Manihot is a New World genus, and it was not established elsewhere until after Europeans transported cassava to Africa early in the 16th century, and later to Asia. It is likely that the vast majority of genes within the species evolved as a result of selection pressures exerted in its place of origin. As cassava breeders look for new traits to meet the changing needs of production, processing and new markets, chances are that the genes to provide those traits will be found in the genebanks from the Americas. Likewise, the biological control agents that co-evolved with pests and diseases affecting cassava and its relatives will also have their highest diversity in the center of origin. This paper highlights some of the outstanding contributions of cassava’s evolutionary homeland to the crop’s improvement in modern times, argues that new technologies will rely even more on the broad base of genetic resources in the Americas, and presents a case for more comprehensive evaluation of major genebanks. Examples are drawn from yield, quality and resistance traits, and from predators and parasites controlling pests in Africa and Asia. Trends in production and in new markets are described as the principal drivers to encourage more extensive and better use of Manihot genetic resources. Projections for climate change also indicate the need for traits that are not present in current varieties. Best-bet approaches are described for finding solutions arising in the crop’s center of origin in the New World.
In nature, the cassava ancestor Manihot esculenta spp flabellifolia does not form storage roots like the cultivated species Manihot esculenta spp esculenta. Specific genetic factors influencing storage root formation include developmental signals, plant hormones, light, and domestication as well. The genetic diversity between these two species was accessed using the Euphorbiace cDNA chip developed at ARS; Fargo, North Dakota, USA. We mined for candidate regulatory genes from those differentially-expressed in the roots of these two species, using specific algorithms and compiled information of gene functionality from current literature. Putative biological pathways containing over-represented genes were identified and a model for storage root formation and flowering behavior was proposed, which highlighted light and hormone responses. Of the 596 genes differentially-expressed (p<0.005), 22 functional groups, including 162 regulatory genes, were identified. Gene Set Enrichment Analysis (SNEA) identified gene sub-sets for biological processes, cellular components, and molecular functions, and putative regulatory genes based on expression targets, binding proteins, and protein modifications. These integrated results indicated central node genes, genes associated with node genes, and their expressed level of regulation (activated or silenced). Among biological pathways visualized by SNEA, regulatory genes such as transcription factors (GA_DELLA) modulating flower set, and Auxin-Responsive genes modulating storage root formation in response to forest shade and open field cultivation of the cultivated species were identified.
The distribution and frequency of single nucleotide polymorphisms (SNPs) is an excellent tool for discerning evolutionary relatedness between cultivated and wild plant genomes. This type of information is scanty for the genus Manihot, and thus limiting systematic approaches in the genetic improvement of cassava. Here, we present a detailed description of the comparative patterns of SNPs in Isoamylase1 (Meisa1) and Glyceraldehyde-3-phosphate dehydrogenase (G3pdh) in 10 accessions of wild (Manihot esculenta subsp. flabellifolia) and 12 accessions of cultivated cassava (M. esculenta). The results show that Meisa1 is more variable in cultivated cassava than that in subsp. flabellifolia, where the 954 bp sequence region differs at 1 in 111 and 250 nucleotides of cultivated and wild species, respectively. Frequency analysis shows that SNPs occurs once every 42 bp in cultivated and 70 bp in wild. Tajima’s D test statistics showed that Meisa1 has been evolving under different selection pressures, diversifying in cultivated and purifying in wild. G3pdh is under diversifying selection in both populations. This may indicate the importance for isoamylase1 in starch quality traits in cassava, a trait which is likely to have been the target for artificial selection by farmers and breeders, in addition to natural selection. This study also suggests that G3pdh may be a good marker for phylogeny study while Meisa1 may be useful for intra and inter-cultivar diversity studies. The coding SNPs that change the amino acid types were identified and the potential implication of the change in protein function is analyzed and discussed.
The cassava germplasm collection in Thailand divides to two phases. First, Rayong Field Crops Research Center (RYFCRC), Department of Agriculture, collected more than 200 accession. Then, in 2001, the same center received the 600 accessions of the germplasm core collection from CIAT, Colombia. RYFCRC maintains the collection in both tissue culture and in the field. In the laboratory, accessions are sub-cultured every 3-4 months. The field planting is also used for characterization, including: the morphological descriptors at three months after planting (MAP) such as color of apical leaves; at six and nine MAP, petiole color, leaf color, number of leaf lobes , length of leaf lobe, width of leaf lobe , lobe margins, petiole length , color of leaf vein, color of stem cortex, color of stem epidermis, color of stem exterior, distance between leaf scars and growth habit of stem. The descriptors to be scored at harvest include plant height, height to first branching, levels of branching, branching habit, angle of branching, dry matter content, starch content and harvest index.
Plant germplasm collections invariably contain varying levels of genetic redundancy, which hinders the efficient conservation and utilization of plant germplasm and is especially of concern in clonally propagated crops including cassava. Identification and probable elimination of duplicates or mislabeled genotypes is important from both genetic and economic point of view. Conventionally, morphological descriptors are used for genotype identification, however, DNA markers specifically microsatellites have proven to be suitable markers for genotype identification as these are not influenced by environment, are co-dominant, reproducible, hyper-variable and abundant in eukaryotes. A Global Crop Diversity Trust (GCDT) funded project has been carried out at IITA to fingerprint the entire germplasm cassava collection using SSR markers to assess genetic redundancy in the collection. About 2400 cassava accessions conserved at IITA field bank have been genotyped with 25 SSR markers, using a PAGE (polyacrylamide gel electrophoresis) and capillary electrophoresis system. Genotype profiling was first carried out with a set of SSR markers using PAGE system to identify potential duplicates and establish a cost-effective system to assess accessions whenever new acquisitions are made. The crucial step was determining a threshold to consider if two accessions were potential duplicates or not. A strategy of comparing genetic distances (GD) based on modified Roger’s genetic distance measure between accessions with a threshold of GD = 0 to 0.15 for at least three SSR markers was used to identify absolute identical (GD = 0) as well as potential duplicate (GD > 0.15) accessions. It was assumed that the accessions that remained different across 3 SSR markers with a GD of more than 0.15 based on PAGE data were unique accessions. Following the above criteria, all 2418 cassava accessions were genotyped initially with 10 SSR markers on PAGE, resulting in a total of 41 alleles with an average of 4.1 alleles per marker. Based on genetic distance, a total of 895 potential duplicates were identified for further genotyping with additional 15 SSR markers (multiplexed into 5 panels of 3 SSRs each) on ABI3100 for capillary electrophoresis. This step of stringent fingerprinting with additional SSRs was carried out to address the same question of differentiating accessions even at 1 bp level through capillary electrophoresis, which otherwise would not be addressed using the PAGE system. The similar concept of genetic distance was used on the data generated from ABI3100 analysis to identify absolute identical accessions. A total of 70 alleles were observed with an average of 4.7 alleles per SSR marker. All the SSR markers used in the present study showed high gene diversity that ranged from 0.23 to 0.75 with an average of 0.49. Based on GD = 0 for at least 3 SSR markers, a total of 355 absolute identical accessions were identified indicating the presence of about 14.7% duplicate accessions in the collection. Results obtained have been compared with available passport and characterization data to identify off-types or mislabeled accessions. The results have also been compared with the recently established cassava core collection based on morphological traits to determine the presence of duplicate accessions. Interestingly, the core collection did not contain any duplicate accession, thus validating the criterion used in the establishment of cassava core collection. The results from this study will allow rationalizing cassava germplasm collection by reducing redundancy, cost-effective germplasm maintenance, and ensuring optimal representation of the genetic diversity of the germplasm collection at IITA. The results also demonstrates that SSR markers, together with the statistical tools for individual identification and redundancy assessment, are technically practical and sufficiently informative to assist the management of tropical plant germplasm collections.
In the genus Manihot, with about 98 species documented, only cassava (M. esculenta Crantz) is cultivated and is considered a major source of food for the human diet in the tropics. Brazil, which is the main center of origin of cassava, has the greatest genetic diversity of the genus. To use the diversity of wild germplasm, Embrapa Cassava & Fruits (CNPMF) established and expanded, since 2005, a collection of wild species of Manihot. The accessions of this collection were obtained from various sources, which include: 1) Seeds and cuttings of accessions from Embrapa Genetic Resources and Biotechnology; 2) Material collected at Embrapa Semi-Arid and at Federal University of ‘Recôncavo da Bahia’; 3) Collection expeditions performed in semi-arid (caatinga) and savanna Brazilian ecosystems; and 4) Plants obtained from seeds produced in the collection, via open pollination. Currently, the field collection has around 605 accessions of 26 species. In this wild germplasm, the following studies are being carried out: 1) Morphological and taxonomic caracterization; 2) Crossing compatibility, development of hybrids and paternity analysis; 3) citogenetics and pollen production and viability; 4) Evaluation of cryopreservation procedures; and 5) Evaluation of gene flow.
Cassava genetic resources conservation is managed through in-situ or ex-situ methods. CIAT maintains more than 6300 cassava accessions under an in vitro storage facility at 26°C, 1000lux, 12/12 photoperiod using less than 65m2. Depending on clone behavior under those conditions, stocks should be planted on fresh medium each 8-12 months. Cryopreservation could allow the maintenance of this collection for the long-term, reduce maintenance and regeneration costs, and minimize the risk of genetic change. CIAT has implemented classical and new techniques on cassava cryopreservation. During recent years, we focused on the ED method and it was tested with the core collection. Some clones have shown recalcitrance to this technique. As part of a collaborative project among CGIAR centers (IITA, CIP, Bioversity and CIAT) with a support of the Global Crop Diversity Trust and GPG-2, a round of technical interactions were facilitated among researchers of participating centers. Recalcitrant clones to ED were tested with the DV method. Data showed that some clones could overcome the recalcitrance. One-hundred lowest responding clones were tested with the new technique and plantlets are being recovered to transfer to soil to be analyzed. If no changes are observed, this technique could be considered as a routine cryopreservation method.
As a major staple crop, cassava (Manihot esculenta) is a very good source of dietary calories for almost half of African people. Cassava tubers and leaves are used mainly for food. The tubers are also raw material for starch and in starch-based industries. Many breeding programs are on-going in Africa and other parts of the world, to improve the traits of end user preference, such as, high tuber yield, pest and diseases resistance, tolerance to abiotic stresses, micronutrients, starch quality, dry matter content, etc. In support of these programs, the IITA Genetic Resources Center (GRC), collaborating closely with Germplasm Health Unit and Cassava Breeding team, is serving as a pre-breeding, a genebank and a germplasm distribution partner. The Genebank at GRC in Ibadan (Nigeria) conserves and distributes germplasm of cassava and its wild relatives held in trust, to support scientific research and new cassava varieties development. Due to clonal nature, cassava germplasm, mainly from Africa, is conserved in the field genebank at Ibadan, Nigeria (3499 accessions) and duplicated in medium term in vitro (slow growth) conservation facility (2787 accessions).
In addition, 673 improved and elite cassava lines developed by the cassava breeding programs are also conserved in medium term in vitro storage. About 290 of these lines (43%) were newly introduced or reintroduced into in vitro system, following a virus cleaning method, for producing virus-free planting material. The virus cleaning method combines heat-treatment, regeneration through meristem culture and virus indexing to ensure freedom from cassava mosaic begomoviruses and cassava brown streak viruses. Clean germplasm is used for distribution to partners and stakeholders on request. Over a period of 2 years (March 2010 to March 2012), in vitro plantlets of 198 accessions of improved cassava varieties were supplied to partners in 5 countries, many of which are located in East and southern Africa. Information on cassava germplasm accessions and the procedure to acquire germplasm from IITA is provided in the webpage, http://genebank.iita.org/.
Cassava (Manihot esculenta spp. esculenta), is a tropical crop cultivated mainly for its starchy tuberous roots. Initiatives for scientific research on cassava is increasing during the last years. As part of a PhD research program, a study on the genetics of cassava domestication was carried out between 2006 and 2010 within a project lead by Wilson Castelblanco and Anna Westerbergh, at the Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden. During 2006 and with close collaboration with cassava researchers at the Centro Internacional de Agricultura Tropical (CIAT), an F2 mapping population was developed by crossing cassava with its proposed wild ancestor Manihot esculenta spp. flabellifolia. Several field trials at CIAT and a greenhouse trial at SLU were used to visualize and quantify trait differences between the cassava and wild ancestor parents and the genotypic/phenotypic segregation in the F2 progeny. The F2 mapping population was used to address the following research questions: i) what are the phenotypic differences between cassava and its wild ancestor? ii) what is the genetic basis (e.g. QTL distribution and number) of trait differences and how does this compare to major crops where selection has been more intense? iii) how is the process of root formation (starch synthesis and allocation) controlled in specific F2 individuals showing great variation in root morphology, and iv) what is the genetic diversity variation in cultivated cassava compared with wild cassava populations in relation to the three major stages of cassava evolution: domestication in the southern Amazon, dispersion within the Americas and introduction into Africa? This paper presents data to answer these questions.
The most prevailing bacterial disease of cassava in all the growing regions of the World is cassava bacterial blight (Xanthomonas axonopodis pv manihotis). Resistance to the disease is found in wild relative Manihot glaziovii native to the Americans. This disease is a major constraint to cassava cultivation and losses can be extremely in regions where susceptible cultivars are grown. To identify a source of resistance to cassava bacterial blight (CBB) from the drought tolerant germplasm introduce, a field screening of introduced tissue culture materials from CIAT were harden and planted in Mingibir, Kano State, Nigeria where the disease pressure for Sudan savannah record highest. A total of 91 genotypes were screened on the field over two years on a single row planting. Four month after planting, the genotypes shows very good vigour (96.15%) and good leaves retention (97.43%) as a good characteristic for drought. Three genotypes (CTS 2B – 64, CTS 2B – 43 and CTS 2A – 30) represents 5.12% of the total genotypes screened on the field showed high resistance to Cassava Bacterial Blight. These genotypes are a good source of resistance to cassava bacterial Blight in this dry agro-ecology.
Assessment of genetic diversity within germplasm provides a valuable source of information for breeding programs. Molecular markers have become an important tool for assessing cassava genetic diversity and degree of relationship among cassava genotypes. Microsatellite or SSR markers are widely used for this purpose because of their co-dominant nature, high polymorphism, technical simplicity and reproducibility. Recently, alternative SSR markers have been developed from public expressed sequence tag (EST) databases because it is fast, cost-effective and has a high level of transferability between related species. In this study, a total of 49 EST-SSR primers were successfully designed from an EST database using PRIMER 3 program, and used to detected polymorphism within 29 samples of M. esculenta Crantz from 15 countries. Nine markers revealed polymorphism between M. esculenta samples with the number of alleles ranging from two to four per locus. The average unbiased and direct count heterozygosity were 0.4901 (ranges from 0.3522 to 0.7193) and 0.5674 (ranges from 0.2414 to 1.000), respectively. Two of nine (ESSR26 and ESSR28) showed significant (P < 0.05) deviations from Hardy–Weinberg equilibrium (HWE). No significant linkage disequilibrium (LD) was observed between pairs of loci. Cross-transferability of Manihot species (M. chlorosticta, M. carthaginensis, M. filamentosa and M. tristis, M. esculenta Crantz) and subspecies (M. esculenta Crantz ssp. Flabellifolia) was evaluated. The results showed that all nine markers were amplified successfully. Of these, six and two markers showed polymorphism in M. esculenta Crantz ssp. Flabellifolia and M. tristis, respectively. In addition, all genotypic data were applied for genetic cluster analysis of Manihot species and subspecies. Within M. esculenta, the results showed that the closet genetic distance was found between the samples from Ecuador and Colombia, while the samples from Brazil and Argentina were the most divergent. Between Manihot species, the results indicated that the genetic distance ranged from 0.0397 to 1.4491. The samples of M. chlorosticta and M. esculenta Crantz ssp. flabellifolia were the closest groups, while M. tristis was the most divergent from M. carthaginensis. The EST-SSR markers and information obtained in this study will be useful in genetic study of the Manihot species and subspecies as well as in molecular breeding of cassava through marker-assisted selection (MAS).
Our research program at EMBRAPA Genetic Resources and Biotechnology exploits natural genetic variation to overcome genetic bottlenecks during domestication and to improve yield and quality of cassava storage root. Here, we integrate our results of landrace genetic diversity, metabolite profiles (sugar and carotenoid) and microarray-based transcript to unveil complex biological and metabolic networks in storage root. Based on correlation analysis, we mined candidate regulatory genes to identify putative biological pathway network that differentiate storage root phenotypes. We also mined candidate genes for changes in expressed genes coding for enzymes in the conversion of sucrose to starch, starch catalytic activity, and carotenoid synthesis as well. Results from this analysis provided evidences to indicate that sugary mutation in cassava storage root is a complex trait involves missing expression of BEI, high expression of gene coding for starch degrading enzymes and specific putative regulatory genes network such as ABI5, SLY, PRL1 and CLPP4. For the case of carotenoid, HPLC carotenoid profiles correlate differentially with specific expressed genes such PSY, PDS and LyCb as well as with specific putative regulatory genes network such as FLC, ABI1, JAR1, MPK4, BRI1 and ATG50240. It was also observed that the gene coding for HSP18.1 and HSP21 are highly expressed in intense yellow root than in white.
The use of osmotic regulators to in vitro germplasm conservation is one of the strategies used to reduce the plant growth and to get the best conditions to an adequate management of the in vitro collections. This work aimed to evaluate the effect of different concentrations of mannitol and sorbitol isolated or in combination with sucrose in reducing the growth of cassava in vitro plants. In order to obtain plants to establish the experiments shoot tips were inoculated in MS medium supplemented with 1,0 mg/L of thiamine, 100 mg/L of inositol, 0,02 mg/L of NAA, 0,04 mg/L of BA, 0,05 mg/L of GA3, 20 g/L of sucrose and 2,4 g/L of Phytagel® with the pH adjusted to 5,8. The cultures were incubated in growth chamber under 27 ± 1 ºC of temperature, 16 h light and light intensity of 22 µEm-2s-1 for 30 days. To conservation study two experiments completely randomized in a factorial scheme (2×3) were performed considering 2 sucrose concentration (0g/L and 20g/L) and three concentrations of sorbitol or mannitol (0g/L; 0,5g/L and 10g/L), using the 8S as basic medium. The plants were incubated under 21 ± 1ºC of temperature, under a photoperiod of 12 h day and light intensity of 2.0 x 107 µmoles. To both experiments the absent of sucrose compromised the plant development. The mannitol showed a strongest reduction effect in comparison with sorbitol. The concentration of 10g/L from both sugars inhibited the growing making evident that the hydric stress promoted was not tolerate by plants affecting their development. The best result was obtained with 20g/L of sucrose without mannitol and sorbitol allowing the plants conservation for 12 months.
Cassava (Manihot esculenta Crantz) is an important tropical tuber crop grown in India. Even though cassava is an introduced crop it got acclimatized to the agro climatic regions in the tropical region of India, which is very similar to the centre of origin of the crop. The Central Tuber Crops Research Institute in India holds a germplasm of 1660 accessions. The present study was conducted during 2009-2011 to identify elite clones among 300 landraces maintained as field gene bank. Starch content ranged from 20-45 % and accessions viz. CI-776, CI-71, CI-760, CI-869 and CI-43 had very high starch. The cyanogen in fifteen sweet cassava varieties ranged from 6.10 – 23.20 µg g-1 as against 24.4 µg g-1 in the standard M4. Sugar content adds taste to the cooked tuber and it ranged from 3.6- 8.9 %. Cooking quality as per standard parameters, based on hardness, mealiness and taste was tested and sixteen accessions showed high rating. The elite landraces with long cylindrical tuber shape were evaluated for fried chip quality based on texture, bite, taste, keeping quality and oil retention. CI 699, CI 883, CI 75, CI 84, CI 702, CI 93 and CI 126. had good fried chip quality. In addtion to quality traits, nutrient use efficiency was studied and seven landraces were found to be NPK efficient. Also six early maturing accessions of six month duration with high yield and dry matter content (>40%) were also identified and are being used in prebreeding programme.
Before a variety is registered as a cultivar and/or granted Plant Breeder’s Rights, its distinctness, uniformity and stability (DUS) is tested using morphological characters (descriptors). In India, the Protection of Plant Varieties and Farmers Rights Authority and Central Tuber Crops Research Institute conducted evaluation trials for identifying the DUS descriptors in cassava. Observations on 66 descriptors proposed by various organizations were recorded on 22 released varieties of cassava for three years. It includes 15 stem, 16 leaf, 11 floral and 16 tuber traits. Besides eight special characteristics like harvest index, biochemical traits, keeping quality and incidence of pests and diseases were also recorded. Type of assessment of characteristics included 3MG, 23MS, 27VG and 13 VS traits. The six characteristics identified for grouping of cassava varieties were (a) Stem: Predominant colour of stem (b) Leaf: emerging leaf colour, petiole colour (c) Tuber: shape, cortex colour, flesh colour. The data collected during 2009-2010, 2010-2011 and 2011-12 were subjected to statistical analysis to study the stability of DUS characters. Reference varieties were identified and maintained with respect to each of the DUS descriptor. In addition to the 22 released varieties, 30 germplasm accessions were also maintained as reference varieties. The unique dus characteristics identified can be used for the characterization and protection of the cassava varieties in future.
Cassava Bacterial Blight (CBB), caused by Xanthomonas axonopodis pv. manihotis (Xam) compromises severely cassava production and thereby food security in several developing countries. CBB incidence and expansion to other cultivated areas is expected to increase in the context of global climatic change. Despite of this real threat, no resistance (R) gene has been isolated to any of the high number of Xam strains isolated in the past or recent years. We initiated an integrated strategy to identify cassava R genes effective against CBB and dissect the molecular bases underlying resistance. The cassava genome sequence was interrogated to identify several Immunity-Related Proteins (IRPs). We will present the genomic organization and evolution of the most representative classes of IRPs. Among them are RXam1 and RXam2, which are encoded by candidate R genes associated with QTLs effective against Xam. The function of these two genes was validated by gene silencing and by association studies based on sequence polymorphisms and responses to Xam in different cassava cultivars. Our results suggest that RXam2 can be considered the first cassava R gene effective to control CBB. By yeast two-hybrid we also aim at deciphering the protein interaction network established during the responses of cassava to Xam. The function of the identified interactors will be discussed. In addition, new markers derived from the IRPs were included in the cassava genetic map and will be linked to known resistance QTLs to Xam. Finally, because of the growing importance of microRNAs (miRNAs) during plant-pathogen interactions, we identified induced and repressed miRNAs. Altogether, our study enabled to draw an overall picture of the molecular bases underlying cassava resistance to CBB, with the aim of guiding new strategies to assist the breeding programs of cassava varieties with enhanced resistance.
Xanthomonas axonopodis pv manihotis (Xam) is the causal agent of cassava bacterial blight (CBB) in all cassava growing area of the world. CBB disease is a major constraint to cassava cultivation, and losses can be extremely severe in regions where highly susceptible cultivars are grown. To build a well organized disease management approach, the genetic diversity of the pathogens population ought to be known. Information is scarce on the genetic diversity of Xanthomonas axonopodis pv manihotis population in Nigeria. Amplified Fragment Length Polymorphism, (AFLP) a novel PCR-based technique was used to characterize the Xanthomonas axonopodis pv manihotis isolates from the middle belt and Northern states of Nigeria. Thirty six strains of Xam and 2 reference strains were tested with eight AFLP primer combination and the data generated were analysed with NTSYS-PC version 2.0. Principal Component Analyses of the data were carried out using SAS version 8.2 to reveal a scatter-gram plot of the isolate. Numerical analysis differentiated the AFLP patterns into eight distinct clusters at 65% similarity coefficient level. Cluster 1, 3 and 4 with 73.7% of the total bacterial strains grouped together while the other clusters had two strains each shared the remaining 26.3%. Cluster 3 had similar strains from different states together and had the 29% of the entire clusters while cluster 4 grouped strains from only two geographically related states together. The genetic analysis presented here contributes to understanding of the Xam population structure in the northern region of Nigeria and will help in developing resistance cassava cultivars for this agro-ecological zone.
Cassava bacterial blight (CBB), caused by Xanthomonas axonopodis pv manihotis (Xam), is a devastating disease producing losses of over 50% in total yields. Despite the importance of CBB for food security, there is a lack of recent studies in elucidating the molecular determinants to CBB resistance. It has been demonstrated that transference of immunity genes between phylogenetically distant plants generates broad spectrum resistance against bacterial pathogens. In addition, the generation of autoactive NB-LRR (Nucleotide-Binding Leucine-Rich Repeats) genes, represents an alternative to produce enhanced resistance in cassava varieties. Our principal aim is to generate durable and broad spectrum resistance to CBB. To accomplish it we are using RXam2, a cassava gene coding for a NB-LRR associated to a resistance QTL to Xam, as well as the genes Xa21 from rice and Bs2 from pepper. Autoactive versions mutated in the MHD motif (NB domain) for both RXam2 and Bs2 were generated through site directed mutagenesis using overlap extension PCR and were confirmed by transient agroinfiltration in cassava and tobacco. Preliminary assays show that these genes have the ability to generate a strong resistance response. These genes were cloned into pCambia1305.2 under a TALE(Xam)-inducible promoter. On the other hand, Xa21 and Bs2 were cloned into pCambia1305.2 under 35S promoter. All these constructions are being employed to transform FEC from the variety 60444.
Cassava Bacterial Blight (CBB), incited by Xanthomonas axonopodis pv. manihotis (Xam), is the most important bacterial disease of cassava, a staple food source for millions of people in developing countries. Here we present a widely applicable strategy for elucidating the virulence components of a pathogen population. We report Illumina based draft genomes for 65 Xam strains and deduce the phylogenetic relatedness of Xam across the areas where cassava is grown. Using an extensive database of effector proteins from animal and plant pathogens, we identify the effector repertoire for each sequenced strain and use a comparative sequence analysis to deduce the least polymorphic of the conserved effectors. These highly conserved effectors have been maintained over 11 countries, 3 continents and 70 years of evolution and as such represent ideal targets for developing resistance strategies.
Cassava bacterial blight (CBB) is a caused by the gram-negative, vascular bacterial pathogen Xanthomonas axonopodis pv. manihotis (Xam) and affects cassava growing regions across Africa, South America and Asia. Symptoms include leaf wilt, vascular necrosis and shoot dieback, and infected crops can suffer losses up to 100% of total yield. Despite significant efforts, breeding for bacterial blight resistance in cassava has not yet generated varieties displaying true resistance to CBB, suggesting that transgenic approaches will be necessary in order to generate strong, durable resistance against Xam infection. We have established an in vitro systemic inoculation system and tested the model African cultivar TMS 60444 with over 30 geographically and temporally diverse Xam strains. Our results revealed that African strains show higher levels of virulence than South American strains, suggestive of Xam co-evolution and adaptation for maximum virulence against regional cassava varieties. Susceptibility of additional varieties from Africa and South America to a subset of these Xam strains is being evaluated to further test this hypothesis. Matrix analysis of Xam virulence and the presence/absence of bacterial effectors identified by Illumina sequencing of Xam strains has revealed several effectors that are likely to play a role in virulence. The relative contribution of defence pathway responses to bacterial blight infection in cassava is being characterized in an effort to better understand the underlying molecular mechanisms for susceptibility to Xam infection. In addition, several transgenic strategies are in progress to engineer CBB resistance, including expression of pathogen recognition receptors EFR (Arabidopsis) and Xa21 (rice), and the R-gene Bs2 (pepper).
RNAi technology has proved effective for imparting resistance to both RNA and DNA plant viruses. The genomes of African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV-UG) were screened to determine the regions most effective for generating pathogen-derived resistance to these geminiviruses. Inverted repeat constructs were generated from the AC4, AC1, AC2, AC3, CP, AV1, BV1 and BC1 regions of ACMV and tested for efficacy to control replication of the homologous virus in transient tobacco assays. Knowledge gained was utilized to produce transgenic cassava plants for four and seven constructs generated from ACMV and EACMV-UG sequences, respectively in the cassava mosaic disease (CMD) susceptible cultivar 60444. An average of 60 independent transgenic events were generated per construct and plants screened to identify low T-DNA copy, siRNA accumulating lines. Approximately ten such events from each construct were transitioned to the greenhouse for replicated viral challenging with infectious clones of ACMV and EACMV (K201). For both virus species, the AC1 and AC2 regions imparted greatest resistance to the homologous virus, providing up to 100% control against inoculation with ACMV and 50-70% for EACMV. No viral DNA could be detected in the resistant plants. Confirmation of resistance to EACMV after two cycles of confined field trials at NaCRRI, Namulongue has demonstrated the predictive value of these greenhouse tests. Transgenic plants of 60444 accumulating siRNAs from both compoments of a fusion construct of the AC1 and AC2 regions of ACMV and EACMV have been produced and shown to possess high levels of resistance to both pathogens.
Cassava production in East Africa is significantly constrained by cassava mosaic disease (CMD). The main causal viruses of CMD in Uganda are the geminiviruses African cassava mosaic virus (ACMV) and the Ugandan strain of East African cassava mosaic virus (EACMV-UG). Plant biotechnology provides opportunity for introgressing new sources of geminivirus resistance into cassava germplasm. Using Agrobacterium-mediated transformation, we generated transgenic plants of the CMD susceptible cultivar 60444 with two inverted repeat constructs of the full length and C-terminal regions of the AC1 gene of EACMV-UG. Transgenic lines were shown to accumulate siRNAs specific to the integrated sequences before being planted in a confined field trial at NaCRRI, Namulonge. Six siRNA lines were tested for virus resistance under field conditions. PCR diagnostics indicated that both siRNA constructs suppressed infection with EACMV-UG over two seasons of testing; the virus being detected in less than 3% of the plants sampled compared to 71% in the control. Most plants developed typical CMD symptoms within three months, but disease was most severe on the non-transgenic 60444. Both ACMV and EACMV-UG were detected in leaves of controls but only the non-targeted ACMV in the siRNA transgenic plants, with the latter associated with mild CMD symptoms. At harvest, shoot and root biomass of siRNA transgenic plants was significantly higher compared to the controls. Stake cuttings were obtained from two best performing lines and replanted to determine capacity to resist EACMV-UG infection across vegetative cycles. After 12 months regrowth, transgenic plants remained free of detectable EACMV-UG, indicating efficacy of RNAi technology to provide resistance against a targeted geminivirus under field conditions.
Cassava mosaic disease (CMD) is caused by a DNA virus complex that includes seven geminivirus species. An earlier study showed that two satellite-like DNAs (SatII and SatIII) with related sequences in the cassava genome can break endogenous CMD resistance and increase disease severity in cassava. We asked if the Sat DNAs also impact viral infection in susceptible (S) and resistant (R) Arabidopsis ecotypes that lack integrated genomic copies of the Sat DNAs. S plants coinoculated with African cassava mosaic virus (ACMV) and Sat DNA showed symptoms at 10-12 dpi, while plants inoculated with ACMV alone had mild symptoms at 21 dpi that never became as severe as those in the presence of the Sats. PCR and gel blot data showed that ACMV DNA accumulated to higher levels in the presence of the SATs. R plants inoculated with ACMV alone or in the presence of the SATs DNA did not show symptoms or contain viral DNA. However, R plants coinoculated with Cabbage leaf curl virus (CaLCuV) and Sat DNA were symptomatic and accumulated CaLCuV DNA at 20-22 dpi. R plants inoculated with CaLCuV or SAT DNA alone never showed symptoms or had viral DNA. Although the Sat DNAs impacted viral infection, we did not detect an increase in Sat DNA levels overtime. These results show that the Sat DNAs function in Arabidopsis and with a heterologous geminivirus to enhance symptoms and break resistance.
Traditional methods of viral diagnostics using virus-specific antibodies and PCR often fail to identify a pathogen. We undertake an alternative approach using siRomics. The plant antiviral defense system based on RNA silencing generates 21-24 nucleotide short interfering RNAs (siRNAs). Emerging evidence from deep-sequencing of short RNAs indicates that viral siRNAs are derived from the entire genome sequence of RNA and DNA viruses and accumulate at high levels. Hence it appears feasible to reconstruct a complete viral genome from viral siRNA species. Bioinformatics algorithms are being developed that allow de novo assembly of eukaryotic genomes and transcriptomes from short sequencing reads. Our current efforts aim at development of a siRomics approach based on siRNA deep-sequencing and de novo assembly for universal diagnostics of plant virus disease. The main advantage of this approach is that it allows fast and reliable identification of the genome sequence of an unknown virus or a new viral strain causing a given disease. I will illustrate our efforts using examples from various patho-systems and, in particular, I will focus on naturally-infected cultivars of Indian cassava investigated in the frame of our Indo-Swiss Collaboration in Biotechnology (ISCB) together with Dr. K. Veluthambi and his team at Madurai Kamaraj University
African cassava mosaic virus (ACMV), East African cassava mosaic Malawi virus (EACMMV), East African cassava mosaic Cameroon virus (EACMCV) and East African cassava mosaic Zanzibar virus (EACMZV) cause cassava mosaic disease (CMD) in sub Saharan Africa. Co-occurrence of these viruses in cassava synergistically enhances disease symptoms and complicates their detection and diagnostic. A technique based on single-tube duplex and multiplex PCR (d&mPCR) was developed for the simultaneous detection of ACMV, EACMMV, EACMCV and EACMZV. Specific amplification of each of the virus species was achieved by four primer pairs designed to target DNA-A sequence components of cassava mosaic begomoviruses (CMBs) in a single tube PCR amplification using DNA extracted from dry-stored cassava leaves. The d&mPCR enabled the simultaneous detection and differentiation of the four CMBs: ACMV (948bp), EACMMV (504 bp), EACMCV (435 bp) and EACMZV (260 bp) in single and mixed infection, and the results from the PCR amplicons sequencing agreed with sequence identities of the respective published virus species. In addition, we report here a new modified Dellaporta et al. (1983) protocol, which was used to extract DNA from dry and fresh cassava leaves with comparable results. Experience from using the d&mPCR techniques shows that time was saved and amount of reagents used were reduced. The d&mPCR is a new tool that will have wide application for quick and extensive leaf sampling with scientists doing virus diagnostics studies, phytosanitary officers monitoring disease spread as well as seed certification and multipliers requiring virus indexing.
Cassava mosaic disease (CMD) is a major constraint on cassava cultivation in Africa. The disease is endemic and is caused by seven distinct cassava mosaic geminiviruses (CMGs), some of them including several variants. From cassava leaf samples presenting CMD symptoms collected in Burkina Faso, four DNA-A begomovirus components were cloned and sequenced, showing 99.9% nucleotide identity among them. These isolates are most closely related to African cassava mosaic virus (ACMV) but share less than 89% nucleotide identity (taxonomic threshold) with any previously described begomovirus. A DNA-B genomic component, sharing 93% nucleotide identity with DNA-B of ACMV, was also characterized. Since all genomic components have a typical genome organization of Old World bipartite begomoviruses, this new species was provisionally named African cassava mosaic Burkina Faso virus (ACMBFV). Recombination analysis of the new virus demonstrated an interspecies recombinant origin, with major parents related to West African isolates of ACMV, and minor parents related to Tomato leaf curl Cameroon virus and Cotton leaf curl Gezira virus. This is the first report of an ACMV-like recombinant begomovirus arisen by interspecific recombination between bipartite and monopartite African begomoviruses.
Cassava mosaic disease (CMD) caused by cassava mosaic geminiviruses (CMGs, Geminiviridae) is a major threat on cassava production throughout Africa. In Madagascar, severe symptoms with high prevalence of CMD were observed. From 700 mostly symptomatic cassava leaves, we undertook molecular characterization of the CMGs involved. The PCR diagnosis confirmed the presence of CMGs in Madagascar and six species were detected with the frequent occurrence of mixed infections. Based on rolling circle amplification, cloning and sequencing, we obtained full genome sequences of 281 DNA-A and 119 DNA-B of CMGs. DNA-A sequences were most closely related to those of African cassava mosaic virus (ACMV), South African cassava mosaic virus (SACMV), East African cassava mosaic virus (EACMV), East African cassava mosaic Cameroon virus (EACMCV), East African cassava mosaic Kenya virus (EACMKV) and a new species named cassava mosaic Madagascar virus (CMMGV). DNA-B sequences were most closely related to those of ACMV, EACMKV, EACMCV and CMMGV. Phylogenetic reconstruction allowed to assess the geographical structure of CMG populations and to determine the recent history of CMG migrations in Madagascar. Taken together, our results point to Madagascar as a potential major center of begomovirus diversity.
Cassava is an important staple food in Africa. Despite its value, production is constrained by pests and diseases. The African Cassava Mosaic Disease (ACMD) transmitted by Bemisia tabaci (Gennadius) is the most damaging disease constraint to cassava production in Africa resulting in significant crop losses. Traditional cassava production usually involves intercropping and cultivar mix. Such diversified agro-ecosystems may often support lower insect pest load than corresponding monocultures. Therefore, manipulation of cropping systems provides an important pest management tool. Two on-station experiments were established at Kwadaso and Ejura during the 2010 cropping season to assess the impact of cassava-cowpea intercrop and cultivar mix on B. tabaci population, and its implications on the incidence and severity of ACMD. Bemisia tabaci was more abundant in Kwadaso than Ejura. It’s abundance on four cassava varieties were higher than on cowpea. At Ejura, its abundance within the different cropping systems was similar. However, at Kwadaso, it varied among the different cropping systems. The incidence and severity of ACMD were also varied with the local variety been the most susceptible. Generally, no significant relationship was established between B. tabaci population and incidence and severity of ACMD, except at Kwadaso, where the abundance of B. tabaci was negatively correlated to the incidence of ACMD.
Genetic variability of the Bemisia tabaci genotypes, the vector of cassava mosaic disease (CMD) was performed through comparison of a portion of the mitochondria cytochrome oxidase I DNA sequence of adult females collected in cassava growing areas of Kenya, Tanzania and Uganda in 2010/11. Five distinct genotypes were obtained hereafter named: Uganda 1-like, southern Africa-like, Kenya distinct, Tanzania distinct and Uganda distinct. Uganda 1-like genotypes were widely distributed in all the three East African (EA) countries. The Ug1-like genotypes had a sequence similarity of 97.2-99.5% with the published Ug1 genotypes and were divergent by 0.4-5.5% amongst each other. The southern Africa-like genotypes were detected for the first time in EA. They shared a sequence similarity of 96.8-99.5% with reference southern Africa genotypes and diverged by 2-5% with each other. These genotypes occurred in coast Kenya and Tanzania mainly, as well as central and northern Uganda. Unlike previous reports which reported the occurrence of Ug2; a genotype associated with huge whitefly populations at the ‘severe epidemic front’ in Uganda in the 1990s, our study did not detected the Ug2 genotypes in any of the three countries. In contrast, three genotypes: Kenya distinct, Tanzania distinct and Uganda distinct that are unlike any previously reported in EA were detected, which diverged by 10.7-41% with the published Ug1 and 9.7-53.4% with each other. The results obtained show greater diversity among cassava whiteflies than was previously anticipated. The implication of such huge diversity to the biology (transmission and spread of cassava viruses) of the whiteflies is significant but is yet to be established.
Cassava is an important food crop in both urban and rural areas in Zambia and it plays a principal role in the food economy. Among the starchy staples, cassava gives a carbohydrate production of about 40% higher than rice and 25% more than maize, this makes cassava the cheapest source of calories for both human and animal feeding (Tonukari, 2004). The crop is grown on 180,000 ha and mostly by small scale farmers. Production per hectare is 5.8 t, lower than Africa average (10 t ha-1)and below most of Zambia’s neighbours; Malawi, Tanzania, Democratic Republic of Congo, Angola (FAOSTAT, 2008). The low cassava productivity is partly due to abiotic and biotic factors. Biotic factors include pests and diseases such as cassava mealybug (McMahon et al., 1995), cassava green mite (CGM), cassava mosaic disease (CMD) and cassava anthracnose disease (CAD). The pests are found wherever cassava is grown in the country. Among the diseases affecting cassava include CAD as one of the most important in Africa (Yaninek, 1994). Though the disease has been reported in cassava fields by farmers, extension agents and other stakeholders in the cassava industry in Zambia, disease status (incidence, severity) has not been evaluated. Because of the economic importance of CAD in Zambia, a survey was conducted in Luapula and Eastern Provinces. Therefore the objective of this study was to determine the incidence and severity of CAD in Zambia. Three months to one year old plants were considered for incidence and severity for the disease. The latitude longitude and altitude for each field was recorded using Global Positioning System (HC sumit etrex). The disease severity for CAD was scored on scale of 1-5 (Muimba, 1982) where 1= no symptoms and 5= wilting, drying up of shoots and young leaves, death of part or whole plant. Leaf samples with CAD symptoms were collected and pressed on newspapers for further laboratory analysis. Incidence for CAD was made in a “Z” configuration. Fifteen plants per field were counted equidistant from each other within the row. Disease severity was determined from whole plants. The data was analysed using statistical package for social sciences (SPSS). There were significant difference (P>0.05) in the CAD severity in the surveyed districts. In Luapula province the mean CAD severity was 1.7. Samfya had the highest CAD severity and Nchelenge had the lowest severity (1.2). The highest incidence for CAD was observed in Mansa district (75%) and lowest in Nchelenge district (21.5%). There were also significant difference (P>0.05) in the CAD severity in the surveyed districts of Eastern province. The mean CAD severity being 1.7. Lundazi had the highest (1.8) and Rufunsa had the lowest (1.5). The incidence for CAD was highest in Chipata district (60%) and least in Rufunsa district (53%).
A study was conducted to investigate post flask survival and viral re-infection of cassava variety 60444 multiplied in ILTAB, Danforth Plant Science Centre, USA. Fifty five percent (55%) of the plantlets survived post flask hardening and weaning in an insect proof house. The plants that survived were assessed for CMD incidence and severity in highly CMD endemic coastal savannah agro-ecological zone in Ghana. Although CMD incidence was first observed three weeks after planting (WAP), scoring was started from the fourth week and thereafter every week until the eighteenth week. Disease incidence (DI) increased rapidly from 3.0% at 4 WAP to 87.01% at 18WAP. Index of symptom severity for all plants (ISSAP) and for diseased plants only (ISSDP) ranged from 1.05 to 2.67 and 2.3 to 3.58 respectively from the fourth week to the eighteenth week. Molecular screening for viruses using DNA-based Polymerase Chain Reaction (PCR) with virus-specific primers JSP001/JSP002, EAB555R/EAB555F and UV-ALIF/ACMV-CPR3 which respectively detects ACMV, EACMV and the Ugandan variant of EACMV revealed the presence of ACMV and EACMV. ACMV was detected in 66.7% of the number of plants tested while EACMV was detected in a mixed infection with ACMV in only one plant (3.3%). The Ugandan variant of EACMV was not detected in any of the plants tested. The present study has shown that tissue culture generated disease-free plants (60444) are highly susceptible to CMD re-infection and thus meristem culture does not confer resistance to susceptible plants.
Twenty-two new cassava genotypes and eight others (used as checks) were evaluated in two cropping seasons (1998/99 and 1999/2000) for resistance to viruses causing Cassava mosaic disease (CMD) in IITA fields located at different agroecological zones of Nigeria. Field experiments were conducted in randomized designs. Disease incidence (DI) and index of symptom severity (ISS) data were obtained monthly for each location and genotype. Leaves with CMD symptoms were also collected during resistance evaluation at each location and virus was indexed by amplification in polymerase chain reaction. Significant differences within and across locations were observed in the reactions of new cassava elite clones to CMD, as revealed by the mean DI and ISS values. The highest (P = 0.05) values of DI and ISS at each location and across locations were recorded on the cultivar ‘Isunikankiyan’. DI across cassava genotypes was significantly (P = 0.05) highest in the Ibadan (22.6%) location, followed by Onne (19.3%). Generally, plants of clones 96/0860, 96/1439, 96/0160, 96/1089A, 96/1632, 96/1613, 96/1708, 96/0191, 96/0249 and 96/1565 had significantly lower values of DI in each location. African cassava mosaic virus in single infection was the predominant causal agent of CMD at all study locations.
Cassava is the most important root crop and the second most important staple after maize in Malawi. It is grown across the country and is a staple food crop for more that 30% of the people along the central and northern shore areas of Lake Malawi. Despite its potential, cassava production is greatly constrained by a number of abiotic and biotic constraints. Biotic constraints such as cassava mosaic disease (CMD), cassava green mite, cassava mealy bug, cassava bacterial blight and cassava brown streak disease (CBSD) are the serious ones. Of these diseases, cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are the most damaging in Malawi. They can reduce tuber yield and quality between 10 and 100% on susceptible cultivars. Previous studies have reported on the occurrence of CMD in Malawi based on few samples collected from research stations and districts. Although CBSD was first reported in 1950 in Malawi and later incidences reported along lakeshores of Malawi. In many cases observation of symptoms expression without comprehensive studies using accurate methods have been used to ascertain occurrence of cassava mosaic begomoviruses and CBSD in Malawi. The aim of this study was to conduct a comprehensive countrywide survey and determine the incidence and severity of cassava virus diseases infecting cassava in Malawi. A diagnostic survey was conducted in 2009 and 2010 to determine the incidence and severity of cassava virus diseases infecting cassava in Malawi. Sixty-eight cassava farmers’ fields were surveyed in 3 regions: Northern, Central and Southern. Our results indicate EACMV and EACMMV occurred predominantly in 14 and 9 districts, respectively, while CBSV and UCBSV were prevalent only in north and central districts. No correlation was observed between whitefly abundance with incidence of CMD and CBSD. These results represent the first comprehensive survey of CMD and CBSD in Malawi. The information on status of virus diseases in Malawi in this study has important applications for breeding of cassava resistant materials, plant quarantine and planting materials multiplication and dissemination.
A survey was conducted to investigate the occurrence of cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) in farmers’ fields in the major cassava growing provinces of Zambia in April-May 2009. Cassava mosaic disease incidence was highest in North-Western (67.4%) and Lusaka (67.3%) followed by Luapula (60.5%) provinces and lowest in Eastern (37.2%), Northern (36.5%) and Western (34.8%) provinces. Disease symptom severity was moderate to severe in Lusaka (3.0), Luapula (2.5) and North-Western (2.5) provinces and low in the rest of the provinces. Adult whitefly (Bemisia tabaci) populations were highest in Lusaka (2.3) and lowest in Northern (0.1) province. Polymerase chain reaction (PCR) results using specific primers for African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV) detected single infections of ACMV and EACMV in 30.8% and 20% of the positive reactions, respectively. Dual infections of EACMV+ACMV were detected in 7.8% of the samples tested. Cassava brown streak virus (CBSV) was not detected in any of the samples and no symptoms suggestive of CBSD were observed in the surveyed fields. This is a first comprehensive assessment of viruses affecting cassava in Zambia.
In India, cassava mosaic diseases are caused by Indian Cassava Mosaic virus (ICMV) and Sri Lankan Cassava Mosaic Virus (SLCMV), which belong to begomoviruses transmitted by whitefly, Bemisia tabaci. SLCMV is now the most prevalent virus in India. Indian cassava genotypes have desirable traits like high yield, high starch content and superior plant architecture. However, the basis for resistance against viruses is narrow and our resistance breeding program at CTCRI uses resistance from a Nigerian cultivar MNga-1(TMS 30001) to produce hybrids with CI 732, a high yielding and high starch content Indian semi-dwarf cultivar. Consequently, several cassava mosaic resistant (CMR) lines were developed. CMR lines exhibited three phenotypes viz., highly susceptible, resistant and recovery types. They were grown in a randomised block along with virus infected lines. Symptom development was scored and virus concentration was measured. A Sybr green qPCR assay was established for SLCMV to quantify the viral DNA. Virus concentration was positively correlated with severity of symptom. Among susceptible breeding lines, viral load and symptoms did not show much variation throughout the growth period. However, in resistant varieties, even though there was no symptom expression, low concentrations of viral DNA was found. In recovery type, although there was severe infection at early stages, the symptom score as well as the virus titre decreased over the growth period.
The effect of mosaic virus disease on starch and tuber yield of five local accessions of cassava was evaluated. “Tomfa” showed the highest (95%) incidence of the disease, index of severity of symptoms (ISSAP) 3.70 as well as (ISSDP) of 3.84 while “Dagarti” did not show any phenotypic expression of the disease throughout the study period. Most of the accessions showed symptoms of the mosaic disease two months after planting and by the fifth week had recovered. However, PCR-based molecular screening 12 months after planting revealed the presence of ACMV in all the accessions while EACMV was observed in Ankrah, Dagarti and AW/17. The mean tuber weight (fresh root weight) and starch yield 12 MAP was significantly (P ≤ 0.05) high in Ankrah but low in Tomfa. However, dry matter content of Dagarti 12 MAP was significantly higher than Ankrah, AW/ 17, Tuaka and Tomfa. The present study has revealed that there is a/ no correlation between mosaic virus disease and starch yield and/ or dry matter content in cassava. Also, PCR-based analysis of the genome is the surest way for the detection of the virus since the absence of phenotypic symptoms might be misleading.
Cassava Bacterial Blight is one of the most problematic diseases affecting this crop. Its causal agent Xanthomonas axonopodis pv. manihotis (Xam) employs effector proteins to manipulate certain processes in the host in order to grow and multiply in it. Effectors can suppress plant defense responses through interaction with components of the immune system. We determined that a Xam effector, HpaF, is required for maximal bacterial virulence, and it is a suppressor of general and specific plant defenses. Additionally, we identified three potential HpaF interactors (HFI1, HFI2, and HFI3), but their function had not been established. Our objective was to elucidate the relevance of these HpaF interactions in the suppression of the basal host defense responses. We used the heterologous system of Pseudomonas fluorescens-Arabidopsis thaliana to induce PAMP-Triggered Immunity and observed that HpaF suppresses this defense response. A reverse genetics approach in Arabidopsis was used to define the importance of HFIs in the defense suppression by HpaF. We propose HFI2 and HFI3 as positive and negative regulators of basal plant defense, respectively. These results highlight the importance of HpaF as a Xam effector and sheds light into the pathogenicity mechanisms of this bacterium.
In cassava, tuber rot disease caused by Phytophthora palmivora is one of the important diseases which causes upto 50 % yield loss in endemic areas. There are no external symptoms and the infected root shows internal brown discolouration and rottening and exhibit foul smell. The early detection and identification of plant borne pathogens has become an integral part of successful disease forecasting and management.The present study focused on the PCR and Nucleic acid spot hybridization based detection of pathogen. Isolates of Phytophthora palmivora were isolated from infected cassava tubers. ITS- PCR followed by sequencing was performed for characterization of the pathogen and a species specific primer was designed. The specificity of the primer was also tested. The primer was proficient in detecting the pathogen in naturally infected tuber and soil samples also. A species specific probe was also developed to detect through Nucleic acid spot hybridization.The probe was developed from the specific PCR template.The quality and specificity analysis of the probe was executed and it seemed to have good probe quality as well as specific. The designed primer and probe were successful in specific detection of the pathogen. The work would be the application of PCR and nucleic acid hybridization based diagnostic assays for detection of the pathogen well in advance so as to ensure that the planting sites as well as planting materials are free of propagules.
Cassava mosaic disease (CMD) is the most significant challenge in cassava production causing yield losses of up to 95%. CMD is caused by cassava mosaic geminiviruses (CMGs) and transmitted by the whitefly Bemisia tabaci. Different cassava cultivars have shown varying levels of CMD resistance with some showing near immunity. Seven cassava cultivars were biolistically inoculated with 50 ng and 10 ng infectious clones of African cassava mosaic virus isolate Cameroon (ACMV-CM) and East African cassava mosaic virus isolate K201 (EACMV-K201), respectively using the Helios® gene gun. A 100% disease incidence was recorded for the two viruses 18 days post infection (DPI) in most cultivars. Cultivars TME3, TME204 and Okoyao showed complete resistance to ACMV-CM, which is known to cause mild symptoms and no virus was detected in leaves of these plants with both PCR and Southern blot analysis. Contrastingly, inoculation with EACMV-K201 resulted in development of CMD severity of up to 4 (scale of 1-5) in all the seven cultivars. Symptom remission was observed for cultivars TME3, TME204 and Okoyao with newer leaves presenting significantly reduced or no symptoms by 35 DPI. Asymptomatic leaves accumulated less virus than symptomatic leaves as determined by Southern blotting. Further studies are underway to understand the natural resistance mechanisms to CMD inherent to TME3 and TME204.
One of the most devastating diseases in cassava is the bacterial blight (CBB), caused by the bacterium Xanthomonas axonopodis pv. manihotis, an important pathogen that can generate losses up to 100%. Diverse bacteria, including the genus Xanthomonas, possess a repertoire of type three effectors (T3E) that are delivered into host cells by the type-three secretion system and play a role in virulence and bacterial fitness. Previous studies in our lab have reported the presence of 19 T3E in Xam CIO151. The aim of this work was to demonstrate the role of diverse effectors of Xam in the pathogenic interaction with cassava. By using the technique of double crossing over, we developed a systematic strategy to obtain single and multiple mutants of specific effectors in Xam CIO151. The mutants were inoculated in the susceptible cultivar of cassava MCOL2215 and symptoms were tested 15 days post-inoculation. ΔavrBs2, ΔhpaF and ΔxopZ showed a reduction in virulence but ΔxopN had no effect on virulence when compared to the wild type. The mutation effects were tested on additional Xam strains, which are representative of the bacterial diversity present in Colombia, and similar results were obtained. These results are critical in the elucidation of the role of type three effectors in Xam virulence and could be useful for the development of durable and sustainable resistance to CBB in cassava.
A molecular epidemiology study of Begomoviruses involved in Cassava Mosaic Disease (CMD) was conducted around Yangambi in North-Eastern DR Congo. Incidence and disease severity were systematically evaluated and compared to results from targeted PCR and sequences obtained from cassava, as well as legumes and whiteflies collected in the visited fields. The results showed that CMD-associated viruses are widely distributed throughout the investigated area. Dual infections were common (66%) in which both ACMV and EACMV species were present. EACMV-UG was predominant in highly infested fields. Sequence analysis showed a rather distribution related to the type of environment in which cassava is grown. The virus isolates were related to the principal ecosystems: moderate severity isolates were found close to the humid forest in which agricultural activity is not intensive and the severe isolates are limited to the secondary forest, in which the cassava is grown more intensively. EACMV isolates are randomly spread through each of the main agro-ecologies. Two virus species were frequently found in whiteflies (59%). The various whitefly biotopes and the season-long presence of cassava make it a region of special interest for studying the spread and development of CMD. Therefore, knowing the constant evolutionary process of begomoviruses, our study focused on the potential contribution of forest plants species to the emergence of different viruses: ACMV and EACMV were detected in two leguminous Fabaceae species (Centrosema pubescens and Pueraria javanica). The wide presence of EACMV-UG and the high incidence and severity of CMD demonstrate that this part of DRCongo continues to be affected by the CMD pandemic.
Cassava are both food and energy crops. Diseases and insects are the major obstacles for cassava production in Thailand. Cassava bacterial blight disease caused by Xanthomonas axonopodis pv. manihotis affecting cassava are currently the major losses of cassava production. The use of resistant varieties for disease prevention is the most effective method. This research is aimed to screen cassava varieties for resistant to cassava bacterial blight disease in the greenhouse and brown leaf spot disease resistant. The severity of disease symptoms were used for assessing the level of disease resistant. The evaluation of cassava germplasm core collection was received from CIAT (International Center for Tropical Agriculture) from 2001. We planted cassava among 2006 – 2010 at Rayong Field Crops Research Center (RYFCRC), Department of Agriculture (DOA) Thailand. The evaluation of cassava bacterial blight caused by Xanthomonas axonopodis pv. manihotis in green house condition inoculated by clipping method under 80 % relative humidity at room temperature. Check the disease severity 1 to 5, every seven days for two months. The results show that, relatively resistant to cassava bacterial blight 3 varieties (MCUB 23, CR 19 and MARG 2), moderately resistant 18 varieties, moderately susceptible 209 varieties and susceptible 244 varieties. The evaluation of cassava brown leaf spot disease (Cercosporidium henningisii ) in field condition. Check the disease severity at the age of 5 months to 12 months every 2 weeks. The evaluated was show that, relatively resistant to cassava brown leaf spot disease 165 varieties, moderately resistant 360 varieties, quite susceptible 1 variety (MCUB 56).
Cassava accounts for up to 60% of the daily calorie intake in sub-Saharan Africa. However, a major constraint to cassava cultivation is the 30-50% yield loss due to cassava mosaic disease (CMD). CMD is caused by several circular ssDNA cassava begomoviruses (CBVs), including African cassava mosaic virus (ACMV); East African cassava mosaic virus and South African cassava mosaic virus (SACMV), found to be endemic to southern Africa. Current strategies for obtaining resistance to CMD are through genetic engineering. The aim of this study is to develop CBV resistant transgenic cassava, based on RNA silencing induction via a pathogen derived resistance mechanism. Mechanism involves transgenic expression of virus-derived hairpins to generate siRNAs that target homologous viral sequences for degradation. The most efficient and reproducible transformation system for cassava is Agrobacterium-mediated transformation of friable embryogenic callus (FEC). In this study, cassava FEC from model cv. TMS60444 and South African land race T200 were transformed with various viral gene silencing constructs derived from selected sequences within the AC1/4 and AC2/3 open reading frames of EACMV, ACMV and SACMV. FECs were co-cultivated with Agrobacterium LBA4404 transformed with pCambia 1305.1 harboring the various constructs. Regenerated plants with single or double transgene copy were selected and Agro-infected with CBVs. Leaf material was collected and symptom severity scored at 12, 32, 55 and 67 days post infection. Viral load will be determined.
Manihot esculenta crantz is a worldwide cultivated crop, an important source of nutrients and a raw material for starch production, compromised by the causal agent of Cassava Bacterial Blight (CBB), Xanthomonas axonopodis pv. manihotis (Xam). Bacterial pathogenicity often relies on the injection into eucaryotic host cells of effectors proteins, via a type III secretion system, a molecular mechanism poorly investigated in cassava-pathogen interaction studies. In Xam, only one gene associated with pathogenicity has been reported: pthB. It belongs to the Transcription Activator Like (TAL) effectors family which interact directly with DNA promoters modulating the expression of target host genes to the benefit of the invading bacteria.Here, we aim to understand the function of pthB trough the pathogenicity of Xam and therefore, identify cassava genes expression modified upon Xam infection. Until now, bioinformatic programs to find TAL targets and two RNAseq experiments comparing cassava plants challenged with Xam vs. Xam ΔpthB have been done, leading to the experimental validation of 30 candidate genes trough semicuantitative and qRT PCR. Those results, together with the transcriptomic data, will constitute an important tool for a better understanding of CBB, its control and an informative way for understanding other cassava-pathogen interactions.
Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) constitute the most formidable threat to cassava (Manihot esculenta Crantz) productivity in African continent. Effective management of CMD and CBSD depend very much on ability to diagnose them and their causal viruses efficiently, accurately and timely at low cost. In sub Saharan Africa capacity to diagnose CMD and CBSD is limited by deficiencies in array of interrelated factors. In 2008 we imitated a project aimed at enhancing the capacity of National Cassava Programs in Tanzania, Kenya, Uganda, Malawi, Rwanda, Mozambique and Zambia to develop diagnostics tools to effectively implement CMD and CBSD management programs. From 2008 to 2012, cassava virus disease diagnostic capacity in terms of human and infrastructure has been significantly enhanced in the project countries. NARs scientists have been trained on various cassava disease diagnostics. Various molecular laboratory disease diagnostic equipments were procured and delivered to NARs labs. As a result of these, cassava mosaic begomoviruses and cassava brown streak viruses as well as their associated vector, Bemisia tabaci have been identified and characterized using standardized and harmonized molecular tools. Cassava disease prevalent and virus distribution maps have been generated by NARs scientists to inform sustainable disease management strategies including provision of support to cassava seed systems and conventional breeding programs.
Farmers in Rwanda still grow local cassava cultivars that are susceptible to cassava mosaic disease (CMD) for a variety of reasons including certain consumer preferred product characteristics. A need was recognized to develop cultural methods to manage CMD on these popular cultivars. An experiment was conducted to study the effect of intercropping a local CMD susceptible cultivar on CMD severity. The experiment was conducted for two seasons from 2008 to 2010 at Rubona Station of the Rwanda Agriculture Board in the Southern Province of Rwanda. Two cassava varieties, Creolinha (local CMD susceptible) and TME 14 (Ndamirabana, improved CMD resistant) were grown. Cropping treatments were; Cassava + bean (for each cassava cultivar), Cassava + maize (for each cassava cultivar), Cassava + bean and maize (for each cassava cultivar), maize and beans, Cassava (for each cassava cultivar), Maize and Beans. The experiment design was randomized complete block design with four replications. The experiment relied on natural infestation of whiteflies. Whitefly populations and CMD severity on cassava were recorded once a month until cassava crop harvest. Intercropping with beans or maize, or both beans and maize reduced CMD severity on the susceptible variety Creolinha but had no effect on the CMD resistant variety TME 14. Therefore cassava intercropping with beans and maize may be employed to reduce CMD severity and cassava crop loss due to the disease in susceptible varieties.
Cassava is an important crop in sub-Saharan Africa. Its production is constrained by diseases & pests e.g. cassava mosaic disease (CMD) whose yield losses has been reported in Uganda since its outbreak in 1990s. Trials to assess yield losses attributed to CMD in Uganda were established in 2005-2007 using ten popular landrace and four improved cassava cultivars. For each cultivar, symptomatic and asymptomatic stems were picked and planted in equal numbers in Randomised Complete Block Design with four replicates. Plots were split between asymptomatic and symptomatic cuttings in a net plot. All plots were treated with Imidacloprid and Cypermethrin to control whitefly vector and prevent CMD spread. CMD symptoms were assessed monthly till harvest. Yield data was recorded at 12 months for root number and root fresh weight. The study measured the effect of severe CMD and compared yield losses on the landraces and improved cultivars, which were checks. CMD severity was highest in the landraces and low in the improved cultivars for both initially symptomatic and asymptomatic plants. CMD severity ranged from 3.3 – 4.1 in the landraces and 2.2 – 2.8 in the improved cultivars for the initially symptomatic plants and from 2.4 – 3.2 in the landraces and 2.0-2.6 in the improved cultivars for the initially asymptomatic plants. More roots were produced by initially asymptomatic than the initially symptomatic plants. Landraces had higher yield losses (25-91%) compared to 6-45% for improved cultivars and suggests that improved varieties are still better for yield and disease resistance while some landraces are still good and suggests why they are still popular with farmers.
An exploratory analysis was conducted on data from 43 cassava clones in a multi-location uniform yield trial at five benchmark sites in Nigeria in 2008 and 2009 to evaluate the number of top yield clones with apparent or real resistance to cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis. Results showed that two clones were resistant to CBB at Ibadan location only though with poor fresh root yield, and majority of clones were susceptible (53% of clones at Ibadan, 88% at Ikenne, 100% at Mokwa, 86% at Ubiaja, 88% at Zaria). Results further confirmed that CBB resistance is negatively correlated to fresh root yield, and fresh top yield. This paper calls for the need to appropriately review CBB assessment in breeding schemes and an appropriate breeding methodology that selects CBB resistance and stable yield, utilized in ensuring that cassava clone released to farmers do not constitute more threat to food security.
Cassava bacterial blight (CBB) and cassava green mite (CGM) were two major biotic threats to cassava production in Nigeria between 1970 to late 80s. However, increased resistance breeding and adoption of improved varieties by farmers in years that followed helped in drastically reducing the impact of both constraints. Recent field observations across the country showed a possible repeat of the 1970 – 80 experience, hence the need for renewed priority attention to CBB and CGM in cassava breeding programme. In this study, we evaluated a total 449 cassava genotypes comprising of 256 landraces or genotypes developed at the National root Crop Research Institute (NRCRI) and 183 breeder lines from the International Institute of Tropical Agriculture (IITA) for resistance to CBB and CGM under field conditions. Of the 449 genotypes evaluated, 114 genotypes (25.4%) comprising of 59 landraces and 55 improved/breeders lines were resistant to CBB. Resistance to CGM was observed in only 73 genotypes (16.3%) comprising of 50 landraces and 23 improved/breeders lines. There was no correlation between CBB and CGM in the evaluated genotypes. However, a total of 7 genotypes comprising of 1 landrace and 6 improved lines had neither CBB nor CGM symptoms throughout the study.
In 1999 a shortage of cassava in Côte d’Ivoire led to a price increase of cassava products in the country. There was no epidemic of Cassava mosaic disease (CMD) in the country at that time, but disease symptoms were unusually severe on infected plants. Our investigations revealed an increasingly complex picture of CMD. We showed evidence for synergism and natural trans-replication that took place between the two geminivirus species, African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV). Secondly, we demonstrated how the synergistic interaction and the inter-species recombinations between ACMV and EACMV have contributed to the emergence of new geminiviruses associated with the extremely severe CMD symptoms observed on cassava plants in Côte d’Ivoire. Thirteen years later, the cassava situation has significantly worsened. Cassava is no longer an “all sufficient food” because its products are no longer accessible to underprivileged communities. Despite its importance as the major staple food in Côte d’Ivoire, Cassava remains an orphan crop to the Ivorian research community and government arenas. We hope to change this situation from the bottom up, by jumpstarting cassava research in the country, by establishing a teaching laboratory at the University of Cocody and by building a University owned cassava research extension center in the outskirt of Abidjan, in one of the most important cassava-growing region of the country. This strategy and other ideas will be discussed.
Tuber rot of cassava is causing yield losses up to 50% in the Southern regions of India. It was identified that the causal agent is an Oomycetes fungus, Phytophthora palmivora. The disease is characterized by brown watery lesions in the tuber with foul smell making it unpalatable. Symptoms are usually noticed only at the time of harvest as there are no above ground symptoms. Rainy season and water logged conditions favor the spread of this pathogen. Pathogen isolation was done using healthy cassava tuber slice as bait and transfer of mycelia to water agar. Carrot agar supported the maximum growth rate of the pathogen at temperature 26±2°C. Sporangia were papillate and ovoid with a short pedicle. The virulence assay by artificial wound inoculation on tubers reproduced symptoms at field conditions. All isolates were highly aggressive. The internal transcribed spacer region (ITS) of the ribosomal DNA sequence analysis showed 99% similarity with other P. palmivora isolates. Though amplified fragment length polymorphism analysis yielded high level of polymorphism among the isolates, cluster analysis did not show any correlation with the geographical area of collection. Our study is the first report on molecular characterization of this pathogen. The present study will pave the way for further studies to understand the population genetic structure, phylogeography, and molecular ecological studies of this destructive pathogen.
Cassava (Manihot esculenta Crantz.) is a major root starch crop grown in India, were it is widely cultivated in Kerala, Tamil Nadu, Andhra Pradesh, Maharashtra and few North Eastern states for food and industrial purposes. Indian cassava mosaic disease (ICMD) is an important disease of cassava and a serious constraint to cassava cultivation. Two viruses cause the disease, Indian Cassava Mosaic Virus (ICMV) and Sri Lankan Cassava Mosaic Virus (SLCMV) with SLCMV now emerging as the dominant virus in Cassava regions. In Indian cassava genotypes, there is limited scope for natural resistance against geminiviruses and hence we investigated the possibilities to use virus derived sequences for development of transgenic resistance in this significant crop. RNA mediated resistance through expression of inverted-repeat dsRNA sequences derived from the virus genome and expression of artificial microRNA expressing short virus sequences from miRNA precurses have recently been proven effective for induction of virus resistance (immunity) against a number of RNA viruses. In contrast, these RNA interference strategies never resulted in immunity of transgenes against geminiviruses. However, it suggests that viral mRNA is target of RNA silencing and that the success of the strategy might depend on the relevance of the target gene for systemic spread of the virus. We have generated a number of gene constructs (artificial micro RNA, inverted repeat sequences of Rep/ TrAP/ gene chimera) to induce resistance against cassava mosaic viruses from India viz., ICMV and SLCMV. Since robust transformation and regeneration methods for cassava are not yet available, all constructs were transferred for transgene expression to Nicotiana benthamiana a susceptible host plant SLCMV and ICMV. Screening of transgenic N. benthamiana carrying amiRNA constructs and inverted repeat constructs by inoculation with SLCMV resulted in a variety of plant responses ranging from susceptibility to resistance. To reach virus resistance against both viruses, ICMV/SLCMV, using a single amiRNA construct was not successful. Several inverted repeat constructs were chosen for further testing in cassava. Transformation of the high starch cassava cv.H226 which is highly susceptible to ICMV/SLCMV is now well underway and at different stages of selection. Results from the transgene experiments to generate virus resistance in N. benthamiana against ICMV/SLCMV will be shown and methods to evaluate the efficiency of RNAi gene constructs by transient gene expression assays in N. benthamiana will be discussed.
Equal to the economic importance, heavy yield loss in cassava was caused by various pathogens and leading to starvation. P. palmivora is causing cassava tuber rot in Southern regions of India which accounts for yield losses up to 50% and thus pose as a serious threat to successful cassava cultivation. The disease is characterized by brown watery lesions in the tuber leading to rot of the tuber with foul smell making it unpalatable. Rainy season and water logged conditions worsen the situation. Symptoms are usually noticed only at the time of harvest because there is no above ground symptom on the foliage or stem. Pathogen isolation was hindered by contaminating population due to the rot condition of the tuber. We used healthy cassava tuber slice as bait and transfer of mycelia to water agar greatly reduced the bacterial contamination. The method was most successful in isolation the pathogen without use of chemicals. Carrot agar supported the maximum growth rate of the pathogen and the temperature 26±2°C was found to be optimum. Sporangia were papillate and ovoid with a short pedicle. The virulence assay was carried out in cassava tuber by artificial wound inoculation method and the symptoms were same as field samples and Koch’s postulates were fulfilled. All isolates were highly aggressive. The internal transcribed spacer region (ITS) of the ribosomal DNA was amplified and the sequence analysis showed maximum similarity (99%) with other P. palmivora isolates. Further amplified fragment length polymorphism (AFLP) analysis yielded high level of polymorphism among the isolates. Cluster analysis did not show any correlation with the geographical area of collection. Since the first report of the disease with phenotypical characterization, our study is the first report on molecular characterization of the pathogen. This is the only report available on cassava tuber rot in India. The disease poses serious threat to the cassava growing regions causing heavy economic loss to the farmers. More attention needs to be paid on controlling the pathogen and also the spread of the disease to other areas. The present study will provide pavement for the further studies to understand the population genetic structure, phylogeography, molecular ecological studies.
Xanthomonas axonopodis pv manihotis (Xam) is the causal agent of cassava bacterial blight, a disease that represents the most limiting problem in this crop. In Colombia, the population structure of Xam was characterized during the 90s. In those studies, processes of pathogen migration and concomitant high diversity index were detected in different regions of the country. With the aim to characterize the current population structure of the pathogen, sampling collections were carried out during the last four years in the Caribbean coast and Eastern plains of Colombia. Xam isolates were characterized using AFLPs. Clustering and population analyses were performed to determine possible distribution patterns of the pathogen. Additionally, genes encoding for the Type Three Effectors (T3E) were sequenced to establish their degree of variability and to assess the presence and nature of potential selection pressures exerted by the host. The AFLPs results show a more diverse and complex population structure of Xam in the Colombian Caribbean coast than in the Eastern plains. On the other hand, a low variation was detected on the T3E genes possibly indicating their importance in pathogenesis. However, most of the isolates that were completely discriminated by AFLPs were also discriminated by the sequences T3E-encoding genes. This study shows a broad overview of populations of Xam in Colombia and it will contribute to improve the existing bacterial blight control practices.
In spite of its economic importance, cassava is one of the least researched among the major crops of the world and the potential for genetic improvement is considerable. Identification of genomic regions underlying traits of interest is a key step in any crop’s improvement but for cassava, this has been rather slow process due to lack of genomic resources and high levels of heterozygosity and clonal propagation system. However, recent advances in sequencing technologies (and the dramatic reduction in costs) has sets the stage for employing modern and more powerful tools to study the genetic architecture of economically important traits in the crop. Genome-wide association study (GWAS) is increasingly being adopted as a more efficient method of finding genes of interest by exploiting existing linkage disequilibrium in a sample of unrelated individuals. GWAS overcomes some key limitations of traditional bi-parental QTL mapping by (i) sampling broader germplasm base to uncover more QTLs and alleles, and (ii) providing higher resolution, often to the gene level and (iii) circumvents the time-consuming process of creating mapping populations. We have recently genotyped-by-sequencing a set of 652 clones representing important breeding lines of IITA, most of which are accompanied by historical phenotypic data from multi-location and multi-year trials. This germplasm set is also being used a training population for a genomic selection project that is being implemented by Cornell University, IITA, NRCRI-Nigeria, and NaCCRI-Uganda. We performed GWAS on this set of germplasm using more than 4000 SNPs distributed across 607 unique cassava genome scaffolds starting focusing on four traits: quantitative resistance to cassava mosaic disease, dry matter content, root-number and pro-vitamin A content. Strong associations between SNP markers and these traits were identified, after accounting for the effect of population structure, and most of these SNPs co-located with previously mapped QTLs as well as genes that are known to influence these traits. We demonstrate that GWAS is a viable approach for high-resolution and efficient mapping of QTLs and genes of interest in the clonally propagated cassava.
The availability of genomic resources enables the application of modern genomics-based approaches to cassava breeding and conservation. Here, single nucleotide polymorphic (SNP) markers are identified and validated and used to detect quantitative trait loci (QTL) associated with tolerance to cassava brown streak disease (CBSD) in the variety ‘Namikonga’. Sequence profiles of expressed sequence tags (ESTs) from three EST sequencing initiatives were combined and filtered on sequence quality. Quality sequences were aligned and embedded in a Windows browser called HarvEST:Cassava which consists of a Unigene set of 22,903 sequences. From these 2,954 putative SNPs were identified. Of these, 1,536 putative SNPs were selected for validation using Illumina’s GoldenGate assay across an array of 53 genotypes. As a result 1,190 SNPs were validated. These SNPs were converted to KBioSciences KasPAR platform. These SNPs, together with SSRs were used to genotype an F1 mapping population between ‘Namikonga’ and ‘Albert’ generated specifically to identify QTL associated with CBSD tolerance. Linkage analysis resulted in a map of 1,837 centi-Morgans (cM) containing 568 markers (434 SNPs and 134 SSRs) distributed across 19 linkage groups. The mapping population was phenotyped over two years for root necrosis and the data analysed with genotyping data to identify QTL. One significant QTL was detected, representing 27% of the variation. A number of smaller QTLs were also detected. The major QTL is currently being validated for use in marker-assisted selection. It is anticipated that the EST database, SNP resources and genetic linkage map will find several applications in the improvement of cassava.
Cassava originated and domesticated in central Brazil in more than 7000 years becoming a so important crop with extraordinary starch yielding and extremely tolerance to drought and barren soil conditions. Genetically, cassava is highly heterozygosity bottlenecked the conventional breeding. In the study, wild ancestor species and cultivars with significant difference in tuber root yield, starch content and reproductive habits were used for whole genome sequencing with the next generation sequencing technology to illustrate the molecular evolution and discover valuable genes in genome and transcriptomic level. Two reference genomes, W14 and KU50 have been assembled with over 70% coverage of genome in size and 97% coverage of gene regions, respectively. An integrated genetic map was constructed by merging contigs, BAC based physic map, BAC end sequenced, chromosomes in situ BAC located and molecular marker linkage maps.
It is revealed that cassava genome is still in higher heterozygosity with self SNP frequency of 1/257 bp for wild species W14 and 1/286 bp for cultivar KU50. There are complicated diversities among W14, KU50 and AM560 (a cultivar selfing S3 generation sequenced by JGI) and it is shown that diversity decreasing in evolution from ancestor to cultivar according to variation evident of SNPs, Indels and Repeats. Large amount of SNPs among wild species and cultivars has been released which available to genotyping and MAS breeding.
Findings relative to special pathways on starch accumulation and drought tolerance were deciphered by deep annotation of genome/transcriptome and verification among 4 genotypes. Some of key genes encoding important enzymes in starch metabolism, carotene biosynthesis as SuSy, INV, PPDK, ADPG and ALDO have been identified in tuber root of cassava. Meanwhile, a series of miRNAs and their targets of mainly transcription factors, signal receptor proteins etc. have been elucidated play important role in cassava adaption to drought and cold stresses. Comparative genomics analysis among cassava, Jatropha and castor bean in Eurphorbiceace found coherence of gene divergence in the most of the biological process and the unique gene families in each species.
Genome sequence, BAC library, starch metabolism, drought tolerance, miRNA
Cassava is an important tropical crop for food security, income generation and industrial application in many Asian and African countries. Despite the global importance of cassava and current global issues such as food crisis and climate changes, there has been little investment in improving cassava production through advanced breeding technology. Here, RIKEN group has developed the following integrative cassava functional genomics platform for the global cassava research community to advance cassava molecular breeding in collaboration with International Center for Tropical Agriculture (CIAT), Mahidol University and Agricultural Genetics Institute (AGI): 1) Full-length cassava cDNA resources (KU50, ECU72 and MPER417-003), 2) High-informatic ESTs using high-throughput sequencers (ECU72, MPER417-003, Huay Bong 60 and Hanatee), 3) Integrative cassava database of international standard, 4) Cassava oligoarray analysis platform containing more than 30,000 genes, and 5) Genetic transformation system in elite Asian cultivar, KU50. These tools will accelerate cassava molecular breeding for high yield and high value cassava in Southeast Asia.
Virus induced gene silencing (VIGS) is a powerful tool to study gene function of unknown plant genes and to induce co-suppression by RNA interference with replicating RNA viruses. The expression of genes or gene fragments via VIGS permits gene function analysis and the study of candidate genes in a simple, fast and robust method prior or as an alternative to the transgenic approach. We have constructed a geminivirus VIGS vector from the genomic DNA A and DNA B components of an East African cassava mosaic virus, cloned within the left and right boarders of a binary vector. The gene to be studied is introduced into the recombinant DNA A genome replacing the viral coat protein which is dispensable for movement in planta. Upon plant inoculation and during infection, the recombinant virus expresses the foreign gene “fragment” and induces the degradation of a homo-/orthologous gene by RNAi. If an endogenous gene is targeted, an altered mutant phenotype resulting from ‘gene knock-outs‘ allows assignment of function to unknown genes. By using the VIGS approach, aspects of interference into the replication of non related viruses and to induce virus resistance in cassava are studied. The definition of minimal sequences for gene silencing and the expression of artificial micro RNA constructs with the VIGS vector are presented to discuss the scope of the method.
Whiteflies (WF) are the major biotic stress that threatens the sustainability of staple crop, including cassava, causing direct damage due to feeding and can obliterate the entire cassava crop. High WF population densities are a key factor in cassava mosaic and cassava brownstreak virus epidemics in Africa. Twelve WF species are serious pests of cassava being the most important Aleurotrachelus socialis (LAC) and Bemisia tabaci (Africa). One of the most potent resistance mechanisms to WF was discovered at CIAT. Wild cassava and several M. esculenta cultivars originating from Ecuador and Peru display significant resistance to WFin the field. On the resistance line, MEcu 72 WF deposit fewer eggs, establish fewer feeding sites, nymph development is delayed, and WF mortality is increased. Two approaches were proposed to unravel the genetic mechanism of white fly resistance (WFR). First, a gene expression profiling, using microarray technology, coupled the subtractive libraries approach. The aim was to capture genes that were diffentially induced during WF attack. Second, the QTL mapping aproach analysis using a segregating popultion between MEcu 72 and MCol 2246 (susceptible to WF). Microarrays technology on challenged and non-challenged WF resistant/susceptible subtractive libraries, as well as, on the 5000 cassava unigen microarray were used to identify differentially expressed genes in cassava during A. socialis attack. The results showed 405 sequences induced by A. socialis at different stages of their life cycle. Based on analysis using the Gene Ontology (GO) and the Arabidopsis thaliana (TAIR) databases, these sequences falled into biological process like defense, cell wall modification, oxidative burst, signal transduction, transport, primary metabolism and photosynthesis. Some of these sequences are part of the signaling pathways regulated by jasmonic acid (JA) and ethylene (ET), which are implicated in the defense response during pathogens and herbivores attack to plants. Our results suggest that WFR is a complex trait, in which more than one genetic region may be involved. To unravel the mechanism of resistance to WF and define the genetic regions involve in the resistant response against A. socialis attack, we propose to take the QTL mapping approach to identify the genetic basis for cassava’s quantitative resistance to A. socialis. This WFR can be used in molecular breeding to accelerate the development of WFR cassava cultivars with field attributes valued by smallholder farmers in Latin America. By understanding the mechanism of resistance to A. socialis, our studies may lead to strategies that will confer resistance to other WF species that today decimate cassava in Africa and Asia. This resistance could also be transferred to plants that serve as WF refuges near cassava plantings, thereby limiting WF population expansion
Illumina deep sequencing technique is a powerful tool for plant biologists to define the plant transcriptome in detail. Except monitoring the genes expression in a quantitative way in a single tissues or cell types, this technique can also be used to globally define the transcription starting site, polyadenylation signals and the possible alternative splicing sites. Utilizing this technique, we successfully examined the photosynthetic differentiation along a developing maize leaf and laser-capture microdissection to profile bundle sheath and mesophyll cells. We observe that 64% and 21% of genes are differentially expressed along the developmental gradient and between mature mesophyll and bundle sheath cells, respectively. Cluster analysis of the data reveals an extremely dynamic transcriptome, with transcripts for cell cycle, primary wall synthesis and basic cellular metabolism at the leaf base transitioning to secondary cell wall biosynthesis and C4 photosynthetic development towards the tip. We also use this technique to monitor the transcriptome changes among the cassava tuber roots developments. The preliminary data indicates a dynamic change of developmental and carbon metabolism related pathways.
The regulation of cassava storage root formation in 4 month-olds roots by Yang et al. (2011) mainly regulated by key enzymes in glycolysis/gluconeogenesis and starch metabolism pathway. However, there are still large gap in our understanding of gene regulation during initiation and early storage root development. Transcription profiling of fibrous, intermediate (dia<0.5cm), and storage root (dia>1cm) at 8 week-olds was investigated using a 60-mer-oligo microarray representing 21,500 expressed genes. The 2,206 genes were highly expressed and only 1,547 genes were annotated in 400 enriched GO terms. Functional analysis showed that significant key processes in intermediate root were developmental, macromolecule metabolism, protein translation and modification processes. Homeostatic, lipid and amino acid metabolism, catabolic, cell cycle, cell death, and external stimuli response were key regulated processes in storage root. Transcription and gene expression were key regulated processes during transition stage from fibrous to intermediate root, while homeostasis and signal transduction were key processes during transition stage from intermediate to storage root. Sets of transcription factors expressed during transition stage will be further analyzed.
Cassava is an important tropical crop with characteristics of high photosynthesis and powerful starch accumulation. And sucrose transportation throughout loading from mesophyll cell to phloem in leaf, long distance movement to unloading from phloem to storage cell in tuber root is key step coordinating source, flow and sink. In this study, Two genotypes, Arg7 and W14 significant different in starch accumulation are used for uncovering sugar loading and unloading mechanism in cassava. It is shown that sucrose is the main form of transport from leave to tuber roots, and there are different sucrose loading and unloading models in cassava based on structural, physiological and expression analysis of SUTs. In leaf, Sucrose loading rely on apoplast transport of SUTs, and SUT1 and SUT2 play more important role than SUT4, and still have symplast transport identified by few distribution and function of plasmodesmata between sieve element-companion cell (SE-CC) compplex and neighboring parenchyma cells. In tuber roots, sucrose unloading mainly depend on symplast transport with large amount of plasmodesmata, and apoplast transport play a minor role with less expression of SUTs. Combining 14C-labeled autoradiography and fluorescein footprinting, and subcelluar localization of SUTs would further confirmed the comparative function of the apoplast and symplast in phloem loading and unloading. These output could provide directions for breeding of high starch varieties.
The Integrated Breeding Platform (IBP) of the CGIAR Generation Challenge Programme (GCP) provides information, analytical tools and related services to plant breeders to design and conduct modern breeding programs. It is intended to boost crop productivity for smallholders in drought-prone environments by exploiting the economies of scale afforded by collective access to modern breeding technologies and informatics tools. The IBP is being developed in collaboration with 14 initial ‘user cases’ – breeding projects for eight crops in 32 developing countries. This ensures IBP development is driven by breeder needs. Primary access to the IBP is through the web-based, user friendly Integrated Breeding Portal (https://www.integratedbreeding.net/). The portal provides access to valuable crop breeding information, trait dictionaries and SNP information. It enables convenient and cost-effective access to breeding services, including useful genetic resources, and quality high-throughput genotyping facilities. The Platform provides purpose-built informatics tools to support breeding logistics, data management, data analysis and decision modelling, as well as open-access third party tools which are all accessible through the portal. The portal also provides tools and online space for the development and support of crop-based communities of practice that promote application of molecular breeding techniques. A multi-year comprehensive training programme supported by the platform is designed to help overcome technical and human resource limitations to integrated breeding in developing countries.
Genotyping-by-sequencing (GBS) uses next generation sequencing, restriction enzymes, and barcoded multiplexing to cost-effectively score large numbers of genetic markers. These markers can then be used to perform genomic selection on Cassava, thus shortening the breeding cycle. To generate a genotypic data set for a test of genomic selection in cassava, we have collected GBS data for a set of 626 clones from IITA’s Genetic Gain population, a set of important clones from IITA’s breeding program. 96-plex GBS libraries were made from PstI-digested DNA and sequenced on the Illumina HiSeq, one lane per library. Over 5000 SNPs in about 900 scaffolds were identified using an analysis pipeline that aligned the GBS reads to the cassava reference genome sequence. After filtration for missing data, departure from Hardy-Weinberg equilibrium, etc., between 1000 and 4000 SNPs remained in the data set, depending on the criteria. We are also testing other restriction enzymes to see if we could improve the distribution of read depths. Over twice as many SNPs were called from ApeKI libraries, and read depth was much less skewed. We continue to optimize the GBS library construction, SNP calling, and SNP filtering in cassava.
The genetic factors responsible for diversity in storage root of cassava are being studied by several groups. The few available studies is disperse and are not sufficient to accurate predictions of genetic determinant or regulation on the large diversity recently observed in our laboratory. With a functional genomic’s based approach, the high throughput microarray technology sounds to be appropriated to gain information at global level to identify differentially expressed genes among landraces of divergent genetic background. To date, most efforts using microarrays to study cassava has been focused on expression profiles with restricted genetic background oriented to diseases, abiotic stress and post harvest physiological deterioration. In addition, it has also been claimed that cDNA chip developed for Euphorbiacea family, based on two species (leaf spurge and cassava), may be a useful tool to study gene expression analysis and diversity in cassava at a global base. Here used microarray data to analyze genetic divergence among cassava landraces representing world germplasm collection representative from CIAT and landraces from Amazon. Out of 161 transcripts, differentially expressed among 9 representative accessions, we identified unique sub set of transcripts related to pigmented, sugary, commercial and Colombian landraces. By focusing on regulatory genes and using Sub Network Enrichment Analysis (SNEA) we identify putative biological pathways that differentiate pigmented and sugary cassava from normal and commercial cassava.
Molecular evolution of a crop has relied predominantly on sequence information in order to model the evolutionary history of genes that determine plant speciation and domestication as well. Phylogenetic trees are based on alignment of DNA or protein sequences, from which evolutionary distances between genes can be inferred. However, while a phylogenetic tree models the history of gene duplication events, it does not, by itself, reflect the evolution of gene function. As more is learned about the regulatory and structural complexity that dictates gene/protein function, it is becoming increasingly clear that additional non-sequence information is important to consider for a more complete understanding of the evolution of function in gene families. A gene’s transcriptional profile may contain critical characteristics of function, including when and where a gene is expressed, and the conditions under which gene expression is manifested. These regulatory properties may be crucial in explaining the key functional differences between related genes whose functions cannot be distinguished from sequence alone, and thus more adequately reflect the functional diversity achieved within gene families. Due to the complexity and diversity of factors influencing gene regulation, sequence-based prediction of a gene’s regulation remains a premature goal. Microarray technology allows for a direct, quantitative measurement of transcriptional response to a given environmental or genetic factor, and is currently the most useful experimental source of large-scale gene expression data. The integration of genomic and transcriptomic data is providing an increasingly detailed picture of molecular evolution by incorporating regulatory behavior into models of the evolution of gene expression and function. Here we report our first step toward understand changes of gene expression to model gene evolutionary function using our cassava domestication model that relies on changes in growth habit, storage root formation and flowering set traits in the cassava ancestor.
Heat shock proteins (HSPs), in plants, are distributed in cytoplasm, endoplasmic reticulum and plastid and are involved in several cell processes presenting simple and multifunctional activities. In our laboratory we are exploiting genetic diversity harbored in pigmented and sugary mutations of cassava to identify heritable variation in genes coding for HSPs in non-green tissue. Here we present contrasted expressed genes that were mined in our Root Expressed Gene Data Base (REGDB), in collaboration with ARS_Fargo, North Dakota, USA. Over 24400 unigenes were analyzed showing two major groups of HSPs. A cytoplasmic/endoplasmic reticulum group associated with high glucose content in the sugary phenotype and a plastidial group associated with carotenoid accumulation in pigmented cassava. Pearson correlation analysis between carbohydrates content and transcript levels showed a total of 66, 111 and 131 transcript significantly correlated with sucrose, glucose and starch content respectively. A total of 467 genes were correlated with b-carotene. Specific transcripts levels resultant from the correlation study showed that HSPs with chaperone functionalities and DNAj protein type, present in cytoplasm of plant cells, showed very high levels of expression in sugary cassava then in normal cassava. For the case of pigmented cassava, the high b-carotene content landrace always showed high level of transcript corresponding to at 18 HSPs belong to the small HSP family.
The typically low root protein content of cassava increases the risk of protein malnutrition in communities relying on it as a staple. Nitrogen assimilation is the first step in protein metabolism and is catalyzed by the enzymes glutamine synthetase (GS) and glutamate synthase (GOGAT). The GS gene family consists of cytosolic GS1 and chloroplastic GS2 while the GOGAT gene family consists of NADH-dependent GOGAT (GLT) and Ferrodoxin-dependent GOGAT (GLU). The current work was undertaken to develop understanding of the molecular features of these gene families in cassava. Transcript sequences of GS and GOGAT genes for A. thaliana were used to query public databases of cassava and other crops for homologues. Multiple alignments and phylogenetic analysis of the homologous sequences were done using online bioinformatic resources and promoter analysis performed using the promoter regions of cassava GS/GOGAT genes. Primers were designed for these genes and total RNA extracted from 3 month-old in vitro cassava plants of cultivars TMS 60444, P1/19 and AR9-2 to test expression of GS/GOGAT genes in leaves, stems and roots using quantitative RT-PCR. Phylogenetic analysis revealed a distinct difference in cassava GLU gene (MeGLU), which did not cluster with other GLU genes from the other crops. Promoter analysis identified predominantly light induced cis-regulatory elements. Transcript quantification further suggested differential tissue-specific expression of GS/GOGAT genes in the three genotypes tested. This study confirms the tissue-specific expression of GS/GOGAT genes in cassava, which has been well documented in Arabidopsis. The structural differences in MeGLU genes need to be studied further to determine how the observed difference would affect protein metabolism in cassava as compared to other crops.
This study is trying to establish the methodology to determine methylation on cassava genomic DNA. The Methylation-Sensitive Amplified Polymorphism (MSAP) could be observing through changes of pattern cleavage of CCGG sequence by Msp I and Hpa II isoschizomers enzymes. Cuts based on 5-methyl occurrences on cytosine position (inner or outer position) on target sequences allow differentiating epigenetic pattern between a control and cryopreserved sample. Preliminary data show a balance between “de novo” and demethylation occurrences. The bands sequentiation, at different methylation levels (1/1, 0/1, 1/0) are developing. With this information it will compare to GenBank to figure out which pathway/genes could be involved in the response (turn on or turn off).These works open a new application of this technique in cassava under different stresses/treatments.
Cassava is an important food crop in sub-Saharan Africa where its production accounts for >50% of the worldwide output. Its production is affected by cassava brown streak disease (CBSD) that is rapidly spreading in Eastern Africa and great lakes region. By exploiting existing sources of resistance a study was undertaken to map quantitative trait loci (QTL) for CBSD tolerance using an F1 mapping population from a cross between Namikonga and Albert. The mapping population was screened against CBSD infection at two locations in Tanzania in 2008. Root necrosis was scored at a scale of 1-5 (no root necrosis and severe necrosis). The F1s and parents were genotyped with 222 informative SSRs at BecA Hub facility in Nairobi. In addition a subsample of the population was genotyped with 1536 SNPs using a GoldenGateTM assay platform. Of the 1536, 600 informative SNPs were included in linkage and QTL analysis using JoinMapTM and MapQTLTM. Mixed-model analysis was further used to associate markers with CBSD tolerance. Interval-based QTL analysis revealed a strong QTL in linkage group 4 of SNP based genetic linkage map explaining 27% of the genetic variations and MEF_c_2120 and MEF_c_1513 SNPs were found closely linked to the QTL. Results from mixed-model marker-trait association analysis of the entire mapping population corroborated those of linkage-based interval mapping. The present work is the first step towards utilization of MAS to back-cross CBSD-tolerance QTLs into susceptible farmer preferred cultivars.
Systemic approaches using either genomic or post-genomic data have been done before for understanding of pathogen responses in plants. Nevertheless, the precise role of many genes has not been explained and an important issue remains to be addressed: To construct resistance protein networks integrating as much available information as possible.
A resistance protein network for an economically important plant as Cassava, brings new possibilities to expand our understanding about the specie’s response to pathogen attacks. The knowledge of A. thaliana is more extensive, thereby a network based on this plant is a good point of reference to validate our method.
We collected all available genomic information for Cassava and A. thaliana from numerous databases; this includes microarrays, miRNA targets, PFAM, GO, etc. Initially, the data were analyzed using classical descriptive multivariate methods. Subsequently, a kernel method allowing the determination of distances between genes was applied to infer partners of potential resistance genes.
Here we present our approach for obtaining, integrating and analyzing several types of genomic data in order to construct a protein network representing interactions of resistance proteins. Our first results on relationship of resistance genes with other candidates to participate in defense processes will be discussed.
The cassava green mite (CGM; Mononychellus tanajoa) is an important pest impacting cassava production in South America and more recently in Africa since its accidental introduction in the 70’s. Our research intends to characterize the natural resistance/tolerance to CGM in the cassava germplasm. Our objectives are: (1) to characterise the development of CGM on susceptible and resistant/tolerant accessions (2) to histologically and phenotypically characterise selected accessions contrasting, and (3) to profile cassava leaf proteome during the establishment of CGM. Bioassays have been established in order to detect differences at both, constitutive and induced response. It includes biological and demographic parameters (v.g. oviposition, longevity, fecundity) that are used to study its biology and construct the CGM life tables. Leaf samples were analysed by electron microscopic to investigate differences between accessions at both leaf epidermis and intern anatomy levels. Dynamic proteome profiling using cutting edge proteomics tools available at ETH Zurich will be performed on cassava leaf material at selected stages of CGM attack. Combined analysis of insect demographic development, phenotype and proteome data from contrasting accessions will be instrumental to elucidate mechanisms involved in cassava defense against CGM.
Cassava brown streak disease has emerged to be the greatest threat to food security in East and Central Africa. It causes root necrosis and serious reduction in cassava harvest and sometimes total crop loss. Efforts to mitigate CBSD currently involves convectional breeding to introgress resistance to farmer preferred cultivars. However, this is limited by the need to grow all F1s to maturity, process that take more than a year to determine the levels of resistance. If molecular markers were found to be associated with the resistance gene(s), then the F1 seeds could be screened and selected at the seedlings stage. Application of MAS in breeding would then provide the accuracy required to efficiently pyramid resistance from different sources thereby delivering a more durable resistance. This project aims to use a segregating population of a cross between tolerant and susceptible cultivars to identify genomic regions associated with tolerance to the disease. Another major objective is to investigate small RNA’s and microRNA’s that have been implicated to play a role in plant defense against pathogens through RNA silencing mechanisms. To achieve this, we will extract total RNA and do cloning from CBSD infected and non-infected resistant and susceptible cassava plants followed by Next generation sequencing on the Roche 454 FLX genome sequencer available at the ILRI-BeCA hub or to outsource illuminar sequencing services. We will use bioinformatic approaches to identify cassava miRNAs and siRNAs. In addition we intent to perform comparative genomics analysis that will involve blast searches using already known miRNAs against Genebank databases including genome survey sequences (GSS), high throughput genomic sequences (HTGS), expressed sequences taqs (ESTs) and non-redundant (NR) nucleotides. It is expected that the discovery and identitification of miRNAs in CBSD free and infected plants will elicit interest and opportunities for their role in CBSD resistant in cassava.
Small RNAs, including microRNas and ta-siRNAs, play a crucial role in stress response in plants, including biotic stress. Some small RNAs are known to respond to bacterial infection in Arabidopsis thaliana but is currently unknown whether these responses are conserved in other plants and whether novel specie-specific miRNAs could have a role in defense. This work addressed the role of miRNAs and ta-siRNAs in the Manihot esculenta (cassava)-Xanthomonas axonopodis pv. manihotis (Xam) interaction. Next-generation sequencing was used for analyzing small RNA libraries from cassava infected and non-infected with Xam. A full repertoire of cassava miRNAs was characterized, which included 56 conserved families and 12 novel families. Targets were predicted in the cassava genome for all families. Some miRNA families’ expression increased in response to bacterial infection, including miRNAs known to mediate defense by targeting auxin-responding factors. Some bacteria-repressed miRNAs included families involved in copper regulation as well as some targeting disease resistance genes. The possibility of additional regulation mechanisms resulting from transitivity (production of secondary siRNA from cleaved targets) and differential loading of miRNA* passenger strand was also addressed. Finally, we identified 54 possible ta-siRNAs loci in cassava, 15 loci were induced and 39 were repressed in response to Xam infection, we predicted targets for these ta-siRNAs in the cassava genome, finding that many of them are directed against transcription factors and auxin response factors. Taken together these results suggest that small RNAs in cassava play an important role in defense against Xam.
Cassava mealybug (Phenacoccus manihoti) is one of the most damaging pests of cassava in Africa. While biological control of mealybug by introducing natural predators has been practiced, breeding of resistant cultivars remains arguably the most effective means of controlling the pests. A diverse collection of cassava genotypes AR9-18, AR12-37, 192B/00068, T200 and TMS60444 including South African genotypes P10/3, P1/19, P4/10, P1/16 and P40/1 were multiplied in vitro and transferred to the glasshouse at twelve weeks. Eight week old seedlings were infested with cassava mealybug (L3 stage) and harvested at four different time-points, 6hrs, 24hrs, 48hrs and 1 month post infestation. Total RNA was extracted from the leaf tissues of both infested and control plants followed by Quantitative Real-time Polymerase Chain Reaction (RT-qPCR) method to detect differential expression of known pest resistant genes. Primers were designed for genes Rag2, MYB1, MYB2, CYP79D1, CYP71E7, MeTI and MI1.2 and their expression tested on cDNA of different cassava genotypes at different time points. Quantitative PCR results showed differential expression of Rag2, MeTI, CYP71E7, CYP79D1 and MYB2 at different time points and between genotypes. The results of RT-qPCR were further used to select two contrasting genotypes for whole transcriptome analysis using Illumina HiScanSQ. The analysis of insect resistant and susceptible cassava transcriptome will be used to identify novel candidate genes and to further study pest resistance pathways.
MicroRNAs (miRNAs) are endogenous ~21nucleotide small RNAs. They play important regulatory roles in plants by targeting mRNAs for cleavage or translation repression. MiRNA-guided gene regulation plays a key role in biological diverse processes in plants; therefore their identification is essential to fully understanding their targets which could lead to great implications for the improvement of cassava production. Computational comparative approaches based on the evolutionary conservation of mature miRNAs have revealed a number of orthologs of known miRNAs in different plant species. A combination of computational homology search for Expressed sequence tags (ESTs) and the miRTour tool was used in this study to identify potential cassava miRNAs. The cassava EST database was blasted to search for putative miRNAs using previously known plant miRNAs from various plant species. A total of 9 potential miRNAs were identified following a range of strict filtering criteria. Using the psRNA Target tool, potential targets were predicted for the newly identified putative miRNAs. The targets appear to be involved in plant growth, development and stress responses. However, compared with the current numbers of identified miRNAs for other species in the plant kingdom, a large number of potential miRNAs remain to be identified in cassava.
Cassava is the most important vegetatively propagated food crop and the second most important food staple in terms of calories per capita for more than 500 million people in Africa. Production of Cassava has been threatening by brown streak disease (CBSD) which causes a loss of 350,000 Mt to the crop in coastal regions of Tanzania. Molecular marker application has been used to combat the disease. Development of a genetic linkage map from an F1 population is a first step in finding markers associated with CBSD resistance. The objective of this study is to provide the basis for identification of molecular markers associated with CBSD tolerance derived from AR40-6, through the construction of a genetic linkage map. 32 SSR markers were used to screening for polymorphism in parents AR40-6; tolerant variety to CBSD and Albert; susceptible variety to CBSD. 10 SSR markers found to be polymorphic and informative were used to genotype 226 individuals to find the integrity of population. ABI 3730 Sequencer used to screen and genotype F1 population and data were scored using GeneMapper 4.0 Software. 159 individuals found to be true crosses, 18 selfs and the rest were offtype. The study is ongoing and the true crosses will be Genotyped by Sequence using 1100 SNP markers. Data obtained will be scored using Join Map 4.1 and hence construction of genetic linkage map. This will be recent SNP based linkage map for CBSD and will represent crucial step in development of Quantitative trait loci.
To improve cassava productivity, it is important to better understand the molecular mechanisms underlying initiation and development of the storage roots. In cassava, tuberization in greenhouse grown plants can be visually characterized at 6 weeks of age as determined by organ swelling and formation of starch containing secondary xylem. Histology was performed to study the anatomy of this unique organ at tuber initiation stages. Gene expression profiles of young storage structures was performed using cDNA microarray from four developmental stages; before visual tuber formation (2 wks after planting), initiation of tuber formation (1 month after planting), filling stage of tuber (2 months after planting) and late stage tuberization (3 months after planting). The glutamic acid-rich protein (Pt2L4) which is involved in secondary growth of xylem was shown as the highest upregulated gene during starch filling stage in late stage tuberous organs. However, this gene was found to also be expressed in xylem tissues of the stem. The expression of patatin family genes were detected at high levels during the initiation stage of tuberization, in addition to others involved in the jasmonic acid pathway. These candidate genes may be involved in the tuberization mechanism, and are currently being more fully characterized to study their function.
Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) that cause cassava brown streak disease (CBSD) continue to decimate cassava production in East Africa, urgently necessitating the identification of new sources of resistance. The cultivar Kaleso is resistant to CBSD under field and glasshouse conditions, and presents a valuable source of virus resistance for cassava breeding. We used Illumina RNA-sequencing to identify genes differentially expressed in this cultivar upon infection by an isolate of CBSV. Quality of the raw data was validated with FastQC, and normalized expression values were filtered using a coefficient of variation cut off to identify genes with highest variability across treatments. Filtered results were grouped using hierarchical clustering to identify sets of genes selectively upregulated in infected Kaleso, but remaining unchanged in control, and infected susceptible cultivar (Albert) treatments. More than 700 genes were identified that were selectively induced in Kaleso in response to CBSV. Genes identified in this category include: enzymes related to the production of secondary metabolites, transcription factors, as well as genes involved in defence, defence signalling pathways and RNA silencing. Interestingly, more than 20 different nucleotide-binding site leucine-rich repeat genes were also identified in this category. Genes identified in this study have potential to improve our understanding of CBSV resistance mechanisms in cassava, but may also be deployed to accelerate CBSV resistance breeding using marker assisted selection.
To evaluate genome-wide expression patterns of developmental or stress-related resistance process of cassava (Manihot esculenta Crantz), a 60-mer oligonucleotide microarray representing 20,840 cassava genes was designed to identify differentially expressed transcripts. Using this platform, we have explored the expression profiling related to storage root development and cold response in cassava. During cassava tuberization, 25 significantly changed pathways were identified. The putative rate-limiting enzymes in these key pathways, for example, enolase, L-lactate dehydrogenase and aldehyde dehydrogenase for glycolysis/gluconeogenesis, and ADP-glucose pyrophosphorylase, starch branching enzyme and glucan phosphorylase for sucrose and starch metabolism, have also been highlighted. The first molecular model for storage root development has been constructed based on the changes of structural scenario and carbon flux (Yang et al., 2011). Meanwhile, the dynamic expression changes reflect the integrative controlling and transcriptome regulation of the networks in the cold stress response of cassava. Many stress-associated genes with a wide range of biological functions have been identified, such as signal transduction components (e.g., MAP kinase 4) and transcription factors (TFs, e.g., RAP2.11). Seventeen major TF families including AP2-EREBP were also involved in the early response to cold stress. As a response to cold stress in cassava, an increase in transcripts and enzyme activities of reactive oxygen species scavenging genes and the accumulation of total soluble sugars (including sucrose and glucose) were also observed. The biological processes involved in the signal perception and physiological response might shed light on the molecular mechanisms related to cold tolerance in tropical plants and provide useful candidate genes for genetic improvement (An et al., 2012). Using the microarray platform, more than hundreds of candidate genes have been identified, proving the huge applicable potential of the technology in cassava functional genomics. It will also provide a valuable resource for cassava community to study the functional genomics of cassava related to different developmental processes, abiotic stress responses and disease resistances.
cassava, microarray, expression profiling, tuberization, cold response, gene discovery
In India, cassava is consumed as a secondary staple along with the staple, rice and many rural poor consume it as the staple in different forms of preparations. Approximately 300 000 tons of sago and starch are also manufactured from cassava roots by nearly 1200 factories. Conventional fertilizer management strategy results in lower fertilizer use efficiency and imbalanced NPK applications. Large scale on farm experiments conducted for the past 9 years have resulted in developing site specific nutrient management (SSNM) technology for cassava cultivation in India. The model QUEFTS was used for determining region specific balanced NPK uptake requirements and recommendations for a target yield of cassava. Minimum and maximum internal efficiencies of N, P and K were estimated as 35 and 80 for nitrogen, 250 and 750 for phosphorus and 32 and 102 for potassium. A linear increase in tuberous root yield with N, P and K uptakes of 17.6, 2.2 and 15.6 kg N, P and K per 1000 kg tuberous root yield was observed. Good agreement between measured and predicted yields was observed while calibrating the model. A nutrient decision support system software (CASSNUM) has been developed in which different modules are available for calculating field specific NPK recommendations for certain yield targets, identifying site specific nutrient disorders and their remedial measures etc.
Six combinations of different NPK doses (0-0-0, 0-90-120, 60-0-120, 60-90-0, 60-90-120 and 90-90-120 kg.ha-1) were tested in 5 sites distributed in Districts of Ouémé, Atlantique, Zou and Couffo in order to determine the doses of nitrogen (N), phosphorous (P) and potassium (K) due for increasing the yields of improved and local cassava varieties in each agro-ecological zone in southern Benin. The trial was carried out during 3 agricultural campaigns with the improved cassava variety BEN 86 052. The experimental design is randomised complete blocks with 4 replicates. From the analysed results it appears that the 60 kg.ha-1 of N, 90 kg.ha-1 of P2O5 and 120 kg.ha-1 of K2O are the most indicated doses to produced improved cassava variety on the degraded land (ferrallitic soils) of Abomey’s plateau region. The yield is about 19 t.ha-1 hirer and 7 t.ha-1 obtain without mineral fertilizers. As for the areas like Toffo, Eglimè, Zouzouvou and Adjohoun, the doses of 90 kg.ha-1 of N, 90 kg.ha-1 of P2O5 and 120 kg.ha-1 of K2O are the most indicated with the yields about 28 t.ha-1 and 8 t.ha-1 without mineral fertilizers contribution. The influence of mineral fertilizers on the fresh cassava roots is more effective on the weight than the number.
Cassava, nitrogen, phosphorus, potassium, yield, Benin.
Cassava (Manihot esculenta Crantz) has gradually changed from human food and animal feed into an industrial raw material for the production of starch, alcohol and many other products. Farms of greater than 10 ha are emerging. Several problems including low soil fertility, scarce and expensive planting materials and inappropriate farming techniques are particularly important for larger farms. Practical understanding of factors that determine cassava production by farmers in Nigeria will not only increase its annual production, but also enhance income generation.
To tackle these challenges, a survey and trainings were conducted from 2005 to 2009 in 74 selected cassava farms in Nigeria. The survey was to evaluate the farm performance based on production practices while trainings on selection and handling of cassava planting material, land preparation, weed control management, rapid multiplication of cassava planting materials, commercial cassava cultivation, harvest and transportation of cassava roots were conducted to improve their performance.
Results from the survey show that the average percentage missing stands was 35.0 % and the average yield was 9.94 t/ha in the assessed farms. No farm had less than 20 % missing stands. More than 50% of the farms had a percentage missing stands ranging from 40 to 50%. After the trainings, there was an increase in yield (25.94 t/ha), with an average yield gap of 16.03 t/ha, while the percentage missing stands decreased to 20.84%. There was a negative and highly significant correlation between the percentage missing stands and the yield before (r = -0.38), after (r = -0.38) the training and the yield gap (r = -0.30) also between the missing stands and trainings (r = -0.72). The correlation between trainings was positive and highly significant to the yield before (r = 0.41), after (r = 0.38) the training and the yield gap (r = 0.28).
Based on these results, we conclude that training of farmers is necessary to boost cassava production in Nigeria. Beyond training, there should be adequate follow up to ensure good implementation of the acquired knowledge by farmers.
farming knowledge, farm performance, training
The study investigated the contribution of intercropping cassava with grain legumes on cassava performance for the three seasons of 2007/08, 2008/09 and 2009/10. Agricultural Research and Development Institute Ukiriguru site was used to carry out the experiment. A cassava legume intercropping experiment was established using RCDB with four replications in a split-plot arrangement for three seasons. Cassava varieties intercropped with cowpeas, green grams and groundnuts and cassava mono crops with and without NPK formed main plot and sub-plots, respectively. Soil samples were taken prior to field preparation in all seasons to determine soil fertility status and legume plant samples for nutrients concentration. Fertilized cassava mono crop showed significantly (p < 0.05) taller plants among cropping systems and in cropping systems x variety interactions. Likewise significant (p < 0.05) differences were observed in stem diameter in cropping systems x variety interaction where fertilized mono crop showed thicker stems compared to the other cropping systems irrespective of the variety. However no significant (p < 0.05) differences in diameter was observed between cropping systems. Significant (p < 0.05) differences in fresh tuber yields were observed between cropping systems where fertilized cassava mono crops had the highest yields (19.6 – 28.5 t ha-1) followed by cassava green gram intercrops (18.2 – 27.1 t ha-1). The amount of N returned to the soil through legume residues was in the order of cowpeas > green gram > groundnuts. Results revealed more benefits from cassava green gram intercropping followed by cassava cowpeas intercropping. Cassava intercropping with green gram or cowpeas is recommended as they have the ability to improve soil fertility and higher economic returns. Improved cassava varieties intercropped with legumes would be the most appropriate measure for sustainable cassava production.
Herbicide-tolerant (HT) crops represent a new breakthrough technology in weed control. Herbicides function by disrupting some essential process in plants as photosynthesis, mitosis, pigment biosynthesis or essential amino-acid biosynthesis. Crops and weeds share these biological processes, but the weed control can be achieved by several mechanisms, including target site modification, metabolic detoxification of the herbicide active ingredients or manipulation of the protective responses of the plant. In producing herbicide-tolerant cultivars by genetic transformation, CIAT developed two approaches to identify non-transgenic herbicide tolerance in cassava. The first approach involves self-pollinating cassava germplasm to produce S1 genotypes, which exposes recessive sources of tolerance to herbicides. The second approach is through the use of molecular markers for the application of TILLING or Eco-TILLING. In our work, we transform the reduction of costs associated to the utilization of HT cassava to calculate an equivalent yield increase, to use this number as an input for the IMPACT partial equilibrium model (IFPRI) and determine the economic impact that this new technology may generate. Ten countries that produce cassava are modeled as pioneers: Brazil, China, Colombia, Ghana, India, Kenya, Nigeria, Thailand, Uganda, and Vietnam. The results show gains for consumers and producers in most countries. In particular, producers from exporting countries that adopt the technology early are benefited, as well as consumers from importing countries.
Weed infestation at early stage causes severe yield losses in cassava. Weeding consumes about 30% of total labour input (about 150-200 man day ha-1). Chemical method of weed control can reduce the dependency on hand weeding. However its effect on cassava root yield and starch content was not much reported. A field experiment on weed management in cassava was conducted during 2010-11 and 2011-12 with hand weeding, pre-emergence and post-emergence application of herbicides and their combinations as treatments in randomized block design with three replications at the Regional Centre of Central Tuber Crops Research Institute, Bhubaneswar, Odisha, India. The results of the experiment revealed that significantly the highest root yield was recorded with four hand weeding (1, 2, 3 and 4 months after planting (MAP)). However, it was statistically comparable with the application of oxyflourfen @ 0.06 kg a.i. ha-1 (pre-emergence) + 2 hand weeding (2 and 3 MAP) and two hand weeding (1 and 2 MAP) + glyphosphate @ 2.0 kg a.i. ha-1 (post-emergence; 3 MAP). However, post emergence application of herbicide reduced the starch content of the roots. The lowest amount of starch content in roots was observed in weedy check and post emergence application of glyphosate at 2 and 3 MAP along with hand weeding. Maximum net return was observed in four hand weeding treatment (1, 2, 3 and 4 MAP). It was followed by pre emergence application of oxyflourfen + 2 hand weeding (2 and 3 MAP).
Utilizing soil for agriculture inevitably leads to changes in soil properties such as nutrient status, pH, organic matter content and physical characteristics. Justifiably, in Nigeria maximizing food production at all costs is still the over-riding motivation due to poverty and the resulting food insecurity; wider environmental impacts and longer-term consequences are easily overlooked. The long-term productivity and sustainability of cassava are especially important, so a priority for soils research is needed to provide the basis for management practices that could avoid irreversible damage to the soil resource. Some soil management practices help agricultural soils store carbon and therefore contribute to climate change mitigation. Our success in responding to the latest challenge of global climate change in cassava production will depend on how we manage this vital resource (soil). This paper examines the different soil management techniques with emphasis on cover crop fallow methods, developing, and integrating living cover crop systems for cassava tuber crop establishment.
Cassava; soil management; sustainability; Climate Change.
The main objective of this paper was to analyze the resource-use efficiency and describe the socio-economics characteristics of cassava-based farmers in Ogun State, Nigeria. One hundred and twenty-five respondents were selected through the multi-stage sampling procedure. Primary data were collected from these respondents through the use of a well structured questionnaire. Descriptive statistics, quantitative and regression analytical techniques were used on the data obtained. The study revealed that 87.2% of the respondents were males, and 84% of them were married. Analysis showed that 61% of the respondents had some form of formal education, while 39% of them have no formal education. Production inputs are still being under-utilized in the study area. There is a statistical significant difference between the mean yield of farmers and the experimental or recommended yield of cassava. Incorporating policy measures for efficient use of production inputs and also to guard against all bids that may stands as obstacles towards efficient use of these production inputs were suggested.
Socio-economics, resource-use efficiency, production inputs.
A field experiment was conducted at the teaching and Research farm of the Cross River University of Technology, Obubra Campus in the Rainforest belt of Nigeria to evaluate the residual effect of poultry droppings on growth and yield of 2 cultivars of cassava. Four rates of poultry manures: 0, 5, 10 and 15 t haˉ1 were applied in 2009 on eggplant field. In 2010, a sectional combination of two cultivars of cassava (TMS30572) as CV1 and TMS 4(2) 1425 as CV2 and the 4 rates of poultry droppings (0, 5, 10, and 15 t haˉ1) were laid out in a randomized complete block design (RCBD) replicated three times. Each plot size measured 4m x 3m (12m²). Results obtained indicated that residual poultry droppings significantly increased the yield of cassava. Poultry droppings at the rate of 15 t haˉ1 produced tallest plants, highest number of harvestable tubers and highest tuber yield (18 t haˉ1) and least yield in the control (6.3 t haˉ1). TMS 30572 produced higher tuber yield (9.8 t haˉ1) than TMS 4(2) 1425 with a yield of 6.5 t haˉ1. Application of poultry manure at rate of 15 t haˉ1on garden egg in a season proceeding cassava cultivation is a promising soil nutrients management practices for increased cassava yield.
Residual Effects, Poultry Droppings and Cassava Varieties
The yield trial for evaluation of suitable casava lines cultivars for cultivated conditions of Lop-Buri province by using 3 recommended cassava cultivars (Sriracha 1, KU 50, HB 60 and HB 80) and 16 elite line from Kasetsart cassava Breeding Project (MKULB 08-2-9, , MKULB 08-2-13, MKULB 08-2-19, MKULB 08-2-22, MKULB 08-2-32, MKULB 08-2-39, MKULB 08-2-45, MKULB 08-2-49, MKULB 08-2-52, MKULB 08-2-58, MKULB 08-2-12, MKULB 08-2-62, MKULB 08-2-65, MKULB 08-2-68, MKULB 08-2-72, MKULB 08-2-77) as conducted at the Lop-Buri research station field was conducted between in February 2010 – March 2011 and between April 2011- March 2012. The results revealed that line MKULB 08-2-32, KU 50, and HB 80 gave highest yield per hectare (50.94, 45.63, 44.31 ton/ha.) while MKULB 08-2-65, MKULB 08-2-32, HB 60 gave highest yield per stem (6.67, 5.59 and 5.06 kg/stem) and HB 60, MKULB 08-2-13, KU 50, Sriracha 1, MKULB 08-2-22, HB 80, MKULB 08-2-39, MKULB 08-2-62 and MKULB 08-2-32 gave root starch content highest (25.22, 25.07, 24.96, 24.62, 24.33, 23.49 and 23.07 % respectively).
Three cassava varieties of Kasetsart University (KU) gave high yield potential in the difference of environmental occurrence. The objective of this study was to determine the highest stability and yield of cassava varieties grown in Lop-Buri, Phetchabun and Nakhon Sawan, Thailand during 2008 to 2010. Eight experiments with three cassava varieties; Kasetsart 50(KU 50), Huay Bong 60(HB 60) and Huay Bong 80(HB 80) were carried out in a Randomized Complete Block Designs (RCBD) with three replications, cassava yield was harvested in ten month after planting. The results showed that various varieties of cassava gave difference in fresh root yield, root per plant and root starch content, the HB 60 gave higher fresh root yield (47.96 ton per hectare) than HB 80 and KU 50 by 37.14 and 31.01 ton per hectare, respectively. The HB 80 gave the highest root per plant and root starch content (8.87 root and 25.4%) followed by HB 60 and KU 50 about 8.66 root, 23.2% and 8.34 root, 23.0%, respectively.
cassava, stability, potential, KU 50, HB 60, HB 80
This ex-post study is conducted in order to analyze the economic importance and effectiveness of research activities on cassava varietal improvement and adoption undertaken by CIAT and national research institutes in Southeast Asia through utilizing an economic surplus analysis method to estimate economic benefits to producers and consumers.
This study conducts an economic evaluation of the research activities leading to cassava varietal development and adoption in Cambodia, China, Thailand, and Vietnam. We calculate consumer and producer surpluses in each country through gathered information on cassava production and sales as well as research projects, and later the results are compared to the research costs so that the effectiveness of R&D activities can be determined. A policy analysis is conducted and strategies proposed from the results.
The preliminary results suggest that for all four countries, research investment has generated significant economic benefits to the producers in the region given the amount of investment. More specifically, we have calculated the net present value (NPV) of $1.28 million, $918.15 million, $9.08 billion, and $626.14 million for Cambodia, China, Thailand, and Vietnam, respectively.
Millipedes as scavengers of dead plant matter serve as beneficial arthropods. Occasionally, when conditions are favourable they develop high populations and invade farms. Millipede infestation have been identified as a major contributing factor to low root yield of cassava in the western region, Ghana. This study was to assess the pest status of millipedes on cassava and to propose management strategies to enhance cassava production. Participatory Rural Appraisal approach, questionnaires, field observations, damage assessment and chemical treatment of cassava cuttings prior to planting has been conducted. The Mpohor Wassa East, Prestea Huni-Valley and Wassa Amemfi East districts have been identified as hot spots for millipedes’ infestation. Although, high numbers of millipedes were found in the soil, the damage on promptly harvested cassava roots were minimal. The damage on planted cassava cuttings was very severe, ranging from 10-100%. The researchers and stakeholders have identified the promotion of farm hygiene, and chemical treatment of cassava cuttings before planting as immediate interventions. Chemical treatment of cassava cuttings through dipping protected over 95% of newly emerging cassava buds from been attacked by the millipedes. Monitored and prompt harvesting of cassava roots is recommended to minimize the damage.
Millipedes, cassava, chemical treatment, farm hygiene
In India, cassava is an important cash crop especially in the southern state of Tamil Nadu, where the soils are mostly Vertisols and are subject to frequent tractor traffic associated with soil tillage and land preparation for planting the stakes. Root rot infection caused by Phytophthora palmivora has been observed in very serious proportions in cassava in these regions and crop loss to the tune of 60 to 80 per cent is reported from many farms. On farm experiments were conducted in farmers’ field to study the problem and to develop remedial measures. The results showed that mechanical manipulation of the plough layer and hard plough pan below it resulted in significant increase in the movement of soil organic carbon and total nitrogen to lower soil layers. A more uniform distribution of water in different soil layers where chisel ploughing was done was also observed. Mechanical manipulation of the plough pan layer by deep ripping resulted in relatively uniform distribution of available N and K to the lower soil layers up to 60 cm. Chisel ploughing along with ridge and furrow method of planting resulted in significantly higher tuber yield and a substantial reduction in root rot infection. The study resulted in developing a management strategy for successful management of root rot of cassava in India.
The Department of Agricultural Research Services (DARS) through Roots and Tuber Crops Commodity Team in collaboration with its partners has developed and released a number of improved cassava varieties along with production packages. Nevertheless, adoption of these technologies by the majority of Malawian rural farmers has been very low due to among others, limited access to improved technologies and disease free planting materials. As entry point, links were established between the DARS and the Department of Crop Development and Extension Services through respective District Agricultural Development Offices (DADOs). The DADOs facilitated selection of lead farmers, and farmer groups who received initial cassava planting materials for further multiplication and distribution. To date, a total of 1893 bundles (50×1m) and 10000 mini sprouts of nine improved cassava varieties have been distributed to the selected beneficiaries. Two major training sessions on cassava multiplication, pest and disease identification and management were conducted to 10 famer groups and 86 selected beneficiaries. These training sessions were beefed up with 42 on-farm demonstrations that have so far been conducted. Follow-up visits to the project sites have revealed that almost all the varieties have been retained by most farmers and farmer groups and more so by those groups that are business oriented. Over the two-year period, the project has also collaborated with other partners in the sector such as FAO, IITA/SARRNET, Millenium Village and WALA Project. This partnership has resulted in expansion of the project initiatives to non-project districts of the country and has created a very big demand for cassava planting materials. As such, Root and tuber Crops Commodity Team has embarked on a massive on station rapid multiplication of newly released sweet cassava varieties that are currently in short supply. In addition, rehabilitation of a tissue culture laboratory at Lunyangwa Agricultural Research Station is under way for cleaning and multiplying planting materials.
cassava, panting materials, varieties, cleaning, seed system
Cassava contributes to about 22 % of Ghana’s Agricultural Domestic Product. Apart from its use as a source of food it also has an extensive use as a raw material for livestock feed and several industrial products. Following the breakdown of ACMVD resistance in Afisiafi cassava variety, several attempts have been made to find a suitable substitute. Hybridization between Afisiafi and ACMVD tolerant genotypes in the BNARI field gene bank produced 6 tolerant hybrids and other 3 hybrids which were evaluated for morphological and agronomic properties. The hybrids and their parental accessions showed normal flowering and fruit set. Hyb-15 showed heterotic effect for dry matter content, starch yield and earliness to flowering which was significantly (p≤0.05) shorter than days to 50 % flowering in Hyb-24. Earliest branched accession did not necessarily, produced the widest canopy spread. AF, however, which branched at the lowest height of 83.7 cm has the potential for being used to smother weeds.
A field experiment was carried out for two years at the National Root Crops Research Institute, Nigeria to ascertain the Zinc fertilizer requirement for cassava fresh tuber yield and quality. The treatments comprised application of Zn fertilizer in the form of ZnO and ZnSO4 on two cassava elite materials namely TMS 30572 and NR 8083. The Zinc rates tested based on initial soils test values for Zn are 0, 2, 4, 6, 8 and 10kg/ha using a split plot design with three replications. The cassava cultivars occupied the main plots and Zn application rates occupied the sub-plots. All agronomic and cultural practices were duly carried out and the experiment was harvested 12 months after planting. Data were collected on growth, fresh tuber yield and yield components. In addition, laboratory analysis was carried out to determine the crude protein, dry matter and starch contents of the fresh tubers; these were later converted to their respective yields in tones per hectare. All the data collected were subjected to analysis of variance for split plot design and significant treatment means separated using Least Significant Difference (LSD) at 5% alpha level. From the result, the plant height, fresh tuber yield and crude protein yield of cassava were significantly affected by Zinc application but not tuber number, dry matter and starch yields. Zinc applied either in the form of ZnSO4 or ZnO at a rate of 6kg Zn/ha was found optimum for both cassava fresh tuber and crude protein yields. The crude protein yield ranged between 1.20t/ha and 1.48t/ha with the highest recorded at the rate of 6kg Zn/ha applied being 43% higher than the control.
The increase in production of crop plants has been slowed by the occurrence of environmental stresses. The significant one is drought. The objective of this study was to determine the effect of irrigation on yield of three cassava cultivars grown on Map Bon, coarse-loamy variant soil at Khao Hin Son Research Station, Chachoengsao, Thailand during November 2010 to October 2011. The experiment was carried out in a split plot design in a Randomized Complete Block Design (RCBD) with three replications. Five irrigation schemes were the main plot; (1) application at the rate of 60 mm per plant per month at 2 to10 months after planting, (2) application at the rate of 60 mm per plant per month at 2 to 4 months after planting, (3) application at the rate of 60 mm per plant per month at 5 to 7 months after planting, (4) application at the rate of 60 mm per plant per month at 8 to 10 months after planting, and (5) application by rain. The sub plot comprised of three cassava cultivars; i.e. KU 50, HB 60 and HB 80. This work provided that treatments with various period of irrigation schemes gave differences in fresh stem weight, fresh leaves weight and fresh root yield but the treatments with application at the rate of 60 mm per plant per month at 8 to 10 months after planting tended to give higher fresh stem weight, fresh leaves weight and fresh root yield by 93, 21 and 13% (37.57, 11.81 and 69.24 ton per hectare) and KU 50 tended to give higher fresh root yield than HB 60 and HB 80 by 68.10, 59.73 and 57.11 ton per hectare, respectively. The application at the rate of 60 mm per plant per month at 2 to 4, 5 to 7 and 8 to 10 months after planting tended to give higher root starch content and HB 80 tended to show higher root starch content (26.47%).
Cassava (Manihot esculenta Crantz) is a major food crop in the tropics particularly in the developing countries of Sub-Saharan region of Africa. Nigeria is the largest producer of cassava in the world; highest levels of production are from the South- South, South-West, and South-Eastern parts of Nigeria with little production from the North Eastern part of the country. Cassava production is declining with attendant increase in food insecurity. A state wide survey was conducted to document cassava production, distribution and utilization in Osun state. The main production areas include the savannah, forest and forest/savannah agro ecological zones of the state with the highest average yield/ha occurring in the savannah zone (18.6tons/ha) and lowest at forest/savannah transition (11.1tons/ha). Major sources of planting materials include farmer owned previous seasons stems (56%) and collection from friends within the neighbourhood (22%), while the least source is from research centres and agro chemical dealers (6.7%). Most farmers (68.7%) claimed that cassava production has reduced significantly within the last five year while some (0.7%) opined that the decline is negligible. Distribution and utilisation of cassava in is Osun state is highly traditional; most of the produce is processed and consumed locally within the farming communities (91.3%) while 1.3% get into industries. Only one high technology cassava flour processing centre was observed in the state. The most important cassava production constraints are shortages of good planting materials and standard collection centres. This study therefore indicates the necessity to improve on the distribution of new healthy and high yielding varieties of cassava as well as establishment of adequate cassava flour processing centres in other to achieve the federal government of Nigeria presidential initiative on cassava production.
Cassava, Production, Processing, Utilisation
The significant environmental stresses is drought. The increase in production of crop plants has been slowed by it. The objective of this study was to determine the effect of dry period irrigation on yield of three cassava cultivars grown on Map Bon, coarse-loamy variant soil at Khao Hin Son Research Station, Chachoengsao, Thailand during November 2010 to December 2011. The experiment was carried out in a split plot design in a Randomized Complete Block Design (RCBD) with three replications. Five irrigation schemes in dry period were the main plot; (1) application by rain, (2) application at the rate of 40 mm per plant per month at 2 to 4 months after planting, (3) application at the rate of 60 mm per plant per month at 2 to 4 months after planting, (4) application at the rate of 80 mm per plant per month at 2 to 4 months after planting, and (5) application at the rate of 100 mm per plant per month at 2 to 4 months after planting. The sub plot comprised of three cassava cultivars; i.e. KU 50, HB 60 and HB 80.
This work provided that treatments with various irrigation schemes gave no differences in fresh stem weight, fresh leaves weight, fresh root yield and root starch content while the KU 50 cultivar with application by rain at 2 to 4 months after planting gave significantly higher fresh root yield by 64.06 ton per hectare. KU 50 cultivar tended to give higher fresh root yield than HB 60 and HB 80 cultivar. Three cassava cultuvars tended to show no differences in root starch content about 31.34 to 31.87%.
production, cassava, irrigation, coarse-loamy variant soil
As a tropical country Indonesia is harshly prone by climate change mainly caused by heat lift and rain decline. Thus, Indonesia abuts hard hitch to nosh people around 240 million. Indonesia main food is rice, to be balances by importing rice 2-3 million tons and wheat 5-6 million tons yearly. Recently show cassava production tends to rise in react to the larger need. Cassava as the most capable carbohydrate source is not only used as basis of food, but also used as raw matter for various industries, fuel and feed. Cassava ruins neglect without any vital support from policy maker to meet the huge order both from domestic and global market. Indonesia imports cassava starch from Thailand at amount of 500,000 – 800,000 ton yearly. Indonesia cassava production in 2011 was roughly 23.4 million tons harvested from 1.2 million hectares with average yield around 19.3 t/ha. As upland crop depends on rain, so it is mostly grown in the early of wet season. There is a firm of fight in upland utilization for cassava with the other crops and forest. To meet the larger demand, hence cassava production must be increased by intensifying the cultural practices to get higher yield. To avoid climate change expanding areas for cassava development by converting forest is not allowed by REDD (Reducing Emission from Deforestation and forest Degradation). Sustaining cassava production by agro-forestry and intercrop is a way out. Cassava intercropping with various cereals and legumes able to help water lack caused by rainfall decline. Early reap is not proper way to escape cassava from water lack, since sustainability of cutting stores becomes a grim problem for the following season. To conserve water, applying manure from animal dunks and beneath crop residues is suggested. In a few sites extra irrigation had been done to evade from drought.
sustainable cassava yield
Cassava brown streak virus (CBSV) and Ugandan brown streak virus (UCBSV) are present in East Africa almost everywhere where cassava is cultivated. The viruses cause similar diseases in cassava although they have distinct molecular and biological features. Cassava cultivars have a differential susceptibility to UCBSV and CBSV and this most probably drives the dissemination of CBSV in cassava growing regions in Africa. While in field situations, symptom expression of cassava is difficult to assess, strikingly different symptom phenotypes are found in the experimental host Nicotiana benthamiana. Severe leaf curl symptoms mark infections of UCBSV while plants infected with CBSV develop severe necrosis and eventually die. Major differences are also manifested in P1 genes of the viruses and we therefore compared the gene silencing suppressor activity of P1 from UCBSV and CBSV isolates in transient assays, to trace relationships between intensity of symptoms and P1 activities. We found considerable differences in suppressor activities and P1 from CBSV isolates were much stronger than those from UCBSV isolates. The most striking suppressor activity was found with the P1 gene of CBSV Tan_70 which was much stronger than silencing suppression of P1 from other CBSV isolates. It needs to be further investigated whether in natural virus situations CBSV isolates with higher P1 activities are more frequently found or even dominate in CBSV populations or mixed infections.
Cassava brown streak disease (CBSD) has recently been reported as the most significant threat to cassava production in East and Central Africa. Two virus species: Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) (Potyviridae: Ipomovirus) have been associated with the occurrence of CBSD in all reported cases. Both species (CBSV and UCBSV) have been reported to occur widely in Kenya, Tanzania and Uganda. Unconfirmed reports of new occurrences in Burundi, eastern Democratic Republic of Congo (DRC) and Rwanda made it essential to conduct rapid field assessments supported with virus diagnostic testing in order to confirm the presence/absence of CBSVs and to quantify the scale of the outbreaks. Field surveys were conducted separately in each country between June 2011 and March 2012. Assessments of farmers’ fields involved the scoring of leaf and root symptoms of CBSVs and the collections of leaf samples for subsequent lab-based diagnostics. PCR-based tests were performed in NARS labs in Burundi (for Burundi and DRC) and Rwanda, and were subsequently supplemented by real-time PCR analyses for species determination at IITA-Tanzania. Testing revealed a high level of congruence (> 90%) with field-based symptom assessments. Only UCBSV was found to occur in all three countries and sequence and phylogenetic analyses demonstrated a high level of homology with previously published UCBSV sequences from Kenya, Malawi and Uganda. Incidences of both foliar symptoms of CBSD and positive virus diagnoses were highest in the Lake Tanganyika shoreline area of western Burundi, followed by south-eastern Rwanda and the northern part of Fizi District in DRC. These results indicate the growing scale of the CBSD pandemic in East and Central Africa and highlight the urgency of implementing effective control measures.
Cassava Brown Streak disease (CBSD) has, and continues to be a major threat to the cassava industry in Uganda. The most economically damaging symptom of CBSD occurs on the roots as a yellow/brown, corky necrosis. However, the onset and development of this necrosis is not known. Therefore, this study was conducted to understand the progression of CBSD root necrosis. The experiment was conducted at Namulonge (central Uganda), where the CBSD pressure and whitefly population is high. Four CBSD susceptible genotypes (TME 204, TMS I92/0067, MH97/2961, and Bamunanika) and five CBSD tolerant genotypes (TME 14, NASE 3, NASE 1, MM96/0686 and 28-TME 14) were used. The experiment was laid out in a split-plot factorial experiment with three replicates. CBSD root necrosis was assessed at 4 months after planting (MAP) and thereafter at monthly intervals until 12 MAP. Results indicated significant differences (P<0.001) among reaction grades (susceptible and tolerant), genotypes and sampling times. CBSD root necrosis commences as early as 4 MAP in susceptible genotypes with a severity of 2 and incidence of 16.67%. These findings have important implications for CBSD breeding particularly when evaluating seedlings and /or clonal plants that often have different number of roots and CBSD management by planting early maturing varieties.
Cassava brown streak disease (CBSD) is a major constraint to cassava production in eastern and central African countries. The disease is caused by two RNA viruses: Cassava brown streak virus (CBSV) and Ugandan Cassava brown streak virus (UCBSV). Natural CBSD resistance has so far not been identified in the cassava germplasm. Here we report on the evaluation of 14 elite cassava lines (selected from the cassava germplasm and breeding programmes) in controlled greenhouse conditions against the two CBSD isolates. We developed a stringent infection method based on top grafting procedures coupled to a reliable virus quantitation to characterize the CBSD resistance. In the resistance screening activities we identified one elite line that remained symptom-free and did not allow viral replication for both CBSD-associated viral species. The CBSD resistant elite line remained symptom-free when tested against combined CBSV and UCBSV infection confirming the high level of CBSD resistance. Transcriptome profiling studies using Illumina sequencing technology were performed on the CBSD resistant elite line to decipher molecular markers associated with CBSD resistance. In the present study we report on cassava genes with differential regulation in cassava elite lines contrasting for CBSD resistance.
The effects of Cassava brown streak virus (CBSV) and Cassava brown streak Uganda virus (CBSUV) infections that cause cassava brown streak disease (CBSD) was studied on three cassava varieties; Albert (CBSD susceptible), Kiroba (tolerant) and Kaleso (field-resistant). The time it took to develop symptoms after graft inoculation as well as severity varied on the cassava varieties; Albert developed severe leaf and root symptoms 1-2 weeks after inoculation, Kiroba in 2-4 weeks but milder root symptoms while Kaleso developed only mild leaf symptoms after 6-8 weeks. The relative amounts of virus titre in each variety estimated by real-time quantitative PCR (qPCR) revealed high virus titres in Albert compared to Kiroba and Kaleso. The mechanism of resistance was further investigated by examining the extent of reversion by making cuttings from top, middle and bottom part of CBSD-infected plants. A greater number of disease-free plants were generated from cuttings made from Kaleso than Kiroba and Albert from all plant parts. Experiments examining the suitability of cassava varieties to feeding and reproduction by the whitefly, Bemisia tabaci, the vector of CBSVs, revealed no significant differences. Difference occurred, however, in the rate of virus transmission by whiteflies in which a small percentage (3%) of Kaleso plants took infection by CBSV while up to 60% of Kiroba and Albert plants were infected. The ability of Kaleso to suppress virus multiplication and spread when challenged by both graft and whitefly inoculations is the indication of innate virus resistance mechanism of Kaleso to CBSVs, and this will be valuable information for developing CBSD resistant varieties.
Cassava production is threatened by the spread of diseases including Cassava Brown Streak Disease (CBSD). Increased severity and distribution of the disease from low to high altitude areas has recently occurred. Breeding for resistance is an important means of minimising the effects of the disease. Using a mapping population of 60 F1s from a cross between Namikonga (tolerant) and Albert (susceptible), QTLs associated with CBSD resistance were identified with a major QTL representing about 27% of the observed variation. Utilizing this QTL will allow selection of progenies that will be 27% more resistant than the susceptible parent while resistance in Namikonga is considered to be 100%. This study aims at improving the accuracy of these QTLs and obtaining a better estimate of their effect by increasing population size from 60 to 250 F1 individuals, genotyping-by-sequencing, genotyping using a higher density of SNP markers in the major QTL region, and identifying candidate resistance genes by characterising sequence variation in QTL region We also propose to determine the association between CBSD symptoms and virus titre in the F1 population. The mapping population has been validated using 15 SSR markers and 305 true crosses identified. Of these, 275 are being phenotyped in a hot spot area in Naliendele, Tanzania.
Cassava Brown Streak Disease (CBSD) is currently the most devastating viral disease of cassava responsible for serious yield loses in East Africa. To improve on cassava productivity in the region, a number of control strategies have been adopted among which is host plant resistance. Applying Marker Assisted Selection to cassava breeding for CBSD resistance is one way of accelerating the selection process of developing improved varieties. Currently Namikonga is considered to be the best source of CBSD resistance. In this study, a Namikonga-derived F1 population was generated by crossing Namikonga with four (4) farmer preferred CBSD susceptible parents; MH96/4271, MM97/2961, NASE 12 and TME 14. Eight hundred and ten (810) F1 full sibs were generated and established in a seedling evaluation trial at Namulonge which is a high CBSD inoculum pressure zone. The mean root CBSD severity per family at harvest was; Namikonga x MH96/4271 (1.82±0.11), Namikonga x TME 14 (2.12±0.20), Namikonga x MM97/2961 (2.55±0.56) and Namikonga x NASE 12 (1.50±0.20) Four hundred and eighty eight (488) plants were advanced to clonal evaluation trial. This is the population which will be used to validate the candidate Molecular markers associated with CBSD resistance in Namikonga.
Development of resistance in cassava against CBSD is still a major challenge in many breeding programs in CBSD affected cassava growing regions in Africa. This can be attributed to its high heterozygosity due to its outcrossing nature. This study was initiated to develop resistance in selected cassava genotypes through inbreeding. Eight genotypes; 182/00661, 130040, TZ/130, Kigoma, TZ/140, 0040, Namikonga and 100142 were selected as parents (S0) for selfing. The selfs (S1) were evaluated in the field for resistance using a disease score of 1-5. Ranksum analysis was adopted as a new method for disease analysis of CBSD resistance by screening and ranking the genotypes according to their level of resistance based on both disease incidence and index of symptom severity of roots. Rank analysis was compared to AUDPC analysis of foliar data in order to select the best performing families. Rank analysis of S1 root data showed that only two families were categorized as moderately resistant (Namikonga and TZ/140) and one family as resistant (0040) while based on AUDPC (foliar data) two families were categorized as moderately resistant (130040 and Namikonga), one family as resistant (0040) and one family as highly resistant (TZ/140). Comparison of S0 and S1 showed that there was a decrease in disease index in S1 than their respective S0 though the difference was not significant. Based on this finding the study demonstrated that more cycles of selfing can lead to development of highly resistant cassava genotypes to both UBSV and CBSV.
Cassava brown steak disease (CBSD) is caused by Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV). Due to its impact on root quality, usability and marketability, CBSD is now considered the most important biotic threat to cassava production in East and Central Africa. Transgenic resistance mechanisms are being explored for management of CBSD. Two RNAi constructs, pILTAB718 (DFull Length-CP) and pILTAB719 (N-terminal CP), were generated from the coat protein (CP) sequence of UCBSV, and transgenic cassava produced in the CBSD susceptible cultivar 60444. Transgenic lines shown to be accumulating CP specific siRNAs were challenged in the greenhouse by grafting to UCBSV-infected rootstocks. Plants for both RNAi constructs proved to be highly resistant to the homologous virus. Seven lines each derived from pILTAB718 and pILTAB719 were planted under confined field trial conditions at Namulonge, Uganda. Development of CBSD leaf symptoms was delayed in the RNAi lines compared to non-transgenic 60444 controls, but reached 100% of plants in all lines except those of p718-005 and p718-001, in which 50% and 95% (n=60) remained symptom free respectively. RT-PCR analysis of leaf samples showed presence of CBSV in 13 of the 14 lines tested but no detectable UCBSV, while plants of line pILTAB718-001 proved to be free of both UCBSV and CBSV. At harvest, storage roots were examined for CBSD symptoms. In lines p718-005 and p718-001 incidence and severity of root damage was significantly low compared to controls, with 109 out of 116 (95%) roots remaining symptom free in plants of p718-001. Data from greenhouse and field studies demonstrate proof of concept for control of CBSD by RNAi technology.
Previously, artificial microRNAs (amiRNAs) were shown to effectively control plant RNA viruses. The use of endogenous microRNA backbone precursors to express ~21 nucleotide sequences complementary to specific viral sequences has become an alternative to the hairpin RNA (hpRNA) to control viruses. The high specificity of amiRNAs may reduce off-target effects that could result from siRNAs generated from hpRNA. The Arabidopsis thaliana miR159a backbone precursor was modified to express amiRNAs targeting conserved regions of Cassava brown streak virus (CBSV) and Ugandan Cassava brown streak virus (UCBSV). RNA sequence encoding P1, Nuclear Inclusion B (Nib) and Coat Protein (CP). The precursors miR159a-P1[CBSV], miR159a-P1[UCBSV], miR159a-NIb[UCBSV] and miR159a-CP[CBSV] were efficiently processed into miRNAs of ~21 nucleotide size in N. benthamiana, detectable by Northern analysis. The maximum level of protection for 3 different N. benthamiana transgenic lines of miR159a-P1[CBSV] and miR159a-CP[CBSV] against CBSV was 72.2%, while that of miR159a-P1[UCBSV] and miR159a-Nib[UCBSV] against UCBSV was 83% and 61% respectively, compared to controls which were infected at 100%. The expression and protection data were found to be heritable and stable using T2 and T3 generations. These results show that amiRNA based approach could be an effective strategy to control cassava brown streak disease in cassava.
During the BioCassava Plus Phase 1 funded by the Bill & Melinda Gates Foundation, we demonstrated that cassava mosaic disease (CMD) resistance can be engineered in transgenic cassava by expression of hairpin-RNAs targeting viral sequences. Here we report on the production of transgenic cassava resistant to both viral species associated with cassava brown streak disease (CBSD), namely cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV). Transgenic cassava lines expressing hairpin RNAs homologous to conserved regions of the CBSV and UCBSV genomes were generated using the cassava genotype model for genetic transformation. Virus resistance was evaluated using the stringent top grafting method to confirm that transgenic lines had stable resistance against both CBSV and UCBSV in multiple experiments with increasing viral loads. In order to tackle both CBSD and CMD the technology has subsequently been mobilized into a farmer-preferred cassava genotype naturally resistant to CMD. All transgenic lines remained immune when inoculated with CBSV and UCBSV. Co-inoculation with geminiviruses did not alter the engineered CBSD resistance. Our work demonstrates that CBSD and CMD resistances can be combined to provide virus resistant farmer-preferred cassava.
Cassava brown streak disease (CBSD) is among the seven most dangerous plant diseases in the world for their impact on food and economic security. It causes losses of up to 100% in harvestable roots in susceptible varieties and reduces the market value of cassava due to necrotic lesions. CBSD is caused by two different virus species, Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV), belonging to the genus Ipomovirus and family Potyviridae. A study was undertaken to determine the proportion of CBSV and UCBSV in Uganda. Ninety-five CBSD symptomatic cassava leaf samples were collected between June and August 2009 from 94 fields of the major cassava growing districts in Uganda. The leaf samples were analysed for presence of CBSV and UCBSV using real-time reverse transcriptase polymerase chain reaction (RT-PCR). Results showed that UCBSV is the more prevalent CBSD-associated virus in Uganda, with 93.6% incidence, whereas only 1.1% of the samples tested positive for CBSV. In 4.3% of the samples, no CBSD associated virus was detected. Contrary to earlier reports for Uganda, Kenya and Tanzania, no dual infections of CBSV and UCBSV were encountered in the current study. In development of the real-time primers it was shown that the majority of UCBSV strains of Uganda could be differentiated from UCBSV strains of Kenya and Tanzania, suggesting Uganda may have a variant of UCBSV. The findings of this study have important applications for breeding of cassava for CBSD resistance, studies on epidemiology and control of CBSD in Uganda.
Cassava mosaic disease (CMD) is caused by cassava mosaic begomoviruses in the family Geminiviridae. are widespread in Kenya causing yield losses of up to 50%. However, limited information is available on their distribution and diversity. A study was conducted with the aim of determining their prevalence, incidence, severity and diversity. A country-wide survey was carried out to collect leaf samples from infected plants; whitefly counts were done to determine their presence and mode of infection. Results showed that there was an average CMD incidence of 55.2% countrywide. Coast Province had the highest incidence of 73.8%. The prevalence of CMD countrywide was 84.6% with Nyanza Province recording the highest prevalence of 96.2%. The spread of CMD by use of infected cuttings was 73.8% compared to spread by whitefly which only accounted for 26.2%. Polymerase chain reaction analysis of the 350 samples collected during the survey confirmed presence of EACMV and ACMV in 51% and 11% of samples, respectively. Dual infection by the two viruses was detected in only 9% of the samples. The remaining 29% samples tested negative although these samples had symptoms. EACMV was detected in all the provinces surveyed while ACMV was mostly prevalent in Western and Nyanza Provinces. However, ACMV was detected in Eastern and Coast Provinces for the first time. The dual infection with EACMV and ACMV was more prevalent in Nyanza Province (4%). The information gained from this study can be used to advise the farmers on the use of disease-free planting material and suitable varieties for the four Provinces. There is need for the characterization of the viruses as well as identification of varieties resistant to these viruses and virus strains.
Cassava, cassava mosaic disease, cassava brown streak disease, incidence, prevalence, severity, Bemisia tabaci, Kenya.
Cassava Brown Streak disease (CBSD), caused by cassava brown streak virus (CBSV), is a major constraint to cassava production in East Africa. Use of resistant cultivar is so far the best option to control CBSD .However, to date there are no varieties resistant to the disease. In this study we use graft inoculation to screen genotypes that can be used in breeding programs to breed resistant varieties. This method enables to study the viral transmission in reverse order. Compared to CBSV transmission by the white fly in the open field , This method ensures that no plant escapes virus inoculation. This research resulted in eight genotypes (72TME14, 109TME14, 28TME14, 432TME14, 132TME14, 52TME14, 67TME14 and 139TME14) . Not all varieties that show no disease symptoms in the field are free from the disease. Moreover we studied the correlation between symptoms seen on plants and the physical presence of the viruses on the leaf samples. With these results we were able to recommend which leaf can be picked as samples for diagnosis purposes. leafs from position 2, 3 and 4 of the cassava plant or not from so young leaves and not so mature leaves are to be picked as samples.
Le manioc, aliment de base des populations congolaises subit depuis les années 90, des attaques dévastatrices de la mosaïque africaine de manioc. Les pertes de rendement sévères ont conduit à une baisse importante de la production avec pour corollaire une diminution de l’offre sur les marchés des grandes agglomérations. L’augmentation des prix qui a suivi occasionné à Brazzaville un mécontentement général de la population notamment chez les femmes qui sont majoritaires dans cette filière. Le gouvernement du Congo appuyé par des partenaires au développement a engagé une action de grande envergure pour éradiquer l’épidémie. Plusieurs projets sont mis en œuvre. Des clones résistants développés par l’IITA ont été introduits et testés dans différentes zones agro écologiques. Les capacités des acteurs sont renforcées. Les clones appréciés par les producteurs sont en cours de multiplication à grande échelle et de distribution aux ménages. Des gains de production sont notés. Des groupements de multiplicateurs de boutures saines sont constitués. La vente des boutures procurent des revenus importants aux membres. Malgré ces effets positifs très visibles, du fait de la faiblesse des services de vulgarisation, la majorité des producteurs ignorent que la maladie, responsable de la perte des rendements est due à un organisme pathogène (virus) transmis par les boutures et par les mouches blanches. Pourtant cette connaissance est capitale pour assurer le succès des campagnes de lutte. La faiblesse des organisations des producteurs est une contrainte majeure. Les interventions n’étant pas coordonnées, les synergies se développent difficilement, les expériences des uns et des autres ne sont pas mis à profit avec le niveau de satisfaction souhaité. En outre, le sous équipement des structures de la recherche agricole qui subissent par ailleurs les contre coups des financements publics ne permettent pas le suivi régulier des clones pour en évaluer le niveau de diffusion et de la perte de la résistance chez certains, en fonction des zones agro écologiques ainsi que de la présence éventuelle d’autres espèces ou souches virales. De plus, le manque d’études socioéconomiques ciblées sur la filière manioc ne permet pas de quantifier les gains induits par la mise en œuvre de tous ces projets ainsi que les impacts survenus particulièrement chez les femmes. Des actions à entreprendre pour lever ces contraintes sont proposées.
mosaïque africaine du manioc, lutte, succès, faiblesse, Congo.
Cassava brown streak disease (CBSD) caused by two viruses, Cassava brown streak virus (CBSV) and Cassava brown streak Uganda virus (CBSUV) of the genus Ipomovirus, family Potyviridae, is the most important disease of cassava in Eastern, South and Central Africa. It causes yield losses of up to 70-100%, and varieties resistant to the disease are not available for cultivation. The objectives of this study was to develop methods for the elimination of CBSVs from three East African cassava varieties (Kaleso, Kiroba and Albert) using a combination of experiments involving tissue culturing, thermal (using different temperature regimes), chemical (using Ribavirin at different concentrations) as well as the combined application of the treatments on tissue cultured cassava plants. The effect of heat treatments varied; exposure at 30 oC and 35 oC produced the maximum number of disease-free plants, which also appear to have positive effect on plant growth and development while plant growth was retarded at 40 oC and most plants died at the highest temperature 45 oC. At 0.21 mM/l ribavirin, plants showed the signs of phytotoxic effects in the form of severe stunting of plantlets, sluggish root development and eventual death of all the plantlets in all three cassava varieties while lower concentrations of 0.15 mM and 0.10 mM were both beneficial for plant growth as well as virus elimination. The combinations of chemo and thermotherapies produced the highest number of disease-free plants in all three varieties; Kaleso (50%), Kiroba (44%) and Albert (35%). These results indicate that in vitro methods can greatly enhance the elimination CBSVs and thus provide a means for CBSD management through the elimination of viruses from popular cassava varieties.
Uniplex and multiplex reverse transcription-polymerase chain reaction (RT-PCR) protocols were developed for the detection of cassava brown streak viruses (CBSVs) in single and mixed infections with cassava mosaic begomoviruses (CMBs) in cassava. CMBs contain ssDNA as their genome (genus Begomovirus, family Geminiviridae) while CBSVs are made up of positive sense ssRNA (genus Ipomovirus, family Potyviridae), and they cause the economically important cassava mosaic and cassava brown streak diseases, respectively, in sub-Saharan Africa. Diagnostic methodologies have long been available for CMBs but they are limited for CBSVs especially in mixed infections. In this study, the two CBSVs, Cassava brown streak virus (CBSV) and Cassava brown streak Uganda virus (CBSUV) occurring singly or in mixed infection with CMBs, African cassava mosaic virus and East African cassava mosaic virus were detected in a single RT-PCR using both previously described and newly designed virus-specific primers. Protocols were highly efficient for detecting CBSVs compared to the existing methods and have great potential to minimize sample handling and contamination. As well as improving the diagnosis of cassava viruses, the development of multiplex RT-PCR protocols have revealed the common occurrence of mixed infections by CBSV and CBSUV in cassava fields of Tanzania and Kenya, which was contrary to the common belief until recently that these two viruses have existed separately. These protocols have implications for diagnosis and epidemiological studies on cassava virus diseases in Eastern Africa.
Cassava is an important source of carbohydrates feeding over 700 million people worldwide. Pests and diseases are considered among the major constraints to cassava production in Africa. Over eight different viruses of cassava have been described in Africa but only two of these cause severe yield losses in East Africa. Currently (CBSD) distribution is being newly reported in the Western region of Kenya where over 90% Cassava mosaic disease (CMD) incidences have been reported. A study was designed to investigate the possible interactions of CMGs and CBSV on the host plant and their effect on the development of symptoms on popular cassava varieties. The possible interactions of Cassava brown streak virus-Uganda (CBSVU) and Cassava mosaic geminiviruses (CMGs) were tested by sap inoculation of 10 Nicotiana benthamiana plants singly and in combination in two trials. At 30 days post inoculation, dual infection of CMD+CBSD showed the highest disease severity (4.7) followed by CBSV-U (4.1) and CMD (3). Symptom development was assessed by graft-inoculation of 4 local popular cultivars with diseased scions and foliar symptoms examined using a scale of 1-5. Disease infection was confirmed by polymerase chain reaction (PCR) for CMGs and reverse transcriptase polymerase chain reaction (RT- PCR) for CBSVU. No significant difference (P>0.05) was observed when the viruses occurred singly compared to significant differences (P<0.05) observed in dual infection on mean severity among the cassava landraces. The study provides the first report of the foliar effect of dual infection of CMD and CBSD in popular cassava landraces and possible synergistic interaction of the two viruses when occurring together.
Cassava (Manihot esculenta Crantz) roots are a staple food for over eight million inhabitants in Rwanda and its leaves constitute an important vegetable. Production of cassava is however constrained by many pests and diseases. Among them cassava mosaic disease (CMD) and is threatened by cassava brown streak disease (CBSD). A survey was carried out in cassava farmers’ fields in 14 Districts representing the major cassava growing areas between 2009 and 2011 to establish disease incidence, prevalence, symptom severity and characterise the cassava viruses. CMD incidence in the affected cassava fields ranged from 6-100% while CBSD proportion of infection was low (1-40%). A total of 283 cassava leaf samples were collected and analysed using universal primers for detection of African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV). PCR analysis results revealed 91% of the analysed samples to be infected by EACMV, 8% by ACMV and 2% by dual infection of ACMV and EACMV. Partial nucleotide sequences of the ACMV coat protein gene and EACMV DNA-B analysis confirmed the PCR results. For the first time occurrence of cassava brown streak Uganda virus (CBSUV) was found in Rwanda but no cassava brown streak virus species was detected in the collected samples. Disease and virus distribution maps are presented here. Results from this study will provide information for disease management strategies as well as cassava virus diagnosis.
Cassava brown streak disease (CBSD) is a major threat to cassava production in Uganda. The disease is caused by two ipomovirus species; Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV), both transmitted by the whitefly vector (Bemisia tabaci). Since the outbreak of the CBSD epidemic in Uganda in 2004, knowledge on its spread in the field is still limited. In this study, three cassava genotypes with varying levels of tolerance to CBSD were used to evaluate the effect of amount of initial inoculum on spread in different disease pressure zones in Uganda. Disease incidences (%), apparent infection rate (r), area under disease progress curves were determined and populations of the whitefly vector Bemisia tabaci monitored on a monthly basis. Initial field inoculum level significantly affected CBSD incidence (P = 0.001), AUDPC and r (P = 0.05). At Namulonge and Kamuli, where disease pressure is high and moderate respectively, disease incidence by seven months was high (>90%) in all the treatments. Even in Lira where disease pressure and vector population are low, there was considerable with higher initial-field inoculum levels resulting to higher incidence levels which signify the importance of inoculum source in disease spread. The high rate of disease spread in Lira despite low vector numbers shows the importance of the vector in dissemination of the disease and further validates the significance of using infected cutting in the spread of CBSD. Both genotype and inoculum level had no effect on CBSD root incidence; however infection time had a significant (P < 0.001) effect in all locations. Yield was least in early infected plants compared to healthy plants, this was due to the fact that early infection reduces tuberisation and retards root fill.
Cassava brown streak disease (CBSD) is a major constraint to cassava (Manihot esculenta) production in Eastern Africa, causing up to 100% yield losses. Marker-assisted selection (MAS) improves selection speed breeding process and reduced population size. Objectives of this study are to (i) verify the integrity of F1 population from a cross between Nachinyaya (CBSD tolerant) and AR37- 80 (CBSD susceptible), and (ii) develop a SNP-based genetic linkage map. Leaf samples of 279 genotypes were DNA isolated, genotyped by ABI 3730 sequencer with 26 SSR markers at BecA, Nairobi. 11 SSRs confirmed 257 true hybrids; two off-types and 12 individuals with missing data. Hybrids and parents, genotyped with 514 SNPs at KBioscience by KASPar technology. SNP-based genetic linkage map was built by JoinMap®4.1 from 238 hybrids, 416 SNPs distributed on 20 linkage groups. A map had 1695cM and 4.1cM average distance between loci. 210 SNPs found common in previous cassava map (Rabbi et al., 2012) and 206 SNPs first mapped. The map will facilitate QTLs analysis in Nachinyaya for CBSD tolerance in MAS and improved food security.
A diagnostic survey was conducted during 2010-11 to provide an assessment of the status of cassava brown streak disease (CBSD) in 90 locations in 12 districts that represent the most important cassava growing areas of Malawi. The results revealed the widespread occurrence of CBSD in the lakeshore areas in the districts of Karonga, Nkhotakota, Nkhatabay, Rumphi, Salima, in a few locations in Zomba, but not in Chitipa, Chiradzulo, Kasungu, Mulanje, Mzimba and Thyolo. The average incidence of leaf and stem symptoms was 26.3% and 13.9%, respectively. There were significant differences between districts with respect to CBSD incidence (χ² = 20.9, P < 0.001) and severity (χ² = 13.9, P < 0.05). Incidence of foliar symptoms and severity were positively correlated (r = 0.90 [n=88], p < 0.05). The average abundance of Bemisia whiteflies was 0.4 adults per top five leaves of sampled plants and there was no significant correlation between whitefly numbers and CBSD incidence. The low abundance of whiteflies was probably due to sampling during the cool, dry season, which is known to be unfavorable for whiteflies. All the local and improved cassava varieties found in CBSD-affected districts were susceptible to CBSD. Diagnostic tests by RT-PCR and nucleotide sequencing of an approximately 280 bp region of the 3′ end of the virus coat protein gene confirmed the occurrence in Malawi of both Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV), known to be involved in CBSD etiology. UCBSV was detected in all CBSD-affected districts, whereas CBSV was only detected in a few locations in Karonga and Rumphi districts in northern Malawi. These results suggest that UCBSV is endemic in Malawi, whilst CBSV may be a relatively recent introduction. Further detailed sequencing of CBSVs is necessary in order to gain a more thorough understanding of the diversity and origin of the two virus species in the country. The finding that CBSVs are present in all major cassava producing regions warrants a comprehensive prevention plan to mitigate the impact of CBSD on cassava production in Malawi.
Cassava Brown Streak Disease (CBSD) has recently caused important losses in cassava field in East Africa because most of the improved cassava varieties deployed in the last years appeared susceptible. The disease is associated with two cassava brown streak viruses, Cassava brown streak virus (CBSV) and Uganda cassava streak virus (UCBSV). Classical symptoms are restricted to the storage roots and therefore it renders early disease diagnostic complicated. The viral genome encodes for ten proteins, the coat protein (CP) being the most conserved sequence amongst the different CBSV isolates. Degenerated primers were used to amplify the full CBSV CP sequence from CBSV-infected cassava collected in Tanzania. In order to evaluate the RNA interference mechanism in this system, different strategies were conducted: The characterized CBSV CP partial sequence was used to produce different expression cassettes. Transgenic cassava lines were produced for the complete set of binary vectors covering the different approaches. Transgenic cassava lines were selected based on transgene copy number and also specific analyses were conducted: relative transcript level and small RNA analysis. The selected transgenic cassava lines were evaluated for CBSV resistance by grafting. Virus tolerance and/or resistance were assessed through CBSV quantification.
The most promising approach to curbing cassava yield losses attributed to cassava brown streak disease (CBSD) is by establishing and deploying resistant cultivars. Association study based on limited population size has established quantitative trait loci (QTL) for CBSD resistance in Namikonga and resistance in other cassava lines such as Nachiyanya among others has been observed. In order to understand the mechanism underpinning CBSD resistance, it is requisite to establish any genetic variations associated with resistance. In this study a genome wide SNP detection and analysis, based on whole genome re-sequencing of resistant and susceptible cassava lines, will be carried out using both traditional (allele counting) as well as the more robust contemporary (probabilistic) computational approaches by different bioinformatics tools. Initial results and the methods utilized in SNP identification and analysis will be presented. Additionally, any variants detected in the QTLs for CBSD resistance that are potential candidates conferring resistance in the CBSD resistant cassava lines will be provided.
Cassava is an important food crop in SSA with a high potential in food and industrial applications. However, it is affected by diseases that result into significant losses on farm. One of these is cassava brown streak disease which affects the foliar morphology and reduces the palatable portion of the root rendering it unfit for both human and animal consumption. The disease results into significant losses in starch yield by deposition of lignified materials in the root and loss of value in terms of starch and relevant dietary fiber. In an ongoing study on the effect of the disease in two trial sites of Kayunga and Namulonge, the percentage losses in different varieties have been computed and the differences in loss due to type of planting material used (diseased or clean) have also been computed. Different reactions have been seen for the varieties TME 14, I/97/0067, TME 204 and MM96/4271 in the two trial sites. It has been observed that the use of clean planting material reduces losses in starch yield by over 50% at different growth periods in different varieties. The dry matter content of diseased and clean materials was not significantly different although it was higher for plots were diseased cuttings were used. Significant differences were observed for cyanogenic content with non diseased materials having high cyanide contents. The starch content was also high for plots were clean planting materials were used. Though varietal differences were observed in different parameters investigated, it was clear that the use of clean planting materials results into higher starch yield hence increasing the economic value of the crop.
The objective of the research is to generate a genetic linkage map from an F1 population of a cross between cultivar Mkombozi (female- as the source of cassava brown streak disease [CBSD] resistance) and TMS 4(2)1425 (male and susceptible) for the detection of QTLs associated with tolerance to CBSD. Specific objectives are: to determine the integrity of mapping population using Simple Sequence Repeat (SSR) markers to eliminate unknown parental combinations. Genotype the mapping population for single nucleotide polymorphic (SNP) markers and generate a genetic linkage map. Currently DNA extraction and SSR genotyping is ongoing in order to fulfill objective one. To date genotyping was done using ten SSR markers (SSRY 51, SSRY52, SSRY38, NS193, SSRY63, SSRY102, SSRY119, SSRY155, SSRY169 and SSRY147). There are 158 individuals that have been identified as true crosses and will be used in SNP genotyping to develop the genetic linkage map for CBSD tolerance.
We are continuously challenged to develop new, more precise, more rapid, more cost effective and more user-friendly diagnostics for crop pests. Why, because to respond rapidly to a pest outbreak is the cornerstone of any mitigation strategy and any action is reliant on a accurate diagnosis of the pest. Yet despite this imperative, inherent difficulties persist on rapid and reliable crop pest identification. This need has been clearly exemplified by the emergence of Cassava brown streak disease (CBSD) and its two associated viruses Cassava brown streak virus (CBSV) and Uganda cassava brown streak virus (UCBSV).
An emerging technology in diagnostics is that of Loop-mediated Isothermal AMPlification (LAMP), which has characteristics in common with PCR (i.e. it amplifies nucleic acid), but differs in one major respect in that it amplifies at a constant temperature (i.e. no thermal cycling). This major difference, in association with a range of dye chemistries for detection of the amplification product, provides for a choice of diagnostic formats suitable for laboratory and field. Under the Great Lakes Cassava Initiative the LAMP technology was successfully applied to the detection of CBSV and UCBSV in formats using the Genie II (real-time instrument suitable for a laboratory) and a dip-stick-styled, Lateral Flow Device (suitable for field use). The application of LAMP in crop pest diagnostics is discussed in relation to the development and use of diagnostics for CBSVs in research, seed certification and surveillance, and for use in environments with limited infrastructure.
Efficient methods for transmitting cassava brown streak disease (CBSD) causal viruses from infected to non-infected cassava plants are essential tools for studying the biology of this important disease, and for assessing resistance in conventional and genetically modified germplasm. A chip bud grafting method has been developed in which axillary buds from CBSD symptomatic plants are grafted onto greenhouse-grown disease-free test material. Using this system, transmission was successfully achieved from source plants of cultivar Ebwanateraka RT-PCR positive for Cassava brown streak virus (CBSV) only, to 6-8 week old disease-free test plants of TME 204, Ebwanateraka and 60444. Across replicated experiments and depending on the genotype, 70-100% of the inoculated plants (n=60) developed CBSD leaf and stem symptoms within 4-6 weeks after bud grafting. Infected plants also developed typical CBSD symptoms in storage root tissues when cultivated for a further 4 months. RT-PCR of leaves sampled from these plants confirmed presence of CBSV in all symptomatic plants. The system described is efficient for use within controlled growth conditions. Each diseased scion plant supplies multiple buds for inoculations and experimental materials can be tested for CBSD transmission as young, uniform plants of the size easily handled in a greenhouse or large growth chamber.
In Cassava, natural resistance against virus isolates and strains of Cassava brown streak virus (CBSV) and Ugandan brown streak virus (UCBSV) is limited. Hence, small RNA mediated post transcriptional gene silencing against CBSV and UCBSV was pursued. Target sequences were carefully chosen to possibly reach immunity to infection against isolates and strains of both virus species. We designed constructs with virus sequences in an inverted repeat orientation (hpRNAi) and constructs harbouring the MIR319a precursor in which the stem sequences had been replaced with virus sequences (amiRNA). We screened F2 plants of transgenic N. benthamiana transformed with our constructs with diverse isolates of CBSV and UCBSV by mechanical inoculation. We found the plants to be immune against homologous virus. Inoculation with heterologous virus, however, resulted in infections, but delayed compared to wild type. The observed resistance of hpRNAi expressing plants (400 nt virus sequences) was similar to amiRNA expressing plants (21nt virus sequences); and, although the sequences for the hpRNAi constructs had been chosen from regions highly conserved between the viruses, we found the resistance to be directed against homologous virus and its strains only. Expression of synthetic genes comprising sequences from either viruses or, expression of multiple amiRNAs also directed against both viruses resulted in broad-spectrum immunity against CBSV and UCBSV.
Virus diagnosis in cassava is important for disease prevention and control. For cassava mosaic begomoviruses and for cassava brown streak ipomoviruses typically molecular methods are used which permit detection and discrimination of virus species and strains. The ultimate purpose of pathogen diagnosis is to support disease management decisions and this determines which of the available methods is to be used. We have developed a suite of assays for virus diagnosis in cassava and compared biological, serological and molecular methods to determine the most adequate method for a diagnostic problem. When virus confirmation is an issue, serological assays provide rapid results in robust test formats that can be easily up-scaled and conducted even under simple laboratory conditions. While PCR, qPCR or LAMP assays reveal high resolutions, their high sensitivity however is associated with lack of robustness and type I (false positives) or type II (false negatives) errors. Hence their usefulness is limited when virus assays have to be conducted in situations with only limited laboratory infrastructure and expertise available. For virus diagnosis in cassava methods developed by several laboratories are on hand. The challenge now is, to incorporate virus indexing in the management decision process. This requires that tests are validated and harmonised protocols are established which is fundamental to certification in seed systems of cassava planting material free of viruses.
According to recent studies on agrobiotech adoption and development in sub-Saharan Africa, local expertise and capacity for regional development of biotech products are essential components for the adoption of biotechnology in Africa. Over a decade of cassava technology transfer has failed to empower African laboratories with cassava genetic transformation platforms. We recently initiated and implemented strategies to effectively establish this technology in Africa. In an initial step, a transformation protocol with improved stability and reduced consumable requirements was optimized by our team (Bull et al., 2009; Niklaus et al., 2011). Optimization of key steps in the transformation protocol was particularly instrumental to ensure effective transfer to African laboratories where conditions are less optimal and stable. We elaborated strategies based on hands-on workshops and training of local scientists for rapid transfer of the technology to BecA (Kenya), MARI (Tanzania) and WITS (South Africa) (Bull et al., 2011; Chetty et al., in press). Routine transformation of the cassava model cultivar has subsequently been used to implement the transformation of farmer- and industry-preferred cultivars (Chetty et al., in press; Zainuddin et al., submitted). Our pioneering success with limited resources paves the way for new development and funding schemes by cooperation agencies and foundations.
Biotechnology has been considered an attractive tool to improve cassava (Manihot esculenta Crantz) for traits such as biotic stress. Despite the establishment of the transformation technology in the mid-90’s, its implementation and continuous maintenance in African laboratories has remained scarce. A major constraint for cassava improvement has been the lack of an efficient and robust transformation and regeneration system, and poor knowledge and technology transfer to African laboratories and farmers, which is an important objective for achieving food security and sustainable crop production on the sub-Saharan African continent. Despite some success achieved in genetic modification of the model cassava cultivar Tropical Manihot Series (TMS), TMS 60444, in some European and U.S. laboratories, the lack of a reproducible and robust protocol has not allowed the establishment of a routine transformation system in sub-Saharan Africa. Here we report the first successful implementation of a robust cassava transformation platform in a South African laboratory and its use for the generation of transgenic T200 cassava, a SA industry-preferred cultivar, which. The complete pipeline from generation of cassava FEC to Agrobacterium-mediated transformation and regeneration of transgenic plants has been established, and efficiencies between T200 and TMS 60444 were compared. Results from our study demonstrated high transformation rates for both T200 (23 transgenic lines from 100 friable embryogenic callus (FEC) clusters) compared with TMS60444 (32 transgenic lines from 100 FEC clusters). The successful establishment of a robust cassava transformation and regeneration system in South Africa demonstrates the relevance of technology transfer to sub-Saharan Africa and highlights the importance of developing suitable and reliable techniques prior to their transfer to laboratories offering less optimal conditions.
Genetic improvement of cassava through conventional breeding is challenging due to its high heterozygosity and low fertility. Genetic engineering can be used to complement traditional breeding methods in crop improvement. So far it has only been possible to transform few cassava cultivars, which have limited agricultural importance. Little effort has been placed on developing transformation systems for African cultivars. In order to exploit the desirable traits of African cultivars as well as to increase the genetic diversity of transformable cultivars, it is important to develop efficient and reproducible transformation system for African farmer-preferred cassava cultivars. In this study, we are trying to establish efficient regeneration and transformation system using seven farmer-preferred cultivars (Albert, Ebwanatereka, Kibaha, Kibandameno, Mkombozi, Serere and TME 14) with the intention of laying a basis for introduction of useful traits. The successful generation of friable embryogenic callus and generation of transgenic plants from two farmer-preferred cultivars (Ebwanatereka and Serere) in addition to the model type cv. 60444 are well established at IITA/BecA hub. In addition, efforts to improve the transformation efficiency and engineering of other cultivars are in progress. The efficient transformation of African cassava cultivars will speed up the development and deployment of enhanced germplasm with desired traits and bring the benefits of genetic engineering to African farmers.
Routine production of large numbers of transgenic plans is required to fully exploit advances in cassava biotechnology and to develop product quality events for regulatory approval and delivery to farmers. Pipeline procedures have been developed and implemented for large-scale production and analysis of transgenic cassava plants. Utilizing A. tumefaciens strain LBA4404, co-culture of friable embryogenic callus (FEC) yields an average of 15 independent transgenic events of cultivar 60444 per cm3 of FEC starting material. This system has been employed to produce more than 2500 transgenic events across 35 different genetic constructs for research into RNAi-mediated resistance to geminivirus and potyvirus pathogens, and many 100s of plants modified for nutritional enhancement. Plants generated are screened for copy number and those possessing 1-2 copies advanced for transgene analysis at the RNA level and subsequent trait performance. Plants produced have proven robust, facilitating proof-of-concept for traits in the greenhouse and through confined field trials in Puerto Rico, Uganda, Kenya and Nigeria. Processes developed for 60444 have been adapted for production of product-quality transgenic plants in the farmer-preferred cultivars TME204 and TME7. Approximately 300 regenerants of TME204, transformed for resistance to cassava brown streak disease, have been recovered and are undergoing screening to identify low copy, vector backbone free, siRNA accumulating events for advancement to product selection field trials. Information presented will illustrate significant progress made in developing and adapting the integrated, scaled-up tissue culture, molecular analysis, quality control and tracking systems required to operate high throughput transgenic platforms for cassava.
A total of 20 Tanzania famer preferred cassava (Manihot esculenta) landraces were assessed for somatic embryo induction, sustainability and subsequently plant regeneration. This assessment was crucial since a successful cassava genetic transformation depend mostly on the regeneration ability and plant recovery of specific genotypes. Leaf lobes were used as explants on MS media (Murashige & Skoog, 1962) supplemented with different concentrations of sucrose (0-6%), copper sulphate (0-2mM), and auxin 2,4-D (8-16mg/l) in the presence of hydrolysate and vitamin B complex. Forty percent of all landraces tested demonstrated capability to undergo somatic embryogenesis and regeneration to plantlets while 10% were able to attain cotyledonary stage, 15% globular stage and 35% ended up to callus stage. On the other hand, RNA interference constructs were developed for genetic transformation for resistance against cassava mosaic disease. Double stranded RNA interference (dsRNAi) constructs one carrying 200 bp of replication associated protein (AC1) and the other one 200 bp of the overlapping region of transcription and replication enhancer protein (AC2/AC3) of East African cassava mosaic virus (EACMV) were developed. We used dsRNA expression vector pGSA1285 (pCAMBIA) whereby the AC1 and AC2/AC3 partial gene sequences were inserted in the sense and antisense orientation separated by Gus intron. The partial gene sequences were derived from EACMV isolated from Tanzanian farmer preferred cassava landraces. The RNAi constructs made will be used to transform selected cassava landraces of importance to Tanzanian local farmers through Agrobacterium mediated transformation. This will be the first genetic transformation of cassava landraces in Tanzania for cassava improvement.
RNAi, somatic embryogenesis, famer preferred cassava, Tanzania
Kasetsart 50 (KU50), probably the most important extensively grown cassava cultivar in the world, has been considered as a recalcitrant cultivar for genetic transformation since only few transgenic plants has been reported using shoot organogenesis approach. Several cassava cultivars, such as 60444, in routine transformation could be used for research purposes but are not farmer-preferred varieties due to vulnerability to viral diseases and other drawbacks. Hence, development of an efficient transformation method for KU50 is in demand. In this study, we reported the successful induction of friable embryogenic calli (FEC) and establishment of embryogenic suspension culture of KU50. After co-cultivated with A. tumefaciens strain LBA4404 harboring the binary plasmid pCAMBIA1301, dozens of transgenic cassava regenerated from transformed embryogenic suspension cells via somatic embryogenesis under the hygromycin selection. Several key steps of transformation procedure have been investigated and optimized, including somatic embryo multiplication on DKW medium, FEC purification and maintenance on friable embryogenic callus medium with decreasing concentration of tyrosine (0.5/0.2/0.1 mmol L-1), size control of suspension FEC (250-500 μm), germination of hygromycin resistant somatic embryos on shoot organogenesis medium containing 4 mg L-1 AgNO3. Transformants were verified by GUS assay and rooting test on basic shoot culture medium supplemented with 10 mg L-1 hygromycin. The development of KU50 transformation method provides a tool for genetic improvement of this economically important cultivar via transgenesis.
cassava cultivar KU50, genetic transformation, friable embryogenic callus, transgenic plants
Inbred progenitors offer multiple advantages to crop improvement, e.g. efficient exploitation of heterosis, identification of useful recessive traits, conservation and exchange of germplasm, production of genetic stocks, and application of molecular tools. Cassava inbreeding through successive self-pollinations was attempted but it is not a practical approach. The Bill and Melinda Gates Foundation is supporting an initiative to produce doubled haploids through microspore/anther and ovule/ovary culture and wide crosses. The project also supports the generation of genetic stocks. Anthers extracted from flower buds were cultured into the modified MS and maintained in the dark. Callus induction was observed after four months of culture initiation. Embryogenesis was also induced from tetrads, microspores and mature pollen. Origin of the calli was determined by histological and SSR marker analysis and results indicate that six out of eight samples had a haploid origin. Unpollinated ovules grew to large size in ways that resembled natural development and enclose structures that could support full embryo development in the cultures. Crosses with castor produced four plantlets. Genetic stocks are developed at IITA and CIAT. Partners in China and Uganda established lab facilities and began implementing the technologies with local germplasm. The current goal is to reliably produce plants from androgenic calli, which are being produced reliably through different means.
A reliable method for measuring the pollen viability is of crucial importance for the application in breeding programs and has not been yet well established for cassava. We compared different methods to estimate the viability of pollen grains of two sub-species of cassava: (i) Manihot esculenta spp. esculenta (Mee) and M. esculenta spp. flabellifolia (Mef). Pollen grains used in this study came from the accessions TN 001 (Mee) and FLA 029V-01 (Mef) held in the genebank of Embrapa Cassava and Fruits. Flowers covered before anthesis were collected around 9:00 am, shortly after anthesis. Four methods were tested: (i) colorimetric tests with the dyes acetic carmine (2%), lugol (2%) and acetic orcein (1%); (ii) in vivo germination by assessing the number of germinated grains on the stigma; (iii) in vitro germination using the culture medium proposed by Mbahe (1994); and (iv) fluorochromatic reaction (FCR), evaluating by fluorescence the pollen tubes developed on stigma. In all methods the pollen viability from Mee was lower than Mef. There was no discrepancy in results among the dyes and all of them showed a high percentage of viable pollen, above 90% for both accessions. The in vivo and in vitro germination methods underestimated pollen viability in both accessions with rates below 20%. FCR method was the most reliable estimator of pollen viability, with percentages of 76 and 81% for TN 001 and FLA 029V-01, respectively.
Dehydration is a crucial step in cryopreservation systems, since the moisture content of the cell has to cover a specific range capable to keep cell integrity during ultra-freezing and rehydration without damaging cellular structures. We evaluated different exposure times in laminar flow hood for dehydration of pollen grains and subsequent viability test. Flowers used in this study came from the accession FLA 001 of Manihot esculenta spp flabellifolia held in the genebank of Embrapa Cassava and Fruits. Anthers were placed in open aluminum foil envelopes and directly submitted to the laminar flow to six different exposure times (15, 30, 45, 60, 120, and 360 minutes). Fifty anthers were used for each treatment and as a control for viability test we used pollen derived from fresh sampled anthers. The initial and final moisture content of pollen grains was determined in all treatments. To evaluate the tolerance to dehydration we tested the pollen viability using the fluorochromatic reaction (FCR) method. The grain moisture content ranged from 86% (in anthers exposed for 15 minutes) to 44% (exposed for 360 minutes). Pollen tubes were developed only in fresh anthers (no dehydration) and the ones dehydrated for 15 minutes. The results show that the pollen of this accession is not tolerant to reduction of moisture content above 14%.
Generation of embryogenic callus is a key step in genetic engineering of many crop species, including cassava. Protocols for generation of friable embryogenic callus (FEC) have been lacking for Ugandan cassava cultivars, thereby delaying their genetic engineering for agronomic and other desirable traits. The objective of this study was to determine conditions suitable for production and regeneration of FEC in the Ugandan cassava cultivars; Aladu and Ebwanateraka, and control cultivar 60444. Immature leaf lobe explants were established on Murashige and Skoog (MS) based media for initiation of organized embryogenic callus (OES). To produce FEC, resulting OES were established on Gresshoff and Doy based callus induction media with varying levels of sucrose, maltose, tyrosine, tryptophan, naphthalene acetic acid (NAA) under light and dark conditions. Subsequently, FEC was subcultured to MS-based embryo maturation and embryo regeneration media. The amino acid tyrosine favoured production of FEC in Aladu and Ebwanatereka, but not in 60444, while 20 g/L of sucrose trigged production of FEC in Aladu and 60444, but 40 g/L of sucrose was superior for Ebwanatereka. Media supplemented with 1 ml/L naphthalene acetic acid NAA facilitated embryo regeneration in Ebwanatereka and 60444, while Aladu responded better to 5 ml/L NAA. Light, tyrosine and sucrose were essential for FEC production in Uganda cultivars while NAA was required for regeneration of somatic embryos.
Cassava is an important source of starch and carbohydrates in Uganda. However, production of most of the Farmer preferred cultivars (FPCs) is greatly constrained by pests and diseases. New conventionally bred resistant varieties have been introduced to sustain production but resistance is often overcome by emergence of new pathogen strains. Genetic engineering of FPCs would allow their preservation and sustainable use. For this to be achieved, transformable FPCs need to be identified. The objective of this study was to evaluate two FPCs; NASE 14 and Ebwanatereka, for production of embryogenic structures. Immature leaf lobes were excised from tissue culture plantlets and plated onto MS medium supplemented with 50 µm Picloram for 28 days at 28°C with 16 hours light. Nine leaf lobes were plated per plate and eight plates were used. The plates were scored for production of organized embryogenic structures (OES). The experiment was repeated twice. Both cultivars produced OES; NASE 14 (28.5%) and Ebwanatereka (26.7%) demonstrating their potential to produce target tissue necessary for transformation. Therefore the production of Friable embryogenic callus for use in genetic engineering can then be explored in these cultivars as an option for their improvement.
Basic knowledge on the reproductive biology of cassava is limited. Proper understanding of embryo development is required, for example, to define the best timing for its rescue in the production of doubled-haploids based on wide crosses. Hundreds of microscope sections of cassava flowers and developing fruits from the time of pollination to 24 days after pollination (DAP) were analyzed with light microscope. Tissue was fixed with a mixture of formaldehyde, acetic acid and ethanol and stained with safranin and fast green. Embryo development seems to be strikingly slow at early stages. Globular embryos were only detected 21 DAP along with early stages of heart-shape embryos, which points to unsynchronized embryo development even in the loculi of the same ovary. Embryos of this stage averaged 117µm in length, while the developing seed reached about 9 mm in length. Perhaps young embryos are easily lost in sections. More advanced (torpedo-shaped) embryos, 229µm long, were found soon thereafter (22 DAP) and some embryos already reached the early cotyledonal stage 24 DAP. Embryos 29 DAP were large enough to be excised, reaching an average length of 2.4mm. Embryos younger than three weeks are too small to find under stereoscope and dissect. If embryo rescue is needed at this early stage of development the in vitro culture of fertilized ovules or ovaries, rather than excised embryos, may be more suitable.
Cassava research activities (such as wide crosses to produce doubled haploids), require rescuing embryos at early stages of development. However, there is limited information on the reproductive biology of this crop. Selection of elite “mother” (pollen recipient) genotypes, proper understanding of embryo growth and definition of the most appropriate timing for embryo rescue is of prime importance. Ongoing research suggested that there are large differences in fruit set and development rate as well as for embryos development between different genotypes. Days after pollination (DAP) was found not to be an adequate predictor of embryo size as their size ranged from almost invisible to 8.7 mm in length 32 DAP even within the same mother genotype. The ideal stage for embryo rescue in cassava was from 32 to 36 DAP, because tissues are not hardened, most embryos are visible (> 0.7mm), their excision without injury is feasible. In vitro growth at this stage had a high success rate. A half MS medium supplemented with 0.5 mg/L GA3, 2% sucrose and 0.2% gelrite proved to be adequate for embryo rescue. Rescuing and culturing younger embryos when they are not readily visible may require the inclusion of other tissue such as embryo sac and even part of the ovary.
Cassava, is the main source of dietary starch and household income for over 70 percent of the population in Democratic Republic of the Congo, it is an important source of employment and income, especialy for women. The genetic improvement of cassava through conventional means is however severely constrained by asynchronous and shy flowering nature of crop.. Considering the limitations for the use of conventional methods in the improvement of this important crop, one such option is induced mutagenesis which offers an opportunity to enhance genetic variability exploitable for the improvement of some agronomic traits such as pests resistance . We present in this study the preliminary data on the determination of the radiosensitivity for Congolese cassava landrace as a prelude to a more detailed work that will include other accessions from wider geographical regions where Cassava grown.
In Vitro culture of Cassava (Manihot esculenta ) var.Boma genotypes obtained by meristems culture were exposed to Cobalt-60 gamma irradiation to determine the optimal doses for eventual use as orientation for selection of effective mutagenic treatements that can induce useful genetic changes.
Nodal segments from vitroplants were irradiated with differents doses (5,10,15,20,25 and 30 Gy) while a control batch was not irradiated, the dose of 6Gy leading to an average 50 percentage damage was determined as the optimal dose. The optimal dose was calculated more precisely using the linear regression equation.
Cassava, gamma irradiation, In vitro culture, radiosensitivity
Cassava is a very important crop in the tropics owing to its high production per unit area and its ability to performance in stressful environment. Its production is however, constrained, among other factors, by diseases including cassava mosaic disease (CMD) and cassava brown streak disease (CBSD). The two viruses are caused by cassava mosaic begomoviruses (CMBs) and Cassava brown streak viruses (CBSVs), respectively. In East Africa, resistance to CMD and CBSD has traditionally been achieved through conventional breeding. However, conventional breeding takes long to obtain a plant with desired traits and it may even be hard to achieve due to heterozygous nature of cassava. Mikocheni Agricultural Research Institute (MARI) initiated transformation of cassava landraces as the first initiative to engineer resistance to CMD and CBSD in Tanzania using friable embryogenic callus (FEC) and somatic embryogenesis methods. Cassava cultivars TMS 60444 was successful transformed with pCAMBIA plasmid containing GUS reporter gene at MARI. The following cassava landraces succesifuly produced somatic embryos under MARI conditions: Paja la mzee (4-6 weeks), Katakya (5-6 weeks), Mahonda (5-7 weeks), Machui (4-8 weeks) and Rushura (5-7 weeks). These landraces are being transformed with RNAi constructs to confer resistance to CMD and CBSD.
Cassava breeding is cumbersome and inefficient compared to other crops. International initiatives recognized the fundamental importance of doubled haploid (DH, plants derived from zygotic haploid cell cultures) for both plant science research and commercial success in plant breeding. DH (inbreeding) in cassava would create a baseline for development of populations aimed at identification of high-value recessive traits, production of genetic stocks, and application of molecular tools in breeding. Inbred progenitors will make breeding, maintenance, exchange, conservation and exploitation of germplasm much more efficient, increasing the impact of genetic transformation and molecular markers, and genetic stocks based on botanical seed easily shared. Most successful use of DH technology in breeding is via anther or microspore culture. Recent reports indicates that gynogenesis may also be a highly efficient approach, especially when androgenesis response is low or recalcitrant, there is a reduced number of microspores per anther, and or the number of DH required per genotype is low, such as in the case of cassava. This work describes a method for ovule and ovary culture. Histological analyses show that unpollinated ovules grow in a way that resembles natural post-fertilization development while cultured in vitro. Media enable ovule enlargement and development of structures that could support embryo development in the cultures.
Cassava starch from nine varieties namely; NR 8082, TMS 97/2205, TMS 97/0162, TMS 92/0057, TMS 98/0505, TMS 92/0326, TMS 30572, TMS 82/0058 and TME 419 were evaluated for their suitability as gelling substitute to conventional gelling agents (Gellan gum and Agar) in medium using cassava shoot tips and nodal segments as explants. Explants were seeded singly into a 15ml cassava multiplication medium gelled either in 0.2% gellan gum, 0.7% agar or 7% starch from the nine cassava varieties. Each treatment was represented by 25 test tubes (15 shoot tips and 10 nodal segments). Cultures were maintained at 28oC ± 2, 16h photoperiod and 30-40μEm-2 s-1 flux intensity supplied by white fluorescent tubes on shelves for four weeks. After 4 weeks in culture, percentage survival of explants irrespective of type ranged from 61.5 to 100 with NR 8082 and TMS 97/2205 cassava starch-gelled medium recording the highest score while the mean number of nodes produced per explant ranged between 3.6 ± 1.43 to 5.33 ± 0.87 for shoot tips and 2.73 ± 0.96 to 4.79 ± 0.97 for nodal segments. The highest mean number of nodes from nodal segments was observed in TME 419 starch-gelled medium. This result is in agreement with earlier findings thus confirming the gelling potential of TME 419 cassava starch in medium for micropropagation of cassava.
TME 419, cassava starch, explants, gelling agent, micropropagation
An important constraint that limits cassava’s full potential is the short shelf life of harvested roots. Cassava roots undergo rapid deterioration 24 – 48 hours after harvest, the so-called post harvest physiological deterioration (PPD) which renders the roots unpalatable and unmarketable. Genetic engineering represents an efficient approach to circumvent the limitations of traditional breeding for vegetatively propagated crops with high degree of heterozygosity such as cassava. PPD is caused when wounds are created as a result of harvesting cassava storage roots. The wounds initiate an oxidative “burst” with subsequent over-accumulation of reactive oxygen species (ROS). Inadequate wound healing and the “rare return to homeostasis from stress” cause prolonged and oxidative damage spreading from the site of injury. Up-regulation of defense-related genes occurs in cassava storage roots post-harvest; but this is insufficient in magnitude and timing to prevent deterioration. Therefore, reduction of the initial oxidative burst in cassava root was tested by constitutively over-expressing enzymes involved in ROS scavenging. Dehydroascorbate reductase (DHAR) is an important enzyme functioning in the generation of ascorbate (AsA), a potent antioxidant protecting plants against oxidative damage. To examine the potential of DHAR to reduce or delay the oxidative stress, we have developed transgenic cassava plants constitutively over-expressing DHAR. The transgenic lines were validated by PCR for the presence of transgenes. The transgenic lines are currently being evaluated for their level of tolerance to PPD and other abiotic stresses such as drought under greenhouse.
Genetic improvement of cassava through conventional breeding is challenging due to its high heterozygosity and low fertility. Genetic engineering can be used to complement traditional breeding methods in crop improvement. So far it has only been possible to transform few cassava cultivars, which have limited agricultural importance. Little effort has been placed on developing transformation systems for African cultivars. In order to exploit the desirable traits of African cultivars as well as to increase the genetic diversity of transformable cultivars, it is important to develop efficient and reproducible transformation system for African farmer-preferred cassava cultivars. In this study, we are trying to establish efficient regeneration and transformation system using seven farmer-preferred cultivars (Albert, Ebwanatereka, Kibaha, Kibandameno, Mkombozi, Serere and TME 14) with the intention of laying a basis for introduction of useful traits. The successful generation of friable embryogenic callus and generation of transgenic plants from two farmer-preferred cultivars (Ebwanatereka and Serere) in addition to the model type cv. 60444 are well established at IITA/BecA hub. In addition, efforts to improve the transformation efficiency and engineering of other cultivars are in progress. The efficient transformation of African cassava cultivars will speed up the development and deployment of enhanced germplasm with desired traits and bring the benefits of genetic engineering to African farmers.
Manihot esculenta Crantz (Cassava) is an important crop in the tropics and subtropics, used not only as a staple food but also as a source of renewable energy (biofuel) and raw material for industry. Cassava is a vegetatively propagated perennial shrub that typically has a 12 month growing cycle. It is also cross pollinated and highly heterozygous. Genetic improvement of cassava could benefit from developing inbred lines which will allow for specific hybrid combinations to be identified using parents with known characteristics. Use of inbred lines will facilitate exploitation of heterosis in cassava. The development of inbred lines in an outcrossing crop like cassava would take many years based on a least 5-6 generations of selfing to achieve over 95% homozygosity. Many cassava lines also show inbreeding depression that make it difficult to maintain inbred lines and continue to self pollinated them. One strategy for the development of inbred lines is the development of double haploid plants that become homozygous with fixed traits in one generation. Techniques to develop haploids and doubled haploids have been identified in other crops like maize and barley but not yet in cassava. As part of a multifaceted strategy to develop doubled haploids, this project seeks to exploit wide crosses coupled with potential chromosome elimination to produce haploids and doubled haploids. The strategy utilizes hybridization between M. esculenta and Ricinius communis. This paper will summarize work in progress at IITA to develop this wide crosses and to characterize the progeny produced from these crosses.
Availability of the homozygous lines will give a great impact in gearing up the crop improvement in cassava. Attempts were made to induce androgenesis in the cultured anthers and the microspores with SM and TMS. Four staminate bud size categories were tested. MS modified liquid medium was used. A heat shock was given prier inoculation. The blended pollen mixture was filtered with a series of meshes and collected the microspores was cultured. Fifty four percent and 36% callus induction was observed in anthers from 2.3-2.6 mm and 2.9-3.2 mm size categories respectively in SM. In TMS greatest response (17%) was observed from the anthers at the 2.3-2.6 size category. Callus development, breaking through the anther wall indicated the androgenesis induction from the microspores within the anther. Greatest percentage of micro-callus was observed in microspores isolated from the flower category of 2.3-2.6 mm. Embryogenesis has been induced from three stages of gametogenesis, tetrads, microspores and mature pollen grains and different stages of micro calli development was identified. Cytological studies conducted with acetocarmine after exine digestion revealed that the multicellular structures have been formed in all three stages of gametes. This is the first report of pollen-derived microcalli in cassava.
Availability of a reliable protocol for doubled haploid (DH) plant production in cassava would accelerate the improvement of this valuable food crop via conventional breeding programs. Haploid culture is a technique that can be used to improve the production and occurrence of the frequency of haploids. Anther culture is the most common technique for DHs production. Attempts were made to develop a protocol for doubled haploid plant production in cassava using this technique. Anthers extracted from the flower buds were cultured into the modified MS medium and maintained in the dark. Callus induction was observed after four months of culture initiation. Origin of the calli was determined by histological and SSR marker analysis. Cultured anthers were subjected to histological analysis after four months of culture initiation. Obtained micrographs clearly showed the formation of multicellular structures within the exine matrix of the pollen grain in the pollen sac. Eight anther-derived calli were subjected to SSR marker analysis. Using seven pre-identified heterozygous SSR, allele status of the anther-derived calli was assessed. The results showed that six out of eight samples had a significant haploid origin.
Promoters for driving effective, targeted gene expression are a prerequisite for modification of cassava storage roots for transgenic biofortification and traits such as modified starch. The heterologus promoters namely patatin, isoflavonone synthase (IFS), granule bound starch synthase (GBSS), sporamin, RolB, and ORF2 were tested, in addition to CaMV 35S were tested for their action in cassava. Each promoter was fused to the uidA reporter gene and used to produce transgenic plants of cassava cultivar 60444. Greenhouse plants were analyzed for GUS expression in shoot and root tissues at 3, 4 and 5 months after planting. CaMV35S promoter driven expression in cassava was strong and constitutive, with a higher level of expression occurring in the shoots than in root tissues. In comparison, potato GBSS, IFS and ORF-2 drove relatively weak expression patterns in cassava with highest expression observed in the fibrous roots, while within tuberous roots, stems and leaves highest activity for these promoters was seen in the vascular tissues. Activity for the sporamin was strongest in the tuberous roots though its expression was significantly less compared to that of CaMV 35S. Rol-B driven activity was strong in most tissues particularly in vascular and dermal regions but not specific to the roots. Patatin driven expression was strongest in the vascular system, especially so in secondary xylem tissues of storage roots where it was comparable to that of the CaMV35S promoter. However, unlike the latter, the patatin promoter drove minimal expression in upper stem areas and in leaves. Results demonstrated that none of the heterologous promoters studied drives specific storage root transgene expression, with all active to some extent in the shoot vascular tissues. However, patatin proved to be a strong promoter in cassava storage roots with minimal expression in shoot tissues and therefore presents a good candidate for driving transgenes of interest in tuberous roots.
To date recalcitrance to genetic transformation in cultivars other than 60444 has proved to be a bottleneck in generating transgenically enhanced cassava varieties for deployment to breeders and farmers. Efforts in our laboratory have focused on adapting the friable embryogenic callus (FEC) system into a wider range of genetic backgrounds. FEC was successfully generated and genetically transformed with an ER targeted version of the green fluorescent protein (GFP) by co-culture with A. tumefaciens strain LBA4404. Whole plants have been regenerated through this method in cultivars TME3, TME7, TME12, TME14 and TME117 from West Africa, and Ebwanateraka, Teraka, TME204, Serere, Aladu and Bao from East Africa, in addition to the common Asian variety MTai16 (Ku50). Variables found to be important in adapting the transformation system included extension of the co-culture time from two to four days and avoiding use of carbenicillin. Robust GFP-expressing plants were established in the greenhouse in all cases except Serere and Ku50, which instead produced weak offtypes of the kind previously reported for cassava regenerated through this system. Production of transgenic TME204 and TME7 has been scaled up to pipeline levels and is now routine, resulting in recovery of hundreds of independent events modified for putative resistance to CBSD and nutritional enhancement respectively. While the FEC system remains challenging in some cultivars, it is proving to be an adaptable tool for production of transgenic cassava across a range of genetic backgrounds.
The suitability of red fluorescent protein (DsRed) as a visual reporter gene for use in cassava genetic transformation was evaluated. Friable embryogenic callus derived from cultivar 60444 was transformed by both Agrobacterium and biolistics, using vectors consisting of ER-targeted DsRed under control of the 35S cauliflower mosaic virus promoter. Fifty callus lines were recovered from a single transformation, out of which 30 callus lines expressed DsRed and 26 were regenerated into healthy plants. High and uniform DsRed expression was observed at the callus, somatic embryo and organs of whole in vitro and soil-grown cassava plants. Unlike analogous plants transgenic for green fluorescent protein (GFP) minimal interference by phenolic compounds and chlorophyll was observed. Detailed imaging of internal structures of the petiole, stem and storage roots were obtained with expression of DsRed compared to GFP, particularly in the storage root. Dual visualization of both genes in a single transformation system was relatively easy when analyzed at their respective wavelengths with the appropriate filters, thereby establishing a system for monitoring two independent marker gene expressions at the same time in the same tissue. No phenotypic impact was observed in highly DsRed expressing greenhouse grown plants, indicating that DsRed presents potential as a tool for studying gene expression in cassava.
Somatic embryogenesis is one of the major pathways used for genetic transformation in most of the plants as it gives true to type and non-chimeric transgenic plants. The two phases of induction and expression of embryogenesis are suggested to be independent of each other and influenced mainly by endogenous hormones and exogenous plant growth regulators (PGRs). In cassava (Manihot esculenta Crantz), which is a very important tuber crop since decades, feeding more than 500 million people of the Tropics and sub-tropics, the genetic modification either for disease resistance or for quality improvement is so far done successfully only through somatic embryogenesis. Conventionally, little improvement has happened to the disease resistance and productivity aspects of this crop due to in breeding depression and the polygenic and recessive nature of many desirable traits. Embryogenesis in cassava is exceptionally important for the developing countries so as to impart superior traits into farmer preferred cultivars using genetic engineering. Indirect somatic embryogenesis using immature leaf lobes and axillary buds have been well established. The process being highly genotype dependent and distinctly variable with laboratory conditions, it was necessary to compare the regeneration ability of these two explants from different African cassava cultivars (Albert, Kibaha, TMS 96/0160, 96/1089A, TME3, TME4, TMS 30572) in comparison with popular Indian cultivars (H226 and H165) in the embryogenesis medium (MS+2mMCuSO4+50mM Picloram). Explant preference for somatic embryogenesis by different cultivars was different. H226 and H165 showed almost 100% response for young leaf lobe explants, but less than 15% on axillary buds. Albert, and TMS 96/0160 showed between 65 and 75% response. Cultivars TME3, TME4, and TMS 30572 showed below 50% response on both the explants used. When Kibaha preferred axillary bud explants (61%), 96/1089A showed high response (77.5%) on leaf lobe. Our findings suggest that in each genotype explants selection plays a major role for optimum outcome.
Towards the androgenesis induction in an in vitro microspore culture for doubled haploid production, the main bottle neck is to switch the normal gametophytic development pathway to a sporophytic one. This switch can be induced by applying a stress pretreatment onto the inflorescences, and visualized with a DAPI staining to show the nuclear division in model plants, such as Hordeum vulgare and Brassica napus, etc. But this method has proven to not be applicable in cassava due to its exine wall which blocked the emission fluorescence from observation. By combing partial digestion of the exine wall and different fluorescence dyes, we finally figured out a method to see through the exine wall and visualize the nuclear division inside the microspore. Using this method, we successfully developed a system for monitoring cassava androgenesis induction. In our study, the sporophytic nuclear division has been initiated, By means of optimizing the pretreatment and culture condition, a doubled haploid production method could be established in near future.
Cassava female flowers contain a single pistil and are devoid of androecium, corolla and calyx. Three carpels of pistil are fused resulting in 3 loculli and a central columella. A short style ends with a three-lobbed, massive stigma with undulated receptive edges. The mature ovule is anatropous and stays single in the loculus. It has a large, parenchymatic nucellus not completely covered with a thick and short inner integument and a longer outer integument. The latter ends with thickenings called elaiosomes or curuncles. The integuments form a micropylar canal that surrounds a nucellar protrusion (nucellar beak), similar in size to the part of nucellus covered by the integuments. The nucellar beak reaches an outgrowth of the columella called an obturator. At maturity, the beak fuses with the obturator completing a transmitting tract (TT) for growing pollen tubes. The TT that starts at the stigma edges, and continues through the style, columella, obturator and the beak can be regarded as an adaptation to hot climates and temporal water deficit. Histolochemical analyses performed with different staining techniques show variability of tissue types and their components including changes following pollen tube passage through the tissue. This is the first study showing detailed histology of the mature cassava female organs prior and post pollination.
Mass propagation by somatic embryogenesis (SE) can be a technique to faster new cassava varieties diffusion to the farmers. Secondary SE cultures were established on solid and liquid media for the clone Rayong 9. Effect of five different cytokinins in secondary SE was tested. 6-benzylaminopurine, kinetin, zeatin, isopentenyladenine and adenine were added at 1 mg/l to the induction and maturation media. From this experiment, it can be concluded that adenine doesn’t have an inhibitory effect at the concentration assessed. Consequently, we tested higher adenine concentrations. The addition of adenine at 1, 5, 20 and 40 mg/l led to similar rates (9 to 13 %). The conversion rate tended to be lower for adenine 10 mg/l. The acclimatization survival rate varies from 40 to 67 %: it tends to be higher for the plantlets issued from adenine concentrations higher than 10 mg/L. However, adenine at 10, 20 and 40 mg/l tended to improve the process relatively to embryoid sizes and plantlet survival rates in the greenhouse.
Climatic change as well as high temperatures and increased water deficit are often associated with drought effects on crop plants. The basis of drought tolerance in cassava is complex and may be driven by diverse adaptive mechanisms and usually of a polygenic nature. Cassava is a hardy crop with relatively high root and foliage production under rain-fed systems and low soil fertility whose production is expanding into semiarid and arid areas. In our study, we are using different strategies to produce varieties that would maintain high productivity in spite of water stress conditions. Firstly we evaluated the response of 13 elite Nigerian varieties putatively regarded as drought-tolerant, 47 Latin America genotypes introduced from CIAT and 90 drought-tolerant genotypes from EMBRAPA at Minjibir in Kano, Nigeria. Across the genotypes, fresh root yields ranged from 20 to 29 t/ha. Also we are seeking to understand the genetic basis for drought tolerance through the identification of genes controlling traits associated in cassava plant response to drought. We have also generated populations which are currently under evaluation in Kano, Nigeria (267 progenies) and another 204 seedlings in a homologous environment in Ghana (Tamale). To enhance phenotyping in controlled conditions, the Generation Challenge Programme has supported the building of state-of-the-art irrigation equipment and weather stations for weather data capturing in Nigeria and Ghana for a proper phenotyping of these populations. The approaches being deployed in screening germplasm and identification of genomic regions responsible for drought tolerance in cassava would lead to faster delivery of climate-smart varieties for poor resource farmers who grow cassava in marginal environments and under most dire economic situations. Such resources and products from this project are veritable tools for exchange among members of the cassava breeding community of practice (CoP) in Africa.
Cassava is a food security crop in drought-prone regions, as well as in regions of with reliable moisture where it has the potential for high yields. To fully exploit the potential use of molecular genomic tools in breeding for drought and water-limited environments, reliable phenotypic traits and methods to measure them are needed. The traits should be well correlated with overall yield performance, heritable, populations should have sufficient genetic variability for the traits, be applicable for high-throughput and economical sampling in field trials, and traits should have a clear-cut and rational explanation for its physiological or molecular function in drought tolerance. Several traits were examined in trials conducted in Brazil and Colombia, including plant height, above ground dry matter accumulation, leaf retention, stomatal conductance, soil water extraction, leaf and stem abscisic acid (ABA) accumulation, concentration of leaf osmotically active solutes, storage root size at the early stage of development, and partitioning index (PI) at an early stage. Several populations were examined, including diverse lines from breeding programs representing a range from drought susceptible to tolerant, and a biparental cross of susceptible X tolerant parents for QTL identification. Despite sampling a diverse range of genotypes, the range in osmotic solute concentration was limited. Stem starch reserves appear to play a role in supplying carbohydrate for survival and recovery after extended dry periods, though to phenotype their role in drought tolerance may require cycles of drought followed by rewatering, which is cumbersome and costly. Given cassava’s tendency to close stomata with just a slight lowering of leaf water potential, measurements of stomatal conductance and leaf ABA can provide sensitive evaluation of genotypes. PI at an early stage (storage root initiation) is correlated with genotypic tendency for partitioning into the harvested sink and holds promise as a valuable trait for drought phenotyping.
Cassava (Manihot esculenta), grown for its bulky starchy root, is an important food security crop in Africa. Cassava stores very well underground with flexible harvest duration often between 7 and 24 months after planting (MAP). However, after harvest, the root suffers from post harvest physiological deterioration (PPD) after 48-72 hours resulting in huge losses in income to farmers especially in rural areas with poor access to markets. The lack of adequate genetic variation in elite gene pools have largely limited breeding efforts to improve cassava for delayed PPD. Complementary breeding initiatives to develop delayed PPD cassava genotypes using induced mutagenesis and gene mining of wild relatives were undertaken. Irradiation with gamma ray at two dosage levels of 12GY and 15 GY were applied to in vitro plantlets of three improved varieties and then micro-propagated to develop M1 population. Delayed PPD found in M. walkerae was introgressed into cassava via backcross, and advanced backcross populations developed were evaluated at 12 MAP for delayed PPD. Results revealed nine M1 mutants with delayed PPD at 14 days after harvest (DAH). Cassava is highly heterozygous and expression of recessive genes or deactivation of gene silencing through mutation are likely reasons for mutant expression in M1. Given that the irradiated plantlets were micro-propagated over three cycles to reduce chimera, some of the mutants may be identical copies of the same genetic material. Evaluation of advanced backcross populations developed from M. walkerae identified 45 genotypes with delayed PPD at 14 DAH indicating that the trait was successfully introgressed from wild relatives into cassava. The two complementary approaches have led to the development of delayed PPD germplasm which would be further tested for trait stability in advanced populations. The germplasm holds promising breeding prospect of improving cassava for delayed PPD to enhance commercialization of the crop.
Cassava storage roots suffer from a rapid post-harvest physiological deterioration (PPD) within 24-48 hours of harvest, which affects their quality and marketability. PPD is a reactive oxygen species (ROS)-mediated process, which the root’s ROS-scavenging systems are insufficient to contain. We have generated independent single-insert transgenic lines of cassava in which the superoxide dismutase (SOD) gene is driven by the root-specific promoter from patatin, with the objective of producing storage roots in which this anti-oxidant enzyme is present at higher than normal levels at harvest. Here we present data on the effects of this construct on the morphology and physiology of the plant and its roots, expression levels of the gene-construct, changes in activity of SOD, and its effects on the storage root’s PPD response.
Cassava resilience is one of its most prized features. Being a perennial crop cassava has a plasticity that allows it to overcome most biotic and abiotic stresses. There is still considerable work to be done understanding the anatomical, biochemical, physiological and/or genetic basis of tolerance to different stresses. Protocols and equipment for measuring the phenotypic responses and proper screening of cassava germplasm (that still remains largely unexplored) need to be developed. The impact of climate change on the environment will likely impose new breeding needs or accentuate old requirements. Rainfall will increase in many cassava growing areas. This will result in higher risks of soil erosion. In other areas, drought may be exacerbated. Herbicide tolerance combined with direct planting would be ideal technologies to overcome these problems. Rapid production of planting material of new varieties adapted to the new environmental conditions will also be required. In other cases, new varieties combining sources of tolerance to different stresses will need to be assembled quickly. The development of partially inbred genetic stocks (to be used as sources of tolerance) will facilitate this process. Improved protocols to reliably screen for tolerance to post-harvest physiological deterioration are under evaluation and is a requirement to exploit the recently found sources of tolerance. Aggressive phenotyping of germplasm is required to develop a complete menu of options to address different biotic and abiotic stresses.
A major constraint to the development of cassava is its short shelf-life due to post-harvest physiological deterioration (PPD) of cassava roots shortly after harvest. In order to identify key pathways and players in the onset of PPD, quantitative proteomics approaches were developed and implemented. The use of isobaric Tag for Relative and Absolute Quantification (iTRAQ) technology generated quantitative proteomics data for nearly 1400 non-redundant proteins (Owiti et al., 2011).
In order to increase proteome coverage we performed a large-scale label-free quantitative proteomics study with cassava roots undergoing PPD. Over 2400 unique proteins were identified with this procedure (Vanderschuren et al., unpublished data). To our knowledge our study represents the most extensive cassava root proteome coverage. For quantitative proteomics analysis, we compared spectral count and MS intensity to list the most abundant proteins in cassava roots as well as to identify novel protein candidates with altered concentration profile during PPD. Enzymatic activities of selected candidates in cassava accessions contrasting for PPD susceptibility were characterized. Our proteomics data is being integrated into the pep2pro database (Baerenfaller et al., 2011) for easy and rapid access by the cassava research community.
Cassava (Manihot esculenta) tubers are rich in starch and serve both as a vegetable and a key stable food in Tropical areas. Careful processing of cassava tubers is required to avoid the risk of cyanide intoxication due to degradation of cyanogenic glucosides. Cyanogenic glucosides are ancient bioactive plant constituents serving as defence compound. Cassava produces the cyanogenic glucosides linamarin and lotaustralin from the amino acids valine and isoleucine, respectively. The entire pathway for cyanogenic glucosides synthesis in cassava has been isolated and characterized. The pathway consists of two membrane bound cytochromes P450, belonging to the CYP79 and CYP71 family and a soluble UDPG-glucosyltransferase. Two homologues of each of these enzymes have been identified. The cells involved in synthesis of the cyanogenic glucosides are found to be located in three distinct areas of the petioles. 1) They are found in the cortex indicating a role in defense, 2) they are found in the phloem parenchyma pointing to a transport downwards in the plant and 3) they are found in the xylem parenchyma. This last position might indicate that cyanogenic glucosides serve as a sink for nitrogen from the xylem sap. Besides serving a protective role, the cyanogenic glucosides may also function as a storage source of reduced nitrogen.
Plants have complex defense systems for combating harsh environmental stresses. Stress acclimation is an effective mechanism that plants have evolved to adapt to changing environment; after underwent stress acclimation, plants are typically more tolerant to adverse stresses. Despite that little is known about the molecular mechanisms of stress acclimation, it is conceivable that a slew of transcriptome variations and rewiring of genetic circuitry occur after stress acclimation. MicroRNAs (miRNAs) have been recognized as key gene regulators in eukaryotes, playing critical roles in development and stress tolerance. Here, we performed a systematic, comprehensive study of miRNAs and their potential roles in cold acclimation in two agri-economic important Euphorbiaceous plants, Cassava (Manihotesculenta) and Castor bean (Ricinuscommunis). Using NextGen Sequencing, we profiled the small noncoding RNA (sncRNA) species and protein-coding genes from the plants that experienced dramatic temperature decrease, that underwent cold acclimation and that grew under normal condition. We identified 61 and 22 novel miRNAs from the sequencing data and experimentally validated 18 in Cassava, respectively. We also identified 36 and 11 differentially expressed miRNAs, many of which were specific to one of the stress conditions. Furthermore, we detected a large number of mRNA genes differentially expressed in plants under cold stresses with and without stress acclimation. Many of these genes were putative targets of miRNAs and had expression variations anti-correlated with the expression of targeting miRNAs. The targeted mRNAs were enriched with functions related to stress, MYB33, TCP2/3/4 and APS1. Our study provided the first results on sncRNA gene regulation in stress acclimation, and shed lights on the role of miRNAs and pathways affected by cold stress and stress acclimation in plants.
Cassava has been identified as hardy crop that can grow on low nutrient and poor soil with little water. Due to expanding dry agro-ecology and short rain for rain-fed agriculture in dry ecology, early bulking cassava has been recognised as an important character for variety in a drought prone agro-ecology. Five released varieties in Nigeria and 29 genotypes from Latin America germplasm were evaluated in Mijinbir Station, Kano State in Nigeria over three years. Randomized complete block design was used with standard 6 X 6 plot size and a local check (Dakata). In this trial we evaluated for the best early bulking varieties from both the local germplasm from Nigeria and others from the centre of origin. Here we show that AR38-8, CR14B-218, CR52A-1 of Latin America origin have fresh root yield ranges from 20 ton ha-1 to 29 ton ha-1,dry root yield 3.8 ton ha-1 to 5.88 ton ha-1, dry matter content 50% to 61% and harvest index 0.43 to 0.59 in the dry ecology.
We investigated the effect of CO2 concentration and water stress on dry mass accumulation in cassava plants grown in greenhouse conditions in 12L pots and maintained with either 390 or 750 ppmof CO2. Two water treatments were applied: (i) consistently well-watered (WW) and, (ii) periodically water deficit (WS), imposed by withholding irrigation. Five 7-day cycles of water deficit were imposed, with each cycle followed by irrigation prior to the start of the next cycle. Plants were harvested 92 days after the initiation of treatments and oven-dried at 70oC until constant mass. The drought greatly reduced the total dry mass (TDM) of plants, showing that five cycles of deficit treatment was quite strong. The treatment 390_WS showed a reduction in TDM of 52% compared to 390_WW, while plants of the treatment 750_WS decreased by only 22% in relation to 750_WW. Also, plants grown under 750_WS produced 61% more TDM than plants grown under 390_WS. The effect of elevated CO2 in reducing the negative effects of water stress was even more evident in the production of dry mass of tuberous roots, since the amount produced by plants under 750_WS was 111% greater than plants grown under 390_WS. Based on these results, we conclude that the increase of the CO2 concentration reduced the effects of drought on dry mass production of cassava.
This study evaluated how different nitrogen forms affect photosynthetic responses of cassava to CO2 concentration. Cassava was grown in 12L pots in a greenhouse (30/25oC day/night) at 390 or 750 ppmof CO2. Three nitrogen treatments were applied: (a) 12 mM NO3-, (b) 6 mM NO3- + 6 mM NH4+, and (c) 12 mM NH4+. At 36 days after treatments began, plants grown under elevated CO2 and fertilized only with NO3- (750_NO3-) exhibited photosynthesis rates similar to plants grown under 390_NO3-. In addition, photosynthesis rates of plants at 390_NO3- were higher than for plants at 750_NO3- when both were measured at the same CO2 concentration (Ca) of 750 ppm. These results indicate photosynthetic acclimation in cassava plants exposed to CO2-enriched atmosphere resulting in reduced photosynthetic capacity. However, photosynthesis rates increased as NH4+ increased in the nutrient solution, such that photosynthetic acclimation was reduced for plants fertilized with only NH4+. This positive effect of NH4+ was not observed in more advanced growth stages, with plants at 750_NH4+ showing toxicity symptoms, plus photosynthesis and dry matter production much lower than plants at 750_NO3-. But 390_NH4+ plants were more affected than 750_NH4+ plants. So, our results indicate that increasing carbon supply can minimize the negative effect of NH4+ on cassava plants.
In the process of modeling the effects of climate change on agricultural production, bio-physical crop models are being combined with future climate scenarios, to draw feasible agricultural yield changes in the mid and long term, and then combined in partial equilibrium models to determine future socioeconomic impacts of climate change. In our work we analyzed the changes in climate over the last 100 years and the likely change in climate up to 2050; assessed the climate suitability of crops in current climate conditions and how suitability will be affected by climate change; estimated the potential impact of these changes in suitability on an economic and socio-economic point of view and proposed some adaptation and mitigation policies for agriculture sector in Thailand. To model the bio-physical response of crops, we used the ECOCROP model, that generates suitability factors. An econometric model was developed to relate the suitability factor to the actual yield levels in different regions of Thailand, adding as explanatory variables geographical conditions, socioeconomic parameters, and management variables, that helped explain the transition from a suitability index to a yield value. From this econometric model, future scenarios were built to analyze the effects of climate change in future cassava production in Tailand. The DREAM partial equilibrium model was used to assess the economic impact of the changes in yield. The results show a favorable change in Cassava production under most climate scenarios analyzed.
Climate change is a global challenge that has a particularly strong effect on developing countries such as Nigeria. This has resulted in sporadic weather patterns in certain areas where cassava is grown. Cassava farmers who are mostly operating at subsistence level in Nigeria are struggling to cope with these erratic changes.
Technologies have been developed in National Root Crop Research Institute Umudike to help ameliorate the impact and enable them continue producing under the present environmental conditions. Some of these include the development of drought tolerant clones such as TMS 98/0505, TMS 98/0581, TMS 98/0510, and TMS 91/02324. These varieties have undergone field evaluations and are being multiplied and distributed to farmers. Also decline in soil fertility is being addressed by development of soil resource base improvement packages which include intercropping cassava with legumes and integrated nutrient management in cassava production system. This paper addresses the detailed packages that have been developed at NRCRI and their importance for sustainable production of cassava in Nigeria.
The study examined the effects of climate change on the biotic reaction and productivity trends of nine improved cassava varieties grown by Nigerian farmers and their implications on Nigeria’s future food security in the past ten years (1990–2000). The result showed that the varieties lost resistance to major cassava pests and diseases (CMD, CBB, CAD, CGM, CM) as years passed by and yield followed the same trend as variations in seasonal changes of rainfall, temperature, sunshine and relative humidity due to climate change. The interactions of climate change, biotic stress and cassava productivity over time showed negative trends in growth and yield of the varieties. The implication is that biotic stress was sufficiently high to mask the resistance to pests/diseases and yield of these varieties grown by poor resource farmers. This indicates that the varieties cannot sustain high productivity, hence affects Nigeria’s future food security. Two varieties (NR 8082 & TMS 30572) were more tolerant to climate induced biotic stress than other varieties because their yields were only 10% lower than initial yields at the time of release. This negative production trend resulting from the interaction of climate change on the resistance and productivity of the varieties calls for additional breeding efforts to develop new varieties and integrated management strategies for sustainable yield that could ensure future food security in Nigeria.
Cassava (Manihot esculenta Crantz) roots initiate deterioration less than 72 hours after harvest due to bulkiness. Post harvest physiological deterioration (PPD) account for significant annual yield losses globally for fresh cassava roots. Lack of varieties with low delayed PPD has been due to loss of genetic variation in available gene pools, which has resulted for the set back in breeding for tolerance for PPD. Wild relative waekarea is a good source of delay PPD and for improving genetic variability improved varieties. In this study, second backcross introduced from CIAT was introduced to NARs in Africa to evaluate and used the selected varieties to breed for delayed PPD in Africa cassava germplasm. Four hundred and sixty nine in vitro PPD genotypes of BC2 polulation from CIAT from the wild relative Manihot wakaerea were multiplied, hardened, weaned, transferred to the field and evaluated for the first year for delayed PPD at the National Root Crops Research Institute (NRCRI), Umudike, Nigeria. Delayed PPD were evaluated at 7, 14 and 30 days after harvest (DAH). Out of the population of the BC2 cassava plants planted on the field, only 53% of the BC2 plants showed good establishment resulting in the evaluation of about 93 BC2 genotypes for delayed PPD. Using specific levels of PPD, results indicate that about 73% of the genotypes were found to have high resistance level of PPD at 7 DAH of which were 49 genotypes while 45 genotypes corresponds to individuals without PPD. Forty-six percent of the genotypes were highly resistant at 14 DAH. Two genotypes maintained 0% at 30 DAH in the half sib populations BIPD280 and BIPD289 respectively. The varieties used are developed from a BC1 population of wakaerea as a donor PPD gene that is highly tolerant to PPD. The second backcross to introgress CMD resistance for African NARs evaluation. There is need to further validate these population for the second year to determine stability of genetic basis and if heritable and to estimate the influence of G x E interaction in trait expression.
Cassava is mostly grown as a raw material for starch industries and to some extent for food in India. Considering the agro-climatic diversity of India that has 15 agro-climatic zones, the present investigation studied the performance of cassava under varying nutrient regimes, micro irrigation-fertigation treatments and very low critical inputs and their impact on the yield and quality of cassava. Four different agro-climatic zones were selected to execute the above trials namely i) Southern plateau (Peddapuram: temperature 25.6oC to 36.2oC and average rainfall 1925.6 mm), ii) West coast plains and hilly terrain region (Yethapur: temperature 19.4oC to 37.6oC and average rainfall 1371.5 mm), iii) Gujarat plains (Navsari: temperature 13.3oC to 37.4oC and average rainfall 507.2 mm) and iv) Western dry region (Udaipur: temperature 5.4oC to 38.2oC and average rainfall 176.4 mm). Under the Integrated Nutrient Management trial, highest tuber yield, 35.33 t ha-1 was obtained at Yethapur, however, the various treatments did not have any significant influence on the Starch content. In the micro irrigation – fertigation trial, highest tuber yield (58.8 t ha-1) was obtained when irrigation at 100% CPE + 100% RDF was applied. The low input techniques gave a maximum tuber yield of 24.64 t ha-1. The potential of cassava as a climate change resilient crop was substantiated in the study by the economic tuber yield and quality under diverse climatic zones.
Cassava (Manihot esculenta Crantz) holds much promise for meeting the need for food security in equatorial regions. While an excellent source of carbohydrate but it contains relatively high concentrations of the cyanogenic glucoside (CNc), and low levels of some essential micronutrients. Eating inadequately processed cassava can cause acute cyanide intoxication and neurological diseases such as konzo. Rising CO2 affects all plants directly, through the process of photosynthesis, and indirectly by changing the climate affecting yield and composition. We compared the cyanogen and micronutrient levels in leaves and tubers of 10 different cassava cultivars growing at three different sites in Mozambique. We found a significant genotype x environment effect on CNc and micronutrient concentration. The degree of water stress at each site was estimated using the ratio of different carbon isotope (d13C). The colonization of roots of all cultivars by arbuscular mycorrhizal fungi was also quantified, and found to be high, indicating that mycorrhizae play a key role in plant nutrient acquisition in these low-input farming systems. To further test the environmental effects, we grew cassava at two temperatures (23°C and 34°C) and imposed a drought treatment, in a factorial design. CNc was significantly higher in the young leaves and tubers of droughted plants. Temperature alone was not associated with any change in CNc, but changes in d13C showed that higher temperatures amplified the effect of drought on CNc. We conclude that cassava is well adapted to cope with global warming, and that water stress is more important in determining CNc than either temperature or rising CO2.
Cassava (Manihot esculenta Crantz) contains two cyanogenic glucosides linamarin and lotaustralin which are bioactivated upon tissue disruption by the sequential action of β-glucosidases (linamarases) and α-hydroxynitrile lyases (HNLs) to release toxic cyanide. Apart from playing an important role in the defence of the plant the liberated cyanide may be further converted into ammonia, asparagine and aspartic acid by β-cyanoalanine synthases (CASs) and β-cyanoalanine hydratases (NIT4s). Thus CASs and NIT4s act as detoxification enzymes and facilitate the recovery of nitrogen stored in the cyanogenic glucosides. In this study we have taken several approaches to analyse the endogenous turnover of linamarin and lotaustralin in cassava. The cellular localisation of linamarase and HNL has been determined in leaves, petioles and stems of a low and a high cyanide cultivar by using specific antibodies combined with confocal microscopy. In addition, the transcript abundance of linamarase, HNL10, two β-cyanoalanine synthases (CASa and CASb) and two β-cyanoalanine hydratases (NIT4.1 and NIT4.2) has been measured along with the levels of linamarin and lotaustralin in four tissues; leaf, petiole, outer and inner part of the stem. An observed variation in transcript and cynanogenic glucoside levels suggest that the compounds either are transported or broken down or a combination of both depending on the tissue localisation.
Scientists compared the expected impacts of climate change on the production of cassava and six other key staple crops in sub-Saharan Africa – potato, maize, bean, banana, millet, and sorghum. According to Schubert ,2012 by 2030, temperature rises of between 1.2 and 2 degrees Celsius, combined with changes in rainfall patterns, will leave cassava in a class of its own, outperforming the other crops overall. In East Africa, for example, it bucks the trend of declining suitability of all other crops in the study, with a 10% increase. In West Africa cassava will hold its ground, significantly outperforming the suitability of potato (-15%), bean (-20%) and banana (-13%). Cassava, along with banana and maize, will see a 5% increase in suitability in Southern Africa, with only Central Africa registering decrease (–1%) –significantly better than the substantial declines expected in potato and bean. Jarvis etal, 2012 from research findings conclude that cassava is actually positively impacted in many areas of Africa, with −3.7% to +17.5% changes in climate suitability across the continent. Conversely, for other major food staples, we found that they are all projected to experience negative impacts, with the greatest impacts for beans (−16% ± 8.8), potato (−14.7 ± 8.2), banana (−2.5% ± 4.9), and sorghum (−2.66% ± 6.45). We then examined the likely challenges that cassava will face from pests and diseases through the use of ecological niche modeling for cassava mosaic disease, whitefly, and brown streak disease and cassava mealy bug. In vitro virus elimination by dissecting the meristems is important in complete virus screening and elimination before field multiplication. Cassava is very good substitute of winter wheat products in Zimbabwe hence it is very important. It can be grown at local level with minimal inputs particularly by smallholder farmers in Zimbabwe. It can be grown using relatively low rainfall which is less expensive and does not require a lot of water or nutrients. It is a very important in Zimbabwe where food shortage looms and prices of food products continue to rise. Cassava is highly nutritious and leaves can be eaten as vegetables. The importance of sweet cassava cannot be underestimated in Zimbabwe especially at smallholder farmer level.
Cassava is an important food crop in SSA, tolerant to drought and high yielding. However, it is affected by heat and moisture stress resulting into significant yield losses. Full understanding of tolerance mechanisms under stresses is necessary to develop tolerant varieties and increase crop yield. In our study, effects of moisture and heat stress on cassava physiology have been investigated. 20 cassava varieties were evaluated in an RCBD in Western Uganda for 12 months and plant phenotypic and biochemical parameters examined. Weather characteristics and data on physical stress response and recovery were recorded. Rainfall ranged between ≤50mm in dry months to ≤200mm in rainy season. On site average temperatures were ≥280C in rainy season ≤380C in dry period. Soils were well drained with significant organic matter and minerals such as nitrogen, calcium and potassium. Irrigation water properties were conducive with water pH, organic matter and salinity in proportionate values. Varietal differences occurred in plant phenotypic characters such as plant height and leaf number which were correlated to ability of plants to tolerate stress and rate of recovery. Biochemical characteristics were strongly correlated to rate of recovery in different cassava varieties. The study identified 4 stay green varieties of I/97/00067, 0686, NASE 2 and NASE 3 tolerant to stress in varying levels and 3 early recovering varieties of 266BAM, Bukalasa and 72-TME 14. These will be characterized further to ascertain the genetic mechanisms behind their tolerance. They will also be considered for uptake by farmers to counteract the impending climate change crises expected in the future.
The increasing importance of cassava (Manihot esculenta), which contain large amounts of potentially toxic cyanogenic glucosides, calls for better understanding of the cyanogenic glucoside biosynthetic pathway and the regulation hereof. In this perspective, putative promoter regions 5’ upstream of CYP79D1, CYP79D2, CYP71E7, a CYP71E7 functional homologue, UGT85K4 and UGT85K5 were cloned into pKGWFS7 vector using gateway technology and agro-transformed into the cassava cultivar Albert. Subsequently, promoter constructs were infiltrated into N. benthamiana leaves and incubated under different light conditions and analysed with a GUS activity assay and GFP fluorescence microscopy. In silico analysis of the promoter regions revealed the presence of core elements involved in basal gene transcription and several cis-acting regulatory elements involved in light, hormone and wound response. Stress studies with different light conditions, hormones, wounding and nutrient were performed on wild type TME12 cultivar and analysed with real-time qPCR and LC-MS to reveal the impact on linamarin and lotaustralin biosynthetic pathway on transcriptional and metabolite level.
To identify traits that can be used for genetic improvement of drought tolerance of cassava, panels of diverse lines were subjected to water deficit in field and controlled-environment conditions. Leaf retention was poorly correlated with storage root weight under stress, as many genotypes shed lower leaves while maintaining a small set of leaves near the shoot apex. In addition, leaf chlorophyll greenness readings were similar in both control and water stressed plants when measured on upper canopy leaves, which permitted many genotypes to maintain canopy-scale photosynthetic capacity during water deficit. Relationships between traits related to water use (canopy temperature, soil water depletion, abscisic acid) indicated that phenotyping for these traits needs to be carefully timed. Leaf sugar contents were correlated with chlorophyll, but were not consistently correlated with yield. In general, genotypes accumulated substantial starch reserves in stems; among genotypes this was correlated with storage root weight. This suggests that genotypes with more stem starch are better able to sustain activities during prolonged stress and recover upon rewatering. Storage root weight was not positively correlated with aboveground biomass, an indicator of canopy photosynthesis, or fibrous root weight, whereas it was strongly correlated with partitioning index for early-stage storage-root growth (PI). Heritability and variation among genotypes were sufficiently high to predict that response to selection would be successful for several traits, including canopy temperature, ABA, and PI. We conclude that PI at an early stage of stress is a valuable trait for phenotyping cassava drought tolerance.
The impact of civil war in Democratic Republic of Congo (DRC) results in a rapid shift in the composition of food demanded by various income categories of households. The post conflict food consumption study conducted in Kivu Provinces reveals the 19.38% of budget share allocated to the consumption of root and tuber crops. The per capita consumption of cassava was 190.54gm, which contributes 762.16 kcal/g/day to the total energy requirement by physically active individual. The lowest per income quartile households consume only about 50% of the average. In Kivu provinces of DRC, 96% of households consumed cassava as ugali, a major recipe from the preparation of cossettes. Likewise, it is also consumed in boiled, grind and fried forms or as special local delicacy called chikwange. The QUAIDS model was used to estimate the determinant factors of demand for roots and tubers with cassava products being an important food type. Factors that positively and significantly affect the consumption of cassava are own price of cassava products, total household income, family size, and agriculture as the primary occupation of the household head. The own price elasticity for roots and tubers was found positive and significant, which contradicts the normal law of demand for staple crops. As expected the change in prices of other food crops (cereals, grain legumes, animal protein, banana and plantain, seasoning products, and beverages) affect negatively and significantly the consumption of cassava. Therefore root and tuber food commodities especially cassava is consumed as mitigating measures against hunger and starvation during the rehabilitation of eastern DRC in the post conflict period. The income elasticities were positive for cassava. This indicates that cassava is normal goods for Kivu provinces. The income elasticity was more than one for the two lowest per income quartiles. This implies that cassava consumption increases with household’s income for the poor of the poor.
Cassava is an important root crop that is grown by resource-poor farmers in marginal areas where its production faces moisture stress constraints. A strategic approach to improve cassava’s tolerance to moisture stress relies on understanding of its molecular mechanisms of drought tolerance for breeding or gene manipulation. This study was carried out to identify drought tolerance candidate genes in cassava. One drought tolerant and one susceptible cassava genotypes were grown in glasshouse under well-watered and water stressed conditions. Ten (10) genes that have been biologically validated and reported to be associated with drought tolerance in other plants such as Arabidopsis and rice were analysed for their expression in cassava in response to water stress using Real-Time PCR. All the ten genes were differentially expressed in response to water stress, four of which (MeALDH, MeZFP, MeMSDand MeRD28) were identified as drought tolerance associated genes because they were exclusively up-regulated in drought tolerant genotype. Studies to biologically validate these four genes and to identify other drought tolerance associated genes will advance understanding of molecular mechanisms of drought tolerance and provide useful information for gene manipulation in cassava.
Cassava, drought, Real-Time PCR, gene expression.
Cassava (Manihot esculenta Crantz) storage roots play an important role not only as a basic food source for the developing countries but also as feedstock for starch and biofuel industries. Cassava roots undergo post-harvest physiological deterioration (PPD) within 24h hours after harvest, thus reducing the crop’s palatability and marketability. PPD is an active physiological process involving changes in gene expression, protein synthesis and accumulation of secondary metabolites. Genome-wide gene expression analysis of PPD process revealed that PPD is an enzymatically mediated oxidative process, and reactive oxygen species (ROS) are at the central of the process (Reilly et al., 2004; Owiti et al., 2011). In this study, co-expression of ROS scavenging enzymes superoxide dismutase (MeCu/ZnSOD) and catalase (MeCAT1) or ascorbate peroxidase (MeAPX2), in transgenic cassava were used to explore the intrinsic relationship between ROS scavenging and PPD occurrence. Transgenic cassava transformed with p54::MeCu/ZnSOD-35S::MeAPX2 and p54::MeCu/ZnSOD-35S::MeCAT1 was produced and confirmed by Southern and qRT-PCR analysis. Under the exposure to ROS-generating reagents methyl viologen (MV) and H2O2, high expression levels and enzymatic activities of Cu/ZnSOD, CAT and APX in the transgenic plants were detected, suggesting that the transgenes were functionally expressed. The levels of oxidative stress indicators, chlorophyll degradation, lipid peroxidation, and H2O2 were dramatically reduced in transgenic lines than those of wild-type. Higher viability and comparable mitochondrial activity in H2O2-treated transgenic protoplasts were also detected by fluorescent dye staining. These results showed that the co-expression of MeCu/ZnSOD and MeCAT1 or MeAPX2 in cassava significantly improved tolerance to abiotic stresses. During PPD occurrence, the enzymatic activities in the storage roots of transgenic lines were highly boosted compared to wild-type, leading to a lower H2O2 concentration. A delay of PPD occurrence for more than 7 days has been detected from harvested transgenic cassava plants. Using fluorescent probes Dihydrorhodamine123 and MitoTracker Deep Red FM, real time monitoring of mitochondrial oxidation was conducted. Our study not only sheds the light for understanding the mechanism of PPD process but also develops an effective approach for delayed PPD and improved abiotic stress resistance in cassava.
cassava, post-harvest physiological deterioration, ROS scavenging, stress resistance
Climate change is a phenomenon which has large effects on the rural farming population. Higher temperatures, lower precipitation, changes in temporal and spatial distribution of rainfall and extreme events, directly influence agricultural production. Despite these undisputable impacts, rather little is known about how smallholder farmer in Africa perceive climate change and which are the elements of change they classify as most serious obstacles for farming. In this Poster we want to present the results of a survey carried out in the Benin Savannah and in the forest regions of Cameroon. We have chosen these two countries to compare different cultural, social, environmental and climatic conditions We will analyse how farmers perceive Climate Change and if they consider these changes as serious obstacles to farming on which they already reacted by modifying cultivation practices. The first interpretation of our results show, that people are well aware of climate change. Nevertheless, the results also seem to proof the assumption that it is difficult for cultivators to distinguish between natural weather fluctuation and climate change. If impacts of climate change were mentioned farmer often referred to obstacles which happened during the last or next-to-last season and very seldom to a long durée.
Cassavas a very important staple food crop in Nigeria and over 100million Nigerians eat it or it’s food products, at least once a day. It is also an established fact that micronutrient deficiency is common among children and reproductive women in most cassava growing regions in Nigeria.
Genes for these micronutrient traits are lacking in the Nigerian cassava germplasm. This means that the genetic improvement of the Nigerian cassava for these traits cannot easily be done through conventional hybridisation and recombination.
Therefore, to improve the nutritional value of the Nigerian cassava clones, these micro-nutrient traits have to be introduced. Genetic transformation techniques, a genetic engineering methodology has proved a useful tool for this purpose. However, genetic engineering as a breeding tool is relatively new in Nigeria and as in many West African countries, is faced with many biosafety challenges.
This presentation therefore looks at the preparation of major stakeholders (regulators and practioners) of Bio-cassava plus Nigeria, in dealing with bio-safety challenges that may arise.
Cry toxins produced by the bacterium Bacillus thuringiensis (Bt) are effective biological insecticides that have been successfully used as a biopesticide for many years. Cry toxins can bind to receptor-like cadherin and insert into the membrane of insect midgut epithelial cells, by which to form pores and cause cellular lysis and fatal damage to the midgut epithelium. The expression of certain Cry toxins in transgenic crops has contributed to an efficient control of insect pests, leading to a significant reduction in chemical insecticide usage. In this study, transgenic cassava plants over-expressing Cry1Aa were used to evaluate the ability of pesticide effect through using Helicoverpa armigera as a model. H. armigera is a type of Lepidopteran pest that feeds on a wide range of plants like cotton and cassava. Insect feeding assays were carried out to test the effects of CryIAa transgenic cassava leaves on the development and survival of H. armigera. Significantly reduction (P < 0.05) of larvae survival and weight were detected on transgenic cassava expressing Cry1Aa in comparison with the non-transformed plants. The high level of CryIAa in transgenic cassava caused the lethal effect, in contrast to the normal growth and development of pupation and adults when fed with the wild-type leaves. Morphological observation on the larval midguts showed that the consumption of Bt cassava deleteriously affected gut integrity of H. armigera. The columnar cells of the midgut epithelium were dramatically damaged and showed loose or disordered structure. Their cytoplasms become highly vacuolated and contained disorganized microvilli. Our study demonstrated the expression of CryIAa is an effective approach for rendering cassava resistant to H. armigera as well as other Lepidopteran insects.
cassava, Cry1Aa, Helicoverpa armigera, insect resistance, toxicological analysis
Delivery of genetically modified cassava to farmers and breeders requires coordinated procedures for production and selection of large numbers of transgenic plants. Regenerated plants must be screened in the laboratory and field to select for events that perform to the desired trait level, that have agronomic performances similar to mother plant material and are best suited to achieve rapid regulatory approval. In addition to operating efficient transgenic plant production, ILTAB at DDPSC has developed simple, high throughput procedures to screen the resulting events at the DNA and RNA levels and deliver elite plants in a timely manner for advancement to confined field testing. Plants are screened for copy number and presence of vector backbone (VBB) using in vitro leaf material within 2-3 weeks of regeneration, allowing those with high T-DNA copy number and VBB sequences to be eliminated from the pipeline system as rapidly as possible. Events passing the above criteria are micropropagation for another , three week to yield sufficient leaf material for analysis of siRNA accumulation or mRNA expression depending on the trait in question. Plants passing these screens are then transitioned to the greenhouse to more fully determine trait and morphological phenotype, with the best performing events being advanced for field trial. Utilizing this process, 2.5 FTE (abbreviate this) have recently produced and analyzed approximately 250 transgenic events of TME204 over a 12 month period, of which 10% have been identified for field testing for resistance to cassava brown streak disease.
Cassava production in East Africa is constrained by cassava brown streak disease (CBSD) and cassava mosaic disease (CMD). The Virus-Resistant Cassava for Africa (VIRCA) project was initiated in 2005 with the goal of applying biotechnology to deliver virus resistant varieties to farmers in East Africa. VIRCA has developed cassava transformation technologies, obtained regulatory approvals and conducted confined field trials (CFTs) in Uganda and Kenya. Through these efforts, proof-of-concept for efficacy of RNAi technology against both diseases has been demonstrated under greenhouse and field conditions. VIRCA is now using this knowledge to generate plants of the farmer-preferred cultivar TME204 engineered for resistance to CBSD. These plants are now being screened to identify candidate lines for field evaluation. A field trial program has been designed to integrate trait selection and agronomic performance trials with the data collection required for compilation of the dossier for regulatory approval of the final CBSD resistant event. These technical components of VIRCA are supported by coordinated communication efforts and comprehensive planning required to ensure expeditious delivery of CBSD – resistant TME204 to farmers in the Lake Victoria region.
Cassava mosaic and cassava brown streak diseases are a major constraint to cassava production in East African. Cassava mosaic disease (CMD) has especially been in the region for over one hundred years and caused a major outbreak in the 1980s that almost halted cassava production around the Lake Victoria region. The disease has been managed through different means, the most important being the use of resistant varieties developed through conventional breeding. However, farmers still use their old cultivars and landraces which are highly susceptible to CMD, mainly because they possess other preferred traits. It is therefore important to improve these farmer preferred varieties without changing the intrinsic characteristics that make the farmers hold on to them. The Virus Resistant Cassava for Africa (VIRCA) project developed and evaluated 11 transgenic lines in a confined field trial in KARI Alupe using two technologies, the gene silencing technology and a G5 binding protein. The aim was to use the technologies to target the farmer preferred cultivars. Four lines developed using the gene silencing technology gave very good disease control and are being evaluated for durability of resistance. The gene silencing technology is now being used to transform and develop transgenic virus resistant lines using farmer preferred varieties.
Cassava is an important food crop in sub-Saharan Africa where its production accounts for >50% of the worldwide output. Its production is affected by cassava brown streak disease (CBSD) that is rapidly spreading in Eastern Africa and great lakes region. By exploiting existing sources of resistance a study was undertaken to map quantitative trait loci (QTL) for CBSD tolerance using an F1 mapping population from a cross between Namikonga and Albert. The mapping population was screened against CBSD infection at two locations in Tanzania in 2008. Root necrosis was scored at a scale of 1-5 (no root necrosis and severe necrosis). The F1s and parents were genotyped with 222 informative SSRs at BecA Hub facility in Nairobi. In addition a subsample of the population was genotyped with 1536 SNPs using a GoldenGateTM assay platform. Of the 1536, 600 informative SNPs were included in linkage and QTL analysis using JoinMapTM and MapQTLTM. Mixed-model analysis was further used to associate markers with CBSD tolerance. Interval-based QTL analysis revealed a strong QTL in linkage group 4 of SNP based genetic linkage map explaining 27% of the genetic variations and MEF_c_2120 and MEF_c_1513 SNPs were found closely linked to the QTL. Results from mixed-model marker-trait association analysis of the entire mapping population corroborated those of linkage-based interval mapping. The present work is the first step towards utilization of MAS to back-cross CBSD-tolerance QTLs into susceptible farmer preferred cultivars.
Smallholder farmers in developing world countries depend upon cassava (Manihot esculenta) as a primary source of calories feeding over 700 million people in Africa, Asia and Latin America. Currently, whiteflies (WFs) are the major biotic stress that threatens the sustainability of cassava. Damage caused by WF feeding can obliterate an entire cassava crop. In addition, high WF densities are a key factor in cassava mosaic geminivirus epidemics. Therefore, identifying the cassava genes that confer resistance to WF infestations and deploying the WFR genes in lines preferred by smallholder farmers will transform approaches to WF control in developing world countries by: enhancing the quality and quantity of cassava, decreasing the losses due to WF feeding and virus transmission, decreasing the use of insecticides, lowering production costs, and improving the health and safety of smallholder farmers. This reaserch will identify the genetic basis for resistance to the whitefly Aleurotrachelus socialisin the cassava line MEuc72. A. socialis resistance is multi-genic and both antibiosis (insect toxicity) and antixenosis (insect deterrence) is displayed. To transfer WFR to cassava with the field attributes valued by smallholder farmers, the genes associated with WFR must be identified.
Despite the importance of cassava as a supplier for caloric needs in several developing countries, little is known about the genetic basis of adaptation, domestication and evolution of this crop. The genus Manihot apparently originated in Mexico and Central America, and rapidly radiated in South America. Cassava, the only crop species within the genus, was probably selected from wild ancestors on the southern edge of the Amazon basin some 6-7,000 years ago. Understanding the genetic structure and evolution of cassava will provide important knowledge to guide the breeding process and produce elite cultivars in shorter times.
In collaboration with BGI and Yale University we performed RAD sequencing on one hundred genotypes with different geographical origins and physiological characteristics. We produced close to 100 Gb of Illumina sequencing data (about 1x per genotype). We are currently using bioinformatic approaches to build a rich set of SNP markers which we will use to guide breeding processes through selection by genotyping. We will also use this information to build a phylogenetic history of the genetic variation discovered in our germplasm, which will be helpful to understand the nature and distribution of genetic diversity in cultivated and wild species. To contribute to the development of the reference genome for cassava, we performed whole genome Illumina sequencing of the reference genotype. We generated over 70 million paired end reads which gave us a total coverage of about 15X. A preliminary analysis of these reads allowed us to join over 500 candidate scaffold junctions in the current reference genome. We plan to continue our sequencing and analysis efforts to make a significant progress in the amount and quality of the genomic tools and databases available for cassava breeders and researchers.
Cassava is an important staple in sub Saharan Africa but its nutritional value both as human food and feeds in the livestock industry is highly undermined by its low protein content (1-2%). Improving cassava for high protein content could help improve the dietary needs of consumers and enhance the market potential of the crop for poor resource farmers who depend on the crop for their livelihood. Initiatives were taken to introgress high protein content from wild Manihot species of cassava (M. esculenta spp flabellifolia) in Latin America. Interspecific hybrids from crosses between Wild cassava species and cassava were conducted at CIAT, Colombia. The hybrids were further developed using advanced backcross scheme involving additional backcross to cassava to generate a BC1 population. The BC1 genotypes were crossed to cassava mosaic disease (CMD) resistant donor (having CMD2 resistance) to develop BC2 populations for deployment to Africa were CMD is endemic. Molecular markers associated with CMD2 resistance were used to select 138 accessions in the BC2 population for CMD resistance and then shipped from CIAT to Nigeria for field evaluation. Evaluation for CMD resistance indicates that about 70% of the selected accessions were resistant to CMD. At 10 Months after planting, %crude protein contents (%CP) were determined using the Kjedahl procedure.
Results of protein analysis revealed %CP ranging from 1.66 – 12.69% in the accessions. The top 13 accessions had %CP levels between 6.3 and 12.9% indicating that protein was successfully introgressed from wild Manihot species into cassava. The identification of these 13 genotypes with high protein and CMD resistance also provide a possibility to effectively use these materials as parents to breed for high protein using elite cassava gene pools in Africa. Some of the LA accessions with high protein content possess yellow pulp signifying high beta carotene thus further enhancing the prospect of improving crop’s nutritional value.
Cassava is an most important food security crop in Africa. The increasing challenge of meeting food demands in Africa requires efficient breeding strategies to rapidly develop high yielding improved varieties. However, the poor funding of national research systems (NARS) in Africa have largely reduced the capacity of NARS to adopt modern breeding strategies. The Generation Challenge Programme as part of its mission to use advanced plant science to improve crops for greater food security in Africa established the Cassava Breeding Community of Practice (CoP) consisting of four countries (Ghana, Nigeria, Tanzania and Uganda) and two CGIAR centers (IITA Nigeria and CIAT, Colombia) as members. The CoP as a model concept for fast tracking marker assisted breeding (MAB) in Africa have resulted in the implementation of MAS and MARS in cassava. Breeding target goals are generally similar in several of the countries, and through integrated efforts of the CoP access by countries to genomic resources ,high through platforms and robust analytical and data management tools have been facilitated. In the CoP, marker-assisted transfer of cassava mosaic disease (CMD) resistant Latin American (LA) cassava germplasm for quality and productivity traits have been shared by countries thus allowing for evaluation of similar germplasm on continent-wide basis. Over 2000 LA genotypes of the same set of families have been distributed among member countries. A significant outcome of the CoP is the release by Nigeria in 2010 of the first MAS developed CMD resistant LA variety in Africa. In Tanzania, two varieties developed based on MAB strategy involving MAS for CMD resistance in combination with field screening for cassava brown streak disease were released. Through coordinated breeding activities embarked in the CoP among countries, similar common breeding goals are being efficiently addressed leading to significant impact on the continent with new additional eight countries set to join in 2012.
An F1 population consisting of 100 individuals, derived from crosses of “Huay Bong 60” by “Hanatee” was developed and used for linkage map analysis. A total of 667 simple sequence repeat (SSR) markers previously developed by the International Center for Tropical Agriculture (CIAT) were screened for polymorphism between the parental lines. There were 171 informative markers that were used to genotype lines in the mapping population. Genotypic data of the F1 samples was used to construct a linkage map using Join Map® 3.0. The map consisted of 158 markers encompassing 988.81 cM, distributed on 21 linkage groups with a mean distance between markers of 6.26 cM. The results indicated that the map constructed in this project has an incomplete coverage of the genome due to the number of linkage groups exceeds of the number of cassava’s gamete chromosome, and the low number of markers in some linkage group. However, the genetic linkage map generated in this study will be useful for genetic studies in cassava particularly for the identification of genetic markers linked to traits of interest, although the complex cassava genome suggests that maybe a long term objective.
Cassava (Manihot esculenta) roots spoils within 48-72 hours after harvest due to postharvest physiological deterioration (PPD) which accounts for significant annual yield losses globally. Cassava is allogamous and highly heterozygous showing high segregation at F1 for several key breeding traits. Unfortunately, the development of delayed PPD varieties has been hampered due to lack of genetic variation in available breeding gene pools. Mutation induction is a proven technology for creating and improving genetic variability in a crop variety. In this study, initiatives were undertaken to use induced mutation to create and breed for delayed PPD in cassava. Two high yielding elite varieties (TMS95/0379 and TMS98/0002) known for resistance to disease and pest were selected as planting materials for induced mutation to develop delayed post harvest deterioration tolerance in cassava. These materials were irradiated at 12 and 15 gamma ray level as in vitro cultures at the International Atomic Energy Agency (IAEA), Vienna, Austria. They were micro-propagated through several cycles to reduce chimera. They were subjected to hardening process and transferred to the field for evaluation for mutants for delayed PPD at the National Root Crops Research Institute (NRCRI), Umudike, Nigeria. Yield and delayed PPD were evaluated at 7 and 14 days after harvest (DAH). Over 2000 M1 cassava plants were initially planted on the field, however, only 50% of the M1 plants showed good establishment resulting in the evaluation of about 824 M1 genotypes for delayed PPD and other important agronomic traits such as yield, dry matter content and harvest index. Phenotypic variation for PPD and other traits were observed within M1 derivatives of the same parental clone suggesting possible genetic variations due to mutation. Similar observation was made for other traits. Traits correlations were highly significant between PPD and other evaluated traits. Results indicate that nine M1 plants showed no physiological post harvest deterioration representing 1% of the evaluated M1 population.
Cassava (Manihot esculenta Crantz) is increasingly becoming an important crop in South Africa (SA), especially in the northern parts of the country bordering Botswana, Zimbabwe, and Mozambique. It is especially well suited in SA as a source of industrial starch because of its high quality starch, equivalent to that of waxy maize, which is not grown locally. There is so far very little molecular breeding work on cassava in SA with the result that its full potential has not been exploited. Although a lot of research on cassava has been done in other regions of the world that could be transferred to SA, the difference in climatic conditions limits the successful transfer of such results. The few studies conducted in the local universities and from neighboring countries indicate that there is a huge potential for promoting cassava for food, feed, and industrial production. Recently, the ARC’s Biotechnology Platform has embarked on two major molecular breeding projects in cassava with a major focus on improving the root protein content and resistance to pests in SA grown cassava genotypes. This article will highlight the objectives of these projects, progress achieved so far and long-term goals. The specific areas of interest where researchers stand to contribute most are further highlighted and discussed.
Cassava is plagued by two important viral diseases one of which is the cassava mosaic disease (CMD) caused by a group of begemoviruses. CMD is transmitted by whitefly, Bemisia tabaci. Yield loss due to this disease can range from close to zero to near 100%. Two genes CMD1, of a polygenic nature and CMD2, a dominant kind, have been identified and mapped on the cassava genome. In order to ensure stability of resistance, there is need to identify more resistance genes to enable pyramiding through the aid of molecular markers. Two new sources of resistance namely TMS 97/2205 and TMS 96/1089A were used to generate 2 bi-parental mapping populations segregating for CMD resistance with TMS 30555 as a susceptible parent. The populations (304 from 97/2205 and 141 from 96/1089A) have been phenotyped on a scale of 1 to 5 and segregation resulted in the distribution of the genotypes in all the five phenotypic classes indicating the suitability of the cross for genetic analysis of CMD resistance. The proportion of resistant genotypes in the population was 65% with a chi square goodness of fit test that supports a 3:1 segregation ratio for resistant vs. tolerant/susceptible phenotypes. Screening of the 3 parental clones with SNP (KASPar) markers resulted in the identification of at least 900 polymorphic markers for each of the populations. These are now being used to genotype the entire populations for identification of QTLs that would prove useful for marker-assisted pyramiding and selection of resistant cassava varieties.
Mutation breeding for Cassava Mosaic Disease (CMD) resistance was carried out from 2007 to 2011. Five putative cassava mosaic disease (CMD) free mutants with zero severity symptoms were discovered and tagged among induced plants. There were no visible bands of amplification when DNA extraction and PCR analyses were done using East African Cassava Mosaic Virus (EACMV) (EAB555F/EAB555R) and African Cassava Mosaic Virus (JSP001/JSP002) specific primers, with molecular sizes of 500 bp and 700 bp respectively. Thus, confirming their mutant status in a very high ACMV pressure zone. The yield potential of these CMD mutants appreciated from 2-8 kg per plant to 7-22 kg per plant and these high yields were attributed to the absence of the cassava mosaic disease.
In Latin America, whiteflies are a pest on many economically important crops including food security crops like cassava. Most species of whiteflies are monophagous (feed on only one host plant). However, a few species are oligophagous or polyphagous. Economic losses are estimated in the hundreds of millions of dollars.
The identification of whitefly species in adult stage is problematic. Morphological differentiation of pupae is one of the better methods for determining identity of species, but it may vary depending on the host plant on which they develop which can lead to misidentifications and erroneous naming of new species. Polymerase chain reaction (PCR) fragment amplified from the mitochondrial cytochrome oxidase I (COI) gene is often used for mitochondrial haplotype identification that can be associated with specific species or its biotypes.
Our objective was to compare morphologically based identification to genetic material extracted from 10 species of whiteflies attacking crops of economic interest in LAC. We compared morphometric traits and DNA barcodes obtained from COI sequences to validate the robustness of the COI gene for species identification in the Aleyrodidae family and to develop a diagnostic kit for the rapid identification of whiteflies. A phylogenic UPGMA tree was constructed using the COI sequence information available in the genebank repository (NCBI) and sequences obtained in this study. This result indicated that the COI gene contains sufficient phylogenetic signal for inferring species-level phylogeny, and thus its potential as diagnostics tool for species identification in the Aleyrodidae family.
Cassava (Manihot esculenta Crantz) is an important food source and industrial feedstock. Accordingly, it ranked fourth among all crops in worldwide production. As a cyanogenic crop, cassava can produce hydrogen cyanide (HCN), a toxic compound, during cell damage which caused health effects such as acute in toxicity, manifested as vomiting, dizziness, etc and environmental toxicity. Even though, HCN can be reduced to the safe levels by proper processing, but it requires labor intensive and time, leading to economic and nutrient losses. In such case, the released HCN still remains in environment. Additionally, shortcut processing can yield toxic products. These cause a serious problem to environment and quality of life. Therefore, improving cassava cultivar for low cyanogen content, and raising knowledge on genes affecting the trait have been focused on. For this reason, this project aimed to identify QTL associated with the cyanogen content in cassava root in an outbred population derived from two divergent varieties which were ‘Hanatee’ (exhibited low cyanogen content) and ‘Huay Bong 60’ (displayed high cyanogen content) using SSR markers.
Cyanogen content of Hanatee, Huay Bong 60 and their F1 progenies were evaluated in 2008 and in 2009 at Rayong province, and in 2009 at Lop Buri province, Thailand using picrate paper kit . Linkage map was constructed based on 303 SSR markers using JoinMap 3.0. QTL analysis affecting cyanogen content was performed by MapQTL 4.0. The result showed that, the cyanogen content of ‘Hanatee’ was lower than ‘Huay Bong 60’ more than two folds in all evaluated environments. The cyanogen content of the population showed continuous variation with transgressive segregation. The correlation coefficients among years and locations were significantly detected, ranked from 0.308 to 0.487. The linkage map consisted of 303 SSR markers, distributed on 27 linkage groups with a map that encompassed 1,328 cM. The average distance between markers was 5.8 cM. Five QTL underlying cyanogen content were detected based on MQM analysis. The LOD scores of detected QTL ranged from 3.77-5.75 and percentage of phenotypic variation explain (PVE) ranged from 15.9-26.0%. Among all the identified QTL, CN09R1 at locus CA141 was the most significantly associated with the cyanogen content trait which showed highest LOD score (5.75) and explained the greatest PVE of 26%. Single marker analysis (KW analysis) were also been considered. The results revealed that all QTL with an exception of CN08R1 were significant in their environments and some QTL also displayed the significant association in other environments. Remarkably, CN09R2 at locus CA344 showed significant of KW in all environments.
The population in this study was sufficient for QTL analysis. It diverged in both phenotypic and genotypic levels. The powerful SSR based genetic linkage map was used for analysis of QTL underlying cyanogen content and five new QTL were successfully identified from 4 linkage groups. The strongest QTL, CN09R1 showed the LOD value of 5.75 and it explained 26.0% of the variation in cyanogen content. There was no common QTL found across years and locations, but single marker analysis of CA344, a marker linked to CN09R2, was significant in all evaluated years and locations.
Cassava (Manihot esculenta Crantz) is a major food crop for more than 500 million people of the world. It has been cultivated for its starchy root that fully with carbohydrate in the tropical and subtropical regions. It has been reported that root yields have a similar correlation with the total number of branches and plant height in root biomass crops such as cassava and potato. Hence, plant architecture is one of the important traits for developing new variety. This study, QTL for plant and first branch height in cassava were identified using an F1 mapping population of a cross between ‘Huay Bong 60’ (female) and ‘Hanatee’ (male). Genetic linkage map of the F1 population was constructed based on 235 informative SSR markers using JoinMap® 3.0 software. The results showed that 156 SSR markers were mapped on 25 linkage groups. Each linkage group had the SSR markers ranged from 2 to 21 loci with an average of 6 loci per linkage group. Map spanned at 845.2 centriMorgan (Kosambi cM) and the mean intervals between markers are 7.9 cM. Phenotypic data of plant and first branch height of the F1 mapping population were measured and recorded at 12 months after planting in 2007 to 2009. Plant and first branch height ranged from 111.5 to 382.7 cm and from 40 to 280 cm, respectively and showed in normal distribution. Data were calculated based on multiple-QTL models (MQM) mapping analysis using MapQTL 4.0 software. Total of 12 QTL were identified on 6 linkage groups consisting of seven QTL for plant height and five QTL for first branch height. Three of 12 QTL (H_R08_II, FB_R09_I and FB_R09_II) had high LOD value and large portion of % phenotypic variation explained (PVE) which were classified as major QTL. Finally, QTL for both of plant and first branch height will be useful and applicable in MAS of cassava and also for the identification of genes controlling these traits.
Cassava (Manihot esculenta Crantz) is a major staple crop for millions of people in East and Central Africa (ECA), mostly in the rural areas. Cassava is the second most important staple crop in Africa after maize, provides a stable food source, particularly for low income, resource-poor farmers, and is used as a high-energy source of feed for livestock. This crop is easy to plant, mature easily and have enormous industrial and economic potentials. In addition, it has have high nutritional energy qualities and the leaves are consumed as vegetables. The largest producers of cassava in the ECA are Uganda, Rwanda, Burundi and Kenya. In yield terms, over 30 million tons of cassava is produced annually in the ECA sub-region which is more than any other staple crop. The importance of cassava as staple crop in Africa has been highlighted at the highest level of African Union. In the New Partnership for Africa’s Development (NEPAD) Comprehensive African Agricultural Development Program (CAADP), cassava is ranked among the high priority crops for agricultural research to contribute to food security and poverty alleviation for the urban and rural poor. Cassava has been prioritized by NEPAD as a ‘poverty fighter’ which will spur industrial development in Africa. The association for strengthening agricultural research in ECA (ASARECA) strategy 2007–2016 points to the fact that the biggest impact on poverty reduction in ECA will come from concentrating on staple crops with cassava ranking highest among the staples with a growing domestic market. In addition, cassava has the potential as a commercial crop for the food, feed, starch, ethanol and biofuels industries as the case in Brazil and Thailand. In ECA, its production stands at 5 tons/ha compared to potential yield of 60 tons/ha. This low yield is attributed to traditional farming practices although there are also reports that indicate that cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) can significantly reduce the potential cassava yield of 60 ton/ha to over 70% loss. Therefore in realisation of the clear livelihood, economic importance and the genetic potential of this crop in the ECA region together with the key constraints to its production, ASARECA through its agrobiodiversity and biotechnology programme has enhanced the utilization of conservation biotechnology techniques to conserve cassava genetic resources and has promoted the use of tissue culture to enhance its utilisation. A certification scheme for tissue culture plantlets have also developed. Proper agronomic practices using clean planting materials can help increase the production of the landraces and farmer preferred naturalized cultivars of these crops. Through a follow project on using low cost tissue culture techniques, quality, pest and disease free germplasm are being supplied to smallholder farmers to increase cassava production.
conservation biotechnology, utilization, cassava, certification, low cost, tissue culture, east and central Africa.
Cassava is one of the staples being targeted for bio-fortification to control micronutrient malnutrition and improve food and nutrition security in Africa. Three selected varieties of bio-fortified cassava roots with appreciable content, retention and bio-availability of pro-vitamin A were processed into gari and assessed for consumer acceptability. Questionnaires on socio-demography and consumers’ preference were administered to 518 regular consumers of gari in a local government in Lagos state, Nigeria. Nine-point hedonic scale was used to assess consumers’ preference for the gari samples, prepared in form of eba on some selected sensory parameters. The participants used, cut across all ages, sex and occupation with 53% female, 69% between 21 and 50 years, 29% had no education and 47% had at least secondary school education. Over 86% of the consumers liked extremely/very much, the gari samples from varieties 01/1412 and 01/1371 fermented for 1 day and roasted at 800C and 1200C respectively in term of all the selected sensory parameters and overall acceptability. They also expressed their willingness to plant, use and consume if available. Cassava bio-fortification seems a technically, economically and sustainably promising approach to control micronutrient deficiencies and compliment other intervention strategies.
Bio-fortification, Cassava, Consumer acceptability, Gari, Preference.
Molecular breeding(MB) or marker assisted breeding is an enhanced tool that allows researchers to look for DNA fingerprintings or markers in plants. Molecular plant breeding helps to expand genetic diversity, characterize genetic architecture, modify gene action, and its methods can be applied to increase selection efficiency. The MB Program utilizes DNA marker technology to aid effective incorporation of valuable traits into plant cultivars. Many important traits in the development of cultivars can be difficult to measure and difficult to make progress with selections in breeding programs. DNA marker technology aids in overcoming these limitations by using a small amount of leaf tissue from a plant to perform an easily interpreted laboratory analysis indicating the likelihood of having the desired trait. Inspite of the promise of this technology, many developing countries have not fully implemented it. Marker Assisted Selection (MAS) laboratories are an integral part of MB and so the implementation of an effective MB program depends on its functionality. In developed countries, latest approaches are routinely applied via advanced technologies whereas developing countries are still taking initial steps in MB techniques. Several limitations in the application of MB include lack of optimal facilities, little or no access to consumables, access to molecular markers and poorly trained personnel. However, through virtual platforms aided by the Generation Challenge Programme (GCP), molecular breeders in Africa now have better access to high standard equipments, advanced laboratory services, capacity building and data management tools. These attempts are geared towards genetic crop improvement in developing countries through functional laboratories. In this presentation, we report current challenges, opportunities and progress made so far by biotechnology platforms in enhancing functional (MAS) laboratory management in Africa using Nigeria as a case study.
The major goal for cassava breeding is the genetic enhancement that aims at increasing cassava productivity through the use of broad-based improved germplasm that combines multiple disease resistance ability with high yield and other desirable traits3 varieties of cassava with pro vitamin A. There is the need to introduce yellow root genotypes that would be suitable for boil and eat and with mealy attributes. In the past in Ghana there were a large number of yellow root cassava that would pound and was used for a major food form in Ghana ‘fufu’ where the yellow colour would replace the use of limited amount of plantains for preparing ‘fufu’. The landraces of yellow root in Ghana and yellow root being bred in IITA genotypes will be assessed for the diversity that exist from the collection a search for the unique genes that control the proViatim A levels and unique genes in the yellow poundable genotypes. Results from this genome wide screening study will form the basis for a planned controlled breeding scheme with pairwise crosses for some genotypes, selfing for some of the genotypes to be used to develop a hybridisation that would allow the tapping of heterosis. The last set of breeding will be the use of some of the genotypes to backcross some advanced bred materials without the poundability trait to improve it using the selection from the study. Information on possible markers responsible for the provitamin A will be identified and used to validate markers that would be useful for marker assisted selection for screening large breeding populations for pVAC traits at the various breeding cycle. The population to be used for the genome wide screening will be Ghanaian gene pool of yellow roots, yellow roots from IITA, yellow root seeds from CIAT and some white roots cassava making a total of 120 genotypes.
This study will allow other cassava breeders from other institutes in Ghana also utilise the genomic facility available to enhance cassava breeding.
CMD, cassava, stability, genotypes, yield.
Molecular basis of cassava resistance to pathogens is poorly understood. The plant immunity related proteins (IRP) involved in pathogen recognition have a limited repertory of conserved domains, being the most important the LRR (leucine rich repeats), NBS (nucleotide binding sites), LysM and kinases. Recent whole genome data availability allows the identification of proteins containing these domains as well as molecular markers, whose development is proposed as a strategy to find and transfer genetic regions between cultivars and for marker assisted selection. Based on a set of IRPs identified by bioinformatic approaches we selected some to map on the cassava genetic map. Primers were designed matching non-coding regions of 46 immunity related genes (IRG) and were used to amplify on DNA from TMS30572 and CM2177-2, two cassava cultivars employed on the construction of the first cassava genetic map. High quality sequences for 25 genes were obtained. Two direct polymorphic amplicons and 80 SNPs were found between these cultivars. Further, a SSR search was performed and 10.802 markers were identified in the 10 Kbp flanking sequences of IRGs coding genes. We have evaluated 33 pairs of primers for 7 groups of genes classified according to the presence of particular functional domains. We have found that 60% of the assessed SRRs are polymorphic in the parent cultivars. Segregation and analysis of these markers are in progress and will be presented.
Cassava (Manihot esculenta Cranz) has played a remarkable role as a major household food and income security crop in the Eastern Africa region. However, cassava’s low nutritional composition has remained a major factor which underrates it as a complete food crop. Notably, vitamin A deficiency (VAD) that ranges from night blindness to Xerophthalmia and Keratomalacia causing total blindness has been noted as a major health hazard in communities where cassava is a major stable (Gichuki et al., 2010; Rice et al., 2004). Nonetheless, global efforts are being made towards nutrient enhancement in cassava, with protein-, iron/zinc- and provitamin A-rich cassava becoming apparent. This initiative is strongly envisaged as a strategy for sustainably addressing malnutrition associated with heavy dependence on cassava for nutrition. In Eastern Africa, plant breeding programmes at the NARS have put considerable efforts towards development of nutrient rich cassava varieties for possible deployment to farmers. We now present the breeding approaches, progress, challenges and prospects of successful deployment and uptake of nutrient enhanced cassava varieties in Uganda, Kanya and Tanzania.
It is advisable to increase protein content in cassava storage root to improve nutritional quality of cassava for human consumption. Protein content in storage roots of cassava (Manihot esculenta Crantz) is low with low range of variability. Search of germplasm collections provided no evidence for genetic variation in protein content mainly due to lacking of reliable quantification procedure used to estimate protein content. As a consequence, conventional breeding techniques have not shown evidence of success in the genetic manipulation of protein content in cassava storage root. Studies in our laboratory have provided evidence showing that variation in total buffer extractable protein (TBEP) content may be genetically manipulated by targeting a sink deposit of functional proteins in CSR tissue that correlates with carotenoid accumulation. These observations allowed us to consider a new strategy for a conventional breeding program. We first searched for the protein sink capacity using genetic diversity of pigmented cassava storage root to recognize the variation in protein content due to carotenoid accumulation followed by crossing contrasting landraces. It included provenance test of the candidate landrace, open pollination, oriented pollination as well as a modified backcross. Results from landraces genetic diversity indicated that we can increase more than 3x TBEP, corresponding to 55% more proteins in the bulk root tissue. With the available segregating population, F1 populations are being analyzed and clones with protein content were selected and new varieties are being tested across contrasting environment.
Dry matter content (DMC) is a key trait, particularly for the industrial uses of cassava. Seasonally dry environments are predominant in many regions of the world where cassava is grown. In these environments, cassava roots are often available only during a few months of the year when roots with acceptable levels of DMC can be harvested (typically before the arrival of the rains, AoR). However, DMC can drop drastically if harvest takes place after the AoR to the point that root quality is unacceptable to the industry. This study aimed to identify cassava germplasm that can be harvested at 16-18 months after planting with relatively high and stable levels of DMC and further improved root yields. Results suggest that there is genetic variability for recovery of DMC after the AoR as well as for the capacity to increase fresh root productivity (duplicate it) after an extended growing cycle. However, special breeding approaches are required to achieve these goals. Development of cassava that can be harvested at different ages in seasonally dry environments is important because it would widen the time processing plants could operate; provide income to farmers at different times during the year; result in increased productivity without a proportional increase in the production costs; and eventually result in cassava germplasm that may better face the uncertainties derived from climate change. Root rot problems may be exacerbated in a long-season crop.
Cassava is a root crop that yields a large amount of extractable starch and is characterized by high yield potential, tolerance to drought and degraded soils, and great flexibility in planting and harvesting. Cassava is now gaining importance as a biofuel crop throughout the tropical countries. One tonne of fresh cassava roots with starch content of >26-28% yields around 140-150 litres, while one tonne of dry chips/flour yields around 430-440 litres of 96% alcohol under ideal conditions. As a profitable biofuel crop, a paradigm shift in productivity and starch yield in cassava needs to be achieved through genetic improvement, especially triploidy breeding. Triploids possessing high yield potential and high starch content will be ideal for biofuel production. The most notable features of the triploids are their high dry matter and starch contents, probably caused by triploidy per se. Triploids also possess good plant type, early harvestability and high adaptability for overcoming the adverse effects of climate change. Farmers’ participatory evaluations resulted in the recommendation of two triploid hybrids, 4-2 and 5-3 having high starch (28-30%) and root yield with stability under different seasons and locations and are fast spreading in the industrial belt. Several high starch hybrids, Tr16-6, Tr30-1, Tr11-8, Tr47-1 and early bulking hybrids, Tr2-18, Tr3-4, Tr2-15, Tr7-5 are under evaluation for transforming cassava into a highly remunerative biofuel crop.
Root quality traits were evaluated in two sites (Namulonge, NL and Nakasongola,NK) using four half-sib families from two farmer preferred (Kakwale, Bamunaanika) and two improved varieties (TME5, NASE10) at NaCRRI,. Genetic and environmental effects were measured for the following root traits:cyanogenic potential (CNP), starch yield (SY), amylose content (AM), reducing sugar content (RSC), swelling power (SP), post harvest deterioration (PPD) 3 and 5 days after harvest and harvest index (HI). There were highly significant differences in family, location and the family-location interaction for CNP with higher values in NK. Bamunanika showed the highest CNP value in NK while NASE10 showed the highest value in NL. Kakwale showed consistently low CNP values across locations. Significant differences were observed in AM in NK only. RSC differed significantly in the two sites with higher values in NL. TME5 in both sites had the highest RSC while NASE 10 had the lowest. Difference in SY for location or for family-location interaction was not significant. HI values for NK were significantly higher than those for NL. There were significant (p< 0.05) differences in PPD between the families. This study revealed with the exception of CNP and DMC, cassava root quality traits performed better in NL (relatively humid) than NK (relatively dryland). Kakwale performed consistently for all traits in the two locations.
Diversity in social and cultural aspects of the beneficiaries of research technologies seems to have significant effects on the rate of adoption of improved cassava cultivars, and it needs to be addressed in a breeding programme. Use of participatory approaches in plant breeding enables researchers to respond more precisely and efficiently to the needs and preferences of resource-poor farmers and their markets. The current study was conducted in order to provide an update on the farmers’ preferred attributes in cassava varieties and to identify researchable needs which can be addressed through conventional breeding. Individual interviews, focused group discussions, preference scoring and matrix ranking were adopted by the study. The study allowed farmers to participate in the collection and evaluation of local and improved cassava germplasm. Findings highlight some of the clones that have been abandoned by farmers and reasons thereof. A list of 9 major desirable attributes was established with slight differences in preference among farmers in the two districts. High root yield, high dry matter, and prolonged underground storability were ranked highly by farmers in Northwestern Province. Leaf retention and stay green ability where more preferred by farmers in Solwezi where there is increasing consumption of cassava leaves as a vegetable. In association with these attributes, insect pests and diseases and tolerance to mole rats were cited as additional preferred varietal attributes while susceptibility to root rots was ranked among the most undesirable attributes, particularly in Mwinilunga. Changes in preferences have occurred among farmers over a period of twenty years. The need for the national root and tuber improvement programme in Zambia to routinely carry out periodical Participatory Rural Appraisal (PRA) studies with all players involved in the cassava value chain is recommended so as to get an update on what farmers, trader, industrialist, and other consumers desire out of new cassava varieties.
Cassava is the second most important staple crop after maize grown and consumed in most areas of Tanzania. Producing areas include the coastal strip along the Indian Ocean, around Lakes Victoria and Tanganyika and shores of Lake Nyasa. The Lake Zone is the highest producer of cassava contributing 37% of the total production in Tanzania but cassava productivity in these areas is only 7.0t/ha below the national average fresh root yield of about 10.5t/ha. Low yield is attributed to diseases and pests and local varieties are susceptible to major virus diseases. Following the emergence of cassava mosaic disease (CMD) pandemic in 1998 in north western Tanzania, caused by the Ugandan variant (UgV), about 900 clones developed by IITA were introduced from Uganda through open an open quarantine facility in 2001. They were evaluated for resistance against CMD and other root yield traits in hotspot areas of the Lake Zone. Farmers’ involvement in participatory evaluation of the genotypes for preferred traits was crucial. Eight genotypes with high root yields, resistance to CMD, high dry matter content that met farmer preferred traits were identified and officially released in 2009 (Meremeta, Mkombozi, Rangimbili, Suma, Belinde, Kasala, Nyakafulo and Kyaka). The varieties were put under multiplication and disseminated to farmers. The varieties have contributed in improving food security and livelihood in the Lake Zone of Tanzania.
Cassava Green Mite (CGM) and Cassava Mealy bug (CMB) are the major insect pests attacking cassava in Malawi and significantly contribute to low yields. The need to develop new improved varieties resistant to insect pests requires knowledge on the mode of gene action controlling the expression of resistant traits to these insect pests. Therefore, a study was carried out to determine combining abilities and mode of gene action for resistance to CGM and CMB by crossing cassava genotypes using a 7 × 7 diallel mating design. The F1 progenies were evaluated in a seedling trial laid in RCBD with two replicates. Results indicated highly significant (P<0.001) general combining ability (GCA) and specific combining ability (SCA) mean squares for CGM, CMB, average root number per plant and fresh root weight (kg plant-1) which signified preponderance of significant variability existing in breeding material attributable to additive and non-additive gene effects. GCA variances for all the traits studied were lower than SCA variances which suggested that non-additive gene action was more important than additive gene action in influencing the studied traits. Mulola was the best general combiner for all the traits; followed by TMS4(2)1425 and 01/1316 for CGM and root number per plant. The best ranking hybrids were Mulola × 01/1313, Silira × TMS4(2)1425, Depwete × Silira, Mulola × Silira, Depwete × Maunjiri and 01/1316 × TMS4(2)1425. Overall, the results suggested that a breeding program that exploits heterosis would be more efficient in incorporating the traits under study for this set of genotypes.
cassava green mite, cassava mealy bug, GCA, gene action, SCA.
Cassava is an important crop in tropical and subtropical countries but its production is affected by biotic stresses particularly cassava mosaic disease (CMD), cassava brown streak disease (CBSD) and cassava green mite (CGM). Eleven cassava advanced lines were screened for resistance to CMD, CBSD and CGM in three consecutive seasons (2009-2011) at Agricultural Research Institute (ARI) Naliendele in Mtwara, Tanzania in a randomized complete block design with three replications. Data on CMD, CBSD and CGM symptoms severity were scored on a scale of 1 to 5 (1 means no disease symptom and 5 severe disease symptoms). Data on root yield and related traits were also collected at harvest. Data were subjected to analysis of variance and treatment means were separated using least significant difference test. There were significant differences for CMD, CBSD root necrosis and CBSD shoot infection among clones. More than 70% of clones scored class 2 or less indicating field resistance against CBSD and CMD. Significant differences were also revealed among clones for fresh root yield, number of roots per plant and harvest index. Improvement of cassava in resistance against these devastating diseases will improve crop productivity and ultimately livelihoods of farmers.
Cassava brown streak disease (CBSD) is a viral disease that affects cassava production in the coastal region of Kenya. Host plant resistance is the most effective way to control CBSD but only one resistant genotype is grown by farmers. Sixty-four genotypes were screened for their reaction to CBSD i in search of new resistance sources by wedge grafting infected scions at two sites. At 6 and 12 months after planting, the incidence (ICBSD), severity (SCBSD), incidence of root necrosis (IRN), and severity of root necrosis (SRN) were rated. Genotypes, sites, and their interaction were highly significant for ICBSD and IRN. Genotypes, and their interaction with rating periods, were highly significant for SCBSD and SRN. SRN showed a positive and significant (P < 0.05) correlation with SCBD and IRN (but low for SCBD and high for IRN), indicating that genotypes with low IRN would also have low SRN, while high SCBSD may not always be associated with SRN. One symptom or combination of CBSD symptoms, namely, leaf chlorosis and blotches, stem lesions and die-back, root necrosis and root constrictions, were observed on some genotypes. Genotypes such as Lml2002/2855 and Lml2002/1838 which previously did not exhibit symptoms of CBSD under field conditions, expressed severe symptoms after inoculation. Genotype 5318/3, followed by Kwl150, Msa140 and Plot14, showed high resistance to root necrosis over the two sites, and may be used as new sources of CBSD root necrosis resistance.
Cassava mosaic disease (CMD), a viral disease transmitted by Bemisia tabacci, is a major economic disease in all the cassava growing regions in sub-Saharan Africa. Breeding for resistance has been an important option to combat the spread and yield reduction associated with CMD. This study was conducted to determine the relative importance of general (GCA) and specific (SCA) combining ability among selected cassava genotypes. A half-diallel mating scheme of seven resistant or susceptible genotypes was used. The parents and their 21 F1 progenies were planted in a Randomised Complete Block Design with three replications in two locations representing forest agroecosystems in Ghana (Ejura and Fumesua). The trials were planted for two seasons. Results of the combined ANOVA revealed the environment effect was significant for yield and CMD score. The ratio between GCA and SCA mean squares for yield, CMD and number of roots was greater than 1.0 indicating the predominance of additive gene action. . Narrow-sense heritability was significant for plant root number and CMD. GCA was significant for CMD. The progenies from crosses Dabodabo x Kwasea, Debor x Lagos and Lagos x Kwasea were the best combinations for CMD resistance.
Food demands for global population have resulted in continued pressure and increased utilization of semi-arid marginal land where drought is frequent. Understanding responses to water stress among cassava genotypes can improve efficiency of selecting cassava varieties that can produce good yields in marginal conditions. 53 cassava clones, collected from drought prone districts of Uganda, were evaluated for their morphology, yield and adaptability to drought stress conditions in replicated field trials. Significant differences (P<0.05) were found among genotypes for all the parameters evaluated. Moisture stress resulted in a decline in harvest index-21.46%, fresh root yield-39.35%, NR-20%, dry matter content-12.4%, RSC-21.6%, LR-26% and PH-15.52%. Water stress had devastating effects on vegetative and yield parameters of cassava, justifying breeding strategies to develop drought tolerant cassava varieties.. Large genetic effects indicated that breeding objectives would be easily achieved. MH96/0686, Magana, Yellow, TME 204, Nyamutukura, MH97/2961 and NASE 12 were least affected by drought. Genotype x Location interaction was highly significant (P<0.05) except for AGB suggesting that selection for genotypes suited to agro-ecological zones with different levels of drought stress is possible. Some genotypes had stable yield and yield components suggesting potential for good adaptation to dry environments.
HarvestPlus began supporting cassava biofortification in Africa in 2004 with the goal of breeding for pro-Vitamin A enriched cassava with 15µg/g fresh weight of beta carotene combined with high yield, high dry matter, pest and disease resistant and good plant type to overcome poverty and hidden hunger among pregnant women and children. In December 2011, the Nigeria variety release committee released the first wave of Vitamin A cassava varieties, IITA TMS I011412, IITA TMS I011371 and IITA TMS I011368. A second wave of genotypes with higher levels of total carotenoids up to 11.7 µg/g fresh weight are in the pipeline with genotype IITA TMS I070593 giving high and stable total carotene content, improved dry matter content and cassava mosaic disease resistance. This paper will review progress made in early breeding stages to continue feeding the pipeline of new biofortified genotypes. Increased attention is focused on end-user preferences such as suitability for consumption of boiled roots. The process of screening large populations for proVitamin A content at the early breeding cycle stages has been enhanced by validation and use of a portable photometer device (iCheckTM Carotene) that allows assessment and selection for total carotenoid content in up to 60 samples per day. Promise for continued genetic gains in proVitamin A content also has been increased by selection among and within elite by elite yellow root crosses, introduction of new genetic diversity from Latin America and by initiation of genomic selection.
cassava, biofortification, proVitamin A, stability, genotype by environment interaction
In most developing countries, children under five years account for a large share of the total disease burden attributable to Vitamin-A Deficiency (VAD). A bold attempt to reduce nutritional deficiency was made through breeding to incorporate beta carotene (pre-cursor for Vitamin A) into cassava, a major staple for the poor/malnourished, thereby providing a cheap and strategic means of addressing VAD in the fight against hunger. In 2010, eleven farmers were selected to participate in a preference and sensory evaluation of 26 cultivars of pro-vitamin-A enhanced cassava at the National Root Crops Research Institute, Umudike, Nigeria.The farmers were trained and assisted by a facilitator to do on-farm assessment of the cultivars as well as sensory evaluation of a processed cassava product popularly known as “gari” from each cultivar. Sensory attributes like gari colour (dry), gari colour (wet), fibre content, smell, taste, texture and starchiness were evaluated. Data generated from the survey were subjected to analysis of variance and the Duncan multiple range test. Results revealed that mean scores of all listed attributes differed significantly (P < 0.05) among the cultivars evaluated. Root size was most outstanding as indicated by the large F-Statistics. However, root shape, root colour, plant size, root structure and bulking pattern weresimilarly important. Furthermore, analysis of the panellist preference ratings showed classification of the cultivars into three clusters on basis of their preference scores. Although results revealed mean scores of all the sensory attributes differed significantly (P<0.05) among the cultivars examined two traits fibre content of the products and gari colour both dry and when seeped/pounded were the most dominant among the sensory attributes. Based on the preference assessment of 26 cassava cultivars for morphological and sensory attributes, it could be deduced that cultivars like NR8082, 01/1412, 05/0303, 05/1559, 05/0100, 05/0127, 05/0327, 05/1631 and 05/1646 consistently emerged as the most preferred cultivars. Interestingly, eight of the yellow root cassava cultivars compared favourably with the control (NR8082) which is a current popular cassava variety with the farmers.
An attempt has been made to increase the root carotenoid levels in cassava through gene pool development in germplasm from IITA and NRCRI. Among 38 cassava pre-release and released varieties in Nigeria, eight promising genotypes were selected on the basis of flowering ability, dry matter, pests and disease resistance and carotenoids content. These were used to develop a crossing block at NRCRI. The eight genotypes were harvested and screened for total carotenoids and dry matter content. Total carotene content ranged from 0.80ug/g to 15.25ug/g flesh weight among the genotypes. Pigmentation in the root parenchyma correlated positively with high carotenoids as determined by a standard colour chart and spectrophotometer readings, but dry matter content was negatively correlated with carotene at the two harvesting periods. Genotype TMS 01/1368 (recently released UMUCASS series) had the highest value of total carotenoids while genotype TMS 98/0505 had the lowest value. In addition, genotype TMS 97/2205 showed the highest dry matter content of 44.39%, while genotype TMS 01/1371 (another UMUCASS series) showed the lowest DMC of 25.31%. Farmers were sensitized to grow more yellow fleshed root cassava to address vitamin A deficiency in Nigeria and to improve their livelihoods.
Carotene, Germplasm, Spectrophotometer, Colour, Vitamins
The demand in Nigeria for cassava has continued to increase as it is widely grown, consumed in various forms and transformed into many industrial products. This demand, however, is challenged by the low yield and yield instability even with increase in the total land area under production. There is a need to explore new selection methods such as what we call the physiological selection method in combination with other known methods. Physiological selection has the ability to fix a yield component which enhances and sustains yield, which depends on a combination of factors. Polycrosses from 10 parents, each superior in at least one physiological character, were obtained and established in the screen house. 100 seedlings per half sib family were selected and transplanted in a single row and data was collected on number of leaves, leaf area, plant height, number and root weight. TMS 92/0052 showed that all measured parameters had positive and highly significant correlations with root weight. Similar results were observed in TMS 30555 but leaf area and leaf area index showed negative and significant correlations with yield. TMS 01/0046 showed root yield positively and significantly related with the leaf number, while other parameters were positive but non-significant. The implications of these results for selection of cassava cultivars will be discussed.
Varieties TMS 98/0581, NR 98/0505, TMS 96/1632, TMS 92/0057 and TMS 94/4779 were treated with (0, 2 and 4% colchicine). The 40 treated stem cuttings per variety were air dried for 24 hours before planting. Different colchicine concentrations influenced cassava growth with number of leaves and plant height increased by increasing colchicine level. The number of branches and length of leaves decreased while the breath and number of leaves increased. The result of the study showed that the cassava varieties used in the experiment were not only sensitive to colchicine treatment, but also exhibited differential responses. The significant increase in the number of leaves accompanied by retrogressive increase in length and breadth may be an indication that polyploidy is a potential method of manipulating photosynthetic area for higher food production as against the over shadowing effect of long and broad leaves. Increase in plant height, leaf length, reduced branching, and development of lateral leaf types with higher sink-strength potential will help in increase starch accumulation and high yield. The overall result suggests that polyploidization with colchicine is a potential method of manipulating plant-architecture for the development of variable genotype for different purposes.
Genetic diversity on starch composition, in cassava storage root, has been accessed for searching to amylose/amylopectin ratio in the world cassava germplasm collection at CIAT, showing low range of variability except the find of a low amylose content access that could be of interest to cassava starch industry. In our laboratory we reported a new class of cassava plant (named sugary) with storage root containing high free sugar as glucose that also carries several different kind of starch composition with variation such amylose free and distinct amylopectin structure as well. An access of sugary cassava, with this particular starch phenotype, when grows outside its place of origin is extremely susceptible to bacterial blight disease (BBD) and produce low yield of storage root and low starch content as well. A conventional breeding program was designed to transfer novel trait to commercial variety in Cerrado region, which included provenance test of the landrace, crosses such self-pollination, open pollination, oriented pollination as well as a modified backcross. Branch size and frequencies were evaluated in F1 plants from those crosses to select clones with equivalent branching pattern of amylopectin, as well as resistance to BBD, high storage root yield and starch content. Results provided new clones confirming the presence of that particular amylopectin structure, increased storage root yield from 8 to 22ton/ha, increased novel starch from 10 to 20% and is free of BBD. A set of new elite clones retaining a novel amylopectin structure has been tested for use in the flotation industrial process in the metallurgy industry, showing an increase of up to 30% more efficiency in the purification of iron ores the main raw material to make steel. Genetic analysis of this particular trait is being carried out with recently obtained F1 populations.
High-value traits are envisioned as a way to strengthen markets for cassava, linking farmers to these markets and assuring the competitiveness of cassava and its products in the future. High-value traits gradually began to be identified. Particularly relevant are two mutations defining new starch quality traits (amylose-free and small granule). These mutations are recessive in nature. It is a challenge for cassava breeders to be able to exploit these recessive traits because of the strong inbreeding depression found in cassava. A method was proposed and tested to exploit recessive traits without noticeable inbreeding depression. The recessive source of a high-value trait is crossed with several elite germplasm adapted to the target environment to produce an F1 generation (the recessive trait is not expressed in this generation). Plants from unrelated F1 families are then crossed to produce a pseudo F2 generation. Inbreeding depression is negligible in this “F2” generation and the recessive trait is recovered in 25% of its genotypes. CIAT, Thai Tapioca Development Institute and Kasetsart University (Thailand) implemented this scheme to develop a waxy starch variety. About 16000 “F2” seeds were germinated and 12,000 seedlings transplanted. A total of 11,192 genotypes produce roots that could be tested for the waxy starch trait (which was recovered in 25.7% of the progenies). Currently few clones are in the advanced yield trials stage.
Three cassava varieties from Kasetsart University are widely grown in Thailand. However, their stability regarding yield components is not well known. The objective of this study was to determine the stability and yield potential of varieties grown in Lop-Buri, Phetchabun and Nakhon Sawan, Thailand during 2008 to 2010. Eight experiments with three cassava varieties; Kasetsart 50 (KU 50), Huay Bong 60 (HB 60) and Huay Bong 80 (HB 80) were carried out in a Randomized Complete Block Design with three replications. Trials were harvested ten months after planting. The results showed important differences in fresh root yield, roots per plant and root starch content. HB 60 gave higher fresh root yield (47.96 t ha-1) than HB 80 and KU 50 (37.14 and 31.01 t ha-1, respectively). HB 80 gave the highest number of roots per plant and root starch content (8.87 roots and 25.4%) followed by HB 60 (8.66 roots and 23.2%) and KU 50 (8.34 root, 23.0%), respectively. Cassava clearly offers a high and stable yield potential.
cassava, stability, potential, KU 50, HB 60, HB 80
Cassava, valued most for its starchy storage root, is an important food and economic crop in Nigeria. A principal constraint to breeding for improved productivity in Nigeria is the narrow genetic base identified in elite cassava varieties released in Nigeria in the 80s and 90s. Early initiatives to introduce Latin American germplasm to Africa and Nigeria were severely hampered by its susceptibility to the cassava mosaic disease (CMD) in the 90s. The discovery and genetic mapping of the CMD2 dominant gene has significantly contributed to the efficient transfer of CMD resistance into Latin American cassava. The LA germplasm consisted of those genotypes developed for CMD resistance using CMD2 gene. A total of 35 pre-selected genotypes of Latin American origin from the clonal evaluation stage in the breeding scheme in Nigeria were evaluated for adaptation and productivity based on disease resistance, yield and tuber characteristics in Nigeria . The randomised complete block design was used for the study in Nigeria in 2010 and 2011. Results showed that there was high variation among the clones for fresh root yield, harvest index, dry matter content and starch. The fresh root yield ranged from 24.00 – 33.00 ton ha-1 with CW 482 – 3 having the highest yield (33.74 ton ha-1) while the highest dry matter content was 34.06 % from CR 15B – 7. The analysis of variance showed a significant difference (P ≤ 0.05) among the evaluated clones for fresh root yield at 12 months after planting. The results indicates that the best four LA genotypes were significantly better in root yield than TMS30572 , a widely grown improved variety used as check in this trial. A good number of the LA genotypes were found to be relatively well adapted with good performance for biotic and agronomic traits which could explored to further improve African germplasm. The LA germplasm would be more beneficial for enhanced productivity if they represent different heterotic group from the African germplasm to maximize heterosis.
Cassava mosaic disease (CMD) is the most important disease of cassava in Africa. The first deployed resistance to CMD, which is thought to be polygenic, was from Manihot glaziovii. However, varieties developed using this source showed increasing susceptibility to CMD. The discovery of the dominant CMD2 made breeding for resistance to CMD more efficient. Monogenic resistance is generally non-durable. Initiatives were taken to build stable resistance in cassava cultivars being developed at National Root Crops Research Institute. Recently, the International Institute of Tropical Agriculture identified new varieties with resistance close to immunity that may represent new sources of resistance to CMD. wo of the varieties TMS98/1089A and TMS97/2205 are being used in crosses with CMD2 varieties to combine both sources of resistance. Seedling nursery evaluation of progenies developed were done at 3, 6, 12 months after planting on a scoring scale of 1 (highly resistant) to 5 (highly susceptible). Genotypes within the range of moderate to high resistance were selected at 12 MAP in 2010 and re-evaluated in 2011. Results showed that 55.5% were highly resistant genotypes; 42.7% were resistant and 1.4% were moderately resistant. The high proportion of the highly resistant genotypes indicate that cross combination of resistant parents resulted in progenies of better and higher resistance to the disease and thus the possibility of enhancing durability. Initiatives are underway to map loci associated with disease resistance.
Cassava is an out-crossing, heterozygous plant that suffers from inbreeding depression (ID). Although inbreeding offers many advantages its effects in cassava are still under-quantified.. A study to assess the performance of S1 progenies of five African cassava varieties (TMS 30572, TME 419, TMS 98/0505, TMS 01/1371 and TMS 98/0002) for six agronomic traits was conducted. The average ID levels were as follows: fresh root yield (FRY 86.55%), fresh foliage yield (FFY 66.38%), harvest index (HI 25.34%), root dry matter content (DMC 14.32%), plant height (PH -25.49%) and vigour (VI 20.83%). The average IDs obtained indicate that HI, DMC and VI were not severely affected. The average for PH in the S1 was not reduced implying no inbreeding depression. Inbreeding depression was highest in FRY and FFY, which are more complex traits than the others. The ID values for FRY and FFY underscore the relative importance of non-additive genetic effects in their inheritance. For each trait, however, individual S1 genotypes that substantially outperformed the non-inbred parents (transgressive segregants for favorable allele combinations) were found. This was observed mainly for PH, DMC and VI where ID values were lower. These results suggest that inbreeding may be strategically important to increase genetic gains and identify useful recessive traits. Advanced self-pollinated generations are currently in development to screen for inbreeding tolerance in cassava to enhance genetic improvement of the crop.
The expression of traits, especially quantitative traits, results from the interaction of genes and the environment. Selection of varieties that are high yielding and consistent in performance across contrasting environments is essential to develop stable varieties. Genotype by environment interaction affects heritability negatively and thus limits progress from selection. The objective of this study was to determine the effect of environment (spatial and or temporal) on the expression of traits in cassava. Fourteen cassava genotypes (with 2 checks) were evaluated for yield parameters as well as for major pests and diseases across two agro-ecological zones (Umudike and Otobi) in Nigeria during two cropping seasons. A randomized complete block experimental design was used with 4 replications. Data were analyzed using SAS and GGE biplot for stability evaluation. Analysis of variance showed genotypes were significantly different in all yield and disease parameters except root rot disease. Differential genotype responses to traits and environments were recorded. TMS 98/2132 had the highest mean in both years and locations although it was not the most stabile genotype.
Cassava is an important food security crop in the semi-arid areas of Kenya. It is grown in Kenya from the lowlands to over 2000 meters above sea level. The last cassava hybridization activities in Kenya occurred in 1955 in the East African Agricultural and Forestry Organisation (EAAFRO). Since then, improvement work has been through direct selection from the local germplasm or introduced tissue culture clones and seed populations from IITA. This has resulted in a number of local and introduced genotypes that are mealy with low cyanide potential with a range of maturity periods (8 to over 18 months) and tolerant to important cassava diseases and pests. In 2002, five local clones and seven IITA introductions were planted at Katumani in a crossing block. Hybridization started in the second week of May 2003 when most clones flowered; however, low temperatures experienced during June/August and drought stress caused seed capsules to abort. Few cross combinations managed to yield 10 seeds or more. A second crossing block comprising four local and seven IITA genotypes was planted in November 2003 at Kiboko where average daily temperatures range from 20°C to 34°C throughout the year and where irrigation is available. Flowering at Kiboko started 108 days after planting and continued for 8 months. Genotype 990130 failed to produce female flowers while genotypes 990127 and 990183 were incompatible with 820001 and 990010. Over 50% of the crossed families produced between 100 and 600 seeds per cross. The large seed number were attributed to the long flowering period, warm temperatures throughout pollination and availability of irrigation. From this preliminary study, it was decided that future crossing blocks will be established at Kiboko unless higher altitude sites such as Katumani will be required to stimulate flowering for genotypes that will not flower at Kiboko.
Vitamin A deficiency (VAD) is a major problem in children and pregnant women. Breeding cassava with enhanced levels of proVitamin A carotenoids in the roots (biofortification) is a cost effective approach to overcome VAD, especially for people who live in rural areas dependent on cassava. The challenge in breeding biofortified cassava is the large number of genotypes that need to be screened for their total carotene content (TCC) to select and advance to the next breeding cycle. An effective, quick, practical and portable device was developed by BioAnalyt (iCheckTM Carotene) to quantify carotenoids. Results from iCheck were compared with TCC values obtained in the laboratory using HPLC and the spectrophotometer. Cassava storage roots were sampled from single plants and from replicated yield trials and analyzed by iCheckTM Carotene along with HPLC or spectrophotometer. Estimates of TCC showed high correlations with R2 values ranging from 0.57 to 0.96 for iCheckTM and spectrophotometer data in four trials. The iCheckTM Carotene can be transported and used at remote field sites and results can be obtained the same day as roots are harvested. At least 60 samples can be processed per day with a small group of trained technicians. The method has been used to facilitate screening of large populations of cassava genotypes at the initial breeding stages.
cassava, biofortification, proVitamin A
The collection of cassava (Manihot esculenta Crantz) in Côte d’Ivoire is composed of local and introduced varieties from various origins. A study concerning its morphological characterization was carried out from 2001 to 2002 at the CNRA’s (Centre National de Recherche Agronomique) research station at Bouaké. It is based on 14 aerial and belowground qualitative descriptors applied to 340 accessions. Descriptors were recorded between 5 and 12 months after planting. Statistical analyses of data (multiple correspondences analysis, Aggregative hierarchical clustering, etc.) grouped the accessions into 8 homogenous classes. Class 1, 99(41)1 type, is composed of many improved varieties (68 %) while class 6, Bonoua rouge type, and class 7, CB type, each contains at least 80 % of traditional cultivars or landraces within the groups. All the clones at yellow flesh were assigned to class 2, Agba bana group. Duplicate accessions account for 25 % of the germplasm. Therefore, the number of accessions could be reduced to 285 morphotypes.
accession; cassava collection; characterization; Manihot esculenta
In spite of diligent efforts by NRCRI, Umudike and IITA to make Nigeria the largest producer of cassava in the world, the adoption rate of elite cultivars by farmers is about 40% and that is unacceptable. In addition, all cassava cultivars presently grown in Nigeria are low in vitamins and protein content and high in cyanogenic potential. A participatory rural appraisal (PRA) and sensory evaluation was conducted in Abia, Imo and Ebonyi states to assess farmers’ preferences for cassava with yellow fleshed root. Almost all the farmers consume cassava or its products at least once daily. More than 50% of farmers have not heard or read of high-carotene enrichment in cassava. Seventeen clones were grown in the surveyed areas, with more that 70% identified as bitter, indicating the relatively high prevalence of bitter cassava. Some of the farmers’ preferred traits include high yield, early maturity, pests and diseases tolerance, yellow fleshed roots, sweetness, high dry matter (DM), easy peeling, marketable roots and roots that keep long in ground without decaying. DM for the most preferred cultivars is above 40% and found to be important in both sweet and bitter cultivars. These traits identified are interrelated. Because farmers select cultivars based on multiple criteria, participatory rural appraisal and selection is essential for a successful breeding programme.
farmers, Nigeria, Vitamin A, cassava, Participatory rural appraisal.
An attempt has been made to increase the root carotenoid levels in cassava through gene pool development in germplasm from IITA and NRCRI. Among 38 cassava pre-release and released varieties in Nigeria, eight promising genotypes were selected on the basis of flowering ability, dry matter, pests and disease resistance and carotenoids content. These were used to develop a crossing block at NRCRI. The eight genotypes were harvested and screened for total carotenoids and dry matter content. Total carotene content ranged from 0.80ug/g to 15.25ug/g flesh weight among the genotypes. Pigmentation in the root parenchyma correlated positively with high carotenoids as determined by a standard colour chart and spectrophotometer readings, but dry matter content was negatively correlated with carotene at the two harvesting periods. Genotype TMS 01/1368 (recently released UMUCASS series) had the highest value of total carotenoids while genotype TMS 98/0505 had the lowest value. In addition, genotype TMS 97/2205 showed the highest dry matter content of 44.39%, while genotype TMS 01/1371 (another UMUCASS series) showed the lowest DMC of 25.31%. Farmers were sensitized to grow more yellow fleshed root cassava to address vitamin A deficiency in Nigeria and to improve their livelihoods.
Cassava, spectrophotometry, carotenoids, genotypes and vitamins
The Integrated Breeding Platform (IBP) is envisioned as a sustainable, web-based, one-stop shop for information, analytical tools and related services to design and carry out breeding projects. The IBP aims to leverage advanced information and communication technologies to enable breeding programmes to accelerate variety development for using molecular marker technologies for various breeding purposes. The platform will also deliver support services to guide and train breeders in accessing and using marker technologies. International germplasm exchange was the engine of the Green Revolution and much of the important information generated from this exchange was only accessible locally in field books or researchers’ files. We show at NRCRI the management of nursery and trial data in the database and application of the Trait Dictionary for standard measurement of the traits. NRCRI is now using IB Fieldbook to generate field books for the 2012 Replicated Yield Trials. Fieldbooks generated for these trials are moved to Samsung Galaxy tablets for data collection. The Galaxy tablet is convenient because data files can easily be transferred, it gives a reasonable time for data collection (up to ten hours) and has little glare while being used in the field for data recording. IBP will facilitate exchange of information and provide the foundation for a second green revolution by seamlessly uniting genetic conservation, evaluation, utilization and exchange.
Vitamin A deficiency is more common in developing countries where impoverished populations lack adequate resources to diversify diets and purchase foodstuffs or supplements. A typical adult-sized cassava meal (500g) can provide adequate calories but is an insufficient source of iron, zinc, vitamin A and protein. To improve the vitamin A content of cassava meals eaten by the populace, 18 high beta-carotene cassava varieties and 2 check varieties (TMS 30572 and TME 419) were evaluated for agronomic parameters, resistance to major pests and diseases, dry matter content and total carotenoids in two seasons. Data were subjected to analysis of variance (ANOVA) and Genotype plus Genotype x Enviroment (GGE) biplot analysis. Significant differences were observed among genotypes for fresh root yield and harvest index. Genotype TMS 05/1570 had fresh and dry root yields of 47.1 t/ha and 21.5 t/ha respectively while TMS 05/1601 had the highest total carotene content of 6.8 μg/g on a fresh weight (FW) basis. Check varieties had approximate total carotenoids of 1.0 μg/g FW. Total carotenoids and colour chart scores were correlated among the genotypes. Breeders can select for carotene content in cassava as well as high agronomic performance in order to enhance adoptability of new pro-vitamin A cassava varieties by farmers.
Stages in a cassava breeding program include: hybridization, seedling nurseries and subsequent evaluation trials based on the breeder’s interest. Materials (genotypes) are lost at each stage of the breeding program which may render a new population inadequate for the intended breeding objective. Loss of materials at different stages of the cassava breeding program was investigated in Nigeria using nine hybrid populations. Seedlings were raised from true seeds and the plants were evaluated at seedling, clonal and preliminary evaluation stages. Loss of materials ranged between 91.2 and 97.4% with an average of 94.1% among the populations. The loss was very high at the early stages (74.3 and 60.7% at hybridization and seedling nursery stages respectively) but drastically reduced as the study progressed (7.11 and 5.12% during clonal and preliminary evaluation trials respectively). This shows that large population sizes are critical in identification of rare recombinants in the development of improved cassava varieties. High loss of materials observed at early stages indicates that hybridization and germination of resultant hybrid seeds are critical stages in a cassava breeding program; hence, the need for generation of large populations so that breeders can have enough materials from which to select the desirable genotypes.
A study was conducted to assess the extent of genetic variability, broad-sense heritability and correlations between three traits (fresh root weight, root number and top weight) in five cassava genotypes across three locations (Fumesua, Pokuase and Ejura) in Ghana for 2 years. Combined analysis of variance revealed highly significant genotypic effects for all the traits; this suggests that some of the genotypes were superior to others in these three cassava traits. Also genotype x environment interaction was significant for all the traits studied, indicating considerable but varying influence of the environment on the expression of the traits. High broad-sense heritability and genetic advance as percent of the mean were observed for fresh root weight, suggesting that the trait is primarily under genetic control and that a simple recurrent phenotypic selection scheme would be rewarding. Phenotypic coefficient of variation values were larger than their corresponding genotypic coefficient of variation values. Correlations between the three traits were highly significant and positive indicating that simultaneous progress for three traits is feasible.
Cassava is an important perennial storage root crop in Uganda. Several cassava cultivars are grown; however, a few are perceived by farmers to be early bulking (ERB). ERB in cassava has increasingly become a major breeding objective in the national cassava breeding programmes in Africa. It is considered a requirement for cassava as an industrial crop and factor increasing cassava storage root yield per unit time. To assess farmers’ understanding of cassava ERB and to identify their cultivar selection criteria, a study was conducted in Busia, Jinja and Mukono districts in Uganda. A sample of 120 smallholder cassava farmers were sampled and interviewed using structured questionnaires and their fields were assessed. Results showed farmers had varied understanding of ERB. They expressed a strong need for improved ERB cultivars asserting they provide quick food, income and escape from late season pests and drought. Farmers’ cassava cultivar selection criteria did not vary among districts. Their selection relied on storage root yield, ERB, resistance to pests and diseases and sweetness. Farmers stressed that ERB cassava cultivars should, in order of importance, have high dry matter content, be sweet, high yielding and resistant to pests and diseases. In order to design a successful breeding programme under smallholder production systems, the farmers’ prevailing production conditions, views and trait preferences should be understood and considered.
The cassava germplasm collection in Thailand was developed in two phases. In the first phase, personnel from Rayong Field Crops Research Center (RYFCRC) from the Department of Agriculture (DOA) collected more than 200 accessions (landraces and improved varieties) from Thailand. In 2001 RYFCRC received 600 accessions (core) of the germplasm collection from CIAT, Colombia. RYFCRC collects and conserves its germplasm collection in two ways: in vitro through established tissue culture protocols and grown in the field. In the laboratory, accessions are subcultured every 3-4 months. Materials in the field are evaluated and characterized for many different traits. Some morphological descriptors, such as color of apical leaves are taken three months after planting. Other traits are evaluated at six and nine months after planting such as petiole color, leaf color, number of leaf lobes, length of leaf lobe, width of leaf lobe, lobe margins, petiole length, color of leaf vein, color of stem cortex, color of stem epidermis, color of stem exterior, distance between leaf scars and growth habit of stem. The descriptors to be scored at harvest are plant height, height to first branching, levels of branching, branching habit, angle of branching, dry matter content, starch content and harvest index.
From a nutritional point of view, cassava’s major advantage is that it is an inexpensive source of carbohydrate. The roots contain negligible amount of protein although substantial amounts are derived from the cassava leaves. Enhancement of cassava’s nutritive value has not been given serious consideration, either in breeding or in processing research. However, since 2004, development partners have provided financial support to HarvestPlus (H+) and BioCassava+, a consortium of organizations working to develop cassava varieties with substantially increased provitamin A carotenoid (β-carotene), protein, iron, and zinc content.
Limited information is available about the current vitamin A status of children aged 2−5 years residing in cassava-based production and consumption areas. Therefore, we conducted a survey to determine nutritional status (stunting, underweight, and wasting) and micronutrient deficiencies (vitamin A and E, iron, and zinc) among children 2−5 years of age. In addition, we also determined the foods consumed. A total of 6 local government areas (LGA), 18 enumeration areas/communities, and 667 households with a child 2−5 years of age were sampled. Blood samples were collected for the determination of biochemical markers using standard methods. Anthropometry and the 24-h dietary recall multiphase methods were used for assessing nutritional status and food consumption, respectively. The data showed that 31.3% of these children were stunted, 7.1% were underweight, and 16.2% were mildly wasted. Of the 31.3% that were stunted, 20.7% were classified as severely stunted. One in four (25%) of children aged 2−5 years were vitamin A deficient. The level of vitamin A deficiency was high at 31.1% in Ika North LGA and 26.5% in Ndokwa West. In all the LGAs except Isoko North, 1 in 5 children aged 2−5 suffered from VAD. Twelve percent of all the children investigated suffered from vitamin E deficiency. Twenty six (26.3%) of children aged 2−5 years suffered from depleted iron stores. Iron-depleted stores were highest among 49−60 months (27.7%) and 25−36 months (26.6%), followed closely by the 37−48 months age group (24.7%) and by the 13−24 months age group (22%). Only 2.5% of 2−5-year-old children suffered from zinc deficiency. Cassava products consumed were Eba and fufu. The number of children that consumed Eba was more than those that consumed rice. The mean intake of Eba is 341 g (n = 669); fufu 121 g (n = 142), and rice 260 g (n = 501). In conclusion, malnutrition and micronutrients deficiency is a public health problem in Delta State. While the proportion of children suffering from malnutrition and micronutrients deficiency varies by LGA, it is a significant public health issue in all LGAs.
No other source of starch is traded in the international markets more than that of cassava. This crop is the second most important global source for starch production (8.0 million t/year) after maize (15.5 million t/year). Key factors for cassava in starch production are its price and quality. However, there were no reported variations for starch functional properties in cassava until the discovery, in 2006, of the amylose-free (waxy) and small-granule mutations. Efforts to exploit these mutations began immediately upon their discovery. Crosses among the sources of these mutations were made and these genotypes (heterozygous for both traits) were self-pollinated or crossed to produce segregating progenies of which about 6% should combine the expression of the two recessive traits. A total of 148 plants (from 19 S1 families) and 89 plants (from 13 “F2” families) were analyzed and not a single individual expressing simultaneously both mutations was found. Results suggest that the two traits are closely linked or their combination is lethal. Interesting segregation for amylose content (ranging from 19 to 42%) was found among different small granule genotypes, suggesting that there may actually be two mutations segregating in the population: granule morphology and amylose content.
Starch is an important renewable raw material with an increasing number of industrial applications. As the most important trait in cassava, the starch quality of storage roots has been paid more attention in cassava research and breeding community. Cassava cultivars showing either high amylose or high amylopectin are desirable for cassava starch industries. Several attempts have been made to obtain waxy or high amylose cassava by mutation breeding (Ceballose et al., 2007, 2008) or genetic engineering (Munyikwa et al. 1997; Koehorst-van Putten et al., 2011). The expression of granule-bound starch synthase I (GBSSI) and starch branching enzymes (SBE), two key enzymes in starch biosynthesis, have been successfully down-regulated by RNA interference in transgenic cassava, respectively. Those transgenic cassava lines have been proved to be waxy or high amylose, ranging from 0-75% in amylose content. Compared to wild-type starch, the physico-chemical properties of those starches have been changed significantly, including granule size, paste temperature, viscosity, freeze-thaw stability, starch-iodine chelates stability, rheological properties, etc. The native starches from those transgenic cassava lines were used to develop novel modified starches, including oxidized starch, gelatinized starch, cross-linked starch, esterified starch, etherified starch and so on. Most properties of novel modified starches were totally different from the traditional modified starch; and several types showed a better performance in certain characters when compared with commercial ones. These studies will not only demonstrate the successful production of starch quality improved cassava by transgenic approach but also provide the raw materials for the development of novel modified starches for industrial applications.
transgenic cassava, starch biosynthesis, gene expression regulation, modified starch
Among starch producing crops, cassava has a higher carbohydrate production than others under suboptimal conditions, more than 163 million tons of cassava starch are produced world-wide each year and are used for direct human consumption, animal feeds and as raw material for a wide range of industrial products. A basic knowledge of starch characteristics and storage process is required to improve cassava starch quality and quatity. This report describes a comparative study of starch granule size distribution and amylose content in cassava storage roots grown under different conditions. Microscopic evaluation reveals that storage roots contain larger starch granules than fibrous roots. The study on the Thai commercial cassava varieties demonstrates the increment of starch granule size from outermost to innermost layers of storage root, while no significant change is observed in amylose content. The effects of developmental stages and growing season on cassava starch reveals that granule size is significantly influenced by both factors, while the amylose contents only fluctuate in a narrow range. The size of the starch granules increases particularly in the first six months after cultivation. Planting cassava in the beginning of the wet season in Asia yields larger granule sizes than planting in the dry season. The significance of this study lies in better understanding optimal growing conditions for improved starch characteristics and production, leading to a better quality agricultural production of this important food and material crops.
A study was conducted comparing the amino acid profiles of 10 commercial varieties (COL) and 15 clones with the highest levels of nitrogen (HIN) over two years of harvests. The highest nitrogen values detected in roots to date are close to 1.30%. The conversion factors of total nitrogen into protein calculated from amino acid profiles was 3.6 ± 0.9 for COL and 2.8 ± 0.2 for HIN. 53.7% of the total nitrogen is measured from protein with no difference between COL and HIN. The remaining 46.3% corresponds to ammonium ions, nucleic acids, or other nitrogenous non-protein molecules. Nitrogen content is 15.1 ± 1.2 and 19.1 ± 0.6% of the protein for COL and HIN, respectively. This difference is explained by a high content of arginine (4 nitrogen atoms per arginine molecule) in HIN clones. For COL, the proteins contained, on average: 23.3% glutamic acid, 15.7% proline, 14.3% arginine, 7.9% aspartic acid, while for HIN: 23.5% glutamic acid, 2.3% proline, 35.5% arginine, 7.9% aspartic acid. A linear correlation was found between the total nitrogen content and the level of arginine in cassava roots. Root protein content based on amino acid profile varied between 1.0% and 2.8% in the clones analyzed. Screening of varieties by the total nitrogen content leads to identify clones that are richest in arginine and not necessarily the richest in protein. Nitrogen alone, therefore, is not adequate to predict protein content.
Department of Agriculture of Thailand has released Rayong 9 variety on 2006. A remarkable hybrid variety hybridize from the cross of high starch content female parent CMR31-19-23 and male parent OMR29-20-118 in 1992 at Rayong Field Crop Research Center (RYFCRC). The outstanding of Rayong 9 is high starch that suitable for ethanol production. Rayong Field Crop Research Center collaborated with Thailand Institute of Scientific and Technological Research (TISTR) to investigate ethanol yield of Rayong 9 compared with four standard checks as Rayong5 Rayong 72 Rayong 90 and Kasetsart 50 in a laboratory at TISTR. Fresh cassava roots at 8, 12 and 18 months were clean, chopped and dried until the moisture of cassava chips were around 10.4-13.3%. Cassava chips were processed to starch by a-amylase and amyloglucoamylase. Saccahromyces cerevisiae TISTR 5596 were used to convert fermentable sugars to alcohol by batch fermentation in 250 ml flask. The maximum yield of ethanol was found in Rayong 9 with every harvesting age especially at 12 months (208 liter/ton of fresh root). The ethanol yield of high starch content varieties Rayong 9 and Rayong 90 were study at a prototype ethanol factory producting 99.5% ethanol with capacity 1,500 litter/day of TISTR. The fresh root 9.5 tons/variety were used to be raw material for converting to ethanol by batch fermentation in 25,000 litre fermentation tank. The result found that Rayong 9 gave the higest ethanol yield 198 liter/ton of fresh root.
Cassava, ethanol, Rayong 9
Vitamin A deficiency and its related diseases constitute major health challenges in most developing countries affecting about 250 million people globally. Recent studies in Nigeria showed that 30% of under-five children were vitamin A deficient. The HarvestPlus research consortium aims to breed and deploy bio-fortified staple crops such as cassava for better nutrition and mitigation of challenges such as vitamin A deficiency. Scientists at Nigeria’s National Root Crops Research Institute (NRCRI), the International Institute for Tropical Agriculture (IITA), Nigeria and the International Center for Tropical Agriculture (CIAT), Colombia developed pro-vitamin A cassava varieties with end-user preferred traits and high agronomic performance. This initiative resulted in a recent release and launch of three cassava varieties with enhanced pro-vitamin A contents to Nigerian farmers. The 3 new varieties (TMS 01/1368, TMS 01/1412 and TMS 01/1371) registered and released as UMUCASS 36, UMUCASS 37 and UMUCASS 38 respectively, were preferred over local checks for cassava food products such as gari and fufu in on-farm participatory evaluations with end-users. The total carotene content of the new varieties ranged between 6 – 8 µg/g FW, based on data collected from 9 multi-environments across 4 agro-ecological zones in Nigeria and 104 farmers in 13 states. The HarvestPlus target for delivery of these varieties is to reach 50,000 households in 4 pilot states in Nigeria and to extend same to other African countries. Modern breeding techniques such as the development of partial inbreds are being deployed to further enhance the beta carotene contents future varieties. The new set varieties must contain high levels of beta carotene in combination with stable post-harvest retention ability, resistance to major pests and diseases and superior yields.
Clonal evaluation stage is the first field trial after seedling evaluation in a conventional breeding cycle of cassava. Yellow root cassava contains carotene, a precursor of Vitamin A which is an essential micronutrient for good health, sight and immune system booster. Twenty-nine yellow root cassava genotypes and two check varieties (TME 419 and TMS 30572) were evaluated for agronomic parameters, response to major pests and diseases of cassava and quality traits at Umudike, South-Eastern Nigeria in 2010/11 cropping season. The experimental design was randomized complete block design replicated twice using a single row plot of 5m for each genotype. The genotypes were evaluated for fresh root yield, dry matter and carotene contents at 12 MAP and the data were subjected to analysis of variance. There were high significant differences among the genotypes for the three parameters. The genotypes showed high resistance to major pests and diseases having severity scores of 1 or 2. Carotene content ranged from 5.0µg/g to 7.1µg/g; fresh root yield ranged from 1.0 to 25.2 t/ha; dry root yield ranged from 0.3 to 9.3 t\ha while dry matter ranged from 19.6% to 40.89%. The genotypes with high carotene content also had high dry matter content ranging from 32% to 40%. The genotypes are currently being evaluated in preliminary trial at the same location after which the top genotypes in relation to all the traits of interest will be selected for multi-locational trial.
clonal, evaluation, yellow root cassava.
Tapioca is a storage-cupboard convenience food obtained from the tubers of cassava (Manihot esculenta Crantz). It is an important staple in many African countries where both Protein Calorie Malnutrition (PCM) and Macro and Macro Nutrients Malnutrition (MMNM) are endemic. The nutritional properties of Moringa oleifera Lam. (MO) are now so well known that there seems to be little doubt of the substantial health benefits to be realized by consumption of Moringa leaf powder in situations where starvation is imminent. Being a product of cassava, tapioca is nutritionally inferior and need to be fortified. This paper reports the nutrient profiles of tapioca fortified with MO leaves. Tapioca was fortified with freshly prepared powder of MO leaves at 12.5 and 25 % of dry weight basis (dwb). Standard methods were used for the determination of nutrient profiles of both fortified and control samples. Nutrients analyzed for include crude protein, fat, ash, carbohydrate and moisture content. Others are phosphorus, calcium, magnesium, potassium, sodium, manganese, iron, copper, zinc, vitamins A, B and C. Unfortified tapioca had significantly lower (p < .05) proximate values (protein: 1.06%; fat: 0.41%; ash: 0.21%). The fortification of tapioca significantly (p < .05) increased the contents of crude protein, phosphorus, fat, ash (%) and vitamins A, B, and C(iu/g) as well as all the monitored macro- and micronutrients. These values increased from 1.06–5.11, 0.07–0.17, 0.41–0.86, 0.21–0.65, 0.08-1.05, 0.06-0.27 and 0.09-0.45 for 12.5% dwb fortified tapioca; and 1.06–6.35, 0.07–0.33, 0.41–1.49, 0.21–1.76,0.08-1.26, 0.06-0.65 and 0.09-1.32 for 25.0% dwb fortified tapioca respectively. Data from this study suggest that fortification of tapioca with MO leaves could produce a cassava based food staple which can furnish the daily requirements of minerals, protein, energy and some vitamins. Tapioca fortified with MO leaves could be used to ameliorate both PCM and MMNM which are endemic not only in Nigeria and other African countries, but also in other cassava consuming developing nations.
Vitamin B6 is an essential nutrient for human health and plant growth. It serves as a cofactor for several proteins in various metabolic pathways, and is a potent antioxidant to scavenge reactive oxygen species. Strategies to increase vitamin B6 accumulation in crop plants have the potential to produce biofortified crops as well as to generate crops with enhanced tolerance against oxidative stress. Here, we report genetic engineering of cassava expressing two Arabidopsis genes essential for de novo biosynthesis of vitamin B6. Vitamin B6 was quantified by a yeast microbiological assay and the vitamers of B6 were further characterized by HPLC. Transgenic cassava showed an over 20-fold increase in vitamin B6 content in leaves and a 4-fold increase in storage roots. Due to their potential higher antioxidant capacity, transgenic lines were tested for tolerance to both biotic and abiotic stress. Interestingly, the transgenic cassava lines displayed improved tolerance to post-harvest physiological deterioration (PPD). Consistent with observations made earlier in Arabidopsis, we also noticed an increase in yield for selected transgenic cassava lines in experiments performed under greenhouse conditions. Currently, the transgenic cassava lines with increased vitamin B6 levels are being tested in the field to evaluate their agronomic performance. Our results demonstrate the potential of vitamin B6 biofortification in cassava and provide new strategies to improve cassava.
Cassava is the most productive crop in terms of energy yield per unit area of land in the low land tropics. Higher incomes for marginal areas of the developing world, where the crop is generally grown, requires the industrialization of the crop and the development of novel industrial products for cassava, with the aid of modern biotechnology. There are several novel products that can be produced from cassava. These include modified starches, such as 100% amylopectin from the down regulation of the granule bound starch synthethase (GBSS) gene. The industrial applications of either pure amylopectin or pure amylose starches, such as the production of high value biodegradable polymers from pure amylose starches or the use of 100% amylopectin in thickeners, pastes, and glues, is a market with unlimited growth potential.
The amylose/amylopectin composition of starches in plants is controlled by three enzymes. The granule bound synthethase (GBSSII), the starch branching enzyme (SBE), and the soluble starch synthase (SSS). Maize, potato, and rice mutants have been found with a defective GBSSII genes that gave rise to amylose free (100% amylopectin), or waxy starches. Anti-sense technology has also been employed to create potato transformants with 70-100% amylopectin via the down-regulation of the GBSSII gene. The two principal starch biosynthesis genes have been cloned at CIAT from root and leaf cDNA libraries. The availability of these starch genes opens up opportunities for producing cassava starches with different 100% amylopectin via anti-sense transformation.
While our project goal is to produce 100% amylopectin starch (waxy starch), in cassava by the down regulation of granule-bound starch synthase (GBSS) via “anti-sense mediated” genetic transformation, our objectives are four-fold:
- Construction of sense and antisense granule-bound starch synthase (GBSS)
- Generation of embryogenic callus for an industrial variety of cassava
- Transformation of one industrial varietiy of cassava with the above constructs.
- Regeneration of transformants and analysis of the roots for waxy starch
While we have concluded the transformation methodology in cassava, we are currently seeking the collaboration of CIAT or any other organization that will be willing to give us the necessary genetic construct.
A large dataset (2129 data points) was developed over the years of research to increase carotenoids content in cassava roots. Correlations were always based on more than 550 data points. Correlations between dry matter content (DMC) and total carotene content (TCC) or β-carotene (TBC) were positive and weak (0.13 and 0.07, respectively). There is no problem, therefore, for producing biofortified cassava with adequate levels of DMC. Correlation between cyanogenic potential (HCN) and TCC was negative suggesting that it is possible to obtain high-carotene with low HCN values. Correlations of data from spectrophotometer and HPLC were very high. TCC and TBC had a high correlation (0.90) suggesting that most carotenoids in cassava roots are β-carotene. Correlations between TCC and TBC with phytoene were relatively high (0.52 and 0.61, respectively). Correlations between TCC and TBC with phytofluene were 0.60 and 0.65, respectively. Correlation between phytoene and phytofluene was 0.96. No case where accumulation of phytoene or phytofluene without parallel levels of carotenoids was observed. Similarly there was no accumulation of phytoene without parallel levels of phtytofluene. There is no evidence, therefore, that accumulation of carotenoids in cassava roots is related to a blockage at the PSY or PDS steps in the carotenoids biosynthesis.
Significant progress has been made increasing carotenoids content in cassava roots. The information was used to test the usefulness of NIRs and the Minolta Chromameter in predicting carotenoids content (and other relevant traits). Quantification was made of fresh root tissue (not lyophilized). The dataset (2129 data points) was first cleaned of outlying or suspicious data points to develop reliable prediction equations. R2 values between NIRs prediction and actual measurements were 0.91 for total carotenoids content (TCC); 0.93 for total β-carotene (TBC), and 0.95 for dry matter content, but is less efficient for cyanogenic potential (0,81). Standard error of cross validation (SECV) for TCC and TBC were (1.191 and 0.837, respectively) while the residual predictive deviations (RPD) were also acceptable (above 3.0). These results suggest that NIRs can be used to reliably predict different variables based on fresh root samples. The Minolta Chromameter can also be used for pre-selection as its R2 values were 0.58 for TCC and 0.64 for TBC. Relative concentration of different carotenoids and precursors did not suggest the existence of a major blockage in the metabolic pathway towards the synthesis of β-carotene. Once phytoene is synthesized most to the different pigments in the metabolic pathway are found, as expected, in correlated proportions.
With the support of HarvestPlus, CIAT and other institutions have been involved in projects to increase total carotenoids content (TCC) and total β-carotene (TBC) in cassava roots. A rapid cycling recurrent selection method was developed and used to increase TCC and TBC. Year-to-year results suggest continuous gains. In the last F1 (seedling) nursery harvested during 2011 a maximum TCC of 25.8 µg/g (fresh weight basis) was quantified in the genotype GM 3732-22, whose dry matter content (DMC) was excellent (39.98%) but only had 12.9 µg/g of TBC (FW). On a dry weight basis this genotype produced 64.5 and 32.2 µg/g of TCC and TBC, respectively. Higher TBC levels were quantified in GM 3742-6 and GM3674-31: 15.0 and 14.2 µg/g FW, respectively (or 36.1 and 44.5 µg/g on a dry weight basis, respectively), with excellent or acceptable DMC (41.5 and 31.9%, respectively). However, these comparisons are affected by year to year variation. Currently the best five clones from each seedling nursery from 2004 to 2010 are grown side by side for comparison. Data are also consistently demonstrating that the rapid progress is genetically based. Preliminary results suggest that concentration of carotenoids increases with age of the plant. A new estimation of heritability based on parent-offspring regression (equivalent to narrow sense h2) was found to be high (0.64), which explains the rapid and consistent gains achieved.
The industrial starch market is undergoing major expansion, but certain specific industrial uses cannot be satisfied by native starches and, therefore, chemical or physical modification is necessary. Mutations in the cassava starch biosynthesis pathways were discovered at CIAT (Cali, Colombia) few years ago. A starch mutation induced by gamma rays radiation resulted in a deeply modified branching pattern of amylopectin as well as other starch characteristics and properties. These modifications include changes in starch granule ultrastructure (e.g. decreased starch crystallinity), a weak organized structure, and increased susceptibility to mild acid and enzymatic raw starch hydrolysis (fastest and most efficient hydrolysis of all studied native starches). This mutation could offer interesting advantages for the production of bioethanol. Surprisingly this mutation also results in increased proportion of amylopectin. Hydrolysis was more dependent on granule morphology than on starch chemical composition. Recent crosses produced segregating progenies whose starch had the small-granule characteristics, but amylopectin content ranged from 19 to 42%. Rapid viscoamylograms of the latter starch showed very distinctive patterns.
Yellow Cassava Roots varieties are being propagated in Nigeria to aid in combating dietary vitamin A deficiency in the country due to their high content of β-carotene (a precursor of vitamin A). Three newly bred yellow roots cassava genotypes: TMS/01/1368, TMS/01/1371 and TMS/01/1412 were assessed for their potential usage in processing into acceptable fufu using the odourless flour technique and by the traditional method. Carotenoids in the intermediate and finished products of these yellow roots were evaluated. Results showed that while the fresh roots had 6.26-7.76 µg/g β-carotene contents TMS 30572 -white root (control) had 0.35 µg/g β-carotene contents, their intermediate products namely grated cassava mash and fermented cassava mash respectively had β-carotene content of 6.24-7.75 µg/g (β-carotene contents retention of 97.68-98.48 %) and 5.97-7.48 µg/g(94.68-96.66%) and final product of the 3 genetypes had 5.41-7.03 µg/g(86.42-90.24%). This implies negligible loss (<0.6%) of carotenoids incurred during grating, less than 5% loss incurred during fermentation of the grated mash and less than 15% loss incurred during the entire process of production of fufu from the yellow cassava roots by the traditional method. The intermediate products using the odourless flour technique had 5.93-7.53 µg/g (carotenoids retention ranged from 94.68-94.73% for grated cassava mash), 1.50-2.12µg/g (21.55-33.87% for fermented cassava flour) and the final product (cassava fufu) had 1.20-2.00µg/g (17.24-31.94%). The losses were mainly incurred during the drying processes. Generally the yellow fufu was more acceptable by the Taste Panel than the fufu produced using the odourless flour technique. The use of traditional method for the production of fufu when using yellow- root cassava genotypes is recommended for maximum utilization of the nutrient in the newly bred yellow cassava genotypes.
Cassava is a starchy food with carbohydrates accounting for 80% of the nutritive value. The levels of protein and micro nutrient are significantly low or absent in the majority of varieties preferred by farmers in various African countries. This is important during periods of food scarcity when most poor households eat cassava starch based diets devoid of any other supplementation. In rural dryland western and coastal Kenya, that food is cassava eaten as gruel, ugali or boiled from fresh roots. The most disadvantaged communities are children under five years of age of whom approximately 30% suffer from vitamin A deficiency.
An ambitious project to enrichen cassava meal has successfully introgressed ADX and PSY genes into cassava line 60444. Evaluation of a confined field trial of four different events show that the genes have been over -expressed in the roots and significantly differ from that of the local check and the wild type. There are also differences between the events when plants are harvested at different plant ages. The results indicate that under AEZ’s similar to Kenya betacarotene levels will be improved when these genes are introgressed into commercial cassava cultivars.
Cassava leaves forms a good accompaniment to staple food for many in the sub Saharan region. A study was carried out to determine total and free amino acids content in tender and mature leaves. Total and free amino acids were analysed by acid hydrolysis and EZ: faast free amino acids kit respectively. The results showed that cassava leaves have essential; isoleucine, leucine, lysine, methionine, phenylalanine, threonine and tryptophan, valine, cystein and non essential amino acids; asparagine, aspartic acid, glutamic acid, glutamine, tyrosine and serine. Total amino acids levels were significantly higher than free amino acids in both tender and mature leaves (p<0.05). Cystein was limiting as total amino acid and not detected as a free amino acid. This shows that the cystein is in protein bound form. Total amino acids content ranged from 340±152-53300±4239 mg/kg and 180±130-27460±5853 mg/kg in tender and mature leaves respectively while free amino acids ranged from 2.6±0.1-1144.5±0.5 mg/kg and 0.6±0.1-583.3±0.9mg/kg in tender and mature leaves respectively. Leaf maturity also significantly influenced total and free amino acids levels as observed in tender leaves registering higher levels of both total and free amino acids. The results revealed that both tender and mature leaves have essential amino acids which could provide the body with the essential nutrients required by the body.
Cassava, total and free amino acids, tender, mature, leaves
In Sierra Leone, Cassava ( Manihot esculenta Crantz) is cultivated throughout the country and is the second staple after rice. It constitutes at the same time a food and revenue crop for producers. However, its production remains a traditional type with a low level of intensification, of which one of the major constraints is the availability of improved planting material. Statistical data also shows that there is a high prevalence of malnutrition, especially among women and children in most cassava producing regions in the country. An estimated 40% of young children suffer from vitamin A deficiency. Iron-deficiency anemia is currently estimated to affect 86% of children under 5 years, and 68% of women of childbearing age. To mitigate these problems, the continuous provision to the farmers of improved varieties that contain the most effective and long term solution to addressing micronutrient deficiencies appears to be solution. The orange fleshed cassava is among plants of more bio available vitamin A sources. Twelve orange-fleshed cassava genotypes were planted in 5 locations representing the rain forest, the forest savanna transition and the savanna zones of the country. Measurements and observations related to pests and diseases, reaction of farmers with respect to agronomic and sensory characteristics were recorded. Tuberous roots were harvested 12 months after planting (MAP) and yield and yield component data also recorded. The analysis of the data including locations and genotypes indicated that the average yield varied from 25-40t/ha. Moyamba and Makeni recorded the best yield of 38 and 40t/ha respectively. The lowest yields were recorded at Kambia (18t/ha). Generally, farmers selected genotypes based on yield, vigorous growth pattern, size of tuber, ease of peel, colour of pulp, cooking and taste. Most genotypes did not show any major disease and pest incidence and severity (score 1 and 2). The best five genotypes selected by most farmers were as follows: 01/1635, 01/1646, 01/1641, 01/1412 and 01/1663.
Genotypes, Orange-fleshed, growth rate, biofortification, sensory, malnutrition.
Changes in body dimensions reflect the overall health and welfare of individuals and populations. Anthropometry is used to assess and predict performance, health, and survival of individuals and to reflect the economic and social wellbeing of populations. It is widely used, inexpensive, and is a non-invasive measure of the general nutritional status of an individual or population group. Limited information is available on the current nutritional status and amount of cassava consumption among children aged 2─5 years residing in cassava-based production and consumption areas. Therefore, we conducted a survey to assess the nutritional status and food consumption of children 2─5 years of age. A total of 6 local government areas (LGA), 18 enumeration areas/communities, 667 households with a child 1─5 years old were sampled. Anthropometry and the 24-h dietary recall multiphase methods were used for assessing nutritional status and food consumption, respectively. The data showed that 31.3% of these children were stunted, 7.1% were underweight, and 16.2% were mildly wasted. Of the 31.3% that were stunted, 20.7% were classified as severely stunted. The level of stunting was similar in the LGAs. When the data were disaggregated by age, severe stunting was more prevalent (30.1%) in the 13─24 months age group and when this was combined with those moderately stunted, the percentage of stunted children in this age group was 41.3%, followed by 34% for the 25─36 months age group. More male children were stunted (34%) compared to female children (29.3%). Cassava products consumed were Eba and fufu. The number of children that consumed Eba was more than those that consumed rice. The mean intake of Eba is 341 g (n = 669); fufu 121 g (n = 142), and rice 260 g (n = 501). In conclusion, malnutrition is a public health problem in Delta State. While the proportion of children suffering from malnutrition varies by LGA, it is a significant public health issue in all LGAs.
Iron deficiency is the world’s most widespread nutritional disorder and affects about 5 billion people in developed and developing countries. It leads to anemia, the severe form of iron deficiency, which affects nearly 2 billion people worldwide. Altogether, 39% of preschool children are anemic. Zinc deficiency in developing countries is a leading cause of illness and ranks fifth in the top 10 risk factors. Worldwide, zinc deficiency is responsible for about 16% of lower respiratory tract infections, 18% of malaria, and 10% of diarrheal disease. Limited information is available about the current iron and zinc status of children aged 2−5 years residing in cassava-based production and consumption areas. Therefore, we conducted a survey to determine the iron and zinc status of 2−5-year-old children. A total of 6 local government areas (LGA), 18 enumeration areas/communities, and 667 households with children aged 2─5 years were sampled. Blood samples were collected by venipuncture for the determination of serum ferritin and zinc using an immunoradiometric assay and atomic absorption spectrometry, respectively. Results obtained indicate that 26.3% of children aged 2−5 years suffered from depleted iron stores. Among the sampled LGAs, iron-depleted stores were highest in children living in Ughelli North (32.1%) followed by children living in Aniocha (29.8%) and Ethiope (27.7%). Iron-depleted stores were highest among 49−60 months (27.7%) and 25−36 months (26.6%), followed closely by the 37−48 months age group (24.7%) and by the 13−24 months age group (22%). Only 2.5% of 2−5-year-old children suffered from zinc deficiency. When the observed value of zinc deficiency was partitioned among the LGAs, zinc deficiency was low with a prevalence of 4.3% in children living in Ethiope LGA. About 7.7% of the children in the 25−36 month’s age range suffered from zinc deficiency followed by 4.9% in the 13−24 months range. In conclusion, iron deficiency is more prevalent and is a public health problem in the target State compared to zinc deficiency. Although the proportion of children with low serum ferritin levels varies by local government areas, low iron store is a significant problem in all LGAs.
Vitamin A deficiency (VAD) is a global problem. It affects more than 100 million children and is responsible for as many as one out of every four child deaths in regions, countries, and communities with a deficiency of vitamin A. Deficiencies of vitamin E in children under 5 may have a negative consequence in terms of immune function. From a nutritional point of view, cassava’s chief advantage is that it is an inexpensive source of carbohydrate. Enhancement of cassava’s nutritive value has not been given serious consideration, either in breeding or in processing research. However, since 2004, development partners have provided financial support to HarvestPlus (H+) and BioCassava+, a consortium of organizations working to develop cassava varieties with substantially increased provitamin A carotenoid (β-carotene), protein, iron, and zinc content. Limited information is available about the current vitamin A status of children aged 2−5 years residing in cassava-based production and consumption areas. Therefore, we conducted a survey to assess the status of vitamins A and E among children 2−5 years of age. A total of 6 local government areas (LGA), 18 enumeration areas/communities, and 667 households with a child 2−5 years of age were sampled. Blood samples were collected for the determination of serum retinol and tocopherol using HPLC. Results indicated that 25% of children aged 2−5 years were vitamin A deficient at the State level. The level of vitamin A deficiency was high at 31.1% in Ika North LGA and 26.5% in Ndokwa West. In all the LGAs except Isoko North, 1 in 5 children aged 2−5 suffered from VAD. Twelve percent of all the children investigated suffered from vitamin E deficiency. When the data were disaggregated by LGAs, vitamin E deficiency was 16.9% in Ika North, 16.3% in Ethiope, and 14.5% in Ndokwa West. Among the LGAs with lower prevalence of vitamin E deficiency were Aniocha (7.1%) and Ughelli North (7.7%). In conclusion, vitamins A and E deficiencies are a severe public health problem in Nigeria. While the proportion of children with low serum vitamin A and tocopherol levels varies across the LGAs, vitamins A and E deficiencies remain a significant public health concern in the State and in all the LGAs.
Dried and ground fractions of peels, leaves and flesh samples of the improved (p746, p768 and p770) and unimproved (WT) cassava cultivars were assessed for their proximate composition, carotenoids, minerals, amino acids and HCN,
Crude protein on DM basis averaged 5.3, 9.6 and 28.5 % for the flesh, peels and leaves, respectively. Generally the genetically improved cassava cultivars contained higher levels of protein (2.4% (WT) and 8.1% (p746) for the flesh), TAA, and other macronutrients compared to unimproved variety. HCN varied in the flesh among varieties and was 96 in WT and 141 mg/kg in p746.
Fiber fractions (NDF, ADF and lignin) were highest in leaves and lowest in flesh. Both total amino acid and individual amino acids concentrations were 2 to 10 times higher in peels fractions compared to flesh of the same variety. Total carotenoid concentration in the flesh was 0.04 mg/kg in WT and 1.01 mg/kg in p746. ß-carotene was the primary carotenoid pigment in the flesh and peels, 75-93% whereas in cassava leaves lutein was 54-64%. Mineral levels were highest in leaves, followed by peels, and lowest in the flesh.
This study revealed nutritional differences between cassava cultivars and plant parts. Furthermore, cassava peels, normally thrown away contained higher nutrients and therefore could be a good source of nutrients in livestock diets
The study was aimed at the nutritional trend of yellow cassava roots analyzed biochemically and consistently for two years at NRCRI in Nigeria. Total carotenoid content (TCC) µgg-1 and percentage dry matter (%DM) content was specifically looked at in some selected genotypes on fresh weight basis. A total of ninety genotypes were analyzed under the NR/05-07 series from 2010 and 2011 planting seasons. The Harvest-Plus Standard Operational Procedure (SOP) was used to conduct the carotenoid analysis while oven drying was used for the dry matter analysis at 700C. The data was analyzed using means and linear regression graphs. The result shows that TCC has a mean of 6.37µgg-1 and 4.98µgg-1 in 2010 and 2011 respectively. More so, the regression showed that there was a negative relationship between TCC and %DM in the first year. However, the relationship became positive in the second year, and this was attributed to too much rainfall in 2011 which affected the carotene level. Nutritionally, the analysis showed that the higher the consumption of yellow-fleshed root cassava, the more the intake of vitaminA but the less the energy in-take.
Fresh cassava roots and leaves cannot be stored for long because they rot within 3-4 days after harvest. Being bulky with about 70 percent moisture content, transportation of the roots and leaves from rural to urban areas for marketing is very difficult and expensive.
Both root and leaf contain varying amounts of cyanide that is toxic to humans and mammals; additionally, they are not palatable. Thus there is a need to process cassava into various products that have increased shelf-life, are easier to transport and market, cost less to transport, contain less cyanide and have improved palatability and nutritional value.
Several traditional fermented foods and beverages are produced at the household level in Rwanda and create local employment opportunity and income generation. The cassava-based fermented foods include; cassava flour & cassava leaf flour.
Literature on Rwanda fermented cassava foods is non-existent. Therefore, the objective of this review is to document the methods by which these Rwandan fermented foods are produced and to devise scientific means to improve their quality and optimize their production methods.
Traditional fermented cassava-based foods, shelf life, nutritive & economical values
The Great Lakes Cassava Initiative (GLCI) reached a scale of 1.35 million vulnerable farmers, many of whom from remote and insecure areas, with clean cassava seeds of improved varieties which were CMD-resistant or CBSD-tolerant. These farmer beneficiaries, along with the various aspects of the seed system activities, were documented in a live database online, that were directly inputted from the field by more than 200 field agents. These field agents were given mini-laptops and given repeated training on the general use of computer as well as specific data entry to document the GLCI field activities. Underpinning this scale and documentation was the innovations developed by the integrated research and development activities of GLCI. The innovations can be broadly categorized as innovations for a large-scale seed system which the context of emergent and existing diseases, innovations to manage this large scale of operations, and innovative M&E system that facilitated the documentation of the results of the GLCI activities. The broad-spectrum of partnerships that designed and implemented the research and implementation was the basis to the success of GLCI in reaching scale and documenting the success. The clearly defined roles and responsibilities and the coordination of these partnerships are the underlying ingredients for the success of these partnerships.
GLCI was a four year project operating across 6 countries. GLCI established a network of more than 50 partners encompassing national and international research, national pant protection, government agricultural extension, and non-governmental organizations tasked with identifying, producing, validating, and delivering improved disease tolerant (cassava mosaic and cassava brown streak) varieties to 1.2 million farming families in East and Central Africa. This paper discusses key lessons learned in planting material production and delivery through five innovative approaches used in the GLCI seed system: decentralized production to attain scale, source site sampling and diagnostic testing to mitigate CBSD risk, the benefits and limitations of visual in-field quality management protocols (QMP) to validate fields before dissemination, and transparent and participatory dissemination processes. Furthermore, the paper presents challenges with these innovations and provides practical suggestions for practitioners which may be applicable to other vegetatively propagated crops.
As a development initiative focused on rehabilitating the cassava crop in the Uganda, the Great Lakes Cassava Initiative (GLCI) project has built from the efforts of the Crop Crisis Control Project (C3P) through strong partnerships and innovative approaches to increase food security and incomes of cassava dependent communities. The four and a half year GLCI project funded by the Bill and Melinda Gates Foundation is focused on strengthening the capacity of 60 local African partners and approximately 1.15 million farmers to address CMD and the emerging CBSD pandemics that threaten food security and incomes of cassava dependent farm families in Burundi, Democratic Republic of Congo, Kenya, Rwanda, Tanzania and Uganda. In Uganda, CRS implements the GLCI project with 6 local partners who cover over 8 districts in eastern and central Uganda. The National Cassava Program of NaCRRI particularly implements the component of Participatory Variety Selection with farmer groups established by the local partners. Through innovative approaches, the project has served 47,082 farm families with clean planting materials, created a net-work of 292 farmer groups and tested 7 new and improved cassava varieties with 24 farmer groups in Uganda. Innovative approaches included partnerships, seed multiplication and dissemination to scale, research and development, information and communication technology (ICT) for monitoring evaluation and learning and mobilization of farmer groups for seed multiplication integrated with saving and internal lending communities (SILC).
Survey studies were conducted in three years (2009-2011) to determine the relationship between Cassava brown streak disease (CBSD) and populations of the whitefly, Bemisia tabaci, in the coastal lowlands of Tanzania. A positive relationship between whitefly population and CBSD incidence was observed. CBSD incidences in different districts varied between seasons and were dependent on whitefly abundance. Strong correlations were observed between CBSD incidence and whitefly abundance in each of the three seasons (2009, r2=0.89; 2010, r2=0.80; 2011, r2 =0.98). Similarly, positive correlations were demonstrated between CMD and whitefly abundance in 2009 (r2=0.92) and 2010 (r2=0.85). In 2011, however, the association was not significant. Fluctuations in whitefly populations in the coastal lowlands and the lack of clean sources of planting material might be the reason for recurrent outbreaks of both CMD and CBSD. In general, the abundance of whiteflies is less than in CMD/CBSD pandemic affected areas of north-western Tanzania. Consequently, there is much potential to address CMD and CBSD in coastal Tanzania by establishing ‘clean’ sources of planting material and strengthening the application of basic phytosanitary measures.
The original aim of the GLCI was to contribute to improved food security through the distribution of high-yielding improved, CMD-resistant cassava varieties. As such it was a scaling out of the C3P project and began with the multiplication of best CMD-resistant clones identified in C3P. As the project began, CBSD [a ‘new encounter’ disease in the Great Lakes Region] was spreading out of Uganda to neighbouring countries, threatening all the target countries for GLCI. The spread of CBSD challenged the assumption that food security could be improved by access to the CMD-resistant planting material. In the absence of any improved varieties with resistance to CBSD, the project had to design and implement measures to prevent the distribution of highly susceptible clones and to prevent the distribution of virus-infected cuttings: 1.The removal from the seed system of the most CBSD-susceptible clones among the CMD-resistant material. 2. Implement virus exclusion measures and a quality management system at the multiplication sites. The presentation reviews how this was done and draws lessons about CBSD management and the implications for cassava seed systems.
The cassava virus diseases, cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are the most important constraints to cassava production in East and Central Africa. A dual pandemic of both diseases has affected large parts of the Great Lakes region in recent years and continues to spread. Extensive regional surveillance work, conducted through various projects over the last two decades, has played a key role in plotting the regional spread of the two diseases, identifying newly affected areas and targeting mitigation efforts. Since 2007, various approaches to disease monitoring have been employed by research institutions under the auspices of the Great Lakes Cassava Initiative (GLCI). Extensive countrywide surveys have been implemented by national research systems in target countries on an annual basis. Farmers and other stakeholders have been involved in localized Digital Early Warning Network (DEWN) and Global Plant Clinic (GPC) assessments designed to provide forewarning of new CBSD outbreaks. Researchers have also conducted ‘Rapid Assessment Surveys’, which have sought to confirm reports of new occurrences of CBSD. Whilst CMD is readily assessed in view of its clear-cut symptoms, CBSD is much more difficult to identify and monitor, since symptoms are cryptic. Experience from the diverse set of surveillance activities conducted has revealed that effective monitoring of CBSD requires the deployment of surveillance teams that are highly experienced in recognition of CBSD symptoms, coupled with the effective application of virus diagnostics. Much success has been achieved through the course of the GLCI project in strengthening both human and physical capacity, which has led directly to the successful completion of a broad set of surveillance activities, and several new reports of occurrences of CBSD in the Great Lakes region.
Investment into the development of effective crop pest diagnostics is rarely matched by investment that ensures their effective and sustainable use. Consequently the returns on investment are often seen as poor and, on occasion, cited as evidence of institutional failure. This is not a condition of the developing world, but common across the world. The challenge around developing and using crop pest diagnostics have been keenly felt under the Great Lakes Cassava Initiative (GLCI) in the detection of the causal viruses of Cassava brown streak disease (CBSD) for research and phytosanitary purposes. Discussion is provided on how the GLCI has risk-proofed the dissemination of cassava planting material against spread of CBSD viruses by the first-use of combining a regional approach to pest risk analysis with field and laboratory testing of cassava for CBSD viruses. A focus is given to the piloting of a bespoke Proficiency Testing Scheme for CBSD viruses in building a ‘Community of Practice’ amongst researchers and plant health personnel. The GLCI has benchmarked for the region, and for others to emulate, the first use of real-time PCR for plant health testing for seed certification purposes, the first use of a Proficiency Testing Scheme to assess laboratory competence and the first use of a regional pest risk analysis to support the safe movement of planting material. For Africa, with its recent history of crop pest epidemics and the hard consequences these have reaped, and as now evidenced once more from CBSD, it is no longer acceptable for ‘business as normal’ in investing only in ‘cures’ without balanced investment in plant health and ‘prevention’. The GLCI over a 4 year period provided healthy cassava material suitable for planting to 1.2 million farmers of the Great Lakes region.
To develop any crop is necessary the development a seed system that supports, in a continuous way, the production of planting material in a comprehensive time and with a competitive price. In all of these processes it needs involve checking points to secure the genetics and phytosanitary status of the material produced. CIAT has developed and implemented different models that integrate in vitro techniques (conventional on solid conditions, massive method through RITA® system and a low-cost system at rural areas) and scaling up at nursery level (mini garden, two nodes cutting and one node-one leaf method) that allow cover up specific demand of farmer associations or at industrial level. The implementation of any system depends on how much material we need to produce to the end user or who wants to implement (their infrastructure, capacity of investment and region). Basically, sustainability it depend market demand, their dynamics and how could interact with other actors and crops on project area. The new model on CGIAR through CRP-RTB project will allow their centers share experiences and reinforce potential methods to apply on other vegetative crops. An overview of these methods will be discussed, paying attention on pros and cons to their implementation.
A research and development project for production of clean, safe and quality cassava seed planting material was carried out by the CATISA, Zambia partners. The CATISA coordinated the Zambian seed multiplication component of the COMESA Regional Agricultural Program (COMRAP) funded by the EC to increase seed availability to farmers in the wake of the financial meltdown. Production of clean cassava seed was initiated at UNZA Tissue Culture laboratory; six MTS low cyanide varieties were multiplied by elite seed multiplication farmers coordinated by small scale entrepreneur NGO in four provinces. Despite reductions in plant survival due to late planting (15-35% reduction), the expected yield of fresh cassava tubers on the 126 hectare crop was at 40mt/ha equaling 5,040mt wet weight or 1,680mt dry weight of cassava flour would be produced. The yield of cuttings increased as the farmers diligently cut the stems and replanted to enlarge their fields at the starting of current season to yield 736 ha of cassava in 2011/2012. Laboratory analyses showed cyanide contents ranging from 5.3-13mg/kg tubers, 6.1-13.7 stems and 2-23mg/kg leaves in two assayed varieties (Kampolomba and Mweru, respectively). Protein content in tubers averaged 3.1 percent, stems 12.3 percent and leaves 29.8%. This project has created nuclei of clean, safe cassava seed material to provide seed to surrounding farmers and start of value addition.
Africa will suffer for much longer as many intervention agencies drag and pull its food security development agenda in different directions that do not add up to solution for the teeming masses that live in the rural areas. This assertion is hinged on several factors affecting ‘’cassava the hunger fighter crop’’ according to the African Union. The Eastern African region is a case in point. There are many agencies trying in their disparate ways to add comfort to the large population of vulnerable households who grow cassava on small acres in small fields with human labour that they often cannot hire and afford. The threat of climate variations and weather fluctuations and the dearth of road and marketing infrastructure have made the food and income sector more difficult than ever. More recently, pest and disease have added to worsen the hunger equation. Only a dedicated re-thinking of the issues in a more holistic and regional way would push the food security agenda forward. The countries concerned are receivers of aid and international assistance with little mettle on how to nationally direct the food security agenda. Today, two major virus diseases are ravaging the cassava crop. Cassava Mosaic Virus and Cassava Brown Streak Virus are able to reduce cassava output to near zero level for most available varieties. The spread of both diseases largely occasioned by stem movements will continue inadvertently as the rural areas are short of stems and food from maize and rice are far from being able to meet domestic needs. Poor weather has cut short the maize harvest in many communities and the rise and leap of cassava into the food economy of the many enclaves of maize utilisation has been an assurance for food security. This trend is increasing as cereal prices and bad weather combine to make them less available on the plates of the poor majority. Regional hardships cannot be handled through isolated national attacks; but would require a concerted effort from all stakeholders to outline science-based solutions no matter how heavy the cost or the time frame needed to address the convoy of complexities involved.
The International Institute of Tropical of Agriculture (IITA) partnered with the Food and Agriculture Organization (FAO) and Total Land Care (TLC) in Malawi to implement a two year project on “Enhancing Food Security in Cassava Based Systems in Malawi”. The project was implemented in a total nine Extension Planning Areas (EPAs) of districts of Lilongwe; Nkhotakota and Salima . Activities included promoting production, on-farm value addition; strengthening capacity of farmers to plan, implement and manage value addition and improve market access; identifying, appraising and promoting entry for cassava and alternative high value farm products for rural and urban markets, conducting promotional campaigns to raise the profile and status of cassava in food security and economic growth; facilitating establishment of linkages between farmer groups and agribusiness service providers and providing training materials for cassava technology to enhance productivity. Despite the short period of implementation, the project contributed towards the rural livelihoods through provision of cassava planting material, training of farmers in cassava production and in acquisition of processing equipment and setting up of processing centers. However, no much value addition at commercial level was achieved mainly because of limited time to strengthen fragmented markets. The present paper is discussing lessons learnt that could be used in future projects.
New cassava varieties resistant to cassava mosaic disease (CMD) were developed by International Institute of Tropical Agriculture (IITA) Ibadan in collaboration with National Root Crops Research Institute (NRCRI) Umudike, Nigeria and rapidly disseminated to farmers to address the potential threat of the disease in the country and to enhance adoption of new cassava cultivars, increase productivity and additionally expand post harvest processing and marketing outlets of cassava products. To achieve these objectives an integrated cassava project was put in place in South eastern Nigeria to provide the requisite operational mechanisms. The project was principally sponsored by government of Nigeria and the Shell Petroleum Development Corporation (SPDC). This paper attempts to x- ray strategies employed by the project to fast track dissemination of the cassava technologies. Results of the study showed that 10 CMD resistant varieties as well as two cassava processing technologies were rapidly disseminated to rural farm groups through well coordinated multi institutional extension delivery mechanisms. Increased adoption and diffusion of the cassava varieties were recorded in the study area while remarkable changes in cassava productivity as well as income generation capacities of farm households were very evident. Furthermore, under the tutelage of the project emerged farmer driven diffusion mechanisms and entrepreneurial endeavours anchored on the new technologies which serve as formidable platform for sustainable rural livelihoods. The success of this project strongly underscores the need to draw the funding and logistic supports from organized private sectors to strengthen the already existing government sponsored extension service in the country. Other options for put up a workable partnership between government and the private sector in funding extension are highlighted in the paper. Also suggested are the necessary policy actions considered vital in creating an enabling environment for the partnerships to thrive.
The traditional multiplication and dissemination new cassava varieties in Nigeria are domiciled in State government-run Agricultural Development Programmes (ADPs). In this system, new cassava varieties were promoted as technology/message in the Small Plot Adoption Trial (SPAT), administered by the Extension Agents (EAs) in collaboration with contact farmers. Though largely successful but requiring about 30 years to achieve appreciable coverage, the rapid transformation of cassava from home-based food security crop to an industrial crop, coupled with emerging business-oriented farmers demanding higher yield and accessing new markets, has necessitated the need for new innovative approaches that ensures near-instant access by a large number of farmers to newly released cassava varieties. This paper reviews the innovative networking and partnership approaches adopted in three donor assisted projects (the Cassava: Adding Value for Africa (C:AVA) Project; the United States Agency for International Development; Marketing Agricultural Revenue and Key Enterprises in Targeted Sites (USAID MARKETS) Project and Harvest Plus (HP) Project) in the last four years to reach over half a million cassava farming households in Nigeria. The general framework of all the approaches is an active multi-stakeholder partnership driven by market demand for specific cassava products where farmers participating in cassava variety multiplication systems in several communities simultaneously graduate to robust commercial stem venture farmers within one season thus ensuring rapid multiplication and self-motivated distribution of new cassava varieties. These approaches hold the key to rapid dissemination of new materials to fast track delivery under poor government support, but more efficient use of donor resources.
Cassava (Manihot esculenta Crantz), an important source of energy in the diets of most tropical countries is rapidly evolving from a subsistence to a commercial and industrial crop (FAO, 2002; Onyeka et al, 2005). The crop has low multiplication ratio which poses a challenge in the efficient distribution of improved varieties to farmers and other users due to insufficient planting materials. Two year experiment was carried out to evaluate the effect of direct planting of two and four node per cassava planting stakes on stem yield and other agronomic attributes. The study was carried out in 2008/2009 and 2009/2010 cropping seasons at the National Root Crops Research Institute’s (NRCRI) research farm, Umudike. Planting materials consisted of Ten newly improved cassava varieties (TMS98/0505, TMS98/0510, TMS98/0581, TMS97/2205, TMS92/0057, TMS92/0326, TME419, NR87184, TMS98/0002, TMS96/1632) collected from the germplasm of NRCRI, Umudike and two farmers preferred varieties (NR8082 and TMS30572) as controls. Two and four node per stake of each variety were planted in 1m x 0.5m planting distance in a plot size of 5×4 meters (20 plant stands) with three replications. Analysis of variance on main treatment effects showed that the number of nodes/stake was highly significant (P<0.001) except for the number of root rots and stalk weight whereas, variety and year recorded high significant variations. Four node/stake planting materials had better mean performance over two nodes for all the attributes measured except in root rot. Also, cassava attributes measured were better in 2010 than in 2009 cropping seasons. Most of the newly released had better performances that the check varieties. Direct planting of two and four node of cassava stems therefore, have a great potential for rapid cassava stem multiplication.
The challenge for cassava industrialization/commercialization in Nigeria include the identification of market opportunities and the organization farmers, processors and traders to respond to the demands of existing and potential markets for cassava. These included linking with appropriate technology developers to match market demand with the required technology to ensure adaptive technology transfer, input supply, improved processing technology and service provision for agro-enterprise development in Nigeria. This study was, therefore, aimed at developing the cassava commodity delivery chain in Nigeria with emphasis on market or demand based interventions using the case of a large cassava starch & glucose processing plant (Tempo Farm) in Western Nigeria. In particular, the processors were identified to face constraints of lack of sufficient fresh cassava roots to feed their factories which is operating below 30% of installed capacity. In the present model, farmers were clustered around large-scale processors sometimes empowered with improved cassava varieties and use of best agronomic practices. Their capacities were enhanced through training programs, demonstration events, and supply of extension publications.
In this model, the cassava agro-processor is at the center of the cassava delivery-chain development. It starts by identifying the market, which is usually an agro-processor with capacity to buy and process cassava roots in commercial volume. It assigns roles to all stakeholders in the cassava delivery chain, thus making every stakeholder an active participant and contributor.
The key tool proposed into this model is the stakeholders’ forum, a platform under which all key players in the chain come together at intervals to discuss matters of mutual interest. These include memoranda of understanding, business plans, contracts and subcontracts. This had worked for selected cassava agro-processors in Nigeria like EKHA Agro (specializes in glucose syrup), MATNA (starch production) both in the south-west, Nigerian Starch Mill (industrial starch) in the south-east, and NOVUM (cassava flour) in the Middle Belt.
The Great Lakes Cassava Initiative (GLCI) project began in Rwanda in April 2008, as to address the cassava disease pandemics. The project is led by Catholic Relief Services (CRS) and operates in 11 districts. CRS’ Rwanda mission in this project was to multiply and disseminate CMD resistant and CBSD tolerant varieties; develop appropriate production packages; and build the capacity of farmers and partners in cassava production practices. In order to achieve its objectives, the project has built a strong partnership with local and International Organizations, the Ministry of Agriculture, Local authorities and xtensionists as well as the National Cassava Committee. To insure a sustainable and scalable cassava seed system that allows farmer to access to Cassava improved varieties which meet farmer and market preferences, the project has also trained and supported its partners in different topics (eg. Cassava, pest and disease control, cassava multiplication and dissemination, group management and training to work with adult learners etc..) who in turn trained farmer groups and individual farmers. Field Agents played an invaluable role in this technologies and innovation transfer to farmers as well as in Monitoring, Evaluation and reporting trough GPS and mini-computers use. The Quality Management Protocol and the improved Voucher system used in this project facilitated the seed dissemination and created a strong relationship between multipliers and the beneficiaries. It has been also a time saving in allowing planting materials to get spread in different zones very quickly. In order to ensure the food security of the thousands of cassava farmers in Rwanda, further research and support is needed to develop cassava varieties that are resistant to Cassava Brown Streak Disease.
The Participatory Variety Selection (PVS) approach was used to provide new varieties from national breeding programs to farmers in six countries that participated in the Great Lakes Cassava Initiative (GLCI) project from 2008/09 to 2011/12 seasons. The countries were Burundi, DR Congo, Kenya, Rwanda, Tanzania and Uganda. Its main objectives were to (a) increase farmers’ awareness and their access to improved varieties; (b) give farmers the opportunity to select their preferred cassava varieties for wider dissemination; (c) accelerate seed dissemination of farmers’ chosen varieties through farmer-to-farmer exchange mechanisms and as extension methodology; and (d) to scale up dissemination and adoption of desirable varieties. The improved clones used were developed in the late 1990s to mitigate the Cassava Mosaic Disease (CMD) pandemic in the Great Lakes region. Therefore, they were never selected for tolerance to Cassava Brown Streak Disease (CBSD) which was only reported to re-occur in Uganda in 2004. After four seasons of evaluation, no single clone was identified to have promising CBSD tolerance in Burundi, DR Congo, Rwanda, Lake Zone of Tanzania and Western Kenya. New clones with proven dual resistance to CBSD and CMD need to be introduced into these areas/countries to mitigate the increasing CBSD threat. Seven clones have shown promising field resistance to CMD and CBSD at high disease hot-spots in Uganda where they were evaluated for just one season. These will be confirmed after the second season evaluation. The data on fresh root yield from all the countries clearly showed that most of the improved clones were highly resistant to CMD and had a significant yield advantage over the local checks and also had acceptable eating qualities. The NARS cassava research programs should use these clones in their breeding programs to generate new cultivars that have high yielding ability along with dual resistance to CMD and CBSD and acceptable end-user characteristics.
At the beginning of the GLCI project, cassava cuttings were produced by 81% of women and girls. The famer groups were essential composed by females.
The harvests obtained were managed by men and badly affected the money in drinks and finding a new wife. Consequently, children don’t go to school, lack of money to buy food and medicines for the family. Thanks to the trainings on gender mainstreaming made by GLCI project, many things have changed: Some male heads of households decided to help their wife in cassava plantations and especially the management of harvesting is done by consensus.
Note: Some scenes of this process are about to be drawn by an artist and will be presented on a poster during the conference:
Scene1: Only the wife and children (female) are involved in house work as: cultivate the field, cook food, collecting firewood…
Scene2: The man spends all the day to cabaret and return at night with drunkenness
Scene 3: A man sells a party of the production to go out with other women, while his children were expelled from school
Scene4: The scene shows the same man working with his family in growing cassava seeds…
Scene5: The man with his wife, go to the market, to sell party of the production and bought school material and share drinking together.
Cassava is the second most important food crop after maize in terms of volume and capita consumption or source of calories in Tanzania. The objective of research and development is to deliver seeds which are high yielding, disease and insect pest tolerant, marketable and consumer preferred. In order to achieve this, good seed system has to be in place. Effort done by research about seed systems are undertaken in biotechnology such as use of tissue culture materials and genetic engineering on vegetative propagated materials. The production and utilization of cassava in the country is constrained mainly by limited access to farmers of quality planting materials of improved cassava varieties, lack of cassava varieties that are resistant to Cassava Brown Streak Disease and Cassava Mosaic Disease and with desirable end users root qualities and low soil productivity as smallholder farmers hardly use fertilizers in cassava cultivation, and poor utilization of cassava peels and high quality cassava flour value chains technologies and innovations. Research is continuing to evaluate the eight received clones potentially CBSD-tolerant varieties, also to evaluate the promising clones from breeding program for CBSD-tolerant for the release process. The document discussed the seed system for varietal development and release as well as the importance of participatory variety selection, disease control, monitoring, training and awareness creation through surveys, multiplication and dissemination approaches.
The National Programme for Roots and Tubers Development (PNDRT) is a Programme elaborated by the Ministry of Agriculture and Rural Development, funded mainly by the International fund for agricultural development (IFAD). Its main objective is to improve food security and enhance the living condition of the rural poors, especially women through the development of Roots and Tubers crops. The programme is nationwide and covers mainly cassava (60%), yams, irish and sweet potato, colocassia and xanthosoma. The total programme’s cost is estimated at 21,6 million US$ for a duration of 8 years (2004-2012). After seven years of implementation the main achievements as far as cassava production, processing, marketing and farmers’ capacity building and organization are hereunder listed:
(i) 85000 rural households have benefited from PNDRT’s support, (ii) approximately 12 000 000 improved variety of cassava stems were distributed to trained farmers. The improved varieties were supplied by the Agricultural Development Research Institute (IRAD) and the International Institute of Tropical Agriculture (IITA). The use of improved varieties (8034, 8017, 8061, 96/1414, 92/0326, 95/0109, etc.) along with the adoption of Integrated Pest Management techniques transfer contributed to the improvement of the yield in rural areas from 10 to 30 t/ha. (iii) In order to add a value to the fresh tuber quantitatively produced, PNDRT has provided farmers with 485 small processing plants for flour, starch, gari, chips, cassava stick, wet flour “waterfufu” production. (iv) 35 stores, 16 sheds, 46 drying slabs and 6 oven were built and handed over to the farmers. (v) A Market Information System has been put in place to link up producers and buyers. Despite the above attractive results which have allowed the beneficiaries to improve food security and their daily life, PNDRT is facing some challenges: (a) the industrialization of cassava processing to meet the need of huge companies like NESTLE (one of PNDRT’s partner) which is willing to buy annually 1500T of cassava native starch, (b) the Programme is due to end in septembre 2012 and in case there’s no fund for an eventual second phase, the activities realized for cassava sub-sector development will no longer continue to impact positively speaking the livelihood of the beneficiaries.
Cassava is an important food security crop in western Kenya. The region produces over 60% of the national cassava production. The small holder farmer’s reliance on informal seed systems failed due to infections of cassava mosaic disease and cassava brown streak disease on local land races. Farmers successfully bulked improved cassava varieties in small decentralized fields that were subjected to an elaborate quality management protocol leading to a participatory field certification by research, extension and the farmer before recommendation of fields for seed cuttings dissemination. Seed markets and beneficiaries were established by local cassava stakeholders in western Kenya. Yield, plant health and accessibility were the main considerations of beneficiaries.
improved varieties, quality Management protocol, dissemination
Africa’s cassava output for the past 20 years has accounted for more than half of the world output. However, its participation in international trade for both low cost (e.g. chips and pellets) and high value added (e.g. starch) cassava products has been insignificant. In fact, in all cassava producing countries in Africa, cassava contribute little more than food security, despite a large potential to generate income and employment as documented in several studies, including one of the largest agricultural commodity sector studies, the Collaborative Study of Cassava in Africa that was carried out throughout the 1990s.
This paper looks at the reasons for missed opportunities in cassava development in Africa through the lenses of a diagnostic methodology for value chain development recently proposed by UNIDO and argues that a comprehensive strategy for cassava agribusiness development holds the key to equitable wealth creation, employment generation and food security for the realization of the cassava potential in Africa.
Cassava value chain is understood as the totality of business units involved in the passage of cassava through specific order of activities, from input supply to primary production, postharvest management, industry-use, and marketing, during which value is added to cassava and the actors make incomes at every stage. In the past three decades, introduction of packages of technologies and innovations to upgrade cassava value chains in Africa has been undertaken through R4D activities. This paper uses case studies to describe the synchronization of the technologies and innovations introduced into the cassava value chains, assessment of the performance, the role of policy initiatives, the transformation that occurred and potential benefits to the cassava value chain actors in the last decade of R4D work on cassava in Africa. Propositions were made for increasing the efficiency of cassava value chains in Africa through targeted research.
This paper describes the value added distribution to all participants in the Brazilian cassava value chain. Data from secondary sources were collected and analyzed to build the cassava value chain. Brazilian production of cassava roots of 24,3 million tons in 2010 accounts for 10,27% of world production, from which 50.2% is used in animal feeding, 33.9% for diverse forms of human consumption, 0.2% for exports, 5.7% for other uses and 10% represents losses. Within the production of cassava roots for human consumption 91.5% is used for flour (“farinha”) production, 8.4% used for starch production and 0.1% for fresh, frozen and minimum processed cassava products consumption. The rent generated by Brazilian cassava sector was estimated in US$ 1.3 billion corresponding to approximately 1% of the gross value of the agricultural production. The sector generates 1 million direct jobs. Cassava in Brazil is mostly cultivated by small farmers with an average size of three hectares. Thus, 74.5% of the cassava farmers cultivate less than 10 hectares, 10% of the farmers between 10 and 100 hectares, 13.3% between 100 and 500 hectares and only 2.2% more than 500 hectares. The technology used for cassava production ranges from traditional production in the north and northeast of the country to semi and mechanized production in the center and south of Brazil. At least five medium to large fabricators of cassava processing equipment and machinery can be identified. The potential for cassava starch uses in Brazil indicates future needs of 1.55 million tons for mixing with wheat flour, exports, paper industry and glucose and fructose syrup production.
Cassava subsector represents a potential pathway out of poverty for many smallholders in developing world. Although precise and ultimate exploitation of cassava has potential to steer total transformation in Uganda, its value chain is not fully known. Contemporary value chain maps provide brief insights of what is done in value chain analysis. However, most analyses in Uganda fall short of cassava chain maps. The study was conducted to map and understand the value chain of cassava in Uganda as the first step in chain analysis. Informal and formal interviews of individuals in industries (food, pharmaceuticals, brewing, paper, textile), schools, hospitals, processor groups, chemical suppliers, supermarkets, border posts, traders and millers were conducted using a rapid reconnaissance approach involving checklists. The data collected were functions, products flow, actors’ roles and values added by each actor, institutions and policies and constraints and opportunities affecting the chain. The cassava chain in Uganda depicted a supply chain than value chains (90% vs 10%, respectively) with information flowing from production to markets (95% vs 5% respectively). The existing cassava-based products were subsistence/semi-commercial ones without significant market shares in the consumer, business and industrial markets. The major actors were farmers, processors, transporters (travelling traders), whole sale traders, retailers, consumers and institutions. All the actors were delinked and uncoordinated with no clear roles along the chain thereby rendering the chain inefficient and exploitations thereof. Cassava was traded majorly in the informal marketing systems without regulations. The volumes of cassava-based chips and flour imported into Uganda exceeded those exported to neigbouring countries. Tenure and customary laws, market dues, infrastructure, standards, investment policies, consumer attitudes and lobbying and advocacy positively or negatively influenced cassava trade. Production diseases, Poor infrastructure, poor quality of the cassava products, unreliable markets, electricity outages, high fuel prices, and illegal and risky market dealings were found to present a challenge to the entire sub-sector. Eliminating common ‘breaks’ in the chain, increasing productivity on-farm, taking advantage of private and public standards to meet quality in international markets, addressing the rare quality traits in cassava for specific end-uses should be tracked rapidly to develop the sub-sector.
Cassava chain map, Value chain, Actors, Products, Markets
The government of Nigeria (GON) introduced policies to encourage the substitution of high quality cassava flour for wheat flour in bread baking from March 2012, starting with 10 percent cassava flour inclusion with a steady increase to 40 percent by 2015. The belief that a growing demand for cassava will spur rural industrial development and contribute to the economic development of producing, processing and trading communities, is the basis for the 40% cassava flour inclusion in bread.
The GON has introduced fiscal incentives to stimulate increased domestic production and processing of cassava. From July 1, 2012, the GON will implement a 65 percent levy on wheat flour, while wheat grain will attract a 15 percent levy. Bakeries that attain 40 percent cassava flour inclusion in bread will enjoy a corporate tax incentive of 12 percent rebate. With effect from March 31, 2012, the importation of cassava flour will be prohibited, and all equipment for processing of high quality cassava flour and flour blending will enjoy a duty free regime. Key players in the sector are the flour millers under the aegis of Flour Millers Association (FMA) of Nigeria, the cassava growers’ Association, and the bakers.
The blending of cassava flour with wheat flour for bread making has occurred in the past, and to some extent is still being done, but is not widespread due to unreliable supply of good quality cassava flour. Managers in the confectionary industry are not familiar with the potential of cassava flour, are not familiar with some of the positive experiences in the past, and do not know what specific recipes have worked and which have not.
From the bakers’ point of view, the most important component of wheat flour is gluten that plays a decisive role in dough formation, gas retention, and the structure of the crumb. When composite flours are used, certain tricks are employed to achieve a properly leavened product in the end. The current limit to the addition of cassava to wheat flour for bread without a change in crumb color, crust color, taste, texture, aroma and overall acceptability is 20 %. To achieve 40% inclusion of cassava flour in bread flour to produce bread that compares favorably with bread from 100% wheat flour, there is a need for continuing research and experimentation with new recipes.
To ensure an uninterrupted supply of high quality cassava flour, the GON has ordered 18 large cassava processing factories capable of processing 1000 tons of cassava roots per day from China; these will later be leased to private sector investors.
Successful implementation of the policy on inclusion of cassava flour in bread will result in a 40% reduction in Nigeria’s wheat imports by 2015, conserve foreign exchange earnings and increase employment; wheat imports are currently estimated at N635 billion (about $4.2bn).
Cassava directly feeds about 30% of the population in Malawi with increasing proportion during lean maize season. Over the years, research in cassava product development for food and alternative uses has demonstrated the diverse uses of cassava. Moving beyond research into development continues to be constrained by lack of awareness about the potential products, seasonality of production leading to unsteady flow of raw materials, poor access to finance and technologies, limited knowledge about quality standards for industrial markets and poor market linkages among value chain actors. This paper highlights the activities of a 3 year project implemented by the Trustees of Agricultural Promotion Program with support from The Alliance for a Green Revolution in Africa. The goal of the project is to increase incomes of the rural households through: increasing productivity of cassava, building the capacity of small and medium Entrepreneurs to increase quantity and quality of starch; and promote use of by-products and other cassava plant components in livestock feed. Malawi imports about 700 tons of starch against domestic production of 150 tons. SMEs fail to take advantage of the existing demand due seasonality of production, poor processing technologies, poor linkages with industrial markets and inadequate knowledge about quality standards. The use of cassava based ingredient in livestock has been constrained by limited awareness, unavailability of raw materials, labor intensiveness of making livestock feed. The current project seeks to support smallholder farmers and SMEs to address these challenges through facilitating access to technologies, finance, expertise and knowledge.
The Cassava: Adding Value for Africa (C:AVA) Project is working in Ghana, Tanzania, Uganda, Nigeria and Malawi. The C:AVA vision for success is to develop sustainable value chains for non-traditional end uses of cassava, most notably for High Quality Cassava Flour (HQCF). It is anticipated that successful delivery of the outputs of the project will improve the livelihoods and incomes of more than 70,000 beneficiaries including smallholder farmers, members of village processing units and workers in processing factories. The C:AVA project approach is based mainly on three key intervention points to develop HQCF values chains: i) ensuring consistent supply of quality raw material, i.e. cassava roots and grits; ii) developing financially viable intermediaries; and iii) ensuring the confidence of end users of HQCF as a food ingredient or industrial raw material. This paper draws stories from four years of implementation. Many valuable lessons have been learned regarding issues of quality assurance, competitiveness throughout the value-chain and the role of private sector champions in development of sustainable market opportunities. C:AVA highlights best practices for creating awareness on project interventions, methods of sharing knowledge and skills across countries and cultures, how best to cope with project management in a constantly changing operational environment as well as pitfalls to avoid when building a value chain. This paper will present in more detail some of the lessons learnt during the implementation of the C:AVA project.
This paper examines and discusses the interplay of gender and diversity in cassava value chain development, particularly in production, agro-enterprise development and marketing. The study is based on the Cassava adding Value for Africa (C:AVA ) project coordinated by the Natural Resources Institute (NRI), University of Greenwich (UoG) and implemented in Uganda, Tanzania, Malawi, Ghana and Nigeria; and the Great Lakes Cassava Initiative (GLCI) coordinated by the Catholic Relief Services (CRS) and implemented in Uganda. Cassava was a priority crop for both food security and source of income for the households. A clear division of roles between men and women in the different parts of the cassava value chain was evident, and changes in the gender roles were prominent. More work and responsibilities are burdened onto women who own and have less access to resources, while the men have become less burdened and have acquired more time for leisure by their use of income from cassava sales. Traditionally considered a female crop for food security, cassava has changed face to become a major male cash crop. On the whole, men spent their incomes on capital investments while the women’s income was basically spent on recurrent expenditures in the home. It was also found that the existing household gender relations highly influenced the allocation of resources, the farming practices, use, control of assets and income; as well as decisions made within the farm households and community. Post-harvest practices reveal clear division of labour, with men mostly engage in uprooting the cassava where big quantities are needed, with peeling and processing are predominantly a female and child roles. Marketing which involves large quantities is usually for the men. Gender and diversity dynamics within the cassava commercial processors and end user industries are analysed and discussed highlighting employment and labour conditions in cassava processing enterprises, ownership, leadership and management positions as well as membership of processors and trade associations. Facilitating and constraining factors for women participation are discussed. Implications and recommendations for gender and diversity sensitive cassava programming are given. These include the need for continued gender responsive agricultural research and technology development in the mechanization of cassava production, cassava processing equipment, post-harvest equipment such as for peeling, information and technology to reduce post-harvest wastage, rural financing and marketing services; agricultural support systems such as training needs in leadership of groups; sensitivity in the women’s labour constraints while designing and reviewing the projects; continued functional adult literacy; collection, documentation and sharing of indigenous knowledge on coping strategies for food security, weather resistant crops to complement cassava, and for early warning signs. Finally, recommendations are made for the formulation of gender responsive qualitative and quantitative indicators to guide the monitoring and evaluation of activities.
This study explored the pattern of information flow in the integrated cassava processing-goat keeping farming systems in Ogun State, Nigeria. A multi-sampling technique was used to select a sample of 160 cassava processors and 80 goat keepers. Data were collected using interview guide. Descriptive and Inferential statistics were used to analyze the data. The results showed that respondents sourced agricultural information from multiple sources. Friends and fellow farmers are prominent information sources for 79.2% of the cassava processors. Goat keepers obtain information mainly from radio (68%), OGADEP (68%), and extension agents (66%). The focused group discussion revealed that other sources of information used by the respondents included FADAMA Facilitators, handouts, veterinary doctors and the internet. The pattern of information flow among farmers is multidimensional, an indication that information flows in many directions: top-down as well as horizontally among fellow farmers. Majority of the processors were aware of the use of drying platforms (74.3%) and black plastic sheets (73.3%) for drying cassava peels. Majority of the goat keepers (88%) were aware of using dried cassava peels to feed goats. The study found that one main constraint to information flow was poor interaction between village extension agents and farmers. The Chi-square test showed significant association between the gender of goat-keepers and awareness of the use of dried cassava peels as supplemental feed for goats (P < .05). There was no significant association between age, income level, educational level, location and keepers’ awareness of using dried cassava peels as supplements for feeding goats. It is recommended that a good communication skill for extension officers is required for effective dissemination of new innovation. Extension service managers should design effective communication strategies on dissemination of information in ways that promote multi-dimensional interactions amongst stakeholders in the target value chain.
Cassava is at present being internationally commercialized with a speed not seen before. This is true in Africa locally and regionally and concerning export from Africa or the West Indies to USA and different parts of Europe. Today fresh roots produced in the Caribbean may be bought in US and Europe, while frozen leaves as well as a selection of white and yellow Gari from Nigeria or Ghana also is available. Commercialization of fresh roots traditionally has been restricted due to their perishable character, calling for immediate processing to products with a longer shelf life. However, also the potential toxicity of roots, leaves and products thereof – as depending on cultivar, growth conditions and processing – traditionally hindered commercialization. The toxicity is in general ascribed to the content of cyanogenic glycosides, although recently coumarin phytoalexins, such as scopoletin, has been pointed to as an additional possibility. Finally, some uncertainty has existed concerning the quail- and quantitative burden of mycotoxins in cassava roots and their products. In conclusion, chemical food safety has played a role in the judgments of especially cassava roots as a food resource internationally. The presentation reviews the knowledge concerning the chemical food safety of cassava roots and root products putting emphasis on among others the low content of especially aflatoxins, a group of indeed very dangerous mycotoxins often found in e.g. maize and maize products.
Smallholder farmers in mountainous areas of northern Vietnam grow cassava on small plots in diversified crop-livestock systems. Cassava is a minor food, but cash income from sales of cassava roots and livestock is important for household food security and livelihoods. Farmers utilize cassava on-farm to feed livestock. They also sell cassava as dried chips, largely for export, or as fresh roots to small-scale rural starch pre-processors, who supply wet starch to food and industrial markets surrounding Hanoi. Farmers who sell fresh roots for local processing can access the fibrous processing residues as low-cost feed resources for intensifying household livestock production. The manure produced can increase food and feed crop yields and generate biogas for household energy supply. The eco-efficiencies of integrated cassava and livestock production and processing systems are being assessed. On-farm cropping trials test new cassava varieties, fertilizer management, and intercropping practices to improve sustainable production on sloping lands. Livestock feeding trials test weight gain from various formulations of locally available feeds. Appreciating mutual benefit, the processor is helping to scale-out successful innovations.
Recent workshops with cassava breeders and economists in Tanzania and Uganda have attempted to marry the state of the art in the national cassava breeding programmes of these two countries with an up-to-date review of value chains for cassava and processed cassava products. Questions addressed included: the current cassava breeding objectives, the history of variety release, and the key traits that have been addressed in breeding? To date a focus on farmer led trait identification seems to have driven breeding in these countries. By connecting the findings of from new value chain analysis with existing breeding programmes it has been possible to revealed some interesting new opportunities to re-caste this programme based on addressing the needs of end users and possible new market opportunities. Emerging findings and possible directions for a new alliance between demand and supply-side ends of cassava value chains will be presented.
Investigations were conducted to characterize six high yielding cassava mosaic disease (CMD) resistant cassava varieties for their differences and similarities in viscoelastic properties and physico-functional characteristics. The viscoelastic properties (pasting temperature, peak viscosity, final viscosity, breakdown viscosity and setback viscosity), and physico-functional characteristics (swelling power, solubility and water binding capacity) were determined using standard analytical methods. The results showed wide variations in viscoelastic properties with values ranging from 270.67-380.67 BU for peak viscosity, 37.17-260 BU for final viscosity, 199.83-282.33 BU for breakdown viscosity, 21.83-98.66 BU for setback viscosity and 2.48-10.51 min time to pasting temperature. Similarly, variations in swelling power, solubility and water binding capacity were noted. Statistical analysis showed significant differences amongst the studied cassava genotypes with Sika variety having exceptionally high viscoelastic characteristics. The differences noted in the viscoelastic properties and physico-functional characteristics of the different cassava genotypes could be used in their selection for specific food and industrial processing applications.
Cassava chips (7% moisture level) produced from cassava root (IITA 94/0561) was stored for 6 months in high density polyethylene bag. Stored chips were coarse milled, rehydrated to 62.51% and seeded with fresh cassava mash (FCM) at levels of 5%, 10% and 20%. The resulting mash was fermented for 72 hr, with pH and total titratable acidity (TTA) monitored every 24 hr, and processed to gari. Yield and swelling capacity of gari were determined. Sensory evaluation was carried out on water soaked gari and gari paste (‘eba’). pH values of fermenting mash decreased by 31-33% in all the samples with increase in fermentation time, with least values of 4.05-5.97 in FCM. TTA values ranged from 0.043-0.063 lactic acid during the period of fermentation. Yield of gari from the seeded chips ranged from 64.4-72.3% and that of FCM was 18.7%. Swelling capacity of gari ranged from 2.0-3.0 ml in FCM and that with 20% FCM, respectively. Sensory evaluation result revealed that gari produced from cassava chips seeded at 10% level is adequate for making ‘eba’ while that seeded at 5% level is adequate for consumption as soaked gari (p<0.05). Use of stored cassava chips with 10% FCM for gari production could be encouraged to reduce postharvest problem of cassava roots and the drudgery of gari processing.
Cassava chips, cassava mash, gari, eba, postharvest losses, storage.
The influences of age at harvest and cultivar on yield and physico-chemical properties of cassava flour and starch yields were evaluated at 8 and 11 Months After Planting (MAP). Ten cassava cultivars originating from Ghana were used in the present study. Agronomic data were collected on plant height, canopy width, and height at branching at 4, 6, 8 and 10 MAP. Data were also collected on Root yield, Harvest index, starch content, starch and flour yields at 8 and 11 MAP. Physico-chemical analysis was carried out on Solubility, Swelling power and Water-binding capacity of flour and starch. The results showed that starch yield ranged from 2.52 – 5.99 t/ha at 8 MAP, and 6.29 – 8.56 t/ha at 11 MAP. Flour yield also ranged from 5.70 – 9.46 t/ha at 8 MAP, and from 10.82 – 12.53 t/ha at 11 MAP. Swelling power of flour ranged from 10.00 – 15.84 g/g at 8 MAP and 12.04 – 18.31 g/g at 11 MAP. Swelling power of starch also ranged from 7.20 – 12.69 g/g at 8 MAP, and from 7.78 – 11.97 at 11 MAP. Water- binding capacity was high and the range was 176.3 – 244.0 % at 8 MAP, and 183.1 – 215.7 % at 11 MAP for flour, whiles that of starch ranged from 68.01 – 77.70 % at 8 MAP, and 62.61 – 76.01 % at 11 MAP. Solubility was also high for both starch and flour, and the values ranged from 66.44 – 78.26 % at 8 MAP, and 45.08 – 72.78 % at 11 MAP for flour, whereas the values for starch were 37.68 – 76.31 % at 8 MAP and 53.04 -74.06 5 at 11 MAP. From the results obtained, it was inferred that, age at harvest significantly affected starch and flour yields (p< 0.05), but not solubility, swelling power and water-binding capacity. Harvesting at 11 MAP produced the highest starch and flour yields in all cultivars studied. Cultivar effect was however not significantly different.
High Quality Cassava Flour in Eastern Uganda is produced by farmer processors through peeling, washing, grating, dewatering, sun drying, milling and packaging appropriately. A significant new growth market exists for its commercial application in the bakery, biscuits, plywood, paperboard, animal feed and starch industries. To penetrate these lucrative end-user markets, the farmer processors’ capability was innovatively strengthened to meet the standard for code of practice for hygiene in the food and drink manufacturing industry and will be certified with a quality mark. The capacity of Pallisa Agri-business Training Association, Popular (Wo)men Knowledge Initiative and Eastern Agro Producers and Processors Association with limited capital was strengthened to meet the required standards by carrying out hazard analysis and establishing systems that met food safety, hygiene and manufacturing standards. This will propel them to sell in national, regional and International markets thereby promising to improve livelihoods and incomes of smallholders who traditionally grow cassava as a famine reserve crop.
High quality cassava flour, farmer processors, quality control,; code of practice, end-user market.
Cyanogens have long been recognized as a toxic component of edible roots of cassava and leaves. The cyanogenic content of the roots can vary from less than 10 to more than 500mg/Kg, measured as hydrogen cyanide (HCN) on a fresh weight bases. Cassava roots are processed by a variety of methods into many different food products, depending on locally available processing resources, local customs and preferences. These different processing methods are expected to affect the cyanogenic content of cassava. To investigate the effect of different processing methods on the chemical characteristics of new cassava varieties, three types of cassava flours were prepared by the method of slicing, grating and reconstitution respectively. Yebeshie and Abasafitaa cassava varieties were processed and their proximate composition, starch, non-glucosidic cyanogens, free cyanide and total cyanogens studied. The slicing method resulted in the highest protein content in both varieties. Starch contents of 65.20% and 63.40% were recorded for flour from the reconstitution method for Yebeshie and Abasafitaa respectively. The lowest total cyanogen of 0.238mg CN equivalent/Kg and free cyanide of 0.058 mg CN equivalent/Kg were observed for flour from Abasafitaa prepared by the reconstitution method. Flours from the slicing methods had the highest non-glucosidic cyanogens followed by flours from the grating method. The reconstitution method can therefore be effectively used to produce cassava flour with a high starch content and lower cyanogenic potential.
Cassava, processing methods, Chemical characteristics
In sub-Saharan African and other tropical countries where cassava is cultivated, breeding programs aim at obtaining varieties that are disease and pest resistant, high yielding, early bulking or have high starch content. Varieties grown for food are tested for suitability in preparing specific dishes. However, the effect that age at harvest or climatic factors such as rainfall pattern have on sensory quality of foods prepared from the cassava varieties is not widely studied. Time of harvesting cassava roots is usually based on maturity characteristics such as bulkiness, mealiness or cooking quality of roots. This study underscores the importance of age at harvest of cassava roots to consumer preference and acceptability of gari prepared from them. Four cassava varieties Afisiafi, Tekbankye, Abasafitaa and Gblemoduade planted in June, were harvested each month from 10 months until 15 months after planting and processed into gari. Samples were subjected to affective sensory evaluation in relation to age at harvest. The sensory attributes evaluated were taste, colour, crispiness, aroma, appearance and overall acceptability. All the sensory attributes were significantly affected (p<0.01) by age at harvest of the cassava roots. Gari prepared from older harvests of 14 months and 15 months after planting were more preferred by panelists to gari from younger harvests. One principal component was extracted that contributed 90% of the variability in the response variables. It was observed from cluster analysis that aroma was the sensory attribute that contributed most to the overall acceptability of gari. This study has the potential to guide in decision making on the optimum harvesting time required for cassava varieties if their roots are to be processed into gari.
Nigeria as the world’s largest producer of cassava, has not made impact in export of cassava products. One of these products is cassava flour. High quality cassava flour could be used to substitute certain percentage of wheat flour in the bakery and confectionary industries. Despite the policy of 10 percent inclusion of cassava flour in baking and confectionary industries in Nigeria, early adopters under the presidential initiative suffered a huge set back due to poor patronage. The present Minister of Agriculture has, however, decided to revisit and transform this subsector through building the High Quality Cassava Flour value-chains. To start this, teams were set up to audit the Cassava Small & Medium Scale Enterprises (SMEs). The objectives were to identify the existing SMEs in Southeast Nigeria, identify the economic factors that have hindered the optimal use of the facility, identify major challenges in the business and determine the production capacities of the mills to meet the ministerial action plan. This audit team comprising of socio economists and engineers visited the SMEs that process cassava into High quality Cassava Flour (HQCF) in the five states that make up the southeast geopolitical zone of Nigeria. The states include; Abia, Anambra, Ebonyi, Enugu and Imo. Information on the location of the processing factories, ownership structure, operations, raw materials requirement, output, production capacity, and marketing information among others were elicited.
A total of seventeen (17) SMEs were identified in the southeast geopolitical zone of Nigeria. However, only ten (10) of this number have the capacity to produce HQCF. Result shows that 60 percent of the SMEs were initiated and owned by individuals while institutional and cooperative ownerships accounted for 20 percent each. Also 50 percent of the HQCF SMEs were operational while the other half were not operational at the time of this audit in Febbruary 2012. Most of the HQCF processing mills (70%) are semi automated and have the capacity to produce 1 to 2 tons/hour. Ten (10) percent are fully automated and capable of producing 3.5 tons of HQCF /hour. Among the numerous challenges facing the processors, product marketing, low prices of products and high cost of diesel were the most serious.
The study was aimed at determining the pattern of consumption of shelf-stable dried cassava fufu among selected respondents in four Local Government Areas in Lagos State, Nigeria. A total of two hundred respondents were interviewed using purposive sampling technique. The data collected were analysed using descriptive statistics and OLS regression analysis. The study found out among others that consumers of dried fufu were married, with a mean age of 34.3 years and monthly income of N36, 418.84. The respondents consumed an average of 5kg of the dried cassava fufu per month. Predominant preferred qualities central to the consumption of dried cassava fufu were colour (80.5%), texture (65.0%), odour and packaging respectively (60.0%). The OLS regression results revealed that dried fufu consumption is significantly affected by income of the household (p<0.01), household size (p<0.01), odour of the product (p<0.05) and education level of the consumers (p<0.01). The study concluded that dried fufu consumption was popular among consumers in the study area especially among the elites. The study recommended among others that adequate consumer awareness and availability of the product would further enhance its acceptability among consumers.
A decade ago CIAT began the search of what it called “High-Value Cassava”. What was then only a promise has gradually became a reality. In the area of starch quality traits an amylose-free (waxy) mutation was identified and has now been successfully introgressed to be released as commercial varieties. Part of this work is financially supported by the private starch sector. A small-granule mutation was also identified and found to be particularly suitable for processes requiring starch hydrolysis (e.g. sweeteners and ethanol). Moreover, CIAT has also identified a high-amylose genotype with as much as 42% amylose (whereas cassava starch typically has around 20%). Breeding methodologies to exploit these traits have been developed and tested. On the nutritional side, during the past decade, the increases in carotenoids content in the roots have been remarkable, and there seems to be no plateau in the progress made. Protocols for efficient selection in carotenoids have also been made. These results demonstrate that Manihot esculenta has many useful traits waiting to be found and also that this crop is capable of rapid responses if proper breeding methodologies are employed. Future work will concentrate on developing herbicide resistance and improving the protocol for assessing post-harvest physiological deterioration in roots.
The influence of different drying techniques on some functional, rheological, microbial, and sensory properties of odourless cassava fufu flour was investigated. Two drying methods (a locally fabricated flash- dryer and sun-drying) were employed for the experiment. Functional properties of the odorless fufu flour processed using the different drying techniques showed no significant differences (p>0.05) for bulk density, swelling power, and water absorption capacity. Results of the gelation temperature showed significant differences in the dried fufu samples, values obtained from the flash dried samples were lower than the sun-dried fufu materials. This suggests that the flash dried samples are suitable as instant products as they can be easily reconstituted. Result obtained for bulk density, swelling power, water absorption capacity, and gelation temperature using sun-drying and flash dryer ranged from, 0.68-0.72g/ml, 9.58-12.75%, 2.0-3.25g/g and 70.50-76.50○C respectively. Most of the rheological characteristics analyzed for sun-dried and flash dried products showed no significant difference, however a significant difference was observed in the results for setback. Total microbial count for flash dried products ranged from 1.5×102 to 4.0×103 and 3.0×103 to 7.30×104 for sun dried-dried. The major bacterial organism isolated from the products using two drying techniques was lactobacillus sp while fungal isolates include Rhizopus stororafu and Aspergilus niger for flash dried and sun-dried materials respectively. The presence of Coliform and Staphylococcus areaus bacteria were detected in sun-dried fufu samples. When subjected to sensory evaluation the dough from sun-dried and flash dried samples differed significantly in terms of colour, stickiness and mouldability. However the all samples were generally accepted by the panelists.
Corn starch is the most widely used excipient in the production of tablets and hence is utilized as disintegrants, fillers or binders. All the starches that are used in the Malawian pharmaceutical industries are imported from South Africa, Zimbabwe, Tanzania, United Arab Emirates, China, India, Kenya and United Kingdom which constitute corn, potato and wheat. Until now, the use of the root crop starches in tablet formation has not been extensively studied in Malawi. Using cassava starches extracted from three different cultivars (Mbundumali, Mulola and Sauti), the effect of native cassava starches as binders on the compression and mechanical properties of ibuprofen tablets was studied. The starches were used as binders for 400 mg ibuprofen tablets produced by wet granulation at the various concentrations (2-8 %w/w) and compressed at different punch settings (23-27). The formed tablets were evaluated for weight uniformity, thickness, hardness, friability and disintegration. Cassava starches, derived from the three cultivars can be used as binders in uncoated ibuprofen tablets under the following operating conditions: punch setting of 24 and binder concentration of 2% w/w. Under such conditions, less friable tablets were produced and reduced amounts of materials were used. Mulola starch is the most appropriate binder for ibuprofen tablets while Sauti starch could be useful when fast disintegration is more essential and a requirement.
Ghana is the sixth largest world producer of cassava and the third largest producer in Africa with a total output of 12.2 million MT/annum. Cassava contributes 22% of national agricultural GDP and has more than two (2) million households involved in tilling over 500,000 Ha of land to produce the crop. The importance of cassava to the national economy can therefore not be underestimated. One of the most recent interventions in the cassava industry in Ghana is the Cassava: Adding Value for Africa (CAVA) Project. This paper highlights challenges in the industry, key interventions by the CAVA Project to address some of the challenges in the industry and the outcome of these interventions. Challenges relating to farmers include: the non-availability of viable markets for the over 30% surplus roots produced annually, the poor road network to farming communities that make movement of raw materials difficult, the very low yields of 10MT/ha as compared to achievable yields of over 20MT/Ha, and the apparent lack of business sense of most subsistence farmers. Processors are challenged with uncompetitive end-product prices, low physical capacities of installed equipment, difficulty in accessing low risk credit for fixed assets and working capital, and poor quality management in processing plants. Challenges in the market end of the value chain include the lack of product diversification, the non-existence of a market-driven development-oriented research and development support, reluctance of the market to appreciate quality and be willing to pay for it, and the lack of a conducive policy environment to drive up-take of cassava products. Three main leverage points of the Cassava: Adding Value for Africa (CAVA) project interventions were the provision of improved high yielding cassava planting material to improve yields and make root pricess more competitive, establishment of a Loan Portfolio Guarantee to ease access to working capital loans for processors to increase supply into the value chain, opening up markets for High Quality Cassava Flour to absorb the increased supply and creating awareness through a mass media campaign. The outcome of these interventions has been a 50% increase in cassava root yields for targeted farmers, over 400% increase in the supply of HQCF, an increase in the number of companies and institutions using HQCF as an extender for plywood adhesives and as a wheat flour substitute for bread and biscuits in educational institutions; as well as the establishment of a National Composite Flour Committee to draft a policy document to enforce the production, marketing and utilization of composite flour as an integral part of Ghana’s bakery culture. A holistic approach to addressing the other challenges is recommended to include, amongst others, the establishment of a national cassava platform to stimulate partnership/collaboration, leverage synergies, and set a national agenda for Research and development in cassava, as well as in production, processing and marketing.
Challenges, cassava, industry, interventions, CAVA.
Product temperature is a very important system parameter as well as an indicator of extrusion process. In this study, the product temperature response of a single screw extruder developed locally was investigated for the extrusion process of the flour of cassava which is grown in Nigeria in large quantity. Response Surface Methodology, stepwise regression, correlation and Analysis of Variance were employed to a factorial experiment in completely randomized design to study the effect of extrusion variables: feed moisture (25, 30, 40%), extruder temperature (40, 70, 100°C) built up by varying the duration of sampling and screw speed (100, 150, 200 rpm) on product temperature. A maximum temperature of 148°C was attained in 30 minutes through viscous dissipation and up to a moisture loss of 55% w.b. Product temperature decreased with increasing moisture content and in duration of operation. Also, Product temperature increased with increase in speed up to 150 rpm but decreased at 200 rpm. Cassava Flour extrudates were found to be more than three times stable than its raw flour while it has a lower and faster moisture loss than other products in previous study. It was easier for cassava to cook/gelatinize under the heat provided by the extruder as revealed by higher solubility and viscosity of the cassava extrudates. The equations relating the various dependent and independent variables were established to predict the performance of the machine. Quadratic coefficients fit the extrusion data very well, better than linear models.
Extrusion, Product temperature, Cassava flour, Process parameters, Nigeria.
Fish, a good and healthy protein source for the family is expensive for the average Nigerian. This research work was done out of the need for alternative processing options for cassava, a high yielding tuber crop in Nigeria and to reduce the cost of fish feeds in fish production in Nigeria. Five blends of cassava flour and other locally sourced feed ingredients (A-E) were processed in a locally developed single screw fish feed extruder (L/D – 12:1, CR – 4.4:1) at different extrusion times (10-30 mins). The quality related parameters studied were product temperature, floatability of feed, dissolving rate and compressive strength. Strength properties were determined using the Instron Testing Machine. Product temperature varies directly with extrusion time. Highest product temperature of 105oC was observed for sample A, while sample E has the lowest, 78oC. All samples except Sample E (having the highest portion of cassava flour) floated in water. None of the samples got dissolved in water but they all became softened. Highest compressive strength was observed for Sample E while the imported feed has the lowest. Sample E is the most brittle while Samples A-D and the imported feed vary in their level of ductility. Sample A is the most ductile. Sample B (with equal portion of cassava and maize) has the nearest values of compression and extension (i.e. 190N and 14.5mm) to the imported feed (192N and 11mm). ANOVA, least significant follow up test result shows that compressive strength is significantly different at 95% confidence interval for Sample E. Moreover, the force-deformation curves obtained from the compression tests follow the usual pattern or shapes (sigmoid) of curves obtained for visco – elastic substances such as biomaterials. Using cassava to supplement fish feed will reduce the high and fluctuating cost of fish feed production. Cereal will be conserved for human and other uses.
Extrusion, Fish feed , Cassava flour, Quality parameters, Nigeria,
Poultry birds need quality feed for efficient production in order to have good returns and maximize profit. A trial was carried out to evaluate the performance of broilers fed cassava peels fortified with moringa leaves (CP:M) at ratio 1:1 as a replacement to wheat bran in graded levels. Five diets were formulated, diet I had 0% CP:M and 20% wheat bran served as control, while in diets II –V the wheat bran portion was replaced at graded levels of 25,50,75 and 100%.One hundred and fifty a week old broiler chicks were divided and randomly assigned to these dietary treatment replicated thrice and lasted for eight weeks.
Results revealed that feed intake and body weight gain of birds on diet I,II,III and IV were significantly higher (P<0.05) than V at both phases. The dry matter, crude protein, ether extract and crude fiber digestibility for diet I,II and III were higher significantly than IV and V. Feed conversion efficiency of those fed diets I-IV were similar and significantly higher(P<0.05) than V. Among the haematological parameters observed the packed cell volume (PCV), haemoglobin(HB) plasma protein(PP) mean cell volume (MCV) and MCHC were significantly affected(P<0.05). Those fed diets I-IV had similar haematological values and these were higher compared to V. The total protein, albumin, cholesterol, urea, glucose and serum alanine transaminase values of all the chicks were within standard range. The organ weights of the broilers which were taken were not affected. The rate of survival was not significantly (P>0.05) affected among the dietary treatments. Conclusively wheat bran could be replaced up to 75% with CP:M without adversely affecting the performance or blood parameters of the broilers.
wheat bran,cassava peels:moringa leaves broilers.
Cassava is the second most important staple crop in Africa next to maize. The crop is grown in 39 African countries of which Nigeria, DR Congo, Angola, Ghana, Mozambique, Tanzania and Uganda are among top ten producers in the world. It is the a major staple food crop for more than 200 million people (over 70% of the population) in the East and Central Africa (ECA) region (ASARECA, 2009). Cassava has been recognized as a powerful poverty fighter both as a food security crop, and through commercialization. It has also recently been recognized as being resilient to the impacts of climate change, including higher temperatures and drought conditions (Jarvis, A., et al, in press). However the ECA region is yet to benefit significantly from the potential of cassava, mainly because of threats from diseases, limited use and low income from the crop.
In recognition of these issues, in 2009 Farm Radio International (FRI) included cassava as part of our African Farm Radio Research Initiative (AFRRI) activities in Uganda. With the involvement of farmers, agriculture officers and National Agricultural Advisory Services (NAADS) coordinators, Akena Cassava and MH 97/2961 cassava varieties were selected as food security improvements in Soroti and Kibaale districts of Uganda respectively. With local partner radio stations and knowledge partners, we implemented Participatory Radio Campaigns (PRCs) in the two districts, aiming to increase knowledge and production of these disease tolerant varieties.
PRCs are farmer-centered radio programs. Farmers participate in selecting the topic of the radio campaign, choose the time of broadcast, and are intimately engaged in the ongoing development of the farm radio programming over a set number of months; including them as central agents of the knowledge-sharing process. Lively and entertaining formats are designed to attract and keep listeners. A key component is the use of ICTs to increase two way communication, such as phone call-outs and SMS alerts to farmers, use of interactive voice response systems and solar MP3 radios with listening clubs. PRCs build up to a decision-making moment and then support farmers as they adopt the new technology.
Farmers in Soroti and Kibaale requested information on Cassava Mosaic Disease (CMD) and Cassava Brown Streak Disease (CBSD) tolerant varieties. The district agriculture offices, research institutions and extension service providers recommended Akena and MH 97/2961 varieties for their CMD resistance and CBSD tolerance, suitability for the selected agronomic conditions and higher yields. FRI and partner radio stations (Voice of Teso & Kagadi Kibaale Community Radio) planned, designed, broadcast and evaluated three Participatory Radio Campaigns (PRCs) about the value chains of the two cassava varieties.
This work studied the extent to which cowpea fortification and co-fermentation will influence the souring production and physico-functional properties of cassava dough during the production of gari. A 4 x 4 factorial design was used to study the effects of fermentation time (0, 24, 48 and 72 hours) and cowpea level (0, 10%, 20%, and 30%) on the souring production (pH and titratable acidity) and physico-functional properties (pasting characteristics, swelling capacity, water absorption capacity and bulk density) of the cowpea-fortified cassava dough. Increasing fermentation time increased titratable acidity, water absorption and swelling capacities but decreased pH from 6.17-4.57 with 48 hours of fermentation. Increasing levels of cowpea fortification reduced the peak viscosity from 583-368 BU, swelling and water absorption capacities, but increased the bulk density from 0.50-0.71% and titratable acidity from 0.018-0.072 g lactic acid/100g. The reduction in pH and increased titratable acidity and peak viscosity at 20% cowpea level after 48 of fermentation suggest that the techniques could be employed to enhance the nutritive value of gari, while enhancing the safety, and improving the flavour and stability of the product.
In southern Malawi, civic engagement in development of cassava crop utilization has been going on since 2000 largely as a result of exposure to chronic food shortage, crop theft as well as HIV/AIDS. The process started as a study focussing on the course of action by which citizens discuss and determine the public good under conditions of chronic stress and limited government capacity. The studies furthermore explored how researchers and farmers together could use and develop a genetic resource that may be regarded as the key to household survival. The process was initiated as a researcher – farmer collaboration but led to emerging institutions and networks reconnecting the community to the wider public realm as well as to the state and private sector. As the villagers took on responsibility for their own individual as well as the collective efforts to develop locally preferred cassava varieties, cassava-based products and product markets, they unveiled organizational powers within the community to create a sustainable, productive and fair relationship between themselves, the market and the agencies of government. During this evolving process, the role of the researchers changed. This farming community is a registered enterprise known as CMRTE (Chinangwa ndi Mbatata Roots and Tubers Association) farmers with 2600 farmers, comprising 67 clubs and 87% women.
Empowering women in rural communities to generate sufficient funds to feed their families has always been a priority to a lot of donor organisations that operate in many low-income countries including Nigeria. A lot of money was therefore injected into cassava commercialisation by organisations such as Shell Petroleum Development Limited (SPDC) in collaboration with USAID for the development of cassava under the Cassava Enterprise Development project (CEDP) during early 2000 in Nigeria. The Rural Women Foundation (RWF) and Asa North Women cooperative group were one of the few organisations that received support from SHELL/USAID to commence cassava commercialization with technical backstopping from IITA. While a lot of fanfare and media attention was drawn to this project which had the potential to be a huge success, managing a cassava fufu factory proved to be a challenge. Some problems encountered during the first year included insufficient supply of cassava raw material at the project site, high transportation costs due to the bulky nature of cassava roots, low production capacity, very bad road network leading to the cassava factory, and frequent breakdown of production machineries. Even with these problems, it became very clear during the first two years that cassava fufu flour is a product that was much in demand and that even within Nigeria, the market was very lucrative. Village politics, displeasure by many male community members at the fact that the cassava factory belonged to a women’s groups and land ownership manipulation lead to a temporary closure of the factory since 2007. Had the factory been handed over to the male members of the community as wished for by the male leaders, the outcome may have been different. This experience shows that although a lucrative opportunity to increase women’s earning power presented itself, it became clear that so long as women do not have rights to own land, problems persevere. Women’s financial independence is inextricably linked to the prevailing patriarchal socio-cultural norms that hamper their progress. This experience by RWF in managing the cassava fufu factory could provide lessons for other African women venturing into agribusiness.
Natural antioxidants delivered through foods can support the inherent antioxidant cadre of human body by acting as free radical scavengers. Carotenoids, anthocyanin, resveratrol, piceid, curcuminoids, tocopherol, ascorbic acid etc. are some of the phytogenic antioxidants readily available in fruits like Pomegranate, Grape pomace and berries and herbs and can have various pharmacological benefits like antimutagenic, antiallergic, anti-inflammatory, antiviral and anticarcinogenic properties. Cassava varieties having high carotene and anthocyanin can also be used. The major problem associated with the antioxidants is their instability to changes in temperature, pH, presence of other chemicals which reduce their bioavailabilty. One method to overcome this problem is to complex them with readily available edible materials. Our earlier experience that starch extracted from a carotene-rich cassava variety invariably possessed a yellow colour prompted us to try complexation of the pigments with starch. Carotene, Anthocyanin Rich Extract and curcumin were stirred into cassava starch and the starch isolated tested for pigment incorporation by Viscometry, NMR and XRD while pigment stability and shelflife by kinetic studies. The results indicated that the pigments can be effectively incorporated into cassava starch. The pigment content and colour retention were satisfactory. The stability of the products could be attributed to formation of inclusion complexes. Initial experiments with nanostarch prepared from cassava starch also showed promise as a matrix for retention of pigments. It is proposed to prepare various food items and carry out evaluation of organoleptic, antioxidant potential and bioavailabilty at Santhigiri Health Research Centre.
Producers and traders are fragmented; transact individually; lack market information and do not benefit from economies of scale. Three pilot-scale sites were initiated at Kibuku, Bukedea and Kiryandongo. Collective processing, bulking and marketing initiatives were employed. Three “umbrella” farmers’ associations composed of 450 members (10 sub-groups per umbrella) were purposively selected. Each sub-group selected a representative for a nucleus demo site. Site members received foundation equipment and tailored hands-on training on management, entrepreneurial skills, networking, quality processing and marketing, and farmer-consumers /millers relations. Roles of the site members included organising production, provision of raw materials, processing, collection and bulking, records keeping, marketing and market intelligence, and equity sharing of proceeds. Chipping and drying on black polyethylene sheet reduced drying time from 7 to 2 days at chips loading rate between 6 and 8 kg/m2. Cassava chip final moisture content: 10.1%, mycotoxin infestation: 0%, total cyanogens limited to ≤ 6ppm. Moisture content, insect pest and mycotoxin infestation changed by +3%, +1.8%, and +0.1pbb respectively over 5 months of bulking. Transaction costs were reduced by 60%. Farmers’ attitude and enthusiasm towards cassava as high income crop improved appreciably; quality standards of dried cassava chips improved; and market-oriented farmer groups better-positioned. Recommendations and future perspectives are discussed.
A study was conducted in three PNDRT regions (Southwest and Littoral, South and Centre, West and Northwest) in Cameroon to document cassava processed products, assess knowledge of cassava processing, identify processing gaps, assess quality of processed products, evaluate use and type of equipment and assess processing constraints among small-holder farmers. A total of twelve small-scale processing units and eight marketer groups with six fabricators were contacted and interviewed. In addition, two operational and two non-operational medium-scale processing factories were visited to assess activities, success and challenges of the operational ones while the non-operational ones were interviewed on reasons behind their folding up. Key informant interviews and focused group discussions were conducted to collect information on their activities. Physical assessment of the processing sites was also used to gather information and local equipment fabricators visited to assess practices, competencies and possibility of empowerment. Results revealed that the cassava value chain in Cameroon is female-dominated, from production through processing to market. Both finished and intermediate products including chips, flour, fufu, gari, starch and other indigenous foods like baton, mintumba, nkolda are produced at small and medium scale. Apart from baton, that was reported processed among groups, other products were reported at individual and household levels. At the latter, production is characterized by small farm size, relying on family labour for processing to meet family food requirements and small portion sold as processed products. The profit margins attained are small due to poor quality products, although labour investments are high compared with those of medium and large-scale processing factories. For any sustainable intervention, establishment of cassava stakeholders’ forum is required where needs of cassava enterprises can be addressed, expand utilization, develop new products, provide basic equipment and reduce drudgery in processing. Market linkage needs strengthening among the stakeholders and national sensitization on cassava processing could be a way to create awareness and get the attention of the government for policy drive. Small-holder farmers are associated with inadequate planning, poor management, lack of know-how and insufficient capital making it very difficult for them to sustain the production of quality cassava products and are ignorant of key issues in market norms and standards. They should therefore be encouraged to produce indigenous foods like baton, mintumba, nkolda etc that are of high demand and value in local markets.
An interaction between urban-demand and rural-supply markets’ prices of gari, a cassava-based product consumed in Nigeria was investigated using an advanced time series econometric technique. Stationarity in prices was probed using the ADF-test while Johansen cointegration and VECM techniques were used to obtain the speed of adjustment coefficients characterizing the system’s long run dynamics. Results revealed non-stationarity in both prices with significant ADF-test statistics (p<0.01). Cointegration between prices was found by both trace- (23.67; p<0.01) and maximum eigenvalue- (20.49; p<0.01) statistics. The VECM confirmed that long-run equilibrium could be restored after exogenous shocks by corrections in the urban market. A clear trend in price leadership was found, with the rural market being dominant for determining the price of the product. Efficiency could be attained in price information transmission among key players if relative price stability was achieved in the rural markets. The study recommended that farmers and processors should be the primary focus of marketing policies and be given the opportunity to make input during formulation and design of programs targeted at them.
Cassava-based, gari, spatial integration, price transmission, rural, urban, markets, Nigeria
Cassava (Manihot esculenta crantz) was one of the leading food security root crops whose production had increased substantially over the last two decades in Nigeria. An advanced time series econometric technique was used to investigate the interaction between the crop’s production and each of the influencing factors, including area devoted to cassava, yield, and weather variables, namely rainfall and temperature. Secondary data collected from two reliable sources for 1961-2008 periods were used for the study. Descriptive statistics, correlation analysis and cointegration, preceded by the Augmented Dickey-Fuller (ADF) test of stationarity, as well as the associated vector error correction model (VECM were used for data analysis. Results revealed that only cassava production and area devoted were integrated of order one, I(1) and conform for use for cointegration analysis. Yield, rainfall, and temperature was each a mere “white noise” being integrated at levels, I(0), and unsuitable for cointegration tests. Cointegration test revealed existence of a long run equilibrium relationship between production and devoted area with trace- and maximum eigenvalue statistics calculated as 20.98 (p<0.01) and 20.92 (p<0.01) respectively. Granger causality test revealed causality from production to cultivated area (F=3.39 p<0.05), but could not reveal from land area to production. The implication of the finding is that past values of cassava production could be used as reliable indicators for predicting the future values of cultivated land area in Nigeria, but not vice versa. Interplay of some other factors would have contributed to past fluctuations in cassava production and there was need to adopt a far-reaching approach in the development of the cassava sector in Nigeria. The recent drive at promoting cassava value-chains is a positive step that should be sustained.
Cassava, production, devoted area, yield, weather conditions, cointegration, Nigeria.
Promoting market-orientation among agricultural producers, more so the smallholder farmers, in developing countries is pivotal for development of effective agribusiness value chains that could supply adequate food. This will involve improving the production and marketing processes as well as capacity for income generation among resource-poor farmers (Otieno et al., 2009). In developing countries, smallholder farmers find it difficult to participate in markets because of a range of constraints and barriers reducing the incentives for participation, which may be reflected in hidden costs that make access to markets and productive assets difficult (Makhura et al., 2001). Transaction costs, that is, observable and non-observable costs associated with exchange, are the embodiment of access barriers to market participation by resource poor smallholders (Coase, 1960; Delgado et al., 1999; Holloway et al, 2000 and Makhura, et al., 2001). Poor infrastructure often increases the transaction costs of market participation (Takeshima, 2008). Policy analysis about market participation and supply decisions leave considerable scope for econometric inquiry (Lapar et al., 2003). In Nigeria, strong demand and the fact that most of the nation’s 150 million people are in the hands of smallholders provides a tremendous opportunity for cassava farmers to participate in the cassava market and increase rural incomes. Unfortunately, recent output has not kept pace with increasing demand, suggesting that barriers prevent rural farmers from participating in the market. Increased transaction costs deter entry of small farmers into the market. This study looks at required interventions aimed at reducing transaction costs to encourage increased farmer participation in competitive markets. This study looks at required interventions aimed at reducing transaction costs to encourage increased farmer participation in competitive markets. Using data from 360 smallholder cassava farmers in South-Eastern Nigeria, this study determined the factors enabling smallholder participation in cassava market and used the findings to identify strategies to promote successful smallholder commercialization. A selectivity model was used and simulated to account for the effects of transaction costs. The study showed that 166 farmers were off-farm sellers, 50 on-farm sellers, 37 off-farm buyers, 12 on-farm buyers and 95 autarkic (neither selling nor buying) households. The stimulus levels were used to ascertain selected factors which were important for seller decisions (off-farm/on-farm) and effect of different policy alternatives. A 10% increase in personal means of transport, road conditions to the nearest town and marketing experience led to a 0.28%, 0.64% and 0.01% increase in sales off-farm respectively. Increase in distance to the nearest town, distance from the house to the market, distance from the house to the farm and cost of transportation by 10% led to a 0.06%, 0.07%, 10.18% and 0.0001% increase in on-farm sales respectively. The results of policy simulations show that if provision of good roads were made to the nearest towns, from the house to the farm and from the house to the market, about 72.40%, 68.81% and 54.62% of the respondents would sell cassava off-farm respectively. The results also indicate that with provision of vehicle loans and dissemination of improved varieties, about 69.90% and 34.72% of the respondents would sell in the market. The study raises policy issues which, when attended to, might reduce these fixed and proportional transaction costs, particularly by enhancing access to information and communication facilities, providing market outlets and bulking centers for farming households. Some constraints require direct policy measures, such as policies dealing with, extension services, education, and then there are those that require stable policy environment for small-scale traders to promote significant farmer response. The conceptual and empirical evidence suggests that interventions aimed at facilitating rural smallholder cooperatives, by reducing transaction costs are central to stimulating market participation.
Transaction Costs, Cassava and Simulations
Le manioc est cultivé dans toutes les régions de Madagascar et en particulier dans les provinces de Fianarantsoa et de Toliary qui fournissent plus de 65 % de la production nationale. Il constitue le deuxième aliment énergétique de base de la population malgache. Le manioc est cultivé sur une superficie de 350 000 hectares avec une production de 2 366 250 tonnes. Les acteurs de cette filière sont les producteurs, les collecteurs, les provendiers et les transformateurs, les exportateurs et les détaillants. Avant les années 60, il y avait 8 féculeries. Aujourd’hui, à côté des petites unités de broyage artisanal, le PROBO (Produit du Boina) à Mahajanga et la FECULERIE de Marovitsika à Moramanga sont les seules usines de transformation des racines de manioc qui existent à Madagascar. Les techniques de production, ainsi que le cycle végétatif de manioc varient selon les régions. Les variétés locales restent encore largement utilisées par les planteurs malgaches bien que des variétés améliorées aient été déjà vulgarisées. Le manioc a de multiples usages. Les tiges sont utilisées comme boutures à planter et servent aussi de fourrage, de paillis pour amender le sol, de combustible. Les feuilles, riches en protéines, pilées fraîches ou séchées et cuites avec de la viande de porc ou de bœuf ou des poissons constituent un plat malagasy renommé appelé « ravitoto ». Les racines fraiches ou sèches, riches en glucides, sont utilisées en alimentation humaine et animale. Les produits dérivés du manioc sont les provendes, la farine et l’amidon ; ils sont utilisés dans différents domaines. A Madagascar, il existe plusieurs méthodes traditionnelles de transformation des racines de manioc. Elles varient d’une région à l’autre et comprennent toute une gamme d’activités. Des combinaisons spécifiques de ces activités permettent d’obtenir un très grand nombre de produits. Il n’existe pas d’organisations de producteurs de manioc, sauf dans les cas d’interventions spécifiques. Les producteurs vendent généralement les tubercules à l’état frais ou secs directement aux consommateurs et aux collecteurs. La filière ne fait pas actuellement l’objet de promotion particulière. Les structures de commercialisation du manioc à Madagascar sont représentées par : les producteurs, les collecteurs, les transporteurs/collecteurs, les grossistes et les détaillants. Concernant l’économie globale de cette filière, le manioc est essentiellement une culture de subsistance bien que la demande locale reste non satisfaite. Le commerce extérieur du manioc n’existe pas à proprement parler. En effet, Madagascar exportait aussi bien du manioc que des produits dérivés sous différentes formes. Actuellement, l’exportation de manioc est devenue insignifiante. A présent, des résultats de recherches sur le manioc sont appliqués dans le domaine agroalimentaire, en particulier dans la biscuiterie, la boulangerie et la pâtisserie. Ainsi, dans ces domaines, la substitution partielle de la farine de blé par celle des racines de manioc est possible ; elle peut alors être intégrée dans la politique de valorisation des cultures à Madagascar. C’est donc une des stratégies nécessaires pour réduire la pauvreté du peuple Malgache avec la mise en relation directe des producteurs aux industries.
Manioc, Transformation, Biscuiterie, Boulangerie, Pâtisserie, Madagascar
Investment in cassava processing technologies has largely been restricted to smallholder processing entrepreneurs benefitting from financial assistance from donors supported by projects in Eastern and Southern Africa countries including Malawi. Large scale private sector involvement and Investment has been low. This has resulted in unsustainable value chains and limited impact on number of beneficiaries. This paper concerns factors that facilitate investment decisions by large scale private sector which create sustainable market and employment opportunities for resource poor households.
Lessons from the implementation of C: AVA project in Malawi have shown that large scale private sector involvement and investment in commercial processing has great potential to unleash benefits to smallholder cassava growers, processors and all players in the value chain. The benefits are cash incomes from direct sales of fresh roots, wet cake, high quality flour, import substitution and creation of new employment opportunities. The enabling factors include (i) good knowledge of appropriate processing technology to promote; (ii) skills to engage and demonstrate benefits of the new technology to potential investors; (iii) market information; (iv) ability to connect new investment to company corporate social responsibilities; (v) creating sustainable supply chain of raw materials; (vi) taking advantage of the political will, (vii) continuous provision of appropriate information and; (viii) understanding of comparative and external factors. Hence private sector participation in the various value chains is critical to creating sustainable markets for growth of agriculture based economies.
To benefit from the enormous industrial potentials of cassava, the Natural Resources Institute (NRI) UK secured funds from Bill & Melinda Gates Foundation (USA) to strengthen the High Quality Cassava Flour (HQCF) value chain in collaboration with public and private institutions in Africa, Nigeria inclusive. This paper reports our experiences from June 2008 till date. The C:AVA Nigeria team carried out activities including the establisment of demonstration plots, baseline study, stakeholder forum and training workshops, stem distribution to new farmer groups, capacity strengthening for village processing groups, practical demonstrattion of the use of HQCF in bread, biscuits and adhesives production as well as the assessment of the drying efficiency of the various flash dryers in the country. At present, C:AVA Nigeria has 85 village processing groups (1,753 individuals) and 100 farmers groups (3,021 individuals) with their members trained on common errors on cassava cultivation and weed management. A total of 20,394 bundles of cassava stems were distributed to farmers within the reporting period. A total 448 village –level processors were trained on production of wet fufu cake, good manuafcturing practices, quality wet cake for HQCF SMEs. Some of the SMEs were trained on mushroom production from cassava peels. There was farmers field day to showcase the performance of the improved varieties distributed as well as the technology transferred. Farmers are now having an average yield of 25 – 35 Tonnes/ Ha. The efficiency of 4 different models of flash dryers was evaluated and the four – cyclone flash dryer was the most efficient at 49% industrial level. A Nigerian Fabricator has been mentored by C:AVA to supply international standard FD to Malawi. C: AVA Nigeria has retrofited of 3 SMEs and will be retrofitting some additional SMEs before the expiration of the project by March 2013. C: AVA collaborated with CTAP to carry out audit on 145 cassava processing SMEs in the country. The next few months will seek to sustain market linkages, retrofits and supply pull of HQCF to bakeries as well as for other industrial products such as biscuits, paperboard, etc.
Cassava (Manihot esculenta Crantz) is traditionally grown by smallholder women farmers for household consumption. In Cameroon, the cultivation of this crop is recently gaining interest among a larger community as it appears to be a source of income generation. This study was carried out at Andom in Eastern Cameroon, to characterize the dynamics of cassava cultivation in the area with the purpose to find efficient improving methods for cassava production. Twenty one farmers were selected in a random manner and interviewed for their field activities for the 2006-2011 periods. A high variation on farm size between 0.1 and 1.68 ha was observed among household farmers. The consumption rate was calculated as equivalent to 191.5 kg dry weight of flour per person in the village and the average productivity was estimated to 7 tons ha-1on a Taking into account the family size and consumption rate, a correlation was made between the total consumption per year and the total production. It was shown that 66% of farmers had surplus of production while 14% had a deficit of cassava. The deficit observed for certain farmers was related to the small size of their cultivated farms. These data show a potential of cassava production in the village that could be improved with efficient labor input, improved soil management and the introduction of improved varieties that yield double of the local varieties. Such improvement should be accompanied by the installation of processing units that could help farmers to commercialize the surplus production in short terms. This will participate to increase the welfare of local farmers.
A study was carried out to determine the quality of silage produced from guinea grass, cassava peels and pineapple waste mixture at different lengths of storage. The materials were mixed into nine different ratios including the three sole feeds and ensiled for 30, 60, 90,120 and 150 days with each treatment replicated three times. A total of one hundred and thirty five bottles (960ml) were used for the ensilage. At the expiration of each length of storage, the silage were opened, mixed and analysed. There was a significant reduction (P<0.05) in the dry matter (DM) and crude protein (CP) content of the silage produced. The DM was reduced from 33.13% after 30 days to 25.45% after 150 days and the CP content of the silage was reduced from 8.80% after 30 days of ensilage to 6.00% after 150 days. The CP, NDF and ADF contents of the silage were significantly higher (P<0.05) that that of the un-ensiled materials. The highest CP content (9.09%) was obtained in sole cassava peel silage and was not significantly different from 8.89% obtained in 75% cassava peel: 25%guinea grass. Sole cassava peel silage also had the highest DM highest (40.99%) while the least DM content (15.20%) occurred in sole pineapple waste silage. The highest value of HCN was obtained in 100%cassava peel silage and the least value in 100% guinea grass. Interaction of length of storage and mixture had significant effect (P<0.05) on DM, CP, EE, NDF, ADF, ADL, CELLULOSE, Hemicellulose, ash and HCN content. 50% cassava peel waste: 25%guinea grass:25% pineapple waste from the 90 to 150 days had the best in terms of lowest HCN. The reduction in chemical composition after 150 days is still within required range for ruminant animal feeds.
silage, guinea grass, cassava
La République Démocratique du Congo est le troisième pays parmi les six plus grands producteurs du manioc dans le monde et le deuxième en Afrique après le Nigeria. Avec sa production de 15Million de tonne par an, la consommation humaine du manioc en R.D.C. est la plus élevée au monde : en effet, un Congolais consomme en moyenne 453 kg de racines fraîches par an, soit 145 kg de farine de manioc. Les feuilles de manioc se placent au premier rang de tous les légumes-feuilles consommés en R.D.C où un ménage de 7 à 8 personnes consomme près de 4 kg de feuilles de manioc par semaine. Comparativement aux racines, les feuilles de manioc sont riches en protéines (6-8 mg/g), en fer (3 mg/l00g), en calcium (200 mg/l00g), en vitamine A (10.000— 13.000 UI) et vitamine C (140 mg/l00g). Cependant, malgré son importance dans l’alimentation humaine (Nourriture pour 90% de la population congolaise) et du bétail en RDC, les techniques de transformation (fermentation) du manioc en RDC, sont en ce jour artisanales, empiriques et rudimentaires conduisant à des produits transformés de qualités douteuses qui ne peuvent pas garantir la sécurité sanitaire des produits du manioc.
En outre, le manioc constitue une source de revenu principal au niveau des ménages. En milieu rural, pour plus de 90% des ménages agricoles en R.D.C les activités commerciales sont essentiellement basées sur les produits de manioc. Cependant, par manque des procédés standardisés, le commerce des produits du manioc est très limité et la majorité des produits sont uniquement accessibles au marché local. La filière manioc en RDC comprend : La production au champ, la transformation, la commercialisation au niveau des grossistes et des détaillants et la consommation au niveau des ménages ou par les industriels. La production est encore à majorité entre les mains des petits producteurs et considéré comme une activité économique du secteur informel. Quelques efforts de modernisation de la transformation sont en train d’être réalisé avec l’appui des partenaires au secteur privé afin d’assainir les produits de manioc CHIKWANGUE et FOUFOU. Toutefois le séchage demeure encore un défi pour l’amélioration des technologies et de produits du manioc.
Tenant compte de l’ampleur de la dépendance des populations congolaises vis-à-vis du manioc et du rôle que le manioc joue sur le plan économique, ainsi que son impact sur la santé de la population il est urgent d’envisager une forte amélioration des techniques de transformation du manioc en milieu paysan et éventuellement dans l’industrie.
Grace à un appui sur la valorisation des résultats innovants de la recherche scientifique, le financement du secteur agricole et en particulier le manioc, ainsi que le soutien continu des efforts des chercheurs, il est possible d’atteindre une production de 42 millions de tonnes en 2020 en RDC. Une attention particulière peut être portée sur : l’utilisation des variétés de manioc génétiquement rentable ( à haut rendement, riches en vitamine A ,et autres nutriments..), l’utilisation des microferments pour la standardisation des procédés de transformation du manioc, l’élaboration des normes de qualités et leur validation par la société internationale de normalisation, la diversification des produits du manioc (amidon, éthanol, farine panifiable etc..,)