Cassava's environmental challenges: The latest science
Bellagio meetings always seem to deliver beyond the already high expectations, and this week’s meeting on a global strategy for cassava research is no exception. Today we spent the day looking at the environmental challenges for cassava in the 21st century. What does climate change mean for cassava? What are the emerging pest and disease problems?
The latest CO2 fertilisation science
Don Ort presented some of the latest findings on CO2 fertilisation in cassava which updates our knowledge on how cassava might respond to a higher CO2 world. In 2009, Australian researchers published a paper showing that cassava actually responded negatively to enhanced CO2, and furthermore showed that cyanide concentrations increase with greater CO2 – a mixed blessing present in other crops too. Don’s results of a FACE experiment on cassava in Illinois seems to contradict those initial findings in Australia – cassava growth and tuber yield seems to increase quite significantly, as expected in theory, and cyanide content is not affected. Findings are unpublished, so I can only go that far in reporting on this. Let’s hope Don publishes this work soon!
Is cassava the adaptation crop for Africa?
I presented some of our results of modelling the response of cassava and other crops to climate change, and provocatively asked if cassava might be the exception to the general rule of thumb that yields will decrease with climate change. Cassava is a highly resistant crop, that once established can endure drought and heat pretty effectively. It also seems to have a differential response to maize, whereby many areas with apocalyptic scenarios for maize yield reductions seem to gain in terms of cassava yield. The concept that cassava could have significant potential in adapting African agriculture is not new – back in 1996 a paper was published by Wilberforce Kamukondiwa in Climate Research outlinging its massive potential. And as Phil Thornton reminded us this week – Africa has some serious challenges to face up to. So cassava continues to appear on the radar screen as a hardy crop that can help in areas where more climate sensitive subsistence crops start to have problems.
There seemed to be general agreement in the room that the pest and disease issue is the big unknown, and likely far greater a constraint than the direct impact of abiotic stresses. More on that follows. But this discussion also highlighted once again the need for data. We simply do not have much data available on multi-environment trials of cassava technologies, or monitoring networks for pest and diseases. All the more reason to promote Open Access Agriculture, something we are pushing for in CIAT and CCAFS.
Cassava pest and disease outlook
It seems that a major constraint today in cassava production across the globe is due to pests and diseases. Diseases are emerging and spreading. In Africa, cassava brown streak disease and cassava mosaic virus are having major impacts. Claude Fauquet attributed the major changes in cassava diseases to climate change, and shifts in distribution and prevalence of vectors, whitefly amongst them.
Tony Bellotti from CIAT also provided an overview of the outlook for major cassava insect pests, and highlighted three major factors impacting on pests across the globe:
- Changes in consecutive dry months: with shorter dry spells you get more mites and mealybugs, less whitefly and vice versa.
- Increased temperatures: shorter development time of insect pests (but also their natural enemies in some cases).
- Changes in management: staggered planting dates, altered cropping patterns, shifting planting dates causing changes in the cycles of arthropods, especially in industrially grown cassava regions.
There are success stories in confronting the challenges of cassava pests. These include identification of genotypes with host plant resistance to whitefly and mites, and management of pests through biological control, such as the parasitic wasp used in the Thai “sting” operation. Tony also mentioned the potential role of wild species in terms of finding host plant resistance to whitefly and mites and highlighted this as one of the areas for future research. There was also the discussion on the need to sequence some wild relative species to identify host resistance genes. Seems like this room in Bellagio is still oozing crop wild relatives after the last meeting….