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Jarvis, Andy; Ramirez-Villegas, Julian; Herrera Campo, Beatriz; Navarro-Racines, Carlos
doi: 10.1007/s12042-012-9096-7
This paper examines the impacts of climate change on cassava production in Africa, and questions whether cassava can play an important role in climate change adaptation. First, we examine the impacts that climate change will likely have on cassava itself, and on other important staple food crops for Africa including maize, millets, sorghum, banana, and beans based on projections to 2030. Results indicate 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, brown streak disease and cassava mealybug. The findings show that the geographic distribution of these pests and diseases are projected to change, with both new areas opening up and areas where the pests and diseases are likely to leave or reduce in pressure. We finish the paper by looking at the abiotic traits of priority for crop adaptation for a 2030 world, showing that greater drought tolerance could bring some benefits in all areas of Africa, and that cold tolerance in Southern Africa will continue to be a constraint for cassava despite a warmer 2030 world, hence breeding needs to keep a focus on this trait. Importantly, heat tolerance was not found to be a major priority for crop improvement in cassava in the whole of Africa, but only in localized pockets of West Africa and the Sahel. The paper concludes that cassava is potentially highly resilient to future climatic changes and could provide Africa with options for adaptation whilst other major food staples face challenges.
Bellotti, Anthony; Herrera Campo, Beatriz; Hyman, Glenn
doi: 10.1007/s12042-011-9091-4
Cassava is attacked by a complex of arthropod pests across the tropical regions of the world where the crop is grown. Root yield losses have been recorded for several pests, including mites, mealybugs, whiteflies, hornworm, lacebugs, thrips and burrower bugs. Agronomic characteristics such as vegetative propagation, a long growth cycle, drought tolerance, staggered planting dates and intercropping contribute to the considerable diversity of pests that feed on the crop. The dynamics of cassava production are evolving as trends in the food, feed and industrial starch sector are leading to an increased demand for high quality starches. The resulting shift to larger scale production units, expansion of cultivated area and modifications in crop management combined with the effects of climate change, especially warmer temperatures and altered rainfall patterns, affect the occurrence and dynamics of arthropod pests in cassava agro ecosystems. Data is presented to describe the effects of temperature and dry seasons on key pest species. Whiteflies, mites and mealybugs register a suitability increase in the same areas in South America: Northeastern Brazil, Northern Argentina, South-Central Bolivia, and Southwest Peru. In Africa increases are projected in Southeast Africa and Madagascar. In Asia, regions with greater projected suitability for these pest species are Coastal India and Southeast Asia. Future trends and important criteria that will influence the severity and management of key pests are discussed.
Ceballos, Hernán; Kulakow, Peter; Hershey, Clair
doi: 10.1007/s12042-012-9094-9
Cassava is an important energy source in the diets of millions of people in tropical and subtropical regions of the world. It is a key subsistence crop, and its industrial uses are steadily growing. In spite of its economic and social relevance, relatively little investment has been made for research on cassava. However, conventional breeding resulted in more stable production through enhanced tolerance to biotic and abiotic stresses; increased productivity, both in fresh root production and increased dry matter content; and, more recently, improvements in qualitative traits such as starch quality and increased carotenoids content. The inbreeding of cassava has been identified as a key step for more efficient genetic improvement of the crop, therefore, research is underway to develop protocol(s) for the production of doubled haploids. Marker-assisted selection has been successfully applied to cassava, but in a more modest scale compared with other crops. More support and emphasis is needed on practical applications of molecular marker technology in cassava improvement. The availability of more efficient genotyping approaches and the cassava genome sequence promise to increase the impact of biotechnology tools on cassava improvement. Efficient and reliable phenotyping of cassava remains a challenging goal to achieve in the near future.
Prochnik, Simon; Marri, Pradeep; Desany, Brian; Rabinowicz, Pablo; Kodira, Chinnappa; Mohiuddin, Mohammed; Rodriguez, Fausto; Fauquet, Claude; Tohme, Joseph; Harkins, Timothy; Rokhsar, Daniel; Rounsley, Steve
doi: 10.1007/s12042-011-9088-zpmid: 22523606
The starchy swollen roots of cassava provide an essential food source for nearly a billion people, as well as possibilities for bioenergy, yet improvements to nutritional content and resistance to threatening diseases are currently impeded. A 454-based whole genome shotgun sequence has been assembled, which covers 69% of the predicted genome size and 96% of protein-coding gene space, with genome finishing underway. The predicted 30,666 genes and 3,485 alternate splice forms are supported by 1.4 M expressed sequence tags (ESTs). Maps based on simple sequence repeat (SSR)-, and EST-derived single nucleotide polymorphisms (SNPs) already exist. Thanks to the genome sequence, a high-density linkage map is currently being developed from a cross between two diverse cassava cultivars: one susceptible to cassava brown streak disease; the other resistant. An efficient genotyping-by-sequencing (GBS) approach is being developed to catalog SNPs both within the mapping population and among diverse African farmer-preferred varieties of cassava. These resources will accelerate marker-assisted breeding programs, allowing improvements in disease-resistance and nutrition, and will help us understand the genetic basis for disease resistance.
López, Camilo; Bernal, Adriana
doi: 10.1007/s12042-011-9092-3
Bacterial Blight is an important disease of cassava, causing losses that have resulted in historical famines in certain growing zones. The disease is caused by Xanthomonas axonopodis pv. manihotis, a gram-negative rod that belongs to the gammaproteobacteria. In this review, we describe the pathosystem and the recent studies that have been undertaken to elucidate both susceptibility and resistance mechanisms in cassava, with the hope of generating resistant plants using biotechnology. We first describe studies of the pathogen, including pathogen population changes through time as well as genomic tools that have recently been generated to determine pathogenicity factors. Secondly, we discuss mechanisms of disease resistance that have been elucidated in recent years and how these mechanisms could be used for the generation of improved plants resistant to CBB.
Taylor, Nigel; Gaitán-Solís, Eliana; Moll, Theodore; Trauterman, Brent; Jones, Tira; Pranjal, Amita; Trembley, Cindy; Abernathy, Vince; Corbin, David; Fauquet, Claude
doi: 10.1007/s12042-012-9099-4
A platform for high-throughput production and analysis of transgenic cassava (Manihot esculenta) has been developed for the variety 60444 and implemented to generate plants expressing traits for nutritional enhancement, modified metabolism, promoter analysis and disease resistance. Over a three and a half year period this system has been utilized to produce more than 3500 independent transgenic plant lines from 50 different genetic constructs within a single laboratory. Plants recovered through this system have proven robust and efficacious for engineered traits under greenhouse conditions and within the first confined field trials of transgenic cassava carried out in Uganda, Kenya, Nigeria and Puerto Rico. Detailed procedures are described for the operation of this platform, including all steps in tissue culture, genetic transformation, copy number estimation, greenhouse establishment for shoot and storage root formation and systems for centralized quality control, transgenic plant tracking and regulatory compliance. In addition to providing reliable transgenic plant production for proof of concept studies in the variety 60444, the systems implemented and described here form the structure for high throughput production of transgenic farmer-preferred cultivars of cassava.
Ayling, Sarah; Ferguson, Morag; Rounsley, Steve; Kulakow, Peter
doi: 10.1007/s12042-012-9093-x
Cassava is a globally important food security and industrial crop produced for food, feed, starch and biofuel. Cassava is drought-tolerant and can grow in poor soils. Roots can be stored in the ground for long periods as part of intact growing plants, allowing flexible harvest times for poor farmers in the tropics. In addition, due to cassava’s inherently high starch content, it is a popular source of carbon for industrial purposes and increasingly biofuel. It is, however, relatively low in nutrients and susceptible to several pests and diseases, including attacks from whitefly, mealybug, green mite, cassava mosaic viruses and cassava brown streak viruses. A number of groups worldwide are working to improve cassava by conventional breeding, by molecular marker-aided breeding, and through the use of transgenic approaches. To facilitate the work of these groups, easy access to up-to-date and integrated information resources are essential to enable knowledge sharing and data mining. Here we review the information resources currently available to breeders and researchers and discuss future directions for the cassava community’s data integration and curation.
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