A method for generating virus-free cassava plants to combat viral disease epidemics in Africa

Here, we report a method to clean cassava plants from viral infections that cause cassava mosaic and brown streak diseases in Africa. Infected plants of resistant or tolerant varieties from Malawi, Mozambique, Kenya, Tanzania and Uganda were cleaned in the UK using a combination of tissue culture, chemotherapy and thermotherapy. In the first cycle of our virus-indexing procedure, we successfully cleaned 27 of the 31 varieties (87%), and after an additional three cleaning cycles, all plants were virus-free. Virus-free tissue-cultured plants were shipped back to Africa for distribution to farmers. This first cross-boundary effort provides important lessons for mitigating the two-major cassava viral diseases

The process and lessons of exchanging and managing in-vitro elite germplasm to combat CBSD and CMD in Eastern and Southern Africa

Varieties with resistance to both cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) can reverse food and income security threats affecting the rural poor in Eastern and Southern Africa. The International Institute of Tropical Agriculture is leading a partnership of five national (Malawi, Mozambique, Kenya, Tanzania and Uganda) cassava breeding programs to exchange the most elite germplasm resistant to both CMD and CBSD. This poster documents the process and the key learning lessons. Twenty to 25 stem cuttings of 31 clones comprising of 25 elite clones (5 per country), two standard checks (Kibandameno from Kenya and Albert from Tanzania), and four national checks (Kiroba and Mkombozi from Tanzania, Mbundumali from Malawi, and Tomo from Mozambique) were cleaned and indexed for cassava viruses at both the Natural Resources Institute in the United Kingdom and Kenya Plant Health Inspectorate Services, in Kenya. About 75 in-vitro plantlets per clone were sent to Genetic Technologies International Limited, a private tissue culture lab in Kenya, and micro-propagated to ≥1500 plantlets. Formal procedures of material transfer between countries including agreements, import permission and phytosanitary certification were all ensured for germplasm exchange. At least 300 plantlets of each elite and standard check clones were sent to all partner countries, while the national checks were only sent to their respective countries of origin. In each country, the in-vitro plantlets were acclimatized under screen house conditions and transplanted for field multiplication as a basis for multi-site testing. Except for Tomo, a susceptible clone, all the clones were cleaned of the viruses. However, there was varied response to the cleaning process between clones, e.g. FN-19NL, NASE1 and Kibandameno responded slowly. Also, clones responded differently to micro-propagation protocols at GTIL, e.g. Pwani, Tajirika, NASE1, TME204 and Okhumelela responded slowly. Materials are currently being bulked at low disease pressure field sites in preparation for planting at 5-8 evaluation sites per country. The process of cleaning, tissue culture mass propagation, exchange and local hardening off/bulking has been successful for the majority of target varieties. Two key lessons derived from the process are that adequate preparations of infrastructure and trained personnel are required to manage the task, and that a small proportion of varieties are recalcitrant to tissue culture propagation

Cassava: The Drought, War and Famine Crop in a Changing World

Cassava is the sixth most important crop, in terms of global annual production. Cassava is grown primarily for its starchy tuberous roots, which are an important staple for more than 800 million people, mostly in sub-Saharan Africa, but also in other parts of Africa, Asia, the Pacific and South America. Cassava is important for both small-scale farmers and larger-scale plantations due to its low requirement for nutrients, ability to tolerate dry conditions and easy low-cost propagation. It is sometimes referred to as the “drought, war and famine crop of the developing world” and reliance upon this crop is expected to increase in the coming years as the global climate changes. As with all crops, cassava presents some challenges which need to be addressed, especially if its production is to continue to expand. We highlight here a number of key issues around the continued and increased reliance upon cassava as a staple food crop. Cassava contains cyanogenic glycosides that release hydrogen cyanide and many cultivars are toxic if not processed before consumption. The degree of toxicity is altered by plant breeding, agricultural practice, environmental conditions and methods of food preparation. We conclude that use of cassava has the potential to help many countries achieve food security in a sustainable manner, in the face of significant environmental change, but that its introduction should be accompanied by appropriate education about its toxicity

Cassava: The Drought, War and Famine Crop in a Changing World

Cassava is the sixth most important crop, in terms of global annual production. Cassava is grown primarily for its starchy tuberous roots, which are an important staple for more than 800 million people, mostly in sub-Saharan Africa, but also in other parts of Africa, Asia, the Pacific and South America. Cassava is important for both small-scale farmers and larger-scale plantations due to its low requirement for nutrients, ability to tolerate dry conditions and easy low-cost propagation. It is sometimes referred to as the “drought, war and famine crop of the developing world” and reliance upon this crop is expected to increase in the coming years as the global climate changes. As with all crops, cassava presents some challenges which need to be addressed, especially if its production is to continue to expand. We highlight here a number of key issues around the continued and increased reliance upon cassava as a staple food crop. Cassava contains cyanogenic glycosides that release hydrogen cyanide and many cultivars are toxic if not processed before consumption. The degree of toxicity is altered by plant breeding, agricultural practice, environmental conditions and methods of food preparation. We conclude that use of cassava has the potential to help many countries achieve food security in a sustainable manner, in the face of significant environmental change, but that its introduction should be accompanied by appropriate education about its toxicity.cassava; cyanide; food security; drought; carbon dioxide; Manihot esculenta ; sustainable agriculture; nitrogen use efficiency

Variations in the Chemical Composition of Cassava (Manihot esculenta Crantz) Leaves and Roots As Affected by Genotypic and Environmental Variation

The purpose of this study was to assess the quality of cassava cultivars, in terms of cyanogenic potential and composition of macro- and micronutrients, sampled from different locations in rural Mozambique. Total cyanide concentrations in fresh cassava tissues were measured using portable cyanide testing kits, and elemental nutrients were later analyzed from dried plant tissue. Variation in cyanogenic potential and nutrient composition occurred both among cultivars and across locations. The majority of cultivars contained >100 ppm total cyanide, fresh weight, and are therefore considered to be dangerously poisonous unless adequately processed before consumption. Leaf cyanogenic and nutrient content varied with plant water status, estimated using carbon isotope discrimination (δ¹³C). The colonization of roots of all cultivars by arbuscular mycorrhizal fungi was also quantified and found to be high, indicating that mycorrhizas could play a key role in plant nutrient acquisition in these low-input farming systems

Surveillance and control of cassava diseases in Africa

International audienceno abstrac

Surveillance and control of cassava diseases in Africa - International meeting results in Pan-African cassava disease network

International audienceCassava is the most important vegetatively propagated food staple crop in Africa. Even if its vegetative propagation through stem cuttings has many advantages, it also represents its Achilles heel. Pathogens are passed from one generation to the next and can easily accumulate, threatening cassava production. Two viral diseases are currently considered to be the greatest global threat to cassava production in Africa. Faced with the gravity of this situation, 43 scientists from African national and regional institutions and international agricultural research centres met in Saint-Pierre, La Réunion Island from 10 to 13 June 2014, to contribute to the surveillance and control of cassava diseases and pests that threaten the food security and livelihoods of millions Africans. The main action was to consolidate and develop a global alliance against cassava diseases in Africa and a strategic action plan with several international initiatives for the coming years. Firstly, the establishment of a Pan-African Cassava Surveillance Network (PACSUN) with an interactive website and an International Cassava Transit Site (ICTS) in La Réunion. Secondly, the development of diagnostic technologies to better identifying viruses, bacteria and vectors, and a comprehensive educational and training plan to support all these activities. (Texte intégral