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