Abstract
Cassava varieties resistant to cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are needed for the food and income security of the rural poor in eastern and southern Africa (ESA). The International Institute of Tropical Agriculture led five national cassava breeding programs (Malawi, Mozambique, Kenya, Tanzania and Uganda) in virus-cleaning and exchanging elite cassava germplasm resistant to both diseases. This paper documents the experiences and lessons learned from the process. Thirty-one clones (25 elite, two standard and four national) were submitted by the five breeding programs to the Natural Resources Institute and Kenya Plant Health Inspectorate Services for virus cleaning and indexing. Subsequently, ca 75 in-vitro virus-indexed plantlets per clone were sent to Genetic Technologies International Limited (GTIL), a private tissue culture (TC) lab in Kenya, and micro-propagated to produce ≥1500 plantlets. After fulfilling all the formal procedures of germplasm exchange between countries ≥300 plantlets per clone were sent to each partner country. National check clones susceptible to CMD/CBSD were sent only to their countries of origin. In each country, the in-vitro plantlets were acclimatized under screen house conditions and transferred to clean isolated sites for field multiplication. All the clones were cleaned of the viruses, except Tomo. The cleaning process was slow for F19-NL, NASE1, and Kibandameno and TC micro-propagation at GTIL was less efficient for Pwani, Tajirika, NASE1, and Okhumelela than for the other clones. Difficulties in cleaning recalcitrant clones affected the timeline for establishing the multi-site evaluation trials in target countries. The initiative is the one of the kind to successfully clean and exchange elite germplasm as a joint action to combat CBSD in ESA. Adequate preparation in terms of infrastructure and personnel are critical to successfully receiving and adapting the indexed in-vitro plants as new germplasm.
Highlights
Cassava (Manihot esculenta Crantz) is one of the most important food staples in sub-Saharan Africa (SSA), ranked as the number one root crop followed by yam and sweetpotato (FAOSTAT 2017)
The crop is threatened by two viral diseases: cassava brown streak disease (CBSD) and cassava mosaic disease (CMD), and these are currently the principal biotic factors affecting production in East and Southern Africa (ESA) (Alicai et al 2007; Legg et al 2011)
While CMD is of economic importance across SSA, CBSD remains localized in ESA, there is a high risk of the disease spreading to West Africa unless contained (Legg et al 2011)
Summary
Cassava (Manihot esculenta Crantz) is one of the most important food staples in sub-Saharan Africa (SSA), ranked as the number one root crop followed by yam and sweetpotato (FAOSTAT 2017). Collaborative efforts with different national cassava breeding programs have identified germplasm resistant or tolerant to CBSD/CMD. These have been evaluated so far under a narrow range of conditions of environment, virus species/strains, and vector abundance (Legg et al 2011). Past experiences of CMD pandemic management have underlined the significance of identifying and deploying host resistance as well as the importance of joint action among partners in the affected countries through elite germplasm exchange (Ntawuruhunga et al 2013). The work was undertaken in the early stages of the project BNew Cassava varieties and Clean Seed to Combat CMD and CBSD^ (5CP), and aimed at exchanging elite germplasm among the five countries most affected by CMD and CBSD for adaptability breeding
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