Novel stable isotope techniques to unravel differences in water use efficiency of cassava cultivars. A key to intensify cassava productivity in Sub-Sahara Africa

Cassava (Manihot esculenta Crantz, Euphorbiaceae) is an important cash and food crop of resource-limited farmers in Africa, Asia, Latin America and the Caribbean. Cassava is principally a smallholder crop and is grown as an intercrop with other main food crops. This PhD research fits within the project African Cassava Agronomy Initiative (ACAI), a 5 year Bill & Melinda Gates Foundation project funded in 5 countries in Africa (Nigeria, Tanzania, DRC, Ghana and Kenya). The overall goal of this thesis is to enhance the resilience of cassava production against droughts, as one of the strategies to intensify its production, at the same time coping with climate change and supplying the processing industry with roots during the entire year, despite re-occurring dry spells. Water use efficiency (WUE) hence serves as a key-entry point and isotope discrimination methods will be tested as a proxy for this in cassava. Studies with other crops suggest that genetic variation in isotope discrimination may be sufficient as a selection criterion for improved water use efficiency. This comprehensive testing of novel stable isotope techniques (13C/12C; 2H/1H and 18O/16O) in unravelling the WUE of various cassava cultivars forms the core of this PhD research. It will allow us to suggest the better cultivars for specific planting times and ecological characteristics.