Enhancing Drought Tolerance in the Climate Resilient Legume Cowpea

Cowpea (Vigna unguiculata) holds important status as a crop that is adapted to marginal growing climates where water is limited.  As such it is a vital grain and fodder legume grown across semi-arid and dry savannah zones of the tropics in sub-Saharan Africa and other regions with similar agro-ecologies. Not only is cowpea more tolerant than most other legume and non-legume crops to drought, heat and poor soil conditions, it also possesses extensive genetic variation for these traits. A central challenge is how to improve cowpea adaptation because it has not been fully optimized for productivity under drought conditions and on poor soils under rainfed conditions. The challenge is complex, particularly as the timing of drought stress in the growth cycle is unpredictable. Cowpea possesses good resistance to vegetative-stage drought, for which QTL have been identified. However, the resistance fails under infection by the ashy stem blight soil fungus Macrophomina phaseolina, and resistance identified to this pathogen also must be incorporated. For protection against terminal drought, drought tolerance traits can be combined with early maturing short-season types which can avoid terminal drought events and produce good grain, but the tradeoff is poor fodder yield and also susceptibility to mid-season drought. Delayed leaf senescence and stay-green traits in cowpea have been identified and their QTL are being exploited for protection from mid-season droughts in longer-cycle cowpeas to promote both grain and fodder yield. Enhanced genomic resources applied to different breeding strategies and coupled with multi-location phenotyping for yield under drought stress are being used to boost cowpea resilience and these approaches will be discussed.