Cowpea cultivation is widespread in West Africa where it is an important source of protein. This study is aimed at determining the effects of water deficit applied at different stages of cowpea development on yield and its components (pod number, seed number, seed yield, aerial biomass yield, harvest index and root biomass of the plant). The experiments were carried out in pots during the rainy season of 2016 under natural conditions of illumination, temperature and relative humidity. Three water regimes were applied to plants at different stages of cowpea development: total suspension of watering at flowering phase (43 days after sowing) (S1); suspension of watering at the beginning of pod formation on the 46th day after sowing (S2); and normal watering as control until harvest (S0). At the water regime level, yield components had higher values in S0 followed by S2. The lowest values were obtained at S1 level. The root to aerial biomass ratios was higher under water deficit than in the control. In conditions of water deficiency, Suvita2, IT96D-610, and ISV128 genotypes gave the highest seed yields and Tiligré the lowest yield. The harvest index showed a genotypic variation according to the water regime. Suvita2 and ISV128 gave the best harvest index in all water regimes. This study may have contributed to the selection of genotypes adapted to drought.
Key words: Cowpea, harvest index, water deficit, yields, Niger.