Evaluation of cowpea for drought tolerance at seedling stage

Cowpea is a health-promoting diploid legume species [Vigna unguiculata (L.) Walp., 2n = 2x = 22]. The annual cowpea production is 5.4 million tons of dry seed globally. Despite the fact that cowpea is one of the most drought-tolerant crops, some genotypes with excellent agronomic traits such as high yield under sufficient water supplies have been reported to be highly drought-susceptible, thus still requiring the need for breeding drought-tolerant cowpea genotypes. Therefore, the objectives of this study were to evaluate drought tolerance in cowpea at seedling stage and to identify drought-tolerant cowpea genotypes. In this study, a total of 331 cowpea genotypes were evaluated for drought tolerance at seedling stage. The experiment was conducted in a greenhouse and repeated 3 times. Drought tolerance phenotyping was conducted using a previously described methodology and a total of 11 traits were analyzed. The experiment was validated by the use of drought-tolerant and susceptible controls. Results showed that: (1) a large variation in the evaluated traits for drought tolerance was identified among the 331 cowpea genotypes, (2) a high correlation was found for traits such as plant greenness score and tolerance to trifoliate leaf chlorosis under drought stress (r = 0.8), whereas no linear correlation was found for traits such as tolerance to trifoliate leaf chlorosis and unifoliate leaf SPAD chlorophyll under non-drought stress (r = 0.0), (3) a total of 21 genotypes were found to be drought-tolerant across different traits, and (4) country of origins could impact drought tolerance in cowpea. The top performing genotypes were repeated using an independent experiment to further validate the data. The results from this study would be of interest in breeding programs aiming at improving drought tolerance in cowpea.