Seedling stage drought screening of candidate cowpea (Vigna unguiculata (L) Walp.) genotypes

Prolonged drought of cowpea at the seedling stage can affect survival and productivity. This study sought to evaluate cowpea genotypes for their resistance to seedling-stage drought stress. Fifteen cowpea genotypes were used in this study. The experiment was a factorial experiment arranged in a Completely Randomized Design with three replications. Drought stress was imposed for 4 weeks after the full expansion of the first trifoliate leaf. Soil Plant Analysis Development (SPAD) chlorophyll meter readings of unifoliate, first, and second trifoliate leaves of each genotype were measured on a weekly basis due to the predictive ability of chlorophyll content on drought tolerance. The data were subjected to ANOVA, and the means were separated at a 5% probability level. Genotypes were ranked according to their tolerance level based on their chlorophyll inflectance index (CII). The results revealed significant genotype by stress interaction effects. Seedling stage screening under water-stressed conditions in combination with measurements of leaf chlorophyll measurements proved to be an effective way for rapid screening of genotypes for drought tolerance. IT14K-1424-12, IT10K-837-1 and IT10K-303-1 had consistently high chlorophyll content under drought stress for unifoliate and trifoliate leaves. These genotypes also fell into one cluster. Based on CII with a threshold of 51% for the fourth week of drought stress of unifoliate and trifoliate leaves, three genotypes (IT14K-1424-12, IT10K-837-1 and IT10K-303-1) were found to have Type I drought-tolerant mechanism. These genotypes could be used in future breeding interventions or released as varieties.