Seedling stage drought-induced phenotypes and drought-responsive genes in diverse cowpea genotypes

Populations developed from crosses between parents contrasting in drought tolerance are used to identify drought-related genetic elements in crops. Easily assayable phenotypes and identification of contrasting genotypes are important components of such studies. We investigated genotypic and phenotypic responses to seedling-stage drought of 14 cowpea [Vigna unguiculata (L.) Walp.] genotypes. Observations on stem greenness, unifoliate senescence, wilting, trifoliate abscission, and anthocyanin accumulation made twice weekly for 30 d after the last watering in greenhouse experiments were compared with survival and recovery dry weights to identify contrasting genotypes. Based on survival and recovery dry weights, four genotypes were identified representing the drought-tolerance spectrum. The genotype IT93K-503-1 was highly tolerant and IT98K-499-39 was tolerant, whereas CB46 was susceptible and 'Bambey 21' was highly susceptible. Genotypes differed in all phenotypic responses assayed. Only stem greenness was correlated with survival and recovery dry weight (r > 0.60). Field drought-induced senescence was correlated with greenhouse stem greenness, survival, and recovery dry weight (r > -0.56). Restriction fragment length polymorphism analysis of 12 drought-related complementary DNAs generated 29 polymorphic bands among the 14 genotypes. Seven of these bands were correlated with different drought-related phenotypes. These findings have utility for improved selection and molecular genetic studies of seedling drought tolerance in cowpea.