Inheritance of drought resistance in cowpea [Vigna unguiculata (L.) Walp.]

Identification of efficient selection criteria remains a major challenge to cowpea breeders in developing drought-resistant cultivars. Simply-measured plant characteristics were evaluated in a series of greenhouse pot experiments for their potential use as selection criteria in screening for drought-resistance in cowpea. Eight traits (delayed leaf senescence, stem diameter, leaf temperature, leaf relative humidity, leaf diffusive resistance, transpiration rate, leaf water potential, and leaf water content) were measured from genotypes, Tvu 11986 (drought resistant) and Tvu 7778 (drought susceptible), following exposure to 15 d of drought stress from flowering to early pod formation stages. Stepwise and linear discriminant analyses revealed that delayed leaf senescence, stem diameter, and leaf temperature were the most important traits in discriminating the two genotypes. The drought-resistant genotype was characterized by prolonged delayed leaf senescence and large stem diameter. Leaf temperature was inconsistent for characterizing drought resistance. The effectiveness and consistency of these traits for discriminating drought resistance were evaluated on 13 genotypes using linear discriminant analysis and cluster analysis. The cross Tvu 11986 x Tvu 7778 was made to generate F1, F2, F3, BC1, BC2, BC1S, and BC2S progenies. Narrow-sense heritability estimates were high for delayed leaf senescence, moderate for stem diameter, and low for leaf temperature. Strong genotypic correlation was observed between delayed leaf senescence and stem diameter. Number of effective factors and F2 segregation ratios indicated that the three traits were simply inherited and controlled by one or two dominant genes. Presence of heterosis for the three traits was observed from generation means analysis. Delayed leaf senescence and stem diameter were identified as the best selection criteria for drought resistance. Backcrossing or pedigree selection should be effective methods to incorporate these traits into improved lines or cultivars.