Responses of seven cowpea (Vigna unguiculata L. WALP) genotypes to 14-day water deficits at various phenological stages

Abstract

Abstract In West Africa, cowpea is a key crop valued for its nutritional, ecological, and economic value. However, this region of the world frequently suffers from drought, which severely compromises the productivity of this species. Varietal selection, one of the most effective approaches to adressing this constraint, requires identifying the most sensitive stages of development and selecting high-performance varieties for breeding programmes. This study evaluated the agronomic responses of seven cowpea genotypes subjected to a 14-day water deficit at four phenological stages (20, 30, 40, and 50 days after sowing) using a completely randomized block design with three replicates under controlled greenhouse conditions, with the aim of identifying genotypes likely to be tolerant at different stages of development and stress levels. Total grain weight (g) per genotype under each water regime was used as the primary performance criterion. Under continuous irrigation (WR0), grain weights ranged from 2.83 ± 0.28 g (KVx150) to 7.80 ± 0.37 g (Waongo), with a mean of 5.39 ± 0.44 g. The early vegetative stage (20 DAS) was the most critical, with a mean grain weight of only 0.29 ± 0.11 g across surviving genotypes, representing an average loss of 94.95% relative to WR0. In contrast, the pod-filling stage (50 DAS) showed the lowest impact, with a mean grain weight of 1.06 g and average losses of 74.65%. Based on drought tolerance indices (GMP, STI, YI), Waongo recorded the highest grain weight across all stress regimes (0.83 g at WR1, 1.76 g at WR2, 2.10 g at WR3, and 1.43 g at WR4), making it the best overall performer. IT93K-503-1 also performed well, with a total grain weight of 6.50 ± 0.30 g under WR0 and a higher hundred-grain weight than Waongo across most regimes, but showed sensitivity to stress applied at 40 DAS (0.90 ± 0.36 g, loss of 86.15%). The performances of Waongo and IT93K-503-1 are attributed to mechanisms ranging from cell turgor maintenance to phenological plasticity, making them suitable candidates for drought breeding programmes.