Assessment of variability in dual purpose large seeded cowpea using multivariate trait analysis

Cowpea (Vigna unguiculata (L.) Walp.) is a key dual-purpose crop in the semi-arid tropics, providing both grain for human consumption and fodder for livestock. However, its production is often constrained by significant genotype × environment interactions under rainfed conditions. This study evaluated 15 large-seeded cowpea genotypes across seven environments in Niger from 2022 to 2024 to assess variability, stability, and adaptability for dual-purpose traits. The evaluated traits included days to first flowering, days to 50% flowering, days to 50% maturity, grain yield, fodder yield, and hundred-seed weight. A mixed linear model was used to estimate best linear unbiased predictions (BLUPs), which were subsequently used to compute three multi-trait selection indices: the multi-trait genotype–ideotype distance index (MGIDI), the multi-trait stability index (MTSI), and the factor analysis and ideotype-design (FAI-BLUP) index. Significant (P ≤ 0.001) effects of genotype, environment, and genotype × environment interaction were observed for all traits. Heritability was high for hundred-seed weight (75%) and moderate for flowering traits (45–60%) but low for fodder and grain yield (23% and 29%, respectively), indicating strong environmental influence. The three indices consistently identified genotypes G13, G1, and G12 as superior, combining high grain yield, fodder yield, and seed size with stable performance across environments. The results demonstrate the effectiveness and complementarity of multi-trait selection indices for identifying stable and high-performing dual-purpose cowpea genotypes under Sahelian conditions.