https://doi.org/10.37229/fsa.fjb.2026.10.28

Drought stress is a major abiotic constraint limiting cowpea (Vigna unguiculata L.) productivity in arid and semi-arid regions. Integrating drought-tolerant germplasm with plant growth-promoting rhizobacteria (PGPR) offers a sustainable approach to improving crop resilience. This study evaluated the drought response of four Egyptian cowpea germplasm accessions conserved at the National Gene Bank of Egypt under contrasting water regimes and PGPR inoculation. Prior to greenhouse evaluation, two Stenotrophomonas rhizophila strains (SprA and SprB) were screened under polyethylene glycol-induced osmotic stress, where both strains exhibited high drought tolerance, while SprB showed superior plant growth-promoting activities. A factorial randomized complete block design with three replications was conducted using four cowpea accessions, four irrigation levels (100, 75, 50, and 25% field capacity), and three PGPR treatments (Rhizobium leguminosarum, Stenotrophomonas strain-1, and strain-2). Nineteen growth, physiological, nutrient uptake, and yield-related traits were evaluated. Three-way ANOVA revealed significant effects of water regime, genotype, PGPR inoculation, and their interactions on most traits. Water deficit markedly reduced growth, nutrient uptake, and yield, whereas PGPR inoculation partially mitigated these effects. Principal component analysis explained 91.30% of the total phenotypic variation, identifying nitrogen and potassium uptake in shoots and roots as the major determinants of drought adaptation. The results demonstrate that nutrient acquisition efficiency, biomass maintenance, and root functionality are key indicators of drought tolerance and valuable selection criteria for breeding resilient cowpea cultivars adapted to water-limited environments. Among the tested PGPR, S. rhizophila strain SprB showed the greatest potential as a bioinoculant for improving cowpea performance under drought stress.