Harnessing plant growth-promoting microorganisms to improve drought resilience in common bean (Phaseolus vulgaris L.)

BACKGROUND: Drought stress is one of the principal abiotic stresses that constrain crops yield across the globe. The current research examines the involvement of PGPM, namely Bacillus subtilis (1211 EMCCN) and Aspergillus niger (ATCC 102), in improving drought tolerance of Phaseolus vulgaris cultivated in soil water contents of 100%, 60%, and 40% field capacity. RESULTS: B. subtilis showed a higher production of indole-3-acetic acid, cytokinin, and ACC deaminase, indicating its strong role in promoting plant growth and mitigating stress. In contrast, A. niger produced more gibberellic acid and enhanced phosphate solubilization. Drought stress significantly reduces plant growth, biomass, chlorophyll content, and relative water content, while increasing electrolyte leakage and oxidative stress markers. Inoculating plants with plant growth-promoting microorganisms (PGPM) alleviated these negative effects, improving growth performance, photosynthetic pigment content, and water status compared to uninoculated plants. The microbial treatments reduced oxidative damage and enhanced antioxidant defense systems, including both enzymatic and non-enzymatic antioxidants. PGPM inoculation also promoted the accumulation of osmolytes and secondary metabolites, aiding osmotic adjustment and redox balance. Multivariate analysis confirmed the positive effects of microbial inoculation in mitigating drought stress. CONCLUSION: Among the tested microorganisms, B. subtilis showed greater effectiveness than A. niger in most of the physiological and biochemical traits measured. Overall, the findings suggest that PGPMs are a promising and sustainable strategy for enhancing drought tolerance and improving the productivity of common beans in water-limited conditions.