Rhizobacteria and Phytohormonal interactions increase Drought Tolerance in Phaseolus vulgaris through enhanced physiological and biochemical efficiency

The cultivation of common beans (Phaseolus vulgaris L.) in semi-arid regions is affected by drought. To explore potential alleviation strategies, we investigated the impact of inoculation with Bacillus velezensis, and the application of acetylsalicylic acid (ASA) via foliage application (FA), which promote plant growth and enhance stress tolerance. A split-split-plot experiment with four replications was conducted, featuring two irrigation levels: full watering (FW, 100% of plant water requirements) and deficit watering (DW, 70% of plant water requirements) as a main plot, two ASA levels (No foliage application (NFA) 0 and 0.5 mM) as sub plot, and bacterial inoculation (BI) versus non-bacterial inoculation (NBI) as sub-sub plot. Results showed that the highest grain yield was achieved with the ASA + BI under FW (3270 kg ha^-¹), a 56% increase compared to the control (2094 kg ha^-¹). Under DW, the ASA + BI increased yield by approximately 30%. ASA significantly increased relative water content under deficit watering, achieving 84% with BI. Chlorophyll a content peaked at 3.11 mg g^{- 1} with full watering, and chlorophyll b content increased by up to 23.8% under deficit watering, indicating improved photosynthetic capacity. Malondialdehyde and hydrogen peroxide levels were reduced to 10.88 and 14.81 µmol g^-¹ fresh weight, respectively, in ASA + BI treatments, demonstrating reduced oxidative stress. Antioxidant enzyme activities were significantly elevated in treated plants under DW. This study demonstrates the potential of microbial and hormonal treatments in boosting drought tolerance in common beans, providing a viable approach for sustaining crop performance under stress conditions.