Snap Bean Plants' Physio-Biochemical Reactions to Plant Growth-Promoting Rhizobacteria to Mitigate the Negative Effects of Drought Stress

Abstract

Abstract Purpose Drought is one of the main devastating abiotic stresses on sustainable agriculture and global food security. Enhancement of abiotic and biotic stress tolerance by plant growth–promoting rhizobacteria (PGPR) has been increasingly documented. However, PGPR have not been employed to manage drought stress in snap bean.Methods Therefore, the current study was conducted to assess the beneficial effects of Azospirillum brasilense, Bacillus megaterium, Rhizobium leguminosarum bv. phaseoli, and Pseudomonas fluorescens on snap bean plants cv. Valentino grown in sandy soil under three levels of irrigation (100, 80, and 60% of the estimated crop evapotranspiration) during the 2020 and 2021 seasons to alleviate the detrimental impacts of drought stress. The experimental design was a split plot with three replications. The irrigation water levels were randomly distributed in the main plots, while the PGPR and non-inoculation treatments were randomly dispersed in the subplots.Results The results showed that drought stress decreased plant growth parameters, leaf elemental content, SPAD readings, relative water content, membrane stability index, yield attributes, and water use efficiency and induced increases in proline content and superoxide dismutase, peroxidase, and catalase activities. PGPR application, particularly Bacillus megaterium, significantly enhanced all growth and yield parameters, improved nutrient content, SPAD readings, and relative water content, lowered membrane damage, and accumulated endogenous proline and antioxidant enzymes, causing drought-tolerance. Yield response factors of all PGPR were lower than those of the check plants, indicating their effectiveness in alleviating the detrimental impacts of drought stress.Conclusion In light of these findings, it could be concluded that the PGPR application, especially Bacillus megaterium, could be utilized as a low-cost and an environment-friendly effective strategy to mitigate the negative effects of drought stress on the growth and productivity of snap bean.