Salt-tolerant growth-promoting bacterium B10 alleviates salt stress and promotes growth in common beans

Soil salinity presents a significant abiotic challenge to agriculture, disrupting the physiological and metabolic equilibrium in common bean (Phaseolus vulgaris L.), thereby inhibiting growth and diminishing yield. This study seeks to screen salt-tolerant plant growth-promoting bacteria that can mitigate salt stress in common beans and to develop a cost-effective and easy-to-operate application technology for microbial agents. This study identified salt-tolerant plant growth-promoting rhizobacteria (PGPR) strains from saline-alkali soils in the Lindian District of Daqing, Heilongjiang, China. Indole-3-acetic acid (IAA) production was quantified using the Salkowski assay, and phosphate solubilization was assessed through gradient dilution techniques. The strains were characterized through morphological, physiological, biochemical, and molecular analyses. Furthermore, pot experiments were conducted to evaluate key growth parameters of P. vulgaris under salt stress conditions. Salt stress markedly diminished the chlorophyll content, carotenoid levels, and antioxidant enzyme activity in non-inoculated plants. In contrast, inoculation resulted in 60.71% increase in plant height, 30.77% increase in root length, 127.50% increase in fresh root weight, and 150% increase in dry root weight. Furthermore, inoculation enhanced chlorophyll content, elevated antioxidant enzyme activity, and improved soil enzyme activity. In conclusion, strain B10, classified as a Bacillus species, represents a promising salt-tolerant PGPR that facilitates the growth of P. vulgaris, enhances soil enzyme activity and enriches beneficial taxa, thereby alleviating the impacts of salt stress. Consequently, B10 is a strong candidate for the development of microbial inoculants for P. vulgaris in saline-alkali soils, providing a viable solution for sustainable agriculture in salt-affected regions.