Abstract
Salinity stress, through restricting water availability and inducing ion toxicity, represents one of the major threats to global agricultural productivity. Although plant growth-promoting bacteria (PGPB) have been widely studied for their ability to alleviate abiotic stresses, the co-inoculation of Stenotrophomonas maltophilia (MN099392) and Rhizobium leguminosarum bv. phaseoli (PP125713) to enhance salt stress tolerance in common bean (Phaseolus vulgaris L.) cultivars has received limited attention. This study aimed to evaluate the effects of co-inoculation with S. maltophilia and R. leguminosarum bv. phaseoli on physiological traits and yield performance of two common bean cultivars (Almas and Pak) under salinity stress. A factorial experiment was conducted based on a completely randomized design with three replications in the research greenhouse of the Faculty of Agriculture, Shiraz University. Treatments included six bacterial inoculations (non-inoculated control, S. maltophilia (P1), Enterobacter hormaechei (P2), R. leguminosarum bv. phaseoli strain Rb-114 (RB), and dual combinations P1 + RB and P2 + RB) and four salinity levels (0.5, 4, 6, and 8 dS m(− 1)). Increasing salinity reduced chlorophyll and carotenoid contents, protein accumulation, and grain yield, while electrolyte leakage, proline concentration, antioxidant enzyme (APX and POD) activities, and ABA content increased. Co-inoculation with P1 + RB effectively mitigated the adverse effects of salinity by enhancing chlorophyll, carotenoids, soluble sugars, IAA, essential nutrients (Mg, Fe, and K), grain weight and nitrogen content. Overall, co-inoculation with S. maltophilia and R. leguminosarum bv. phaseoli significantly improved salinity tolerance, particularly in the Almas cultivar, through enhanced nutrient uptake, maintenance of membrane integrity, and regulation of hormonal balance. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1038/s41598-026-37145-2.