Identification and Evaluation of Rhizobium for Enhancing Plant Growth and Resilience to Drought and Salinity

Rhizobium species are well known for their nitrogen-fixing ability, but their potential as multifunctional biofertilizers for stress mitigation remains underutilized. This study aimed to isolate and characterize Rhizobium strains with plant growthpromoting (PGP) traits and evaluate their effects on plant performance under drought and salinity stress. Twelve bacterial isolates were obtained from root nodules of Vigna radiata and Cajanus cajan, of which ten were confirmed as Rhizobium spp. via 16S rRNA gene sequencing. Among them, strain RZ5 (Rhizobium phaseoli) exhibited superior PGP attributes, including high indole-3-acetic acid (IAA) production (38.6 ± 1.2 µg/mL), phosphate solubilization (2.1 ± 0.1 cm halo), and ACC deaminase activity (28.4 ± 1.1 nmol α-ketobutyrate/mg protein/h). In controlled greenhouse experiments, RZ5 and RZ2 (R. tropici) significantly enhanced shoot and root length, biomass accumulation, and physiological parameters in Vigna radiata under drought and salinity conditions. Inoculated plants maintained higher chlorophyll content (up to 42.1 SPAD units), relative water content (>80%), and lower electrolyte leakage compared to controls. Furthermore, Rhizobium inoculation improved soil nutrient status, including total nitrogen and available phosphorus levels. This is one of the few studies to comprehensively demonstrate the dual role of Rhizobium in both plant growth promotion and abiotic stress mitigation. These findings underscore the potential application of native Rhizobium strains as climateresilient biofertilizers for sustainable agriculture.