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Abstract

Plant growth-promoting rhizobacteria (PGPR) inhabiting the rhizosphere play a significant role in improving plant growth and physiological performance through the production of diverse bioactive metabolites. Halophytic plants growing in saline environments harbor salt-tolerant rhizobacteria that may possess important plant growth-promoting traits. The present study aimed to isolate and characterize PGPR from the rhizosphere of Sesbania sesban and evaluate their effects on seed germination and seedling growth of maize (Zea mays L.) and mung bean (Vigna radiata L.). A total of five rhizobacterial strains Ss1 (Bacillus sp.), Ss2 (Staphylococcus sp.), Ss3 (Enterococcus sp.), Ss4 (Staphylococcus sp.), and Ss5 (Micrococcus sp.) were isolated and screened for plant growth-promoting traits, including indole-3-acetic acid (IAA) and cytokinin production, nitrogen fixation, phosphate solubilization, and salt tolerance. All isolates were Gram-positive and produced both IAA and cytokinins. However, none exhibited nitrogen-fixing ability in semi-solid malate medium, while only one isolate showed phosphate solubilization in Pikovskaya medium. Auxin production ranged from 211.84 µg mL⁻¹ in isolate Ss1 (Bacillus sp.) to 63.79 µg mL⁻¹ in isolate Ss2 (Staphylococcus sp.), whereas cytokinin production varied between 271.35 and 253.56 µg mL⁻¹. All isolates tolerated up to 3% NaCl but failed to grow at 5.5% NaCl. Germination assays with surface-sterilized maize seeds showed increased root and shoot lengths and biomass compared with the control. Similarly, pot experiments with mung bean demonstrated improved chlorophyll content, seedling growth, and biomass after 15 days. These results suggest that S. sesban-associated rhizobacteria, including Ss1 (Bacillus sp.), Ss2 (Staphylococcus sp.), Ss3 (Enterococcus sp.), Ss4 (Staphylococcus sp.), and Ss5 (Micrococcus sp.), have potential as bioinoculants for improving crop growth under saline conditions.

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