Halotolerant plant growth-promoting rhizobacteria from rice and wheat in sodic soils: Characterization for their potential to alleviate salt stress

Abstract

Soil salinity and alkalinity present critical constraints to agricultural productivity, particularly in arid and semi-arid regions. This study characterized the rhizospheric microbial communities and isolated halotolerant plant growth-promoting rhizobacteria (HT-PGPR) from rice (Oryza sativa L.) and wheat (Triticum aestivum L.) cultivated in sodic soils with variable salinity levels. Soil physicochemical and biochemical analyses revealed significant correlations between soil sodium content and microbial activity parameters. Serial dilution and selective media techniques identified bacterial and fungal populations with varying tolerance to sodium chloride (0.5-5%), sodium carbonate (1-2.5%), and sodium bicarbonate (1-2.5%) concentrations. Rice rhizosphere exhibited higher bacterial populations (19.1-38.3 × 104 cfu/g) compared to wheat (10.5-65.2 × 104 cfu/g), while wheat showed increased fungal diversity (17.5-80.5 × 103 MPN/g). Among the isolates, 30–40% demonstrated tolerance to 5% NaCl, indicating potential as HT-PGPR candidates for biofortification and saline soil amelioration. Microbial biomass carbon and nitrogen showed positive associations with soil enzyme activities, particularly dehydrogenase (14.25-25.34 µg TPF/g/day) and alkaline phosphatase (9.7-15.6 µg PNP/g/day) in rice. These findings suggest that selected halotolerant isolates possess multifunctional traits including salt tolerance and potential nutrient-solubilizing capacity, making them promising candidates for biofertilizer development and sustainable agriculture in salt-affected regions.