Isolation, characterization and symbiotic performance evaluation of soybean (Glycine max) nodulating rhizobia from different districts of Bangladesh

Abstract

Rhizobia can meet up nitrogen requirement of legumes by biological nitrogen fixation through symbiosis. The main objective of this study was to find out the morpho-physiological diversity of indigenous soybean nodulating rhizobia and to find effective rhizobial strains for enhancing better soybean production at different environmental conditions. Fourteen rhizobial strains were isolated and studied their morph-physiological characteristics; evaluated their nodulation and symbiotic efficiency at potted soil. Among the strains, seven were slow growing, four were intermediate to slow growing and three were fast growing. The strains exposed creamy, milky-white and transparent single colonies between 1.17 and 3.67 mm in diameter after 3 to 7 days on growth medium. Twelve strains were alkali producers and only two strains were acid producers. Most of them tolerated both acidic pH (4.0 and 5.0) and alkaline pH (9.0 and 10.0) conditions. All strains tolerated to 1.0% NaCl but none of them survived at 5.0% salt stress. They retained their normal growth up to 37oC but most of them showed growth susceptibility at 45oC and growth was inhibited at 50oC. The strains were inoculated as treatments on soybean plants to compare their performance on growth of soybean along with urea and control treatment. Overall, rhizobial treatments significantly increased nodulation and growth of soybean plants over recommended dose of urea and negative control. Diverse rhizobial strains were associated with soybean root nodules in Bangladesh. The strains SB-27, SB-28 and SB-212 were very effective and produced almost double plant dry matter weight over some other strains, dose of urea and negative control. The physical stress tolerant and highly symbiotic strains deserve to be effective as bio-fertilizer for soybean crop production.