Abstract

Nine fast-growing bacteria were isolated from mung bean nodules and characterized with plant growth promoting properties. All the isolated bacteria were able to colonize mung bean root at varying level of 3 × 10³ to 3 × 10⁷ cfu (0.1 mg)^-1 root, whereas, bacterial isolates M2, M4, M5 and M6 showed high biofilm formation ability on abiotic surface. None of them was able to nodulate mung bean plant when reinoculated. Bacterial isolate M2 was found to be an efficient indole acetic acid producer (28.3 µg mL^-1), whereas M6 was an excellent phosphate solubilizer (21.8 µg mL^-1). Two isolates, M1 and M3, were able to fix nitrogen. 16S rRNA gene sequence analysis of potential isolates revealed that bacterial isolates M2 and M6 showed maximum similarity with Bacillus subtilis, M4 with Bacillus simplex and M5 with Agrobacterium tumefaciens. Further, the impact of co-inoculation of these non-rhizobial bacteria withBradyrhizobium sp. MN-S on nodulation, plant growth and grain yield of mung bean was also assessed. Generally, co-inoculation significantly improved nodulation and grain yield compared with Bradyrhizobium sp. MN-S alone inoculation. The enhancement due to co-inoculation in nodule number and nodule dry weight was 78 and 127%, respectively when compared with the Bradyrhizobium sp. MN-S alone. Co-inoculation combination of Bradyrhizobium sp. MN-S with B. subtilis M6 performed best by increasing 22% grain yield, while the rest combinations also benefited plants non-significantly. The results show that non-rhizobial plant growth promoting bacteria improve nodulation and grain yield of the legumes upon co-inoculation with crop specific rhizobia.

Key words: Mung bean, nodulation, non-rhizobial, endophytes, co-inoculation.