Evaluation of Bacillus and Rhizobium Strains to Enhance the Growth of Vigna radiata (L.) under Drought Stress

Abstract

In the present study, strains of Bacillus and Rhizobium were evaluated for their efficacy to produce auxin and to enhance the growth of Vigna radiata (L.) under drought stress. Colorimetric analysis indicated the production of auxin in bacterial culture supernatants in the presence of 0, 200, and 500 µg ml-1 L-tryptophan. At 500 µg ml-1 of L-tryptophan, B. subtilis Z-24, and B. simplex Z-38 produced significant levels of 41.4 and 24.8 µg ml-1 auxin, respectively. High Performance Liquid Chromatography (HPLC) also detected the auxin production by bacterial strains. In vitro rooting assay also recorded maximum increase in number of lateral roots with B. simplex Z-02, over control. For pot trials, seeds treated with single and mixed bacterial cultures were grown under 28%, 20%, and 10% field capacities (FC) of loamy soils. At 28% FC (normal water level), maximum increase of 28% dry weight was observed for R. rosettiformans Z-30; as compared to respective control. At 10% FC (highest water stress), significant increases of 87% and 70% in fresh weight and root length were recorded by B. cereus Z-59 and B. simplex Z-37, respectively. In case of mixed culture, C-3 (Z-38, Z-20, and Z- 30) and C-2 (Z-59, Z-20, and Z-23) were the most effective to enhance up to 68% dry weight and 13% shoot length of plants under drought stress (10% FC). Results showed that Bacillus and Rhizobium strains have the potential to produce auxin and improved the growth of mung beans under drought stressed conditions.