Stress-tolerant antagonistic rhizobacteria isolated from the medicinal plant iTinospora cordifolia/i

摘要

Medicinal plants harbor a large number of beneficial microorganisms. Stress tolerance is an important attribute while screening bacteria for developing microbial inoculants. In the present studies, salt-tolerant bacteria isolated from the rhizosphere of the medicinal plant Tinospora cordifolia were screened for multiple plant growth promoting activities, antagonism against fungal pathogens and stress tolerance. A total of 25 morphologically distinct salt-tolerant bacteria were isolated on nutrient agar plates with 2.5% NaCl from the rhizosphere of Tinospora cordifolia growing in Jalandhar, Punjab, India. Twelve salt-tolerant bacterial isolates showing phosphate solubilization zones ranging from 3–12 mm on modified Pikovskaya agar were screened for the production of auxins, 1-aminocuclopropane 1-carboxylate (ACC) deaminase, ammonia and hydrogen cyanide. Of these 12 salt-tolerant and phosphate-solubilizing isolates, auxin production was shown by all isolates, ACC-deaminase activity by 7 isolates, ammonia production by 8 isolates and hydrogen cyanide (HCN) by 5 isolates. Phosphate solubilization in liquid medium ranged from 26 to 151 μg/ml, while auxin production ranged 10.7 to 31 μg/ml. Five bacterial isolates showing all plant growth-promoting activities were screened for antagonism against the phytopathogens Fusarium moniliforme, Fusarium verticillioides, Curvularia lunata and Alternaria alternata and the abiotic stress conditions of salinity, temperature, pH and calcium salts. The bacterial isolate T1B1, which shows multiple plant growth promoting activities and stress tolerance, was identified as Bacillus sp. based on phenotypic characteristics and 16S rRNA gene sequencing. The bacterial isolate T1B1 was selected as a potential candidate for the development of microbial inoculants for stressed environments.