Stress-tolerant antagonistic rhizobacteria isolated from the medicinal plant Tinospora cordifolia

Abstract

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.

Culturable Stress-Tolerant Plant Growth-Promoting Bacterial Endophytes Associated with Adhatoda vasica

“…Similar results were observed earlier while screening stresstolerant Pseudomonas strains from Lahaul and Spiti valley in Himachal Pradesh, India (Vyas et al 2009). Many reports are available on screening rhizobacteria for PGP properties; however, limited reports have shown the selection of bacteria based on stress tolerance along with other activities for the development of microbial inoculants (Vyas et al 2009;Vyas and Kaur 2018). Selection of bacteria based on stress tolerance is important as bacterial screened in vitro fail to give same response in field due to the stress imposed by the environmental conditions (Vyas et al 2009;Vyas and Kaur 2017;Kaur et al 2018).…”

“…Bacterial endophytes are important components of sustainable agriculture playing a significant role in the nutrition of plants in view of their capability to produce large array of agriculturally important metabolites. However, different biotic and abiotic factors affect the performance of these microorganisms (Vyas et al 2010;Das et al 2015;Vyas and Kaur 2018). Abiotic stresses include temperature, pH, moisture status, salinity, and salts present in soils.…”

“…The performance of plant growth-promoting bacteria is constrained by the stress generated by environmental factors including temperature, desiccation, pH, alkalinity/acidity, and salinity in the soil (Vyas et al 2010;Das et al 2015;Vyas and Kaur 2018). Salinity is a major stress-limiting plant growth, crop productivity, and performance of microorganisms in soils (Dodd and Pérez-Alfocea 2012).…”