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

Abstract

Endophytes are potential source of various novel compounds that help to promote plant growth, eliminate plant pathogens, and enable the plant to resist stress-like conditions. The present study aimed at selecting stress-tolerant bacterial endophytes with plant growth-promoting ability from Adhatoda vasica. Salt-tolerant bacterial endophytes were isolated on nutrient agar with 2.5% NaCl from the leaves of Adhatoda vasica collected from Manipur, India. The isolates were screened for stress tolerance, plant growth-promoting traits, antagonism against fungal phytopathogens and plant growth promotion. Sixteen morphologically distinct salt-tolerant bacterial endophytes were isolated from Adhatoda vasica. All bacterial endophytes showed auxin production while phosphate solubilization was shown by 81% isolates, siderophore production by 75%, ACC deaminase by 43.8% isolates, HCN by 50% isolates, and ammonia by 62.5% isolates. Four bacterial isolates showed antagonistic activity against all the test fungal phytopathogens Fusarium verticillioides (MTCC 3322), Curvularia lunata (MTCC 283), and Alternaria alternata (MTCC 1362). Dendrogram generated based on stress tolerance of the bacterial isolates against salinity, temperature, pH, and calcium salts showed 3 clusters and two independent branches. Two bacterial isolates identified based on phenotypic features and 16S rRNA gene sequencing as Bacillus thuringiensis A1B3 and Bacillus sp. A1B6 significantly increased the growth parameters of pea and maize in comparison to uninoculated control in pots under natural conditions. The attributes of stress tolerance, antagonism against fungal pathogens, and plant growth promotion indicated the potential of Bacillus thuringiensis A1B3 and Bacillus sp. A1B6 to be used as microbial inoculant in agriculture under stressed environment.