Rhizobacteria Associated with Spilanthes acmella Murr. Confer Drought-Tolerance and Plant Growth Promotion

Plant growth-promoting rhizobacteria (PGPR) exhibit biocontrol and biofertilzer traits and help plants survive adverse environmental conditions. In this study, the rhizobacteria are explored for their ability to tolerate drought stress and their potential to act as plant growth promoters. Herein, we have isolated bacterial strains from the rhizosphere of Spilanthes acmella Murr. (toothache plant) found in the Shivalik hills region of Himachal Pradesh. We screened nine drought-tolerant culturable bacteria by analyzing their ability to survive in varying concentrations of polyethylene glycol (PEG) (10% 50%), which is further supported by their 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity and their ability to release exopolysaccharides (EPS). Strains having these activities are identified by 16S rDNA analysis, which reveals that they belong to four different bacteria genera, namely Klebsiella, Enterobacter, Burkholderia, and Pantoea. These isolates also harbor plant growth-promoting traits such as solubilization of phosphate, production of indole-3-acetic acid (IAA), siderophore, ammonia, hydrogen cyanide (HCN), and antifungal activity. The Enterobacter cloacae showed maximum drought tolerance among all the other isolates. We found that the drought stress of 60% PEG inhibited wheat seedlings' growth, but the bacterization with the isolated strains stimulated seedling growth. Hence we conclude that these drought-tolerant PGPR from the rhizosphere of S. acmella Murr. can be utilized to enhance the survival and growth of plants under drought stress. The isolated strains not only exhibit the drought-tolerant ability but also show the biocontrol and biofertilizer traits. Inoculation of these strains could help the plant survive under adverse environmental conditions.