Isolation, characterization and plant growth-promoting effects of sorghum [Sorghum bicolor (L.) moench] root-associated rhizobacteria and their potential role in drought mitigation.

Drought is a major constraint throughout the world, and it creates a major yield loss by changing the plant metabolic process. However, the negative effects of drought on plant growth and development were alleviated by using plant growth-promoting bacteria. With these backgrounds, the study was conducted to identify the drought-tolerant endophytic bacteria and to know their plant growth promotion (PGP) effect on sorghum plants under drought conditions. From sorghum root, Acinetobacter pittii, Bacillus lichiniformis, Bacillus sp., Pseudacidovorax intermedius, and Acinetobacter baumannii strains were isolated and identified through 16S rRNA sequencing. These strains had higher levels of proline, protein, exopolysaccharides (EPS), 1-aminocyclopropane-l-carboxylic acid (ACC) deaminase, indole-3-Acetic Acid (IAA), and gibberellic acid (GA). An experiment was carried out in the laboratory to evaluate the effects of three drought-tolerant strains, A. pittii, Bacillus sp., and P. intermedius, on the growth of sorghum seedlings. Whereas root length (RL), shoot length (SL), seedling vigor index (SVI), and total dry matter production (TDM) were more in the Bacillus sp., and P. intermedius inoculated plants in both stress and non-stress condition. Principle component analysis revealed that Bacillus sp. and P. intermedius improved the growth characteristics and protect the seedling from water stress situations. A correlation study between the variables showed a positive significant correlation between all variables except root: shoot ratio (RSR) and SL. Variable RSR was not significantly correlated with GP, GRI, and SL; SVI and TDM showed a non-significant correlation with RSR.