Seed priming and subsequent inoculation of drought-tolerant plant growth-promoting rhizobacteria Bacillus tropicus KH90 improves rice (Oryza sativa L.) plant health under drought and non-drought conditions

Drought stress adversely affects productivity by altering plant health. Plant growth-promoting rhizobacteria (PGPR) can boost plant health and induce plant tolerance against various unfavorable conditions. This study aimed to screen drought-tolerant rhizobacteria with potent multi-PGP traits from previously isolated strains and evaluate the isolates’ efficacy on the enhancement of rice seed growth parameters under drought and non-drought conditions. Five isolates (KK21, MK66, BH73, BH74, and KH90) were found to be drought-tolerant with multi-PGP traits under both drought and non-drought conditions. The isolates also showed efficient oxidative stress mitigation features like proline accumulation, SA-production, and antioxidant (PPO, PO, and CAT) activities. The FTIR research revealed the presence of several functional groups in KH90-produced EPS under stressed and non-stressed circumstances. Using 16S rRNA gene sequencing, the drought-tolerant isolates were identified as Bacillus cereus KK21, Lysinibacillus fusiformis MK66, Bacillus luti BH73, Bacillus aerius BH74, and Bacillus tropicus KH90. Primed seeds performed better than unprimed seeds in terms of germination percentage, seedling height, and vigor index when grown in both drought and non-drought conditions. However, further plant inoculation with KH90 increased leaf relative water, photosynthetic pigments, and proline content and decreased electrolyte leakage and malondialdehyde contents in rice leaves under both drought and non-drought conditions. The results showed that drought-tolerant Bacillus tropicus KH90 with multi-PGP-traits is able to improve rice plant health in both normal and drought-stressed conditions by reducing the physiological damage caused by the stress. This gave credence to the idea that this strain may be used to manage drought stress.