Bacillus cereus: an effective bio-inoculant for promoting salt stress tolerance of rice seedlings under saline soil conditions

Plant growth-promoting rhizobacteria (PGPR) are a powerful tool to maintain sustainable agriculture and promote plant resistance to biotic and abiotic types of stress. Salinity, a major abiotic stress hampers plant growth, development, and yield. Salt-tolerant PGPR are effective agents for ameliorating salinity effects on rice plants. The present study endeavored to isolate, determine halotolerant ability, characterize Plant Growth Promoting (PGP) traits, and finally observe the effect of PGPR strain on plant growth promotion of rice plants under saline and non-saline conditions. Based on the 16S rRNA gene sequencing technique, the rhizobacterial strain DB2 was identified as Bacillus cereus ATCC 14579(T) from NCMR, NCCS Pune. To check the growth-promoting ability, the strain was inoculated with two rice genotypes named Chinsurah Nona I (salt tolerant-non aromatic) and Badshabhog (aromatic) under polyhouse conditions. Results showed a significant increment in relative water content (RWC), total chlorophyll content (TCC), root length (RL), and shoot length (SL) in both rice genotypes inoculated with DB2 under both saline and non-saline conditions. Under non-saline conditions enhancement of RWC, TCC, RL, and SL was better in DB2 inoculated Chinsurah Nona I than in Badshabhog inoculated with DB2. Whereas, DB2-inoculated Badshabhog showed more recovery of RWC, TCC, RL, and SL than DB2-inoculated Chinsurah Nona I under saline conditions. Under salt stress conditions, inoculation with the rhizobacterial strain showed a significant reduction in electrolytic leakage (EL) in rhizobacteria inoculated with both rice genotypes. Moreover, DB2 inoculation showed a significant reduction in Na+ content in the roots of Chinsurah Nona I (44.6%) and Badshabhog (24.5%) rice genotypes. The present study has indicated that the application of salt-tolerant PGPR may be an effective and sustainable solution for rice cultivation under salt-stress conditions.