Preliminary evaluation of halotolerant PGPRs for promoting maize growth under salt stressed gnotobiotic conditions

Salinity stress is one of the critical factors that limits agricultural productivity particularly in the arid to semi-arid regions worldwide. Elevated concentrations of soluble salts especially NaCl cause osmotic stress, ionic stress and imbalance in the uptake of essential nutrients. Use of salt tolerant rhizobacterial isolates have gained much attention now-a-days on account of their environment friendly nature and effectiveness. Therefore, current study was executed to isolate salt tolerant bacteria from the rhizosphere of maize and check their salt tolerance and plant growth promotion under salinity stress. Selected isolates were further investigated in a growth room trial to compare their efficiency in improving growth and physiology of maize. Salinity stress caused a significant reduction in all the measured traits however, inoculation of rhizobacteria modulated its effects and improved maize growth. Among different strains, SUA-14 caused maximum increment in the shoot length (41%), root length (96%), shoot fresh (1.8 fold) and dry weight (1.3 fold), root fresh (1.76 fold) and dry weight (2 fold), salt tolerance index (1.6 fold), chl 'a' contents (2.6 fold) and chl 'b' contents (2.3 fold) as compared to its respective uninoculated control. Whereas, rhizobacterial strain SHM-5, SHM-13 and SUA-14 showed statistically nonsignificant response in terms of increasing carotenoid contents by 1.8 fold in comparison with their corresponding control. Pearson correlation coefficient showed a strong positive correlation between growth and physiological attributes under salinity stress. On the basis of PCA, SUA-14 found to be the most efficient strain followed by SHM-13. Using 16 S rRNA sequencing, SUA-14 and SHM-13 were identified as Acinetobacter and Bacillus species respectively.