Alleviation of the adverse effect of salinity stress by inoculation of plant growth promoting rhizobacteria isolated from hot humid tropical climate

The present study was conducted to evaluate the effect of salt tolerant plant growth promoting bacteria on the growth of Oryza sativa under salinity stress. For this, a total of 82 rhizobacteria isolated from the rhizosphere soils were evaluated for their salt tolerance ability. A subset of 12 isolates, which showed growth at 15% NaCl (w/v) was further evaluated for plant growth promotion (PGP), extracellular enzyme production and antagonistic ability. The results revealed that isolates PHL3 and BHK2 showed statistically significant inhibition of mycelial growth of Macrophomina sp. and Sclerotium rolfsii respectively, while 11 isolates produced amylase and protease, 10 isolates showed cellulase and siderophore production. Four isolates (BRC8, BRC12, PHL3 and BHK2) showed positive to all three PGP traits tested whereas, 8 isolates (BRC8, BRB5, PHK1, BHKn1, BRC3, BHL1, PHL3 and PRL3) showed positive for production of any four enzymes tested. The multi potential salt tolerant isolates were identified as to genus Bacillus, Agrobacterium, Alcaligenes, Lysinibacillus and Pseudomonas using microbial identification system (Biolog) and 16S rRNA gene sequencing. The effects of these bacteria on the plumule and radicle length of O. sativa (var. CARI Dhan 3) were determined under salinity of 0-15 dS m−1 in jar assay. Based on the plumule and radicle length in the jar assay, seven isolates were further evaluated for their plant growth parameters under glasshouse conditions. The results revealed that Pseudomonas aeruginosa (PRR1 and PHL3) and Lysinibacillus sp. (BPC2) effectively enhanced the growth of paddy seedlings under salinity stress. Overall, it was found that the strain P. aeruginosa (PRR1) showed better results in germination percentage (111.11%), shoot length (74.44%) and root length (152.47%), over the control. These results suggest that the use of salt-tolerant plant-growth-promoting bacteria may provide an effective cultivation of paddy (O. sativa) in salinized agricultural lands.