Amelioration of Salinity Stress by Bacillus Species as Promoters of Plant Growth in Saline Soil

Abstract

Salinity is a major factor of osmotic stress of the high salt in the rhizosphere, which limits plant growth and development. The uptake of salt inhibits the physiological and metabolic processes of plants and severely impacts agricultural productivity. About 62 million hectares (20%) of the world’s irrigated land are affected by salinity. In vitro and in vivo bioassays reveal that some salt-tolerant plant-associated Bacillus spp. enhance plant tolerance to salinity. The roots and fresh weight of plant seedlings showed better growth promotion significantly by the application of Bacillus species in the saline environment. However, the precise mechanism of higher tolerance of plants to salinity by Bacillus spp. is still poorly understood. Salt-tolerant plant growth-promoting Bacillus species, viz., B. oryzicola YC7007, B. velezensis, B. licheniformis SA03, B. safensis ZY16, B. megaterium, B. pumilus, B. firmus SW5, B. subtilis SU-12, B. amyloliquefaciens, B. aryabhattai MS3, B. cereus, and B. aquimaris DY-3 enhance salinity tolerance of plants through inducing plant gene/protein/pattern recognition receptors against salt stress. Out of different genera of salt-tolerant bacteria such as Pseudomonas, Enterobacter, Agrobacterium, Streptomyces, Klebsiella, and Ochromobacter, Bacillus show the highest performances in enhancing plant tolerance to salinity. This chapter summarizes current knowledge on the amelioration of salinity stress in plants by plant growth-promoting Bacillus species.