Alleviation of Drought Stress by Plant Growth-Promoting Rhizobacteria (PGPR) in Crop Plants: A Review

Water deficit is the major constraint among all stresses, which affects agricultural production worldwide. Food production is getting reduced due to drought stress which is unable to feed an ever-increasing population. The development of drought-resistant plant varieties or transgenic plants to increase food production is costly and time-consuming, also the fully adoption of new technique is not acceptable, so any sustainable way is required. The use of plant growth promoting rhizobacteria (PGPR) for the improvement of plant growth under environmental stress is a sustainable and inexpensive way. PGPRs provide various direct mechanisms like phytohormone synthesis, phosphate solubilization, nitrogen fixation, and exopolysaccharide production as well as indirect mechanisms like hydrogen cyanide, 1-aminocyclopropane-1-carboxylate deaminase, siderophore, and antibiotics production which enhances plant growth under environmental stress. Due to their multiple traits, the search for suitable and rhizosphere-competent PGPR becomes interesting and can be used as inoculants for biofertilization and biocontrol purposes in agriculture, forestry, and environmental rehabilitation.