Direct and Indirect Mechanisms of Growth Promotion by Plant Growth Promoting Rhizobacteria

The current agro-model relies heavily on agrochemical use, which can cause environmental and soil pollution. There is a need to promote environmental sustainability while ensuring food security. This can be achieved through rhizobacterial application, thereby reducing our reliance on synthetic agrochemicals. The direct mechanisms of growth promotion by plant growth-promoting bacteria (PGPR) include phytohormone production, nitrogen (N) fixation, nutrient solubilization, and siderophore production and exopolysaccharide production. The indirect mechanisms of growth promotion by rhizobacteria involve the inhibitory effect on pathogens and species that negatively impact plant growth and productivity. Rhizosphere organisms can protect plants against soilborne pathogens through various mechanisms, which include antibiotic production, production of volatile organic compounds (HCN and ammonia), production of enzymes and biosurfactants, direct competition of food and space with pathogens, and induced resistance. The application of plant growth-promoting rhizobacteria (PGPR) for growth promotion has continued to gain traction due to its environmental friendliness.