Role of Plant Growth-Promoting Rhizobacteria (PGPR) for Crop Stress Management

Abstract

Crops under both abiotic and biotic stress are the major constraints on productivity. A number of factors like physical disorders, disease susceptibility, toxicity, hormonal imbalance, and nutritional deficiency interfere with the growth and development of plant under stress condition. Under these circumstances, rhizoremediation with the help of the plant growth-promoting rhizobacteria can mitigate stress-induced adverse effects on crop productivity. Plant growth-promoting rhizobacteria and their associated molecules play dual role by affecting both nutrition and resistance concomitantly through overlapping mechanisms. These free-living plant growth-promoting rhizobacteria actively colonize plant roots, exerting beneficial effects using their own metabolism or by directly affecting the plant metabolism. Rhizobial symbiosis has great agricultural importance in terms of improving soil fertility and crop productivity due to their synergistic as well as antagonistic interactions with other microbes in the soil environment. Plant growth-promoting rhizobacteria trigger elicitors, produce siderophores which deprive iron nutrition, and also induce cell wall-degrading extracellular enzymes as defense responses against plant pathogens. PGPR have the ability to induce the secretion of phytohormones, volatile compounds, antibiotics, and toxins which play an important role in plant growth. Rhizobacteria trigger N-acyl homoserine lactones (AHLs) like autoinducer molecules to regulate the gene expression as a part of quorum sensing. Other than these, plant growth-promoting rhizobacteria stimulate endogenous hormones of hosts to enhance stress tolerance. The mutualistic symbiosis triggers NOD factors and NOP effectors, while nonsymbiotic bacterial molecules enhance plant nutrient acquisition and growth. Here in this chapter, we have discussed and reviewed comprehensively the effectivity and mechanisms of plant growth-promoting rhizobacteria for enhancing crop productivity under different stress conditions.