Chapter 11 - Role of plant growth–promoting rhizobacteria in sustainable agriculture

Abstract

The changing environmental conditions have created an immense pressure on the plants, due to various biotic (pests and diseases) and abiotic stresses (salinity, drought etc.). Many plants of commercial importance are grown in monoculture and require amendments to get proper growth and yield, as well as to provide protection against biotic and abiotic stresses. To combat with these stresses, plant growth–promoting rhizobacteria (PGPR) present in the rhizosphere play a crucial role. They promote the plant growth by providing nutrients, hormones, and other plant growth substances. The carbon-rich root exudates provide nutrients to the microbes present in the rhizosphere. PGPR possess diverse functions such as symbiosis, nitrogen fixation, phosphate solubilization, etc. They include different strains of the genera, among which Bacillus and Pseudomonas spp. are extensively studied due to the production of a wide spectrum of antibiotics, efficient rhizosphere colonization, and potential to control soil-borne pathogens. PGPR are having the ability to protect plants from various diseases and pests by inducing systemic resistance (ISR). Beneficial rhizobacteria mainly secrete antibiotics such as lipopeptides, polyketides, and antifungal metabolites antagonistic to plant pathogens and lead to the accumulation of phenolic compounds, phytoalexins, and activation of defense enzymes/genes to provide resistance against pests. Among the abiotic stresses, aridity stress imparted by drought, high temperature, and salinity is the most prominent abiotic stress limiting plant growth and productivity. This can be mitigated through exopolysaccharides producing rhizobacterial strains. Rhizobacteria also decrease the fertilizer input and promote plant growth by solubilizing the fixed nutrients and by providing the hormones and other growth-promoting substances.