Insight of Mechanism of Action of Plant Growth Promoting Rhizobia in Leguminous Crops: A Review

Abstract

World demand for food supply is burgeoning day by day and the need of the hour is to escalate yield per unit area per unit time. Nevertheless, to meet such enormous demand for food, inclination toward inorganic fertilizers has bolstered. It would not only be exorbitant but could grievously degrade the environment through climate change or via contamination of water bodies. There is a need to look for surrogate tactics for climate-resilient agriculture. The microorganisms particularly those that reside in the rhizosphere can play a pertinent role in ameliorating yield without having any detrimental effect on the environment. These organisms are called plant growth-promoting rhizobacteria (PGPR); these can be ePGPR or iPGPR depending on their location whether inside the host plant or outside the host plant. Further, Plant growth promoting rhizobia can play a significant role in improving soil health and enhancing yield through their symbiotic association with legume plants via biological nitrogen fixation (BNF), phosphate solubilization, phytohormone production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity or siderophore production. In the neoteric era, a myriad liquid or charcoal carrier-based formulations of PGPR as microbial inoculants are accessible in the market. However, liquid formulations of microbial inoculants have specific advantages over charcoal-based formulations. Furthermore, dual inoculation or amalgamation of microbial inoculants has a synergistic effect on individuals in crop production. Wherefore, this review will provide a concise account of legume-rhizobial symbiosis, various mechanisms of action of microbes associated with legumes in addition to BNF, the benefits of liquid microbial inoculants and the significance of co-inoculation of symbiotic and other microbial inoculants. The realization attained from the present review herein will further help the fellow scientist to conceive better research ideas keeping in view the multifaceted characteristics of rhizobia.