Legume Plant Growth-Promoting Rhizobacteria (PGPRs): Role in Soil Sustainability

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The interactions of plants with different microorganisms in the rhizosphere have varied effects on plant health, productivity, and soil fertility. Numerous types of bacteria play certain vital roles in agriculture production systems by way of establishing different types of relationships that are commonly called as plant growth-promoting rhizobacteria (PGPRs). These PGPRs have multiple roles that have positive impact on plant physiological activities and defense mechanism against biotic and abiotic stresses. Such effects may include symbiotic and asymbiotic N fixation and mobilization; production of siderophores, phytohormones, and antibiotics; counteracting the effect on various pathogenic fungi; solubilization of soil phosphate; and production of growth-promoting indole acetic acid (IAA). Besides, under various stress situations (such as drought, salinity, and metal toxicity), these PGPRs not only halt the deleterious effects of such stresses but also make the plant grow and develop normally. PGPRs through production of ACC (1-aminocyclopropane-1-carboxylate) deaminase can successfully deter the detrimental stress effect of ethylene, enabling the plants to grow normally by alleviating the harmful effect of this. The toxic effects of higher concentration of heavy metals can also be counteracted through PGPRs. These favorable microorganisms reduce the chemical load in rhizosphere and also have multiple synergistic effects on the plant growth and efficacy of other microorganism. Recently, PGPRs have become the most important tool for use as biofertilizers because they provide sustainability of agroecosystems. As the understanding of these PGPRs is increasing, it has become quite evident that apart from legumes, these are also contributing cereals and other nonlegume host crops in a variety of ways. Eco-friendly PGPRs have now become a very important supplement for agriculture production and soil health with involvement of minimal cost. In the light of this background, various aspects of PGPRs biotechnology with special reference to legumes are reviewed and discussed in this chapter.