Role of Phosphate-Solubilizing Bacteria in Legume Improvement

Abstract

Microbial communities inhabiting soil or rhizosphere play important roles in growth and development of plants. Of these, phosphate-solubilizing bacteria (PSB) play fundamental roles in biogeochemical phosphorus cycling in agro-ecosystems. Phosphate-solubilizing microbes transform the insoluble phosphorus to soluble forms by acidification, chelation, exchange reactions, and polymeric substances formation. The use of phosphate-solubilizing microbes in agronomic practices helps not only to offset the high cost of phosphatic fertilizers but also to mobilize insoluble phosphorus in the fertilizers and soils to which they are applied. And hence, application of such naturally occurring organisms possessing multiple growth-promoting activities hold greater promise for increasing the productivity of crops including legumes. Another agronomically promising organism is rhizobia which are known exclusively for its ability to form symbiosis with legumes and enrich nitrogen pool of soil, can also facilitate plant growth by synthesizing plant growth regulators and solubilizing insoluble phosphorus besides providing nitrogen to plants. In addition, under low nitrogen fertilizer inputs, availability of phosphorus is a major factor restricting the rate of N-2-fixation in legumes. The combined inoculation of N-2-fixers, PSB, and mycorrhizal fungi could be more effective than single organism for providing a more balanced nutrition for legume plants under conditions of reduced nutrient inputs. In this chapter, the strategic and applied research conducted so far to understand as to how PSB along with other symbionts enhance nutrient availability to legumes and concomitantly improve yield are reviewed and discussed. The application of synergically interacting yet phylogenetically diverse microbes is likely to help sustaining the legume productivity in different agricultural production systems.