Abstract
Most soils contain large reserves of total phosphorus (P), but its fixation and precipitation with soil constituents cause a major P-deficiency and severely restrict the growth and yield of plants. The use of chemical P-fertilizers is obviously the best means to circumvent P-deficiency, but their use is always limited due to its spiraling cost. In order to increase the availability of P and to reduce the use of chemical fertilizers, solubilization of insoluble P by phosphate-solubilizing microorganisms has provided an alternative to chemical phosphatic fertilizer. Besides P, these organisms promote the growth of plants by N2 fixation, enhancement of other plant nutrients, synthesizing phytohormones, suppressing plant diseases (bio-control) and reducing the toxicity of ethylene through 1-aminocyclopropane-1carboxylate (ACC) deaminase. In this chapter, attention is paid to understanding the fundamental and molecular basis as to how precisely these microbes, notably bacteria and fungi, help plants to grow better in P-deficient soils. Effective use of such microbes is likely to result in an ideal cropping system with a lesser impact on the environment through decreased application of chemical fertilizers.