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Phosphate Solubilizing Microorganisms - Some bacteria, e.g., Thiobacillus, Bacillus, etc., convert nonavailable inorganic phosphorus present in soil into an available form utilizable by crop plants. These bacteria also produce iron chelating substances, called siderophores, which chelate the iron present in the root zone.

As a result, this iron becomes nonavailable to harmful microorganisms and, in this manner, crop plants are protected from them. In addition, certain fungi, e.g., Glomus, etc., form associations with plants roots; these are called mycorrhiza.

The fungus may be located at the root surface (ectomycorrhiza) or it may be present inside the roots (endomycorrhiza). These fungi convert nonavailable phosphorus into an available form, produce growth promoting substances and also protect against soil pathogens.

These microorganisms are yet to be exploited on a commercial scale. An example of commercial application of mycorrhizal fungi is found in Citrus in U.S.A.; seedlings are inoculated with the fungus in nurseries before being transplanted into the field.

Seedlings that are inoculated with mycorrhizal fungi, called AMF (arbuscular mycorrhizal fungi) survive better after transplanting (often mortality may be reduced to zero or near zero) and grow faster. AMF are being exploited gainfully in India for establishing trees and other plants on lands that are deficient in nutrients, e.g., wastelands or degraded lands, and on flyash overburdened sites.
Even in case of crops like vegetables and flowers, use of AMF can increase yields by about 30-50%. AMF are mass-produced in association with roots of potted plants, roots of plants grown in aquaculture (soil less culture), and roots cultured in vito.