Özet:

Phosphorus is one of the major plant nutrients limiting plant growth. Available P is generally not sufficient maximum crop yields because most P in soils exists in insoluble forms. A large portion of inorganic phosphates applied to soil as fertilizer is rapidly immobilized after application and becomes unavailable to plants. Large quantities of chemical fertilizes are used to replenish soil N and P, resulting in high costs and severe environmental contamination. In agriculture, it is important to make full use of microorganisms in order to reduce the use of chemical fertilizers as much as possible. Increasing and extending the role of biyofertilizers would reduce the need for chemical fertilizers and decrease adverse environmental effects. Several bacte-ria may also solubilize inorganic phosphate, making soil phosphorus other wise remaining fixed available to the plants due to excretion of organic acids and through other mechanisms. The principal mechanism for mineral phosphate solubilization is the production of organic acids, and acid phosphatases play a major role in the mineralization of organic phosphorous in soil. The success of biofertilizer inoculum depennds various factors such as quality of inoclum, crops and cultivars, temperature, moisture regimes, soil composition, inoculation and application technique, available of the utilizable substrates and level of fertilization. This reviev has shown that there is huge potential for use of PGPR as biofertilizing agents for a wide variety of crop plants in a wide range of climatic and edaphic conditions. In particularly, researches must be investigate the phytohor-mone production by PGPR, production of enzymes which decrease phytohormone productionoby the host, root development and morphology resulting in greater root surface area for the absorption of nutrients or enhance host-symbiont relationships.

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