Process of rock phosphate solubilization by Aspergillus sp PS 104 in soil amended medium.

Aspergillus sp PS 104, a soil isolate had excellent potential to solubilize rock phosphate in vitro. The process was influenced by the presence of various concentrations of local loess (red soil). The simultaneous occurrence, in our experiment, of high levels of solubilized phosphate and synthesized citric acid, together with the lowest reached pH values, confirmed the role of citric acid in the phosphate solubilization mechanism. When the soil was present, phosphate release was better correlated than citrate synthesis with H+ concentration. Changes in soluble phosphate concentration did not follow a sigmoid pattern. The ability of organism to release phosphatase was also studied. An interesting relationship was observed between the two processes of phosphate mobilization: citric acid synthesis and phosphatase production.

Rhizobia as a biological control agent against soil borne plant pathogenic fungi.

Rhizobia promote the growth of plants either directly through N2 fixation, supply of nutrients, synthesis of phytohormones and solubilization of minerals, or indirectly as a biocontrol agent by inhibiting the growth of pathogens. The biocontrol effect of rhizobia is due to the secretion of secondary metabolites such as antibiotics and HCN. Siderophore production in iron stress conditions provides rhizobia an added advantage, resulting in exclusion of pathogens due to iron starvation.