Siderophore mediated phosphate solubilization and promotion of nodulation in legumes

Abstract Phosphate is an essential nutrient for plant development present in unavailable form. Its solubilization in soil is mediated by several mechanisms. The biological way to solubilize complex phosphate salts is by the help of microbes. Paraburkholderia sp. igkv1 isolated from soil is a potent phosphate solubilizing bacterium. It showed phosphate solubilization up to 1.71 µgml⁻ ¹dayl⁻ ¹ and acid hydrolase activity of 1406 µg pnp released g⁻ ¹ soil. It also improved nodulation by 1.9-folds and 3-folds in pigeonpea and chickpea respectively when inoculated with Bradyrhizobium sp. BRP2. To ascertain the role of metabolites in improving nodulation a series of experiments were conducted under controlled condition and field conditions. Organic acids and siderophore mediated phosphate solubilization were performed in the present study and it was found that 600 mg/l siderophore solubilized insoluble phosphate upto 176µgml⁻ ¹ invitro. Under controlled condition, siderophore (1mM) increased 2.4-folds nodulation in chickpea as compared to organic acids. A detailed characterization of siderophore was carried out that revealed presence of a unique chromophore hydroquinidine in siderophore. Succinic acid increased the siderophore level up to 139 mg/l in liquid culture (y = 0.6178x + 63.779). Siderophore solubilized different phosphate salts in the order Ca₃(PO₄)₂>FePO₄ > AlPO₄. Under field condition varied concentration of siderophore resulted in significant increase in the grain yield of soybean by 1.63-folds. Study suggest that PSB can enhance both P and N use efficiency of crops through secretion of siderophore.