Perspectives of Phosphate Solubilizing Microbes for Plant Growth Promotion, Especially Rice - A Review

Phosphorus (P) is the second (to nitrogen) important macronutrient, a constituent of the essential macromolecules like DNA, RNA, ATP, phospholipids etc., major repository of chemical energy and indispensable at all growth stages of plants including rice. The rice crop requires around 6.4 kg P2O5 (2.8 kg P) per ton of grain yield and at neutral pH, P availability is optimum. Phosphate solubilizing microbes viz. Bacillus, Pseudomonas, Azotobacter, Aspergillus spp. recycle the nutrients like N, P, C, K, S, Fe etc. and promote plant growth and development. Different endophytes like Rhizobium, Azospirillum, Pseudomonas spp., epiphytes like Rhizobium, Pantoea spp., rhizospheric organisms like Bacillus, Pseudomonas, Erwinia spp. and entomopathogens viz. Beauveria, Metarhizium, Nomuraea spp. mineralize insoluble P for P accessibility to plants. Soil enzymes also solubilize organic phosphates to available forms. Oxidation of glucose to gluconic acid, production of organic and inorganic acids, ammonia, H2S, etc. are major mechanisms for acid production and P mineralization by microbes. So, phosphate solubilizing microbes would be important biofertilizers as they promote plant growth, improve soil health and protect plants from different pathogens without affecting the environment. This has led to formulation and commercialization of several P-solubilizing microbial biofertilizers.