Characterization of Native Phosphorus Solubilizing Fungal Species and Development of a Phosphorous Biofertilizer Formulation for Rice Cultivation

Inoculation of plants with phosphate solubilizing microorganisms (PSM) is a promising strategy to improve plant absorption of phosphorus (P) and thereby to reduce the usage of chemical P fertilizer. However, in Sri Lankan context, only a limited number of P biofertilizers has been identified. The objective of the study was to develop a low-cost P biofertilizer for rice cultivation in the low country wet zone. A phosphate solubilizing fungal isolate (Bentota isolate) isolated from rice rhizosphere was used to develop the P biofertilizer and the fungus was identified as Penicillium oxalicum through DNA sequencing. P solubilization ability of the fungus was tested in Pikovskaya’s Broth Medium. Phosphate content released to the culture medium by P. oxalicum after seven days of incubation was 402.43 μg mL^-1. A low-cost growth medium with rice husks and rice seeds as the main ingredients was developed for mass multiplication of P. oxalicum was able to produce a sufficient colony count and survived up to 4 months in the growth medium maintaining a final population size of 22.7 x 10⁸ CFU g^-1 at room temperature and 33.5 × 10⁸ CFU g^-1 at 8 °C without losing the P solubilizing ability. The efficacy of the P biofertilizer was evaluated under field condition. Results revealed that the bioferlizer can reduce chemical P fertilizer usage by 50% without a yield reduction and can be used as alternative P fertilizer for rice cultivation in the Low Country Wet Zone in Sri Lanka.