Isolation and selection of solubilizing phosphate soil fungi native to Coahuila state, Mexico

Background and Aims: Phosphorus deficiency in crops is generally remediated through the application of fertilizers. However, this practice is costly and deteriorates the environment. The use of biofertilizers such as phosphate-solubilizing fungi is a promising alternative. The objective of the present study was to isolate and select native phosphate-solubilizing soil fungi from Coahuila state, Mexico, with potential to be used as biofertilizers. Methods: Fungal strains were isolated using the soil-particle washing technique. The selection of phosphate-solubilizing strains was performed in a Sundara medium with tricalcium phosphate, and phosphate-solubilizing capacity was visually detected based on the presence of hyaline halos. The qualitative evaluation was carried out by calculating the solubilization index. In the quantitative evaluation, the cultures were incubated for 25 days in liquid medium, and soluble P, pH, and fungal biomass were measured every five days. Key results: A total of 271 strains of fungi were isolated. Of these isolates, 52.76% tested positive for phosphate solubilization in the qualitative evaluation. With regard to solubilization efficiency, the values ranged from 2.06-6.85. The strains Sp. Mz54, Aspergillus sp. 4C19, Penicillium sp. Mu73, Penicillium sp. Mu77, and Penicillium sp. A56 presented the highest solubilization efficiency indices (t<0.005). In the quantitative evaluation, the strain Penicillium sp. Mu73 solubilized the highest quantity of phosphorus (83.26 mg l(-1)) (t<0.005). According to the regression analyses, the phosphorus concentration increased as the pH decreased (r(2) =0.81). Conclusions: The strain Penicillium sp. Mu73 has high potential for use as a biofertilizer because it solubilizes a high amount of phosphorus under in vitro conditions.