Molecular characterization of phosphate solubilizing fungi Aspergillus niger and its correlation to sustainable agriculture

Aim: The present study aimed to investigate the phosphate solubilization potential of agriculturally important fungi, i.e., Aspergillus sp. isolated from the rhizosphere of healthy plants in Abha city, SaudiArabia. Methodology: Sixteen Aspergillus sp. isolated and tested for phosphate solubilization potential were identified by 5.8S-ITS region sequencing and characterized by 11 ISSR-PCR markers. Finally, the highest phosphate solubilization potential isolates were used in field experiments on cucumber and tomato plants. Results: All Aspergillus niger isolates showed 96-100% similarity to A. niger strains available at GenBank database, Isolate ASAB-5 was most efficient at solubilizing phosphate on Pikovskaya's medium, with a solubilization index of 2.67, and 235.22 mg l(-1) of solubilized phosphate. ISSR-PCR markers revealed is total 142 bands in all isolates, with about 32.3% showing monomorphism and 67.6% polymorphism. Based on genetic similarity and intraspecies variability, the Aspergillus isolates were grouped into two different clusters with about 67.9% genetic similarity. The results of field experiments showed no significant difference between seeds treated with culture filtrate or conidial suspension of ASAB-5; however, both differed remarkably from untreated seeds. Interpretation: The current study confirms the existence of several useful phosphate solubilizing fungi in plants, which may serve as potential biological fertilizers. They are safer than chemical fertilizers and increase the bioavailability of soil phosphates for plants.