Isolation and characterization of rhizomicrobial isolates for phosphate solubilization and indole acetic acid production

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Recently, public concerns regarding the use of agrochemicals have increased due to the environmental impacts and potential risks to human health. The application of beneficial microorganisms is a novel technology to improve plant health and productivity and has therefore been extensively studied as an alternative strategy for biocontrol. In our study, 122 microbial isolates were obtained from the rhizosphere of Panax ginseng and subsequently tested in vitro for phosphate solubilization and indole acetic acid (IAA) production. Pikovskaya’s medium was used to estimate rhizomicrobial isolates to solubilize tricalcium phosphate [Ca3 (PO4)2]. Among all the investigated strains, 82 % of rhizospheric fungi showed phosphate solubilization activity; however, only 57.1 % of the rhizobacteria isolates showed phosphate solubilization ability. For IAA production, 64.7 % of the tested rhizofungi isolates were able to produce the phytohormone; however, only 47.62 % of the rhizobacteria isolates exhibited IAA production. Among all investigated species, Pseudomonas fluorescence and Azotobacter chroococcum showed the highest phosphate solubility demonstrating 885.4 and 863.4 μg mL−1, respectively. Mucor sp. produced 42.3 μg mL−1 of IAA in Czapek’s tryptophan medium, and the highest fungal species to solubilize the inorganic phosphate (237.5 μg mL−1) was estimated by Penicillium sp. Rhizobacteria were more effective than rhizofungi in phosphate solubilization and IAA production. This study introduces some potent species in terms of phosphate solubilization and IAA production which could be likely to improve soils’ quality and promote plant growth.