Isolation and evaluation of plant growth-promoting characteristics of phosphate solubilizing fungi from Iranian soils

The application of phosphate solubilizing fungi (PSF) is a biological and eco-friendly method to increase phosphorus availability from insoluble sources. The aim of this study was to obtain PSFs that can be used as biological agent in order to increase soil phosphorus and improve plant growth. Initially, 144 PSFs isolates were isolated from the soil of corn fields (0-30 cm) in Fars, Kermanshah, and Khorasan Razavi provinces, Iran. Among them, 27 isolates showed the maximum solubilizing ability of tricalcium phosphate (TCP). Based on molecular analysis, different genera were identified as Aspergillus (7.5%), Talaromyces (44.4%), Penicillium (44.4%) and Cladophialophora (3.7%). This is the first report of Cladophialophora as mineral phosphorus solubilizing agent. The maximum phosphate solubilizing ability in solid media was represented by Talaromayces pinophilus strain MFA (hallo to colony diameter is 4.11 mm), whereas this ability was manifested by Talaromayces verruculosus strain PF 157-2 (23.8 mg/l), Talaromayces pinophilus strain MFA (20.7 mg/l), Aspergillus tubingensis strain PF 140-2 (20.50 mg/l) and Talaromayces pinophilus strain FB (20.04 mg/l) in liquid media respectively. Aspergillus tubingensis strain PF 140-2 and Talaromayces pinophilus strain 1FB showed the maximum auxin (9.2 mg/l) and siderophore (ratio of halo zone diameter to colony diameter: 4.44 mm) production ability respectively. The maximum amount of hydrogen cyanide (grade 4) was produced by Penicillium oxalicum strain PF 83-1. These results confirmed that PSF especially Talaromayces pinophilus strain MFA, Talaromayces verruculosus strain PF 157-2, Aspergillus tubingensis strain PF 140-2 and Talaromayces pinophilus strain 1FB can be introduced as biological agents which could increase soil phosphorus availability and improve plant growth.