Isolation and characterization of potassium solubilizing <i>Aspergillus</i> species isolated from saxum habitats and their effect on maize growth in different soil types
Raji Muthuraja, Thangavelu Muthukumar
Abstract
Potassium (K) is an important nutrient for plant growth. However, less than 2% of K in the soil exists in plant-available forms. Further, fungi inhabiting saxicolous habitats are infrequently examined for their plant growth-promoting ability. Therefore, in this study, we isolated K solubilizing fungi (KSF) from saxicolous habitats and screened them for their ability to produce plant growth hormones, organic acids, and siderophore that may facilitate plant growth. Seventy-two saxicolous fungal isolates were screened for their K solubilization in Aleksandrow medium amended with mica. Of these, eight potential KSF isolates resembling Aspergillus species based on 18S rRNA gene sequencing were selected for further screening. Three of these KSF isolates KSF-07 (Aspergillus terreus), KSF-55 (Aspergillus niger), and KSF-69 (Aspergillus violaceofuscus) produced different organic acids (ascorbic, acetic, benzoic, citric, malic, and oxalic acid), indole acetic acid (0.678–46.326 µg L−1), and siderophore (46.66–65.26 PSU) under in vitro conditions. The three Aspergillus species solubilized 56.56−59.80 mg L−1 of K from mica and 33.97–39.19 mg L−1 from potassium aluminum silicate. Inoculation of KSF and mica amendment significantly improved plant growth and K uptake by maize and also enhanced the KSF populations in post-harvest soil. Pearson's correlation analysis revealed the existence of a significant negative correlation between soil pH and available K. Among the KSF isolates screened, A. violaceofuscus (KSF-69) presents an excellent prospect as a bio-inoculant for improving crop growth in different soil types.