Diversity of the Phosphate Solubilizing Fungi (PSFs) Population from the Soybeans Rhizosphere in the Noun Valley, Western Highlands of Cameroon

Abstract

Soil beneficial microorganisms like bacteria and fungi play a key role on soil properties, nutrients availability and fertility. Phosphate solubilizing fungi (PSFs) in plants rhizosphere have the ability to convert insoluble organic and inorganic phosphate into soluble form and make the phosphorus available to the plants. Many soils in West and North-West of Cameroon lack soluble phosphate for plants growth, development and productivity. The main objective of this study was to evaluate the diversity of phosphate solubilizing fungi under the soybean’s rhizosphere in the Noun Valley, Western Highlands of Cameroon. Fifteen soybeans rhizosphere samples were randomly collected in five localities of the Noun Valley, and analyzed. Fungi isolation was done by serial dilution plate method on nutrient agar plates (PDA) amended with antibiotic, and PSF selection were done on Pikovskaya’s agar (PVK) media. The phosphate (P) solubilization efficiency was done on PVK broth and modified Pikovskaya’s broth amended with Al(PO4). Functional activities such as metabolites and enzymes production ability were assessing. Fungi diversity was done through macroscopic and microscopic features observation, (colony colors, mycelia shape, growth and sporulation rate, mycelia branching pattern and spores’ organization). From 178 isolates obtained from the fifteen sampling sites, 148 strains grouped in four genera (Rhizopus spp., Aspergillus spp., Penicillium spp. and Trichoderma spp.) and 15 fungi species, showed phosphate solubilization ability. The solubilization efficiency (SE) and P-released were done at temperature range of 25°C- 30°C and at pH range of 6-7. The SE ranged between 96. 59% and 15.7% on agar media while the amount of P released in broths ranged from 15.45 to 2.64 mg/L depending on isolates, the broth and the incubation time. Among these, Rhizopus sp. (15.45mg/L) showed the highest solubilization efficiency, followed by Aspergillus sp., Trichoderma sp. and Penicillium sp. With 13.46 mg/L, 12.03 mg/L and 9.19 mg/L respectively. The entire PSF were able to produce organic acid and showed cellulose hydrolysis activity. Therefore, these fungi species from soybeans rhizosphere are potential PSF for the solid and liquid formulation of PSF based-biofertilizers.