In vitro selection of phosphate solubilizing strains of Trichoderma spp.

Abstract

Phosphorous (P) is considered to be the macronutrient with the lowest availability for plants in the majority of tropical soils, and is thus a limiting factor for vegetal growth. The application of Phosphoric Rock (PR) has been widely studied in order to satisfy its requirement in crops, but the quantity of liberated P is too low to satisfy demand. A viable alternative for managing this problem is the use of rhizospheric microorganisms that solubilize P (PSM) in chemically unavailable forms. In the search for microorganisms that solubilize phosphates, studies report that Trichoderma spp., in addition to their effects as pathogen biocontrollers, also exhibit phosphodissolvent capacities. The objective of this investigation was to evaluate in vitro strains of Trichoderma spp. isolated from rhizospheres of beans and corn with phosphate solubilizing abilities. Different strains of Trichoderma were isolated and selected from rhizospheric soil and rhizospheres. Three medium types were evaluated utilizing both solid and liquid media in order to determine their biometric characteristics, relative efficiency of solubilization of PR, bioacidulant capacity of the culture medium, and concentration of P in solution. In liquid media, these fungi were inoculated with and without PR, the quantity of soluble P was quantified, and the pH was taken. There were significant differences with respect to mycelial growth between solid media with and without the presence of PR, solubilization halos, and relative efficiency of solubilization in relation to incubation time. Liquid media with and without PR showed significant differences with respect to the quantity of soluble P. The pH of these media was inversely proportional to the quantity of soluble P, as the probable principle mechanism of dissolution of PR is the production of organic acids.