Rock phosphate solubilization by the ectomycorrhizal fungus <I>Laccaria fraterna</I> and its associated mycorrhizal helper bacterial strains

Abstract

Phosphorus (P) is mostly present in the form of insoluble phosphates in soil and so plants cannot utilize it. Plant roots are often associated with mycorrhizal fungi and other microorganisms that effectively can absorb P and other elements from the soil. In the present study, few mycorrhizal helper bacterial (MHB) strains such as Pseudomonas putida, Erwinia herbicola and Bacillus subtilis were isolated and identified from surface sterilized basidiomata and mycorrhizosphere of an ectomycorrhizal fungus Laccaria fraterna association with Eucalyptus globu­lus. To evaluate phosphate solubilization of the fungus and its MHB strains, they were grown on rock phosphate (RP) and tricalcium phosphate as sole P sources in Pikovskaya’s liquid medium. The fungus and its MHB showed varying levels of phosphate solubilization activity in the presence of different carbon and nitrogen sources. These fungus and MHB had the potential to solubilize these phosphates by decreasing the pH and confirmed that phosphate solubilization is accompanied by acid production. Thus, the evidence that fungus and MHB strains do convert insoluble phosphates such as RP into soluble forms, may not only replace expensive phosphorous fertilizer in agriculture field but also lead to better mobilization of the fertilizers added to soils.

Keywords: Ectomycorrhizal fungi, Laccaria fraterna, mycorrhizal helper bacteria, phosphate solubilization, rock phosphate.

African Journal of Biotechnology, Vol 13(25) 2524-2530