The most important plant species employed in reforestation programs depend on ectomycorrhizal fungi for their establishment and growth. The exploitation of this symbiosis to improve forest productivity requires fungal inoculants in a large scale level. To develop such a technology it is necessary to define the optimal composition of the culture medium for each fungus. With these objectives in mind, the effect of the composition of the culture medium on biomass production of the ectomycorrhizal fungus Pisolithus microcarpus (isolate UFSC-Pt116) was studied. The original composition of two culture media, already employed for cultivation of ectomycorrhizal fungi, was submitted to several variations with the C/N ratio as the main variable. A variation of the Pridham-Gottlieb medium was the most efficient for the production of biomass. Therefore, it was submitted to a factorial assay where glucose, peptone and yeast extract components were the factors analyzed. Results showed that the glucose concentration may be increased up to 40 % in order to promote higher biomass production. Peptone had a positive effect on this variable, whereas yeast extract promoted a deleterious effect. These results indicate that it is advisable to eliminate yeast extract from the medium and replace it with peptone prior to use.

The utilization of rocks as fertilizers is limited by their low solubility. However, solubilization may be achieved by some micro-organisms, such as ectomycorrhizal fungi (ECMf). The aim of this study was to evaluate the potential of seven isolates of ECMf to solubilize two rocks, alkaline breccia and granite, and to liberate potassium and phosphorus for Eucalyptus dunnii seedlings under greenhouse conditions. Fungal inoculants were produced in a peat-vermiculite-liquid medium mixture and added to the planting substrate at 10 %. Rocks were ground up and added at 0.500 mg and 16.0 mg per plant, as a source of phosphorus and potassium, respectively. Other nutrients were added and E. dunnii seeds were sown. Control plants, non-inoculated, were fertilized with the same amount of phosphorus and potassium using soluble forms. After 90 days, the plant height, shoot dry weight, root length, phosphorus and potassium contents, and mycorrhizal colonization were evaluated. Alkaline breccia was more efficient than granite as a source of phosphorus and potassium for the plants, and may be an alternative to conventional fertilizers. Isolates UFSC-Pt22 (Pisolithus sp.) and UFSC-Pt186 (Pisolithus microcarpus) were the most efficient in promoting plant growth, mainly when combined with alkaline breccia to replace potassium and phosphorus fertilizers, respectively.