Effect of pH on the in vitro growth of ectomycorrhizal fungi collected from Pinus radiata plantations

Abstract

In this study, the effect of the pH on the in vitro growth of the ectomycorrhizal fungi Rhizopogon luteolus, Suillus bellinii and Suillus luteus, collected from Pinus radiata was evaluated. The fungal cultures were grown on solid BAF (Biotin-Aneurin-Folic acid agar) medium with pH adjusted to 4.8, 5.8, 6.8 and 7.8 and incubated for 32 days at 24±1 ºC. During the incubation, the radial growth rate (mm/day) was determined and the area of the colonies (cm2) and the pH changes of the media were also determined at the end of incubation period. The results showed that a variation of pH from 4.8 to 7.8 affected significantly the growth rate and the final area of colonies of R. luteolus and S. luteus. For R. luteolus: the highest rate of growth and colony area occurred at pH 5.8 and 6.8; while for S. luteus, the highest growth rate and colony area were observed at pH 4.8 and 5.8, respectively. When the changes in the pH cultures at the end of incubation period were investigated, it was observed that all fungal species reduced the pH of the media acidifying it in a lesser or larger extent, being this effect more intense for the cultures with higher initial pH. These results suggest that the pH of culture medium is determinant of the in vitro behaviour of the ectomycorrhizal fungal species. This is very important for the selection of new ectomycorrhizal species for large-scale inoculum production for application in programs of plant mycorrhization in forest nurseries.