The effects of glyphosate on the in vitro linear growth of selected microfungi from a boreal forest soil.

Glyphosate-based herbicides are used extensively in forestry and agriculture to control broadleaf plant competition. A review of the literature offers conflicting results regarding the impact of glyphosate on fungal growth. This study investigated the effects of 7 glyphosate concentrations (1, 2, 5, 10, 50, 100, and 1000 microg*mL-1) of Roundup (35.6% glyphosate) on the number of colony-forming units (CFUs) of soilborne microfungi from a boreal forest soil sample and on the in vitro linear growth of 20 selected species of microfungi representative of this boreal forest soil. Concentrations of glyphosate at 50 microg*mL-1 and higher significantly decreased the number of CFUs observed. At glyphosate concentrations equal to 5 microg*mL-1, 13 fungal species exhibited colony diameters less than 50% than that of their respective controls. Several species showed an inhibition of pigmentation and sporulation when subjected to glyphosate concentrations of 1 microg*mL-1. Differential sensitivity was observed among species at the various concentrations, suggesting the possibility of a shift towards tolerant species of fungi when they are exposed to glyphosate.