Effects of Herbicides on in vitro Growth of Mycorrhizae of Pine (Pinus spp.)

Abstract

Effects of various herbicides on growth of ectotropic mycorrhizal fungi were determined over a 3-week period on modified Melin-Norcrans agar amended with the herbicides at rates of 0, 1, 3, 5, 10, 40, 80, 100, and 500 μg active ingredients/ml. Considerable variation in effect was observed among the herbicides for certain fungi and among the fungi for certain herbicides. All of the test fungi grew in the presence of each of the test herbicides at a rate of 80 μg/ml, and some growth was observed at the 500 μdg/ml rate in a majority of the herbicide-fungus combinations. Significant decreases (P = 0.05) in growth were observed for specific herbicide-fungus combinations at herbicide rates of 1 and 3 μg/ml; however, 50% or greater decreases in fungal colony areas were observed in only 12 of 112 of the combinations at such low rates. The herbicides, in decreasing order of activity against the fungi, were: diphenylethers > dinitroanilines > s-triazines > substituted amides > perfluidone [1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide]. With few exceptions, the herbicide concentrations necessary to affect fungal growth significantly were considerably higher than would be expected to occur in soil treated with the test herbicides at recommended application rates.