Effect of pesticides on ectomycorrhizae ofPinus sylvestris seedlings

Summary Knowledge of the effect of pesticides on the formation of forest tree mycorrhizae is important as pesticides are nowadays used in forestry. The effect of the fungicide Dithane M-45 and the herbicide Gramoxone on the growth ofPinus sylvestris L. seedlings and on the development of their mycorrhizae was studied. Investigations involved seedlings inoculated with pure cultures of mycorrhizal fungi in flasks with perlite under aseptic conditions, in Mitscherlich pots filled with perlite under semi-aseptic conditions, and on peat substrate in outdoor beds. No change in seedling growth and the mycorrhiza formation occurred when water suspension of the fungicide Dithane M-45 was used at the recommended dose. The highest rates of this fungicide had no phytotoxic effect although the growth of treated seedlings was reduced due to complete or partial inhibition of mycorrhizal formation. In contrast, even low doses of Gramoxone reduced the growth of the inoculated and non-inoculated seedlings which were more sensitive than their mycorrhizal fungi. The soil sterilization of outdoor beds with an application of a water suspension of Dithane M-45 at recommended doses reduced mycorrhizal development and seedling growth. Seedlings inoculated simultaneously with pure cultures ofSuillus granulatus showed a slightly better growth than untreated controls.