FUNGICIDE BIODEGRADATION BY ECTOMYCORRHIZAL FUNGI.

Tarja Laatikainen & Helvi Heinonen-Tanski, Department of Environmental Sciences, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland. (tlaatika@messi.uku.fi)

Chlorothalonil and propiconazole are commonly used fungicides for seedling protection at forest nurseries in Finland. Chlorothalonil is used against Scleroderris canker (Gremmeniella abietina) and Pine needle blight fungus (Lophodermium seditiosum) and it is applied as soon as seedlings are taken out from greenhouse, and these treatments are repeated in 3 weeks intervals to late autumn. Propiconazole is used against Scleroderris canker and the mouldiness (Phacidium infestans, etc.) during overwinter cold storage and it is applied to seedlings at late autumn before snow covering. Total amount of applied chlorothalonil and propiconazole in every growth period can be up to 10 kg/ha (a.i.) and 0.5 kg/ha (a.i.), respectively, or even more. Therefore, there can be cumulative amounts of both fungicides in containers where these seedlings are growing. Unknown amounts of these fungicides can also be washed off through containers into forest nursery soil by rain and when snow is smelting.

The capability of ectomycorrhizal fungi of forest trees to degrade chlorothalonil and propiconazole was studied with liquid pure culture tests. The fungi used were Amanita muscaria (2 strains), Hebeloma spp., Paxillus involutus and Suillus bovinus. The 5 % v/v inoculum was grown in 100 ml liquid 2-strength MN-solution in glass flasks. The culture flasks were incubated at room temperature in a dark and they were manually shaken daily. After one week there was visible amount of mycelium in each culture flask and at that time a fungicide at the concentration of 0.1 ppm or 1 ppm was applied into the flasks. Experiments were carried out in triplicate. The first samples of mycelia were taken one week after and the sampling was repeated three times at the interval of a week, except A. muscaria samples applied with propiconazole which were taken up to six times. The samples were filtered through glass filter with vacuum and then freeze-dried for ergosterol measurements. Ergosterol is main sterol in most fungi and it is an important cell wall component present only in alive fungal cells. Therefore, ergosterol content will indicate the amount of alive fungal cells from total fungal mass.

In principal, ergosterol content of mycelia decreased with time, except in control and propiconazole groups of A. muscaria which grew slower than other tested fungi and their ergosterol contents, i.e. fungal growth, were still increasing after four weeks. Chlorothalonil treatment of 1 ppm exterminated A. muscaria already at the beginning and there were no detection of ergosterol at all. In general, both fungicides decreased amount of total fungal mass (and ergosterol content) compared to control groups. The growth of one strain of A. muscaria was slightly enhanced by propiconazole at the concentration of 1 ppm as well as the growth of P. involutus by chlorothalonil at the concentration of 0.1 ppm.

Biodegradation of chlorothalonil and propiconazole will be discussed later.