BIOLOGICAL MODE OF ACTION OF SOIL-APPLIED FLUTRIAFOL IN CONTROLLING TAKE-ALL OF WHEAT

The mode of action of flutriafol (a sterol-inhibiting, triazole fungicide) against Gaeumannomyces graminis var. tritici (causal agent of take-all of wheat) was investigated with agar plate tests, soil sandwich experiments and pot experiments to determine the effect of the fungicide on growth of the fungus on agar, in soil and on disease, respectively. All fungicide concentrations generally reduced growth of G. graminis on agar but pathogenicity remained unaffected. Flutriafol reduced saprophytic growth of the fungus through unsterilised soil at concentrations equivalent to 200 and 2000 g a.i. ha-1, but only at 2000 g a.i. ha-1 in autoclaved soil. At 200 g a.i. ha-1 it also reduced survival of the fungus in colonised oat grains. Take-all was reduced by all fungicide concentrations in unsterilised soil, but only by 2000 g a.i. ha-1 in autoclaved soil, and excluding this concentration, < 1-mu-g g-1 flutriafol was detected in the plant roots. Control of take-all with flutriafol appears to be achieved by a protective effect, the fungicide reducing saprophytic survival and growth of G. graminis and not by a therapeutic effect resulting from uptake of the fungicide by the host.