Co-application of Difenoconazole with Thymol Results in Suppression of a Parastagonospora Nodorum Mutant Strain Resistant to this Triazole

Abstract

Results of in vitro study of thymol, a natural chemosensitizer, as a potential agent for overcoming of difenoconazole resistance of Parastagonospora nodorum causing glume and leaf blotch of wheat are first reported. The level of difenoconazole resistance of a natural mutant PNm1 strain with low sensitivity to the Dividend fungicide (a.i. difenoconazole) was determined by the cultivation of this isolate on potato dextrose agar in the presence of the fungicide at sub-lethal and lethal (in relation to the initial fungicide-sensitive strain) concentrations. A principal possibility of the thymol use to overcome resistance of P. nodorum to DMI (demethylation inhibitors) fungicides is shown. Co-application of this compound with Dividend SC, 3 % resulted in a significant reduction of resistance of the mutant strain and enhancement of its sensitivity to difenoconazole up to the level corresponding to the initial non-resistant isolate.