A Multi-aspect Comparative Investigation on the Use of Strobilurin and Triazole - based Fungicides for Winter Wheat Disease Control

Fungicides continue to be essential for the effective control of plant diseases. The azoles class of fungicides has been the leading agents for the control of fungal pathogens of plants since their introduction in the mid 1970s. This class of fungicides is also called sterol demethylation inhibitors (DMIs) because they inhibit the formation of cytochrome P450 sterol 14 alpha-demethylase (450 14DM), an enzyme required for the biosynthesis of ergosterol. Ergosterol is an important compound required for fungal membrane integrity and cell cycle progression (Dahl et al., 1987). DMIs represent one of the largest groups of systemic fungicides that have been used to control agriculturally important fungal pathogens (Zhan et al., 2006). In the mid 1980s, the first DMIs fungicide propiconazole has been investigated and introduced in the agronomic practice of Lithuania for winter wheat disease control (Šurkus et al., 1988) and currently 10 DMIs active substances alone or in mixtures are registered for cereal disease control. In spite of their long-term use, a widespread resistance to azoles in plant pathogenic fungi has not occurred. The shift to decreasing sensitivity propiconazole to Phaeosphaeria nodorum the causal agent of Stagonospora blotch of wheat has been reported since 1994 (Peever et al, 1994) although until 1994 only minor changes in the sensitivity of Mycosphaerella graminicola populations – c.a. Septoria leaf blotch, to DMIs fungicides in European countries was confirmed (Turner et al., 1996). The slightly resistant field isolates were not cross-resistant to the DMI fungicides, which act at a different stage of sterol biosynthesis (Hollomon, 1994). Sometimes the crossresistance is only partial. Whilst cross-resistance extends to all DMIs (Gisi et al., 2004) a recent rapid decline in the efficacy of some DMIs fungicides in controlling powdery mildew and Septoria leaf blotch of wheat has been noted. Some fungicides, notably epoxyconazole and prothioconazole, are still very effective in controlling M. graminicola (Cools & Fraaije, 2008). In the beginning of 90s a new class of fungicides, generated on the basis of the fungus Strobilurus tenacellus secondary metabolites was developed (Ammermann et al., 1992; De Vleeschauwer et al., 1996). Strobilurins, with a chemistry based on a natural product from a mushroom, are fungicide of new generation and proved to be quite effective, protective, eradicant and potential broad-spectrum substances against foliar diseases of winter wheat.