SBI-fungicides : fungicidal effectiveness and resistance in «Botrytis cinerea»

Abstract

In vitro fungitoxicity tests with 14 sterol biosynthesis inhibitors (SBIs) showed that the SBIs pyrifenox, flusilazol, propiconazole, triflumizole and fenpropimorph applied at the low concentration of 1 µg ml-1 inhibited the mycelial growth of wild-type and mutant strains of Botrytis cinerea that were resistant to the benzimidazoles, to the dicarboximides and to a mixture of benzimidazole+phenylcarbamate (carbendazim+diethofencarb). The SBIs tested exhibited higher effectiveness against the wild-type and mutant strains of B. cinerea compared with some widely used botryticides, such as the dicarboximides iprodione, procymidone and chlozolinate, the aromatic hydrocarbons quintozene, chloroneb and tolclofos-methyl, and the relatively new fungicides cyprodinil and fenhexamid. Only benomyl and fludioxonil presented higher effectiveness than the SBIs. In planta pot experiments with preventive applications of the commercial products Dorado 20 EC (pyrifenox), Punch 40 EC (flusilazol), Tilt 25 EC (propiconazole), Corbel 75 EC (fenpropimorph) and Trifmine 30 EC (triflumizole) showed that lesions of cucumber seedlings by all the abovementioned strains of B. cinerea were completely inhibited at low SBI concentrations of 0.05–0.1 g a.i. l-1. After chemical mutagenesis with N-methyl-N-nitro-N-nitrosoguanidine (MNNG), only strains with low resistance (Rf 6–9, based on MIC values) to triadimefon were isolated at a mutation frequency of 3.9 10-5. Cross-resistance studies with other SBIs showed that these triadimefon-resistant strains exhibited positive cross-resistance (Rf 2–10) to the other C-14 demethylase inhibitors (DMIs), but not to the morpholine fungicides fenpropimorph or tridemorph. Study of fitness of DMI-resistant strains showed that these mutation(s) were pleiotropic, with significant adverse effects on characteristics determining phytopathogenic fitness such as rate of mycelial growth, sporulation, conidial germination and pathogenicity on cucumber seedlings. The results indicate that some SBI-fungicides are suitable for use in resistance management programmes against grey mould.