Reduced Sensitivity to Sterol-Inhibiting Fungicides in Field Isolates ofVenturia inaequalis

Abstract

For eight sterol-inhibiting fungicides, minimal inhibitory concentrations for preventing colony formation by individual conidia were four to eight times higher for isolates of Venturia inaequalis from one West German orchard [apple] than for isolates from either a second West German orchard or orchards in the United States. Reduced activity was exhibited to BAS 454 06 F (1-(2,4-dichlorophenyl)-2-(1H-1,2-triazol-1-yl)), bitertanol, CGA 71818 (1-[2-(2,4-dichlorophenyl)-pentyl]-1H-1,2,4-triazole), DPX H6573 (bis(4-fluorophenyl)methyl(1H-1,2,4-triazol-1-yl methyl)silane), etaconazole, fenarimol, Ro 15-1297 (1-(2,4-dichlorophenyl)-2-(3-pyridinyl)-ethanone O-methyloxime), and triflumizole. Isolates with reduced senstivity to sterol inhibitors did not show increased sensitivity to dodine. Genetic analysis of nine isolates with reduced sensitivity indicated that reduced sensitivity was determined by a single gene.