Reduced sensitivity to carbendazim in isolates of <i>Botrytis allii</i>

Abstract

Fifty isolates of Botrytis allii causing onion botrytis neck rot were obtained from onion seed and bulbs throughout New Zealand and tested for their sensitivity to carbendazim (benzimidazole) fungicide in a mycelial growth study Agar plates amended with carbendazim at 6 or 8 different concentrations were inoculated with an 8 mm disc of mycelium of each of the isolates and incubated in the dark at 20C Radial growth of the colonies was measured after 4 days EC₅₀ (effective concentration required to give half of maximum growth) values were estimated by fitting logistic curves with growth as a proportion of the maximum growth Of the 50 isolates 16 were identified as resistant 32 as sensitive and two had a variable response The estimated EC₅₀ values for the isolates that were sensitive ranged from 0006 to 0053 g/ml active ingredient It is recommended that New Zealand onion growers closely follow the current benzimidazole resistance management strategy