A comparative study of fungicide sensitivity assays

Abstract: Fungal pathogens are able to develop resistance against most single-site fungicides such as the dicarboximides and the anilinopyrimidines when used exclusively on highly susceptible cultivars with inadequate cultural practices to support control. It was therefore imperative to assay the sensitivity of Western Cape Botrytis cinerea populations to iprodione and pyrimethanil. Traditional methods of fungicide sensitivity testing involves measuring mycelial growth and conidial germination on plates, but these methods are expensive and time consuming, leaving prospects for more rapid methods of fungicide sensitivity monitoring. This study made comparative use of two microassays, namely a microtiter test and a microbioassay. For the microtiter test, conidia from B. cinerea were challenged in 96 well microtiter plates with different concentrations of iprodione and pyrimethanil. Conidial germination was read with a microplate photometer (microtiter plate reader). For the microbioassays, conidiospores of B. cinerea were incubated on glass slides containing fungicide amended media of equal concentrations used in the microtiter tests and the germ tube lengths were measured. Data resulting from these two methods were compared to determine possible disparity between methods. This forms part of a larger study to establish a rapid fungicide sensitivity monitoring system for the South African pome fruit industry.