Barak, E., Department of Environmental Biology, University of Guelph, Guelph, ON, NIG2WL, Canada, Lady Davis Trust, Jerusalem, Israel
Edgington, L.V., Department of Environmental Biology, University of Guelph, Guelph, ON, NIG2WL, Canada

Six isolates of Botrytis cinerea were studied for their cross-resistance to seven fungicides. Fungicide inhibition of mycelia growth followed the order: iprodione, chlorothalonil (EC50 0.2-8.5 fiM), captafol, thiram (1-18 JUM), captan, etem, and folpet (4-130 nM). Inhibition of spore germination usually required lower amounts of the chemicals but relatively similar concentrations were needed for all fungicides (ECJ0 0.06-1 juM), except for iprodione, which was ineffective at this stage of fungal development (ECJ0 40-370 /xM). Significant cross resistance among all isolates was demonstrated both for mycelia growth and spore germination with captan, folpet, captafol, etem, thiram and chlorothalonil. No cross resistance was observed with iprodione. It is suggested that cross resistance may be due to excessive production of thiols which detoxify the fungicides. Thus, if resistance develops against any one of these multisite fungicides, the others will also likely prove to be ineffective. © Taylor & Francis Group, LLC.