Activity of zoxamide against European isolates of Phytophthora infestans

摘要

Zoxamide is a single-site inhibiting non-systemic fungicide recently registered in Europe for the control of potato late blight. Potato leaf discs sprayed with a range of zoxamide concentrations were used to test the sensitivities of Phytophthora infestans isolates never exposed to zoxamide and of isolates obtained from European field trials in nine countries (1997-2000). Isolates varied in sensitivity with mmnrniTp. inhibitory concentration values from 0.5 to >20 mg/litre. Sensitivity of isolates was not affected by zoxamide treatment and was unrelated to phenylamide resistance. Selected isolates exhibiting a range of in vivo sensitivities were tested in vitro using poisoned agar plates; all proved very sensitive (EC_(50) values 12-88 mu g zoxamide/litre). A scanning microscopy study showed that on the potato leaf surface zoxamide acts after germination, inhibiting further development of hyphae and preventing production of sporangiophores and sporangia.