A survey of resistance to the dicarboximide fungicides inBotrytis cinerea

Abstract

Isolates of Botrytis cinerea Pers.: Fr. collected from a range of crops in New Zealand, were tested for resistance to the dicarboximide fungicides by measuring radial growth on agar media amended with iprodione. In addition, each isolate was tested for resistance to the benzimidazole fungicides, by growing on medium amended with carbendazim, and for sensitivity to high osmotic pressure, by growing on medium amended with 0.68 M NaCl. In outdoor crops (grape, kiwifruit, strawberry, boysenberry) dicarboximide-resistant strains were found on only 2 of the 18 properties examined, one a vineyard and the other a strawberry planting. In neither instance was any loss of disease control apparent. No dicarboximide resistance was found on the single glasshouse grape property sampled, but on glasshouse vegetable crops (tomato, French bean, cucumber) dicarboximide resistance was found on all 7 properties. In these vegetable houses resistant strains were often predominant and in some instances there appeared to be a loss of disease control. In total, 150 of the 649 isolates tested were dicarboximide-resistant. They were all of low-level resistance (EC", for radial growth 100 mg/litre) and with only one exception, all were abnormally sensitive to high osmotic pressure. Some other physiological properties of a subsample of isolates representing all fungicide response types (dicarboximide-sensitive or -resistant and benzimidazole-sensitive or -resistant) were examined. Strains resistant to iprodione were cross-resistant to dichlozolinate, procymidone, vinclozolin, and dicloran. Dicarboximide-resistant strains did not differ, as a group, from sensitive strains in radial growth rate, sporulation, or sclerotial production. It is suggested that the presence of low-level dicarboximide-resistant strains in a crop may lead to a loss of fungicide efficacy and hence to a loss of disease control when conditions are conducive to development of B. cinerea.