Osmotic sensitivity of fungal variants resistant to dicarboximide fungicides

Abstract

Fungicide-resistant variants of Botrytis cinerea, Penicillium expansum and Aspergillus nidulans were selected on media amended with the dicarboximide fungicide iprodione. A total of 58 were scored for osmotic sensitivity by comparing the extent to which their radial growth was inhibited by adding 0.68 m sodium chloride to the basal medium with that of their parents. The majority (49) were abnormally osmotically sensitive, but within this group there was no consistent relationship between degree of osmotic sensitivity and degree of fungicide resistance. The remaining nine osmotically insensitive variants were, however, all of only low fungicide resistance. The radial growth rates and conidiation of the resistant variants were very diverse, and bore no obvious relationship either to their degree of osmotic sensitivity or to their degree of fungicide resistance. Two of the A. nidulans variants were almost aconidial on basal medium, but conidiated abundantly on medium amended with iprodione. The correlation between osmotic sensitivity and dicarboximide resistance is discussed in relation to the infrequent occurrence, to date, of practical problems associated with dicarboximide resistance.