Bioassays for Induction of Dicarboximide Fungicide-Resistance with Filtrate of the Resistant Strains of Botrytis cinerea

Abstract

Induction of dicarboximide fungicide-resistance by pre-culturing in the filtrates of the field resistant strains (IHES-2 and CAES-4) of Botrytis cinerea was examined by two bioassay methods. In the protoplast bioassay method, the regeneration frequencies of the mycelial protoplasts of the sensitive strain (IPCR-1) pre-treated with IHES-2 and CAES-4 filtrates, respectively, were 2.7 and 2.4% on the medium containing the fungicide, which were about tenfold higher than that by pre-treatment with IPCR-1 filtrate. In another method, IPCR-1 conidia were shaking-cultured in IHES-2 and CAES-4 filtrates for 3 days, respectively, and each of the conidia was harvested as a mycelial ball like structure (MBS). The MBSs pre-cultured in these filtrates formed the colonies about three times as many as those with IPCR-1 filtrate. From the two different bioassays, the induction of dicarboximide fungicide-resistance with the filtrates of the resistant strains was confirmed. Especially, MBS bioassay method may be a useful one for bioassays of filamentous fungi, in which it is hard to statistically detect the effects of physiologically active substances because of the morphogenic changes in the growth cycle.