Similarities in the antifungal activities of fenpiclonil, iprodione and tolclofos-methyl against Botrytis cinerea and Fusarium nivale

Fenpiclonil [4‐(2,3‐dichlorophenyl)pyrrole‐3‐carbonitrile], a new agricultural fungicide, is a structural analogue of the antibiotic pyrrolnitrin used as an antimycotic in animals. Its spectrum of antifungal activity is similar to that of iprodione and tolclofos‐methyl, which are representatives of dicarboximide and aromatic hydrocarbon fungicides. Laboratory mutants of Botrytis cinerea and Fusarium nivale were simultaneously resistant to fenpiclonil, iprodione and tolclofos‐methyl and they showed an increased susceptibility to high osmotic pressure (sodium chloride, glucose). Strains of B. cinerea, collected in Champagne vineyards, which were resistant to dicarboximides were not resistant to fenpiclonil and tolclofos‐methyl. The antioxidant α‐tocopheryl acetate, and the cytochrome P‐450 inhibitors piperonyl butoxide and tebuconazole antagonized the fungitoxicity of fenpiclonil and iprodione in a wild‐type strain of B. cinerea. The uncoupling activity of fenpiclonil, iprodione and tolclofos‐methyl was detected in mitochondria from both a wild‐type strain and a laboratory mutant of B. cinerea. The concentrations effective towards this process were greater than those inhibiting the mycelial growth of wild‐type strains. These results suggest that fenpiclonil, iprodione, tolclofos‐methyl and related fungicides have the same biochemical mode of action. However, a primary effect on respiration, previously considered for pyrrolnitrin, seems to be improbable.