Efficacy of Carpropamid Against Mutants of Magnaporthe Grisea at Codon 75 on Scytalone Dehydratase

In 2001, Pyricularia oryzae isolates, showing reduced sensitivity to scytalone dehydratase inhibitors, were collected from the Matsuura river area in Saga prefecture, Japan. A single-point mutation causing substitution of one amino acid in scytalone dehydratase was found in those isolates. However, the blast control efficacy of carpropamid in the field has not been completely lost in the area where the mutant isolate is dominant. The results of inoculation tests suggest that enhancement of host defense responses, the other mode-of-action of carpropamid, may contribute to the residual efficacy of carpropamid against the mutants.