2022 Volume 2022 Issue 73 Pages 76-80
In 2018, approximately 80% of the apple cultivation areas in Hokkaido were affected by apple scabs. Furthermore, in 2017, DMI-resistant strains of Venturia inaequalis were found in Japan. Therefore, we investigated the sensitivity of V. inaequalis in Hokkaido to DMI. Eighty-two isolates were collected from the apple orchards in Hokkaido. We conducted culture medium tests for difenoconazole and fenarimol sensitivity, and the half maximal effective concentration (EC50) values were calculated. In addition, allele-specific polymerase chain reaction (PCR; Yaegashi et al. 2020) was used to detect the Y133F substitution on all isolates. Allele-specific PCR confirmed that approximately 80% of all isolates had the Y133F substitution. The culture medium tests showed that the EC50 values were higher for isolates with the Y133F substitution than those without this substitution. When the isolates were inoculated and sprayed with difenoconazole and fenarimol fungicides, the fungicides showed effects on the isolates without the Y133F substitution but not on those with the Y133F substitution. Thus, we found that DMI-resistant strains of V. inaequalis were present in Hokkaido.
