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<p>Apple scab, caused by <i>Venturia inaequalis</i>, is a major apple disease, primarily managed through repeated applications of site-specific fungicides. To assess the current resistance status in Japan, the sensitivity of 1234&#xa0;<i>V.</i><i> inaequalis</i> isolates collected from commercial apple orchards between 2018 and 2025 to five fungicide classes (methyl benzimidazole carbamates [MBCs], quinone outside inhibitors [QoIs], demethylation inhibitors [DMIs], anilinopyrimidines [APs], and succinate dehydrogenase inhibitors [SDHIs]) was comprehensively evaluated using agar-based sensitivity assays, bioassays, and molecular diagnostics. Resistance to MBC, QoI, DMI, and AP fungicides was widespread; however, SDHI resistance was not detected. All isolates were resistant to MBC fungicides, with the predominant E198A mutation in the <i>β-tubulin</i> gene. The QoI resistance-associated G143A mutation in the <i>cytochrome b</i> gene was detected in 77.5% of isolates, indicating fixation of complete resistance in the population. Approximately 75% of the isolates exhibited the Y133F mutation in <i>CYP51A1</i>, which is associated with reduced sensitivity to DMI fungicides. Sensitivity assays for the AP fungicide cyprodinil revealed broadened EC₅₀ distribution, and bioassays demonstrated partial reduction in control efficacy against isolates exhibiting reduced sensitivity. This represents the first report of AP resistance in <i>V. inaequalis</i> in Japan. By contrast, SDHI fungicides showed unimodal EC₅₀ distributions and no resistance-associated amino acid substitutions in <i>sdhB</i>, <i>sdhC</i>, or <i>sdhD</i>. Multiple-fungicide resistance was prevalent, with many isolates resistant to three (57.7%) or four (10.5%) fungicide classes. These results indicate that chemical control alone is becoming increasingly ineffective, emphasizing the need for integrated disease management strategies for sustainable apple scab control.</p>

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Sensitivity to major fungicide classes and occurrence of multiple fungicide resistance in Venturia inaequalis populations in Japan

  • 期刊论文

  • 发表日期：

    2026年7月8日

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  • Kazuyuki Hirayama

摘要

Apple scab, caused by Venturia inaequalis, is a major apple disease, primarily managed through repeated applications of site-specific fungicides. To assess the current resistance status in Japan, the sensitivity of 1234 V. inaequalis isolates collected from commercial apple orchards between 2018 and 2025 to five fungicide classes (methyl benzimidazole carbamates [MBCs], quinone outside inhibitors [QoIs], demethylation inhibitors [DMIs], anilinopyrimidines [APs], and succinate dehydrogenase inhibitors [SDHIs]) was comprehensively evaluated using agar-based sensitivity assays, bioassays, and molecular diagnostics. Resistance to MBC, QoI, DMI, and AP fungicides was widespread; however, SDHI resistance was not detected. All isolates were resistant to MBC fungicides, with the predominant E198A mutation in the β-tubulin gene. The QoI resistance-associated G143A mutation in the cytochrome b gene was detected in 77.5% of isolates, indicating fixation of complete resistance in the population. Approximately 75% of the isolates exhibited the Y133F mutation in CYP51A1, which is associated with reduced sensitivity to DMI fungicides. Sensitivity assays for the AP fungicide cyprodinil revealed broadened EC₅₀ distribution, and bioassays demonstrated partial reduction in control efficacy against isolates exhibiting reduced sensitivity. This represents the first report of AP resistance in V. inaequalis in Japan. By contrast, SDHI fungicides showed unimodal EC₅₀ distributions and no resistance-associated amino acid substitutions in sdhB, sdhC, or sdhD. Multiple-fungicide resistance was prevalent, with many isolates resistant to three (57.7%) or four (10.5%) fungicide classes. These results indicate that chemical control alone is becoming increasingly ineffective, emphasizing the need for integrated disease management strategies for sustainable apple scab control.