Effect of isofetamid on SDHI-resistant isolates of <i>Botrytis cinerea</i>

Tests of sensitivity to isofetamid conducted with <i>Botrytis cinerea</i> isolated from Hokkaido (2011-2016) and other districts in Japan (2017-2018) revealed the absence of isolates with reduced sensitivity. Isolates of <i>B. cinerea</i> with mutation H272Y/R in sdhB, collected in Germany and Japan, resulted in high and moderate resistance to boscalid and many other succinate dehydrogenase inhibitors (SDHIs), respectively. However, these isolates were as sensitive as wild-type isolate to isofetamid. In contrast, isolate BC-50 [P225F] and BC-49 [H272L] caused moderate to high resistance to isofetamid. Considerable differences in mycelial growth, conidiation, conidial germination, and pathogenicity were not observed between these resistant isolates and sensitive isolates. A competitive assay between resistant isolate BC-50 [P225F] and BC-49 [H272L] and B05.10 [wild type], however, revealed the disappearance of resistant isolates after several generations of mixed incubation in <i>in vitro</i> and <i>in vivo</i> conditions.