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Updated: Jan 9, 2026
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Published on: September 28, 2021
Effect of isofetamid on SDHI-resistant isolates of Botrytis cinerea
Yuzuka Abe1, Yoshitake Desaki1, Nanami Kuwahara1
1Central Research Institute, Ishihara Sangyo Kaisha, Ltd.
Abstract:
Tests of sensitivity to isofetamid conducted with Botrytis cinerea isolated from Hokkaido (2011-2016) and other districts in Japan (2017-2018) revealed the absence of isolates with reduced sensitivity. Isolates of B. cinerea 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 in vitro and in vivo conditions.
Insights
Isofetamid remains effective against Botrytis cinerea, showing no reduced sensitivity in recent Japanese isolates. While some mutations confer resistance to other succinate dehydrogenase inhibitors (SDHIs), these mutations do not affect isofetamid sensitivity, though specific mutations can cause resistance.
Area of Science:
- Agricultural Science
- Plant Pathology
- Mycology
Background:
- Botrytis cinerea is a significant plant pathogen causing gray mold disease.
- Succinate dehydrogenase inhibitors (SDHIs) are crucial fungicides for controlling B. cinerea.
- Monitoring fungicide resistance in plant pathogens is essential for sustainable agriculture.
Purpose of the Study:
- To assess the sensitivity of Botrytis cinerea isolates to isofetamid.
- To investigate the impact of specific SDHI resistance mutations on isofetamid sensitivity.
- To evaluate the fitness of isofetamid-resistant B. cinerea isolates.
Main Methods:
- Fungicide sensitivity testing of B. cinerea isolates from Japan and Germany.
- Molecular analysis of sdhB gene mutations (H272Y/R, P225F, H272L).
- Competitive assays under in vitro and in vivo conditions.
Main Results:
- No reduced sensitivity to isofetamid was observed in Japanese B. cinerea isolates (2011-2018).
- SDHIs resistance mutations (H272Y/R) did not confer cross-resistance to isofetamid.
- Specific mutations (P225F, H272L) caused moderate to high resistance to isofetamid.
- Resistant isolates exhibited reduced fitness, disappearing in competitive assays.
Conclusions:
- Isofetamid maintains efficacy against B. cinerea, even in isolates resistant to other SDHIs.
- Specific mutations conferring isofetamid resistance also reduce fungal fitness.
- Isofetamid is a valuable tool for managing B. cinerea, with resistance development unlikely to be rapid.
