Treatment with succinate dehydrogenase inhibitor Y12196 protects strawberries from boscalid-resistant Botrytis cinerea with the H272R mutation in SDH B

Gray mold, caused by Botrytis cinerea, poses a significant threat to the strawberry industry worldwide. B. cinerea is a high-risk pathogen in the sense of fungicide resistance. The sensitivities of B. cinerea isolates collected from Zhejiang Province, China, to the succinate dehydrogenase inhibitors (SDHIs) boscalid and Y12196 were determined based on discriminatory dose or 50% effective concentration (EC50). Of the 42 isolates collected in 2018, 15 were resistant to boscalid (35.7%), and 3 were resistant to Y12196 (7.1%). Among the 84 isolates collected in 2019, the EC50 values for boscalid ranged from 0.097 to 54.162 mg/L, while the EC50 values for Y12196 ranged from 0.284 to 20.147 mg/L. Sequence analysis showed that the B. cinerea isolates carrying P225F (proline -> phenylalanine) and N230I (asparagine -> isoleucine) mutations in SDH subunit B exhibited cross-resistance between boscalid and Y12196. However, boscalid-resistant isolates with a point mutation at position 272 of SDH B (H272R, histidine -> arginine) were more sensitive to Y12196. Consistent with this, Y12196, but not boscalid, could successfully inhibit the growth of B. cinerea carrying the H272R mutation (BcSDH(B-H272R)) on detached strawberries and leaves. Molecular docking simulations further revealed that the hydrogen bonds and pi-pi interactions were formed between Y12196 and BcSDH(B-H272R), but not between boscalid and BcSDH(B-H272R), explaining why the boscalid-resistant B. cinerea H272R mutant isolates were sensitive to Y12196. Together, our results suggested that Y12196 could effectively control boscalid resistance associated with the H272R mutation.