Resistance Risk and Resistance-Related Point Mutations in Target Protein Cyt b of the Quinone Inside Inhibitor Amisulbrom in Phytophthora litchii

Amisulbrom is a novel quinone inside inhibitor, which exhibits excellent inhibitory activity against phytopathogenic oomycetes. However, the resistance risk and mechanism of amisulbrom in Phytophthora litchii are rarely reported. In this study, the sensitivity of 147 P. litchii isolates to amisulbrom was determined, with an average EC50 of 0.24 +/- 0.11 mu g/mL. The fitness of resistant mutants, obtained by fungicide adaption, was significantly lower than that of the parental isolates in vitro. Cross-resistance was detected between amisulbrom and cyazofamid. Amisulbrom could not inhibit the cytochrome bc1 complex activity with H15Y and G30E + F220L point mutations in cytochrome b (Cyt b) in vitro. Molecular docking indicated that the H15Y or G30E point mutation can decrease the binding energy between amisulbrom and P. litchii Cyt b. In conclusion, P. litchii might have a medium resistance risk to amisulbrom, and a novel point mutation H15Y or G30E in Cyt b could cause high amisulbrom resistance in P. litchii.

Automated summary

This study found that the broad-spectrum fungicide Amisulbrom exhibited excellent inhibitory activity against the grass armyworm, but the resistance risk and mechanism in the grass armyworm are rarely reported. The sensitivity of 147 grass armyworm isolates to Amisulbrom was determined, with an average EC50 of 0.24 +/- 0.11 mu g/mL. Resistance mutants obtained through fungicide adaption showed significantly lower fitness than the parental isolates in vitro. Cross-resistance was detected between Amisulbrom and Cyazofamid. In vitro studies showed that Amisulbrom could not inhibit the cytochrome bc1 complex activity with H15Y and G30E + F220L point mutations in cytochrome b (Cyt b). Molecular docking indicated that the H15Y or G30E point mutation can decrease the binding energy between Amisulbrom and grass armyworm Cyt b. In conclusion, the grass armyworm may have a medium resistance risk to Amisulbrom, and a novel point mutation H15Y or G30E in Cyt b could cause high resistance to Amisulbrom in the grass armyworm.