Activity and Point Mutation G699V in PcoORP1 Confer Resistance to Oxathiapiprolin in Phytophthora colocasiae Field Isolates

The oxysterol-binding protein inhibitor oxathiapiprolin is a new fungicide for controlling oomycetes diseases. Besides, laboratory mutagenesis oxathiapiprolin-resistance among phytopathogenic oomycetes in the field remains unknown. Here, the sensitivity of 97 P. colocasiae isolates to oxathiapiprolin was examined that were collected between 2011 and 2016. We obtained a baseline sensitivity with a mean EC50 value of 5.2639 x 10-4 mu g mL-1. We showed that 6/32 isolates collected in Fujian Province from 2019 to 2020 were resistant to oxathiapiprolin without a significant fitness penalty on sporulation, vegetative growth, and virulence of the field isolates. The oxathiapiprolin resistance field isolates contained the point mutation glycine to valine at 699 in PcoORP1. The point mutation G699V was verified to confer resistance of P. colocasiae to oxathiapiprolin using the CRISPR/Cas9 system. The mutation G699V decreased the binding affinity between oxathiapiprolin and PcoORP1. These results will improve our understanding of the mechanism of P. colocasiae resistance to oxathiapiprolin under field conditions.

Automated summary

In this study, the sensitivity of 97 P. colocasiae isolates to the fungicide oxathiapiprolin was examined. It was found that 6 out of 32 isolates collected in the field showed resistance to oxathiapiprolin, and the resistance was associated with a point mutation in the PcoORP1 gene. The mutation was verified to confer resistance using the CRISPR/Cas9 system.