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 EC 50 value of 5.2639 × 10 -4 μg 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.