Pseudoperonospora cubensis in China: Its sensitivity to and control by oxathiapiprolin

Abstract The novel fungicide oxathiapiprolin has potential for the control of downy mildew of cucumber, which is caused by Pseudoperonospora cubensis . In this study, an in vitro bioassay with detached leaves was used to determine the baseline sensitivity to oxathiapiprolin for 77 Ps . cubensis isolates from 11 provinces in China. The baseline sensitivity curve was continuous, and the average EC 50 value was 2.23 × 10 −4  μg ml −1 . In field trials, the control of downy mildew of cucumber was greater with oxathiapiprolin at 20 or 30 g a.i. ha −1 than with dimethomorph at 262.5 g a.i. ha −1 . Oxathiapiprolin was taken up by cucumber roots and transported upwards to stems and leaves. The full length of PscORP1 , the gene that encodes the target protein of oxathiapiprolin in Ps . cubensis , was sequenced for the first time. Our results suggested that oxathiapiprolin will be an excellent alternative fungicide for control of cucumber downy mildew. However, as Ps . cubensis is a high-risk pathogen, resistance development to oxathiapiprolin should be monitored and managed.