Study on fungicide resistance of Pseudoperonospora cubensis to azoxystrobin

Azoxystrobin is a strobilurin fungicide, it has a broad antimicrobial spectrum and high activity, but at the same time the agent also runs the risk of becoming a resistance agent. In order to understand the resistance of the cucumber downy mildew's(Pseudoperonospora cubensis) sensitivity to azoxystrobin, 36 cucumber downy mildew isolates were tested using the leaf disk floating method.The isolates were collected from 13 production areas over eight provinces: Heilongjiang, Jilin, Liaoning,Beijing, Shandong, Jiangsu, Hubei and Guangdong. EC50 of Pseudoperonospora cubensis to azoxystrobin was 0.0107-0.2408 μg· m L- 1and the average EC50 was 0.1004 μg· m L- 1. Of the 36 strains, 26 had a medium level of resistance, nine had low resistance, one was sensitive and none were highly resistant. The resistance level of Shandong Province strains to azoxystrobin was the highest and the resistance levels of other provinces' resistant strains to azoxystrobin were relatively low.