Study on the Sensitive Baseline of Pseudoperonospora cubensis to the Strobilurin Fungicide Azoxystrobin

Nineteen isolates of Pseudoperonospora cubensis were sampled from different regions in which the strobilurin fungicide had never been used. The toxicity of azoxystrobin to P. cubensis was assayed with leaf disk floating method. The EC50 values were in the range of 11.72×10-5~9.340×10-3 μg/mL, the sensitive baseline of P. cubensis to a strobilurin fungicide, azoxy-strobin, was determined as 2.317×10-4 μg/mL based on the mean EC50 value to the most sensitive isolate from Dingxing, Hebei.