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 EC_(50) 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 EC_(50) value to the most sensitive isolate from Dingxing, Hebei.