Sensitivity And Resistance Risk Assessment Of Phytophthora Capsici Leonian To Azoxystrobin

Azoxystrobin, developed by Syngenta (Zeneca) company, was the first product of the strobilurin fungicides. It combines high level and broad-spectrum of fungicidal activity with excellent safety in the environment. Strobilurin fungicides inhibit mitochondrial respiration in fungi at a specific site on complex III and break energy synthesization of fungi. Strobilurins were called QoI as they combined with Qo part of Cyt b. This kind of fungicide was widely used because of their novel action mechanism and non-cross-resistance with . However, the frequency of spontaneous resistant mutation was high according to several research reports. It's easy to form resistant-population in high fungicidal selection pressure.Pepper blight (Phytophthora capsici Leonian) is one of the most serious diseases on China pepper produce. Aimed to control the popularity of pepper blight, fungicidal workers are searching new fungicides for the widely resistance to traditional Oomycete-fungicides occurred in field. So, it is essential to embark on sensitivity and resistance risk assessment of Phytophthora capsici Leonian to Azoxystrobin.48 single-sporangia isolates of Phytophthora capsici, causing capsicum epidemic disease, were collected and separated from Nanjing, Jiangsu Province and Hexian, Anhui Province where QOIs and Qils had not been used previously. Sensitivities of different morpha of P. capsici life cycle to azoxystrobin were determined. Mycelial growth of P. capsici was least affected by azoxystrobin, with mean EC50 value 21.041 ± 14.397 μg/mL ranging from 1.225 to 86.1 μg/mL. Activity of azoxystrobin EC50 was lower than that of metalaxyl 47.7 times. The mean EC50 values of the azoxystrobin inhibiting sporangia formation and germination of P. capsici were 0.161 ±0.126 μg/mL and 0.155±0.023 μg/mL ranging from 0.006 to 0.996 μg/mL and 0.053 to 0.334 μg/mL, respectively. Its activity was 516.8 folds as that of metalaxyl. Germination of encysted zoospores of P. capsici was most sensitive to azoxystrobin, and EC50 distributed from 0.018 to 0.111 μg/mLwith mean value 0.057±0.011 μg/mL. This value was 142.4 times lower than that of metalaxyl.Mutants UV-17 and H4-V3 of Phytophthora capsici Leonian were gained by...