Sensitivity of Pseudoperonospora cubensis to dimethomorph, metalaxyl and fosetyl-aluminium in Shanxi of China.

摘要

Cucumber downy mildew, caused by the fungal pathogen Pseudoperonospora cubensis, is a devastating disease in Shanxi Province, China. Fungicides dimethomorph, metalaxyl and fosetyl-aluminium have been used in the disease management. In this study, 143 isolates of P. cubensis were collected from different geographic locations of Shanxi, and examined for their corresponding sensitivities to these fungicides using the leaf disc bioassay method. The EC 50 values of the isolates to dimethomorph, metalaxyl and fosetyl-aluminium ranged from 0.0006 to 5.85 g/ml (mean=1.01 g/ml, SD=1.27), 0.0869 to >500.00 g/ml (mean=85.97 g/ml, SD=95.61 for the range of 0.0869-458.10 g/ml) and 0.0066-114.50 g/ml (mean=7.89 g/ml, SD=15.33), respectively. Over 80% isolates showed the EC 50 values to dimethomorph <2.0 g/ml. This study is the first to report high levels of resistance to metalaxyl in P. cubensis populations in Shanxi Province, and seven isolates were found to be extremely high resistant with EC 50 values >500 g/ml. The most P. cubensis isolates showed a normal distribution of EC 50 range between 0 and 18 g/ml to fosetyl-aluminium, and a few high resistant isolates were found. No cross-resistance was found between any fungicides used in this study. The concept of resistance index (RI) was used to determine the resistance level to each fungicide for sub-population of the pathogen in each district of Shanxi Province.