Differential sensitivity to fungicides in Czech populations of Pseudoperonospora cubensis

摘要

During the growing seasons of 2001 and 2002, 42 isolates of Pseudoperonospora cubensis were collected from nine regions of Czech Republic and screened for tolerance or resistance to fungicides. The effectiveness of three frequently used fungicides (Previcur 607 SL /propamocarb/, Aliette 80 WP /fosetyl-Al/, Ridomil Plus 48 /metalaxyl/) was tested at five concentrations, using a floating disc bioassay. Fungicide effectiveness varied considerably. Propamocarb was the most effective as all isolates weresensitive to all concentrations (607-9712 mu g a.i./ml). Fosetyl-Al was also effective, as most isolates were controlled by the optimal concentration (1600 ug a.i./ml). However, the occurrence of isolates collected in 2001 that sporulated at low concentrations (400 and 800 mu g a.i./ml) of this fungicide could indicate that selection for tolerance is occurring in the population, but this was not re-observed on the P. cubensis isolates collected in 2002. Metalaxyl was ineffective, as 93% of the isolatesshowed resistance to the optimal concentration (200 mu g a.i./ml) of this fungicide, and the other 7% of isolates were tolerant. Profuse and/or limited spo-rulation of 88% of the isolates was also observed on 400 and 800 ug a.i./ml solutions, i.e. concentrations 2x and 4x times higher than optimal. A substantial shift to highly resistant strains was evident in the Czech P. cubensis population in 2001 and 2002.