Resistance of Pseudoperonospora cubensis to flumorph on cucumber in plastic houses |
| |
Authors: | S S Zhu X L Liu Y Wang † X H Wu P F Liu J Q Li S K Yuan N G Si |
| |
Institution: | Department of Plant Pathology, College of Agronomy and Biotechnology, China Agricultural University, Beijing 100094;;Center of Agrochemicals for Biological and Environmental Technology, Institute for the Control of Agrochemicals, Ministry of Agriculture, Beijing 100026;and;Shenyang Research Institute of Chemical Industry of China, Shenyang 110021, China |
| |
Abstract: | Plastic-house experiments were conducted over a 2-year period (2004–05) to estimate the effects of successive applications of flumorph or a mixture of flumorph with mancozeb to cucumber plants on selection for flumorph resistance in the downy mildew oomycete, Pseudoperonospora cubensis . Application of flumorph alone favoured the selection of resistant isolates of Ps. cubensis . Resistant populations were detected at a frequency of 2·5% after six successive applications of flumorph alone in a plastic house in 2004. Resistant isolates were also detected (4·8%) after eight successive applications of the mixture of flumorph and mancozeb in 2004, although the mixture gave significantly better disease control than flumorph alone and produced a slight delay in the development of resistance. In a second cucumber crop in the same plastic houses in 2004, the frequency of resistant isolates increased to 100% after three successive applications of flumorph or four of flumorph + mancozeb. Under laboratory conditions, most flumorph-resistant isolates showed high levels of resistance and their levels of pathogenicity and sporulation were as high as that of wild-type isolates. Flumorph showed cross-resistance with dimethomorph and iprovalicarb, but not with azoxystrobin, cyazofamid, cymoxanil or metalaxyl. These studies suggest a high risk for the occurrence of resistance to flumorph in Ps. cubensis in cucumber crops under plastic-house conditions. |
| |
Keywords: | baseline fungicide sensitivity CAA fungicides cucumber downy mildew Cucumis sativus fungicide resistance |
|
|