Biology of Plasmopara viticola - Approach to a biological control of grapevine downy mildew

Plasmopara viticola, the causai agent of grapevine downy mildew is very well adapted to its host pianI. Therefore it is very difficult to develop methods for the biological control which meet the requests of ecological viticulture. One of the possibilities for a biological control of grapevine downy mildew is the usage of the natural resistance potential of the European cultivars of Vitis vinifera, more exactly the induced resistance. Another way is the use of specific inhibitors which either stop the infection process or have an effect on the interaction of the pathogen with the host pianI. Whereas generai information about the resistance reactions in plants is available and the first results were also won for vine, the knowledge about inhibitors is very scanty. The basic prerequisite to develop methods and strategies for the biological control of grapevine downy mildew is a comprehensive knowledge about the biology of P. viticola, especially so with respect to the interaction between pathogen and host. Since P. viticola is well adapted to the host plant, the development of biological methods is a scientific and technical challenge. P. viticola is indigenous in the south-eastern part of North America with a damp warm climate where it can be found on different autochtonous Vitis species. Due to the coevolution of the pathogen and the host a balanced relationship exists between the pathogen's virulence and the host's resistance. In contrast the European Vitis vinifera cultivars are highly susceptible for P. viticola; they have got in contact with the pathogen only 120 years ago and no adaptation has been developed in this short period of time. According to our hypothesis, a lack of a fast recognition of the pathogen results in a delayed resistance response of V. vinifera cultivars. The growth and development of P. viticola is \.ery fast on the host plant and reproduction as well as propagation potential is high. In addition, the growing conditions of grapevine, e.g. regional coverage of viticulture, dense canopy and humid climate, promote epidemic