OSCAR, a national observatory to support the durable deployment of disease-resistant grapevine cultivars

The cultivation of disease-resistant grapevine cultivars makes it possible to reduce considerably the number of pesticide treatments applied in viticulture. The recent, but increasingly widespread deployment of these cultivars raises several important issues. The first concerns the qualitative potential of the cultivars and their marketing. The second issue is more generally important and concerns the management of durability of resistance. Several cases of erosion or breakdown of resistance have already been reported in Europe. The evolution of pathogen populations targeted by varietal resistance should therefore be closely monitored, to ensure that grapevine resistance remains effective in the long term. Another key issue is the design of the cropping system, which should be adapted to resistant cultivars so as to maintain production objectives, promote the durability of resistance and minimize the use of pesticides. INRA has set up the National Observatory for the Deployment of Resistant Cultivars (OSCAR; http://observatoire-cepages-resistants.fr) to meet these challenges. OSCAR is a participative network based on plots in production situations planted by growers. The participative dimension of the network promotes the sharing of experiences relating to agronomic behavior, the potential for mechanization, ease of cultivation and wine quality. This observatory also monitors the emergence of new diseases or of virulent strains. Powdery and downy mildew (diseases targeted by varietal resistance) isolates are collected and tested under laboratory conditions, to monitor changes in population aggressiveness. We present here the first results obtained for the 34 plots of OSCAR monitored in 2017. This observatory is currently being extended to a larger number of plots in France and other European countries. The data obtained will be fed into mathematical models to determine the effects of deployment strategies and landscape features on the epidemiological dynamics of resistance erosion.