Current status of Xanthomonas ampelina in Spain and susceptibility of Spanish cultivars to bacterial necrosis1

The causal agent of bacterial necrosis of vine, Xanthomonas ampelina, was first recorded in Spain in 1978 on grapevines in the region of Zaragoza, where the total infested area is now around 9000 ha. The disease was later recorded in Rioja where small foci of around 50 ha were found, and in Galicia, where it exists in the area of Ribeiro and Pontevedra. Surveys done in other grapevine-growing areas of the country have not led to the detection of the disease. The symptoms described in Spain are the same as those in other countries and bacterial necrosis has not, at present, been identified on table grapes. Losses resulting from the disease are closely linked to climatic conditions and the drought of these last few years has practically eliminated symptoms of X. ampelina in Aragon and the area of Rioja. Chemical control of the disease through the use of cupric formulations is not sufficient during rainy years with favourable conditions, and the best method for preventing the disease seems to be the use of resistant cultivars or those displaying weak susceptibility. A 3-year experimental field study of the varietal susceptibility of 30 Spanish cultivars has shown that Airén, Garnacha tintorera, Juan Ibáñez and Vidadillo are the most susceptible. Cardinal, Garnacha negra, Mazuela, Merseguera, Monastrell and Trepat are the least susceptible of all the cultivars studied. A parallel study of the susceptibility of plants grown in vitro has been undertaken and may be useful for rapid testing of varietal susceptibility.