Flavescence Doreé (FD) is a chronic grapevine yellow disease that leads to the decline of grapevine, especially noble grapevine (Vitis vinifera L.). Grapevine yellow is caused by the quarantine phytoplasma of the subgroups16S rRNA V-C in V-D. Phytoplasma is transmitted by the vector American grapevine leafhopper (Scaphoideus titanus Ball), by feeding on vines. The most common symptoms of FD on infected plants are the curling of vine leaves downwards, yellowing of leaves at white and reddening of leaves at red varieties and discoloration of leaf surfaces and leaf veins, the leaves are fragile and when they fall, the stalk remains on the vine, there is dropping of clusters, the yield is reduced and with lower quality. In Slovenia, FD symptoms are visible after the infection from the beginning of July and thus gradually become more pronounced towards autumn. The disease inhibits conductivity and growth of phloem and xylem tissues, which are responsible for the transfer of organic and inorganic substances and water to plants. Smaller vessels form in places where the tissue is not conductive. There is a lack of periderm, an accumulation of lipids in the chloroplasts of the leaf parenchyma, the absence of corky cambium and a lack of lignin. The yield is reduced, the bunches may dry prematurely. The wine is of lower quality, there are noticeable differences in the sensory, with highest acidity and minerals in the wine. This chronic blockage of the xylem can eventually cause the vine to fail. In Slovenia, we have many problems with FD, as it is widespread in all three winegrowing regions. To reduce the FD spreading various measures can be applied such as mandatory treatment of vines with insecticides, with which we try to reduce the population of the American grapevine leafhopper, removing infected vines as well as host plants from vineyards, planting of uninfected grafts, timely detection of infected plants and controlled transfer of plant vegetation, propagating material and more. Measures are important in rootstocks nurseries, vineyards with mother vines and nurseries, where stricter conditions for disease control must be taken into account, as the disease can spread quickly with infected planting material. The most effective measure for the elimination of FD phytoplasma is the treatment of planting material with hot water (50 °C for 45 min), which will become a necessary practice in Slovenia as well.
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