The grapevine yellows Flavescence dorée (FD) is a quarantine disease, which causes great damage in viticulture in southern Europe and spreads further and further north. The symptoms of the disease are a yellowing and curling of the leaves, drying, shrinking and falling berries, as well as lack of lignification of the shoots. It is caused by phytoplasmas, which are transmitted very efficiently from wine to wine by the introduced American grapevine leafhopper Scaphoideus titanus. An epidemic outbreak of the disease occurs when phytoplasma and leafhopper coincide. So far, neither phytoplasma nor leafhopper have been detected in grapevine in Germany. However, the disease is already widespread in Burgundy and S. titanus has been found in Alsace since 2016. The risk is therefore high that soon the Palatinate viticulture will be affected.
Since the 1990s it has been known that in the Palatinate a closely related phytoplasma to FD is found in grapevine: the Palatinate Grapevine Yellows Phytoplasma (PGY). Genetic variants of this phytoplasma are widespread in Germany - but not in grapevine but in alder. PGY is transmitted to grapevine from various alder leafhoppers but can not be propagated there as long as S. titanus is absent.
FD / PGY phytoplasma variants that can be efficiently transmitted by S. titanus may already be present in the alder trees in Germany. For an outbreak of FD, only a transmission from alder to grapevine and a spread from vine to vine by S. titanus is needed. This epidemiological relationship is shown schematically in Fig. 1.
Vineyards near alders therefore have a particularly high risk of being attacked by FD / PGY. In collaboration with the working group on Environmental Systems of the Institute of Agroecology, a GIS-based analysis of the presence of alders close to grapevine was carried out in Palatinate. The purpose of the risk map is to help vine growers, advisors and researchers to identify high-risk vineyards and to monitor them for infestation with a yellows disease. Through this the early detection of an occurrence of FD and the prevention of further spread is intended.
Fig. 1 Way of transmission of PGY/FD phytoplasmas from alder to grapevine