In the 1950s, INRA led the way in the identification of the agent and insect vector of flavescence dorée. Now, it has made significant advances in understanding the biology of these organisms. New findings have enabled the development of a specific detection test for the disease and have opened the way for new, non-insecticide methods to control it. At present, flavescence dorée cannot be cured: it can only be treated by uprooting infected vines, management of grapevine nurseries and insecticide control of the vector.
Serious consequences to agriculture
Flavescence dorée is a highly contagious quarantine disease that is incurable in grapevines. Typically, it causes leaves to yellow and grapes to shrivel. It is found across most wine-producing areas in southern Europe. It may cause significant harvest losses and may compromise the sustainability of vineyards. At present, compulsory control measures are in effect covering more than half of France’s total vineyard area.
An unusual pathogen
As with other yellows diseases, flavescence dorée is caused by phytoplasma, small bacteria in the Mollicutes class that lack cell walls. Phytoplasmas are intracellular obligate parasites that reproduce in plant phloem tissue and in associated phloem-feeding insects. The main phytoplasma vector for flavescence dorée is the leafhopper Scaphoideus titanus. By feeding on an infected plant and then feeding on other plants, the vector spreads the disease through the vineyard, in much the same way as the Anopheles mosquito transmits malaria in humans. Long-distance dissemination is, however, largely the result of the transport of infected propagative material by humans.
Research needed to find treatments
Existing treatment methods rely on uprooting infected vines, monitoring grapevine nurseries for the disease and insecticide control of the vector. Treatment measures are compulsory, polluting, costly and run counter to wine industry moves to reduce pesticide use. Compulsory control measures also represent an enormous problem for organic winegrowers and for wineries in the process of converting to organic agriculture.
Consequently, it is essential in the short term to find methods to better control flavescence dorée and to develop treatment alternatives that use less insecticide. To do so, a better understanding is needed of the pathogen, the vector and the mechanisms that govern interaction between phytoplasma, leafhopper and grapevine.
A new research dynamic at INRA Bordeaux-Aquitaine
At INRA Bordeaux, two research units are jointly working on flavescence dorée’s triangular system: phytoplasma–leafhopper vector–grapevine. The first research unit (1) is looking at the phytoplasma, its origins, the evolution of epidemics, and its interaction with its plant and animal hosts. The second unit (2) is studying the insect vector, its behaviour in relation to the host plant and the history of its introduction and spread in Europe.
(1) Fruit Biology and Pathology Joint Research Unit (UMR 1332 BPF), “Mollicutes” team
(2) Vineyard Health and Agroecology Joint Research Unit (UMR 1065 SAVE)
INRA’s important role in the study of the flavescence dorée epidemic
Since the 1950s, INRA has led the way in the study of the disease, both in terms of identifying its nature and discovering its vector. Subsequent research has looked at the fight to control flavescence dorée and to better understand the mechanisms regulating it. Research was largely carried out in Bordeaux and in Dijon. INRA Sophia-Antipolis conducted experiments on organic treatment methods, although they have not yet proven successful.