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Impacts écophysiologiques de l’Esca : résilience des ceps et effet des modes de taille

Abstract : Esca is a grapevine trunk disease that is characterized by the formation of necrosis in the inner wood and the erratic expression of foliar symptoms from one year to another. The key to understand why healthy wood tissues become necrotic in mature grapevines lies in the identification of the factors that influence the pathogenic behaviour of Esca-related fungi, or other microorganisms such as bacteria, and their ability to degrade woody tissue. Current viticultural management practices, such as vine pruning, generate open wounds, which increase the risk for grapevines to get infected with Esca-related pathogens. In this context, a first approach consisted in monitoring the expression of Esca over several growing seasons (3 years) by measuring its impact on grapevine physiology. Discrimination between healthy and symptomatic plants based on the surveillance of foliar indicators (e.g., photosynthetic activity, stomatal conductance, phenolic composition) was not efficient for early detection of the disease. Significant differences were observed only at the same time, or just following the expression of the first foliar Esca symptoms. On the contrary, sap flow measurements were effective in the detection of symptomatic vines several weeks before the appearance of any foliar symptoms. This monitoring method could therefore become an interesting tool for the early detection of Esca. A second approach consisted in comparing two types of pruning practices. After 3 years of monitoring, all studied physiological parameters appeared to be homogeneous for all grapevines. Nonetheless, early differences were recorded in the desiccation cones, which would suggest that the "conventional" pruning method probably limited sap flow movement, unlike a pruning system that takes into account the natural stem vessel connectivities. Finally, we can hypothesize that the interactions linking internal symptoms (i.e. necrosis in the wood) and external ones (i.e. foliar symptoms) would be located within sap conducting system, suggesting that xylem vessels are a privileged site to study Esca disease.
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Loris Ouadi. Impacts écophysiologiques de l’Esca : résilience des ceps et effet des modes de taille. Ecologie, Environnement. Université de Bordeaux, 2019. Français. ⟨NNT : 2019BORD0434⟩. ⟨tel-02862055⟩

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