Grapevine trunk diseases like esca and Eutypa dieback are affecting grapevines worldwide. They cause wood rot from pathogenic fungi and spectacular leaf symptoms like tiger-stripe scorch patterns for esca and dwarf canopy for Eutypa dieback (Figure 1). These diseases reduce vine yields and increase the risk of plant death. However, there is still a gap in our understanding of the extent of these diseases at large scale, and the factors that cause the spread of disease to vary. France has monitored leaf symptoms of esca and Eutypa dieback since the early 2000s. This vineyard surveillance followed a resurgence of the esca disease, probably following the ban in 2001 on the use of sodium arsenite, which was the only treatment available despite its toxicity. From 2003 to 2022, the prevalence (proportion of vineyards with at least one symptomatic plant) and incidence (proportion of symptomatic plants) of these diseases were monitored in all the main French vineyards.
Researchers combined databases from 13 French wine regions, recording leaf symptoms of esca and Eutypa dieback from 2082 plots and 36 cultivars over 20 years. They used the database to show how often esca and Eutypa dieback occurred in France. Esca was found in 74% of plots each year, with 3% incidence. Eutypa dieback occurred in 41% of plots, with 1.4% incidence. Eutypa dieback mainly affected the cultivar “Ugni blanc” and disease incidence has decreased over the years, probably in response to efficient cultural practices (dead wood removal from the plots) and climate change. Esca is still a big problem in France. It affects many cultivars and wine regions and disease incidence has tended to increase over the years, despite esca incidence never exceeding 4%.
Second, researchers used statistics to understand how different factors affect the prevalence and incidence of esca leaf symptoms in France. This approach revealed several findings:
- the cultivar identity affects the prevalence of esca. Some are less susceptible (in that case there are many plots with 0% symptomatic plants), while others are more susceptible.
- esca incidence changes from year to year. This is likely due to climate factors that affect both wood fungal communities and plant physiology.
- plot age affects esca incidence. Plots less than 10 years old and over 30 years old had fewer disease symptoms than plots between 10 and 30 years old. This non-linear effect had never been quantified, despite it being well-known in viticulture. Certain traits known to differ with plant age, such as plant metabolism, wood properties, and wood microbial communities, may be involved. So far, however, it has not been possible to explain why older plants become as resistant as younger ones. Could it be because the weakest vines are replaced by new ones, leaving the strongest behind? We need to do more research with vines of different ages.
Lucas Etienne, Frédéric Fabre, Davide Martinetti, Elise Frank, Lucie Michel, Valérie Bonnardot, Lucia Guérin-Dubrana, Chloé E. L. Delmas published this work in Plant Pathology Journal:
TITLE IMAGE: An analysis of a large French database on grapevine trunk diseases (2003-2022) showed higher esca incidence after 2012 and a decrease in Eutypa dieback. It also indicated a non-linear effect of plot age on esca.
