Chloé Delmas

Research Director at the UMRs for vineyard health and agroecology at INRAE-ISVV

Published in *Terre de vins* No. 76 – March/April 2022

Tree decline is not a recent problem. However, it has only recently become a matter of national concern...

For a long time, wood diseases were seen as the sole cause of mortality, but it is now recognised that this decline is attributable to a combination of factors. It has only been tackled in a coordinated manner since 2016, through the national plan to combat vine decline, which brings together the industry and the research community. Within this framework, since 2017 I have been studying the interaction between several biotic (diseases) and abiotic (drought, climate) factors, and their consequences for vine physiology. I have taken a particular interest in esca, one of the main wood-decay diseases in France, and in the role of the environment in this disease. Our understanding of it remains very limited, as it involves a complex interplay of pathogens.

Vine decline is caused by a variety of factors, including wood diseases and the climate, and requires a comprehensive approach to prevent it more effectively.

How are you making progress in understanding ESCA and its links to tree decline?

We are facing technical and technological limitations. It is impossible to replicate the leaf symptoms in the laboratory, as the specific fungus or fungi responsible have not been identified, and the symptoms are generally observed on vines over 10 years old. To overcome these limitations, we have transplanted vines from long-affected plots into pots so that we can study them, in particular using X-ray imaging. We have around a hundred vines over 30 years old, sourced from INRAE’s experimental vineyards in Bordeaux. This has enabled us to observe natural leaf symptoms of esca at the same time as they appear in the vineyards, and with the same likelihood of occurrence. We demonstrated for the first time that these symptoms were associated with a loss of water conduction in the vessels of the leaves and current-year shoots. This phenomenon is caused by blockages, known as thylloses, which the plant develops as a defence against attack. We then proved that moderate to severe drought completely inhibited the expression of the symptoms.

What are the prospects for research into the topic of tree decline?

Nous utilisons ce dispositif expérimental pour tester l’impact d’autres conditions environnementales sur les pathogènes, telles que différentes conditions de fertilisation azotée. Nous avons aussi commencé à mener un travail de modélisation statistique à l’échelle régionale et nationale, pour étudier le rôle des facteurs climatiques dans l’expression des symptômes de maladies du bois. Et ce, pour prédire à terme le risque d’expression de symptômes ou de dépérissement selon les climats futurs et les terroirs viticoles.