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Mail : biovanni.bortolami@inrae.fr
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Sujet de thèse

The effect of pathogens on the water and carbon economy of grapevines: implications for the grapevine dieback crisis (2017-2020)

• encadrants : Chloé Delmas, Gregory Gambetta (UMR EGFV)
• financement : Plan National Dépérissement du Vignoble (FranceAgrimer, projet Physiopath)

Résumé

Climate change is expected to have critical impacts on agro-ecosystems through decreased yields and increase plant mortality resulting from a combination of drought, heat stress, and pathogen attacks [1-3]. In viticulture, grapevine dieback is an increasing problem caused by a large range of abiotic and biotic factors having large economic consequences [4]. Grapevine dieback affects 75% of vineyards in France and is characterized by a yearly decrease in yield and/or death of plants. However, the causes leading to grapevine dieback are not clearly identified and the underlying physiological mechanisms are still unknown. In the context of climate change, two questions remain un-explored: Does drought amplify or restrain the spread of vascular and foliar pathogens? Do vascular and foliar pathogens amplify droughtinduced mortality?

Drought can modify pathogenesis either through effecting plant susceptibility, or through a combined effect of drought and disease on plant physiology [5]. The combined effect of abiotic and biotic stresses on plant physiology, especially on the carbon balance, is likely dependent on the type of pathogen (e.g. vascular, biotroph or necrotrophe) [6-7]. Theoretically, two mechanisms can explain drought-induced plant mortality: hydraulic failure or carbon starvation [8]. Both mechanisms could be affected by pathogen infection through effects on water transport and/or carbon balance [7].

The aim of this thesis is to understand the underlying mechanisms leading to grapevine dieback, especially leaf wilting, leaf senescence, and vine mortality, by studying the physiological responses of grapevines to drought and pathogen infections. The experimental approaches will be transdisciplinary including plant pathology and physiology methods. The doctorate, of three years’ duration, will consist of:

• compiling data from the literature and field surveys to realize a meta-analysis on the impact of multiple stresses (e.g. drought and pathogens) on plant physiology,
• conducting greenhouse experiments using various grapevine varieties and multiple stress treatments (drought, shading, infection with different types of pathogen) assessing pathogen symptoms, plant physiology (growth, transpiration, gas exchange, xylem pressures, hydraulic conductivities),
• conducting metabolic analyses to determine non-structural carbohydrate reserves, carbon versus nitrogen ratio, and phytohormone leaf contents,
• participating in related experiments as part of the greater project team, and
• analysing and synthesizing data producing both research manuscripts and technical documents to communicate our results to the scientific community as well as the viticulture community.

The results, obtained using a transdisciplinary approach at the crossroads of pathology and physiology, will reveal the role of disease, plant hydraulics, and carbon stress in the growing problem of grapevine dieback.

Publications significatives

G. Bortolami, G. A. Gambetta, S. Delzon, L. J. Lamarque, J. Pouzoulet, E. Badel, R. Burlett, G. Charrier, H. Cochard, S. Dayer, S. Jansen, A. King, P. Lecomte, F. Lens, J. M. Torres-Ruiz, C. E.L. DelmasExploring the Hydraulic Failure Hypothesis of Esca Leaf Symptom Formation. Plant Physiology Nov 2019, 181 (3) 1163-1174; DOI: 10.1104/pp.19.00591