Investigating esca susceptibility in a range of Vitis vinifera L. cultivars through a physiopathology-based approach

<div> Perennial plant dieback involves complex interactions between pathogens and plant ecophysiology [1] . While the effects of environmental conditions are becoming better characterised, understanding intraspecific variation in susceptibility to dieback remains a challenging area of research, and requires to combine plant physiology and pathology to elucidate underlying mechanisms across genotypes. Here, we carried out an integrative work to investigate underlying mechanisms of grapevine varietal susceptibility to esca, a complex vascular disease leading to dieback. We used a common garden planted with 46 cultivars grown in homogeneous conditions [2] . We characterised plant hydraulic and wood anatomical traits, carbon assimilation, starch storage, metabolic and microbial wood composition, in both asymptomatic and esca-symptomatic plants. We found that genotypes with the lowest stomatal conductance and leaf minimal conductance tend to have lower susceptibility to esca. The genotype had a significant effect on theoretical hydraulic conductivity (Kth), xylem ray parenchyma area and marginally on the aperture fraction of intervessel pits, albeit not related to physiological or epidemiological varietal patterns. Differences in stem metabolome and microbial communities of asymptomatic plants from contrasting genotypes were not related to esca susceptibility. Comparing asymptomatic and esca-symptomatic plants, we revealed a clear response syndrome to esca, involving reduced leaf gas exchanges, starch storage and Kth, stem metabolic modifications, but no changes in microbial communities. However, these responses were only marginally modulated by symptom severity and varietal susceptibility to esca. These results reveal the complexity to pinpoint major traits explaining the large gradient of varietal susceptibility to esca in grapevine, but suggest a key role of cultivar ecophysiology. Integrative studies unravelling plant-microorganism-environment interactions within the trunk are the next step if we are to understand the mechanisms underlying complex woody plant diseases. </div>