## 4 Discussion
To the best of our knowledge, the xylem anatomical properties associated with red-berried and white-berried cultivars represent new information in the field. However, further studies are needed to confirm these data and understand whether this anatomical feature has an important role in plant physiology or in plant-pathogen interactions. In this study we examined the relationship between these characteristics and incidence of esca symptoms, as previously assessed by [22] in the same experimental field for the same grapevine cultivars. For the relationships among vessel sizes and densities with esca incidence previously detected on the same grapevines, no linear relationship was observed for either the red-berried or white-berried cultivars. Previous investigation indicated that cultivars with larger vessels might be more susceptible to inoculated _P. chlamdospora_[34], one of the putative agents of esca, according to both pathogen concentration and wood necrosis lesions. In the present study, we referred to the esca symptoms observed in the field, which are known to involve several fungal species [5; 11; 52]. On the other hand, sometimes the presence of pathogens involved in esca was not resolved after the manifestation of symptoms. Grapevine trunk diseases have unpredictable discontinuity in the expression of foliar symptoms year by year [2; 8; 53; 54]. Even after their first appearance, foliar symptoms do not develop systematically and cannot be predicted from year to year, which indicates that several factors, including the type of rootstock and environmental factors, are probably involved in their development [5]. However, a correspondence with esca susceptibility in some cultivars occurred in several works. The highest esca incidence was reported for 'Cabernet Sauvignon', 'Sangiovese', and 'Sauvignon Blanc', with lower incidence for 'Montepulciano' 'Merlot' and 'Chardonnay', [22; 23; 55; 56]. Recent study yielded evidence that parenchyma cells play an active role during esca pathogenesis, expanding into the vessel lumen, secreting extracellular compounds, and eventually occluding the vessel, but no positive correlation between the severity of esca leaf symptoms and leaf vascular occlusions was observed. The authors suggested that symptom development was associated with vascular occlusions that are likely elicited at a distance from the pathogen niche localized in the trunk [57]. In our work, the overall average value of vessel diameter measured among the red-berried and white-berried cultivars showed that the white-berried cultivars have larger vessel sizes than the red-berried cultivars. A similar trend was observed among the red-berried and white-berried cultivars relative to the overall disease incidence observed by [22]. Then, although no significant relationship between disease incidence and xylem vessel dimensions was observed for the singular cultivars, the average values suggest a greater susceptibility of the white-berried cultivars that, according to our investigation, showed larger xylem vessel dimensions. Further investigations including a greater number of cultivars will be needed to verify this relationship. In this regard, the OIV [58] reported that in Italy the incidence of trunk disease depends on the varietal susceptibility: on plants of 15 to 18 years, corresponding to the age of plants analysed in this work, the average incidence can fluctuate from around 12% to 19% for the white-berried cultivars, and around 8% to 10% for the red-berried cultivars [23; 59]. This suggests that some relationship among vessel dimensions and esca incidence might exist.