Grapevine trunk diseases are a threat to table- and grape-wine cultivation worldwide. Phaeomoniella chlamydospora (Pch) is a vascular fungus recognized as one of the most important pathogens associated with grapevine trunk diseases. The relationships between xylem vessel features and Pch susceptibility of 10 table- and 17 wine-grape genotypes, as well as 3 rootstocks, were investigated by image analysis of 50 µm cross-sections and artificial Pch inoculation on one-year-old vine cuttings. Vessels were grouped in the diameter classes 1–30, 31–60, 61–90, 91–120, and >120 µm. Among the table-grape varieties, ‘Sable’, ‘Timco’, and ‘Red Globe’ showed higher densities of large vessels (>120 μm) than ‘Italia’, ‘Sugar Crisp’, and ‘Sugraone’. Among the wine-grape varieties, ‘Minutolo’, ‘Montepulciano’, ‘Primitivo’ CDTa19, and ‘Verdeca’ showed higher densities of large vessels than ‘Aglianico’, ‘Nero di Troia’, ‘Sangiovese’, and ‘Susumaniello’. In the rootstocks, the vessel diameters were 50.8, 54.0, and 60.9 μm for ‘34 E.M.’, ‘140 Ruggieri’, and ‘1103 Paulsen’, in that order. For table-grape varieties, Pch was re-isolated from 13.3% for ‘Sugar Crisp’ and ‘Sugraone’ cuttings up to 93.3% for ‘Timco’. For wine-grape varieties, Pch re-isolation ranged from 51.1% (‘Bombino nero’, ‘Negroamaro’ D15, and ‘Sangiovese’) to 81.1% (‘Montepulciano’), while for the rootstocks, the values were from 33 to 51%. A principal component analysis (PCA) revealed a positive correlation between the frequencies of large vessels and Pch re-isolation. In addition, in wine grapes and rootstocks, higher Pch re-isolation frequencies in the lateral parts of cuttings were correlated (r = 0.79) to a higher frequency of large vessels. The results highlight relationships between grapevine xylem vessel sizes and susceptibility to P. chlamydospora that are worthy of further research.
