Performance of Georgian Grapevine Varieties in a Vineyard Infected by Flavescence Dorée Phytoplasma in Piedmont, Northwestern Italy

In Europe, Flavescence dorée (FD), the only epidemic disease within the phytoplasma-associated grapevine yellows complex (GY), reduces productivity and has a negative impact on berry composition and wine quality. Recent studies have shown that Georgian Vitis vinifera L. varieties have low susceptibility to Bois noir (BN), another GY disease. This study investigated the performance of some Georgian grapevine varieties in a highly FD-affected area in Piedmont (northwestern Italy), exploring their susceptibility to FD and testing their oenological potential through berry and wine quality analyses. Activities, conducted in a case-study vineyard containing central–western European, Georgian, and PIWI (fungus-resistant grape varieties) varieties, included field surveys and molecular analyses. Mortality and infection percentage index were significantly higher in Georgian and central–western European varieties, respectively. All Georgian varieties exhibited none or mild symptoms without a reduction in the number of symptomless berries. Only the FD phytoplasma (FDp) genotype M54 was identified in infected grapevines, suggesting that differences in symptom severity were related to a variety-specific response to infection. Despite infection, Georgian varieties maintained stable berry and wine quality parameters, showing no significant changes in acidity, sugar content, and flavor profile. Thus, Georgian varieties had great oenological potential and responded well to both FDp infection and local agroecosystem conditions.