Eugenol, widely distributed in various plants including cloves, is a well-known powerful antifungal and antibiotic molecule that is concentrated in hybrid grapevines, notably in the cultivar Baco blanc (Vitis vinifera x Vitis riparia x Vitis labrusca) created by F. Baco in the 19th century. Under biotest conditions, by assessing fruit rot incidence and severity, we confirmed that this variety is highly resistant to Botrytis cinerea by comparing with two Vitis vinifera cultivars, also of prime importance in the Armagnac region: Folle Blanche and Ugni Blanc. The marked varietal resistance was also confirmed in the vineyards and may arise from differential chemical feature of the berry skin. The Baco blanc berry skin was highly concentrated in eugenol, notably at veraison (1118 to 1478 μg/kg), contrarily to the two other cultivars (e.g. Ugni Blanc 22 to 28 μg/kg). Furthermore, significant intra-varietal differences in B. cinerea resistance among six Baco blanc clones were shown in terms of incidence and severity of fruit rot and/or sporulation. These differences in resistance were related to different fruit chemical composition, including the berry skin eugenol content. Finally, a significant negative correlation was highlighted between the fruit technological maturity and the skin eugenol content, allowing us to propose eugenol as a key fruit skin biomarker of the ontogenic resistance of the hybrid cultivar, Baco blanc, to such a major necrotrophic pathogen in grapevine.Read less <