Grape Phenolic Composition Analysis of ‘Tempranillo Tinto’ and ‘Graciano’ Grapevine Clones

Climate change poses an increasing threat to viticulture sustainability, particularly in traditional wine regions, where varietal regulations restrict the adoption of new cultivars. Elevated temperature and water deficit may alter anthocyanin accumulation and the broader phenolic profile of ripening berries, directly affecting wine colour, structure, and quality. In this context, exploring intra-varietal diversity may help to identify clones with a favourable phenolic profile that could contribute to adaptation strategies within existing varietal regulations. We report the first comprehensive monomeric phenolic profiling, by UHPLC-QqQ-MS/MS, of grape berries from eleven Vitis vinifera L. ‘Tempranillo Tinto’ clones (two seasons) and seven ‘Graciano’ clones (three seasons), from old vineyards in La Rioja (Spain). Six phenolic classes were quantified: hydroxycinnamic acids, hydroxybenzoic acids, flavonols, flavanols, stilbenes, and anthocyanins. Multivariate analysis of variance, linear mixed-effects models, principal component analysis, and hierarchical cluster analysis were used to characterize clonal diversity. Significant clone effects were detected for all six phenolic classes in ‘Graciano’ and four in ‘Tempranillo Tinto’. In ‘Graciano’, clone GR_1250 was distinguished by elevated flavonol and anthocyanin levels, whereas GR_1265 showed the highest flavanol and hydroxybenzoic acid content. In ‘Tempranillo Tinto’, clone TT_1041 stood out for its higher flavanol and hydroxybenzoic acid concentrations, whereas TT_767 had elevated anthocyanin levels. Two to four distinct phenotypic clusters were identified within each variety. These results confirm substantial intra-varietal phenolic diversity in both cultivars and identify clonal selections with differential phenolic profiles that may be useful for quality-oriented clonal selection, particularly when integrated with agronomic, phenological, sanitary and wine-level information.