Modification of skin anatomy and phenolic compounds of Tannat grapes along ripening by abscisic acid foliar applications

The ‘Tannat’ grapevine variety is known for its high polyphenolic content in grapes but low anthocyanin extractability. Secondary metabolite accumulation during ripening is influenced by a complex interplay of environmental factors and plant responses. While scientific literature indicates that abscisic acid (ABA) applications at veraison can modify the polyphenolic content of grapes, the effects can vary based on the dosage and climatic conditions. However, limited literature exists on the changes of grape skin anatomy in response to exogenous ABA applications during ripening. This study aimed to investigate the effects of ABA applications on ‘Tannat’ grapevines on the grape skin anatomy and polyphenolic compounds during ripening at two different locations. The results demonstrate that location was a key factor that significantly affected grape polyphenol content, under temperate-warm climate conditions and temperate, sub-humid nights (TSH) resulting in higher phenolic compound levels. Additionally, warm climates favored anthocyanin extractability. Grape skin cell typologies evolve differentially; while empty cells (type I) were independent of the climatic conditions, cells with anthocyanin accumulations (type II, III, IV and V) vary based on their polymerization degree in response to the climate conditions. ABA applications increased the total anthocyanin contents in the grapes harvested in the TSH location but did not affect their content in the WH site. The evolution of the anatomy of skin cells of ‘Tannat’ can help to better adjust ‘Tannat’ vineyard management in different viticulture regions (canopy management, exogenous ABA treatments, irrigation) and to improve wine production techniques (maceration days for anthocyanins extractability, aging of wines, etc.).