The Effects of NAA and GA3 Applications at Preflowering and Preveraison Stages on Sugar–Acid Metabolism and Wine Quality in Marselan Grapes: Integrated Insights from Transcriptomic and Metabolomic Analyses

Exogenous plant growth regulators are increasingly applied in viticulture, yet their roles in grape ripening and wine quality remain unclear. In this study, Marselan grapevines were treated with naphthaleneacetic acid (NAA) or gibberellic acid (GA3) at preflowering and preveraison stages, and sugar–acid metabolism and wine sensory traits were evaluated through integrated transcriptomic and metabolomic analyses. Results revealed that NAA applied before flowering upregulated genes for cell expansion and sugar–acid metabolism, increasing alcohols and organic acids, producing wines with high acidity and fresh, fruity aromas. GA3 before veraison enhanced pigment and volatile-aroma pathways, elevating alcohols and esters, resulting in wines with rich floral and ripe-fruit notes and fuller body. Sensory evaluation confirmed that NAA wines were crisp with higher acidity, while GA3 wines had a fuller body and complex aromas. These stage-specific molecular findings provide a framework for precision viticulture and targeted modulation of wine aroma profiles.