## 4 Discussion  
Among the C6/C9 substances, (E)-2-hexanal and hexanal were the most abundant aroma compounds [14]. 1103P mainly promoted the accumulation of these two compounds, which led to a significant increase in the total C6/C9 substance concentration (Table S6). [PERSON] found that 1103P significantly increased the concentration of C6/C9 compounds in Chardonnay [15]. A recent study also indicated that 1103P has more aromatic compounds, abundant green-vegetable/astringent notes, and more defect-causing compounds [44]. These studies support our findings, and our results further demonstrate that 1103P confers more C6/C9 compounds to grape berries, particularly in vintages with high rainfall. SO4 reduced the content of most compounds in grape berries, but 5A had a relatively minor impact on the aroma components of CS grape berries. This might be due to the imbalance  
Figure 8: The concentration of 1-hexanol in wine in 2019 and 2020 (**A**); The concentration of 1-hexanol and hexanal in berries in three vintages (**B–D**). Note: different letters mean significant differences among the four treatments on the basis of [PERSON]’s multiple range test as \(p<0.05\). between vegetative growth and reproductive growth. The more vigorous vegetative growth of CS/1103P and CS/SO\({}_{4}\) might have changed the metabolic flow of some aroma compound precursors, thus having a greater impact on the aroma components of CS grape berries, especially in years with more rainfall. The vegetative growth of CS/5A was more consistent with that of own-rooted, so the composition characteristics of its aroma compounds were also more similar. In wine, we found that 1103P increased the levels of C6/C9 alcohols and acids while decreasing the levels of higher alcohols, benzenes, esters, and volatile phenolic compounds compared to own-rooted. It has been shown that Merlot wine made from the Merlot/SO\({}_{4}\) combination has a lower higher alcohols content [17]. Among the many compounds, it was found that the concentration levels of compounds in the grape and wine do not consistently correspond to each other, which was mainly caused by the complex winemaking process. Many compounds undergo transformation losses during the fermentation process. When we used OPLS-DA to fit models for grape berry and wine compounds from different rootstock combinations, we found that the fitted model for wine was better than the fitted model for grape berry. This showed that the differences in aroma substances between different graft combinations were amplified by fermentation, and it was clear that we were able to successfully build a reliable fit model when differentiating wines. This was partly due to the fermentation process creating more complex aromas in the wines, and as the number of compound species increases, the dependent variable used to evaluate differences between grafted combinations and CS also increases, making it easier to construct a reliable model. Furthermore, the sensory aroma profile of wine emerged from complex binding phenomena between volatile constituents and matrix macromolecules [45]. Fermentation aromas were more closely related to the grape's primary metabolites, such as sugars, acids, and amino acids, and differences in the grape's primary metabolites could also cause changes in the wine's aroma composition. Interestingly, among the many complex compounds, we found that the C6/C9 substances in grapes and wine had a better correspondence. Among them, 1103P greatly raised the overall amount of C6/C9 compounds in both grapes and wines, and this difference was also consistent across different years. This variation might be because C6/C9 compounds were very abundant in grapes. Grapes reduced C6/C9 aldehydes to C6/C9 alcohols during the fermentation process, allowing them to enter the wine without complex interference. Although the selection of yeast strains and fermentation conditions would also affect the reduction efficiency, the precursor concentration in the fruit was the most fundamental determining factor.