## 4 Discussion  
The influence of rootstocks on the TSS was measured, showing that the berries on grafted vines accumulated higher TSS than those on the own-rooted Merlot berries, which is inconsistent with previous reports [4; 8]. However, TSS of Marselan berries was decreased by rootstocks (5 BB and 1103P). In addition, the values of berry TSS/TA in scion-rootstocks MT-5 BB, MT-1103P, MT-SO4, MN-5 BB, and MN-1103P were lower than those in the own-rooted samples. This result is consistent with previous studies [8; 32], which suggests that rootstock 101-14 could delay the maturity of Chardonnay berries. However, it is worth noting that this statement cannot be used as a single criterion to judge berry ripeness. Under the same condition, the TSS/TA levels of Merlot and Marselan scion-rootstocks were lower than those of the own-rooted samples. Rootstocks accelerated the ripening of Merlot berries when they significantly increased TSS and TA. Conversely, rootstocks hindered the ripening of the Marselan berries when they decreased TSS but increased TA levels. Rootstock had different effects on different scions. Significantly, rootstocks (5 BB, 1103P, and SO4) harmed the aroma of Merlot wine. Rootstocks markedly reduced the content of C6 aldehydes (hexanal and _(E)_-2-hexanal), increased the content of C6 alcohols (hexanol), and decreased the total amount of C6 compounds in Merlot wines. In addition, C6 volatile compounds were converted from acetate compounds to aldehydes and finally to alcohols during early, middle, and late berry developmental stages, respectively. In the later stages of berry development, alcohols dominated, followed by aldehydes [33]. The main aroma component of MT wine was aldehydes, which was different from Merlot scion-rootstocks, where the main aroma component was alcohol. Previous studies have determined that berry ripening stages by the alcohol-aldehyde ratio: alcohols usually have a higher herbaceous odor than related aldehydes [33; 34]. The alcohol-aldehyde ratio of Merlot wines from scion-rootstocks was significantly increased, indicating that rootstocks promote berry ripening in Merlot, which may be one of the reasons why the total amount of aroma in grafted rootstocks was lower than that in own-rooted Merlot. Rootstocks had a certain effect on the terpene content, for example, the total amount of terpen in MT-1103P was higher than that in MT, while the content of lanlool in MT-SO4 was significantly higher than that in MT. Meaningfully, rootstocks had a positive effect on the aroma of Marselan wine, indicating a significant increase in the total amount of C6 compounds. Rootstocks observably increased the content of C6 aldehydes, while rootstock 5 BB decreased the content of C6 alcohols and rootstock 1103P increased the content of C6 alcohols. Rootstock 5 BB markedly increased geraniol content, and the total terpene content of MN-5 BB was higher than that of MN. Rootstocks significantly increased the aldehydes content of Marselan wine but decreased the alcohol-aldehyde ratio, which may be one of the characteristics of rootstock prolonging the ripening of Marselan. That might be one of the reasons why the total aroma of wines was higher in the grafted combination than in own-rooted samples. In terms of total volatile compounds, rootstocks prominently reduced the aromas of Merlot and significantly increased the aromas of Marselan, consistent with the results of volatile-related gene expression levels. For Merlot, the expression of aroma genes in scion-rootstocks was generally lower than that in own-rooted samples, while the expression levels of _VvLoXA; VvGT7_ from MT-5 BB; and _VvLinNer1, VvGT7_, and _VvGT9_ from MT-1103P were higher than those from own-rooted samples. This resulted in a generally negative impact of the rootstock on the volatiles in Merlot wines, which is consistent with previous studies [18].