## 2 Results and Discussion
### Effects of Rootstocks on Derivy Flavonoids  
With few exceptions, minor differences in flavan-3-ol concentrations and proportions in grape skins emerged among grafted and own-rooted vines (Supplementary Figure S2), which is consistent with previous research [4; 27; 30]. In particular, 101-14, Riparia Gloire, and SO4 had almost no influence on total flavan-3-ol concentrations in the two seasons. Besides, the season factor dominated the effects of 110R, 5A, 5 BB, and Harmony on flavan-3-ol concentrations. Contrarily, a recent study showed that 'Merlot' grafted onto SO4, 101-14, and 110R presented higher concentrations of proanthocyanidins in skins in one growing season. The differences in the rootstock effects on flavan-3-ols may be affected by scion cultivars and climatic differences, and further studies are necessary to understand this [31]. Notably, in this study, Ganzin 1 slightly reduced almost all the individual flavan-3-ol concentrations, indicating that Ganzin 1 tended to inhibit the accumulation of flavan-3-ols in grape skins. Interestingly, all the rootstocks except 110R imparted negative effects on epicatechin-3-O-galate concentrations and proportions; besides, significant decreases were observed in 2016 (Supplementary Figure S2). Therefore, we speculate that the accumulation of epicatechin-3-O-galate may be responsive to the graft. It was reported that catechin concentrations significantly differed among different grafted Thompson Seedless' vines [7]. By contrast, in this study, rootstocks had no marked effects on catechin concentrations and proportions, which may be ascribed to the scion cultivar differences. In this study, flavonol concentrations and the proportions were not affected by the rootstocks, except Harmony (Figure 2). Quercetin, as the most abundant flavonoid in 'Thompson Seedless', was also not statistically affected by different rootstocks [7]. Notably, 5A, Harmony, and Riparia Gloire increased the concentrations of all the individual flavonols in the two seasons, even though increases were not significant (Figure 2). These observations suggested that 5A, Harmony, and Riparia Gloire tended to promote flavonol biosynthesis. \begin{table}
\begin{tabular}{c c c c c} \hline
**Source of** & **Berry Weight** & **Total Soluble Solids** & **Tittatable acidity** & \\
**Variation** & **(g/100 Berries)** & **(\({}^{\text{a}}\)Brix)** & **(g/L)** & **pH** \\ \hline
**Rootstock (R)** & & & & \\ CS & 133.82  & 20.10 ab & 5.55 & 3.50 \\ CS/101-14 & 133.64 & 19.73 ab & 6.44 & 3.38 \\ CS/110R & 127.52 & 20.05 ab & 5.48 & 3.39 \\ CS/5A & 144.87 & 19.35 ab & 5.12 & 3.35 \\ CS/5 BB & 137.27 & 19.65 ab & 6.01 & 3.35 \\ CS/Ganzin 1 & 153.33 & 20.1 ab & 5.39 & 3.56 \\ CS/Harmony & 134.17 & 20.55 a & 5.18 & 3.46 \\ CS/Riparia Gloire & 142.64 & 19.6 ab & 4.68 & 3.42 \\ CS/SO4 & 130.00 & 18.28 b & 6.11 & 3.42 \\
**Vintage (V)** & & & & \\
2015 & 123.74 b & 20.24 a & 5.97 & 3.46 \\
2016 & 147.62 a & 19.08 b & 5.39 & 3.38 \\
**Significance** \({}^{\text{b}}\) & ns  & ns  & ns & ns & ns \\ \hline \end{tabular}
\end{table} 
Table 2: Effects of rootstocks on physiochemical parameters of mature berries in two seasons (2015-2016). In agreement with previous studies [4; 11; 30], rootstocks did not significantly affect anthocyanin concentrations in mature berries in this study (Figure 3). Nonetheless, few and minor differences in anthocyanin concentrations among grafted and own-rooted vines were found. Generally, the effects of grafted vines, except CS/SO4, on anthocyanin concentrations depended on seasons in this study. In 2015, except for SO4, all the rootstocks showed slight positive effects on anthocyanin accumulation. Notably, 'Merlot' and 'Shiraz' grafted onto 110R both possessed higher concentrations of anthocyanins than ungrafted grapevines in the previous studies [31; 32]. However, in 2016, anthocyanin concentrations were slightly reduced by rootstocks, except 5 BB and 110R, which exhibited a negligible influence.