Flavonoids are important metabolites of wine grapes, which have important effects on the qualities of the grape fruits and their wines. In this study, the effects of different rootstocks on the physicochemical parameters and flavonoid substances of Tannat (Vitis vinifera L.) grapes were studied to provide the theoretical basis for the selection and utilization of rootstocks.

In the present research, Tannat shoots were used as scions and were greenwood grafted on four different kinds of rootstocks, including 1103P, 101-14, SO4, and Beta. On the bases of the analysis of the basic physicochemical parameters (total soluble solid content, titratable acid, pH, and 100-berry weights) of the commercial mature grape berries of these grapevines grafted on different rootstocks, the compositions and contents of the flavonoids in the corresponding grape berries were detected by using high performance liquid chromatography-mass spectrometry (HPLC-MS), in the three vintages of 2016, 2017 and 2019.

The rootstocks had little effect on the 100-berry weights of the Tannat grapes; the contents of the total soluble solids were higher in the combination of Tannat/101-14, as well as the own-rooted Tannat; the titratable acids of the grape juice of the Tannat/101-14 and the Tannat/Beta combinations were higher than the own-rooted Tannat grapes. In the part of flavonoids, the contents of anthocyanins and flavonols in the Tannat/SO4 combination was the lowest in all of these combinations; the concentrations of anthocyanins and flavonols in the Tannat/101-14 combination and the own-rooted Tannat were higher than those of other combinations; the concentrations of flavanols in the skins of the Tannat/101-14 combination was higher. In addition, the concentrations of anthocyanins and flavonols in the Tannat/ 11103P combination was lower, but the content of flavanols in the skins of the Tannat/1103P combination was relatively high. Besides, the results of two-factor ANOVA of the year and the rootstock showed that the rootstocks had significant effects on all types of anthocyanins. All the four rootstocks showed a tendency of reducing the anthocyanins of peonidin, petunitin, malvidin, non-acylation, acetylation and coumaric acylation. In the mature fruits, the quercetins were the most abundant flavonols, followed by myricetins, while syringetins and laricitrins accounted for a smaller proportion. Rootstocks had a significant effect on the myricetins and laricitrins, which reduced the contents of myricetin and laricitrin to different degrees. Through the establishment of OPLS-DA (Orthogonal Partial Least Squares Discrimination Analysis) model, it was found that the Tannat/101-14 combination was mainly distinguished by the malvidin anthocyanin compared with the own-rooted grapes. The main difference compounds of Tannat/Beta combination were anthocyanins of malvidin, delphinidin and acetylation, the total flavanols and quercetin compounds. The difference compounds of the Tannat/SO4 combination were anthocyanins of malvidin, delphinidin, acetylation, and quercetins. The Tannat/1103P combination mainly consisted of acetylated anthocyanins and quercetins.

In Beijing region, all the four rootstocks (1103P, SO4, Beta, and 101-14) showed a tendency of reducing the flavonoid concentrations, including anthocyanins of peonidin, petunitin, malvidin, non-acylation, acetylation, coumaric acylation quercetins, and laricitrins. The rootstock '101-14' was beneficial to the accumulation of anthocyanins, flavonols and flavanols in fruit skins, which was conducive to the improvement of the wine quality, so it was recommended to be used. However, Tannat grapes grafted with SO4 had less flavonoid accumulation, which was not recommended to be used.