Background: In viticulture, rootstock genotype plays a critical role to improve scion physiology, berry quality and to adapt grapevine (Vitis vinifera L.) to different environmental conditions. This study aimed at investigating the effect of two different rootstocks (1103 Paulsen-P-and Mgt 101-14-M) in comparison with not grafted plants-NGC-on transcriptome (RNA-seq and small RNA-seq) and chemical composition of berry skin in Pinot noir, and exploring the influence of rootstock-scion interaction on grape quality. Berry samples, collected at veraison and maturity, were investigated at transcriptional and biochemical levels to depict the impact of rootstock on berry maturation. Results: RNA-and miRNA-seq analyses highlighted that, at veraison, the transcriptomes of the berry skin are extremely similar, while variations associated with the different rootstocks become evident at maturity, suggesting a greater diversification at transcriptional level towards the end of the ripening process. In the experimental design, resembling standard agronomic growth conditions, the vines grafted on the two different rootstocks do not show a high degree of diversity. In general, the few genes differentially expressed at veraison were linked to photosynthesis, putatively because of a ripening delay in not grafted vines, while at maturity the differentially expressed genes were mainly involved in the synthesis and transport of phenylpropanoids (e.g. flavonoids), cell wall loosening, and stress response. These results were supported by some differences in berry phenolic composition detected between grafted and not grafted plants, in particular in resveratrol derivatives accumulation. Conclusions: Transcriptomic and biochemical data demonstrate a stronger impact of 1103 Paulsen rootstock than Mgt 101-14 or not grafted plants on ripening processes related to the secondary metabolite accumulations in berry skin tissue. Interestingly, the MYB14 gene, involved in the feedback regulation of resveratrol biosynthesis was upregulated in 1103 Paulsen thus supporting a putative greater accumulation of stilbenes in mature berries.

Different types of oenotannins were added to Vitis vinifera cv. Sangiovese grapes of various composition and the resulting wine color parameters were measured, including intensity, hue, total phenol index, monomer anthocyanin content, and colored polymeric pigment content. Oenotannins were also tested during pre-and postfermentation on grapes harvested in 2003 from two growing areas. Grapes from the 2004 harvest were tested at different ripeness using only oenotannins exhibiting the best wine color stabilization in 2003. The response of different oenotannins varied according to grape characteristics, with gallnut and grape seed tannins most reliably stabilizing and increasing color intensity even after six months of storage. The same tannins positively affected wine color stabilization, an effect further enhanced in wine produced from less ripe grapes. Timing of oenotannin addition and grape characteristics had a significant effect on color intensity and stabilization. The estimation of grape phenolic maturity may allow for improved wine color characteristics by tailoring the use of oenotannins.

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Despite phenotypic plasticity that allows the adaptation to harsh environments, when vines experience severe abiotic stresses, they can suffer from metabolic damages affecting grape production and quality. Grafting is an affordable strategy to mitigate these negative consequences since the rootstock can increase the drought tolerance in the scion. This work explored the effects of pre-veraison water deficit on vines grafted on different rootstocks (Mgt 101-14 and 1103 Paulsen) to obtain physiological, biochemical, and molecular information about the influence on grape quality. Repeated measurements were carried out to assess vine physiology, production, technological maturity, and berry phenolic composition. qRT-PCRs were executed on berry skins at maturity to assess the expression levels of ten genes and five miRNAs involved in the phenylpropanoid pathway. Water stress caused significant alterations in grape technological maturity. The rootstock effect was not detected in primary metabolism while it was well defined in the accumulation of phenolic compounds in berries (such as anthocyanins). Finally, significant differences were identified in gene and miRNA expression between water-stressed and well-watered vines. In conclusion, the response to water stress can be modulated by rootstocks, which mainly act by regulating secondary metabolism, especially in grapes.