Terpenoid profiles and biosynthetic gene expression pattern in Asti DOCG white muscat grapes at ripening as affected by different canopy management protocols

Aim: The main goal of this study was to find an efficient canopy management to limit the high temperature-related aroma losses of White Muscat grapes, and consequently to preserve the quality standards of Asti DOCG wines.

Methods and Results: Four different strategies have been tested in two vineyards of the Asti DOCG production area: pre-flowering leaf removal (m1), post-berry set leaf removal (m2), leaf removal at veraison (m3), and clusters thinning (m4). Control vines (m0) did not receive any thinning or defoliation. Grapes were collected at four time points: seven days before the commercial harvest, at the commercial harvest scheduled for “Asti spumante” wine, at the commercial harvest scheduled for “Moscato” wine and overripening. Free and glycosylated terpenoids content (GC-MS) as well as the expression of key genes involved in terpenoids biosynthesis and metabolism (RT-qPCR) were analysed separately in skin and pulp. The results revealed a peak of volatile accumulation, which occurred early and late throughout the sampling times. The treatments m3 and m4 were, in general, those more effective in enhancing the aroma profiles in both tissues analysed. Correspondingly, in these grapes, specific genes, such as VvDXS3 and VvGT14 resulted up-regulated. Other genes, such as VvHDR, showed different expression pattern resulting, in general, more expressed in pulp than skin, regardless the applied treatment.

Conclusions:

Based on these preliminary trials carried out in a specific production area of White Muscat, it seems that m3 and m4 treatments had a significant effect on the volatile’s accumulation in both grape skin and pulp. m1 treatment resulted to be the less effective in inducing changes in the aroma profile and the terpenoid biosynthetic pathway.

Significance and Impact of the Study: Moscato d’Asti DOCG is one of the most characteristic enological products of Piemonte (North-West Italy) wine grapes-growing area. It comes exclusively from White Muscat grapes which are exalted by the climatic and geographical conditions of the production area. Indeed, the interactions between vine and environment, limestone terrain and micro-climate typical of hilly zones leads to a characteristic fruity and sweety aroma. The characteristic aroma of Muscat wine is attributed to the presence of specific terpenoids, mainly linalool, nerol, geraniol, trans-piran linalool oxide and citronellol. The grapevine terpenoids pathway is strongly regulated by endogenous and environmental factors and among them, temperature and light exposure plays a crucial role. As recently observed, the content of these compounds is strongly decreasing due to the increasing temperatures. Higher temperature during the growing season is forcing growers to find ways to reliably control grape composition preserving the typical aroma of Asti DOCG wines. The present study could offer important information to address grower’s choice in term of canopy management that are better suited to the changing climate.