Effects of vine top shading on the accumulation of C6/C9 compounds in 'Cabernet Sauvignon’ (Vitis vinifera L.) grape berries in northwestern China

The Xinjiang Uygur Autonomous Region is an arid and semi-arid region with low rainfall and strong sunlight; thus, grape berries in this region accumulate sugar content rapidly, and the ripening process is shorter than that in other regions. Although previous studies illustrated that altered sunlight conditions could influence the aroma profiles of grape berries, less attention has been paid to the effect of vine top shading on volatile compounds under a dry-hot climate.We focused on the effects of vine top shading on the concentrations of linolenic and linoleic acids, as well as their metabolites, the C6/C9 compounds, in grape berries. Four vine top shading treatments at veraison (ripening onset) and post-veraison (skin full coloration) were performed by reducing solar exposure to the grapevines by 20% and 50% respectively. Apart from (E)-2-hexenal in the 20% shading treatment of 2016, (E)-2-hexenal were not promoted by the 50% shading and 20% shading treatments during veraison to harvest in both of the vintages. By contrast, the influence of vine top shading from post-veraison till harvest was different between the two vintages; these C6 compounds were decreased in both of the shading treatments in 2016, whereas most of them were promoted in 2017, possibly related to daily sunshine hours in this period. In addition, the C9 compound nonanal with very low concentration exhibits a significant difference among various treatments by two-factor analysis of variance. As for linolenic acid and linoleic acid, two types of C6 compound biosynthetic precursors, four shading treatments all reduced their concentration, except for linolenic acid in the 50% shading treatment of 2016. Moreover, it appeared to have no apparent correlation between the variations of two precursors and their volatile metabolites, indicating that there is a complex impact of vine shading on C6 compound biosynthesis.Vine top shading at veraison can reduce the accumulation of some C6 compounds in grape berries, but no consistent consequence was attained for the vine shading at pre-veraison. The findings indicate the significance of grapevine solar exposure management at veraison in controlling the level of C6 compounds in a dry-hot region like Xinjiang. © 2021 Society of Chemical Industry.