Rootstock and irrigation modify berry aroma characteristics in 'Merlot' and 'Sangiovese' grapevines

Rootstocks can modify scion response to water stress in grapevines, but little is known about the combined effect of rootstock and deficit irrigation on berry quality. An experiment was performed on 5-year-old potted grapevines (Vitis vinifera L. 'Merlot' and 'Sangiovese') to compare the effect of two rootstocks ('SO4' and '1103P') and three irrigation regimes (full irrigation, FI; regulated deficit irrigation 1, RDI 1; regulated deficit irrigation 2, RDI 2) on fruit quality and their aroma characteristics. Cultivar and rootstock combinations were subjected to water stress from fruit set through veraison and from veraison through harvest in RDI 1 and RDI 2 vines, respectively, whereas they were fully irrigated for the rest of the irrigation period. Control grapevines (FI) were fully-irrigated throughout the entire season. In 'Merlot' and 'Sangiovese', the total aroma concentrations ranged from 3 to 8 mu g g(-1) and 2 to 5 mu g g(-1) of berry fresh weight, respectively. In both cultivars, monoterpenes were higher in RDI 1 vines, particularly on 'SO4' (+10% than '1103P'), whereas water stress imposed after veraison negatively affected monoterpenes concentrations in 'Sangiovese' vines (-25% with respect to control plants). Benzene derivatives and C-13-norisoprenoids were enhanced in both cultivars by RDI 1 treatment, with some differences between rootstocks: benzene derivatives showed greater values in SO4 rootstock, C-13-norisoprenoids were higher in '1103P'. Water deficit was applied before veraison also induced higher concentrations of vanillins and phenols in 'Sangiovese' berries. This was particularly evident in 'SO4'-grafted vines, which showed higher values with respect to 'Sangiovese' vines grafted on '1103P' (+45%, average between the two aromas classes). Deficit irrigation may be a useful tool to enhance grape aroma, although the rootstock-scion combination can magnify or inhibit this effect.