Evolución de la composición y síntesis de compuestos fenólicos de plantas de Marselan sometidas a regulación fuente/fosa en dos terroir vitícolas del sur de Uruguay

Viticulture in Uruguay has undergone constant evolution, driven by the pursuit of higher quality and its integration into the international market. In this context, the Marselan variety, a cross between Grenache Noir and Cabernet Sauvignon, has demonstrated high oenological potential. However, scientific information regarding its behavior under different terroirs and agronomic management practices remains scarce. This study aims to analyze the impact of source-sink regulation on berry ripening and the synthesis of secondary metabolites in two viticultural regions in southern Uruguay.

The study was conducted during the 2020-2021 season in commercial vineyards located in Los Cerrillos and Garzón, two regions with marked differences in soil and climate. A randomized complete block experimental design was used, with three treatments: (1) control treatment (TC) with no intervention, (2) pre-flowering leaf removal (DPF) performed at Eichhorn and Lorenz phenological stage 17, and (3) fruit set leaf removal with crop thinning (DC+R) performed at stage 27, followed by cluster thinning between stages 33 and 35 of the same scale. Berry samples were collected at three time points before harvest, analyzing soluble solids, acidity, pH, total polyphenols, anthocyanins, and tannins. Total polyphenols were analyzed using the Folin-Ciocalteu method, measuring absorbance at 765 nm. Total anthocyanins were quantified using the Riberéau-Gayon and Stonestreet (1965) method, measuring absorbance at 520 nm. Tannins were determined through the methylcellulose precipitation method according to Sarneckis et al. (2006), with readings taken at 280 nm using a spectrophotometer. These methods allowed for the evaluation of the concentration and evolution of different phenolic compounds at three key moments during berry ripening.

The results showed that the DC+R treatment increased the accumulation of soluble solids, total polyphenols, and anthocyanins in both locations, with a more pronounced effect in Los Cerrillos, where it accelerated berry ripening and enhanced the synthesis of secondary metabolites. The DPF treatment exhibited terroir-dependent behavior: in Los Cerrillos, it had no significant impact on phenolic compound accumulation or berry ripening, whereas in Garzón, it reduced yield and promoted the synthesis of total polyphenols and anthocyanins in the berries.

The findings of this study highlight the importance of managing the source-sink relationship through leaf removal and crop load adjustment techniques tailored to specific terroir conditions. These strategies optimize ripening and improve the oenological quality of Marselan grapes, contributing to the production of high-end wines and the development of the Uruguayan wine industry.