The Douro Demarcated Region (DDR) has peculiar edaphoclimatic characteristics that provide a suitable terroir for premium wine production. As climate change effects continue to emerge, ensuring productivity and quality becomes increasingly important for viticulturists, as those directly determine their profits. Cultural approaches, such as the use of biostimulants, are actively being developed to mitigate abiotic stress. The main objective of this work was to assess the effect of foliar sprays of a seaweed (Ascophyllum nodosum) based extract (ANE) and glycine betaine (GB) on grape berry quality, bioactive compounds, and antioxidant activity. A trial was installed in a commercial vineyard (cv. Touriga Franca) in the Douro Superior (Upper Douro) sub-region of the Douro Demarcated Region. In 2020, a total of three foliar sprayings were performed during the growing season, namely at pea-size, bunch closure, and veraison. There was a positive effect of both biostimulants (ANE and GB) on the physiological and biochemical performance of cv. Touriga Franca exposed to summer stress. In general, the GB 0.2% spraying was the most promising treatment for this grape cultivar, as it increased berry quality, the concentration of bioactive compounds (total phenolics, flavonoids and ortho-diphenols), and the antioxidant activities. These results revealed the efficacy of biostimulants sprayings as sustainable viticultural practice, improving berry quality under summer stress conditions.

Plant-based extracts have been recently employed as sustainable tools to improve biotic and abiotic stress tolerance and increase grape quality. However, knowledge about the effect of these extracts on secondary metabolism compounds, that are fundamental for grape and wine quality, is still scarce. In this study, a trial was installed in an experimental vineyard with the variety Touriga Franca located at University of Trás-os-Montes e Alto Douro, Baixo Corgo sub-region of the Douro Demarcated Region, in two growing seasons: 2019 and 2020. Foliar sprayings with the natural products, nettle extract (NE) and Japanese knotweed extract (JKE), were tested to evaluate their effect on downy mildew incidence and severity, on grapevines bioactive compounds contents and antioxidant activity, at veraison and harvest. NE and JKE have stimulated an improvement in the concentration of total carotenoids in leaves and the concentration of total phenolics in berries along with an improved concentration of total phenolics and flavonoids in leaves and berries. Thus, it was verified that these extracts enhance grapevines bioactive compounds and antioxidant capacity and, consequently, the physiological performance of the plant and the quality of the berries. Considering the challenges posed by climate change in the Mediterranean basin viticulture sector, the use of plant extracts might represent a sustainable tool to mitigate the increasing severity of drought, often associated to heatwaves and high irradiation. Moreover, downy mildew incidence results suggest that an integrated disease management approach combining conventional control with alternative fungicides can be used in the future for a more sustainable viticulture.

Climate change will pose a challenge for the winemaking sector worldwide, bringing progressively drier and warmer conditions and increasing the frequency and intensity of weather extremes. The short-term adaptation strategy of applying biostimulants through foliar application serves as a crucial measure in mitigating the detrimental effects of environmental stresses on grapevine yield and berry quality. The aim of this study was to evaluate the effect of foliar application of a seaweed based biostimulant (A. nodosum – ANE) and glycine betaine (GB) on berry quality, bioactive compounds, antioxidant activity, and elucidated their action on the secondary metabolism. A trial was installed in a commercial vineyard (cv. ‘Touriga Franca’) in the Cima Corgo (Upper Corgo) sub-region of the Douro Demarcated Region. A total of four foliar sprayings were performed during the growing season: at flowering, pea size, bunch closer, and veraison. There was a positive effect of GB in the berry quality traits. Both ANE and GB increased the synthesis of anthocyanins and other phenolics in berries and influenced the expression of genes related to the synthesis and transport of anthocyanins (CHS, F3H, UFGT, MATE1 and GST). So, they have the potential to act as elicitors of secondary metabolism, leading to improved grape quality, but also sets the foundation for sustainable agricultural practices in the long run.