Forcing vine regrowth in vitis vinifera cv. touriga nacional at Douro region

Context and purpose of the study - Douro Region, characterized by a Mediterranean climate type and schist soils, is subjected to water and heat stresses conditions during summer. In some locations, the temperatures registered during berry maturation, lead to fruit ripen during warmer months, increasing the degradation of organic acids, tannins and phenolics that can negatively affect the quality of wines. Forcing vine regrowth is a new practice, being currently tested in Mediterranean countries, that aims to shift fruit ripening to cooler months of the year by pruning the plants after fruit set - Crop Forcing (CF) - removing all the leaves and bunches and leaving five buds per shoot, in order to reduce the negative effect of high temperatures during berry maturation on its quality.

Material and methods - This work aims to study the effect of forcing vine regrowth in cv. ‘Tourigarepla Nacional’ under Regulated Deficit Irrigation conditions, in vines irrigated with 30% of the evapotranspiration. Three modalities were established: vines with no forcing regrowth (Control - CTRL), vines with CF set 15 days after fruit set (CF15) and plants with CF performed 30 days after fruit set (CF30). The effects on phenology, canopy development, berry development and fruit composition were assessed.

Results - Plants subjected to CF15 were severely damaged after phenological stage of full bloom due to exceptional conditions to downy mildew (Plasmopara viticola) infections, boosted by the new phenological stages due to crop forcing. On the other hand, the crop forcing modality CF30 registered a delay of nearly two months in all phenological stages, since fruit set until harvest. Shorter internodes (50%) and lower leaf area (35%) were observed in CF30 when compared to the CTRL plants at ripening stage. The number of shoots at fruit set was also significantly different between the three treatments, with higher values in CF modalities and lower values in CTRL plants. In terms of yield, comparing CF30 (harvested in November, 27th) and CRTL (harvest in October, 6th), it was found that CF reduced the number of bunches (39%), the number of berries per bunch and the average berry weight (60%). Moreover, berries from the forced crop modalities (from grapes) had a pH slightly lower (3.35), higher titratable acidity (8.82 g/L) and lower ˚Brix (17.02˚Brix) when compared to CRTL, with pH values of 3.74, titratable acidity of 4.16 g/L and Brix of 23.93˚. Despite these results, further study should be carried out to evaluate the long-term effects of CF and its applicability depending on the climatic conditions for each year.