Aplicación de deshojado en prefloración en las variedades Syrah y Tannat: Análisis de la influencia sobre las variables de rendimiento, composición, sanidad y estructura del hollejo

This study evaluated the effect of preflowering leaf removal (DPF) and the application of Prohexadione calcium (PCa) on vegetative development, yield components, grape composition, sanitary status, and berry skin histological structure in the grapevine cultivars Tannat and Syrah under the edapho-climatic conditions of southern Uruguay. The effect of the treatments on vegetative parameters was generally limited, although some differences were observed. Potential exposed leaf area showed no significant differences among treatments within each cultivar but differed between cultivars, with higher values in Syrah. The proportion of exposed clusters also did not differ significantly among treatments in both cultivars. The number of leaf layers remained within optimal ranges; however, in Syrah the treatments reduced canopy density compared with the control. Regarding yield components, the number of clusters per plant was not affected by the treatments, indicating that differences were mainly determined by genotype, with higher cluster numbers in Syrah. Average cluster weight showed no significant differences, although slight decreasing trends were observed under Prohexadione calcium in Syrah and under pre-flowering leaf removal in Tannat. Yield per plant was not significantly modified by the treatments, and Syrah exhibited higher productivity than Tannat. Prohexadione calcium significantly reduced berry weight in Syrah, whereas pre-flowering leaf removal did not produce significant changes. In Tannat, however, early leaf removal significantly reduced berry size. Physiological responses related to cluster compactness were not statistically significant. Berry growth followed a normal developmental pattern, although in Syrah the application of Prohexadione calcium limited final berry growth. With respect to berry composition, soluble solids increased normally during ripening, with no differences among treatments at harvest. Total acidity decreased progressively in both cultivars without final differences among treatments, while pH increased throughout ripening and was only slightly affected by the treatments. Phenolic composition showed cultivar-dependent responses: in Tannat, anthocyanin potential and total polyphenol index increased following early leaf removal, whereas in Syrah the responses were more moderate. The histological structure of the berries, specifically cuticle thickness, epidermis thickness, hypodermis thickness, and total epicarp thickness, did not show significant differences among treatments or between cultivars, indicating a strong structural stability of these tissues. However, the number of skin cells displayed a differential response within each cultivar. In Tannat, the highest values were observed in the control treatment and decreased under early leaf removal, while in Syrah the treatments, particularly Prohexadione calcium, produced significant increases in this parameter. Overall, the results demonstrate that the evaluated vineyard management practices effectively modified canopy structure and certain parameters related to technological and enological grape quality, with cultivar-specific responses. Nevertheless, yield and sanitary status were strongly influenced by environmental conditions during the growing season. This work provides original information at the national level regarding the interaction between agronomic management, berry skin anatomy, and phenolic composition in Tannat and Syrah, contributing to a better understanding of their enological potential under the edapho-climatic conditions of southern Uruguay.