[en] Background and aims: The economic regulation of yield is becoming more important as pressure increases to consistently produce high-quality fruit and manage production costs. The main goal of this study was to verify whether early leaf removal may be an efficient technique to regulate crop yield and to improve cluster microclimate as well as grape and wine quality in Mediterranean Vitis vinifera cultivars. Methods: Early leaf removal was manual and mechanically conducted at two timings (pre-bloom and fruit-set) in Tempranillo, Graciano and Mazuelo cultivars. The effects of early defoliation on yield components, leaf growth, canopy porosity and fruit health were assessed. Moreover, the impact on grape and wine composition as well as on the wine sensory properties was also studied. Results: Early leaf removal induced a significant decrease of fruit set, cluster weight and yield per vine. As a result, looser clusters of less number of berries were obtained. Berry weight was found to be similar or smaller than that of control but of increased relative skin and skin-to-pulp ratio. A leaf recovery response to defoliation was showed by the vines, leading to similar or even increased leaf-to-fruit ratios. Cluster exposure and canopy porosity were substantially improved, favoring a diminishment of Botrytis rot. In terms of grape composition, both technological and phenolic maturities were improved, leading to more alcoholic wines of higher anthocyanin and polyphenol (hidroxycinnamic acids and flavonols) concentrations, as well as of better mouthfeel sensory properties. Furthermore, when no biotic stress (such as Botrytis) was present, early leaf removal induced higher concentrations of resveratrol in the wines. Both timing and modality of defoliation were important in reducing yield components as well as in improving grape and wine quality and the more pronounced effects were observed for the pre-bloom and mechanical treatments, respectively. Hand removal of 4 leaves was overall ineffective in altering yield components and grape and wine composition. Conclusions: Early leaf removal may be an efficient and valid strategy for grapevine crop regulation. It is an important viticultural technique easy to be mechanically performed in order to substantially improve grape and wine quality in cultivars Tempranillo, Graciano and Mazuelo. Significance of the study: Early defoliation might become a novel, powerful and efficient technique to regulate grapevine yield and improve grape and wine quality. Its easiness of mechanization may be very interesting for the grape and wine industry, and may become an economically important alternative to traditional, expensive, and labor intensive practices, such as manual cluster thinning.

[es] Introduccion y objetivos: La regulacion del rendimiento del vinedo es una cuestion de gran importancia en la viticultura actual, a medida que crece la presion por producir uva de calidad a unos costes sostenibles. El objetivo principal de este trabajo era verificar si el deshojado precoz puede ser una tecnica eficaz para regular la produccion de uva, mejorar el microclima de los racimos asi como la calidad de la uva y del vino en variedades de vid caracteristicas de la viticultura mediterranea. Metodologia: Se realizo un deshojado en dos epocas (pre-floracion y cuajado) de forma manual y mecanica, en las variedades de vid (Vitis vinifera L.) Tempranillo, Graciano y Mazuelo. Se estudio los efectos del deshojado precoz sobre los componentes de la produccion, el desarrollo vegetativo, la porosidad de la canopy y el estado sanitario de los frutos. Asimismo, se estudio el impacto del deshojado sobre la composicion de la uva, del vino y de sus caracteristicas sensoriales. Resultados: El deshojado precoz redujo significativamente la tasa de cuajado, el peso del racimo y la produccion de uva por cepa. Se obtuvieron racimos mas sueltos, con menor numero de bayas. Estas eran de menor o igual peso de baya pero con mayor proporcion de hollejos y ratio hollejo/pulpa. En respuesta a la defoliacion las cepas mostraron un crecimiento vegetativo compensatorio, que se tradujo en el mantenimiento e incluso incremento de la relacion hoja/fruto. La porosidad de la canopy y la exposicion de los racimos mejoraron sustancialmente y favorecieron una menor incidencia de Botrytis. Mejoro significativamente el grado de madurez tecnologica y fenolica en la uva, que dio lugar a vinos con mayor grado alcoholico, antocianos y polifenoles (acidos hidroxicinamicos y flavonoles), asi como mejores caracteristicas organolepticas en boca. Ademas, en ausencia de un estres biotico como la Botrytis, el deshojado precoz condujo al aumento de la concentracion de resveratrol en vino. La epoca y modo de ejecucion tuvieron un efecto importante en la reduccion de los componentes de la produccion asi como en la mejora de la calidad de la uva y del vino, observandose los efectos mas acusados en las cepas deshojadas en pre-floracion, y de forma mecanica, respectivamente. El deshojado manual de 4 hojas fue en general insuficiente para alterar los componentes de la produccion o la composicion de la uva y del vino. Conclusiones: El deshojado precoz es una estrategia valida y eficaz para regular el rendimiento productivo de la vid. Ademas, es una importante practica viticola, facil de mecanizar, para mejorar sustancialmente la calidad de la uva y del vino en las variedades Tempranillo, Graciano y Mazuelo. Importancia e impacto: El deshojado precoz podria convertirse en una novedosa, potente y eficaz tecnica para regular el rendimiento productivo y mejorar notablemente la calidad de la uva y del vino. Su facil mecanizacion puede ser de gran importancia para el sector vitivinicola, ya que puede resultar una alternativa economicamente competitiva a las costosas practicas manuales tradicionales, como el aclareo manual de racimos.