Ensuring a well-ventilated bunch zone is a key target of canopy management in viticulture, facilitating spray penetration and reducing the spread of fungal diseases. To achieve this aim, the use of mechanical leaf removal systems available since the early 1990s became increasingly widespread under central European conditions. However, apart from positive phytosanitary impacts, leaf removal alters canopy microclimate substantially. While some research has been conducted on the effects of such canopy management techniques on red grape quality, their effects on fruit quality of white varieties have rarely been investigated. The objective of this thesis was to provide a deeper understanding of the microclimatic influence on grape quality at different stages of berry development, with a focus on the white grape cultivar Riesling (Vitis vinifera L.). An optimized protocol for high-throughput FTIR measurements and other state of the art analysis were used to quantify compounds relevant for grape and wine quality. Three different approaches to create samples from variable microclimatic conditions were evaluated: The removal of leaves in the bunch zone to maximize bunch exposure, the complete shading of bunches using opaque boxes and the utilization of the natural variance of the microclimatic conditions within homogenous vineyards. The effect of microclimate manipulation on different classes of phenolic substances was large in the case of flavonols, and rather small in the case of flavanols and hydroxycinnamic acids. The only effects of microclimatic conditions on flavanol and hydroxycinnamic acid concentration were observed when leaf removal or shading were conducted directly after berry set. Radiation exposure at any developmental stage led to a rapid increase of flavonol concentration in the berry skin, whilst without radiation the synthesis of flavonols was inhibited completely. The concentration of amino acids was strongly negatively correlated with the concentration of phenolic substances. Bunches shaded during the ripening phase had barely detectable monoterpene concentrations, and re-illumination during the last weeks of ripening only increased their concentration by 2-fold, representing just 20 % of the concentration of the control treatment. In the same time period, flavonol concentration recovered rapidly to levels comparable to those of the control. Although monoterpenes accumulate only at later stages of ripening, the most important period for their synthesis is around veraison, when the expression of monoterpene biosynthetic genes is at a maximum. Microclimate also influences the optical properties of a berry, mainly because of their effects on chlorophyll and carotenoid synthesis as well as degradation and phenol accumulation. Sorting berries by their VIS-spectra led to subsamples of significantly different composition of aroma compounds organic acids and amino nitrogen. The common factor behind these compositional and optical differences seems to be the berry microclimate, which is in accordance with our other studies. These findings may be technically exploited in targeted berry sorting operations for premium winemaking or to remove undesired fruit prior to fermentation.
Verknüpfung zu Publikationen oder weiteren Datensätzen
