Impact of light exposure on compositional development of white Riesling (Vitis vinifera L.)
Abstract
The aim of this study was to investigate the effect of leaf removal during two developmental stages on the compositional development of white Riesling (Vitis Vinifera L.). During the 2011 and 2012 growing seasons, a field trial (Vitis vinifera L. cv. Riesling Gm 198-25 grafted on SO4) was conducted in which light conditions were manipulated by a) complete shading through the application of light-impermeable boxes on the bunches or b) full light exposure through defoliation of the bunch zone. Both treatments were applied shortly after the onset of berry size expansion (modified E-L 27 ; (Coombe, 1995)) and at the onset of veraison (E-L 34) and compared to a non-manipulated control. While temperature and humidity in the boxes were similar to the values measured in the ambient, PAR measured in the boxes only reached about 1 % of total PAR. Results showed that berry skin phenolics increased, and malic acid and amino acid concentration increased with decreasing radiation interception after veraison, while concentration of sugars did not vary significantly between the treatments. The E-L27 defoliation treatment showed a higher concentration of phenolics compared to the E-L 34 defoliation treatment. The increase in berry skin phenolics could be explained by an increase in quercetines, while none of the treatments showed an effect on the concentration non-flavonoid phenols. These findings are consistent with data aquired in previous seasons. The application of shading and defoliation at E-L 27 did not induce significant changes in berry amino acid and malic acid concentration compared to defoliation or shading at E-L 34. Defoliation was shown to decrease bunch rot infection and to increase sunburn incidence in comparison to the control treatment. However, no differences in sunburn incidence and bunch rot infection were detected between early and late defoliation.
Publication date: 07/09/2026
Issue: GiESCO 2013
Type: Oral
Authors
1 Institute of General and Organic Viticulture
2 Institute of Wine Chemistry and Beverage Technology; University Geisenheim, 65366, GEISENHEIM, Germany
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Keywords
light exposure, berry composition, phenolics, defoliation, shading