Abstract
Girdling is a traditional horticultural practice applied at fruit set or other phenological stages, and is used mostly as a vine management. In grapevines, it is used primarily for table grapes to improve berry weight, sugar content, color, and to promote early harvest. The objective of this study was to evaluate the effect of trunk girdling applied at veraison, in ‘Cabernet Sauvignon’ wine grapes (Vitis vinifera L.), on agronomical and physiological parameters during vine development from the onset of ripening (veraison) to harvest, and additionally to quantify the effect of girdling on primary and secondary metabolism. Girdling was applied 146 days after pruning (dap) at veraison, when berry sampling for metabolomics and agronomical evaluations commenced, with a further three sampling dates until harvest, at 156 dap (30% maturation, 10 days after girdling-dag), 181 dap (70% maturation, 35 dag), and 223 dap (commercial harvest, 77 dag). Skin/pulp and seed tissues were extracted separately and metabolomics was performed using one-dimensional proton nuclear magnetic resonance (1D 1H NMR) spectroscopy and high performance liquid chromatography (HPLC-DAD). At harvest, girdling significantly increased stomatal conductance (gs) in vines, decreased glutamine concentrations, and increased anthocyanin and flavonol concentrations in the skin/pulp tissues of grape berries. Berry weight was reduced by 27% from 181 dap to harvest, and was significantly higher in grapes from girdled vines at 181 dap. Sugars, organic acids, and other amino acids in skin/pulp or seeds were not significantly different, possibly due to extra-fascicular phloem vessels transporting metabolites from leaves to the roots. Using a metabolomics approach, differences between skin/pulp and seeds tissues were meaningful, and a greater number of secondary metabolites in skin/pulp was affected by girdling than in seeds. Girdling is a simple technique that could easily be applied commercially on vine management to improve berry color and other phenolics in ‘Cabernet Sauvignon’ grapes.
Highlights
‘Cabernet Sauvignon,’ originating from France, is the most important grape variety used for red wines, varietal, or blended in all winegrowing regions worldwide
Vine management practices should be evaluated for their ability to reduce cycle and harvest time in order to retain grapes with optimal characteristics, which include a high concentration of sugars and phenolics, balanced acidity and pH, and reduced volume loss due to shriveling
In grapevines, girdling is normally applied at fruit set or veraison, depending on whether the objective is to increase berry size, reduce cycle duration, or promote metabolite accumulation (Harrell and Williams, 1987; Roper and Williams, 1989; Böttcher et al, 2018). This technique is typically used for table grapes sold as fresh fruit; to our knowledge, the influence of girdling on grapevine development, berry weight, and primary and secondary metabolism in ‘Cabernet Sauvignon’ grapes intended for winemaking has not yet been investigated. The application of this technique to winemaking grapevines at veraison should increase the concentration of phenolic compounds and sugars in grape berries, and reduce the growing season to allow for early harvest, avoiding volume loss during the winemaking process (Keller et al, 2006)
Summary
‘Cabernet Sauvignon,’ originating from France, is the most important grape variety used for red wines, varietal, or blended in all winegrowing regions worldwide. This technique is typically used for table grapes sold as fresh fruit; to our knowledge, the influence of girdling on grapevine development, berry weight, and primary and secondary metabolism in ‘Cabernet Sauvignon’ grapes intended for winemaking has not yet been investigated The application of this technique to winemaking grapevines at veraison should increase the concentration of phenolic compounds and sugars in grape berries, and reduce the growing season to allow for early harvest, avoiding volume loss during the winemaking process (Keller et al, 2006). HPLC is largely used to determine phenolics in grapes and wines, with easy identification of the anthocyanins, flavonols, flavanols and hydroxycinnamic acids in a single run at different wavelengths (Peng et al, 2002; Oberholster et al, 2013; Garrido-Bañuelos et al, 2019b; Girardello et al, 2019)
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