Background & Aim
Sunburn is a physiological disorder that reduces grape quality and vineyard yield. It is the result of excessive sunlight and high temperatures. As climate change continues to increase air temperatures, reports of sunburn damage in vineyards worldwide are becoming more frequent. Grapes produce secondary metabolites (carotenoids, polyphenols and aroma compounds) to counter photo-oxidative stress and acclimate to higher radiation environments.
This study evaluated changes in these compounds during ripening when grapes were exposed post-flowering (ED) and at véraison (LD), and compared them to a non-defoliated control (ND).
Methods & Results
ND contained more terpineol and violaxanthin, and the defoliated treatments contained more zeaxanthin, carotene, C6 compounds and flavonoids. ED berries adapted better to higher-light environments, displayed larger changes in secondary metabolite concentrations and lower levels of sunburn damage than LD berries did. The composition of berries with increasing sunburn damage was evaluated for the first time. Berries with no damage had the lowest concentrations of flavonoids and oxidized glutathione, and the highest concentrations of chlorophyll and terpineol. As damage increased, destruction of photosynthetic pigments, increase in polyphenols and loss of aroma compounds were evidenced. A significant effect of temperature and developmental stage on grape composition was also observed.
Significance of the study
This study provides a holistic overview of changes in secondary metabolites experienced by grape berries when exposed to excessive light, how these vary along development and how they affect sunburn incidence.
Reference: Gambetta, J.M.; Romat, V.; Schmidtke, L.M.; Holzapfel, B.P. Secondary Metabolites Coordinately Protect Grapes from Excessive Light and Sunburn Damage during Development. Biomolecules 2022, 12,42.
This abstract is republished in its original form, with headings inserted, as permitted by the following Creative Commons licence: https://creativecommons.org/licenses/by-nc-nd/4.0/
Image credit: PG Goussard