ARS | Publication request: Environmental Influences on Ripening and Phenolics in Grapes

Submitted to: Proceedings of Plant Growth Regulation Society of America
Publication Type: Proceedings
Publication Acceptance Date: November 15, 2010
Publication Date: March 20, 2011
Citation: Tarara, J.M., Lee, J. 2011. Environmental Influences on Ripening and Phenolics in Grapes. Proceedings of Plant Growth Regulation Society of America. CD-ROM.

Technical Abstract: During the past decade, we refined our understanding of the effects of solar radiation and temperature on grape ripening, especially in dark-skinned cultivars used for wine. In three separate studies, we deployed up to ten combinations of berry temperature and exposure to solar radiation, then assessed analytically the outcome on groups of phenolic compounds in the berries that are of most interest to the grape and wine industry: flavonol-glycosides, anthocyanins, and proanthocyanidins (condensed tannins). Concentrations of flavonol-glycosides increased with exposure to solar radiation, but these compounds were insensitive to field temperatures. High berry temperatures, or a combination of low light and high berry temperature, decreased the total concentration of anthocyanins at harvest. At equal temperatures, shaded and sunlit berries differed in the proportions of acylated derivatives and dihydroxylated anthocyanins. Berry temperature was positively associated with higher concentrations of skin proanthocyanidins at the onset of ripening, although this difference was not borne out at harvest. When the diurnal fluctuation in berry temperature was reduced by cooling the berries during the day and heating them at night, the onset of ripening was accelerated. The consequences for wine quality from many of these compositional changes are not yet understood. Biological perspective and a summary of microclimate drivers of fruit quality are presented.