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United States Department of Agriculture

Agricultural Research Service

Title: Sunlight and Temperature Effects on Merlot Berries

Authors
item Spayd, Sara - WSU
item Tarara, Julie
item Mee, David - WSU
item Ferguson, John

Submitted to: Practical Winery and Vineyards
Publication Type: Trade Journal
Publication Acceptance Date: October 15, 2003
Publication Date: January 15, 2004
Citation: SPAYD, S., TARARA, J.M., MEE, D., FERGUSON, J.C. SUNLIGHT AND TEMPERATURE EFFECTS ON MERLOT BERRIES. PRACTICAL WINERY AND VINEYARDS. Pages 19-46, 82.

Technical Abstract: Anthocyanin and phenolic profiles of berry skins from Vitis vinifera cv. Merlot in the Yakima Valley of Washington were influenced by sun exposure and temperature in 1999 and 2000. Total skin monomeric anthocyanin (TSMA) concentrations were higher in 2000 than in 1999 in any given treatment. Berry temperature was increased as much as 13 C above ambient and shaded cluster temperatures when clusters were exposed to sunlight, regardless of aspect for north-south oriented rows. However, maximum fruit temperatures (sometimes exceeding 40 C) were higher for clusters on the west side of the canopy because ambient temperatures were higher in the afternoon. East-exposed clusters had higher TSMA concentrations than west-exposed or shaded clusters. To separate light and temperature effects, west-exposed clusters were cooled to the temperature of shaded clusters and shaded clusters were heated to the temperature of west-exposed clusters. Exposure to sunlight increased TSMA concentrations regardless of temperature in both years. In 1999 and 2000, cooling sun-exposed clusters increased TSMA concentrations. Heating shaded clusters decreased TSMA concentrations in 1999, but had no effect during the cooler ripening period of 2000. Decreased TSMA concentrations in berry skins from west-exposed clusters were due to temperature and not due to UV radiation. Exposure to solar radiation increased concentrations of the 3-glycosides of quercetin, kaempferol, and myricetin. In 2000, sun-exposed clusters, regardless of aspect, had almost ten times greater concentrations of total flavonols than shaded clusters. Blocking UV significantly reduced individual and total flavonol concentrations, while temperature had little to no effect on their concentrations.

Last Modified: 10/30/2014
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