UBC Theses and Dissertations
Stop and smell the grapes : altering cultivar-typical aromas in ‘Gewürztraminer’ (Vitis vinifera L.) berries via regulated deficit irrigation and crop load management Kovalenko, Yevgen
Grape growers use viticultural practices such as deficit irrigation and crop load management via cluster thinning to improve phenolics and aromas in red grapes and wines; however, the impact of these practices on grape terpenes – key aromatics for quality in wines – remains largely unknown. I performed two three-year studies to investigate the effect of deficit irrigation and crop load management strategies on the accumulation of terpenes in Gewürztraminer grapes grown in the Okanagan Valley (BC, Canada). Yield and grape sugars were reduced by deficit irrigation treatments; however, effects were minimal when the deficit was applied late in the season. Applying late deficit allowed to save ~30% of irrigation water compared to standard irrigation. Total free terpenes were not affected by deficit irrigation treatments, but the concentration of key terpenes for the aroma of Gewürztraminer wines, such as geraniol and citronellol, was significantly increased in grapes exposed to water deficit late in the season. This irrigation treatment did not affect the expression of terpene genes, suggesting that the increased concentration of specific terpenes was not regulated at the transcriptional level. Reducing the crop load stimulated sugar accumulation, particularly if this reduction was applied early in the season. Reducing the crop load early during the season also increased the terpene levels before the commercial harvest (20-21 oBrix), but had no effects at harvest, suggesting a faster accumulation of terpenes during ripening. The peak of expression of several terpene synthases occurred before the commercial harvest. Expression of two terpene synthases was increased in grapes of grapevines subjected to crop load reduction early in the season. My studies indicate that it is possible to modulate terpenes in vineyards by managing irrigation and crop load. However, I observed that the seasons had a stronger effect on terpenes than the treatments investigated.
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