Assessing the impact of temperature on grape phenolic metabolism Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8336h635j

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  • Many climatic factors influence grape berry composition including nutrient status, water availability, biotic stress, sun exposure and temperature. Previous research examined the effects of many factors listed above and much progress has been made. It is often difficult, however, to separate effects that typically confound each other, such as sun exposure and temperature. Increasing exposure of a berry to the sun will lead to some degree of heating unless the temperature is otherwise maintained. In this study berry temperatures where manipulated independent of sun exposure, necessarily separating the two effects. The objective of this study was to assess the impact of fruit temperature on the phenolic metabolism of grape berries (Vitis vinifera L. cv. Merlot) grown under field conditions with controlled exposure to sunlight. While similar studies have focused on production and accumulation of anthocyanins our primary focus was on proanthocyanidins or ‘tannins’. Here we report the effects of modulating daytime and nighttime temperatures as well as damping the diurnal temperature range. Furthermore, research was broken into two phases: berry set to véraison (phase I) and véraison to commercial harvest (phase II). This was to assess the effects of treatments during two discrete phases of berry development characterized by accumulation of distinct phenolic metabolites. Samples collected at véraison indicated that damping the diurnal temperature fluctuation advanced the onset of ripening. Those berries were larger (doubledamped: 0.753±0.015 vs control: 0.512±0.034 g/berry) and more colored than all others. Phenolic material from grape seed and skin was quantified and characterized using three chromatography methods. Proanthocyanidin accumulation at véraison was linearly related to heat summation over the developmental period with nighttime heating yielding the highest concentration and daytime cooling yielding the lowest (night-heat: 1.46±0.13 vs day-cool: 0.97±0.09 mg/berry). Damping the diurnal temperature fluctuation reduced proanthocyanidin mDP (double-damped: 21.8±1.0 vs control: 28.0±1.7). Day-Cooling resulted in an increase in the concentration of flavonols at the end of phase I yet a decrease at the end of phase II. The goal of this work is to provide researchers with additional information regarding climatic factors influencing phenolic biosynthesis and to provide grape growers with tools to better manage their crop.
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