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A rootstock trial was established in 1997 at the OSU Woodhall vineyard, located in the Southern Willamette Valley, which included two experiments. The first experiment was a factorial of four varieties grafted on to 9 rootstocks, and also as ungrafted vines (a split-plot design). The second experiment was a randomized complete block design of Pinot noir on 19 rootstocks, and ungrafted vines. Evaluation of these experiments was conducted in order to assess rootstock impact on vine physiological performance, and fruit and wine composition, between 2002 and 2005.
While there were changes in gas-exchange and the hydraulic properties of the scion in response to the different rootstocks, these changes were not directly linked to vine size. Some rootstocks could not cope with the large water demand that their larger canopies required, while other rootstocks appeared to have reduced canopy size as a strategy of drought avoidance. Evidence also indicated that Vitis rootstocks can induce changes to the scion stomatal behavior under drought conditions.
The vegetative growth potential of the rootstock appeared to interact with the scion, affecting the hydraulic properties and water status of the vines, as well as fruit composition. Sugars levels across all rootstocks were very similar, provided that rootstocks achieved an adequate leaf area to fruit ratio, suggesting that rootstock growing cycles are not necessarily different. Juice titratable acidity (TA) increased with vegetative growth. Skin tannin (proanthocyanidin) concentration was independent of the vigor imposed by the different rootstocks. Skin proanthocyanidin (mg/berry) was highest for 125AA, 1616C, and 420A, while 161-49C, Schwarzmann, 3309C and Riparia Gloire had the lowest tannin content. Rootstocks SO4, 8B, 420A, and 140Ru had higher levels of anthocyanins. Differences in berry weight were not related to the concentration of skin tannin or total anthocyanin (mg/kg fruit) found.
In order to produce wine lots from the different rootstocks, a micro-scale fermentation technique was developed. Based upon chemical and spectral analyses, this technique approximated the results obtained with a commercial red wine fermentation.
In 2005, Pinot noir wines were made from all rootstocks. The wine phenolic profile did not entirely reflect fruit composition, since extraction of skin components into wine varied greatly with the rootstock. These results suggest that there was a direct effect of the rootstock on fruit and wine chemistry, rather than a consequence of differences in crop size, vine vigor or berry weight. |
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