Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 17, 2011
Publication Date: December 1, 2011
Citation: Shellie, K. 2012. Interactive effects of deficit irrigation and berry exposure aspect on Merlot and Cabernet Sauvignon in an arid climate. American Journal of Enology and Viticulture. 62:462-470. Interpretive Summary: Regulated deficit irrigation (RDI) is an irrigation practice used to vary the water status of the vine at particular phenological stages with the goals of enhancing water use efficiency and controlling vine vigor. Cabernet Sauvignon and Merlot are two of the most widely planted, red-skinned wine grape cultivars in the world, each accounting for 3% of world wine grape production and are also the most widely planted red-skinned cultivars in the Snake River Valley AVA. The present study was conducted to test the main and interactive effects of irrigation amount, genotype and fruit canopy location on vine phenology, shoot growth, midday leaf water potential, berry growth, yield components, and berry composition at harvest. This paper reports results from a field trial conducted with own-rooted grapevines in an arid climate over a four-year period. Fruit canopy location affected the berry weight and skin anthocyanin content of Cabernet Sauvignon and the concentration and content of skin anthocyanins and concentration of juice hexose sugars in Merlot. Deficit-irrigated vines had lower skin total phenolic content than standard-irrigated vines due to their reduced berry weight. This was especially pronounced in Cabernet Sauvignon. Water deficit had no effect on skin tannin concentration or content in either cultivar . Cabernet Sauvignon had a higher concentration and content of skin total tannins and phenolics than Merlot. The subtle differences in cultivar response to water deficit and striking influence of canopy location on skin anthocyanin content observed under the climatic conditions of this study have two important implications for production. Under the conditions of this study, optimum water use efficiency and vigor control will likely be achieved by imposing less of a water deficit on Cabernet Sauvignon relative to Merlot. Cultural practices that reduce fruit exposure during the warmest part of the day or enhance canopy microclimate homogeneity would most likely increase the uniformity of berry composition within the vine canopy.
Technical Abstract: Deficit irrigation is used to control vine vigor and enhance water use efficiency yet few studies have compared cultivar response to water deficit in a warm, arid climate with a high amount of solar radiation and measured the interactive effects of water deficit, cultivar and fruit canopy location. Own-rooted Cabernet Sauvignon and Merlot grapevines were exposed to a standard or 50% of standard (deficit) amount of irrigation in a multi-year field trial in the arid Western Snake River Plain of Idaho (USA). Interactive effects were observed between cultivar and irrigation amount for berry size, juice titratable acidity and skin total phenolic content and between cultivar, irrigation amount and fruit canopy location for skin anthocyanin concentration and content. Berry fresh weight and skin total phenolic content at harvest was lower in Cabernet Sauvignon than Merlot when vines were supplied with 50% less water. Exposed fruit located on the west-facing side of the vine canopy had less skin anthocyanin content per berry than east-facing fruit. Cultivar differences in phenology, shoot length, and seed number per berry were not affected by irrigation amount. Results suggest that Cabernet Sauvignon is more sensitive than Merlot to water deficit under the climatic conditions of this study and that reduction in canopy microclimate differences between the east and west side of the canopy could increase vine uniformity in berry composition.