ARS | Publication request: Water Deficit Effect on Ratio of Seed to Berry Fresh Weight and Berry Weight Uniformity in Winegrape cv. Merlot

Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 4, 2010
Publication Date: August 1, 2010
Citation: Shellie, K. 2010. Water deficit effect on ratio of seed to berry fresh weight and berry weight uniformity in winegrape cv. Merlot. American Journal of Enology and Viticulture. 61(3):414-418.

Interpretive Summary: Small berry size is widely acknowledged as a favorable attribute for production of red wine. Recent research has shown that water deficit during berry development alters the concentration of constituents and composition of the berry and that these changes influence wine sensory qualities. Uniform berry size is another desirable attribute for wine production. Water deficiency is known to inhibit berry growth, but it is unknown whether it also reduces the variability in weight among berries at maturity. The objective of this research was to determine whether water deficit prior to veraison alters the relative proportions of seed to berry fresh weight in cv. Merlot and to determine whether water stress decreased the variability in berry weight at maturity. Vine water status had no significant influence on berry weight uniformity at maturity but it did increase the ratio of seed to berry fresh weight independent of berry size. Results from this study reveal two new pieces of information of importance to winemaking concerning the relationship between vine water status and grape attributes. Water management cannot be used as a tool to enhance berry size uniformity at maturity. The berry size distribution observed in this study for a seeded grape cultivar was similar to the size distribution of a seedless grape cultivar suggesting that berry size variability is established very early in fruit development. The second piece of new information is that berries grown under a water deficit contained at least 8% more seeds and greater seed to total berry fresh weight than berries from well-watered vines. Berries from water deficient vines will therefore contain more seed relative to skin-derived compounds available for extraction during fermentation.

Technical Abstract: Field-grown grapevines cv. Merlot (Vitis vinifera L.) were differentially irrigated in a randomized block design during two growing seasons to maintain a high or low level of vine water stress between fruit set and harvest. Detached berries from clusters harvested at maturity were individually weighed and their weight distribution was used to analyze weight uniformity within each irrigation regime and obtain a sample of light, medium and heavy berries of identical weight from vines under each level of irrigation. Berry weight within each irrigation regime was distributed normally and vine water status had no significant influence on weight uniformity at harvest. The coefficient of variation for berry fresh weight averaged 28% each year. The seed fresh weight of berries from vines with lowest midday leaf water potential was at least 8% heavier, contained a greater number of seeds and had a greater ratio of seed to berry weight. This change was independent of berry weight. Results have implications for winemaking because a greater ratio of seed to berry weight may alter the quantity of seed relative to skin-derived compounds available for extraction during fermentation.