Issue link: http://winesandvines.uberflip.com/i/137110
GRAPEGROWING The science behind our findings is that grape berries cannot get unlimited sugar solution supply through the phloem. This long-distance transport from leaves (sugar factory) to berries is sophisticated, and the "language" of their communication is hydrostatic pressure. Similar to the mechanism in the xylem, yet actively regulated, phloem sap from the leaves to the berries also follows a pressure gradient. When phloem delivers sugar solution into berries, incompressible water flows into the berries along with unloaded sugars, and the pressure is also transmitted into the berries. If the pressure could not be released, as was the case of treated clusters in our experiments, increased pressure in the berries would become a signal telling the leaves to stop sending more sugar solution. This is why decreased sugar accumulation and delayed ripening in treated clusters was observed. Additionally, if the pressure exerted on the skin exceeds its extensibility, berries will crack as found in the experiment. Grape berries have more than one pathway that ensures the important sugar-delivery process will not be disturbed easily. By measuring berry special delivery transpiration, we have found that it varies markedly with changes in environmental conditions. Any decrease in air temperature or increase in humidity reduces berry transpiration. Therefore, berry transpiration is evidently not a Irrigation and rainfall Figure 3. Clusters with restricted transpiration (right) ripened more slowly than untreated clusters (left). INCLINE CLUSTER SORTING Every element of our incline sorting table was developed and tested with guidance from premier winemakers. ■ Superior speed control ■ Multiple models to fit crush pad needs ■ Ozone and UV-resistant food-grade belt ■ Remote on/off and speed control ■ Easy, thorough cleaning H I G H - P E R F O R M A N C E C R U S H PA D E Q U I P M E N T www.pnlspecialties.com ■ p. 707 573 3141 1650 Almar Pkwy, Santa Rosa, CA 95403 04.18.13 P&L Specialties Wines & Vines 3.5x4.875" 1/4-Page BW 66 p racti c al w i ne ry & v i ne yard J U LY 20 13 reliable pathway to dispose of excess phloem water. But grape berries have another pathway, xylem backflow, to ensure the continued delivery of sugar solution through the phloem and avoid cracking. To conclude, berry transpiration and xylem backflow are both necessary during berry development. When one or both pathways are restricted, the unbalanced berry water "account" causes delayed ripening, reduced sugar accumulation and increased cracking. ■ ■ f. 707 573 3140 Lic. in CA/OR/WA A R M S T R O N G C R E AT E S Irrigation and rainfall are events in a vineyard that most directly influence berry water balance. It is important to note that supplying water directly to the soil by drip irrigation has different effects than supplying water to the canopy (overhead sprinkler irrigation or rainfall). When roots take up water from the soil, how much water will be delivered into the berries is controlled by pressure gradients, as explained above. However, with overhead irrigation or rainfall, water is intercepted by the canopy. This increases canopy and cluster zone humidity, and thus decreases berry transpiration.