2007 Annual Report 1a.Objectives (from AD-416) 1. Determine if early-season irrigation and water stress are associated with changes in grape berry xylem connection to the vine. 2. Determine if late-season irrigation and water stress are associated with changes in grape berry volume. 3. Determine if berry water can flow back to the vine under conditions of water stress. 1b.Approach (from AD-416) Pot-grown grapevines with very distinct genetic backgrounds will be used for this study. Soil moisture will be altered independently of air humidity by using drip irrigation. We will attempt to modify the xylem connection between the berries and the rest of the vine by varying soil moisture deficit during bloom and early berry development. Irrigation treatments will include regulated deficit irrigation (RDI), partial rootzone drying (PRD), and abundant irrigation (no water stress). The vines will then be subjected to dry-down and rewatering cycles before and after veraison. Determine the influence of soil moisture on changes in berry volume and final berry volume. Individual clusters will be dipped in water beakers to assess the potential for direct absorption of water through the berry skin. Berry diameter will be monitored continuously using pressure transducers coupled to a data logger. Simultaneously, leaf water potential will be monitored non-destructively using a leaf psychrometer system. Meteorological conditions will be recorded with temperature and relative humidity sensors to calculate the air vapor pressure deficit during experiments. Documents Grant with Washington State University. 3.Progress Report This report serves to document research conducted under a grant agreement between ARS and Washington State University. Additional details of research can be found in the report for the parent project 5358-21000-034-00D, Production Systems to Promote Yield and Quality of Grapes in the Pacific Northwest. Dr. Keller and collaborators conducted the following research towards the agreements objectives: We subjected pot-grown Vitis vinifera (cv. Merlot) and Vitis labruscana (cv. Concord) to water deficit during the lag phase of berry growth and used electronic transducers to monitor changes in berry diameter. In a second experiment, shoots with their bases immersed in a solution of the xylem-mobile dye basic fuchsin were pressurized using a pressure chamber to determine if the dye could be forced into post-veraison berries. In addition, excised berries were immersed in distilled water with or without the skin or pedicel sealed to test if water can be absorbed through the skin and if sugars can be lost from the berries through the pedicel. Finally, we built a device that enabled us to separately extract sap from the berry apoplast (xylem, cell walls and intercellular spaces) and the symplast (mainly cell vacuoles), which was then analyzed for its chemical composition. . We have shown that the xylem connection between grape berries and the shoot remains open during ripening. In the first year of this project we found that, given sufficient root pressure, the backflow of xylem water from the berries to the shoot could be stopped and even reversed. We also obtained unequivocal evidence for our hypothesis that phloem influx into grape berries suddenly increases at veraison (beginning of ripening), even in the face of severe water deficit stress. We also found that solutes imported via the phloem are accumulated in the berry cell walls along with their accumulation (storage) in the mesocarp cells. This finding confirms our hypothesis that solute accumulation in the berry apoplast is responsible for the decrease in driving force for xylem water movement into ripening grape berries. There were some striking differences in the behavior of Merlot and Concord berries, but it is premature to speculate about the implications of these disparities in apoplast solute contents. Another important finding is that while late-season (preharvest) irrigation does not seem to induce increases in berry size, it does prevent berry shrinkage due to water stress. Thus growers may use irrigation close to harvest as a tool to maintain yield without significantly altering berry constituents. On the other hand, we demonstrated that water can be absorbed through the berry skin, which may result in cracking (splitting) of berries and subsequent loss of sugar and other solutes, which would effectively ‘dilute’ grape quality. These results open up interesting questions about the role of rainfall and/or overhead sprinkler irrigation in potential fluctuations in both berry size and quality. ADODR Statement: The ADODR met with the cooperating PI and project personnel at meetings during the year and discussed results through phone calls, e-mail, and in person.