Xuemin Hou, Kenneth Shackel,* and Mark Matthews 
*Department of Plant Sciences, University of California, Davis, Davis, CA 95616 (kashackel@ucdavis.edu)

The hydraulic connection of the grape (Vitis vinifera Chardonnay) berry and its parent vine changes over berry development between pre- and postveraison and is a critical element for understanding the response of berry size and expansive growth to changes in vine water status. The hydraulic conductance pathway has been estimated using excised material, but estimates vary greatly and span over one order of magnitude. Here we used a nondestructive approach, applying pres-sure steps to the root system of a non-transpiring vine in dry soil to manipulate shoot water status, while simultaneously measuring the change in stem water potential of the shoot and the change in berry diameter. Postveraison hydraulic conductance was ~10% of preveraison conductance, consistent with previous research showing hydraulic conductance decreasing over berry development. The estimated pre- and postveraison conductance was similar to the lower conductance values previously reported and indicated that low hydraulic conductance postveraison could minimize water backflow from the berry to the parent vine. This study provides the first in situ estimate of hydraulic conductance between the berry and the stem, and the method should be applicable to other plants to study water relations between fruit and parent plant.

Funding Support: California Table Grape Commission, UC Davis Department of Plant Sciences, UC Davis Graduate Group in Horticulture & Agronomy, UC Davis Office of Graduate Studies, China Scholarship Council, Curtis J. Alley Memorial Research Scholarship, Robert L. Balzer Scholarship, Horace O. Lanza Scholarship, Wine Spectator Scholarship, and Henry A. Jastro Graduate Research Award