Project Number: 5358-21000-041-05
Project Type: Grant

Start Date: Sep 24, 2007
End Date: Sep 30, 2009

Objective:
1. Test whether the shoot number/vigor relationship in grapevines is caused by hydraulic limitation. 2. Determine if the vulnerability of vines to water stress increases with increasing shoot number. 3. Develop practical recommendations for planting density, pruning and irrigation management.

Approach:
The study will be conducted with field-grown grapevines (Vitis vinifera L. cv. Merlot) planted on their own roots in 1999 at WSU¿s Irrigated Agriculture Research and Extension Center in Prosser, WA. The vines are cordon-trained and spur-pruned, permitting great flexibility in terms of bud numbers. One hundred vines will be pruned in winter and shoots will be thinned after budbreak. The vines will be deficit-irrigated after bloom, so that they experience repeated dry-down/rewatering cycles. In order to detect effects of shoot numbers on vine response to water deficit, irrigation water will be applied at the first sign of leaf wilting following each dry-down episode. Soil moisture will be monitored using neutron probes, with PVC access tubes installed equidistant between drip emitters. The crop load will be kept relatively constant over the entire range of shoot numbers; this will be done by cluster thinning after bloom where necessary. We will employ a regression approach with frequent measurements on vines with widely varying shoot numbers. This should enable us to determine potential threshold shoot numbers and quantitative relationships between shoot number, hydraulic resistance, carbon assimilation, and vigor. Documents Grant with Washington State University. Formerly 5358-21000-034-23G (12/2008).