2006 Annual Report 4d.Progress report. This report serves to document research conducted under a grant agreement between ARS and Cornell 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. Lailiang Cheng and collaborators conducted the following research towards the agreement: The overall objective of this project was to understand the underlying physiological mechanism of leaf chlorosis in Concord vines and develop practical measures growers can use to overcome the problem in WA vineyards. During the first year of this project, we have. 1)collected leaf samples from three vineyards in central WA that have consistently had chlorosis problems to determine the Fe status in chlorotic leaves;. 2)set up a controlled pH experiment to determine the effect of pH on leaf function and chlorosis of Concord vines; and. 3)conducted an experiment on potted vines to determine the effectiveness of FeEDDHA application in alleviating Fe-deficiency-induced leaf chlorosis at a high soil pH (7.6). Our results clearly indicate that. 1)chlorotic leaves from WA vineyards have significantly lower active Fe compared with green leaves;. 2)high soil pH induces leaf chlorosis in Concord vines;. 3)roots of Concord vines are able to upregulate ferric chelate reductase activity to compensate for the decreased Fe availability at high soil pH whereas leaf ferric chelate reductase activity is decreased by high soil pH; and. 4)FeEDDHA is very effective in alleviating leaf chlorosis induced by high soil pH, which strongly suggests that FeEDDHA, a fertilizer commercially available, may have a good potential in combating the chlorosis problem.