2007 Annual Report 1a.Objectives (from AD-416) Determine the physiological mechanisms by which ‘Concord’ vines in central WA vineyards accumulate enough total iron in leaves, yet develop chlorosis. Develop practical solutions to overcoming the chlorosis problem of ‘Concord’ in WA vineyards. Develop a new test to measure physiologically active iron in ‘Concord’ grape leaves for diagnosis of Fe-deficiency. 1b.Approach (from AD-416) We will first collect both chlorotic leaves and normal leaves from 3 ‘Concord’ vineyards in WA to confirm that chlorotic leaves have lower active Fe than normal leaves, then: 1. Determine the physiological mechanisms by which ‘Concord’ grape leaves accumulate the same or even high level of total iron, yet develop chlorosis, on high pH soils; 2. To determine the effectiveness of FeEDDHA application on alleviating Fe-deficiency induced chlorosis in ‘Concord’ vines in a pot study at pH 8.0 and in a vineyard in central WA; 3. Determine the tolerance of rootstocks to Fe-deficiency for ‘Concord’ and the mechanism of tolerance; 4. Develop a new diagnostic test to measure physiologically active iron in ‘Concord’ grape leaves. Documents Grant with Cornell University. 3.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. Cheng and collaborators conducted the following research towards agreement objectives 1, 2, and 3: High soil pH induces leaf chlorosis in Concord vines. Roots of Concord vines are able to increase ferric chelate reductase (FCR) activity in response to the decreased Fe availability at high soil pH, which helps maintain root Fe assimilation at high soil pH. However, the Fe assimilated by FCR cannot be effectively utilized by leaves because leaf FCR activity is decreased by high soil pH. An increase in root-medium pH did not raise xylem sap pH, but decreased Fe and citrate to some extent. Xylem malate was highest at pH 6.6, and decreased both above and below this pH. Lower active Fe decreased midday CO2 assimilation and PSII quantum efficiency, as well as night respiration. Malate content increased as active Fe increased to 1.0 mg m-2, and then decreased as active Fe exceeded this level. Citrate increased linearly as active Fe decreased, and was an order of magnitude lower than malate content. These results suggest that leaf FCR activity may limit Fe assimilation to a greater extent than root FCR activity. The decreased leaf aconitase activity under Fe-deficiency is the most likely cause of the increase in citrate levels. Greater activity of the other glycolytic and TCA enzymes under Fe-deficiency may help to funnel carbon into the mitochondria and enhance NAD(P) reduction. Citrate levels (and the citrate:malate ratios) in the xylem exudate and leaf were much lower when compared with other species, and may be linked to Fe-inefficiency of ‘Concord’. The results from the field trial in central WA indicate that FeEDDHA application has significantly decreased the degree of canopy chlorosis and increased leaf active Fe content, but it appears that its effect was not as strong as what was observed in the study with potted vines. This may have something to do with the way FeEDDHA was applied. Clearly more work is needed on the optimal rate before any recommendation is made to growers; and We have developed an analytical test for measuring physiologically active Fe in ‘Concord’ grape leaves using dried leaf tissues. Strong correlations were found between leaf active Fe content and leaf photosynehtic capacity. This method will provide effective diagnosis of Fe-deficiency. Smith, B. R. and L. Cheng, 2007 Iron Assimilation and Carbon Metabolism in ‘Concord’ Grapevines Grown at Different pHs. J. of Am. Soc. for Hort. Sci. 132(4):473-483. 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.