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Yi Zhang, Tracey Mechlin and Imed Dami

The purpose of this study was to investigate the influence of foliar application of abscisic acid (ABA) on grapevine dormancy, specifically to: 1) determine the optimum foliar application concentration of ABA and 2) evaluate the morphological and physiological changes of greenhouse-grown grapevines in response to exogenous ABA application. Vitis vinifera ‘Cabernet Franc’ and Vitis spp. ‘Chambourcin’ with different leaf ages (40, 50, 80, 100, 110, and 120 days) were subjected to foliar ABA application at different concentrations (0, 100, 200, 400, 600, 800, 1600, and 3200 mg·L−1) and to a cold-acclimated regime. Concentrations of 800 mg·L−1 or higher were phytotoxic and the optimum concentrations were between 400 and 600 mg·L−1. Optimum concentrations of ABA inhibited shoot growth and advanced growth cessation, periderm formation, and leaf senescence, which led to advanced dormancy in both cultivars. In this study, it was concluded that exogenous ABA induced endodormancy because single cuttings (not paradormant) under favorable growing conditions (not ecodormant) were used. Furthermore, grapevine response to ABA was influenced by leaf age and cold treatment. ABA was effective in inhibiting shoot growth and increasing periderm formation in the young vines with 40- to 50-day old leaves and the old grapevines with 80- to 120-day old leaves. However, ABA was effective in inducing early shoot cessation, leaf senescence and abscission, and dormancy in old vines with 100- to 120-day old leaves only. The advanced morphological and physiological changes induced by exogenous ABA mimicked those triggered by environmental cues during the cold acclimation process. It was suggested that advancing the cold acclimation process using foliar ABA application may be beneficial for long-season grape cultivars grown in regions with short growing seasons and early fall frost events.