Abscisic acid (ABA) has a key role in some plant species under low-temperature stress (LTS). In this study the effects of ABA at four concentrations (0, 50, 100 and 200 μΜ) on electrolyte leakage (EL), visual damage index, soluble carbohydrate, proline, total phenolic compound and relative water content (RWC) of leaves of ‘Sultana’ grapevines were studied under LTS (0, 4 and −4 °C). Moreover, to further elucidate the efficiency of foliar ABA on freezing tolerance, some relevant morpho-physiological changes were evaluated at three sampling dates: September, October and November. The increase in cane and leaf EL and the visible symptoms of leaf damage caused by LTS were minimized by the application of ABA. Moreover, in ABA-treated vines, specifically at 200 μM, the contents of soluble carbohydrate, proline and total phenolic increased and the RWC decreased. These alterations in ABA-induced metabolism alleviated the deleterious effects of LTS on ‘Sultana’ grapevine. Freezing tolerance of ABA-treated vines improved within each sampling date in autumn. Foliar application of ABA at 200 μM decreased LT50 in September, October and November by −2.6, −3.6 and −3.9 °C, respectively, as compared to those of control vines. This study also demonstrated that ABA was effective in shoot growth inhibition, leaf abscission and periderm development, indicating that ABA treatments advanced cold acclimation in grapevines. Increased fall freezing tolerance induced by foliar ABA application may be beneficial in nurseries, new established vineyards and for late-bearing cultivars in regions with fall frost events.
