Previous studies have demonstrated that the freezing tolerance (FT) of grapevine was enhanced by foliar application of exogenous abscisic acid (exo-ABA), a treatment which might be incorporated into cultural practices to mitigate cold damage in vineyards. To investigate the underlying mechanisms of this response, a two-year (2017 and 2018) study was conducted to characterize the effects of exo-ABA on greenhouse-grown 'Cabernet franc' grapevine. In control grapevines, both physiological (deeper dormancy) and biochemical (sugar accumulation in buds) changes occurred, indicating that grapevines initiated cold acclimation in the greenhouse. Compared to control, exo-ABA decreased stomatal conductance 2 h after application. Two weeks post application, exo-ABA treated grapevines showed accelerated transition of grapevine physiology during cold acclimation (increased depth of dormancy, decreased bud water content and enhanced bud FT), relative to control. Exo-ABA induced the accumulation of several sugars in buds including the raffinose family oligosaccharides (RFOs), and the RFO precursor, galactinol. The expression of raffinose and galactinol synthase genes was higher in exo-ABA treated grapevine buds, compared to control. The new findings from this study have advanced our understanding of the role of ABA in grapevine FT, which will be useful to develop future strategies to protect grapevines from cold damage.

In this study we characterized the influence of genotype and bud position on seasonal changes in freezing tolerance (FT, LT50) and soluble sugars especially raffinose, in buds of field-grown cold-sensitive Cabernet franc (CF, Vitis vinifera) and cold-tolerant Couderc 3309 (C-3309, V. riparia x V. rupestris) and Concord (CD, V. labruscana) over two years and the influence of artificial deacclimation. Generally basal buds were more FT and the cold-hardy cultivars CD and C-3309 had the lowest LT50 compared to the cold-sensitive CF. Among all sugars, fructose, glucose, sucrose, raffinose, and stachyose had strong correlation with LT50 but there were distinctive responses associated with bud position and cultivar that were related to raffinose. Basal buds accumulated the most raffinose, and raffinose concentrations were 2- to 3- fold higher in the cold-hardy than those in the cold sensitive cultivar. Furthermore, cold hardy cultivars CD and C-3309 started accumulating raffinose with decreasing photoperiod and prior to exposure to cold temperature resulting in an early increase of FT. These results suggest that affinose accumulation might be an early step in the process of cold acclimation that coincides with early development of FT. It is concluded that bud raffinose concentration might be a useful detection tool and a metabolic marker during the early stages of cold acclimation to distinguish various Vitis genotypes with contrasting FT.

Economic losses due to cold weather events are a major constraint to the expansion of premium but cold-sensitive winegrape cultivars in colder regions, such as Ohio (USDA) Plant Hardiness Zones 6b–5b (−17.8 to −26.1 °C) (ARS-USDA 2012). The purpose of this study was to determine whether a foliar application of abscisic acid (ABA) could increase the freezing tolerance (FT) of field-grown ‘Pinot gris’ grapevines (Vitis vinifera), and whether the effectiveness of ABA treatments can be influenced by the phenological timing of the application. Mature ‘Pinot gris’ grapevines were treated with a foliar application of ABA at a concentration of 0 mg L⁻¹ (control), or 400 mg L⁻¹ at vine phenological stages corresponding to véraison, post-véraison, and postharvest. ABA application did not affect yield components, fruit composition, or vegetative growth, but caused early leaf senescence, leaf abscission, and advanced dormancy that led to increased FT of ‘Pinot gris’ during the dormant season. The phenological timing of application influenced ABA effectiveness, with spray applications made at véraison and post-véraison being the most effective. It was concluded that a foliar application of ABA increased bud FT during the dormant season, and thus, ABA is a potential cultural practice tool for mitigating economic losses from cold injury in production regions with damaging cold events.

The purpose of this study was to develop a method to increase freezing tolerance of field-grown grapevines using foliar application of abscisic acid (ABA). The specific objectives were to evaluate the morphological and physiological changes of field-grown Vitis vinifera Cabernet franc grapevines in response to exogenous ABA application and to determine an optimum timing for foliar application of ABA that results in enhanced freezing tolerance. Cabernet franc grapevines grown at two locations were treated with 400 and 600 mg/L ABA at different stages of development corresponding to veraison and 20, 30, 40, and 55 days postveraison. ABA did not affect yield components or basic fruit chemical composition. However, it enhanced anthocyanin concentration, advanced dormancy, decreased bud water content, and ultimately increased freezing tolerance under simulated freezing events. The increased freezing tolerance by ABA was confirmed by assessing bud injury following natural freezing events of −19°C and −23°C in two locations. The effectiveness of ABA may have been enhanced by application timing, which was optimum at veraison and 20 to 30 days postveraison. Results suggest that ABA application has the capacity to enhance dormancy and increase freezing tolerance and can be used as a prophylactic tool to protect against winter injury of grape cultivars grown in cold regions.

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.