Cold Hardiness of New Apple Cultivars of Commercial Importance in Canada

Abstract

Six new apple cultivars were evaluated for cold hardiness in early December and February for two consecutive winters, relative to traditional cultivars ‘Golden Delicious’, ‘Mutsu’ (winter tender) and ‘McIntosh’ (hardy). Pieces of dormant current season’s shoots were frozen in a series of test temperatures from -20°C to -40°C in a programmable freezer. Ratings of tissue browning in the xylem were used to assess injury after thawing. The temperature of incipient damage (TID), the warmest temperature at which a cultivar began to show injury, was obtained from survival curves by non-linear regression. TID varied significantly among cultivars, but generally not with the time of the dormant period. Overall, the cultivars could be placed in groups based on relative winter hardiness as follows: ‘Aurora Golden Gala’ (very tender) < ‘Mutsu’, ‘Jonagold’, (tender) < ‘Ambrosia’, ‘Golden Delicious’ and ‘Gala’ (intermediate) < ‘Northern Spy’, ‘McIntosh’ (hardy), and ‘Honeycrisp’ (very hardy). These data indicate nearly a 10°C range in winter hardiness amongst the nine cultivars studied, depending on the sampling date. The cultivars, ‘Ambrosia’ and ‘Aurora Golden Gala’ appear to be particular winter tender; ‘Aurora Golden Gala’ appears more tender than ‘Mutsu’ and ‘Jonagold’ while ‘Ambrosia’ is similar to ‘Golden Delicious’– all of which are considered relatively tender in Ontario and British Columbia. ‘Honeycrisp’ demonstrated the greatest winter hardiness. Based on these finding, it would be prudent to consult long-term climate normals and to take into account the frequency of extreme weather events for potential susceptibility to winter injury particularly prior to establishing the new tender cultivars ‘Aurora Golden Gala’, ‘Ambrosia’, and ‘Gala’.