Winter Hardiness Measurements on 15 New Apple Cultivars

Abstract

Fifteen new cultivars from the 1995 NE-183 planting were evaluated for cold hardiness in November and February for three consecutive winters, relative to ‘Golden Delicious’ (winter tender) and ‘Spartan’ (hardy). Pieces of dormant current season's shoots were frozen to a series of test temperatures from −20°C to −36°C in a programmable freezer. In the final year, major scaffolds and trunks of certain cultivars from the NE-183 trial, plus ‘Royal Gala’ and ‘Summerland McIntosh’, were also tested, to establish the correlation between the hardiness of shoots and other parts of the tree. Ratings of tissue browning in the xylem and bark were used to assess injury after thawing. The temperature of incipient damage (TID), i.e. 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 not with sampling season. Overall, cultivars with shoots similar to ‘Golden Delicious’ in hardiness were: ‘Arlet’, ‘Cameo’, ‘Orin’, ‘Golden Supreme’ and ‘Suncrisp.’ ‘Ginger Gold’, ‘GoldRush’, ‘Sunrise’ and ‘Braeburn’ had TIDs intermediate between ‘Golden Delicious’ and ‘Spartan’. Clones with shoots as hardy as ‘Spartan’ were: ‘Pristine’, ‘Fortune’, ‘Honeycrisp’, ‘Yataka’, ‘Fuji’ and NY 75414-1. Trunks were less hardy than shoots (had higher TID), and scaffolds tended to be intermediate. For the NE-183 trees, the TID of shoots and scaffolds, and the TID of trunks and scaffolds, from the same trees were significantly correlated. The TID for trunks and shoots was not correlated (R=0.24, p=0.29). This appeared to be attributable to deviations in the hardiness among tissues of several cultivars, especially ‘Fuji’ and ‘Fortune’, which had hardy shoots but tender trunks. In contrast, the TID for trunks, scaffolds and shoots of ‘Royal Gala’ and ‘Summerland Mclntosh’ were all significantly and highly correlated (R > 0.90). The development of non-destructive methods to measure the hardiness of the trunk might improve the assessment of cultivar hardiness.