Cold hardiness in the USDA malus core germplasm collection

A group of 200 Malm accessions representing a 'core' of the complete collection held by the Plant Genetic Resources Unit of the U.S. Department of Agriculture at Geneva, New York, were studied. The core collection was established at five geographically diverse sites in the United States (Minnesota, Illinois, North Carolina, Washington, New York) in 1994. In the winter of 1995-96, the planting in Minnesota was exposed to several episodes of low temperatures ranging from -30° to -38°C. Winter injury and amount of flowering were rated in May 1996. Among the hardiest entries were accessions of M. baccata, M. halliana, M. kansuensis, M. toringoides, M. micromalus, M. prattii, M. prunifolia, M. sieboldü, M. ioensis and M. spectabilis. Among the hardiest accessions of M. pumila were cultivars from Canada, Russia and the northern US including 'Macfree', 'Haralson', 'Delicious', 'Brightgold', 'Petrel', 'Keepsake', 'Empire', 'Yellow Transparent', 'Novosibirsk! Sweet' and an 'Antonovka' selection.