RELATIONSHIP BETWEEN CERTAIN METHODS AND PROCEDURES OF TESTING FOR WINTER INJURY OF OUTDOOR EXPOSED SHOOTS AND ROOTS OF APPLE TREES

Abstract

Techniques of evaluating winter injury of apple shoots and roots were tested after the trees were exposed to natural outdoor freezing. The findings were compared with results of hardiness tests of similar trees following artificial freezing treatments previously reported.Two-year-old apple trees of Northern Spy, McIntosh and Antonovka on Malus robusta 5 rootstock were kept in pots outdoors during the winter of 1958–1959. The lowest air and soil temperatures recorded that winter were −26.0°F. and −1.0°F. respectively. Comparable control trees were kept in a storage cellar at a constant temperature of 32 ± 3°F.An electrical resistance method was compared with two procedures for obtaining the electrical conductance of roots and of terminal, median and basal portions of twigs. A highly significant correlation existed between the conductivity and resistivity methods of testing. These methods and procedures are both sufficiently sensitive and consistent to warrant their use in studies of the effect of winter weather on various plant parts. However, the resistance method is preferable because it is much simpler.The differences in the injury to the three varieties, to the three portions of the twigs, and following the two exposure treatments, were highly significant. Highly significant interactions were also found between varieties and treatments, between twig portions and treatments, and between varieties and twig parts. No significant differences were found between replications. The importance of these variances in terms of winter injury is discussed.