COMPACT MUTANTS OF APPLE INDUCED BY IONIZING RADIATION

Abstract

Mutations of compact habit of growth were induced in selected apple varieties by acute irradiation with gamma rays from a Co60 source at doses ranging from 3750 rad to 7500 rad. The rate of mutation was high. In trees of the McIntosh variety, repropagated from irradiated material, the percentage of total vegetative (tree or leaf) mutants was 9.8 and the percentage of compact mutants 5.2. The compact mutants were characterized by shortened internodes and reduced tree size. Various degrees of growth reduction were induced by the radiation treatment. Most of the compact mutants produced fruit of an undesirable shape, often flattened, irregular, and grooved. However, mutants were selected which combined the desirable compact growth habit with fruit that was characteristic of the variety.