SPONTANEOUS MUTATION AS A SOURCE OF CLONAL VARIATION ON DECIDUOUS FRUITS

Trees of a clone of the same age and growing under the same conditions should be identical. Variations within a clone are largely due to topophysis, virus infection and genetic instability. As an introduction to the symposium the latter aspect is briefly reviewed. Mutations may affect genomes, chromosomes or genes. Their expression depends on the genes involved and the genetic background. Instability of a gene may depend on other (mutagenic) genes or on the conditions in the tissue (paramutation). Because of the periclinal structure of the meristem, somatic mutations are usually limited to certain histogenetic layers. Separation from the normal tissue is possible by adventitious bud formation. Various methods are mentioned. When tissue culture in volving regeneration of buds from an undifferentiated callus is used, the incidence of mutations may be quite high as it seems to be affected by the presence of synthetic growth regulators and their quantitative ratios. The practical implications are briefly discussed.