The characteristics and stability of a range of Cox's Orange Pippin apple mutants showing different growth habits

Summary

Seven hundred and fifty gamma-irradiated scions of Cox's Orange Pippin apple were grown to produce a V₁ generation and were then multiplied to produce a V₂ of 13 158 individual trees. 272 obvious vegetative mutants, mainly dwarf or compact types, were found in this population and classified according to growth habit. These were propagated to produce clones of the mutant types (V₃) and a study of these clonal mutants as compared with their original (V₂) characteristics showed that while the vast majority of the selected mutants produced dwarf or compact clones, no clear indication of final cropping performance could be drawn from the original phenotype of the selected V₂ mutants.

The majority of mutants produced were not of commercial value, and the main reasons for the rejection of V₃ clones depended, in many cases, on the phenotype of the V₂ selection. Thus while all types of V₂ mutant produced approximately the same proportion of acceptable trees, the reason for the rejection of the V₃ clones varies with the V₂ phenotype. Therefore selection can be carried out at an early stage in a mutation breeding programme to reduce the proportion of certain unwanted types such as mericlinal chimaeras that otherwise are carried forward to yield trials. From the orchard trials of 82 mutant clones, 24 were short-listed for possible commercial introduction. All were derived from the less extreme mutant types.