Open-pollinated seed of 500 genotypes of commercial cultivars, breeding selections and wild species of apples (Malus x domestica) was collected from overseas mixed-clone repositories . This is to generate the first generation of the new `Apple Breeding Population' . Subsequent generations will be intercrossed in a pair-crossing design . Recurrent selection for general combining ability (GCA) is the breeding method used for genetic improvement of the Breeding Population . Every parent in the control-pollinated breeding population is tested for GCA using a polycross mating design.
The best individuals of the Breeding Population, intensively selected between families using the polycross GCA estimates, and also within families are intermated to produce a `Cultivar Production Population' . Trees selected from this have then to be evaluated in grafted clonal tests before commercial release .
Each generation, a new Breeding Population of 500 genotypes is selected from the pair-cross families, based on parental GCA values (from polycross tests), full-sib family means and individual performance and then intercrossed . Greatest emphasis will be on within-family selection not between-family, so as to avoid reducing the effective population size .