Molecular markers (isozyme and DNA) have been used to map apple and have helped to elucidate the inheritance of some morphological traits. In this project random amplified polymorphic DNA (RAPD) and isozyme markers were used to create maps for `Wijcik McIntosh, a columnar (reduced branching) sport of `McIntosh' and NY 75441-67, an advanced selection from the multiple disease resistance breeding program. NY 75441-67 is resistant to scab source of resistance from M. floribunda) and resistant to cedar apple rust. `Wijcik McIntosh' is being used in the breeding program as a source of the dominant gene, Co, for reduced branching, but there is also interest in this genotype because of the tremendous variation in plant form observed in progenies segregating for columnar habit. Some of these form variants may be of greater commercial interest than the parental material. Morphological traits examined in this progeny included plant height, stem diameter, suckering, branching habit, spur production, and internode length. The usefulness of molecular markers to pre-select for components of plant form is being examined. Molecular markers promise to aid our understanding and manipulation of quantitative morphological traits.
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