Isozymes in North American Malus (Rosaceae): Hybridization and Species Differentiation

Isozyme phenotypes of Malus fusca, a native of western North America, differ strik- ingly from those of eastern North American sect. Chloromeles. Isozyme phenotypes vary little between the three taxa recognized within sect. Chloromeles: M. angustifolia, M. coronaria, and M. ioensis. Phe- notypes of seedlings from native taxa did not share diagnostic allozymes with the cultivated apple, M. x domestica, indicating little gene flow from the latter into native Malus. Isozyme patterns do, however, support earlier conclusions based on morphology that M. platycarpa and the flowering cultivar 'Kola' are hybrids of sect. Chloromeles and the domesticated apple, and that M. dawsoniana is a hybrid of the domesticated apple and M. fusca.