Genetic Variation and Distribution of Pacific Crabapple

By: Kanin J. Routson, Gayle M. Volk, Christopher M. Richards, Steven E. Smith, Gary Paul Nabhan, and Victoria Wyllie de Echeverria

ABSTRACT. Pacific crabapple [Malus fusca (Raf.) C.K. Schneid.] is found in mesic coastal habitats in Pacific northwestern North America. It is one of four apple species native to North America. M. fusca is culturally important to First Nations of the region who value and use the fruit of this species as food, bark and leaves for medicine, and wood for making tools and in construction. However, little is known about either distribution or genetic diversity of this species. To correct this deficiency, we used habitat suitability modeling to map M. fusca habitat types with species occurrence records. The species apparently occupies at least two distinct climate regions: a colder, drier northern region and a warmer, wetter southern region. Total area of modeled habitat encompasses ’356,780 km2 of low-lying areas along the Pacific coast. A total of 239 M. fusca individuals sampled from across its native range were genetically compared using six microsatellite markers to assess for possible geographic structuring of genotypes. The primers amplified 50 alleles. Significant isolation by distance was identified across the ’2600 km (straight line) where samples were distributed. These results may help establish priorities for in situ and ex situ M. fusca conservation.

Wild apple species (Malus Mill.) are native throughout temperate climes of Asia, Europe, and North America (Brown, 2012; Luby, 2003). They offer promising sources of genetic diversity for apple breeding (Brown, 2012) and also provide a wildlife habitat and serve as a direct food source for humans. Four Malus species are native to North America. Three species occur in eastern and midwestern United States and eastern Canada: M. angustifolia (Aiton) Michx. is native from southern New Jersey to Florida, M. coronaria (L.) Mill. from Ontario to South Carolina, and M. ioensis Alph. Wood Britton ranges from Minnesota to Texas. These have been determined to be closely related based on isozymes (Dickson et al., 1991). The species native to the Pacific northwestern North America, M. fusca, is the sole geographic, morphological (Van Eseltine, 1933), chemical (Williams, 1982), and genetic outlier among the North American taxa.


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