Application of genetic and spatial analyses to identify collection priorities for wild Malus species

The USDA-ARS National Plant Germplasm System has 33 species of wild Malus, many of which were acquired from plant explorations performed over the past 30 years. The phylogenetic relationships among these species were determined by chloroplast sequencing (1681 bp from four regions). Five primary clades of species were identified. Malus x domestica and the primary progenitor species, M. sieversii, M. orientalis, M. sylvestris, and M. prunifolia were localized within one of the two clades specific to species of Chinese origin. Malus fusca, native to the western US and Canada, also localized within this Chinese clade. The other three Malus clades originate from Taiwan (M. doumeri), southern Italy (M. florentina), and central/eastern North America (M. ioensis, M. coronaria, M. angustifolia). Genetic diversity and admixture of individuals within each clade and species was evaluated using nuclear microsatellite markers. Together these data provide the basis for integrating genetic structure information with species range distribution modeling approaches to prioritize novel collection sites.