Malus sieversii: A Diverse Central Asian Apple Species in the USDA-ARS National Plant Germplasm System

There are several Central Asian Malus species and varieties in the USDA-ARS National Plant Germplasm System (NPGS) apple collection. Malus sieversii is the most comprehensively collected species native to Central Asia. Other taxa such as M. sieversii var. kirghisorum, M. sieversii var. turkmenorum, M. pumila, and M. pumila var. niedzwetzkyana have primarily been donated to the collection by other institutions and arboreta. We sought to determine if genetic and/or phenotypic differences among the individuals that make up the gene pools of these taxa in the NPGS exhibit unique characteristics. Genetic data, based on microsatellite analyses, suggested that the diversity within each taxa is significantly greater than that among taxa. Trait data also revealed very few differences among taxa, the primary characteristic being the dark red fruit coloration and tinted flesh color of the accessions assigned to M. pumila var. niedzwetzkyana resulting from a known single-gene mutation in anthocyanin production. We found that M. sieversii is a highly diverse species with a range in genetic and phenotypic trait variation that includes the characteristics of the other Central Asian taxa of interest. We conclude that the gene pools that comprise the accessions within the NPGS Central Asian Malus collection are highly overlapping with respect to both phenotypic traits and genotypic characters. The mountains of Central Asia have forest species that include Malus sieversii (Ledeb.) M. Roem., a highly diverse apple crop wild relative. The Russian scientist Vavilov ex- plored the forests of Central Asia in the 1920s and made note of the wide range of M. sieversii phenotypes, suggesting that this region, includ- ing Kazakhstan, Kyrgyzstan, Tajikistan, and western China, is a center of origin for the domesticated apple (Luby et al., 2001; Wan et al., 2011; Yan et al., 2008). Malus sieversii grows in a wide range of habitats, including areas with hot summers and short winters as well as those with long, severe winters in the Tien Shan Mountains (Dzhangaliev, 2003). Wild populations are found in montane, scrub, humid as well as dry continental forests and in diverse stream habitats in xeric areas (Forsline et al., 2003). Malus sieversii trees are phenotypically diverse, offering variation in the time of flowering, quantity and quality of fruit, ripening period, fruit biochemical composition, tree architecture, winter and