Technical Abstract: Plant explorers have visited Russia, Turkey, Kazakhstan, and China over the past twenty years to find populations of the wild relatives of apple (Malus). Seeds from wild populations of M. sieversii, M. orientalis, M. hupehensis, M. kansuensis, M. toringo, M. bhutanica, M. transitoria, and M. zhaojiaoensis have been planted at the USDA-ARS-National Plant Germplasm System (NPGS) Plant Genetic Resources Unit in Geneva, NY. Malus sieversii and M. orientalis seedling trees have been screened for disease resistance and evaluated for genetic diversity based on microsatellite markers and ploidy levels have been identified for the species native to China. Genetic diversity analyses reveal that most of the overall genetic structure in these species is partitioned among individual families but that significant regional differentiation exists. Some accessions exhibit high levels of resistance to apple scab (Venturia inaequalis Cooke), cedar apple rust (Gymnosporangium juniperi-virginianae Schwein) as well as fire blight (Erwinia amylovora Burrill) and could be very valuable in disease resistance breeding programs. Genotypic data for microsatellite markers is publicly available in the new molecular observation tables in the Germplasm Resources Information Network (GRIN) database (http://www.ars-grin.gov/npgs/).