Technical Abstract: Quince, Cydonia oblonga Mill., is a close relative of apples (Malus sp.) and pears (Pyrus sp.) in the Rosaceae family. It has been cultivated for thousands of years in central Asia and the Middle East for its fruit, and for hundreds of years as a dwarfing rootstock for pears. The USDA-ARS National Clonal Germplasm Repository in Corvallis, Oregon has assembled a diverse living Cydonia collection that includes wild collected accessions, landrace genotypes and named cultivars from the center of origin in the Middle East and Central Asia. One self-rooted tree each of 125 accessions is maintained in a 1 hectare orchard. Trees were evaluated annually from 2006 to 2010 for incidence of naturally occurring diseases including Fabraea leaf and fruit spot (Diplocarpon mespili (Sorauer) B. Sutton (=Fabraea maculata)), powdery mildew (Podosphaera sp.), rust (Gymnosporangium sp.) and fire blight (Erwinia amylovora (Burrill) Winslow et al). A standard rating system of 1 (no disease) to 9 (severe symptoms) was used for all diseases. No fungicides were applied to trees. Fabraea leaf spot is prevalent most years at the site and plant response ranged from highly susceptible to resistant. Rust and powdery mildew occurred in some years when environmental conditions were suitable. Fire blight infections were not common and strikes were removed when observed. Many quince clones exhibited resistance to individual fungal pathogens. Several selections including ‘Limon’ from Turkey, TE-2-73 and ‘Rannyaya Tange’ from Turkmenistan, and ‘Kuganskaya’ from Ukraine exhibited resistance to all three fungal diseases. The NPGS quince collection, with diverse representation that includes much of Cydonia’s natural wild and cultivated distribution, is an important source of genes for adaptation to the diseases that attack this crop.