Heirloom apple cultivars represent an important specialty crop for producers and a genetic resource for the dessert apple industry. These cultivars are plagued with misidentifications, which hinders utilization and long-term preservation. Phenotypic identification, used for centuries, is unable to distinguish among the thousands of existing U.S. heirlooms. DNA profiling provides an objective basis for cultivar identification. Washington State University’s “MyFruitTree” (myfruittree.org), built upon the RosBREED project and with international collaborations, has accumulated a DNA profile dataset of thousands of apple individuals focused on the U.S. genepool. Users submit leaf samples for trees of interest, and MyFruitTree’s cost-recovery research opportunity determines the cultivar identity (or reveals their uniqueness and pedigree position). However, a common and valid question is, “How do you know that is the correct identity?” The core panel of robustly identified cultivars was based on public breeding germplasm, modern cultivars, and their ancestors, which were DNA profiled in the RosBREED project last decade. Since then, examined trees from collections in the U.S. and abroad have greatly expanded the number of DNA profiles with cultivar labels. But those labels are not always correct, especially when a tree is derived from only a single source. Therefore, a system was derived for assigning confidence to the cultivar labels associated with DNA profiles. Cultivar name evidence is assembled in the categories of provenance, phenotype, and genotype for both the DNA-profiled tree and the historically named cultivar, and congruence is examined. This system is applied at two levels: streamlined and comprehensive. The streamlined approach for the current DNA profile dataset efficiently determined whether each individual belongs confidently in the “Reference Panel” or is relegated to “Accessory Profiles” pending further evidence. A Reference Panel was assembled of hundreds of U.S. heirlooms (and more than a thousand close relatives from other regions). The comprehensive approach involves attention from a transdisciplinary tribunal of experts who carefully weigh evidence that an apple individual – often a proposed new discovery of an otherwise lost heirloom – is indeed a historically named cultivar. As MyFruitTree accumulates more DNA profiles submitted by cultivar collection managers and apple enthusiasts nationwide, the cultivar name assignment system is being applied to unidentified trees with strong provenance evidence of cultivar status. Establishing accurate cultivar identities of valued trees via DNA profiling is providing the critical foundation for a coordinated national effort to sustain preservation and utilization of apple crop diversity.
