Progress on the molecular characterization of the USDA National Pear Collection

The US Department of Agriculture, Agricultural Research Service maintains 2,378 accessions of Pyrus and 478 wild pear relatives in an orchard at the National Clonal Germplasm Repository (NCGR) in Corvallis, Oregon. A set of 10 simple sequence repeats (SSR) and an array of 70,000 single nucleotide polymorphism (SNP) markers have been used to identify and eliminate duplicates and mislabeled trees and to ensure a diverse collection of true-to-type heritage cultivars and their wild relatives. The reference SSR-based database now contains genotypes from 497 accessions and has allowed us to identify unknown pear trees in four collections across four US states. Fire blight is a worldwide disease problem and one of our projects focuses on developing diagnostic markers for resistance to this devastating pathogen that can help identify genotypes to use in breeding new cultivars. Future work includes comparing the SSR-based genotypes of important pear cultivars preserved at the NCGR across European collections to obtain a global view of heritage pear genetic resources, increasing the number of genotypes in the SSR-based reference database, and confirming SNP-determined duplicates through phenotypic evaluation. Conservation and characterization of pear genetic resources at the NCGR is a global effort.