Flow Cytometry and DNA Microsatellite Analysis Detect and Identify Triploid Pyrus Cultivars

The U.S. Department of Agriculture (USDA), Agricultural Research Service (ARS), National Clonal Germplasm Repository (NCGR), Corvallis, OR, maintains an international collection of diverse pear (Pyrus L.) genetic resources. All Pyrus species are primarily diploid, with a base chromosome set of x = 17 (2n = 2x = 34), however, some cultivars are triploid (2n = 3x = 41) or tetraploid (2n = 4x = 68). Flow cytometry was performed on 725 genebank pear accessions to assess ploidy, and 91% were found to be diploid. Of the 62 triploid accessions, two were Asian (Pyrus pyrifolia) cultivars, 56 were European (P. communis) cultivars and four were interspecific hybrids. Simple sequence repeat (SSR) or microsatellite-based profiles were generated for 20 triploid accessions and  reference pear cultivars at NCGR using a standard fingerprinting set of 12 SSR markers developed by the European Cooperative Programme for Plant Genetic Resources. The triploid accessions included pairs of same name cultivars (P. communis ‘Batjarka’ and ‘Karamanlika’) obtained from different sources, and a sample of P. communis ‘Obican Vodenac’ growing at the Appalachian Fruit Research Station (AFRS). SSR loci generated three alleles for each of the triploid accessions, thus confirming triploidy. Cultivars with the same name had the same fingerprints and are therefore duplicates. Cultivars Batjarka and Kajzerka were misidentified and Obican Vodenac from AFRS did not match that cultivar from NCGR. SSR fingerprints of ‘Batjarka’ and ‘Katjzerka’ matched those of two other genotypes: ‘Erabasma’ and ‘Karamanlika’, respectively. The presence of either one or two alleles at each of the 12 SSR loci for ‘Obican Vodenac’ from AFRS indicated that it was diploid and not true-to-name. The use of SSR markers for genetic fingerprinting confirmed triploidy in pear genebank accessions and resolved three cases of mis-identification. The NCGR genebank provides propagation material for breeding and genetic research by on-line request through the USDA ARS Germplasm Resources Information Network (GRIN).