Ploidy of USDA World Pear Germplasm Collection Determined by Flow Cytometry

• Published in: Acta horticulturae no. 1094; pp. 75 - 81
• Main Authors: Postman, J, Bassil, N, Bell, R
• Format: Journal Article
• Language: English
• Published: International Society for Horticultural Science 01.01.2015
• Subjects: alleles; aneuploidy; clones; crossing; cultivars; diploidy; DNA fingerprinting; flow cytometry; gene banks; genetic markers; genotype; germplasm; germplasm conservation; Germplasm Resources Information Network; growers; hybrids; leaves; microsatellite repeats; pears; pollen; pollinators; propagation materials; Pyrus; tetraploidy; trees; triploidy; Oregon
• ISSN: 0567-7572
• DOI: 10.17660/ActaHortic.2015.1094.6

Living germplasm collections representing world diversity of pear (Pyrus L.) are maintained by the US Department of Agriculture at the National Clonal Germplasm Repository (NCGR) in Corvallis, Oregon, USA. Flow cytometry was performed on young leaf tissue from 1,284 genebank accessions to assess ploidy, and 93% were found to be diploid (2n=2x=34). All pear wild relative species examined were diploid. The European and interspecific hybrid cultivar collections included 85 triploid trees out of 997 tested. Only three Asian cultivars of 166 were found to be triploid. One European cultivar was tetraploid and one was aneuploid (2.3x). Six pear clones received as purported tetraploids were determined to be diploid, and two were chimeral, having both tetraploid and diploid tissue. Many of the pear cultivars identified as triploid were not previously known as such. Simple sequence repeat (SSR) or microsatellite-based profiles were generated for 19 triploid accessions and reference pear cultivars using a standard fingerprinting set of 12 SSR markers. Two to nine of the 12 SSRs generated three alleles in the triploid accessions, thus supporting the triploid determination. The use of flow cytometry to determine ploidy combined with SSR markers for genetic fingerprinting helped to confirm synonymy in several pear accessions. Ploidy results permitted the elimination of misidentified accessions that should have represented triploid or tetraploid genotypes. Knowledge about the ploidy of genebank accessions will help growers avoid using triploids as pollinizers and breeders avoid using sterile pollen when making crosses. The NCGR genebank provides propagation material for breeding and genetic research by on-line request through the USDA Germplasm Resources Information Network (GRIN).