Submitted to: Acta Horticulturae
Publication Type: Abstract Only
Publication Acceptance Date: 1/20/2001
Publication Date: 12/31/2002
Citation: POSTMAN, J.D., SUGAR, D. ELIMINATION OF VIRUSES FROM THE USDA PYRUS GERMPLASM COLLECTION. ACTA HORTICULTURAE. 2002. 596:529-530. Interpretive Summary: The national genebank for pears in the U.S. is maintained by the US Department of Agriculture, Agricultural Research Service at the National Clonal Germplasm Repository in Corvallis, Oregon. This collection represents world diversity for pears and includes over 1700 accessions representing all of the know species of pears in the world as well as many hybrids and selections. The orchard collection consists of nearly 1500 unique kinds of pears including 100 Asian and 700 European cultivars. Pear trees are screened for the presence of latent virus diseases by grafting them onto virus-sensitive "indicator" varieties that produce distinct symptoms. More than 60% of the pear cultivars received at the repository were found to be infected with one or more virus. Infected trees are put through a virus-elimination procedure that involves growing the plants for several weeks at elevated temperatures (near 100 degrees F) followed by propagation of the tiny shoot tips. Since the beginning of this work in 1983, more than 400 virus infected pear trees have been replaced with new trees that have tested negative for the presence of viruses. Nearly 90% of the pear cultivars at the repository are now available to researchers and nurseries as virus tested plants. More information about the National Plant Germplasm System pear collection is available at: http://www.ars-grin.gov/cor/pyrus/pyrinfo.html
Technical Abstract: The national genebank for Pyrus in the U.S. is maintained by the United States Department of Agriculture, Agricultural Research Service at the National Clonal Germplasm Repository in Corvallis, Oregon. This collection represents world diversity for pears and includes over 1700 accessions representing the 26 major taxa of Pyrus and their hybrids. Clonal genotypes are stored as orchard trees with approximately 10% of the collection backed up as in vitro cultures. Wild species are represented as orchard trees and as seed collections. Clonal accessions are screened for latent viruses by graft inoculation to a range of woody indicator plants. Since 1983 more than 650 virus-infected pear clones have been detected in the collection. Infected clones are subjected to alternating temperature heat-therapy followed by apical meristem culture to generate virus-free replacement plants. More than 400 virus infected clones have been replaced with heat-treated meristem derived trees. Presently, 77% of the clonal Pyrus accessions and more than 86% of the pear cultivars at the U.S. pear genebank are available as virus tested trees.