|Waterworth, Howard - RETIRED - USDA|
Submitted to: Acta Horticulturae
Publication Type: Abstract Only
Publication Acceptance Date: November 20, 2000
Publication Date: N/A
Technical Abstract: Approximately 150 accessions of temperate fruit tree germplasm are imported annually into the US through the US Department of Agriculture's National Plant Germplasm Quarantine Center in Beltsville, MD. These accessions are destined for USDA and university researchers, commercial interests, national repositories, and private citizens. A wide range of tests is conducted for viral and sub-viral pathogens. Pome fruits are tested for latent viruses using graft bioassays, while bioassays and ELISA are used to test stone fruit germplasm for viruses. Particular effort is made to prevent the introduction of plum pox virus; stone fruits are treated by grafts onto the woody indicators GF 305, Prunus tomentosa, and shirofugen plum, and the indicators are subsequently tested by ELISA and mechanical inoculation to herbaceous hosts. A recent advance is the incorporation of PCR techniques with nested, broad-spectrum primers to test for phytoplasmas such as apple proliferation, pear decline, and peach X diseases. Tissue bot hybridizations with cRNA probes are used to test for several viroids, including peach latent mosaic, apple scar skin, and pear blister canker viroids. The incorporation of molecular procedures has resulted in changes in US regulations, so that accessions received as dormant budwood may be eligible for provisional release after about one year in quarantine. Efforts continue to incorporate procedures that improve the reliability of quarantine testing and/or reduce the time accessions are held in quarantine. Notably, experiments are in progress to introduce PCR testing for cherry green ring mottle virus, and the apple latent viruses.