ISHS Acta Horticulturae 550: XVIII International Symposium on Virus and Virus-like Diseases of Temperate Fruit Crops - Top Fruit Diseases
ADVANCES IN QUARANTINE TESTING OF TEMPERATE FRUIT TREE GERMPLASM AT USDA |
| Authors: | G.R. Kinard, H.E. Waterworth, R.G. Mock |
| Keywords: | Bioassay, Hybridisation, Plum pox, PCR |
| Abstract:
Approximately 150 accessions of temperate fruit tree germplasm are imported annually into the USA 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. 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. The procedure is applied to extracts from both dormant budwood and leaf midribs. Use of the former allows for rapid testing before the germplasm is established and, in the case of pomes, before it is grown in the field. Tissue or dot blot hybridisations 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 USDA regulations, so that accessions received as dormant budwood may be eligible for provisional release after about one year in quarantine. During this period, the accessions are tested for all described quarantine pathogens at least once, and twice for some, such as plum pox virus and phytoplasmas. Efforts continue to incorporate procedures that improve the reliability of quarantine testing and 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. Infected accessions are usually subjected to therapeutic procedures. Electronic records are maintained on all accessions, which are publicly available on the world wide web in the germplasm resources information network (GRIN). Germplasm released from USDA quarantine is generally available upon request, free of charge, to scientists in the USA and throughout the world. | |
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