Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 20, 2005
Publication Date: February 20, 2005
Citation: Postman, J.D., Denoma, J., Reed, B.M. 2005. Detection and elimination of viruses in usda hop (humulus lupulus) germplasm collection. Acta Horticulturae. 668:143-148. Interpretive Summary: The United States Department of Agriculture, Agricultural Research Service (ARS) maintains a collection of more than 250 unique hop plants at its gene bank in Corvallis, Oregon. The ARS stores its hop collection as potted plants in insect-proof screenhouses to prevent insects from spreading viruses from plant to plant. Hop plants were tested for 6 common hop viruses using a laboratory test called "ELISA". Nearly all hop plants that came from field collections were found to be virus infected and 63% of infected plants contained 2 or more viruses. A technique called "heat therapy" combined with propagation of tiny shoot tips (less than 1 mm long) was used to produce new virus-free plants. Heat therapy involves growing plants for several weeks at temperatures around 100 degrees Fahrenheit. New plants grown from these heat-treated shoot tips were tested and nearly all were found to be free of viruses. The ARS hop gene bank presently includes 125 varieties that are now free of common hop viruses.
Technical Abstract: The United States Department of Agriculture (USDA), Agricultural Research Service (ARS) maintains a collection of Humulus germplasm at its National Clonal Germplasm Repository (NCGR) in Corvallis, Oregon, for the conservation and improvement of hop genetic resources. About 268 clonal accessions and seedlings are maintained as potted plants in a screen house. A 'core' subset of 84 genotypes is also maintained in vitro under cold storage. Clonal accessions were tested by ELISA for Apple mosaic ilarvirus (ApMV), Arabis mosaic nepovirus (ArMV), Hop latent carlavirus (HpLV), American hop latent carlavirus (AHLV), Hop mosaic carlavirus (HpMV), and Prunus necrotic ringspot ilarvirus (PNRV). Ninety-eight hop clones out of 200 were found to be virus infected. HpMV was the virus most commonly detected (67% of infected plants), followed by HpLV (51%), AHLV (50%), and ApMV (28%). ArMV and PNRV were not detected. More than 60% of infected accessions contained 2 or more viruses, and more than 25% contained 3 or more. Cultivars 'Wye Target', 'Vojvodina', 'Shinsuwase', 'Cascade' and 'USDA 21119' were infected with all 4 viruses. Alternating temperature heat-therapy and apical meristem culture were used to eliminate viruses from infected plants. Infected plants were grown for 2 weeks at temperatures alternating between 38°C and 30°C every 4 hours. Apical meristems 0.5mm or smaller were dissected and grown in vitro until large enough to transfer to soil in the glasshouse. Following a natural dormant period, plants were retested by ELISA. Of 182 plants regenerated from heat treated meristems, none tested positive in subsequent virus assays. Presently, the NCGR maintains 125 unique hop genotypes that have tested negative for all of these hop viruses.