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Emergence, origins, and potential control points for new viruses affecting ornamental crops.
J. HAMMOND (1). (1) USDA-ARS, USNA, Floral and Nursery Plants Research Unit, Beltsville, MD, U.S.A.

The introduction of new species and varieties is important to the ornamentals industry, yet new materials bring risks of new viruses or viroids that may affect other ornamentals or even agronomic crops. Changes in production practices over recent decades also affect the introduction and prevalence of virus diseases; among these is a shift from seed production to large-scale vegetative propagation of many industry staples such as petunia, and changes of scale from local origin and production of relatively small numbers of plants to large-scale globally distributed production. Unrooted cuttings may be produced at one location, with rooting and plug production at a second facility, and finishing at a third location before distribution to a retail outlet. Distributed production facilitates introduction and dissemination of new viruses, and the transmission of viruses between diverse crops and different continents. A single mother plant can yield thousands of infected cuttings, which may not show visible symptoms before reaching flowering size at the wholesale or retail outlet. Recently-emerged viruses include <i>Alternanthera mosaic virus</i>, found in phlox in 1997 and now known to infect ornamentals in at least 17 diverse genera; Viola white distortion associated virus, a novel ilarvirus affecting pansies; and multiple carlaviruses. More sensitive, wide spectrum detection methods, applied early in the crop production cycle, may minimize new virus introduction and spread.

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