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Virus Diseases of Orchids
This article was published originally on 4/12/1996Viruses are among the smallest organisms that cause plant diseases. They can be seen only when magnified thousands of times. Although they are simple organisms, made up only of nucleic acid and a protein coat, viruses cause devastating diseases.
More than 25 viruses have been reported to infect orchids. The two most common orchid viruses are cymbidium mosaic virus and odontoglossum ringspot virus.
There are, however, some symptoms that are frequently associated with virus diseases. Typical virus symptoms include yellow, brown, or black spots or line patterns on foliage, with discolored areas often sunken. Brown or yellow rings (ringspots) or a mosaic pattern of yellow and green coloration on foliage are characteristic of virus infections. Flowers may show brown streaks or color break. Color break describes a discoloration of flowers, usually seen as lighter intensity line patterns. (Some orchids show symptoms of color break from genetic mutations, not virus infection.)
Methods used to diagnose orchid viruses include serology, plant bioassays, and electron microscopy. ELISA test kits, based on serological techniques, are now commercially available for many of the viruses that can infect orchids. These kits can be purchased and run by a grower. There are also commercial companies that will test plant samples for the presence of viruses. Plant bioassays involve inoculating a set of susceptible "indicator plants" with extract (ground tissue and sap) from a suspect plant and watching for characteristic symptoms to develop. Electron microscopy allows for the visualization of characteristic virus particles in plant cells. Unlike serological kits and plant bioassay techniques, however, electron microscopy methods involved specialized training and facilities.
In the future, as genetic engineering techniques continue to be developed, orchids that are resistant to certain viruses may become available.
Year of Publication:
IC-475(8) -- April 12, 1996