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Transcript
OREGON June 1971 ORNAMENTAL AND Vol. 15, Issue 1 NURSERY DIGEST Page 1,2 Thomas C. Allen Department of Botany and Plant Pathology Oregon State University Corvallis, OR GARDEN, EASTER LILIES INFECTED BY VIRUSES I have not examined an Easter or garden lily in Oregon that did not contain at least one virus. Lily researchers in Denmark and Holland report a similar situation with their home-grown lilies. Therefore, Oregon cannot be blamed for the virus content in lilies. The blame must be placed on the lily itself and its method of propagation. Any crop that is vegetatively propagated, such as lilies, is bound to contain viruses. For instance, potatoes grown in Oregon have at least one and probably two viruses. Good control programs protecting plants from insect vectors of viruses and removing plants with obvious virus symptoms can reduce viruses in lilies. Even if all lily plants with virus symptoms are removed, virus-infected plants which appear to be healthy will be present. Some plants may have been infected recently and the virus has not built up enough to cause symptoms, and some viruses do not produce plant symptoms. In both of these cases, symptoms are not visible and the viruses are spread unknowingly by growers. One virus affects lilies universally One lily virus, aptly named the "lily symptomless virus," appears to infect lilies universally. Why should we be concerned about a virus that does not visibly affect a plant? The concern is not for the present appearance of the virus-infected lily, but for the future, knowing that symptoms will show under certain environmental conditions. F. P. McWhorter, Professor Emeritus of Plant Pathology at Oregon State University, told me of an experiment with Ace lilies infected with a virus disease named curl-stripe. When the infected lilies were harvested from coastal fields, half of them were replanted in the Willamette Valley and appeared healthy. Yet the other half, planted along the coast, showed curl-stripe symptoms. Thus, the grower along the coast had to pay for roguing the diseased plants, while the Willamette Valley grower saved his money. Subsequently, bulbs from both areas were forced in greenhouses for Easter lily production. The forcing environment favored curl-stripe symptom expression. Now the formerly healthy appearing bulbs from the Willamette Valley produced many more plants with curl-stripe than the rogued coastal lot. The virus content was originally equal in both lots, but symptom expression depended upon environmental conditions. When I have taken curl-stripe diseased plants into a greenhouse, the plants consistently recovered and appeared healthy. When symptomless, the virus was called " lily symptomless virus"; when leaves curled and were striped, the virus was called "curl-stripe virus." Obviously, the virus did not change, but was one virus. Serology and electron microscopy have confirmed this conclusion. The length of the virus particles from healthy Ace lilies and those diseased with curl-stripe was the same, 640 nanometers (nm). When magnified 57,000 times, these virus particles appear about 1½ inches long (Figure 1). In comparison, a 6-foot-tall man magnified 57,000 times would have a height of 65 miles. Virus particles 640nm long also have been associated with Lilium longiflorum ‘Nellie White,’ L. speciosum with mild mottle symptoms, L. wilsoni, various hybrid garden lilies, and tulips with tulip breaking or tulip mosaic. Necrotic fleck caused This same lily virus when combined with cucumber mosaic virus caused necrotic fleck in Ace and Nellie White lilies. Since neither virus alone causes symptoms under some environmental conditions, the presence of one or the other virus in a healthy-appearing lily is a potential hazard. Figure 1. Electromicrograph of virus particles extracted from a curl-stripe diseased Ace lily. Virus particles have been plated with a platinum: palladium alloy to enhance contrast and create a shadow. Magnification is 57,000X. Another virus found in Oregon lilies has particles 750nm long. Lilies infected with this virus are immediately recognized as virus diseased by the bright yellow mottled leaves. This virus is present in hybrid garden lilies, in tulips, and in Ace lilies with classical fleck disease. In this latter disease, the 640nm virus and cucumber mosaic virus also are present. In some plants of L. wilsoni and tulips, both the 750nm virus and the 640nm virus are present. When ultrathin sections of leaves containing the 750nm virus are examined, pinwheel or tubular inclusions are present (Figure 2). These inclusions are characteristic of viruses 750nm long. Serological tests indicate that this is the tulip virus. Figure 2. Electromicrograph of pinwheel (PW) and tubular (T) inclusions within a leaf cell of the hybrid garden lily ‘Bright Star.’ These configurations are characteristic of a 750nm virus infection Magnification is 35,100X. Thus, we know there are at least three distinct viruses in Oregon lilies. None are unique to Oregon, and the three viruses are associated with various virus diseases whose names do not indicate the virus involved. All three viruses are aphid or vegetatively transmitted and therefore are controllable. Oregon Ornamental and Nursery Digest was published from 1957 to 1975 by the Agricultural Experiment Station, Oregon State University, Corvallis. Pesticide Use - Due to constantly changing laws and regulations, no liability for the suggested use of chemicals in this reprint is assumed. Pesticides should be applied according to label directions on the pesticide container. Permission to Reprint material appearing in the Oregon Ornamental and Nursery Digest is granted with the request that you credit the source: Oregon Ornamental and Nursery Digest, date, volume, issue, page numbers. Do not excerpt or reprint in such a manner as to imply the author's endorsement or criticism of a product or concept. Nondiscrimination - The information in the Oregon Ornamental and Nursery Digest is provided with the understanding that no discrimination is intended and that listing of commercial products implies no endorsement by the authors. Criticism of products or equipment is neither intended nor implied.