Rose rosette virus (rose rosette disease)

Taxonomy

Domain	Viruses
Realm	Riboviria
Kingdom	Orthornavirae
Phylum	Negarnaviricota
Subphylum	Polyploviricotina
Class	Bunyaviricetes
Order	Elliovirales
Family	Fimoviridae
Genus	Emaravirus

Scientific Name

Emaravirus Rose rosette virus

Scientific Name Synonyms

Emaravirus Rose rosette virus

Common Name

Rose rosette virus (RRV)

Author: Mary Ann Hansen, Virginia Tech

Reviewed by: Anton Baudoin, Virginia Tech

Pathogen

Rose rosette virus is a member of the Emaraviridae, a group of eriophyid mite-transmitted viruses. It is a negative-strand, multipartite RNA virus consisting of four to eight separate RNA particles. Double membrane-bound particles are seen with electron microscopy in infected rose tissue. Rose rosette virus was detected in 84 of 84 rose plants showing symptoms of rose rosette disease and in 0 of 30 asymptomatic rose plants by Laney, et al. (2011) and is thus has been identified as the cause of rose rosette disease.

Symptoms and Signs

Symptoms of rose rosette disease (RRD) are highly variable, depending on the species or cultivar of rose affected. This variability can complicate diagnosis. Symptoms can include rapid elongation of new shoots, followed by development of witches’ brooms or clustering of small branches. Leaves in the witches’ broom are small, distorted, and may have a conspicuous red pigmentation, although red pigmentation is not a consistent symptom. Canes on some species or cultivars develop excessive growth of unusually soft and pliable red or green thorns that may stiffen later. When this symptom is present, it is diagnostic for RRD. Symptomatic canes may also be noticeably thicker than the parent cane from which they emerged, or they may grow in a spiral pattern. Flowers may be distorted with fewer petals than normal, and flower color may be abnormal. For example, flowers that are normally a solid color may be mottled. Buds may abort, be deformed, or be converted to leaf-like tissue. Infected rose plants often die within one to two years.

When all of the above symptoms are present, diagnosis is relatively straightforward. However, a diseased plant may exhibit few of these symptoms, especially in the early stages of the disease. Some symptoms, such as leaf coloration, may be subtle. Although some diseased plants develop very obvious red pigmentation, others exhibit a less striking reddish-pink color on leaf undersides or along the margins of otherwise green leaves. Because the new leaves of many rose cultivars normally have reddish pigments, it may be difficult to determine whether the reddish color is abnormal or not. Therefore, it is important to continue to monitor symptoms on suspect roses. On RRD-infected plants, the reddish color does not go away, whereas on healthy plants, the reddish color usually disappears as the leaf matures.

Witches’ brooms on some diseased plants may be an unusual color of green that can be mistaken for symptoms of a nutrient deficiency. However, nutrient deficiency should affect the whole plant. If these symptoms appear only on parts of the plant, they are probably not due to nutrient deficiency and RRD is more likely. The witches’ broom symptom itself is not necessarily diagnostic for rose rosette disease. This symptom can also occur in response to certain types of herbicide injury. For example, if glyphosate, the active ingredient of the herbicide Roundup, contacts green tissue of rose plants in the fall, it is translocated to the buds, and symptoms do not become evident until those buds emerge the following spring. Witches’ brooms with yellow, narrow leaves on clusters of shoots are typical of glyphosate injury. The commonly used broadleaf herbicides 2,4-D, dicamba and several others, can also cause leaf distortion on roses. Unless plants are injured again, symptoms of herbicide injury should disappear by the following year. Also, herbicides do not induce the red coloration typical of many rose rosette infections.

Other symptoms of rose rosette disease that may be expressed include blackening and death of the canes on some cultivars, short internodal distances, and blind shoots (shoots that do not produce a flower). Rose rosette-infected plants may also show increased susceptibility to powdery mildew.

Ecology and Spread

The disease is transmitted by the eriophyid mite, Phyllocoptes fructiphilus, or by grafting. The wild multiflora rose (Rosa multiflora) is very susceptible to the disease and is a common source of inoculum. Cultivated roses planted downwind of infected multiflora rose are especially at risk because the mite vector travels on wind currents from infected to healthy plants. Some growers have observed symptoms on previously healthy plants within four weeks of being planted downwind of diseased multiflora rose. The causal agent of rose rosette disease is not soil-borne, so it is possible to successfully plant healthy roses in beds where diseased plants have been removed. However, because the pathogen is systemic in infected plants, the virus may persist in RRD-infected root pieces that remain in the soil. If plants regrow from these old root pieces, as multiflora rose is apt to do, they can serve as an inoculum source for healthy plants. Therefore, it is important to thoroughly remove symptomatic plants and ensure that infected plants are not allowed to regrow from old, infected root pieces.

Geographic Distribution

As of 2013, rose rosette disease has been found only in North America. It has been found in California, Wyoming, and Utah, from Nebraska south to Texas, in Iowa, Missouri, and Arkansas, and in most states east of the Mississippi River. With the exception of Connecticut, it has not yet been found in New England to date. The disease is also reported in Manitoba, Canada.

Management

Cultural Control

No effective control is available for rose rosette disease on existing, infected plants. Preventing disease spread is the main recommended method of control. Because multiflora rose (Rosa multiflora) commonly serves as a source of inoculum, it is important to remove all multiflora rose in the vicinity of where cultivated roses are grown. It is generally recommended that multiflora rose be removed within a 100-meter radius of cultivated rose nurseries and gardens. Locations where individual multiflora rose plants have been removed should be monitored for regrowth, and any regrowth should be promptly removed and destroyed. Multiflora rose over larger areas is difficult to control and complete removal may be impractical.

To prevent infection of new transplants, avoid planting cultivated roses on hilltops or downwind of known multiflora rose plantings where the cultivated rose transplants are more susceptible to invasion by the mites. Space plants so that canes and leaves do not touch each other. Eriophyid mites do not have wings and must crawl from plant to plant. Proper spacing makes it more difficult for the mites to move within a planting.

Any suspect roses should be removed and destroyed immediately or monitored for continued symptoms and removed as soon as presence of RRD is ascertained. In some areas, burning is permitted and can be used to destroy diseased plants. If burning is not allowed in the area, plants should be bagged and removed. Diseased plants that have been uprooted should not be allowed to remain in the vicinity of healthy roses because they can continue to serve as a source of inoculum. Fallen leaves or other debris from infected rose plants should also be thoroughly removed because mites that survive on plant debris could spread to new transplants. To avoid spreading mites that may be present on plant debris, avoid using leaf blowers to remove fallen leaves.

Chemical Control

Although there is no chemical compound that will directly control rose rosette virus, effective control of mites with certain miticides may reduce the risk of spread. Be aware that miticides registered for control of spider mites typically do not control the eriophyid mites that transmit RRD. Use of miticides in the absence of cultural controls is not recommended. One way to use a miticide as an additional tool in a control program is to focus sprays on plants that surround spots where diseased plants have been removed. These are the most likely plants to which mites from within a planting would have moved. Consult your local extension specialist or agent for recommendations relevant to your particular state. Remember: the label is the law.

Resistance

R. multiflora is the species that appears to be most susceptible to RRD. However, many species and selections of cultivated roses are also highly susceptible, and no cultivars have been proven to be resistant. Although the native species Rosa setigera is reported to be resistant to the disease, one grower has reported increased susceptibility to powdery mildew on plants of R. setigera, which could indicate some level of infection by the RRD pathogen. The species Rosa bracteata (also called the McCartney rose), which exists as a weed in southern states, is susceptible to RRD but resistant to feeding by the mites that transmit the disease. It may be possible, through breeding techniques, to incorporate this mite resistance into cultivated roses in the future. In the meantime, it would be wise to assume that all cultivated roses are potentially susceptible to the disease.

Diagnostic procedures

Because symptoms of RRD can be confused with those of herbicide injury from glyphosate, it is important to obtain background information on the timing of disease development and the history of herbicide use near affected plants when trying to diagnose the disease by symptoms alone. One symptom that appears to be diagnostic for RRD, if present, is the presence of canes of large diameter emerging from canes of smaller diameter.

Laboratory tests for diagnosing RRD include demonstration of transmission of symptoms from affected stems grafted onto healthy plants, as well as use of molecular techniques for detection of the virus. It can take months to obtain results with the grafting technique, whereas use of reverse transcription and polymerase chain reaction can be done in a relatively short period of time. Refer to the article, How We Test for Rose Rosette in Oklahoma, by Jen Olson for details on extracting viral RNA, and performing reverse transcription and PCR for detecting RRV. Note that diversity among viral isolates could potentially cause a false negative result. If a symptomatic plant tests negative, it would be a good idea to re-test with a different set of primers.

Some have also used identification of the eriophyid mite vector as a means of diagnosis of RRD; however, presence of the mite does not confirm presence of the virus. Also, the mites are very small and may be difficult to find on the plant even if they are present.

Resources and References

• Allington W.B., Staples R., Viehmeyer G. 1968. Transmission of rose rosette virus by the eriophyid mite Phyllocoptes fructiphilus. J. Econ. Entomol. 61(5): 1132-1140.
• Dominiak-Olson, J. and E. Rebek. Rose Rosette Disease. Oklahoma State University Extension EPP 7329.
• Laney, A. G., Keller, K. E., Martin, R. R., and Tzanetakis, I. E. 2011. A discovery 70 years in the making: characterization of the Rose rosette virus. J Gen Virol 92:1727-1732.
• Nassuth, A., Pollari, E., Helmeczy, K.,Stewart, S., and Kofalvi, S. 2000. Improved RNA extraction and one-tube RT-PCR assay for simultaneous detection of control plant RNA plus several viruses in plant extracts. J. Vir. Meth. 90:37–49.
• Olson, J. 2012. How We Test for Rose Rosette in Oklahoma NPDN News 7(6): 4-7.

Acknowledgments

• National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30708 as part of "Diagnostic Image Series Development for Supporting IPM in the Southern Region" (USDA-NIFA-RIPM-003351)