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 ...
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.
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 ...
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.
