EPLP-010 6/14 Rose Rosette Disease Demystified Kevin Ong, Associate Professor and Extension Plant Pathologist Molly Giesbrecht, Extension Associate (Plant Pathology) Dotty Woodson, Extension Program Specialist; Laura Miller, County Extension Agent–Tarrant County Texas A&M AgriLife Extension Service, The Texas A&M University System What do we know? The disease has been around Rose rosette disease, a lethal rose disease with no for more than 70 known cure, has recently increased in the Dallas-Fort years. As early as Worth area. Many people who grow and enjoy roses the 1940s, symp- as well as landscapers who take care of them are con- toms of witches’ cerned about how to protect their plants and confused broom (growth of by all the information available from various sources a tight, brush-like on the Internet, in publications, and from the media. cluster of plant So, what do we know about this disease? shoots) (Fig. 1) The following review of information from peer- were described on reviewed (evaluated by experts in the field) articles in roses in Manitoba, scientific journals summarizes what we know so far. Canada (Conners, 1941). In the United Figure 2. Witches’ broom effect on States, rose plants a flower cluster. Distorted flowers in Wyoming with and increased, atypical reddish color similar symptoms on the buds. were described in 1942 (Thomas and Scott, 1953), and the disease was subsequently found in other states. In 1990, George Philley reported the disease in East Texas. It appeared in the Dallas-Fort Worth area in the mid-1990s and has expanded there in the last 2 to 3 years. Symptoms associated with rose rosette disease include: • Witches’ broom (Fig. 2) • Malformed flowers and leaves Figure 1. Witches’ broom–the cluster and bunching of • Excessive leaf growth and thorniness abnormal plant shoots. • Extreme red discoloration of plant tissue (Fig. 3) 1 (negative strand RNA virus), in symptomatic roses. The virus occurred in 84 out of 84 symptomatic plants (Laney et al, 2011). This study also resulted in a genetic test to detect the virus. However, the procedure can be tedious. Several diagnostic clinics, including the Texas Plant Disease Diagnostic Lab, are testing a modified, easier-to-use detection method. The Oklahoma Plant Disease and Insect Lab and the Texas Plant Disease Diagnostic Lab are two National Plant Diagnostic Figure 3. Malformed shoots, smaller leaves, and increased Network-affiliated labs that can test for the rose rosette red discoloration. virus using PCR methods. • Lateral shoot elongation (abnormal lengthening What is so bad about a virus? of side branches/twigs) • Enlarged/thickened stems There is no effective way to treat a virus on an -in However, symptoms vary on different rose types fected plant because the virus may be systemic (spread and cultivars. For example, red shoots do not occur in throughout the plant) and not a localized infection. some ornamental rose varieties, and multiflora roses When symptoms occur on only part of the plant, the do not exhibit the excessive thorns. disease may be localized, or it may be systemic but asymptomatic on other parts of the plant. What causes rose rosette? Pruning the infected part may eliminate the pathogen if the infection is localized, but, if systemic, Researchers have suspected that mite damage, the infection will persist. Mites carrying the virus can phytoplasma, or a virus causes rose rosette disease. continue feeding on all parts of the rose and carry the • Eriophyid mites virus to uninfected rose tissues. Transmission experiments using eriophyid mites collected from asymptomatic roses did not result in What do studies show about how appreciable rose rosette symptoms (Armine et al, rose rosette disease is transmitted? 1988), making it unlikely that the eriophyid mite’s • Grafting experiments (Thomas and Scott, feeding causes the damage all by itself. 1953; Epstein and Hill, 1995; Armine et al., 1988). • Phytoplasma Grafting experiments on many different roses Phytoplasma (a specialized group of bacteria that did not always result in transferring the rose rosette infect plants) has long been considered a major can- symptoms. Species and plant tissue age may have didate for the cause of the disease. Research articles some influence; disease transmission was more effi- from Poland (Kaminska et al, 2001), India (Chaturve- cient on rapidly growing tissue. di et al, 2009), and China (Gao et al, 2008) demon- • Eriophyid mite, Phyllocoptes fructiphilus strated the presence of a phytoplasma (from the aster (Allington et al. 1968, Armine et al, 1988). yellows family) causing rose rosette-like symptoms. But, there are no reports of phytoplasmas in symp- To test the mites’ ability to transmit the disease, tomatic roses in the United States. In an experiment researchers took mites from infected, symptomat- where symptomatic plants were treated with antibiot- ic plants and introduced them onto healthy plants. ics, rose rosette symptoms persisted (Epstein and Hill, Although the disease was not always transmitted, the 1995). Antibiotics should have killed or suppressed results suggest that the eriophyid mites can effectively the phytoplasma. transmit the disease for about 10 days. Experiments using eriophyid mites harvested from healthy plants • Virus and transferred to healthy plants did not result in rose In 2011, a research group from the University rosette symptoms, suggesting that mite damage alone of Arkansas detected a new virus, an Emaravirus does not cause the symptoms. 2 • Mechanical transmission experiments If the virus is systemic and can get into the roots, To find out whether pruning practices might it may be able to move to adjacent plants or new transmit the disease, leaf sap and juice, made by plants through the root graft. This theory has not grinding infected plant parts, were rubbed on the been scientifically confirmed. leaves of healthy plants. This did not result in rose rosette symptoms (Allington et al, 1968). Why can’t I leave it alone Other experiments using contaminated razor and see if it recovers? blades to wound healthy plants also did not result in Sometimes rose rosette disease does not kill the rose rosette symptoms. Stab inoculation, using a con- rose but stunts it. Although it may recover on its own, taminated needle to wound healthy plants, resulted in it is highly unlikely, and the infected rose can serve as rose rosette symptoms in two out of 120 tries (Epstein a virus reservoir. Theoretically, eriophyid mites can and Hill, 1995), showing that mechanical transmis- transmit the virus from a diseased plant to other roses. sion is possible but highly unlikely. How does the mite spread? How is this disease currently If plant parts are touching, it is possible that the identified and/or confirmed? mites could walk from one plant to the next. Move- The following methods are used to diagnose rose ment for longer distances is thought to occur passive- rosette disease: ly by wind (Keifer, 1975; Epstein et al., 1997) or by • Field identification based on symptoms (The piggybacking on other insects (Shvanderov, 1975). reliability of symptoms is an issue since herbi- cide damage, insect damage, and nonbiological Do we know conclusively that environmental conditions—such as wind, the eriophyid mite is transmitting temperature, and sun—can mimic rose rosette symptoms.) the rose rosette virus? • Detection of eriophyid mites along with disease No published study clearly demonstrates that the symptoms eriophyid mite (Phyllocoptes fructiphilus) actually • Electron microscopy to identify virus-like par- carries the rose rosette virus. Evidence from mite ticles and soluble, membrane-bound particles transmission studies suggests that the eriophyid mites (Rohozinski et al, 2001; Ahn et al, 1996; Silvestro are carrying and transmitting some disease-causing and Chapman, 2004) agent from the diseased plant. • PCR analysis using molecular methods to detect the virus (see more below) Can the virus move through root grafts? Are my roses “clean” if the genetic The more apt question is whether adjacent roses detection test is negative? will graft their roots together. Many have said that Not necessarily. The genetic test detects the pres- this is unlikely, but Golino (2005) demonstrated ence of the virus on the sample. Typically, even though possible root grafting by using a herbicide on a plant symptomatic plant tissue is usually used for the test, and observing the mortality of the adjacent roses. An only a small portion of the plant is sampled. The sam- experiment where researchers grafted pieces of roots ple does not show the extent that the virus is distribut- from an infected plant onto a healthy rose resulted in ed throughout the plant. The sample may contain no rose rosette symptoms on the new plant, suggesting viruses or viruses below the detection limit of the test. that root tissue can harbor the virus (Armine et al, If infection is suspected, additional sampling and con- 1988). tinued monitoring for symptoms and mites is advised. 3 What is the best way to deal Epstein A. H. and Hill J. H. 1995. “The Biology of with rose rosette disease? Rose Rosette Disease: A Mite-Associated Disease of Uncertain Aetiology.” Journal of Phytopathology Based on the current information about the disease 143:353–360. and its presumed vector, the best management practic- Epstein, A. H., Hill, J. H., and Nutter, F. W. Jr. 1997. es are: “Augmentation of Rose Rosette Disease for Bio- • Remove confirmed and/or symptomatic plants control of Multiflora Rose (Rosa multiflora).” Weed quickly. Science 45(1): 172–178. • Treat nearby plants with miticide to reduce the Gao, R., Zhang, G. M., Lan, Y. F., Zhu, T. S., Yu, X. Q., probability of disease transmission by eriophy- Zhu, X. P., and Li, X. D. 2008. “Molecular Char- id mites. But, this will not stop the virus if it is acterization of Phytoplasma Associated with Rose already in the plant.