By Kathleen Phillips
Halfway through a five-year, $4.6 million grant to combat rose rosette disease in the U.S., the national research team studying it is encouraged by the amount of information learned but admits having a way to go before finding how to overcome the deadly problem.
Rose rosette was observed on wild roses as early as the 1940s, but it was not until 2011 that scientists definitively identified the cause as being from a new virus in the novel genus Emaravirus transmitted by the microscopic eriophyid mite, according to Dr. David Byrne. Now the virus is killing commercial rose varieties.
Symptoms, which can show up as early as 17 days from exposure to infected mites or as many as 279 days after, include “witches’ brooms, excessive thorniness, enlarged canes, malformed leaves and flowers.” Ultimately, the rose plant dies.
The team is pursuing three issues: the virus, the mite and rose plant resistance to the disease, according to Byrne, professor of Rosa and Prunus Breeding and Genetics for Texas A&M AgriLife Research, College Station, and Rose Rosette Disease Project director. And now they are soliciting help from people who like to grow roses as well.
“It is a citizen scientist approach,” said Dr. Kevin Ong, team member and director of Texas A&M AgriLife Extension Service’s Texas Plant Disease Diagnostic Lab in College Station. “We are trying to engage the people who have an interest in roses in general and give them the opportunity to participate in a national research project.”
Because of the many components to the problem, the research team represents not only many states but a variety of expertise from entomology to pathology to plant breeding.
“We’re still learning about the mite and the virus,” Byrne said. “And now we are seeing rose rosette not only on multiflora (wild) roses, which are considered invasive, but also on commercially cultivated roses.”
Because of that, researchers now consider all roses susceptible to the disease until proven otherwise. That calls for a massive monitoring effort, he said.
“The main purpose of monitoring is to try to gather information to identify sources of resistance or tolerance,” Byrne said. “It’s been somewhat frustrating from a breeding point of view because it takes two or three years to determine if something is resistant.”
He said as the national research project begins its fourth year, the field trials planted the first year are just now providing data that could lead to developing resistant varieties.
“We’re up to about 500 different roses planted for evaluation and I also have collected data on probably close to 700 already. The vast majority are susceptible,” Byrne said. “We’re in the verification mode now, because some varieties that had been thought to be resistant are turning out to be susceptible.”
The researchers are turning to molecular techniques to develop markers to use in the analysis for marker-assisted selection for breeding, which theoretically can decrease the breeding cycle by half, he said.
“What’s more important is we can decrease by 80 percent the number of plants we have to put out in the field,” he said. “That is a huge saving and potentially will allow us to look at more seedlings, which will accelerate the breeding process as well.”
Meanwhile, other team members on the national project, which was funded by a U.S. Department of Agriculture Specialty Crop Research Initiative grant, are turning to rose enthusiasts to help monitor and validate reports of the disease across the U.S.
“There is a need for development of new detection methods, so as our research collaborators develop new detection methods, we test them on real samples to make sure they work in the real world,” Ong said. The methods are also validated at an Oklahoma State University lab.
Ong said his role on the project is also to educate the public about the disease, which will help monitor its location, so his team created a website http://roserosette.org as a clearinghouse for information.
“The website also is a portal so that people can take pictures and submit them into the database. A verifier on the team looks at the photo to determine whether the plant depicted has rose rosette,” Ong said.
The site is designed for mobile phones or tablets so a person can easily take a picture while looking at the plant, he said.
“When a picture is submitted, the site captures the location and a verifier is notified to make a decision about the image,” Ong explained. “Yes, it is rose rosette; no, it is not rose rosette; or we are not sure or we would like to get more information or a sample. Those are the three possible answers.”
Verifiers can ask for a physical sample for confirmation, if necessary, he said. All images are maintained in the online database for future reference by variety to help researchers and the public document those varieties proven susceptible.
To help people learn what to look for, Ong published a series of factsheets available at http://bit.ly/roserosettefacts. Several other affected states also have information linked on the rose rosette website.
The team is also trying to develop better tools to detect the virus and presence of the mite.
To track the mite, all the reports of rose rosette have been put on a map to get a sense of the mite’s distribution and movement, Byrne said. Researchers know that the microscopic mite travels in the wind and has been known to move 300 feet a year. There appears to be a northern and a southern range, which in Texas is roughly at Interstate 20, below which cases of rose rosette are rare.
“In the last two or three years, we have confirmed it in some Texas counties south of I-20, but it might’ve just been brought in from somewhere,” Ong said.
The researchers said people can look at rose plants now as new growth and flowering often occurs in early fall, but late-spring examinations are ideal for finding signs of rose rosette.
“It’s been exciting to see this national effort come together,” Byrne said. “We are trying to understand the epidemiology and environmental factors of the disease development and spread. Hopefully, we will have even more information by the end of this year.”