Certain species of maple have earned a nasty reputation that plant breeder Ryan Contreras aims to change.
Norway and Amur maples are known to “escape cultivation” — a euphemism for becoming invasive — leading to restrictions in some parts of the U.S.
The problem has caused demand for these species to drop steeply over the past decade, with some nurseries reporting declines of up to 90 percent, said Contreras, associate professor of ornamental plant breeding at Oregon State University.
Creating sterile cultivars of these maples may allow them to regain their former popularity in New England and elsewhere.
Meanwhile, Contreras is also breeding for sterility in other maple varieties commonly grown in Oregon to save them from a similar fate.
“We want to restore one market while maintaining the other,” he said.
Sterility can theoretically be achieved in maples with the same method that was used to create seedless bananas and watermelons — developing a plant with three sets of chromosomes instead of two.
In such plants, called triploids, the odd number of chromosomes prevents them from evenly splitting and pairing off during sexual reproduction, often preventing the formation of viable seed.
The process of creating triploids is time-consuming, though. Contreras first used chemical agents to create maples with four chromosome sets, then crossed them with maples with two chromosome sets.
“It renders them highly infertile but we don’t know yet to what degree,” he said. “We won’t know until these plants start flowering.”
In Contreras’ view, it’s easier to repopularize a once-common variety, such as Norway and Amur maples, than to educate landscapers and other plant buyers about an entirely new one.
This philosophy has also spurred his breeding of cotoneaster, a flowering plant in the rose family, to withstand fire blight.
While it’s not a major problem in Oregon, pressure from the bacterial pathogen is strong in the Eastern U.S., where cotoneaster was once a prevalent landscape plant.
Due to their susceptibility to fire blight, demand for cotoneasters has dried up, Contreras said. “It’s completely fallen out of favor.”
Even so, nursery growers still know how to cultivate the plant and landscapers remain familiar with it, he said.
Contreras is hoping to restore the cotoneaster’s marketability with three cultivars that have been virtually symptom-free when exposed to the disease.
“The testing is ongoing,” he said. “We want to confirm that under many environments and disease pressures, they’re going to continue to perform as we’ve seen them perform.”
To that end, Contreras is cooperating with researchers at Kansas State University and Virginia Tech to see if his cotoneasters will thrive in other regions. The University of California-Davis is also analyzing their disease resistance and evaluating their drought tolerance.
Filling a niche
By focusing on long-term research that confers beneficial agronomic traits, Contreras is trying to fill a niche that’s largely unoccupied by private breeders.
His goal isn’t to complete with private companies that release new branded varieties every year.
“To make a splash, there needs to be lots of marketing behind it,” he said.
Even when his ultimate goal is breeding a cultivar that’s sterile or disease resistant, Contreras must nonetheless select for plants that are attractive.
“We throw away thousands of plants because they don’t look good. They’ve got to look good,” he said.
A successful cultivar must be appealing to consumers, adaptable to production agriculture and easy to propagate, Contreras said. “If it doesn’t have those three things, then it’s pointless,” he said.
Contreras grew up on a farm in eastern North Carolina, raising hay, hogs and laying hens, then pursued a higher education in horticulture.
“For a while, I wanted to have a nursery, but I cured myself of that,” said Contreras.
While working at a nursery in college, the potential for financial calamity steered him toward a career in academia.
During his college years, Contreras took a deep dive into peanut breeding, but ended up returning to ornamental plants.
The genetics of peanuts and other major field crops have already been extensively researched, but the nursery industry still has a vast unexplored territory.
“Landscape plants are my passion. There’s very little known about the genetics of woody plants,” Contreras said. “Everything we’re learning is new.”
Occupation: Ornamental plant breeder
Hometown: Corvallis, Ore.
Family: Wife, Megan, and two young children
Education: Bachelor’s degree in horticultural science from North Carolina State University in 2002, master’s degree in horticultural science from North Carolina State University in 2006, doctorate in horticulture from the University of Georgia in 2009.