Where science meets serendipity

Tom Ranney has an addiction, but not one he wants to kick. He spends his waking hours imagining plants that don’t exist yet, theorycrafting, and developing new strategies and approaches to breeding. When he sleeps, he dreams about it.

Ranney is currently the J.C Raulston Distinguished professor at North Carolina State University, where he’s been a staff member for 27 years. You can find him at his lab within the Mountain Horticultural Crops Research Station, which is where the magic happens. The rush of inventing something completely new is what hooked Ranney on breeding.

“Every cross you make is a genetic roll of the dice,” he says. “You can’t ever completely predict what you’re going to get. It’s science coupled with serendipity, which adds to the intrigue.”

However, he didn’t always know he wanted to be a breeder. While working toward his bachelor’s degree at Ohio State University, Ranney found summer work with a tree service, which exposed him to the world of urban agriculture and municipal forestry. He attended graduate school at Cornell University for horticulture and plant protection. Early on in his faculty career, he began screening plants for better pest resistance and adaptability. From there, the next logical step is figuring out how to combine some of those desirable traits. As Ranney says, that’s basically plant breeding.

The process

Ranney has developed nearly 30 new plant introductions through the Mountain research lab, including Javelin pear, a J. Frank Schmidt introduction known for purple foliage and a tight column, and Invincibelle Spirit, the Hydrangea arborescens introduced through Spring Meadow Nursery and central to a campaign that has raised nearly $1 million for breast cancer research.

One of the many aspects of plant breeding that fascinate Ranney is how it integrates many different disciplines. To be a good breeder, you must know plants inside and out. It involves horticulture, genetics, pathology, entomology, and ecology. A well-rounded skillset is necessary to evaluate the germplasm and genetic diversity of plants you’re researching.

There are several factors that Ranney considers when picking a potential breeding idea. But it always comes back to crop improvement. Sometimes opportunities present themselves through particular diseases or an insect problem – something that can be solved by plant breeding. His work often aims to enhance disease or insect resistance, regional adaptability (like cold-hardiness), or reducing invasiveness or weediness. There are also plenty of commercial angles to breeding, like the potential for making more compact forms, fragrant, or reblooming varieties of popular plants. When picking a breeding target, broad genetic diversity is the No. 1 trait he looks for in a group of plants. That raw genetic material is crucial, and helps with “crossability,” that enables him to create fertile hybrids that can continue to move through generations.

He also solicits input from friends in the nursery industry to help prioritize goals and focus his efforts.

A recent example is the collaboration with fellow North Carolinians John and Jill Hoffman of Hoffman Nursery that led to a seedless miscanthus. Hoffman was interested in improving miscanthus by enhancing ornamental features and reducing weediness. Maiden grass is very common along the roadsides of North Carolina and has been grown in nurseries for more than 100 years. But reseeding had always been a problem. The creation of a highly infertile form was a major development and the project was a major undertaking. Over the course of 10 years, Ranney created triploids over multiple generations. The result of the partnership with Hoffman and Star Roses and Plants is My Fair Maiden, a large, bold, cold-hardy miscanthus that is highly infertile.

Photo by Julie McMillan

Never satisfied

As with most of his projects, there is a next step. Variegated patterns, new sizes – just because there is a patent pending does not mean Ranney is by any means “done” with the seedless miscanthus project.

“There is no such thing as a perfect plant, so you always have opportunities to make improvements,” Ranney says. “We’re always prioritizing, strategizing, identifying our objectives. In the short term we may be able to achieve some of those objectives, but some of our breeding strategies might have a 10- to 20-year time horizon.”

New products can be spun off all along that process and timeline. For instance, Ranney’s lab is currently doing a lot of breeding work on magnolias. The opportunities to combine increased cold-hardiness with evergreen traits, different flower colors, or with fragrance, could easily be the endeavor of a lifetime.

“That’s why we have graduate students,” he jokes. “To carry on!”

One of the toughest parts of plant breeding is evaluating your selections. It’s easy to generate lots of plants in a breeding program, but it is complicated and time-consuming to narrow them down to the very best. Ranney starts by selecting as early as possible to reduce numbers, and looks to identify plants that have superior characteristics. The picks begin growing in containers, and the plants that turn out best go to the field for further testing.

In the field, Ranney and his team identifies the plants that are superior as candidates for introduction. From there, the potential introductions are sent to multiple sites throughout the U.S. for evaluation.

Getting input from many sources is important at this point. Ranney often brings in industry experts from North Carolina Nursery & Landscape Association to provide perspective on commercial potential. Then, ultimately, it’s a judgment call. Is the plant unique enough, does it have desirable traits that would make it worthy of a commercial introduction? Think big. Depending on your grower partners, you might want to broaden your target range.

“You might find a plant does really well in Japan, but it might not do well in Oregon,” Ranney says. “It makes it complicated, because you’re working toward evaluating global potential and there are a lot of different environments out there.”

Globe trotting

Like many breeders, Ranney is an accomplished plant hunter. He’s worked with nurserymen in Japan, collected with collaborators in China, and has made many trips to Europe to take advantage of the similar climate.

“Our plant collecting is different than others in that we try to network with plant people, arboretums, botanical gardens, and nurseries around the country that might have unique germplasm, plants that have particular traits that could be useful to our breeding efforts,” he says.

For instance, Ranney is working on developing seedless pears trees but also wants to enhance other traits – specifically red flower color.

On one of his trips to Japan, Ranney found a Pyrus pyrifolia called ‘Ohara beni’ that had that elusive red flower.

“It’s got the darkest red color I’ve seen,” he says. “It’s red in bud and does open up to a white flower eventually.”

Getting that tree imported in the U.S. and through quarantine was a long process, but now ‘Ohara beni’ is a parent in several crosses in Ranney’s breeding program.

The future of plant breeding

Photo by Julie McMillan

The Mountain Crop Improvement (MCI) Lab is the home of Ranney’s research, and while product development is a part of what happens there, the education and training of undergraduate and graduate students is another major component of the university breeding program. Ranney works with undergraduate students in the lab’s summer internship program. Students actually do independent research projects in that program. They also get to attend research conferences and interact with graduate students and faculty.

Ranney is very optimistic about the future of his particular niche of the horticulture industry.

“In many regards, we’re in the golden age of plant breeding,” Ranney says. “Never before have we had as many opportunities. Right now, we’ve got access to germplasm we’ve never had from around the world. Never before have we had such an understanding of plant genetics and access to modern tools like tissue culture and molecular markers. There are more people now engaged in plant breeding in university, private and commercial, than ever before. But what’s really exciting to me, is the future is going to keep getting better with the new advanced breeding techniques. Particularly the genome editing technologies that are coming out now are going to revolutionize plant breeding in the future.”

These tools and techniques, often lumped under gene editing technologies, have massive implications for breeders. The CRISPR-Cas system, for example, allows users to either delete or replace segements of DNA very precisely. Ranney says the system is low-cost, effective, and offers the potential to confer virus resistance or create sterile plants by knocking out critical reproductive pathways. It can extend shelf life of flowers by modifying ethylene pathways, or create plants that are more compact or dense, rebloom, or reduce invasiveness.

“We’re in a very good spot right now, but the opportunities are just going to skyrocket in the future.”

For more: www.ces.ncsu.edu/fletcher/mcilab/index.html