Dec 5, 2017
RosBREED 2 halfway toward improved parent plants

Apple cultivars with ancient genetic resistance to the industry’s scourge of fire blight, and peaches with a consumer-friendly texture are just two of many targets that researchers with the RosBREED 2 program have in their sights.

Researchers in 12 different states are halfway through RosBREED 2, a five-year research effort into traditional breeding members of the rose family, which also include strawberries, blackberries, pears, peaches and sweet and tart cherries.

University of Minnesota Horticulture Professor Jim Luby, known for his work on Honeycrisp, is a member of the RosBREED program.

“The same gene that makes a cherry red, makes an apple red and makes a peach red,” said Michigan State University’s Amy Iezzoni. “It’s been pretty easy for us to get tests for red color.”

Broadly, the effort is focused on identifying disease-resistant genes in members of the rose family and combining those traits with fruit quality. An earlier, four-year phase of the grant targeted genes to improve fruit quality.

By isolating genes responsible for such desirable traits, devising methods to test plants in the field for the DNA traits, and even breeding a new generation of parent plants, the researchers hope to empower breeders and shorten the time span needed to commercialize new cultivars. Iezzoni, who co-directs the project along with Cameron Peace of Washington State University, calls the process “DNA-informed breeding.”

“Basically, RosBREED’s goal is to make breeding more efficient,” she said. “We can be very deliberate.” Traditional fruit tree breeding is a time-consuming and lengthy process requiring as much as 20 years per generation. But DNA tests developed by RosBREED research can be used to screen plants in breeding programs, selecting from hundreds of siblings the few who carry the parent plants’ desirable genes.

“We know the cassette of genes that make Honeycrisp crisp, and you can select that in the progeny,” she said.

A changing market

It’s difficult to talk about RosBREED without discussing Honeycrisp.

Discovered in 1960 and released in 1991, the large-celled crunchy fruit showed the value of varieties tailored to consumer tastes. The breakout variety also has shortcomings, such as poor storage, that make it ripe for further improvement by breeders. Despite its widespread success, Honeycrisp’s family tree wasn’t known until 26 years after it was released. The University of Minnesota graduate student who published the family tree this year relied on RosBREED data in his work.

The apple’s success has changed the industry. Growers now well understand the value of improved cultivars – and so they’re receptive to researchers’ work.

USDA-ARS Research Plant Pathologist Jay Norelli, a team leader in RosBREED, has seen a lot change in the industry in the last five to 10 years.

“Now, marketers really want new cultivars,” he said. “Growers are now much more interested in what kind of traits are going to be coming into new cultivars in the future.”

Michigan State University Professor Amy Iezzoni examines a sweet cherry tree as part of the RosBREED program.

Tough apples

Norelli, who’s based at the USDA station in Kearneysville, West Virgina, has been developing disease resistance into apple cultivars, attacking that problem from a couple of different angles.

One angle is crossing Red Delicious with Splendor, hoping to capture the disease resistance from Red Delicious and the fruit quality from Splendor. A Purdue research team is trying for similar results with Enterprise and Goldrush. RosBREED’s objective in these cases is to “develop an elite group of parent plants with pyramided resistance genes,” Norelli said. He’s hoping to finish the project by the end of RosBREED grant cycle.

Also by the end of RosBREED 2, he hopes to have breeding lines with increased blue mold and fire blight resistance.

Another angle of attack looks much farther back. Wild apples in Kazakhstan are thought to be a living ancestor to the modern apple, but are resistant to fire blight. Genetic material of these apples was brought back to the United States more than 20 years ago, and now Norelli is supervising research into finding fire blight resistance material in those genetic models. Results from that work, he said, are probably six to eight years away, beyond the end of RosBREED 2.

That long-term timetable comes despite Norelli’s ability to practice “accelerated breeding” with apple trees that fruit very rapidly. He said about two to three generations of breeding (“back crossing”) are needed to increase genetic stability. When it comes to disease, “growers want immediate solutions,” he said, but largely they seem enthusiastic and positive about his work.

Jim McFerson, director at the Washington State University Tree Fruit Research and Extension Center, said there’s a lot of work yet to be done, and commercialization – developing the actual cultivars that growers would use – will depend on individual breeding programs around the country. “We can’t promise the world,” he said. “While we’ve accomplished a lot, the point is we have a lot to do.”

But that doesn’t make the projects already in the research pipeline any less thrilling. One project being pursued is the sweet cherry with genetic resistance to powdery mildew.

“It’s an exciting time to be a researcher in specialty crops,” he said.

Reliable peaches

Iezzoni is excited about a project to give peaches consistent texture and softness.

Ksenija Gasic, associate professor of horticulture at Clemson University, is working on RosBREED to address postharvest issues in peaches, but separately has been working on getting peaches to ripen more evenly.

Currently, growers are re-harvesting the same orchard five to seven times to collect peaches as they ripen and before they soften, while at the grocery store peaches are anywhere from rock hard to overripe, and consumers are taking home a mix.

Ksenija Gasic, associate professor of horiticulture at Clemson University, and Guido
Schnabel, Clemson plant pathologist, join others on work with blossoming peach trees
as part of the RosBREED program.

“You take them home and three people take three peaches, and each have a different experience,” Gasic said.

Gasic is looking at mutant and sport varieties of plum for insight into improving peach consistency. Peach cultivars ripening their fruit consistently, or peaches able to be uniformly softened at the grocery store, could change the game for growers and consumers.

The possibility of a vastly improved fruit – an industry-changer like Honeycrisp – is what the researchers and breeders would like to deliver to growers, McFerson said.

“You always wonder what’s going to get the fruit quality to the next level,” Iezzoni said. “There are some things within the breeding programs that I think are going to bring things to the next level.”

Stephen Kloosterman, assistant editor


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