Michigan State University creates annotated Montmorency sour-cherry genome

Researchers at Michigan State University have recently created an annotated genome for the Montmorency, the variety that dominates the sour cherry industry in the United States. 

This discovery will help researchers and breeders find genes and markers associated with various traits much faster than in the past, said MSU assistant professor Courtney Hollender, whose lab led the generation of the annotated genome.

This genetic map will help breeders chart a path to a better tart cherry, but there are other obstacles to overcome in this research.

When Hollender's team announced the Montmorency genome in 2023, it was the result of about four years of work. Scientists had already deciphered the sweet cherry genome, and Hollender's team—specializing in the genetics, development, and physiology of fruit trees—wanted to map the Montmorency genome to accelerate some of their research projects.

It wasn't as easy as initially thought. Led by Charity Goeckeritz, then one of Hollender's graduate students, the team discovered that Prunus cerasus, the sour cherry species, has twice the number of chromosomes as sweet cherry, Prunus avium, making gene mapping a more complex task, Hollender said. 

Now, having overcome this particular breeding hurdle, the next step is to hire a sour cherry breeder. 

Amy Iezzoni, MSU horticulture professor, had been the nation's only cross cherry breeder for decades until her retirement in 2021. Since then, the industry has been awaiting a successor, but MSU's budget constraints have delayed action. 

Hollender said the situation should change soon. The College of Agriculture and Natural Resources at MSU will post a new breeder position in the near future, likely in 2025. The exact job description has not yet been defined, but it will include cherry breeding, genetics, and genomics. It may also include peach breeding.

MSU staff are still maintaining a subset of the germplasm collection created by Iezzoni. Extension specialist Nikki Rothwell stated that this spring, elite cherry selections are scheduled to be planted at the MSU Northwest Michigan Horticulture Research Center. 

From her home in northwest Michigan, the heart of cherry country, Iezzoni continues to patiently manage advanced cherry selections. She has always intended to bridge the gap between herself and her successor, but the process is taking longer than initially expected.

“I’m trying to ensure that selections with commercial potential are cared for,” Iezzoni said. “The good news is that things are happening.”

Once a new breeder is hired, the next step will be to identify traits that address Montmorency’s weaknesses. Michigan grower Dave Smeltzer listed the “big four” desired traits: later blooming, greater compactness, more uniform color, and resistance to cherry leaf spot. 

Montmorency has proven vulnerable to spring frosts, which have become more frequent in Michigan over recent decades, causing some massive crop losses. That’s why the industry needs a later-blooming variety. Smeltzer said even one or two days “can make a big difference.” 

Montmorency also tends to become soft and bruise easily and doesn’t always color uniformly, making it less desirable for processors. Additionally, it is susceptible to cherry leaf spot, the main problem in Michigan’s industry. Iezzoni said two of her advanced selections appear to be tolerant of the disease.

Even if a breeder could find a new and improved variety that addresses all these problems, the next hurdle, perhaps the biggest, remains. Smeltzer called it the million-dollar question: Can the industry afford to replace Montmorency?

Cherry growers have been so dependent on Montmorency for so long that replacing it won’t be easy, said Utah grower Marc Rowley.

It’s not just the cost of new plantings for an industry struggling to make a profit. The industry has spent a lot of time and money marketing Montmorency’s health benefits, and virtually all growing and handling processes revolve around this variety. Any new variety would need to promise a significant increase in yield and quality for growers to seriously consider replacing it.

“Even if we found more resistant or later-blooming varieties, it wouldn’t be an easy solution,” said Michigan grower Juliette King McAvoy. “They would still need to fit into a specific production and processing niche.”

But to survive in the long run, the American cherry industry needs a better fruit, said Smeltzer.

Source: Good Fruit Grower
Image: Battistini Vivai

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