Dec 3, 2019

Michigan research hunts new tart cherry traits

Michigan loves growing Montmorency cherries, but the state isn’t above looking at what other varieties have to offer.

Firmer fruit, more sugar, freestones, earlier harvest and better tolerance of cherry leaf spot are among some of the traits targeted by Amy Iezzoni who this summer at the Michigan State University (MSU) Clarksville Research Center gave a presentation on her ongoing work breeding cherries. The goal isn’t a new niche variety for consumers, but rather traits desired by the growers.

“In the past, the cherry leaf spot tolerance has been a major thing they’d like,” said Iezzoni, a horticulturalist who’s worked with MSU plant pathologist George Sundin on the issue over the years.

A severe outbreak occurred in Michigan tart cherries during the mid-1990s. The disease is caused by the fungus Blumeriella jaapii, and shows up as reddish to purple spots that turn brown. Sweet cherries are tolerant of the disease, while wild cherries are naturally resistant. The trick is to incorporate resistance into the tart cherries. Iezzoni’s found that a truly resistant cultivar needs multiple genetic mechanisms defending against cherry leaf spot.

An earlier harvest could help growers dodge some pest pressure from spotted wing drosophila (SWD), she said. SWD, which will lay eggs in most small fruits, cycle through several generations every summer. Unlike some other crops affected by SWD, with tart cherries the goal is to simply cut down on the amount of pest prevention, “so you’re not living on the tractor and paying for the sprays,” Iezzoni said. The trick for adjusting the cherries’ harvest time is to not push bloom earlier, thus risking crop loss to spring freeze damage.

An “air” freestone cherry is one trait that Iezzoni showed off at the Clarksville Research Center. The flesh of the cherry clung only to the suture, or outside ridge of the stone, with an air-filled pocket around the rest of the stone.

“That is unusual to find in cherry, but it does exist,” she said. The trait could make it easier to pit Montmorency cherries that are used for processing.

Better firmness in a cherry could lead to better fruit quality. Higher sugar could help the flavor, although it won’t reduce the fruit’s acid. A niche variety called Jubileum, a Hungarian cherry that Iezzoni said was used in crosses for her research, has the color of a Bing cherry while being smaller like a Montmorency cherry. Jubileum is much more firm than a tart cherry and sweet, with a brix score of 21, she said.

Jubileum, however, is not a high-yielding variety, she said. And no matter what traits are being added, the toughest trait to keep in the variety is its high-yielding characteristic, Iezzoni said.

“It takes a while to document exactly what the fruit set is going to be,” she said. Tonnage needs to be examined in the orchard.

The RosBREED research project – a USDA-funded multi-state effort that recently ended its fifth and final year – refined techniques and tools that are speeding up her research.

“RosBREED was instrumental in giving me the knowledge and tools to select for the genetic traits more efficiently,” Iezzoni said.

Heading into the winter, she’s looking at the data on the offspring of experimental crosses and planning what crosses to make next season.

“Choosing parents is a big decision,” she said.

— Stephen Kloosterman, associate editor