Plum acreage remains small across the eastern United States. In Michigan, only about 20 growers—only two with more than ten acres—sell plums through local roadside farm and farmers’ -markets in the season after sweet cherries and before apples.
“It’s a niche market, not a large market, but it has a gourmet quality about it,” says Bill Shane, at the Southwest Michigan Horticultural Research and Extension Center near Benton Harbor. Shane breeds peaches, but works with growers as they keep evaluating plum varieties that have that gourmet appeal and are productive in their climate. It takes skillful growers to produce plums, he says.
One person who is optimistic about the future of plums is Dr. Brian Smith, who breeds plums at the University of Wisconsin at River Falls. So far, his reputation hinges on one plum cultivar named Black Ice, released in 2006. The plum is large, round, sweet, very dark—and bred in a climate where winter low temperatures can hit 40 degrees below zero.
“Black Ice is the only plum I’ve released so far, but I have more in the pipeline,” Smith said.
Plums grown in the Midwest have never measured up in size and quality to those of California. Black Ice, however, has many of the -characteristics of California plums while being quite winter hardy.
Black Ice was bred from a California plum (Z’s Blue Giant) and a winter hardy cherry plum. Black Ice arrived with a dark purple-black tender skin, juicy red flesh, and semifreestone pit, and ripened two to three weeks earlier than any other large quality plum for the Midwest.
Black Ice trees are naturally semidwarf. Many plum trees are not self–fertile, and the preferred pollinizer for Black Ice is Toka, but Compass and Alderman also work.
Smith is unusual as a breeder because his job description is two-thirds teaching and one-third cooperative extension specialist serving the state’s commercial fruit growers. Research and plant breeding aren’t mentioned but support the rest of his position. He works each year making crosses and evaluating the results—almost like a hobby that’s become a passion. He said he became interested in plant breeding as a youngster working with his father on new watermelon varieties for the family’s farm in South Dakota.
“All I do is make interspecific crosses,” he said. “Some hybrids I work with have five species in them.”
Floyd Zaiger in California was the pioneer who built a thriving nursery business on interspecific stone fruit crosses. And Smith does it much the same way. What makes stone fruits so interesting to Smith is that they will cross across species lines, sometimes creating fertile offspring, so peaches, cherries, plums, and apricots can all contribute genes to make new kinds of fruits. That’s what excites Smith. “There is so much -germplasm to work with,” he said.
The fruit produced by Zaiger Genetics is not well suited to the climate of the northeastern quadrant of the United States. Even the breeding program at Vineland, Ontario, is geared to producing fruit for the U.S. Department of Agriculture’s Hardiness Zone 5, Smith says, and he wants fruit that will thrive in zones 3 and 4.
He is shooting for 3. This last winter, the most severe in the Midwest in 20 years, showed that Black Ice is not as hardy as he had first thought, but hardy enough for zone 4. That makes it quite a bit hardier than peaches and hardier than either the Japanese or European plums.
Black Ice has the eating quality of Japanese dessert plums and ripens about August 5, making it a true summer fruit, he said.
Because of the ability to hybridize stone fruits across species lines, there is a catalogue full of traits that can be incorporated into a new fruit, Smith says. Plums come in many colors (red, yellow, blue), in sizes from golf balls to peaches, and in shapes from round to oval.
Some plums were native to his region of North America. While fruit is small and quality is poor, Smith has used them to obtain the winter hardiness and drought tolerance he wants.
A key problem, he says, is that Japanese plums, which are suited for California, are not hardy enough. And European plums, which are somewhat hardier than peaches, are hexaploid (having six sets of chromosomes), not diploid (two sets) like other stone fruits, so their genetics are not accessible in interspecific -breeding programs.
Smith has 30 acres of land available for his breeding work and also greenhouse space. All of his 400 parent trees grow in containers ranging from 5 to 25 gallons in size.
In the fall, Smith moves all containerized parental trees into large walk-in coolers. After they harden off and acquire their chilling hours, Smith moves them to the greenhouse in February and March where he can force early bloom and then hybridize amongst them. All the buds in balloon stage on a tree are emasculated and then carefully hand-pollinated later with pollen from the -chosen parent.
The secret in interspecific breeding is persistence, he says. Keep searching and never give up. You never know where a cross will produce a fertile hybrid with high -quality.
Smith is hoping to release two new stone fruits in the near future, one a small, round, plum-apricot cross that, he says, has “unique flavor, the richness of an apricot and the sweetness of a plum.” He also has a new yellow plum with a rosy blush that “has amazing sweetness and -flavor.”
International Plant Management, the Lawrence, Michigan, company headed by Wanda Heuser Gale, is working with Smith. The company works with breeders and nurseries to commercialize new varieties.
“The whole plum market is not a big deal,” said Wally Heuser. “But Brian Smith is a very interesting guy and he’s working with some very interesting stuff. He puts out a very hardy plum.”
International Plant Management is also working with Cornell University to commercialize some cherry varieties left by Dr. Bob Andersen when he retired and the Cornell breeding program in stone fruits was discontinued. Andersen also did plum breeding. Now, most plum breeding work is done at Vineland and in Ralph -Scorza’s USDA breeding program at the Appalachian Fruit Research Station at Kearneysville, West Virginia.
Plums were once bred at University of Minnesota, where the Alderman variety originated. Now, Smith says, “I’m the only breeder in the 24 states around us.”
In May this year, Smith received the outstanding faculty award for his work as a professor of horticulture and extension educator.