University of Wisconsin-River Falls

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Jan. 16, 2004

UW-River Falls Professor Develops Hardy Midwestern Plum

Commercial plums from California now have a hardy Midwestern cousin. University of Wisconsin-River Falls plant breeder Dr. Brian R. Smith has developed a plum cultivar that stands up to Wisconsin's winters and produces fruit to rival its sun-kissed kin. Smith, a professor of horticulture at UW-River Falls and a state commercial fruit specialist with UW-Extension, created the new cultivar by crossing a plum variety adapted to Wisconsin's frigid winters with a Japanese dessert plum. The new hybrid yields fruit as large and tasty as any California-grown plum from the grocery store, he says, but also withstands subzero temperatures and sports a more easily managed semi-dwarf growth habit.

He hopes one day to see plums join apples, cherries, and strawberries as a commercial Wisconsin fruit crop.

"Commercial plum production is almost non-existent in the state right now primarily because most of your higher quality plums aren't winter hardy, bloom too early in the spring, and require long growing seasons," says Smith. "The goal of my breeding program has been to develop commercial plum cultivars for growing in this climate."

To protect the plum cultivar and facilitate its commercialization, a patent application has been filed by the WiSys Technology Foundation, Inc., an organization that patents and licenses intellectual property for the 25 campuses of the UW System other than UW-Madison.

Besides boasting the most extensive fruit breeding program in the UW System, UW-River Falls also hosts the only plum breeding project in a 24-state surrounding area. Yet when Smith launched the endeavor in 1991, no one had bred plums in the Midwest for over 55 years. To find a source of winter-hardy genetic stock to blend with conventional California-grown varieties, Smith therefore looked to cultivars developed 100 years ago by pioneering plum breeders and planted by homesteaders on family farms. Other sources of germplasm came from wild plum varieties.

One type of plum he selected for his breeding experiments was the cherry plum, a hybrid whose lineage includes wild plum species adapted to northern climes. The cultivar Smith is patenting through WiSys is a cross between a cherry plum and a conventional California dessert plum.

To develop new cultivars, Smith has at his disposal a collection of 350 potted plum trees he maintains at UW-River Falls. After selecting the trees he wants to interbreed, he collects and stores pollen from each male parent tree, transferring it eventually by hand to the flowers of each female parent to achieve the desired hybridizations. If a plant bears fruit as a result of his efforts, he collects its seeds and stores them under conditions that simulate winter, a process called stratification.

After stratification, the seeds begin to germinate. Smith plants the seedlings in pots and begins growing them in a greenhouse, transferring them the following summer to the field. He then waits patiently anywhere from two to 12 years for the plants to mature and produce fruit. Many seedlings never do, succumbing instead to the ravages of Wisconsin's climate.

Once the survivors reach maturity, Smith evaluates them for fruit size and quality, winter hardiness, resistance to disease, and yield, among other traits. If a tree performs well, he propagates it by budding or some other asexual cloning method. If these cloned plants continue to do well, he finally considers the tree as a candidate for cultivar status and possible commercial production.

The plum cultivar being patented by WiSys has been under development for about 10 years; in addition, another 10 potential cultivars are "looking pretty good," says Smith, although he's not ready to release them. The next step for his first plum cultivar will be a round of testing by commercial growers under their own field conditions. Smith is also testing various methods for asexually propagating the cultivar in collaboration with UW-Madison horticulture professor Brent McCown.

Eventually plum trees could be grown commercially in several areas of the state, Smith says, especially in more temperate places such as the Door County peninsula where cherries are now grown, or on high bluffs, less prone to frost, where farmers currently plant apple trees. "Although, as we develop more frost resistance into these varieties, site selection will become less of an issue," he adds.

Only time will tell if Smith's breeding experiments bear fruit for the Midwest's farm economy, but that is the ultimate goal. "My research is a long-term investment in the health of Wisconsin's and the Midwest's ag sectors," he says. "My hope is that plums will someday be a crop that helps farmers diversify their operations, improve their profitability and stay competitive."

Consumers deserve high quality dessert plums," he adds, "rather than the typical low-grade plums shipped here from the Southwest less fresh by 1,500 miles."


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