Apr 30, 2015
Quicker cranberries: Breeding research seeks to shorten variety development process

Researchers at the USDA Agricultural Research Service’s Cranberry Genetics and Genomics Lab at the University of Wisconsin-Madison have made significant advances in the past year toward the development of a state-of-the-art, genetic, marker-assisted selection program that will greatly reduce the number of years it takes to develop new cranberry varieties, said UW-Madison graduate student Brandon Schlautman.

Schlautman is a research assistant working with Juan Zalapa, an assistant professor in the UW-Madison Department of Horticulture and a USDA-ARS research geneticist, to establish a marker-assisted selection program that will allow researchers to use genetic information to predict a cranberry seedling’s potential fruit quality and yield prior to planting that seedling in the field for evaluation.

When combined with a new cranberry breeding system being developed in cooperation with UW-Madison cranberry breeder Eric Zeldin that uses very high seedling densities, marker-assisted selection should reduce the amount of field space, the financial investment and the number of years it takes to develop new cranberry varieties, Schlautman told cranberry growers attending the 2015 Wisconsin Cranberry School.

Compared to almost all other commercially grown crops, cranberries are relatively undomesticated. The cranberry industry relies on only a handful of cultivars that are wild selections, or first- or second-generation hybrids of those wild selections, Schlautman said.

Many cranberry varieties grown today originated in the 1800s.

“Early cranberry growers just walked across the bogs, and when they found a good plant they brought it home and planted it and shared it with their neighbors,” Schlautman said.

Examples of these early wild selections include: Howes, discovered in 1843 in Massachusetts; McFarlin, discovered in 1874 in Massachusetts; Searles, discovered in 1893 in Wisconsin; and Ben Lear, discovered in 1900 in Wisconsin.

USDA initiated a cranberry breeding program in 1929 in response to an outbreak of false blossom disease. From this breeding program, six varieties were developed of which Stevens – released in 1950 – became the most widely planted cultivar.

About 50 percent of Wisconsin cranberry acreage is planted with Stevens, which is a cross of McFarlin and Potters Favorite, a wild selection discovered in 1895 in Wisconsin Rapids.

It would be another 50 years before the first second-generation cranberry hybrids would be released. In 2003, UW-Madison released HyRed, a cross between Stevens and Ben Lear. Soon after, Rutgers University released Crimson Queen (Stevens x Ben Lear), Demoranville (Franklin x Ben Lear) and Mullica Queen (Lemunyon x No. 35).

While growers no longer cultivate wild cranberry vines, one Wisconsin cranberry grower – Ed Grygleski Sr. of Tomah – began breeding cranberry hybrids in the 1970s to develop varieties that produced higher yields. He released GH1 in 2004 and BG in 2012.

Causing the long delays in releasing new cranberry hybrids is the need to establish long-term test plots on cranberry growers’ marshes, which requires intensive and expensive management to evaluate the progeny over many years. By using marker-assisted selection and a high-density field nursery, researchers hope to dramatically decrease the length of time it takes to develop new cranberry hybrids, Schlautman said.

Comparing cranberries to corn, Schlautman noted that it took 10,000 years for the ancestor of corn – teosinte – to evolve from a grass-type plant producing ears with a dozen kernels to today’s corn hybrids, with ears yielding about 800 kernels.

“They didn’t go from teosinte to corn in one generation. It took a long time. The goal of marker-assisted selection is to trace the inheritance of important traits through multiple generations and select the best crosses without having to grow all the plants in the field, so that when a new cultivar is in demand we can have it ready,” Schlautman said.

Marker-assisted selection will allow cranberry breeders to generate genetic information for individual seedlings. With that information, breeders can predict the potential yield, vigor, disease resistance, length of maturity, fruit quality and other traits at the seedling stage. Only those seedlings judged to have the potential to become new cultivars will undergo field evaluation.

In the past year, more than 700 individual markers have been developed and validated by Schlautman and others working in the Cranberry Genetics and Genomics Lab. These markers will serve as important landmarks in developing a genetic map to begin the search for the locations of genes involved in various traits of agronomic importance, Schlautman said.

“These markers work kind of like GPS coordinates to help us find what we’re looking for in the cranberry genetic code,” Schlautman said.

Additionally, more than 370,000 DNA sequence variations have been identified and are being integrated into the genetic map to continue the search for important genes to incorporate in the marker-assisted selection program.

In theory, marker-assisted research will allow cranberry breeders to develop complex schemes allowing multiple crosses to combine many desirable traits, such as early maturity, large fruit size and disease and insect resistance.

Schlautman also said breeders will be able to perform multiple generations of marker-assisted selections over a shorter time period, rather than a single generation of phenotypic selection over a 50-year period, as was practiced in the past.

One of the biggest limitations to establishing a marker-assisted program is the identification of genes with important agronomic traits. In order to effectively perform this step, Schlautman said it is important that cranberry researchers collaborate among themselves, growers and industry leaders in deciding which traits are most in need of immediate improvement.

In order to increase their capacity to analyze more plants each year and increase their efficiency in evaluating traits in order to identify genes, Schlautman also said the genetics lab is experimenting with other new technologies, including imaging technologies for measuring plant vigor, fruit color and fruit shape.

“Right now, we probably have cultivars that can support the industry for the next few years, and it’s not essential for us to release a new variety right away,” Schlautman said. “But in the meantime, we can keep making additional crosses to make progress so that when the time comes that a new cultivar is in demand, we have it ready and it’s 10 to 15 generations ahead instead of just one generation.”

Lorry Erickson, FGN Correspondent

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