World renowned for the development of the 'Lights' series of cold hardy deciduous azaleas, the Woody Landscape Plant Breeding and Genetics program at the University of Minnesota was formally initiated in 1954. The program has been responsible for the release of over 40 cold hardy woody landscape plants, which have served to significantly expand the palette of plant materials available for landscape use in the upper Midwest.

Cultivar releases from the program have included large stature shade trees, flowering trees, shrubs, roses and thirteen members of the 'Lights' series of deciduous azaleas. For a complete list of woody plant cultivars released from the U of M program, including pictures, see (http://www.maes.umn.edu/maesinfo/releases/releaseinfo.html).

Development of landscape plants suitable for use in USDA Plant Hardiness Zones 3 and 4, with winter temperature range from -29ºC to -40ºC, continues to be an overarching objective of the program. Advanced selections from our own breeding efforts and previously untested plant groups are routinely tested for cold hardiness in controlled laboratory freezing tests. As an additional part of our effort to produce new cold hardy woody plants, project scientist Steve McNamara is field screening large seedling populations of marginally hardy landscape taxa including Cornus florida, Cerdidiphyllum japonicum, Acer pseudosieboldianum, and Taxodium distichum looking for 'outliers' with exceptional cold hardiness, suitable for northern landscapes.

Another new project effort is directed towards the development of powdery mildew resistant deciduous azaleas. As an initial step in the process, graduate student Michael Long is screening forty-one deciduous azalea cultivars in replicated field plots in Minnesota and Ohio to identify mildew tolerant or resistant cultivars for use in future breeding efforts. Liner-sized plants of most of the cultivars being screened in the field are also being screened in growth chamber experiments. We want to determine whether the same resistance/susceptibility reactions occur in the growth chamber that we see in the field experiments. If this is the case, we can accomplish powdery mildew screening on a smaller scale, in the off-season, at a cost savings to the breeding project. Future work will involve screening seedlings collected from populations of deciduous azaleas native to the eastern United States.

Our native environments contain huge reservoirs of potential woody landscape plants. We are interested in identifying, collecting, and evaluating clonal and seedling accessions of promising woody taxa. Several promising candidates include Acer pensylvanicum and Cornus alternifolia as small statured shade tolerant trees, Staphylea trifolia and Viburnum lentago as shrubs and Potentilla tridentata, Cornus canadensis, and Gaultheria procumbens as groundcovers. The list grows by the day!

Along with identifying meritorious plants, other questions will need to be answered such as; how can the plant be most economically propagated, how can the plant be best managed and produced in the nursery and how is the plant best grown in the landscape. Such questions are best addressed in a team approach with the Nursery Plant Production team.

From the relatively straightforward processes of fingerprinting or uniquely identifying individual plants, to tagging horticulturally significant traits to aid the plant breeding process and a myriad of tasks in between, molecular markers have become nearly indispensable tools in plant breeding and genetics. Molecular markers are finding a place in the Woody Landscape Plant Breeding project at the University of Minnesota as well. Graduate student Nicole Gardner used Inter Simple Sequence Repeat (ISSR) markers to produce unique fingerprints for a collection of twenty-eight vining Clematis cultivars. In addition, the markers identified true hybrids among progenies arising from crosses between several non-vining shrubby Clematis species.

Some of the earliest cultivars released from the Woody Landscape Plant Breeding project were roses resulting from a sideline breeding project initiated by Robert A. Phillips and Dr. L.E. Longley who were running the chrysanthemum breeding project in the 1940s. In 1990, former lead scientist Dr. Harold Pellett and project scientist Kathy Zuzek reinitiated the rose breeding program at the University of Minnesota. Objectives for the project include developing Zone 4 hardy shrub roses with attractive repeat blooms, blackspot tolerance and attractive plant habit. Several advanced selections that fulfill all of these objectives are currently being readied for entry in regional trials.

A new rose project involves a diversity characterization of the black spot fungus, Diplocarpon rosae. Graduate student Vance Whitaker is collecting black spot isolates from across eastern North America. He will characterize the molecular diversity of the fungal isolates with Amplified Fragment Length Polymorphism (AFLP) primers.  A diverse collection of rose genotypes will be inoculated with the black spot isolates to determine the race diversity of the isolates (race differentiation).  Results from the study will allow us to identify black spot resistance genes in rose germplasm and begin the process of incorporating these genes into cold-hardy shrub rose cultivars.

For additional information concerning the Woody Landscape Plant Breeding and Genetics Research team at the University of Minnesota or cultivar releases from the program contact Stan C. Hokanson.