Woody Landscape Plant Breeding and Genetics 

Project Leader:  Dr. Stan Hokanson, Associate Professor, Department of Horticultural Science, University of Minnesota

Research Scientists

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 to breed trees and shrubs capable of withstanding Minnesota's harsh climate. Since that time, the program has been responsible for the release of 46 cold hardy woody landscape plants. 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.

Development of landscape plants suitable for use in USDA Plant Hardiness Zones 3 and 4, with a winter temperature range from -29ºC to -40ºC, continues to be an overarching objective of the program. Many plant are routinely tested for cold hardiness in controlled laboratory freezing tests. Additionally, project scientist Steve McNamara is field screening large seedling populations of marginally hardy landscape taxa including Cornus mas (Corneliancherry dogwood), Cerdidiphyllum japonicum (Katsura tree), Acer pseudosieboldianum (Korean Maple), Taxodium distichum (Baldcypress), and Ulmus parvifolia (Lacebark elm) looking for 'outliers' with exceptional cold hardiness.

We believe a number of native species have great potential for use as landscape plants.  We are currently collecting and growing many seedling populations.  Field trials are conducted to evaluate many desirable characteristics among the seedlings.  Promising individual selections will be clonally propagated and evaluated for potential introduction.  Some of the species currently being evaluated include Ceanothus americanus (New Jersey tea), Cercis canadensis (Eastern redbud), Cornus alternifolia (Pagoda dogwood), Lindera benzoin (Spicebush), Ribes aureum var.villosum (Clove currant), and Staphylea trifolia (American bladdernut).

From the relatively straightforward process of developing DNA fingerprints as a means of uniquely identifying individual plants, to tagging horticulturally significant traits to aid the plant breeding process, the tools of molecular biology have become nearly indispensable in plant breeding and genetics. The Woody Landscape Plant Breeding and Genetics project at the University of Minnesota has utilized molecular markers for several recent projects.  Former graduate student Nicole Gardner used Inter Simple Sequence Repeat (ISSR) markers to produce unique fingerprints for a collection of twenty-eight vining Clematis cultivars.  Her results will provide Clematis breeders and growers with a means of verifying the true identities of similar-looking cultivars and will also facilitate the breeding of exciting new Clematis hybrids.  Current graduate student, Vance Whitaker.utilized Amplified Fragment Length Polymorphism (AFLP) markers to characterize the molecular diversity and the geographical patterning in the fungal organism Diplocarpon rosae, which causes rose blackspot, one of the major disease of roses worldwide.  Results from that work will aid in developing blackspot disease resistance breeding programs.  

In addition to working on rose black spot, our project also has been investigating several other plant disease complexes in an ongoing effort to develop plants that are not only aesthetically pleasing but also resistant / tolerant to disease.  Former graduate student Michael Long identified deciduous azalea cultivars and species with superior resistance / tolerance to powdery mildew.   Another study is focusing on Pagoda dogwood (Cornus alternifolia), the only tree dogwood capable of withstanding Minnesota's harsh winter climate.  In collaboration with Dr. Bob Blanchette (Forest Pathology) we have isolated and cultured a fungal pathogen that attacks this tree.  In collaboration with Dr. Jennifer Juzwik (USDA Forest Service) we are developing a screening protocol to identify canker-resistant seedlings.

Some of the earliest cultivars released from the Woody Landscape Plant Breeding and Genetics program 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, the rose breeding program at the University of Minnesota was reinitiated by former project scientist Kathy Zuzek. Objectives for the project include developing USDA Zone 4 hardy shrub roses with attractive repeat blooms, blackspot tolerance and attractive plant habit. Three recurrent blooming, small-stature polyantha cultivars, Northern Accents SvenTM, Northern Accents OleTM, and Northern Accents LenaTM, have been introduced and will be available to the public in summer of 2007.  Additional advanced selections are currently being evaluated in regional trials.

In an effort to develop and introduce new and exciting landscape plants to the public, exotic plants capable of proliferating, spreading, and establishing in natural ecosystems have been inadvertantly introduced.  Such invasive plants are capable of replacing native plant species and precipitating large scale changes in ecosystems.  The best place to deal with the problem of invasive plants is at the breeding and evaluation stage of plant introduction.  Our project, with funding provided by the Minnesota Nursery and Landscape Association, is currently studying the reproductive biology and life history characteristics of two introduced, and potentially invasive, maple species, Amur maple (Acer ginnala) and Norway maple (Acer platanoides).  By comparing the biological behavior of these species with that of native maple species such as sugar maple (Acer saccharum) and red maple (Acer rubrum), we hope to gain a better understanding of the characteristics that lead to a plant's tendency to become invasive.  This information should ultimately help us predict which plants are most likely to become invasive and to select against traits linked to invasiveness when breeding new trees and shrubs.

Attractive trees and shrubs beautify our landscapes, benefit the environment, and improve our overall quality of life.  However, Minnesota's rigorous climate presents a formidable challenge to the growth and survival of many desirable landscape plant species.  After 50 years of research, the Woody Landscape Plant Breeding and Genetics program remains committed to the long-term goal of developing exciting new plant varieties that are both beautiful and well adapted to Minnesota and other northern regions.

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