Woody Landscape Plant Breeding

Development of landscape plants suitable for use in USDA Plant Hardiness Zones 3 and 4, with a winter temperature range from -29ºC to -40ºC, is the overarching objective of the program. We test plant cold hardiness in controlled laboratory freezing tests. Project scientist Steve McNamara field screens large seedling populations of marginally hardy landscape taxa including such as Cornelian cherry dogwood (Cornus mas), Katsura tree (Cerdidiphyllum japonicum), Korean Maple (Acer pseudosieboldianum),Bald Cypress (Taxodium distichum), and Lacebark elm (Ulmus parvifolia). He looks 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)
• Staphylea trifolia (American bladdernut)

From the straightforward process of developing DNA fingerprints to identify individual plants, to tagging horticulturally significant traits to aid the plant breeding process, the tools of molecular biology are 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. 

For example, graduate student Nicole Gardner used Inter Simple Sequence Repeat (ISSR) markers to produce unique fingerprints for a collection of 28 vining Clematis cultivars. Her results will give clematis breeders and growers a way to differentiate similar-looking cultivars. They will also help with breeding exciting new Clematis hybrids. 

Graduate student Vance Whitaker used Amplified Fragment Length Polymorphism (AFLP) markers to characterize the molecular diversity and the geographical patterning in the fungal organism Diplocarpon rosae. This organism causes rose blackspot, one of the major disease of roses worldwide. Results from that work will help programs working to breed plants that can resist the disease.  

Our project investigates several plant disease complexes to develop plants that are both aesthetically pleasing and disease resistant or disease tolerant.  Former graduate student Michael Long identified deciduous azalea cultivars and species with superior resistance or tolerance to powdery mildew.  Another study looks at Pagoda dogwood (Cornus alternifolia), the only tree dogwood capable of withstanding Minnesota's harsh winter climate. Working with Dr. Bob Blanchette, a forest pathologist, we have isolated and cultured a fungal pathogen that attacks this tree. Together with Dr. Jennifer Juzwik of the 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 resulti. These came 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 project scientist Kathy Zuzek restarted the rose breeding program at the University of Minnesota. It worked to develop shrub roses that were hardy to USDA Zone 4, had attractive repeat blooms and habit and could resist blackspot. Three recurrent blooming, small-stature polyantha cultivars, Northern Accents SvenTM, Northern Accents OleTM, and Northern Accents LenaTM, were introduced in 2007.

Sometimes, this work results in plants that could adversely affect the local ecosystem, such as invasives. The best place to deal with the problem of invasive plants is at the breeding and evaluation stage.  Our project, with funding provided by the Minnesota Nursery and Landscape Association, studied the reproductive biology and life history characteristics of two such species, Amur maple (Acer ginnala) and Norway maple (Acer platanoides). We determined that they are invasive and should not be planted in Minnesota. We did this 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 do this to gain a better understanding of the characteristics that lead to a plant's tendency to become invasive.  

This information helps us to predict which plants are likely to become invasive. We then 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. Minnesota's rigorous climate make it hard for many landscape plant species to grow and survive. 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 the northern region of the USA.