Selecting and Testing Elms: the Wisconsin Elm Breeding Program

Selecting and testing elms for urban areas has required a substantial commitment of land, greenhouse space, equipment and labor over thirty years time. The development and continued survival of this program has depended primarily upon satisfying and education/basic research function; the production of improved cultivars has been an important but secondary product. Although resistance to Dutch elm disease @ED) has been a major focus of the selection and testing program, crown architecture, leaf characters, and resistance to other pests have also been emphasized. Many elements of the testing program have been developed to accelerate the early screening of plant material. We believe that long-term tree breeding and testing programs are both possible and desirable and can lead to the development of superior trees for urban areas. A program of selecting and breeding elms for use in urban landscapes was initiated in Wisconsin in 1957. In its formative years, emphasis was placed upon assembling ‘elm germplasm from throughout the north temperate region, establishing field trials to evaluate adaptability to the north central United States climate, and screening of well-adapted materials for resistance to Dutch elm disease @ED). The initial motivation for creating an elm research program in Wisconsin was widespread public alarm at the decimation of American elm (Ulmus americana) population in urban areas. However, politics alone could not sustain a viable program and 21 justification for continuing elm research involved a transition from short -term fungicide and chemotherapy work to long -term breeding and host -pathogen studies. Our most important product continues to be the training of graduate students and the discovery of basic facts about elm biology and the nature if host -pathogen interactions. Unlike other scientists whose research results in ideas to be disseminated in journals, we also produce a tangible product, the disease -resistant, ornamentally attractive elm. However, it is important to note that this latter product alone could not justify the continued involvement of the university in selecting and testing elms. METRIA:7 PROCEEDINGS A BIOLOGICAL BASE FOR TESTING Every plant breeding program depends upon a source of raw materials from either wild populations or from germplasm accessions in public or private collections. In 1957, the only sources of “improved” elm germplasm were the Dutch breeding program at Wageningen, and the U.S.D.A. program, then at Columbus, Ohio, but subsequently moved to Delaware, Ohio. Materials received from the Dutch program have been evaluated here in Wisconsin for many years, but most such introductions have not been sufficiently hardy in our north central United States climate. Cultivars from the Wageningen program have been marketed in the United States (e.g. ‘Groeneveld’), but their use is limited to hardiness zones 5-7. The Dutch germplasm base has emphasized Ulmus glabra, u. carpinifolia, and other species better adapted to maritime climates. Thus, a germplasm base adapted to harsh continental climate was sought for use in the Wisconsin program. Many accessions of Eurasian species, especially u. pumila and g. japonica had the requisite adaptability to the north central region, and also possessed moderate to high levels of resistance to Dutch elm disease. A great deal of work completed during the 1960’s involved the creation and evaluation of various hybrid combinations using Siberian elm (v. pumila) as a source of DED resistance. Some hybrids developed during this 22 period were, and continue to be, useful as cultivars and as breeding materials. Despite its many other flaws, Siberian elm continues to be the major source of DED resistance genes for virtually all hybrid elm cultivars in use today. A great deal of intuition was also acquired during this period, and continues to guide our choice of parents for breeding, as well as our choice of research problems. We have continued to add to our earlier germplasm base with additional accessions of these species, but also u. parvifolia, u. laciniata and other Eurasian species in a continuing search for new and useful germplasm. However, continued expansion of the germplasm base poses a maintenance dilemma. Although new germplasm especially from geographic regions not previously studied (e.g. People’s Republic of China) is of vital importance, the continued introduction of new accessions, together with new progeny arrays from systematic breeding, places a great strain on program resources. This dilemma leads (inevitably) to a hierarchy of activities with respect to germplasm use.