US National Arboretum


Floral and Nursery Plants Research Unit

Dr. Richard T. Olsen

Research Geneticist
{Beltsville, MD}

1. Genetic Improvement of Landscape Trees for Disease and Pest Tolerance, Non-Invasiveness, and Ornamental Traits

2. Genetic Resources, Evaluation, and Information Management of Woody Landscape Plant Germplasm

The urban tree breeding program develops cultivars of urban landscape trees with improved stress-, disease-, and pest-tolerances as well as non-invasiveness to minimize naturalization and gene-introgression into native populations.  The urban tree breeding program enhances both common and underutilized tree genera, including Acer, Catalpa, Celtis, Chionanthus, Nyssa, Tsuga, and Ulmus.   

The integration of germplasm collection and management, with a breeding program, facilitates long-term research directed at the systematic improvement of important tree genera for the nursery industry.  Research includes the analysis of genetic diversity in cultivated plant material and identification of unique provenances to broaden the gene pool, the improvement of storage and regeneration techniques for poorly studied genera, and coordinates with taxonomists on genera with classification or nomenclatural problems.

In order to maintain and enhance genetic diversity in urban forests, new tree species adapted to urban conditions and superior cultivars of established tree species must be evaluated and bred for tolerance to existing abiotic and biotic stresses as well as introduced pathogens and pests.  There is a continual need for large shade trees in the urban forest, as well as smaller trees for height restricted planting areas.

The urban tree breeding program takes a systematic approach to developing new tree cultivars for the nursery industry and urban forest, beginning with the identification and establishment of novel germplasm as breeding stock.  This germplasm is evaluated for tolerance to abiotic stresses, resistance to specific diseases and pests.  Breeding objectives and goals are established for priority genera, which may include testing interspecific and intergeneric crossabilities, elucidating breeding barriers and mechanisms for overcoming them, the development of polyploids and interploid hybrids to limit invasiveness, the development of molecular markers for verifying hybridity and determining modes of inheritance for resistances and ornamental traits.  Hybrid progeny are evaluated for desired ornamental traits and stress tolerances, with elite germplasm distributed to academic and industry cooperators for evaluation, selection, and introduction as novel urban tree cultivars.

Catalpa project:  Established a long-term Catalpa breeding project to develop powdery mildew resistant, cold-hardy Catalpa and ×Chitalpa cultivars, with novel ornamental traits.  Conducted crosses to elucidate self-compatibility, and determine interspecific and intergeneric compatibilities and ploidy barriers.  Evaluated new taxa and hybrids for powdery mildew susceptibility and inheritance of ornamental traits.  With Dr. Joseph H. Kirkbride, Jr., investigating taxonomic problems in Catalpa nomenclature and implications for cultivated plants in the nursery industry.

Nyssa project: Redirected a Nyssa (black gum) breeding program towards evaluation of novel hybrids for resistance to leaf spot, improved branch architecture and habit and autumn color.  Currently, we are growing large F2 populations that are segregating for desired traits.  Collaborate with Drs. Amy Rossman and Drew Minnis (USDA-ARS Systematic Mycology and Microbiology) on the molecular identification and characterization of the leaf spot organism affecting Nyssa.

Tsuga project:  Hemlocks, particularly the eastern or Canadian hemlock (Tsuga canadensis), are an important component of native and cultivated landscapes in New England, the mid-Atlantic, and Appalachian regions.  The introduced hemlock woolly adelgid (Adelges tsugae) is devastating these populations, as well as the rarer Carolina hemlock (Tsuga caroliniana).  The U.S. National Arboretum established a hemlock breeding program in the 1990’s to incorporate the resistance of Asian species into our native hemlocks.  Successful crosses have been obtained between T. caroliniana and T. chinensis, and several other Asian species; however, there appears to be a hybridization barrier with T. canadensis.  In collaboration with Michael E. Montgomery (USDA-Forest Service, Center for Forest Health Research), our hybrids have been evaluated in the field, and currently in containers, using artificial infestations.

Chionanthus project: Preliminary investigations into Chionanthus breeding, looking at species relationships and potential areas for improvement.  Molecular markers derived from Chinese fringetree (Chionanthus retusus) by Reneé S. Arias et al (USDA-ARS Genomics and Bioinformatics Research Unit) will be used to determine genetic diversity and relationships in cultivated and native populations of Chionanthus as well as to clarify pollination and reproductive biology in the genus and related genera.


Peer reviewed publications:

Brummer, E.Charles, W.T. Barber, S.M. Collier, T.S. Cox, R. Johnson, S.C. Murray, R.T. Olsen, R.C. Pratt, and A.M. Thro. 2011. Plant breeding for harmony between agriculture and the environment. Frontiers Ecol. Environ. 9:561-568.

Kirkbride, J.H. and R.T. Olsen. 2011. Identity of Catalpa tibetica (Bignoniaceae). J. Bot. Res. Inst. Texas 5:625-631.

Kirkbride, J.H. and R.T. Olsen. 2011. Neotypification of Catalpa speciosa (Bignoniaceae). Taxon 60:1760-1763.

Whittemore, A.T., and R.T. Olsen. 2011.  Ulmus americana (Ulmaceae) is a polyploidy complex. Amer. J. Bot. 98:754-760.

Arias, Renee, N. Techen, T. Rinehart, R. Olsen, J. Kirkbride, and B. Scheffler. 2011. Development of SSR markers for Chionanthus retusus (Oleaceae) and effective discrimination of closely related taxa.  Hortscience 46:23-29.

Minnis, Andrew M., A.Y. Rossman, and R.T. Olsen. 2011. Mycosphaerella nyssicola revisited: a species distinct from M. punctiformis. Mycotaxon 115:311-322.

Minnis, Andrew M., A.Y. Rossman, D.F. Farr, and R.T. Olsen. 2010. Sphaerographium nyssicola Minnis, Rossman & D.F. Farr, sp. nov.  Persoonia: Molecular Phylogeny and Evolution of Fungi 25:122-123.

Trueblood, C., T.G. Ranney, N.P. Lynch, J.C. Neal, and R.T. Olsen. 2010. Evaluating fertility of triploid clones of Hypericum androsaemum L. for use as non-invasive landscape plants. Hortscience 45:1026-1028.

Olsen, Richard T. and A. T. Whittemore. 2009. Validation of the hybrid flowering cherry Prunus ×incam  (Rosaceae). Novon. 19:490-493.

Ma, Hongmei, M.Kramer, R. Olsen, and M. Pooler. 2009. Evaluation of flowering cherry species, hybrids, and cultivars using SSR markers. J. Amer. Soc. Hort. Sci. 134:435-444.

Montgomery, Michael E., S.E. Bentz, and R.T. Olsen. 2009.  Evaluation of hemlock (Tsuga) species and hybrids for resistance to Adelges tsugae (Hemiptera: Adelgidae) using artificial infestation.  Journal of Economic Entomology. 102:1247-1254.

Olsen, Richard T., T.G. Ranney, and Z. Viloria.  2006.  Reproductive behavior of induced allotetraploid ×Chitalpa and in vitro embryo culture of polyploidy progeny.  J. Amer. Soc. Hort. Sci. 131:716-724.

Olsen, Richard T., T.G. Ranney, and D.J. Werner.  2006.  Fertility and inheritance of variegated and purple foliage across a polyploidy series in Hypericum androsaemum L.  J. Amer. Soc. Hort. Sci. 131:725-730.

Olsen, Richard T., T.G. Ranney, and C.S. Hodges.  2006.  Susceptibility of Catalpa, Chilopsis, and hybrids to powdery mildew and catalpa sphinx larvae.  HortScience 41:1629-1634.

Olsen, Richard T., J.M. Ruter, and M.W. Reiger.  2002.  Photosynthetic responses of container-grown   Illicium L. taxa to sun and shade.  J. Amer. Soc. Hort. Sci. 127:919-924.

Dirr, M.A., J.A. Adkins, and R.T. Olsen.  2002.  Magnolia zenii Cheng. ‘Pink Parchment’. HortScience 37:709-710.

Non-peer reviewed publications:

Olsen, Richard T. and J.H. Kirkbride. 2010. Manchurian catalpa Catalpa bungei. Arnoldia 68(2):75-76.

Ranney, T.G. and R.T. Olsen.  2009. Breaking the color barrier: the classic Annabelle hydrangea now comes in pink. Nursery Notes 43(2):44-45.

Olsen, Richard T.  2008.  Redefining Catalpa: exploring diversity and breeding novel urban trees. Comb. Proc. Intl. Plant Prop. Soc. 58:306-309.

Olsen, Richard T. 2008.  Evaluation of a 15-year-old Carolina silverbell provenance trial. Proc. 53rd Ann. SNA Res. Conf. 53:27-31.

Robbins, J., M. Widrlechner, R. Olsen, S. Reed, A. Meerow, K. Hummer, P. Bretting, P. Allenstein, and M. Krautmann.  2008.  Gene banks offer breeders access to germplasm. Nursery Management & Production 24(5):53-58.

Olsen, Richard T.  2008.  Prunus ×sieboldii.  American Nurseryman 207(6):66.

Bentz, S.E., M.E. Montgomery, R.T. Olsen.  2008.  Resistance of hemlock species and hybrids to hemlock woolly adelgid, p.137-139. In: B. Onken and R. Reardon (comp.).  Fourth Symposium on Hemlock Woolly Adelgid in the Eastern United States, 12-14 February 2008.  USDA Forest Service, FHTET-2008-01.  Hartford, Connecticut.

Pooler, Margaret, and R. Olsen.  2006.  Outside the box – breeding of not-so-common woody landscape plants at the U.S. National Arboretum.  Comb. Proc. Intl. Plant Prop. Soc. 56:300-302.

Ranney, Thomas, D. Touchell, R. Olsen, T. Eaker, N. Lynch, and J. Mowrey.  2006.  Progress in breeding non-invasive nursery crops.  Proc. 51st Ann. SNA Res. Conf. 51:597-598.

Olsen, Richard T. and A.C. Bell.  2005.  History of beach vitex cultivation: a potential invasive ornamental.  Proc. 50th Ann. SNA Res. Conf. 50:531-533.

Olsen, Richard T., T.G. Ranney, and D.J. Werner. 2005.  Inheritance of ornamental foliage characteristics in diploid, triploid, and tetraploid Hypericum androsaemum L.  Proc. 50th Ann. SNA Res. Conf. 50:648-650.

Olsen, Richard T. and T.G. Ranney.  2005.  Breeding for non-invasive landscape plants.  N.C. Nursery Short Course 6:8-12.

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