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Associate Professor, Ornamental Plant Breeding
My teaching and research focuses primarily on woody nursery and landscape plants. In addition to spring and fall woody plant identification courses, I teach a course on plant growth and development. Research in my lab is mostly applied in nature and we work closely with the nursery industry to try and develop new plants that work well in production and serve the needs of growers and gardners alike. Some of the crops we are working on include:
- Cape hyacinth
- Flowering currant
- Portugese and common cherrylaurel
Department of Horticulture
4017 Ag and Life Sciences BldgCorvallis, OR 97331-7304
My research program involves several areas of ornamental plant breeding and cultivar development. Of primary interest is the development of sterile forms of nonnative species that are of economic importance to Oregon growers to prevent escape from cultivation. Primary techniques to achieve sterility/reduced fertility include develoment of triploids using ploidy manipulation, as well as mutagenesis by exposing seeds or meristems to physical and chemical mutagens.
We are also trying to develop new cultivars that have increased insect and disease resistance. My program conducts basic research in traditional genetics, cytogenetics, and molecular cytogenetics to support the applied breeding program with the goal of developing plants that are attractive to consumers and easy for growers to produce.
HORT 226. Landscape Plant Materials I: Deciduous Hardwoods and Conifers. Fall. 4 credits
HORT 226e. Landscape Plant Materials I: Deciduous Hardwoods and Conifers. Fall - Online. 4 credits
HORT 228. Landscape Plant Materials II: Spring Flowering Trees and Shrubs. Spring. 4 credits
HORT 228e. Landscape Plant Materials II: Spring Flowering Trees and Shrubs. Spring - Online. 4 credits
HORT 301. The Biology of Horticulture. Fall. 3 credits
HORT 301e. The Biology of Horticulture. Fall & Spring - Online. 3 credits
Ph.D. Horticulture, The University of Georgia - Athens, Georgia - December 2009
M.S. Horticultural Science, North Carolina State University - Raleigh, North Carolina - June 2006
B.S. Horticultural Science, North Carolina State University - Raleigh, North Carolina - December 2002.
Assistant Professor, Oregon State University, Department of Horticulture. 40% Teaching / 35% Research. December 2009 - present
Graduate Research Assistant, University of Georgia, Athens, Georgia, Department of Horticulture. 2006 - 2009
Graduate Research Assistant, North Carolina State University, Raleigh, Department of Horticultural Science. 2004 - 2006
International Plant Propagators Society
American Society for Horticultural Science
American Conifer Society
American Penstemon Society
American Rhododendron Society
Mara came to the program in 2010 after a number of years working with a canola breeding program in private industry. She has a degree in nursery and landscape from Colorado State University. Mara manages greenhouse, container, and field plots; collects much of our data; and generally helps keep things running smoothly.
Jason Lattier - Ph.D. Student
- Interspecific and intersectional hybridization in Syringa
- Linkage mapping of Syringa section Pubescentes
- Hibiscus syriacus breeding to develop sterile cultivars and investigation of heritability of various floral traits
- Cytology and flow cytometry of selected woody nursery crops
Kim Shearer-Lattier - M.S. Student
- Genome size and ploidy level survey in Acer
- Interspecific hybridization in Penstemon to improve adaptibility to cultivation
- Mutagenesis of Galtonia candicans to improve form and reduce lodging
Justin Schulze - M.S. Student
- Assessing the carbon budget of 22x and 44x Prunus laurocerasus 'Otto Luyken' in container production
- In vivo polyploidization of Prunus lusitanica
- Interspecific hybridization of P. laurocerasus x P. lusitanica
Hsuan Chen - Ph.D. Student
- Using GISH to identify parental contribution among hybrids of Hibiscus syriacus and H. paramutabilis
- Developing new hybrids of Hibiscus with novel floral chracteristics
Joseph Rothleutner - M.Sc. - Genome Sizing and Fire Blight Resistance Screening in Cotoneaster. Current Position: Tree Improvement Specialist at the Morton Arboretum in Chicago
Jon Dempster: Fertility and morphological observations of 2x, 3x, and 4x crabapples including 'Prairiefire' and its polyploid derivatives.
Aleen Haddad: Genome size analysis in Acer: Comparing methods of sample handling and preparation
Rebecca Reeve: In vivo polyploidization of Hibiscus syriacus using diffferent mitotic inhibitors and application techniques
Geena Quinones: Non-targeted mutagenesis of Carpenteria californica using varying rates of gamma radiation
Morgan Chan: Field evaluation and herbarium voucher collection for 49 species of Cotoneaster
Tucker Doyle: In situ chromosome doubling of four Oregon native plants of varying growth forms
Tiffany Pham: In vitro polyploidization of Hydrangea macrophylla
Keith Lukowski: Mapping the woody flora of Oregon State University
Coral Cummings: Viability and longevity of Prunus laurocerasus and P. lusitanica pollen under varying storage conditions
Imogene Hollis: Propagation and cataloguing newly received accessions for the Ornamental Plant Breeding Program
I accept graduate students for Horticulture
Refereed Journal Articles (*authored by student)
- Contreras, R.N. and M.W. Friddle. 2015. 'Oregon Snowflake' flowering currant. HortScience 52(2):320-321.
- *Rothleutner, J.J., R.N. Contreras, V.O. Stockwell, and J.S. Owen, Jr. 2014. Screening Cotoneaster for resistance to fire blight by artificial inoculation. HortScience 49(12):1480-1485.
- Contreras, R.N., J.M. Ruter, and D.A. Knauft. 2014. Flower, fruit, and petiole color of american beautyberry (Callicarpa americana L.) are controlled by a single gene with three alleles. HortScience 49(4):422-424. (HortScience Cover)
- Schwartz, B.M., R.N. Contreras, K.R. Harris-Schultz, D.L. Heckart, J.B. Peake, and P.L. Raymer. 2013. Discovery and characterization of a turf-type triploid seashore paspalum. HortScience 48(12):1424-1427.
- Contreras, R.N., J.M. Ruter, J.S. Owen, Jr., A. Heogh. 2013. Chlorophyll, carotenoid, and visual color rating of japanese-cedar grown in the southeastern United States. HortScience 48(12):1452-1456.
- Schwartz, B.M., K.R. Harris-Schultz, R.N. Contreras, C.S. Hans, W.W. Hanna, and S.R. Milla-Lewis. 2013. Creation of artificial triploid and tetraploid centipedegrass using colchicine and breeding. Intl. Turfgrass Soc. Res. J. 12:327-334.
- Contreras, R.N., J.S. Owen, W.W. Hanna, and B.M. Schwartz. 2013. Evaluation of seven complex Pennisetum spp. hybrids for container and landscape performance in the Pacific Northwest. HortTechnology 23(4):525-528.
- Landgren, C., J.S. Owen, and R.N. Contreras. 2013. Evaluating soil and foliar fertilization of Abies nordmanniana under container and field production. Scandinavian J. For. Res. http://dx.doi.org/10.1080/02827581.2012.762939
- Contreras, R.N., R. Golembiewski, J. Velez. 2013. Are Learning Styles, Study Habits, and Performance Correlated in Woody Plant Identification Students? HortTechnology 23(1):130-133.
- Schwartz, B.M., K.R. Harris-Schultz, C.S. Hans, R.N. Contreras, and S.A. Jackson. 2013. Creation of Hexaploid and Octaploid Zoysiagrass with Colchicine and Breeding. Crop Science 53:2218-2224.
- Vining, K.J., R.N. Contreras, M. Ranik, and S.H. Strauss. 2012. Genetic methods for mitigating invasiveness of woody ornamental plants: Research needs and opportunities. HortScience 47(9):1210-1216.
- Contreras, R.N. 2012. A simple chromosome doubling technique is effective for three species of Cupressaceae. HortScience 47(6):712-714.
- Contreras, R.N., J.M. Ruter, J. Conner, Y. Zeng, and P. Ozias-Akins. 2012. Confirmation of hybridity using GISH and determination of 18S rDNA copy number using FISH in interspecific F1 hybrids of Tecoma (Bignoniaceae). Genome 55(6):437-445. (doi: 10.1139/g2012-030)
- Contreras, R.N., R. Determann, and M. Friddle. 2011. Differences in winter browning among japanese-cedar cultivars are not due to variation in ploidy levels. HortScience 46(11):1465-1467.
- Contreras, R.N. and J.M. Ruter. 2011. Genome size estimates and chromosome numbers of Callicarpa L. (Lamiaceae). HortScience [46 (4): 567-570.
- Contreras, R.N., J.M. Ruter, and B.M. Schwartz. 2010. Oryzalin-induced polyploidy in Cryptomeria japonica (Thunb. ex L.f.) D. Don (Cupressaceae). HortScience 45(2):316-319.
- Contreras, R.N. and J.M. Ruter. 2009. Sulfuric acid scarification of Callicarpa americana (Lamiaceae) seeds improves germination. Native Plants Journal 10(3):283-286.
- Contreras, R.N., J.M. Ruter, and W.W. Hanna. 2009. An oryzalin-induced autoallooctoploid of Hibiscus acetosella Welw. ex Hiern. ‘Panama Red’ (Malvaceae). J. Amer. Soc. Hort. Sci. 134(5):553-559.
- Contreras, R.N. and T.G. Ranney. 2008. New opportunities for breeding fragrant rhododendrons. J. Amer. Rhododendron Soc. 62(4):201-202.
- Contreras, R.N., T.G. Ranney, and S.P. Tallury. Reproductive behavior of diploid and allotetraploid Rhododendron L. ‘Fragrant Affinity’. 2007. HortScience 42(1):31-34.
- Contreras, R.N., T.G. Ranney, S.R. Milla-Lewis, and G.C. Yencho. 2007. Investigating parentage and hybridity of three azaleodendrons using AFLP analysis. HortScience 42(3):740–743.
Conference Proceedings (*authored by student)
*Lattier, K.S. and R.N. Contreras. 2015. Non-targeted mutagenesis of Galtonia candicans Decne. through exposure to ethyl methanesulfonate. Combined Proceedings of the International Plant Propagators' Society 65. (Accepted)
*Schulze, J. and R.N. Contreras. 2015. Effect of ploidy level on vegetative propagation of two cytotypes of Prunus laurocerasus L. ‘Schipkaensis’. Combined Proceedings of the International Plant Propagators' Society 65. (Accepted)
*Lattier, K.S. and R.N. Contreras. 2015. Chemical mutagenesis of Galtonia candicans Decne. results in altered morphology and reduced fertility. Proc. 60th Ann. SNA Res. Conf. 60:XXX-XXX (Accepted)
R.N. Contreras and M.W. Friddle. 2015. Fire blight resistance among interspecific and interploidy F1 hybrids of Cotoneaster. Proc. 60th Ann. SNA Res. Conf. 60:XXX-XXX (Accepted)
Contreras, R.N., J. Rothleutner, and V. Stockwell. 2014. Breeding for fire blight resistance and sterility in Cotoneaster. Proceedings of the 13th International Workshop on Fire Blight. Acta Hort. 1056:221-223.
Contreras, R.N., M. Friddle, and J.D. Lattier. 2013. Relative fertility and ploidy levels of selected rose of sharon cultivars. Proc. 58th Ann. SNA Res. Conf. 58:232-236.
*Rothleutner, J.J., R.N. Contreras, and V. Stockwell. 2012. Evaluation of fire blight resistance of 31 species of Cotoneaster. Proc. 57th Ann. SNA Res. Conf. 57:276-278.
Contreras, R.N. and J.M. Ruter. 2010. Induced polyploidy in Japanese cedar. Proc. 55th Ann. SNA Res. Conf. 55:25-29.
Contreras, R.N. and J.M. Ruter. 2008. Preliminary efforts to induce polyploidy in Cryptomeria japonica. Proc. 53rd Ann. SNA Res. Conf. 53:159-161.
Contreras, R.N. and J.M. Ruter. 2007. New Callicarpa species with breeding potential. Proc. 52nd Ann. SNA Res. Conf. 52:327-329.
Contreras, R.N., T.G. Ranney, S.P. Tallury and S.R. Milla. 2005. Using molecular markers to investigate parentage of azaleodendron hybrids. 2005. Proc. 50th Ann. SNA Res. Conf. 50:632-635.
Contreras, R.N. and T.G. Ranney. 2004. New opportunities for breeding allopolyploid azaleodendrons. Proc. 49th Ann. SNA Res. Conf. 49:552-554.
Abstracts and Posters (*authored and presented by student)
*Lattier, J.D. and R.N. Contreras. 2014. Colorimetric phenotyping of tetraploid progeny exhibiting incomplete dominance for flower color. Independent Plant Breeders Conference. Grand Rapid, MI
*Shearer-Lattier, K. and R.N. Contreras. 2014. Non-targeted mutagenesis of Galtonia candicans by exposing seeds to EMS. Independent Plant Breeders Conference. Grand Rapid, MI, October 30 – November 2, 2014.
Contreras, R.N. and L. Meneghelli. 2013. In Vitro Chromosome Doubling of Prunus laurocerasus ‘Otto Luyken’. Proc. 109th Ann. Amer. Soc. Hort. Sci. Res. Conf. HortScience 48(9):S411. (Abstr.)
Schwartz, B.M., R.N. Contreras, W.W. Hanna, and S.A. Jackson. 2013. Manipulating the Chromosome Number of Zoysiagrass. ASA-CSSA-SSSA Abstracts 2013. (Abstr.)
Schwartz, B.M., R.N. Contreras, K.R. Harris-Schultz, J.B. Peake, and P.L. Raymer. 2012. Identification or Creation of a Putative Triploid Seashore Paspalum. ASA-CSSA-SSSA Abstracts 2012. (Abstr.)
*Rothleutner, J.J. and R.N. Contreras. 2012. Variable Fire Blight Resistance Among 31 species of Cotoneaster. Proc. 109th Ann. Amer. Soc. Hort. Sci. Res. Conf. HortScience 47(9):S366 (Abstr.)
Einhorn, T., Gibeaut, D., Contreras, R.N., and Whiting, M. 2012. Polyploidy of cells in sweet cherry fruit. Proc. 109th Ann. Amer. Soc. Hort. Sci. Res. Conf. HortScience 47(9):S387 (Abstr.)
Gibeaut, D., R. Contreras, T. Einhorn, and M. Whiting. 2011. Cropload affects the size, but not the number or polyploidy of cells in sweet cherry fruit. Washington State Horticultural Association 107th Annual Meeting, Wenatchee, WA, December 5-7, 2011.
Contreras, R.N., J.M. Ruter, J. Conner, Y. Zeng, and P. Ozias-Akins. 2011. Interspecific hybridization in Tecoma Juss. (Bignoniaceae): Confirmation of hybridity using GISH and morphology. HortScience 46(9):S320. (Abstr.)
*Rothleutner, J.J. and R.N. Contreras. 2011. Genome size estimates for Cotoneaster spp. HortScience 46(9):S386 (Abstr.)
Schwartz, B., K. Harris, R.N. Contreras, and W. Hanna. 2010. Colchicine-induced tetraploidy in centipedegrass. ASA-CSSA-SSSA Abstracts 2010 (in press). (Abstr.)
Contreras, R.N. 2010. Breeding methods to reduce the invasive potential of nursery crops. HortScience 45(8):S29 (Abstr.)
Contreras, R.N. and John M. Ruter. 2010. Fruit color in American beautyberry is controlled by a single gene. HortScience 45(8):S280 (Abstr.)
Contreras, R.N. and John M. Ruter. 2009. An oryzalin induced polyploidy from a hybrid of Hibiscus acetosella x H. radiatus(Malvaceae) exhibits reduced fertility and altered morphology. Proc. 106th Ann. Amer. Soc. Hort. Sci. Res. Conf. HortScience 44(4):1177.
Contreras, R.N. and John M. Ruter. 2008. Evaluation of Callicarpa spp. for ornamental potential. Proc. 105th Ann. Amer. Soc. Hort. Sci. Res. Conf. HortScience 43(4):1266.
Contreras, R.N. and Thomas G. Ranney. 2006. Reproductive behavior of diploid and allotetraploid azaleodendrons. Proc. 66th Ann. SR-ASHS Res. Conf. HortScience 40(3):497-498.
Trade Publications (*authored by student)
*Shearer Lattier, K. and R.N. Contreras. 2015. Penstemon breeding in the Willamette Valley: A lesson in flexibility. Bulletin of the American Pestemon Society (Accepted).
Contreras, R.N. and J.D. Lattier. 2014. Improving a garden classic. Digger, August:47-50.
Contreras, R.N. and M. Horn. 2014. Breeding to improve garden performance of Penstemon in the Willamette Valley: early stages. Bulletin of the American Pestemon Society 73:68-72.
Contreras, R.N. and G. McAninch. 2013. Back from the ban: new Buddleja cultivars receive exemption under ODA amendment. Digger, October:33-36.
Contreras, R.N. and T. Rinehart. 2012. An express route to perfection. Digger, August: 47-50.
*Rothleutner, J.J. and R.N. Contreras. 2012. Celebrating Cotoneaster. Digger, January:33-36.
Contreras, R.N. and J.S. Owen. 2011. The Economy of Water. Digger, August:139-144.
Contreras, R.N. 2011. Bred for success. Digger March:41-45.
Contreras, R.N. 2010. Bridging the gap: A new partnership between Oregon State University and LPDC designed to continue cultivar development. Landscape Plant News
Contreras, R.N. and J.M. Ruter. 2010. Developing an evergreen, evergreen: Winter browning in Japanese cedar. Amer. Conifer Soc. Quarterly J. 27(1):19-23.
Contreras, R.N. and John M. Ruter. 2009. Callicarpa evaluation and breeding at The University of Georgia Tifton Campus. Landscape Plant News 20(2):3-5.
Contreras, R.N. and John M. Ruter. 2008. Evaluation of Callicarpa spp. for utilization in a breeding program. Georgia Green Industry Association Journal. May/June 32-33.
Awards and Honors
2013 College of Agricultural Sciences Savery Outstanding Young Faculty Award
2015 College of Agricultural Sciences R.M. Wade Award for Excellence in Teaching