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Assistant Professor, Ornamental Plant Breeding
My research focuses on ornamental plant breeding using traditional, cytogenetic, and molecular tools. Some of my projects include:
- Induced polyploidy and backcrossing to develop sterile triploid Norway maple and common cherrylaurel
- Mutation breeding in Galtonia candicans, Sarcococca confusa, Ribes sanguineum, Prunus laurocerasus, and Berberis thunbergii
- Polyploidy in arborvitae to develop non-winter browning forms and increase insect resistance
- Interspecific hybridization among common and portugese cherrylaurels to develop disease resistant and sterile forms
- Developing disease resistant and reblooming lilacs
- Using interspecific and interploidy level crosses combined with traditional disease screening to develop new cotoneaster cultivars that are sterile, drought tolerant, and disease resistant
- Interspecific hybridization in Philadelpus to develop novel culivars that exhibit new combinations of ornamental traits including inflorescence architecture and fragrance
- Developing compact Hibiscus syriacus cultivars that are sterile with new combinations of traits
- Improving garden performance of Penstemon for the Willamette Valley
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 invasive species that are of economic importance to Oregon growers. 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.
Another area of focus is to identify cultivars or selections 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 / 60% 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
Jason Lattier - Ph.D. Student
- Embryo culture to recover interspecific hybrids in Prunus and Syringa
- 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.Sc. Student
- Evaluating fertility of tetraploid and M1 japanese barberry populations
- Developing polyploids of Trachelospermum from in vitro treatments
- Genome size and ploidy level survey in Acer
- Interspecific hybridization in Penstemon to improve adaptibility to cultivation
Joseph Rothleutner - M.Sc. - Genome Sizing and Fire Blight Resistance Screening in Cotoneaster. Current Position: Tree Improvement Specialist at the Morton Arboretum in Chicago
I accept graduate students for Horticulture
- Ribes sanguineum ‘Oregon Snowflake’
Refereed Journal Articles
- 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.
Contreras, R.N. 201X. Ornamental Plant Breeding at Oregon State University. Combined Proceedings of the International Plant Propagators' Society (Accepted).
Contreras, R.N., J. Rothleutner, and V. Stockwell. 201X. Breeding for fire blight resistance and sterility in Cotoneaster. ActaHort. Proceedings of the 13th ISHS Congress on Fire Blight (Accepted).
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
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 (Accepted) (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.
Contreras, R.N. and M. Horn. 2014. Breeding to improve garden performance of Penstemon in the Willamette Valley: early stages. The Penstemaniac: Newsletter of the American Pestemon Society (Accepted).
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