Ryan  Contreras
Ryan  Contreras
Ryan  Contreras
Ryan  Contreras


Norway maple
ploidy manipulation
japanese barberry
sweetbox shrub
flowering currant
flow cytometry
Ryan Contreras
Assistant Professor, Ornamental Plant Breeding

My research focuses on ornamental plant breeding using traditional, cytogenetic, and molecular tools. Some of my projects include:

  • Developing sterile triploid Norway maple and common cherrylaurel
  • Mutation breeding in Galtonia candicans, Sarcococca confusa, and Ribes sanguineum
  • Polyploidy in arborvitae to develop novel forms 
  • Interspecific hybridization among common and portugese cherrylaurels to develop disease resistant and sterile forms
  • Developing disease resistant and reblooming lilacs via intra- and intersectional hybridization
  • New cotoneaster cultivars that are sterile, drought tolerant, and disease resistant
  • New Philadelpus hybrids that exhibit new combinations of traits with an emphasis on fragrance
  • Compact Hibiscus syriacus cultivars that are sterile with new combinations of traits
  • Improving garden performance of Penstemon for the Willamette Valley
OSU Campus
Department of Horticulture
4017 Ag and Life Sciences Bldg
Corvallis, OR 97331-7304
United States
(541) 737-5462


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.

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 / 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

Professional Memberships

International Plant Propagators Society

American Society for Horticultural Science

American Conifer Society

American Penstemon Society

American Rhododendron Society

Graduate Students


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

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


Joseph Rothleutner - M.Sc. - Genome Sizing and Fire Blight Resistance Screening in Cotoneaster.  Current Position:  Tree Improvement Specialist at the Morton Arboretum in Chicago

Undergraduate Researchers


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


Cultivar Releases


  • Ribes sanguineum ‘Oregon Snowflake’ PPAF


Refereed Journal Articles




  • 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.
  • 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.
  • 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.






  • Contreras, R.N. and T.G. Ranney. 2008. New opportunities for breeding fragrant rhododendrons. J. Amer. Rhododendron Soc. 62(4):201-202.



Conference Proceedings

Lattier, J.D. and R.N. Contreras.  2014.  Hybridization Studies in Lilacs (Syringa L.).  Proc. 59th Ann. SNA Res. Conf. 59:229-234.

Contreras, R.N.  2014.  Ornamental Plant Breeding at Oregon State University.  Combined Proceedings of the International Plant Propagators' Society 63. <http://www.pubhort.org/members/ippsue?session=>

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 

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 (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.


Trade Publications

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