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Ryan Contreras

ryan.contreras [at]

Office: 541-737-5462

Agricultural & Life Sciences

Agricultural & Life Sciences 4031

2750 SW Campus Way

2750 SW Campus Way
Corvallis, OR 97331

Program Overview

My research focus is landscape 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 reduced seedling production include ploidy manipulation, mutagenesis seeds or meristems, and wide hybridization.

We conduct fundamental research in traditional genetics, cytogenetics, molecular genetics, and genomics to support the applied breeding program with the goal of developing plants that are attractive to consumers, easy for growers to produce, and resilient in modern landscapes.  The end goal is to develop new cultivars that have increased insect and disease resistance combined with superior aesthetics.


  • HORT 301. Growth and Development of Horticultural Crops. Fall. 3 credits
  • HORT 310e. Principles of Plant Propagation. Winter - Online. 3 credits
  • HORT 311. Plant Propagation. Winter. 4 credits

Team Members

Project Leader - Ryan Contreras
  • Ph.D. Horticulture, The University of Georgia - 2009
  • M.S. Horticultural Science, North Carolina State University - 2006
  • B.S. Horticultural Science, North Carolina State University - 2002
  • Professor, Oregon State University, Department of Horticulture. 40% Teaching / 55% Research. September 2021 - current.
  • Associate Head, Oregon State University, Department of Horticulture. April 2021 - current.
  • Associate Professor, Oregon State University, Department of Horticulture. 40% Teaching / 55% Research. September 2016 - September 2021.
  • Assistant Professor, Oregon State University, Department of Horticulture. 40% Teaching / 35% Research. December 2009 - September 2016
  • 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
Awards and Honors
  • 2021 American Society for Horticultural Science Outstanding Cross-commodity Publication Award
  • 2020 American Society for Horticultural Science - Research Division Vice President-Elect
  • 2019 Oregon Association of Nurseries President’s Five Star Award
  • 2018 Oregon Association of Nurseries Distinguished Education Award
  • 2018 Western Region Award for Excellence in College and University Teaching in the Food and Agricultural Sciences
  • 2016 Oregon Association of Nurseries President’s Five Star Award
  • 2015 R.M. Wade Award for Excellence in Teaching and Registry of Distinguished Teachers
  • 2013 College of Agricultural Sciences Savery Outstanding Young Faculty Award
Research Assistants 

Ivory Knutson

Cara Lucker


Current Graduate Students

Keen Maher - PhD student - Physiology and gene expression among synthetic polyploids.

Past Students

  • Dan Blanchard - M.S. 2023 - Developing mapping and database tools for the Oregon State University landscape.  Current Position:  Instructor and Curator of Collections, Oregon State University, Corvallis, OR.
  • Adigun McLeod - M.S. 2023 - The effects of ploidy manipulation on 'I3' hemp.
  • Cara Still - M.S.  2023 - Reproductive behavior and pollinator attraction of Buddleja cultivars.  Current Position:  Faculty Research Assistant, Ornamental Plant Breeding Program, Oregon State University, Corvallis, OR.
  • Kristin Neill - M.S. 2020 - Phenotyping Ornamental Plants: Case Studies in Disease Resistance of Cotoneaster and Fruit Quality Attributes from Vaccinium ovatumCurrent Position:  Horticulturist at Amazon Spheres, Seattle, WA.
  • Hsuan Chen - Ph.D. 2018 - Developing Tools for Hardy Hibiscus and Lilac Breeding: Quantile Regression, Cytogenetics, Interspecific Hybridization, Somatic Hybridization, and Marker-Trait Association.  Current Position:  Assistant Professor, Horticultural Science, NC State, Raleigh.
  • Jason Lattier - Ph.D. 2017 - Breeding and Genetics of Lilacs and Hardy Hibiscus. Current Position: Director and Curator Caine Conservatory, High Point University, North Carolina.
  • Justin Schulze - M.S. 2017 - Breeding, Production, and Morphophysiology among Cytotypes of Common and Portuguese Cherrylaurel. Current Position: Plant Breeder and Horticulturist with Bailey Nurseries, Inc., Watkinsville, GA.
  • Kim Shearer - M.S. 2016 - Inducing and evaluating phenotypic and cytometric variation in landscape plants: Observations from Acer, Galtonia, and Penstemon. Current Position: Curator of Living Collections and Manager Chicagoland Grows at the Morton Arboretum, Chicago, IL.
  • Joseph Rothleutner - M.S. 2012 - Genome Sizing and Fire Blight Resistance Screening in Cotoneaster. Current Position: Director of Horticulture and Facilities at Santa Barbara Botanic Garden, CA.

Undergraduate Researchers and Interns


  • Benjamin Fischer - 2024 Beginning researcher program.  Using SSRs to determine parentage of hybrid maples


  • Ashley Sander - 2023 intern
  • Claire Kepner - 2023 intern
  • Madelaina DiPasquale.  Phenology and propagation of Camellia grown in Corvallis, OR.
  • Josh Ashcraft.  Phenology of the maple germplasm collection including synthetic polyploids at OSU Ornamental Plant Breeding
  • Ty Seely. Analysis of pollen from 22x, 33x, 44x, and 22x+44x common cherrylaurels.
  • Patrice Woodworth. Ploidy analysis of seedlings dervied from 4x Acer ginnala & Acer platanoides and 2x+4x Hydrangea macrophylla.
  • Gwyn Alanko: Ploidy analysis of maple seedlings derived from tetraploid parents.
  • Sawyer Hurd: Intern and assistant on mockorange breeding to evaluate fragrance, flowering, and form among newly developed hybrids
  • 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

Cultivar Releases

Styrax japonicus 'ORSTSTYx1' PPAF

Philadelphus 'ORSTPHILx1' PPAF Swan Lake®

Vaccinium ovatum 'Cascade Jewel' PPAF

Hibiscus syriacus 'ORSTHIB5x1' PPAF Petite Pink Flamingo™

Cotoneaster ×suecicus 'Emerald Beauty' PP32,308

Cotoneaster ×suecicus 'Emerald Sprite' PP31,719

Ribes sanguineum 'Oregon Snowflake' PP26763

Publications (*indicates student author)


Contreras, R.N. 2024.  Styrax japonicus 'ORSTSTYx1'. HortScience.  59(6):745-746.


Contreras, R.N.  2024.  Hibiscus syriacus 'ORSTHIB5x1' PPAF Petite Pink FlamingoTM.  HortScience. 59(6):743-744. 


Contreras, R.N.  2024.  Philadelphus 'ORSTPHILx1' PPAF Swan Lake®.  HortScience.  59(3):429-430.


Contreras, R.N.  2024.  Vaccinium ovatum 'Cascade Jewel' PPAF.  HortScience.  59(4):503-504.



Chen, J., Sun, Y., Oki, L.R., Sisneroz, J.A., Reid, K., Nackley, L.L., Contreras, R.N., Kim, S., Schuch, U.K., Haver, D.L., Stuke, M., Fron, A., Kopp, K., Jones, S.B., & Hipps, L. 2023.  Climate-ready landscape plants: garden roses trialed at reduced irrigation frequency in Utah, USA. HortTechnology 33(5):477-492.


Contreras, R.N.  2023.  'Emerald Sprite' and 'Emerald Beauty' cotoneasters.  HortScience 58(10):1190–1191.


*Still, C.M., J. Snelling, S. Mehlenbacher, and R.N. Contreras.  2023.  Buddleja cultivar identification using microsatellite markers.  HortScience 58(9):1055–1056.


*McLeod, A., R.N. Contreras, M. Halstead, and K. Vining.  2023.  In vivo and in vitro chromosome doubling of 'I3' hemp.  HortScience 58(9):1018–1022.


Miller, C. T., Drewery, M., Waliczek, T. M., Contreras, R. N., & Kubota, C. 2023. Engaging Undergraduate Students in Research. HortTechnology, 33(1):1-7.



*Chen, H. and R.N. Contreras.  2022.  Near-Hexaploid and Near-Tetraploid Aneuploid Progenies Derived from Backcrossing Tetraploid Parents Hibiscus syriacus × (H. syriacus × H. paramutabilis).  Genes. 13(6):1022.   doi: 10.3390/genes13061022


*McLeod, A., K. Vining, T. Hoskins, and R.N. Contreras. 2022.  Impact of Indole-3-butyric Acid Concentration and Formulation and Propagation Environment on Rooting Success of ‘I3’ Hemp by Stem Cuttings.  HortTechnology. 32(3):321-324. 


*Lattier, J.D. and R.N. Contreras.  2022.  Flower forms and ploidy levels impact fertility in althea.  HortScience 57(4):558- 570. 


*Neill, K.E. and R.N. Contreras.  2022.  Does Inducing Tetraploidy in Vaccinium ovatum Improve Fruit Traits and Plant Architecture?  HortScience.  57(2):312-318.



*Melsen, K., M. van de Wouw, and R.N. Contreras.  2021.  Mutation breeding in ornamentals.  HortScience. 56(10):1154-1165.


*Neill, K.E., R.N. Contreras, V.O. Stockwell, *H. Chen.  2021.  Screening Cotoneaster sp. for resistance to fire blight using foliar inoculation with two strains of Erwinia amylovora.  HortScience 56(7):824-830.



Contreras, R.N. and T.C. Hoskins.  2020.  Developing triploid maples.  Horticulturae 6(4)70.


Hoskins, T.C., *J.D. Lattier, and R.N. Contreras.  2020.  Sowing green seed without stratification does not shorten juvenility or increase plant size in common lilac (Syringa vulgaris).  HortScience 55(11):1781-1787.


*Lattier, J.D. and R.N. Contreras.  2020.  Segregation of flower color and eyespot in althea.  J. Amer. Soc. Hort. Sci. 145(4):215-227  (JASHS Cover)


Contreras, R.N. and *Shearer, K.  2020.  Exposing seeds of Galtonia candicans to ethyl methanesulfonate (EMS) reduced inflorescence height, lodging, and fertility.  HortScience 55(5):621-624


*Chen, H., J.D. Lattier, K. Vining, and R.N. Contreras.  2020.  Two SNP markers identified using GBS are associated with remontancy in a segregating F1 population of Syringa meyeri ‘Palibin’ x S. pubescens ‘Penda’ Bloomerang®.  J. Amer. Soc. Hort. Sci. 145(2):104-109


*Petter, J., P. Ries, A. D’Antonio, and R.N. Contreras.  2020.  A Tree Selection Survey of Tree City USA Designated Cities in the Pacific Northwest.  Arboriculture & Urban Forestry.  46(5):371-384


*Petter, J., P. Ries, A. D’Antonio, and R.N. Contreras.  2020.  How are managers making tree species selection decisions in the Pacific Northwest of the United States?  Arboriculture & Urban Forestry.  46(2):148-161.




Hoskins, T. and R.N. Contreras.  2020.  Exposing seeds of Sarcococca confusa to increased concentrations and durations of ethyl methanesulfonate reduced seed germination, twinning, and plant size.  HortScience 54(11):1902-1906.


Graebner, R.C., H. Chen, R.N. Contreras, K.G. Haynes, and V.R. Sathuvalli.  2019.  Identification of a high frequency of triploid potatoes from tetraploid x diploid crosses.  HortScience 54(7)1159-1163.


*Lattier, J.D., H. Chen, and R.N. Contreras.  2019.  Variation in genome size, ploidy, stomata, and rDNA signals in althea (Hibiscus syriacus L.).  J. Amer. Soc. Hort. Sci. 144(2):130-140.


Vining, K.J., I. Pandelova, K. Hummer, N. Bassil, R.N. Contreras, K. Neill, H. Chen, A.N. Parrish, and B.M. Lange.  Genetic diversity survey of Mentha aquatica L. and Mentha suaveolens Ehrh., mint crop ancestors.  Genetic Resources and Crop Evolution 66(4):825-845.


*Chen, H., L. Xue, T. Li, and R.N. Contreras.  2019.  Quantile regression facilitates simultaneous selection of negatively correlated floral traits among BC1F1 progeny of the male fertile hybrid cultivars Lohengrin and Resi (Hibiscus syriacus x H. paramutabilis).  J. Amer. Soc. Hort. Sci. 144(1):70-76.



Contreras, R.N. and K. Shearer.  2018.  Genome size, ploidy, and base composition of wild and cultivated Acer.  J. Amer. Soc. Hort. Sci. 143(6):470-485.



*Lattier, J.D. and R.N. Contreras.  2017.  Ploidy and genome size in lilac species, cultivars, and interploid hybrids.  J. Amer. Soc. Hort. Sci. 142(5):355–366. doi: 10.21273/JASHS04189-17


*Lattier, J.D. and R.N. Contreras.  2017.  Intraspecific, interspecific, and interseries cross-compatibility in lilac.  J. Amer. Soc. Hort. Sci. 142(4):279-288. (JASHS cover).


*Lattier, J.D., H. Chen, and R.N. Contreras. 2017. Improved method for enzyme digestion of root tips for cytology. HortScience 52(7):1029-1032.


*Schulze, J.A., J.D. Lattier, and R.N. Contreras.  2017.  In vitro germination of immature Prunus lusitanica seed.  HortScience 52(8):1122-1124.

*Schulze, J.A. and R.N. Contreras.  2017.  In vivo chromosome doubling of Prunus lusitanica and preliminary morphological observations.  HortScience.  52(3):332-337.

*Schulze, J.A., R.N. Contreras, and C.F. Scagel.  2017.  Comparing vegetative propagation of two ‘Schipkaensis’ cherrylaurel ploidy levels.  HortTechnology 27(1):69-72. 


Contreras, R.N. and L. Meneghelli.  2016.  In vitro chromosome doubling of Prunus laurocerasus 'Otto Luyken' and 'Schipkaensis'. HortScience 51(12):1463-1466.

*Rothleutner, J.J., M.W. Friddle, and R.N. Contreras.  2016.  Ploidy levels, relative genome sizes, and base pair composition in Cotoneaster.  J. Amer. Soc. Hort. Sci. 141(5):457-466.


Contreras, R.N. and M.W. Friddle.  2015. ‘Oregon Snowflake’ flowering currant.  HortScience 50(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)


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., 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.

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.

Schwartz, B.M., K.R. Harris-Schultz, C.S. Hans, R.N. Contreras, and S.A. Jackson.  2013.  Creation of hexaploid and octoploid zoysiagrass using colchicine and breeding.  Crop Science 53:2218-2224.

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.  Published online 7 Jan 2013.  doi:10.1080/02827581.2012.762939

Contreras, R.N., R. Golembiewski, J. Velez.  2013.  Evaluation of study habits of plant identification students. HortTechnology 23(1):130-133.


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 in several species of Cupressaceae. HortScience 47(6):712-714.

Contreras, R.N., J.M. Ruter, J. Conner, Y. Zeng, and P. Ozias-Akins. 2012.  Interspecific hybridization in Tecoma Juss. (Bignoniaceae):  Confirmation of hybridity using GISH and determination of 18s rDNA copy number using FISH in F1 hybrids. 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 tetraploidy in Cryptomeria japonica (Cupressaceae).  HortScience 45(2):316-319.


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 J.M. Ruter.  2009.  Sulfuric acid scarification of Callicarpa americana (Lamiaceae) seeds improves germination.  Native Plants J. 10(3):283-286.


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, S.R. Milla-Lewis, and G.C. Yencho.  2007.  Investigating parentage and hybridity of three azaleodendrons using amplified fragment length polymorphism analysis.  HortScience 42(3):740-743.

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.