Ryan Contreras

Associate Professor, Ornamental Plant Breeding
Send an Email

Office: 541-737-5462
Other: ryan.contreras@oregonstate.edu
Fax: 541-737-3479

Agricultural & Life Sciences

Agricultural & Life Sciences 4031

2750 SW Campus Way

2750 SW Campus Way
Corvallis, OR 97331

Program Overview

My teaching and research focuses on woody nursery and landscape plants. I teach spring and fall woody plant identification courses, growth and development of horticultural crops, and plant propagation. Research in my lab is closely aligned 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:

  • Amur, trident, and Norway maples
  • Fragrant sweetbox
  • Flowering currant
  • Arborvitae
  • Portugese and common cherrylaurel
  • Lilacs
  • Cotoneaster
  • Mockorange
  • Althea
  • Katsuratree
  • Vaccinium
  • Deutzia
Email ryan.contreras@oregonstate.edu


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. 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.


  • 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. Growth and Development of Horticutural Crops. Fall. 3 credits
  • HORT 301e. Growth and Development of Horticutural Crops. Fall & Spring - Online. 3 credits
  • HORT 311. Plant Propagation. Winter. 4 credits
  • HORT 311e. Plant Propagation. Winter - Online. 4 credits

Team Members

Project Leader - Ryan Contreras
  • 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.
  • Associate Professor, Oregon State University, Department of Horticulture. 40% Teaching / 35% Research. September 2016 - current.
  • 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
  • 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 Assistant - Tyler Hoskins

Tyler is a native Oregonian who has degrees from Clackamas Community College, George Fox, and Virginia Tech. The latter is where he honed his expertise in managing water and nutrients in soilless substrates of nursery crops - earning his M.S. with former Oregon State professor, Jim Owen. Tyler expertly manages the growing operation for the breeding program from propagation, to containers, field production, irrigation, and fertilization.

Current Graduate Students

Kristin Neill - M.S. Student
  • Recurrent selection to improve fruit and landscape qualitities of evergreen huckleberry.
  • Interploidy and intersubgeneric hybridization in Cotoneaster.

Past Students

  • Hsuan Chen - Ph.D. 2018 - Developing Tools for Hardy Hibiscus and Lilac Breeding: Quantile Regression, Cytogenetics, Interspecific Hybridization, Somatic Hybridization, and Marker-Trait Association
  • Jason Lattier - Ph.D. 2017 - Breeding and Genetics of Lilacs and Hardy Hibiscus. Current Position: Post Doctoral Researcher at the US National Arboretum. Beltsville, MD.
  • Justin Schulze - M.S. 2017 - Breeding, Production, and Morphophysiology among Cytotypes of Common and Portuguese Cherrylaurel. Current Position: Breeder and Horticulturist with Bailey Nurseries, Inc. at their PII location in 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: Tree and Shrub Breeder 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 at the Lincoln Park Zoo, Chicago, IL

Undergraduate Researchers and Interns


  • Lena Wilhelm.  Assessing ploidy variation of Berberis nervosa over its geographic distribution:  preliminary observations from the collections of the OSU Herbarium.
  • Patrice Woodworth
  • Amy Kessler
  • Josh Ashcraft


  • Ty Seely. Analysis of pollen from 22x, 33x, 44x, and 22x+44x common cherrylaurels.
  • Patrice Woodworth. Ploidy analysis of seedlings dervied from 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

I accept graduate students for Horticulture

Curriculum Vitae: 

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Do you accept grad students?: 
I accept graduate students for Horticulture
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OSU Main Campus
My Publications


Journal Article

J. D. Lattier and Contreras, R., Intraspecific, Interspecific, and Interseries Cross-compatibility in Lilac, Journal of the American Society for Horticultural Science, vol. 142, no. 4, pp. 279 - 288, 2017.
J. D. Lattier, Chen, H., and Contreras, R., Improved Method of Enzyme Digestion for Root Tip Cytology, HortScience, vol. 52, no. 7, pp. 1029 - 1032, 2017.
J. D. Lattier and Contreras, R., Ploidy and Genome Size in Lilac Species, Cultivars, and Interploid Hybrids, Journal of the American Society for Horticultural Science, vol. 142, no. 5, pp. 355 - 366, 2017.


Journal Article

J. J. Rothleutner, Friddle, M. W., and Contreras, R., Ploidy Levels, Relative Genome Sizes, and Base Pair Composition in Cotoneaster, Journal of the American Society for Horticultural Science, vol. 141, no. 5, pp. 457 - 466, 2016.