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 gardeners alike. As the nursery industry grows an incredible diversity of crops, we try to address a diverse suite of plants from low growing shrubs or groundcovers to large shade trees. This interest in serving the needs of the industry has led me to initiate projects on nearly 50 genera.
My research program involves several areas of 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 achieve sterility/reduced fertility include development of triploids using ploidy manipulation, as well as mutagenesis by exposing seeds or meristems to physical and chemical mutagens.
My lab conducts 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.
Adigun McLeod: Ploidy manipulation and genomics of industrial hemp
Cara Still: Reproductive behavior and pollinator attraction of Buddleja cultivars
Dan Blanchard: Developing mapping and database tools for the Oregon State University landscape
Raven Hartley: Evaluating propagation and production systems in new nursery crops
*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. https://doi.org/10.21273/HORTTECH05016-21
*Lattier, J.D. and R.N. Contreras. 2022. Flower forms and ploidy levels impact fertility in althea. HortScience. 57(4):558-570. https://doi.org/10.21273/HORTSCI16478-21
*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. https://doi.org/10.21273/HORTSCI16332-21
*Melsen, K., M. van de Wouw, and R.N. Contreras. 2021. Mutation breeding in ornamentals. HortScience. 56(10):1154-1165. https://doi.org/10.21273/HORTSCI16001-21
*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. https://doi.org/10.21273/HORTSCI15872-21
Contreras, R.N. and T.C. Hoskins. 2020. Developing triploid maples. Horticulturae 6(4)70. https://doi.org/10.3390/horticulturae6040070
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. https://doi.org/10.21273/HORTSCI15328-20
*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 https://doi.org/10.21273/JASHS04824-19. (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 https://doi.org/10.21273/HORTSCI14775-19.
*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 https://doi.org/10.21273/JASHS04847-20.
*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 https://doi.org/10.48044/jauf.2020.027.
*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. https://doi.org/10.21273/HORTSCI14428-19
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.
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 L. Meneghelli. 2016. In vitro chromosome doubling of Prunus laurocerasus 'Otto Luyken' and 'Schipkaensis'. HortScience 51(12):1463-1466.
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.
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., 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. 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. https://doi.org/10.21273/HORTSCI.42.3.740