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ARS Home » Pacific West Area » Corvallis, Oregon » Forage Seed and Cereal Research Unit » Research » Publications at this Location » Publication #418832
Research Project: Development of Plant and Molecular Resources to Improve Performance, Utility, and Tolerance of Cool Season Grasses and Legumes

Location: Forage Seed and Cereal Research Unit

Title: EPSPS gene amplification in a glyphosate-resistant population of Italian ryegrass (Lolium multiflorum) from Oregon

Author
item RIBEIRO, VICTOR - Oregon State University
item BERRY, PETE - Oregon State University
item CREED, TIM - Oregon State University
item BARROSO, JUDIT - Oregon State University
item MALLORY-SMITH, CAROL - Oregon State University
item Gallagher, Joseph

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2024
Publication Date: 10/31/2024
Citation: Ribeiro, V.H., Berry, P., Creed, T.B., Barroso, J., Mallory-Smith, C.A., Gallagher, J.P. 2024. EPSPS gene amplification in a glyphosate-resistant population of Italian ryegrass (Lolium multiflorum) from Oregon. Pest Management Science. 81(2):1060-1066. https://doi.org/10.1002/ps.8508.
DOI: https://doi.org/10.1002/ps.8508

Interpretive Summary: Herbicide resistance can result in unreliable control of weeds and can be caused by different molecular sources. Lolium multiflorum (annual ryegrass, Italian ryegrass), grown as both a crop and a weed in Oregon, is known to have several forms of resistance to the herbicide glyphosate. When a new glyphosate-resistant Italian ryegrass population was tested for molecular sources of resistance, it carried many copies of the EPSPS gene, the gene encoding the glyphosate target-site enzyme. Although this mechanism of glyphosate resistance has been previously reported, this is the first time we have seen it in the grass seed production region of Oregon, where it has the potential to cross-pollinate with annual ryegrass crops. Understanding which forms of glyphosate resistance are present in specific species can inform best practices for herbicide use and weed management.

Technical Abstract: BACKGROUND Lolium multiflorum Lam. (Italian ryegrass, annual ryegrass) is both a weed and a crop in Oregon. Because it is commonly managed using chemical controls, herbicide-resistant populations have arisen within the seed production region. A glyphosate-resistant population was identified within Yamhill County, Oregon, in a fallow field previously cropped with perennial ryegrass. RESULTS A dose-response study revealed that the glyphosate-resistant population OR12 was 9.2-fold more resistant to glyphosate than the susceptible population. No EPSPS amino acid substitutions known to confer glyphosate resistance were observed via gene sequencing. Quantitative PCR of genomic DNA revealed a mean 30-fold increase in EPSPS gene copies in the OR12 population. Biomass after glyphosate treatment was correlated with EPSPS gene copy number of individual plants. CONCLUSION This is the first known report of glyphosate resistance associated with EPSPS gene amplification to arise in L. multiflorum populations in Oregon.