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

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 evolved within the seed production region. A glyphosate‐resistant population was identified in Yamhill County, Oregon, in a fallow field previously cropped with perennial ryegrass. RESULTS Dose–response studies showed that the glyphosate‐resistant population, OR12, was nine‐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 polymerase chain reaction (qPCR) 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. © 2024 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.