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Title: EPSPS gene amplification in glyphosate-resistant in Italian ryegrass (Lolium perenne ssp. multiflorum) populations from Arkansas, USA

Author
item SALAS, REIOFELI - University Of Arkansas
item SCOTT, ROBERT - University Of Arkansas
item Dayan, Franck
item BURGOS, NILDA - University Of Arkansas

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2015
Publication Date: 3/11/2015
Publication URL: https://handle.nal.usda.gov/10113/62420
Citation: Salas, R.A., Scott, R.C., Dayan, F.E., Burgos, N.R. 2015. EPSPS gene amplification in glyphosate-resistant in Italian ryegrass (Lolium perenne ssp. multiflorum) populations from Arkansas, USA. Journal of Agricultural and Food Chemistry. 63:5885-5893. DOI:10.1021/acs.jafc5b00018

Interpretive Summary: Evolution of resistance to glyphosate is an increasing problems in agriculture. Glyphosate-resistant Italian ryegrass was first identified in Arkansas, USA in 2007. This report provides additional information on the level of resistance and resistance mechanisms in six populations from that state. The resistant biotypes were 7 to 19 times less sensitive to glyphosate than the susceptible population. There was no different in uptake and translocation of glyphosate, and no mutation in the EPSPS gene known to be associated with resistance to glyphosate was detected. Resistance is associated with a great increase in the number of copies of the EPSPS gene. Plants surviving the recommended dose of glyphosate contained at least 10 copies.

Technical Abstract: Glyphosate-resistant Italian ryegrass was detected in Arkansas, USA in 2007. In 2014, 45 populations were confirmed resistant in eight counties across the state. The level of resistance and resistance mechanisms in six populations was studied to assess the severity of the problem and identify alternative management approaches. Dose-response bioassays, glyphosate absorption and translocation experiments, herbicide target (EPSPS) gene sequence analysis, and gene amplification assays were conducted. The dose causing 50% growth reduction (GR50) was 7 to 19 times higher for the resistant than the susceptible population. Uptake and translocation of 14C-glyphosate was similar in resistant and susceptible plants and no mutation in the EPSPS gene known to be associated with resistance to glyphosate was detected. Resistant plants contained 11-fold to >100-fold more copies of the EPSPS gene than the susceptible plants, while the susceptible plants had only one copy of EPSPS. Plants surviving the recommended dose of glyphosate contained at least 10 copies. The EPSPS copy number was positively related to glyphosate resistance level (r=80). Resistance mechanisms could be location-specific. Suppressing the mechanism for gene amplification may overcome resistance.