Identification of Glyphosate Resistance in Lolium rigidum Gaudin

Glyphosate resistance was found in Lolium rigidum Gaudin (Rigid ryegrass, LOLRI) inSouth Africa. Suspected glyphosate-resistant L. rigidum populations were collected andgrown under greenhouse conditions. The plants were sprayed with a range of doses of glyphosate35 days after planting and shoot dry biomass was determined 17 days after herbicidetreatment. Based on the dose-response experiment conducted in the greenhouse,one population of L. rigidum suspected to be resistant to glyphosate was approximately 5.3fold more resistant than susceptible population. The other population was 2.8 fold moreresistant than susceptible population. Difference between the two suspected resistant populationswas 1.9 fold. All plants were treated with glyphosate (1000 g a.i. ha-1) and shikimicacid was extracted 2, 4 and 6 days after treatment. The plants of susceptible populationsaccumulated more shikimic acid than other two populations.