Investigating the Resistance of Annual Ryegrass (Lolium rigidum) Biotypes Collected from Wheat Fields of Fars Province to Pinoxaden Herbicide

In order to investigate the resistance level ofannual ryegrass (Lolium rigidum) biotypes to Pinoxaden herbicide, greenhouse and Petri dish bioassay studies based on CRD with 4 replications were conducted at Weed Research Department of Iranian Research Institute of plant Protection during 2008 and 2009. The resistance level of biotypes was determined in pot trials, while the herbicide dose required for 50% reduction of coleoptile length of the susceptible biotypes (GR50) as well as the susceptibility and resistance level of biotypes were studied in Petri dish bioassay trials. The experiments were conducted on 12 annual ryegrass biotypes collected from wheat fields of Fars province. The susceptible (FS) and 11 suspected to resistant biotypes (including ES1, ES2, ES3, ES4, ES5, M1, M2, M3, F1, FJ and FI2) were sprayed at 2- to 4-leaf stage by applying 0-32 times of recommended dose of Pinoxaden herbicide including 0. 45, 90, 180, 360, 720 and 1440 g ai ha-1 in greenhouse experiments. The germinated seeds were also exposed to 0, 0.4, 0.8, 1.6, 3.2, 6.4 and 12.8 g ai l-1 in Petri dish bioassay experiments. The percentage of dry matter and plant survival of each biotype was calculated compared to the untreated control and the resistance level was determined four weeks after herbicide application in greenhouse experiments. The percentage of coleoptile length of biotypes compared to the control was assessed 7 days after treating the germinated seeds with herbicide in Petri dish bioassays and the resistance level of biotypes were calculated. The results of greenhouse and Petri dish bioassay studies indicated that 4 biotypes including ES4, M2, F1 and FJ were resistant to Pinoxaden herbicide. As a general conclusion, most of the studied biotypes were sensitive pionoxaden.