Role of Ile-2041-Asp in conferring high-level resistance to clodinafop-propargyl in winter wild oat (Avena ludoviciana) populations

Winter wild oat is an important and troublesome weed in wheat fields. Herbicides that inhibit the enzyme acetyl-coenzyme A carboxylase (ACCase inhibitors) have been widely used to control grass weeds such as wild oat in Iran, which has resulted in evolution of resistance to theses herbicides in wild oat. Whole-plant dose-response assay with 10 doses (from 0 to 32 times of the recommended rate, 64 g ai ha-1) was conducted to determine resistance level (RI) to clodinafop-propargyl (EC 8%) in 15 resistants and one susceptible wild oat populations from Fars and Khuzestan in southwest Iran. To evaluate the mechanism of resistance in resistant populations, cleaved amplified polymorphic sequence (CAPS) and derived cleaved amplified polymorphic sequence (dCAPS markers were used). The results of dose-response experiment clearly revealed that four (M2, M3, S4 from Fars and R5 from Khuzestan) out of fifteen populations were highly resistant to clodinafop-propargyl, where these populations were not even controlled over the range of 32 times of clodinafop-propargyl recommended rate. Therefore, resistance level in above population was greater than 21/93, the highest estimated RI for AN13. Three populations (M1, S1 and F3 from Fars) showed moderate resistance to clodinafop-propargyl with RI, 5-10. Based on molecular approaches, two known mutations (Ile-1781-Leu and Ile-2041-Asp) were identified in resistant populations. Results of a robust molecular assay demonstrated that the Ile-2041-Asp substitution occurred in M2 and R5 populations and the Ile-1781-Leu substitution occurred in the R5 population and 6 other populations; S1 S2, S3, S4, ES1 from Fars and AN13 from Khuzestan. This is the first report of a winter wild oat population carrying the both mutations in the world. Interestingly, this study revealed that Ile-2041-Asp substitution is associated with conferral of high-level resistance to clodinafop-propargyl and possibly other herbicides from FOPs family in winter wild oat.