Cross and multiple resistance patterns to 10 ACCase and three ALS inhibitor herbicides were detennined in 16 Iranian winter wild oat populations. Molecular assays were carried out using the (d)CAPS method to study the four ACCase target-site mutations. Metabolism-based resistance was perfonned using malathion (a cytochrotne P450 inhibitor). Various resistance levels (from 1.50 to >21.93) to clodinafop-propargyl were observed among the populations. Resistance patterns to ACCase inhibitors indicated that the ES I population was only resistant to fenoxaprop-p-ethyl (FX) and diclofop-methyl (DC), while the S3, S4, AN6 and AN9 showed cross-resistance to boils mentioned herbicides and clodinafop-propargyl (CD). The MI. M3, SI and S2 populations were resistance to the three mentioned herbicides (FX, DC, CD), as well as quizalofop-p-teficyl (QZ). The M2 and R5 showed cross-resistance to all previous herbicides (FX. DC. CD. QZ) and haloxyfop-r-methyl (HX). The M4, F3 and SHT1 had cross-resistance to some fops and sethoxydim, while the SHT1 showed cross-resistance to cycloxydim, as well. The AN13 showed cross-resistance to all fop and dim herbicides except clethodim. Furthermore, the SI, S2. S4 and F3 showed also multiple resistance to some ALS-inhibiting herbicides. The AN6 indicated cross-resistance to all ALS inhibitors including sulfosulfuron+metsulfuron and iodosulfuron+mesosulfuron (diflufenican). Molecular assays demonstrated that the SI, S2, S3, S4, ES I and AN13 populations carrying a mutation at the Ile-1781-Leu position, while the M2 having a mutation at the Ile-2041-Asn position. Simultaneously, R5 involved both the Ile-1781-Leu and Ile-2041-Asn mutations. The metabolic study results indicated that malathion application increased the efficacy of sulfosulfuron+metsulfuron from 30.65% to 43.18% in the AN6 and F3, while malathion led to increasing of iodosulfuron+mesosulfuron efficacy from 26.90% to 50.28% in the SI and AN6 populations, respectively. Overall, the study demonstrates both target-site and enhanced metabolism mechanisms associating with various patterns of resistance in the studied winter wild oat accessions.

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