Evaluation of the Winter Wild oat (Avena ludoviciana Durieu.) Resistance Trend to Acetyl coA carboxylase Inhibitor Herbicides in Fars Province’s Wheat Fields of Fars Province

Wild oat (Avena ludoviciana Durieu.) is one of the most important weeds in wheat fields. The wheat farming relies on chemical control. Most of the registered herbicides for these fields are in group of Acetyl CoA carboxylase (ACCase). These group of herbicides are the most effective ones on weed control with low active ingredients and low toxicity for mammalians, so have extensive application all over the world. To date, 49 were detected resistance to ACCase inhibitor herbicides, respectively (Heap, 2021). Resistance to herbicides in Avena spp. have been reported in wheat fields of Iran, repeatedly. The first resistance report to ACCase inhibitors was in 2006. This study was conducted on some Avena ludoviciana Durieu. populations collected in 2014 from wheat fields (in Fars province) which their weed herbicide resistance had been studied in 2009 (Sasanfar, 2017). The aim of this study was to investigate the effect of chemical management on control of resistant winter wild oats and the trend of resistance evaluation.

In order to monitor resistance, 11 suspected Avena ludoviciana Durieu. populations collected from Marvdasht, Estahban, sepidan and a sensitive population by 8 herbicides of Acetyl CoA carboxylase group. Also the resistance index was measured in response to 9 doses of clodinafop propargyl in dose-response test. Greenhouse studies (resistance screening and dose-response tests) were conducted with five replications. The individual’s fresh weight reduction related to untreated control and survival percentages were evaluated, 28 days after herbicide applications. Based on screening data, resistant populations were classified with R classification system (Moss et al., 2007) and three-parameter log-logistic model was fitted to dose-response data. Some molecular markers were used to detecting mutations confering herbicide resistance in ACCase enzyme gene. At the end, the results of assays were compared with the same ones reported in the past resistance survey of these fields to understand the resistance trends.

All populations were resistant to three fop herbicides used in this study: clodinafop propargyl, fenoxaprop-p-ethyl and diclofop methyl. Cross-resistance of three populations of mavdasht (M1, M2 and M4) was confirmed and M1 and M2 populations, were cross resistant to pinoxaden. Results of applying sulfonylureas herbicides indicated that multiple herbicide resistance was occurred in ES2, ES4 and M4 populations (Table 3). Results of dose-response tests showed that, despite susceptible population ED50 was 22.37 g ai/ha, the range of measured ED50 in resistant populations were between 81.2 to 270.9 g a. i/ha; so the RI values for the most resistant population, ES4, to clodinafop propargyl herbicide based on fresh weight as percentage of untreated control is more than 12 and for the weakest resistant population, S2, was 3.8. Resistance in some populations could not be measured because herbicide doses up to 32 times more than recommended dose could not reduce their fresh weight under 50%. According to survival percentage data, the most resistant population was M3 from Marvdasht (Table 4) but evaluated ED50 values of S2, ES2, ES3 and ES4 were less than the values evaluated on the base of fresh weight. It seems that this populations seeds are not uniform but their resistant plant individuals have good growth rate and could be crop competitive in fields.The resistance report on seeds collected in 2009 shows no resistance to dims and den herbicides in any population; except M4 which was resistant to sethoxydim. In our survey (on seeds collected in 2014) Marvdasht populations were resistant to all three fop herbicides and cross-resistance to sethoxydim, cycloxydim and pinoxaden. The molecular studies confimed three Ile-1781, Ile-2041 and Trp-2027 mutations in resistant individual plants of wild-oat (A. ludoviciana) populations. Comparison of the results of these two studies showed, Although, the resistance-endowing ACC gene mutations in two populations M2 and S1 collected in 2009 and 2014 were the same; but have changed in other populations in these two years. The 1781 and 2027 mutations were observed in Estahban and Marvdasht populations collected in 2014 for the first time, respectively.

Resistance trend survey confirmed the expansion of cross resistance spectrum to three herbicide families (fops, dims and den) and enhanced resistance indexes, suggesting longtime integrated management instead of chemical control is needed.