Tracing Resistance of Weeds to Aryloxyphenoxypropionate (ACCase), Acetolactate Synthase (ALS) and Synthetic Auxcins Herbicides in Shoushtar Wheat Fields

Since the first compilation of herbicide-resistant weeds in 1982, the number of reported herbicide-resistant species has increased significantly. Iudosulfuron-methyl-sodium mesosulfuron-methyl mefenpyr diethyl, sulfosulfuron and tribenuron-methyl, acetolactate synthase (ALS) inhibiting herbicides, clodinafoppropargyl, aryloxyphenoxypropionate (ACCase) inhibiting herbicides and 2,4-D〣, synthetic auxcins herbicides are registered in Iran for post emergence control of broadleaf and some grass weeds in wheat (Triticumaestivum L.). In southwest Iran, Khouzestan province, the appearance of wild oat (AvenaludovicianaDurieu), littleseedcanarygrass (Phalaris minor Retz) and wild mustard (SinapisarvensisL.) populations with different degrees of resistance to mentioned herbicides has been reported previously in last decade. A reliable seedling bioassay was developed and tested for the rapid screening for resistance to aryloxyphenoxypropionic (APP) herbicides in some.populationsspecialy grass weed. This paper describes a rapid and reliable seedling test to detect APP-resistant A. ludoviciana,Phalaris minor and Sinapisarvensisbiotypes in order to determine their frequency within a population. This test has also been developed in order to discriminate between APP, ALS and synthetic auxcin -resistant biotypes.
Suspected resistant and susceptible seeds of wild oat, littleseedcanarygrass and wild mustard to iodosulfuron-methyl -sodium mesosulfuron-methyl mefenpyr diethyl, sulfosulfuron and tribenuron-methyl, clodinafoppropargyl and 2,4-D〣 were collected from wheat fields, Shoushtar, southwestern of Iran in 2014 – 2015 growing season. The wild oat and littleseedcanarygrass seedspregerminated in petri dishes. Single doses of clodinafop (1.25 and 0.080 mg ai L-1) were used for the R- and S- populations of wild oat and littleseedcanarygrass, respectively. These experiments were carried out by placing 5 pre-germinated seeds in a 7-cm-diam petri dish containing one piece of filter paper and 5 ml of distilled water or solutions having concentration of clodinafop. The petri dishes were placed in the germinator. The coleoptiles length of seedlings was measured 7 days after treatment (DAT). The pregerminated seeds of wild mustard were sown in pots and irrigated regularly to avoid any moisture stress. Ten days after planting (DAP), they were thinned to two seedlings per pot. Twenty days after weed emergence, seedlings of the pots were subjected to iodosulfuron-methyl-sodium mesosulfuron-methyl mefenpyr diethyl (18 g ai ha-1), sulfosulfuron (19.95 g ai ha-1) and tribenuron-methyl (15 g ai ha-1) and 2,4-D〣 (200 g ai ha-1) application. The sprayer was calibrated to deliver 338 L ha-1 at pressure of 2 atm. The aboveground biomass was harvested 28 days after treatment (DAT) and weighed. Then, distribution map of resistant and susceptible populations in fields was drawn using GIS 9.3 software.
The results showed that eleven, eight, two and one wild mustard populations were confirmed resistant (RRR), probably resistant (RR), possibly resistant (R?) and susceptible (S) to sulfosulfuron based on “R” ratings system. In addition, three, twelve, three and four wild mustard populations were confirmed resistant, probably resistant, possibly resistant and susceptible to iodosulfuron-methyl-sodium mesosulfuron-methyl mefenpyr diethyl. For tribenuron-methyl, seven, twele and three populations were confirmed resistant, probably resistant, possibly resistant and other populations were susceptible. Meanwhile, whole populations were susceptible to 2,4-D MCPA. Seven days after clodinafop treatment, a clear difference in symptoms was observed between the R- and S- populations. Clodinafop affected the cleoptile length of S- and R-populations of wild oat and littleseedcanarygrass differentially. As, thirty three, fifteen and one wild oat populations were confirmed resistant, probably resistant, possibly resistant and other populations were susceptible. Finally, eight, five and three littleseedcanarygrass populations were confirmed resistant, probably resistant, possibly resistant and other populations were susceptible. Distibution map of populations showed that confirmed, probably, possibly resistant populations were dispersed as uniformaly in the region. As shown in the map, distribution of populations was in the center of region.
The results obviously demonstrated that R- and S-populations could be discriminated by the pregerminated seed, whole plant assays. It could be concluded that 2,4-D〣, iodosulfuron-methyl-sodium mesosulfuron-methyl mefenpyr diethyl were more potent than other AlS herbicide group for wild mustard control. Moreover, awareness of distribution map of resistant and susceptible populations could help for better management and prevention the further spread of the populations. We believe that more populations must be studied to determine exact distribution of resistant and susceptible populations in southwest Iran. Finally, extensionists based on distibution maps of resistant populations could recommend herbicides that prevent or delay herbicide resistance development.