| Summary: | Species of <i>Phalaris</i> have historically been controlled by acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides; however, overreliance on herbicides with this mechanism of action has resulted in the selection of resistant biotypes. The resistance to ACCase-inhibiting herbicides was characterized in <i>Phalaris brachystachys</i>, <i>Phalaris minor,</i> and <i>Phalaris paradoxa</i> samples collected from winter wheat fields in northern Iran. Three resistant (R) biotypes, one of each <i>Phalaris</i> species, presented high cross-resistance levels to diclofop-methyl, cycloxydim, and pinoxaden, which belong to the chemical families of aryloxyphenoxypropionates (FOPs), cyclohexanediones (DIMs), and phenylpyrazolines (DENs), respectively. The metabolism of <sup>14</sup>C-diclofop-methyl contributed to the resistance of the <i>P. brachystachys</i> R biotype, while no evidence of herbicide metabolism was found in <i>P. minor</i> or <i>P. paradoxa</i>. ACCase in vitro assays showed that the target sites were very sensitive to FOP, DIM, and DEN herbicides in the S biotypes of the three species, while the R <i>Phalaris</i> spp. biotypes presented different levels of resistance to these herbicides. ACCase gene sequencing confirmed that cross-resistance in <i>Phalaris</i> species was conferred by specific point mutations. Resistance in the <i>P. brachystachys</i> R biotype was due to target site and non-target-site resistance mechanisms, while in <i>P. minor</i> and <i>P. paradoxa</i>, only an altered target site was found.
|
|---|