A novel mutation in SoIAA20 confers cross-resistance to 2,4-Dichlorophenoxyacetic acid and other auxinic herbicides in Sonchus oleraceus.

background2,4-Dichlorophenoxyacetic acid (2,4-D) and other auxinic herbicides are important for weed control in cropping systems globally. Weeds with resistance to 2,4-D and other auxinic herbicides have evolved, including several populations of Sonchus oleraceus from multiple sites in Australia. We report the underlying mechanism in these populations that gives rise to auxinic herbicide resistance.

resultsWe studied a total of three susceptible and eight resistant Sonchus oleraceus populations. All resistant populations had a deletion of three amino acids flanking the degron sequence of an Aux/IAA gene, SoIAA20, which was not found in the three susceptible populations. The eight populations with the resistant allele were also resistant to dicamba, fluroxypyr and clopyralid. The resistant plants also had reduced movement of 2,4-D out of the treated tissues compared to susceptible plants.

conclusionThe paired deletion flanking the degron region of SoIAA20 likely provides resistance to 2,4-D by restricting the movement of 2,4-D from the treated tissue to the rest of the plant. We hypothesise that this deletion keeps the 2,4-D bound to the target site. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.