An <scp> ALA 122 THR </scp> substitution in the <scp>AHAS</scp> / <scp>ALS</scp> gene confers imazamox‐resistance in <scp> Aegilops cylindrica </scp>

BACKGROUND Wheat growers have limited herbicide options to manage Aegilops cylindrica Host (jointed goatgrass), with many relying on mesosulfuron or imazamox in Clearfield™ winter wheat. Both imazamox and mesosulfuron inhibit acetohydroxyacid synthase/acetolactate synthase (AHAS/ALS). In 2015, a suspected imazamox resistant biotype of Ae. cylindrica was found in eastern Washington. RESULTS Imazamox and mesosulfuron were applied to the suspected resistant and susceptible Ae. cylindrica biotypes in increasing application rates to evaluate herbicide dose needed to cause 50% growth reduction (GR50 ). The imazamox resistant biotype had a GR50 of 308.5 g ai ha-1 and was more than 5000 times more resistant to imazamox than a known susceptible biotype with a GR50 of 0.06 g ai ha-1 . The Ae. cylindrica resistant biotype was also resistant to mesosulfuron, with an GR50 of 46.82 g ai ha-1 , which was five times more than the susceptible GR50 of 8.6 g ai ha-1 . Sequencing of the AHAS/ALS gene revealed an Ala122 Thr substitution in the herbicide binding region of the AHAS/ALS gene on the D genome of Ae. cylindrica. The resistance trait was inherited as a dominant trait, and the Ala122 Thr co-segregates with the resistance phenotype. CONCLUSIONS An Ala122 Thr substitution in the AHAS/ALS gene on the D genome of Ae. cylindrica confers resistance to imazamox in Ae. cylindrica. &#169; 2021 Society of Chemical Industry.