Extensive use of triallate, a preemergence herbicide used for wild oat (Arena fatua L.) control in cereal crops, has selected for resistant (R) wild oat populations. Triallate is thought to be activated via metabolic sulfoxidation to create the more potent triallate sulfoxide. Treatment of R and susceptible (S) wild oat lines with [1-14C]triallate showed that triallate is metabolized to the same primary endproduct, 2,3,3-trichloropropene sulfonic acid, in both types. However, the rate of triallate metabolism was more than 12-fold slower in R than in S plants. Dose response studies indicated that although R plants were 6- to 20-fold more resistant than S plants to triallate treatment, both types were equally sensitive to in vitro synthesized triallate sulfoxide. In addition, [1-14C]triallate sulfoxide was metabolized to the same endproducts and at the same rate in R and S plants. The data indicate that resistance is conferred by a reduced rate of triallate sulfoxidation and represent the first documented case of herbicide resistance in plants conferred by reduced metabolism.
Bibliographical noteFunding Information:
This work was partially supported by the Montana Agricultural Experiment Station, the Monsanto Company, and the Montana Noxious Weed Trust Fund. We thank Dr. Amy Hackett and the Monsanto Co. for the kind gifts of [14C]triallate and 14C-labeled TCPSA. The excellent technical assistance of Tracey Myers is much appreciated.