TRIALLATE RESISTANCE IN AVENA-FATUA L IS DUE TO REDUCED HERBICIDE ACTIVATION

Extensive use of triallate, a preemergence herbicide used for wild oat (Avena fatua L.) control in cereal crops, has selected for resistant (R) wild oat populations. Triallate is thought to be activated via met abolic sulfoxidation to create the more potent triallate sulfoxide. Tr eatment of R and susceptible (S) wild oat lines with [1-C-14]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 p lants. Dose-response studies indicated that although R plants were 6- to 20-fold more resistant than S plants to triallate treatment, both t ypes were equally sensitive to in vitro synthesized triallate sulfoxid e. In addition, [1-C-14]triallate sulfoxide was metabolized to the sam e endproducts and at the same rate in R and S plants. The data indicat e that resistance is conferred by a reduced rate of triallate sulfoxid ation and represent the first documented case of herbicide resistance in plants conferred by reduced metabolism. (C) 1996 Academic Press.