Target-site resistance to trifluralin is more prevalent in annual ryegrass populations from Western Australia.

BACKGROUND Trifluralin is widely used in Australia as one of the important pre-emergence herbicides to control annual ryegrass (Lolium rigidum Gaud.) populations. Trifluralin resistance evolution and mechanisms have been identified in some ryegrass populations. RESULTS In this study, 21 putative resistant field survey populations from Western Australian were screened with trifluralin, and 90% (19 out of 21) contained individuals surviving 480 g/ha trifluralin treatment. Twelve populations contained individuals possessing the known α-tubulin resistance mutations at Val-202, Thr-239 and Arg-243 in TUA4, plus multiple potential resistance mutations in TUA4 pending for genetic confirmation. Three populations only had individuals carrying newly identified (but uncharacterised) mutations in TUA3/TUA4. Radioactive work found that six populations evolved metabolic resistance to trifluralin, and at least four of them also possessed the known and/or putative target-site mutations. CONCLUSION These results confirm that a high incidence of resistance to the dinitroaniline herbicide (trifluralin) is present, and target-site tubulin mutations make a major contribution to resistance in these annual ryegrass populations. Co-evolution of both target-site and non-target-site resistance to per-emergence herbicides warrants diverse management tactics. This article is protected by copyright. All rights reserved.