Mechanisms of multiple herbicide resistance in Lolium rigidum

Abstract

Herbicide-resistant populations of Lolium rigidum infest more than 8,000 farms in southern Australia. These populations may be resistant to one or more herbicides from many modes of action including inhibitors of lipid biosynthesis, branched-chain amino acid biosynthesis, photosynthesis, tubulin polymerization, carotenoid biosynthesis, or aromatic amino acid biosynthesis. The mechanisms of resistance have been extensively studied, and populations with herbicide-insensitive acetyl-coenzyme A carboxylase and acetolactate synthase enzymes are known. In addition, many populations have the ability to rapidly metabolize a number of herbicides from several different modes of action. In contrast, the mechanism of resistance to glyphosate is due to neither an insensitive target site, nor to more rapid glyphosate metabolism. L. rigidum populations readily accumulate multiple resistance mechanisms and this creates major difficulties in managing this ubiquitous grass weed.