Pyroxasulfone Resistance in Lolium rigidum Conferred by Enhanced Metabolic Capacity

Abstract

Author ContributionsRB and AP designed and performed the experiments. RB, AP, TG, SP wrote the manuscript.\n\nOne sentence summaryThis study provides novel insight into herbicide resistance conferred by GST-based detoxification to allow proactive intervention to minimize weed resistance evolution.\n\nAbstractThe evolution of herbicide-resistant weed populations in response to synthetic herbicide selective pressure is threatening safe weed control practices achieved by these molecules. In Australia multiple-resistant populations of annual ryegrass (Lolium rigidum) are effectively controlled by soil-applied herbicides which provide adequate weed control.\n\nIn this study we define the mechanistic basis of the experimentally-evolved resistance to the soil-applied herbicide pyroxasulfone in a L. rigidum population. TLC and HPLC-MS provide biochemical confirmation that pyroxasulfone resistance is metabolism-based with identification and quantification of pyroxasulfone metabolites formed via a glutathione conjugation pathway in pyroxasulfone-resistant L. rigidum plants. The observed over-expression of two putative resistance-endowing GST genes is consistent with pyroxasulfone-resistance in parental plants (P6) and positively correlated to pyroxasulfone resistance in F1 pair-cross progenies. Thus, a major detoxification mechanism involves glutathione conjugation to pyroxasulfone and GST over-expression in pyroxasulfone-resistant L. rigidum plants. The definition of the genetic basis of metabolic resistance in weeds can be a first crucial step towards chemical means to reverse resistance and improve long-term weed resistance management.