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The Lolium genus encompasses many species that colonize a variety of disturbed and non-disturbed environments. Lolium perenne L. spp. perenne , L. perenne L. spp. multiflorum , and L. rigidum are of particular interest to weed scientists because of their ability to thrive in agricultural and non-agricultural areas. Herbicides are the main tool to control these weeds; however, Lolium spp. populations have evolved multiple- and cross-resistance to at least 14 herbicide mechanisms of action in more than 21 countries, with reports of multiple herbicide resistance to at least seven mechanisms of action in a single population. In this review, we summarize what is currently known about non-target-site resistance in Lolium spp. to acetyl CoA carboxylase, acetohydroxyacid synthase, microtubule assembly, photosystem II, 5-enolpyruvylshikimate-3-phosphate synthase, glutamine synthetase, very-long chain fatty acids, and photosystem I inhibitors. We suggest research topics that need to be addressed, as well as strategies to further our knowledge and uncover the mechanisms of non-target-site resistance in Lolium spp. [ABSTRACT FROM AUTHOR]

Multiple-herbicide resistant (MHR) weeds are a global problem and a looming threat to weed control in crops. MHR weeds express a specific phi class glutathione transferase (MHR-GSTF) which seems to contribute to herbicide resistance. The present work aims to investigate the structure and catalytic properties of the MHR-GSTFs from different grass weeds and crops (Alopecurus myosuroides , Lolium rigidum , Hordeum vulgare , Triticum aestivum). Recombinant MHR-GSTFs were expressed in E. coli and purified by affinity chromatography. Kinetic analysis of substrate specificity using a range of thiol substrates and xenobiotic compounds suggested that all enzymes display a broad range of specificity and are capable of detoxifying major stress-induced toxic products. Notably, all tested enzymes exhibited high activity towards organic hydroperoxides. The crystal structure of MHR-GSTF from Alopecurus myosuroides (Am GSTF) was determined by molecular replacement at 1.33 Å resolution. The enzyme was resolved with bound glutathione sulfenic acid (GSOH) at the G-site and succinic acid at the H-site. The enzyme shows conserved structural features compared to other Phi class GSTs. However, some differences were observed at the C-terminal helix H9 that may affect substrate specificity. The structural and functional features of Am GSTF were compared with those of the homologue crop enzymes (Hv GSTF and Ta GSTF) and discussed in light of their contribution to the MHR mechanism. • MHR weeds are a global problem and a looming threat to weed control in crops. • MHR weeds express a specific phi class GST which contributes to herbicide resistance. • The properties of the MHR-GSTFs from different grass weeds and crops were studied. • Recombinant MHR-GSTFs are capable of detoxifying stress-induced toxic metabolites. • The structure of a GSTF from A. myosuroides was determined by X-ray crystallography. [ABSTRACT FROM AUTHOR]

Italian ryegrass (Lolium multiflorum Lam.) is a highly competitive grass weed capable of severely infesting wheat fields worldwide. In recent years, Chinese farmers are finding it increasingly difficult to control L. multiflorum when using acetyl-CoA carboxylase (ACCase)-inhibiting herbicides. Accordingly, clarifying the resistance pattern of putative resistant populations of L. multiflorum is important for selecting alternative herbicides for effective weed control. In this study, a putative resistant L. multiflorum population, HN-03, which apparently has survived clodinafop-propargyl treatment under the recommended field application rate, was collected from a wheat field in Zhumadian, Henan, China. Whole-plant bioassay revealed that the HN-03 population had evolved high-level resistance to clodinafop-propargyl. Sequencing of the ACCase gene revealed a point mutation, of TGG to TGT, at codon position 1999, causing a Trp-to-Cys substitution in the resistant plants. The HN-03 population also exhibited cross-resistance to fenoxaprop- P -ethyl, clethodim, and pinoxaden and multiple-resistance to mesosulfuron-methyl and bixlozone, but it remained susceptible to cypyrafluone. Pre-treatment with piperonyl butoxide and malathion considerably increased the susceptibility of the HN-03 population to fenoxaprop- P -ethyl and mesosulfuron-methyl, by 25.3% and 36.6%, respectively. This study shows the L. multiflorum population HN-03 has evolved multiple herbicide resistance due to both a target-site mutation and P450s-mediated enhanced metabolism. Cypyrafluone can be used as an alternative herbicide to control resistant L. multiflorum , and it might be potentially helpful for improving the management of herbicide resistance in other aggressive weeds. [Display omitted] • A Chinese L. multiflorum population was found resistant to clodinafop-propargyl. • Cross- and multiple-resistance patterns were determined for the population. • Target-site gene mutation was detected in the resistant plants. • P450s-involved enhanced metabolism also played a role in resistance phenotypes. [ABSTRACT FROM AUTHOR]

Multiple-herbicide resistance (MHR) in barnyardgrass (Echinochloa crus-galli) is a threat to rice production. The Ala-205-Val mutation in acetolactate synthase (ALS) conferred resistance to several ALS inhibitors in the E. crus-galli population AXXZ-2; consequently, ALS-inhibitors were unable to control this noxious weed species. In the present study, the sensitivity to acetyl-coenzyme A carboxylase (ACCase) herbicides and other herbicides having different modes of action was evaluated to determine an effective strategy for chemical weed control. Compared with that of the reportedly sensitive population JLGY-3, the AXXZ-2 population showed differential resistance to three ACCase-inhibitors (cyhalofop-butyl, fenoxaprop-P-ethyl, and pinoxaden), in addition to quinclorac and pretilachlor. A novel substitution (Asp-2078-Glu) in ACCase was detected as the main target-site resistance mechanisms in the AXXZ-2 population. Structural modeling of the mutant ACCase protein predicted that Asp-2078-Glu confers resistance to three ACCase inhibitors by reducing the binding affinity between them and the ACCase protein. To the best of our knowledge, this is the first study to report that the novel Asp-2078-Glu mutation confers resistance to several ACCase inhibitors. Target-site mutations in ALS and ACCase were detected in this MHR population. Except for quinclorac, pretilachlor, ALS inhibitors, and the three ACCase inhibitors, a number of herbicides remain effective in controlling this MHR E. crus-galli population. Unlabelled Image • A novel mutation (Asp-2078-Glu) in ACCase conferred target-site resistance to ACCase herbicides. • Structural modeling partialy explain why the mutation conferred the unique cross-resistance pattern to ACCase herbicides. • Potential chemical management strategy for this MHR population was generated. [ABSTRACT FROM AUTHOR]