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The effectiveness of bensulfuron-methyl in controlling Schoenoplectiella juncoides (Roxb.) Lye has significantly decreased in rice fields in China. Hence, a bensulfuron-methyl-resistant S. juncoides population (W15) was collected from Dandong City, Liaoning Province, China, to investigate the underlying resistance mechanisms. Whole-plant dose-response experiments and ALS activity assay confirmed that W15 has evolved high-level resistance to bensulfuron-methyl compared with the susceptible S. juncoides population (W4). Molecular analysis revealed a Pro-197-Ser mutation in ALS1 , while there was no significant difference in the relative ALS gene expression between W15 and W4. LC-MS/MS analysis showed W15 metabolized bensulfuron-methyl more rapidly than W4. Furthermore, bensulfuron-methyl resistance in W15 was significantly alleviated by malathion and 4-chloro-7-nitrobenzoxadiazole (NBD-Cl). Glutathione S -transferase activity was higher in W15 than in W4. Meanwhile, W15 displayed cross-resistance to halosulfuron-methyl and multi-resistance to MCPA-Na. In summary, these findings demonstrated for the first time that both target- and non-target-site resistance are relevant in the resistance of S. juncoides to bensulfuron-methyl. [Display omitted] • Schoenoplectiella juncoides has evolved high-level resistance to bensulfuron-methyl in Liaoning, China. • A Pro-197-Ser mutation was found in bensulfuron-methyl-resistant Schoenoplectiella juncoides. • Increased metabolism enhances Schoenoplectiella juncoides resistance to bensulfuron-methyl. • Bensulfuron-methyl-resistant Schoenoplectiella juncoides exhibited resistance to halosulfuron-methyl and MCPA-Na. [ABSTRACT FROM AUTHOR]

The evolution of herbicide resistance in weeds has emerged as one of the most serious threats to sustainable food production systems, which necessitates the evaluation of herbicides to determine their efficacy. The first herbicide resistance case in the Iberian Peninsula was reported about 50 years ago, wherein Panicum dichotomiflorum was found to be resistant (R) to atrazine in Spanish maize fields. Since then, herbicide resistance has evolved in 33 weed species, representing a total of 77 single-herbicide-resistance cases in this geographic area: 66 in Spain and 11 in Portugal. Changes in agricultural practices, namely the adoption of non-tillage systems and the increased use of herbicides, led to the selection of weed biotypes resistant to a wide range of herbicides. Nowadays the most important crops in Spain and Portugal (maize, winter cereals, rice, citrus, fruits, and olive orchards) are affected, with biotypes resistant to several mechanisms of action (MoAs), namely: ALS inhibitors (20 species), ACCase inhibitors (8 species), PS II inhibitors (18 species), and synthetic auxin herbicides (3 species). More recently, the fast increase in cases of resistance to the EPSPS-inhibiting herbicide glyphosate has been remarkable, with 11 species already having evolved resistance in the last 10 years in the Iberian Peninsula. The diversity of resistance mechanisms, both target-site and non-target-site, are responsible for the resistance to different MoAs, involving point mutations in the target site and enhanced rates of herbicide detoxification, respectively. More serious are the 13 cases reported with multiple-herbicide resistance, with three cases of resistance to three–four MoAs, and one case of resistance to five MoAs. Future research perspectives should further study the relationship between management strategies and the occurrence of TSR and NTSR resistance, to improve their design, develop monitoring and diagnostic tools for herbicide resistance, and deepen the study of NTSR resistance. [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]