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Summary Populations of Polypogon fugax have developed resistance to many acetyl‐CoA carboxylase (ACCase)‐inhibiting herbicides. This resistance threats the effectiveness and sustainability of herbicide use. In our previous research, a field P. fugax population exhibited GST‐based metabolic resistance to the widely used ACCase‐inhibiting herbicide quizalofop‐p‐ethyl. Here, in this current study, we identified and characterized two GST genes (named as PfGSTF2 and PfGSTF58) that showed higher expression levels in the resistant than the susceptible population. Transgenic rice calli overexpressing PfGSTF2, but not PfGSTF58, became resistant to quizalofop‐p‐ethyl and haloxyfop‐R‐methyl. This reflects similar cross‐resistance pattern to what was observed in the resistant P. fugax population. Transgenic rice seedlings overexpressing PfGSTF2 also exhibited resistance to quizalofop‐p‐ethyl. In contrast, CRISPR/Cas9 knockout of the orthologue gene in rice seedlings increased their sensitivity to quizalofop‐p‐ethyl. LC–MS analysis of in vitro herbicide metabolism by Escherichia coli‐expressed recombinant PfGSTF2 revealed that quizalofop (but not haloxyfop) was detoxified at the ether bond, generating the GSH‐quizalofop conjugate and a propanoic acid derivative with greatly reduced herbicidal activity. Equally, these two metabolites accumulated at higher levels in the resistant population than the susceptible population. In addition, both recombinant PfGSTF2 and PfGSTF58 can attenuate cytotoxicity by reactive oxygen species (ROS), suggesting a role in plant defence against ROS generated by herbicides. Furthermore, the GST inhibitor (NBD‐Cl) reversed resistance in the resistant population, and PfGSTF2 (but not PfGSTF58) responded to NBD‐Cl inhibition. All these suggest that PfGSTF2 plays a significant role in the evolution of quizalofop resistance through enhanced herbicide metabolism in P. fugax.

A 28 days pesticide degradation experiment was conducted for broccoli ( Brassica oleracea L. var. italica Planch) and pakchoi ( Brassica chinensis L.) with three pesticides (chlorantraniliprole (CAP), haloxyfop-etotyl (HPM), and indoxacarb (IXB)) to explore the effects of biochar on pesticide environmental fate and rhizosphere soil diversity. Rice straw biochar (RB) was applied to soil at a 25.00 t ha −1 dosage under greenhouse conditions, and its effects on the degradation of three pesticides in vegetables and in soil were investigated individually. Overall, RB application effectively facilitated CAP and HPM degradation in broccoli by 13.51–39.42% and in broccoli soil by 23.80–74.10%, respectively. RB application slowed the degradation of CAP, HPM and IXB in pakchoi by 0.00–57.17% and slowed the degradation of CAP in pakchoi by 37.32–43.40%. The results showed that the effect of RB application on pesticide degradation in crops and soil was related to biochar properties, pesticide solubility, plant growth status, and soil characteristics. Rhizosphere soil microorganisms were also investigated, and the results showed that biochar application may be valuable for altering bacterial richness and diversity. The effect of biochar application on pesticide residues in crops and soil was influenced by the vegetable variety first, and the second was pesticide characteristics. RB applied to soil at a 25.00 t ha −1 dosage under greenhouse conditions is recommended for broccoli production to ensure food safety. Our results suggested that biochar application in soil could reduce pesticide non-point source pollution, especially for highly soluble pesticides, and could affect soil microorganisms.

This study was developed based on a goosegrass [Eleusine indica (L.) Gaertn.] population from Primavera do Leste, MT, Brazil, with resistance to multiple herbicide modes of action (5-enol-pyruvylshikimate-3-phosphate synthase [EPSPS] inhibition: glyphosate; acetyl-coenzyme A carboxylase [ACCase] inhibition: aryloxyphenoxypropionate chemical group). The objective was to identify possible mechanisms of resistance associated or not with herbicide sites of action. Several experiments and analyses were carried out with the contribution of different laboratories and institutions. The results obtained allowed us to conclude that: (1) the Asp-2078-Gly mutation conferred resistance to ACCase inhibitors, without overexpression of ACCase or changes in herbicide absorption and translocation; (2) overexpression of EPSPS, Thr-102 and Pro-106 mutations, and changes in absorption and translocation are not involved in E. indica resistance to glyphosate; (3) the metabolism of glyphosate in resistant E. indica plants requires further studies to elucidate the final destination of this herbicide in these plants. The mechanism of resistance of E. indica biotypes to ACCase-inhibiting herbicides was elucidated: it involves a change in the action site. However, the mechanism of resistance to EPSPS inhibitors was not conclusive, indicating that some hypotheses, mainly those regarding the metabolism of glyphosate in resistant plants, require further testing.

Spartina alterniflora is one of the most noxious invasive plants in China and many other regions. Exploring environmentally friendly, economic and effective techniques for controlling Spartina alterniflora is of great significance for the management of coastal wetlands. In the present study, different approaches, including mowing and waterlogging, mowing and tilling and herbicide application, were used to control Spartina alterniflora . The results suggest that the integrated approach of mowing and waterlogging could eradicate Spartina alterniflora , the herbicide haloxyfop-r-methyl could kill almost all the Spartina alterniflora , and the integrated approach of mowing and tilling at the end of the growing season was a perfect way to inhibit the germination of Spartina alterniflora in the following year. However, no matter which control approach is adopted, secondary invasion of Spartina alterniflora must be avoided. Otherwise, all the efforts will be wasted in a few years.

ABSTRACT Sequential crops may be affected by herbicide residuals in the soil. In corn crop there are reports of problems when the crop is sown soon after application of ACCase-inhibiting herbicides. The aim of this study was to evaluate safety intervals for the application of ACCase-inhibiting herbicides before sowing corn in different soils. Two experiments were conducted in a greenhouse, and in the field conditions. In both, the experimental design were completely randomized in factorial scheme 6x4+1 (6 periods of application x 4 herbicides + 1 control) with five replications. The treatments were: haloxyfop-P-methyl (124.7 g ha-1), clethodim – formulation 1 (192 g ha-1), quizalofop-P-ethyl (100 g ha-1) and clethodim formulation 2 (192 g ha-1) in applications at 15, 10, 5, 3, 1 and 0 days before sowing in sandy and clayey soil. In the greenhouse, formulations based on clethodim were more safety in both types of soils, and safety intervals for clethodim-based herbicides were 5 days and greater than 15 days for quizalofop-P-ethyl and haloxyfop. Haloxyfop should not be applied on day of sowing in clay soil. In the field none of the treatments compromised the development and yield of the crop, even when applied on the day of sowing.

In compliance with Article 43 of Regulation (EC) No 396/2005, the European Food Safety Authority (EFSA) received a mandate from the European Commission to perform a targeted review of the existing maximum residues levels (MRLs) for the active substance haloxyfop‐P to check whether the existing EU MRL in onions, sunflower seeds and soya beans (covering codex maximum residue limits (CXLs) or import tolerances) and the proposed import tolerance MRLs in linseeds, rapeseeds/canola seeds are safe for consumers and can eventually be maintained in the MRL Regulation after the expiry of the approval of the active substance. EFSA screened these MRLs considering the toxicological reference values established during the EU peer review process for the renewal of the approval of haloxyfop‐P and identified chronic consumer intake concerns for two diets when for the remaining plant and animal commodities, the input values were at the LOQ. Fall‐back MRLs could not be proposed, but the additional information provided by EURLs allowed to resolve the chronic intake concerns using lower validated LOQs for a range of plant commodities and milk. EFSA concludes that the existing EU MRLs in soya beans and onions, the CXL in sunflower seeds and the proposed import tolerances in linseed and rapeseed/canola seeds are not expected to pose a risk to consumers. However, to guarantee consumer's safety regarding the chronic exposure to haloxyfop‐P residues, the enforcement LOQs in several plant commodities and milks would have to be lowered to the levels reported by the EURLs.

Digitaria insularis poses a significant challenge in weed control due to its perennial habit, dense clumping growth, and the widespread presence of herbicide-resistant biotypes. Our research investigates whether single or multiple herbicide resistance biotypes of D. insularis experience fitness costs, specifically affecting their germination. To determine the resistance factor, a dose-response curve was employed using glyphosate and haloxyfop-P-methyl herbicides separately in a completely randomized design (CRD) with four replicates per dose (nine doses total). Shoot dry mass was measured at 100 days after herbicide application (DAA), with control assessments performed at 14, 28, and 42 DAA. Subsequently, a separate CRD experiment examined the germination rate as a function of temperature and photoperiod for each biotype. This factorial scheme tested six temperatures across three biotypes (susceptible and two resistant types) under three light exposure periods (0, 8, and 12 hours). Germination percentage and the germination speed index (GSI) were calculated for 14 days, with counts of healthy seedlings recorded daily. Statistical analysis confirmed the resistance/susceptibility of the biotypes based on the dose-response curve. For the susceptible and simple resistance biotypes, the most favorable temperatures for germination were 20, 30 and 40 °C, at which the highest germination percentages and a higher germination speed index were observed. On the other hand, for the biotype with multiple resistance, the temperatures of 25, 30 and 35 °C were more favorable, promoting superior results in both parameters studied.

Understanding the mechanism of herbicide resistance is fundamental for designing sustainable weed control strategies and exploiting herbicides rationally. Shortawn foxtail is a problem grass weed infesting several important crops in China. The repeated use of acetyl-CoA carboxylase (ACCase)-inhibiting herbicides has resulted in herbicide resistance in this weed. The ACCase gene of resistant individuals of a shortawn foxtail population (JSLS-1) has an Ile-2041-Thr mutation. F2 generation seeds, originated from the same heterozygous plant, were harvested, and two homozygous mutant (JSLS-1RR) and wild (JSLS-1SS) populations for the Ile-2041-Thr mutation were obtained. In whole plants, the JSLS-1RR population conferred high resistance to fenoxaprop and clodinafop, moderate resistance to haloxyfop, low resistance to pinoxaden, and no obvious resistance to clethodim and sethoxydim, compared with JSLS-1SS and a proven susceptible population (HNXY-1). A derived cleaved amplified polymorphic sequence (dCAPS) marker was developed to rapidly detect the rare Ile-2041-Thr mutation in the shortawn foxtail population. This is the first report of the cross-resistance pattern of Ile-2041-Thr mutation, and the robust dCAPS marker could quickly detect this mutation in shortawn foxtail. Nomenclature: Clethodim, clodinafop, fenoxaprop, haloxyfop, pinoxaden, sethoxydim, shortawn foxtail, Alopecurus aequalis Sobol.

Control of glyphosate-resistant (GR) junglerice is a challenging task in eastern Australia. There is limited information on the efficacy and reliability of alternate herbicides for GR populations of junglerice, especially when targeting large plants and when temperatures are high. A series of experiments were conducted to confirm the level of glyphosate resistance in three populations of junglerice and to evaluate the efficacy of alternate herbicides for the control of GR junglerice populations. The LD50 of glyphosate of B17/7, B17/34, and B17/35 populations was found to be 298, 2,260, and 1,715 g ae ha–1, respectively, suggesting that populations B17/34 and B17/35 were highly resistant to glyphosate. Glyphosate efficacy was reduced at high-temperature (35 C day/25 C night) compared with low-temperature conditions (25 C day/15 C night), suggesting that control of susceptible populations may also be reduced if glyphosate is sprayed under hot conditions. Preemergence herbicides dimethenamid-P (1,000 g ai ha–1) and pendimethalin (1,500 g ai ha–1) provided 100% control of GR populations (B17/34 and 17/35). Postemergence herbicides, such as clethodim (60 or 90 g ai ha–1), glufosinate (750 g ai ha–1), haloxyfop (52 or 78 g ai ha–1), and paraquat (400 or 600 g ai ha–1), applied at the four-leaf stage provided 100% control of GR populations. For larger junglerice plants (eight-leaf stage), postemergence applications of paraquat (400 or 600 g ai ha–1) provided greater weed control than clethodim, glufosinate, and haloxyfop. A mixture of either glufosinate or haloxyfop with glyphosate provided poor control of GR junglerice populations compared with application of glufosinate or haloxyfop applied alone. Efficacy of glufosinate and haloxyfop for the control of GR populations decreased when applied in the sequential spray after glyphosate application. This study identified alternative herbicide options for GR junglerice populations that can be used in herbicide rotation programs for sustainable weed management. Nomenclature: Clethodim; dimethenamid-P; glufosinate; glyphosate; haloxyfop; paraquat; pendimethalin; junglerice; Echinochloa colona (L.) Link

The acetyl-coenzyme A carboxylase (ACCase)-inhibiting cyclohexanedione herbicide clethodim is used to control grass weeds infesting dicot crops. In Australia clethodim is widely used to control the weed Lolium rigidum. However, clethodim-resistant Lolium populations have appeared over the last 5 years and now are present in many populations across the western Australian wheat (Triticum aestivum) belt. An aspartate-2078-glycine (Gly) mutation in the plastidic ACCase enzyme has been identified as the only known mutation endowing clethodim resistance. Here, with 14 clethodim-resistant Lolium populations we revealed diversity and complexity in the molecular basis of resistance to ACCase-inhibiting herbicides (clethodim in particular). Several known ACCase mutations (isoleucine-1781-leucine [Leu], tryptophan-2027-cysteine [Cys], isoleucine-2041-asparagine, and aspartate-2078-Gly) and in particular, a new mutation of Cys to arginine at position 2088, were identified in plants surviving the Australian clethodim field rate (60 g ha⁻¹). Twelve combination patterns of mutant alleles were revealed in relation to clethodim resistance. Through a molecular, biochemical, and biological approach, we established that the mutation 2078-Gly or 2088-arginine endows sufficient level of resistance to clethodim at the field rate, and in addition, combinations of two mutant 1781-Leu alleles, or two different mutant alleles (i.e. 1781-Leu/2027-Cys, 1781-Leu/2041-asparagine), also confer clethodim resistance. Plants homozygous for the mutant 1781, 2078, or 2088 alleles were found to be clethodim resistant and cross resistant to a number of other ACCase inhibitor herbicides including clodinafop, diclofop, fluazifop, haloxyfop, butroxydim, sethoxydim, tralkoxydim, and pinoxaden. We established that the specific mutation, the homo/heterozygous status of a plant for a specific mutation, and combinations of different resistant alleles plus herbicide rates all are important in contributing to the overall level of herbicide resistance in genetically diverse, cross-pollinated Lolium species.