Cross-resistance pattern to ACCase-inhibiting herbicides in a novel Trp1999Leu mutation American sloughgrass (Beckmannia syzigachne) population

The mutation Asp-376-Glu in the ALS gene confers resistance to mesosulfuron-methyl in Beckmannia syzigachne

Understanding the mechanisms by which weeds develop herbicide resistance is crucial for managing resistance effectively and optimizing herbicide use. Beckmannia syzigachne, a harmful grass weed prevalent in wheat and rice-wheat rotation areas, poses a significant threat to crop productivity. A field herbicide resistance survey identified a resistant population with a new ALS mutation (Asp-376-Glu). The Glu-376-Asp population displayed varying resistance levels to seven ALS herbicides, verified using the dCAPS method. qRT-PCR analysis showed that no significant difference existed in the ALS gene expression between the Asp-376-Glu and S populations. P450 and GST inhibitors failed to reverse resistance to mesosulfuron-methyl, suggesting no involvement of P450- and GST-based metabolic resistance. Molecular docking indicated that the Asp-376-Glu mutation reduces the binding affinity between ALS-inhibitors and BsALS. The findings provide valuable insights into herbicide resistance mechanisms for weed resistance control.

The Cys-2088-Arg mutation in the ACCase gene and enhanced metabolism confer cyhalofop-butyl resistance in Chinese sprangletop (Leptochloa chinensis)

Acetyl-CoA carboxylase (ACCase)-inhibiting herbicides are among the most commonly used herbicides to control grassy weeds, especially Leptochloa chinensis, in rice fields across China. Herein, we collected a suspected resistant (R) population of L. chinensis (HFLJ16) from Lujiang county in Anhui Province. Whole plant dose response tests showed that, compared with the susceptible (S) population, the R population showed high resistance to cyhalofop-butyl (22-fold) and displayed cross-resistance to metamifop (9.7-fold), fenoxaprop-P-ethyl (18.7-fold), quizalofop-P-ethyl (7.6-fold), clodinafop-propargyl (12-fold) and clethodim (8.4-fold). We detected an amino acid substitution (Cys-2088-Arg) in the ACCase of resistant L. chinensis. However, ACCase gene expression levels were not significantly different (P > 0.05) between R plants and S plants, without or with cyhalofop-butyl treatment. Furthermore, pretreatment with piperonyl butoxide (PBO, a cytochrome P450 monooxygenase (CYP450) inhibitor) or 4-chloro-7-nitrobenzoxadiazole (NBD-Cl, a glutathione-S-transferase (GST) inhibitor), inhibited the resistance of the R population to cyhalofop-butyl significantly (by approximately 60% and 26%, respectively). Liquid chromatography tandem mass spectrometry analysis showed that R plants metabolized cyhalofop-butyl and cyhalofop acid (its metabolite) significantly faster than S plants. Three CYP450 genes, one GST gene, and two ABC transporter genes were induced by cyhalofop-butyl and were overexpressed in the R population. Overall, GST-associated detoxification, CYP450 enhancement, and target-site gene mutation are responsible for the resistance of L. chinensis to cyhalofop-butyl.

Evolution of ACCase-inhibitor resistance in Chloris virgata is conferred by a Trp2027Cys mutation in the herbicide target site

BACKGROUND

Chloris virgata is a troublesome weed in tropical regions. With the evolution of glyphosate resistance in key grass species, acetyl CoA carboxylase (ACCase) inhibitors have become a commonly used tool in soybean production areas in Brazil. We assessed if suspected resistant populations exhibited cross resistance to the different classes of ACCase inhibitors and investigated the resistance mechanisms in C. virgata.

RESULTS

Dose-response experiments revealed resistance to haloxyfop-methyl and pinoxaden, with 432- and 3-fold resistance, respectively, compared to susceptible populations. Due to the lack of genetic resources for C. virgata, we sequenced, assembled, and annotated the genome using short-read Illumina technology. The k-mer analysis estimated a genome size of approximately 336 Mbp, with BUSCO completeness of 97%, and over 36 000 gene models were annotated. We examined if ACCase copy number variation and increased gene expression were involved in the resistance phenotype and found no difference when compared to a susceptible population. A mutation was detected in ACCase that encodes for amino acid position 2027, resulting in a tryptophan-to-cysteine (Trp2027Cys) substitution. We found the resistant population absorbed 11.4% less herbicide and retained 21% more herbicide on the treated leaf compared to the susceptible population. We developed a genotyping assay targeting the resistance-endowing Trp2027Cys substitution for quick resistance diagnosis.

CONCLUSION

A Trp2027Cys amino acid substitution in ACCase confers resistance to haloxyfop and pinoxaden in C. virgata. We provide important insights into the evolutionary history of C. virgata and a draft genome as a useful resource to further our understanding of the biology in the genus Chloris. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A pH-responsive MOF-functionalized hollow mesoporous silica controlled herbicide delivery system exhibits enhanced activity against ACCase-herbicide-resistant weeds

BACKGROUND

Weeds grow aggressively in agricultural fields, leading to reduced crop yields and an inability to meet the growing demand for food. Herbicides are currently the most effective method for weed control. However, the overuse of herbicides has resulted in the evolution of resistance mutants and has caused environmental pollution. Therefore, new technologies are urgently required to address this global challenge.

RESULTS

We report a copper-benzene-1,4-dicarboxylate metal organic framework (Cu-BDC MOF)-functionalized carboxyl hollow mesoporous silica (HMS-COOH) delivery system for the pH-controlled release of the acetyl-CoA carboxylase (ACCase)-inhibiting herbicide quizalofop-p-ethyl (QE). The delivery system (QE@HMS@Cu-BDC) enabled the efficient control of barnyard grasses that are susceptible and resistant to ACCase-inhibiting herbicides, which showed 93.33% and 88.33% FW control efficacy at 67.5 g ha-1 , respectively. With the lowest pH value (3), QE and copper ion were released slowly to total 70.30% and 78.55% levels (respectively) from QE@HMS@Cu-BDC after 89 h. QE@HMS@Cu-BDC showed better absorption, conduction, transportation and ACCase activity inhibition performance than that of QE emulsifiable concentrate (EC) in both susceptible and ACCase-herbicide resistant barnyard grasses. In addition, with the safener effect of carrier HMS@Cu-BDC and the aid of the safener fenchlorazole-ethyl (FE), the application of QE@HMS@Cu-BDC was shown to mitigate the damage caused by QE to rice plants.

CONCLUSION

This work found that the new material HMS-COOH@Cu-BDC can be used to mitigate herbicide-induced oxidative stress and improve rice plant safety. Futhermore, the QE@HMS-COOH@Cu-BDC constructed in this research might be used as an efficient nanopesticide formulation for weed controls in paddy rice fields. © 2023 Society of Chemical Industry.

Cross-resistance of barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] to aryloxyphenoxypropionate herbicides

Managing emerged weeds that have evolved resistance to acetyl CoA carboxylase (ACCase)-inhibiting herbicides is a challenging task. A dose-response experiment was conducted on barnyardgrass biotypes resistant (R) and susceptible (S) to three aryloxyphenoxypropionate herbicides cyhalofop-butyl (CyB), fenoxaprop-ethyl (FeE), and quizalofop-ethyl (QuE) along with investigations into the potential resistance mechanism of these biotypes. The tested R barnyardgrass biotypes had strong resistance to CyB and FeE (resistant/susceptible ratio: 7.9-14.4) but weak resistance to QuE (resistant/susceptible ratio: 2.4-3.1). Absorption, translocation, and total metabolism of CyB and QuE were not associated with differences among S and R barnyardgrass biotypes. However, differences between S and R barnyardgrass were observed in production of active acid forms of each herbicide (cyhalofop-acid and quizalofop-acid). Production of cyhalofop-acid was >1.6-fold less in R barnyardgrass (3-8%) for 24 h after herbicide application than in the S barnyardgrass (8-16%). Meanwhile, production of quizalofop-acid was less in R barnyardgrass (< 14%) throughout the study period than in the S barnyardgrass (< 22%). Sequencing results of ACCase gene showed no difference between S and R barnyardgrass. Overall results show that a non-target-site resistance mechanism altering metabolism of CyB and QuE likely contributes to resistance of the barnyardgrass biotypes to these herbicides.

Multiple resistance to ACCase- and ALS-inhibiting herbicides in black-grass (Alopecurus myosuroides Huds.) in China

Two black-grass (Alopecurus myosuroides Huds.) populations (R2105 and R1027) that were suspected to be resistant to clodinafop-propargyl, an acetyl-CoAcarboxylase (ACCase) inhibitor, were found in winter wheat fields in China. Research was carried out to investigate whether resistance to clodinafop-propargyl was present and the molecular mechanism of herbicide resistance in these two populations. Dose-response assays confirmed high level resistance to clodinafop-propargyl in both R2105 and R1027 populations, with resistance indexes 25.1 and 22.1. ACCase gene sequence comparison revealed three amino acid mutations (Trp-1999-Leu, Ile-2041-Asn, or Asp-2078-Gly) in R2105 population and Ile-2041-Asn mutation in R1027 population. Sensitivity to other herbicides assays indicated that R2105 and R1027 populations were cross resistant to fenoxaprop-P-ethyl and multiple resistant to pyroxsulam and mesosulfuron-methyl. The ALS gene sequence analysis revealed that all resistant individuals in R2105 and R1027 populations had the Trp-574-Leu mutation. Applying malathion, significantly decreased the rate of metabolism of clodinafop-propargyl in both R2105 and R1027 populations. This is the first report of multiple resistance to ACCase- and ALS-inhibiting herbicides conferred by target-site mutations and enhanced metabolism in black-grass in China.

Pollen-mediated flow of herbicide resistance genes in Beckmannia syzigachne

BACKGROUND

Beckmannia syzigachne (Steud.) Fernald has evolved herbicide resistance due to the long-term sole use of herbicides and has become a dominant weed in wheat fields in the middle and lower reaches of the Yangtze River in China. In addition to the selection pressure imposed by herbicides, pollen-mediated gene flow (PMGF) has been reported to cause the spread of herbicide resistance between populations within a certain range in some farmland weeds. It is not clear whether the same is true for the self-pollinated grass weed B. syzigachne.

RESULTS

In this study, we confirmed and quantified the level of PMGF in B. syzigachne through concentric circle planting and herbicide resistance tests. Results show that when the B. syzigachne pollen donor was close to the recipient (0.5 m), the average gene flow was 0.66%. Gene flow was detected as far as 10 m (the farthest distance studied) and decreased exponentially with increasing distance, which could be described by a double exponential decay model. Temperature also affected gene flow, whilst the average level of gene flow in all directions of wind was similar and wind speed caused insignificant difference in gene flow.

CONCLUSION

The results of this study confirmed that PMGF can occur between B. syzigachne populations in adjacent fields. Although the level of resistance spreading by pollen was low, especially across long distance, the results were relevant for smallholding farms, which is the dominant form of agricultural operation in China. It is therefore important to take proactive measures and integrate chemical and ecological weed control methods to prevent the spread of resistant B. syzigachne via both seeds and pollens. © 2022 Society of Chemical Industry.

Intra- and cross-field dispersal of Beckmannia syzigachne seed by a combine harvester

BACKGROUND

Beckmannia syzigachne (Steud.) Fernald has become a dominant weed that has evolved resistance to major herbicides used in the wheat fields of rice-wheat double cropping areas of the middle and lower reaches of the Yangtze River, China. Seed dispersal occurs over long distances via irrigation water. As mechanical harvesting services popularize, there is concern that combine harvesters could play an increasing role in B. syzigachne seed dispersal.

RESULTS

Random sampling of 30 combine harvesters at wheat harvest determined that an average of 8000 B. syzigachne seeds remain in the combine after wheat harvesting, predominantly on the metal plate. These seeds could potentially be transported into adjacent fields. A double exponential model predicted that seeds remaining on the metal plate could be dispersed over 7885 m² into the next field. Within a field, the number of fallen seeds and their dispersal distance were positively correlated to panicle density. Combines spread seeds away from the source potentially creating new weed patches. During irrigation and rotary tillage ploughing, 70% of B. syzigachne seeds scattered in the field floated on the water surface and were moved away by the wind.

CONCLUSION

Both wheat combine harvesters and water flow effectively spread B. syzigachne seeds. Areas with high B. syzigachne population density should be carefully harvested separately, and the metal plate should be carefully cleaned to prevent spreading the weed across fields and region. Floating B. syzigachne seeds displaced to field edges by water can be physically removed with nets to prevent further distribution by water.

The Ile-2041-Val mutation in the ACCase gene confers resistance to clodinafop-propargyl in American sloughgrass (Beckmannia syzigachne Steud)

BACKGROUND

Exploring the mechanisms of herbicide resistance in weeds is an important part of designing resistance management strategies and rationalizing herbicide use. Beckmannia syzigachne is one of the most important agricultural weeds in China. Long-term use of acetyl-CoA carboxylase (ACCase)-inhibiting herbicides has led to the evolution of herbicide resistance in B. syzigachne. ACCase-inhibiting herbicides comprise three chemical families: aryloxyphenoxypropionates (APPs), cyclohexanediones (CHDs) and phenylpyraxoline (DENs).

RESULTS

Based on whole-plant dose-response experiments, a B. syzigachne population (BS-R) was confirmed to be 12- and 20-fold resistant to the APP herbicides quizalofop-P-ethyl and clodinafop-propargyl, and 2.2-, 2.8- and 2.8-fold resistant to fenoxaprop-P-ethyl, the CHD herbicide sethoxydim and the PPZ herbicide pinoxaden, respectively, compared with its susceptible counterpart (BS-S). Resistance to clodinafop-propargyl in the BS-R population could not be reversed by the known cytochrome P450 (CYP450) inhibitor malathion and the glutathione S-transferase (GST) inhibitor 4-chloro-7-nitrobenzoxadiazole. In addition, no difference in CYP450 and GST activity was confirmed between the BS-R and BS-S populations. ACCase gene sequencing revealed an Ile-2041-Val mutation in the BS-R population. A derived cleaved amplified polymorphic sequence marker was developed for rapid detection of the specific Ile-2041-Val mutation. Correlation quantification of resistance in homo- and hetero-resistant versus wild-type plants showed that resistance to clodinafop-propargyl in this population is conferred by the Ile-2041-Val mutation.

CONCLUSION

Unlike previous reports on the unique cross-resistance pattern conferred by the 2041 mutation, this study demonstrates that the Ile-2041-Val mutation in BS-R population confers resistance to certain ACCase-inhibiting APP, CHD and PPZ herbicides in B. syzigachne. © 2021 Society of Chemical Industry.

Pro-197-Ser Mutation in ALS and High-Level GST Activities: Multiple Resistance to ALS and ACCase Inhibitors in Beckmannia syzigachne

American sloughgrass (Beckmannia syzigachne Steud.) is one of the most troublesome weeds infesting wheat and canola fields in China. Some biotypes cannot be controlled, either by acetolactate synthase (ALS) or acetyl coenzyme A carboxylase (ACCase) inhibitors, which are the main herbicides for controlling this weed. However, very few studies have investigated multiple resistance mechanism in B. syzigachne. In this study, a B. syzigachne biotype with a high resistance to ALS inhibitors we have reported was also showed relatively lower resistance to ACCase inhibitors, with a resistance index around 7. RNA-seq analysis was used to investigate the factors responsible for multiple resistance, and 60,108 unigenes were assembled by de novo transcriptome assembly and then annotated across eight databases. A Pro-197-Ser mutation was identified in the ALS gene by SNPs analysis and validated by PCR, while no mutation was identified in the ACCase gene. Nineteen candidate metabolic genes were screened and their overexpression was confirmed by qPCR. The expression of GST-T3 and GST-U6 in resistant plants ranged from 7.5- to 109.4-folds than that in susceptible ones at different times after two kinds of herbicide treatment. In addition, GST activities in resistant plants were 3.0-5.0 times higher than that in susceptible plants. Other novel resistance factors also showed high correlation with multiple resistance which included four genes encoding disease resistance proteins, a transcription factor (MYC3), and one gene conferring blight resistance. In this research, a B. syzigachne biotype was confirmed to have evolved multiple resistance to ACCase and ALS inhibitors. The Pro-197-Ser mutation in ALS gene and high-level GST activities were confirmed responsible for the multiple resistance. Characterized disease-resistance proteins, transcription factor, and blight-resistance proteins may play an essential role in these multiple herbicide resistance.

Identification and expression of main genes involved in non-target site resistance mechanisms to fenoxaprop-p-ethyl in Beckmannia syzigachne

BACKGROUND

Non-target-site resistance (NTSR) to herbicides is a serious threat to global agriculture. Although metabolic resistance is the dominant mechanism of NTSR, the molecular mechanisms are not yet well-characterized. This study aimed to uncover the likely metabolism-related genes in Beckmannia syzigachne (American sloughgrass) resistant to fenoxaprop-p-ethyl.

RESULTS

Ultra-performance liquid chromatography - tandem mass spectrometry experiments showed that the resistant American sloughgrass biotype (R, SD-04-SS) showed enhanced degradation of this herbicide compared to the susceptible biotype (S, SD-12). R and S biotype were harvested at 24 h after fenoxaprop-p-ethyl treatment to conduct RNA sequencing (RNA-Seq) analysis to investigate the likely fenoxaprop-p-ethyl metabolic genes. The RNA-Seq libraries yield 417 969 980 clean reads. The de novo assembly generated 115 112 unigenes, of which 57 906 unigenes were annotated. Finally, we identified 273 cytochrome P450s, 178 oxidases, 47 glutathione S-transferases (GSTs), 166 glucosyltransferases (GTs) and 180 ABC transporter genes to determine the likely fenoxaprop-p-ethyl metabolism-related genes in R biotype. Twelve overlapping up-regulated genes in the R biotype (fenoxaprop-p-ethyl-treated R/non-treated R, fenoxaprop-p-ethyl-treated R/fenoxaprop-p-ethyl-treated S) were identified by RNA-Seq and the results were validated using qRT-PCR. Ten were identified as fenoxaprop-p-ethyl metabolism-related genes, including three P450s (homologous to CYP71D7, CYP99A2 and CYP71D10), one GST (homologous to GSTF1), two GTs (homologous to UGT90A1 and UGT83A1) and four oxidase genes.

CONCLUSION

This work demonstrates that the NTSR mechanism by means of enhanced detoxification of fenoxaprop-p-ethyl in American sloughgrass is very likely driven by herbicide metabolism related genes. The RNA-Seq data presented here provide a valuable resource for understanding the molecular mechanism of NTSR in American sloughgrass. © 2020 Society of Chemical Industry.