Aryloxyphenoxypropionate Herbicides Research Articles

TREATMENT WITH FLUAZIFOP-P-BUTYL HERBICIDE INDUCES OXIDATIVE STRESS IN PHASEOLUS VULGARIS L.

Fluazifop-p-butyl is an aryloxyphenoxy-propionate herbicide used for broad-spectrum weed control in Phaseolus vulgaris and other legume crops. In this study, field experiment was conducted to evaluate some physiological responses of Phaseolus vulgaris to herbicide treatment. Parameters measured includes: whole plant biomass, chlorophyll content, lipid peroxidation, relative water content of the leaves, carbohydrate content of the leaves, and antioxidant enzymes activities. The results showed that fluazifop-P-butyl significantly decreased the plant biomass, relative water content of the leaves, total chlorophyll and carbohydrate contents of the treated plant compared with the control. In contrast, there was a significance increase in malondialdehyde level as well as activities of antioxidant enzymes. The results of this work showed that herbicides caused physiological disorders in non-target plants by inducing oxidative stress that may lead to poor growth and yield.

Magnetic ZIF-8-Based Mimic Multi-enzyme System as a Colorimetric Biosensor for Detection of Aryloxyphenoxypropionate Herbicides.

In the present study, a magnetic mimic multi-enzyme system was developed by encapsulating the aryloxyphenoxypropionate (AOPP) herbicide hydrolase QpeH and alcohol oxidase (AOx) in zeolitic imidazolate framework (ZIF-8) nanocrystals with magnetic Fe3O4 nanoparticles (MNPs) to detect AOPP herbicides. The structural, protein loading capacity and loading ratio, porosity, and magnetic properties of QpeH/AOx@mZIF-8 were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen sorption, and vibrating sample magnetometry. An AOPP herbicide colorimetric biosensor made with QpeH/AOx@mZIF-8 had the highest sensitivity toward quizalofop-P-ethyl (QpE) with a limit of detection of 8.2 μM. This system was suitable to detect two other AOPP herbicides, including fenoxaprop-P-ethyl (FpE) and haloxyfop-P-methyl (HpE). The practical application of the biosensor was verified through quantitative analysis of QpE residues in industrial wastewater and field soils. Furthermore, QpeH/AOx@mZIF-8 exhibited excellent long-term storage stability (at least 50 days), easy separation by magnet, and reusability (at least 10 cycles), supporting its promising role in simple and low-cost detection of AOPP herbicides in real environmental samples.

Detecting the effect of ACCase-targeting herbicides on ACCase activity utilizing a malachite green colorimetric functional assay

AbstractResearch was conducted using a functional malachite green colorimetric assay to evaluate acetyl-coenzyme A carboxylase (ACCase) activity previously identified as resistant to sethoxydim and select aryloxyphenoxypropionate (FOPs) herbicides, fenoxaprop, and fluazifop. Two resistant southern crabgrass [Digitaria ciliaris (Retz.) Koeler] biotypes, R1 and R2, containing an Ile-1781-Leu amino acid substitution and previously identified as resistant to sethoxydim, pinoxaden, and fluazifop but not clethodim was utilized as the resistant chloroplastic ACCase source compared with known susceptible (S) ACCase. Dose-response studies with sethoxydim, clethodim, fluazifop-p-butyl, and pinoxaden (0.6 to 40 µM) were conducted to compare the ACCase–herbicide interactions of R1, R2, and S using the malachite green functional assay. Assay results indicated that R biotypes required more ACCase-targeting herbicides to inhibit ACCase activity compared with S. IC50 values of all four herbicides for R biotypes were consistently an order of magnitude greater than those of S. No sequencing differences in the carboxyltransferase domain was observed for R1 and R2; however, R2 IC50 values were greater across all herbicides. These results indicate the malachite green functional assay is effective in evaluating ACCase activity of R and S biotypes in the presence of ACCase-targeting herbicides, which can be used as a replacement for the 14C-based radiometric functional assays.

Identification of herbicide resistance OsACC1 mutations via in planta prime-editing-library screening in rice.

Base-editing-library-induced high density nucleotide substitutions have been applied to screen functional mutations in plants. However, due to limitations in the scope and conversion specificity of base editors, many desired mutations at pivotal protein sites may be overlooked. Here, we developed a prime-editing-library-mediated saturation mutagenesis (PLSM) method to substantially increase the diversity of amino acid substitutions at target sites for in planta screening. At six conserved residues of OsACC1, 16 types of herbicide-resistance-endowing mutations were identified. Most of these mutations exhibit reliable tolerance to aryloxyphenoxypropionate herbicides and have not been reported or applied in rice breeding. In addition, the advantage of PLSM was further shown by comparing the base-editing-mediated mutagenesis at the selected targets. The PLSM method established in this study has great potential for the direct evolution of genes related to agronomically important traits for crop improvement.

Dynamics of the Degradation of Acetyl-CoA Carboxylase Herbicides in Vegetables.

(1) Background: Aryloxyphenoxy-propionates and cyclohexanediones are herbicides most widely used in dicot crops worldwide. The main objective of the study was to determine the dynamics of herbicide residues in carrot, lettuce, cauliflower, and onion in order to suggest a low level of residues in harvested vegetables. (2) Methods: Small plot field trials were carried out in four vegetables in the Czech Republic. The samples of vegetables were collected continuously during the growing season. Multiresidue methods for the determination of herbicide residues by LC-MS/MS were used. Non-linear models of degradation of individual herbicides in vegetables were calculated using the exponential decay formula. Action GAP pre-harvest intervals for the 25% and 50% maximum residue limit (MRL) and 10 µg kg−1 limit (baby food) were established for all tested herbicides. (3) Results: The degradation dynamics of fluazifop in carrot, onion, and cauliflower was significantly slower compared to quizalofop and haloxyfop. The highest amount (2796 µg kg−1) of fluazifop residues was detected in cauliflower 11 days after application. No residue of propaquizafop and cycloxydim was detected in any vegetable samples. (4) Conclusions: Aryloxyphenoxy-propionate herbicide (except propaquizafop) could contaminate vegetables easily, especially vegetables with a short growing season. Vegetables treated with fluazifop are not suitable for baby food. Lettuce and cauliflower treated by quizalofop are not suitable for baby food, but in onion and carrot, quizalofop could be used. Propaquizafop and cycloxydim are prospective herbicides for non-residual (baby food) vegetable production.

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

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). 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. 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.

Control of Volunteer Enlist Corn in Enlist E3 Soybean

Recent development of Enlist corn allows the use of 2,4-D choline (Enlist One), glyphosate (Roundup PowerMax), glufosinate (Liberty), and aryloxyphenoxypropionate (FOPs) herbicides for controlling grass and broadleaf weeds. However, volunteer Enlist corn plants can cause infestation in subsequent Enlist E3 soybean (resistant to 2,4-D, glyphosate, and glufosinate) in areas where a corn-soybean rotation is commonly practiced. The main objective of this research was to determine the effectiveness of cyclohexanedione (DIMs) herbicides alone or in tank-mixtures with Enlist One for Enlist corn control in Enlist E3 soybean. A field study was conducted in the 2020 growing season at the Kansas State University Agricultural Research Center (KSUARC) near Hays, KS. Enlist corn hybrid DKC62-53 was planted at 17,420 seeds/a on May 13, 2020. Enlist E3 soybean variety P30T92E was planted at 152,000 seeds/a in a perpendicular direction to corn on May 20, 2020. Herbicide treatments, including clethodim (Select Max) and sethoxydim (Poast Plus) were tested alone or in tank-mixtures with Enlist One as early POST (EPOST, 8- to 12-inch tall corn), or late postemergence (POST) (12- to 30-inch tall corn). Results indicated that Select Max applied EPOST alone provided an excellent, season-long control (95 to 99%) and highest biomass reduction (up to 100%) of volunteer Enlist corn in Enlist E3 soybean. However, volunteer corn control was significantly reduced when Enlist One was tankmixed with Poast Plus. Volunteer corn control was low to moderate (50–85%) with all late postemergence (LPOST) programs tested. Soybean grain yield did not differ among EPOST treatments (39 to 44 bu/a), while grain yield was significantly lower (~ 34 bu/a) for LPOST treatments. These results suggested that the EPOST application of Select Max and Poast Plus can effectively control volunteer Enlist corn infestation in Enlist E3soybean. However, adding Enlist One could compromise the efficacy of Poast Plus herbicide.

Characterization of an enantioselective esterase from the quizalofop-ethyl-transforming strain of Sphingobium sp. QE-1

The enantioselective catabolism of the two enantiomers of the aryloxyphenoxypropionate (AOPP) herbicide, quizalofop-ethyl (QE), in environment by microorganisms is of great interest. In this study, Sphingobium sp. strain QE-1, capable of transforming both enantiomers of QE, was successfully isolated. A novel gene qeH, encoding an esterase capable of initially transforming (R)/(S)-QE to (R)/(S)-quizalofop acid [(R)/(S)-QA], was cloned. QeH showed the highest identity (36.9%) to the β-lactamase MT1414, and the purified QeH displayed optimal activity for (R)-QE at 40 °C and pH 7.0. QeH preferentially hydrolyzed (R)-QE than (S)-QE. Based on molecular docking analyses, the distance between the ligand molecule and the coordination atom was shorter when (R)-QE occupied the active sites as compared to that of (S)-QE, which resulted in a stronger ligand binding affinity for (R)-QE. Besides the two enantiomers of QE, QeH could also convert many other AOPP herbicides with different catalytic efficiency (clodinafop-propargyl > fenoxaprop-P-ethyl > fluazifop-P-butyl > cyhalofop-butyl). This study will enhance our understandings of the enantioselective catabolism of AOPP herbicides by microorganisms.

Comparative Transcriptome Analysis Revealing the Different Germination Process in Aryloxyphenoxypropionate-Resistant and APP-Susceptible Asia Minor Bluegrass (Polypogon fugax).

Herbicide-resistant mutations are predicted to exhibit fitness cost under herbicide-free conditions. Asia minor bluegrass (Polypogon fugax) is a common weed species in the winter crops. Our previous study established a P. fugax accession (LR) resistant to aryloxyphenoxypropionate (APP) herbicides, which also exhibited germination delay relative to the susceptible accession (LS). A comparative transcriptome was conducted to analyze the gene expression profile of LS and LR at two germination time points. A total of 11,856 and 23,123 differentially expressed genes (DEGs) were respectively identified in LS and LR. Most DEGs were involved in lipid metabolism, carbohydrate metabolism, amino acid metabolism, and secondary metabolites biosynthesis. Twenty-four genes involved in carbohydrate and fatty acid metabolism had higher relative expression levels in LS than LR during germination. Nine genes involved in gibberellin (GA) and abscisic acid (ABA) signal transduction showed different expression patterns in LS and LR, consistent with their different sensitivity to exogenous hormones treatments. This study first provided insight into transcriptional changes and interaction in the seed germination process of P. fugax. It compared the differential expression profile between APP herbicides resistance and susceptible accessions during germination, which contributed to understanding the association between herbicide resistance and fitness cost.

Control of glyphosate/glufosinate-resistant volunteer corn in corn resistant to aryloxyphenoxypropionates

AbstractCorn-on-corn production systems, common in highly productive irrigated fields in South Central Nebraska, can create issues with volunteer corn management in corn fields. EnlistTM corn is a new multiple herbicide–resistance trait providing resistance to 2,4-D, glyphosate, and the aryloxyphenoxypropionate herbicides (FOPs), commonly integrated in glufosinate-resistant germplasm. The objectives of this study were to (1) evaluate ACCase-inhibiting herbicides for glyphosate/glufosinate-resistant volunteer corn control in Enlist corn and (2) evaluate the effect of ACCase-inhibiting herbicide application timing (early POST vs. late POST) on volunteer corn control, Enlist corn injury, and yield. Field experiments were conducted in 2018 and 2019 at South Central Agricultural Laboratory near Clay Center, NE. Glyphosate/glufosinate-resistant corn harvested the year prior was cross-planted at 49,000 seeds ha–1 to mimic volunteer corn in this study. After 7 to 10 d had passed, Enlist corn was planted at 91,000 seeds ha–1. Application timing of FOPs (fluazifop, quizalofop, and fluazifop/fenoxaprop) had no effect on Enlist corn injury or yield, and provided 97% to 99% control of glyphosate/glufosinate-resistant volunteer corn at 28 d after treatment (DAT). Cyclohexanediones (clethodim and sethoxydim; DIMs) and phenylpyrazolin (pinoxaden; DEN) provided 84% to 98% and 65% to 71% control of volunteer corn at 28 DAT, respectively; however, the treatment resulted in 62% to 96% Enlist corn injury and 69% to 98% yield reduction. Orthogonal contrasts comparing early-POST (30-cm-tall volunteer corn) and late-POST (50-cm-tall volunteer corn) applications of FOPs were not significant for volunteer corn control, Enlist corn injury, and yield. Fluazifop, quizalofop, and fluazifop/fenoxaprop resulted in 94% to 99% control of glyphosate/glufosinate-resistant volunteer corn with no associated Enlist corn injury or yield loss; however, quizalofop is the only labeled product as of 2020 for control of volunteer corn in Enlist corn.

Haloxyfop-P-methyl induces developmental defects in zebrafish embryos through oxidative stress and anti-vasculogenesis

Haloxyfop-P-methyl, an aryloxyphenoxypropionate herbicide, is widely used to eliminate unwanted plants by inhibiting lipid synthesis and inducing oxidative stress. Since haloxyfop-P-methyl targets are limited within plants, few negative side effects on non-target crops have been reported. However, dissolved haloxyfop-P-methyl in rain or groundwater contaminates aquatic environments and affects marine ecosystems. In the present study, treatment with haloxyfop-P-methyl for 48 h induced developmental deficiencies in the eyes and bodies of the zebrafish embryos as a whole and was also linked to increases in the incidence of pericardial edema. Additionally, haloxyfop-P-methyl treatment decreased hatching ratio, embryo viability, and heart rate, while simultaneously increasing the expression levels of apoptotic and inflammatory genes. Moreover, haloxyfop-P-methyl hampered vasculogenesis in the embryos through down-regulation of functional genes, and disruption of vessel formation caused neurodegeneration in the olig2-positive notochord. Collectively, this study newly discovered the oxidative stress-related toxic mechanism of haloxyfop-P-methyl during embryonic development through anti-vasculogenesis, which suppresses neurogenesis of the notochord. This toxicity assessment of haloxyfop-P-methyl on embryogenesis may contribute to establishment of safety profiling of herbicide and to support hazard control in aquatic environment.

A CRISPR-Cas9-mediated domain-specific base-editing screen enables functional assessment of ACCase variants in rice.

A CRISPR-Cas9-mediated domain-specific base-editing screen enables functional assessment of ACCase variants in rice.

Screening of Fungi Isolates for C-4 Hydroxylation of R-2-Phenoxypropionic Acid Based on a Novel 96-Well Microplate Assay Method.

R-2-(4-Hydroxyphenoxy)propionic acid (R-HPPA) is a pivotal intermediate for the synthesis of aryloxyphenoxypropionate (APP) herbicide. To rapidly screen microbial isolates with the capacity of hydroxylating R-2-phenoxypropionic acid to R-HPPA from various environmental samples, a convenient and safe 96-well microplate assay method with sodium nitrite (NaNO2) as chromogenic reagent was proposed and optimized. The optimum assay conditions were as follows: the detection wavelength was 420nm, the concentration of NaNO2 solution was 6.0g/L, color reaction temperature was 60°C, the pH of the NaNO2 solution was 2.4, and the reaction time was 40min. With the aid of this method, screening for microorganisms with C-4-specific hydroxylation activity of R-PPA was conducted. As a result, 23 strains among 3744 single colonies isolated from various samples exhibited the hydroxylation activity. Among these strains, the highest bioconversion rate was achieved by Penicillium oxalicum A5 and Aspergillus versicolor A12, respectively. After 72-h cultivation in shake flask, their conversion rates of R-HPPA from 10g/L R-PPA reached 21.18% and 40.24%, respectively. The established method was effective in rapid screening of microbes capable of biosynthesizing R-HPPA through hydroxylation of R-PPA, and the obtained two fungi species could be potentially used for R-HPPA production.

Sensitivity of weedy rice populations to Quizalofop

Abstract Background: Rice lines displaying resistance to quizalofop-p-ethyl (quizalofop), an acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicide, were developed to facilitate control of imidazolinone-resistant weedy rice (red rice), as well as other susceptible grasses. Objective: To assess the sensitivity of weedy rice accessions from Brazil to quizalofop. Methods: Two bioassays were conducted on the greenhouse from March to June 2016, in a completely random design with a two-factor factorial combination of treatments and four replications. The factor A was weedy rice accession and factor B was quizalofop rates (0, 25 and 50 g a.i. ha-1). It was assessed a total of 84 genotypes in the two bioassays, composed of 78 weedy rice accessions, 4 rice cultivars, and 2 lines resistant to aryloxyphenoxypropionate (AOPP) herbicides. Quizalofop was applied the 2-leaf stage. Weedy rice control was evaluated at 28 and 22 days after treatment (DAT), respectively for bioassay I and II, using a scale of 0% (no control) to 100% (dead). Results: All weedy rice accessions were susceptible to quizalofop, being controlled 100% with 50 g a.i. ha-1. Rice lines SC 964 and SC 965, resistant to AOPP herbicides, were not injured by quizalofop. Conclusions: quizalofop is an effective tool for weedy rice control in ACCase-resistant rice.

Trp2027Cys mutation evolves in Digitaria insularis with cross-resistance to ACCase inhibitors

Sourgrass (Digitaria insularis) is one of the most problematic weeds in South America because glyphosate resistance is widespread across most crop production regions. Acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicides have been intensively used to manage D. insularis, which substantially increased selection pressure for this class of herbicides. We confirmed resistance to ACCase herbicides in a D. insularis population from Brazil and characterized its molecular basis. Resistant plants showed high level of resistance to haloxyfop (resistance factor, RF = 613-fold), low level of resistance to pinoxaden (RF = 3.6-fold), and no resistance to clethodim. A target-site mutation, Trp2027Cys, was found in the ACCase sequence from resistant plants. A protein homology model shows that the Trp2027Cys mutation is near the herbicide-binding pocket formed between two ACCase chains, and is predicted to obstruct the access of aryloxyphenoxypropionates (FOP) herbicides to the binding site. A qPCR-based single nucleotide polymorphism genotyping method was validated to discriminate susceptible (wild-type Trp2027) and resistant (mutant Cys2027) alleles. All resistant plants were homozygous for the mutation and the assay could be used for early detection of resistance in D. insularis field samples with suspected resistance to ACCase inhibitors.

Computational and experimental investigations on the interactions of aryloxy-phenoxy-propionate herbicides to estrogen receptor alpha in zebrafish.

When the amount of pesticide exceeds the self-purification ability of the environment, it will be enriched in the human body through the atmosphere, soil, water circulation, etc., threatening human health. Aryloxy-phenoxy-propionate (APP) herbicides are a class of acetyl-CoA carboxylase (ACCase) inhibitor herbicides, widely used in field-weeding of soybean, cabbage, peanut and other crops. However, due to the water circulation, surface runoff and the agronomic practices such as watering irrigation, APP herbicides have the risk of polluting water and destroying the living environment of aquatic organisms. In this paper, a multistep framework combining homology modeling, molecular docking and molecular dynamic simulations were adopted to explore the interactions between APP herbicides and zebrafish estrogen receptor α (ERα) to investigate the estrogenic activities of the herbicides. The structure of zebrafish ERα was modeled by homology modeling, using the human's estrogen receptor α (PDB ID:2YJA) as the template. Then, eight typical APP herbicides were selected to dock with the zebrafish ERα, and it was determined that there were clear interactions between the herbicides and the receptor. The binding patterns of Quizalofop-P-ethyl (QPE), Clodinafop-propargyl (CP) and Haloxyfop-P (HP) with ERα were further investigated by molecular dynamics and binding free energy calculation. The results showed the van der Waals force and electrostatic force were the main driving forces for maintaining the stability of the complex system. In order to verify the theoretical prediction, an exposed experiment was conducted to study the effects of different concentrations of herbicides on VTG level of zebrafish in vivo and the results were consistent with the computational method. The results of this study revealed the mechanism of the action between APP herbicides and zebrafish estrogen receptors, and also provided ideas for optimizing the herbicides.

Development and Validation of a Liquid Chromatography–Tandem Mass Spectrometry Method for Multiresidue Determination of 25 Herbicides in Soil and Tobacco

In the cultivation of tobacco, crop rotation patterns, such as tobacco/rice or tobacco/corn, are widely used. However, the use of herbicides in the rice or corn phase can lead to their being taken in during the tobacco phase by inner conduction action. In the present study, to monitor the use of herbicides in tobacco, a sensitive and simple analytical method coupled with liquid chromatography-tandem mass spectrometry (LC–MS/MS) has been established for determination of 25 herbicides in soil as well as fresh and flue-cured tobacco leaf. The herbicides analyzed include six aryloxy phenoxy propionate herbicides (APPs) and 19 sulfonylureas herbicides (SUs). The samples were extracted using acetonitrile and purified using C18 sorbent before analysis. Optimum separation of the analytes was achieved using an Agilent Eclipse XDB-C18 column at 40 °C and gradient elution with acetonitrile and 0.1% aqueous formic acid as the mobile phase at a flow rate of 0.8 mL min−1. The limits of quantification and detection are in the ranges 0.08–1.00 mg kg−1 and 0.024–0.30 mg kg−1, respectively, and matrix effects in the range − 70 to 50% were achieved. The recovery rates obtained from spiked soil and tobacco leaf samples ranged from 72.32 to 116.83% with intra-day and inter-day relative standard deviations of 0.44–11.55%. In addition, the method developed was applied to the determination of herbicides residues in actual soil and tobacco samples, revealing that the proposed method can detect trace amounts of APPs and SUs in soil as well as in fresh and flue-cured tobacco leaf.

Toxic Mechanisms of Aryloxyphenoxypropionates in Target and Non-target Organisms

Herbicides are substances used to control unwanted plants-weeds. They can be classified into several classes by mechanism of action. This review describes the members of aryloxyphenoxypropionate herbicides, their pharmacokinetic properties, metabolism and their mechanism of phytotoxicity in target weeds as well as in non-target organisms. Two major toxicity mechanisms are described. The first is by inhibition of lipid synthesis. This is achieved by inhibiting the rate limiting step of lipid biosynthesis catalyzed by acetyl CoA carboxylase. The second mechanism is by induction of oxidative stress. This is achieved by generation of reactive oxygen species which in excess can cause oxidative damage to macromolecules and cellular structures especially the membrane lipids. Loss of vital membrane lipids alters the fluidity of membrane, loss of cellular contents and eventually cell death and death of the entire plant.

Growth, fecundity, and competition between aryloxyphenoxypropionate-resistant and -susceptible Asia Minor bluegrass (Polypogon fugax)

AbstractAsia Minor bluegrass (Polypogon fugax Nees ex Steud.) is a problem grass weed of winter crops in China, where a population has become resistant to aryloxyphenoxypropionate (APP) herbicides. The mechanism of resistance is due to an Ile-2041-Asn mutation of the ACCase gene. Screen house experiments were conducted to study the growth, fecundity characteristics, and competitive ability of this aryloxyphenoxypropionate-resistant (APP-R) biotype compared with a susceptible (APP-S) biotype. When grown under noncompetitive conditions, the APP-R P. fugax developed more rapidly than the APP-S plants, with earlier tiller and panicle emergence and seed shedding; the APP-R P. fugax set seeds nearly 12 d earlier than the APP-S biotype. APP-R and APP-S biotypes had similar aboveground dry weight before the flowering stage. Fecundity of the APP-R biotype was similar to the APP-S biotype (8.57 g seeds plant−1 and 0.17 g seeds panicle−1 versus 8.22 g seeds plant−1 and 0.13 g seeds panicle−1, respectively). Ultimately, the relatively slower-developing APP-S P. fugax had 50% more shoot dry weight than the APP-R plants. Relative competitiveness among the APP-R and APP-S P. fugax biotypes was investigated through replacement series experiments. No difference in competitive ability was measured between APP-R and APP-S biotypes on the basis of shoot dry weight before the tillering stage. These results indicate that there is no apparent fitness penalty for the APP-R P. fugax. The shorter growth cycle of APP-R with no apparent fitness penalty suggests that growers will need begin weed control earlier and possibly include vegetative crops with an even shorter growth cycle in their rotations.

Target-site resistance to cyhalofop-butyl in bearded sprangletop (Diplachne fusca) from China

AbstractBearded sprangletop [Diplachne fusca(L.) P. Beauv. ex Roem. & Schult. ssp.fascicularis(Lam.) P. M. Peterson & N. Snow] is a noxious annual grass weed of paddy fields, distributed in coastal regions of the Jiangsu and Hebei provinces in China. Cyhalofop-butyl has been widely used to control grass weeds since 2006 in China. Overreliance on cyhalofop-butyl has led to the evolution of resistant weeds. In this study, the resistance level and cyhalofop-butyl resistance mechanisms were investigated in the putative resistant (JSHH) population. The dose–response experiments showed that the JSHHD.fuscapopulation had evolved 8.9-fold resistance to cyhalofop-butyl. Acetyl-CoA carboxylase (ACCase) sequencing revealed a point mutation (GGC to GCC) at amino acid position 2096, resulting in a Gly-2096-Ala substitution in the resistant population. To our knowledge, this is the first case of cyhalofop-butyl resistance inD.fuscaand the first report of a target-site mutation conferring resistance to ACCase-inhibiting herbicides inD.fusca. In addition, the resistantD.fuscapopulation (JSHH) with the Gly-2096-Ala mutation was cross-resistant to the aryloxyphenoxypropionate herbicide metamifop, the cyclohexanedione herbicide sethoxydim, and the phenylpyrazolin herbicide pinoxaden.