Protoporphyrinogen Oxidase Research Articles

Molecular Modeling Study and Proposition of Novel Diaryl Ether Derivatives as Protoporphyrinogen Oxidase Inhibitors

Molecular Modeling Study and Proposition of Novel Diaryl Ether Derivatives as Protoporphyrinogen Oxidase Inhibitors

Design, Synthesis of Novel Pyrimidine Derivatives Containing Alkenyl Moieties With Herbicidal Activities

ABSTRACTTo identify lead compounds with potent herbicidal activity, a range of pyrimidine derivatives containing alkenyl groups were designed, synthesized, and characterized using nuclear magnetic resonance (NMR) spectroscopy and high‐resolution mass spectrometry (HRMS). The synthetic pathways for producing these compounds involved substitution reactions, cyclization, hydrolysis, and other processes. The starting materials for each reaction step were readily accessible, facilitating synthesis. The purification of the final product was straightforward, yielding approximately 80%, under mild reaction conditions. Moreover, a pot culture experiment was employed to assess the herbicidal efficacy of the aforementioned compounds. Compounds 6a, 6b, 6h, and 6j demonstrated a significant inhibition against Amaranthus retroflexus, comparable to fomesafen at 150 g a.i./hm2. This suggests that these compounds hold promise as potential lead structures for herbicidal agents. The docking results indicated that the binding energies of compound 6a with protoporphyrinogen oxidase (PPO) were both negative and spontaneous, with numerous interaction active sites. Thus, it is speculated that compound 6a is a PPO inhibitor.

Patterns of herbicide resistance in Raphanus raphanistrum revealed by comprehensive testing and statistical analysis.

Raphanus raphanistrum causes $40 million total revenue losses annually in Western Australia partly due to its historically-documented ability to evolve herbicide resistance to multiple modes of action. In this study, 376 field-sampled populations of R. raphanistrum were tested for resistance to 21 herbicides applied at the recommended label rate. Eight treatments were herbicide mixtures with two, three or four modes of action. A total of 7199 individual resistance tests were conducted across 4 years by screening approximately 104 000 individual seeds and seedlings. The mean survival of individuals within a population for all standalone herbicides was 9%, whereas survival was significantly decreased to 3.5% with a herbicide mixture. Some herbicides such as triasulfuron (herbicide Group 2), 2,4-D (Group 4) or diflufenican (Group 12) were highly impacted by resistance, with frequencies of resistant populations being > 50%. Conversely, there was negligible resistance to glyphosate (Group 9) or protoporphyrinogen oxidase (PPO) inhibitors (tiafenacil, saflufenacil + trifludimoxazin, fomesafen: Group 14), and pre-emergence herbicides (i.e., atrazine or mesotrione: Groups 5 and 27, respectively) remained largely effective. Binary, ternary or quaternary mixtures of Groups 4, 6, 12 and 27 herbicides reduced the frequency of high-level resistant populations to 7.1%, 3.8% or 0%, respectively. The cost-effective control of R. raphanistrum remains a challenge due to herbicide resistance. Raphanus raphanistrum management relies heavily on herbicide uses not yet compromised by resistance, such as pre-emergence herbicides (atrazine, fomesafen, mesotrione), glyphosate, and mixtures of two, three or four modes of action including bromoxynil, diflufenican, MCPA, picolinafen, pyrasulfotole and topramezone. Strategies that integrate effective herbicide use patterns, novel modes of action and efficiently-mechanized non-chemical weed control options (i.e., seed destructors) can completely constrain the selection of herbicide resistance in this highly adaptable species. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Amphiphilic Cationic Carbon Dots for Efficient Delivery of Light-Dependent Herbicide.

The inefficient delivery of herbicides causes unpleasant side effects on the ecological environment. Protoporphyrinogen oxidase (PPO)-inhibiting herbicides rely on the presence of external light to exert the activities and thus their performance in the field is extremely susceptible to the light environment. Here, taking acifluorfen (ACI) as a model PPO-inhibiting herbicide to enhance efficacy by boosting the utilization rate of sunlight, amphiphilic cationic CDs (CPC-CDs) from cetylpyridinium chloride (CPC) as a precursor, is first prepared as a supplementary light source generator, and subsequently co-assembled with ACI through non-covalent bond interactions to obtain the stable fluorescent nanoparticles (ACI@CPC-CDs). ACI@CPC-CDs with fascinating physicochemical properties can penetrate the leaves of weeds through the stomata and undergo a long-distance transport in the cell intervals. Under low light intensity, CPC-CDs can be applied as the internal light source to promote the formation of more singlet oxygen to damage the leaf cell membrane, consequently improving the herbicidal activity of ACI. Moreover, the safety evaluation of ACI@CPC-CDs demonstrates no risk to non-target organisms and the environment. Therefore, this work offers a promising strategy for the efficient delivery of light-dependent PPO-inhibiting herbicides and opens new insights into the application of CDs in the development of sustainable agriculture.

Resistance to protoporphyrinogen oxidase inhibitors in giant ragweed (Ambrosia trifida).

Giant ragweed (Ambrosia trifida L.) is one of the most troublesome weed species in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] cropping systems. Following numerous reports in 2018 of suspected herbicide resistance in several Ambrosia trifida populations from Wisconsin, our objective was to characterize the response of these accessions to acetolactate synthase (ALS), enolpyruvyl shikimate phosphate synthase (EPSPS), and protoporphyrinogen oxidase (PPO) inhibitors applied POST. Four accessions (AT1, AT4, AT6, and AT10) exhibited ≥ 50% plant survival after exposure to the cloransulam 3× rate. Two accessions (AT8 and AT10) and one accession (AT2) exhibited ≥ 50% plant survival after exposure to glyphosate and fomesafen 1× rates, respectively. The AT10 accession exhibited multiple resistance to cloransulam and glyphosate. The AT12 accession was 28.8-fold resistant to fomesafen and 3.7-fold resistant to lactofen. A codon change in PPX2 conferring a R98L substitution was identified as the most likely mechanism conferring PPO-inhibitor resistance. To our knowledge, this is the first confirmed case of PPO-inhibitor resistance in Ambrosia trifida globally and we identified the genetic mutation likely conferring resistance. Proactive and diversified integrated weed management strategies are of paramount importance for sustainable long-term Ambrosia trifida management. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Design, Synthesis, and Herbicidal Activity of Novel Tetrahydrophthalimide Derivatives Containing Oxadiazole/Thiadiazole Moieties.

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) has a high status in the development of new inhibitors. To develop novel and highly effective PPO inhibitors, active substructure linking and bioisosterism replacement strategies were used to design and synthesize novel tetrahydrophthalimide derivatives containing oxadiazole/thiadiazole moieties, and their inhibitory effects on Nicotiana tobacco PPO (NtPPO) and herbicidal activity were evaluated. Among them, compounds B11 (Ki = 9.05 nM) and B20 (Ki = 10.23 nM) showed significantly better inhibitory activity against NtPPO than that against flumiclorac-pentyl (Ki = 46.02 nM). Meanwhile, compounds A20 and B20 were 100% effective against three weeds (Abutilon theophrasti, Amaranthus retroflexus, and Portulaca oleracea) at 37.5 g a.i./ha. It was worth observing that compound B11 was more than 90% effective against three weeds (Abutilon theophrasti, Amaranthus retroflexus, and Portulaca oleracea) at 18.75 and 9.375 g a.i./ha. It was also safer to rice, maize, and wheat than flumiclorac-pentyl at 150 g a.i./ha. In addition, the molecular docking results showed that compound B11 could stably bind to NtPPO and it had a stronger hydrogen bond with Arg98 (2.9 Å) than that of flumiclorac-pentyl (3.2 Å). This research suggests that compound B11 could be used as a new PPO inhibitor, and it could help control weeds in agricultural production.

Mapping of flumioxazin tolerance in a snap bean diversity panel leads to the discovery of a master genomic region controlling multiple stress resistance genes.

Effective weed management tools are crucial for maintaining the profitable production of snap bean (Phaseolus vulgaris L.). Preemergence herbicides help the crop to gain a size advantage over the weeds, but the few preemergence herbicides registered in snap bean have poor waterhemp (Amaranthus tuberculatus) control, a major pest in snap bean production. Waterhemp and other difficult-to-control weeds can be managed by flumioxazin, an herbicide that inhibits protoporphyrinogen oxidase (PPO). However, there is limited knowledge about crop tolerance to this herbicide. We aimed to quantify the degree of snap bean tolerance to flumioxazin and explore the underlying mechanisms. We investigated the genetic basis of herbicide tolerance using genome-wide association mapping approach utilizing field-collected data from a snap bean diversity panel, combined with gene expression data of cultivars with contrasting response. The response to a preemergence application of flumioxazin was measured by assessing plant population density and shoot biomass variables. Snap bean tolerance to flumioxazin is associated with a single genomic location in chromosome 02. Tolerance is influenced by several factors, including those that are indirectly affected by seed size/weight and those that directly impact the herbicide's metabolism and protect the cell from reactive oxygen species-induced damage. Transcriptional profiling and co-expression network analysis identified biological pathways likely involved in flumioxazin tolerance, including oxidoreductase processes and programmed cell death. Transcriptional regulation of genes involved in those processes is possibly orchestrated by a transcription factor located in the region identified in the GWAS analysis. Several entries belonging to the Romano class, including Bush Romano 350, Roma II, and Romano Purpiat presented high levels of tolerance in this study. The alleles identified in the diversity panel that condition snap bean tolerance to flumioxazin shed light on a novel mechanism of herbicide tolerance and can be used in crop improvement.

Noncovalent interactions between quinoxalines and protoporphyrinogen oxidase (PPO): a computational case study for herbicidal applications

Noncovalent interactions between quinoxalines and protoporphyrinogen oxidase (PPO): a computational case study for herbicidal applications

Variegate porphyria onset as neurovisceral manifestation and unusual sensory impairment distribution. Case report

Background: Acute hepatic porphyrias are heme metabolism disorders presenting with a broad clinical spectrum, including neurovisceral manifestations. Peripheral neuropathy is one of the most frequent complications in porphyrias and can correspond about 40 % of the neurovisceral manifestations, and it is mainly attributed to the ALA and PBG accumulation neurotoxicity. The hallmark of an acute porphyric attack is an acute motor axonal neuropathy accompanied by autonomic dysfunction. Sensory impairment is infrequent, and when present, it is classically described as the stocking-glove pattern or, more rarely, a “bathing suit” proximal distribution pattern. Objective: To report a variegate porphyria case in a young patient with unusual sensory manifestations. Methods: A 27-year-old man, previously healthy, present in context of possible arbovirus infeccion with severe abdominal pain, followed by dysautonomia due to orthostatic hypotension, change in urine color and, the emergence of sensory impairment in the trunk and proximal region of the four limbs about twenty days from onset. Dysestesia was severe and marked. Results: Positive clinical features and a urinary exposure test to sunlight corroborate in request genetic testing for acute hepatic porphyrias, with a positive mutation of the PPOX gene in heterozygosis. Discussion: Clinical manifestations with initial presentation of severe dysautonomia followed by sensory changes demarcate neurovisceral involvement of variegate porphyria, adopting an "old-bathing-suit costume" sensory pattern throughout its evolution.

Novel Uracilphenyl sulfonamide-based inhibitors of protoporphyrinogen oxidase: Design, synthesis, and herbicidal activity

Herein, we aimed to develop effective herbicidal compounds by synthesizing 26 novel uracil derivatives containing sulfonamide groups based on the active group splicing principle, with saflufenacil as the reference compound. The structures of the final products were confirmed through 1H NMR, 13C NMR, and HRMS analyses. According to the results, 21 and 19 compounds exhibited outstanding (80 %-100 %) and 60–100 % control efficacies against broadleaf weeds (Zinnia elegans and Abutilon theophrasti) at concentrations of 150 g/hm2 and 37.5 g/hm2, respectively. Notably, compound 2a demonstrated 100 % control efficacy against Zinnia elegans even at the lowest tested concentration of 9.375 g/hm2. On the other hand, the examined compounds exhibited minimal efficacy against other grass weeds, such as Setaria glauca and Echinochloa crusgalli. Furthermore, molecular docking analysis revealed that compound 2a formed hydrogen bonds with Protoporphyrinogen Oxidase (PPO).Studies of the electrostatic potential analysis of the molecular surface showed that the highly active compounds 2a and saflufenacil have similar charge distributions, which may play an important role in the docking of the compounds with their target receptors.These findings offer valuable insights and guidance for developing more effective herbicides, paving the way for future advances in weed control tactics.

Design, Synthesis, and Herbicidal Evaluation of Pyrrolidinone-Containing 2-Phenylpyridine Derivatives as Novel Protoporphyrinogen Oxidase Inhibitors.

In this work, a series of pyrrolidinone-containing 2-phenylpyridine derivatives were synthesized and evaluated as novel protoporphyrinogen IX oxidase (PPO, EC 1.3.3.4) inhibitors for herbicide development. At 150 g ai/ha, compounds 4d, 4f, and 4l can inhibit the grassy weeds of Echinochloa crus-galli (EC), Digitaria sanguinalis (DS), and Lolium perenne (LP) with a range of 60 to 90%. Remarkably, at 9.375 g ai/ha, these compounds showed 100% inhibition effects against broadleaf weeds of Amaranthus retroflexus (AR) and Abutilon theophrasti (AT), which were comparable to the performance of the commercial herbicides flumioxazin (FLU) and saflufenacil (SAF) and better than that of acifluorfen (ACI). Molecular docking analyses revealed significant hydrogen bonding and π-π stacking interactions between compounds 4d and 4l with Arg98, Asn67, and Phe392, respectively. Additionally, representative compounds were chosen for in vivo assessment of PPO inhibitory activity, with compounds 4d, 4f, and 4l demonstrating excellent inhibitory effects. Notably, compounds 4d and 4l induced the accumulation of reactive oxygen species (ROS) and a reduction in the chlorophyll (Chl) content. Consequently, compounds 4d, 4f, and 4l are promising lead candidates for the development of novel PPO herbicides.

Discovery of Pyridyl-Benzothiazol Hybrids as Novel Protoporphyrinogen Oxidase Inhibitors via Scaffold Hopping.

In order to discover novel protoporphyrinogen oxidase (PPO) inhibitors with excellent herbicidal activity, a series of structurally novel 6-(pyridin-2-yl) benzothiazole derivatives were designed based on the scaffold hopping strategy. The in vitro experiments demonstrated that the newly synthesized compounds exhibited noteworthy inhibitory activity against Arabidopsis thaliana PPO (AtPPO), with IC50 values ranging from 0.06 to 1.36 μM. Preliminary postemergence herbicidal activity tests and crop safety studies indicated that some of our compounds exhibited excellent herbicidal activity and crop safety. For instance, compound (rac)-7as exhibited superior herbicidal activities to commercially available flumioxazin (FLU) and saflufenacil (SAF) at all the tested concentrations and showed effective herbicidal activities even at a dosage as low as 18.75 g ai/ha. Meanwhile, compound (rac)-7as showed good crop safety for wheat at a dosage as high as 150 g of ai/ha. Although the absolute configuration of compound 7as has no obvious effect on its herbicidal activity, compound (R)-7as showed a slightly higher crop safety than compound (S)-7as. Molecular simulation studies of Nicotiana tabacum PPO (NtPPO) and our candidate compounds showed that the benzothiazole moiety of compounds (R)-7as or (S)-7as formed multiple π-π stacking interactions with FAD, and the pyridine ring generated π-π stacking with Phe-392. Our finding proved that the pyridyl-benzothiazol hybrids are promising scaffolds for the development of PPO-inhibiting herbicides.

Physiological and transcriptomic strategies related to photosynthesis of rice in response to vanadium stress

Vanadium (V) is recognized as an environmental contaminant that affects plant growth and development. However, the photosynthetic response of plants to V stress at molecular level remains unclear. In this study, we examined the photosynthetic responses of two rice varieties (Oryza sativa L.) with diverse V tolerance under various V levels (0, 10, 20, 30, and 40 mg L−1) using physiological, cytological, and transcriptomic approaches. Our findings indicated that V stress significantly reduced the photosynthetic rate and chlorophyll content in both genotypes, with the V-sensitive rice displaying a more pronounced reduction. Furthermore, we observed numerous plastoglobuli, deformed stroma, and ruptured thylakoid membranes in the chloroplasts of the V-sensitive rice. In transcriptome analysis, we found 34 differentially expressed genes of 21 enzymes potentially affect chlorophyll metabolism. Among them, most of the genes involved in chlorophyll biosynthesis and phototoxic intermediate degradation were down-regulated under V stress, while chlorophyll degradation-related genes exhibited up-regulation. In addition, the different expression levels of genes encoding uroporphyrinogen III synthase (UROS), protoporphyrinogen oxidase (PPO), chlorophyllase (CLH), pheophorbide a oxygenase (PAO), and red chlorophyll catabolite reductase (RCCR) between the two rice varieties may indicate a potential tolerance mechanism in rice plants in response to V stress. Overall, this study contributes to our understanding of the molecular mechanisms underlying plant tolerance to V toxicity, while also highlighting potential targets for improving plant tolerance in V-contaminated soils.

Bifenox induces hepatotoxicity and vascular toxicity in zebrafish embryos via ROS production and alterations in signaling pathways

Existing evidence shows that currently used pesticides pose toxicological risks to exposed wildlife. Chemically, bifenox belongs to diphenyl ethers, a well-known group of herbicides. Its mechanism of action primarily involves inducing lipid peroxidation and blocking protoporphyrinogen oxidases. Toxicity of diphenyl ether herbicides has been elucidated in animal cells; however, in vivo toxicological evaluations of bifenox are required to determine its unexpected effects. This study aimed to determine the negative effects of bifenox, and its effects on higher eukaryotes. We found that early stages of zebrafish embryo exposed to bifenox demonstrated increased mortality and physiological defects, based on the LC50 value. Bifenox severely inhibited blood vessel growth by reducing key elements of complex connectivity; fluorescently tagged transgenic lines (fli1a:EGFP) showed morphological changes. Additionally, transgenic lines that selectively identified hepatocytes (fabp10a:DsRed) showed reduced fluorescence, indicating that bifenox may inhibit liver development. To evaluate the level of oxidative stress, we used 2′,7′-dichlorofluorescein diacetate (DCFH-DA) probes in zebrafish embryos to identify the underlying mechanisms causing developmental damage. Our findings demonstrate that exposure to bifenox causes abnormalities in the hepatic and cardiovascular systems during zebrafish embryogenesis. Therefore, this study provides new information for the evaluation of toxicological risks of bifenox in vertebrates.

Exposure to acifluorfen induces developmental toxicity in the early life stage of zebrafish

Acifluorfen, a selective herbicide from the diphenyl ether family, targets broad leaf weeds. Diphenyl ether inhibits chlorophyll production in green plants by inhibiting protoporphyrinogen oxidase (PPO), causing cellular damage. Despite its known impacts on plants, the influence of acifluorfen on zebrafish embryo development remains unclear. In this study, we explored the LC50 of acifluorfen in early-stage wild-type zebrafish, determining it to be 54.99 mg/L. Subsequent examinations revealed morphological changes in zebrafish, including reduced body length. Using the cmlc2:dsRED transgenic model, we observed heart dysfunction in acifluorfen-exposed zebrafish, marked by an enlarged heart area, edema, and decreased heart rate. In response to dose-dependent acifluorfen exposure, the inhibition of angiogenesis in the brain was observed in transgenic zebrafish models (fli1a:eGFP). Organ malformations, specifically in the liver and pancreas, were noted, in lfabp:dsRED;elastase:eGFP transgenic models, indicating reduced organ size in acifluorfen-exposed zebrafish. Furthermore, acifluorfen heightened the expression of apoptosis-related genes (casp8, casp9, and tp53) in zebrafish embryos. We then determined whether acifluorfen affected the viability of zebrafish liver (ZFL) cells based on its effects on liver development in vivo. The results indicated that the proliferation of ZFL cells decreased significantly in a dose-dependent manner. Additionally, acifluorfen-treated ZFL cells exhibited a slight increase in apoptotic cells stained with annexin V and propidium iodide. In summary, these findings establish a baseline concentration for acifluorfen's effects on aquatic ecosystems and non-target organisms.

Design, Synthesis, and Biological Activity of Novel Phenyltriazolinone PPO Inhibitors Containing Five-Membered Heterocycles.

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) catalyzes the oxidation of protoporphyrinogen IX to protoporphyrin IX, which is a key step in the synthesis of porphyrins in vivo. PPO inhibitors use protoporphyrinogen oxidase as the target and block the biosynthesis process of porphyrin by inhibiting the activity of the enzyme, eventually leading to plant death. In this paper, phenyl triazolinone was used as the parent structure, and the five-membered heterocycle with good herbicidal activity was introduced by using the principle of substructure splicing. According to the principle of bioisosterism, the sulfur atoms on the thiophene ring were replaced with oxygen atoms. Finally, 33 phenyl triazolinones and their derivatives were designed and synthesized, and their characterizations and biological activities were investigated. The in vitro PPO inhibitory activity and greenhouse herbicidal activity of 33 target compounds were determined, and compound D4 with better activity was screened out. The crop safety determination, field weeding effect determination, weeding spectrum determination, and crop metabolism study were carried out. The results showed that compound D4 showed good safety to corn, soybean, wheat, and peanut but poor selectivity to cotton. The field weeding effect of this compound is comparable to that of the commercial herbicide sulfentrazone. The herbicidal spectrum experiment showed that compound D4 had a wide herbicidal spectrum and a good growth inhibition effect on dicotyledonous weeds. Molecular docking results showed that compound D4 forms a hydrogen bond with amino acid residue Arg-98 in the tobacco mitochondria (mtPPO)-active pocket and forms two π-π stacking interactions with Phe-392. This indicates that compound D4 has stronger PPO inhibitory activity. This indicates that compound D4 has wide prospects for development.

Dual plastid targeting of protoporphyrinogen oxidase 2 in Amaranthaceae promotes herbicide tolerance.

Plant tetrapyrrole biosynthesis (TPB) takes place in plastids and provides the chlorophyll and heme required for photosynthesis and many redox processes throughout plant development. TPB is strictly regulated, since accumulation of several intermediates causes photodynamic damage and cell death. Protoporphyrinogen oxidase (PPO) catalyzes the last common step before TPB diverges into chlorophyll and heme branches. Land plants possess two PPO isoforms. PPO1 is encoded as a precursor protein with a transit peptide, but in most dicotyledonous plants PPO2 does not possess a cleavable N-terminal extension. Arabidopsis (Arabidopsis thaliana) PPO1 and PPO2 localize in chloroplast thylakoids and envelope membranes, respectively. Interestingly, PPO2 proteins in Amaranthaceae contain an N-terminal extension that mediates their import into chloroplasts. Here, we present multiple lines of evidence for dual targeting of PPO2 to thylakoid and envelope membranes in this clade and demonstrate that PPO2 is not found in mitochondria. Transcript analyses revealed that dual targeting in chloroplasts involves the use of two transcription start sites and initiation of translation at different AUG codons. Among eudicots, the parallel accumulation of PPO1 and PPO2 in thylakoid membranes is specific for the Amaranthaceae and underlies PPO2-based herbicide resistance in Amaranthus species.

Design, Synthesis, and Herbicidal Activity of Substituted 3-(Pyridin-2-yl)Phenylamino Derivatives.

To discover protoporphyrinogen oxidase (PPO) inhibitors with robust herbicidal activity and crop safety, three types of substituted 3-(pyridin-2-yl)phenylamino derivatives bearing amide, urea, or thiourea as side chain were designed via structure splicing strategy. Postemergence herbicidal activity assessment of 33 newly prepared compounds revealed that many of our compounds such as 6a, 7b, and 8d exhibited superior herbicidal activities against broadleaf and monocotyledon weeds to commercial acifluorfen. In particular, compound 8d exhibited excellent herbicidal activities and high crop safety at a dosage range of 37.5-150 g ai/ha. PPO inhibitory studies supported our compounds as typical PPO inhibitors. Molecular docking studies revealed that compound 8d provided effective interactions with Nicotiana tabacum PPO (NtPPO) via diverse interaction models, such as π-π stacking and hydrogen bonds. Molecular dynamics (MD) simulation studies and degradation studies were also conducted to gain insight into the inhibitory mechanism. Our study indicates that compound 8d may be a candidate molecule for the development of novel herbicides.

Herbicide‐resistant weeds from dryland agriculture in Argentina

AbstractWe reviewed and performed a quantitative synthesis on herbicide‐resistant weeds from rain‐fed crops in Argentina. Twenty‐four weed species distributed in the main extensive crops (soybean, maize, wheat, barley, oilseed rape, sunflower, chickpea and peanut) have evolved herbicide resistance. Of the total, 54% are grasses, 88% are annual species and 63% are cross‐pollinated species. The most representative families were Poaceae with 54% resistant species, followed by Brassicaceae with 17%, and Asteraceae with 13%. Buenos Aires, Santa Fe and Córdoba were the provinces with the most documented cases of resistance (35%, 33% and 30%, respectively). The proportion of cases resistant to pre‐emergence herbicides was 10%, whereas the proportion of cases resistant to post‐emergence herbicides was 90%. Glyphosate was the herbicide with the highest incidence (92%) of resistance among weed species, followed by 29% of species that evolved resistance to ALS‐inhibiting herbicides. Whereas resistance to auxin‐like herbicides comprised 17% of the weed species, acetyl‐CoA carboxylase (8%) and protoporphyrinogen oxidase (4%) inhibiting herbicides showed the least incidence of resistance evolution among weeds. The highest number of resistant species was identified in soybean (19), followed by maize (13), wheat/barley (10) and fallow (9). Weed species with a higher number of resistant populations to a higher number of herbicide mode of action were Amaranthus hybridus, A. palmeri, Lolium multiflorum and Raphanus sativus. The change in the production system since the mid‐1990s, based on the use of herbicides (glyphosate mainly) to control weeds, is likely to account for the notorious increase in the average rate of evolution of herbicide‐resistant weeds in Argentina.

Common ragweed (Ambrosia artemisiifolia L.) accessions in the Mid-Atlantic region resistant to ALS-, PPO-, and EPSPS-inhibiting herbicides

Abstract Common ragweed is a troublesome weed in many crops. Farmers and crop advisors in the coastal Mid-Atlantic region have reported inadequate control of common ragweed in soybean fields with glyphosate and other herbicide modes of action. To determine whether herbicide resistance was one of the causes of poor herbicide performance, 29 accessions from four states (Delaware, Maryland, New Jersey, and Virginia) where common ragweed plants survived herbicide applications and produced viable seeds were used for greenhouse screening. Common ragweed seedlings from those accessions were treated with multiple rates of cloransulam, fomesafen, or glyphosate, applied individually postemergence (POST). All accessions except one demonstrated resistance to at least one of the herbicides applied at twice the effective rate (2×), 17 accessions were two-way resistant (to glyphosate and cloransulam, or to glyphosate and fomesafen), and three-way resistance was present in eight accessions collected from three different states. Based on the POST study, five accessions were treated preemergence (PRE) with herbicides that inhibit acetolactate synthase (ALS), and two accessions were treated with herbicides that inhibit protoporphyrinogen oxidase (PPO). All accessions treated PRE with the ALS inhibitors chlorimuron or cloransulam demonstrated resistance at the 2× rates. Both accessions treated PRE with the PPO inhibitor sulfentrazone had survivors at the 2× rate. When the same accessions were treated PRE with fomesafen, one had survivors at the 2× rate, and one had survivors at the 1× rate. Results from these tests confirmed common ragweed with three-way resistance to POST herbicides is widespread in the region. In addition, this is the first confirmation that common ragweed accessions in the region are also resistant to ALS- or PPO-inhibiting herbicides when applied PRE.