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In this study, the hydrolysis of diclofop‐methyl (DM) in aqueous system and the bioaccumulation of its main metabolite, Diclofop (DA), in the tubifex worms were investigated using enantioselective high‐performance liquid chromatography. With the addition of tubifex, rapid hydrolysis was observed for DM. It is revealed that the hydrolysis of DM in the water and the accumulation of DA in the worms were both enantioselective. Meanwhile, either the hydrolysis amount or the levels of enantioselectivity were influenced by the tubifex. After incubated for 24 h, about 94.6% of the DM was hydrolyzed and the enantiomer fraction of metabolite (DA) deviated from 0.5 with R‐DA significantly higher than S‐DA. The enantiopure S‐DM and R‐DM and S‐DA and R‐DA were incubated, and enantiomerizations were detected between the two DM enantiomers with S‐form inversing into R‐form and vice versa. It was found that the S‐DM exhibited a higher tendency to invert than the R‐DM. [ABSTRACT FROM AUTHOR]

Context: Annual ryegrass (Lolium rigidum) is a major weed of crop production in southern Australia that readily develops resistance to herbicides. Resistance increases both yield losses and control costs associated with this species. Aims: This study aimed to gauge the extent and distribution of resistance to herbicides in L. rigidum across south-eastern Australian grain production systems by collecting seed from randomly selected fields. Methods: A total of 1441 weed populations were collected through random surveys conducted over 5 years across 13 agricultural regions of four states with these samples then tested for resistance to eight herbicides from six modes of action. Key results: Resistance to diclofop-methyl and sulfometuron-methyl was most common, being present in 64% and 63% of populations respectively. Glyphosate resistance was present in 4% of populations collected. Only 15% of populations collected were susceptible to all herbicides tested. Large differences in resistance occurred between the 13 regions surveyed with resistance to diclofop-methyl ranging from 15% to 86% of populations and sulfometuron-methyl from 12% to 96%. Resistance to post-emergent herbicides tended to be higher than pre-emergent herbicides. Multiple resistance was common with 60% of populations collected having resistance to two or more herbicide modes of action. Conclusions: There were significant differences in the extent of multiple resistance in L. rigidum populations collected from individual regions suggesting that the rates of resistance evolution have differed between regions. Implications : The high incidence of herbicide resistance in L. rigidum populations randomly collected from south-eastern Australian cropping fields highlights the need for the adoption of additional weed control practices to mitigate the impact of this species on grain production systems. Herbicide resistant weeds are a major threat to crop production, with annual ryegrass being the major species of concern in Australia. Surveys of south-eastern Australia conducted over a 5 year period found over 60% of populations were resistant to two or more herbicide groups and only 15% of ryegrass populations were susceptible to all tested herbicides. The high level of resistance found across south-eastern Australia highlights the need for farmers to adopt non-herbicide practices, in conjunction with herbicides, to control this species. [ABSTRACT FROM AUTHOR]

Diclofop-methyl, an aryloxyphenoxypropionate (AOPP) herbicide, is a chiral compound with two enantiomers. Microbial detoxification and degradation of various enantiomers is garnering immense research attention. However, enantioselective catabolism of diclofop-methyl has been rarely explored, especially at the molecular level. This study cloned two novel hydrolase genes (dcmA and dcmH) in Sphingopyxis sp. DBS4, and characterized them for diclofop-methyl degradation. DcmA, a member of the amidase superfamily, exhibits 26.1–45.9% identity with functional amidases. Conversely, DcmH corresponded to the DUF3089 domain-containing protein family (a family with unknown function), sharing no significant similarity with other biochemically characterized proteins. DcmA exhibited a broad spectrum of substrates, with preferential hydrolyzation of (R)-(+)-diclofop-methyl, (R)-(+)-quizalofop-ethyl, and (R)-(+)-haloxyfop-methyl. DcmH also preferred (R)-(+)-quizalofop-ethyl and (R)-(+)-haloxyfop-methyl degradation while displaying no apparent enantioselective activity towards diclofop-methyl. Using site-directed mutagenesis and molecular docking, it was determined that Ser175 was the fundamental residue influencing DcmA's activity against the two enantiomers of diclofop-methyl. For the degradation of AOPP herbicides, DcmA is an enantioselective amidase that has never been reported in research. This study provided novel hydrolyzing enzyme resources for the remediation of diclofop-methyl in the environment and deepened the understanding of enantioselective degradation of chiral AOPP herbicides mediated by microbes. [Display omitted] • Sphingopyxis sp. DBS4 degrade rac -diclofop-methyl with obvious enantioselectivity. • Two novel diclofop-methyl hydrolase genes, dcmA and dcmH , were cloned and expressed. • DcmA prioritized (R)-(+)-diclofop-methyl degradation. • DcmA is the first enantioselective amidase for AOPP herbicide degradation. [ABSTRACT FROM AUTHOR]

Different Lolium species, common weeds in cereal fields and fruit orchards in Chile, were reported showing isolated resistance to the acetyl CoA carboxylase (ACCase), acetolactate synthase (ALS) and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibiting herbicides in the late 1990s. The first case of multiple resistance to these herbicides was Lolium multiflorum found in spring barley in 2007. We hypothesized that other Lolium species may have evolved multiple resistance. In this study, we characterized the multiple resistance to glyphosate, diclofop-methyl and iodosulfuron-methyl-sodium in Lolium rigidum, Lolium perenne and Lolium multiflorum resistant (R) populations from Chile collected in cereal fields. Lolium spp. populations were confirmed by AFLP analysis to be L. rigidum, L. perenne and L. multiflorum. Dose-response assays confirmed multiple resistance to glyphosate, diclofop-methyl and iodosulfuron methyl-sodium in the three species. Enzyme activity assays (ACCase, ALS and EPSPS) suggested that the multiple resistance of the three Lolium spp. was caused by target site mechanisms, except the resistance to iodosulfuron in the R L. perenne population. The target site genes sequencing revealed that the R L. multiflorum population presented the Pro-106-Ser/Ala (EPSPS), Ile-2041-Asn++Asp-2078-Gly (ACCase), and Trp-574-Leu (ALS) mutations; and the R L. rigidum population had the Pro-106-Ser (EPSPS), Ile-1781-Leu+Asp-2078-Gly (ACCase) and Pro-197-Ser/Gln+Trp-574-Leu (ALS) mutations. Alternatively, the R L. perenne population showed only the Asp-2078-Gly (ACCase) mutation, while glyphosate resistance could be due to EPSPS gene amplification (no mutations but high basal enzyme activity), whereas iodosulfuron resistance presumably could involve non-target site resistance (NTSR) mechanisms. These results support that the accumulation of target site mutations confers multiple resistance to the ACCase, ALS and EPSPS inhibitors in L. multiflorum and L. rigidum from Chile, while in L. perenne, both target and NTSR could be present. Multiple resistance to three herbicide groups in three different species of the genus Lolium in South America represents a significant management challenge.

SUMMARY: Rapid and widespread evolution of multiple herbicide resistance in global weed species endowed by increased capacity to metabolize (degrade) herbicides (metabolic resistance) is a great threat to herbicide sustainability and global food production. Metabolic resistance in the economically damaging crop weed species Lolium rigidum is well known but a molecular understanding has been lacking. We purified a metabolic resistant (R) subset from a field evolved R L. rigidum population. The R, the herbicide susceptible (S) and derived F2 populations were used for candidate herbicide resistance gene discovery by RNA sequencing. A P450 gene CYP81A10v7 was identified with higher expression in R vs. S plants. Transgenic rice overexpressing this Lolium CYP81A10v7 gene became highly resistant to acetyl‐coenzyme A carboxylase‐ and acetolactate synthase‐inhibiting herbicides (diclofop‐methyl, tralkoxydim, chlorsulfuron) and moderately resistant to hydroxyphenylpyruvate dioxygenase‐inhibiting herbicide (mesotrione), photosystem II‐inhibiting herbicides (atrazine and chlorotoluron) and the tubulin‐inhibiting herbicide trifluralin. This wide cross‐resistance profile to many dissimilar herbicides in CYP81A10v7 transgenic rice generally reflects what is evident in the R L. rigidum. This report clearly showed that a single P450 gene in a cross‐pollinated weed species L. rigidum confers resistance to herbicides of at least five modes of action across seven herbicide chemistries. [ABSTRACT FROM AUTHOR]

Different Lolium species, common weeds in cereal fields and fruit orchards in Chile, were reported showing isolated resistance to the acetyl CoA carboxylase (ACCase), acetolactate synthase (ALS) and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibiting herbicides in the late 1990s. The first case of multiple resistance to these herbicides was Lolium multiflorum found in spring barley in 2007. We hypothesized that other Lolium species may have evolved multiple resistance. In this study, we characterized the multiple resistance to glyphosate, diclofop-methyl and iodosulfuron-methyl-sodium in Lolium rigidum , Lolium perenne and Lolium multiflorum resistant (R) populations from Chile collected in cereal fields. Lolium spp. populations were confirmed by AFLP analysis to be L. rigidum , L. perenne and L. multiflorum. Dose-response assays confirmed multiple resistance to glyphosate, diclofop-methyl and iodosulfuron methyl-sodium in the three species. Enzyme activity assays (ACCase, ALS and EPSPS) suggested that the multiple resistance of the three Lolium spp. was caused by target site mechanisms, except the resistance to iodosulfuron in the R L. perenne population. The target site genes sequencing revealed that the R L. multiflorum population presented the Pro-106-Ser/Ala (EPSPS), Ile-2041-Asn++Asp-2078-Gly (ACCase), and Trp-574-Leu (ALS) mutations; and the R L. rigidum population had the Pro-106-Ser (EPSPS), Ile-1781-Leu+Asp-2078-Gly (ACCase) and Pro-197-Ser/Gln+Trp-574-Leu (ALS) mutations. Alternatively, the R L. perenne population showed only the Asp-2078-Gly (ACCase) mutation, while glyphosate resistance could be due to EPSPS gene amplification (no mutations but high basal enzyme activity), whereas iodosulfuron resistance presumably could involve non-target site resistance (NTSR) mechanisms. These results support that the accumulation of target site mutations confers multiple resistance to the ACCase, ALS and EPSPS inhibitors in L. multiflorum and L. rigidum from Chile, while in L. perenne , both target and NTSR could be present. Multiple resistance to three herbicide groups in three different species of the genus Lolium in South America represents a significant management challenge. [ABSTRACT FROM AUTHOR]

According to Article 12 of Regulation (EC) No 396/2005, EFSA has reviewed the maximum residue levels (MRLs) currently established at European level for the pesticide active substance diclofop. To assess the occurrence of diclofop residues in plants, processed commodities, rotational crops and livestock, EFSA considered the conclusions derived in the framework of Commission Regulation (EC) No 33/2008, as well as the European authorisations reported by Member States (including the supporting residues data). Based on the assessment of the available data, MRL proposals were derived and a consumer risk assessment was carried out. Although no apparent risk to consumers was identified, some information required by the regulatory framework was missing. Hence, the consumer risk assessment is considered indicative only and the MRL proposals derived by EFSA still require further consideration by risk managers. [ABSTRACT FROM AUTHOR]

Weeds are one of the main threats to crop yield. Field experiments were carried out to investigate the efficiency of bio-stimulants (amino acid, humic acid, gibbrillic acid) and weed control methods (clethodium, fluzifop-butyl, clodinafop-propargyl, diclofop-methyl and two hand hoeing) as well as their interactive effects on garlic plant and weeds in Nubaria, Egypt. Application of amino acids at the concentration 100 ppm caused markedly increases in dry weight weeds species under investigation compared with control. Clodinafop-propargyl treatment coefficient has exceeded the rest of the treatments in reducing the narrow weeds accompanying the garlic plants. Application of clethodium treatment produced the maximum values of growth, blub yield and yield attributes. Moreover, two hand hoeing produced the maximum values of photo synthetic pigments and biochemical constituents. The interaction between bio-stimulants and weed control had a significant effect on total dry weight of narrow-leaved weeds, average bulb weight and bulb garlic yield. Clethodium herbicide integrated with amino acid at the concentration 100 ppm application produced the maximum values of garlic blub yield. It can be suggested that the use of clethodium or diclofop herbicide combined with amino acid has better the growth and yield of garlic plants under newly reclaimed soil conditions. [ABSTRACT FROM AUTHOR]

Introduction Soil herbicides residue in agroecosystems is one of the important problems due to herbicides application. However herbicides residue in soil extend the period of weed control. Nevertheless, it may persist longer than desired and injure subsequent crops in rotation. Herbicides vary in their potential to persist in the soil. Some herbicides such as sulfonylurea herbicides are very persistent. Among registered herbicides for weed control in wheat fields in Iran, Sulfonylurea (e.g. sulfosulfuron and metsulforon-methyl+sulfosulforon) and aryloxy phenoxy propionate (e.g. Diclofop-methyl, fenoxaprop-p-ethyl) are more important groups. With regard to the persistence of mentioned herbicides in soil, sulfonylurea herbicides may create problems in crop rotation. Since chickpea (Cicer arietinum L.) is one of important crops in rotation with wheat in Iran and the effect of sulfosulfuron, metsulforon-methyl+sulfosulforon, diclofop-methyl and fenoxaprop-p-ethyl on its growth, nodulation, and nitrogen fixation have not been studied yet. This study was conducted to investigate the effects of mentioned herbicides residue in soilon growth, nodulation, and nitrogen fixation of chickpea genotypes in controlled conditions. Material and Methods In order to study the effects of soil residue of some sulfonylurea and aryloxy phenoxy propionate herbicides on growth, nodulation and nitrogen fixation of chickpea (Cicer arietinum L.), a pot experiment was conducted using factorial arrangement in a completely randomized design with three replications. Factors included herbicide type in four levels (diclofop-methyl, fenoxaprop-p-ethyl, sulfosulfuron and metsulforon-methyl+sulfosulforon), herbicides residue in soil in eight levels (0, 2.5, 5, 10, 15, 20, 30, and 40 percent of recommended dose for each herbicide) and chickpea genotypes in three levels (Hashem, ILC 482, and KaKa). After mixing the herbicide solution with prepared soil and planting, plants were maintained until the beginning of reproductive stage. In the early stage of reproductive, shoot biomass and root biomass, number of root node and total nitrogen content of plants were measured. The data were statistically analyzed using variance analysis, and differences among mean values of treatments were compared by Duncan test (p≤0.05) in SAS. For determination the dose of herbicides required to reduce 50% of plants response (ED50), the dose response curves were fitted simultaneously using the following three-parameter logistic model. f(x,(b,d,e))= d/(1+exp⁡〖{b(log⁡(x)-log⁡〖(e))}〗 〗 ) Where f is the response (above ground dry weight, root dry weight and node dry weight), d is the upper limit, b is the curve slope, e denotes the dose required to give a response halfway between the upper and lower limits (ED50); and x is the herbicide concentration in soil. The validity of the above model and the comparison between the parameters were made using F-test for lack-of-fit with a 5% level of significance. Results and Discussion Results showed that sulfonylurea (sulfosulfuron and metsulforon-methyl+sulfosulforon) and aryloxy phenoxy propionate (diclofop-methyl, fenoxaprop-p-ethyl) had the highest and the lowest effect on mentioned traits of plants, respectively. By increasing of sulfonylurea herbicides residue in soil, all measured traits decreased significantly (p≤0.01). However, soil residue of aryloxy phenoxy propionates herbicides did not significantly affect on chickpea genotypes. The lowest ED50 (0.0025 mg kg-1 soil) and the highest ED50 (0.0047 mg kg-1 soil) of sulfosulfuron herbicide soil residue for shoot biomass, were observed in Hashem and ILC482 genotypes, respectively and the lowest ED50 (0.0057 mg kg-1 soil) and the highest ED50 (0.0837 mg kg-1 soil) of metsulforon-methyl+sulfosulforon herbicide soil residue, were observed in ILC482 and KaKa genotypes, respectively. Considering the results of the study, it can be noted that Hashem genotype showed more sensitivity to sulfosulfuron and metsulforon-methyl+sulfosulforon herbicides soil residue compared to the other genotypes. Generally, results of this experiment showed that soil residue of sulfosulfuron and metsulforon-methyl+sulfosulforon herbicides had significant and negative impact on chickpea growth. On the other hand, chickpea genotypes had different sensitivity to soil residue herbicides. Conclusion Results indicated that it is necessary to look the interval time in chickpea planting in rotation of wheat-chickpea. Moreover, selection of less sensitive chickpea genotypes to soil residue of sulfosulfuron and metsulforon-methyl+sulfosulforon herbicides could be useful in their residue management. Key words: Chickpea genotypes, Diclofop-methyl, Fenoxaprop-p-ethyl, Metsulforon-methyl+sulfosulforon, Sulfosulfuron

A better knowledge of the intertwined effects of herbicides on plant physiology and microbiome as well as nutrient biogeochemical cycles are needed for environmental management. Here we studied the influence of herbicide diclofop-methyl (DM) on the rice root microbiome and its relationship with N cycle. To do so, we exposed rice seedlings to 100 μg/L DM and studied rhizosphere microbiota using MiSeq-pyrosequencing, root exudation by GC–MS, and denitrification activity by 15 N isotope-tracing and qRT-PCR. The richness and diversity of rhizosphere microorganisms, significantly increased after DM exposure combined with an increase in root exudation of amino acids, sugars, and fatty acids. Transcription of denitrification-related gene and denitrification rate increased significantly in the rice rhizosphere. Our results suggest that DM strongly influenced the root exudation of bacteria nutrients, which affected root microbiome community and potentially influenced N cycle in rice rhizosphere. [ABSTRACT FROM AUTHOR]

Weed control failures due to herbicide resistance are an increasing and worldwide problem significantly impacting crop yields. Herbicide resistance due to increased herbicide metabolism in weeds is not well characterized at the genetic level. An RNA-Seq transcriptome analysis was used to identify genes conferring metabolism-based herbicide resistance (MBHR) in a population (R) of a major global weed (Lolium rigidum), in which resistance to the herbicide diclofop-methyl was experimentally evolved through recurrent selection from a susceptible (S) progenitor population. A reference transcriptome of 19,623 contigs was assembled using 454 sequencing technology on a cDNA library and annotated using UniProt and Pfam databases. Transcriptomic-level gene expression was measured using Illumina 100 bp reads from untreated control, mock, and diclofop-methyl treatments of R and S. Due to the established importance of cytochrome P450 (CytP450), glutathione-S-transferase (GST), and glucosyltransferase (GT) genes in MBHR, 11 contigs with these annotations and higher constitutive expression in untreated R than in untreated S were selected as candidate genes for hypothesis testing, along with 17 additional differentially expressed contigs with annotations related to metabolism or signal transduction. In a forward genetics validation experiment, higher constitutive expression of nine contigs co-segregated with the resistance phenotype in an F2 population, including 3 CytP450, 3 GST, and 1 GT. At least nine genes with heritable increased constitutive expression are associated with MBHR trait. In a physiological validation experiment where 2, 4-D pre-treatment induced diclofop-methyl protection in S individuals due to increased metabolism, seven of the nine genetically-validated contigs were significantly induced. These data help explain accumulation of resistance-endowing genes and rapid evolution of MBHR, and provide the opportunity to improve diagnostics of MBHR using molecular tools such as transcriptional markers.

Diclofop-methyl (DM), a common post-emergence herbicide, is frequently used in agricultural production. Silver nanoparticles (AgNPs) are one of the most widely used nanoparticles, and as such, have been detected and monitored in several environmental systems. Here we investigated the interactive effects of DM and AgNPs on the physiological morphology, photosynthesis and antioxidant system of Arabidopsis thaliana . Our results demonstrated that a 1.0 mg/L DM treatment had no significant effect on the fresh weight of plant shoots and the content of total chlorophyll and anthocyanin. However, a 0.5 mg/L AgNPs treatment was found to significantly inhibit plant growth and chlorophyll synthesis, and was found to cause more severe oxidative damage in plants compared to the effects observed in a hydroponic suspension in which DM and AgNPs were jointly present. Meanwhile, the relative transcript levels of photosynthesis related genes ( psb A, rbc L, pgrl1 A and pgrl1 B) in the combined group were found to be slightly increased compared to transcript levels in the AgNPs group, in order to maintain ATP generation at relatively normal levels in order to repair light damage. One explanation for these observed antagonistic effects was that the existence of DM affects the stability of AgNPs and reduced Ag + release from AgNPs in the mixed solution. Thereupon, the Ag + -content was found to decrease in shoots and roots in the combined group by 15.2% and 9.4% respectively, compared to the AgNPs group. The coexistence of herbicides and nanomaterials in aquatic environments or soil systems will continue to exist due to their wide usages. Our current study highlights that the antagonistic effects between DM and AgNPs exerted a positive impact on A. thaliana growth. [ABSTRACT FROM AUTHOR]

Lolium rigidum Gaud. is the most prevalent and damaging grass weed of winter cereals in Spain. L. rigidum infestations are frequently treated with herbicides and, consequently, populations have evolved resistance. In 2012–2013 a random survey was conducted across cereal cropping areas of the Castilla-León and Cataluña regions to establish the distribution and frequency of herbicide resistance in L. rigidum populations to chlortoluron (Photosystem II inhibitor), chlorsulfuron (Acetolactate synthase inhibitor) and diclofop-methyl (Acetyl CoA Carboxylase inhibitor), commonly used herbicides for L. rigidum control in Spain. The results of this survey were compared with the results of a previous survey conducted in 2000–02. Resistance to PSII and ALS-inhibiting herbicides was common: 51% and 92% of the accessions collected from Castilla-León and Cataluña respectively were resistant to chlortoluron, while 75% of accessions from both regions were resistant to chlorsulfuron. Resistance to ACCase was more widespread in Cataluña, where 83% of accessions were classified as resistant, than in Castilla-León where 74% of the populations were still classified as susceptible to diclofop-methyl. These results show that resistance levels to all three herbicides had increased in Castilla-León since 2000 and to chlortoluron and chlorsulfuron in Cataluña. The accessions were also treated with the double dose (2X) of each herbicide. The percentage of L. rigidum that now exhibits multiple herbicide resistance has increased considerably, especially in Cataluña where 75% of the accessions were resistant to multiple herbicides, therefore herbicide sustainability and resistance management present a great challenge. [ABSTRACT FROM AUTHOR]

Diclofop-methyl is a selective post-emergence graminicide from the phenoxy propionate group of herbicides to be developed for control of wild oats, millets, and other annual grass weeds. Diclofop-methyl usage is limited in various grass weed species due to its toxic effect and exposure risks. However, total annual usage of is approximately 750.000 pounds in United States, and more in Asia. Therefore, we aimed to investigate diclofopmethyl's toxic potentials in vitro and the following assays were used; MTT assay for cytotoxicity, comet assay for genotoxicity, generation of reactive oxygen species (ROS), malondialdehyde (MDA) and glutathione (GSH) for the potential of oxidative damage in mouse embryo fibroblast (NIH/3T3) cell line. Diclofop-methyl was observed to reduce the cell viability in a concentration manner and the half maximal inhibitory concentration (IC50) value was 301.7 μM. Diclofop-methyl caused DNA damage and oxidative stress at the concentrations between 12.5-400 μM. Tail intensities were at the range of 1.24 - 58.21% with increasing concentrations, which are approximately ≤ 1.63-fold of the negative control. Also, MDA levels were increased ≥3 11.4-fold of the negative control that denotes lipid peroxidation was induced. However, there was no significant increment in the ROS and GSH levels at all concentrations. In view of the fact that ROS has not been detected, despite its level of MDA proffers, the idea that oxidative damage may have been caused by other mechanisms. Our results indicate that diclofopmethyl was cytotoxic, genotoxic and might have oxidative damage potential in vitro conditions. [ABSTRACT FROM AUTHOR]

Diclofop-methyl (DM), a widely used herbicide in food crops, may partly contaminate the soil surface of natural ecosystems in agricultural area and exert toxic effects at low dose to nontarget plants. Even though rhizosphere microorganisms strongly interact with root cells, little is known regarding their potential modulating effect on herbicide toxicity in plants. Here we exposed rice seedlings (Xiushui 63) to 100 μg/L DM for 2 to 8 days and studied the effects of DM on rice rhizosphere microorganisms, rice systemic acquired resistance (SAR) and rice-microorganisms interactions. The results of metagenomic 16S rDNA Illumina tags show that DM increases bacterial biomass and affects their community structure in the rice rhizosphere. After DM treatment, the relative abundance of the bacterium genera Massilia and Anderseniella increased the most relative to the control. In parallel, malate and oxalate exudation by rice roots increased, potentially acting as a carbon source for several rhizosphere bacteria. Transcriptomic analyses suggest that DM induced SAR in rice seedlings through the salicylic acid (but not the jasmonic acid) signal pathway. This response to DM stress conferred resistance to infection by a pathogenic bacterium, but was not influenced by the presence of bacteria in the rhizosphere since SAR transcripts did not change significantly in xenic and axenic plant roots exposed to DM. The present study provides new insights on the response of rice and its associated microorganisms to DM stress. [ABSTRACT FROM AUTHOR]

Main conclusion : Global warming will increase the incidence of metabolism-based reduced herbicide efficacy on weeds and, therefore, the risk for evolution of non-target site herbicide resistance. Climate changes affect food security both directly and indirectly. Weeds are the major biotic factor limiting crop production worldwide, and herbicides are the most cost-effective way for weed management. Processes associated with climatic changes, such as elevated temperatures, can strongly affect weed control efficiency. Responses of several grass weed populations to herbicides that inhibit acetyl-CoA carboxylase (ACCase) were examined under different temperature regimes. We characterized the mechanism of temperature-dependent sensitivity and the kinetics of pinoxaden detoxification. The products of pinoxaden detoxification were quantified. Decreased sensitivity to ACCase inhibitors was observed under elevated temperatures. Pre-treatment with the cytochrome-P450 inhibitor malathion supports a non-target site metabolism-based mechanism of herbicide resistance. The first 48 h after herbicide application were crucial for pinoxaden detoxification. The levels of the inactive glucose-conjugated pinoxaden product (M5) were found significantly higher under high- than low-temperature regime. Under high temperature, a rapid elevation in the level of the intermediate metabolite (M4) was found only in pinoxaden-resistant plants. Our results highlight the quantitative nature of non-target-site resistance. To the best of our knowledge, this is the first experimental evidence for temperature-dependent herbicide sensitivity based on metabolic detoxification. These findings suggest an increased risk for the evolution of herbicide-resistant weeds under predicted climatic conditions. [ABSTRACT FROM AUTHOR]

O objetivo deste trabalho foi investigar o grau de tolerância de cultivares de trigo e aveia aos herbicidas diclofop-methyl, fenoxaprop-ethyl e haloxyfop-methyl, visando a utilização seletiva desses produtos para controlar espécies gramíneas infestantes dessas culturas. Foi instalado um experimento de campo e outro de casa-de-vegetação. Os tratamentos testados no experimento de campo foram diclofop-methyl (540 g/ha), fenoxaprop-ethyl (180 g/ha), haloxyfop-methyl (120 g/ha) e uma testemunha sem tratamento herbicida, aplicados sobre as cultivares 'CTC-1', 'UFRGS-7' e 'UPF-16' de aveia branca, e em aveia-preta. No experimento de casa-de-vegetação testaram-se três doses de fenoxaprop-ethyl (0, 90 e 120 g/ha), aplicadas sobre sete cultivares de trigo ('BR-23', 'BR-35', 'BR-38', 'E-16', 'E-40', 'E-49' e 'E-52'), aveia-branca, aveia-preta e azevém. Como resultados do ensaio de campo, constatou-se que todos os herbicidas testados controlaram com eficiência (acima de 90%) as cultivares de aveia-branca. A aveia-preta mostrou alta sensibilidade ao fenoxaprop-ethyl e ao haloxyfop-methyl e alguma tolerância ao diclofop-methyl; já o trigo mostrou-se tolerante ao diclofop-methyl e ao fenoxaprop-ethyl. Em casa-de-vegetação, as cultivares de trigo 'BR-38', 'E-16', 'E-49' e 'E-52' apresentaram níveis aceitáveis de fitotoxicidade para fenoxaprop-ethyl a 90 g/ha, enquanto as demais cultivares ('BR-23', 'BR-35' e 'E-40') apresentaram danos moderados ao herbicida. Já fenoxaprop-ethyl a 120 g/ha causou aumento no nível de fitotoxicidade para as cultivares de trigo, exceto para 'E-16' e 'E-52'. O azevém mostrou-se tolerante ao herbicida fenoxaprop-ethyl. Conclui-se que existe potencial de uso do herbicida fenoxaprop-ethyl em lavouras de trigo para controlar seletivamente aveia-branca e aveia-preta. O herbicida diclofop-methyl apresenta controle elevado de aveia-branca e reduzido de aveia-preta. Haloxyfop-methyl não evidenciou seletividade ao trigo, controlando com eficiência as gramíneas testadas.The objective of this study was to investigate the tolerance levels of wheat and oat cultivars to the herbicide diclofop-methyl, fenoxaprop-ethyl and haloxyfop-methyl, aiming the selective use of these chemicals to control grass species that may infest these crops. Two experiments have been performed, one at field condition and another in the greenhouse. Treatments tested in the field were diclofop-methyl at 540 g/ha, fenoxaprop-ethyl at 180 g/ha, haloxyfop-methyl at 120 g/ha, plus a check without herbicide treatment, applied on Avena sativa cultivars 'CTC-1', 'UFRGS-7' and 'UPF-16', and on Avena strigosa. In the greenhouse experiment, three rates of fenoxaprop-ethyl (0, 90 and 120 g/ha) have been tested, applied on seven wheat cultivars ('BR-23', 'BR-35', 'BR-38', 'E-16', 'E-40', 'E-49' and 'E-52'), on aots, Avena strigosa and ryegrass. As results of field trial, it was detected that all herbicides tested controlled efficiently (over 90%) oat cultivars. Avena strigosa showed high sensitivity to fenoxaprop-ethyl and haloxyfop-methyl, and some tolerance to diclofop-methyl, whereas wheat showed tolerance to diclofop-methyl and fenoxaprop-ethyl. In the greenhouse, wheat cultivars 'BR-38', 'E-16', 'E-49' and 'E-52' presented cceptable levels of injury to fenoxaprop-ethyl at 90 g/ha, while the other cultivars ('BR-23', 'BR-35' and 'E-52') presented moderate injury to the herbicide. On the other hand, fenoxaprop-methyl at 120 g/ha caused increased injury levels to all wheat cultivars, except 'E-16' and 'E-52'. Ryegrass showed tolerance to fenoxaprop-ethyl . It was concluded that it is possible to use fenoxaprop-ethyl herbicide in wheat fields for selective controle of oats and A. strigosa. Diclofop-methyl presents high levels of oats control, but reduced control of A. strigosa. Haloxyfop-methyl did not prove selective for wheat, controlling with efficiency the grasses tested.

Pesticides and related environmental contaminants have always been threated to human health due to their intrinsic toxicity. In the context of this contribution, the interaction between diclofop-methyl (DM) enantiomers and human serum albumin (HSA) has been characterized by steady state and three-dimensional fluorescence, molecular modeling, circular dichroism (CD) and ultraviolet-visible (UV-vis) spectroscopy. The binding constants significantly showed the binding was enantioselective and HSA had higher affinity for S-DM. The thermodynamic parameters of the binding reaction (ΔG, ΔH and ΔS) clearly signified that hydrophobic effects and H-bonds contribute to the formation of DM-HSA complex. The alterations of protein secondary structure in the presence of DM enantiomers were confirmed by CD spectroscopy, UV-vis and three-dimensional fluorescence spectroscopy. In addition, both fluorescence probe study and molecular modeling simulation evidenced the binding of DM enantiomers to HSA primarily took place in subdomain IIIA (Sudlow's site II). This investigation highlights the binding mechanism, specific binding sites and binding region of DM enantiomers on human serum albumin at the first time. Besides, such task can provide important insight to the interaction of the physiological protein HSA with chiral aryloxyphenoxypropionate herbicides and give support to the human health risk assessment. [ABSTRACT FROM AUTHOR]

An efficient and reliable enantioseparation method by high-performance liquid chromatography (HPLC) for the chiral herbicide diclofop-methyl (DM) and its primary metabolite diclofop (DC) was developed and validated, and the biological process of the enantiomers in loach liver microsomes (LLM) in vitro was investigated. The enantiomers of DM and DC were first separated on an immobilized-type stationary phase of Chiralpak IC. The best resolutions were achieved under the chromatographic condition of n -hexane/IPA/TFA 96:4:0.1(v/v/v) at 20 °C with each R s > 2 and the two pairs of enantiomers could be eluted in about 10 min. The extraction recoveries of the analytes from LLM were 79.6–108.9% with RSD ≤ 11.5%. The enzyme kinetics of DM enantiomers were different, with the K m value 320.7 for (S)-DM and 392.1 for (R)-DM. The metabolism experiment in vitro showed DM underwent a rapid phase-I metabolism with or without NADPH, indicating the esterases in liver played a dominant role. No interconversion between the two enantiomers was observed by single-enantiomer incubation. The preferential degradation of (S)-DM was confirmed with the half-time ( t 1/2 ) of (S)-DM 5.27 min and 21.2 min for (R)-DM. DC enantiomer was generated by its corresponding ester form and could not be further degraded during the incubation. It was the first study on biotransformation of DM and DC enantiomers in LLM in vitro . The results may help to evaluate the ecological risks of chiral pesticides. [ABSTRACT FROM AUTHOR]

Weed control failures due to herbicide resistance are an increasing and worldwide problem that significantly affect crop yields. Metabolism-based herbicide resistance (referred to as metabolic resistance) in weeds is not well characterized at the genetic level. An RNA-Seq transcriptome analysis was used to find candidate genes that conferred metabolic resistance to the herbicide diclofop in a diclofop-resistant population (R) of the major global weed Lolium rigidum. A reference c DNA transcriptome (19 623 contigs) was assembled and assigned putative annotations. Global gene expression was measured using Illumina reads from untreated control, adjuvant-only control, and diclofop treatment of R and susceptible (S). Contigs that showed constitutive expression differences between untreated R and untreated S were selected for further validation analysis, including 11 contigs putatively annotated as cytochrome P450 (CytP450), glutathione transferase ( GST), or glucosyltransferase ( GT), and 17 additional contigs with annotations related to metabolism or signal transduction. In a forward genetics validation experiment, nine contigs had constitutive up-regulation in R individuals from a segregating F2 population, including three CytP450, one nitronate monooxygenase ( NMO), three GST, and one GT. Principal component analysis using these nine contigs differentiated F2-R from F2-S individuals. In a physiological validation experiment in which 2,4-D pre-treatment induced diclofop protection in S individuals due to increased metabolism, seven of the nine genetically validated contigs were induced significantly. Four contigs (two CytP450, NMO, and GT) were consistently highly expressed in nine field-evolved metabolic resistant L. rigidum populations. These four contigs were strongly associated with the resistance phenotype and are major candidates for contributing to metabolic diclofop resistance. [ABSTRACT FROM AUTHOR]

Lolium rigidum (annual or rigid ryegrass) is a widespread annual weed in cropping systems of southern Australia, and herbicide resistance in L. rigidum is a common problem in this region. In 2010, a random survey was conducted across the grain belt of Western Australia to determine the frequency of herbicide-resistant L. rigidum populations and to compare this with the results of previous surveys in 1998 and 2003. During the survey, 466 cropping fields were visited, with a total of 362 L. rigidum populations collected. Screening of these populations with the herbicides commonly used for control of L. rigidum revealed that resistance to the ACCase- and ALS-inhibiting herbicides was common, with 96% of populations having plants resistant to the ACCase herbicide diclofop-methyl and 98% having plants resistant to the ALS herbicide sulfometuron. Resistance to another ACCase herbicide, clethodim, is increasing, with 65% of populations now containing resistant plants. Resistance to other herbicide modes of action was significantly lower, with 27% of populations containing plants with resistance to the pre-emergent herbicide trifluralin, and glyphosate, atrazine and paraquat providing good control of most of the populations screened in this survey. Ninety five per cent of L. rigidum populations contained plants with resistance to at least two herbicide modes of action. These results demonstrate that resistance levels have increased dramatically for the ACCase- and ALS-inhibiting herbicides since the last survey in 2003 (>95% vs. 70-90%); therefore, the use of a wide range of integrated weed management options are required to sustain these cropping systems in the future. [ABSTRACT FROM AUTHOR]

Background The auxinic herbicide 2,4-D amine is known, in vitro, as a cytochrome P450 inducer. The current study uses 2,4-D pre-treatment, at the whole plant level, to study mechanism(s) of non-target site based herbicide resistance to the ACCase-inhibiting herbicide diclofop-methyl in Lolium rigidum. Results The 2,4-D pre-treatment caused up to 10-fold shift in LD50 and GR50 in dose-response to subsequently applied diclofop-methyl in a herbicide susceptible L. rigidum population. Foliar uptake and translocation of 14C-diclofop-methyl did not differ in 2,4-D pre-treated versus untreated plants. HPLC analysis revealed that de-esterification of diclofop-methyl to toxic diclofop acid was similar, but further metabolism of diclofop acid to non-toxic metabolites was significantly (1.8-fold) faster in 2,4-D pre-treated than untreated plants. HPLC profile of major polar metabolites was similar when L. rigidum and diclofop-methyl tolerant wheat were compared, but wheat metabolised diclofop acid three-fold faster than L. rigidum. In addition, 2,4-D pre-treatment also induced cross-protection against the ALS-inhibiting herbicide chlorsulfuron, and the known P450 inhibitor malathion can reverse this effect. Conclusions Protection against diclofop-methyl provided by 2,4-D pre-treatment in susceptible L. rigidum is associated with higher rates of herbicide metabolism, mirroring that identified in field-evolved, non-target site-based diclofop-methyl resistant populations. 2,4-D may induce higher level expression of herbicide-metabolising genes hence providing protection, and therefore, this 2,4-D induction system can be used, in combination with other genomic approaches, to assist isolating cytochrome P450 and other genes that are involved in herbicide metabolism and endow herbicide resistance in L. rigidum. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

ABSTRACT Lolium rigidum is an obligately cross-pollinated, genetically diverse species and an economically important herbicide resistance-prone weed. Our previous work has demonstrated that recurrent selection of initially susceptible L. rigidum populations with low herbicide rates results in rapid herbicide resistance evolution. Here we report on the mechanisms endowing low-dose-selected diclofop-methyl resistance in L. rigidum. Results showed that resistance was not due to target-site ACCase mutations or overproduction, or differential herbicide leaf uptake and translocation. The in vivo de-esterification of diclofop-methyl into phytotoxic diclofop acid was rapid and similar in resistant versus susceptible populations. However, further metabolism of diclofop acid into non-toxic metabolites was always faster in resistant plants than susceptible plants, resulting in up to 2.6-fold lower level of diclofop acid in resistant plants. This corresponded well with up to twofold higher level of diclofop acid metabolites in resistant plants. The major polar metabolites of diclofop acid chromatographically resembled those of wheat, a naturally tolerant species. Clearly, recurrent selection at reduced herbicide rates selected for non-target-site-based enhanced rates of herbicide metabolism, likely involving cytochrome P450 monooxygenases. [ABSTRACT FROM AUTHOR]

Abstract: The cyto- and genotoxicological potency of diclofop-methyl (herbicide) and lindane (insecticide) was screened using Allium cepa L. test. Onion roots were exposed for 24h to three doses, representing ¼, ½ and EC50 concentrations of each pesticide. Some microscopic endpoints as: mitotic and phase indexes, interphase nuclear volume and chromosomal aberration rate and types were evaluated. The results showed obvious concentration-dependence. Mitotic index decreased to 45-59% and 24-37%, while interphase nuclear volume was reduced to 49-54% and 36-42%, for diclofop-methyl and lindane respectively. Abnormal cell's frequency was considerably increased, too. Physiological and clastogenic types of chromosomal aberrations, as: stickiness, c-mitosis, c-anaphase, fragment and bridges, multipolarity and laggard chromosomes were observed in all corresponding concentrations. Data of this study showed that both analyzed pesticides (commonly used for decades in Albanian agriculture) can potentially induce cyto/genotoxic effect on crops and ultimately damage biota and human health. [Copyright &y& Elsevier]

Abstract: Sterile oat (Avena sterilis) is the most widely distributed, abundant and harmful weed in the winter cereals grown in Greece. Its effective control has relied for the past three decades upon the ACCase-inhibiting herbicides. However, recently many growers in northern and central Greece have experienced reduced sterile oat control after the application of fenoxaprop-p-ethyl or clodinafop-propargyl. Preliminary screening indicated that less than 80% of the treated plants in 36 and 43 out of 125 sterile oat accessions were killed (R, resistant) by the application of the four times the recommended dose of fenoxaprop-p-ethyl (R-Fx) or clodinafop-propargyl (R–Cd), whereas less than 80% of the treated plants in 29 of them were killed by both herbicides applied at four times the recommended dose. Also, more than 80% of the treated plants in 42 and 35 accessions were killed by the four times the recommended dose (r, partially resistant) of fenoxaprop-p-ethyl (r-Fx) or clodinafop-propargyl (r-Cd), respectively. Finally, more than 80% of the treated plants in 47 and 47 accessions were killed (S, susceptible) by the recommended dose of fenoxaprop-p-ethyl (S-Fx) or clodinafop-propargyl (S-Cd), respectively, whereas more than 80% of the treated plants in 36 of these accessions were killed by the recommended dose of both herbicides. The whole-plant dose-response method used to evaluate 17 R-Fx and five S-Fx accessions showed that 16, 17, 11, and two R-Fx accessions were cross-resistant to clodinafop-propargyl, diclofop-methyl, tralkoxydim, and pinoxaden, respectively. In particular, more than 50% of the treated plants in 12, 12, 17, and three accessions survived the respective application of the four times the recommended dose of fenoxaprop-p-ethyl, clodinafop-propargyl, diclofop-methyl, and tralkoxydim. Regarding pinoxaden, 3, 17 and 20% of the treated plants in three accessions survived its application at four times the recommended dose. All R and the S accessions were effectively controlled by the recommended dose of imazamox and mesosulfuron-methyl + iodosulfuron methyl-sodium. These results strongly suggest that cross-resistance to ACCase-inhibiting herbicides has been developed for sterile oat. Therefore, measures should be taken for crop rotation when possible or rotational use of the available ALS- and ACCase-inhibiting herbicides in order to reduce the potential for development of sterile oat multiple resistance. Regarding the accessions with cross-resistance to APP, CHD and PPZ, these could be effectively controlled by the application of mesosulfuron-methyl + iodosulfuron methyl-sodium. [Copyright &y& Elsevier]

Abstract: This experiment studied the behaviour of diclofop-methyl (DM) and its main metabolite, diclofop (DC), during the pickling process. DM showed obvious enantioselective degradation in the pickled cabbage in the pickling process, with a half-life of 4.95days for (+)-(R)-DM but less than 12h for (−)-(S)-DM. In addition, the stereoselective degradation of DM also led to the enantioselective formation of DC. Therefore, (−)-(S)-DC showed a higher residue level than (+)-(R)-DC in both pickled cabbage and its brine. Rac-DC was added into the cabbage used for pickling to study the behaviour of the enantiomers of DC; no enantioselective degradation was observed either in the pickled cabbage or in the brine. DM and DC were configurationally stable in the process, showing no interconversion of (−)-(S)- to (+)-(R)- enantiomer, or vice versa. This research provides information for evaluating the risk of food safety and environmental pollution at the enantiomer level. [Copyright &y& Elsevier]

Diclofop-methyl (DM) is a chlorophenoxy derivative used in large quantities for the control of annual grasses in grain and vegetable crops. In this study, the genotoxic effects of DM were investigated by measuring chromosomal aberrations (CAs) in mouse bone-marrow cells and CA and the comet assay in human peripheral lymphocytes. Mice were treated with 15.63, 31.25, 62.5, and 125 mg/kg body weight of DM intraperitoneally for 24 hours, and 15.63-, 31.25-, 62.5-, 125-, and 250-µg/mL concentrations were applied to human lymphocytes for both 24 and 48 hours. In in vivo treatments, DM significantly, but not dose dependently, increased the total chromosome aberrations, compared to both negative and solvent controls. Cell proliferation was significantly, but not dose dependently, affected by all doses. In in vitro treatments, DM (except 15.63 µg/mL) significantly and dose dependently increased the frequency of chromosome aberrations. Also, 250 µg/mL of 48-hour treatment was found to be toxic. Cell proliferation was significantly and dose dependently affected by DM applications, when compared to negative control. In in vitro treatments, DM significantly decreased the mitotic index only at the highest concentration for 24 hours, and 62.5- and 125-µg/mL concentrations for 48 hours. In the comet assay, a significant and dose-dependent increase in comet-tail intensity was observed at 62.5-, 125-, and 250-µg/mL concentrations. The mean comet-tail length was significantly increased in all concentrations. Our results demonstrate that DM is genotoxic in mammalian cells in vivo and in vitro. [ABSTRACT FROM AUTHOR]

Abstract: Lolium rigidum is the most prevalent and damaging grass weed of winter cereals in Spain. L. rigidum infestations are frequently treated with herbicides and, consequently, populations have evolved resistance. The objective of this study was to determine the extent and frequency of herbicide resistance in L. rigidum populations in Spain to the selective herbicides chlortoluron, diclofop-methyl and chlorsulfuron, commonly used for its control in-crop, and to glyphosate. The response to these herbicides was evaluated on 123 accessions surveyed randomly across cereal cropping areas of the regions of Castile and León, Catalonia and Andalusia. The fresh weight and the frequency of undamaged plants were calculated for each accession and herbicide. At the regional level, higher frequencies of accessions displaying resistance occurred in Catalonia, an intensively cropped region with a greater herbicide selection pressure. Of concern is that in this region the 60% of the accessions displayed some level of resistance to the ALS-inhibiting herbicide chlorsulfuron. The 6.9% of the accessions found in Castile and León with some resistance to glyphosate could also indicate an incipient problem of resistance to this herbicide. For the other herbicides and regions the majority of the accessions remained susceptible. The possible mechanisms of herbicide resistance development in L. rigidum accessions (target-site versus non-target-site resistance) and their variation among regions was discussed. This study can be used to generate herbicide resistance-management schemes for farmers, based upon the herbicide the site and the potential for resistance development. [Copyright &y& Elsevier]

Abstract: The stereoselective degradation of the racemic diclofop-methyl and its chiral degradation product, diclofop (the hydrolysate of diclofop-methyl), in cole has been investigated. Both enantiomers of diclofop-methyl and diclofop were extracted by organic solvent and detected by chiral high-performance liquid chromatography–diode array detector (DAD). Cellulose-tris-(3,5-dimethylphenylcarbamate)-based chiral column was used for the chiral separation of the four enantiomers applying a mixture of n-hexane and 2-propanol (98:2) concluding 0.1% TFA as mobile phase at a flow rate of 1.0mL/min. The assay method was linear over a range of concentrations (0.5–250mgL−1), and the mean recovery was more than 60% for all the enantiomers. The limit of detection for all the enantiomers was 0.2μgg−1 in plant. Racemic diclofop-methyl was foliar sprayed to cole. Stereoselective behaviour was observed in the diclofop-methyl degradation process. The (S)-diclofop-methyl dissipated faster than (R)-diclofop-methyl. In the case of diclofop, the generation and degradation rates of (S)-enantiomer were higher than (R)-enantiomer in the plant. [Copyright &y& Elsevier]

The genotoxic potential of the commercial herbicide Illoxan (containing 284 g/L diclofop-methyl) was determined by using chromosome aberrations in Allium cepa root tip cells. The EC50 value was determined as 150.00 mg/L using a root growth inhibition test and then the roots were treated with 37.50, 75.00, and 150.00 mg/L concentrations for 12, 24, and 48 h. The results indicated that Illoxan significantly increased the abnormal cell frequency at all concentrations and treatment periods when compared with their controls, and this increase was dose-dependent for the 24 and 48 h treatments. On the other hand, Illoxan significantly decreased the mitotic index (MI) in all treatments when compared with their controls. The decrease in the mitotic index was slightly dose-dependent for the 24 and 48 h treatments. Illoxan did not affect the percentage of mitotic stages. For the pretreated root tips, Illoxan (except 37.50 mg/L at 12 and 24 h) significantly increased the frequency of abnormal cells in a dose-dependent manner. This study indicates that Illoxan decreased the mitotic index and produced clastogenic and aneugenic types of abnormalities in Allium cepa root tip cells. The data obtained in this study showed that plant bioassays can be used as an important test battery to detect possible genotoxicity of chemicals. [ABSTRACT FROM AUTHOR]

Gas chromatograph–mass spectroscopic identification of intermediate products in the degradation of diclofop-methyl and the kinetics of the reaction has been investigated. Formation of 4-[(2,4-dichlorophenoxy) phenoxy] ethane and (2,4-dichlorophenoxy) phenol was investigated. The other intermediate products are 2,4-dichlorophenol, 2,4-dichlorobenzene, phenol and acetic acid have been ascertained. The decrease in the concentration of the parent/intermediate compounds is followed by UV–vis spectral study and the supportive information on the functional groups in the intermediates has been obtained from IR-spectroscopy. Degradation process proceeds with oxidation–reduction reaction by the attack of OHyph name="rad" />, O2 − free radicals, which are photogenerated on the UV-light illuminated TiO2/BaTiO3 photocatalysts particles in aqueous medium. In this presentation another wide band gap semiconductor BaTiO3 is shown to have comparable photocatalytic efficiency. The oxidizing agents are added to accelerate the rate of the reaction by enhancing the formation of free radicals. Based on the intermediates formed in the process of degradation, a suitable mechanism has been proposed. [Copyright &y& Elsevier]

Abstract: The stereoselective degradation of the racemic diclofop-methyl in Chinese cabbage and several agricultural soils had been investigated. Both the enantiomers were analyzed by organic solvent extraction and validated by chiral high-performance liquid chromatography-diode array detector (DAD). Cellulose-tris-(3,5-dimethylphenylcarbamate)-based chiral column was used for the chiral separation of the two enantiomers applying a mixture of n-hexane and 2-propanol (90:10) as mobile phase at a flow rate of 1.0mL/min. The elution order of the two enantiomers was distinguished by a JASCO 2000 HPLC-circular dichroism (CD) system and the first elution was (−)-enantiomer while the other was (+)-enantiomer. Racemic diclofop-methyl was fortified into 10 types of agricultural soils and foliar applied to Chinese cabbage. The assay method was linear over a range of concentrations (0.5–250mgL−1) and the mean recovery was more than 80% for both enantiomers. The limit of detection for both enantiomers was 0.1μgg−1 in soil and plant samples. The results of the stereoselectivity degradation of diclofop-methyl enantiomers in soil showed that the (−)-enantiomer was dissipated faster than the (+)-enantiomer in two typical soils and this enantioselectivity may be caused by microorganism, but no stereoselectivity was observed in other soils. In Chinese cabbage plant, (+)-enantiomer accumulated and eliminated faster than its antipode. [Copyright &y& Elsevier]

Abstract: Field experiments were conducted for 2 years to evaluate the effectiveness of certain herbicides on wild-oat (Avena sterilis L.) in wheat (Triticum durum L.). Results showed that tralkoxydim (0.3la.i.ha−1), imazamethabenz-methyl (0.5 and 0.63la.i.ha−1) and the mixture of imazmethabenz-methyl (0.38la.i.ha−1) and isoproturon (0.5la.i.ha−1) increased wheat grain yield up to the level of the weed-free control. In contrast, when used alone both isoproturon (1 and 1.5la.i.ha−1) and dimethenamid (1.8la.i.ha−1) reduced grain yield below that of the weed-infested control. The highest average straw yield was with imazamethabenz-methyl (0.38la.i.ha−1). Considering total wheat yield (grain and straw), imazamethabenz-methyl (0.38la.i.ha−1), imazamethabenz-methyl/isoproturon mixture, fenoxaprop-ethyl (0.09la.i.ha−1) and tralkoxydim (0.3la.i.ha−1) gave similar yield to that of the weed-free control. Imazamethabenz-methyl (0.5 and 0.63la.i.ha−1), imazamethabenz-methyl/isoproturon mixtures (0.38+0.5 or 0.38+0.75la.i.ha−1), diclofop-methyl (0.9la.i.ha−1) and fenoxaprop-ethyl (0.09la.i.ha−1) were most effective against A. sterilis. Imazamethabenz-methyl (0.5 and 0.63la.i.ha−1) severely reduced A. sterilis population, tiller number and dry weight compared with the weed-infested control. Poor A. sterilis control was obtained using dimethenamid, difenzoquat and isoproturon. However, while most herbicides increased growth of broadleaved weeds, isoproturon alone and its mixtures with imazamethabenz-methyl were most effective against these weeds. Based on grain and straw yields obtained, dimethanamid, isoproturon, diclofo-methyl, and difenzoquat appeared somehow phytotoxic to crop plants and lowered wheat yield beyond the weed-infested control. [Copyright &y& Elsevier]

Cyclodextrins (CDs) possess a hydrophilic external surface and a hydrophobic cavity. They are thus highly soluble and, in the meantime, effectively form inclusion complexes with hydrophobic organic compounds to enhance their solubilities. In this study, the complexation between modified β -CDs and the herbicide diclofop-methyl (DM), (2-(4-(2,4-dichlorophenoxy)-phenoxy) propionate), was investigated. The complexation was confirmed by the shifts in the wavelengths of maximum ultra violet (UV) absorption and fluorescence excitation/emission. The deuterium isotope effects indicate that in the presence of β -CDs the solubility of DM was lower while that of diclofop was higher in D 2 O than in H 2 O, suggesting the primary role of hydrophobic interactions in complexation. The solubility of DM was enhanced in the presence of β -CDs, the extent of which depended on the modification of β -CDs. The complexation reduced the hydrolysis of DM and hence increased its stability. The small inconsistency in the power of β -CDs between hydrolysis retardation and solubilization suggests that hydrolysis was affected by the properties of β -CDs and the configuration of DM in the complexes. Use of β -CDs may thus result in the mobilization of soil DM. Properly modified β -CDs may be utilized as formulation additives for improved delivery of DM and for enhanced environmental remediation. [ABSTRACT FROM AUTHOR]

Application of a series of sublethal rates of diclofop-methyl (DM) herbicide to cloned individuals of Lolium multiflorum Lam increased their level of resistance to this herbicide.Under controlled environmental and field conditions, individuals of L. multiflorum genotypes herbicide-acclimated with 35 and 70 g a.i. ha-1 diclofop-methyl rates showed up to 80% survival and produced more aboveground biomass when exposed to four times higher rates compared to herbicide non-acclimated plants. The acquired increase in individual herbicide tolerance was not transmitted to their offspring, denoting the nature of acclimation response.The lack of transmission of resistant traits to the progeny highlights that exposure to sublethal rates of herbicide in susceptible individuals allowed for the expression of pre-existing cytoplasmatic information or simultaneously induced and selected extra-nuclear contents associated with resistance. The potential mechanisms through which induced tolerance may occur in L. multiflorum plants treated with sublethal concentrations of diclofop-methyl are discussed.Any recommendation or attempt to control weeds by reducing herbicide rates to increase economic returns and reduce the risk of environmental contamination should (a) acknowledge the potential acclimation responses in target plants and (b) be made and based on long-term studies. [Copyright &y& Elsevier]

Abstract: The mechanism of resistance to diclofop-methyl in three Italian populations of Lolium spp. (two resistant and one susceptible) was investigated. The major proportion of R-1 (Tuscania 1997) and R-2 (Roma 1994) plants (approximately 80%) survived after herbicide treatment by emitting new tillers from the crown. Both resistant (R-1 and R-2) and susceptible (Vetralla 1994) Lolium spp. populations were target-site sensitive. No difference in diclofop-methyl absorption by shoots of resistant and susceptible biotypes was observed. At the dose corresponding to 1× the recommended field rate, a relatively higher metabolism was found in R-2 biotype. In contrast, at the doses 2× and 10× the field rate no difference in herbicide metabolism between susceptible and resistant biotypes was observed. At all the three herbicide doses (1×, 2×, and 10× the field rate) 48h after the treatment (HAT), the total amount of metabolites produced by wheat was more than three times higher than that produced by resistant and susceptible ryegrass biotypes. At the doses 1× and 2× the field rate, the herbicide translocation was different in the susceptible biotypes compared to resistant biotypes. The total amount of the radiolabel found 48 HAT in culm and root was approximately twice in susceptible biotype than in resistant biotypes. Susceptible and resistant ryegrass biotypes differed in the capability of their roots to acidify the external medium. Susceptible biotype acidified the external solution at approximately 6 times the rates of the resistant biotypes. In the present study, the mechanism responsible for resistance in the investigated resistant biotypes was not univocally identified. Indirect evidence supports the possible involvement of herbicide sequestration or immobilization. [Copyright &y& Elsevier]

Hydrolytic degradation of the herbicide diclofop-methyl was investigated in the multi-pH deionized water, natural aquatic systems and soil suspensions. Resulting data indicated that the herbicide was stable in the acidic and nearly neutral solutions for at least 15 d. The herbicide diclofop-methyl rapidly dissipated in the natural aquatic systems and soil suspensions with half-lives less than 4 d. Methyl-CD (partially methylated β-cyclodextrin) improved its hydrolytic degradation in the pH 8 deionized water and natural aquatic systems while humic acid inhibited its hydrolytic degradation at the same conditions. But dissolved organic matter in the natural aquatic systems and soil suspensions increased its hydrolysis. Two catalysis mechanisms were introduced to describe the effects of cyclodextrin and organic matter on its hydrolytic metabolism. Though inorganic ions maybe improved its hydrolysis reaction in the natural aquatic systems, Fe^{2+} and Cu^{2+} did not form complexes with the herbicide and had poor influences on its hydrolytic degradation whether cyclodextrin was added or not. [ABSTRACT FROM AUTHOR]

The mechanisms of herbicide resistance were investigated in two diclofop-methyl-resistant Lolium spp. populations from central Italy, Roma ’94 and Tuscania ’97. These two populations were compared with two susceptible Italian populations (Vetralla ’94, Tarquinia ’97) and a resistant and a susceptible population from Australia, SLR31 and VLR1. The activity of acetyl Co-A carboxylase (ACCase) extracted from susceptible (S) or resistant (R) individuals from the Italian populations was inhibited by both aryloxyphenoxypropanoate (diclofop acid and fluazifop acid) and cyclohexanedione (sethoxydim) herbicides. Diclofop-methyl was rapidly de-esterified to diclofop acid at a similar rate in both R and S populations. In all populations, diclofop acid was subsequently degraded to other metabolites. The rate of degradation of diclofop acid was not significantly faster in R than in S populations; however, diclofop acid was degraded more completely in Roma ’94 and Tuscania ’97 compared with the S populations. Application of the mixed-function oxidase inhibitor 1-aminobenzotriazole (ABT) significantly enhanced diclofop-methyl toxicity towards both R populations, but not in S populations. However, enhanced herbicide metabolism does not completely account for the measured resistance level. A mechanism other than an altered ACCase and enhanced herbicide metabolism appears to be responsible for resistance to diclofop-methyl in Roma ’94 and Tuscania ’97. [ABSTRACT FROM AUTHOR]

The effect of three herbicides, diclofop-methyl (DM), imazamethabenz-methyl (IM) and fenoxaprop-ethyl (FE), was investigated at the recommended rate (×) and double the recommended rate (2×) in a durum wheat crop. FE had the smallest effect on root system characteristics, while IM had the greatest effect. For all herbicides, the double rate treatment gave a greater statistical reduction than the single rate for root system characteristics. FE had the smallest effect on the activity of aerobic microorganisms, while DM gave the greatest reduction, 10 days after application, and all three herbicides reduced earthworm abundance. DM gave the smallest reduction in the number of tillers and in plant height, while the double rate of IM gave the greatest reduction. For all three herbicides, double the recommended rate resulted in a significant reduction in the weight of 1000 seeds, while no statistically significant deviations were noted at the recommended rate. Finally, the use of all three herbicides resulted in significantly lower statistical yields compared to the sample (control plot), although there were no significant statistical differences among them, for either recommended or double recommended rates. [ABSTRACT FROM AUTHOR]

Populations of Lolium spp. collected in central Italy were screened for resistance to acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides and compared with known susceptible and resistant Lolium rigidum (Gaud.) populations from Australia. Populations Roma’94 and Tuscania’97 were up to 8- and 7.5-fold more resistant to diclofop-methyl, respectively, than susceptible populations in pot experiments. However, populations Tarquinia’97 and Vetralla’94 were not resistant. Diclofop-methyl resistance levels in the Italian populations were lower than in the Australian populations SLR31 and WLR96 (16.5 and > 64 times more resistant than S respectively). In an agar germination test, Tuscania’97 showed low levels of cross-resistance to fluazifop-p-butyl, whereas no cross-resistance was found in the Roma’94 population. [ABSTRACT FROM AUTHOR]

Esters of substituted phenoxy-phenoxy propionic and constitute a new class or herbicides that are effective against gramineous weed and crop species. Slight changes in chemical structure alter drastically the spectrum of weeds controlled by this class of herbicides. Wheat (Triticum aestivum L.) is resistant to diclofop-methyl (methyl 2-[4-(2',4'-dichlorophenoxy)phenoxy] propanoate) (DM) and clofop-isobutyl (isobutyl 2-[4-(4'-phenoxy)phenoxy] propanoate) (CI), oat (Avena sativa L.) and wild oat (Avena fatua L.) are susceptible to DM but resistant to C], and corn (Zea mays L.) is susceptible to both compounds. The antagonism of IAA-induced elongation in the coleoptile straight growth test was determined to measure biological activity of the herbicides. The basis for the differential responses by gramineous species was related to the metabolism and detoxication of the herbicides in coleoptiles. Growth of wheat coleoptiles was relatively unaffected by both compounds. oat coleoptile growth was inhibited by DM but not by CI, but corn coleoptile growth was inhibited equally by both compounds. Coleoptiles and excised shoots of the three species rapidly hydrolyzed both compounds to their respective acids (diclofop, clofop). The acids were conjugated to a water-soluble ester conjugate or they were hydroxylated in the chlorine-substituted phenyl ring and conjugated as a phenolic conjugate. Aryl hydroxylation is a detoxication mechanism in resistant plants. Plants resistant to DM or CI contained low concentrations of the parent ester and the free or bound (ester conjugate) acid and a high concentration of free or bound (phenolic conjugate) aryl hydroxylated acid in coleoptile and shoot tissues. Differential responses by the three gramineous species to DM and CI arc due apparently to differences in their detoxication mechanism. The enzyme for aryl hydroxylation in oat appears to have a higher affinity for the 4-chlo- than for the 2,4-dichloro-substituted moiety. Therefore, oat hydroxylated clofop rapidly and was tolerant to CI but the limited ability of oat to hydroxylate diclofop resulted in oat being extremely susceptible to DM. [ABSTRACT FROM AUTHOR]

Growth of the second leaf of susceptible wild oat (Avena fatua L.) was inhibited within 2 days after treatment with the herbicide, diclofop-methyl, in the 1-½ leaf stage. Leaf growth of resistant wheat (Triticum aestivum L.) was unaffected by diclofop-methyl. In wild oat, chlorosis developed 1 day after leaf growth was inhibited. Foliar absorption of diclofop-methyl was similar between wild oat and wheat with 67 and 61% of the recovered radioactivity from [14C]diclofop-methyl being absorbed by wild oat and wheat, respectively, after 4 days. Wild oat was equally sensitive to the methyl ester and acid forms of the herbicide when the compounds were injected into the stem. Wheat was unaffected by both forms when treated similarly. Very little diclofop-methyl and diclofop (combined total of 10 to 12% in wild oat and 5 to 7% in wheat) remained in plant tissues 2 days after leaf treatment in both susceptible and resistant plants. Therefore, the active form of the herbicide must inhibit growth of susceptible plants very rapidly and at relatively low concentrations. Diclofop-methyl was rapidly hydrolyzed to diclofop by wild oat and wheat, Wild oat predominantly conjugated diclofop to an ester conjugate hut wheat hydroxylated the 2,4-dichlorophenyl ring and formed a phenolic conjugate. The formation of the different conjugates between wild oat and wheat was the most significant difference in metabolism between the two species. Nearly 60 and 70% of the methanol-soluble radioactivity was present as water-soluble conjugates in wild oat and wheat, respectively, 4 days after treatment. [ABSTRACT FROM AUTHOR]

The metabolism of the herbicide, diclofop-methyl (methyl-2-[4-(2',4'-dichlorophenoxy)phenoxy]propanoate, in cell suspensions of resistant diploid wheat (Triticum monococcum L.) was determined 1, 8, and 24 h after treatment with 14C-diclofop-methyl. The 14C-labeled products were identified by thin layer chromatographic comparisons to appropriate standards. Eight hours after treatment with 5 μM diclofop-methyl in 0.8% acetone (neither of which were toxic to the cell suspensions) 87.2% (84.0% methanol soluble, 3.2% methanol insoluble) of the total 14C recovered (90.4%) was in the cells and 12.8% was in the medium. Major metabolites found in methanol extracts of the cells were diclofop (2-[4-(2',4'- dichlorophenoxy)phenoxy]propionic acid), diclofop hydroxylated at an undetermined position on the 2,4-dichlorophenyl ring (ring-OH diclofop), and conjugates of ring-OH diclofop. Acid hydrolysis of the conjugated metabolite(s) yielded ring-OH diclofop and diclofop. Twenty-four hours after treatment 70-75% of the total 14C recovered was present as conjugated metabolites. With the exception of ring-OH diclofop, all metabolites present in the cells were also recovered from the medium. A metabolite found in low concentrations in the medium that yielded diclofop upon hydrolysis was identified as an ester conjugate. Toxic concentrations of diclofop-methyl (10 and 20μM) had no effect on the metabolism of the herbicide, although the rate of uptake was slower than for cells treated with 5 μM herbicide. The products of diclofop-methyl metabolism in cell suspensions of T. monococcum were compared to previous data from T. aestivum intact plant metabolism of diclofop-methyl. [ABSTRACT FROM AUTHOR]

The site of action of the postemergence graminicide, diclofop-methyl (DM), in susceptible plants is possibly the plasmalemma. Indole-acetic acid (IAA)- and fusicoccin (FC)-induced net proton excretion in Avena coleoptiles was inhibited by the free acid, diclofop. However, net proton excretion recovered within 2 h when 2,4-dichlorophenoxy acid (2,4-D) was added simultaneously with diclofop. Diclofop depolarized the membrane potential (Em) within 12 min but the Em recovered within 30 min when diclofop was removed and replaced with either IAA or 2,4-D. The inhibition of IAA-induced coleoptile growth by DM and the membrane effects of its acid, diclofop, were partially reversed by 2,4-D if it was added shortly after treatment of the tissue. These results are consistent with the reversal of DM injury in whole plants with 2,4-D. [ABSTRACT FROM AUTHOR]