Development of a Green Single Drop Microextraction Based on Deep Eutectic Solvent and HPLC-UV for Trace Residue Analysis of Three Frequent-Used Pesticides.

Background: A green sample preparation method named deep eutectic solvent-based single drop microextraction (DES-SDME) was developed and optimized for determining trace metribuzin, dichlorvos, and fenthion. Methods: Two hundred seventy experimental runs were performed, and the optimal values of the five influential factors in the DES-SDME method were determined. The design of the study was based on one factor at a time and the peak area of high-performance liquid chromatography was used as a benchmark for comparing analysis results. Results: After optimizing the effective factors, the linearity range, detection limit and quantification limit of the method were determined by drawing calibration curves for the studied analytes. Conclusion: The results indicated the success of the developed method in obtaining acceptable figures of merit as a green preparation method with accuracy and precision.

A new series of acylhydrazones derived from metribuzin with modulated herbicidal activity.

This paper reports the preparation and herbicidal evaluation of a small library of acylhydrazones based on the synthetic herbicide metribuzin. The hydrazone linkage easily obtained by reaction of metribuzin with aliphatic and aromatic aldehydes, masks efficiently the exocyclic amino group, thereby altering significantly H-bonding with the receptor and increasing the lipophilicity relative to the parent herbicide. The structures of all compounds, including key stereochemical issues on conformation and E/Z configuration around the C[bond, double bond]N bond were thoroughly elucidated by spectroscopic methods, and unambiguously corroborated by X-ray diffraction analysis. The herbicidal assays using an aliphatic and an aromatic acylhydrazone were performed on tomato and rapeseed plants grown in greenhouse. Our results demonstrate, regardless of rate application, that such acylhydrazone formulations do not alter the selectivity of metribuzin. Moreover, the herbicide activity was even higher in the alkyl derivative than that achieved by commercial metribuzin, thus suggesting that this substance can be applied with no need of combination with chemical coadjuvants, unlike most formulations of commercially available herbicides. Therefore, the study shows the promising effect of chemical derivatization of a common herbicide as metribuzin, to improve the herbicide activity without compromising selectivity, and allowing the farmers its use in crop protection safely and effectively.

Accelerated degradation of micro-pollutant by combined UV and chlorine dioxide: Unexpected inhibition of chlorite formation.

UV/chlorine dioxide (ClO2) process can be intentionally or accidently conducted and is potentially effective in micro-pollutants degradation. UV irradiation can promote ClO2 decay and subsequently result in the formation of reactive radicals. Hence, the co-exposure of ClO2 and UV exhibited a synergetic effect on metribuzin (MET) degradation. The MET degradation was promoted by UV/ClO2 with a rate of 0.089 min-1 at pH 7.5, which was around 2.4 folds the total of rates caused by single ClO2 (0.004 min-1) and single UV (0.033 min-1). Reactive radicals mainly HO• and reactive chlorine species were involved in the acceleration effect, and contributed to 59%-67% of the total degradation rate of MET during UV/ClO2 under pHs 5.5-7.5. Among them, HO• was the predominant contributor and the contribution rate gradually rose under higher pH. Chlorite (ClO2-) and chlorate (ClO3-) formation has been the major concern of ClO2 oxidation. However, a comparison of their formation during UV/ClO2 and ClO2 oxidation is rarely reported. Herein, during MET degradation by ClO2, only ClO2- was identified with the highest amount of 1.17 mg L-1. Conversely, during MET degradation by UV/ClO2, only ClO3- was identified with the highest amount of 0.68 mg L-1, showing an upward trend with prolonging treatment time. Furthermore, organic halogenated DBPs formation after 24 h post-chlorination with UV/ClO2 and ClO2 pre-treatments was comparatively evaluated. Organic DBPs formation after post-chlorination was higher with UV/ClO2 pre-treatment compared to ClO2 pre-treatment. The overall concentration of DBPs produced with 30 min UV/ClO2 pre-treatment was about 4.5 times that with 1min UV/ClO2 pre-treatment. This study provided useful reference for the application of UV/ClO2 in micro-pollutants degradation.

Peer review of the pesticide risk assessment of the active substance metribuzin.

The conclusions of the EFSA following the peer review of the initial risk assessments carried out by the competent authorities of the rapporteur Member State, Estonia, and co-rapporteur Member State, Germany, for the pesticide active substance metribuzin and the assessment of application to amend existing residue definition are reported. The context of the peer review was that required by Commission Implementing Regulation (EU) No 844/2012, as amended by Commission Implementing Regulation (EU) No 2018/1659. The conclusions were reached on the basis of the evaluation of the representative use of metribuzin as a herbicide on potato and soybean (field use). The reliable end points, appropriate for use in regulatory risk assessment, are presented. Missing information identified as being required by the regulatory framework is listed. Concerns are reported where identified.

Transcriptomic profiling of near-isogenic lines reveals candidate genes for a significant locus conferring metribuzin resistance in wheat.

BACKGROUND: Weeds reduce wheat yields in dryland farming systems. Herbicides such as metribuzin are commonly used to control weeds. However, wheat has a narrow safety margin against metribuzin. Standing crops such as wheat with weeds in the same field can also be killed by the same dose of metribuzin. Therefore, it is important to identify metribuzin resistance genes and understand the resistance mechanism in wheat for sustainable crop production. A previous study identified a significant metribuzin resistance wheat QTL, Qsns.uwa.4 A.2, explaining 69% of the phenotypic variance for metribuzin resistance. RESULTS: Two NIL pairs with the most contrasting performance in the metribuzin treatment and different in genetic backgrounds were compared using RNA sequence analysis, identifying nine candidate genes underlying Qsns.uwa.4 A.2 responsible for metribuzin resistance. Quantitative RT-qPCR further validated the candidate genes, with TraesCS4A03G1099000 (nitrate excretion transporter), TraesCS4A03G1181300 (aspartyl protease), and TraesCS4A03G0741300 (glycine-rich proteins) identified as key factors for metribuzin resistance. CONCLUSION: Identified markers and key candidate genes can be used for selecting metribuzin resistance in wheat.

Assessing the Stability of Herbicide-Tolerant Lentil Accessions (Lens culinaris Medik.) under Diverse Environments.

Assessing the adaptability and stability of herbicide-tolerant lentil accessions to two broad-spectrum post-emergence herbicides in multi-environment trials has become a must in a breeding program to improve its selection. The adaptability and stability of 42 herbicide-tolerant lentil accessions were investigated using five stability parameters under eight different environments. Significant Genotype-Environment (GE) interaction was found for days to flowering (DFLR), days to maturity (DMAT), and seed yield per plant (SY). The analyzed stability parameters such as Cultivar superiority, Finlay-Wilkinson, Shukla, Static Stability, and Wricke's Ecovalence ranked the tested accessions differently, confirming the importance of using a combination of stability parameters when evaluating the performance of a group of accessions. GGE biplot of the SY trait accounted for 60.79% of sums of squares of the GE interaction and showed that cool and high rainfall environments are ideal for testing the agronomic performance of tolerant accessions. The GGE biplot of SY showed that IG4605(19), IG195(6), and IG156635(12) were specifically adapted to one mega environment, whereas IG70056(38) was identified as a superior line having a high and stable yield. These lines should be included in lentil crossing programs to develop herbicide-tolerant cultivars adapted to diverse environments.

Application of molecularly imprinted electrochemical sensor for trace analysis of Metribuzin herbicide in food samples.

Metribuzin (MTZ) is an important herbicide widely used in fields and represents a big threat to the environment and health. Herein, an electrochemical sensor was designed for its detection in commercial product (Egyscor® 70%), spiked tomatoes and potatoes samples with recovery values ranging from 97.12 to 103.41%. Bulk-polymerized MTZ molecularly imprinted polymer (MIP) was developed, using itaconic acid (functional monomer), ethylene glycol dimethacrylate (cross-linker) at an optimum molar ratio 1:5:30, respectively. Differential pulse voltammetry was used to examine the optimization variables of the MIP based sensor such as the variation of (template: monomer: cross-linker) ratio, accumulation time, multi walled carbon nanotubes amount, pH and scan rate, while cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the sensor. The sensor showed selective adsorption ability and a good linearity over the concentration range of 0.2 ng/mL to 21.429 µg/mL, with LOD and LOQ of 0.1 pg/mL and 0.3 pg/mL, respectively.

Scrutinizing the interaction between metribuzin with glutathione reductase 2 from Arabidopsis thaliana: insight into the molecular toxicity in agriculture.

As one of the triazine herbicides with widespread usage in agriculture, metribuzin exerted nonnegligible hazardous effects on plants via excessive accumulation of reactive oxygen species and destruction of antioxidant enzymes, but the underlying harmful mechanism of metribuzin-induced oxidative damage to plants has never been exploited. Here, Arabidopsis thaliana glutathione reductase 2 (AtGR2) was employed as the biomarker to evaluate the adverse impacts of metribuzin on plants. The fluorescence intensity of AtGR2 was decreased based on the static quenching mechanism with the prediction of a single binding site toward metribuzin, and the complex formation was presumed to be mainly impelled by hydrogen bonding and van der Waals forces from the negative ΔH and ΔS. In addition, the loosened and unfolded skeleton of AtGR2 along with the increased hydrophilicity around the tryptophan residues were investigated. Besides, the glutathione reductase activity of AtGR2 was also destroyed due to structural and conformational changes. At last, the severe inhibiting growth of Arabidopsis seedling roots was discovered under metribuzin exposure. Hence, the evaluation of the molecular interaction mechanism of AtGR2 with metribuzin will establish valuable assessments of the toxic effects of metribuzin on plants.

Toxicity assessment of metribuzin and its amelioration through plant growth regulators in Vigna radiata (L.) R. Wilczek.

The present experiment was conducted to evaluate the metribuzin-induced stress response in Vigna radiata and to explore the ameliorative role of exogenous application of plant growth regulators (PGRs) against metribuzin toxicity by assessing important biochemical and yield parameters. Prior to the field experiment, dose standardization experiments were performed, and EC50 was calculated for metribuzin. On day 21, field grown V. radiata plants were treated with graded concentrations of metribuzin (0-1000 mg [Formula: see text]). Plants treated with 600 mg [Formula: see text] (EC50) and 1000 mg [Formula: see text] (highest dose) of metribuzin were co-treated individually and simultaneously with gibberellic acid-3 (GA), indole-3 acetic acid (IAA), and salicylic acid (SA). After 7 days of treatment, leaf tissues were analyzed for biochemical parameters, whereas those related to yield were recorded during harvest. The result of this study indicated that metribuzin treatment to V. radiata resulted in increase in lipid peroxidation and reduce chlorophyll and carotenoid contents as well as yield parameters. However, metribuzin-treated plants induced proline accumulation and activity of antioxidant enzymes. Exogenous application of GA, IAA, and SA significantly reduced lipid peroxidation and increased contents of photosynthetic pigments, proline, and antioxidant enzymes thereby increasing yield parameters. It was observed that during metribuzin stress, SA exhibited a better ameliorative response out of the three exogenously applied PGRs, while the combined use of all PGRs exhibited much improved ameliorative response on biochemical and yield parameters of plants.

Effect of the Ni3TeO6 phase in a Ni2Te3O8/expanded graphite composite on the electrochemical monitoring of metribuzin residue in soil and water samples.

Growing food demand and climate change have led to the development of various pest control agents to increase crop yields. Although pesticides help meet the food demand, they cause harm to human health and the environment. Metribuzin (MTBZ) is one of the common herbicides used for controlling weeds. Therefore, monitoring MTBZ residues in soil and water bodies is essential for decreasing risk to the environment and human health. This paper reports a highly selective and sensitive electrochemical sensor electrode based on a Ni3TeO6-phase-integrated Ni2Te3O8/expanded graphite (referred to here as NTO-eGR) composite for the detection of MTBZ. The NTO-eGR composite was prepared by a one-step low-temperature hydrothermal method and characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and electron microscopy techniques. The Ni3TeO6 phase was found to be an active component in the NTO/eGR composite, which exhibited satisfactory analytical performance in MTBZ detection with a sensitivity of 1.454 µA µM-1 cm-2. Moreover, the NTO-eGR electrode exhibited high selectivity to MTBZ even in the presence of a five-fold excess of interfering species in water and soil samples. The studies on practical applicability revealed that NTO-eGR exhibits good reproducibility with a relative standard deviation of 2.67% (n = 5). Moreover, good recoveries of greater than 90% were achieved in the determination of MTBZ in soil and water samples. Hence, the NTO-eGR sensor electrode is highly suitable for the rapid on-site determination of MTBZ.

High Doses of Pesticides Induce mtDNA Damage in Intact Mitochondria of Potato In Vitro and Do Not Impact on mtDNA Integrity of Mitochondria of Shoots and Tubers under In Vivo Exposure.

It is well known that pesticides are toxic for mitochondria of animals. The effect of pesticides on plant mitochondria has not been widely studied. The goal of this research is to study the impact of metribuzin and imidacloprid on the amount of damage in the mtDNA of potato (Solanum tuberosum L.) in various conditions. We developed a set of primers to estimate mtDNA damage for the fragments in three chromosomes of potato mitogenome. We showed that both metribuzin and imidacloprid considerably damage mtDNA in vitro. Imidacloprid reduces the rate of seed germination, but does not impact the rate of the growth and number of mtDNA damage in the potato shoots. Field experiments show that pesticide exposure does not induce change in aconitate hydratase activity, and can cause a decrease in the rate of H2O2 production. We can assume that the mechanism of pesticide-induced mtDNA damage in vitro is not associated with H2O2 production, and pesticides as electrophilic substances directly interact with mtDNA. The effect of pesticides on the integrity of mtDNA in green parts of plants and in crop tubers is insignificant. In general, plant mtDNA is resistant to pesticide exposure in vivo, probably due to the presence of non-coupled respiratory systems in plant mitochondria.

Characterisation of a 4A QTL for Metribuzin Resistance in Wheat by Developing Near-Isogenic Lines.

Wheat (Triticum aestivum L.) production is constantly affected by weeds in the farming system. Chemical-based weed management is widely practiced; broad-spectrum herbicides such as metribuzin have been successfully used to control weeds in Australia and elsewhere of the world. Breeding metribuzin-resistant wheat through genetic improvement is needed for effective control of weeds. Quantitative trait loci (QTLs) mapping efforts identified a major QTL on wheat chromosome 4A, explaining up to 20% of the phenotypic variance for metribuzin resistance. The quantitative nature of inheritance of this QTL signifies the importance of near-isogenic lines (NILs), which can convert a quantitative trait into a Mendelian factor for better resolution of the QTL. In the current study, NILs were developed using a heterogeneous inbred family method combined with a fast generation-cycling system in a population of Chuan Mai 25 (resistant) and Ritchie (susceptible). Seven pairs of NILs targeting the 4A QTL for metribuzin resistance were confirmed with a molecular marker and phenotyping. The resistant allele from the resistant parent increased metribuzin resistance by 63-85% (average 69%) compared with the susceptible allele from the susceptible parent. Segregation analysis in the NIL pairs for thousand grain weight (TGW) (g), biomass per plant (kg), tillers per plant, plant height (cm), yield per plant, and powdery mildew visual score (0-9) indicated that these traits were linked with metribuzin resistance. Similarly, TGW was observed to co-segregate with metribuzin resistance in most confirmed NILs, signifying that the two traits are controlled by closely linked genes. The most contrasting NILs can be further characterised by transcriptomic and proteomic analyses to identify the candidate genes responsible for metribuzin resistance.

Comparative transcriptome analyses for metribuzin tolerance provide insights into key genes and mechanisms restoring photosynthetic efficiency in bread wheat (Triticum aestivum L.).

Weeds are the biggest threat to cropping system sustainability in wheat. Metribuzin is a versatile herbicide for broad-spectrum weed management. Understanding key genes, mechanisms and functional markers are essential to develop higher metribuzin tolerant wheats. We identified Chuan Mai 25 (tolerant) and Ritchie (susceptible) as contrasting genotypes to metribuzin stress through dose-response analyses. Transcriptome sequencing using NovaSeq 6000 RNA-Seq platform identified a total of 77,443 genes; 59,915 known genes and 17,528 novel genes. The functional enrichment analysis at 0 h, 24 h and 60 h herbicide exposure revealed that endogenous increase of metabolic enzymes, light-harvesting chlorophyll proteins, PSII stability factor HCF136 and glucose metabolism conferred metribuzin tolerance. The validation of DEGs using RT-qPCR and QTL mapping confirmed their responsiveness to metribuzin. Transcription factors MYB, AP2-EREBP, ABI3VP1, bHLH, NAC are significantly expressed during metribuzin stress. Transcripts with significant enrichments revealed 114 SSRs for genomic selection. The master regulators provide promising avenues for enhancing metribuzin tolerance.

Metribuzin-induced non-adverse liver changes result in rodent-specific non-adverse thyroid effects via uridine 5'-diphospho-glucuronosyltransferase (UDPGT, UGT) modulation.

Metribuzin is a herbicide that inhibits photosynthesis and has been used for over 40 years. Its main target organ is the liver and to some extent the kidney in rats, dogs, and rabbits. Metribuzin shows a specific thyroxine (T4) profile in rat studies with T4 increases at low doses and T4 decreases at higher doses. Only the T4 decreases occur together with histopathological changes in the thyroid and weight changes of liver and thyroid. A set of experiments was conducted to investigate metribuzin's endocrine disruptor potential according to European guidance and regulations. The results indicate that a liver enzyme modulation, i.e. of the uridine 5'-diphospho-glucuronosyltransferase (UDPGT, UGT), is most likely responsible for both increased and decreased plasma thyroxine level and for thyroid histopathological observations. Animals with high T4 levels show low UGT activity, while animals with low T4 levels show high UGT activity. A causal relationship was inferred, since other potentially human-relevant mode of action (MOA) pathways were excluded in dedicated studies, i.e. inhibition of deiodinases (DIO), inhibition of thyroid peroxidase (TPO) or of the sodium importer system (NIS). This liver metabolism-associated MOA is considered not relevant for human hazard assessment, due to species differences in thyroid homeostasis between humans and rats and, more importantly, based on experimental data showing that metribuzin affects UGT activity in rat but not in human hepatocytes. Further, we discuss whether or not increased T4 levels in the rat, in the absence of histopathological changes, should be considered as adverse and therefore used as an appropriate hazard model for humans. Based on a weight of evidence approach, metribuzin should not be classified as an endocrine disruptor with regard to the thyroid modality.

Sulfur precursor and citric acid effect on SnS2 nanoparticles and their influence on the photodegradation activity of selected organic compounds.

Semiconductor nanoparticle-mediated photocatalysis is an attractive option for water decontamination, being the semiconductors as SnS2 with a bandgap in the visible region, the most promising materials. In the present work, we evaluated the influence of important parameters in the photocatalytic application of SnS2 nanoparticles. Our results show that the presence of citric acid (used as a capping agent) restricts the formation of hexagonal nanoparticles. We also demonstrated that using thioacetamide as a sulfur source results in smaller nanoparticles than thiourea, 24.0 nm and 616 nm respectively. Moreover, small hexagonal nanoparticles play a key role in the photocatalytic activity of SnS2 nanoparticles. Compared with TiO2 performance, SnS2 nanoparticles exhibited faster kinetics for methyl orange (MO) degradation, Kapp = 0.0102 min-1, and 0.029 min-1, respectively. We proved that SnS2 is capable of breaking the azo bond of methyl orange by direct reduction. Furthermore, our analyses indicate that SnS2 nanoparticles do not degrade atrazine and imazapic, but the photocatalytic route of metribuzin competed with photolysis, resulting in a particular transformation product that was not obtained with light irradiation only. We demonstrated that SnS2 nanoparticles have high bond selectivity for azo breaking. Furthermore, they represent an advance for the development of designed materials (such as heterostructures), where the properties of SnS2 can be tuned.

Efficacy of embedded metribuzin and tribenuron-methyl herbicides in field-grown vegetable crops infested by weeds.

The purpose of the present study was to investigate the efficacy of the experimental formulations of the metribuzin (MET) and tribenuron-methyl (TBM) herbicides embedded in the matrix of degradable poly-3-hydroxybutyrate blended with wood flour in field-grown tomato and beet crops infested by weeds. There is a necessity to develop environmentally friendly and effective means to protect plants because of the shortcomings of the free herbicide forms such as the environmentally unsafe spray application of solutions and suspensions of the widespread metribuzin and tribenuron-methyl herbicides, removal from soil during watering events and rains, and transport to natural aquatic environments, where the herbicides accumulate in the trophic chains of biota. Free TBM is also rapidly inactivated in soil and metabolized to nontoxic products in plants. The efficacy of experimental formulations of metribuzin and tribenuron-methyl embedded in the matrix of degradable poly-3-hydroxybutyrate blended with wood flour was tested in field-grown tomato and beet crops infested with weeds. Application of metribuzin resulted in the highest productivity of tomatoes (2.3 kg/m2) and table beet (3.4 kg/m2), improved biometric parameters of tomato fruits and beet roots, and caused reduction in nitrate nitrogen concentrations in them. The mode of herbicide delivery did not affect sugar contents, but application of both metribuzin and tribenuron-methyl induced a 1.7-fold and 1.4-fold, respectively, increase in vitamin C concentrations in tomato fruits and beet roots relative to the vegetables grown on the subplots treated with free herbicides and the intact plants. Embedded herbicides can be used as preemergence herbicides in the field. Fig. a Graphical abstract.

Aqueous chlorination of herbicide metribuzin: Identification and elucidation of "new" disinfection by-products, degradation pathway and toxicity evaluation.

A widely used herbicide, metribuzin, was evaluated for degradation, mineralization and disinfection by-products (DBPs) formation during aqueous chlorination. In addition, to assess the toxicity effects of chlorination on metribuzin solution the following tests were performed: acute toxicity using Artemia salina nauplii; cell viability using MTT assay; estrogenicity using a re-engineered Bioluminescent Yeast Estrogen Screen (BLYES) and a constitutively bioluminescent strain (BLYR); mutagenicity and developmental toxicity using Q(SAR) methodology. Metribuzin at 10 mg·L-1 was degraded by chlorination, achieving 93% of removal at 30 min of reaction. TOC analysis showed that the herbicide does not suffer complete mineralization, even after 24 h of contact with free chlorine. Seventeen DBPs were detected and their structural formulae were elucidated by high resolution mass spectrometry. Toxicity effects for chlorinated solutions increased when compared to the unreacted metribuzin solution. DBPs were more toxic to Artemia salina nauplii, increasing around 20% on nauplii mortality. It was also observed high estrogenicity to human receptors in BLYES assays and mutagenic and developmental toxicant effects to animals and humans in Q(SAR) methodology, suggesting that DBPs are potentially more toxic than the precursor metribuzin. Metribuzin solutions at 10 mg·L-1 showed equivalent 17-ß-estradiol values ranged from 0.061 to 6.71 µg·L-1 after to be chlorinated at different reaction times.

Mechanistic basis for synergism of 2,4-D amine and metribuzin in Avena sterilis.

The combination of herbicides with different modes of action has been adopted not only to improve weed control but also to increase the environmental sustainability of plant-protection products. In this study, we showed a synergistic effect of the auxin herbicide 2,4-D amine with the PSII-inhibiting herbicide metribuzin to control the global grass weed wild oat (Avena sterilis) population and investigated the underlying mechanisms. Pretreatment with 2,4-D amine did not change the foliar absorption of metribuzin but did increase metribuzin translocation to the roots and new leaves, although enhancement of the metribuzin metabolism was also observed. Considering that the expression level of the target site psbA gene is significantly higher in leaves than in roots, increased metribuzin translocation to new leaves is likely the major cause of the observed synergism, even though enhanced metribuzin metabolism may offset the metribuzin efficacy. This is the first report on the synergistic mechanism between 2,4-D amine and metribuzin in weed control.

QTL Mapping Using a High-Density Genetic Map to Identify Candidate Genes Associated With Metribuzin Tolerance in Hexaploid Wheat (Triticum aestivum L.).

Tolerance to metribuzin, a broad-spectrum herbicide, is an important trait for weed control in wheat breeding. However, the genetics of metribuzin tolerance in relation to the underlying quantitative trait loci (QTL) and genes is limited. This study developed F8 recombinant inbred lines (RILs) from a cross between a highly resistant genotype (Chuan Mai 25) and highly susceptible genotype (Ritchie), which were used for QTL mapping of metribuzin tolerance. Genotyping was done using a diversity arrays technology sequencing (DArTseq) platform, and phenotyping was done in controlled environments. Herbicide tolerance was measured using three traits, visual score (VS), reduction of chlorophyll content (RCC), and mean value of chlorophyll content for metribuzin-treated plants (MCC). A high-density genetic linkage map was constructed using 2,129 DArTseq markers. Inclusive composite interval mapping (ICIM) identified seven QTL, one each on chromosomes 2A, 2D, 3A, 3B, 4A, 5A, and 6A. Three major QTL-Qrcc.uwa.2AS, Qrcc.uwa.5AL, and Qrcc.uwa.6AL-explained 11.39%, 11.06%, and 11.45% of the phenotypic variation, respectively. The 5A QTL was further validated using kompetitive allele-specific PCR (KASP) assays in an F3 validation population developed from Chuan Mai 25 × Dagger. Blasting the single-nucleotide polymorphisms (SNPs) flanking the QTL in the wheat reference genome RefV1.0 revealed SNP markers within or very close to annotated genes which could be candidate genes responsible for metribuzin tolerance. Most of the candidate genes were related to metabolic detoxification, especially those of P450 pathway and xenobiotic transmembrane transporter activity, which are reportedly key molecules responsible for herbicide tolerance. This study is the first to use specially developed populations to conduct QTL mapping on the metribuzin tolerance trait. The three major QTL and candidate genes identified in this study could facilitate marker-assisted metribuzin breeding in wheat. The QTL could be fine-mapped to locate the genes responsible for metribuzin tolerance, which could be introgressed into elite wheat cultivars.

Biological effects of the free and embedded metribuzin and tribenuron-methyl herbicides on various cultivated weed species.

The present study addresses the herbicidal activity and biological effects of the metribuzin (MET) and tribenuron-methyl (TBM) herbicides used to control various weed species (Amaranthus retroflexus, Sinapis arvensis, and Leucanthemum maximum). The effects of the free herbicides and the herbicides embedded in granules of degradable polymer poly-3-hydroxybutyrate [P(3HB)] blended with birch wood flour were compared. Metribuzin, regardless of the form, caused 100% mortality of the three weeds by day 21. The herbicidal activity of tribenuron-methyl was lower than that of metribuzin, but the embedded TBM was superior to the free herbicide in the length and strength of its action on the weeds. Both metribuzin forms dramatically decreased the main parameters of fluorescence: maximum quantum yield of photosystem-II [Y(II)max], maximum quantum yield of non-photochemical quenching [Y(NPQ)max], and maximum rate of non-cyclic electron transport [ETRmax] and concentrations of chlorophyll a and b. The effect of the embedded TBM on the photosynthetic activity of the weeds was lower in the first two weeks of the growth of herbicide-treated plants but lasted longer than the effect of the free TBM and increased over time. Embedding of metribuzin in the matrix of degradable blend did not decrease its herbicidal activity.