Phenotypic Characteristics and Occurrence Basis of Leaf Necrotic Spots in Response of Weedy Rice to Imazethapyr.

Weedy rice is the most challenging weed species to remove in rice production. We found a novel phenotype of seedling leaves which rapidly generates necrotic spots in response to imidazolinone herbicides in weedy rice, but its influencing factors and formation basis are still unknown. In this study, we used the leaf necrotic spot-producing type of weedy rice as the material. First, leaf necrotic spots were defined as physiological and vacuole-mediated cell necrosis by microscopic examination. The imazethapyr concentration was positively correlated with the degree of necrotic spots occurring, while the action site was in accordance with necrosis using herbicide stability tests combined with fluorescence parameters. Furthermore, transcriptome analysis revealed significant differences in the gene expression of endoplasmic reticulum stress and the lipid metabolism membrane structure damage pathway during necrosis, as confirmed by transmission electron microscopy. The light-temperature test also showed that high temperature and intense light could promote the appearance of necrotic spots. These experimental results are helpful in clarifying the process and basis of imazethapyr in inducing the rapid generation of necrotic spots in rice leaves and providing new insight into understanding the mechanism of response to imidazolinone herbicides and the control of weedy rice.

Investigation of Imidazolinone Herbicide Resistance Gene with KASP Markers for Japonica/Geng Rice Varieties in the Huanghuaihai Region of China.

Rice is a staple food for more than half of the global population due to its food security and sustainable development. Weeds compete with crops for sunlight and indispensable nutrients, affecting the yield and quality of crops. Breeding herbicide-tolerant rice varieties paired with herbicide application is expected to help with weed control. In this study, 194 Japonica/Geng rice varieties or lines collected from the Huanghuaihai region of China were screened by Kompetitive Allele-Specific PCR (KASP) markers based on four mutation sites within OsALS1 (LOC_Os02g30630), which is the target of imidazolinone (IMI) herbicides. Only the OsALS1627N haplotype was identified in 18 varieties, including the previously reported Jingeng818 (JG818), and its herbicide resistance was validated by treatment with three IMIs. To investigate the origin of the OsALS1627N haplotype in the identified varieties, six codominant PCR-based markers tightly linked with OsALS1 were developed. PCR analysis revealed that the other 17 IMI-tolerant varieties were derived from JG818. We randomly selected three IMI-tolerant varieties for comparative whole-genome resequencing with known receptor parent varieties. Sequence alignment revealed that more loci from JG818 have been introduced into IMI-tolerant varieties. However, all three IMI-tolerant varieties carried clustered third type single nucleotide polymorphism (SNP) sites from unknown parents, indicating that these varieties were not directly derived from JG818, whereas those from different intermediate improved lines were crossed with JG818. Overall, we found that only OsALS1627N from JG818 has been broadly introduced into the Huanghuaihai region of China. Additionally, the 17 identified IMI-tolerant varieties provide alternative opportunities for improving such varieties along with other good traits.

Targeting Colon Cancer Cells with Pyrazino-Imidazolinone Derivatives: Synthesis, Molecular Docking, and in Vitro Evaluation of Anti-Proliferative and Pro-Apoptotic Activities.

We report the synthesis, spectroscopic characterization, molecular docking and biological evaluation of nine pyrazino-imidazolinone derivatives. These derivatives were evaluated for their anticancer activity against three cancer cell lines: 518A2 melanoma, HCT-116, and HCT-116 p53 knockout mutant colon carcinoma. The MTT assay was employed to assess their effectiveness. Among the nine compounds tested, four compounds (5 a, 5 d, 5 g, and 5 h) exhibited promising antiproliferative activity specifically against HCT-116 p53-negative cells (IC50 0.23, 0.20, 2.07 and 58.75 µM, respectively). Interestingly, treatment with the 3,4-dimethoxyphenyl derivative 5a resulted in a significant increase (199 %) in caspase activity in HCT-116 p53-negative cells compared to untreated cells while the bromo-pyrazine derivative 5d demonstrated (190 %) increase. These findings suggest that compounds 5a and 5 d induce p53-independent apoptotic cell death. Additionally, in silico molecular docking studies with EGFR and tyrosinase proteins indicated that compounds 5 d and 5 e have the potential to bind to important anticancer drug targets.

Effective Striga control and yield intensification on maize farms in western Kenya with N fertilizer and herbicide-resistant variety.

Context: Maize production in western Kenya is limited by the spread of parasitic weed Striga hermonthica and depletion of soil nutrient stocks. Nitrogen (N) fertilizer and imidazolinone resistant (IR) maize are key elements in the agronomic toolbox to control infestations and enhance yields. Research question: The circumstances under which their use, individually or combined, is most effective on farmer fields have not been well documented. Inappropriate management decisions and low returns on investments arise from this knowledge gap, causing hunger and poverty in smallholder communities to persist. Methods: Experiments were carried out on 60 fields in three different agroecosystems of western Kenya using full-factorial treatments with non-herbicide treated maize (DH) and herbicide treated maize (IR), and N fertilizer omission and application. Trials were stratified on a field with low and high soil fertility within individual farms and repeated over two seasons. Results: Cultivating IR maize instead of DH maize decreased the emergence of Striga with 13 shoots m-2 on average while applying N fertilizer on DH maize led to a reduction of 5 shoots m-2 on average. Decreases of Striga by use of IR maize and N fertilizer were between 6 and 23 shoots m-2 larger at the site with high levels of infestation than at the sites with medium or low emergence. Input of N fertilizer increased grain harvests by 0.59 ton ha-1 on average while use of IR maize enhanced the productivity with 0.33 ton ha-1 on average. Use of N fertilizer had similar yield effects in all three sites, whereas use of IR maize at the site with high Striga emergence increased maize production by 0.26-0.39 ton ha-1 more than at the sites with medium or low emergence. Conclusions: The greater Striga responses to IR maize and the greater yield responses to N fertilizer demonstrate their use could be optimized according to field conditions and management goals. Combining IR maize and N fertilizer has larger added yield benefits where their individual effects on grain productivity are smaller. Significance: Findings from this study indicate that farmers in western Kenya require guidance on how to align the use of herbicide resistant maize and inorganic N inputs with the level of Striga infestation and maize yield on their fields for effectively controlling the pernicious weed and enhancing food production.

Development of Simultaneous Analytical Method for Imidazolinone Herbicides from Livestock Products by UHPLC-MSMS.

A simultaneous analytical method, which used LC/MSMS for imidazolinone herbicides from livestock products (egg, milk, beef, pork, and chicken) for monitoring, was developed with a QuEChERS preparation. A weighed sample (5 g) in a 50 mL conical tube was added to 0.1 M potassium phosphate dibasic solution (5 mL) and shaken for 10 min. After shaking, 0.5 mL of 6 N HCl and 5 mL of acetonitrile were added, and this solution was shaken for 10 min. Additionally, QuEChERS extraction salts (original method, 4 g MgSO4, 1 g NaCl) were added to the sample in a 50 mL conical tube. The mixture was strongly shaken for 1 min and centrifuged at 3000× g for 10 min. The acetonitrile layer was purified with dSPE (150 mg MgSO4, 25 mg C18) and was centrifuged at 13,000× g for 5 min. The supernatant was filtered with a membrane filter (pore size: 0.2 µm) before analysis. The ME (%, matrix effect) range for almost all analytes was −6.56 to 7.11%. MLOD (method limit of detection) and MLOQ (method limit of quantitative) values were calculated by the S/N ratio. MLOQs were 0.01 mg/kg. The linear correlation coefficients (R2) were >0.99 with the range of 0.5~25 µg/kg for all of the imidazolinone herbicides. The recoveries (of imidazolinone herbicides) were in the range of 76.1~110.6% (0.01 mg/kg level), 89.2~97.1% (0.1 mg/kg level), and 94.4~104.4% (0.5 mg/kg level). These are within the validation criteria (to recover 70−120% with RSD <20%). The method demonstrated the simple, rapid, high throughput screening and quantitative analysis of imidazolinone herbicide residues for monitoring in livestock products.

Toxicological effects of active and inert ingredients of imazethapyr formulation Verosil® against Scenedesmus vacuolatus (Chlorophyta).

Imazethapyr, a selective systemic herbicide, is widely used in agriculture and it is frequently detected in water bodies close to application areas. Like other agrochemicals, imazethapyr is commercialized in formulations containing a mixture of additives that increase the effectiveness of the active ingredient. These complex mixtures may cause adverse effects on non-target primary producers, such as microalgae, when they reach freshwater bodies. The aim of this study was to assess the effects, separately, of the formulation Verosil®, the formulation additives, and technical-grade imazethapyr, in the acidic form or as ammonium salt, on the microalga Scenedesmus vacuolatus (Chlorophyta). Verosil®, formulation additives, and acid imazethapyr significantly inhibited the growth of S. vacuolatus (Verosil® > formulation additives > acid imazethapyr) and caused morphological alterations from 2 mg L-1, 4 mg L-1, and 60 mg L-1 onwards, respectively. Verosil® and formulation additives caused the most adverse effect including membrane disorganization, cytoplasm contraction, cell wall thickening, thylakoidal membrane disaggregation, and starch granule accumulation. In addition, Verosil® and formulation additives increased the chl a/chl b ratio, indicating possible alterations in photosystems as a stress response. The carotene/chl a ratio was also increased in microalgae exposed to both Verosil® and formulation additives, suggesting an antioxidant response to these toxic compounds. All these results support the hypothesis that the formulation additives contribute significantly to the toxicity and alterations caused by the commercial formulation Verosil® on S. vacuolatus.

Toxicity of the herbicides used on herbicide-tolerant crops, and societal consequences of their use in France.

In France, the implementation of mutant herbicide-tolerant crops and the use of the related herbicides - sulfonylureas and imidazolinones - have triggered a strong societal reaction illustrated by the intervening actions of environmentalist groups illegally mowing such crops. Trials are in progress, and therefore should be addressed the questions of the environmental risks and the toxicity of these herbicides for the animals and humans consuming the products derived from these plants. Regulatory authorities have allowed these mutant and herbicide-tolerant plants arguing that the herbicides against which they resist only target an enzyme found in 'weeds' (the acetolactate synthase, ALS), and that therefore all organisms lacking this enzyme would be endowed with immunity to these herbicides. The toxicological literature does not match with this argument: 1) Even in organisms displaying the enzyme ALS, these herbicides impact other molecular targets than ALS; 2) These herbicides are toxic for animals, organisms that do not possess the enzyme ALS, and especially invertebrates, amphibians and fish. In humans, epidemiological studies have shown that the use and handling of these toxins are associated with a significantly increased risk of colon and bladder cancers, and miscarriages. In agricultural soils, these herbicides have a persistence of up to several months, and water samples have concentrations of some of these herbicides above the limit value in drinking water.

A Novel Imidazolinone Derivative with 5-Arylidene and 2-Substituted Mercapto Group as Potent Anti-Hepatitis C Virus Compound.

Here six novel imidazolinone derivatives have been synthesized and the compound 4b containing 5-para-methoxy-phenylidene and 2-thioalkylation terminal substitution with 3'-cyano-2',6'-dimethylphenyl showed the best anti-HCV activity and the lowest cytotoxicity. Selectivity index (SI=CC50 /IC50 ) for the 4b was determined as 36, indicating that compound 4b was highly selective towards HCV.

Novel Mutation in the Acetohydroxyacid Synthase (AHAS), Gene Confers Imidazolinone Resistance in Chickpea Cicer arietinum L. Plants.

Chickpea (Cicer arietinum L.) is an important crop in crop-rotation management in Israel. Imidazolinone herbicides have a wide spectrum of weed control, but chickpea plants are sensitive to acetohydroxyacid synthase (AHAS; also known as acetolactate synthase [ALS]) inhibitors. Using the chemical mutagen ethyl methanesulfonate (EMS), we developed a chickpea line (M2033) that is resistant to imidazolinone herbicides. A point mutation was detected in one of the two genes encoding the AHAS catalytic subunit of M2033. The transition of threonine to isoleucine at position 192 (203 according to Arabidopsis) conferred resistance of M2033 to imidazolinones, but not to other groups of AHAS inhibitors. The role of this substitution in the resistance of line M2033 was proven by genetic transformation of tobacco plants. This resistance showed a single-gene semidominant inheritance pattern. Conclusion: A novel mutation, T192I (T203I according to Arabidopsis), providing resistance to IMI herbicides but not to other groups of AHAS inhibitors, is described in the AHAS1 protein of EMS-mutagenized chickpea line M2033.

Evidence for the Application of Emerging Technologies to Accelerate Crop Improvement - A Collaborative Pipeline to Introgress Herbicide Tolerance Into Chickpea.

Accelerating genetic gain in crop improvement is required to ensure improved yield and yield stability under increasingly challenging climatic conditions. This case study demonstrates the effective confluence of innovative breeding technologies within a collaborative breeding framework to develop and rapidly introgress imidazolinone Group 2 herbicide tolerance into an adapted Australian chickpea genetic background. A well-adapted, high-yielding desi cultivar PBA HatTrick was treated with ethyl methanesulfonate to generate mutations in the ACETOHYDROXYACID SYNTHASE 1 (CaAHAS1) gene. After 2 years of field screening with imidazolinone herbicide across >20 ha and controlled environment progeny screening, two selections were identified which exhibited putative herbicide tolerance. Both selections contained the same single amino acid substitution, from alanine to valine at position 205 (A205V) in the AHAS1 protein, and KASP™ markers were developed to discriminate between tolerant and intolerant genotypes. A pipeline combining conventional crossing and F2 production with accelerated single seed descent from F2:4 and marker-assisted selection at F2 rapidly introgressed the herbicide tolerance trait from one of the mutant selections, D15PAHI002, into PBA Seamer, a desi cultivar adapted to Australian cropping areas. Field evaluation of the derivatives of the D15PAHI002 × PBA Seamer cross was analyzed using a factor analytic mixed model statistical approach designed to accommodate low seed numbers resulting from accelerated single seed descent. To further accelerate trait introgression, field evaluation trials were undertaken concurrent with crop safety testing trials. In 2020, 4 years after the initial cross, an advanced line selection CBA2061, bearing acetohydroxyacid synthase (AHAS) inhibitor tolerance and agronomic and disease resistance traits comparable to parent PBA Seamer, was entered into Australian National Variety Trials as a precursor to cultivar registration. The combination of cross-institutional collaboration and the application of novel pre-breeding platforms and statistical technologies facilitated a 3-year saving compared to a traditional breeding approach. This breeding pipeline can be used as a model to accelerate genetic gain in other self-pollinating species, particularly food legumes.

Selective Inhibition of Wild Sunflower Reproduction with Mugwort Aqueous Extract, Tested on Cytosolic Ca2+ and Germination of the Pollen Grains.

Wild sunflower (Helianthus annuus L.) is an invasive species widely distributed in several regions of the world, where it shares a large area with domesticated sunflower. The imidazolinone-tolerant sunflower enables the control of problematic weeds (such as Xanthium spp., Brassica spp., wild sunflower) with imidazolinone herbicides (Clearfield® production system) in cultivated sunflower crops, but could facilitate the gene transfer of herbicide resistance, from cultivated sunflower to wild sunflower, generating hard-to-control weed biotypes or herbicide-resistant populations. The development of new practices that involve the selective inhibition of reproduction structures, such as pollen granules, could be an innovative strategy to minimize outcrossing and the origin of weed-crop hybrids in Clearfield® production systems. In this study, the effects of mugwort (Artemisia vulgaris L.) aqueous extract on cytosolic Ca2+ and the germination of pollen grains collected from conventional, wild and IMI-tolerant sunflower were tested. The results showed that mugwort deregulated Ca2+ homeostasis and markedly reduced the germination of conventional and wild sunflower pollen, but not IMI-tolerant pollen. The HPLC analysis revealed the presence of phenolic acids belonging to the hydroxycinnamic and benzoic classes in the mugwort extract. Hydroxycinnamic acids (caffeic and ferulic) deregulated the cytosolic Ca2+ of conventional and wild sunflower pollen, but not those which were IMI-tolerant, similar to mugwort extract. Selective inhibition of wild sunflower pollen in the Clearfield® sunflower crop contributes to a possible new weed management strategy, reducing the wild sunflower reproduction by seed, minimizing the potential risks of outcrossing with the formation of weed-crop hybrids. The Ca2+ selective chelating activity of caffeic or ferulic acids provides elements to be investigated for their possible use as an alternative to mugwort extract.

The effect of microplastics on behaviors of chiral imidazolinone herbicides in the aquatic environment: Residue, degradation and distribution.

The pollution of aquatic environments by microplastics and herbicides has become a global concern. This study was focused on imazamox, imazapic, and imazethapyr sorption to polypropylene microplastics in water. And the potential effects of microplastics on herbicide enantiomer degradation and distributions in water, sediment, and water-sediment microcosms were investigated. Adsorption experiment results indicated that herbicide sorption to microplastics involved both chemisorption and physical adsorption. Degradation experiment results indicated that microplastics could markedly increase herbicide persistence in water and sediment. Marked stereoselective degradation was not found for the three herbicides in water and sediment, but stereoselective degradation of imazapic in water containing microplastics was found. The water-sediment microcosms experiment results indicated that microplastics have significant effect on stereoselectivity degradation and distribution in water and water-sediment microcosms for imazapic, and have little effect on stereoselectivity behaviors of imazamox and imazethapyr in water-sediment systems. Furthermore, the microcosm experiment results also indicated that herbicides can partition between water and microplastics and that microplastics could affect herbicide persistence and distributions in aquatic environments. The present study provides new insights into the fate of chiral pollutants in aquatic environments containing microplastics, and contributes to understanding behaviors of herbicides and microplastics in aquatic environments.

Insight into the adsorption mechanisms of ionizable imidazolinone herbicides in sediments: Kinetics, adsorption model, and influencing factors.

To reveal the adsorption mechanisms of imazamox, imazapic, and imazethapyr on sediment and batch experiments were carried out in this study. The adsorption kinetics of three imidazolinone herbicides on sediment were accurately described by the pseudo-second-order kinetic model(R2 > 0.9004). The values of adsorption capacity (Qe.cal) were ranged from 0.0183 to 0.0859 mg kg-1 for three herbicides. Adsorption equilibrium was reached within 24 h for three herbicides on sediment, and well fitted by the Freundlich model(R2 > 0.9561). The KF of values for adsorption obtained sediment samples were ranged from 0.2501 to 1.322 L1/n mg1-1/n kg-1for three herbicides. These results indicated that intraparticle diffusion and external mass transport were the main rate controlling steps of the adsorption of herbicides on sediment and that the chemical adsorption was dominant during the adsorption processes. The calculated hysteresis coefficient H were 0.9422,0.7877 and 0.744 for imazmox, imazapic and imazethapyr in raw sediment, respectively, indicating that there is a hysteresis in desorption. The influences of solution pH and sediment organic carbon content on the imidazolinone herbicide adsorption behaviors were also examined. Which shown that the adsorption process for herbicides was highly pH-dependent and adsorption efficiency was closely related to the organic matter content of the sediment, suggesting that electrostatic interactions played crucial roles in the adsorption behavior between sediment and imidazolinone herbicides, and the herbicides were mostly absorbed by the amorphous materials of sediment. These research findings are important for assessing the fate and transport of imidazolinone herbicides in water-sediment systems.

A Two-in-One Strategy: Target and Nontarget Site Mechanisms Both Play Important Role in IMI-Resistant Weedy Rice.

The introduction of Clearfield technology allows the use of imidazolinone (IMI) herbicides to control weedy rice. Imidazolinone herbicides stop the acetolactate synthase (ALS) enzyme from synthesizing branched-chain amino acids, resulting in the death of the plant. Since the launch of Clearfield technology in Malaysia in 2010, many farmers have replaced traditional cultivars with Clearfield (CL) rice lines (MR220-CL1 and MR220-CL2). This technology was initially effective; however, in recent years, local farmers have reported the reduced efficacy of IMI herbicides in controlling the spread of weedy rice. Under IMI herbicide treatment, in previous weedy rice studies, the target-site resistance (TSR) mechanism of the ALS gene has been suggested as a key factor conferring herbicide resistance. In our study, a combination of ALS gene sequencing, enzyme colorimetric assay, and a genome-wide association study (GWAS) highlighted that a non-target-site resistance (NTSR) can be an alternative molecular mechanism in IMI-resistant weedy rice. This is supported by a series of evidence, including a weak correlation between single nucleotide polymorphisms (SNPs) within the ALS exonic region and ALS enzyme activity. Our findings suggest that the adaptability of weedy rice in Clearfield rice fields can be more complicated than previously found in other rice strains.

Use of the imazapic herbicide applied alone or tank mix with imazapyr as growth regulator of lawns

Successive mowing are the major maintenance costs of lawns. Thus, both the expenditure with mowing and the visual and physiological aspect of the lawn have led to the search for alternatives to mechanical management. Thus, this work aimed to study the effects of different rates of imazapic herbicide applied alone or combined with imazapyr as a growth regulator of Bahiagrass (Paspalum notatum) and St. Augustine grass (Stenotaphrum secundatum). The experimental design was a randomized block with four replicates, and the treatments consisted of six rates of imazapic herbicide (35; 70; 105; 140; 175 and 210 g a.i. ha-1) for both species, three rates of imazapic + imazapyr in tank mix (15.57 + 5.25; 23.625 + 7.875; 32.5 + 10.5 g a.i. ha-1) for Bahiagrass and four rates of imazapic + imazapyr mixture (7.875 + 2.625; 15.57 + 5.25; 23.625 + 7.875; 32.5 + 10.5 g a.i. ha-1) for St. Augustine grass. The effect of the treatments was evaluated by observing visible injury symptoms, canopy height, height and number of inflorescences and total dry matter of clippings. Applications of imazapic alone or combined with imazapyr were effective in reducing plant height, number and height of inflorescences and total amount of dry matter of clippings produced by Bahiagrass plants. Imazapic provided satisfactory control of St. Augustine growth, but its utilization caused an increase in the number of inflorescences present in the lawns.

Synthesis and in vitro carbonic anhydrases and acetylcholinesterase inhibitory activities of novel imidazolinone-based benzenesulfonamides.

New imidazolinone-based benzenesulfonamides 3a-e and 4a-e were synthesized in three steps and their chemical structures were confirmed by 1 H NMR (nuclear magnetic resonance), 13 C NMR, and high-resolution mass spectrometry. The benzenesulfonamides used were sulfacetamide (3a, 4a), sulfaguanidine (3b, 4b), sulfanilamide (3c, 4c), sulfadiazine (3d, 4d), sulfamerazine (3e), and sulfathiazole (4e). The compounds were evaluated against carbonic anhydrase (CA) and acetylcholinesterase (AChE) enzymes to obtain possible drug candidate/s. The lead compounds of the series were 3a and 4a against human CA (hCA) I, whereas 3d and 4a were leads against hCA II in terms of Ki values. Series 4 includes more effective CAs inhibitors than series 3 (except 3d). Series 4 compounds having a nitro group (except 4d) were 3.3-4.8 times more selective inhibitors than their corresponding analogues 3a-d in series 3, in which hydrogen was located in place of the nitro group, by considering Ki values against hCA II. Compounds 3c and 4c, where the sulfanilamide moiety is available, were the leads in terms of AChE inhibition with the lowest Ki values. The use of secondary sulfonamides was a more effective modification on CA inhibition, whereas the primary sulfonamide was the effective substitution in terms of AChE inhibitory potency.

Dissipation and phytotoxicity of imazethapyr and imazamox in soils amended with ß-cyclodextrin-chitosan biocomposite.

Use of imazethapyr and imazamox has been an environmental concern due to their high persistence, water solubility, residue build up and potential to injure the succeeding crops. Hence, it is necessary to develop effective decontamination technology. In present study, effect of ß-cyclodextrin-chitosan biocomposite (LCD) amendment in soil on dissipation of imazethapyr and imazamox and their phytotoxicity on succeeding crop was evaluated. The influence of different experimental variables viz. extractant solution and its concentration, liquid to soil ratio, amount of soil and soil type on dissipation of imazethapyr and imazamox was assessed through chemical assays. Irrespective of herbicide formulation and application rate, amendment of soils with LCD increased the dissipation rate of herbicide and the residues were below the detection limit (<0.005 µg g-1) within 5 to 15 days in aridisol, entisol, inceptisol A, inceptisol B, inceptisol C and 7 to 21 days in alfisol and vertisol. Amendment of soils with LCD significantly reduced the growth inhibition of Brassica juncea (L.) Czern and improved the soil biological activity as evident from increase in dehydrogenase activity and soil bacterial count. Amendment of soils with LCD could be a promising, economically feasible and environmentally benign soil decontamination strategy for imazethapyr and imazamox contaminated soils.

Cultivar variation for imazamox resistance in wheat (Triticum aestivum L.): Insights into enzymatic assays for early selection.

Acetohydroxyacid synthase (AHAS, E.C. 2.2.1.6) is the target site of several herbicide classes including imidazolinones. Imidazolinone resistance in wheat is conferred by two major genes AhasL-D1 and AhasL-B1. The objective of this work was to evaluate the in vitro and in vivo AHAS activity and plant growth in response to imazamox of nine wheat cultivars. Dose-response curves for two-gene resistant cultivars were significantly different from the single-gene resistant and susceptible cultivars in the in vitro AHAS assay. Resistance levels at the in vivo AHAS and whole-plant assays for resistant cultivars were >10-fold higher than susceptible cultivars. Moreover, in vivo dose-response curves showed differences among cultivars with the same number of resistance genes. It was concluded that in the in vitro AHAS assay cultivar variability was due to differences in target-site sensitivity while the in vivo AHAS assay reflected the resistance at whole-plant level. Both in vitro and in vivo AHAS dose-response curves could be useful tools when exploring mechanisms involved in imidazolinone resistance in different wheat genetic backgrounds and for the selection of higher resistant genotypes.

Sublethal application of various sulfonylurea and imidazolinone herbicides favors outcrossing and hybrid seed production in oilseed rape.

BACKGROUND: Acetolactate synthase (ALS)-inhibiting herbicides from the chemical families of sulfonylureas and imidazolinones are used worldwide. However, drift or sprayer contamination from some sulfonylurea herbicides causes a high level of male sterility in cruciferous species, especially oilseed rape (OSR). In this paper, we evaluated the gametocidal effects of 27 ALS-inhibiting herbicides that were sprayed on OSR plants at the bolting stage. RESULTS: OSR anther development was very sensitive to sublethal exposure to most ALS-inhibiting herbicides. The application of 18 out of the 20 tested sulfonylureas (except ethametsulfuron and ethoxysulfuron), two imidazolinones (imazethapyr and imazamox), and one sulfonylamino-carbonyltriazolinone (flucarbazone-sodium) at suitable rates could induce male sterility. Eight of the herbicides, including chlorsulfuron (at application rates of 60-120 mg/ha), halosulfuron-methyl (300-600 mg/ha), sulfosulfuron (400-600 mg/ha), triflusulfuron-methyl (500-750 mg/ha), pyrazosulfuron-ethyl (150-225 mg/ha), nicosulfuron (200-300 mg/ha), imazethapyr (750-1125 mg/ha), and imazamox (400-800 mg/ha), could induce over 90% male sterility and over 60% relative outcrossed seed set in six cultivars with different origins. These eight chemicals could be used as new gametocides for hybrid seed production. This study also examined the possibility of external application of these gametocides on several unstable Polima cytoplasmic male sterile and thermosensitive genic male sterile lines. Although the outcrossed seed set of the treated lines was slightly reduced, the gametocide application significantly increased the seed purity of the resulting hybrid. CONCLUSION: The finding of the gametocidal effects of most sulfonylureas and imidazolinones are of great importance for developing new functions for ALS-inhibiting herbicides. The application of gametocides will also greatly promote the safe utilization of environment-sensitive male sterility in hybrid seed production. Unexpectedly, the application of three triazolopyrimidines (florasulam, flumetsulam, and penoxsulam) and one pyrimidinylthiobenzoate (bispyribac-sodium) did not cause male sterility, although these herbicides obviously inhibited the activity of ALS and plant growth. This result suggests that inhibition of ALS activity does not always lead to male sterility in plants, and these gametocides may also inhibit other biological functions vital for microspore development.

Behavior of imidazolinone herbicide enantiomers in earthworm-soil microcosms: Degradation and bioaccumulation.

Imidazolinone herbicides are a group of chiral herbicides that are widely used to control weeds in crops. Despite their wide use, few studies on the behavior of enantiomers in terrestrial systems have been reported. In this study, the bioaccumulation of imazamox, imazapic, and imazethapyr enantiomers in earthworm and their degradation in soils were assessed using earthworm-soil microcosms. The bioaccumulation of the three herbicides in earthworm was not significantly enantioselective. Imazamox and imazethapyr did not significant stereoselective degradation in soil (p > 0.05), while the enantioselectivity of the degradation of imazapic was significant (p < 0.05). Furthermore, biota to soil accumulation factor (BSAF) values were also calculated for three herbicides. Relationships between BSAF values and organic matter content of soil and log KOW of herbicides were investigated. The BSAFs values were negatively correlated with the log KOW of herbicides, and were positively correlated with organic matter content of soil in earthworm-soil microcosms. These relationships indicated that chemical hydrophobicity (Kow) and organic matter content of soil were good predictors to estimate the bioavailability of imidazolinone herbicides to earthworm.