Photolysis of chlorsulfuron and metsulfuron-methyl in methanol

Photolysis of chlorsulfuron and metsulfuron-methyl was studied in methanol under UV light. Their rates of primary photolysis followed first-order kinetics. The main photoproducts were identified as 2-methoxy-4-methyl-1,3,5-triazin-6-amine, 2-chloro-benzenesulfonamide and methyl 2-(aminosulfonyl)benzoate, which entailed the cleavage of the two N–C ureic bonds. Further photolysis of benzenesulfonamide derivatives involved oxidation of −NH₂, cyclisation with loss of CH₃OH, and scission of the C–S bond A trace of methyl o-mercaptobenzoate was also detected. The corresponding photolysis pathways of chlorsulfuron and metsulfuron-methyl were tentatively proposed. © 1999 Society of Chemical Industry     

Kinetics and hydrolysis mechanism of chlorsulfuron and metsulfuron-methyl

In acidic media, hydrolysis of chlorsulfuron and metsulfuron-methyl occurs via two consecutive reactions which were followed by ultraviolet spectrophotometry. For these two reactions, the pseudo-first-order rate constants increase proportionally to the concentration of hydronium ion in the more acidic media and to the square of this concentration at higher pH values. A kinetic study by HPLC shows that the first reaction leads to the formation of 4-methoxy-6-methyl-1,3,5-triazin-2-amine and (o-chlorophenylsulfonyl) carbamic acid for chlorsulfuron or (o-methoxycarbonylphenylsulfonyl) carbamic acid for metsulfuronmethyl. The second reaction is the conversion of these sulfonylcarbamic acids to sulfonamides and carbon dioxide. The complete lack of saccharin and of o-sulfamoyl benzoic acid proves that the ester function of the methoxycarbonyl group is stable. The lack of general acid-base catalysis and a solvent deuterium isotope effect less than unity are consistent with a rate-determining cleavage of the protonated substrate. In the basic pH range (10–14) a single reaction occurs, the nucleophilic substitution of the methoxy group on the triazine by a hydroxide group.     

Adsorption and degradation of chlorsulfuron and metsulfuron-methyl in soils from different depths

Adsorption and degradation rates of chlorsulfuron and metsulfuron-methyl were measured in soil taken from depths of 0–20, 20–40 and 40–60 cm at eight sites. Adsorption of both herbicides was negatively correlated with soil pH, and positively correlated with soil organic matter content. When two soils with very high organic matter were excluded from the calculations, the correlations with organic matter content were no longer statistically significant but those with soil pH were affected only slightly. Degradation rates of both herbicides generally decreased with increasing depth in the soil and were positively correlated with microbial biomass and negatively correlated with soil pH. The possible significance of the results to persistence of the herbicides in the field is discussed.     

The relative movement and persistence in soil of chlorsulfuron, metsulfuron-methyl and triasulfuron

Summary. Adsorption and degradation rates of triasulfuron in 8 different soils were negatively correlated with soil pH and were generally lower in subsoils than in soils from the plough layer. The half-life at 20°C varied from 33 days in a top soil at pH 5·8 to 120 days in a subsoil at pH 7·4. Adsorption distribution coefficients in these two soils were 0·55 and 0·19, respectively. Movement and persistence of residues of chlorsulfuron, triasulfuron and metsulfuron-methyl were compared in a field experiment prepared in spring 1987. Triasulfuron was less mobile in the soil than the other two compounds. Residues of all three herbicides were largely confined to the upper 40–50 cm soil 148 days after application. With an initial dose of 32 g ha⁻¹, residues in the surface soil layers were sufficient to affect growth of lettuce and sugar-beet sown approximately one year after application. Laboratory adsorption and degradation data were used with appropriate weather data in a computer model of herbicide transport in soil. The model gave good predictions of total soil residues during the first five months following application, and also predicted successfully the maximum depth of penetration of the herbicides into the soil during this period. However, more herbicide was retained close to the soil surface than was predicted by the model. The model predicted extensive movement of the herbicides in the soil during winter but did not predict that residues sufficient to affect crop growth could be present in the upper 15–20 cm soil after one year.     

Response of imidazolinone-tolerant and -susceptible volunteer oilseed rape (Brassica napus L.) to ALS inhibitors and alternative herbicides

BACKGROUND: Imidazolinone-tolerant oilseed rape (Brassica napus L.) varieties are currently grown in Canada, North America, Chile and Australia with high acreage. A Europe-wide introduction has started and will be pushed further for both spring and winter varieties. The primary aim of this study was to evaluate the impact of imidazolinone tolerance for future volunteer oilseed rape control in subsequent crops, particularly winter wheat. RESULTS: A greenhouse bioassay showed cross-tolerance of imidazolinone-tolerant oilseed rape towards sulfonylureas, triazolopyrimidines and sulfonylaminocarbonyltriazolinones (resistance factors between 5 and 775), with a homozygous variety expressing a much higher tolerance level compared with a heterozygous variety. Calculated ED₉₀ values suitable for controlling tolerant plants were always much higher than the recommended herbicide dose. Generally, results were confirmed under field conditions, but with higher efficacies than expected in some cases (e.g. florasulam). Herbicides with an alternative mode of action were found to be effective in controlling imidazolinone-tolerant volunteers in subsequent winter wheat crops. CONCLUSION: Herbicide strategies have to be adjusted for volunteer control in subsequent crops if imidazolinone-tolerant oilseed rape varieties are to be grown. However, agronomic tools (harvest date, harvest technique, tillage) should be used conscientiously in the first place to keep volunteer oilseed rape densities at the lowest possible level. Copyright © 2012 Society of Chemical Industry     

Determination of the sulfonylurea herbicides chlorsulfuron and metsulfuron-methyl in soil,water and plant material by gas chromatography of their pentafluorobenzyl derivatives

The measurement of the sulfonyl urea herbicides, chlorsulfuron and metsulfuron-methyl as pentafluorobenzyl derivatives has been investigated and the kinetics of reaction optimised. The reaction product was identified by mass spectroscopy as N,N-bis(pentafluorobenzyl)-2-chlorobenzenesulfonamide. Amounts of herbicide derivative as low as 0·1 pg per injection can be detected. Suitable conditions for both packed and capillary chromatography are given. Application of the method to residue determination is discussed and the method is shown to be suitable for residues in soil and water but less so for plant material.     

Response of maize (Zea mays L.) inbred lines and hybrids to chlorsulfuron

Twenty inbred maize lines, raised in a growth chamber, were treated with 0 or 1 ng g^?1 of chlorsulfuron which caused a variable reduction in root-length. In a second experiment, all crosses (reciprocals included) among two tolerant lines (T: Va85 and Mes44) and two susceptible lines (S: B73 and B79) were raised in a growth chamber together with the parental lines and exposed to 0,0×5 or 1 ng g^?1, The interaction of reciprocal effects x rates was not significant for all traits, The T × S hybrids showed an intermediate response between the T × T and S × S responses for root-length and dry weight. Interaction (hybrids vs. parental lines) × rates was not significant for all traits. These results indicate that susceptibility to chlorsulfuron is not controlled by extra-nuclear factors and that additive gene actions prevail. Four crosses (one T × T, two T × S and one S × S) were further investigated at nine rates from 0 to 1 ng g^?1. The responses confirmed the intermediate behaviour of T×S hybrids, resulting in a GR₂₀ of 0×07, 0×55 and 0×94 ng g^?1 for S × S, T × S and T × T, respectively. In a third experiment, the four crosses previously considered were grown in the field with parental lines and treated at five rates from 0 to 1·12 g a.i. ha^?1. Effects on shoot height and dry weight were consistent with root effects found in growth chamber experiments.     

Interference between triazine-resistant Brassica napus and Panicum miliaceum

Atrazine carryover often limits growers to production of atrazine-tolerant crops the year following application, and allows the increase of triazine-tolerant weed species such as Panicum miliaceum L. (wild proso millet). Tiriazine-resistant Brassica napus L. cv. ‘Triton’ (oilseed rape) was tested to characterize the nature of interspecific interference with P. miliaceum. In a greenhouse study, atrazine at 2.2 kg ha^?1 depressed oilseed rape fruit (siliqua) number and fruit dry weight, and delayed flowering, but did not significantly affect height or weight of shoots, Oilseed rape fruit weight was reduced at 200 P. miliaceum plants m^?2. fruit number and shoot weight were inhibited at 400 weeds m^?2. and height was reduced and flowering delayed at 600 weeds m^?2. Number and weight of fruits were reduced by one-third after 8 weeks of interference as compared to oilseed rape grown with the weed for 4 weeks. Oilseed rape height was reduced by 29% and shoot weight by 55% by 600 weeds m^?2 and 2–2 kg ha^?1 atrazine, while fruit number and weight were reduced by 72%. Oilseed rape shoot weight was reduced by 74% by 600 weeds m^?2 for 12 weeks of interference, while fruit number and weight were reduced by 85% and 82%. respectively. In a field study, fluazifop reduced early season P. miliaceum cover by 72%, but did not increase oilseed rape cover. Mid-season P. miliaceum shoot weight was decreased by 97% by fluazifop and oilseed rape shoot weight was increased by 34%. P. miliaceum control increased oilseed rape biomass by 38% at 89 days, but biomass of oilseed rape sown at 11.2 kg ha^?1 with 2.2 kg atrazine ha^?1 was not decreased by P. miliaceum interference at 89 days.     

A Cluster of Major Specific Resistance Genes to Leptosphaeria maculans in Brassica napus

ABSTRACT Two types of genetic resistance to Leptosphaeria maculans usually are distinguished in Brassica napus: qualitative, total resistance expressed at the seedling stage and quantitative, partial resistance expressed at the adult plant stage. The latter is under the control of many genetic factors that have been mapped through quantitative trait loci (QTL) studies using 'Darmor' resistance. The former usually is ascribed to race-specific resistance controlled by single resistance to L. maculans (Rlm) genes. Three B. napus-originating specific Rlm genes (Rlm1, Rlm2, and Rlm4) previously were characterized. Here, we report on the genetic identification of two novel resistance genes, Rlm3 and Rlm7, corresponding to the avirulence genes AvrLm3 and AvrLm7. The identification of a novel L. maculans- B. napus specific interaction allowed the detection of another putative new specific resistance gene, Rlm9. The resistance genes were mapped in two genomic regions on LG10 and LG16 linkage groups. A cluster of five resistance genes (Rlm1, Rlm3, Rlm4, Rlm7, and Rlm9) was strongly suggested on LG10. The relation between all these specific resistance genes and their potential role in adult-plant field resistance is discussed. These two Rlm-carrying regions do not correspond to major QTL for Darmor quantitative resistance.     

Response of wild Brassica juncea populations to glyphosate

BACKGROUND: Wild Brassica juncea (L.) is a troublesome arable land weed and ruderal. It is critical to understand the responses of this weed to herbicides, because the assessment of its susceptibility profile has important ecological and evolutionary consequences for future cultivation of herbicide-tolerant oilseed rape. The response of 31 wild populations from different geographic origins in China to glyphosate was evaluated with two bioassay methods, and variable responses were found in initial studies. Dose-response assays were conducted to characterize the extreme populations further, and shikimate accumulation in vivo was determined using a spectrophotometric method. RESULTS: On the basis of ID(50) values, the resistance ratios (R/S) were 5.85 and 4.19 for two glyphosate-resistant B. juncea populations in germination tests, whereas they were 4 times more resistant to glyphosate in spray tests. There were differences in shikimate accumulation patterns between the two biotypes. Shikimate concentrations in resistant populations began to decline from 6 days after treatment (DAT), while they increased continually in susceptible populations. CONCLUSION: The results obtained suggest that the populations responded differentially to glyphosate, and this variability may provide the genetic basis for evolution of individuals with increased resistance to glyphosate, with important implications for herbicide resistance management, especially in the context of risk assessment of glyphosate-tolerant crops.     

Identifying seedling and adult plant resistance of Chinese Brassica napus germplasm to Leptosphaeria maculans

Blackleg disease of canola/rapeseed (Brassica napus), caused by the devastating fungal pathogen Leptosphaeria maculans, can significantly influence B. napus production worldwide, except for China, where only the less aggressive L. biglobosa has been found associated with the disease. The aim of this study was to characterize both seedling resistance (major gene resistance, R gene resistance) and adult plant resistance (APR) from a collection of Chinese B. napus varieties/lines (accessions) to L. maculans. Evaluation of seedling resistance was carried out under a controlled environment, using 11 well‐characterized L. maculans isolates as differentials. The identification of APR was performed under multiple field environments in western Canada. R genes were detected in more than 40% of the accessions tested. Four specific R genes, Rlm1, Rlm2, Rlm3 and Rlm4 were identified, with Rlm3 and Rlm4 being the most common genes, while Rlm1 and Rlm2 were detected only occasionally. Results of field evaluation indicated significant variations among field locations as well as accessions; a large portion of the B. napus accessions, regardless of the resistance level observed at the seedling stage, showed high to moderate levels of APR under all environments tested. This study highlights that both R gene resistance and APR are present in Chinese B. napus germplasm and could be potential sources of resistance against blackleg caused by L. maculans if the pathogen ever becomes established in China.     

Major Gene and Polygenic Resistance to Leptosphaeria maculans in Oilseed Rape (Brassica napus)

The most common and effective way to control phoma stem canker (blackleg) caused by Leptosphaeria maculans in oilseed rape (Brassica napus) is through the breeding of resistant cultivars. Race specific major genes that mediate resistance from the seedling stage have been identified in B. napus or have been introgressed from related species. Many race specific major genes have been described and some of them are probably identical in B. napus (allotetraploid AACC) and the parental species B. rapa (diploid AA). More work is needed using a set of well-characterised isolates to determine the number of different major resistance genes available. In some B. napus cultivars, there is resistance which is polygenic (mediated by Quantitative Trait Loci) and postulated to be race non-specific. Many of these major genes and Quantitative Trait Loci for resistance to L. maculans have been located on B. napus genetic maps. Genes involved in race specific and polygenic resistance are generally distinct.     

Degradation of primisulfuron-methyl and metsulfuron-methyl in soil

A newly developed chemical assay was used to determine the degradation in soil of two sulfonylurea herbicides, primisulfuron-methyl and metsulfuron-methyl, under both controlled and field conditions. The results from the chemical assay were compared with those from traditional bio-assays for determination of persistence in the field. Phytotoxic effects of these herbicides were not observed after 6 weeks following application to an acidic (pH 5.7) soil with high organic matter content (7.3% o.c). Half-lives of 13 to 29 days were measured for primisulfuron-methyl at different soil-water contents and temperatures while those for metsulfuron-methyl ranged from 8 to 36 days. The rate of degradation of metsulfuron-methyl was more sensitive to temperature than that of primisulfuron-methyl. Persistence in the field was shorter than expected considering the results from the controlled environment studies. However, determination of the persistence by both chemical assay and bioassay methods produced very similar results.     

Resistance to a highly aggressive isolate of Sclerotinia sclerotiorum in a Brassica napus diversity set

Sclerotinia stem rot (SSR) of oilseed rape (OSR, Brassica napus), caused by Sclerotinia sclerotiorum, is a serious problem in the UK and worldwide. As fungicide‐based control approaches are not always reliable, identifying host resistance is a desirable and sustainable approach to disease management. This research initially examined the aggressiveness of 18 Sclerotinia isolates (17 S. sclerotiorum, one S. subarctica) on cultivated representatives of B. rapa, B. oleracea and B. napus using a young plant test. Significant differences were observed between isolates and susceptibility of the brassica crop types, with B. rapa being the most susceptible. Sclerotinia sclerotiorum isolates from crop hosts were more aggressive than those from wild buttercup (Ranunculus acris). Sclerotinia sclerotiorum isolates P7 (pea) and DG4 (buttercup), identified as ‘aggressive’ and ‘weakly aggressive’, respectively, were used to screen 96 B. napus lines for SSR resistance in a young plant test. A subset of 20 lines was further evaluated using the same test and also in a stem inoculation test on flowering plants. A high level of SSR resistance was observed for five lines and, although there was some variability between tests, one winter OSR (line 3, Czech Republic) and one rape kale (line 83, UK) demonstrated consistent resistance. Additionally, one swede (line 69, Norway) showed an outstanding level of resistance in the stem test. Resistant lines also had fewer sclerotia forming in stems. New pre‐breeding material for the production of SSR resistant OSR cultivars relevant to conditions in the UK and Europe has therefore been identified.     

光敏型氯磺隆与普通氯磺隆的控草效果比较

比较了光敏型氯磺隆与普通氯磺隆不同剂量对各种杂草的控制效果。结果显示在低剂量下,普通氯磺隆的控草效果略高于光敏型氯磺隆。在中量、高量和倍量下,两种制剂控草效果差异不大。     

Verticillium longisporum and V. dahliae: infection and disease in Brassica napus

Verticillium wilt of oilseed rape ( Brassica napus ) is caused primarily by Verticillium longisporum and has become a serious problem in northern Europe. In order to evaluate whether V. longisporum and V. dahliae differ in their interaction with oilseed rape, phenotypical and molecular assessments were made. Oilseed rape plants for fungal assessments were inoculated with V. longisporum and V. dahliae via root-dipping and samples were taken from roots, stems, leaves, flowers, pods and seeds during plant development. The infection by V. longisporum was found to start mainly in lateral roots and root-hairs, followed by colonization of the xylem vessels and extensive spread in stems and leaves, whereas V. dahliae infected the main roots and remained in the region below the cotyledon node of the plants. Re-isolation studies, together with PCR analysis of samples taken from early growth stages through to fully ripe plants, showed that the onset of flowering was a critical phase for V . longisporum to colonize plants. No seeds infected with V. longisporum were found. Mycelial growth from V. dahliae but not V. longisporum was significantly reduced on media containing tissue from a low glucosinolate B. napus genotype compared with growth on media containing tissue from a high glucosinolate cultivar. The results of this study suggest that V. longisporum favours B. napus as host and that the transition from the vegetative to the generative phase is of importance for the spread of the fungus in oilseed rape plants.     

Metabolic effects in rapeseed (Brassica napus L.) seedlings after root exposure to glyphosate

Metabolic effects in rapeseed (Brassica napus L.) seedlings after root exposure to sublethal concentrations of glyphosate were examined in order to evaluate the possibilities of using a response pattern in plants as a measure of exposure to glyphosate through the growth media, more sensitive than the well-known biomarker shikimate. Rapeseed seedlings were grown in hydroponic nutrient solutions containing varying sublethal concentrations of glyphosate (1–50 μM). After 9 days of glyphosate exposure, the shoots of the seedlings were analysed with respect to the effects on selected metabolites downstream from the primary affected metabolite shikimate, which accumulated linearly in response to glyphosate exposure (from 0 to ∼126 μmol/g DW). The selected metabolites analysed, comprising the free amino acids, and the glucosinolates derived therefrom, showed complex patterns in response to glyphosate exposure. Most noteworthy was though that they responded at the lowest concentrations of exposure to glyphosate (1 μM), where no visual effects, decrease in shoot DW or shikimate could be detected, indicating that a biomarker response more sensitive than that of shikimate can be established for plants exposed to glyphosate.