Aspects of the selective phytotoxicity of methazole. II. Behaviour in plants following root exposure

The absorption, translocation and degradation of methazole were examined in onion, Stellaria media, Matricaria matricarioides and Veronica persica grown in culture solution. After a short period of initial rapid uptake, all four species absorbed herbicide and water in the same proportions. Translocation of herbicide to the shoots was directly proportional to transpiration, but the apparent solute concentration in the xylem was less than that in the external solution and varied between the species. A smaller percentage of the total absorbed herbicide was translocated to the shoot in V. persica, the most tolerant species. Methazole was relatively stable in M. matricariodes and was degraded slowly to 3-(3,4-dicnlorophenyl)-1-methylurea (DCPMU). It was degraded rapidly to DCPMU in the other three species and this accumulated in onion and S. media. In V. persica DCPMU was degraded further to 3-(3,4-dichlorophenyl) urea (DCPU). Methazole was not an active inhibitor of photosynthesis by isolated spinach chloroplasts. Both DCPMU and DCPU inhibited photosynthesis but DCPMU was 200-times more active than DCPU. Variations in the concentrations of DCPMU in the shoots of the different species largely accounted for the variations in their response to methazole applied pre-emergence.     

The degradation of methazole in soil. II. Studies with methazole,methazole degradation products and diuron

[¹⁴C]-Labelled methazole, 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU), 1-(3,4-dichlorophenyl)urea (DCPU), and diuron were incubated in soil at 20°C and field capacity soil moisture content. Decomposition followed first-order kinetics; half-lives for degradation of these four compounds were 2.4, 144, 30 and 108 days respectively. The amount of DCPMU and DCPU that could be extracted decreased with time and the decrease was accompanied by the generation of an equivalent amount of ¹⁴CO₂. This was not so in the studies with diuron and methazole, however, and the decrease in the concentrations of radioactivity extracted from soil treated with these compounds could not be entirely accounted for as carbon dioxide. It is concluded that the unextractable radiochemical that was present was DCPMU. Methazole appeared to be degraded through DCPMU to 3,4-dichloroaniline (DCA) with the production of only traces of DCPU.     

Comparative uptake and metabolism of methazole in prickly sida and cotton

The comparative uptake and metabolism of ¹⁴C-labeled 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (methazole), a herbicide, in prickly sida (Sida spinosa L.) and cotton (Gossypium hirsutum L.) were investigated as physiological bases for herbicidal selectivity, using thin layer chromatography, autoradiography, and liquid scintillation counting. Prickly sida and cotton readily absorbed and translocated ¹⁴C from nutrient solution containing [¹⁴C]methazole. Only acropetal translocation of ¹⁴C was observed. Methazole was rapidly metabolized to 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU) and other metabolites by both species. Although metabolism appeared to be qualitatively the same, quantitative differences between species were evident. Methazole was converted to DCPMU (also phytotoxic) more readily by prickly sida than cotton; however, DCPMU was more readily detoxified to 1-(3,4-dichlorophenyl) urea (DCPU) by cotton than prickly sida. More ¹⁴C per unit weight was present in the prickly sida shoots than in cotton shoots. Also, a larger portion of the methanol-extractable ¹⁴C was herbicidal in the shoots of prickly sida than of cotton. Thus, the differential tolerances of prickly sida and cotton to methazole may be explained, in part, by differential uptake and metabolism of methazole and DCPMU.     

Metabolic fate of methazole in purple and yellow nutsedge

The mechanisms for the tolerance of purple nutsedge (Cyperus rotundus L.) and susceptibility of yellow nutsedge (Cyperus esculentus L.) to methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] were studied. Both species absorbed and translocated[¹⁴C]methazole and metabolites from nutrient solution; however, greater amounts of ¹⁴C per unit weight were detected in yellow than in purple nutsedge. Although intact plants and excised leaves of both species rapidly metabolized methazole to DCPMU [1-(3,4-dichlorophenyl)-3-methylurea], detoxification of DCPMU to DCPU [1-(3,4-dichlorophenyl) urea] occurred more slowly in yellow than in purple nutsedge. Compared to yellow nutsedge, a greater percentage of the radioactivity in purple nutsedge was recovered as polar products. Polar products were converted to the free forms of the parent herbicide and to phytotoxic DCPMU by proteolytic enzyme digestion. Based on the findings of this study, at least three mechanisms (differential absorption, metabolism, and formation of polar products) account for the differential tolerance of these two species to methazole.     

Metabolic fate of bioxone in cotton

The metabolic fate of the ¹⁴C-labeled herbicide, 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (bioxone), in cotton (Gossypium hirsutum L. “Acala 4-42-77”) was studied using thin-layer chromatography, autoradiography, and counting. Bioxone-¹⁴C was readily metabolized by cotton tissue to 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU) and 1-(3,4-dichlorophenyl)urea (DCPU). Leaf discs metabolized bioxone-¹⁴C rapidly; 12 hr posttreatment, 65% of the ¹⁴C in methanol extracts was in forms other than intact herbicide. Excised leaves treated through the petiole with either heterocyclic ring-labeled or phenyl ring-labeled herbicide contained little bioxone-¹⁴C after 1 day; DCPMU was formed early then decreased with time. DCPU accounted for 55–70% of the ¹⁴C in excised leaves 3 days posttreatment. In intact plants treated via the roots, the herbicide was rapidly metabolized in the roots to DCPMU and DCPU; little or no intact herbicide was translocated to the leaves. Little radioactivity accumulated in the roots with time; the radioactivity in the leaves accounted for 80–90% of the methanol-soluble ¹⁴C 47 days posttreatment. Most of the ¹⁴C in the leaves was recovered as DCPU (50–60%) and unidentified polar metabolite(s) which remained at the origin of the thin-layer plates (30–40%). The percentage of radioactivity which remained in cotton residue after methanol extraction increased with time. Digestion of the plant residues with the proteolytic enzyme pronase indicated that some of the nonextractable ¹⁴C may be DCPMU and DCPU complexed with proteins. Similar metabolic patterns were noted after treatment with either heterocyclic ring-labeled or phenyl ring-labeled bioxone-¹⁴C. Generally, bioxone was metabolized to DCPMU which in turn was demethylated to DCPU. The herbicide and DCPMU were 20 times as toxic as DCPU to oat (Avena sativa L.), a susceptible species.     

Aspects of the selective phytotoxicity of methazole. I. Measurements of species response, spray retention and leaf surface characteristics

The responses of onion (Allium cepa). Veronica persica, Matricaria matricarioides and Stellaria media to post-emergence applications of methazole were measured in field and glasshouse experiments. Stellaria media was the most susceptible species and V. persica the least. Plants of all species became more tolerant the larger they were at the time of treatment, and this was most pronounced in onion. Onion generally retained less spray per unit of dry weight than the other three species and retention was less on old compared with young plants, whereas with the weed species, this did not change appreciably with age. There was a progressive increase in the amount of structured crystalline wax on successive onion leaves which resulted in larger contact angles between droplets and the leaf surfaces and lower spray retention per unit of dry weight. There was less wax development on the leaf surfaces, increased spray retention, and increased susceptibility to methazole in onion treated pre-emergence with ethofumesate thus confirming that these factors are interrelated. While the increased tolerance of onion to methazole with age could be explained in part by decreased retention of herbicide, this was not so for the weed species, and other factors must determine their change in tolerance with age.     

The degradation of methazole in soil. I. Effects of soil type,soil temperature and soil moisture content

[¹⁴C]-Labelled methazole was incubated in six soils at 25°C and with soil moisture at field capacity. Under these conditions, methazole was unstable, the concentration declined following first-order kinetics with half-life values in the soils ranging from 2.3 to 5.0 days. The main degradation product was 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU) which was more stable than the parent compound. After about 160 days, DCPMU accounted for 30 to 45% of the initial methazole concentration. Degradation of methazole and DCPMU was affected by soil temperature and moisture content. With methazole, half-lives in one soil at field capacity moisture content and temperatures of 25, 15 and 5°C were 3.5, 8.7 and 31.1 days respectively. The half-life at 25°C was increased to 5.0 days at 50% of field capacity and 9.6 days at 25% of field capacity. A proportion of the initial radioactivity added to the soil could not be extracted and this proportion increased with time. After 160 days this unextractable radioactivity accounted for up to 70% of the amount applied.     

The environmental fate of diuron under a conventional production regime in a sugarcane farm during the plant cane phase

BACKGROUND: Field studies of diuron and its metabolites 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU), 3,4-dichlorophenylurea (DCPU) and 3,4-dichloroaniline (DCA) were conducted in a farm soil and in stream sediments in coastal Queensland, Australia. RESULTS: During a 38 week period after a 1.6 kg ha(-1) diuron application, 70-100% of detected compounds were within 0-15 cm of the farm soil, and 3-10% reached the 30-45 cm depth. First-order t(1/2) degradation averaged 49+/-0.9 days for the 0-15, 0-30 and 0-45 cm soil depths. Farm runoff was collected in the first 13-50 min of episodes lasting 55-90 min. Average concentrations of diuron, DCPU and DCPMU in runoff were 93, 30 and 83-825 microg L(-1) respectively. Their total loading in all runoff was >0.6% of applied diuron. Diuron and DCPMU concentrations in stream sediments were between 3-22 and 4-31 microg kg(-1) soil respectively. The DCPMU/diuron sediment ratio was >1. CONCLUSION: Retention of diuron and its metabolites in farm topsoil indicated their negligible potential for groundwater contamination. Minimal amounts of diuron and DCMPU escaped in farm runoff. This may entail a significant loading into the wider environment at annual amounts of application. The concentrations and ratio of diuron and DCPMU in stream sediments indicated that they had prolonged residence times and potential for accumulation in sediments. The higher ecotoxicity of DCPMU compared with diuron and the combined presence of both compounds in stream sediments suggest that together they would have a greater impact on sensitive aquatic species than as currently apportioned by assessments that are based upon diuron alone.     

Anaerobic microbial degradation of selected 3,4-dihalogenated aromatic compounds

Anaerobic microbial degradation of selected 3,4-dihalogenated aromatic compounds was studied in medium inoculated with pond sediment. Sediment samples were collected from a diuron-treated pond. Diuron was dehalogenated at the para position, forming CPDMU as the sole degradation product. DCPU was similarly dehalogenated at the para position, forming MCPU as the only degradation product. Linuron degradation resulted in four products: one, CPMMU, was the result of biological dehalogenation at the para position; another, DCPMU, was the result of chemical degradation; and the other two products were unidentified. Chlorbromuron degradation formed three unidentified products. Stam, an acylanilide, was degraded, forming two products, one of which was possibly 3-chloropropioanilide. CIPC and an unidentified compound were formed from DCIP. No degradation of parent compounds or appearance of degradation products were detected in mixtures of each test compound and sterile sediment except linuron.     

Persistence of methazole activity in soil

Methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] was applied post-emergence at 2-1 kg/ha to crops of onion (Allium cepa L.) grown on a sandy loam and the activity present in the surface 0–5 cm of soil assessed by bioassay. In spring-sown crops, activity at harvest varied from 25 to 78% of the initial acitivity in different years; losses were restricted by low temperature and low rainfall. In autumn-sown crops, little loss occurred during winter and most of the activity remained in the surface 0-5 cm. The results emphasize the need for caution in choice and timing of following crops.     

Bacterial Blight of Welsh Onion : A New Disease Caused by Xanthomonas campestris pv. allii pv. nov.

In June of 1998, a new bacterial disease was observed on Welsh onion in Okinawa Prefecture, Japan. Infected plants in nursery boxes were stunted with tip dieback, and heavily infected plants died. In fields, the disease appeared on leaves as irregular gray spots or elliptical spots with creases in the center. These spots enlarged and spread rapidly continued cloudy or rainy weather, and formed blight lesions on outer leaves. Yellow mucoid bacterial colonies were consistently isolated from these lesions. The causal bacterium was identified as a pathovar of Xanthomonas campestris on the basis of bacteriological properties. The bacterium was pathogenic to Welsh onion, onion, but nonpathogenic to chive, Chinese chive and hyacinth. Of Liliaceae plants, which contain Welsh onion and onion, only hyacinth has been reported as a host for the genus Xanthomonas, namely X. campestris pv. hyacinthi. However, strains of X. campestris pv. hyacinthi were not pathogenic against either Welsh onion or onion. From these results, the bacterium isolated from Welsh onion is considered to be a new pathovar of X. campestris, and the name of X. campestris pv. allii pv. nov. is proposed. A strain MAFF 311173 is designated as the pathotype strain. Received 29 March 2000/ Accepted in revised form 4 July 2000     

Residues of diuron and phytotoxic degradation products in aquatic situations. I. Analytical methods for soil and water

Thin-layer and gas-liquid chromatography, ultraviolet analysis and bioassay with Chlorella spp. have been used to investigate the pathway of degradation of diuron to phytotoxic derivatives when diuron was used as a soil-residual herbicide in irrigation canals. Observations suggest that 1-(3,4-dichlorophenyl)-3-methylurea and 1-(3,4-dichlorophenyl)urea make a contribution to total residues equivalent to a maximum of about 40 and 55%, respectively, of diuron concentrations. Application of a phyto-toxicity rating suggests that in this environment, measurement of diuron specifically would underestimate the total phytotoxicity of residues by a maximum of about 7%.     

八种十字花科寄主植物真叶和子叶的化学成分及其对小菜蛾生长发育及生理代谢的影响

为明确小菜蛾Plutella xylostella对寄主植物真叶和子叶的适合度,于室内测定8种十字花科植物改良青杂3号、改良露头青、陕油0913、甘杂1号、超级火箕青、四月慢、绿球66和中花尖叶芥蓝真叶和子叶的营养物质和次生代谢物质的含量,并测定取食后小菜蛾幼虫的取食选择性、发育历期、蛹重、保护酶和解毒酶活性。结果显示,8种寄主植物真叶的可溶性糖、总氨基酸、单宁、类黄酮和总酚含量之间差异显著,且大部分均显著高于其子叶,8种寄主植物子叶的可溶性糖、总氨基酸、单宁、类黄酮和总酚含量之间也差异显著。小菜蛾3龄幼虫偏好取食真叶;取食8种寄主植物真叶后成虫前期的发育历期为12.3～16.3 d,取食子叶后成虫前期的发育历期为14.3～18.6 d;取食子叶的蛹重明显低于取食其真叶;取食8种寄主植物真叶的小菜蛾幼虫体内超氧化物歧化酶（superoxide dismutase,SOD）、过氧化物酶（peroxidase,POD）、过氧化氢酶（catalase,CAT）、谷胱甘肽S-转移酶（glutathione S-transferase,GST）、羧酸酯酶（carboxylesterase,Car...     

Absorption, translocation and metabolism of pyridate in a tolerant crop (Zea mays) and two susceptible weeds (Polygonum lapathifolium L. and Chenopodium album L.)

Absorption, translocation and metabolism of ¹⁴C-pyridate were compared in tolerant maize. moderately susceptible Polygonum lapathifolium and susceptible Chenopodium album. Foliar absorption was limited in all species, but comparatively higher penetration levels were observed in younger leaves of dicotyledonous species. The absorbed radioactivity was not very mobile and translocation appeared mainly sym-plastic. Herbicide selectivity could not be explained on the basis of absorption and transport. Chenopodium and P. lapathifolium degraded pyridate and formed unstable water-soluble conjugates that easily released a phytotoxic metabolite. By contrast, more stable unidentified water-soluble metabolites were found in maize. That metabolic difference could explain the selectivity of pyridate.     

Pathogenicity of <Emphasis Type="Italic">Stemphylium vesicarium</Emphasis> from different hosts causing brown spot in pear

Stemphylium vesicarium (teleomorph: Pleospora herbarum) is the causal agent of brown spot disease in pear. The species is also able to cause disease in asparagus, onion and other crops. Saprophytic growth of the fungus on plant debris is common. The objective of this study was to investigate whether isolates of S. vesicarium from different hosts can be pathogenic to pear. More than hundred isolates of Stemphylium spp. were obtained from infected pear fruits, dead pear leaves, dead grass leaves present in pear orchard lawns as well as from necrotic leaf parts of asparagus and onion. Only isolates originating from pear orchards, including isolates from dead grass leaves, were pathogenic on pear leaves or fruits in bioassays. Non-pathogenic isolates were also present in pear orchards. Stemphylium vesicarium from asparagus or onion, with one exception, were not pathogenic to pear. Analysis of the genetic variation between isolates using Amplified Fragment Length Polymorphism (AFLP) showed significant concordance with host plants. Isolates from asparagus or onion belonged to clusters separate from the cluster with isolates from pear or grass leaves collected in pear orchards. Multilocus sequencing of a subset of isolates showed that such isolates were similar to S. vesicarium.     

Seed banks of soils under vegetable cropping in England

Estimates of viable weed seeds in soil samples taken in 1968–1975 from 89 vegetable fields in England gave a median value of 4120 m^?2 in 0–15 cm. Poa annua, Stellaria media and Matricaria matricarioides occurred most frequently, and nine species accounted for 72% of all seeds found. The numbers of seeds were lower than those from a survey made a decade earlier but the species occurring most frequently were the same; M. matricarioides, however, appeared to have increased in relative importance.     

Absorption and translocation of 14C-3,6-dichloropicolinic acid in Cirsium arvense (L.) Scop.

Experiments were conducted in a growth cabinet to investigate the absorption and translocation of ¹⁴C-3, 6-dichloropicolinic acid by Cirsium arvense (L.) Scop. (Canada thistle, creeping thistle), a sensitive species. Applications were made, either to the middle four leaves of 12-cm-tall vegetative plants grown under low (40%) and/or high (>95%) relative humidity (r.h.), or to four upper or lower leaves of 30-cm-tall flowering plants grown under low r.h. Following application to vegetative plants, absorption and translocation of ¹⁴C-3,6-dichloropicolinic acid was rapid and was approximately doubled by high r.h. High r.h. increased the amount of radioactivity retained by the treated leaves or translocated to the shoots but did not affect greatly the amount retained in the roots. The herbicide was highly mobile, with over half of that absorbed, translocated out of the treated leaves after two days. The apex accumulated most of the radioactivity, while approximately 8% was recovered from the roots. The absorption and translocation patterns were similar to those reported in the literature for picloram in C. arvense. Absorption of 3,6-dichloropicolinic acid was greater in vegetative than in flowering C. arvense plants, and placement of herbicide on lower leaves tended to decrease the amount of radioactivity recovered from shoot apex and increase the amount recovered from the roots. Approximately 15% of the applied radioactivity could not be recovered from treated plants by 2 days after treatment.     

Aantasting van ui doorPhytophthora porri

Phytophthora porri was isolated from onion leaves causing leaf spots which resemble those of the white tip disease of leek. This is the first report of onion plants being attacked and damaged byP. porri.     

Fusarium oxysporum,F. proliferatum and F. redolens associated with basal rot of onion in Finland

In recent years in Finland, Fusarium infections in onions have increased, both in the field and in storage, and Fusarium species have taken the place of Botrytis as the worst pathogens causing post‐harvest rot of onion. To study Fusarium occurrence, samples were taken from onion sets, harvested onions and also from other plants grown in the onion fields. Isolates of five Fusarium species found in the survey were tested for pathogenicity on onion. Fusarium oxysporum was frequently found in onions and other plants, and, of the isolates tested, 31% caused disease symptoms and 15% caused growth stunting in onion seedlings. Fusarium proliferatum, a species previously not reported in Finland, was also identified. Over 50% of the diseased onion crop samples were infected with F. proliferatum, and all the F. proliferatum isolates tested were pathogenic to onion. Thus, compared to F. oxysporum, F. proliferatum seems to be more aggressive on onion. Also some of the F. redolens isolates were highly virulent, killing onion seedlings. Comparison of the translation elongation factor 1α gene sequences revealed that the majority of the aggressive isolates of F. oxysporum f. sp. cepae group together and are distinct from the other isolates. Incidence and relative proportions of the different Fusarium species differed between the sets and the mature bulbs. More research is required to determine to what extent Fusarium infections spoiling onions originate from infected onion sets rather than the field soil.     

Fungitoxicity of 6H-pyrazolo[3,4-c][l,2,5]thiadiazine-2,2-dioxides

A base-promoted cyclisation of 4-nitroso-5-benzylsulphonamidopyrazoles (VII) afforded 6 H -pyrazolo[3,4-c][1,2,5]thiadiazine-2,2-dioxides (VIII). They were tested in vitro for antifungal activity against a series of phytopathogenic fungi of different taxonomic classes. Five of the compounds had noteworthy activity; in particular 6H-3-phenyl-5-methyl-7–(3,4-dichlorophenyl) pyrazolo[3,4-c][1,2,5]thiadiazine-2,2-dioxide (VIIIc) at the concentration of 200 mg litre^?1 completely inhibited the growth of Pythium ultimum, Corticium solani and Sclerotinia minor.