Uptake and translocation of carpropamid in rice (Oryza sativa L)

Translocation of the antiblast compound, carpropamid, was investigated in rice using [¹⁴C]carpropamid. When applied to the seed, carpropamid was not only readily absorbed but was translocated to different parts of the seedlings emerging from treated seeds. A substantial portion of fungicide appeared to be exuded onto the leaf surface. In 21‐day‐old plants grown from [¹⁴C]carpropamid‐treated seeds, 27.2% of the radioactivity isolated from leaves was present on the surface of lamina. This exuded fraction is probably responsible for its action as a fungal anti‐penetrant compound. Following 30‐min root dipping of 14‐day‐old seedlings, carpropamid was rapidly absorbed and translocated throughout the seedling. Its intra‐laminar distribution was uniform as determined by autoradiography. Only a small fraction (<2%) of fungicide applied to the foliage was translocated beyond the site of application within the treated leaf. Translocation was primarily apoplastic. Approximately 54% of the radioactivity recovered from leaves was in the form of carpropamid. At least seven radiolabelled metabolic products were observed by TLC. Only 8.3% of radioactivity applied through the seeds could be recovered from 21‐day‐old seedlings. © 2001 Society of Chemical Industry     

Bioassays using detached tobacco leaves to determine the sensitivity of Peronospora tabacina to fungicides

Two bioassay methods are described which use detached tobacco leaves to measure the sensitivity of Peronospora tabacina to systemic fungicides. Tobacco leaves (13–15 cm²), treated with fungicides before or after detachment from the plant, were inoculated with sporangia in water drops and, after incubation in beakers and Petri plates, the disease severity and/or production of sporangia was determined 4–7 days after treatment with the fungicides. Of 15 systemic fungicides applied to detached leaves, eight N-phenylamides at 0.066?1.0 μg ml^?1 controlled blue mould; metalaxyl was the most effective fungicide. Isolates of P. tabacina, collected in the field from tobacco plants grown in soil treated with metalaxyl, were not resistant to the fungicide applied to detached leaves prior to inoculation. The fungicide, applied to leaves before detachment, was used to measure the efficacy of five systemic N-phenylamide fungicides sprayed on the basal and unsprayed distal portions of the leaves. Blue mould was controlled on the basal portion of the leaf by all the fungicides at 0.66?1.0 μg ml^?1, but it required the application of 3–30 times more chemical on the basal portion to achieve comparable blue mould control on the distal part of the leaf.     

Uptake and distribution of [14C]metalaxyl by detached tobacco leaves

When the petioles of detached tobacco leaves (10–17 cm²) were incubated in aqueous solutions containing [¹⁴C]metalaxyl, uptake of the fungicide was dependent on the temperature and photoperiod. Detached leaves took up 78% more [¹⁴C]metalaxyl at 26°C than at 16°C. The rate of uptake in the light at 21°C was linear, but after an additional 20h in the dark, there was only twice as much fungicide in the leaves. Different sized leaves contained the same amount of fungicide per cm² area. Uptake by detached leaves of the ¹⁴C-labelled anilide lactones ofurace and RE-26940 [2-methoxy-N-(tetrahydro-2-oxo-3-thienyl)acet-2′,6′-xylidide] was similar to that of metalaxyl. At the concentration of metalaxyl (66 ng ml^?1) that controlled blue mould (Peronospora tabacina) on detached tobacco leaves, the amount of fungicide in the leaves was found to be 7.25 ng. Autoradiography showed that the distribution of [14C]metalaxyl in detached leaves after incubation for 23h was uniform, although higher concentrations of the label were present in the smaller veins of the leaves.     

Is the accumulation of a systemic fungicide at the infection site related to its eradicative action?

Restricted areas of Avena sativa leaves were infected with Puccinia coronata. The systemic fungicide [³H]triarimol was later applied to the roots of these plants. The fungicide did accumulate at the infection sites when applied 14 days after inoculation, but not when applied 4 or 9 days after inoculation. It is concluded that the accumulation of the fungicide at the infection zone is a result of enhanced evaporation from leaf tissues (probably) because the epidermis was broken after pustule formation.     

Dissipation of propiconazole residues in and on wheat (Triticum aestivum L.)

In a 2-year investigation, the dissipation of residues of the fungicide propiconazole from winter wheat straw and leaves was measured by periodic sampling of the green plant material from several plots that had been sprayed with ‘Tilt 2.50EC’ at three different rates. The fungicide deposits on straw and leaves at day 0 were approximately one-quarter of the dose applied on all treatment plots, and this fraction did not differ significantly between three dosage rates. The fungicide residues disappeared rapidly, and the half-life of the fungicide on straw and leaves was approximately 5 days. At harvest time, the fungicide residues in grain and soil were negligible, but the residues remaining on straw and leaves were considerable, especially at higher spraying rates than the recommended dosage.     

Carbon Fixation and Partitioning in Coffee Seedlings Infested with <Emphasis Type="Italic">Pratylenchuscoffeae</Emphasis>

The objective was to study CO₂ fixation and photoassimilate partition in coffee (Coffea arabica) seedlings infested with the lesion nematode Pratylenchus coffeae. Seedlings infested with 0, 1000 and 8000 Pratylenchus coffeae nematodes were exposed to ¹⁴CO₂ and the incorporation and distribution of radioactivity were followed in the roots, stems and leaves. Fresh mass, pigments, soluble sugars, sucrose and specific radioactivity of sucrose in the plant parts were determined. At the highest level of infestation almost all the parameters were significantly changed showing the carbon fixation in the leaves and partitioning to the roots were decreased. Since lesion nematodes are not sedentary and do not form feeding sites that could be characterised as metabolic sinks, it is suggested that their damage is more readily expressed by the leaves, through a reduction in photosynthesis and phloem transport.     

Fate of [14C]daminozide and [14C]maleic hydrazide in American elm (Ulmus americana L.)

Radiolabelled daminozide and maleic hydrazide (MH) were injected into American elm seedlings, kept in nutrient solution, to determine their translocation pattern and metabolic fate. Both compounds were rapidly translocated to all parts of the plant. After 21 days, 13% of the applied ¹⁴C was exuded into the nutrient solution from the roots of the plants treated with MH. Using gel-filtration and thin-layer chromatographic techniques, it was determined that daminozide did not form any metabolite, and that MH was converted into a MH-sugar complex. A significant amount of ¹⁴C was unextractable from the plant tissue.     

Uptake,distribution and metabolic fate of 3H-triforine in plants .I. Short-term experiments

Most of the label, present in the roots of bean, tomato and barley seedlings after short-term root-treatment with ³H-triforine, appeared only weakly adsorbed on to the root tissue and was desorbed after transplanting in fungicide-free soil. Label taken up accumulated almost exclusively in the leaves present at the time of treatment; all leaves expanding after termination of the treatment remained virtually devoid of radioactivity. In “adult” plants label was usually present in a concentration gradient from roots to youngest leaves; in tomato plants, however, distribution of label was rather irregular. Time-course studies with bean and barley plants revealed that the aerial parts were gradually supplied with label, from old to youngest leaves, the maximum relative accumulation of radioactivity slowly moving acropetally. Under the experimental conditions chosen, triforine was converted nearly quantitatively to one metabolite, which almost certainly is different from any known non-enzymic breakdown product of the fungicide.     

The distribution and degradation of chlormequat in wheat plants

The distribution and degradation of chlormequat chloride (2-chloro 1,2-¹⁴C ethyltrimethylammonium chloride) was determined after uptake by the roots of summer wheat seedlings. This plant regulator was readily translocated from the roots to the above ground parts and converted into choline. Choline was further metabolized to betaine which upon demethylation yielded finally glycine and serine. Both amino acids were incorporated into a protein fraction.The occurrence of radioactively labeled glycine and serine in the amino acid pool and the evolution of ¹⁴CO₂ from chlormequat treated plants indicated that serine was formed from glycine under the release of ¹⁴CO₂ during photorespiration.One week after the uptake period 82% of ¹⁴C chlormequat taken up by the roots was recovered as the parent compound or as breakdown products in wheat plants. In addition 5% of the amount taken up by the roots was released as ¹⁴CO₂ by the leaves.Fifty per cent of the total amount of chlormequat originally present in roots and leaves was already metabolized after 7.5 days. No evidence has been obtained for the presence of unchanged chlormequat or an unknown metabolite in the nucleic acid or protein fraction.     

Factors affecting benfuresate activity against purple nutsedge (Cyperus rotundas L.)

Benfuresate (2-3-dihydro-3,3-dimethylbenzofu-ran-5-yl ethanesulfonate) is a selective herbicide for the control of purple nutsedge in cotton. Under outdoor conditions, purple nutsedge was sensitive to benfuresate incorporated in soil up to eight days after initiation of shoot sprouting from the tuber. Older seedlings recovered from the damage. During the period of susceptibility to benfuresate, young shoots more sensitive than the roots. Under controlled environmental conditions, benfuresate applied directly to apical buds developing from the tuber caused severe damage to the treated bud and induced abrupt development of axillary buds. Negligible amounts of the applied herbicide were translocated from the treated part to the other buds and roots. Application of the herbicide to fully developed leaves had no effect, probably because of its rapid metabolism and low basipetal mobility. Its relatively high volatility may also contribute to its low foliar post-emergence activity. Tubers also absorbed herbicide vapours. Root uptake of ¹⁴C-benfuresate resulted in a rapid accumulation of ¹⁴C in the shoot, which had no effect on the purple nutsedge plant, regardless of concentration. The herbicide is rapidly converted, mainly to a non-phytotoxic polar product. These results may explain the high sensitivity of the weed to benfuresate at early growth stages, and the lack of sensitivity in mature plants.     

Efficacy of metalaxyl for blue mould control and its persistence on tobacco

Foliar sprays of metalaxyl, benalaxyl, and cymoxanil plus mancozeb gave better control of blue mould (Peronospora tabacina) than mancozeb alone applied as a spray, or metalaxyl applied to the soil. Before flue-curing, the mean values of metalaxyl residues in tobacco leaves were significantly higher from foliar spray treatments (5.09 μg g⁻¹), than from soil treatments (0.93 μg g⁻¹). Residues had decreased after flue-curing (foliar spray treatment 2.51 μg g⁻¹; soil treatment 0.69 μg g⁻¹), especially on samples taken in September. Curing considerably reduced metalaxyl residues in all cases. Residues of mancozeb ranged from 59.5 to 224.2 μg g⁻¹ before flue-curing and from 11.0 to 22.1 μg g⁻¹ after flue-curing. All these residues were calculated on a dry weight basis. Imidazolidine-2-thione (ethylenethiourea) residues from mancozeb were always below the sensitivity limit of the method used.     

Systemic movement in cucumber plants and control of cucumber gray mould by a new fungicide,S-7131

Carbon-14-labelled S-7131 (N-(3′,5′-dichlorophenyl)-1,2-dimethylcyclopropane-1,2-dicarboximide) penetrated into the treated leaves of cucumber plants, moved to the stem and was then translocated both upwards and slightly downwards. Also through roots the fungicide was readily taken up and translocated to aerial parts. Autoradiographs showed that S-7131 had a tendency to accumulate at the leaf margin. In experiments with cucumber plants bearing flowers and fruits it was shown that S-7131 hardly moved from foliage to flowers and fruits. TLC analysis of radioactive extracts showed that S-7131 moved within plants in the unaltered form. Bioassay tests confirmed that systemic movement of S-7131 contributed to its high efficacy in disease control.     

Impact of foliar nickel application on urease activity,antioxidant metabolism and control of powdery mildew (Microsphaera diffusa) in soybean plants

Nickel (Ni) is a cofactor for urease, an enzyme that breaks down urea into ammonia and carbon dioxide. This study aimed to evaluate the physiological impact of Ni on urea, antioxidant metabolism and powdery mildew severity in soybean plants. Seven levels of Ni (0, 10, 20, 40, 60, 80 and 100 g ha^?1) alone or combined with the fungicides fluxapyroxad and pyraclostrobin were applied to soybean plants. The total Ni concentration ranged from 3.8 to 38.0 mg kg^?1 in leaves and 3.0 to 18.0 mg kg^?1 in seeds. A strong correlation was observed between Ni concentration in the leaves and seeds, indicating translocation of Ni from leaves to seeds. Application of Ni above 60 g ha^?1 increased lipid peroxidation in the leaf tissues, indicative of oxidative stress. Application of 40 g ha^?1 Ni combined with 300 mL ha^?1 of fungicide reduced powdery mildew severity by up to 99%. Superoxide dismutase, catalase, peroxidase and urease enzyme activity were greatest under these conditions. Urea concentration decreased in response to Ni application. Urease activity in soybean leaves showed a negative correlation with powdery mildew severity. The leaf Ni concentration showed a positive correlation with the urease and a negative correlation with powdery mildew severity. The results of this study suggest that urease is a key enzyme regulated by Ni and has a role in host defence against powdery mildew by stimulating antioxidant metabolism in soybean plants.     

Fate of [14C]Mancozeb in Egg Plants (Solanum melongena L.) during Summer under Sub-tropical Conditions

The fungicide mancozeb belongs to ethylenebis(dithiocarbamate) group of fungicides which is used to control brown and black rust, leaf spot, leaf blight, downy mildew etc. on a variety of plants including egg plants, tomato, potato and others. [¹⁴C]mancozeb, when applied to the foliage of egg plants (Solanum melongena L.) during summer months, dissipated very rapidly with a half-life of only 10·6 days. Ethylenethiourea (ETU), ethyleneurea (EU), ethylenethiuram disulfide (ETD), ethylenethiuram monosulfide (ETM) were the metabolites of [¹⁴C]mancozeb detected in all the plant parts at different times after the treatment. The amount of ETU in fruits after fourteen days of treatment was only 206 μg kg^?1 which is below the maximum permissible level and ultimately came down to 4·6 μg kg^?1 after 42 days. EU was found to be the predominant metabolite, suggesting the breakdown of unstable ETU to relatively stable EU under subtropical conditions.     

Resistance to metalaxyl in isolates of the sunflower pathogen Plasmopara halstedii

Plasmopara halstedii isolates showing an atypical reaction to metalaxyl were collected in France, in 1995 and 1996, and tested in the laboratory for their level of sensitivity to this fungicide. Primary and secondary infections caused by one of these isolates were not controlled by the metalaxyl concentration registered for seed treatment. The EC₅₀ of this isolate was 12 800 mg a.i. kg^-1 compared with 22 mg a.i. kg^-1 for sensitive isolate, indicating a 582-fold decrease in sensitivity to the compound. There was no reduction in the agressiveness of the resistant isolate. Using other anti-oomycete fungicides, it appeared that propamocarb, contact fungicides (fluazinam, folpet, mancozeb) and the mixed formulations dimethomorph + mancozeb, cymoxanil + mancozeb and ofurace + folpet were effective against primary infections made with metalaxyl resistant and sensitive isolates, but not against secondary infections. Metalaxyl mixed with fluazinam, folpet or mancozeb was more effective against primary infections with the resistant isolate than metalaxyl alone. The EC₅₀ of five other isolates ranged from 5 800 to 32 900 mg a.i. kg^-1, indicating a variability in metalaxyl sensitivity of resistant sunflower downy mildew isolates. This is the first report of physiological resistance to metalaxyl in Plasmopara halstedii.     

Deterrent effects of some botanical products on oviposition of the cowpea bruchid Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Extracts from nine plant materials were tested in choice and no-choice tests as oviposition deterrents for cowpea bruchid, Callosobruchus maculatus (F.) on chickpea, Cicer arietinum L. Seed treatment with 0.1% crude extract of materials resulted in a significant reduction in ovipositional preference of the bruchid. The highest repellency was found in Rhazya stricta leaves (82%), Azadirachta indica seeds (76.8%), Heliotropium bacciferum aerial parts (59.2%) and citrus peels (58.6%). Progeny production was significantly reduced: only 11.5, 11.9, 12.4, 13.4 and 14.8% of the eggs deposited reached adulthood in R. stricta, neem seeds, Piper nigrum, citrus peels and H. bacciferum, respectively. F1 females laid significantly fewer eggs in response to R. stricta, neem seeds, Eugenia caryophyllata cloves, H. bacciferum, citrus peels and P. nigrum. Percentage reduction in F₂ progeny ranged between 71.4% with R. stricta-treated seeds and 24.5% in the P. nigrum treatment.     

Resistance to acylalanines in Phytophthora infestans in The Netherlands1

In The Netherlands in 1980 a severe late-blight epidemic involving metalaxyl-resistant strains of Phytophthora infestans did considerable damage to the potato crop. As a consequence metalaxyl or metalaxyl-containing products were withdrawn from the Dutch fungicide market for the control of potato late blight. In 1981 the majority of the P. infestans isolates obtained from various parts of the country were sensitive to metalaxyl. In three areas where metalaxyl mixtures were used on a relatively large scale metalaxyl-resistant strains dominated the population. Incidental use of metalaxyl mixtures in 1982 and 1983 showed adequate late-blight control and, when in 1984 an early and in some areas severe epidemic developed, a metalaxyl/mancozeb mixture was reintroduced for curative application in combination with conventional fungicides. Although disease control was adequate, resistant strains were present in a small number of fields. Whether resistant strains will increase in frequency and threaten the usefulness of mixtures of acylalanines will heavily depend on how well potato farmers adopt strategies involving a limited use of mixtures of acylalanines in a spray schedule with conventional late-blight fungicides.     

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.     

Resistance to acylalanines in Pseudoperonospora cubensis1

Resistance to acylalanine fungicides in Pseudoperonospora cubensis, the downy mildew of cucurbits, is reviewed. Insensitive strains of the fungus predominated during the second year of metalaxyl application in cucumber glasshouses in Greece and Israel. Resistance was detected either on detached cucumber leaves floated on metalaxyl solutions or on potted plants treated (sprayed or drenched) with this fungicide. Metalaxyl-resistant strains of P. cubensis showed good pathogenicity and fitness, and competed favorably with the sensitive strains in the absence of the fungicide. A synergism between these two biotypes resulted in an increased virulence of the resistant forms on metalaxyl-treated plants. Metalaxyl-resistant strains of the pathogen exhibited cross resistance to other acylalanine fungicides. Strains resistant to acylalanines and to the chemically unrelated oomycete-fungicides fosetyl-Al and propamocarb were isolated in Israel, as well. In Greece, however, protective sprays with fosetyl-Al, cymoxanil and mancozeb gave good control of cucumber downy mildew when the pathogen was resistant to metalaxyl. P. cubensis is the first case of fungus which developed resistance to acylalanines in the field.     

Uptake of iprodione and control of diseases on potato stems

When applied to the roots of potato plants growing in different soils iprodione became systemic in the plants. Although iprodione was adsorbed on the soils tested, sufficient fungicide was present in potato stems to prevent infection by Phoma exigua var. foveata on all plants except those grown in peat soils. The amount of fungicide present in the aerial parts of the plant was related to the soil/water distribution coefficients. Application of iprodione to the sprouts of seed potato tubers prior to planting decreased the incidence and severity of infection by Rhizoctonia solani (stem canker) and Polyscytalum pustulans on stem bases.