Root exudation of diclofop-methyl and triasulfuron from foliar-treated durum wheat and ryegrass

In this study, we evaluated the release of diclofop-methyl and triasulfuron from the roots of foliar-treated ryegrass and wheat. The study with ¹⁴C-diclofop-methyl indicated a basipetal translocation of foliar-applied herbicide in wheat and ryegrass. No root exudation from ¹⁴C-diclofop-methyl-treated wheat plants was observed, while 20 days after treatment (DAT) 0.2–0.9% of radioactivity absorbed by ryegrass was found exuded in the growing medium. Root exudation was stimulated three to six times by the presence of untreated wheat or ryegrass sharing the growing medium with diclofop-methyl-treated ryegrass. No subsequent uptake of exuded radiolabel by untreated plants (ryegrass or wheat) in the same pot with ¹⁴C-diclofop-methyl-treated ryegrass was observed. The study with ¹⁴C-triasulfuron indicated a basipetal translocation of foliar-applied herbicide in wheat and ryegrass and also into the growing medium. By 20 DAT, 0.5–4.2% of radioactivity absorbed by wheat or ryegrass was found exuded in the growing medium. The presence of untreated plants (wheat or ryegrass) in the same pot as triasulfuron-treated ryegrass or wheat induced exudation seven to 32 times more. The study also revealed a subsequent uptake of exuded compounds by untreated wheat or ryegrass sharing the medium of ¹⁴C-triasulfuron-treated plants. This study has demonstrated for the first time that the root exudation of exogenous compounds can be related to plant arrangement in pots. The implication is that herbicide root exudation and transfer, a form of allelopathy, could be significant in the field. A precise estimation of environmental fate, unexpected ecological side effects and residual activity of herbicides may require quantification of such exudation.     

Phytotoxic activity of root absorbed glyphosate in corn seedlings (Zea mays L.)

Growth chamber experiments were conducted in order to study the absorption, translocation and activity of glyphosate when applied to roots with aqueous solution avoiding any glyphosate–substrate interaction. Corn seedlings at the first leaf stage were set up in individual graduated cylinders containing different solutions of ¹⁴C-glyphosate (0–30 mg ae kg⁻¹). After 26 h of root exposure, plants were transferred to fresh nutrient solution and grown for the next 5 days. After harvest, plants were separated into seed, root, mesocotyle, coleoptile, cotyledon, first leaf and all new leaves (apex), and quantified ¹⁴C radioactivity contained in each part. Glyphosate uptake was only 11% of the theoretical mass flow into the plant. The amount of glyphosate translocated from roots was positively correlated with plant uptake ( P  < 0.01). Total plant fresh weight presented a logistic response to glyphosate amounts, including a growth stimulant effect (hormesis), when plants absorbed less than 0.6 µg. The treated plants presented a normal pattern of glyphosate allocation, with the apex the principal sink, accumulating more than 38% of mobilized glyphosate. When corn plants absorbed more than 0.6 µg they showed a decrease in growth. The relatively high glyphosate quantities allocated in the new leaves showed the relevance of the symplastic pathway in the translocation process for root absorbed glyphosate.     

Uptake and translocation of imazethapyr in peas as affected by parasitism of Orobanche crenata and herbicide application methods

[¹⁴C]-Imazethapyr was applied as a seed treatment and at plant pre-emergence and post-emergence to peas ( Pisum sativum L.) parasitized by Orobanche crenata Forsk. Herbicide uptake increased with time regardless of the application method. Uptake reached about 98%, 89%, 81% and 94% of the total herbicide applied for the seed coating, seed soaking, pre-emergence and post-emergence treatments respectively. Herbicide translocation within the host plants consistently differed between O. crenata -infected and non-infected plants. High levels of ¹⁴C activity were accumulated by parasitic plants from the host. In non-infected pea plants, pods were stronger sinks for imazethapyr than the other parts of the plant, regardless of the application method. The herbicide distribution in the pea plant: O. crenata complex showed the same pattern regardless of the application methods. However, accumulation of radioactivity in the parasite was lower with pre-emergence and post-emergence application than with the seed treatments. In addition, radioactivity concentration in O. crenata plants was slightly higher when [¹⁴C]-imazethapyr was applied to pea seeds by coating than by soaking.     

TRANSLOCATION STUDIES WITH ENDOTHAL-14C IN POTAMOGETON NODOSUS POIR.

Summary. Plants of Potamogeton nodosus, a submersed aquatic, were treated with the di-sodium salt of 7-oxabicyclo(2,2,l)heptane-2,3-dicarboxylic acid-¹⁴C (endothal-¹⁴C). Gross radioautographs showed that the ¹⁴C label moved from mature photosynthesizing leaves and accumulated in the apices and developing secondary plants. Similar results were obtained with mid-leaf, stem (internode) and winter-bud applications. No move-ment of radioactivity occurred following root treatment. The results indicate symplastic translocation of endothal-¹⁴C when applied to the leaf, stem or winter bud. It is suggested that endothal can cause the death of plants by direct injury to root tissues subsequent to absorption.
Recherches sur la migration de l'endothal-¹⁴C dans le Potamogeton nodosus Poir.     

Effect of take-all root infections on nitrate uptake in winter wheat

The effect of take-all root lesions on nitrate uptake of wheat was investigated in two experiments under controlled conditions. Plants were supplied with a nutrient solution labelled with ¹⁵N during stem elongation and flowering to assess the distribution of the isotopic tracer in the different plant organs, and particularly in root segments located on both sides of take-all lesions. The ¹⁵N atom percentage excess measured in root segments located below lesions longer than 1 cm was reduced on average by half compared with that in healthy roots and root segments above lesions, reflecting a reduction in nitrogen uptake by these root segments. This reduction probably resulted from the invasion and breakdown of phloem vessels by the fungus hyphae, interrupting energy supply and thus the uptake process. Severely infected plants showed an increase in the uptake rate per unit of efficient root, which appeared to be a compensatory response to reduction of efficient root biomass in order to satisfy shoot nitrogen demand. However, this compensatory response was insufficient to ensure nitrogen accumulation equivalent to that of healthy plants, as reductions in nitrogen accumulated in roots and aerial parts at flowering were up to 56 and 49%, respectively, for plants with more than 50% of the root system below lesions longer than 1 cm.     

THE EFFECT OF SIMAZINE ON THE PHOTOFIXATION OF CO2 AND ON TRANSLOCATION OF ASSIMILATES IN NORWAY SPRUCE (PICEA ABIES)

Summary. A method of exposing seedlings of Norway spruce (Picea abies (L.) Karst.) to ¹⁴CO₂ is described. Within the 1st hr alter ¹⁴CO₂ exposure, no translocation of the ¹⁴C out of the treated branch could be observed. After a 24-hr period, however, the ¹⁴C in dormant seedlings had been translocated basipetally to part of the root system only, with no lateral diffusion of the ¹⁴C-compounds in the stem. About a week after exposure, both symplastic and apoplastic patterns of translocation had caused a more uniform distribution of ¹⁴C. In seedlings at active internode elongation, the translocation patterns were fundamentally identical to those in dormant seedlings, but the active shoot growth had led to a more uniform distribution of the ¹⁴C.
Simazine at 20 ppm had apparently stimulated both the photofixation of ¹⁴CO₂ and the rate of translocation of the ¹⁴C-assimilates. At 30 ppm, however, simazine had blocked the translocation of nutrients to the roots. On the other hand, the ¹⁴CO₂ uptake was not influenced. The simazine incubation had apparently no influence on the synthesis of cationic photosynthate.     

Distribution of 14C-glyphosate in legumes parasitised by Orobanche crenata

Absorption and translocation of ¹⁴C-glyphosate was evaluated under controlled conditions in peas ( Pisum sativum L.) and broad beans ( Vicia faba L.) parasitised or not by crenate broomrape Orobanche crenata Forsk.). Absorption increased with time up to 12 days after treatment, and reached about 50% of the ¹⁴C-glyphosate applied. Three days after treatment 70–85% of the total herbicide absorbed had been translocated out of the treated leaflet. There was no consistent differ ence in absorption and translocation between infected and non-infected plants 12 days after treatment. The ¹⁴C-glyphosate concentration in the root system increased with time in broad beans. In peas it remained more or less constant from 3 days after treatment. Generally, pods were stronger sinks for glyphosate than other parts of the plant. Herbicide accumulation in broomrape increased with its growth stage, and the parasite was a much stronger sink for glyphosate than the legume root system.     

Optimizing foliar activity of glyphosate on Bidens frondosa and Panicum maximum with different adjuvant types

The influence of non-ionic (X-77) and organosilicone (L-77) adjuvants and of methylated seed oil (MSO) on the uptake, translocation and efficacy of glyphosate was investigated in Bidens frondosa L. and Panicum maximum Jacq. In addition, the physicochemical properties of adjuvants and adjuvant + glyphosate aqueous solutions were determined. Significantly lower surface tension and contact angle values were obtained with aqueous solutions of L-77 alone and with glyphosate. Over a 48-h time course, it was observed that >50% of applied ¹⁴C-glyphosate was absorbed within 15 min in B. frondosa with L-77. At 6 h and thereafter, ¹⁴C glyphosate absorption was significantly higher with MSO compared with X-77 in B. frondosa . In P. maximum , uptake and translocation of ¹⁴C-glyphosate + adjuvant were increased in general up to 48 h after treatment application, except with L-77, which showed no improvement in uptake – instead there was a significant reduction compared with no treatment with L-77. This indicated its antagonistic effect on this grass species. The lower values of ¹⁴C-glyphosate in P. maximum also confirmed that adjuvant effects were species specific. In the efficacy studies, glyphosate formulated with L-77 achieved significantly higher control of B. frondosa , while there was no control of P. maximum with this treatment. This confirmed antagonism in glyphosate absorption into P. maximum by L-77. Furthermore, significantly higher control of tested plants was recorded with MSO in comparison to X-77, which confirms the solubilizing or humectant nature of MSO.     

THE SELECTIVE ACTION OF PICLORAM IN RED MAPLE AND WHITE ASH

Summary. White ash ( Fraxinus americana L. ) trees, 2 years of age, treated continuously with 10 ppm picloram (4-amino-3,5,6-trichloropicolinic acid) in nutrient culture were only slightly injured after 4 weeks whereas red maple ( Acer rubrum L.) trees were killed after only 2 weeks treatment.
When the roots were exposed to 10 ppm ¹⁴C-picloram, the rate of root uptake, acropetal translocation in the stem, and accumulation in the leaves was much lower in the susceptible red maple than in the tolerant white ash. The foliar penetration and translocation of ¹⁴C-picloram applied to the leaves was very slight but similar in both species. Although a radiolabelled picloram metabolite was isolated from plant extracts, it was formed at equal rates in both species.
It was concluded that the tolerance of white ash was not related to lower rates of picloram uptake or faster rates of picloram detoxication. It was postulated that the high susceptibility of red maple was due to a blockage of the xylem by picloram which caused death by a dessication of the leaves and upper stems.
Action sélective du piclorame sur Fraxinus amerieana L. et Acer rubrum L.     

Effects of nitrogen, phosphorus, potassium and calcium nutrition on strawberry anthracnose

The effects of a range of concentrations of four nutrients – nitrogen, phosphorus, potassium and calcium – in fertilizer solutions on the severity of anthracnose on strawberry cv. Nyoho cultivated under a noncirculation hydroponics system were determined after inoculation with Colletotrichum gloeosporioides . Crop growth and tissue nitrogen, phosphorus, potassium and calcium contents of the entire above-ground parts of the plant were also investigated. Elevated nitrogen and potassium concentrations in the fertilizer solution increased disease severity in contrast to phosphorus and calcium. Treatment with either NH₄ or NO₃ nitrogen was not significantly different. The dry weight of the strawberry plants increased significantly with elevated concentrations of nitrogen ( R ² = 0·9078) and phosphorus ( R ² = 0·8842), but was not influenced by the elevated amounts of potassium ( R ² = 0·8587) and calcium ( R ² = 0·6526) concentrations.     

AN AUTORADIOGRAPHIC STUDY OF THE MOVEMENT OF 14C-LABELLED ASSIMILATES IN THE DEVELOPING WHEAT PLANT

Summary. ¹⁴CO₂ together with autoradiographic techniques was used to stuy the movement of labelled carbon within wheat plants at different stages in their development. Movement of ¹⁴C about the plain was found to be extensive in the early stages, gradually bccoming more localized until at a stage after ear emergence there was little transference of labelled carbon between tillers within a 24-hour period.
In the early stages of development ¹⁴C from leaves on the main shoot was transported throughout the plant but accumulated in greatest amounts in the meristematic regions. Assimilates produced by the leaves of newly formed tillers were distributed mainly to the meristematic regions of those tillers although labelled carbon was moved in into the rest of the plant. In the later stages of development of each tiller the labelled assimilate was restricted to the tiller itself and to any very young tillers associated with it. After car emergence the pattern of distribution of the labelled carbon from the youngest and second youngest leaves was found to differ. Movement was predominantly towards the ear from the flag leaf and towards the root system from the leaf below the flag.
It was noticed that mature leaves accumulated some labelled material and the possibility that this occurred via the transpiration stream following migration from phloem to xylem, as is the case with some of the case with some of the translocated herbicides, was investigated, but no indication of xylem transference was obtained.
The possible application of these studies to investigations into the relationship between the movement natural assimilates and of translocated herbicides is discussed.     

THE INTERRELATIONSHIP BETWEEN TILLERS AND RHIZOMES OF POA PRATENSIS L.—AN AUTORADIOGRAPHIC STUDY

Summary. The main shoot or selected tillers of seedling plants of Poa pratensis L. were supplied with ¹⁴CO₂ and the distribution of ¹⁴C-assimilates was followed by autoradiography. The primary tillers were initially supplied with ¹⁴C-assimilates from the main shoot but, once established, became independent of the parental shoot for carbohydrates. Similarly, developing rhizome-tillers were supported by the main shoot and established primary tillers but soon became self-supporting, Defoliation of all the tillers of the plant but one led to the defoliated primary and rhizome tillers being supplied with radiocarbon from the remaining intact shoot. Thus, although the primary tillers and rhizome-tillers in the intact plant appear to be physiologically independent, the entire tiller-rhizome system may be re-integrated after defoliation, allowing assimilate redistribution. P. pratensis may be regarded as a convenient link between the non-weedy herbage grasses which generally lack rhizomes and the weedy rhizomatous grasses typified by Agropyron repens (L.) Beauv.
Etat des relations entre les talles et les rhizomes de Poa pratensis L. Etude autoradiographique     

THE MOVEMENT OF PARAQUAT IN PLANTS

Summary. A qualitative study of the movement of the herbicide paraquat from droplets applied to leaves of tomato plants, using ¹⁴C-methyl-labelled and ¹⁴C-ring-labelled paraquat dichloride and di(methylsulphate), has shown that it moves in the xylem with the transpiration stream. The chemical is as well transported from young leaves as from mature ones, and will move through a steam-ringed petiole. The enhancement of the amount of paraquat transported from the treated leaves which occurs when treated plants are kept in darkness for a period following treatment and then exposed to light, is probably due to the greater movement into the xylem through undamaged tissue which can occur in the dark. Once the chemical has been absorbed into treated leaves, light-induced damage is required for significant movement through the rest of the plant to take place, but the damage then inhibits further entry of paraquat into the xylem. The movement of paraquat in broad bean and maize is essentially similar, though the enhancement of movement by a period of darkness after application is much less marked.
La migration du paraquat dans les plantes     

Effects of the safeners CGA 154281, oxabetrinil and fenclorim on uptake and degradation of metolachlor in corn (Zea mays L.) seedlings

Summary. The influence of three crop safeners on the uptake and degradation of ¹⁴C-metolachlor was investigated in two corn varieties. Following application of herbicide and safener together to seedling shoots the concentrations of non-metabolized ¹⁴C-metolachlor in the tissues was found to be lower in the tolerant variety LG 9 than in the susceptible variety 211A. The difference between varieties was due to differences in both uptake and degradation of ¹⁴C-metolachlor.
Following shoot application most of the radioactivity was retained in the coleoptile and the mesocotyl. Two hours after application 95% of the herbicide had been degraded in coleoptiles and mesocotyls, whereas approximately 20% of non-metabolized ¹⁴C-metolachlor was present in the enclosed developing shoot leaves. In both corn varieties the safener CGA 154281 caused a substantial lowering of tissue levels of parent ¹⁴C-metolachlor. This was primarily due to an enhanced degradation. Glutalhione- S -transfer-ase (GST) enzyme activity in shoot tissues was found to be enhanced in both varieties by CGA 154281. Oxabetrinil and fenclorim were less effective than CGA 154281 both in reducing tissue levels of non-metabolized ¹⁴C-metolachlor and in enhancing GST activity in either variety.     

SHOOT ZONE UPTAKE OF SOIL-APPLIED HERBICIDES IN PISUM SATIVUM L.

Summary. The effects of localized herbicide placement at different internodes of pea ( Pisum sativum L. cv. Alaska) shoots below the soil surface after plant emergence were studied by removing the soil from around the shoots and replacing with herbicide-treated soil. The first internode proved insensitive to linuron, diuron, atrazine and simazine at 4·5 kg/ha, while treatment of the second and third internodes markedly reduced plant growth 4–6 days after treatment. Separate exposure of the first internode alone, and the second and part of the third together to ¹⁴C-labelled atrazine indicated no difference in herbicide metabolism. However, a two- to threefold increase in ¹⁴C uptake and movement to the foliar parts occurred when the second and part of the third internode was treated, as compared to first internode treatment. Thus the differential sensitivity of the internodes to atrazine, and possibly to the other herbicides, may be because the more mature first internode allows less uptake and subsequent movement to the foliar parts.
Absorption dans la zone des tiges des herbicides appliqués dans le sol chez Pisum sativum L.     

Visual and PCR assessment of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) cultivars

Methods to assess light leaf spot ( Pyrenopeziza brassicae ) on winter oilseed rape cultivars were compared in laboratory, controlled-environment and field experiments. In controlled-environment experiments with seedling leaves inoculated at GS 1,4, the greatest differences in percentage area affected by P. brassicae sporulation were observed with inoculum concentrations of 4 × 10³ or 4 × 10⁴ spores mL⁻¹, rather than 4 × 10² or 4 × 10⁵ spores mL⁻¹, but older leaves had begun to senesce before assessment, particularly where they were severely affected by P. brassicae . In winter oilseed rape field experiments, a severe light leaf spot epidemic developed in 2002/03 (inoculated, September/October rainfall 127·2 mm) but not in 2003/04 (uninoculated, September/October rainfall 40·7 mm). In-plot assessments discriminated between cultivars best in February/March in 2003 and June in 2004, but sometimes failed to detect plots with many infected plants (e.g. March/April 2004). Ranking of cultivar resistance differed between seedling experiments done under controlled-environment conditions and field experiments. The sensitivity of detection of P. brassicae DNA extracted from culture was greater using the PCR primer pair PbITSF/PbITSR than using primers Pb1/Pb2. P. brassicae was detected by PCR (PbITS primers) in leaves from controlled-environment experiments immediately and up to 14 days after inoculation, and in leaves sampled from field experiments 2 months before detection by visual assessment.     

VERTICAL DISTRIBUTION OF HERBICIDES IN SOIL AND THEIR AVAILABILITY TO PLANTS: SHOOT COMPARED WITH ROOT UPTAKE

Summary. Turnip, lettuce and ryegrass seedlings showed toxicity symptoms following shoot exposure to atrazine, linuron and aziprotryne at soil concentrations less than would be obtained from normal field applications. Responses following shoot exposure to simazine and lenacil were much less. Root exposure to all five herbicides caused seedling death at concentrations lower than those required for 'shoot-zone' toxicity. Pronamide and chlorpropham were tested against ryegrass only and at the concentrations examined were toxic only when localized in the shoot zone. Root exposure suppressed root growth, but the shoots were able to grow normally if the soil was kept sufficiently moist. Shoots contained more ¹⁴C-atrazine at emergence after shoot exposure compared with root exposure, but there was little subsequent uptake from the shoot zone. There was extensive uptake from the root zone after emergence. In the shoot-zone treatments, concentrations in the plant were high at emergence but were rapidly diluted by plant growth, whereas with root exposure, they increased throughout the experiments. The possible significance of these results to herbicide bebaviour under field conditions is discussed.
La distribution verticale des herbicides dans le sol et leur disponibilité pour les plantes: absorption comparée par la partie aèrienne et par les radnes     

TRANSLOCATION OF 14C-ASSIMILATES AND 3-AMINO-1,2,4-TRIAZOLE AND ITS METABOLITES IN AGROPYRON REPENS

Summary. Translocation of 3-amino-1,2,4-triazole-5-¹⁴C (¹⁴C-aminotriazole) was compared to that of ¹⁴C-assimilates in couch grass ( Agropyron repens (L.) Beauv.) at three different growth stages.
Assimilates of ¹⁴CO₂ were translocated from the treated shoot to other shoots and rhizomes at the 2–3-leaf and 3–4-leaf stages of development. Much less labelled material was translocated into untreated shoots at the 5-leaf stage. More ¹⁴C-assimilates were translocated to the roots than to untreated shoots at all developmental stages. The translocation patterns of ¹⁴C-aminotriazole and ¹⁴C-assimilates were similar.
Two metabolites, A and B, were formed from ¹⁴C-aminotriazole, which chromatographed identically to previously described metabolites in Cirsium arvense (L.) Scop. A was further metabolized into B. Labelled aminotriazole and its two metabolites were translocated throughout the plants. Metabolite A was phytotoxic when concentrated and re-applied to couch grass, but its properties were not those of Unknown II from Cirsium arvense. They were the same as those of Unknown III. Whether or not metabolite A and Unknown III are identical was not established.
Migration des substances assimilables marquées au ¹⁴ C, du 3 amino-1,2,4-triazole et de ses métabolites chez Agropyron repens     

A RAPID BIOASSAY FOR SIMULTANEOUS IDENTIFICATION AND QUANTITATJON OF PICLORAM IN AQUEOUS SOLUTION

Summary. When seeds of lettuce ( Lactuca sativa L.) were placed on small squares of filter paper moistened with solutions of picloram (4-amino-3,5,6-trichloropicolinic acid), the degree of inhibition on of root and hypocotyl elongation 72 hr later was related to picloram concentration. Inhibition was a useful parameter in determining quantities of picloram ranging from 0·03 to 7·2 μg. (Growth stimulation occurred from 0·00072 to 0·0072 μg. After paper chromatography of plant exudates containing ¹⁴C-labelled picloram, location and quantities of picloram on the chromatograms were determined by the lettuce bioassay and compared with determinations by the methods of ultraviolet light sensitivity, ¹⁴C 4π strip scanning and 14 C dilution calculations. R_f values determined lay all methods were identical, and the quantitative determination by the bioassay agreed closely with the calculations based on the amount of ¹⁴C detected by liquid scintillation counting.
Un essai biologique rapide d'idntification et de dosage de piclorame en solution aqueuse     

Detection of corn stunt spiroplasma in vivo by ELISA using antisera to extracts from infected corn plants (Zea mays)

Antisera were raised in rabbits to extracts from healthy corn plants and from plants infected with corn stunt spiroplasma (CSS); they were prepared by partially purifying sap or tissue homogenates from whole stems by differential centrifugation and filtration. The titres of CSS-specific antibody in the antisera to diseased plant extracts (DPE) were monitored by spiroplasma deformation tests. After cross-absorption against healthy plant extracts, the DPE antisera detected cultured CSS at concentrations exceeding 10⁶ cells/ml, compared with less than 10⁵ cells/ml for homologous antiserum, and reacted more strongly against extracts from diseased than from healthy plants. A comparison of techniques for extracting diseased plant tissues showed that the reaction of stems and midribs against cultured CSS antiserum was two to three times stronger if the samples were lyophilized before extraction. When extracts from lyophilized tissues were used as test antigens the DPE antisera discriminated between diseased and healthy corn stems, midribs and roots as effectively as antiserum to cultured CSS. Preliminary attempts to detect CSS in its vector, Dalbulus maidis , were complicated by non-specific reactions of insect tissue extracts but concentrations equivalent to at least one CSS-infected insect/ml of sample were detected by antiserum to cultured CSS.