Basis for antagonism of paraquat phytotoxicity to barley by MCPA dimethylamine*

MCPA dimethylamine in a mixture with paraquat reduced the disruptive effects of paraquat on leaf cell membrane integrity in excised barley (Hordeum vulgare L.) leaf segments. Uptake or translocation of ¹⁴C-paraquat over 24 h was not affected when mixed with either MCPA dimethy-lamine or MCPA mixed butyl ester. In treatments followed by a period of dark, uptake and translocation of ¹⁴C-paraquat was increased compared to treatments followed by a period of light. A mixture of technical paraquat dichloride and technical MCPA dimethylamine in aqueous solution yielded a dark brown precipitate. All of the paraquat ion was present in the supernatant. The absorption spectrum of the supernatant exhibited a strong maximum of 390 nm and a lesser one at 610 nm. The spectrum was close to that produced by aqueous mixtures of paraquat and dimethylamine. In greenhouse studies the phytotoxicity of the supernatant to barley was less than an equivalent amount of paraquat alone and equal to that of the complete paraquat-MCPA dimethylamine mixture. The presence of dimethylamine alone resulted in an early enhancement of paraquat activity. Spot application of an aqueous suspension of the precipitate to rapeseed (Bras sica campestris L.) resulted in slight epinastic effects but these were considerably less than when an equivalent amount of MCPA acid was applied. The effects of the precipitate were restricted to the treated leaf whereas the effects of MCPA acid were evident throughout the plant. The results suggest a chemical interaction between the dichloride salt of paraquat and the dimethylamine salt of MCPA with the production of two compounds with comparatively less biological activity.     

Agronomic effects from the control of Agropyron repens in barley by pre-harvest application of glyphosate

Pre-harvest application of glyphosate in barley at 1·44 and 0·72 kg ha^?1 was compared with post-harvest application at 1·44 kg ha^?1 at six sites in south-east Scotland, three sprayed in 1980 and three in 1981. Both levels of pre-harvest application gave consistent 95–99% control of A. repens compared with 0–76% control from post-harvest application. Yields of crops grown in 1981 were significantly increased after all the 1980 pre-harvest treatments and after one post-harvest treatment. No significant depressions in grain germination were recorded from the lower rate of pre-harvest application but one significant depression was recorded from the higher rate. Combine harvesting throughput at a given grain loss level was significantly improved by pre-harvest application and moisture content of grain at harvest was significantly reduced by up to 2·5%. Wheeling losses from pre-harvest spraying ranged from 1 to 5%. Crop yield increases in the year after spraying compensated for herbicide and application costs plus any yield losses through tractor wheelings.     

Observed and predicted changes over eight years in frequency of barley powdery mildew avirulent to spring barley in France and Denmark

Aerial populations of Blumeria graminis f.sp. hordei were studied in two French and two Danish regions from 1991 to 1999, at a time of year when only winter barley was present. A high frequency of genotypes not able to grow on the spring-sown crop of the previous growing season (denoted 'spring-avirulent') was observed in most years and regions. This frequency increased with increasing proportion of winter barley; it was highest in France and decreased in general over the 8-year period. Most of the spring-avirulent genotypes possessed the V _{a 22} virulence gene, matching a resistance that has never been present in barley cultivars grown in Europe. A hypothetical cropping system, including winter- and spring-sown crops with three resistance genes altogether, was constructed to mimic the utilization of host cultivars in the four regions. Results from a mathematical model simulating changes in the composition of the pathogen population in this system, demonstrated that selection solely due to host resistance genes, i.e. without assuming any cost of virulence, might lead to such results as those observed. The changes in frequency of spring-avirulent genotypes and the frequency of unnecessary virulence genes may be predicted from the proportion of the barley area sown with winter barley, the use of resistance genes in the cultivars, the initial composition of the pathogen population, and hitch-hiking due to gametic disequilibria.     

Effects of surfactants and simulated rainfall on the efficacy of the Engame formulation of glyphosate in johnsongrass, prickly sida and yellow nutsedge

The effects of surfactants and simulated rain were investigated on the efficacy of Engame and Roundup Ultramax formulations of glyphosate on johnsongrass ( Sorghum halepense L.), prickly sida ( Sida spinosa L.) and yellow nutsedge ( Cyperus esculentus L.). Flame surfactant provided the greatest enhancement of Engame efficacy and the effect was species-dependent. Flame enhanced the activity of Engame on johnsongrass and yellow nutsedge but not on prickly sida. Engame and Engame plus Flame were more active than Roundup Ultramax on a glyphosate acid-equivalent basis on johnsongrass without rain, and on yellow nutsedge with or without rain. The Engame and Roundup Ultramax activities on johnsongrass were similar with rain, and rain occurring between five and 30 min after treatment diminished their activities to < 38% of the control. With the addition of Flame surfactant, Engame activity on johnsongrass increased, such that 50% and 80% of the control were realized, even with rain occurring between five and 15 min after treatment, respectively. Engame and Roundup Ultramax provided better control of prickly sida than of johnsongrass following a rain event. The addition of Flame surfactant to Engame did not enhance the activity on prickly sida. Yellow nutsedge control with Engame and Engame plus Flame was greater than with Roundup Ultramax and rain had little effect on control regardless of the length of the rain-free period. These results demonstrated that the activities of Engame, Engame plus Flame and Roundup Ultramax were species-dependent and surfactant-dependent.     

Simulation modelling to understand the evolution and management of glyphosate resistance in weeds

BACKGROUND: A simulation model is used to explore the influence of biological, ecological, genetic and operational (management) factors on the probability and rate of glyphosate resistance in model weed species. RESULTS: Glyphosate use for weed control prior to crop emergence is associated with low risks of resistance. These low risks can be further reduced by applying glyphosate in sequence with other broad-spectrum herbicides prior to crop seeding. Post-emergence glyphosate use, associated with glyphosate-resistant crops, very significantly increases risks of resistance evolution. Annual rotation with conventional crops reduces these risks, but the proportion of resistant populations can only be reduced to close to zero by mixing two of three post-emergence glyphosate applications with alternative herbicide modes of action. Weed species that are prolific seed producers with high seed bank turnover rates are most at risk of glyphosate resistance evolution. The model is especially sensitive to the initial frequency of R alleles, and other genetic and reproductive parameters, including weed breeding system, dominance of the resistance trait and relative fitness, influence rates of resistance. CONCLUSION: Changing patterns of glyphosate use associated with glyphosate-resistant crops are increasing risks of evolved glyphosate resistance. Strategies to mitigate these risks can be explored with simulation models. Models can also be used to identify weed species that are most at risk of evolving glyphosate resistance.     

Biological evidence for a 1:1 Ca2+:glyphosate association in deposit residuals on the leaf surface of barley

It has long been known that calcium ion antagonizes glyphosate, but it was not clear whether the stoichiometry of their interaction is 1:1 or 1:2. Two independent methods were used to determine which stoichiometry was the most probable. First, dose–response curves of barley ( Hordeum vulgare L.) plants treated with glyphosate were determined in the presence of 0, 1.25, 2.5, 5 and 10 mM CaCl₂. The doses of 'free' glyphosate (=not inactivated by calcium ion) were computed using the assumptions of 1:1 and 1:2 stoechiometries. The response curves were redrawn as a function of 'free' glyphosate. Analysis showed that the 1:2 hypothesis could be rejected, whereas the 1:1 hypothesis was highly probable. Second, kinetics of glyphosate penetration into barley leaves were determined in the presence of 0, 2.5 and 10 mM CaCl₂. The concentrations of 'free' glyphosate were computed as above. The kinetics of glyphosate penetration at these concentrations were established and were compared to the kinetics of glyphosate penetration in the presence of CaCl₂. Again, the 1:2 hypothesis was rejected, whereas the 1:1 hypothesis was more probable. These results strongly suggest that the stoichiometry of the Ca²⁺:glyphosate association is 1:1 in deposit residuals on the leaf surface.     

Uptake by roots and translocation to shoots of two morpholine fungicides in barley

Despite being lipophilic, morpholine fungicides are systemic in plants. Such transport may be explicable by their protonation (pKa∽7·5) at the pH of plant compartments to yield the more polar cation. This behaviour might be a useful attribute to be incorporated into other classes of lipophilic pesticides. To understand quantitatively the behaviour of the morpholine fungicides, the uptake by roots and transport to shoots in barley of two such ¹⁴C-labelled compounds, dodemorph and tridemorph, were investigated using bathing solutions of differing pH. At pH 5, uptake and transport were small, but increased by approximately two orders of magnitude at pH 8. Tridemorph, the more lipophilic of the two compounds, was highly accumulated by roots at pH 8 and moderately translocated to shoots. In contrast, dodemorph was translocated to shoots at pH 8 with remarkable efficiency, moving into the xylem across the endodermis at 23 times the efficiency of water, though accumulation in roots was less than that of tridemorph. Behaviour at 24 h was largely similar to that at 48 h for both compounds, indicating that uptake and translocation are equilibrium processes maintained over time. Transport to shoots for each compound was directly proportional to the concentrations accumulated in the roots, except at low pH where partitioning into root solids became proportionately more important with such material not being directly available for transport to the xylem across the endodermis. Uptake and transport of these basic fungicides are explained in terms of their partitioning and of their accumulation in acidic plant compartments by ion trapping as the protonated form; this behaviour is discussed in relation to the pKa and lipophilicity of these compounds. © 1998 Society of Chemical Industry     

Physicochemical factors affecting the uptake by roots and translocation to shoots of amine bases in barley

The uptake by barley roots from nutrient solution and subsequent transport to shoots of two series of amine bases were measured over 6 to 72 h. The compounds were chosen to span systematically ranges of lipophilicity (assessed using 1-octanol/water partition coefficients, K_ow) and pKa that would include commercial pesticide amines. In a series of six substituted phenethyl amines, strong bases with pKa∽9·5, all the compounds were strongly taken up by roots from solutions of pH 8·0; uptake declined substantially as the pH was lowered to 5·0, especially for the compounds of intermediate lipophilicity (log K_ow 2 to 3). This uptake could be ascribed to three processes: (i) accumulation of the cation inside the root cells due to the negative charge on the plasmalemma, as given by the Nernst equation and important only for the polar compounds which have low permeation rates through membranes; (ii) accumulation into the vacuole by ion-trapping, which was the dominant process at high pH for all compounds and at all pH values for the compounds of intermediate lipophilicity; (iii) partitioning on to the root solids, substantial only for the most lipophilic compounds. Translocation to shoots was proportional to uptake by roots, this ratio being independent of external pH for each compound and being optimal for the compounds of intermediate lipophilicity. Such proportionality was also observed in a series of three weaker bases of intermediate lipophilicity, in which compounds of pKa 7·4 to 8·0 were also well taken up and translocated whereas the very weak base 4-ethylaniline (pKa 5·03) was much less so. Tests with quaternised pyridines confirmed that organic cations move only slowly through membranes. The observed behaviour of the amines could be modelled reasonably well assuming that transport within the plant was dominated by movement across membranes of the non-ionised species, and this appeared to be true even for the most lipophilic phenethylamine (log K_ow 4·67) studied, though its long-distance movement would be as the protonated species. © 1998 Society of Chemical Industry     

Spatial and temporal changes in acetolactate synthase activity as affected by new herbicide ZJ0273 in rapeseed, barley and water chickweed

Propyl 4-(2-(4,6-dimethoxypyrimidin-2-yloxy)benzylamino)benzoate (ZJ0273), derived from a precursor compound pesticide (a derivative of 2-pyrimidinyloxy-N-aryl benzoate), is a novel herbicide used in the rapeseed field. This paper studied the differential tolerance or susceptibility of four plant species viz. Brassica napus L. (rapeseed), Hordeum vulgare L. (barley), Malachium aquaticum (L.) Fries (water chickweed), and Alopecurus aequalis Sobol. (equal alopecurus), to various concentrations of ZJ0273, based on the rate of inhibition of acetolactate synthase (ALS) activity. Brassica napus was observed as the most tolerant among four species in which ALS activity in vivo was hardly affected by ZJ0273 at 100 mg/L (recommended dose in the rapeseed field). In contrast, H. vulgare was found to be more susceptible which was reflected in the relative decline of ALS activity and lower biomass production even under at a lower rate of 10 mg/L of ZJ0273. The two weed species exhibited moderate susceptibility as compared to H. vulgare. The present study confirmed that ZJ0273 at 100 mg/L is the optimal dose of herbicide for rapeseed field. Seedling stage was critical in determining the tolerance of crops and susceptibility of weeds which indicated that over seven leaf stage was much safer for rapeseed whereas the two leaf stage juvenile water chickweed was more susceptible to the same rate of ZJ0273. Spatial and temporal variations in ALS activity as affected by 100 mg/L ZJ0273 in water chickweed, rapeseed and barley also suggested that the synchronized sampling based on the tissue position and seedling stage was necessary to examine precisely, the special difference in tolerance or susceptibility to ALS-inhibiting herbicide. The uppermost younger leaf seemed to be the most appropriate sample for evaluation. Furthermore, the variant tendency of ALS activity from different parts of plants between monocotyledons and dicotyledons to ZJ0273 treatments showed differential response which revealed some possible mechanism related to the altered absorption and translocation of the herbicide.     

Physico-chemical factors affecting uptake by roots and translocation to shoots of weak acids in barley

The uptake from solution of maleic hydrazide, flamprop and a series of phenoxyacetic acids by roots, and their subsequent translocation to shoots, was measured in barley. Both uptake and translocation increased as the pH of the solution decreased, the magnitude of the change varying amongst the chemicals tested. Uptake by roots could be accounted for by the ion-trap mechanism, which assumes that entry of the chemicals occurs largely by passive diffusion of the undissociated form of the acids, with passage of the anions across the cell membranes being very slow. The ratio of the permeability of the cell membranes to the undissociated and dissociated forms of the acids was estimated from the accumulation in roots, and in the phenoxyacetic acid series this ratio was maximal (4×10⁵) for compounds of intermediate lipophilicity. Maleic hydrazide and flamprop had much lower ratios, 1.8×10² and 10³ respectively; the value for flamprop was much less than for phenoxyacetic acids of similar lipophilicity, such as 2, 4- dichlorophenoxyacetic acid, indicating that lipophilicity may not be the sole factor determining the behaviour of weak acids in plants. Translocation to shoots was approximately proportional to the chemical concentrations in the roots.     

Fate of glyphosate in soil and the possibility of leaching to ground and surface waters: a review

The very wide use of glyphosate to control weeds in agricultural, silvicultural and urban areas throughout the world requires that special attention be paid to its possible transport from terrestrial to aquatic environments. The aim of this review is to present and discuss the state of knowledge on sorption, degradation and leachability of glyphosate in soils. Difficulties of drawing clear and unambiguous conclusions because of strong soil dependency and limited conclusive investigations are pointed out. Nevertheless, the risk of ground and surface water pollution by glyphosate seems limited because of sorption onto variable-charge soil minerals, e.g. aluminium and iron oxides, and because of microbial degradation. Although sorption and degradation are affected by many factors that might be expected to affect glyphosate mobility in soils, glyphosate leaching seems mainly determined by soil structure and rainfall. Limited leaching has been observed in non-structured sandy soils, while subsurface leaching to drainage systems was observed in a structured soil with preferential flow in macropores, but only when high rainfall followed glyphosate application. Glyphosate in drainage water runs into surface waters but not necessarily to groundwater because it may be sorbed and degraded in deeper soil layers before reaching the groundwater. Although the transport of glyphosate from land to water environments seems very limited, knowledge about subsurface leaching and surface runoff of glyphosate as well as the importance of this transport as related to ground and surface water quality is scarce.     

Effect of ammonium sulphate and related salts on the phytotoxicity of dichlorprop and other herbicides used for broadleaved weed control in cereals

In glasshouse experiments, additions of 10–100 g 1^?1 ammonium sulphate enhanced the phytotoxicity to broadleaved weeds and cereals of several water-soluble herbicides applied post-emergence in 75–300 1 ha^?1 with hydraulic nozzles. Studies with dichlorprop potassium salt and chickweed Stellaria media (L.) Vill. examined interactions between ammonium sulphate and environmental, application and formulation factors. Simulated rainfall immediately after spraying greatly reduced dichlorprop activity, whether or not ammonium sulphate was present. However, when there was an interval of 2–24 h between spraying and rainfall, the additive increased phytotoxicity. Surfactants tended to reduce dichlorprop phytotoxicity to Stellaria media, both in the presence and absence of ammonium sulphate. Certain other inorganic salts including sodium sulphate also enhanced phytotoxicity. Applications by rotary atomizer in very low spray volume (15 1 ha^?1, 250–280 μm drops) were less effective than conventional 150 1 ha^?1 applications. When very low volume application was used, addition of ammonium sulphate or nitrate tended to reduce activity further. In the field, ammonium sulphate significantly increased the effects against weeds of a commercial dichlorprop potassium salt formulation applied conventionally in 200 1 ha^?1 spray volume. Neutralized phosphoric acid had a similar effect but a mixture of this additive and ammonium sulphate reduced phytotoxicity. Both additives slightly increased dichlorprop injury to barley.     

Fungicide and nitrogen applications in relation to the improvement of disease control and yield in winter barley

In crops of winter barley, cvs Igri and Halcyon, crop structure and intensity of foliar diseases were altered by delaying the main top dressing of nitrogen until mid-April. A single application of fungicide then was sufficient to decrease substantially the severity of fungal disease and improve grain yield at harvest.
Disease control and yield responses were greatest when fungicides were applied during a 3-week period after the main nitrogen application in April. No additional yield benefits were obtained by making two fungicide applications at growth stage (GS) 31 and GS 39.     

Relationships between lipophilicity and the distribution of non-ionised chemicals in barley shoots following uptake by the roots

Determinations were made of the distribution of two series of non-ionised chemicals, ^O-methylcarbamoyloximes and substituted phenylureas, in barley shoots, following uptake by the roots from solution. The concentrations in basal and central shoot sections became constant after 24 to 48 h for all but the most lipophilic chemical studied, and were then greatest for the more lipophilic chemicals. Amounts in the leaves generally increased up to 72 or 96 h, when degradation balanced translocation. The accumulation of chemical in the lower section of shoots can be ascribed to a partitioning process similar to that in roots, the chemical being partitioned between the shoot and the xylem transpiration stream; this uptake could be estimated from the octan-1-01/water distribution coefficients, and was predicted to be greatest for compounds for which log K_ow=4. 5.     

建立中国草原生态补偿机制的依据、原则及配套政策研究

重林轻草、重政府投入轻民间参与、重有形价值轻无形价值已经成为我国生态建设中的普遍现象。本文从研究草地的价值贡献和我国草地严重的退化与沙化现状出发,分析了进行草原生态补偿的必要性和紧迫性,并在此基础上提出了对草原生态补偿的理论依据、原则和相应的政策建议。     

Fusaric acid: phytotoxicity and in vitro production by Fusarium oxysporum f.sp. lilii,the causal agent of basal rot in lilies

The production of phytotoxins byFusarium oxysporum f.sp.lilii, a pathogen causing bulb and scale rot in lilies, was investigated. To determine the toxic activity of culture filtrate, a bioassay with in vitro grown scale bulblets or with callus was set up. The fungus produces toxic components in different culture media. The highest toxicity was observed in Czapek Dox medium. HPLC and GC/MS analyses revealed the presence of fusaric acid at toxic concentrations in this medium. The production of fusaric acid in time coincides with the increase of toxic activity in the culture filtrate. It is concluded that at least part of this toxicity is due to fusaric acid.     

Mechanical transmission of maize rayado fino marafivirus (MRFV) to maize and barley by means of the vascular puncture technique

Maize rayado fino marafivirus (MRFV) was mechanically transmitted to kernels of three Costa Rican maize cultivars by the vascular puncture technique. A transmission rate of up to 43.2% was obtained for cultivar HC-57. The rate of MRFV transmission to maize was possibly affected by the morphology of the kernel, which may influence physical access to the vascular tissue after water imbibition. Transmission to maize was confirmed by western blot and immunosorbent electron microscopy. By slight modifications of the procedure, MRFV was also transmitted to barley. This is the first report of MRFV infecting a species outside the supertribe Andropogonodae. Virus infection and replication in barley were confirmed by RT-PCR detection of MRFV RNA and by detection of the virus by ELISA.     

A modified clean-up for the determination of glyphosate and its metabolite residues in lentils using high pressure liquid chromatography and post-column fluorogenic labelling

An analytical method is presented for the analysis of glyphosate and its metabolite (aminomethyl)phosphonic acid (AMPA), in lentil samples. They were extracted from powdered samples with water and chloroform. The aqueous layer was acidified and passed through a cation exchange column. The eluate was made basic, passed through an anion exchange column in the hydroxide form and discarded. The latter column was eluted with hydrochloric acid (0.3 M) which was collected, evaporated under vacuum to 1 ml, diluted with water to 10 ml, filtered and analysed for glyphosate and metabolite using a liquid chromatograph with a post-column reactor and a fluorescence detector. The limit of detection, average recovery and coefficient of variation (CV) were 0.08 μg g^?1, 92.5% and 7.3% for glyphosate and 0.1 μg g^?1, 92.5% and 8.3% for AMP A. The detector response was found to be linear within the range 20–400 ng.     

Evaluation of various methods for the detection of barley yellow dwarf virus by the tissue-blot immunoassay and its use for virus detection in cereals inoculated at different growth stages

Various modifications of the tissue-blot immunoassay (TBIA) for the detection of barley yellow dwarf virus (BYDV, luteovirus) were compared. Similar results were obtained by using three different labelled molecules; goat anti-rabbit antibodies conjugated to alkaline phosphatase, protein A conjugated with alkaline phosphatase and goat anti-rabbit antibodies conjugated with colloidal gold. Blocking the nitrocellulose membrane with polyvinyl alcohol for 1 min was effective and allowed the procedure to be shortened by one hour. TBIA was sensitive enough to detect BYDV in old dry tissue wich had been soaked in water for 1 h.BYDV was monitored by TBIA in wheat, oat and barley after inoculation at heading, flowering and grain filling growth stages. The later the inoculation date, the greater the chance of detecting the virus in stem bases rather than in the upper part of the stem. The later the inoculation the less virus moved, from the inoculated tiller to other tillers of the same plant.