Optimizing diquat efficacy with the use of adjuvants

Optimizing diquat efficacy with the use of adjuvants may broaden the spectrum of weed control, but relevant research towards this direction is limited. Field and greenhouse experiments were conducted to evaluate the effect of diquat applied alone and with six commercial adjuvants (surfactants and oil-based adjuvants) on various weed species. Diquat effect was evaluated in two field experiments on natural populations of common lambsquarters (Chenopodium album L.), prostrate knotweed (Polygonum aviculare L.) and burning nettle (Urtica urens L.) along with two greenhouse trials on rigid ryegrass (Lolium rigidum L.). In field or greenhouse experiments, all the adjuvants significantly increased the control of C. album, P. aviculare, and L. rigidum, from 48, 42 and 7%, up to 82, 74 and 67%, respectively, in terms of fresh weight reduction, but to a different extent for each adjuvant. U. urens was totally (100%) controlled in terms of visual estimation either with diquat or with diquat plus any adjuvant. The differences in the effect of diquat applied with adjuvants mainly depended on the weed species examined and they were not proportional to the surface tension reduction of the spray solution caused by the adjuvants. Overall, the surfactants and the oil-based adjuvants examined in this study considerably enhanced the effect of diquat; this can broaden the spectrum of weed control against broadleaf and grass weeds in orchards and non-crop areas. The results are discussed in relation with the classification of the adjuvants.     

The influence of additives on the penetration of foliar applied growth regulator herbicides

The possibilities are demonstrated of increasing the activity of foliar applied growth regulator herbicides by mixing them with chemicals which injure the cuticle or epidermis. S, S, S-Tributyl phosphorotrithioate (“DEF”) increases the effects of picloram, 2,4,5-T and mecoprop salts on four woody species, privet (Ligustrum ovalifolium Hassk.), poplar (× Populus gelrica Ait.), bluegum (Eucalyptus globulus Labill.) and guava (Psidium guajava L.). Mixtures with esters of the herbicides are not synergistic and often antagonistic. DEF, tributyl phosphorotrithioite, a number of alkyl and aryl phosphates and phosphites and potassium ethyl xanthate enhance the phytotoxicity of picloram solution on dwarf bean (Phaseolus vulgaris L.). Mixtures of picloram with tributyl phosphorotrithioite, tributyl phosphate, mixed acid butyl phosphates, trimethyl phosphate and mixed isomers of tritolyl phosphate are synergistic when applied to guava foliage. Tributyl phosphate and mixed acid butyl phosphates interact similarly with picloram on privet and tributyl phosphate increases the effects of foliar applied mecoprop salt on guava. The mode of action of the additives is not fully understood but there is evidence that DEF facilitates the entry of water soluble growth regulator herbicides into leaves and has little effect on the rate at which the herbicides move through the plant. Tributyl phosphate and mixed acid butyl phosphates are suggested for practical use in herbicide formulations to control woody plants, as they are relatively cheap and non-toxic.     

Auswirkungen des Herbizids Basta® auf die Weinrebe und den Falschen Mehltau

A field experiment was conducted in order to analyse the effects of the herbicide Basta^® with glufosinate-ammonium as the active ingredient (that inhibits specifically the enzyme glutamine-synthetase) on the grapevine plant and the infestation with Plasmopara viticola, the downy mildew pathogen. The herbicide was applied at sublethal concentrations and the toxic effects on leaves and berries based on different quality parameters were estimated. Low concentrations of glufosinate-ammonium (<?0,625?mM) did not affect the chlorophyll and amino acid concentrations in leaves. This was also the case for the content of salicylic acid and phenolic compounds. Furthermore, must parameters such as sugars (glucose and fructose), acids (tartaric acid, malic acid, total acids and volatile acids), and alcohol (ethanol and glycerine) also remained unchanged compared to the fungicide-treated or untreated control, whereas the concentrations of nitrogenous components metabolically available to yeasts increased with increasing concentrations of glufosinate-ammonium. The amount of berries harvested at the end of the experiment depended on the glufosinate-ammonium concentration applied. The harvest was highest when glufosinate-ammonium was applied as a 0.1?mM solution and differed not significantly from the fungicide-treated control, but decreased with increasing herbicide doses. However, the infestation of leaves with P. viticola was significantly reduced by the application of the herbicide, even though not each infection was eradicated due to the non-systemic mode of action of the herbicide. The particular influence of the herbicide onto this host-parasite interaction still remains unclear. Since applications of glufosinate-ammonium at low concentrations seem not to affect grapevine plants negatively, but were able to reduce the infestation with downy mildew, the specific mode of action may reveal new alternatives for the control of fungal pathogens.     

Inhibition of chitin synthesis by two 1-(2,6-disubstituted benzoyl)-3-phenylurea insecticides. II

The knowledge of the biochemical mode of action of 1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea (diflubenzuron) is presented, explaining the insecticidal effect. Like its structural analog, 1-(2,6-dichlorobenzyl)-3-(3,4-dichlorophenyl)urea (Du 19111), it inhibits chitin synthesis in the cuticle of larvae. Virtually complete inhibition was demonstrable 15 min after the application of diflubenzuron. Neither diflubenzuron nor Du 19111 has any effect upon chitinase activity either in vivo or in vitro. The insecticidal effect upon the cuticle, therefore, must be explained as an inhibition of chitin synthesis and not as an activation of chitin degradation. In contrast to the action of Du 19111, no accumulation of N-acetylglucosamine occurs upon treatment of larvae with diflubenzuron. Similarities and differences in the mode of action of both compounds are discussed, together with other effects reported in the literature.     

Suppression of conidial germination and appressorial formation by silicate treatment in powdery mildew of strawberry

The mode of action of soluble silicon against strawberry powdery mildew (Sphaerotheca aphanis var. aphanis) was investigated in four experiments. First, silicon-treated leaves from plants grown with silicate (Si+) and control leaves were excised, inoculated with conidia, and subsequent germination and formation of appressoria in a petri dish was assessed after 24 h. The germination rate was 49.7% on Si+ leaves, and was 67.2% on control leaves (t-test, P < 0.01). Second, we soaked cellulose membranes in various solvents and then placed the membranes on 4% water agar, dusted the membranes with conidia, and examined after 12 h. No difference was apparent between any treatment and the control (distilled water). Third, strawberries growing hydroponically with additional silicon in the medium were inoculated with conidia, and leaves were observed with a scanning electron microscope 1–2 days after inoculation. Germ tubes and secondary hyphae were shorter and had fewer branches on Si+ leaves than on the control. Moreover, penetration appeared to be inhibited. Fourth, the cuticle was separated from leaves from plants grown as in the third experiment, placed on water agar, and dusted with conidia. Germination of conidia, observed with a light microscope, on Si+ leaves was suppressed markedly to 40%–60% of that of the control. These results suggested that soluble silicon induced physiological changes in the cuticle layer after absorption by the plant. In addition, soluble silicate reduced germination of conidia, formation of appressoria, and possibly the penetration of powdery mildew.     

Penetration of triolein and methyl oleate through isolated plant cuticles and their effect on penetration of [14C]quizalofop-ethyl and [14C]fenoxaprop-ethyl

The penetration of two model seed oil compounds, [¹⁴C]triolein (TRI) and [¹⁴C]methyl oleate (MEO) through plant cuticles and their effects on the penetration of [¹⁴C]quizalofop-ethyl and [¹⁴C]fenoxaprop-ethyl were investigated. Experiments were carried out using isolated cuticles from rubber plant (Ficus elastica Roxb.) leaves and from tomato (Lycopersicon esculentum Mill,) and pepper (Capsicum annuum L.) fruits. Chemicals were deposited in droplets on to cuticle discs maintained on agar blocks under controlled conditions. TRI and MEO were used at 1% (V/V). The transfer of radiolabel through cuticles was negligible for TRI and varied from 6 to 13% after 72 h, according to species, for MEO, The penetration results obtained for quizalofop-ethyl (0.084 mg mL^-1) and fenoxaprop-ethyl (0.189 mg mL^-1) were very similar and varied according to species. The greatest diffusion intoagar was observed for pepper (12.8% and 10.7% after 72 h, for quizalofop-ethyl and fenoxaprop-ethyl respectively), the lowest for rubber plant cuticles (1.4 and 1.3% respectively). Addition of MEO produced significant increases in the penetration of quizalofop-ethyl and fenoxaprop-ethyl through rubber plant and tomato cuticles. TRI had an enhancing effect on the two herbicides only with rubber plant cuticles. Results are discussed with particular consideration of the variations between plant species and the possible mode of action of seed oil adjuvants.     

几种除草剂和助剂对苜蓿Medicago sative出苗和生长的影响

在温室条件下研究了几种苗前除草剂单用或混用对苜蓿出苗和生长的影响,以及不同叶龄苜蓿对苗后除草剂的反应及添加助剂对药效的影响。结果表明:咪唑乙烟酸在60~120 g/hm2剂量下,于苗前施用,对苜蓿出苗和幼苗生长都有明显的抑制作用。咪唑乙烟酸(30 g/hm2)与二甲戊灵(495 g/hm2)混用,对苜蓿的药害显著降低。苗后施用除草剂对苜蓿的安全性与叶龄密切相关。咪唑乙烟酸以30~60 g/hm2剂量在苜蓿3叶期施用,对苜蓿安全;在120 g/hm2用量下,对5叶期的苜蓿无明显药害。乳氟禾草灵(130~260 g/hm2)和丙炔氟草胺(75~150 g/hm2) 无论是3叶期还是5叶期施用,对苜蓿幼苗都有严重的药害。与咪唑乙烟酸单用时比较,药液中添加1.0 mL/L 的平平加-15和AM-100及5.0 mL/L的SDP,对苜蓿幼苗生长无明显影响。     

Recent developments in our understanding of the plant cuticle as a barrier to the foliar uptake of pesticides†

The plant cuticle is a highly complex membrane which forms the outer surface of the aerial portion of plants. The nature of the plant cuticle is reviewed with particular regard to its action as a potential barrier to the penetration of pesticide molecules; the role of the cuticular waxes is highlighted. The physicochemical properties of the cuticle influence the behaviour of spray droplets and, in turn, may affect the rate and efficiency of cuticle penetration. The permeation of active ingredients is influenced by their solubility characteristics as indicated by octanol/water (log K_ow) and cuticle/water (K_cw) partition coefficients. Penetration of hydrophilic compounds (low log K_ow) may be enhanced by hydration of the cuticle, while transcuticular transport of non-polar solutes (high log K_ow) is increased by factors which reduce wax viscosity. The use of in-vitro models involving isolated cuticle membranes, isolated cuticle waxes, or isolated leaves has helped to focus on the activities of the cuticle in the absence of other physiological factors. Using these systems, the role of the waxes as a transport-limiting barrier has been identified and the factors influencing sorption, permeance and desorption examined. The action of surfactants, in vitro and in vivo, has been briefly addressed in regard to their role in facilitating cuticle penetration; other steps involving surfactant/solute/cuticle are complex, and synergy appears to depend on a number of factors including test species, concentration of active ingredient, surfactant type and concentration. Adjuvants may greatly influence the surface properties of the droplet, predispose the cuticle to solute transport, and enhance pesticide activity. The nature of these complex inter-relationships is discussed. © 1999 Society of Chemical Industry     

Abrasive und hydrophil/lipophile Effekte unterschiedlicher inerter Stäube im Einsatz gegen Schadinsekten am Beispiel des Kornkäfers Sitophilus granarius L.

Modern research on the insecticidal effects of inert dusts as a stored-grain protectant and for plant protection purposes began in the 1920s. The main advantage of inert dusts is their low-mammalian toxicity. One group of inert dusts used for pest control is diatomaceous earth (DE). DE has been tested as a whole and evaluated as a Group 3 carcinogen by the International Agency for Research on Cancer (IARC). A Group 3 listing indicates that DE is not classifiable as to its carcinogenicity to humans, since definitive conclusions cannot be drawn from the research conducted to date. DE is a form of naturally occurring amorphous silica that can kill insects by ab/adsorbing the lipids such as waxes and triglycerides of the outer cuticle layer by direct contact. When the thin, waterproof layer is lost, the insect looses water and dies. Desiccation follows Ficks law of diffusion into the surrounding atmosphere. In addition to its desiccant action the theory that DE works abrasively to rupture insect cuticles has been proposed. To evaluate the abrasive effects of DE we have tested 27 inert dusts with different surface properties. Materials were compared based on the time needed to kill 50% (LT₅₀) of Sitophilus granarius weevils in laboratory experiments. Substances with hydrophilic and/or hydrophobe properties were significantly more effective against S.?granarius than substances which are mainly abrasive. There is a strong correlation between LT₅₀ and weight loss (=?water loss) of insects (p?=?0.014). Particle size played only a secondary role (p?=?0.077). Commercial DE formulations and activated charcoal (Carbopal MB4) were the most effective hydrophilic substances tested. The most abrasive substances were corundum and silica sand with small particle sizes. It is concluded, that those materials were effective because of a good coverage of the insects outer cuticle and existing shear stress. All results presented are discussed in context of the insecticidal mode of action of inert dusts and possible registration of silica based formulations as biocide.     

Cytology of infection of apple leaves by Diplocarpon mali

Diplocarpon mali, the causal agent of Marssonina leaf blotch of apple, causes severe defoliation during the growing season. Little information is available on the mode of infection and the infection process. In this study, the infection strategies of D. mali in apple leaves were investigated using fluorescence and electron microscopy. Conidia attached to leaf surface apparently by mucilage and germinated on both sides of leaves 6 h post-inoculation (hpi). The pathogen penetrated the cuticle by infection pegs formed either in germ tubes or appressoria in 6 hpi, and then formed haustoria in host epidermal and mesophyll cells accompanied by extension of subcuticular and intercellular hyphae. Five days post-inoculation (dpi), the intracellular hyphae were observed. At the same time, the subcuticular hyphal strands (SHS) were produced as a means for fast expansion and reproduction. About 7 dpi, acervuli formed on inoculated leaves. This was the first observation that D. mali formed haustoria and SHS as infection strategies. Our results suggest that D. mali may behave like a hemibiotroph, which can use both biotrophic and necrotrophic strategies to establish infections on apple leaves.     

Modelling penetration of plant cuticles by crop protection agents and effects of adjuvants on their rates of penetration

A theory of cuticular penetration of crop protection agents (CPAs) is presented, which incorporates properties of cuticles and cuticular waxes as well as properties of active ingredients and adjuvants. Based on this theory, two models are developed which are analytical in the sense that they help to quantify and understand (i) differences in permeability among cuticles from different species, (ii) effects of properties of CPAs on permeabilities of cuticles and rates of uptake and (iii) the effects of adjuvants on properties of cuticles and rates of uptake of CPAs. The models can be used to predict rates of uptake of CPAs as affected by properties of cuticular waxes, active ingredients and adjuvants. However, before this can be done, a constant, two parameters and at least two variables must be estimated. Properties of cuticles are accounted for by the constant D⁰/Δx and the parameter β′. The former, the ratio of the mobility of a hypothetical molecule having zero molar volume (D⁰x) divided by the path length (Δx) across the cuticle, has the dimension of velocity (ms^?1) and is independent of the solubility of the CPA. The latter is a measure of size selectivity of the cuticle. Differences in permeabilities of cuticles from different species increase with increasing size of active ingredients due to size selectivity (β′). Removing cuticular waxes from Citrus cuticles increased D⁰/Δx by a factor of 2042, while β was not affected. Differential solubility of CPAs is considered part of the driving force and at least two different partition coefficients are needed to account for differences in solubilities in cuticular waxes, cutin, water and the formulation residue on the surface of the cuticles. Adjuvants are solvents in the formulation residue on the leaf surface once the carriers (water and other volatile solvents) have evaporated and certain adjuvants also act as accelerators; they penetrate the cuticle and increase D⁰/Δx. Thus, accelerators increase rates of uptake and this effect depends on two factors, (i) the intrinsic activity of the accelerator and (ii) rate of penetration into the cuticle, because the active ingredients follow the accelerator front across the cuticle. Since accelerators penetrate from the formulation residue into the cuticle, the volume of the formulation residue decreases with time. This maintains high concentrations of CPAs in the formulation residue and, thus, maximum driving forces and rates of penetration. To utilise fully this dual accelerator effect, it is necessary to match velocities of penetration of accelerators and active ingredients accurately.     

Tolerance to paraquat-mediated oxidative and environmental stresses in squash (Cucurbita spp.) leaves of various ages

Paraquat is labeled for row-middle application on cucurbits, but drift to crop foliage is inevitable. Experiments were conducted to determine whether differential tolerance to paraquat existed among leaves of various ages in Cucurbita spp. (squash) and other plants, and to examine whether leaves tolerant to paraquat are also tolerant to other herbicides and abiotic stresses. Physiological responses to paraquat, including antioxidant activity, were investigated in squash leaves to identify mechanisms of paraquat tolerance. Although the level of paraquat tolerance differed by leaf age, cultivar, and species, the level of paraquat injury was lower in younger leaves than in older leaves in 14 of 18 squash cultivars and 5 of 12 other species tested. Cellular leakage and lipid peroxidation were consistently lower in the youngest leaf (leaf 4) than in the older leaves. Quantum yield and relative chlorophyll content were the same in all leaves of nontreated plants. Epicuticular wax content was higher in the youngest leaf than in leaves 1, 2, and 3 of cv. ‘Joongangaehobak’ and ‘Wonbiaehobak’. However, leaf cuticle content was not consistent with leaf ages. Differential leaf response to paraquat was partially correlated with the change in catalase, peroxidase, ascorbate peroxidase (APX), and glutathione reductase activities in nontreated and treated leaves. The APX activity in the youngest leaf was generally 2 times higher than in leaves 1-3 in both nontreated and treated plants. Ascorbate antioxidant levels were also higher in the youngest leaf than those in leaves 1-3. Leaves tolerant to paraquat were also tolerant to diquat and to abiotic stresses, low temperature and drought. However, tolerance to oxyfluorfen, which has a different mode of action than paraquat and diquat, was higher in older than in younger leaves. Higher tolerance to paraquat-mediated oxidative and abiotic stresses in young leaves of most squash cultivars might contribute to the differential prevention of oxidative damage in leaves of various ages.     

Finite dose diffusion studies: I. Characterizing cuticular penetration in a model system using NAA and isolated tomato fruit cuticles

A finite dose diffusion system was employed to study cuticular penetration of 2‐(1‐naphthyl) [1−¹⁴C]acetic acid (NAA) from simulated spray droplets through enzymatically isolated tomato fruit cuticles (Lycopersicon esculentum Mill cv Pik Red). Isolated cuticles were mounted on diffusion half‐cells with the cell wall surfaces facing a 20 mM citric acid receiver solution (pH 3.2, volume 2.9 ml, prepared with deionized water). A 5‐µl donor droplet containing NAA at 100 µM in 20 mM citric acid buffer (pH 3.2) was applied to the outer surface. Penetration was monitored by repeated sampling of the receiver solution. NAA penetration was characterized by (1) an initial lag phase of about 2.3 h, (2) a phase of nearly constant maximum rate of penetration averaging 6.3% of applied NAA h⁻¹ (equivalent to 0.032 nmol h⁻¹) and (3) a plateau phase approaching an asymptote at 81.2% of applied NAA (equivalent to 0.406 nmol) at 120 h. Within 1 h after application droplets appeared dry on visual inspection. Immediately after droplet drying, 7.0% of the applied NAA was sorbed to the cuticle, but only 0.5% penetrated into the receiver solution, indicating that penetration occurred almost exclusively from the apparently dry deposit. At 120 h, 5.2% of the NAA applied was associated with the deposit and 4.3% with the cuticle. The distribution of maximum rates of penetration was log‐normal, but penetration at 120 h followed a normal distribution. Cuticle thickness (estimated 5–25 µm) had no significant effect on NAA penetration. Maximum rates of penetration through pepper fruit and citrus and ficus leaf cuticles were 4.9‐, 2.6‐ and 0.1‐times that through tomato fruit cuticles. At 120 h, penetration averaged 85.5, 79.5 and 34.7% for pepper, citrus and ficus cuticles, respectively. Extracting epicuticular and embedded waxes increased NAA penetration rates through tomato fruit cuticle more than three‐fold, but had little effect on penetration at 120 h (71.0 vs 87.7% for cuticular vs dewaxed cuticular membranes). The maximum penetration rate and total penetration were found to be useful parameters in describing the penetration time‐course. © 2000 Society of Chemical Industry     

降雨及助剂对咪唑乙烟酸药效的影响

以苘麻Abutilon theophrasti为测试植物,研究了施药后降雨和助剂对咪唑乙烟酸除草活性的影响。结果表明,咪唑乙烟酸有较好的耐雨性,药后2 h内无降雨,可保持相当的防效,药后4~8 h内无降雨,与无降雨的没有显著差异。添加非离子表面活性剂能明显提高咪唑乙烟酸的除草活性。其中增效作用从大到小依次为:AM-100＞PPJ-15＞OP-10＞SDP,咪唑乙烟酸的IC50值分别比未加助剂处理的下降了33.6%、35.4%、29.5%和17.1%。咪唑乙烟酸的用量越低,助剂的增效作用越明显。     

Study of the enhancement of herbicide activity and rainfastness by an organosilicone adjuvant utilizing radiolabelled herbicide and adjuvant

‘Sylgard® 309’ organosilicone surfactant is a very effective adjuvant for broadleaf weed control with a number of herbicides. It is also effective in providing rainfastness lo these post-emergence herbicide applications. To elucidate the basis for herbicide activity enhancement and rainfastness, the absorption of [¹⁴C]acifluorfen, [¹⁴C]bentazone and [¹⁴C]‘Sylgard 309’ were studied. Non-ionic surfactants and crop oil concentrates were used as adjuvants with [¹⁴C]acifluorfen and [¹⁴C]bentazone, respectively, for purposes of comparison. Maximum absorption of [¹⁴C]acifluorfen and [¹⁴C]bentazone was obtained within 15 min after herbicide application with the organosilicone, versus ≥ 24 h with the convenlional adjuvants. [¹⁴C]-Organosilicone absorption closely paralleled that of the [¹⁴C]-herbicides. The organosilicone appears to exert its action by increasing greatly herbicide absorption. The enhancement effect did not appear to be a function of reduced surface tension. Rainfastness appeared to be a result of greatly accelerated herbicide penetration through the leaf cuticle in the presence of the organosilicone.     

The biochemical and physiological effects and mode of action of AC 222,293 against Alopecurus myosuroides Huds. and Avena fatua L

AC 222,293 was found to exert its mode of action through inhibition of acetolactate synthase, the first enzyme in the biosynthetic pathway of the branched chain amino acids. In vitro AC 222,293 was found to be only a very weak inhibitor of the enzyme, in contrast to the potent inhibition by the free acid, suggesting that action of the herbicide in vivo is dependent on deesterification. Enzyme preparations from susceptible Avena fatua and Alopecurus myosuroides and tolerant wheat (cultivar Fenman) were all equally sensitive with an I₅₀ of approximately 5 · 10⁻⁷ M. Inhibition of treated plants is prevented when valine, leucine, and isoleucine are supplied via the nutrient solution. Prominent secondary effects are inhibition of DNA synthesis and cell division and the action of the herbicide is characterised by cessation of leaf growth.     

Effects of nonionic surfactants on cuticular sorption and penetration of 2, 4-dichlorophenoxy acetic acid

Surfactants increase the uptake of some foliar-applied chemicals to a greater extent than would be expected from their effects on surface tension and spray coverage. This study of the uptake of 2, 4-D [(2, 4-dichlorophenoxy)acetic acid] evaluated the effect of surfactants on penetration through and sorption by isolated cuticles of apple leaves. [¹⁴C]2, 4-D was placed in glass chambers affixed to enzymatically isolated adaxial apple leaf cuticles after the cuticle segments had been treated with various surfactants. The same surfactant pretreatments were included in sorption studies in which cuticle segments were immersed in [¹⁴C]2, 4-D for 96 h. Quantities of 2, 4-D passing through or sorbed by the cuticle were determined. Similar experiments were conducted with unaltered cuticles and cuticles dewaxed with chloroform. The hydrophile-lipophile balance (HLB) of polyethylene-glycol-based surfactants was inversely related to the sorption of those surfactants by the cuticles and penetration of 2, 4-D. Sorption of 2, 4-D by apple leaf cuticles was unaffected by surfactant pretreatment. Dewaxed cuticle membranes showed a similar response to 2, 4-D penetration and sorption following the surfactant pretreatment.     

Inhibition of prepenetration processes of the powdery mildew Golovinomyces orontii on host inflorescence stems is reduced in the Arabidopsis cuticular mutant cer3 but not in cer1

The obligate biotrophic fungus Golovinomyces orontii causes powdery mildew (PM) disease on its host Arabidopsis thaliana. Most research on the G. orontii–Arabidopsis pathosystem uses rosette leaves as experimental materials, so little is known about the behavior of G. orontii on other Arabidopsis organs. We thus conducted microscopic analyses of the PM infection process on leaves, stems, fruits and roots of Arabidopsis. Adaxial and abaxial surfaces of mature rosette leaves supported G. orontii infection, but growth was somewhat suppressed on cauline leaves. Prepenetration processes (germination and appressorium formation) were strongly inhibited on stems, fruits and roots. To test the effect of alterations in the Arabidopsis cuticle on the inhibition of prepenetration processes on stems, we used cuticle mutants of Arabidopsis eceriferum (cer) cer1 and cer3. Both mutants had been characterized for reduction in cuticular wax, but our chlorophyll leaching assay revealed increased cuticle permeability only in cer3. Mature rosette leaves and stems of cer1 and cer3 were inoculated, and prepenetration inhibition on stems was found to be significantly reduced in cer3 but not in cer1. We discuss the function of the cuticle in prepenetration inhibition, as well as our finding on suppression of G. orontii growth and reproduction on cer3 rosette leaves.     

Foliar uptake of pesticides—Present status and future challenge

Uptake of pesticides into plant foliage varies with plants and chemicals, and can be greatly influenced by adjuvants and environmental conditions. It is known that the penetration of pesticides into plant leaves is related to the physicochemical properties of the active ingredients, especially molecular size and lipophilicity. However, the uptake rate of a compound cannot be predicted by either of them or even combination of them. For a specific chemical, uptake varies greatly with plant species and there is no simple method at the moment to quickly evaluate the leaf surface permeability of a plant. Various adjuvants are being used to increase the penetration of pesticides into target plant foliage, but their effects vary with chemicals and plant species. The mechanisms of action of adjuvants in enhancing pesticide uptake remain unclear despite the effort made during the last three decades. Modern analytical and microscopic techniques provide powerful tools to deepen our understanding in this field. However, a more multidisciplinary approach is urgently needed to elucidate the transcuticular diffusion behaviour of pesticides and the mode of action of adjuvants. A better understanding of the foliar uptake process should lead to a more rational use of pesticides and minimize their negative impact on the environment.     

吲哚乙酸引导下三唑醇在大豆植株中的传导与积累研究初报

将吲哚乙酸与三唑醇发生酯化反应后生成的吲哚乙酸三唑醇酯 ,在0.5 mmol/L浓度下水培和喷雾处理6~8叶期大豆植株,同时以相同浓度的三唑醇及其与吲哚乙酸的混合物为对照,色谱法测定不同时间植株不同部位吲哚乙酸三唑醇酯和三唑醇的含量。结果表明,与对照相比,吲哚乙酸三唑醇酯在大豆中具有明显的双向传导和向根部积累的特点。喷雾处理后,在12~60 h之间内吸量和根部积累量均出现最大值。