Influence of metolachlor and the metolachlor protectant CGA 43089 on the biosynthesis of epicuticular waxes on the primary leaves of Sorghum bicolor Moench

Epicuticular wax synthesis by the primary leaf of Sorghum bicolor seedlings is inhibited when the germinating seeds are treated with 5 ppm metolachlor before germination. The composition of the free and esterified primary alcohols plus free and esterified fatty acids and aldehydes have been analysed. The predominant alcohol (75%) had 32 carbons while the 28- and 30-carbon homologues accounted for 78% of the fatty acids. Treatment of the germinating seeds with metolachlor strongly inhibited formation of the C₂₈, C₃₀ and C₃₂ alcohols. Synthesis of C₃₀ and C₃₂ fatty acids was decreased while that of the C₂₆ homologues was somewhat elevated. Simultaneous treatment of the germinating seed with metolachlor and the herbicide protectant CGA 43089 (α-[cyanomethoximino]-benzacetonitrile) resulted in normal wax synthesis. The results lead to the conclusion that the protectant prevents metolachlor from inhibiting synthesis of the dominating C₂₈ to C₃₀ chain-length constituents of the sorghum epicuticular wax.     

The effect of CGA 43089 as a safener of metolachlor in sorghum (Sorghum bicolor) (Recordings of elongation rates on single sorghum leaves)

The influence of metolachlor [2-chloro-6-ethyl-N-(2-methoxyl-methylethyl)acet-o-toluidide] on sorghum (Sorghum bicolor Moench.) is first demonstrated in order to be able to show the difference observed when this herbicide is applied together with CGA 43089. The effect of various concentrations (in nutrient solution) and of various exposure times on the elongation rate of single leaves is demonstrated. The safener CGA 43089 (x-(cyanomethoximino)-benzacetonitrile] showed no effect on the elongation rates when used in normal concentrations. The combined application of safener and metolachlor (concentration ratio 1:3) prevented the growth reductions due to metolachlor. When the safener was applied before metolachlor the safening action was as good as that of the combined application. When the safener was applied 1 or 2 days after the herbicide the safening effect was diminished. Plant uptake of the safener over a period of 3 days was sufficient to prevent the action of metolachlor but the safening effect was reduced when the interval between the end of safener application and the beginning of the herbicide application was increased. The conclusion drawn regarding the mode of action is that CGA 43089 does not interfere with herbicide uptake into the plant. The safener is, however, able to reduce the active amount of herbicide when present at the right time at the site of effect.     

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.     

Metolachlor (2-chloro-N-[2-ethyl-6-methylphenyl]-N-[2-methoxy-l-methylethyl] acetamide) and the metolachlor safener CGA 43089 [α-(cyanomethoximino)-benzacetonitrile] in sorghum seedlings: Correlations between morphological effects and ethylene formation

Treatment of germinating sorghum [Sorghum bicolor (L.) Moench] seeds with the grass herbicide, metolachlor (2-chloro-N-[2-ethyl-6-methylphenyl]-N-[2-methoxy-1-methylethyl] acetamide), causes growth retardation, promoted by thickening of the first leaf and thus inhibition of unfolding of secondary leaves, and increased ethylene production. Sorghum seeds pretreated with the safener CGA 43089 [α-(cyanomethoximino)-benzacetonitrile] exhibit neither morphological deformations nor ethylene production upon metolachlor treatment. Aminoethoxyvinylglycine [l-2-amino-4-(2-aminoethoxy)-trans-3-butenoic acid], a specific inhibitor of ethylene formation in higher plants, decreases ethylene formation by metolachlor-treated sorghum seedlings; the observed deformations, however, remain unchanged. Sorghum control seedlings which grow against a covering plate build up ethylene concentrations as after herbicide treatment, but without induction of the morphological symptoms. These observations suggest that the plant hormone ethylene is a symptom and not the inducer of the morphological effects visible after metolachlor treatment of sorghum seedlings.     

The role of the abaxial leaf surface waxes of Lolium spp. in resistance to Erysiphe graminis

Field and glasshouse observations of Lolium spp. grasses indicated that the lower, abaxial, leaf surface was rarely infected by powdery mildew ( Erysiphe graminis ) even when the upper, adaxial, surface was densely colonized. Experiments showed that conidia of two strains of E. graminis , one from Lolium and one from Avena , germinated equally well on both surfaces of Lolium and Avena leaves, but that the subsequent growth and development of germlings was impaired on the lower surface of Lolium leaves, so that most formed only multiple short germ tubes or an abnormal long tube, and only c. 25% or fewer formed infection structures. This contributes to the apparent resistance of the lower Lolium leaf surface to powdery mildew and may help to explain why the disease is relatively unimportant in UK ryegrass crops, since infection structures develop at a high frequency on only 50% of the leaf area, i.e. the upper surface. Scanning electron microscopy showed that the epicuticular waxes on the lower Lolium leaf surface form amorphous sheets. This contrasts with the crystalline plate waxes seen on the upper surface of Lolium leaves and on both surfaces of oat leaves. However, when the lower Lolium leaf surface was washed with chloroform to remove epicuticular wax, normal germling and infection structure development was obtained on the wax-free surface. This suggests that the sheet waxes prevent the pathogen gaining access to features of the cuticular membrane which trigger normal germling development.     

The role of infection time in the differential response of sorghum cultivars to Striga hermonthica infection

Striga hermonthica is an important parasitic weed that severely reduces yields of sorghum in sub‐Saharan Africa. Pot experiments with the sensitive sorghum cultivar CK60‐B and the tolerant Tiémarifing were conducted in 1999 and 2000 to investigate the role of infection time on the interaction between sorghum and Striga hermonthica. Timing of Striga inoculation was used to establish delays of one and two weeks in first attachment of the parasite. In 1999, early Striga inoculation resulted in a relatively early first Striga attachment on CK60‐B. Although first infection of Tiémarifing occurred one week later, an identical final number of emerged Striga plants was observed. Plants of CK60‐B were more severely affected and supported a higher total Striga biomass. Only with this cultivar the interaction between host and parasite was significantly affected by delayed infection. Parasite biomass was most sensitive and already significantly reduced following a 1‐week delay in infection time. With a further 1‐week delay, an additional reduction in parasite biomass was accompanied by a strong and significant increase in total and panicle dry weight of the host plant. In 2000, first infection of CK60‐B was relatively late and occurred simultaneously with first infection of Tiémarifing and no significant effect of delayed infection on Striga biomass or host‐plant performance was observed. The results indicate that the influence of delayed infection strongly depends on actual infection time and confirm that earlier observed differences in time of first infection between the two cultivars do contribute to the more tolerant response of Tiémarifing to Striga infection.     

The uptake of surfactants into wheat

The time course of uptake has been determined for seven poly(oxyethylene) surfactants, and one anionic surfactant (sodium dodecyl sulphate), into the leaves of wheat plants grown in a phytotron. Uptake was relatively rapid during an initial period of 24 h for six of the eight surfactants; after this period, the uptake rate was lower, and total uptake after 48 h was in the range 80-91% for those six surfactants. The other two compounds, sodium dodecyl sulphate and cetostearyl alcohol-22EO condensate (hexadecan-1-ol/octadecan-1-ol ethylene oxide condensate; average number of ethylene oxide units 22) were barely taken up at all. The observed time course for uptake was consistent with a complex process based on more than one rate-determining process. The physical properties of the surfactants are discussed in relation to their observed uptake behaviour. The surfactant deposit areas, measured by microscopy, were concluded to be not particularly relevant in interpreting the uptake results. Uptake was not related to surfactant chain length, but the physical form of the hydrated surfactant on a leaf surface appeared to influence uptake behaviour.     

Ergot resistance in sorghum in relation to flowering, inoculation technique and disease development

Ergot is an important disease of sorghum (Sorghum bicolor) in parts of Africa and Asia. Studies were conducted to determine the relationship between flowering biology and ergot infection, and to develop an artificial field-screening technique to identify ergot resistance in sorghum. Spikelets resisted infection after anthesis, but each day's delay in anthesis after inoculation supported 8-3% more ergot. The screening technique consisted of three components: trimming of panicles to remove pollinated spikelets before inoculation, a single inoculation of trimmed panicles, and panicle bagging for 7-10 days. Inoculated panicles were evaluated by a qualitative visual rating method (on a 1-5 scale) and a quantitative spikelet counting method. Selected accessions from the world collection of sorghum germplasm were screened at Karama Research Station, Rwanda, for two seasons and 12 ergot-resistant lines were identified. These were also resistant at ICRISAT Centre, India.     

Studies on the sorghum grain midge,Contarinia sorghicola Coquillet,in relation to environmental influence

Abstract

Biology, ecology and damage potential of the sorghum midge, Contarinia sorghicola Coquillet, were studied at Coimbatore, India. The life cycle of the midge was shorter in summer than winter: Johnson grass, Sorghum halepense and pearl millet, Pennisetum americanum served as alternate hosts for the sorghum midge. Seasonal incidence studies revealed that four peak infestations occurred in crops sown in April, June, August and October. Midge developmental stages were quite active all through the year with no diapause, Peak adult midge attraction to the light trap was recorded at 21.00 hours. However, adult midges were found to be quite active only in the daytime in the field. There was no relationship between adult midge catches from the light trap and the population recorded in the field. Morning relative humidity and wind velocity were negatively associated with the population of midge attracted to the light trap. An increased percentage of midge population was recorded in the light trap during the new moon and second quarter phases of moon. Sticky traps were not efficient in trapping adult midges. One pair of adult midge per earhead caused 16–9% grain damage.     

Analysis of foliar uptake of pesticides in barley leaves: Role of epicuticular waxes and compartmentation

Uptake of pesticides into barley leaves was measured under controlled conditions. Leaves detached from plants were submerged in aqueous solutions of ¹⁴C-labelled (2,4-dichlorophenoxy)acetic acid, triadimenol, bitertanol and pentachlorophenol. Uptake was biphasic. A short (30-min) period with high rates of uptake was followed by uptake that proceeded more slowly and was steady over hours. Compartmentation of pesticides was studied by desorbing pentachlorophenol from leaves previously loaded with [¹⁴C]pentachlorophenol. From the uptake and desorption kinetics it was concluded that penetration of pesticides proceeds as follows: the compounds are first sorbed at the surface of epicuticular wax aggregates where they are in contact with the donor solutions. Solutes then diffuse through the surface wax aggregates into the cuticle. Equilibrium between donor solutions, surface wax and cuticle is established in about 30 min. After this time the amounts of solutes in these compartments no longer increase. Uptake after this time represents penetration into the leaf cells. This fraction of the pentachlorophenol is retained irreversibly, while that sorbed in wax and cutin can be desorbed again. All compounds were sorbed in cuticular waxes and partition coefficients wax/water were determined. On a mass basis only 5 to 10% of the amounts sorbed in cutin are sorbed in wax. This comparatively low solubility in wax contributes to the barrier properties of cuticular waxes. The other determinant of permeability is the very low mobility of solutes in cuticular waxes.     

The role of phytohormones in relation to bakanae disease development and symptoms expression

Fusarium proliferatum, the causal agent of bakanae disease was found to be up-regulated gibberellic acids (GAs) in bakanae diseased rice plants and thereby contributing to the different types of symptoms observed associated with the disease. The up- and down regulation of GAs, IAA and ABA were studied in susceptible (MR 211) and resistant (BR3) varieties artificially inoculated with F. proliferatum at different times after inoculation. The increase in GAs including fungiproduced GA3 and IAA were higher in inoculated MR 211 rice plants (GAs = 26%, IAA = 40.39%) as compared to resistant BR3 (GAs = 19%, IAA = 4.27%), 7 days after inoculation (disease score 1, S-1) in whole plant sample analysis. The increase were higher in both roots and leaves but not in the stem, thus the main symptom observed as stunting of the susceptible plants at disease score 1. However, 14 days after inoculation (disease score 3, S-3), both phytohormones were observed to increase in whole plant sample analysis as well as in all plant parts sampled. This increasing effect was found associated with elongation of internodes and chlorosis of leaves in susceptible plants of MR 211. As the symptoms progressed to disease score 5 (S-5, after 21 days of inoculation) susceptible plants of MR 211 were started to collapse and lodged due to over elongation, and finally dead followed by a decrease in GAs and IAA but an increase in ABA. In resistant variety BR3, marginal up regulation of GAs and IAA were observed only at 21 days after inoculation in stems with no typical symptom of bakanae disease.     

A scanning electron microscope study of glyphosate deposits in relation to foliar uptake

The effects of several formulations on foliar uptake of glyphosate, and on the morphology of glyphosate deposits on leaves, were examined in Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.). [¹⁴C]glyphosate, in the form of the free acid or the isopropylamine salt (IPAS), was applied to foliage alone or with various adjuvants. Uptake of all glyphosate IPAS formulations was greater than that of the corresponding acid formulation. Addition of ‘Tween 20’ enhanced the uptake of glyphosate IPAS compared to glyphosate alone, but had no effect on the uptake of glyphosate acid. Ammonium sulfate and the ‘Roundup’ formulation blank increased the uptake of glyphosate acid and IPAS to 2-3 times that of herbicide alone. Surface deposits, as observed by scanning electron microscopy, varied with the formulation of the herbicide, although there were no differences between the acid and IPAS formulations. Glyphosate alone initially formed a deposit with both crystalline and smooth, amorphous areas. Later in the treatment period (48 and 72 h after application), the deposit was almost entirely crystalline. The addition of ‘Tween 20’ or of formulation blank resulted in the formation of a more amorphous, non-crystalline deposit. Herbicide solutions containing ammonium sulfate dried to form a highly crystalline deposit. However, crystals similar to those of glyphosate alone were not visible in these deposits. The ability of these adjuvants to prevent or delay crystal formation may play a role in their enhancement of herbicide uptake.     

酿酒高粱品种、组合及亲本的丝黑穗病抗性鉴定

为了明确不同类型的酿酒高粱材料对西南地区丝黑穗病的抗性和促进抗丝黑穗病品种的选育,采用土壤接菌法对107份材料进行了丝黑穗病抗性鉴定;根据抗性鉴定结果,比较了酿酒高粱杂交组合与其亲本对丝黑穗病的抗性,并对供试菌种进行了致病力分析.结果显示:在感病对照恢1植株平均病株率为67.65％时,有13个不育系、6个保持系、10个恢复系、28个杂交组合的病株率为0,达免疫水平,其中,酿酒高粱不育系和杂交组合所占比例较大,分别为86.67％和75.68％;恢复系中免疫类型所占比例较小,为24.39％;常规品种和组合中无免疫类型;杂交高粱对丝黑穗病的抗性属显性遗传;泸州丝黑穗病菌具有较强的致病力.     

Dynamics of conidial adhesion and elicitor uptake in relation to pisatin accumulation in aqueous droplets on the endocarp of pea pods

The adhesion of conidia of Monilinia fructicola to, and uptake of a biotic elicitor (pea-M. fructicola diffusate preparation) and two abiotic elicitors (actinomycin-D and CuCl₂) by endocarp tissue of pea pods has been investigated in relation to the elicitation of pisatin. Conidia were found to rapidly adhere to the endocarp surface and were not readily dislodged by washing. The dynamics of elicitor uptake from the bathing solutions varied with the elicitor treatments. In the case of the biotic elicitor, bioassays of the solutions remaining on the endocarp surface for residual elicitor activity indicated there was a gradual loss of elicitor from the bathing solution. By 10 h, approximately 41% of the original elicitor activity had disappeared from the bathing solution. Direct measurement of actinomycin-D in the bathing solution showed that uptake appeared to begin about 6 h after its application. On the other hand, direct measurement of Cu²⁺ in the bathing solution showed that approximately 60% of the original concentration of Cu²⁺ rapidly disappeared from the bathing solution in the first 30 min.The results highlight the need for sustained contact between plant and fungus or elicitor in the bathing fluid of the infection-droplet or of the elicitor solution for the maximum outcome of the pisatin response.     

The mode of action of glufosinate in algae: The role of uptake and nitrogen assimilation pathways

The purpose of this work was to investigate the in-vivo mode of action of glufosinate in comparison with that of the known glutamine synthetase inhibitor, methionine sulfoxmine, in photoautotrophic microorganisms. Using the eukaryotic green alga Chlorella fusca (Shih. & Krauss) and the cyanobacterium Anacystis nidulans (Kratz & Myers), currently developed [¹⁵N]NMR pulselabelling techniques have been employed to study the inhibition of ammonia assimilation. The results show that, while methionine sulfoximine immediately blocks glutamine synthesis, glufosinate action requires an induction process in both organisms investigated, possibly indicating the de-novo synthesis of an amino acid membrane carrier. In addition, the observed ability of C. fusca to incorporate nitrogen into glutamate under glutamine synthetase-inhibiting conditions is explicable by an anabolic function of a glutamate dehydrogenase in this organism. This might explain the large differences in observed species sensitivity to glufosinate exposure.     

The role of pH for ionic solute uptake by the non-aerial hypocotyl of mung bean plants

Journal of Plant Diseases and Protection - The non-aerial hypocotyl is an exceptional fast pathway for the uptake of soil-applied pre-emergent herbicides or systemic actives with soil mobility...     

The development of anthracnose symptoms on sorghum genotypes in the Nigerian savanna

Journal of Plant Diseases and Protection - The development of sorghum anthracnose symptoms was monitored on 17 sorghum genotypes of diverse origins during two rainy seasons in the savanna of...     

加工方法对异丙甲草胺水乳剂物理稳定性的影响

通过分析Turbiscan Lab分散稳定性分析仪短期扫描图谱,以及测定所制备的水乳剂液滴平均粒径和Zeta电位,研究了不同加工方法(油水相添加顺序和乳化剂添加位置不同)对异丙甲草胺水乳剂物理稳定性的影响。结果发现:采用乳化剂添加在油相中的反相乳化法(方法 A)制备的水乳剂,短期扫描图谱中背散射光强度随时间降低的幅度很小,液滴平均粒径最小,Zeta电位绝对值最大,加速试验(54℃±2℃,14 d)后外观均一,稳定性最好;采用乳化剂添加在水相中的反相乳化法(方法 B)制备的水乳剂稳定性次之;采用乳化剂添加在水相中的直接乳化法(方法 C)和乳化剂添加在油相中的直接乳化法(方法 D)制备的水乳剂,试样短期扫描图谱中背散射光强度随时间均发生明显变化,顶部及中下部背散射光强度随时间呈更加明显的下降趋势,液滴平均粒径均较大,Zeta电位绝对值较小,加速试验后外观不均一,上层析水,下层产生少量沉淀,其中采用方法 C制备的水乳剂稳定性最差。表明采用不同加工方法制备的同一配方异丙甲草胺水乳剂的稳定性存在显著差异,以乳化剂添加在油相中的反相乳化法制备的水乳剂稳定性最好。     

Performance and uptake of some carbendazim-producing fungicides applied as seed treatments to spring barley,in relation to their physicochemical properties

The performance of carbendazim and its chemical precursors benomyl, thiophanatemethyl and methyl 4-(2-aminophenyl)-3-thioallophanate ( I ) ( “NF48” ) as systemic fungicidal seed treatments on barley was investigated. In field trials all treatments significantly decreased smut (Ustilago nuda) at 3.2 g kg^-1 of seed; the order of effectiveness was I > benomyl > thiophanate-methyl > carbendazim. Control of barley mildew (Erysiphe graminis) followed a similar pattern but results were less clear-cut. Measurements of uptake and translocation from seeds, treated with radiolabelled fungicide and planted in pots of Woburn soil in a controlled environment room, showed that seedlings accumulated much more I than the other compounds over 28 days. This substantial early uptake into leaves could explain why I was particularly effective against smut in the field trials. Comparisons of amounts taken up. with solubility in water, octanol/water partition coefficient, extent of adsorption on soil and pK_a values suggested that the effects of these properties on availability in the soil solution may be more important than their influence on penetration into the root in determining relative uptake and disease control in the case of localised applications such as seed treatments.     

The effective dominance of resistance genes in relation to the evolution of resistance

Field selection for a rare insecticide resistance (R) gene can be substantially delayed if R is rendered effectively recessive [if all or most heterozygotes ( R + ) are killed by the field dosages] and if a representative sample (+ +, R +, RR) of the population is permitted to escape exposure. The relationship between heterozygote mortality and escape in influencing selection rates has been considered at various frequencies of R. The cases when mating precedes selection, and when selection precedes mating, have been calculated using computer simulations. It is concluded that when R genes are rare it is advantageous (a) to apply the highest possible doses of insecticide in such a form that all exposed insects pick up an amount sufficient to kill all or most heterozygotes, (b) to apply the insecticide to adults after they have mated, rather than to younger adults or to larvae, and (c) to ensure that the proportion of insects given the opportunity to escape contact is as high as practical considerations allow. Once resistance is obvious (when samples are brought into the laboratory for tests), the R gene frequency will have risen to a level which makes the suggested strategy no longer valuable. Alternative strategies are briefly discussed.