Fungicide modes of action and resistance in downy mildews

Among oomycetes, Plasmopara viticola on grape and Phytophthora infestans on potato are agronomically the most important pathogens requiring control measures to avoid crop losses. Several chemical classes of fungicides are available with different properties in systemicity, specificity, duration of activity and risk of resistance. The major site-specific fungicides are the Quinone outside inhibitors (QoIs; e.g. azoxystrobin), phenylamides (e.g. mefenoxam), carboxylic acid amides (CAAs; e.g. dimethomorph, mandipropamid) and cyano-acetamide oximes (cymoxanil). In addition, multi-site fungicides such as mancozeb, folpet, chlorothalonil and copper formulations are important for disease control especially in mixtures or in alternation with site-specific fungicides. QoIs inhibit mitochondrial respiration, phenylamides the polymerization of r-RNA, whereas the mode of action of the other two site-specific classes is unknown but not multi-site. The use of site-specific fungicides has in many cases selected for resistant pathogen populations. QoIs are known to follow maternal, largely monogenic inheritance of resistance; they bear a high resistance risk for many but not all oomycetes. For phenylamides, inheritance of resistance is based on nuclear, probably monogenic mechanisms involving one or two semi-dominant genes; resistance risk is high for all oomycetes. The molecular mechanism of resistance to QoIs is mostly based on the G143A mutation in the cytochrome b gene; for phenylamides it is largely unknown. Resistance risk for CAA fungicides is considered as low to moderate depending on the pathogen species. Resistance to CAAs is controlled by two nuclear, recessive genes; the molecular mechanism is unknown. For QoIs and CAAs, resistance in field populations of P. viticola may gradually decline when applications are stopped.     

Physiological and biochemical modes of action of the diphenylether aclonifen

Aclonifen belongs to the diphenylether (DPE) chemical family among which potent herbicides with a photodependent mode of action can be found. For years aclonifen has been used in several types of cultures. However its biochemical mode of action remains unclear although it was listed as a carotenoid synthesis inhibitor by the Herbicide Resistance Action Committee (HRAC). As a matter of fact, corn seedling leaves treated with 10⁻⁴ M aclonifen and maintained in the dark no longer contained carotenoids but showed an accumulation of a compound having all the characteristics of phytoene. That demonstrated aclonifen ability to inhibit the desaturases catalyzing the transformation of phytoene into carotenoids. Moreover, aclonifen (5 × 10⁻⁵ M) was responsible for a photodependent cell destruction (necrosis) of cucumber cotyledons typically due to protoporphyrin IX accumulation. The same phenomenon was demonstrated in aclonifen-treated etiolated corn seedlings (10⁻⁴ M) that showed an accumulation of protoporphyrin IX, reaching 62 ng/g of leaf fresh mass and reactive oxygen species production under light. On these two cases (cucumber cotyledons and etiolated corn seedlings), aclonifen was acting as a typical DPE, as demonstrated by the accumulation of protoporphyrin IX. As a whole, aclonifen was shown here, to act on two different biochemical pathways including carotenoid synthesis on the one hand, as well as protoporphyrinogen oxidase, in the chlorophyll synthesis pathway, on the other for the same range of concentrations.     

Biochemical mode of action of the acaricide fenazaflor

The active ingredient of ‘Lovozal’ (fenazaflor) is hydrolysed in solution to 5,6-dichloro-2-trifluoromethyl-benzimidazole (DTFB). Rat liver mitochondria were uncoupled by fenazaflor after a lag phase, while uncoupling by DTFB was immediate, and a similar situation occurred with mitochondria isolated from Tetranychus telarius L. (This is the first report of isolation of mite mitochondria.) Since both compounds ultimately have the same uncoupling activity, it is likely that fenazaflor exerts its effect only after hydrolysis to DTFB. Living mites showed a stimulation of respiration of 70% on addition of either fenazaflor or DTFB before death occurred, suggesting that the acaricidal effect of fenazaflor is due to uncoupling of oxidative phosphorylation after hydrolysis to DTFB.     

农村宅基地置换模式的差异性及其机理分析

基于对江苏省、河北省50个乡镇的调查数据,利用多元Probit模型,对农村宅基地置换模式差异性所在及其形成的内在机理进行了分析。结果表明:当前农村宅基地置换主要采用置换商品房、置换小产权房以及置换宅基地三种模式,具有显著的区域差异性。土地稀缺程度、农地流转稳定程度、非农就业机会和社会保障稳定程度是导致农村宅基地置换模式差异性产生的主要原因。土地稀缺程度、农地流转稳定程度、非农就业机会以及社会保障稳定程度较高的地区,倾向于采用置换商品房模式进行置换;反之,则倾向于采用置换宅基地模式进行置换。因此,在推进农村宅基地置换工作时,应因地制宜,综合衡量选取适宜的宅基地置换模式,保证农村宅基地置换工作的顺利推进和农民的置换福利性不受损失。     

The relationship of metabolism studies to the modes of action of herbicides

Metabolism studies are necessary in the understanding of the mode of action of herbicides, their loss of activity and their selectivity. Molecular change of a herbicide may involve photochemical degradation, and non-enzymic or enzymic reactions that normally inactivate, but in some cases activate, a compound. Molecular change resulting in activation is discussed with regard to the (2,4-dichlorophenoxy)-alkanoic acids, the pyridines paraquat and diquat, the anilides benzoylprop-ethyl and flamprop-methyl, and the thiocarbamates. Inactivation due to metabolism is reviewed with regard to herbicides applied to soil and foliage. Of the soil-applied herbicides, the 1,3,5-triazines and the nitrile dichlobenil are exemplified as cases in which selectivity may be due largely to interspecific differences in metabolism. Of the foliage-applied translocated compounds, the metabolism of the phenoxyalkanoic acid herbicides has been extensively investigated and may involve conjugation, side-chain degradation or extension, ring hydroxylation and protein binding. The mode of action of glyphosate, asulam, dalapon and aminotriazole in perennial weeds is discussed with particular reference to their metabolism.     

无机化合物对南方根结线虫作用方式的研究

利用体外生物测定方法检测碳酸氢铵、硫酸铜和氯化铁在供试浓度下对南方根结线虫2龄幼虫（Meloidogyne incognita J2）存活的影响,以及药剂对其运动行为、个体发育、呼吸及体液外渗等的影响。结果表明,3种化合物在LC90浓度下使南方根结线虫2龄幼虫50% 致死时间不超过10.14 h,90%致死时间不超过22.66 h,离体条件下均对南方根结线虫2龄幼虫存活有强烈的抑制作用,显著降低了其运动行为,使其体长缩短、透明尾变长。并且,药剂处理均降低了线虫的呼吸作用,线虫悬浮液的电导率明显高于对照。     

Biochemical aspects of the fungitoxic and growth regulatory action of fenarimol and other pyrimidin-5-ylmethanols

The C-14 demethylation of the sterols, dependent on cytochrome P-450, and the C-22(23) desaturation of sterols are reactions in the ergosterol biosynthesis pathway that are regarded as primary target sites in the toxicity of fungicides of the pyrimidin-5-ylmethanol type. Currently, there is no evidence for target sites in other pathways of comparable sensitivity, although the failure of added ergosterol to reverse the fungitoxicity suggests the existence of such sites. The mitochondrial respiratory systems in Ustilago maydis and Aspergillus nidulans are insensitive to this type of fungicide and are not regarded as primary targets of fungitoxicity in these organisms. Appreciable evidence indicates that the primary targets in higher plant growth regulation are reactions, dependent on cytochrome P-450, that assist in the conversion of kaurene to kaurenoic acid in the gibberellin (GA) biosynthesis pathway. Growth retardation by high concentrations of pyrimidin-5-ylmethanols, which is not reversable by GA, apparently involves action at sites outside the GA biosynthesis pathway. The data derived from various studies of the mechanisms of fungitoxicity and growth regulation suggest that any undetected primary targets of the pyrimidin-5-ylmethanols are likely to be haem enzymes, similar to the cytochrome P-450 involved in sterol C-14 demethylation.     

Biochemical and pathogenic differences between Kenyan and Brazilian isolates of pseudomonas syringae pv. garcae

Isolates of Pseudomonas syringae pv. garcae from Kenya and Brazil differed in pathogenic and biochemical characters. In inoculations on Coffea arabica var. SL28 from Kenya, only the Kenyan isolates were virulent. The Kenyan isolates were not bacteriocin producers while the Brazilian isolates were active producers comparable to P. s. syringae from lilac ( Syringa vulgaris ). Pigment production separated the two types of P. s. garcae isolates distinctly. The Kenyan isolates produced the UV fluorescent yellow-green siderophore while the Brazilian isolates produced a nonfluorescent brown diffusible pigment on King's B medium. API-20NE diagnostic kits were largely ineffective in distinguishing between biochemical reactions of P. s. garcae isolates from Kenya and Brazil or between these and P. s. syringae . Syringomycin activity on lemon and Geotrichum candidum distinguished P. s. syringae from P. s. garcae isolates. It is concluded that P. s. garcae (as represented by the seven cultures from the National Collection of Plant Pathogenic Bacteria, Harpenden, UK) exists in at least two strains, the Kenyan isolates comprising one strain while the Brazilian isolates comprise one or more distinct strains.     

Efficacy of fungicides with various modes of action in controlling the early stages of an Erysiphe necator-induced epidemic

BACKGROUND: Limiting the use of fungicides is due to become an important issue in managing Erysiphe necator (Schwein) Burrill infections in vineyards. The authors determined how three fungicides currently used by vine growers could be managed to control the early stages of an E. necator‐induced epidemic. RESULTS: Leaf‐disc bioassays and field experiments suggested that the protectant quinoxyfen induced minor disruption in E. necator development, but compounds with protectant and curative properties (tebuconazole and trifloxystrobin) caused significant, although different, disruption during E. necator‐induced epidemics. Bioassays showed that each of the antifungals were most effective at different stages of fungal development, tebuconazole before sporulation and trifloxystrobin after sporulation of the colonies. Results from the bioassay also highlighted likely occurrences in the field, where several stages of fungal development are encountered simultaneously. CONCLUSION: The present findings were complementary: leaf‐disc tests showed when the fungicides were most effective at inhibiting E. necator infection cycles; the field trial provided results in terms of incidence and severity of disease on bunches without reference to the pathogenic cycle development. A protection strategy combining the different types of fungicide under study is suggested. Copyright © 2010 Society of Chemical Industry     

Regime dynamics of hydrochemical and toxicological parameters of the Irtysh River in Kazakhstan

Since the Irtysh River flows through the important economic,ecological and social territories of China,Kazakhstan and Russia,the water quality issues growingly draw the attention of the water authorities from these countries.Therefore,a detailed study of the hydrochemical regime and toxicological indicators in Kazakhstan was carried out for understanding the regime dynamics of water quality and its affect factors.The combined assessment of maximum permissible concentration(MPC)of chemical components and biotesting method were proposed and performed for the study area.The results clearly showed that the concentrations of single chemical component at different locations are mostly under MPC standard in a basin scale.However,the watershed surface runoff and tributary stream flow from mining industry areas had high concentration of heavy metals and had significant impact on the water quality near Ust-Kamenogorsk.Furthermore,even the stream water generally meet MPC standard,the results of biotesting method show the toxicity level of water sample is lethal for the test objects of phytoplankton and Daphnia.The survival rates of most water samples are lower than 46.7%.Hereby,this study strongly suggests using combined water assessment methods to evaluate the water quality.     

Ecological effect assessment by species sensitivity distribution for 38 pesticides with various modes of action

Species sensitivity distributions (SSDs) of 38 pesticides with various modes of action were analyzed as a higher-tier ecological effect assessment based on collected acute toxicity data. Then the 5% hazardous concentrations (HC₅) based on each SSD were calculated as the predicted no-effect concentrations for aquatic ecosystems. The differences between HC₅ and registration criteria were small (within ten-fold) for 35 of the 38 pesticides. However, there were more than ten-fold differences for a fungicide and two herbicides. These results suggest that the current effect assessment scheme could underestimate the effect of such pesticides. This could be caused by differences in sensitivity of specific properties of the mode of action.     

Studies on the modes of action of n-alkylguanidines and triorganotins on photosynthetic energy conservation in the pea and the unicellular alga Chlamydomonas reinhardi Dangeard

The pea (Pisum sativum L.) and the CW 15 (cell wall-less) strain of the unicellular alga Chlamydomonas reinhardi Dangeard were used to investigate the modes of action of two n-alkylguanidines and several triorganotin salts on reactions associated with photosynthetic energy conservation. The two n-alkylguanidines, n-octylguanidine and n-dodecylguanidine, affected state 3 (ADP stimulated) noncyclic electron transport of pea chloroplasts in a concentration-dependent manner, viz, energy transfer inhibition at low concentrations, uncoupling of electron transport from photophosphorylation at intermediate concentrations, and direct inhibition of electron transport at relatively high concentrations. The Ca²⁺-dependent ATPase (EC 3.6.1.5) activity of C. reinhardi chloroplast fragments was inhibited by both n-alkylguanidines over concentration ranges similar to those required to affect state 3 electron transport in pea chloroplasts. Dodecylguanidine required lower concentrations than octylguanidine to produce similar effects in both assays. The triorganotins produced uncoupler-reversible inhibition of the state 3 electron transport of pea chloroplasts in a sucrose medium and uncoupled the electron transport in a medium containing high chloride concentrations, as shown by their stimulation of both the light-induced transmission changes and the decay of the light-induced pH gradients of chloroplast suspensions. The inhibition of the Ca²⁺-dependent ATPase activity of C. reinhardi by most of the triorganotins was correlated to their inhibition of the growth of the alga on agar medium under different trophic conditions. The efficacies of the tri-n-alkyltins in all the assays used generally increased along the homologous series.     

Fate of endosulfan in rats and toxicological considerations of apolar metabolites

[¹⁴C]Endosulfan, α or β isomers separately, was administered to rats as a single oral dose and as a dietary supplement for 14 days. No appreciable differences were observed in the fate of the two isomers. Five days after the single dose, 75% of the dose had been voided in the feces and 13% in the urine. Of the total radiocarbon consumed in the diet after 14 days, 56% had been eliminated in the feces and 8% in the urine. Bile collection studies showed that up to 47% of a single oral dose was eliminated from the liver via this route; enterohepatic circulation was not apparent. Maximum [¹⁴C]endosulfan equivalents in body tissue occurred in the kidney and liver, 3 and 1 ppm, respectively, after 14 days of feeding 5 ppm of endosulfan. Apolar metabolites in the excreta and/or tissues were a minor portion of the total residues and consisted of the sulfate, diol, α-hydroxy ether, lactone, and ether derivatives of endosulfan. The sulfate was slightly more toxic to mice than endosulfan, while the other products were less toxic. Neither endosulfan nor its metabolites were active in the Salmonella mutagenicity test. Endosulfan in the diet of rats for 28 days at 50 ppm did not induce liver oxidase enzymes, alter liver or kidney weights, or influence the rate of weight gain of the animals.     

氟啶胺等杀菌剂对不同发育阶段小麦赤霉病菌的毒力及其作用方式

为筛选高效防治小麦赤霉病的药剂,采用菌丝生长速率法和孢子萌发法测定了5种杀菌剂对不同发育阶段小麦赤霉病菌的毒力,并测定了田间接种条件下对小麦赤霉病的保护和治疗效果。结果表明,氟啶胺对小麦赤霉病菌菌丝生长、孢子萌发、芽管伸长和产孢的毒力均较高,EC_(50)≤0.249μg/m L;咯菌腈可抑制该病菌菌丝生长、芽管伸长和产孢,EC_(50)≤0.881μg/m L,但对孢子萌发几乎无抑制作用;菌毒清对分生孢子萌发、芽管伸长和产孢的毒力稍低,EC_(50)在5.726~10.244μg/m L之间,但高于其对菌丝生长的毒力;甲基硫菌灵和嘧菌酯对各发育阶段病菌的毒力均较低。在田间,接种前3 d施药,咯菌腈和氟啶胺对小麦赤霉病的保护效果较好,200 g(a.i.)/hm~2处理的效果在80.01%以上,可作为保护剂在发病前使用;菌毒清在接种前3 d和接种后3 d使用时保护效果和治疗效果均较高,200 g(a.i.)/hm~2处理的防效均在69.99%以上,既可作为保护剂在发病前使用,也可作为治疗剂在发病后使用。     

Susceptibility of adult Coccinella septempunctata (Coleoptera: Coccinellidae) to insecticides with different modes of action

Five insecticides (pyriproxifen, imidacloprid, deltamethrin + heptenophos, lambda-cyhalothrin and Bacillus thuringiensis Berliner subsp. tenebrionis) were examined in the laboratory for their acute detrimental side-effects at field rates on adult seven-spot ladybird beetle, Coccinella septempunctata L. The toxicity of the preparations was determined by measuring the acute surface contact effects (dried spray on leaves of Philadelphus coronarius L.), except for B. thuringiensis where mixed pollen was treated. Four to six concentrations were tested (pyriproxifen 12.5, 25, 50, 100, 200, 400 mg AI litre(-1); imidacloprid 62.4, 125, 250, 500 mg AI litre(-1); deltamethrin + heptenophos 26.4, 53.1, 106.3, 212.5 mg AI litre(-1); lambda-cyhalothrin 1.1, 3.4, 10, 30 mg AI litre(-1); B. thuringiensis 1.5, 3.0, 12.0, 48, 192, 768 mg AI litre(-1)), with 22 adults exposed per concentration. All tests were conducted in the laboratory of the Plant Protection Department (University of Debrecen, Hungary) at 22-25 degrees C, 40-60% RH, under a 16:8 h light:dark photoperiod in 1998-1999. Data were analyzed by probit analysis, probit transformation and analysis of variance. According to different categories of evaluation, pyriproxifen, imidacloprid and B. thuringiensis subsp. tenebrionis seem to be safe for C. septempunctata adults but the other two preparations were moderately harmful to them, which requires further semi-field or field tests to measure their real effect under field conditions.     

Studies on the mode of action of asulam in bracken (Pteridium aquilinum L. Kuhn) II. Biochemical activity in the rhizome buds

The effect of asulam (methyl (4-aminobenzenesulphonyl) carbamate) on the synthesis of RNA and protein was investigated in bracken sporeling plants and excised rhizome bud tissue. Foliage application of asulam (4.4 kg/ha) reduced the RNA levels in frond buds and young fronds within 3 days, while protein levels were significantly reduced after 14 days. A significant reduction in respiratory activity of buds was observed after 2 weeks, the level of inhibition being 54% after 8 weeks. During a 3-h incubation period, O₂ uptake by excised bud issue was stimulated by 5 and 10 ppm asulam and inhibited by higher concentrations; ₃₂P uptake was inhibited at all concentrations. Asulam (5 ppm and above) inhibited bud growth and reduced RNA and protein levels in incubated buds (20 h at 30°C), and the incorporation of [₁₄C]orotic acid into RNA and [₁₄C]leucine into protein. Reduction of RNA levels and inhibition of [₁₄C]ladenine incorporation into RNA in buds occurred entirely in the ribosomal and supernatant fractions of the cellular extract. Inhibition of RNA synthesis by asulam (50 ppm) as measured by [₁₄C] orotic acid incorporation into RNA was completely antagonized by CEPA (3-chloroethylphosphonic acid) (50 ppm) and partially by 2,4-D (2,4-dichlorophenoxyacetic acid) (50 ppm) and GA (Gibberellic acid) (50 ppm). These results suggest that the interference of asulam with RNA and protein synthesis at the metabolically active sinks (rhizome buds) could be one of its major mechanisms of action in bracken.     

嗜卷书虱和嗜虫书虱体内磷酸酯酶的生化与毒理学特性比较

采用药膜法对嗜卷书虱和嗜虫书虱进行生物测定,从5种杀虫剂对两种书虱的LC50可以看出,嗜卷书虱对两种拟除虫菊酯类药剂较嗜虫书虱敏感,嗜虫书虱对丁硫克百威较为敏感,而对有机磷类药剂的作用两种书虱的敏感性相似.两种书虱体内酸性磷酸酯酶(ACP)和碱性磷酸酯酶(ALP)的活力比较结果表明:嗜卷书虱和嗜虫书虱体内ACP的比活力为分别14μmol/mg·30 min和2.2 μmol/mg·30 min,ALP的比活力分别为0.092μmol/mg·30 min和0.046μmol/mg·30 min.经方差分析,两种书虱ACP和ALP的比活力之间均存在显著性差异(p<0.05).动力学参数比较结果显示,两种书虱ACP的Vmax值之间的差异达到显著水平,而ALP的Km值之间存在显著性差异.离体试验结果表明,5种药剂对磷酸酯酶的作用各不相同,个别药剂在低浓度下表现诱导作用,说明磷酸酯酶在不同外源毒物的解毒代谢过程中所起的作用有所不同.     

Interaction between optical isomerism and plant pharmacological action,change of modes of action and chirality of 1-(α-methylbenzyl)-3-p-tolylurea

The optical isomers, (R)-1(α-methylbenzyl)-3-p-tolylurea ((R)-MBU) and (S)-1-(α-methylbenzyl)-3-p-tolylurea ((S)MBU), which are analogues of daimuron [1-(α,α-dimethylbenzyl)-3-p-tolylurea], a herbicide for Cyperaceae weeds and a safener for paddy rice, exhibited different biological responses. These two physiological properties of daimuron were observed separately in (R)-MBU and (S)-MBU. Only (R)-MBU had herbicidal activity against Cyperaceae weeds, while the (S)-isomer was a more effective safener against bensulfuron-methyl (BSM) injury of rice seedlings than was (R)-MBU. (S)-MBU promoted root growth of rice seedlings, but the (R)-enantiomer inhibited root growth. (S)-MBU was a more potent inhibitor than (R)-MBU on PS II reaction of spinach broken chloroplasts. Furthermore, (S)-MBU and (R)-MBU showed cross intergenus selective phytotoxicity among the Gramineae plants, Oryza sativa L. (rice, cv. Tsukinohikari, japonica), Triticum aestivum L. (wheat, cv. Norin No. 61) and Echinochloa crusgalli var. frumentacea Wight, on root growth inhibition in the dark.