Biological Mode of Action of the Fungicide, Flusulfamide, Against Plasmodiophora brassicae (clubroot)

Flusulfamide (2, 4-dichloro-,,-trifluoro-4-nitro-m-toluenesulfonanilide) was investigated for its mode of action against Plasmodiophora brassicae Woronin. Seedlings of Chinese cabbage (Brassica rapa L. subsp. pekinensis) were grown for 14 and 21 days in soil infested with P. brassicae and then transplanted into soil containing flusulfamide (0.9µg a.i.g^–1 dry soil). Clubroot was not suppressed by this treatment, indicating that the fungicide is ineffective against P. brassicae established within cortical cells of the host root. Where seedlings were grown in soil infested with resting spores which had previously been treated with flusulfamide, root-hair infection and club formation were suppressed. This indicates that flusulfamide directly acts against resting spores. When placed in root exudates of Chinese cabbage, untreated resting spores germinated at a high frequency while flusulfamide-treated resting spores hardly germinated at all. Use of the Evan's blue staining assay indicated that flusulfamide-treated resting spores remained viable. Flusulfamide was detected by high performance liquid chromatography on resting spores treated with flusulfamide for 30min. This indicates that the chemical is adsorbed onto resting spores. These results suggest that flusulfamide suppresses clubroot disease by inhibiting germination of P. brassicae resting spores through adsorption onto their cell walls.     

Pyrethroid resistance monitoring in European populations of pollen beetle (Meligethes spp.): a coordinated approach through the Insecticide Resistance Action Committee (IRAC)

BACKGROUND: Pollen beetle (Meligethes spp.) is a major pest of European oilseed rape crops. Its resistance to pyrethroid insecticides has been recorded in samples of beetles collected in Europe since at least 1999, and problems with the control of the beetle in the field have been widely reported. In 2007, a Pollen Beetle Working Group was formed through the Insecticide Resistance Action Committee (IRAC) in order to coordinate efforts for surveying pyrethroid resistance development. RESULTS: The results of the first 3 years of the pollen beetle pyrethroid susceptibility survey using a laboratory test are presented in this paper. Resistant beetle samples were collected from 20 of the 21 countries surveyed, with a general trend of increasing frequency and spread of resistant samples in European oilseed‐rape‐growing regions. CONCLUSION: Pyrethroid‐resistant beetles dominate in Western and Central Europe and are becoming established in the North and East, the main oilseed‐rape‐growing areas of Europe. The development and spread of pyrethroid‐resistant pollen beetles highlights the need for effective management strategies for oilseed rape insect pests. Copyright © 2011 Society of Chemical Industry     

杀菌剂抗性监测研究进展

使用现代选择性杀菌剂防治植物病害是保证农作物高产、稳产的重要措施之一,但是现代杀菌剂很容易出现抗性而导致化学防治失败．使农业生产蒙受巨大损失。本文从杀菌剂的抗性检测和治理技术等方面概述杀菌剂的抗性研究进展。     

杀菌剂抗性分子检测技术的研究进展

靶标病菌基因突变是许多内吸性杀菌剂出现抗性的根本原因,检测与抗药性相关的靶标病菌基因突变对阐明抗药性发生的分子生物学机制及进行早期诊断具有重要意义。目前已成功用于检测靶标病菌抗药性菌株的分子检测技术有6种:等位基因特异性扩增、限制性片段长度多态性、等位基因特异性寡核苷酸杂交、单链构象多态性、实时定量PCR、变性高效液相色谱分析。这些技术能够快速、灵敏地检测田间早期出现的抗药性或抗药性种群的发展动态,在病害的可持续管理系统中科学使用杀菌剂方面发挥着重要作用。     

Genetic Control of Resistance to the Piperidine Fungicide Piperalin in Ustilago maydis

Mutants of Ustilago maydis resistant to the piperidine fungicide piperalin were isolated in a mutation frequency of 2.4 × 10^–5 after UV-irradiation and selection on media containing 50gml^–1 piperalin. Genetic analysis with 15 such mutant isolates resulted in the identifications of two unlinked chromosomal loci, the U/ppl-1 locus with two allelic genes (U/ppl-1A and U/ppl-1B) and the U/ppl-2 locus. The U/ppl-2 and U/ppl-1A mutations are responsible for two levels of moderate and high resistance to piperalin (resistance factor, Rf: 54 and 135, respectively, based on effective concentration causing a 50% reduction in the growth rate, EC₅₀), while the U/ppl-1B mutation gives only a small reduction (approximately 8-fold) in piperalin sensitivity. Cross-resistance studies with other SBIs shows that the major gene (U/ppl-2 and U/ppl-1A) mutants are resistant to fenpropidin (Rf: 43 and 68), fenpropimorph (Rf: 261 and 283) and tridemorph (Rf: 9 and 10), but not to the inhibitors of C-14 demethylase (DMIs) and squalene epoxidase. The minor gene mutation U/ppl-1B codes a low-level of resistance (approximately 5—12-fold) to the above morpholine-type fungicides, but in contrast with the major gene mutations it increases 2–10 times the sensitivity to triazoles: triadimefon, triadimenol, propiconazole and flusilazole. Crosses between mutants carrying the U/ppl-genes with compatible isolates carrying the U/fpd, U/fpm or U/tdm mutations, which have been identified in previous genetic works for resistance to morpholine-type fungicides, yielded, with the exception of U/ppl-2 ×U/fpm-2 cross, a large number of recombinants with wild-type sensitivity, indicating that the mutant genes involved in these crosses, were not allelic. An additive gene effect was observed only between nonallelic minor genes U/ppl-1B and U/fpm-1B or U/tdm-1,2. Studies of the fitness of piperalin-resistant isolates showed that the reduced sensitivity of major gene mutants was not associated with changes on the phytopathogenic fitness determining characteristics, such as growth in liquid culture and pathogenicity on young corn plants. Conversely, the minor gene mutation U/ppl-1B appeared to be pleiotropic, having significantly adverse effects on the phytopathogenic fitness.     

The Abrasive Action of a Copper-based Fungicide on Four Different Nozzle Tips

Abstract

The abrasive action of a copper fungicide on four nozzles commonly used in Nigeria when spraying cocoa for black pod control was evaluated. The spray solution flocculated and the nozzles frequently blocked indicating the need for an efficient filter. The single hollow cone type nozzle and the variable spray nozzle were the most highly abraded.     

多杀菌素的作用机理及其抗药性的研究进展

多杀菌素是一类新的杀虫剂,具有高效、低毒、选择性强、对环境安全的特点。其作用机制是通过激活烟碱型乙酰胆碱受体(nAChR),使正常昆虫神经细胞去极化,也可通过抑制γ-氨基丁酸受体(GABAR)使神经细胞超极化。本文综述了多杀菌素作用机理及其抗药性的研究进展。     

多杀菌素的作用机理及其执药性的研究进展

多杀菌素是一类新的杀虫剂,具有高效、低毒、选择性强、对环境安全的特点.其作用机制是通过激活烟碱型乙酰胆碱受体(nAChR),使正常昆虫神经细胞去极化,也可通过抑制γ-氨基丁酸受体(GABAR)使神经细胞超极化.本文综述了多杀菌素作用机理及其抗药性的研究进展.     

杀菌剂银泰防治小麦纹枯病研究

采用室内离体平皿法和田间小区试验测定了植物源农用杀菌剂银泰 (有效成分 :4 -丁酰基苯酚 )对小麦纹枯病菌 Rhizoctonia cerealis生长的抑制作用和对该病害的防治效果。结果表明 ,20%银泰乳油在 0～ 100μg/mL范围内随着浓度提高对小麦纹枯病菌的抑制作用增强 ,其 EC50 和 EC95分别为 36.11和 97.66μg/L;EC95明显小于对照药剂井冈霉素的检测数值 (327.6 4μg/L )。20%银泰乳油 200、400和 800mg/L防治小麦纹枯病的效果分别为 85.8%、89.3%和 92.3% ,与对照药剂甲基硫菌灵 400mg/L的防效 (87.0% )相当。     

Fungicide resistance inBotrytis cinerea isolates from strawberry crops in Huelva (southwestern Spain)

The severity of disease caused byBotrytis cinerea in strawberries is very high and chemical control is common practice; low residue levels of chemical products are required. Thus, it is important to be aware of the development of fungicide resistance in order to choose the best strategies of chemical control. In the present study we evaluated the response of 36B. cinerea isolates against eight different fungicides. The isolates were sampled twice, at the beginning and the end of the season, in 11 commercial strawberry fields located in the area of Huelva (Spain). In addition, two reference isolates, SAS56 and SAS405, were evaluated. The proportion of isolates resistant to benomyl was very high (86%). Resistance to dicarboximides was detected in 44% of the isolates and resistance to pyrimethanil in 25% of the isolates. Different degrees of sensitivity to captan and dichlofluanid were recorded. No resistance was found to diethofencarb plus carbendazim. http://www.phytoparasitica.org posting Sept. 18, 2002.     

利用微生物杀菌剂防治马铃薯黄萎病

马铃薯黄萎病是一种重要的世界性土传兼种传维管束病害,危害大且防治困难。利用活体微生物杀菌剂是防治作物土传病害的有效措施之一。本研究通过盆栽试验评价了微生物杀菌剂枯草芽胞杆菌可湿性粉剂对马铃薯出苗和生长的安全性,在河北省马铃薯主产区开展田间小区试验,研究了该制剂有效防治马铃薯黄萎病的使用方法和适宜施用剂量,并在河北省涞源县、围场县和永年区3县区分别开展了田间示范应用。盆栽试验和田间试验结果表明,枯草芽胞杆菌可湿性粉剂15、30和45 kg/hm²拌种处理对马铃薯出苗安全,对马铃薯生长没有不良影响;田间小区试验表明,在围场县试验田中,该制剂30 kg/hm²拌种处理单独使用或30 kg/hm²拌种加15 kg/hm²初花期滴灌使用均能显著减轻马铃薯黄萎病的发生,分别增产15.53%和17.10%;在新乐市试验田,枯草芽胞杆菌可湿性粉剂30 kg/hm²拌种处理显著增加马铃薯产量16.38%。田间示范应用结果表明,枯草芽胞杆菌可湿性粉剂30 kg/hm²拌种处理在涞源县和围场县防治马铃薯黄萎病效果显著,防效分别为84.22%和72.93%,两地分别显著增产24.30%和9.27%;在邯郸市永年区,相比化学药剂对照处理,枯草芽胞杆菌可湿性粉剂30 kg/hm²拌种处理显著增加马铃薯产量19.73%。本研究表明,枯草芽胞杆菌可湿性粉剂对马铃薯黄萎病具有显著的防治效果和显著的增产效果,为该制剂在马铃薯生产中高效应用提供了科学依据。     

Selection for Fungicide Resistance Within a Growing Season in Field Populations of Phytophthora infestans at the Center of Origin

ABSTRACT The central highlands of Mexico should provide an optimal testing ground for evaluating the potential threat of selection for resistance to fungicides in the population of Phytophthora infestans. We evaluated the hypotheses that exposure to the fungicides azoxystrobin, cymoxanil, dimethomorph, fluazinam, mancozeb, metalaxyl, and propamocarb hydrochloride would lead to (i) a shift in the sensitivity distributions (i.e., selection) and (ii) a lower genotypic diversity of the population. We compared populations from unsprayed plots with populations that had been exposed to several applications of each of the fungicides within a single field season. This study provides novel baseline data and shows that the Toluca valley P. infestans population has a wide range of sensitivities to the fungicides fluazinam, cymoxanil, dimethomorph, metalaxyl, and propamocarb. Directional selection toward resistance combined with a reduction in genetic diversity of the P. infestans population was observed only for the fungicide metalaxyl. The results obtained provide direct experimental support for continuing vigilance regarding further introductions of exotic strains of P. infestans into the United States.     

The Relationship Between Pathogen-induced Systemic Resistance (ISR) and Multigenic (horizontal) Resistance in Plants

Plants have developed mechanisms to successfully co-exist in the presence of pathogenic organisms. Some interactions between plants and pathogens are based on recognition of specific elicitor molecules from avirulent pathogen races (avr gene products), which is described in the gene-for-gene resistance theory. Another type of resistance, multigenic (horizontal) resistance, is a less well-studied phenomenon that depends upon multiple genes in the plant host. All plants possess resistance mechamisms which can be induced upon pre-treatment of plants with a variety of organisms or compounds. This general phenomenon is known as induced systemic resistance (ISR). At least in some plant species, ISR depends on the timely accumulation of multiple gene products, such as hydrolytic enzymes, peroxidases or other gene products related to plant defences. The pre-treatment of plants with an inducing organism or compound appears to incite the plant to mount an effective defense response upon subsequent encounters with pathogens, converting what would have been a compatible interaction to an incompatible one. Our studies in three plant–pathogen systems clearly document that multigenic-resistant plants constitutively express specific isozymes of hydrolytic enzymes that release cell wall elicitors, which in turn may activate other defense mechanisms. ISR induces constitutive accumulation of these and other gene products prior to challenge. ISR is known to function against multiple organisms, and there is no specificity observed in the accumulation patterns of defense-related gene products when ISR is induced. It is therefore hypothesized that the constitutive accumulation of specific isozymes of hydrolytic enzymes, or other defense related gene products, is an integral part of both multigenic resistance and the phenomenon of ISR. Further, plants in which ISR has been activated appear to move from a latent resistance state to one in which a multigenic, non-specific form of resistance is active.     

Inhibition of Methionine Biosynthesis in Botrytis cinerea by the Anilinopyrimidine Fungicide Pyrimethanil

When mycelium of Botrytis cinerea was treated with low concentrations of the anilinopyrimidine fungicide pyrimethanil the total amount of free amino acids increased. Qualitative variations were also induced: alanine, glutamine, lysine, glycine, histidine, asparagine, arginine, threonine and moreover, α-aminobutyrate and β-alanine were accumulated; cyst(e)ine, valine, leucine and citrulline were reduced. When mycelium of B. cinerea was incubated with Na₂[³⁵S]O₄, pyrimethanil at 1·5 μM induced a decrease of [³⁵S]methionine and simultaneously an increase of [³⁵S]cystathionine. These data indicate that the anilinopyrimidine fungicide pyrimethanil inhibits the biosynthesis of methionine and suggest that the primary target could be the cystathionine β-lyase. © 1997 SCI.     

Resistance Risk Assessment of Cereal Eyespot, Tapesia Yallundae and Tapesia Acuformis, to the Anilinopyrimidine Fungicide, Cyprodinil

Eyespot pathogens, Tapesia yallundae and Tapesia acuformis, were isolated from two trial sites in the UK over several years. Both sites were treated with 2 applications per year of cyprodinil (a new anilinopyrimidine fungicide), prochloraz and a mixture of cyprodinil with prochloraz. One trial site was exposed to cyprodinil for 3 years, and the second for a total of 11 years, including 5 years before the trial was initiated. Control of eyespot and sensitivity to cyprodinil were monitored. During the first 3 years of the trial, disease control with all fungicide treatments ranged from 43% to 82%. At the site, where the trial was extended for a further 3 years, control then began to decline but no practical resistance was detected. The decline in control by both fungicides suggests that factors other than reduced sensitivity might be involved. Field isolates of both T. yallundae and T. acuformis with reduced sensitivity to cyprodinil were found predominantly in plots treated with cyprodinil. A reduction in sensitivity to cyprodinil was identified in the population from cyprodinil-treated plots in two years out of six, and in the population from mixture plots in the final year. No obvious trends could be identified and in-vivo studies showed control of most isolates with reduced sensitivity could be regained by increasing the dose to one tenth of the recommended field rate. Analysis of progeny from sexual crosses involving a sensitive isolate and a field isolate with an ED₅₀ value higher than the baseline sensitivity range indicated that a single gene controlled the reduction in sensitivity to cyprodinil in one T. yallundae isolate. There is clearly a resistance risk in eyespot to cyprodinil. The reduction in sensitivity is monogenic in inheritance and at a significant level in some isolates, but any shift in sensitivity in field populations has so far been gradual.