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1.
Accumulation of [14C] fenarimol by mycelium ofPenicillium italicum was studied with isolates having varying levels of laboratory resistance to fenarimol. All resistant isolates tested showed a significantly lower accumulation than the wild-type isolate.Various metabolic inhibitors enhanced accumulation to relatively high levels in both wildtype and resistant isolates. it indicates that accumulation is governed by two processes viz. a non-mediated influx and an energy-dependent efflux. A relatively high fenarimol efflux in resistant isolates probably accounts for low accumulation and for fenarimol resistance. One of the inhibitors which annihilated fenarimol efflux and enhanced fenarimol accumulation was sodium orthovanadate. The synergistic action of fenarimol and orthovanadate to both wildtype and resistant isolates in crossed-paper strip bioassays is probably related to the effect of the latter compound on fenarimol accumulation. Synergistic action between the chemicals in control ofPenicillium decay of oranges could not be detected.Samenvatting De accumulatie van [14C]fenarimol door mycelium vanPenicillium italicum werd bestudeerd bij isolaten met een uiteenlopende graad van laboratorium-resistentie tegen fenarimol. Alle getoetste resistente isolaten vertoonden een lagere opname dan de wild-stam.Verschillende antimetabolieten verhoogden de accumulatie tot relatief hoge waarden die voor gevoelige en resistente isolaten ongeveer gelijk waren. Deze waarneming duidt erop dat accumulatie wordt bepaald door twee processen: nonmediated influx en energie-afhankelijke efflux. Een hogere fenarimol efflux in resistente isolaten vormt waarschijnlijk de verklaring voor de lagere accumulatie en voor het resistentiemechanisme. Een van de remmers die de fenarimolefflux te niet doet, en de accumulatie van fenarimol verhoogt, is natriumorthovanadaat. De synergistische werking van fenarimol en orthovanadaat tegen zowel wild-type als resistente isolaten in crossed-paper strip biotoetsen houdt waarschijnlijk verband met het effect van laatstgenoemde stof op de accumulatie van fenarimol. Synergistische werking van deze verbindingen bij de bestrijding vanPenicillium-rot op sinaasappels werd niet waargenomen.  相似文献   

2.
Imazalil differentially inhibited dry weight increase of 10-hour-old germlings of wild-type and DMI-resistant isolates ofPenicillium italicum in liquid malt cultures. EC50 values ranged from 0.005 to 0.27 μg ml?1. In all isolates ergosterol constituted the major sterol (over 95% of total sterols) in the absence of the fungicide. Therefore, DMI-resistance cannot be associated to a deficiency of the C-14 demethylation enzyme in the ergosterol biosynthetic pathway. Imazalil treatment at concentrations around EC50 values for inhibition of mycelial growth resulted in a decrease in ergosterol content and a simultaneous increase in 24-methylene-24,25-dihydrolanosterol content in all isolates. A correlation existed between the imazalil concentration necessary to induce such changes in sterol composition and the EC50 values for inhibition of mycelial growth of the different isolates. The reason for the differential effects of imazalil on sterol composition in the variousP. italicum isolates may be due to decreased accumulation of the fungicide in the mycelium and to other yet non-identified mechanisms of resistance.  相似文献   

3.
Imazalil differentially inhibited dry weight increase of 10-hour-old germlings of wild-type and DMI-resistant isolates ofPenicillium italicum in liquid malt cultures. EC50 values ranged from 0.005 to 0.27 g ml–1. In all isolates ergosterol constituted the major sterol (over 95% of total sterols) in the absence of the fungicide. Therefore, DMI-resistance cannot be associated to a deficiency of the C-14 demethylation enzyme in the ergosterol biosynthetic pathway. Imazalil treatment at concentrations around EC50 values for inhibition of mycelial growth resulted in a decrease in ergosterol content and a simultaneous increase in 24-methylene-24,25-dihydrolanosterol content in all isolates. A correlation existed between the imazalil concentration necessary to induce such changes in sterol composition and the EC50 values for inhibition of mycelial growth of the different isolates. The reason for the differential effects of imazalil on sterol composition in the variousP. italicum isolates may be due to decreased accumulation of the fungicide in the mycelium and to other yet non-identified mechanisms of resistance.Imazalil remt differentieel de toename in drooggewicht van 10-uur-oude gekiemde sporen van wild-type en DMI-resistente isolaten vanPenicillium italicum in vloeistofcultures van moutextract. De EC50 waarden voor groei van de verschillende isolaten lopen uiteen van 0,005 tot 0,27 g ml–1. In afwezigheid van het fungicide is in alle isolaten ergosterol het belangrijkste sterol (meer dan 95% van het totaal). DMI-resistentie kan daarom niet in verband staan met deficiëntie van het C-14 demethyleringsenzym in de ergosterol biosynthese. Imazalilbehandeling van mycelium bij concentraties rond de EC50 waarde voor groeiremming, resulteerde bij alle isolaten in een afname van het ergosterolgehalte en een gelijktijdige toename van het gehalte aan 24-methyleen-24,25-dihydrolanosterol. Er bestaat dus een nauwe correlatie tussen de imazalilconcentratie die noodzakelijk is om vergelijkbare veranderingen in sterolsamenstelling te induceren en de EC50 waarde voor remming van myceliumgroei van de verschillende isolaten. De differentiële effecten van imazalil op de sterolsamenstelling van de verschillendeP. italicum isolaten kunnen worden veroorzaakt door verminderde accumulatie van het fungicide in het mycelium en door andere, nog niet geïdentificeerde resistentiemechanismen.  相似文献   

4.
Metabolism of imazalil (1-[2-(2,4-dichlorophenyl)-2-(2-propenyloxy)ethyl]-1H-imidazole) inPenicillium italicum isolates with a wild-type sensitivity and with various degrees of resistance to sterol demethylation inhibitors was studied in liquid cultures. The metabolite 1-[2(2,4-dichlorophenyl)-2-(2,3-dihydroxypropyloxy)ethyl]-1H-imidazole (R42243) was detected in the culture filtrate after prolonged incubation. The metabolism occurred in the propenyl side chain of imazalil probably through epoxidation and hydratation. This is the first report of such a conversion of imazalil in fungi. R42243 was much less toxic toP. italicum than imazalil. Therefore, the metabolism can be regarded as a detoxification step. Both wild-type and resistant isolates metabolized imazalil, but metabolism by resistant isolates was faster than by the wild-type isolate. This is probably caused by a relatively strong inhibition of growth of the wild-type isolate by the fungicide. Results indicate that the detoxification of imazalil does not operate as a mechanism of resistance. This conclusion was confirmed by the fact that resistant isolates showed cross-resistance to miconazole and R42243, which had a similar structure as imazalil except for the propenyl side chain.  相似文献   

5.
Isolates ofPenicillium italicum with differential levels of resistance to imazalil were obtained via step-wise mass selection of conidia of the fenarimol-resistant isolate E300-3 on imazalilamended PDA. Three out of five selection steps were successful. The resistance level to imazalil of isolates acquired after the two last selection steps was on average 122 and 197. The differential level of resistance was also apparent in decay control on oranges by imazalil inoculated with the various isolates. The isolates showed a similar cross-resistance pattern to other fungicides which inhibit C-14 demethylation of sterols (DMIs), although the level of resistance to these fungicides was significantly higher. All isolates displayed negatively-correlated cross-resistance to tridemorph and dodine. Most isolates had a normal virulence on oranges. In competition experiments with mixed-inocula of the wild-type and a resistant isolate, the proportion of the wild-type increased in successive generations on untreated oranges and the proportion of the resistant isolate increased on imazalil-treated oranges. The lower competitive ability of the resistant isolate on untreated oranges may be due to a decrease in spore production as compared with the wild-type.Since isolate E300-3 was obtained in two selection steps on fenarimol-amended PDA, the isolates obtained in the last selection steps on imazalil-amended PDA may have at least five different genes for resistance to DMIs. This is consistent with resistance to DMIs being under polygenic control, with the genes involved having an additive interaction, although this is not the only possible explanation of the results.  相似文献   

6.
Imazalil had no effect on the initial growth of mycelia of Penicillium italicum (for 10 hr) or Aspergillus nidulans (for 2 hr). In P. italicum during this period neither respiration nor cell permeability was affected, but uptake of [32P]phosphate, [14C]leucine, or [14C]uridine was partially inhibited. The initial (5 hr) inhibition of substrate uptake coincided with a 50% reduction in ergosterol content. Within 0.5 hr, incorporation of [14C]acetate into C-4-desmethyl sterols was strongly inhibited in mycelia of A. nidulans treated with 0.5 μg/ml of imazalil. However, radioactivity in C-4-methyl and dimethyl sterols exceeded that of control cultures. Concentrations of imazalil as low as 0.005 μg/ml caused short-term (1 hr) declines of incorporation into desmethyl sterols and increases into the C-4-methyl and dimethyl sterols. Incorporation into phospholipids, triglycerides, and free fatty acids was not affected. These data suggest that the primary antifungal action of imazalil is inhibition of demethylation in the biosynthesis of ergosterol.  相似文献   

7.
Laboratory isolates ofPenicillium italicum with varying levels of resistance to fenarimol were obtained via mass selection of conidia on fenarimol-amended PDA. All fenarimol-resistant isolates showed cross-resistance to other fungicides which inhibit ergosterol biosynthesis (bitertanol, etaconazole, fenapanil, and imazalil), but not to fenpropimorph. In contrast, all isolates with a relatively high degree of resistance to fenarimol, exhibited increased sensitivity to fenpropimorph (negatively correlated cross-resistance). The varying degrees of resistance to ergosterol biosynthesis inhibitors (EBI's) suggest that different mutations for resistance are involved. Isolates with a high degree of resistance were selected from conidial populations of isolates with a low resistance level. This indicates that in sich strains different mutations for resistance are present simultaneously.Somein vitro growth parameters of resistant isolates slightly differed from those of the wild type. Virulence of most resistant isolates on oranges was visually normal and in competition experiments with mixed inocula of wild-type and resistant isolates, the latter could still be isolated after five successive infection cycles on fungicide-free oranges. Nevertheless, the proportion of resistant conidia in the successive inocula gradually decreased.Decay of oranges inoculated with EBI-resistant isolates could still be controlled by a curative dip treatment with imazalil at dosage rates recommended in practice (500 g ml–1). However, with the highly resistant isolates, decay control was not complete at half this dosage, indicating only a marginal control at the full dosage rate.On the basis of the results described it is assumed that at a high selection pressure of EBI's in practice, gradual accumulation of different mutations for resistance, together with selection of normal fitness may eventually lead to loss of control ofPenicillium decay. Therefore, desease control strategies with a low selection pressure of EBI's are advisable.Samenvatting Laboratoriumisolaten vanPenicillium italicum met uiteenlopende resistentieniveau's tegen fenarimol werden verkregen door massaselectie van conidiën op fenarimolbevattende PDA. Alle fenarimol-resistente isolaten vertoonden kruisresistentie tegen andere fungiciden die de ergosterolbiosynthese remmen (bitertanol, etaconazool, fenapanil, imazalil), maar niet tegen fenpropimorf. Alle isolaten met een relatief hoge graad van fenarimolresistentie waren zelfs gevoeliger voor dit laatste fungicide (negatief gecorreleerde kruisresistentie). De uiteenlopende graden van resistentie tegen ergosterolbiosynthese remmers (EBI's) suggereren dat verschillende mutaties een rol kunnen spelen. Isolaten met een hoge resistentiegraad werden geselecteerd in conidiënpopulaties van isolaten met een lage resistentiegraad. Dit duidt erop dat in dergelijke stammen verschillende mutaties gelijktijdig aanwezig zijn.Er werden kleine verschillen in parameters voorin vitro groei tussen resistente en gevoelige isolaten geconstateerd. De virulentie van vrijwel alle stammen op sinaasappels was normaal; in competitie-experimenten met mengpopulaties van gevoelige en resistente isolaten konden laatstgenoemde isolaten nog na vijf oppenvolgende infectiecycli op fungicide-vrije sinaasappels worden geïsoleerd. Desalniettemin nam het percentage resistente conidiën in de opeenvolgende inocula geleidelijk af. Penicillium-rot op sinaasappel, geïnoculeerd met EBI-resistente isolaten, kon nog worden bestreden door een curatieve dompelbehandeling met imazalil bij een dosering die in de praktijk wordt aanbevolen (500 g ml–1). Bij een halvering van deze dosering werd echter op sinaasappels, geïnoculeerd met de hoog-resistente isolaten nog rot waargenomen, hetgeen erop duidt dat de bestrijding bij de volle dosering slechts marginaal is.Op grond van de beschreven resultaten kan worden verondersteld dat in de praktijk onder hoge selectiedruk van EBI's een geleidelijke accumulatie van verschillende mutaties, gepaard gaande met selectie van een normale fitheid, kan plaatsvinden, hetgeen uiteindelijk zou kunnen leiden tot onvoldoende bestrijding vanPenicillium-rot. Bestrijdingsstrategieën met een lage selectiedruk van EBI's zijn daarom wenselijk.  相似文献   

8.
The selective fungitoxic actions of prochloraz (an imidazole) and a triazole fungicide, quinconazole (3-(2,4-dichlorophenyl)-2-(1 H- 1,2,4-triazol-1-yl)- 4(3H)-quinazolinone: II ), were studied with selected phytopathogenic fungi. With the exception of Ustilago maydis, all the fungi tested were more sensitive to prochloraz than to II. A number of DMI-resistant mutants of Penicillium digitatum and P. italicum showed positive cross-resistance to both DMIs, but except for P. italicum isolate H17, the levels of resistance to II were much higher than to prochloraz. The generally higher toxicity of prochloraz to the fungi investigated, as compared to II , could not be ascribed to the slightly higher accumulation of prochloraz. With regard to prochloraz, there was no general correlation between the sensitivity of the fungi tested and the amount of fungicide accumulated. A similar situation was evident for II. However, the DMI-resistant mutants of P. italicum did show a reduced accumulation of both azoles, which may account for a low level of acquired DMI-resistance in this fungus. Since accumulation levels of the test compounds in the isolates with different degrees of resistance were the same, additional mechanisms of resistance may be involved in isolates with relatively high degrees of DMI-resistance. No detectable amounts of fungicide metabolites were found in most fungi tested over a 16-hour incubation period. Therefore, fungal metabolism is not generally responsible for the differences in sensitivity between fungi to each azole tested. It also does not generally explain the differential toxicities of prochloraz and II to each individual species. The exception to this was Rhizoctonia solani which metabolized prochloraz to a non-fungitoxic compound. This correlated with its low prochloraz sensitivity.  相似文献   

9.
Uptake of [14C]fenarimol (30 μM) by mycelium of wild-type Aspergillus nidulans was characterized by a rapid initial accumulation during the first 10 min of incubation with the fungicide and a subsequent gradual release with time. Uptake appeared to be the result of influx and efflux. Influx of fenarimol could not be inhibited by low temperature, anaerobiosis, starvation of mycelium, or incubation with several respiratory inhibitors and is, therefore, a passive process. Under identical test conditions efflux activity was severely inhibited and should, therefore, be regarded as an energy-dependent mechanism. After prolonged incubation (90 min) an equilibrium between influx and efflux was established, resulting in an energy-dependent permeability barrier, since uptake could instantaneously be enhanced by addition of oligomycin or N,N′-dicyclohexylcarbodiimide. It also indicates that efflux activity is inducible; this hypothesis is supported by the observation that pretreatment of mycelium with unlabeled fungicide prevented subsequent uptake of [14C]fenarimol. Uptake by fenarimol-resistant mutants J146, M193, and R264 of A. nidulans, all possessing the imaB gene for resistance, was relatively low and almost constant in time. In this case, uptake appeared to be considerably enhanced by low temperature, anaerobiosis, starvation of mycelium, and incubation with respiratory inhibitors. Low uptake by these mutants is ascribed to a higher energy-dependent efflux activity for fenarimol compared with the wild-type strain. Upon inhibition of the barrier activity, net uptake resulted from remaining passive influx, which in that case may be as high as in the wild-type strain. The results suggest that both wild-type and fenarimol-resistant mutants possess an energy-dependent efflux mechanism with different efficiencies to excrete fenarimol and probably other chemicals to which cross-resistance or collateral sensitivity is present.  相似文献   

10.
Fenarimol-resistant laboratory isolates of Penicillium italicum exhibit a high degree of cross-resistance to triazoles, a low degree of cross-resistance to imazalil and a low degree of negatively-correlated cross-resistance to morpholines. The cross-resistance to triazoles is ascribed to a differential accumulation level of these SBI fungicides in wild-type and fenarimol-resistant isolates. As in the case of fenarimol, the relatively low accumulation level of triazoles in resistant isolates is probably caused by the operation of a constitutive, energy-dependent efflux from mycelium, which hinders the triazoles from reaching their site of action in sterol biosynthesis. The accumulation level of imazalil and morpholines did not differ among wild-type and fenarimol-resistant isolates. This may be related to the fact that these fungicides at physiological pHs occur in a protonated form. The lack of a differential accumulation level can be the reason for the deviating cross-resistance patterns of these fungicides.  相似文献   

11.
Mycelial uptake of [14C]fenarimol (10 μg/ml) by 20 fenarimol-resistant mutants of Aspergillus nidulans was compared with uptake by wild-type strain 003. Uptake of the fungicide during the initial 10 min of incubation was significantly lower in all mutant strains than in the wild-type strain indicating that resistance is related with reduced uptake. Upon prolonged incubation a gradual decrease of accumulated radioactivity in the wild-type strain was observed. A few mutants displayed resistance to unrelated chemicals such as p-fluorophenylalanine or d-serine; this phenomenon appeared not to be due to a decreased uptake of the corresponding natural amino acids. Incorporation of [3H]adenine and [14C]leucine by mycelium of mutant M193 was hardly inhibited after 5 hr of incubation with the fungicide, whereas a distinct effect was found with the wild-type strain. At this time also fungitoxicity to the wild-type strain became apparent. Probably, this effect is indirectly caused by inhibition of ergosterol biosynthesis. Mycelium of mutant M193 incorporated [14C]acetate slightly less effectively than the wild-type strain. After 2 hr of incubation with this radiochemical leakage of [14C]acetate metabolites from mycelium of the mutant strain was observed. This indicates that resistance might be correlated with increased excretion of fungal metabolites, which in turn may be related with reduced fitness of fenarimol-resistant mutants.  相似文献   

12.
The ED50 values and resistance factors of 20 fungicides that all act as inhibitors of the C-14 demethylation of 24-methylenedihydrolanosterol were determined for one wild-type and four resistant strains of Ustilago avenae. All fungicides were cross-resistant to each other; however, the resistance factors varied considerably, ranging from 50 (triadimenol) to 2·2 (miconazole). A tentative structural requirement for low resistant factors was the presence of two phenyl rings separated from each other by at least three atoms. Labeling of lipids with [14C]acetate in the absence and presence of the inhibitors and subsequent sterol analysis revealed that the variable resistance factors were not related to the presence of a second target site. In spite of reported second modes of action of fenarimol, tebuconazole or miconazole, accumulation of C-14 sterol precursors in both sensitive and resistant isolates was necessary to accomplish growth inhibition.  相似文献   

13.
The majority of fenarimol-resistant laboratory isolates ofAspergillus nidulans, Cladosporium cucumerinum, Penicillium expansum, P. italicum, andUstilago maydis testedin vitro, displayed a moderate degree of negatively correlated cross-resistance to dodine. A limited number of isolates also possessed an increased sensitivity to guazatine. Colonies of fenarimol-resistant isolates ofA. nidulans with increased sensitivity to dodine showed sector formation on dodine-amended agar. Subcultures from these sectors appeared to have the wild-type sensitivity to dodine and fenarimol. The results indicate that fenarimol resistance and increased sensitivity to dodine are closely linked. The potential practical significance of the results is discussed.  相似文献   

14.
Fenarimol-resistant isolates ofPenicillium italicum with cross-resistance to imidazole and triazole fungicides which inhibit ergosterol biosynthesis were tested for their sensitivity to fenpropimorph. Radial growth tests on PDA showed that the isolates (n=6) lacked cross-resistance to fenpropimorph or displayed enhanced sensitivity to the fungicide (negatively correlated cross-resistance). Control of blue mold decay of oranges incited by the wild-type isolate could be achieved by dipping fruits in suspensions of fenpropimorph at a concentration of 100 mg ml–1. Decay of oranges incited by the fenarimol-resistant isolates was controlled at the same or at a lower concentration (30 mg ml–1), thus showing that the normal or increased sensitivity to fenpropimorph is also expressed under in vivo conditions.Samenvatting Fenarimol-resistente isolaten vanPenicillium italicum met kruisresistentie tegen imidazool-en triazoolfungiciden die de ergosterolbiosynthese remmen, werden getoetst op hun gevoeligheid voor fenpropimorf. Radiale groeiproeven op PDA toonden aan dat de isolaten (n=6) geen kruisresistentie bezaten met fenpropimorf of een verhoogde gevoeligheid voor het middel vertoonden (negatief gecorreleerde kruisresistentie). Op sinaasappels konPenicillium-rot, veroorzaakt door het wild-type bestreden worden door middel van een dompelbehandeling met fenpropimorf bij een dosering van 100 g ml–1). Bestrijding van rot veroorzaakt door fenarimil-resistente isolaten werd verkregen bij dezelfde of een lagere dosering (30 g ml–1); aldus werd aangetoond dat de normale of verhoogde gevoeligheid voor fenpropimorf ook in vivo tot uiting komt.  相似文献   

15.
Venturia nashicola isolates with a high level of resistance to carbendazim showed either increased sensitivity or were resistant to theN-phenylformamidoxime compoundN-(3,5-dichloro-4-propynyloyphenyl)-N′-methoxyformamidine (DCPF). Isolates with an intermediate or low level of carbendazim resistance were resistant to DCPF. Increased sensitivity to DCPF was also associated with a high level of carbendazim resistance inBotrytis cinerea but not with a moderate resistance level. Increased sensitivity to DCPF was not observed in carbendazim resistant isolates ofGibberella fujikuroi.Binding of [14C]DCPF in cell-free mycelial extracts of the highly carbendazim-resistant and DCPF-sensitive isolate ofV. nashicola was higher than in those of DCPF-resistant isolates that were either highly-resistant, intermediately resistant, or weakly resistant to carbendazim or were sensitive to carbendazim. [14C]carbendazim binding in extracts of highly carbendazim-resistant isolates ofB. cinerea was lower than that in extracts of sensitive isolates, whereas [14C]DCFP binding was higher. A decreased [14C]carbendazim binding was also observed in extracts of carbendazim-resistant isolates ofG. fujikuroi, binding of [14C]DCPF, however, was similar in extracts of both carbendazim-resistant and sensitive isolates.  相似文献   

16.
An assay for measuring ergosterol synthesis in cell-free extracts of the filamentous plant pathogen Botrytis cinerea is described. The extracts capable of synthesizing C4-desmethyl sterols from [2- 14 C]mevalonate were derived by mechanical disruption of young conidial germlings in a Bead-Beater apparatus. The C4-desmethyl sterol fraction consisted of three distinct compounds and totalled 39% of the non-saponifiable lipids formed. Ergosterol accounted for 63% of the C4-desmethyl sterols. Only small amounts of C4-monomethyl sterols were synthesized, while C4, 4-dimethyl sterols made up 29% of the non-saponifiable lipids. The latter fraction mainly consisted of lanosterol (54%) and eburicol (28%). The cell-free system had a narrow pH optimum for synthesis of C4-desmethyl sterols of pH 7.3–7.4. Cell-free synthesis of C4-desmethyl sterols was inhibited by the imidazole fungicide imazalil, concomitant with an accumulation of eburicol. The IC50 value (concentration of fungicide which inhibited cell-free synthesis of C4-desmethyl sterols by 50%) was 9.1 × 10 ?9 M. These results are consistent with the hypothesis that imazalil is a potent inhibitor of the cytochrome P450-dependent sterol 14x-demethylase of B. cinerea. The method described may be used to screen compounds biochemically for inhibition of sterol synthesis in an agriculturally important plant pathogen.  相似文献   

17.
Several strains ofAspergillus nidulans, Cladosporium cucumerinum andPenicillium italicum with known resistance to ergosterol biosynthesis inhibitors were tested for resistance to three dicarboximides. Negligible levels of resistance to iprodione and vinclozolin were observed in one out of three strains ofA. nidulans. Two out of three strains ofC. cucumerinum displayed a low resistance to iprodione, and a high resistance to procymidone and vinclozolin. The latter strains were also moderately resistant to the isoflavonoid phytoalexins medicarpin and pisatin, but sensitive to the antibiotic pimaricin. All sixP. italicum strains examined displayed wild-type sensitivity to all three dicarboximides; the two of these tested in thin-layer chromatographic bioassays proved to be resistant to pimaricin.Iprodione and vinclozolin induced energy-dependent fenarimol efflux inA. nidulans. In line with this observation, in crossed-paper strip assays iprodione and fenarimol antagonized each other in their toxicity towardsA. nidulans; towardsC. cucumerinum, on the other hand, these fungicides behaved independently.The implications and practical consequences of the phenomena observed are briefly discussed.Samenvatting Verscheidene tegen ergosterolbiosyntheseremmers resistente stammen vanAspergillus nidulans, Cladosporium cucumerinum enPenicillium italicum werden getoetst op resistentie tegen dicarboximiden. Eén der drie onderzochte stammen vanA. nidulans bezat enige resistentie tegen iprodione en vinchlozoline. Twee van de drie onderzochte stammen vanC. cucumerinum vertoonden een lage graad van resistentie tegen iprodione en een zeer hoge tegen procymidone en vinchlozoline. Ze waren ook enigermate resistent tegen de fytoalexinen medicarpine en pisatine, maar gevoelig voor het antibioticum pimaricine. Alle onderzochte stammen vanP. italicum waren voor de drie getoetste dicarboximiden even gevoelig als het wild-type; voorzover onderzocht, bleken deze stammen resistent tegen pimaricine.Iprodione en, hoewel in mindere mate, vinchlozoline induceerden energieafhankelijke efflux van fenarimol inA. nidulans. In overeenstemming hiermee antagoneerden iprodione en fenarimol elkander in hun activiteit ten opzicht vanA. nidulans. Ten opzichte vanC. cucumerinum gedroegen deze fungiciden zich onafhankelijk van elkaar.De practische consequenties van de waargenomen verschijnselen worden kort aangeduid.  相似文献   

18.
Buffers and leaf discs of mature tobacco (Nicotiana tabacum L.) were utilized to study [14C]-ethylene and 14CO2 evolution from radiolabeled ethephon, (2-chloroethyl)phosphonic acid. Metabolic fate of [14C]ethephon in leaf discs was investigated by use of thin-layer chromatography, high-voltage paper electrophoresis, autoradiography, and liquid scintillation spectroscopy. The evolution of labeled ethylene generally increased with increasing buffer pH, buffer volume, and dosage of [14C]ethephon. [14C]Ethylene was evolved, increasingly with time, from [14C]ethephon either added to the buffer or applied to leaf discs. The rate of [14C]ethylene evolution was maximum during the first day and leveled off on the fourth day. More than 50% of the total [14C]ethylene evolution over a 96-hr period was recovered during the first 24 hr after [14C]ethephon application. No 14CO2 was evolved when [14C]ethephon was degraded in the presence of buffer or leaf discs. Only ethephon itself, and no detectable metabolite thereof, was discovered in the methanolic extract of the leaf disc tissue. An insignificant amount of 14C activity (approximately 2% of the extracted 14C) was detected in the residue. By means of gas chromatography, it was confirmed that in buffers and tobacco leaf tissue ethephon breaks down to release ethylene but not CO2.  相似文献   

19.
Quinone outside inhibitors (QoIs) and succinate dehydrogenase inhibitors (SDHIs) are major groups of agricultural fungicides. However, resistance to some of these fungicides has been reported in a Japanese population of Puccinia horiana, the causal agent of chrysanthemum white rust disease. Because their mechanisms are not well understood, we investigated the existence of mutations in QoI and SDHI target protein-encoding genes. Eight out of nine isolates from cultivated chrysanthemum carried L275F and L299F amino acid substitutions in cytochrome b, the target protein of QoIs. These isolates showed 23- and 17-fold higher EC50 values for the QoI fungicides azoxystrobin and kresoxim-methyl, respectively, in basidiospore germination inhibitory tests, while they were hypersensitive to another QoI, famoxadone. All nine isolates were resistant to SDHI oxycarboxin and carried the I88F substitution in SdhC. This substitution was orthologous to the SdhC-I86F substitution found in some Brazilian isolates of the soybean rust fungus, Phakopsora pachyrhizi, showing reduced sensitivity to some SDHIs. Although the rarity of wild-type sensitive isolates, the subsequent limited number of comparisons between wild types and mutants, and a difficulty in applying reverse genetic analysis to this obligate parasite, are obstacles in making definitive conclusions, L275F and L299F in cytochrome b and SdhC-I88F are suspected to be responsible for the different patterns of sensitivity to QoI and for oxycarboxin-resistance in P. horiana, respectively.  相似文献   

20.
In a lysimeter experiment, [3-14C]metamitron was sprayed in a preemergence treatment of sugar beets, corresponding to approx 4.9 kg metamitron (7 kg Goltix)/ha. After 6 months, the beets contained metamitron equivalents amounting to 0.1 mg/kg fresh wt, calculated on the basis of the specific radioactivity of the [3-14C]metamitron employed. Radioactivity was also detected in the pure sugar isolates. The 14C activity represented approx 0.2 mg metamitron equivalent/kg pure sugar. Since the specific radioactivities of the sugar fractions were too low to employ physicochemical methods, a microbial degradation was used to investigate whether the radiocarbon was incorporated in the sucrose molecule. Microorganisms (Proteus vulgaris) degraded [U-14C] sucrose and the sugar isolates at the same 14CO2 release rates under strictly controlled experimental conditions. This result indicates that about one fourth of the carbon from the C-3 position of the triazine ring of the metamitron, found in the sugar beets at harvest time, is partly being used as a substrate in the production of sucrose possibly via assimilation of mineralized 14CO2.  相似文献   

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