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1.
Control of lettuce downy mildew (Bremia lactucae) with phenylamide fungicides has failed in some intensive lettuce-producing areas in Northern Italy since Spring 1993. Before then, these chemicals and particularly metalaxyl, provided the best disease control. The sensitivity of Bremia lactucae isolates collected in such areas to metalaxyl was evaluated in the laboratory. These strains grew and sporulated profusely on lettuce seedlings treated with 100 and 200 ppm of metalaxyl, whereas sensitive control strains were completely inhibited when treated with fungicide concentrations ranging from 0.5–1 ppm. Thus in Italy occurrence of resistance to phenylamide fungicides in Bremia lactucae has also been demonstrated, as in almost all the countries where these chemicals were previously authorised. Subsequently, a demonstration of occurrence of resistance was made and the virulence pattern of several strains (resistant and sensitive to metalaxyl) was characterised using differential NL series containing the 13 DM resistant genes or R factors. The results suggest the occurrence of a new pathotype in Italy different from all the 16 NL Bremia lactucae races studied.  相似文献   

2.
Resistance to phenylamide fungicides in thePhytophthora infestans population in the Netherlands decreased from a level of 77% of the samples containing resistant strains in 1980 to 0% in 1986 with decreasing use of metalaxyl, the only phenylamide fungicide registered for use against late blight in this country. Use of metalaxyl decreased because the fungicide alone and combinations of metalaxyl with preventive late blight fungicides were not commercially available from 1981 through the first part of the potato growing season of 1984. When metalaxyl was made available again in August 1984 in a mixture with mancozeb and from 1985 in a mixture with almost full rates of maneb and fentinacetate its use remained limited because growers were advised to apply the combination only two times per season in critical situations only to control the severe late blight epidemics of 1984 and 1985. Moreover application on seed potato crops was not allowed. In 1986 the combination was hardly used because the mild epidemic was easily controlled by preventive compounds only.In 1987 and 1988 phenylamide resistance increased to 16 and 42%, respectively, inherent to a general use of the combination in both years in most potato growing regions of up to two applications to combat a very severe epidemic.In lots of seed potatoes harvested in 1988 the percentage of blighted tubers yielding resistant isolates significantly differed from 13% for regions where seed potatoes are predominantly grown for table and processing crops to 41% for a region where predominantly starch potatoes are grown, both as seed and production crops. The more intensive use of metalaxyl combinations in the latter area through the years as compared to the other areas is assumed to be responsible for the higher incidence of resistance.In most years application of the combination induced a significant shift in the population to resistance as is indicated by the higher frequency at which resistant isolates were present in leaf samples taken from treated fields or tuber samples from the harvested crop.The strategy adopted by Dutch potato growers to combat phenylamide resistance in late blight, involving limited use of metalaxyl mixtures to a maximum of two times in critical situations only, has kept up to now resistance in the population at a level at which metalaxyl still significantly contributes to the efficacy of the combination in controlling the disease. Never-theless the observed increase in resistance in the population of 1988 after two consecutive late blight years indicates that this may change if severe epidemics occur each year.  相似文献   

3.
In The Netherlands in 1980 a severe late-blight epidemic involving metalaxyl-resistant strains of Phytophthora infestans did considerable damage to the potato crop. As a consequence metalaxyl or metalaxyl-containing products were withdrawn from the Dutch fungicide market for the control of potato late blight. In 1981 the majority of the P. infestans isolates obtained from various parts of the country were sensitive to metalaxyl. In three areas where metalaxyl mixtures were used on a relatively large scale metalaxyl-resistant strains dominated the population. Incidental use of metalaxyl mixtures in 1982 and 1983 showed adequate late-blight control and, when in 1984 an early and in some areas severe epidemic developed, a metalaxyl/mancozeb mixture was reintroduced for curative application in combination with conventional fungicides. Although disease control was adequate, resistant strains were present in a small number of fields. Whether resistant strains will increase in frequency and threaten the usefulness of mixtures of acylalanines will heavily depend on how well potato farmers adopt strategies involving a limited use of mixtures of acylalanines in a spray schedule with conventional late-blight fungicides.  相似文献   

4.
Bioassays testing the fungicide sensitivity against metalaxyl of Peronospora tabacina isolates collected in German tobacco fields in 2005 revealed the presence of two phenotypes, resistant and sensitive. DNA fingerprints using SSR and minisatellite primers allowed separation of the samples into two groups. The differences in amplification patterns coincided with the sensitive and resistant reaction of the isolates in metalaxyl bioassays. New primers were developed which allowed PCR-based detection of P. tabacina and differentiation of the metalaxyl-sensitive and the metalaxyl-resistant phenotype, respectively. Screening of recent blue mold isolates from Germany and other European countries for metalaxyl sensitivity with leaf disk bioassays coincided completely with the PCR-based identification of the two phenotypes. In Germany, exclusively resistant isolates were found between 2002 and 2004. These still dominate. Since 2005 the co-occurrence of sensitive isolates has been shown. No similar monitoring has been done in any other European country. However, we found the resistant phenotype reaction in a French isolate of 2004 and in two out of three Italian isolates in 2007. Two isolates from Poland and Bulgaria in 2007 were sensitive to metalaxyl. For all 58 isolates tested since 2002 the metalaxyl bioassay-based resistance type and the PCR-based tests for sensitive and resistant genotype coincided. Using genotype-specific primers for future population studies may help to trace the sources of the pathogen from which yearly propagation starts.  相似文献   

5.
Single-oospore progeny from matings between field isolates of Phytophthora infestans either highly resistant or sensitive to metalaxyl were analysed for fungicide sensitivity in vitro, mating type and, in some cases, allozyme variation at the locus for glucosephosphate isomerase ( GPI-1. ) In each cross the majority of first-generation (F1) progeny showed intermediate sensitivity to metalaxyl. Frequency distributions were skewed towards sensitivity and a few progeny were either wholly sensitive or resistant phenotypes. Allozyme analysis of F1 progeny from a cross between parents of Dutch and Mexican origin showed that c. 10% were selfs of both parents and of parental phenotype for metalaxyl sensitivity. The selfs of the A2 but not the Al parent segregated for mating type. Two backcross generations to the metalaxyl-resistant Dutch parent gave unexpected phenotypic frequency distributions and aberrant ratios for genotypes at the GPI-I locus.
Progeny of another backcross between an F1 isolate of intermediate sensitivity and its sensitive Egyptian parent gave a 1:1 ratio for sensitive: intermediate phenotypes. F2 progeny from a related sibmating between intermediate phenotypes segregated in a ratio close to 1:2:1 for sensitive: intermediate: resistant phenotypes. Segregation was also observed among sexual progeny of an intermediate self-fertile isolate from the backcross generation but not among progeny of a resistant self-fertile phenotype. Mating type segregated in both cases.
These data are consistent with resistance to metalaxyl in P. infestans being governed by a single nuclear locus exhibiting incomplete dominance. This hypothesis is discussed in relation to the incidence of resistance to metalaxyl in natural populations of P. infestans.  相似文献   

6.
Mutants of Phytophthora parasitica Dast. more or less resistant to dimethomorph or metalaxyl were obtained by treating mycelium with ultraviolet radiation. Some metalaxyl-resistant mutants exhibited levels of resistance (i.e. the ratio between the EC50 values for the mutant and the wild-type strain) greater than 100, but those observed in the dimethomorph-resistant mutants never exceeded 25. Most mutants retained their resistance after sub-culturing on unamended agar medium. Single zoospore clones derived from a metalaxyl-resistant and a dimethomorph-resistant mutant, selected as amongst the most resistant, had levels of resistance similar to those of the parental strains. The metalaxyl-resistant mutants were also resistant to the related phenylamide fungicides, furalaxyl and benalaxyl, but remained sensitive to dimethomorph. The dimethomorph-resistant mutants were not resistant to phenylamide fungicides. The pathogenicity of some metalaxyl- or dimethomorph-resistant mutants on tobacco leaves was similar to that of the wild-type strains.  相似文献   

7.
In 1981 metalaxyl-resistant Phytophthora infestans was found in 44% of the 63 crops examined in south-west Scotland. In 1982, when fungicides containing acylalanines (metalaxyl or ofurace) were not used in the area, it was detected in 15%. Metalaxyl-resistant strains were found in several crops which had been sprayed only with non-acylalanine fungicides or had received no fungicidal treatment. In neither year was resistance associated with a significant breakdown of disease control.
Metalaxyl-resistant isolates of the blight fungus were obtained from tubers from crops in which resistance was detected on the foliage.
In detached leaf experiments, resistant isolates retained their ability to grow on leaves treated with 100 μg/ml of metalaxyl after 52 weekly transfers on untreated leaves, and produced sporangia on leaves treated with up to 2000 μg/ml of metalaxyl or ofurace. In mixtures with sensitive sporangia the proportions remained stable after nine weekly transfers on untreated leaves. However, at concentrations as low as 50 μg/ml, metalaxyl and ofurace reduced the extent of colonization and the numbers of sporangia produced by resistant isolates by an average of 50%.  相似文献   

8.
Groves CT  Ristaino JB 《Phytopathology》2000,90(11):1201-1208
ABSTRACT A wide range of commercially formulated fungicides cause in vitro effects on mating behavior in specific isolates of Phytophthora infestans, the causal agent of late blight of potato and tomato. Four isolates of P. infestans representing each of the four common US genotypes, US-1, US-6, US-7, and US-8 and varying in their sensitivity to metalaxyl, were exposed to a variety of fungicides used to control late blight in petri dish assays at concentrations ranging from 1 to 100 mug a.i./ml. Exposure of each of these normally heterothallic single mating type isolates of P. infestans to 9 of the 11 commercial fungicide formulations tested resulted in the formation of oospores after 2 to 4 weeks. The highest numbers of oospores were formed on media amended with Ridomil 2E (metalaxyl) and Ridomil Gold EC (mefenoxam) at 0.1 to 10 mug a.i./ml, averaging as many as 471 and 450 oospores per petri dish, respectively. Several other fungicides including Maneb, Manzate (Mancozeb), Curzate (cymoxanil + mancozeb), and Acrobat MZ (dimethomorph + mancozeb) also induced oospore formation, producing from 0 to 200 oospores per plate at fungicide concentrations from 0.1 to 10 mug a.i./ml. The metalaxyl resistant isolates formed oospores in response to the fungicides more often than the metalaxyl sensitive isolates. No oospores were formed on media amended with Bravo (chlorothalonil) or Tattoo C (chlorothalonil + propamocarb HCl) and these compounds completely suppressed growth of the isolates at 0.1 and 1 mug a.i./ml. Three metalaxyl resistant A2 isolates mated with both A1 and A2 isolates after exposure to the fungicides Ridomil 2E and Ridomil Gold EC. Alterations in mating type expression were also observed in a metalaxyl sensitive A1 isolate after exposure to Benlate (benomyl). Copious amounts of chemicals are applied annually to potato and tomato production areas to control late blight. Our results indicate that a wide range of chemically diverse fungicides can induce normally heterothallic metalaxyl resistant isolates of P. infestans to form oospores in vitro after short exposures to the fungicides.  相似文献   

9.
A total of 743 single-lesion isolates of Phytophthora infestans were collected in summer 2003 from Denmark, Finland, Norway and Sweden. Most of the isolates were tested for mating type, and subsets were tested for sensitivity to fungicides and virulence (host specific pathogenicity). Approximately 60% of the isolates were A1 mating type in each country. Both mating types were present in 40% of the fields where more than one isolate was tested, indicating strong potential for sexual reproduction. The proportion of metalaxyl-resistant isolates dropped to under 15% from the 60% observed in the early 1990s in Norway and Finland, possibly due to lower selection pressure because of decreased use of metalaxyl. Propamocarb-HCl sensitivity remained unchanged in the Nordic countries compared to the situation in 1997–2000 in Finland. Four isolates collected from Finland and Sweden were able to sporulate in the presence of this fungicide at a concentration of 1000 mg L−1. In Norway and Finland the frequencies of virulence factors and pathotypes remained nearly unchanged since the 1990s, but the mean number of virulence factors per isolate increased from 5·6 to 6·3. In Denmark and Sweden virulence factors 2 and especially 6 were more common than in Norway and Finland. In addition, in the Swedish population the frequencies of pathotypes were quite even while in other countries pathotype 1,3,4,7,10,11 was most prevalent.  相似文献   

10.
Plasmopara halstedii isolates showing an atypical reaction to metalaxyl were collected in France, in 1995 and 1996, and tested in the laboratory for their level of sensitivity to this fungicide. Primary and secondary infections caused by one of these isolates were not controlled by the metalaxyl concentration registered for seed treatment. The EC50 of this isolate was 12 800 mg a.i. kg-1 compared with 22 mg a.i. kg-1 for sensitive isolate, indicating a 582-fold decrease in sensitivity to the compound. There was no reduction in the agressiveness of the resistant isolate. Using other anti-oomycete fungicides, it appeared that propamocarb, contact fungicides (fluazinam, folpet, mancozeb) and the mixed formulations dimethomorph + mancozeb, cymoxanil + mancozeb and ofurace + folpet were effective against primary infections made with metalaxyl resistant and sensitive isolates, but not against secondary infections. Metalaxyl mixed with fluazinam, folpet or mancozeb was more effective against primary infections with the resistant isolate than metalaxyl alone. The EC50 of five other isolates ranged from 5 800 to 32 900 mg a.i. kg-1, indicating a variability in metalaxyl sensitivity of resistant sunflower downy mildew isolates. This is the first report of physiological resistance to metalaxyl in Plasmopara halstedii.  相似文献   

11.
Propamocarb (Previcur-N; propyl-[3-dimethylamino-propyl] carbamate-monohydrochloride) was testedin vivo against 32 field isolates ofPhytophthora infestans from six countries. Fungicide dosages required to achieve 90% control of the blight ranged between 676 and 1530 ppm a.i. in potted potato (cv. ‘Alpha’) plants and between 1135 and 2648 ppm in potato tuber slices. Isolates from Israel were less sensitive to the fungicide than isolates from Europe or North America. Toxicity of propamocarb was not related to resistance or sensitivity to phenylamide fungicides (e.g. metalaxyl). Nevertheless, most metalaxyl-resistant isolates from Israel were less sensitive to propamocarb than most metalaxyl-sensitive isolates from this country. Monocyclic epidemics conducted with the 20 Israeli isolates in the field showed that 1081–2012 ppm of the fungicide was required to achieve 90% control of the disease. Laboratory experiments revealed that the fungicide was poorly active against sporangial germination and had a limited curative efficacy. It exhibited a translaminar translocation in leaves but a poor acropetal or basipetal systemicity from foliage. Propamocarb + mancozeb mixtures (1:1, v/w) were synergistically effective in controlling the blight. Growers in Israel use tank mixtures of propamocarb (Dynone) and mancozeb to combat late blight in potato fields where phenylamide-resistant isolates ofP. infestans are prevalent.  相似文献   

12.
为了明确我国不同地区马铃薯晚疫病菌对甲霜灵和精甲霜灵的抗性状况,2007-2009年从河北、黑龙江、吉林、辽宁和内蒙古马铃薯主产区采集马铃薯晚疫病菌,采用菌丝生长速率法和叶盘漂浮法测定其对甲霜灵的敏感性,采用叶盘漂浮法测定其对精甲霜灵的敏感性.结果表明:以菌丝生长速率法检测的380株晚疫病菌中和以叶盘漂浮法检测的222株晚疫病菌中对甲霜灵的抗性菌株分别占80％和73.5％;菌丝生长速率法检测结果显示,河北省对甲霜灵的抗性菌株所占频率从2007年的100％降为2008年的66.4％,2009年又回升至74.2％,而吉林和黑龙江两省对甲霜灵的抗性菌株分布频率呈上升趋势.叶盘漂浮法检测的95个菌株中对精甲霜灵的抗性菌株占54.5％,其中河北省40个菌株对精甲霜灵的中间型菌株占优势(62.5％),抗性菌株仅占34.9％,而其他4省55个菌株对精甲霜灵的抗性菌株占优势(69.1％).受检测的北方五省(区)马铃薯晚疫病菌群体中对甲霜灵和精甲霜灵的抗性菌株已占优势,马铃薯晚疫病菌已普遍对甲霜灵及精甲霜灵产生抗性.在对甲霜灵和精甲霜灵普遍产生抗性的地区,应优先选用与甲霜灵、精甲霜灵作用机理不同的药剂防治马铃薯晚疫病.  相似文献   

13.
The occurrence of metalaxyl-resistant isolates of Pseudoperonospora cubensis, the causal agent of downy mildew in cucurbits, was surveyed during 1980–1984 subsequent to their first appearance in December 1979. Metalaxyl use was abandoned in mid-1981 and resistant isolates diminished in late 1981. Metalaxyl use was renewed in 1982 and a gradual increase in frequency of resistant (R) strains was detected. In 1983, 31 out of 40, and in 1984, 43 out of 47 isolates tested were highly resistant to the fungicide with 65 and 91% of them, respectively, collected from plastic houses or fields not treated with metalaxyl. The survey indicates a rapid build-up of R strains of the fungus and the need for alternative chemicals for combating downy mildew in cucurbits.  相似文献   

14.
Phytophthora infestans is the most important potato pathogen worldwide. Various alternatives have been used to control the pathogen, including continuous applications of phenylamide fungicides which has caused a rapid development of resistance in populations of P. infestans. Despite the importance of the disease, metabolite profiling of fungicide-resistant P. infestans has not been reported. In vitro resistance of Phytophthora infestans isolates to metalaxyl was characterized and metabolic changes in resistant isolates were evaluated at low (0.5 mg/L) and high (100 mg/L) concentrations of the fungicide. About 70% of the isolates tested showed resistance to metalaxyl and a total of 49 metabolites were differently expressed in resistant isolates growing in the presence of the fungicide. Principal components analysis revealed a distinct metabolite profile of resistant isolates exposed to both low and high levels of metalaxyl. The main metabolites responsible for the clustering in both fungicide concentrations included fatty acids such as hexadecanoic and octadecanoic acids, sugars such as glucose and fructose, aminoacids such as proline and valine, and organic acids such as butanedioic and propanoic acids. Potential resistance-related metabolic pathways are mostly involved in the regulation of the pathogen’s membrane fluidity and included the fatty acid biosynthesis as well as the glycerophospholipid metabolism pathways. This is the first metabolomic-based characterization of fungicide resistance in plant pathogens.  相似文献   

15.
 2003~2005年,从云南省德宏州新兴冬作马铃薯主产区采集的马铃薯晚疫病病样中分离纯化到86株致病疫霉菌,对其代表性菌株的表型特征进行了较系统的研究。交配型实验结果表明:所测定的62个菌株都属于A1交配型,未发现A2交配型或自育型菌株。毒性基因鉴定、监测及生理小种组成分析显示:德宏州存在所有已知可鉴定的毒性基因,而且生理小种组成非常复杂;所测定的66个菌株可区分出36个生理小种,其中,出现频率最高的小种为1,2,3,4,5,6,7,8,9,10,11,占被测菌株的18.18%,在主产区潞西县和盈江县均有分布。对60个菌株的甲霜灵抗性测定结果表明:56.67%的菌株表现为敏感,25.00%的菌株中抗,18.33%的菌株对甲霜灵有抗性。本文对此实验研究结果作了初步的分析和讨论。  相似文献   

16.
In winter/spring 1984 resistance to metalaxyl developed in Phytophthora infestans within tomato greenhouses in Preveza, Greece. The appearance of resistant isolates followed continuous applications of metalaxyl and prevalence of weather conditions favourable for late blight. The majority of resistant isolates grew on tomato leaf discs floated on solutions containing 100 μg/ml metalaxyl whereas sensitive isolates were inhibited at concentrations of 0.1 μg/ml.
In trials within polyethylene tunnels metalaxyl had no effect on the development of the late blight induced by resistant strains but both a mixture of this fungicide with mancozeb and mancozeb alone, gave satisfactory control of the disease when applied in a 7-day schedule.  相似文献   

17.
ABSTRACT Previous studies indicated that incompletely dominant loci determine insensitivity by oomycetes to phenylamide fungicides such as metalaxyl. To compare the bases of insensitivity in different strains of the late blight pathogen, Phytophthora infestans, crosses were performed between sensitive isolates and isolates from Mexico, the Netherlands, and the United Kingdom that displayed varying levels of insensitivity. Segregation analyses indicated that metalaxyl insensitivity was determined primarily by one locus in each isolate, and that two of the isolates were heterozygous and the other homozygous for the insensitive allele. Metalaxyl insensitivity was also affected by the segregation of additional loci of minor effect. DNA markers linked to insensitivity were obtained by bulked segregant analysis using random amplified polymorphic DNA (RAPD) markers and the Dutch and Mexican crosses. By studying the linkage relationships between these markers and the insensitivity in each cross by RAPD or restriction fragment length polymorphism analysis, it appeared that the same chromosomal locus conferred insensitivity in the Mexican and Dutch isolates. However, a gene at a different chromosomal position was responsible for insensitivity in the British isolate.  相似文献   

18.
A total of 2691 single-lesion isolates of Phytophthora infestans was established from samples of late-blight disease from 354 commercial and garden/allotment sites in Scotland, England and Wales over four growing seasons, 1995–98. The A2 mating type was rare (3·0% of isolates) and was detected at only 34 sites. In vitro tests of sensitivity to the phenylamide fungicide metalaxyl showed that 316 sites yielded isolates with some insensitivity (resistant and/or intermediate); these were more often commercial sites than garden/allotment sites. Over the four seasons, the frequency of isolates with intermediate fungicide sensitivity increased, while the frequency of resistant phenotypes decreased. Resistant isolates were always of A1 mating type. A subset of 1459 isolates from 326 sites was analysed for molecular diversity. Mitochondrial DNA (mtDNA) haplotype Ia predominated (91·0% of isolates); haplotype IIa was present at 54 sites and both haplotypes at 33 sites. The multilocus RFLP probe RG57 detected 30 fingerprints. Four fingerprints were particularly common (RF002, RF006, RF039 and RF040) and 10 were unique to a single site in a single year. The three commonest fingerprints (RF039 > RF002 > RF006) were of A1 mating type and the fourth (RF040) was A2. RF002 isolates were resistant to the phenylamide metalaxyl and were more common in Scotland than in England and Wales. Small sample sizes limited the usefulness of estimates of diversity. Although approximately half of all sites appeared to be colonized by RF039 genotypes, some sites (both commercial and garden/allotment) showed a higher diversity, having both common and unique genotypes. The genotypic diversity within isolates collected from commercial sites and those from garden/allotment sites were similar. The contributions of sexual reproduction and alternatives to sex to the generation of variation are discussed.  相似文献   

19.
烟草黑胫病菌抗甲霜灵突变体的诱导及其适合度研究   总被引：1，自引：0，他引：1  
室内离体条件下采用药剂诱导法,获得了11个烟草黑胫病菌抗甲霜灵突变体;检测了所有抗药突变体的抗药稳定性及抗性水平;比较了3个低抗和1个高抗突变体的适合度。结果表明:在2~20 μg/mL范围内,抗药突变体的发生频率随甲霜灵诱导浓度的增加而提高;所有抗药突变体的抗药性都能稳定遗传;11个抗药突变体中,10个为低抗突变体(抗性水平3.55~13.9倍,平均8.60倍),1个为高抗突变体(抗性水平510倍);低抗菌株20M-001、10M-003、10M-006和高抗菌株10M-004的适合度指数分别为0.56、0.38、0.38和0.87;抗药突变体的适合度指数与抗性水平不相关。  相似文献   

20.
The nature of virulence in isolates of Bremia lactucae from South Devon   总被引：1，自引：1，他引：0  
Nine isolates of Bremia lactucae from South Devon showed the presence of virulence factors against all 11 resistance factors available in lettuce, but no insensitivity to metalaxyl. The virulence phenotype of a single–sporangium isolate of the fungus changed from VI, 3, 4 and 7 to 1, 2, 3, 4, 6 and 7 after it was maintained on Lobjoit Green Cos (RO) for 10 months.  相似文献   

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