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1.
We collected 247 isolates of Cercospora kikuchii from soybean seeds with typical purple stain symptoms from 15 prefectures in Japan. Of the 247 isolates, 93 were sensitive to thiophanate-methyl, a benzimidazole used to control this soybean disease; the remaining 154 were highly resistant to the fungicide. To examine genetic variability among the population of 247 isolates, we developed amplified fragment length polymorphism (AFLP) markers. An AFLP primer pair generated DNA fingerprint polymorphisms among the sample isolates, and with the unweighted pair-grouping method to cluster arithmetic means of the similarity coefficients among all pairs of the fingerprint patterns, the isolates were divided into four lineages (I to IV). Of the 247 isolates, 225 belonged to lineage I, including all isolates that were resistant to thiophanate-methyl. To determine whether the resistance of these isolates was related to mutations in the β-tubulin gene, we amplified partial nucleotide sequences of the gene from 29 representative isolates, including 12 that were resistant to thiophanate-methyl, by means of the polymerase chain reaction. The resistant isolates had identical nucleotide sequence with a one-step change at codon 198, in which the amino acid glutamic acid had been replaced by alanine. The evidence thus suggests that thiophanate-methyl resistance might have arisen in lineage I, the largest of the four lineages. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession numbers AB214511 to AB214515  相似文献   

2.
Fusarium head blight of wheat is caused by a disease complex comprised of toxigenic pathogens, predominantly Fusarium spp., and a non-toxigenic pathogen Microdochium nivale, which causes symptoms visually indistinguishable from Fusarium and is often included as a causal agent of Fusarium head blight. Four field trials are reported here, including both naturally and artificially inoculated trials in which the effect of fungicide treatments were noted on colonisation by Fusarium and Microdochium, and on the production of deoxynivalenol (DON) mycotoxin. The pathogen populations were analysed with quantitative PCR and samples were tested for the presence of the mycotoxin DON. Application of fungicides to reduce Fusarium head blight gave a differential control of these fungi. Tebuconazole selectively controlled F. culmorum and F. avenaceum and reduced levels of DON, but showed little control of M. nivale. Application of azoxystrobin, however, selectively controlled M. nivale and allowed greater colonisation by toxigenic Fusarium species. This treatment also lead to increased levels of DON detected. nobreak Azoxystrobin application two days post-inoculation increased the production of DON mycotoxin per unit of pathogen in an artificially inoculated field trial. This result indicates the potential risk of increased DON contamination of grain following treatment with azoxystrobin to control head blight in susceptible wheat cultivars. This is the first study to show differential fungicidal control of mixed natural pathogen populations and artificial inoculations in field trials.  相似文献   

3.
Green fluorescent protein (GFP)‐expressing transformants were used to investigate the effects of strobilurin fungicide azoxystrobin on Mycosphaerella graminicola infection. Azoxystrobin treatments (125 or 250 g AI ha?1) were applied at various stages of the infection process under controlled conditions. GFP transformants showed conserved in vitro sensitivity to azoxystrobin and pathogenicity. Azoxystrobin controlled over 90% of M graminicola infections when applied before or during penetration of the pathogen (15% of the incubation phase). Azoxystrobin also impaired the growth of intercellular hyphae in M graminicola post‐penetration infection stages when applied at up to 50% of the incubation phase. Incubating infections observed in treated leaves were viable, but their growth was impaired and they did not induce necrosis under controlled conditions. Reduction by half of azoxystrobin dosage had little or no effect on azoxystrobin efficiency in controlling M graminicola. The contribution of post‐penetration fungistatic effect to azoxystrobin curative properties toward M graminicola in a field situation is discussed. © 2001 Society of Chemical Industry  相似文献   

4.
To investigate the frequency distribution of purple seed stain of soybean caused by Cercospora kikuchii in two experimental fields in 2004, we set up rows 75 cm apart and sowed two asymptomatic seeds at each of positions 20 cm apart in each row. We sowed purple-stained seeds infected with the pathogen as inocula at four points instead of asymptomatic seeds in each field. We assessed disease incidence in harvested seeds by counting the numbers of purple-stained and asymptomatic seeds. To determine the spatial distribution of the disease, we grouped the field points into analytical units of several sizes. Beta-binomial and binomial distributions described the distribution patterns of purple-stained seeds. The smallest value of α, a beta-binomial parameter, occurred with analytical units that contained three or nine points next to each other within a single row, suggesting that these units showed the most aggregated distribution of the disease, each of the patches of seeds infected with C. kikuchii could be defined approximately by the area covered by three or nine points (75 × 60 or 75 × 180 cm), and the disease tended to infect plants next to each other within rows.  相似文献   

5.
Temporal variation in Fusarium oxysporum f. sp. vasinfectum (Fov) populations was determined by comparing the genetic diversity of pathogen isolates recovered from three consecutive cotton crops (2002, 2004 and 2006) in the Boggabilla area of New South Wales, Australia. A total of 288 isolates were collected, among which 25 distinct AFLP genotypes were identified. These genotypes were classified into two main groups corresponding to known vegetative compatibility groups (VCG)—01111 and 01112. The Fov populations were dominated by four genotypes (I-A, I-B, II-A, II-B) that accounted for 87.5% of the isolates. Significant temporal variation was observed in both sampled fields with 6.8% and 10.7% of total genetic variation being attributed to differences among collections in different years. Genetic diversity based on Nei’s gene diversity and the Shannon-Wiener index increased over time. Significant changes in the frequency of the dominant Fov genotypes were observed in one field, where genotype I-A declined from 84.8% to 40.0% over the study period (2002–2006), while genotype I-B increased from 7.6% to 35.4%. Strong inter-genotype competition was detected in glasshouse bioassays with 93.4% of symptomatic plants sampled from dual inoculation trials being infected by single genotypes. Competition was differentially mediated by cotton cultivars as the competitive ability of pathogen genotype I-B was enhanced on the resistant cultivar Sicot 189 relative to the susceptible cultivar Siokra 1–4. This suggests that host-mediated inter-genotype competition may play an important role in temporal variation in Fov populations in the field.  相似文献   

6.
In 2014 and 2015, a total of 151 tobacco brown spot (Alternaria alternata) isolates were collected from Guizhou Province in China to evaluate their resistance to the benzimidazole thiophanate-methyl, the carbamate diethofencarb, and the dicarboximide procymidone. Resistance to thiophanate-methyl and diethofencarb was observed in all isolates. Resistance to all the three fungicides, thiophanate-methyl, diethofencarb, and procymidone was detected at a frequency of 6.0%. The F167Y single mutation in the β-tubulin gene was found to be associated with resistance to thiophanate-methyl,but no mutation was found in the coiled-coil region of the histidine kinase-encoding gene OS1, a fungal gene for dicarboximide resistance. Procymidone applied at the rate of 20 mg l?1 inhibited spot lesion formation on tobacco leaves with an efficacy of 51.7% for the low resistance (LR) isolates and 74.2% for the procymidone-sensitive isolates. Thiophanate-methyl applied at 100 mg l?1, however, slightly promoted the expansion of disease lesions with an efficacy of ?7.7%. Azoxystrobin applied at 10 and 20 mg l?1 provided efficacies of 91.1 and 100%, respectively, regardless of whether the isolates were thiophanate-methyl resistant or procymidone-LR. Further studies suggested that azoxystrobin exhibited excellent protective activity and good curative activity against A. alternata in plants. The baseline sensitivity to azoxystrobin was then determined. In the presence SHAM, the mean EC50 values for conidial germination inhibition were 0.49?±?0.22 (Mean?±?SD) mg l?1. Interestingly, no resistance was recovered through UV irradiation or Agrobacterium tumefaciens-mediated mutagenesis. This research indicated widespread resistance to thiophanate-methyl and diethofencarb, low frequency of (6.0%) resistance to procymidone in A. alternata populations from tobacco, and suggested that azoxystrobin could potentially constitute a good alternative for the management of tobacco brown spot disease.  相似文献   

7.
BACKGROUND: Azoxystrobin [methyl (E)‐2‐{2‐[6‐(2‐cyanophenoxy)pyrimidin‐4‐yloxy]phenyl}‐3‐methoxyacrylate], a strobilurin fungicide, is a broad‐spectrum, systemic and soil‐applied fungicide. Azoxystrobin has been registered for rice cultivation in India, but no information is available on its leaching behaviour in Indian soils. Therefore, leaching behaviour of azoxystrobin was studied in packed and intact soil columns under different irrigation regimes. RESULTS: Azoxystrobin did not leach out of the 300 mm long columns after 126 and 362 mm rainfall. After percolating water equivalent to 362 mm rainfall, azoxystrobin leached down to 10–15 cm (packed columns) and 15–20 cm (intact columns) depth. Azoxystrobin was not detected in the leachate from the packed column leached with 94.5 mL water every week (140 mm rainfall per month) during the 28 weeks of the study period. However, azoxystrobin acid, formed by azoxystrobin degradation, was detected in the leachate after 18 weeks. At the end of the study, azoxystrobin had leached down to 5–10 cm depth, and only 60% of initially applied azoxystrobin was recovered from the soil. CONCLUSION: The results indicate that azoxystrobin is fairly immobile in sandy loam soil, but azoxystrobin acid, a major metabolite of azoxystrobin, is quite mobile and may pose a threat of soil and groundwater contamination. Copyright © 2009 Society of Chemical Industry  相似文献   

8.
Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most destructive wheat diseases in China. Yunnan Province, located in south-western China, possesses unique features of geography, climate, wheat growth and stripe rust epidemics, different from main epidemic regions in China. The isolates of this pathogen were collected from nine counties in Yunnan Province during February to May of 2008. Used as a comparison, isolates were also collected from five counties of Gansu Province, the province important in inter-regional stripe rust epidemics in China. Amplified fragment length polymorphism (AFLP) method was applied to study the population genetics of the pathogen among different populations in these two provinces. Forty one AFLP genotypes were obtained from 150 isolates and the genotype qj3 showed the highest frequency in Yunnan Province. While 22 genotypes were detected from 40 isolates, no genotype showing as predominant was identified in Gansu Province. Genotypic diversity in Gansu Province was higher than that in Yunnan Province. A free recombination signature was detected in Gansu Province but not in Yunnan Province. We concluded that the population of P. striiformis in Yunnan Province can be considered as a clonal population.  相似文献   

9.
Selection within populations of Phytophthora infestans was investigated by comparing the aggressiveness of single‐lesion isolates on detached leaflets of four potato cultivars with differing levels of race‐nonspecific resistance to P. infestans. The isolates included 23 representative of Northern Ireland genotypes from the early 2000s, used to inoculate previously reported field trials on competitive selection (2003–2005), plus 12 isolates recovered from the 2003 trial. The cultivars were those planted in the previous trials: Atlantic (blight‐susceptible) and Santé, Milagro and Stirling (partially resistant). Very highly significant variation for latent period, infection frequency and lesion area was found between genotypes and cultivars; differences between genotypes were more marked on the more resistant cultivars, but no one genotype was the most aggressive across all. Detached leaflets were also inoculated with mixtures of isolates from each genotype group at three sporangial concentrations: differences in aggressiveness between genotypes were more apparent at lower concentrations and on the more resistant cultivars. Genotype groups that were the most aggressive on the more resistant cultivars tended to be those selected by the same cultivars in the field. A mixture of all isolates of all genotypes was used to inoculate detached leaflets of the same cultivars. With one exception, single spore isolates recovered from any one leaflet belonged to a single genotype, but different genotypes were recovered from different cultivars. Phytophthora infestans isolates from Northern Ireland showed significant variation for foliar aggressiveness, and pathogen genotypes exhibited differential aggressiveness to partially resistant cultivars and interacted competitively in genotype selection.  相似文献   

10.
为评价烟草赤星病致病菌链格孢Alternaria alternata对嘧菌酯的抗性风险,以敏感菌株J6为试材,通过菌丝药剂驯化和分生孢子紫外诱变诱导抗性突变体,并对抗性突变体的生物学特性进行了研究,同时对抗性突变体与敏感菌株线粒体的细胞色素b基因 (cyt b) cDNA序列全长进行了测序分析。结果表明:经药剂驯化未获得抗性突变体,而紫外诱变共获得7株抗性突变体,突变频率约为0.007%,抗性水平分别为5.27、8.28、25.28、12.82、6.14、9.28和52.91倍。适合度研究表明,抗性突变体与敏感菌株的分生孢子萌发能力及致病力相当,但分生孢子产生量均高于敏感菌株,菌丝生长速率除突变体6-1外均快于敏感菌株。cyt b基因cDNA序列分析表明:有4株抗性突变体在不同位点上发生了核苷酸突变,其中突变体6-7 cyt b的249位和871位碱基由T突变为C,但其编码的氨基酸未发生突变;突变体6-8 cyt b的734位碱基由T突变为C,引起所编码的245位丙氨酸突变为缬氨酸 (V245A);突变体6-9 cyt b的510位碱基由T突变为A,所编码的170位由精氨酸替代了丝氨酸 (S170R);突变体6-11 cyt b的732位碱基由T突变为A,所编码的244位由苯丙氨酸替代了亮氨酸 (L244F),其776位碱基由T突变为C,所编码的259位由丙氨酸替代了缬氨酸（V259A）,其1 156位碱基由A突变为G,所编码的氨基酸未发生变化。研究结果初步表明,烟草赤星病菌对嘧菌酯存在潜在的抗药性风险,其cyt b基因的点突变与其对嘧菌酯的抗药性有关。  相似文献   

11.
In light of growing environmental concerns, surveys of fungicide resistance are needed to ensure efficient control of fungi and avoid unnecessary treatments. Investigations of fungicide resistance in Fusicoccum amygdali are scarce despite the economic impacts of this pathogen in peach and almond orchards. Thiophanate-methyl has been registered for more than 20 years to control F. amygdali but no resistance has been reported to date. This propesticide is metabolized by fungi into carbendazim, a β-tubulin inhibitor. Sensitivity to carbendazim of nine populations of F. amygdali from French orchards was assessed using germination bioassays. Also, resistance levels of 63 strains isolated from four populations were evaluated using mycelial growth assays. The underlying mechanism of resistance was investigated by sequencing the β-tubulin gene, the molecular target of thiophanate-methyl, in a set of isolates with different levels of sensitivity to carbendazim. Cross-resistance to thiophanate-methyl and to another β-tubulin inhibitor, diethofencarb, was also assessed in carbendazim-sensitive and -resistant strains. Isolates highly resistant to carbendazim were found in one of the nine orchards studied. Sequencing showed that resistant phenotypes carry a mutation in the β-tubulin gene leading to E198K substitution. Positive cross-resistance to thiophanate-methyl was confirmed and no negative cross-resistance to diethofencarb was identified in the phenotyped isolates, which were all resistant to this active substance. To our knowledge, this is the first report of resistance to thiophanate-methyl in F. amygdali. The high level of resistance of isolates sampled in one population is of concern, although the limited geographical scope of resistance suggests its recent emergence.  相似文献   

12.
9种杀菌剂对西瓜炭疽病菌的室内毒力测定及配比试验   总被引：3，自引：0，他引：3  
为筛选防治西瓜炭疽病的高效低毒杀菌剂, 缓解和治理生产中病菌对药剂的抗性, 在室内离体条件下采用生长速率抑制法及孢子萌发抑制法测定了9种杀菌剂对西瓜炭疽病菌( Colletotrichum orbiculare )的毒力。结果表明, 嘧菌酯、咪鲜胺和甲基硫菌灵对病原菌菌丝生长的EC50在0.093 3~0.118 2 mg/L之间, 均小于1 mg/L, 表明西瓜炭疽病菌对上述杀菌剂比较敏感; 百菌清、烯肟菌酯和戊菌唑的EC50在2.310 1~5.925 9 mg/L, 病菌对药剂的敏感程度相对较低; 代森锰锌、恶霉灵和多菌灵的EC50分别为36.876 3、74.466 6和99.898 5 mg/L, 抑菌活性较差。孢子萌发试验中, 嘧菌酯、咪鲜胺和甲基硫菌灵对病菌孢子萌发的抑制活性最高, EC50在0.069 4~0.167 2 mg/L之间; 百菌清、烯肟菌酯、代森锰锌的抑制活性次之, EC50在1.853 0~9.503 9 mg/L之间; 多菌灵的抑制活性相对最低, EC50为99.335 3 mg/L。将两种不同作用机理的杀菌剂嘧菌酯与咪鲜胺按照2∶1的比例混配, 联合毒力测定和评价结果表明两者混配对抑制西瓜炭疽病菌具有增效作用。  相似文献   

13.
Since 2007, serious damage to tomato from leaf mould caused by Passalora fulva has frequently been observed in commercial greenhouses in Gifu Prefecture, Japan. One of the factors relating to this damage was suspected to be a decrease in azoxystrobin sensitivity of the pathogen. Biological and molecular studies were conducted to characterize fungicide resistance. In in vitro sensitivity tests using mycelial homogenate placed on fungicide‐amended medium, the minimum inhibitory concentrations (MIC) of azoxystrobin for mycelial growth of the isolates divided into two ranges, 0.031–0.5 mg L?1 and 8–32 mg L?1. Isolates with MICs within the two ranges were considered as sensitive and resistant, respectively, to azoxystrobin because, in in vivo tests, the percentage protection conferred by this fungicide (100 mg a.i. L?1) against these isolates was 89.7–100% and 4.5–31.1%, respectively. Resistant isolates had a replacement of phenylalanine with leucine at codon 129 (F129L) in cytochrome b. Forty‐five percent of the 271 isolates collected from 63 tomato greenhouses from 2007 to 2008 were resistant to azoxystrobin. In many greenhouses where the isolation frequency of resistant isolates was 80% or more, azoxystrobin had been used twice per crop for approximately 6 years. In 2012, 27% of the 405 isolates collected were resistant to azoxystrobin, and there was a marked difference in the frequency of occurrence of resistant isolates in the field populations between the three locations sampled. The occurrence of azoxystrobin‐resistant P. fulva isolates (F129L mutants) inflicted considerable damage on greenhouse tomatoes.  相似文献   

14.
Carbendazim-resistant (RS) and control (CS) strains ofFusarium sporotrichioides Sherb., previously developed in our laboratory, were exposed to graded concentrations of azoxystrob in in broth media under shake-culture conditions for 2, 3, 4 and 8 days. Azoxystrobin concentrations were 0, 1, 10 and 100 mg 1-1 broth and cultures were incubated at a constant 25°C. Mycelial growth was significantly affected by strain (P<0.01), azoxystrobin concentration (P<0.001) and incubation time (P<0.001). Combined results for the four incubation times showed that CS yielded higher mycelial mass than RS (P<0.01) only in the absence of azoxystrobin. At fungicide additions of 1, 10 and 100 mg P-1 mycelial growth was reduced (P<0.001) with minimal strain differences (P>0.05) at all three doses of azoxystrobin. Significant (P<0.05 or better) strain-fungicide interactions were recorded in trichothecene production following exposure to azoxystrobin. At 4 and 8 days of incubation, the 10 mg 1-1 addition of azoxystrobin stimulated T-2 toxin synthesis (P<0.05) only in RS cultures. In contrast, T-2 toxin enhancement in CS cultures occurred only on day 8 but at a lower level of azoxystrobin (1 mg1-1). Thus, the stimulation of T-2 toxin synthesis depended upon strain and azoxystrobin level. Production of diocetoxyscirpenol (DAS) was affected by a more complex set of interactions. Overall means showed that, in comparison with initial values (on day 2 or 3), DAS output maximized significantly(P<0.05) on day 4 in RS cultures and on day 8 in CS. Marked strain effects were observed on exposure to the 10 mg 1-1 level of azoxystrobin. At this level, DAS production was enhanced in RS only after 4 (P<0.01 ) and 8 (P<0.05) days of incubation, while in contrast, CS reduced DAS production. As with T-2 toxin, DAS production in CS was stimulated (P<0.05 or better) only at low exposure levels of azoxystrobin. In the case of neosolaniol (NEO), however, the main effect of strain was significant (P<0.05), with CS producing consistently more of the mycotoxin than RS on day 4 of the experiment. At this point, the NEO:T-2 toxin ratio was also higher in CS (0.63) than in RS (0.12), a feature reported by us previously. In conclusion, the present investigation has shown for the first time that the development of resistance to one fungicide can affect trichothecene production inF. sporotrichioides on exposure to a second fungicide. These results have been incorporated into a new classification scheme for fungicide efficacy which is also presented in this paper. http://www.phytoparasitica.org posting Oct. 7,2001.  相似文献   

15.
Mutants of Botrytis cinerea with moderate and high resistance to pyraclostrobin, a Qo inhibitor of mitochondrial electron transport at the cytochrome bc 1 complex, were isolated at a high mutation frequency, after nitrosoguanidine mutagenesis and selection on medium containing pyraclostrobin and salicylhydroxamate (SHAM), a specific inhibitor of cyanide-resistant (alternative) respiration. Oxygen uptake in whole cells was strongly inhibited in the wild-type strain by pyraclostrobin and SHAM, but not in the mutant isolates. Cross-resistance studies with other Qo and Qi inhibitors (QoIs and QiIs) of cytochrome bc 1 complex of mitochondrial respiration showed that the mutation(s) for resistance to pyraclostrobin also reduced the sensitivity of mutant strains to other QoIs as azoxystrobin, fluoxastrobin, trifloxystrobin and picoxystrobin, but not to famoxadone and to the QiIs cyazofamid and antimycin-A. An increased sensitivity of pyraclostrobin-resistant strains to the carboxamide boscalid, an inhibitor of complex II, and to the anilinopyrimidine cyprodinil, a methionine biosynthesis inhibitor, was observed. Moreover, no effect of pyraclostrobin resistance mutation(s) on fungitoxicity of the hydroxyanilide fenhexamid, the phenylpyrrole fludioxonil, the benzimidazole benomyl, and to the phenylpyridinamine fluazinam, which affect other cellular pathways, was observed. Study of fitness parameters in the wild-type and pyraclostrobin-resistant mutants of B. cinerea showed that most mutants had a significant reduction in the sporulation, conidial germination and sclerotia production. Experiments on the stability of the pyraclostrobin-resistant phenotype showed a reduction of resistance, mainly in moderate resistant strains, when the mutants were grown on inhibitor-free medium. However, a rapid recovery of the resistance level was observed after the mutants were returned to a selective medium. Studies on the competitive ability of mutant isolates against the wild-type parent strain, by applications of a mixed conidial population, showed that, in vitro, all mutants were less competitive than the wild-type strain. However, the competitive ability of high resistant mutants was higher than the moderate ones. Pathogenicity tests on cucumber seedlings showed that all mutant strains tested exhibited an infection ability similar with the wild-type parent strain. Preventive applications of the commercial product of F-500 25EC (pyraclostrobin) were effective against lesion development on cotyledons by the wild-type, but ineffective, even at high concentrations, against disease caused by the pyraclostrobin-resistant isolates. Boscalid (F-510 50WG) was found equally effective against the disease caused by the wild-type or pyraclostrobin-resistant mutants. This is the first report indicating the appearance of B. cinerea strains resistant to QoI fungicides by the biochemical mechanism of site modification and the risk for field resistance.  相似文献   

16.
采用菌丝生长速率法测定了采自云南省5个三七主要产区的34株三七圆斑病原菌槭菌刺孢Mycocentrospora acerina (R. Hartig) Deighton对嘧菌酯、咪鲜胺和苯醚甲环唑的敏感性,并对不同敏感性菌株进行了生存适合度测定。结果表明:咪鲜胺、嘧菌酯及苯醚甲环唑对所有供试槭菌刺孢的菌丝生长均有明显的抑制作用,3种杀菌剂的EC50值分别在0.03~1.91 mg/L、0.18~2.36 mg/L和0.45~2.15 mg/L之间,即该菌株对咪鲜胺的敏感性对高于嘧菌酯和苯醚甲环唑;低敏感性菌株的致病力和菌丝生长速率与敏感性菌株间无显著差异,说明供试槭菌刺孢菌株在当地均具有较高的生存适合度。  相似文献   

17.
Forty-six (1.5%) of nearly 3000 isolates of Mycosphaerella graminicola assayed in vitro were resistant to the QOI fungicide azoxystrobin, but on sub-culturing only ten remained resistant. Cross-resistance extended to other QOIs, but varied between different isolates. In planta the resistant isolates were not well controlled, especially at lower azoxystrobin dose rates. Propyl gallate, an inhibitor of alternative oxidase, potentiated the activity of azoxystrobin in vitro so that resistance was no longer observed. The growth of resistant strains in the presence of azoxystrobin led to alternative oxidase activation. This increased flexibility in respiration allows resistant strains to survive in the presence of a QOI fungicide. Under these conditions, selection for target-site mutations can occur. Using QOIs preventatively reduces the risk of resistance since the alternative oxidase cannot by itself generate all the energy needed for germination and early infection.  相似文献   

18.
To mitigate the impact and dissemination of clubroot in western Canada, canola (Brassica napus) producers have relied on clubroot resistance traits. However, in 2013 and 2014, new strains of the clubroot pathogen, Plasmodiophora brassicae, emerged that are virulent on most clubroot‐resistant (CR) canola genotypes. Novel strains of the pathogen were inoculated onto two susceptible canola cultivars, one resistant line and six CR cultivars. Although all cultivars/lines showed a susceptible response to inoculation with the new strains of P. brassicae, the severity of disease reaction, root hair infection rates and the amount of P. brassicae DNA present in each canola genotype varied depending on the strain. In addition, the effect of inoculum density on disease severity and gall formation was recorded for one of these new strains on a universally susceptible Chinese cabbage cultivar and one susceptible and 10 resistant canola genotypes. Although root galls were observed at an inoculum density of 103 spores per mL of soil, clear differentiation of susceptible and resistant reactions among canola cultivars/lines was not observed until the inoculum density reached 105 spores mL?1. At a spore density of 106 spores mL?1 and above, all cultivars/lines developed susceptible reactions, although there was some differentiation in the degree of reaction. This study shows the potential to develop a unique disease profile for emergent clubroot pathotypes and shows a useful range of spore densities at which to study new P. brassicae strains.  相似文献   

19.
采用孢子芽管长度法,测定了采自河北省不同地区的88个梨黑星病菌 Venturia nashicola 菌株对氟硅唑的敏感性,并测定了10个相对敏感菌株和5个相对抗性菌株对甲基硫菌灵、醚菌酯、福美双和苯醚甲环唑的敏感性。结果表明:不同地区黑星病菌对氟硅唑的敏感性存在一定差异,平均EC50值为(1.3821±0.9276)μg/mL;氟硅唑对未使用过麦角甾醇生物合成抑制剂(EBI)类杀菌剂的75个梨黑星病菌菌株的平均EC50值为(1.1676±0.6128)μg/mL,最大值是最小值的16.91倍,其敏感性分布频率呈连续性单峰曲线,且符合正态分布,故可作为敏感基线用于监测田间梨黑星病菌对氟硅唑的敏感性变化。不同菌株对5种药剂的敏感性相互关系分析表明,氟硅唑和苯醚甲环唑之间呈显著正相关,但与醚菌酯、甲基硫菌灵和福美双之间均不存在交互抗性关系。  相似文献   

20.
Passalora blight of anise, caused byPassalora malkoffii (Bubák) U. Braun, is an important disease of anise in Turkey. The disease affects all the aboveground parts of plants including flower clusters. Infected seeds have dark, linear stromata. Detection of the pathogen on seeds was studied by the blotter method, agar method, washing test and sowing infected seeds in disease-free soils. The pathogen was recovered only by the washing test and to a limited extent by water agar + seed decoction agar. Sixteen of 24 seed samples from diseased regions were found to be infected. The pathogen was not detected by any other methods. However, several indigenous fungi,e.g. Alternaria alternata, were isolated, which may have prevented the growth of the pathogen. Seed washings of infected seed samples had typical spores of the pathogen up to 106 conidia per gram of seed. Transmission of the pathogen was shown by sowing infected seeds in disease-free field soils in two locations where anise had not been grown previously. Azoxystrobin, chlorothalonil + carbendazim and flutriafol seed treatments at 0.04 g a.i. kg−1 seed, 1.0 g + 4.5 g a.i. kg−1 seed and 0.015 g a.i. kg−1 seed reduced the disease by 92.5%, 89.6% and 36.2% in 2002 and by 78.9%, 75.8% and 41.2% in 2003, respectively. Three foliar applications of axosystrobin, chlorothalonil + carbendazim and flutriafol at the rates of 187.5 g a.i. ha−1, 1500 g + 6750 g a.i. ha−1 and 31.3 g a.i ha−1 reduced disease incidence by 92.5%, 86.0% and 96.8% in 2002 and by 97.5%, 90.8% and 97.0% in 2003, respectively. http://www.phytoparasitica.org posting May 17, 2005.  相似文献   

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