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1.
Triticale (xTriticosecale) is a new host for powdery mildew (Blumeria graminis) being not infected by this pathogen in Germany before 2001. To evaluate population structure of the pathogen and race-specific resistances in the host, 694 isolates were collected in 12 states of Germany in the years 2007 to 2009 on triticale. They were tested by a newly developed initial differential set of 20 triticale cultivars. Corresponding virulences were found for all differentials except for cultivar Grenado. In total, 272 different virulence phenotypes (=pathotypes) were detected. The virulence complexity of the isolates ranged from 6 to 19 of 20 possible virulences with a mean of 15. In all years, a high level of diversity of the powdery mildew populations was observed with Simpson indices in the range 0.95 to 0.97. The distribution of the pathotypes was even across Germany with an Evenness index in the range 0.82 to 0.88. A set of 19 isolates with different virulence pathotypes and 10 cultivars were selected to be used to identify race-specific resistances of triticale cultivars and breeding lines. Some cultivars susceptible to most of the isolates in seedling stage were moderately resistant in adult-plant stage. The high diversity and complexity of the pathotypes found in German powdery mildew populations as well as an increasing acreage of only a few dominating triticale cultivars accelerate the adaptation of the pathogen to race-specific host resistances suggesting restricted durability only. More durable resistance might be achieved by combining new effective race-specific (qualitative) resistance genes with race-nonspecific (quantitative) resistances effective in the adult-plant stage that are already available.  相似文献   

2.
为明确不同栽培模式下葡萄霜霉病菌Plasmopara viticola的遗传结构、遗传多样性及遗传分化水平,于2014-2015年定期采集露地和避雨2种栽培模式下的葡萄霜霉病菌菌株,利用6对SSR引物对该病菌基因型、遗传多样性及遗传分化进行对比分析。结果表明,露地和避雨栽培模式下葡萄霜霉病菌群体的Nei’s基因多样性指数大于0.14,香农多样性指数大于0.31,2种栽培模式下群体具有丰富的遗传多样性,但避雨栽培模式可显著降低群体等位基因数和等位基因频率。露地栽培模式下该病菌群体的流行模式呈现中等水平无性繁殖,2年初侵染和再侵染对病害流行的贡献率分别约占26.1%和73.9%;避雨栽培模式下葡萄霜霉病菌群体的流行模式则呈现高等水平无性繁殖,初侵染和再侵染对病害流行的贡献率分别约占4.3%和95.7%。卵孢子的形成对于葡萄霜霉病菌种群遗传变异和有效越冬起着关键的作用。2014-2015年露地栽培模式下葡萄霜霉病菌群体的主效流行基因型对病害流行的贡献率分别为44.5%和51.8%;而其在避雨栽培模式下葡萄霜霉病菌群体的贡献率分别可达84.2%和87.1%。同一年份的露地和避雨栽培模式下葡萄霜霉病菌群体的主效基因型种类相同,2个群体间的等位基因频率呈现显著正相关性,且二者之间存在频繁的基因交流,推测避雨栽培模式下葡萄霜霉病的初侵染源自于避雨设施附近的露地栽培病株上再侵染形成的飞散传播孢子囊。  相似文献   

3.
Powdery mildew populations were analysed to determine the effects of a resistance elicitor and cultivar mixtures on genetic complexity and diversity. Isolations were made from a range of spring barley monocultures and mixtures in a field trial, and characterised for virulence and RAPD profile. In a second trial, isolates were taken from a single mixture from untreated and resistance elicitor-treated areas and from the components of the mixture in monoculture. The mildew population was not only highly heterogeneous for virulence characteristics, but also proved heterogeneous within pathotypes for molecular markers, indicating the major impact of sexual recombination on population structure and the lack of clonal dominance. Various diversity measurements were compared and the value of dissimilarity measurement for revealing genetic distance within a population was highlighted. There was a trend towards increasing complexity as the season progressed, but there was no consistent relationship between cultivar or mixture, disease control treatment, fertiliser treatment, replicate or position in trial, and pathogen genotype. Whilst the resistance elicitor did reduce mildew by 78% in the first trial, and there was no interaction with fertiliser level in its expression, control was substantially less in the second trial. There were no differences between mildew isolates from elicitor and control treatments. It was felt that more effective and consistent resistance elicitors need to be developed before it can be stated that they are unlikely to be eroded by selecting resistant or adapted mildew genotypes.  相似文献   

4.
The effect of the use of different doses of the fungicide fenpropimorph on populations of barley powdery mildew Blumeria ( Erysiphe ) graminis f. sp. hordei was investigated in a laboratory selection experiment. A sample from the Danish aerial population of powdery mildew was split into populations, and these were kept separately for 31 generations on susceptible barley seedlings treated with fungicide at two concentrations, as well as on a control. Samples from these populations were tested for their resistance to fenpropimorph and their virulence spectra. There was a large amount of environmental variation in the ED50 values used to measure fungicide resistance. In both treated populations, the average level of fungicide resistance increased, this increase being faster and greater in the population treated with the high dose. The diversity of pathotypes of the treated populations decreased, with the decline being more rapid in the population treated with the high dose, where one pathotype dominated the population after 31 generations. This pathotype was apparently not the fittest in the population treated with the low dose. This implies that knowledge of ED50 is not sufficient to predict pathotype evolution under different fungicide treatments. The dominant pathotype in the high-dose treatment may not have been clonal, as there was evidence of two levels of fungicide resistance. The large environmental variation observed in estimated ED50 values for resistance towards fenpropimorph may help to explain why this resistance has evolved at a slower rate than resistance towards other fungicides.  相似文献   

5.
Aggregation in the distribution of pathotypes of Erysiphe graminis f.sp. hordei , the barley powdery mildew pathogen, was investigated in field plots of 'Golden Promise', 'Proctor' and 'Tyra'. 'Golden Promise' and 'Proctor' have no effective mildew resistance alleles, whereas 'Tyra' has Mla1 , which was only effective against a proportion of the mildew population. Isolates of mildew were sampled according to a grid sampling scheme and their virulence spectra ascertained in order to group them according to pathotype. The populations were very diverse, and evidence for aggregation (quantified using join counts) was found only in the 'Tyra' plots, at distances of up to 1m. This aggregation was reduced in a subsequent sample. The results are consistent with a model in which mildew epidemics are started by a large number of initial infections, which then form diffuse, overlapping aggregations of clones. These aggregations then become more diffuse, so that the amount of aggregation reduces with time. The greater amount of aggregation seen in the 'Tyra' plots might have been caused by there being less initial inoculum with virulence towards that cultivar.  相似文献   

6.
Net form of net blotch caused by Pyrenophora teres f. teres (Ptt) is a major foliar disease of barley (Hordeum vulgare) worldwide. Knowledge of the evolution of Ptt pathogen populations is important for development of durable host-plant resistance. This study was conducted to investigate changes in genetic structure of a Ptt population within a barley field during three cropping years. The susceptible barley cultivar Henley was inoculated with Ptt isolate NB050. Leaf samples were collected during the years 2013–15 and 174 single spore Ptt isolates stored. Genotyping using Diversity Arrays Technology markers identified that 25% of isolates were clones of the inoculated isolate and 75% of isolates were multilocus genotypes (MLGs) differing from the original inoculated genotype. The novel genotypes probably originated from a combination of windborne spores from neighbouring fields, infected seed and sexual recombination in the field. The rapid change in the genotypic composition of the Ptt population in this study suggests adaptive potential of novel genotypes and demonstrates the need for barley breeders to use multiple sources of host-plant resistance to safeguard against resistance being overcome.  相似文献   

7.
The fatty acid composition of sunflower downy mildew, Plasmopara halstedii, was compared to other parasitic Oomycetes and to pathogenic fungi associated with sunflower by gas chromatographic analysis. P. halstedii revealed a characteristic profile differing from all other samples by the dominance of 5Z,8Z,11Z,14Z,17Z-eicosapentaenoic acid. The infraspecific variation between the isolates of sunflower downy mildew was low: no correlation was visible between fatty acid profiles and isolates of different pathotypes or from different geographic origins. Lipids from hyphae, zoosporangia and oospores of the pathogen contained the same fatty acids, though the content of 5Z,8Z,11Z,14Z,17Z-eicosapentaenoic acid was significantly lower in oospores. The taxonomic and diagnostic value of the fatty acid profile in P. halstedii is discussed.  相似文献   

8.
A large collection of German rye leaf rust isolates was analysed to characterize the diversity, spatial variation and temporal dynamics of virulences. Virulence-avirulence phenotypes (=pathotypes) were determined on 23 host differentials. We found 93 pathotypes among 177 single-uredinial isolates in 2000, 201 pathotypes among 437 isolates in 2001, and 125 pathotypes among 213 isolates in 2002. In total, the 827 analyzed isolates represented 317 pathotypes. Frequency of virulences on the individual differentials varied from 2% to 97%. Eight of the differentials showed a high resistance level with virulence frequencies <10%. Virulence complexity of the isolates ranged from 3 to 21 with a mean of nine. The percentages of highly virulent isolates (>14 virulences) increased from 4 to 15% during the sampling period. A high level of virulence diversity was observed within and between individual sampling sites with Simpson indices around 0.9. Evenness indices ranged from 0.88 to 0.92. Four of the five most frequent pathotypes were found in each year but their frequency never exceeded 10%. Isolates with unusual virulence combinations could be clearly separated by principal component analysis. Location-specific pathotype frequencies were revealed in each year, but the frequency patterns varied across years. On four fields a considerable increase of highly virulent pathotypes occurred within 6 weeks during the epidemic. The high diversity of pathotypes as well as the fast accumulation of highly virulent pathotypes favour the adaptation of the pathogen to race-specific host resistances. More durable resistance might be achievable by combining new effective race-specific resistances with adult-plant and/or race-non-specific quantitative resistances.  相似文献   

9.
大麦白粉病菌遗传学研究进展   总被引：1，自引：0，他引：1  
大麦白粉病是由布氏白粉菌属大麦专化型活体寄生菌Blumeria graminis f.sp.hordei（Bgh）引起的真菌病害,在全球大麦种植区普遍发生,危害日趋严重。大麦白粉病菌与寄主之间存在着“基因对基因”的关系,分化为不同的生理小种或致病型。由于病原菌基因突变、重组和流动以及寄主的选择作用,大麦Bgh种群毒性、致病型频率和分布不断发生变化。随着分子生物学技术飞速发展,应用分子标记已对30多个Bgh无毒基因位点进行了连锁作图分析,已克隆了Bgh无毒基因AVRk1和AVRa10,Bgh全基因组测序现已完成。文章综述了大麦白粉病菌的侵染循环、遗传分化及其无毒基因的定位、克隆和致病机制研究进展,并探讨了基于病原菌毒性进化和基因组解码信息获得持久控制大麦白粉病的有效手段。  相似文献   

10.
Barley (Hordeum vulgare L.) is an important cereal crop and powdery mildew, caused by Blumeria graminis f. sp. hordei, is one of the most serious diseases that occurs on barley throughout the world. In the Middle East, which is the centre of diversity for barley and its pathogens, the wild barley–powdery mildew pathosystem co-evolves resulting in many specific resistances in the host as well as corresponding virulences in the pathogen. Many specific resistances have been used in European breeding programmes and a centre of pathogen diversity has arisen also especially in central Europe. This short review briefly summarizes the use of host resistances derived from wild barley and land races including the durable resistance gene mlo. The use of powdery mildew pathogenicity for studying new and unknown specific resistances and for identifying resistances in commercial varieties is described. However, highly heterogeneous wild barley is also characterized as a valuable source of minor genes for powdery mildew resistance. These might be exploited by barley breeders especially for winter barley improvement where the non-specific resistance gene mlo cannot be used.  相似文献   

11.
A field experiment with barley powdery mildew ( Blumeria graminis f.sp. hordei ) was designed in order to study how the time of arrival of inoculum in the field influenced pathotype frequencies in the resulting populations. Three isolates belonging to pathotypes that were absent or rare in the local aerial inoculum were used to inoculate field plots of winter barley cv. Plaisant. Two successive inoculations with different combinations of the three isolates were performed with an approximately two-generation delay, and frequencies of inoculated pathotypes were assessed four and nine generations after the first inoculation. Pathotypes of the first inoculated isolates generally persisted throughout the period of sampling; this is described as an 'early arrival' effect. During the epidemics the inoculated isolates were not replaced by isolates from the natural airborne inoculum. Pathotype frequencies depended mainly on the time of arrival of inoculum in the plot, but frequencies also depended on the isolate that had been inoculated. The most frequent isolate, GL1, belonged to the clonal lineage dominant in powdery mildew populations on winter barley in the north of France. These results confirmed that the composition of a powdery mildew population in a field is largely determined by the composition of the initial inoculum.  相似文献   

12.
Airborne conidia of Erysiphe graminis f.sp. hordei were sampled in three regions and a single locality in the northern part of France for 2 years. Sampling was carried out in early spring, in late spring and in autumn, in order to separate the effects of winter barley cultivars, carrying few specific resistance alleles, and of spring barley cultivars, carrying diverse resistance alleles, on the structure of the pathogen population. Although complex pathotypes with three to 10 virulences were selected by spring cultivars, simple pathotypes, including a pathotype with the single unnecessary virulence allele Va22 , which formed a clear majority of the samples, remained dominant in early spring, when winter but not spring cultivars were growing. In early spring, simple pathotypes were more prevalent in the north, where the winter cultivars represented 90% of the barley acreage, than in the east, where winter cultivars represented 65%. In the west, the frequency of simple pathotypes was limited compared to the north, possibly because of the resistance allele Mlg in winter cultivars. The high frequency of simple pathotypes in early spring could be explained by a differential adaptation between simple and complex pathotypes or by delayed epidemics on spring cultivars compared to winter cultivars.  相似文献   

13.
Diversity of powdery mildew pathogens infecting pea (Pisum sativum) in the US Pacific Northwest was investigated using both molecular and morphological techniques. Phylogenetic analyses based on rDNA ITS sequences, in combination with assessment of morphological characters, defined two groups of powdery mildews infecting pea. Group I (five field samples and three glasshouse samples) had ITS sequences 99% similar to those of Erysiphe pisi in GenBank and exhibited simple, mycelioid type of chasmothecial appendages typical of E. pisi. Erysiphe pisi is normally considered as the powdery mildew pathogen of pea. Group II (four glasshouse samples and two field samples) had ITS sequences 99% similar to those of E. trifolii and produced chasmothecia with dichotomously branched appendages similar to those of E. trifolii. There are fourteen nucleotide differences in the ITS region between the two groups. The correlation of rDNA ITS sequences with teleomorphic features for each of the two groups confirms their identity. Repeated samplings and artificial inoculations indicate that both E. pisi and E. trifolii infect pea in the US Pacific Northwest. Erysiphe trifolii is not previously known as a pathogen of pea. The existence of two distinct powdery mildew species infecting pea in both glasshouse and field environments may interfere with the powdery mildew‐resistance breeding programmes, and possibly explains putative instances of breakdown of resistance in previously resistant pea breeding lines.  相似文献   

14.
Leaves of Xanthium strumarium infected with downy mildew were collected in the vicinity of a sunflower field in southern Hungary in 2003. Based on phenotypic characteristics of sporangiophores, sporangia and oospores as well as host preference the pathogen was classified as Plasmopara angustiterminalis. Additional phenotypic characters were investigated such as the size of sporangia, the number of zoospores per sporangium and the time-course of their release. Infection studies revealed infectivity of the P. angustiterminalis isolate to both X. strumarium and Helianthus annuus. Inoculation of the sunflower inbred line, HA-335 with resistance to all known P. halstedii pathotypes, resulted in profuse sporulation on cotyledons and formation of oospores in the bases of hypocotyls. Infections of sunflower differential lines often led to damping-off. Molecular genetic analysis using simple sequence repeat primers and nuclear rDNA sequences revealed clear differences to Plasmopara halstedii, the downy mildew pathogen of sunflower.  相似文献   

15.
The barley powdery mildew pathogen, Blumeria graminis f. sp. hordei (Bgh), exists in numerous haplotypes and displays significant differences in fungicide sensitivity. It causes considerable yield losses throughout the world. Microsatellite SSRs are useful tools to study the population level and biogeographic aspects of intraspecific diversity, but so far none have been defined for Bgh. Here, eight polymorphic microsatellite loci were identified and characterized. Primer pairs amplifying the loci were then applied to 111 isolates of Bgh from Australia. The number of alleles per locus ranged from 4 to 13, and Nei's genetic diversity ranged from 0·25 to 0·76. The microsatellite primers detected several clones among the isolates and defined 97 unique haplotypes. There was little evidence for regional genotypic subdivision, suggesting that gene flow may not be restricted among geographic regions. All data was consistent with high levels of genetic diversity, potentially resulting from random mating and spread within each region.  相似文献   

16.
为掌握新疆主要植棉区棉花黄萎病的发生现状及其病原菌大丽轮枝菌Verticillium dahliae的落叶型菌系分布以及遗传变异情况,于2015年对26个新疆主要植棉区棉花黄萎病的发生情况进行了随机调查,统计新疆大丽轮枝菌的培养性状,利用大丽轮枝菌落叶型特异引物D1/D2、INTD2F/INTD2R与非落叶型特异性引物ND1/ND2、INTNDF/INTNDR对新疆大丽轮枝菌菌系进行互补鉴定,并对部分菌系的遗传变异进行简单序列重复区间(inter simple sequence repeat,ISSR)分析。结果表明:2015年新疆棉花黄萎病发病田比例为54.0%,其中病情指数在10.0以上的发病田与2013年持平,而病情指数在20.0以上的严重发病田比例为10.8%,比2013年增加3.8个百分点;新疆大丽轮枝菌的培养性状以菌核型为主,比例为70.1%,菌丝型与中间型比例分别为13.4%和16.5%;新疆大丽轮枝菌落叶型菌系比例为53.2%,26株菌株的来源地全部检出落叶型菌系;聚类分析结果显示,当遗传相似系数为0.66时,新疆大丽轮枝菌落叶型与非落叶型菌系聚为2个谱系,菌系地理来源、培养性状与大丽轮枝菌的遗传分化无明显相关性。  相似文献   

17.
The causal agent of cucurbit powdery mildew in southeastern Spain has been investigated since 1996. Of the 139 single-spore isolates obtained, all were identified asSphaerotheca fusca. Four physiological races (1, 2, 4 and 5) of the pathogen were detected. During the survey, a population shift ofS. fusca was observed: race 1 was progressively replaced by other races. In addition, race coexistence was observed in several cucurbit greenhouses. Four host range patterns or pathotypes were distinguished among the isolates ofS. fusca. All isolates were highly aggressive on melon and especially on zucchini cultivars. No clear relationships between races and pathotypes could be established, although isolates virulent on watermelon were preferentially associated with race 1. These data show an apparent heterogeneity ofS. fusca populations in southeastern Spain that should be analyzed further. http://www.phytoparasitica.org posting Aug. 9, 2002.  相似文献   

18.
Worldwide Puccinia striiformis f. sp. tritici (Pst) epidemics have been reported to be driven by few genetic lineages, while a high diversity is evident at the Pst Himalayan centre of diversity. This study investigated the relationship between pathotype diversity and genetic structure in Nepal, the eastern Himalayan region, which has been largely unexplored. Despite the high genetic diversity and recombinant structure detected through microsatellite genotyping, characterization of virulence phenotypes for 62 isolates identified only eight pathotypes, with two pathotypes predominant over all the populations. This is in contrast to the Pakistani and Chinese recombinant populations, where high pathotype diversity is associated with genetic diversity. The most prevalent Nepali pathotype was not a unique clonal lineage, but was represented by seven multilocus genotypes from four distinct genetic subgroups, suggesting strong directional selection on virulence genes, resulting in convergent pathotypes in distinct genetic groups. This convergent selection is discussed in comparison with clonal French and recombinant Pakistani populations. Additionally, the Nepali Pst population carried virulence to 17 out of 24 tested yellow rust resistance genes (Yr), with the absence of virulence to Victo and Early Premium and resistance genes Yr5, Yr10, Yr15, Yr24 and Yr26. Virulence to Yr2, Yr7, Yr27 and YrSu were fixed in all isolates, in line with the deployment of these resistance genes in Nepal. The results reflect the influence of resistance gene deployment on selection of virulence and pathotypes in a recombinant pathogen population, which must be considered in the context of durable resistance gene deployment.  相似文献   

19.
Genotypic diversity in barley powdery mildew populations in northern France   总被引：1，自引：0，他引：1  
Caffier  Brändle  & Wolfe 《Plant pathology》1999,48(5):582-587
Diversity in populations of Erysiphe graminis ( Blumeria graminis ) f.sp. hordei was studied with virulence and molecular markers. Isolates were sampled in two locations in northern France from a winter barley cultivar (Plaisant) and a spring cultivar (Caruso). Only a few pathotypes (determined by virulence markers) were common. The rest of the population was diverse. Diversity within common pathotypes, estimated by five RAPD and two SCAR markers, was generally high, except for one pathotype, which was frequent on Plaisant. This pathotype carried only one virulence, Va22, out of the 11 virulences tested. It appeared as a clonal lineage, which had occurred previously, at least in 1992, in northern France, demonstrating survival of asexual lineages in populations that often reproduce sexually.  相似文献   

20.
DNA isolated from the formae speciales of Erysiphe graminis that grow on barley, wheat, rye and oats was studied using restriction endonucleases and DNA/DNA hybridization procedures. DNA fragments were purified by molecular cloning and a few containing repeated sequences were used to demonstrate the many variations in restriction fragments both within and between the four formae speciales. In an analysis of six single-colony isolates of the barley mildew pathogen collected from different UK sites in different years, more than a quarter of the fragments scored varied among isolates. One isolate, with an uncommon pathogenicity character, differed from the remainder in the distribution of DNA bands. Isolates of rye mildew were also distinct from one another but isolates of oat mildew from a population of similar size appeared to belong to a single clone.
It is concluded that the chromosomes of E. graminis contain many families of dispersed repeated sequences and that there may be extensive polymorphism for restriction endonuclease cleavage sites associated with these repeats. Such unselected polymorphisms could be useful in helping to understand and discriminate among the factors affecting population structure in the pathogen as it responds to different agricultural practices.  相似文献   

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