Diversity,spatial variation,and temporal dynamics of virulences in the German leaf rust (<Emphasis Type="Italic">Puccinia recondita</Emphasis> f. sp. <Emphasis Type="Italic">secalis</Emphasis>) population in winter rye

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.     

Evidence of host‐range expansion from new powdery mildew (Blumeria graminis) infections of triticale (×Triticosecale) in France

This study aimed to determine whether powdery mildew caused by Blumeria graminis is an endemic pathogen of triticale (×Triticosecale: Triticum × Secale), emerging as a result of recent changes in its pathogenicity, or whether it is a new pathogen, possibly resulting from hybridization between ff. spp. tritici and secalis. A secondary aim was to consider breeding practices that may have favoured this emergence. Phylogenetic analyses based upon six genes revealed the close relatedness of the novel entity and the ff. spp. tritici and secalis, but the IGS marker finally grouped together the isolates collected on triticale and on wheat, supporting the scenario of a recent host‐range expansion from wheat to triticale. Pathotype analyses concluded that virulence spectra of B. graminis infecting triticale were new in comparison to those observed for other reference formae speciales, and lack of fungicide resistance in triticale isolates strengthens the hypothesis of no or little genetic exchange between wheat and triticale populations of powdery mildew. This adaptation may follow the breakdown of plant resistance genes, which are probably not very diverse in current triticale cultivars since this criterion was not considered as a major one until recent years. Moreover, the complex selection and genetics of this hybrid cereal makes it difficult to predict the transmission of powdery mildew resistance genes.     

Racial diversity and complexity in regional populations of Erysiphe graminis f.sp. hordei in France over a 5-year period

The evolution of race patterns in three French regional populations of the barley powdery mildew pathogen Erysiphe graminis f.sp. hordei over a 5-year period showed rapid adaptation to newly introduced host resistance genes. In all three regions, the main change consisted of the replacement of initially abundant races by pathotypes differing markedly from them by their virulence gene combinations. This explained the increase in diversity during the first 3 years of the survey, when the second group of pathotypes became more common in the populations, and its subsequent decrease due to the decline of the first group of races. The mean number of virulence genes per isolate did not vary noticeably over time in the three populations, remaining at about four out of 12 genes tested. However, the distribution of the isolates into virulence complexity classes was greatly modified, fitting a binomial distribution by the end of the study, although significant deviations were apparent in the first 2 years (1986 and 1987). The data indicate that selection, migration and recombination are the most important factors shaping race structure and evolution in powdery mildew populations, and that mutation is of limited significance. No convincing evidence was obtained for the existence of stabilizing selection sensu Vanderplank as the mechanism limiting virulence complexity. Implications regarding spatial and temporal deployment of race-specific resistance genes to control powdery mildew are discussed.     

The Hordeum vulgare subsp. spontaneum–Blumeria graminis f. sp. hordei pathosystem: its position in resistance research and breeding applications

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.     

High diversity, low spatial structure and rapid pathotype evolution in Moroccan populations of Blumeria graminis f.sp. hordei

Limited information is available about the spatial distribution and evolution of Blumeria graminis f.sp. hordei populations in North African countries, such as Morocco. Frequencies of virulence alleles in B. graminis populations are mainly driven by selection exerted by host resistance genes in addition to neutral processes such as migration and genetic drift. In Morocco, in contrast to Europe, there has been no systematic deployment of resistant cultivars, although some R genes are present in the traditional varieties. This is expected to result in the evolution of pathotypes with virulence to different R genes, and higher diversity in Morocco compared to Europe. To test this, we used 24 differential cultivars to characterise 72 isolates from Morocco in 2009. We assessed diversity and spatial structure of pathotypes and compared them to past isolates from the same area (collected in 1992). There was a high diversity of pathotypes. Isolates from 2009 were distinct from isolates from 1992, due to loss of virulence to Mla12, increased virulence to Mla8, Mla3 and Mlk1, and decreased virulence to Mla6, Ml(Ru2), Mlg and MlLa. Many virulences were different from those observed in European and Asian populations of B. graminis. At the spatial scale investigated, airborne dispersal and a lack of strong selection in the host population likely prevented the formation of population structure and allowed the accumulation of high isolate diversity. The evolution of novel and distinct pathotypes since 1992 is likely attributable to gene flow from Europe and selection by the host population in Morocco.     

2013年我国部分麦区小麦白粉菌群体对温度敏感性及其与毒性的关系

 研究小麦白粉病菌群体对温度的敏感性及其与毒性的关系,可为气候变化背景下小麦白粉病的长期发生趋势预测和防治提供依据。本研究对2013年采自云南、四川、河南、北京和陕西五省（市）的小麦白粉菌标样进行分离纯化,获得90个单孢子堆分离物,采用小麦离体叶段法进行温度敏感性测定,并利用32个已知抗病基因品种（系）进行毒性测定,且对两者之间的相关性进行分析。结果表明,供试菌株ET50分布于19.78℃~25.15℃,平均ET50为23.22℃,其中73.34%的供试菌株ET50值介于22℃到24℃之间,小于22℃的菌株占10%,大于24℃的菌株占16.67%。利用Popgen1.32软件对5个省（市）小麦白粉病菌群体的毒性进行多样性分析,结果表明五省市小麦白粉菌群体毒性水平上的多样性指数 H 值为0.237 0,其中四川群体毒性多样性水平最高,Nei’s基因多样性指数 H 值为0.221 2,河南群体最低, H 值为0.197 5。小麦白粉菌群体对温度敏感性与毒性多样性相关性分析结果表明,ET50与毒性多样性（ H 和 I 值）间存在显著的负相关。     

The importance of non‐penetrated papillae formation in the resistance response of triticale to powdery mildew (Blumeria graminis)

Triticale is the intergeneric hybrid between wheat and rye. With the expansion of the triticale growing area, powdery mildew has emerged and become a significant disease on this new host. Recent research demonstrated that this ‘new’ powdery mildew on triticale has emerged through a host range expansion of powdery mildew of wheat. Moreover, isolates sampled from triticale still infect their previous host, wheat, but isolates sampled from wheat hardly infect triticale. Race‐specific and adult‐plant resistance have been identified in triticale cultivars. The main objective of this study was to characterize the cellular basis of powdery mildew resistance in triticale. Commonalities with resistance responses in other cereals such as wheat, barley and oat are discussed. A detailed comparative histological study of various resistance responses during cross‐inoculation of either virulent or avirulent wheat and triticale isolates on both hosts was carried out. The present data provide evidence that for incompatible interactions, the formation of non‐penetrated papillae is the predominant resistance response, while the hypersensitive response (HR) acts as a second line of defence, to cut the fungus off from nutrients, if penetration resistance fails. It is not clear yet what causes the slower growth and reduced colony size of triticale isolates when inoculated on wheat. Possibly, post‐penetration resistance mechanisms, other than HR, are switched on during these (semi‐) compatible interactions. Molecular studies on gene expression and gene function of defence‐related genes might reveal further insights into the genetic basis of these resistance responses.     

大麦白粉病菌遗传学研究进展

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。     

Virulence variation of cucurbit powdery mildews in the Czech Republic – population approach

Kosman diversity models were applied to analyses of virulence (disease reaction patterns) variation of 115 isolates of two cucurbit powdery mildew (CPM) species, Golovinomyces orontii (Go) and Podosphaera xanthii (Px), collected in the Czech Republic from 2010 through 2012. Diversity within and distances between Go and Px populations and each other in a spatio-temporal context and with regard to original host plant species were analyzed based on virulence patterns of individual isolates on a set of 21 melon (Cucumis melo L.) race differential genotypes. Significant differentiation among the Go and Px pathogen populations was revealed, and the results clearly demonstrate and confirm that the set of differential C. melo genotypes is well composed because of high differentiation capacity. Differentiation of pathogens among years was significant for both species. No significant difference between Go isolates from different host plant species was established due to high variability among Go isolates, but there was significant host-specific differentiation among Px isolates. Differentiation of pathogens among regions was not detected. These results revealed high virulence variation in isolates of Go and Px, and their spatio-temporal fluctuations. High diversity in virulence of Go isolates supports the treatment of Go as a complex of different (sub)species with distinct virulence factors. Similar relationships of selected Go isolates in a UPGMA dendrogram in a previously reported multigene phylogenetic tree support the logic and suitability of the Kosman assignment based approach to population studies of organisms with asexual or mixed modes of reproduction. The approach applied in this study provides a complex view of virulence structures of powdery mildew populations, and when combined with race determination and denomination on melon, it may serve as a base to understandvirulence variation of these CPM species from a spatio-temporal viewpoint.     

Analysis of diversity in populations of plant pathogens: the barley powdery mildew pathogen across Europe

Understanding population genetics and evolution within species requires recognition of variation within and between populations and the ability to distinguish between the potential causes of an observed distribution of variation. For this aim several established indices of diversity, and a novel one, were applied to population samples of the barley powdery mildew pathogen,Erysiphe graminis f. sp.hordei. Random spore samples were obtained from the air along transects through regions of interest across large parts of Europe in 1990. Significant geographical differences in diversity of virulence genotypes occurred among regional sub-samples. Diversity was highest in the samples from eastern Germany, Denmark and Austria, whereas the lowest values were found in the samples from Italy, southern France and parts of western Germany. Diversity in the pathogen population was generally related to the degree of diversification of host resistance in time and space, although there was considerable variation in ranking among different measures of diversity. Sensitivity to sample size proved to be the major problem with the use of several established indices of diversity. Working with very large sample sizes we used multiple random subsamples of various smaller sizes to determine how the mean index values changed with changing sample size. The Shannon index proved to be considerably affected by sample size, in contrast to the Simpson index that was therefore used as a global measure of diversity. Limits of confidence were estimated for the Simpson index using the bootstrap method of numerical resampling. The two aspects contributing to global diversity, richness and evenness, were considered separately to allow meaningful interpretation of the Simpson index. Random sub-sampling was used to reduce the influence of sample size differences for these measures. Dissimilarity, a novel measure of diversity for use in plant pathology, indicates the average number of major genes for host resistance against which pathotypes in a sample respond differently. It is thus able to account for the genetic relationship among pathotypes, which is not considered by any other index. The approaches developed in this study help to compare major forces driving evolution of large-scale populations of the barley mildew pathogen.     

Occurrence of races and pathotypes of cucurbit powdery mildew in southeastern Spain

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.     

The Race-Specific Resistance Gene to Powdery Mildew, MlRE, Has a Residual Effect on Adult Plant Resistance of Winter Wheat Line RE714

ABSTRACT Race-specific resistance genes to powdery mildew have been extensively used in wheat breeding programs, but the complete resistance they provide breaks down when confronted by pathogen isolates with matching virulence. However, when overcome, some race-specific genes have a residual action leading to a reduction of the symptoms. Our objective was to determine if the resistance genes MlRE and Pm4b have a residual effect on adult plant resistance (APR) and on vernalized seedling plant resistance (VPR) in the line RE714. Individuals from two populations (double haploid [DH] and F(3) families) were genotyped for the race-specific genes MlRE and Pm4b and assessed for their resistance under field conditions at the adult plant stage (in 1996 and 1997 for the DH lines and in 1997 for the F(3) families). Vernalized seedlings of the DH population were tested with four powdery mildew isolates. Only the MlRE gene had a significant effect (dominant type) on APR. Neither MlRE nor Pm4b had a significant effect on VPR. The dominant residual effect of the defeated race-specific gene MlRE was a component of APR in the line RE714.     

Intrapathotype diversity for aggressiveness and pathogen evolution in cultivar mixtures

ABSTRACT A model was developed and used to study the consequences of diversity for aggressiveness within pathotypes on pathogen evolution in two-component and four-component cultivar mixtures. It was assumed that, within a pathotype, a proportion of the isolates would have higher or lower spore efficacy than the average on a given host genetic background. Two situations were examined in which the pathogen can have either independent or negatively correlated values for spore efficacy on different cultivars. In the latter case, a pathogen genotype more aggressive than the average on a host genotype was always less aggressive on other host genotypes. In the simulations, isolates with greater aggressiveness relative to a host genotype were selected for and increased in frequency. However, because simple pathotypes always reproduced on the same host genotype whereas complex pathotypes were able to grow on several hosts, selection was faster for simple pathotypes. Pathotypes with two different levels of diversity for aggressiveness were compared with nondiversified pathotypes. In order to make comparisons, the effect of a 5 and 10% cost of virulence on the development of complex pathotypes was simulated. In general, increased diversity within pathotypes reduced the rate of increase of complex pathotypes in host mixtures, and this effect was stronger with greater frequencies of autodeposition of pathogen spores.     

Comparison of Genetic and Virulence Diversity of Melampsora larici-populina Populations on Wild and Cultivated Poplar and Influence of the Alternate Host

ABSTRACT The aims of this study were, first, to compare the genetic and virulence diversity between populations of the rust fungus Melampsora larici-populina on wild and cultivated poplar stands and, second, to investigate the influence of the presence of the alternate host of the pathogen, larch, on which its sexual reproduction occurs, on these diversities. Nine French M. larici-populina populations collected from poplar trees in autumn and four populations collected from larch trees during the following spring were analyzed using both virulence factors and neutral markers. In all, 30 pathotypes were identified within the 13 populations studied. The pathotypic structure clearly distinguished the cultivated stands with high richness and complexity from the wild stands with low richness and complexity. High linkage disequilibria between virulences indicated preferential virulence associations, probably due to selection by the host. In all, 19 random amplified polymorphic DNA (RAPD) markers were used, which revealed a very high genetic diversity in the 743 isolates analyzed. The nine populations from poplar appeared moderately differentiated, indicating long-distance gene flow, and no isolation by distance was found. Linkage disequilibria between RAPD markers generally were low, indicating frequent recombination, but they were not lower in populations located near larch, probably due to long-distance dispersal.     

Virulence structure of the <Emphasis Type="Italic">Blumeria graminis</Emphasis> DC.f. sp. <Emphasis Type="Italic">avenae</Emphasis> populations occurring in Poland across 2010–2013

The aim of the present study was to determine the virulence structure of powdery mildew of oats (Blumeria graminis DC.f. sp. avena) in Poland in the years 2010–2013. For this purpose, powdery mildew isolates were collected from three experimental stations in Poland. To assess the virulence of the isolates, eight oat varieties with different responses to the pathogen were used. The results showed that a significant proportion of powdery mildew isolates found in Poland overcame the resistance genes of varieties Bruno (Pm6), Jumbo (Pm1) and Mostyn (Pm3). In contrast, lines Av1860 (Pm4), Am27 (Pm5) and Cc3678 (Pm2) were completely resistant to all pathogen isolates involved in the experiment. Changes constantly occurring in the powdery mildew population perfectly reflect diversity indexes, which were the smallest in the first year of observation, where in the following years these parameters were significantly higher. It is worth noting that the presence of powdery mildew is seasonal and local, which is reflected in the prevalence of the disease in a defined area of the country.     

江苏省水稻品种对水稻细菌性条斑病抗性鉴定及评价

为明确江苏省水稻条斑病菌致病力分化状况和不同类型水稻品种对条斑病抗感特性,在孕穗期采用针刺接种法对徐淮稻区2007—2009年采集分离获得的45株条斑病菌进行致病力测定,根据病原菌在6个水稻鉴别品种IRBB4、IRBB5、IRBB14、IRBB21、IR24和金刚30上的抗感反应划分致病型,从中选择具有代表性的3种不同致病型条斑病菌,并鉴定了240个不同类型的水稻品种对条斑病的抗感性。根据菌株在鉴别品种上的抗感反应将供试菌株划分为8个致病型,其中优势致病型为C3致病型,所占比例为35.5%;大多数菌株与鉴别品种间表现出弱互作关系,少数菌株表现出强互作关系。粳稻品种对条斑病的抗性明显高于籼稻,但常规粳稻和杂交粳稻对强致病力菌抗性比例仅为59.8%和37.5%。表明水稻细菌性条斑病流行仍具有潜在的威胁。     

2009—2010年河南省小麦白粉菌群体毒性及其遗传多样性分析

利用40个鉴别寄主对河南省5个小麦产区的44个单孢子堆纯化分离的小麦白粉病菌进行毒性鉴定分析,并采用多基因家系法进行了遗传多样性分析。结果显示,供试群体对Pm8、Pm1、Pm3a、Pm3b、Pm3c、Pm3f、Pm3e、Pm5、Pm6、Pm7、Pm17、Pm19、Pm34等抗病基因的毒性频率分别达到90%以上,已不能再作为抗源利用;对Pm12、Pm16、Pm21、Pm18、Pm2、Pm2＋6、Pm2＋MLD、Pm5（Mli）、Pm23、Pm30、Pm4a等基因的毒性频率低于15%,仍可以在抗病育种中加以利用;河南省的小麦白粉病菌存在地理之间的差异,同时病菌在地区之间有自西南向东北/东方向的传播。表明省内群体中存在着丰富的遗传多样性。     

Stability and variability of virulence of Phytophthora infestans assessed in a ring test across European laboratories

Determining virulence towards race‐specific resistance genes is a prerequisite to understanding the response of pathogen populations to resistant cultivars, and therefore to assess the durability of these resistance genes and the performance of resistance management strategies. In Phytophthora infestans, virulence testing began shortly after the introduction of R‐genes from Solanum demissum into S. tuberosum cultivars. However, the characteristics of R‐gene expression, the sensitivity of the phenotype to environmental and physiological parameters, and the diversity of experimental protocols make the comparison of data from different studies problematic. This prompted European teams working on P. infestans diversity to: (i) design a joint protocol, using detached leaflets from greenhouse‐grown plants of a shared set of differential cultivars inoculated with standardized suspensions of inoculum, and (ii) assess the performance of this protocol in a blind ring test involving 12 laboratories and 10 European isolates of the pathogen. A high level of consensus in the determination of virulence/avirulence to R1, R3, R4, R7, R8, R10 and R11 was achieved among the collaborators, showing that the protocol could be robustly applied across a range of laboratories. However, virulence to R2, R5 or R9 was detected more frequently in some laboratories, essentially from northern Europe; these genes are known to be highly sensitive to host and environmental conditions. The consensus determination was often markedly different from the original virulence phenotype of the isolates, suggesting virulence instability in stored P. infestans isolates. This indicates that creating reliable core collections of pathogen isolates with known virulences could be difficult.     

Virulence phenotypes of Blumeria graminis f. sp. hordei in South Africa

Virulence analysis of 224 isolates of Blumeria graminis f. sp. hordei (barley powdery mildew) from South Africa was performed. The isolates were collected from eight fields and a greenhouse in 2004 and 2007. The isolates were tested for virulence on a set of 20 differential varieties. All isolates were virulent on the resistance genes Mla8 and Ml(Ch) and avirulent for the resistance genes Mla3, Mla6, Mla7, Mla9, Mla13, Mla23, Mlp1 and MlaN81. Virulence frequencies of field isolates for the resistance genes Mla12 + MlaEm2, Mlat, Mla22, Mlk1 and Mlh were 52.9–99.5 % and for Mla1 + MlaAl2, MlLa, Mlra, Mlg + MlCP and Ml(Ru2) were 0.5–23.5 %. In total, 46 pathotypes were detected in the field and seven other pathotypes in the greenhouse. Only nine pathotypes were found in both years, but they included 61.8 % of the isolates. The predominant pathotype represented 15.9 % of the isolates, and was the only one common to all three field populations. The average relative virulence complexity per field isolate increased from 0.405 in 2004 to 0.486 in 2007. Two powdery mildew metapopulations in geographically distant and separated areas (North West and Western Cape) were deduced. The South African population of Blumeria graminis f. sp. hordei had unique virulence frequencies and virulence associations when compared to populations from other parts of the world.     

大麦白粉菌种群毒性监测及抗性材料鉴定

2005和2006年从我国冬大麦区采集和分离大麦白粉菌单胞菌株729个,利用Pallas近等基因系进行致病型鉴定和群体毒性频率分析.同时,利用分离得到的不同致病型菌株,通过抗谱分析的方法鉴定了328份大麦品种(系)的白粉病抗性和抗病基因.结果显示:大麦白粉菌群体对抗病基因Mlal Mla(A12)、Mla3、Mla6 Mla14、Mla7 Mla(No3)、Mla7 Ml(Lg2)、Mla9 Mlk、Mla9、Mlal3 MlaRu3、Mlpl、Mlg(Cp)和mlo5的毒性频率为0;对Mla12 MlaEm2、Mla7 Mlk、Mlat Mla8、Mla10MlaDu2和Mlk1的毒性频率很低,分别为0.1%、0.4%、0.9%、2.8%和4.2%.两年共鉴定出不同的致病型21个,致病型000、001和003在两个年度皆为优势致病型.所鉴定的328份材料绝大多数感病,仅37份抗病材料,能明确推导出抗白粉病基因的品种(品系)很少,这些品种(品系)含有的抗白粉病基因为Mr(Bw)Mla8、Mlg、Mira Mla8、Mla9 Mla1、Mla Mla(A12)和mlo5.