The application of high-throughput AFLP's in assessing genetic diversity in Fusarium oxysporum f. sp. cubense

Fusarium oxysporum f. sp. cubense (Foc) is responsible for fusarium wilt of bananas. The pathogen consists of several variants that are divided into three races and 21 vegetative compatibility groups (VCGs). Several DNA-based techniques have previously been used to analyse the worldwide population of Foc, sometimes yielding results that were not always consistent. In this study, the high-resolution genotyping method of AFLP is introduced as a potentially effective molecular tool to investigate diversity in Foc at a genome-wide level. The population selected for this study included Foc isolates representing different VCGs and races, isolates of F. oxysporum f. sp. dianthi, a putatively non-pathogenic biological control strain F. oxysporum (Fo47), and F. circinatum. High-throughput AFLP analysis was attained using five different infrared dye-labelled primer combinations using a two-dye model 4200s LI-COR automated DNA analyser. An average of approx. 100 polymorphic loci were scored for each primer pair using the SAGA^MX automated AFLP analysis software. Data generated from five primer pair combinations were combined and subjected to distance analysis, which included the use of neighbour-joining and a bootstrap of 1000 replicates. A tree inferred from AFLP distance analysis revealed the polyphyletic nature of the Foc isolates, and seven genotypic groups could be identified. The results indicate that AFLP is a powerful tool to perform detailed analysis of genetic diversity in the banana pathogen Foc.     

HOST-PATHOGEN INTERACTIONS IN NATURAL POPULATIONS OF LINUM MARGINALE AND MELAMPSORA LINI: I. PATTERNS OF RESISTANCE AND RACIAL VARIATION IN A LARGE HOST POPULATION

Populations of wild flax, Linum marginale and its associated rust fungus Melampsora lini growing at Kiandra, New South Wales, Australia, were sampled during the 1986–1987 growing season. Thirteen different races of M. lini were detected in a sample of 96 isolates. The distribution of isolates was uneven: race A comprised 73% of the samples; race N, 8%; and race H, 5%; while the remaining races were represented by only one or two samples. The dominance of race A increased over the course of the growing season, comprising 67% of the early season samples and increasing to 78% for those collected late in the season. The overall diversity of the pathogen population decreased late in the growing season, but this trend was not statistically significant. The average virulence of individual isolates of the pathogen population increased during the growing season. This trend was most pronounced among the minor races, where the mean number of differential hosts infected increased from 4.58 for early season samples to 5.12 and 5.08 for mid and late season samples, respectively. In contrast to the virulence pattern in the pathogen, the L. marginale population displayed a more even distribution of resistance. In a sample of 67 plants 10 resistance phenotypes were detected from their pattern of resistance/susceptibility to seven pathogen isolates. No phenotype had a frequency that exceeded 30%. Resistance phenotypes were randomly distributed on both a population level and on a fine scale.     

Differentiation of Physiologic Races of the Rice Blast Fungus, Pyricularia oryzae Cav. by PAGE-electrophoresis

Eighty-three isolates of the rice blast fungus (Pyricularia oryzae) were tested with respect to genetic diversity and the possibility of race differentiation by electrophoresis. The fungus was genetically very heterogeneous. The isolates were differentiated into 6 races by pathogenicity on race differential varieties. There was little correlation between pathogenicity and zymogram types of one particular enzyme such as esterase, phosphatase or catalase. The isolates were divided into 14 groups by the combination of the zymogram types of the three enzymes. The isolates in the same group showed similar pathogenicity. A new method is proposed which differentiates the blast fungus races by the combination of zymogram type of enzymes. The details, are discussed.     

Genetic comparison of Ug99 with selected South African races of Puccinia graminis f.sp. tritici

Using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) marker analyses, the genetic structure of selected South African wheat stem rust races was compared with Ug99. SSR analysis divided the population into two distinct groups with 24.5% similarity between them. A local race, UVPgt55 (North American race notation TTKSF), grouped with Ug99 (TTKSK) with a 100% similarity. When AFLP data were included, the same groups were found, but with an increased similarity of 66.7%. Although the SSR data were unable to distinguish between all individual isolates, the AFLP data alone and in combination with the SSR data discriminated between the isolates. The grouping of individual isolates resembled the pathogenicity profile of the different races. On the basis of its similarity with Ug99, it was concluded that UVPgt55 was most probably an exotic introduction into South Africa, whereas the other races specialized locally through mutational adaptation.     

Detection of Races 1 and 2 of Fusarium solani f. sp. cucurbitae and their Distribution in Watermelon Fields in Tunisia

A crown, foot and fruit rot of watermelon has been observed in most of the watermelon production areas in Tunisia. A survey conducted from 2000 to 2001 allowed the isolation of 291 isolates which were identified as Fusarium solani. These isolates were identified as F. solani f. sp. cucurbitae (Fsc) and races 1 and 2 characterized on the basis of pathogenicity tests on watermelon seedlings and muskmelon fruits. These results were confirmed by counts of the number of septa in the macroconidia. About 271 isolates were identified as Fsc race 1, 12 isolates were identified as Fsc race 2 and eight isolates were not pathogenic. Race 1 is widely distributed in watermelon production areas in Tunisia and race 2 has a lower incidence but it is present in the north, the middle and southern Tunisian watermelon cropping areas. Additionally, a study to compare the virulence of 122 isolates of Fsc race 1 showed different degrees of virulence among them. This is the first report of Fsc races 1 and 2 in Tunisia.     

Detection of Cochliobolus heterostrophus races in South China

Cochliobolus heterostrophus is the causal pathogen of the southern corn leaf blight (SCLB). There are three known races: race O, race C and race T. To determine which C. heterostrophus races comprise the field population in southern China and to assess diversity of these strains in terms of virulence, 200 isolates from diseased plants were collected in nine provinces/municipalities. All were race O, that is, no race T or race C isolates were found. Sixty race O isolates that sporulated well were chosen for further analysis. Virulence was measured using the integral optical density (IOD) of leaf lesions on four maize inbred lines. UPGMA cluster analysis of AFLP markers was applied to the 60 race O isolates plus control race O, T and C strains. Phylogenetic distribution, geographic location and virulence were not correlated. These results can provide valuable information for guidance in early warning and disease control.     

DNA addition or deletion is associated with a major karyotype polymorphism in the fungal phytopathogen Colletotrichum gloeosporioides

Summary A 1.2 Mb minichromosome resolved by pulsed-field electrophoresis was present in two independent race 3 isolates of Colletotrichum gloeosporioides causing Type B anthracnose specifically on Stylosanthes guianensis cv. Graham in Australia. This chromosome was absent in duplicate isolates representing races 1, 2 and 4 which infect other S. guianensis cultivars. A gene library was prepared specifically from the 1.2 Mb mini-chromosome and ten independent DNA clones unique to this chromosome were identified by differential hybridisation to whole chromosome probes. All of the ten selected probes hybridised only to the 1.2 Mb minichromosome unique to the race 3 isolates but not to any chromosome in isolates of the other races. These ten probes also hybridised only to restriction-digested DNA of race 3 and were thus both chromosome- and strain-specific for Type B C. gloeosporioides. Hybridisation analysis of NotI fragments of the 1.2 Mb minichromosome with these sequences indicated that they were not tightly clustered on the chromosome. These data demonstrate that the variation in the occurrence of the 1.2 Mb minichromosome did not arise by rearrangement of the genome of a progenitor strain but involved either large scale deletion or addition of DNA. The 1.2 Mb minichromosome did not contain a cloned high-copy-number repeat sequence present on all other mini- and maxichromosomes, suggesting addition from a genetically distinct strain. All ten chromosome-specific DNA probes hybridised to a 2.0 Mb chromosome in all races of C. gloeosporioides causing Type A anthracnose on Stylosanthes spp. including S. guianensis. Restriction fragment length polymorphism analysis demonstrated that only 15% of the hybridising restriction fragments of the Type A 2.0 Mb chromosome and the 1.2 Mb Type B race 3 minichromosome were identical. This indicated that it is unlikely that the 1.2 Mb minichromosome of the race 3 Type B pathogen was recently introgressed from-the Type A pathogen.     

I. Pathogenic variation in fungi and bacteria and mycorrhizal compatibility: Variation in Pseudomonas morsprunorum and the selection of cherry cultivars resistant to bacterial canker

During 1971 and 1972 leaf spot infection caused by Pseudomonas morsprunorum was far more severe on the cv. Roundel than on the normally more susceptible cv. Napoleon, and Roundel supported higher leaf surface populations of the pathogen. This unprecedented reversal in the established field performance of the two cultivars was associated with the presence on the trees of a colony variant (race 2) of P. morsprunorum that differed from the forms of the organism previously described (race 1) in physiological, pathological and phage sensitivity characteristics. In inoculation experiments race 2 isolates showed some specificity for Roundel and race 1 isolates for Napoleon. This difference was reflected in the distribution of the races on trees of the two cultivars growing in experimental plots and commercial orchards. Similar interactions between race and host genotype were observed amongst progeny from breeding programmes and material originally selected for resistance to bacterial canker after inoculation with race 1 proved susceptible to race 2. Three distinct groups of isolates with the colony characteristics of race 2 have been identified and one of these has affinities with Pseudomonas syringae. Group 1 isolates, corresponding to P. morsprunorum and comprising non-fluorescent forms, were the most virulent in pathogenicity tests and accounted for the majority of race 2 infections in the field.     

Genetic Diversity and Pathogenicity of Fusarium oxysporum f.sp. melonis Races from Different Areas of Italy

Fusarium wilt caused by Fusarium oxysporum f.sp. melonis (FOM) is a devastating disease of melon worldwide. Pathogenicity tests performed with F. oxysporum isolates obtained from Italian melon‐growing areas allowed to identify thirty‐four FOM isolates and the presence of all four races. The aims of this work were to examine genetic relatedness among FOM isolates by race determination and to perform phylogenetic analyses of identified FOM races including also other formae speciales of F. oxysporum of cucurbits. Results showed that FOM race 1,2 was the most numerous with a total of eighteen isolates, while six and nine isolates were identified as race 0 and 1, respectively, and just one isolate was assigned to race 2. Phylogenetic analysis was performed by random amplified polymorphic DNA (RAPD) profiling and by translation elongation factor‐1α (TEF‐1α) sequencing. The analysis of RAPD profiles separated FOM races into two distinct clades. Clade 1, which included races 0, 1 and 1,2, was further divided into ‘subclade a’ which grouped almost all race 1,2 isolates, and into ‘subclade b’ which included race 0 and 1 isolates. Clade 2 comprised only race 2 isolates. The phylogenetic analysis based on TEF‐1α separated FOM from the other formae speciales of F. oxysporum. Also with TEF‐1α analysis, FOM races 0, 1 and 1,2 isolates grouped in one single clade clearly separated from FOM race 2 isolates which grouped closer to F. oxysporum f.sp. cucumerinum. RAPD technique was more effective than TEF‐1α in differentiating FOM race 1,2 isolates from those belonging to the closely related races 0 and 1. Both phylogenetic analyses supported the close relationship between the three different FOM races which might imply the derivation from one another and the different origin of FOM race 2.     

Genetic diversity in the blackberry rust pathogen, Phragmidium violaceum, in Europe and Australasia as revealed by analysis of SAMPL

Indigenous to Europe, the blackberry rust fungus Phragmidium violaceum was introduced to Australia and subsequently appeared in New Zealand, with the most recent authorised introductions to Australia specifically for the biological control of European blackberry. Markers for ‘selective amplification of microsatellite polymorphic loci’ (SAMPL) were developed for studying the population genetics of P. violaceum. Modification of one of the two SAMPL primers with a HaeIII adapter (H) revealed significantly greater levels of genetic variation than primers used to generate AFLPs, the latter revealing little or no variation among 25 Australasian and 19 European isolates of P. violaceum. SAMPL was used to describe genetic variation among these 44 isolates of P. violaceum from 51 loci generated using primer pairs (GACA)₄ + H–G and R1 + H–G. The European isolates were more diverse than Australasian isolates, with 37 and 22 % polymorphic loci, respectively. Cluster analysis revealed geographic clades, with Australasian isolates forming one cluster separated from two clusters comprising the European isolates. However, low bootstrap support at these clades suggested that Australian isolates had not differentiated significantly from European isolates since the first record of P. violaceum in Australia in 1984. In general, the results support two hypotheses. First, that the population of P. violaceum in Australia was founded from a subset of individuals originating from Europe. Second, that P. violaceum in New Zealand originated from the Australian population of P. violaceum, probably by wind dispersal of urediniospores across the Tasman Sea. The application of SAMPL markers to the current biological control programme for European blackberry is discussed.     

Pathotypes of Plasmodiophora brassicae, the cause of clubroot, in Australia

Variation in pathogenicity of Plasmodiophora brassicae in Australia was studied using the European Clubroot Differential series of brassica hosts. From 41 collections of P. brassicae originating from important vegetable brassica production regions in Victoria, Western Australia, Tasmania, Queensland and New South Wales, 23 triplet codes were generated. These were more similar to populations of P. brassicae reported from the USA than those from Europe. The most common Australian pathotypes had triplet codes of 16/3/12 and 16/3/31 and were each assigned seven times to pathogen collections originating from three states of Australia. Other codes that occurred more than once were 16/2/31, which was assigned to six collections from four states of Australia, and 16/19/31, which was assigned twice to collections originating from Western Australia.     

Races and virulence of Fusarium oxysporum f.sp. cubense on local banana cultivars in Kenya

Virulence of 31 Kenyan isolates of Fusarium oxysporum obtained from bananas showing symptoms of Panama disease was tested against the differential banana cvs Bluggoe, Gros Michel, Dwarf Cavendish, and two other local cvs Muraru and Wang'ae. Seventeen isolates were assigned to either race 1 or race 2 of F. oxysporum f.sp. cubense (FOC). Race 4 was not apparent in this sample of 31 isolates from Kenya as none were pathogenic to cv. Cavendish, and no wilted Cavendish have been observed in field surveys in Kenya. Races could not be assigned to 12 isolates as they were virulent on more than one differential cultivar, and two were apparently not pathogenic. All isolates assigned to races 1 and 2 belonged to the VCG bridging complex 0124/5/8/20, but some other isolates belonging to this VCG complex could not be assigned to race. All five isolates assigned to VCG 01212 could not be assigned to known races. Considerable variability thus exists within FOC isolates within this region. Local cultivars of banana showed differential resistance to the pathogen. The interaction of cultivars and isolates on the level of disease was significant. Overall, cv. Wang'ae was the most susceptible to most of the isolates tested, regardless of their race, and could therefore be used as a reference cultivar in pathogenicity tests of isolates of FOC in the East African region. Of the cultivars tested that are widely grown on smallholder farms in Kenya, Muraru was the least susceptible.     

Molecular and physiological diversity among Verticillium fungicola var. fungicola

The genetic and physiological variability of Verticillium fungicola var. aleophilum responsible for Agaricus bisporus dry bubble disease in North America is well documented but little is known about the var. fungicola affecting European crops. Variability was assessed within this variety and compared with that reported for the var. aleophilum. Eighteen isolates of V. fungicola var. fungicola and four var. aleophilum isolates were analysed for DNA polymorphism, mycelial growth, response to biochemicals produced by A. bisporus, fungicide resistance, and pathogenicity assessed by direct inoculation on sporophore or casing contamination. RAPD and AFLP markers delineated three French isolates from a homogeneous group containing the other var. fungicola isolates, but no correlation could be drawn between DNA polymorphism and the various traits studied. The var. fungicola isolates were more susceptible than the var. aleophilum isolates to the antibiosis effect of A. bisporus. Only mycelial growth rate at 23 °C could explain the variability in aggressiveness among the European isolates. The putative effect of the post-incubation temperature on contamination during mushroom cultivation was discussed. This work emphasized that, like the American var. aleophilum, the var. fungicola in Europe is genetically homogeneous, but physiological diversity exists, especially in France where it could be related to less standardized cultural practices.     

Chloroplast DNA Transgresses Species Boundaries and Evolves at Variable Rates in the California Closed-Cone Pines (Pinus radiata, P. muricata, and P. attenuata)

We studied phylogenetic relationships among populations and species in the California closed-cone pines (Pinus radiata D. Don, P. attenuata Lemm., and P. muricata D. Don) via chloroplast DNA restriction site analysis. Data on genetic polymorphism within and among 19 populations in the three species were collected using9 to 20 restriction enzymes and 38 to 384 trees. Because only five clades and extremely low intraclade diversity were found, additional phylogenetic data were collected using a single representative per clade and two outgroup species, P. oocarpa Schiede and P. jeffreyi Loud. In total, 25 restriction enzymes were employed and approximately 2.7 kb surveyed (2.3% of genome). The five clades recognized were Monterey pine, knob-cone pine, and the southern, intermediate, and northern races of bishop pine. On the basis of bootstrapping, both Wagner and Dollo parsimony analyses strongly separated the northern and intermediate races of bishop pine from the southern race; knobcone pine from Monterey and bishop pines; and the closed-cone pines from the two outgroups. Approximate divergence times were estimated for the lineages leading to knob-cone pine and to the intermediate and northern populations of bishop pine. The position of Monterey pine relative to bishop pine within their monophyletic clade was unresolved. Surprisingly, Montery pine and the southern race of bishop pine were much more similar to one another than was the southern race of bishop pine to its conspecific intermediate and northern races. Both the Monterey and southern bishop pine lineages also evolved severalfold more slowly than did the knobcone pine and intermediate-northern bishop pine lineages. These results differ significantly from a recent allozyme study, corroborating previous observations that chloroplast genome phylogeny can depart substantially from that of nuclear genes.     

Pathogenicity and its alternation with both morphological and genetic variation in Plasmopara halstedii (sunflower downy mildew)

Morphological, pathogenic and genetic variation was studied in seven Plasmopara halstedii (sunflower downy mildew) isolates of several races using five singlezoosporangium isolates per pathogen isolate. Aggressiveness criteria were analysed in one sunflower inbred line showing a high level of quantitative resistance. Genetic relationships were detected between the single zoosporangium isolates using 12 expressed sequence tags (EST)-derived markers. Analysis of the five single zoosporangium isolates for P. halstedii isolates showed variability within pathogen isolates for all aggressiveness criteria, but not for all pathogen isolates. Isolates of races 100 and 3xx were characterised with shorter latent period and higher sporulation density than the isolate of races 7xx. All pathogen isolates showed high percentage infection values and caused a large reduction in seedling size except for one isolate involved in dwarfing. There was no relation between zoosporangia form or size and race virulence profiles or aggressiveness criteria. There was no intra-genetic variation for all pathogen isolates, but it was observed an important genetic variation between single zoosporangium isolates of all races. No correlation was detected between pathogenicity traits and EST genotypes.     

Genetic evidence for the origins of range disjunctions in the Australian dry sclerophyll plant Hardenbergia violacea

Aim The distribution of genetic variation in the Australian dry sclerophyll plant Hardenbergia violacea (Fabaceae) is examined in the context of Pleistocene climate change in order to identify likely refugia. Particular consideration is given to the origin of range disjunctions in South Australia and Tasmania, and to determining whether the Tasmanian population is indigenous or recently introduced from mainland Australia. Location Southeastern Australian mainland and Tasmania. Methods A combination of chloroplast polymerase chain reaction–restriction fragment length polymorphism and genomic amplified fragment length polymorphism (AFLP) marker systems was used to examine the genetic structure of 292 individuals from 13 populations across the range of H. violacea in southeastern Australia. Results Hardenbergia violacea populations in Tasmania and southern Victoria were characterized by low, almost monotypic chloroplast diversity. New South Wales showed higher haplotype diversity and haplotype sharing among widely distributed populations. Principal coordinates analysis (PCoA) of the AFLP data found a strong latitudinal cline in AFLP variation from northern New South Wales south to Tasmania. The Tasmanian population formed an isolated and somewhat disjunct genetic cluster at one end of this cline. However, the South Australian population was an exception to the clinal variation shown by all other populations, forming a highly disjunct cluster in the PCoA. Within‐population genetic diversity was low in both disjunct populations. Main conclusions The genetic evidence indicates that the Tasmanian population is likely to be indigenous and probably the product of vicariance, which was followed by range contraction at the Last Glacial Maximum or an earlier glacial event. The deep phylogenetic disjunction in South Australia is evidence of a much earlier separation on mainland Australia. The chloroplast structure indicates that, during the Pleistocene, H. violacea underwent broad‐scale recolonization in southern Victoria and Tasmania, possibly from a large continental refugium in eastern New South Wales. We conclude that H. violacea, and presumably the sclerophyll communities in which it occurs, have undergone multiple range contractions to large continental refugia during different Pleistocene glaciations in southeastern Australia.     

Reaction of some wheat cultivars and breeding lines to Puccinia striiformis f. sp. tritici hot races in Iran

Many physiological races of Puccinia striiformis f. sp. tritici which cause stripe rust in wheat can be determined in different parts of the world. The emergence of new races with different pathogenicity which happens very quickly breaks cultivars resistant and cause disease. Therefore, breeding cultivar for resistance to different pathogenic races should be continued. In this research, pathogenicity of two isolates collected from two regions of Iran were determined by using wheat yellow rust differential lines, which indicated race 70E50A+ and 6E18A+ The responses of 30 wheat genotypes were separately evaluated in the forms of randomized complete block design with three replicates in the seedling stage under greenhouse condition. The components of resistance including latent period and infection type were recorded. Results indicated genotypes were evaluated in terms of both traits and were significant at 1% level. Also, the results from pathogenicity study indicated of effective gene/s included Yr1, Yr2+, Yr3, Yr4, Yr5, Yr10, Yr15, Yr24, Yr26, YrSP, YrND, YrSD and YrSU. From the genotypes studied in the greenhouse condition, 39% of the genotypes showed complete resistance to both races. Probably, resistance genes, Yr32 and YrCV, or the other unknown genes which are types of seedling resistance are either alone or in combination of one another cause strength in resistant genotypes.     

Characterization of emerging populations of Fusarium oxysporum f. sp. conglutinans causing cabbage wilt in China

Fusarium oxysporum f. sp. conglutinans (FOC) causes Fusarium wilt, a disease of cabbage that has brought about significant economic loss throughout northern China since it was first detected in 2001. To characterize the Chinese FOC isolates, we compared the cultural characteristics, pathogenicity and races between the Chinese isolates and the type strains (race 1: 52,557 and race 2: 58,385). The Chinese FGL‐03‐6 isolate had cultural characteristics similar to those of strain 52,557, including colony growth rate, colony and spore characteristics and responses to temperature changes, while the strain 58,385 grew faster, produced more pigment and spores and was more adaptable to temperature fluctuations. The lethal temperature for all strains was 60°C, and the optimal temperatures for pathogen growth on potato dextrose agar and pathogenicity on plants were 25°C and 25 to 30°C, respectively. Tests for race and pathogenicity indicated that different cabbage cultivars had similar resistance reactions to FGL‐03‐6 and 52,557. However, the pathogenicity of FGL‐03‐6 was similar to that of 58,385, which infected quickly and caused more severe disease symptoms. This study further provides information regarding characterizing different strains of F. oxysporum f. sp. conglutinans.     

AFLP Linkage Map of the OomycetePhytophthora infestans

Here we present the first comprehensive genetic linkage map of the heterothallic oomycetous plant pathogenPhytophthora infestans.The map is based on polymorphic DNA markers generated by the DNA fingerprinting technique AFLP (Voset al.,1995,Nucleic Acids Res.23:4407–4414). AFLP fingerprints were made from single zoospore progeny and 73 F1 progeny from two field isolates ofP. infestans.The parental isolates appeared to be homokaryotic and diploid, their AFLP patterns were mitotically stable, and segregation ratios in the F1 progeny were largely Mendelian. In addition to 183 AFLP markers, 7 RFLP markers and the mating type locus were mapped. The linkage map comprises 10 major and 7 minor linkage groups covering a total of 827 cM. The major linkage groups are composed of markers derived from both parents, whereas the minor linkage groups contain markers from either the A1 or the A2 mating type parent. Non-Mendelian segregation ratios were found for the mating type locus and for 13 AFLP markers, all of which are located on the same linkage group as the mating type locus.     

Pathogenic divergence of Central European and Australian populations of Blumeria graminis f. sp. hordei

Hosts and pathogens have adapted their response to each other through genetic changes that have arisen during the course of their co‐evolution. In developed countries the longevity of varieties is often short; new varieties frequently possess novel genes with specific resistance to pathogens. The latter must adapt to the resistance genes to maintain pathogenicity. To study this adaptation, 50 Central European and 50 Australian isolates of Blumeria graminis f. sp. hordei (Bgh) were tested on 50 barley differential varieties with different specific resistance genes. All the Central European isolates differed from each other in their virulence combinations and belonged to 50 various pathotypes, whereas Australian isolates comprised 37 pathotypes. None of the pathotypes detected in Central Europe was identical or similar to any of those in Australia. This can be attributed to the much higher number of virulences in Central European isolates that developed over a long period of contact with a range of host varieties containing specific resistance genes. This has led to a gradual divergence of the Australian and the European Bgh populations. In Europe, unlike Australia, new specific resistance genes are still widely used in breeding barley varieties and the divergence of both populations will continue.