Characterisation of <Emphasis Type="Italic">Phytophthora infestans</Emphasis> isolates collected from potato in Estonia during 2002–2003

A collection of 101 isolates of Phytophthora infestans, obtained from seven sampling sites representing central, east and south-east Estonia during 2002 and 2003 were assessed for several phenotypic and genotypic markers. All 101 isolates were assessed for virulence and resistance to metalaxyl. Virulence to each of the 11 classic resistance genes was found among the tested isolates. The mean number of virulences per isolate was 6.3, with a very low frequency of virulence against resistance genes R5 (5%) and R9 (14%). The most common pathotypes were 1.3.4.7.8.10.11 and 1.3.4.7.10.11, representing altogether 12% of the studied strains. In terms of metalaxyl resistance, 30 resistant, 52 intermediate and 19 sensitive isolates were found. A subgroup of 50 isolates was assessed for mating type, allozymes [glucose-6-phosphate isomerase (Gpi) and peptidase (Pep)], DNA fingerprints with probe RG57 and mtDNA haplotype. Of this subset, 30 were A1 and 20 were A2. Collections from three of the seven fields contained both mating types. Allozyme analysis did not reveal any polymorphism. However, 19 diverse RG57 fingerprints were detected, and two mitochondrial DNA haplotypes, Ia and IIa, were detected. By combining the mating type, mtDNA haplotype and RG57 fingerprint data, 26 multilocus genotypes were identified, of which 18 were detected only once. Genotypic diversity measured by the normalised Shannon diversity index was high (0.76). The large number of multilocus genotypes and the presence of both mating types in some fields indicate that sexual reproduction may take place in Estonian populations of P. infestans.     

Population structure of Sclerotinia sclerotiorum in crop and wild hosts in the UK

Sclerotinia sclerotiorum is an important pathogen of many crop plants which also infects wild hosts. The population structure of this fungus was studied for different crop plants and Ranunculus acris (meadow buttercup) in the UK using eight microsatellite markers and sequenced sections of the intergenic spacer (IGS) region of the rRNA gene and the elongation factor 1‐alpha (EF) gene. A total of 228 microsatellite haplotypes were identified within 384 isolates from 12 S. sclerotiorum populations sampled in England and Wales. One microsatellite haplotype was generally found at high frequency in each population and was distributed widely across different hosts, locations and years. Fourteen IGS and five EF haplotypes were found in the 12 populations, with six IGS haplotypes and one EF haplotype exclusive to buttercup. Analysis of published sequences for S. sclerotiorum populations from the USA, Canada, New Zealand and Norway showed that three of the IGS haplotypes and one EF haplotype were widely distributed, while eight IGS haplotypes were only found in the UK. Although common microsatellite and IGS/EF haplotypes were found on different hosts in the UK, there was evidence of differentiation, particularly for one isolated population on buttercup. However, overall there was no consistent differentiation of S. sclerotiorum populations from buttercup and crop hosts. Sclerotinia sclerotiorum therefore has a multiclonal population structure in the UK and the wide distribution of one microsatellite haplotype suggests spatial mixing at a national scale. The related species S. subarctica was also identified in one buttercup population.     

French isolates of Phytophthora infestans from potato and tomato differ in phenotype and genotype

Prior to 1996, the A2 mating type of Phytophthora infestans was not detected on potato in France, but was found at one site on tomato in 1995. This finding lead to the question of the extent of differences and relationships existing between the populations of P. infestans present on each host. A collection of 76 isolates collected in France, mainly in 1996, from potato and tomato was characterised for mating type, allozyme genotype at the Gpi and Pep loci, and mitochondrial DNA haplotype; 74 of these isolates were also characterised for multilocus RFLP fingerprint, and 62 for virulence. All isolates except four showed allozyme genotypes (Gpi 90/100 or 100/100, Pep 83/100 or 100/100) and mtDNA haplotypes (Ia or IIa) characteristic of the populations introduced into Europe in the late 1970s. The four exceptions were isolates collected from tomato in Southern France in 1988-1991, which showed some characteristics of the former European populations (Gpi 86/100, Pep 92/100, mtDNA Ib). Both mating types were present among the collections from both hosts, but isolates with the A2 mating type were found on potato only in one garden crop, adjacent to tomato. Nine different RG57 fingerprints were observed, with a greater diversity among tomato isolates. Furthermore, tomato and potato collections differed markedly in the frequencies of genotypes present. Finally, tomato isolates generally had a lower virulence complexity than potato isolates. These data suggest that P. infestans populations on tomato and potato are largely separated, despite the occurrence of limited gene flow.     

Clonality in Sclerotinia sclerotiorum on Infected Cabbage in Eastern North Carolina

ABSTRACT Eighty-four isolates of Sclerotinia sclerotiorum from four cabbage production fields in North Carolina and 16 isolates from an experimental cabbage field plot in Louisiana were DNA-fingerprinted and tested for mycelial compatibility. In a comparison with 594 unique DNA fingerprints of S. sclerotiorum from Canadian canola, no fingerprints were shared among Canadian, North Carolina, and Louisiana populations. DNA fingerprints from the North Carolina sample were distinctive from those of the Canadian and Louisiana samples, with significantly more hybridizing fragments in the 7.7- to 18-kilobase range. Forty-one mycelial compatibility groups (MCGs) and 50 unique DNA fingerprints were identified from the North Carolina sample. Three MCGs and three fingerprints were identified from the Louisiana sample. From the North Carolina sample, 32 MCGs were each associated with a unique fingerprint; of these, there were 11 clones (i.e., cases in which two or more isolates belonged to the same MCG and shared the same DNA fingerprint). Six clones sampled from two or more fields represented approximately 29% of the total sample (24 of 84 isolates), with six clones recovered from fields 75 km apart. There were 10 cases in which one MCG was associated with more than one DNA fingerprint and two cases in which one DNA fingerprint was associated with more than one MCG. The small sample from Louisiana was strictly clonal. The North Carolina sample had a clonal component, but deviated from one-to-one association of MCG with DNA fingerprint to an extent consistent with more recombination or transposition than the other two populations sampled.     

Phenotypic and genotypic diversity in Phytophthora infestans on potato in Great Britain, 1995–98

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

田间水稻单个病斑中稻瘟病菌的遗传多样性

根据93个单病斑中分离的227个单孢菌株样品的分析，研究了来自同一定殖系统(同一病斑)中稻瘟病菌不同单孢菌株(同源菌株)的遗传变异。在致病性分析的样品中，仅有5个病斑分离的10个单孢菌株在所有鉴别品种上表现同源菌株有完全相同的致病反应，并且有完全相同的DNA指纹图谱带型；另有13个病斑上分离的32个单孢菌株的同源菌株不仅属于不同的生理小种，而且在1～3个单基因品种上也有不同的致病反应。用rep—PCR指纹图谱和致病型分析67个病斑的157个单孢样品中的同源菌株具有完全相同的DNA指纹图谱；13个病斑中分离的27个单孢样品中同源菌株具有显著差异的指纹图谱；8个病斑分离的27个单孢菌株样品中同一来源样品中部分样品有相同的指纹图谱带型，部分样品却有不同的指纹图谱。同源菌株之间有完全相同致病性其指纹图谱亦相同或有很小的差异；通常，致病性差异很大的同源菌株其指纹图谱差异也很大。作者认为来自同一定殖系统中的不同单孢菌株存在的遗传变异与病菌的异核现象或自然状态下不同遗传背景菌株同时侵染造成同一病斑有关。     

Molecular marker analysis of European Setosphaeria turcica populations

Setosphaeria turcica is the causal agent of northern corn leaf blight, a foliar maize disease of worldwide economic importance. In Europe, its severity increases. To investigate the pathogen's population-genetic structure in central Europe, a total of 80 isolates was sampled in Germany, Switzerland, France, Austria, and Hungary and investigated with 52 random amplified polymorphic DNA (RAPD) markers. The mating type of the isolates was determined in testcrosses. Among the 73 isolates from maize there were 26 different RAPD haplotypes. All isolates with identical haplotype are considered clonemates. The haplotype shared by most members was represented by 22 isolates from Germany, Switzerland, and France, indicating high fitness and substantial migration. Only a single clone had members in both southeastern Austria and southwestern Switzerland, suggesting that the Alps constitute a major barrier for this pathogen. Several haplotypes differed by only one or two RAPD bands from the predominant haplotype and may have arisen by mutation. Few other clonal lineages were detected. The evolution of some haplotypes could not be explained by mutation alone. Sexual recombination may rarely occur. In population samples from Germany, Switzerland, and France, mating type MAT2 was predominating, while most isolates from Austria and Hungary had MAT1. Seven isolates from Johnson grass (Sorghum halepense), an alternative host of S. turcica, were clonemates and very different in RAPD haplotypes from all isolates collected from maize.     

Genotypic variability and aggressiveness of Bipolaris oryzae in the Philippines

The genotypic diversity of a collection of 352 isolates of Bipolaris oryzae obtained from 11 locations in the Philippines was estimated. The isolates could be divided into 50 haplotypes based on variation in microsatellite DNA with a moderately high genotypic diversity value of 0.88. Thirty nine haplotypes were represented by three or fewer isolates, whereas 80 % of the isolates belonged to only eight haplotypes, each containing 10 to 88 isolates indicating the prevalence of clonality. AMOVA revealed that the greatest variation was associated with the brown spot isolates collected within provinces (50.81 %), among varieties within provinces (48.17 %) and within ecosystems (49.33 %). Intensive sampling from a single field showed that the population was mostly clonal with about 98 % of the isolates belonging to a single VNTR haplotype. However, isolates within this haplotype exhibited a continuous range of aggressiveness when inoculated onto susceptible rice variety IR72. Several types of lesions were observed in the field during sampling, but the isolates obtained from each type of lesion produced a range of different lesion types when inoculated onto leaves of IR72, indicating that the type of lesion observed in the field was not related to the genotype of the pathogen. These results show that rice fields across the Philippines may contain B. oryzae isolates with considerable genotypic diversity, but an individual field may have both clonal and unique genotypes.     

Measuring Immigration and Sexual Reproduction in Field Populations of Mycosphaerella graminicola

ABSTRACT A field experiment was conducted to determine the relative contributions of immigration and sexual reproduction to the genetic structure of Mycosphaerella graminicola populations during the course of an epidemic. The genetic structure of M. graminicola populations sampled from wheat plots inoculated artificially with 10 isolates was compared with control plots infected naturally by airborne ascospores. Restriction fragment length polymorphisms (RFLPs) were used to test the randomness of associations among loci, and DNA fingerprints were used to identify clones. All isolates in the control plots had unique genotypes and RFLP loci were at gametic equilibrium, findings consistent with random mating. The proportion of isolates in the inoculated plots with DNA fingerprints that differed from the 10 inoculated isolates increased from 3% in the early to 39 and 34% in the mid- and late season, respectively. The degree of gametic disequilibrium was higher in the mid-season than in the late-season population. By the end of the growing season, we estimate that 66% of the isolates in the inoculated plots were asexual progeny of the 10 inoculated isolates, 10% were immigrants, and 24% were sexual recombinants. The proportion of infections caused by ascospores increased over the growing season.     

Ribotyping of EntomopathogenicVerticittium lecanii in Japan

To estimate the genetic diversity in 30 isolates ofVerticillium lecanii from aphids, whiteflies, mite and black pine in Japan, including two commercialized strains (Mycotal and Vertalec), DNA polymorphisms in ribosomal DNA of those isolates were analyzed using polymerase chain reaction (PCR). The internal transcribed spacer (ITS) and intergenic spacer (IGS) regions of the nuclear ribosomal RNA gene of each isolate were analyzed by PCR-RFLP (restriction fragment length polymorphism). The size of the PCR product from the ITS region was ~ 580 bp in 27 of the isolates. A 600 bp ITS product was detected in Mycotal and Vertalec. One Japanese isolate produced both the 580 bp and 600 bp products. Enzymatic digestion of the ITS region with Sau3A I,Msp I,Hae III andRsa I revealed RFLPs that consisted of eight haplotypes. Mycotal and Vertalec were specific haplotypes that differed from other isolates. The Japanese isolates had a complex relationship with the original host, but we identified several specific haplotypes common to an aphid origin. Ten distinct IGS haplotypes were detected in the IGS region, some of which were associated with aphid and whitefly origins. These results suggest that the haplotype of rDNA RFLP analysis can be used for studying genetic diversity inV. lecanii.     

Genetic structure and phylogeny of Italian and Czech populations of the cucurbit powdery mildew fungus Golovinomyces orontii inferred by multilocus sequence typing

Cucurbit powdery mildew caused by Golovinomyces orontii is a serious disease that affects cucurbit crops in temperate areas. In northern Italy, the species is responsible for the early infections at the beginning of the growing season. However, chasmothecia have never been recorded in Italy and the impact of either asexual or sexual reproduction of G. orontii remains to be determined. To investigate and compare the genetic structure of Italian populations with those from the Czech Republic, where chasmothecia are sporadically recorded, seven housekeeping gene fragments (tef‐1α, csI, ITS, H3, tub2, IGS and mtLSU) were amplified and used in a multilocus sequence typing (MLST) approach. The four‐gamete test was performed to detect recombination between and within populations. Phylogeny was inferred using both Bayesian and minimum evolution analyses. Results from MLST revealed the presence of 141 single nucleotide polymorphisms and the existence of 13 different haplotypes. Phylogenetic analysis revealed the existence of two main distinct phylogenetic groups that were also highly genetically different, confirming that G. orontii is a species complex. Recombination was detected within both the phylogenetic groups and the geographical populations, indicating that sexual reproduction could have occurred. However, considering the lower haplotype diversity and the high frequency of ST3 (17 isolates) and ST7 (eight isolates) haplotypes, the Italian population could be predominantly clonal, while sexual reproduction may occasionally occur due to the introduction of genotypes similar to those from the Czech Republic.     

Population structure and genetic diversity suggest recent introductions of Dothistroma pini in Slovakia

Dothistroma pini is one of two pathogens causing Dothistroma needle blight (DNB), a foliar disease of pines. The species was redefined in 2004 and subsequently recorded in several European countries. In Slovakia, the first report of the pathogen was in 2013. In this study, the population structure, genetic diversity, and reproductive mode of 105 isolates collected from 10 localities and seven hosts were determined in Slovakia. Species-specific mating type markers, ITS haplotype determination, and 16 microsatellite markers were used to characterize and genotype the isolates. Overall, 15 unique multilocus haplotypes (MLHs) based on microsatellite markers and three ITS haplotypes were identified. Three independent methods (DAPC, STRUCTURE, EDENetwork) separated the isolates into two distinct population clusters corresponding with ITS haplotypes. A high level of clonality was recorded suggesting that conidia are the primary source of pathogen dispersal. The low genetic diversity, predominantly asexual reproductive mode of the pathogen, and the fact that most isolates were collected from introduced tree species and native species in artificially planted urban greenery, supports the hypothesis that D. pini has been recently introduced into Slovakia.     

High Genetic Similarity Among Populations of Phaeosphaeria nodorum Across Wheat Cultivars and Regions in Switzerland

ABSTRACT Phaeosphaeria nodorum was sampled from nine wheat fields across a 30-km transect representing three geographical regions in Switzerland to determine the scale of genetic differentiation among subpopulations. Three different wheat cultivars were sampled three times to determine whether differences in host genotype correlated with differences among corresponding pathogen populations. Seven restriction fragment length polymorphism (RFLP) loci and one DNA fingerprint were assayed for each of the 432 isolates in the collection. DNA fingerprints differentiated 426 unique genotypes. Though absolute differences were small, five RFLP loci exhibited significant differences in allele frequencies across the nine sub-populations. Gene diversity within all subpopulations was high (H(T) = 0.51), but only 3% of the total genetic variation was distributed among the nine subpopulations. When subpopulations were grouped according to geographical region or host cultivar, less than 1% of the genetic variation was distributed among groups, suggesting widespread gene flow and the absence of pathogen adaptation to specific wheat cultivars. Tests for gametic equilibrium within subpopulations and across the entire Swiss population supported the hypothesis of random mating.     

The Northern Ireland Phytophthora infestans population 1998–2002 characterized by genotypic and phenotypic markers

A total of 204 isolates of Phytophthora infestans from Northern Ireland, almost all from commercial potato crops, were collected over 5 years (1998–2002). Phenotypic diversity was assessed using mating type and metalaxyl resistance; genotypic diversity was assessed using two allozyme loci (glucose-6-phosphate isomerase, Gpi, and peptidase, Pep ), mitochondrial DNA haplotype and the multilocus RFLP probe RG57. All isolates were A1 mating type and Gpi 100/100 . The majority were Pep 100/100 , but four Pep 83/100 and six Pep 96/100 isolates were identified. Three mtDNA haplotypes were detected; haplotype IIa was the most common, but each year up to 2001 its frequency declined, with a concomitant increase in Ia isolates. Three isolates had the rare haplotype IIb, but this was only detected in 1998. Metalaxyl resistance and mtDNA haplotype were markedly associated: most haplotype Ia isolates were metalaxyl-resistant, whereas haplotype IIa was more commonly associated with metalaxyl sensitivity. Analysis of a subsample of 91 isolates revealed nine RG57 genotypes, three associated exclusively with haplotype IIa and six exclusively with haplotype Ia. The most common RG57 genotype (51% of isolates) comprised both metalaxyl-resistant and -sensitive haplotype IIa isolates. However, of haplotype Ia isolates, all metalaxyl-resistant phenotypes belonged to one of four RG57 types, one of which was the second most frequent overall (29% of isolates), while all metalaxyl-sensitive isolates belonged to one of two other types. The P. infestans population in Northern Ireland appears to consist of a limited number of clones related to, but differentiated from, the populations in mainland Britain and elsewhere in Europe.     

Evidence for Natural Selection in the Mitochondrial Genome of Mycosphaerella graminicola

ABSTRACT Pathogenicity assays were combined with restriction fragment length polymorphism (RFLP) markers in the mitochondrial and nuclear genomes to compare Mycosphaerella graminicola populations adapted to bread wheat (Triticum aestivum) and durum wheat (T. turgidum) in the Mediterranean Basin. The majority of isolates had unique nuclear DNA fingerprints and multilocus haplotypes. Only six mitochondrial DNA (mtDNA) haplotypes were identified among 108 isolates assayed. There were minor differences in frequencies of alleles at nuclear RFLP loci between the two host-adapted populations, but differences in the frequencies of mtDNA haplotypes were highly significant (P < 0.0001). mtDNA haplotype 1 dominated on the isolates adapted to bread wheat, and its frequency was twice as high as for the isolates adapted to durum wheat. mtDNA haplotype 4, which contained a unique approximately 3-kb insertion, was detected only in isolates showing specificity toward durum wheat and was the dominant haplotype on this species. We propose that the low mitochondrial diversity in this pathogenic fungus is due to a selective sweep and that differences in the frequencies of mtDNA haplotypes between the two host-adapted populations were due to natural selection according to host species.     

Comparison of Chinese and Japanese A1 isolates of <Emphasis Type="Italic">Phytophthora infestans</Emphasis>

The mating type, glucose-6-phosphate isomerase (Gpi) and peptidase (Pep) genotypes, RG57 fingerprint, and mitochondrial DNA (mtDNA) haplotype of Chinese isolates of Phytophthora infestans collected in Hebei and Gansu in 1996 were compared with those of Japanese isolates collected during 1997–2000. The Chinese isolates were divided into four genotypes, one of which was identical to the dominant Japanese genotype, A1-A (mating type A1; Gpi 100/100; Pep 100/100; RG57 100010001100110100011001110: 1–25, 14a, and 24a; and mtDNA haplotype IIa). Comparison of the genotypes with reported data revealed that some completely and partially identical genotypes occur in Russia and parts of Europe. The other two A1 genotypes and one A2 genotype were also detected in Gansu (Gpi 100/100, Pep 100/100, and mtDNA haplotype Ia), which were regarded as unique to this region.     

Genetic differentiation of Magnaporthe oryzae populations from scouting plots and commercial rice fields in Korea

A previous study of the diversity and population structure of the rice blast fungus, Magnaporthe oryzae, over a 20-year period in Korea, found novel fingerprint haplotypes each year, and the authors hypothesized that populations might experience annual bottlenecks. Based on this model, we predicted that M. oryzae populations would have little or no genetic differentiation among geographic regions because rice blast is commonly found throughout Korea each year and M. oryzae would have to disperse from small populations surviving annually between rice crops. To test this hypothesis, we sampled M. oryzae from rice fields in eight provinces in Korea in a single year (1999). In four provinces, we sampled from a set of rice cultivars commonly grown in commercial fields (group I); because of low disease incidence in four other provinces, we could not sample from commercial fields and instead sampled from scouting plots of different cultivars set up for detecting new pathotypes of M. oryzae (group II). All isolates were genotyped with DNA fingerprint probes MGR586 and MAGGY, a telomere-linked gene family member TLH1, the PWL2 host specificity gene and mating type. Fingerprint haplotypes clustered into two distinct lineages corresponding to the two sets of cultivars (groups I and II), with haplotype similarities of 71% between lineages and >76% within lineages. Isolates from the same cultivar within group I were genetically differentiated among locations, and isolates within the same location were differentiated among cultivars. Differentiation for TLH1 and PWL2 was significant (P < 0.03), but not as strong as for fingerprint markers. Similar analyses were not possible among group II isolates because too few isolates were available from any one cultivar. All isolates were in the same mating type, Mat1-1, ruling out sexual reproduction as a source of novel haplotypes. When the 1999 samples were compared with the historical samples from the previous study, haplotypes of group I formed a separate cluster, while those of group II clustered with haplotypes from the historical sample. Altogether, geographic subdivision, monomorphism of mating type, and correlation of haplotypes to sets of cultivars are not consistent with the hypothesis of repeated turnover of haplotypes. Instead, the previous correlations of haplotypes to year might have been caused by inadequate sampling of haplotypes each year, highlighting the need for studies of population genetics to be conducted with systematic samples collected to address specific questions.     

Population structure of rice blast isolates resistant to scytalone dehydratase inhibitors in Mie Prefecture and implications for their origin

In Mie Prefecture in Japan, rice blast isolates resistant to melanin biosynthesis inhibitors targeting scytalone dehydratase (SDH) were first observed in 2005. To analyze the distribution of the resistant isolates, 527 isolates were collected from wide areas in this prefecture during 2006 and 2007. Almost half of the isolates collected (233 of 527 isolates) carried a point mutation in the SDH gene conferring the resistant phenotype. To compare population structures of resistant and sensitive isolates, we analyzed the isolates with repetitive-element-based PCR DNA fingerprinting using a single primer complementary to a sequence in the terminal inverted repeat of transposable element Pot2. A majority of the resistant isolates were classified into a single DNA fingerprint haplotype, Mie1. Despite its prevalence in the resistant isolates, Mie1 was not found in the sensitive isolates. Furthermore, in a dendrogram constructed from the DNA fingerprint data, Mie1 and six other haplotypes formed a cluster composed of resistant isolates alone. These results suggest that the resistant isolates that belonged to the Mie1 haplotype had migrated from regions outside Mie Prefecture and selectively propagated in a short period in this prefecture.     

Characterization of some Asian isolates of Phytophthora infestans

A total of 401 isolates of Phytophthora infestans were collected from eight Asian regions (Korea, India, Taiwan, Indonesia, Thailand, Nepal, China and Japan) between 1992 and 2000 – 318 from potato and 83 from tomato. The isolates were analysed for mating type, metalaxyl resistance, RG57 fingerprinting, mitochondrial DNA (mtDNA) haplotype and the polymorphism of three allozyme loci, i.e. glucose-6-phosphate isomerase ( Gpi ), peptidase ( Pep ) and malic enzyme ( Me ). The isolates were multilocus-genotyped based on RFLP (RG57) fingerprint, dilocus allozyme genotype, mtDNA haplotype and mating type. Twenty multilocus genotypes were identified among 125 isolates. Of these genotypes, 14 had not been previously reported. Some of the multilocus genotypes were common to isolates from several geographical regions, suggesting migration. The metalaxyl-resistant isolates belonged to the multilocus genotypes JP-1, JP-2, and JP-3. Multilocus genotypes coexisting in a single field were found in following regions: Thailand (1994), central China (1996), Nepal (1997) and Japan (1998 and 2000). The possible origins of certain genotypes are discussed, including the possibility of sexual recombination within the P. infestans populations in Nepal and perhaps Thailand.