The recent history of Puccinia striiformis f.sp. tritici in Denmark as revealed by disease incidence and AFLP markers

Disease observations and amplified fragment length polymorphism (AFLP) markers were used to study recent developments in the Puccinia striiformis f.sp. tritici population in Denmark. The fungus appeared spontaneously at 10 locations in Denmark in 1997 after it was not observed under natural conditions in 1996. The pattern of disease development and prevailing winds suggested that the fungus reappeared by airborne spores from the south or west. In 1998, disease incidence was more evenly distributed throughout the country. Forty-eight single lesion isolates were collected from most crops where the disease was observed in these years; all except one from 1997 belonged to two pathotypes that were not previously detected in the country, and both possessed the newly discovered Yr17 virulence. The isolates were characterized with AFLP markers together with 28 isolates representing eight of 13 pathotypes observed prior to 1996. Initial screening of 240 Pst I/ Mse I AFLP primer combinations on four isolates showed that a primer combination, on average, revealed 0·4 polymorphisms between any isolate pair. A selection of 21 primer combinations resulted in 28 AFLP markers, which revealed 16 AFLP phenotypes among all 76 isolates. The two Yr17- virulent pathotypes consisted of three AFLP phenotypes, which were observed in both 1997 and 1998; the two most frequent AFLP phenotypes occurred at most sampling locations and often within the same crop. AFLP diversity was larger among samples collected prior to 1996, and also in this period most AFLP phenotypes were observed at different sampling locations. These results are consistent with the features of an entirely asexually reproducing pathogen dispersed by aerial spores across large areas.     

Studies on the origin,spread, and evolution of an important group ofPuccinia recondita f. sp.tritici pathotypes in Australasia

Wheat brown rust pathotype (pt) 104-2,3,(6),(7), 11 was first detected in Australasia in Victoria during 1984. Although it appeared similar to a pre-existing pathotype, 104-2,3,6,(7), detailed greenhouse test revealed nine pathogenic differences between the two rusts. Six differences involved contrasting virulence/avirulence for the resistance genes/specificitiesLr12, Lr27+Lr31 andLr16, and three uncharacterised genes, present in the wheat cultivars Gaza and Harrier, and in triticale cultivar Lasko. Differences in partial virulence between the pathotypes were found for the genesLr2a, Lr13 andLr26. A comparison of the phenotypes for 13 isozyme systems in the two pathotypes revealed two differences, including aPgm2 allele in pt 104-2,3,(6),(7),11 not found in other contemporary AustralasianPuccinia recondita f. sp.tritici pathotypes. On the basis of these differences, it was concluded that pt 104-2,3,(6),(7),11 was introduced into the Australasian region before or during 1984.Seven variants of pt 104-2,3,(6),(7),11, that differed by single virulences, were detected during 1984–1992. Pt 104-2,3,(6),(7),11 and a derivative pathotype with virulence forLr20 underwent rapid increases in frequency, largely displacing pathotypes which predominated before 1984. Although first detected in eastern Australia, both pathotypes spread to New Zealand, and the derivative pathotype appeared in Western Australia. The rapid spread and increase of these pathotypes could not be explained by host selection. Pt 104-2,3,(6),(7),11 and derivatives may therefore be more aggressive than other contemporary Australasian pathotypes.Abbreviations NSW New South Wales - Prt Puccinia recondita f. sp.tritici - Qld Queensland - SA South Australia - WA Western Australia     

Virulence and Molecular Diversity in Cochliobolus sativus

ABSTRACT Spot blotch, caused by the fungal pathogen Cochliobolus sativus, is an important disease of barley in many production areas of the world. To assess genetic diversity in this pathogen, a worldwide collection of C. sativus isolates was evaluated for virulence on barley and DNA polymorphism. Three pathotypes (0, 1, and 2) were identified among the 22 isolates tested in this study and the 36 isolates characterized previously on three barley differentials (ND5883, Bowman, and NDB112) that differ in their resistance to C. sativus. Pathotype 2, which exhibits high virulence on cv. Bowman, was only found in North Dakota, whereas the other two pathotypes occurred in many other regions of the world. Genetic diversity of the 58 C. sativus isolates, together with isolates of three related pathogenic Cochliobolus spp. (C. heterostrophus, C. carbonum, and C. victoriae) was analyzed using amplified fragment length polymorphism (AFLP) markers. A total of 577 polymorphic AFLP markers were recorded among the 70 isolates of the four Cochliobolus spp. using eight primer combinations. Cluster analysis revealed distinct groups corresponding to the four different species, except in one case where race 0 of C. carbonum was placed in an outgroup that may belong to a different species. In C. sativus, 95 polymorphic AFLP markers were detected with the eight primer pairs used, and each isolate exhibited a unique AFLP pattern. Allelic diversity in the pathotype 2 group was lower (0.10) than in the pathotype 0 (0.23) and pathotype 1 (0.15) groups, indicating that pathotype 2 may have arisen more recently. Cluster analysis did not reveal a close correlation between pathotypes and AFLP groups, although two AFLP markers unique to pathotype 2 isolates were identified. This low correlation suggests that genetic exchange may have occurred through parasexual recombination in the fungal population. Some isolates collected from different regions of the world were clustered into the same AFLP group, suggesting that migration of the fungal pathogen around these regions has occurred.     

Assessment of biological and molecular variability between and within field isolates of Plasmodiophora brassicae

Plasmodiophora brassicae is an obligate biotroph that causes clubroot, one of the most damaging diseases of crucifers. Differential cultivars and random amplified polymorphic DNA markers were used to assess the extent of genetic diversity among nine single-gall populations of P. brassicae and 37 single-spore isolates (SSI) derived from four of those field samples. Isolates were classified into eight pathotypes, and each isolate was associated with a unique molecular genotype. Virulence and DNA polymorphisms were detected within and between field isolates, and among SSIs from different pathotypes, hosts and geographical origins. The relatively high level of genetic diversity among field isolates was similar to that among SSIs derived from a single-club field isolate. Molecular and pathogenicity-based classifications were not clearly correlated, but isolates belonging to pathotype P1 were clustered. Two RAPD markers were specific to pathotype P1. The finding that genetic differences can occur in P. brassicae field isolates will be an important consideration in resistance genetic studies and in choosing breeding strategies to develop durable clubroot resistance.     

小麦条锈菌水源11类群的RAPD分析及SCAR标记的建立

鉴于水源11类群近年来一直处于优势地位,为简化其检测手段,本研究利用RAPD技术对该类群的8个主要致病类型进行了多态性分析,以寻找其中主要流行类型的特异性分子标记。结果如下:共筛选出10个碱基随机引物190条,其中94条可得到稳定清晰的扩增图谱,用该94条引物进行RAPD分析,发现各致病类型间遗传变异丰富;以引物S1410扩增得到了水源11-4的特异性DNA条带;以引物S1412和S1304扩增得到了水源11-14的特异性DNA条带;对引物S1304扩增得到的特异性DNA条带回收、克隆和测序,设计了1对19bp/18bp的引物,并成功地将其转化为对水源11-14特异的SCAR标记。以上结果表明,通过规模筛选来寻找小麦条锈菌生理小种的特异性DNA片段,并将其转化为稳定的SCAR标记,有可能建立起中国小麦条锈菌流行生理小种的快速分子鉴定体系。     

Development of simple sequence repeat markers for the classification of the clubroot pathogen <Emphasis Type="Italic">Plasmodiophora brassicae</Emphasis>

Clubroot disease caused by Plasmodiophora brassicae is one of the most serious diseases in cruciferous crops. To classify isolates, we developed simple sequence repeat (SSR) markers for P. brassicae. Twenty-four Japanese isolates were used in this study: 12 isolates of an unknown pathotype from the Kyoto Prefecture, as well as 12 isolates of known pathotypes, including three single-spore lines. From the 12 isolates from Kyoto Prefecture, 11 were classified into either pathotype 2 (three isolates) or 4 (eight isolates). We designed 23 SSR markers based on the P. brassicae genome, of which 11 markers from intergenic regions showed polymorphisms in the 24 isolates. Many haploid isolates belonging to pathotypes 2 and 4 were monomorphic, and typical alleles were detected in some isolates not belonging to pathotype 4. Two bands were detected for eight SSR loci in five isolates, indicating that different genotypes were mixed in these isolates. We constructed a phylogram based on the 11 polymorphic SSRs. Pathotypes 2 and 4 formed a cluster, from which pathotypes 3 and 1 were successively placed. These results strongly suggest a close genetic relationship between isolates in pathotypes 2 and 4, consistent with our finding that isolates in these two pathotypes were found at one collection site. In combination with pathotype classification and other marker systems, the SSR markers can be used for more detailed analyses to improve the control of clubroot disease.     

Genetic variation among asexual progeny of Phytophthora infestans detected with RAPD and AFLP markers

Genotypic variation among 32 single-zoospore isolates (SZI) of Phytophthora infestans , derived asexually from two hyphal-tip parental isolates (PI-105 and PI-1) of the US-8 genotype, was assessed with 80 random amplified polymorphic DNA (RAPD) primers and 18 amplified fragment length polymorphic DNA (AFLP) primer pairs. In previous investigations, the SZIs from parental isolate PI-105 showed high levels of virulence variability and were differentiated into 14 races, whereas the SZIs from PI-1 showed identical virulence to the parent. The purpose of this investigation was to determine if phenotypic variation observed among SZIs of P. infestans could be detected at the DNA level in these isolates. Polymorphism was detected with 51 RAPD primers and with all 18 AFLP primer pairs in PI-105 SZIs. In SZIs from PI-1, polymorphism was also detected with 25 RAPD primers and 17 AFLP primer pairs. Cluster analysis using the unweighted pair-group method with arithmetic averages (UPGMA) separated the SZIs from parent PI-105 into six virulence groups, 11 RAPD groups and three AFLP groups. Cluster analysis of PI-1 SZIs, which all belong to the same virulence group, differentiated them into four RAPD groups and six AFLP groups. No close correlation among RAPD, AFLP and virulence groups could be established within the two progenies of SZIs. Results of this study suggest that there is a considerable level of inherent genetic variability among SZIs derived asexually from the same parental isolate. The possible mechanisms and implications of this genetic variation are discussed.     

Gene and Genotypic Diversity of Phytophthora cinnamomi in South Africa and Australia Revealed by DNA Polymorphisms

Phytophthora cinnamomi isolates from South Africa and Australia were compared to assess genetic differentiation between the two populations. These two populations were analysed for levels of phenotypic diversity using random amplified polymorphic DNAs (RAPDs) and gene and genotypic diversity using restriction fragment length polymorphisms (RFLPs). Sixteen RAPD markers from four decanucleotide Operon primers and 34 RFLP alleles from 15 putative loci were used. A few isolates from Papua New Guinea known to posses alleles different from Australian isolates were also included for comparative purposes. South African and Australian P. cinnamomi populations were almost identical with an extremely low level of genetic distance between them (D_m=0.003). Common features for the two populations include shared alleles, low levels of phenotypic/genotypic diversity, high clonality, and low observed and expected levels of heterozygosity. Furthermore, relatively high levels of genetic differentiation between mating type populations (D_m South Africa=0.020 and D_m Australia=0.025 respectively), negative fixation indices, and significant deviations from Hardy–Weinberg equilibrium, all provided evidence for the lack of frequent sexual reproduction in both populations. The data strongly suggest that both the South African and Australian P. cinnamomi populations are introduced.     

小麦条锈菌鉴别寄主和小种命名现状

 中国是世界上小麦条锈病最大的流行区之一,也是限制中国小麦生产的最严重病害之一,特别是当条件适于其发生时会造成巨大的产量损失.小麦条锈菌小种生理专化性研究及小种监测是掌握小麦条锈菌及其毒性变化动态、抗病基因有效性及病害流行预测预报的重要依据,是治理由此病原菌引起的小麦条锈病的基本环节之一.由于地域、条锈菌群体结构、研究水平和历史等的差异,目前国际上不同国家和地区采用相应的小麦条锈菌鉴别寄主和小种命名方法.中国、美国和印度均使用了各自不同的小麦条锈菌鉴别寄主,并采用了相应的小种命名体系,例如从1957至2002年,中国利用10多个鉴别寄主已鉴定和命名了32个小种和30多个致病类型,美国利用10多个鉴别寄主已鉴定和命名了80个小种;另一类是采用1972年Johnson提出的二进制国际小种命名法,这种体系包括了国际鉴别寄主和欧洲鉴别寄主,象一套鉴别寄主被整体使用,欧洲、中东、亚洲、非洲和南美国家及澳大利亚和新西兰均采用此体系监测小麦条锈菌变化,是一套被最为广泛接受和使用的小麦条锈菌小种鉴别方法和命名系统,但随着研究深入和各国实际情况差异等原因,不同研究人员加入了不同的辅助鉴别寄主,以更能准确和实际地反映本国和地区的现实情况,为生产服务,本文对此现状进行了分析和比较.由于此病菌具有长距离气传和扩散的特点(地区间、国家间和洲际间),因而也讨论了未来小麦条锈菌鉴别寄主组成、小种命名方法和研究结果的交流和比较等实际问题.     

Variation in genotype, pathotype and anastomosis groups of Colletotrichum lindemuthianum isolates from Mexico

Patterns of variation were determined in anastomosis, pathotype and genotype of Colletotrichum lindemuthianum samples collected from individual plants of common bean cultivars from four locations in the Mexican highlands. In Chihuahua, 22 polymorphic AFLP bands in isolates taken from a single plant identified five distinct genotypes. In Michoacán, nine genotypes were identified based on a total of only six polymorphic bands. Combined cluster analysis of all isolates from individual plants grouped them geographically. In Chihuahua, in isolates from 16 individual plants, only nine genotypes were identified and all samples were found to belong to the same anastomosis group. However, analysis of selected isolates revealed two new pathotypes not reported previously from Chihuahua (races 449 and 467). In contrast, in Michoacán all 13 isolates from individual plants were found to have distinct genotypes, and in Mexico State only two pairs of isolates among 20 samples had identical genotypes. Although no pathotype variation was determined, five anastomosis groups were identified in Michoacán and three in Mexico State. These results suggest that patterns of variation in genotype and anastomosis groups are complex in the different locations sampled, and that no strong relationship exists between genotype, pathotype or anastomosis group.     

Differentiation of Cotton-defoliating and Nondefoliating Pathotypes of Verticillium dahliae by RAPD and Specific PCR Analyses

Severe Verticillium wilt of cotton in southern Spain is associated with the spread of a highly virulent, defoliating (D) pathotype of Verticillium dahliae. Eleven of the D and 15 of a mildly virulent, nondefoliating (ND) pathotype were analyzed by random amplified polymorphic DNA (RAPD) using the polymerase chain reaction (PCR). Six of 21 primers tested generated pathotype-associated RAPD bands. Another 21 V. dahliae isolates were compared in blind trials both by RAPD-PCR using the six selected primers and pathogenicity tests on cotton cultivars. There was a 100% correlation between pathotype characterization by each method. Unweighted paired group method with arithmetic averages cluster analysis was used to divide the 47 V. dahliae isolates into two clusters that correlated with the D or ND pathotypes. There was more diversity among ND isolates than among D isolates, these latter isolates being almost identical. ND- and D-associated RAPD bands of 2.0 and 1.0kb, respectively, were cloned, sequenced, and used to design specific primers for the D and ND pathotypes. These pathotype-associated RAPD bands were present only in the genome of the pathotype from which they were amplified, as shown by Southern hybridization. The specific primers amplified only one DNA band of the expected size, and in the correct pathotype, when used for PCR with high annealing temperature. These specific primers successfully characterized V. dahliae cotton isolates from China and California as to D or ND pathotypes, thus demonstrating the validity and wide applicability of the results.     

Puccinia striiformis f.sp. tritici in Australasia: pathogenic changes during the first 10 years

Pathogenic attributes of the wheat stripe rust pathogen were monitored in annual surveys from the first recording of this disease in Australia in 1979. During the 10-year period to 1988,15 different pathotypes were detected in Australia and New Zealand. The pathotypes included some of economic importance to commercial wheat cultivars and others with no obvious selective advantage to aid their survival. Single-gene mutations were the most likely causes of variation. The implications of these results on pathogenicity surveys and breeding for resistance are discussed.     

Genetic Diversity in South American Colletotrichum gloeosporioides Isolates from Stylosanthes guianensis, a Tropical Forage Legume

The degree of genetic diversity of 127 Colletotrichum gloeosporioides isolates from Stylosanthes guianensis genotypes in South America was measured at the molecular level by random amplified polymorphic DNA (RAPD) with nine arbitrary primers of 10 bases, and by restriction fragment length polymorphism (RFLP) with a non-LTR (long terminal repeats) retrotransposon DNA sequence. The RAPD products revealed scorable polymorphism among the isolates, and a total of 80 band positions were scored. Sixty-three of the 127 isolates were clustered into 13 distinct lineages usually correlating with geographic origin. Where isolates from various regions were clustered together, most had identical host genotype origin. The pathogen population sampled from Carimagua, Colombia, a long-time Stylosanthes breeding and selection site, with a savanna ecosystem, was highly diverse. A set of 12 S. guianensis genotype differentials was used to characterize pathogenic variability of 104 isolates and their virulence patterns were grouped into 57 pathotypes. However, when they were tested on four Australian differentials, they grouped into 11 pathotypes. As shown in previous studies, no strict correlations existed between genetic diversity measured by RAPD or RFLP, and pathotype defined by pathogenicity pattern on the differentials. Southern blot analysis of the 127 isolates revealed 23 hybridizing fragments, resulting in 41 fingerprint patterns among the 127 isolates. Relationships between RFLP and RAPD variables were examined using Spearman's Rank Correlation Coefficient, which showed that the two measures of genotypic variation are in agreement.     

Assessment of Diversity in Claviceps africana and Other Claviceps Species by RAM and AFLP Analyses

ABSTRACT Genetic diversity among isolates of Claviceps africana, the sorghum ergot pathogen, and isolates of other Claviceps spp. causing ergot on sorghum or other hosts, was analyzed by random amplified microsatellite (RAM) and amplified fragment length polymorphism (AFLP) analyses. Of the RAM primer sets tested, one revealed polymorphism in C. africana isolates, with Australian and Indian isolates possessing a unique fragment. AFLP analysis, in addition to clearly distinguishing Claviceps spp., revealed polymorphisms in C. africana. A group of isolates from the United States, Puerto Rico, and South Africa exhibited 95 to 100% similarity with one another. Several isolates from Isabela, Puerto Rico were 100% similar to an isolate from Texas, and another isolate from Puerto Rico was identical with one from Nebraska. Australian and Indian isolates showed greater than 90% similarity with isolates from the United States., Puerto Rico, and South Africa. A number of polymorphisms existed in the United States group, indicating that the recently introduced population contains multiple genotypes. Isolates of C. sorghicola, a newly described sorghum pathogen from Japan, were very distinct from other species via RAM and AFLP analyses, as were isolates from outgroups C. purpurea and C. fusiformis. Both RAM and AFLP analysis will be useful in determining future patterns of intercontinental migration of the sorghum ergot pathogen, with the AFLP method showing greater ability to characterize levels of intraspecific variation.     

Clonality and long-distance migration of Puccinia striiformis f.sp. tritici in north-west Europe

The biotrophic fungus Puccinia striiformis f.sp. tritici , a basidiomycete that causes yellow rust on wheat, is spread by wind-dispersed spores. Analysis of amplified fragment length polymorphism (AFLP) variation showed that the fungus frequently migrates between the UK, Germany, France and Denmark. There is no biological evidence for sexual or parasexual reproduction under natural conditions, and this was supported by the lack of recombination, as revealed by AFLP, over the time and area represented by the samples in this study. A phylogeographic analysis revealed that there was effectively a single, clonal population in the four countries, up to 1700 km apart, consistent with a 'continent-island' model in which Denmark is the recipient of migrants from other countries. In five cases, specific pathogen clones were dispersed between the UK and Denmark, and on at least two recent occasions clones were also spread from the UK to Germany and France, causing outbreaks of yellow rust on wheat cultivars that were previously resistant to the disease in these countries. The agronomic consequences of migration were enhanced because of the limited genetic diversity for yellow rust resistance in wheat cultivars in the area. These results demonstrate that long-distance migration of pathogen clones, coupled with low diversity in the host species, may cause previously useful resistance genes to become ineffective for disease control on a continental scale.     

Genetic variability within Phaeoisariopsis griseola from Central America and its implications for resistance breeding of common bean

The genetic and virulence variability of 112 isolates of Phaeoisariopsis griseola , collected from various locations in Central America, were studied using seven random amplified polymorphic DNA (RAPD) primers and 12 common-bean differential genotypes. Broad molecular diversity ( H  = 0·92) among isolates was found using RAPD markers. Fifty pathotypes were identified on 12 differential bean genotypes, 29 of which were represented by only one isolate. Only 18 pathotypes were found in two or more countries. Pathotype 63-63 was the most virulent and caused leaf spots on all 12 common-bean differential genotypes. Comparison of virulence phenotypes and RAPD profiles to known Andean P. griseola isolates confirmed that all isolates belonged to the Mesoamerican group. Pairwise comparison between individual RAPD loci showed that the majority were in gametic phase linkage disequilibrium, revealing that P. griseola maintains a genetic structure that is consistent with asexual reproduction. The molecular and virulence diversities of P. griseola isolates from Central America imply that using single resistance genes to manage angular leaf spot is inadequate and stacking resistance genes may be necessary to manage the disease effectively.     

中国条锈菌新小种条中30、31号的研究

本文报道了1991年以来对新小种条中30、31号鉴定与致病性的研究。继1991年发现对绵阳系成株小麦有致病力的、对Hybrid46有毒的新致病类型91—1,1993年又发现了新的致病类型93—1。根据它们对我国鉴别寄主的反应,命名为条中30、31号。与条中28、29号相比,新小种具有更宽毒性基因组成和更高的相对寄生适合度值,它们对我国生产品种、高代品系和重要抗源有更广的致病范围。证实两个新小种的出现和发展是绵阳系小麦抗条锈变异的主要因素,建议加强对新小种抗病育种和流行预测的研究。     

Genetic Diversity in Australian Populations of Puccinia graminis f. sp. avenae

ABSTRACT Sequence-tagged microsatellite profiling was used to develop 110 microsatellites for Puccinia graminis f. sp. tritici (causal agent of wheat stem rust). Low microsatellite polymorphism was exhibited among 10 pathogenically diverse P. graminis f. sp. tritici isolates collected from Australian cereal growing regions over a period of at least 70 years, with two polymorphic loci detected, each revealing two alleles. Limited cross-species amplification was observed for the wheat rust pathogens, P. triticina (leaf rust) and P. striiformis f. sp. tritici (stripe rust). However, very high transferability was revealed with P. graminis f. sp. avenae (causal agent of oat stem rust) isolates. A genetic diversity study of 47 P. graminis f. sp. avenae isolates collected from an Australia-wide survey in 1999, and a historical group of 16 isolates collected from Australian cereal growing regions from 1971 to 1996, revealed six polymorphic microsatellite loci with a total of 15 alleles. Genetic analysis revealed the presence of several clonal lineages and subpopulations in the pathogen population, and wide dispersal of identical races and genotypes throughout Australian cereal-growing regions. These findings demonstrated the dynamic population structure of this pathogen in Australia and concur with the patterns of diversity observed in pathogenicity studies.     

全国小麦秆锈菌生理小种种群动态分析(1990~1994)

1990～1994年5年间一共分离鉴定了小麦秆锈菌菌株1224个,鉴定出21C3CKH、21C3CKR、21C3CTR、21C3CTH、21C3CPH、21C3CPR、21C3CFH、21C3CFR、34C2MKH、34C2MKR、34C2MKK、34C2MFK、34C2MFR、34MKG、34MFG、34MFK、34C1MKH、34C1MKR、34C1MFH等19个致病类型,分布于云南、福建、四川、贵州、湖南、湖北、浙江、上海、江苏、陕西、河南、河北、甘肃、内蒙古、吉林、辽宁、黑龙江、青海等18个省、市、自治区。涉及种植1000hm~2以上的绵阳20、绵阳19、绵阳15、绵阳11、扬麦三号、扬麦四号、扬麦五号、浙麦一号、浙麦二号及阿勃、晋2148、川麦八号、川育四号、川育十四、川麦20、西幅四号、西幅七号、蜀万831、宛7107、宝丰一号、小堰六号、苏麦三号等品种和近年来育出的部分新品系和高代材料,特别是在地处小麦秆锈菌易变区四川省首次发现了对小麦秆锈菌单抗基因Srll有毒力的21C3CTR等致病类型。     

Specific Detection of Tomato Pathotype of Verticillium dahliae by PCR Assays

Verticillium dahliae Klebahn is the causal agent of tomato wilt disease. Isolates of V. dahliae can be classified based on pathogenicity to tomato, but the pathotypes are indistinguishable in morphology. We designed PCR primers for specific detection of isolates pathogenic to tomato (tomato pathotype) from the sequences of a pathotype-specific gene, vdt1. With the primer pair Tg5/Tc3, a PCR product (approximately 3.2 kb) specific to tomato pathotype was amplified from the genomic DNA of isolates. Using the primer pair, a tomato pathotype isolate was specifically detected from hypocotyls of inoculated tomato and eggplant. On the other hand, no amplification was observed from non-tomato pathotype isolates of V. dahliae, some other wilt pathogens of tomato and a healthy host plant. Therefore, the primer pair can be useful for pathotype-specific detection of V. dahliae as well as for diagnosis of wilt disease of tomato plant. Received 7 September 2001/ Accepted in revised form 3 December 2001