Host Range Specificity in Verticillium dahliae

ABSTRACT Verticillium dahliae isolates from artichoke, bell pepper, cabbage, cauliflower, chili pepper, cotton, eggplant, lettuce, mint, potato, strawberry, tomato, and watermelon and V. albo-atrum from alfalfa were evaluated for their pathogenicity on all 14 hosts. One-month-old seedlings were inoculated with a spore suspension of about 10(7) conidia per ml using a root-dip technique and incubated in the greenhouse. Disease incidence and severity, plant height, and root and shoot dry weights were recorded 6 weeks after inoculation. Bell pepper, cabbage, cauliflower, cotton, eggplant, and mint isolates exhibited host specificity and differential pathogenicity on other hosts, whereas isolates from artichoke, lettuce, potato, strawberry, tomato, and watermelon did not. Bell pepper was resistant to all Verticillium isolates except isolates from bell pepper and eggplant. Thus, host specificity exists in some isolates of V. dahliae. The same isolates were characterized for vegetative compatibility groups (VCGs) through complementation of nitrate nonutilizing (nit) mutants. Cabbage and cauliflower isolates did not produce nit mutants. The isolate from cotton belonged to VCG 1; isolates from bell pepper, eggplant, potato, and tomato, to VCG 4; and the remaining isolates, to VCG 2. These isolates were also analyzed using the random amplified polymorphic DNA (RAPD) method. Forty random primers were screened, and eighteen of them amplified DNA from Verticillium. Based on RAPD banding patterns, cabbage and cauliflower isolates formed a unique group, distinct from other V. dahliae and V. albo-atrum groups. Minor genetic variations were observed among V. dahliae isolates from other hosts, regardless of whether they were host specific or not. There was no correlation among pathogenicity, VCGs, and RAPD banding patterns. Even though the isolates belonged to different VCGs, they shared similar RAPD profiles. These results suggest that management of Verticillium wilt in some crops through crop rotation is a distinct possibility.     

Vegetative Compatibility Groups of Verticillium dahliae in Israel: Their Distribution and Association with Pathogenicity

A collection of 565 isolates of Verticillium dahliae, recovered between 1992 and 1997 from 13 host plant species and soil at 47 sites in Israel, was tested for vegetative compatibility using nitrate-nonutilizing (nit) mutants. Three vegetative compatibility groups (VCGs) were found and identified as VCG2A (28 isolates), VCG2B (158 isolates), and VCG4B (378 isolates) by using international reference strains. One isolate was heterokaryon self-incompatible. Of the VCG2B isolates, 92% were recovered from the northern part of Israel and 90% of VCG4B isolates were recovered from the south, with some overlap in the central region. Isolates of the minor group VCG2A were geographically scattered among the two major VCGs. Isolates of the same VCG resembled one another more than isolates from different VCGs based on colony and microsclerotial morphology, temperature responses, and, partially, pathogenicity. Different pathotypes were defined among 60 isolates tested, using cotton (cv. Acala SJ-2) and eggplant (cv. Black Beauty) as differentials. All isolates in VCG2A and 86% of the isolates in VCG4B, irrespective of their origin, induced weak to moderate symptoms on cotton and moderate to severe symptoms on eggplant and were similar to the previously described cotton nondefoliating patho-type. In contrast, all cotton isolates in VCG2B caused severe foliar symptoms, stunting, and often death, but little or no defoliation of inoculated cotton plants. These were defined as a cotton defoliating-like pathotype and induced only weak to moderate symptoms on eggplant. We concluded that vegetative compatibility grouping of V. dahliae in Israel is closely associated with specific pathogenicity and other phenotypic traits.     

Vegetative compatibility groups within Verticillium dahliae isolates from different hosts in Greece

Forty-four isolates of Verticillium dahliae obtained from different diseased hosts were tested by vegetative compatibility group (VCG) analysis to investigate their genetic relatedness and correlate the results with four VCGs (1, 2, 3, 4) previously described. Based on complementarity of nit mutants, only three VCGs were identified from the Greek isolates. Seventeen isolates were assigned to VCG 2 (A or B), two to VCG 3 and eight to VCG 4 (A or B). The 17 remaining isolates could not be grouped to any of the three VCGs. All isolates belonging to a distinct VCG complemented strongly with at least one of the two tester strains of that group, or with several strains of the Greek collection belonging to that VCG.     

Vegetative compatibility groups in <Emphasis Type="Italic">Verticillium dahliae</Emphasis> isolates from olive in western Turkey

Verticillium wilt, caused by Verticillium dahliae, is the most serious disease in olive cultivation areas in western Turkey. Two hundred and eight isolates of V. dahliae from olive (Olea europea var. sativa) trees were taken for vegetative compatibility analysis using nitrate non-utilizing (nit) mutants. One isolate did not produce a nit mutant. Nit mutants of 207 isolates were tested against tester strains of internationally known vegetative compatibility groups (VCGs) 1A, 2A, 2B, 3, 4A and 4B, and also paired in many combinations among themselves. One hundred and eighty nine of the isolates (90.9%) were strongly compatible with T9, the tester strain of VCG1A, and thus were assigned to VCG1A. Eight isolates were assigned to VCG2A and four isolates to VCG4B. One isolate was heterokaryon self-incompatible (HSI) and five isolates could not be grouped to any of the VCGs tested. Pathogenicity assays were conducted on a susceptible olive cultivar (O. europea cv. Manzanilla) and a susceptible local cotton cultivar (Gossypium hirsutum cv. Çukurova 1518). Both cotton and olive inoculated with all VCG1A isolates showed defoliating symptoms in greenhouse tests. This is the first report on VCGs in V. dahliae from olive trees in Turkey which demonstrates that VCG1A of the cotton-defoliating type is the most commonly detected form from olive plants in the western part of Turkey.     

Vegetative Compatibility Groupings of Verticillium dahliae from Cotton in Mainland China

One hundred and fourteen isolates of Verticillium dahliae obtained from cotton and eggplant in mainland China were successfully assigned to two vegetative compatibility groups (VCGs) except for one self-incompatible isolate. Eleven isolates were strongly compatible with T9, the tester strain of the cotton defoliating pathotype, forming a linear growth of wild type with abundant microsclerotia and dense mycelia between compatible nitrate-nonutilizing mutants. The remaining 102 isolates were grouped into the non-defoliating VCG2, although the strength of the reaction varied; some isolates were strongly compatible with the tester strain while others were only slightly compatible. All VCG1 isolates including T9 showed the same defoliating symptom in greenhouse inoculation tests. This study confirmed the presence of the defoliating pathotype (VCG1) of V. dahliae in mainland China.     

Vegetative-compatibility groups in Verticillium dahliae from Israel

Nitrate-nonutilizing (nit) mutants were used to determine vegetative compatibility among 34 isolates of Verticillium dahliae from cotton, potato, olive, eggplant, chrysanthemum and tomato from 12 sites in Israel. Based on the formation of complementary heterokaryons, 33 isolates were assigned to two vegetative- compatibility groups (VCGs): one VCG contained 15 isolates from cotton, eggplant, chrysanthemum and olive; and the other VCG contained 18 isolates from potato, olive and cotton. The status of an additional isolate from tomato, which was compatible with both VCGs, remained unclear. In a limited pathogenicity test with 10 isolates, two (from tomato and eggplant) were pathogenic on tomato, eggplant and cotton; most isolates from cotton were pathogenic on cotton and eggplant only; and one from cotton was non-pathogenic. Fewer isolates were pathogenic on tomato than on cotton or eggplant. The diversity of vegetative compatibility found in our V. dahliae collection is comparable to that found in studies of American populations.     

Genetic and Virulence Diversity in Verticillium dahliae Populations Infecting Artichoke in Eastern-Central Spain

ABSTRACT Severe Verticillium dahliae attacks have occurred in artichoke crops in the Comunidad Valenciana region of eastern-central Spain since the late 1990s. Knowledge of genetic and virulence diversity in the pathogen population is a key factor for the management of the disease through disease risk assessment as well as development and use of resistant cultivars. V. dahliae isolates from artichoke (109 isolates) and cotton (three isolates) in that region were characterized by vegetative compatibility grouping (VCG), and specific polymerase chain reaction assays using three sets of primer pairs that differentiate the cotton-defoliating (D) and -nondefoliating (ND) V. dahliae pathotypes. In all, 35 and 39 V. dahliae isolates representative of the identified VCGs and geographic origins were tested for virulence to artichoke cvs. Nun 6374 and Nun 9444, and cotton cv. Acala SJ-2, respectively. Four VCGs were identified among 107 artichoke isolates, and 2 isolates were heterokaryon self-incompatible: VCG1A (one isolate), VCG2A (31 isolates), VCG2B (72 isolates), and VCG4B (three isolates). The three cotton isolates were VCG1A. Isolates in VCG2B were distributed across the region and were the most prevalent isolates in the northern part. Conversely, 83.9% of isolates in VCG2A were recovered from the southern part of the region. Two subgroups of isolates were identified in VCG2B based on heterokaryon compatibility with either international or local tester isolates, which further showed diversity in the amplification of 334- and 824-bp DNA fragments which are markers of the D and ND pathotypes, respectively. Virulence of isolates to artichoke and cotton correlated with VCG but the pattern of correlation varied with the host. VCG1A isolates from artichoke and cotton induced defoliation in cotton but not in artichoke. Collectively, isolates of VCG2B and VCG4B were the most virulent and isolates of VCG1A or HSI were the least virulent to artichoke; but isolates of VCG1A were more virulent to cotton than those of any other VCG. Also, molecular subgrouping in VCG2B determined by amplification of the 334- and 824-bp markers correlated with virulence of isolates to the two hosts tested.     

Molecular Variability Within and Among Verticillium dahliae Vegetative Compatibility Groups Determined by Fluorescent Amplified Fragment Length Polymorphism and Polymerase Chain Reaction Markers

ABSTRACT A degree of genetic diversity may exist among Verticillium dahliae isolates within vegetative compatibility groups (VCGs) that bears phytopathological significance and is worth investigating using molecular tools of a higher resolution than VCG characterization. The molecular variability within and among V. dahliae VCGs was studied using 53 artichoke isolates from eastern-central Spain, 96 isolates from cotton, 7 from cotton soil, and 45 from olive trees in countries of the Mediterranean Basin. Isolates were selected to represent the widest available diversity in cotton- and olive-defoliating (D) and -nondefoliating (ND) pathotypes, as well as for VCG. The VCG of 96 cotton and olive isolates was determined in this present study. Molecular variability among V. dahliae isolates was assessed by fluorescent amplified fragment length polymorphism (AFLP) analysis and by polymerase chain reaction (PCR) assays for DNA fragments associated with the D (462 bp) and ND (824 bp) pathotypes, as well as a 334-bp amplicon associated with D pathotype isolates but also present in some VCG2B isolates. Isolates from cotton were in VCG1A, VCG1B, VCG2A, VCG2B, and VCG4B and those from olive trees were in VCG1A, VCG2A, and VCG4B. Artichoke isolates included representatives of VCG1A, VCG2A, VCG2B (including a newly identified VCG2Ba), and VCG4B. AFLP data were used to generate matrixes of genetic distance among isolates for cluster analysis using the neighbor-joining method and for analysis of molecular variance. Results demonstrated that V. dahliae isolates within a VCG subgroup are molecularly similar, to the extent that clustering of isolates correlated with VCG subgroups regardless of the host source and geographic origin. VCGs differed in molecular variability, with the variability being highest in VCG2B and VCG2A. For some AFLP/VCG subgroup clusterings, V. dahliae isolates from artichoke grouped in subclusters clearly distinct from those comprising isolates from cotton and olive trees. In addition, VCG2B isolates from artichoke formed two distinct clusters that correlated with PCR markers of 334 bp (VCG2B(334)) or 824 bp (VCG2B(824)). Artichoke isolates in the VCG2B(334)/2beta(334) cluster were molecularly similar to isolates of VCG1A. The molecular difference found among artichoke isolates in VCG2B correlates with virulence of isolates to artichoke and cotton cultivars demonstrated in a previous study.     

Vegetative Compatibility amongVerticillium dahliae Isolates from Watermelon in Greece

Vegetative compatibility among 17 isolates ofVerticillium dahliae obtained from watermelon, originating from eight regions of Greece, was investigated using complementation tests between nitrate-nonutilizing(nit) mutants. Among 529 chlorate-resistant sectors obtained, only 107 werenit mutants. These mutants were paired with tester strains (from Greece and other countries) of previously described vegetative compatibility groups (VCGs), and also were paired in many combinations among themselves. All isolates were self-compatible. Sixteen isolates were found to belong to VCG2. Only isolate V75 could not be assigned to a VCG, because the threenit mutants obtained from it showed negative reactions with the tester strains of four VCGs and with complementary mutants from other isolates. Based on this sample, we conclude that the population ofV. dahliae from watermelon in Greece is homogeneous in respect to VCG.     

A PCR-based 'molecular tool box' for in planta differential detection of Verticillium dahliae vegetative compatibility groups infecting artichoke

A multiplex-nested-PCR procedure was developed for in planta detection of Verticillium dahliae isolates infecting artichoke and assessment of their vegetative compatibility groups (VCGs). PCR markers were identified and assigned to V. dahliae VCGs, including: i) a 334 bp marker amplified from VCG1A or VCG2B³³⁴ isolates; ii) a 688 bp marker amplified from VCG2A or VCG4B isolates; and iii) a 688 bp and a 964 bp PCR marker amplified from VCG2B⁸²⁴ isolates. The infecting V. dahliae VCGs were identified in artichoke tissues according to specific patterns of amplified markers after two rounds of PCR. The PCR-based 'molecular tool box' was first optimized using DNA extracted from artichoke plants artificially inoculated with isolates representative of known VCGs. Thereafter, the efficiency of the molecular procedure was tested using DNA extracted from naturally-infected artichoke plants showing a range of symptom severity as well as from symptomless plants. The novel multiplex-nested-PCR assay was clearly superior in detecting the pathogen compared to conventional isolation procedures, and in addition was informative about the VCGs. Moreover, the PCR method allowed the detection and VCG identification of V. dahliae infections in symptomless but infected plants, which had yielded false negatives when checked by microbiological isolation procedures. This 'molecular tool box' has uncovered the presence of several V. dahliae VCGs infecting the same artichoke plants in the Comunidad Valenciana Region. In addition, it is useful for genetic and pathogenicity diversity studies of V. dahliae populations infecting artichoke, and may help in predicting the severity of verticillium wilt epidemics.     

Vegetative compatibility groups ofVerticillium dahliae from cotton in the southeastern anatolia region of Turkey

Eighty isolates ofVerticillium dahliae from the southeastern Anatolia region and 20 isolates from the east Mediterranean region from wilted cotton plants were used for vegetative compatibility analysis employing nitrate non-utilizing mutants and reference tester strains of vegetative compatibility groups (VCGs) 1A, 2A, 2B, 3, 4A and 4B. Of the 100V. dahliae isolates, 49 were assigned to VCG1A, 39 to VCG2B, nine to VCG2A and three to VCG4B. Pathogenicity assays were conducted on susceptible cotton cv. Çukurova 1518 in the greenhouse. All VCG1A isolates induced defoliation and all VCG2B isolates caused partial defoliation symptoms. Isolates of VCG2A and VCG4B caused typical symptoms of leaf chlorosis without defoliation. This is the first report on VCGs ofV. dahliae in the southeastern Anatolia region of Turkey, which demonstrates that VCG1A of the cotton-defoliating type and VCG2B of the partially defoliating type are prevalent in this region.     

Vegetative compatibility groups inVerticillium dahliae isolates from cotton in Turkey

Verticillium dahliae Kleb. with a complicated genetic diversity is a widely distributed major pathogen resulting in cotton wilt, which causes high economic losses in cotton lint production in the cotton belt of Turkey. A collection of 70 TurkishV. dahliae isolates (68 from wilted cotton plants in 28 districts and two from watermelon plants in two districts) were tested for vegetative compatibility by observing heterokaryon formation among complementary nitrate-nonutilizing (nit) mutants. The mutants were tested against international reference tester isolates and also were paired with one another. Thirty-nine isolates were assigned to vegetative compatibility group (VCG) 2B, 19 to VCG2A and three to VCG4B. One isolate was self-incompatible and eight others could not be assigned to any of the identified VCGs because theirnit mutants showed negative reactions with the tester isolates of four VCGs or theirnit mutants reverted back to the wild type. This is the first report of VCGs inV. dahliae from cotton in Turkey.     

Aggressiveness of Verticillium dahliae isolates from different vegetative compatibility groups to potato and tomato

Aggressiveness of Verticillium dahliae isolates from three vegetative compatibility groups (VCGs) was tested on potato and tomato. VCG4B was the most aggressive to potato and VCG2A was the most aggressive to tomato; VCG2B was the least aggressive to both potato and tomato. In potato, disease incidence, symptom severity and colonization index of stem segments were significantly higher in plants inoculated with VCG4B isolates than in those inoculated with VCG2B and VCG2A isolates. Inoculation with VCG4B and VCG2A decreased plant height and fresh weight more than inoculation with VCG2B. In tomato, VCG2A caused significantly more severe symptoms than either VCG4B or VCG2B. The colonization index in tomato plants inoculated with VCG2A was also significantly higher than in those inoculated with VCG4B and VCG2B. Similar patterns of relative aggressiveness were observed in potato and tomato when the pathogenicity of isolates of various VCGs, each originating from a specific host (cotton, potato or eggplant), was compared.     

Differentiation ofVerticillium dahliae populations on the basis of vegetative compatibility and pathogenicity on cotton

Complementary auxotrophic nitrate-nonutilizing (nit) mutants were used to investigate vegetative compatibility within 27 strains ofVerticillium dahliae isolated from several hosts originating from Africa, Asia, Europe and the United States. Using about 500nit mutants generated from these strains, three vegetative compatibility groups, 1, 2 and 4, were identified. Simultaneously, virulence of each strain was assessed on cultivars ofGossypium hirsutum, G. barbadense andG. arboreum, based upon Foliar Alteration Index (FAI) and Browning Index (BI) estimation. The strains in VCG1 were of both the cotton-defoliating pathotype and race 3 (on cotton) but were non pathogenic on tomato; those in VCG2 and VCG4 were of the nondefoliating pathotype and belonged to different races on cotton and on tomato. Hyaline mutants deriving from parental wild-type strain showed differences in pathogenicity but were always assigned to the parental VCG. A relationship was established between VCGs and the taxonomic position of host plants. Data fromnit pairings indicated that the sub-populations ofV. dahliae (VCGs) may not be completely isolated genetically.     

Vegetative compatibility and pathogenicity of <Emphasis Type="Italic">Verticillium dahliae</Emphasis> isolates from chrysanthemum in Turkey

A collection of 30 strains of Verticillium dahliae, recovered during 2004–2006 from 12 cultivars of chrysanthemum (Chrysanthemum morifolium) in five districts of İzmir province in Turkey, was assigned to vegetative compatibility groups (VCGs) based on pairings of complementary nitrate-nonutilizing (nit) mutants induced on a chlorate-containing medium. Of these strains, nine were assigned to VCG1, seven to VCG2A, 11 toVCG2B and one to VCG4B. The remaining two strains could not be tested for vegetative compatibility because of their inability to yield nit mutants. Pathogenicity tests conducted by the root-dip method, demonstrated that wilt of chrysanthemum in Turkey is caused by V. dahliae, and most strains in VCG1 were significantly more aggressive to chrysanthemum than those in VCGs 2 and 4B. This is the first known study in the world of the VCGs of V. dahliae isolates from chrysanthemum.     

Genetic diversity of the entomopathogen<Emphasis Type="Italic">Verticillium lecanii</Emphasis> on the basis of vegetative compatibility

Forty-three isolates ofVerticillium lecanii from insects, phytopathogenic fungi and other substrates were tested for vegetative compatibility by observing heterokaryon formation among complementary nitrate-nonutilizing (nit) mutants.nit mutants were isolated from 42/43 strains examined. Twenty-one isolates were self-incompatible, and the remaining 21 isolates were divided into 14 vegetative compatibility groups (VCGs): ten containing only a single strain each, and the remaining four containing two to four isolates each. Members of isolates in each of these VCGs all shared the same IGS haplotype. Further, the isolates within a VCG were correlated with one another in part by fragment patterns of mt-LrDNA, -SrDNA, Bt-2 and H4 region, by PCR-RFLP and -SSCP, but not by dsRNA. Two isolates belonging to VL-J2 have high virulence to aphids, whereas strains from VL-J1 lack this character. These findings indicate that two VCGs (VL-J1 and -J2) may originate from two distinct clonal lineages. Alternatively, high VCG diversity and HSI frequency ofV. lecanii might be associated with an array of distinct lineages. These data not only suggest relationships among DNA polymorphisms, virulence, and VCG, but also demonstrate genetic heterogeneity ofV. lecanii. http://www.phytoparasitica.org posting Sept. 30, 2003.     

Region-wide analysis of genetic diversity in Verticillium dahliae populations infecting olive in southern Spain and agricultural factors influencing the distribution and prevalence of vegetative compatibility groups and pathotypes

Severity of Verticillium wilt in olive trees in Andalusia, southern Spain is associated with the spread of a highly virulent, defoliating (D) Verticillium dahliae pathotype of vegetative compatibility group 1A (VCG1A) but the extent of this spread and the diversity of the pathogen population have never been documented. VCG typing of 637 V. dahliae isolates from 433 trees in 65 orchards from five olive-growing provinces in Andalusia indicated that 78.1% were of VCG1A, 19.8% of VCG2A, 0.6% of VCG2B, 1.4% of VCG4B, and one isolate was heterokaryon self-incompatible. A single VCG prevailed among isolates within most orchards but two and three VCGs were identified in 12 and 3 orchards, respectively, with VCG1A+VCG2A occurring in 10 orchards. VCG1A was the predominant VCG in the three most important olive-growing provinces, and was almost as prevalent as VCG2A in another one. Molecular pathotyping of the 637 isolates using specific polymerase chain reaction assays indicated that VCG1A isolates were of the D pathotype whereas isolates of VCG2A, -2B, and -4B were of the less virulent nondefoliating (ND) pathotype. The pathotype of isolates correlated with the disease syndrome affecting sampled trees. Only three (seq1, seq2, and seq4) of the seven known sequences of the V. dahliae-specific 539- or 523-bp amplicon were identified among the 637 isolates. Distribution and prevalence of VCGs and seq sequences among orchards indicated that genetic diversity within olive V. dahliae in Andalusia is higher in provinces where VCG1A is not prevalent. Log-linear analysis revealed that irrigation management, source of irrigation water, source of planting stock, and cropping history of soil were significantly associated with the prevalence of VCG1A compared with that of VCG2A. Multivariate analyses using a selected set of agricultural factors as variables allowed development of a discriminant model for predicting the occurrence of D and ND pathotypes in the area of the study. Blind tests using this model correctly indentified the V. dahliae pathotype occurring in an orchard. The widespread occurrence and high prevalence of VCG1A/D pathotype in Andalusia have strong implications for the management of the disease.     

Genetic and pathogenic characterization of <Emphasis Type="Italic">Verticillium dahliae</Emphasis> isolates from eggplant in Turkey

During 2005 to 2007, eggplant fields in 19 provinces from three different regions (western, southern and southeastern Anatolia regions) of Turkey were surveyed for Verticillium wilt. Sixty-seven isolates of Verticillium dahliae from wilted eggplants were collected and used for vegetative compatibility analysis using nitrate non-utilizing mutants and reference tester strains of vegetative compatibility groups (VCGs) 1A, 2A, 2B, 3, 4A and 4B. Among all isolates, 33 (12 from western, 15 from southern and six from southeastern Anatolia) were assigned to VCG2B, 23 (four from western, eight from southern and 11 from southeastern Anatolia) to VCG2A, six (four from southern, one from western, and one from southeastern Anatolia) to VCG4B and five (one from western, one from southern and three from southeastern Anatolia) to VCG1A, whereas VCG3 and VCG4A were not defined among isolates. In order to test if there is a correlation between VCG and pathogenicity in V. dahliae, pathogenicity of 30 isolates, representing the four multimember VCGs, were tested on Solanum melongena cvs. ‘Kemer’ and ‘Aydın Siyahı’ in an unheated greenhouse. All isolates were found to be pathogenic on both cultivars and there was no difference in susceptibility between the two cultivars. VCG4B isolates collectively led to higher vascular discoloration index (VDI) on both cultivars and higher disease severity index (DSI) on ‘Kemer’ compared with other VCGs. Similarly, VCG1A caused lower VDI on both cultivars and lower DSI on ‘Kemer’. Isolates within each of VCGs 1A, 2A and 4B caused similar VDI on both cultivars. Isolates of VCG2B were found to vary in their VDI values on both cultivars. To the best of our knowledge, the present study is the first report of natural infections of eggplant by VCG1A.     

Phylogenetic analysis of Verticillium dahliae vegetative compatibility groups

The evolutionary relationships among Verticillium dahliae vegetative compatibility (VCG) subgroups VCG1A, VCG1B, VCG2A, VCG2B, VCG4A, VCG4B, and VCG6 were investigated by parsimony analysis of amplified fragment length polymorphism (AFLP) fingerprints and sequences of six DNA regions (actin, beta-tubulin, calmodulin, and histone 3 genes, the ITS 1 and 2 regions of the rDNA, and a V. dahliae-specific sequence), using 101 isolates of diverse host and geographic origin. Polymorphisms in gene sequences among isolates of different VCGs were very low and individual gene genealogies provided very little resolution at the VCG level. The combined analysis of all DNA regions differentiated all VCG subgroups except for isolates in VCG1A and VCG1B. VCG clonal lineages in V. dahliae and evolutionary relationships among them were resolved independently by analyses of AFLP fingerprints, multiple gene genealogies, and the combined data set of AFLP fingerprinting and multiple gene genealogies. Two main lineages (I and II) were identified with lineage II comprising two closely related subgroups of VCGs. Lineage I included VCG1A, VCG1B, and VCG2B334; and lineage II included, VCG2A and VCG4B (subclade 1); and VCG2B824, VCG4A, and VCG6 (subclade 2). VCG subgroups were monophyletic except for VCG2B that appeared polyphyletic. Limiting the parsimony analysis either to AFLP fingerprints or DNA sequences would have obscured intra-VCG differentiation. Therefore, the dual approach represented by the independent and combined analyses of AFLP fingerprints and DNA sequences was a highly valuable method for the identification of phylogenetic relationships at the intraspecific level in V. dahliae.     

Vegetative Compatibility Groups in Verticillium dahliae Isolates from the Netherlands as Compared to VCG Diversity in Europe and in the USA

In a study of vegetative compatibility in Verticillium dahliae in the Netherlands, a collection of 45 isolates including representatives from woody hosts, several horticultural crops and from the soil of potato fields was examined. In addition an effort was made to compare vegetative compatibility groups (VCGs) from different countries. The results of this study indicate that VCG diversity in V. dahliae in the Netherlands is limited. Only two VCGs were detected: VCG NL-I and VCG NL-II. The former is the predominant VCG for isolates from tree hosts. However, Verticillium wilt in trees can be caused by isolates from both VCGs. It is suggested that the predominance of VCG NL-I in tree hosts is the result of the origin of the tree and the cropping history of its growing site, rather than trees being preferential hosts for isolates from this VCG. Comparison of VCG testers from the Netherlands, from several other European countries and from the USA show that in Europe two major VCGs are present. The first one, including NL-I, is compatible with USA VCG 3 and VCG 4, whereas the second one, including NL-II, is compatible with USA VCG 1 and VCG 2. These groups are not completely separated; in some cases, testers formed heterokaryons with VCG testers from both main groups. Because of the presence of these bridge isolates and because mutants from the same isolate differ in ability to form heterokaryons, it is emphasised that careful selection of isolate testers is an essential step to get a clear picture of VCG diversity.