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.     

Genetic variability and virulence among Verticillium albo-atrum isolates from hop

Verticillium wilt, caused by Verticillium albo-atrum or V. dahliae, is an important disease of many worldwide crop species. In Europe, V. albo-atrum isolates infecting hop express different levels of virulence, inducing mild or lethal disease syndromes, and it is therefore an attractive model for studying the virulence of this pathogen. In this work, eleven amplified fragment length polymorphism (AFLP) primer combinations were used to analyze genetic variability among 55 V. albo-atrum hop isolates from four European hop growing regions, as well as isolates from other hosts and V. dahliae isolates. Cluster analysis divided V. albo-atrum and V. dahliae isolates into two well-separated groups. Within the V. dahliae cluster, isolates were separated without host specific grouping, although no host adapted isolates were included. In V. albo-atrum, the alfalfa isolates were distinct from isolates of other hosts, where a high association with virulence was observed in hop and tomato isolates. All lethal hop isolates were genetically different from mild hop isolates. The lethal hop isolates from England and Slovenia expressed the same virulence phenotype, although they showed a different AFLP pattern. The mild hop isolates formed two subgroups, to which isolates clustered irrespective of geographical location. These data suggest multiple origins of V. albo-atrum hop isolates, and the possible appearance of new virulent isolates in the future in other hop growing regions.     

Genetic Relationships Among Verticillium dahliae Isolates from Cotton in Greece Based on Vegetative Compatibility

Vegetative compatibility groups of a collection of 71 Greek Verticillium dahliae isolates obtained from cotton plants were tested. Nit mutants were generated from single spore wild strains by selecting chlorate-resistant sectors on minimal medium amended with potassium chlorate, 25g/l. These mutants were tested against tester strains from the USA and Greece of the previously described VCGs 1, 2, 3 and 4. Forty-six of 71 isolates belonged to VCG2, because they were able to anastomose with the testers of this group, two isolates belonged to VCG4 and one to VCG1, while the 22 remaining strains could not be assigned to any of the identified VCGs. Our data demonstrated that wilt of cotton is caused only by V. dahliae in Greece, and VCG2 is the most commonly detected VCG. Some strains were found to be more virulent to cotton than other strains from the same VCG. This is the first report of VCG1 of Verticillium in Greece.     

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.     

Vegetative compatibility and pathogenicity of<Emphasis Type="Italic">Verticillium dahliae</Emphasis> isolates from the aegean region of Turkey

A total of 101Verticillium dahliae isolates were recovered from cotton plants at 57 sites in the Aegean region of Turkey between 2003 and 2004. Isolates were tested for vegetative compatibility by observing heterokaryon formation among complementary nitrate-nonutilizing (nit) mutants. Forty-six isolates were assigned to VCG 1, 12 to VCG 2A, 33 to VCG 2B and four to VCG 4B. The remaining six isolates could not be tested for vegetative compatibility because of their inability to yieldnit mutants. All isolates recovered were tested for pathogenicity on cotton cultivars Acala SJ-1 and Deltapine 15-21 by the stem-injection method. The isolates of VCG 2 and 4B, irrespective of their origin, induced weak to severe symptoms on cotton and were similar to the previously described cotton non-defoliating pathotype. In contrast, all cotton isolates of VCG1 caused severe foliar symptoms, stunting, defoliation and often death. This is the first report on VCG 1 ofV. dahliae in Turkey. http://www.phytoparasitica.org posting May 4, 2007.     

Plant Host Range of Verticillium longisporum and Microsclerotia Density in Swedish Soils

Verticillium longisporum is a soil-borne fungal pathogen causing vascular wilt of Brassica crops. This study was conducted to enhance our knowledge on the host range of V. longisporum. Seven crop species (barley, oat, oilseed rape, pea, red clover, sugar beet and wheat) and five weed species (barren brome, black-grass, charlock, cleavers and scentless mayweed) all common in southern Sweden were evaluated for infection by response to V. longisporum. Oat, spring wheat, oilseed rape, scentless mayweed and charlock inoculated with V. longisporum in a greenhouse showed stunting to various degrees close to the fully ripe stage. Based on the extent of microsclerotia formation, explants were separated into four groups: for pea and wheat, <5% of the samples had formed microsclerotia; for scentless mayweed, 5–10%; for oat, 10–20%; and for charlock and oilseed rape >80%. The results suggest that plant species outside the Brassicaceae can act as reservoirs of V. longisporum inoculum. Soil inoculum densities in nine fields were monitored over a period of 12 months, which ranged from 1 to 48 cfu g⁻¹ soil. Density of microsclerotia was lowest just after harvest, reaching its maximum six months later. No significant correlation between inoculum density in soil and disease incidence on oilseed rape plants was found. However, the data suggest that a threshold of 1 cfu g⁻¹ soil is needed to cause disease on oilseed rape. Species identification based on microsclerotia morphology and PCR analysis showed that V. longisporum dominated in soil of seven, and V. dahliae in two of the nine fields studied.     

江西棉黄萎病发生及防治

江西棉黄萎病1996年传入,至目前发生的均为非落叶型弱致病菌系,其发生规律及危害趋势与枯萎病基本相同,损失率一般在10％-30％。防治上宜选育和推广抗病品种及其他防治措施应急。     

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.     

Cultural Characteristics, Pathogenicity and Vegetative Compatibility of Fusarium udum Isolates from Pigeonpea (Cajanus cajan (L.) Millsp.) in Kenya

Seventy-nine single-spore isolates of Fusarium udum, the causal agent of wilt disease of pigeonpea, from Kenya, India and Malawi were characterized according to their cultural characteristics, pathogenicity and vegetative compatibility group (VCG). The isolates exhibited high variation in pathogenicity on a wilt-susceptible pigeonpea variety, and in mycelial growth and sporulation on potato dextrose agar medium. The 79 isolates were categorized into two virulence groups, two groups of radial mycelial growth and four groups of sporulation. Radial mycelial growth showed a moderate negative correlation (r = –0.40; P = 0.01) with sporulation. However, mycelial growth and sporulation had no correlation with virulence. Pairings between complementary nitrate non-utilizing (nit) mutants of F. udum generated on chlorate containing minimal medium revealed that all the isolates belonged to a single VCG (VCG 1) with two subgroups, VCG 1 I and VCG 1 II. Vegetative compatibility was independent of cultural characteristics and pathogenicity. This is the first report of vegetative compatibility in F. udum.     

Detection of the Defoliating Pathotype of Verticillium dahliae in Infected Olive Plants by Nested PCR

Spread of Verticillium wilt into newly established olive orchards in Andalucía, southern Spain, has caused concern in the olive industry in the region. This spread may result from use of Verticillium dahliae-infected planting material, which can extend distribution of the highly virulent, defoliating (D) pathotype of V. dahliae to new areas. In this study, a molecular diagnostic method for the early in planta detection of D V. dahliae was developed, aimed especially at nursery-produced olive plants. For this purpose, new primers for nested PCR were designed by sequencing a 992-bp RAPD marker of the D pathotype. The use of the specific primers and different nested-PCR protocols allowed the detection of V. dahliae pathotype D DNA in infected root and stem tissues of young olive plants. Detection of the pathogen was effective from the very earliest moments following inoculation of olive plants with a V. dahliae pathotype D conidia suspension as well as in inoculated, though symptomless, plants.     

Pathogenicity and Virulence of the Two Dutch VCGs of Verticillium dahliae to Woody Ornamentals

Two experiments were performed in two consecutive years to test whether isolates of different vegetative compatibility groups (VCGs) differ in their ability to cause disease in woody ornamentals, to study the host specificity of the isolates and to get an insight into disease development in woody hosts. A range of woody ornamental plant species, including Acer campestre, Acer platanoides, Acer pseudoplatanus, Catalpa bignonioides, Cotinus coggygria, Robinia pseudoacacia, Rosa canina, Syringa vulgaris and Tilia cordata, were root-dip inoculated with six isolates of Verticillium dahliae, belonging to the two VCGs that occur in the Netherlands (VCG NL-1 and VCG NL-2). Isolates belonging to each VCG caused severe symptoms of verticillium wilt in most plant species tested. Disease progress differed between plant species, but was generally the same for the two VCGs. No overall differences in virulence were observed between the two VCGs for external wilt symptoms, number of dead plants, or shoot length. No significant VCG × plant species interactions were present for these characteristics. However, isolates of VCG NL-1 caused more vascular discolouration than did isolates of VCG NL-2. Isolates within VCGs often differed considerably in their virulence to certain hosts, as shown by highly significant isolate × plant species interactions. Isolates were more virulent on their original host. These findings imply that VCG identification does not contribute to disease prediction for a range of woody hosts.     

甲基营养型芽胞杆菌AL7对棉花黄萎病的盆栽防治效果及定殖能力

为了探明甲基营养型芽胞杆菌AL7对棉花黄萎病的防治效果及其定殖能力,本文利用盆栽接种试验研究了菌株AL7对棉花黄萎病的防治效果;将带四环素抗性的pGFP78质粒转入到菌株AL7中,分析了菌株AL7在棉花根围土壤中、根部组织内的定殖情况。结果表明,菌株AL7对棉花黄萎病的盆栽防治效果为77.1%。pGFP78质粒转入后对菌株AL7的生长没有明显影响,仍具有游动性和产生物膜。定殖检测结果表明,菌株AL7能够在棉花根围土壤中及根系组织内长期定殖,接种5 d时定殖数量最高,达6×10~6cfu/g土,接种80 d后根围土壤中的定殖数量仍维持在2×10~6 cfu/g,根系组织内的定殖量为6×10~4 cfu/g。利用激光共聚焦显微镜观察验证,接种7 d后菌株AL7已经进入到棉花根部的中柱鞘细胞,能够在棉花根内大量定殖。     

Genetic and Molecular Characterization of Verticillium dahliae Isolates from Woody Ornamentals in Belgian Nurseries

Isolates of Verticillium dahliae were collected from affected trees (Acer spp., Tilia spp. and Robinia spp.) and soils in Belgian ornamental nurseries. Nitrate non-utilizing mutants were produced and vegetative compatibility groups (VCGs) were classified based on complementation tests with reference tester strains. Of the 30 isolates analysed, 12 were classified as VCG2B and 18 as VCG4B following the American classification. In order to distinguish VCG2B from VCG4B, specific polymerase chain reaction primers were designed based on the sequence of a VCG2B-associated Direct Amplification of Minisatellite-region DNA (DAMD) band generated with the core sequence of the phage M13 minisatellite DNA. Using this test, amplification products were generated for all the VCG2B isolates characterized in this study. In contrast, no signal was seen on ethidium–bromide agarose gel for VCG4B isolates. Pathogenicity tests were carried out in a glasshouse on maple-rooted cuttings inoculated with conidial suspensions of V. dahliae belonging to both groups (VCG2B/VCG4B). Some strains proved to be highly aggressive, while others did not. However, these different behaviours were not correlated with the VCGs.     

检疫性轮枝菌及其近似种的鉴定

 大丽轮枝菌(Verticillium dahliae)和黑白轮枝菌（V. albo-atrum）在世界范围内引起多种作物的黄萎病,属于我国重要进境植物检疫对象。本研究对采自我国部分地区和CBS保存的多种植物病原性轮枝菌,包括黑白轮枝菌、大丽轮枝菌及其变种大丽轮枝菌长孢变种(V. dahliae var. longisporum)、三体轮枝菌(V. tricorpus)、变黑轮枝菌(V. nigrescens)和云状轮枝菌(V. nubilum),采用生物学特性观察,结合rDNA-ITS序列分析的方法,进行了比较和分析。结果表明：不同种类轮枝菌在休眠结构形态上具有一定差异,部分菌株不产生任何休眠结构。各供试菌株在15～25℃范围内均可生长,但黑白轮枝菌在30℃下生长受到强烈抑制,而其他菌株受影响较小。对供试菌株rDNA-ITS序列分析结果表明植物病原性轮枝菌可聚为9个分支,包括三体轮枝菌、变黑轮枝菌、云状轮枝菌、V. theobromae、大丽轮枝菌、大丽轮枝菌长孢变种和3个不同的黑白轮枝菌分支,黑白轮枝菌、大丽轮枝菌及其长孢变种亲缘关系较近。采用生物学性状结合rDNA-ITS序列分析能够更加有效地将两种检疫性轮枝菌从其他植物病原性轮枝菌中区分出来。     

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.     

Phytotoxicity on cotton ex-plants of an 18.5 kDa protein from culture filtrates of Verticillium dahliae

A phytotoxic protein that evokes the typical symptoms of Verticillium wilt disease in seedlings of Gossypium hirsutum L. (Upland cotton) was isolated from culture filtrates of Verticillium dahliae. The protein was purified by ammonium sulfate precipitation, Sephadex-G100 fractionation, and native PAGE. The 18.5 kDa protein, designated VD18.5, appears to be a single subunit protein with an isoelectric point between 3 and 5. VD18.5 induces symptoms of leaf dehydration, chlorosis, necrosis and stem discoloration in seedlings of the disease susceptible cotton cultivar Siokra 1–4. The LD₅₀ of VD18.5 on protoplasts of Siokra 1–4 was 18 μg mL⁻¹. VD18.5 had no noticeable effect on Pima S-7, which is a disease resistant cultivar. Phytotoxic activity was partially destroyed at high temperature and was abolished by digestion with proteinase K. Mass spectrometry fingerprinting and protein sequence data from VD18.5 yielded no significant matches when submitted to the Mascot search engine and NCBI non-redundant protein databases, respectively. These results suggest that VD18.5 is a novel protein that may be involved in the development of some of the symptoms associated with Verticillium wilt disease in the cotton plant.     

Dry mycelium of<Emphasis Type="Italic">Penicillium chrysogenum</Emphasis> induces resistance against verticillium wilt and enhances growth of cotton plants

Dry mycelium (DM) ofPenicillium chrysogenum and its water extract (DME) were examined for their effects on induced resistance against Verticillium wilt and plant growth of cotton in the greenhouse. Soil application of 0.1–5% DM or 0.5–5% DME provided significant protection against the wilt, relative to the control. As neither DM nor DME inhibited mycelial growth ofVerticillium dahliae in vitro, it is suggested that the disease-controlling effects of DM or DME are attributed to induced resistance. DME (5%), as well as DME treated with chloroform or cold acetone, were as effective as 2% DM in reducing disease severity of Verticillium wilt, implying that the resistance-inducing substance(s) in DM are mostly water-soluble, with neither proteins nor lipids likely to be responsible for the induction of resistance. No significant difference in root colonization withV. dahliae was found between control-inoculated and 2% DM- or 5% DME-inoculated plants. However, colonization of hypocotyls and epicotyls was drastically suppressed by either 2% DM or 5% DME relative to the control. Treatments with 2% DM or 5% DME significantly increased ionically-bound peroxidase (POX) activity in roots, hypocotyls and the second leaf of cotton plants, with the hypocotyls expressing the highest increase. Soil application of DM or DME increased plant height, fresh and dry weight of inoculated and non-inoculated cotton plants, relative to their corresponding controls. It is concluded that DM may be used in cotton crops to promote plant growth and to induce resistance againstV. dahliae. POX might be associated with the defense against Verticillium wilt. http://www.phytoparasitica.org posting Jan. 9, 2002.     

Contribution to the taxonomy and pathogenicity of fungicolous Verticillium species. II. Pathogenicity

In recent years in the Netherlands a second mushroom species,Agaricus bitorquis, which prefers higher temperatures thanA. bisporus and is less susceptible to certain diseases, is often commercially grown.Verticillium fungicola var.fungicola, the causal agent of dry bubble, is responsible for considerable damage in crops ofA. bisporus. InA. bitorquis, however, dry bubble has hardly been noticed, but brown spots due toV. fungicola var.aleophilum resulted in inferior mushroom quality. The latter variety also caused brown spots ina. bisporus, but to a minor degree. In variety Les Miz 60 ofA. bisporus, however, it also induced fruit-body deformation in a way different from dry bubble. Verticillium psalliotae, isolated fromA. bitorquis in England, induced more confluent brown spots inA. bitorquis. In the netherlands, where moreA. bitorquis is grown than in other countries,V. psalliotae has not yet been encountered in crops ofA. bitorquis. V. psalliotae, which has a high temperature optimum for mycelial growth, likeV. fungicola var.aleophilum andA. bitorquis, did not infectA. bisporus in our trials.Artificial infection ofA. bisporus orA. bitorquis could not be accomplished with the following related and/or fungicolous fungi:Verticillium lamellicola, V. fungicola var.flavidum, V. biguttatum, Nectriopsis tubariicola, Acremonium crotocinigenum andAphanocladium album.Samenvatting Vooral in Nederland wordt sinds een aantal jaren naastAgaricus bisporus ook de warmteminnende champignonsoortAgaricus bitorquis geteeld, die minder vatbaar is voor bepaalde ziekten. TerwijlVerticillium fungicola varfungicola in de teelt vanA. bisporus droge mollen en daardoor veel schade veroorzaakt, komen in de teelt vanA. bitorquis geen droge mollen voor maar wel bruine vlekken, die tot kwaliteitsverlies en dus schade leiden. De vlekken bleken veroorzaakt te worden doorV. fungicola var.aleophilum. Deze schimmel veroorzaakte ook inA. bisporus bruine vlekken, hoewel in minder ernstige mate, maar in het ras Les Miz 60 vanA. bisporus bovendien misvormde champignons, die wel op droge mollen leken, maar daaraan niet gelijk waren.OokV. psalliotae, in Engeland geïsoleerd vanA. bitorquis met vlekken, veroorzaakte wat meer samenvloeiende, bruine vlekken inA. bitorquis. In Nederland, waar meerA. bitorquis geteeld wordt dan in andere landen, isV. psalliotae nog niet aangetroffen in teelten vanA. bitorquis. InA. bisporus kon geen kunstmatige infectie worden verkregen metV. psalliotae, die net alsV. fungicola var.aleophilum enA. bitorquis warmteminnend genoemd zou kunnen worden.Met de volgendeVerticillium-achtige of van paddestoelen geïsoleerde schimmels kon evenmin op kunstmatige wijze een infectie worden opgeroepen inA. bisporus ofA. bitorquis: Verticillium lamellicola, V. fungicola var.flavidum, V. biguttatum, Nectriopsis tubariicola, Acremonium crotocinigenum enAphanocladium album.     

Vegetative compatibility of cotton-defoliating <Emphasis Type="Italic">Verticillium dahliae</Emphasis> in Israel and its pathogenicity to various crop plants

Verticillium dahliae isolates recovered from a new focus of severe Verticillium wilt of cotton in the northeast of Israel were tested for vegetative compatibility using nitrate non-utilizing (nit) mutants and identified as VCG1, which is a new record in Israel. Other cotton isolates of V. dahliae from the northern and southern parts of the country were assigned to VCG2B and VCG4B, respectively. VCG1 isolates induced severe leaf symptoms, stunting and defoliation of cotton cv. Acala SJ-2, and thus were characterized as the cotton-defoliating (D) pathotype, whereas isolates of VCG2B and VCG4B were confirmed as the earlier described defoliating-like (DL) and non-defoliating (ND) pathotypes, respectively. This is the first record of the D-pathotype in Israel. The host range of representative isolates of each VCG-associated pathotype was investigated using a number of cultivated plants. Overall, the D isolates were more virulent than DL isolates on all tested host plants, but the order of hosts (from highly susceptible to resistant) was the same: okra (Hibiscus esculentus local cultivar), cotton (Gossypium hirsutum cv. Acala SJ2), watermelon (Citrullus lanatus cv. Crimson Sweet), safflower (Carthamus tinctorius cv. PI 251264), sunflower (Helianthus annuum cv. 2053), eggplant (Solanum melongena cv. Black Beauty), and tomato (Lycopersicon esculentum cv. Rehovot 13). The pattern of virulence of ND isolates differed from that of D and DL isolates, so that the former were highly virulent on eggplant but mildly virulent on cotton. Tomato was resistant to all cotton V. dahliae isolates tested. RAPD and specific PCR assays confirmed that the D isolates from Israel were similar to those originating from other countries.     

Incidence of Verticillium wilt of artichoke in eastern Spain and role of inoculum sources on crop infection

Surveys of 94 artichoke fields throughout the artichoke production areas of Comunidad Valenciana (eastern Spain) were conducted from 1999 to 2002 to determine the incidence and distribution of Verticillium wilt.Verticillium dahliae was isolated from 80.9% of the sampled fields, and detected in all artichoke-growing areas, with a mean disease incidence of 53.8% infected plants. The disease was found to cause severe damage to cv. ‘Blanca de Tudela’, which is the most important artichoke cultivar grown in Spain, and was also observed on the seed-propagated cv. ‘Imperial Star’. In field trials to study the role of infected planting material and soil inoculum on infection of artichoke plants during the cropping season,V. dahliae was transmitted from infected stumps to the plants, confirming that the use of infected stumps could have greatly contributed to the dissemination of the pathogen. Inoculum density ofV. dahliae in soil had an effect on crop infection, in that a higher number of microsclerotia per gram of soil resulted in a higher percentage of infected plants. In addition, yield of cv. Blanca de Tudela was significantly affected byV. dahliae infection, showing that a higher percentage of infection corresponded with lower yield. http://www.phytoparasitica.org posting July 21, 2005.