Incidence and pathogenicity of races and isolates of Verticillium dahliae in Crete, southern Greece

Classification of 32 Verticillium dahliae isolates originating from 19 plant species in eight different botanical families to races and determination of host range pathogenicity were carried out. The physiological races of isolates were identified using the two differential tomato cultivars ??Belladonna?? (susceptible to both races 1 and 2 of V. dahliae) and ??Ace 55VF?? (resistant to race 1, susceptible to race 2 of V. dahliae). Among these isolates, 14 were race 2 (43.8%), 12 race 1 (37.5%) and six nonpathogenic (18.7%) on tomato. The host range pathogenicity of isolates was determined using four differential hosts (eggplant, turnip, tomato (Ve ^? ) and sweet pepper). Among isolates, five were pathogenic to both eggplant and turnip (15.6%), 21 to eggplant, turnip and tomato (65.6%), five to eggplant, turnip, tomato and sweet pepper (15.6%) and one was pathogenic to eggplant, turnip and sweet pepper (3.2%). The pathogenicity of isolates on the aforementioned five hosts was investigated on the basis of external symptoms and by calculating the relative areas under disease progress curves (relative AUDPC). Results showed that eggplant was the most susceptible, followed by turnip and tomato cv. Belladonna, while sweet pepper and tomato cv. Ace 55VF were less susceptible to all the isolates used. The pathogenicity of isolates varied from highly to mildly virulent on eggplant and turnip while on Belladonna, Ace 55VF and sweet pepper it varied from highly virulent to nonpathogenic. Belladonna exhibited a similar level of susceptibility to races 1 and 2 of V. dahliae, but was more susceptible than Ace 55VF to race 2. Interestingly, the isolates originating from eggplant were clearly more virulent than those originating from tomato and black nightshade on all solanaceous plants tested.     

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.     

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.     

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.     

Weed hosts of <Emphasis Type="Italic">Verticillium dahliae</Emphasis> in cotton fields in Turkey and characterization of <Emphasis Type="Italic">V. dahliae</Emphasis> isolates from weeds

A weed survey conducted in 2004 and 2005 in Aydin province of Turkey showed that Solanum nigrum, Xanthium strumarium, Amaranthus retroflexus, Portulaca oleracea, Sonchus oleraceus and Datura stramonium were the most prevalent weeds in the cotton fields exhibiting Verticillium wilt. Verticillium dahliae Kleb. was recovered from A. retroflexus and X. strumarium in those cotton fields. This is the first report of V. dahliae occurring naturally in A. retroflexus in Turkey. Pathogenicity tests on cotton and weeds showed that the virulence of V. dahliae isolates from weeds was higher on cotton plants than on weeds, with the disease severity ranging from 31.7% to 98.0%. Disease severity of V. dahliae isolates was 54.7–93.9% on eggplant, 23.7–51.6% on cucumber and 11.0–16.4% on tomato, whereas it did not cause any disease symptoms, or only low levels, on pepper and bell pepper. Two vegetative compatibility groups (VCGs) were identified among seven tested weed isolates: VCG2A (two isolates) and VCG2B (three isolates) using international reference strains.     

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.     

Pathogenicity, vegetative compatibility and RAPD analysis of Fusarium oxysporum isolates from tobacco fields in Extremadura

Fusarium wilt of tobacco could be caused by Fusarium oxysporum f. sp. batatas or f. sp. vasinfectum since f. sp. nicotianae was rejected because there was no evidence of isolates specific to tobacco. Forty isolates of F. oxysporum from soil and plants from tobacco fields in Extremadura (south-western Spain) were characterized by pathogenicity on burley and flue-cured tobacco, for vegetative compatibility group (VCG), and by random amplified polymorphic DNA (RAPD). Isolates from burley were identified as race 1 of F. oxysporum f. sp. batatas based on pathogenicity on tobacco, sweet potato and cotton, and those from flue-cured as race 2. Most isolates from soil were heterokaryon self-incompatible (HSI) and the remaining isolates from soil and tobacco were grouped into four VCGs: VCG 1 (5 isolates from burley), VCG 2 (17 isolates from flue-cured and 4 from soil), VCG 3 (2 isolates from flue-cured) and VCG 4 (2 isolates from soil). This is the first report of the two races and VCGs of F. oxysporum f. sp. batatas in Spain. Analysis of RAPD revealed two clusters (C-I and C-II) related to race and VCGs. C-I included race 1 (VCG 1) isolates from burley and nonpathogenic (VCG 4 or HSI) isolates from soils. C-II included nonpathogenic (VCG 2) and race 2 (VCG 2 or VCG 3) isolates from flue-cured. VCG and RAPD markers were effective in distinguishing race 2 from race 1, suggesting that there are two genetically differentiated groups of F. oxysporum f. sp. batatas on tobacco in Extremadura.     

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.     

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.     

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.     

Verticillium wilt of olive in Turkey: a survey on disease importance,pathogen diversity and susceptibility of relevant olive cultivars

A comprehensive survey on the prevalence and incidence of Verticillium wilt of olive in Turkey has been conducted over 6 years (2003–2008). Vegetative compatibility group (VCG) assessment and PCR-based molecular pathotyping were used to evaluate the distribution of the defoliating (D) and nondefoliating (ND) pathotypes of Verticillium dahliae in surveyed areas. Pathogen prevalence was 35% of all olive orchards inspected and incidence of the disease reached 3.1%. VCG1A was predominant (29.3%) and infected all major cultivars grown in Turkey. The other two VCGs detected (2A and 4B) were of minor relevance (4.9% and 0.9%, respectively). Disease incidence caused by VCG1A infections was higher (ranging from 1.1% to 6.9%) than that caused by VCG2A and VCG4B in 10 provinces (Manisa, Aydin, Kahramanmaras, Izmir, Mugla, Kilis, Denizli, Gaziantep, Mardin and Balikesir). However, VCG2A and 4B were more prevalent (and responsible for higher disease incidence) than VCG1A in three provinces (Hatay, Osmaniye and Bursa). Finally, VCG1A isolates were found in all provinces except Canakkale, and simultaneous presence of the three VCGs was only verified in Hatay province. An artificial inoculation bioassay (19 representative V. dahliae isolates included) revealed that VCG1A (13) isolates as a group were more aggressive and caused defoliation, whereas VCG2A (5) and VCG4B (1) isolates induced milder symptoms. Within a VCG group, virulence varied among isolates infecting the same olive cultivar and this virulence was also related to the differential susceptibility of the cultivars (‘Manzanilla’, ‘Ayvalik’ and ‘Gemlik’) tested. Molecular pathotyping allowed the identification of D (VCG1A) and ND (VCG2A/4B) pathotypes, which correlated with results from pathogenicity tests. Remarkably, the V. dahliae VCG1A/D pathotype population infecting olive in Turkey was molecularly different from that one previously identified in Spain.     

Origin of Race 3 of Fusarium oxysporum f. sp. lycopersici at a Single Site in California

ABSTRACT Thirty-nine isolates of Fusarium oxysporum were collected from tomato plants displaying wilt symptoms in a field in California 2 years after F. oxysporum f. sp. lycopersici race 3 was first observed at that location. These and other isolates of F. oxysporum f. sp. lycopersici were characterized by pathogenicity, race, and vegetative compatibility group (VCG). Of the 39 California isolates, 22 were in VCG 0030, 11 in VCG 0031, and six in the newly described VCG 0035. Among the isolates in VCG 0030, 13 were race 3, and nine were race 2. Of the isolates in VCG 0031, seven were race 2, one was race 1, and three were nonpathogenic to tomato. All six isolates in VCG 0035 were race 2. Restriction fragment length polymorphisms (RFLPs) and sequencing of the intergenic spacer (IGS) region of rDNA identified five IGS RFLP haplotypes, which coincided with VCGs, among 60 isolates of F. oxysporum from tomato. Five race 3 isolates from California were of the same genomic DNA RFLP haplotype as a race 2 isolate from the same location, and all 13 race 3 isolates clustered together into a subgroup in the neighbor joining tree. Collective evidence suggests that race 3 in California originated from the local race 2 population.     

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 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.     

马铃薯黄萎病病原菌营养亲和群、生理小种、交配型鉴定以及致病力差异分析

为明确引起马铃薯黄萎病的大丽轮枝菌Verticillium dahliae的遗传变异和致病力的差异,对从内蒙古及其周边地区马铃薯发病株上分离得到的29株大丽轮枝菌的营养亲和群、生理小种和交配型进行了测定,利用伤根接种法进行致病力分化研究。结果表明,供试的29株马铃薯大丽轮枝菌菌株被划分为VCG2B、VCG4B和VCG4A三个营养亲和群,其菌株数分别为11、2和16株;供试的29株菌株均鉴定为单一的2号生理小种和MAT1-2-1交配型。供试的29株大丽轮枝菌菌株间致病力存在一定的差异,其中NCP-1菌株的致病力最强,病情指数为83.33;而NWS-5菌株的致病力最弱,病情指数仅为10.85;不同营养亲和群菌株的平均致病力也存在显著差异,VCG4B型菌株的平均致病力最高,平均病情指数为67.18;其次为VCB2B型菌株,平均病情指数为42.50,而VCG4A型菌株致病力最弱,平均病情指数仅为20.54。     

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.     

Characterization of a Regional Population of Fusarium oxysporum f. sp. niveum by Race, Cross Pathogenicity, and Vegetative Compatibility

ABSTRACT Eighty-eight isolates of Fusarium oxysporum f. sp. niveum, collected from wilted watermelon plants and infested soil in Maryland and Dela-ware, were characterized by cross pathogenicity to muskmelon, race, and vegetative compatibility. Four isolates (4.5%) were moderately pathogenic to >/=2 of 18 muskmelon cultivars in a greenhouse test, and one representative isolate also was slightly pathogenic in field microplots. The four isolates all were designated as race 2, and were in vegetative compatibility group (VCG) 0082. Of the 74 isolates to which a VCG could be assigned, 41 were in VCG 0080, the VCG distributed most widely; 27 were in VCG 0082, and were distributed in half of the 20 watermelon fields surveyed; and 6 were in the newly described VCG 0083, and were restricted to three fields. Among the isolates in VCG 0080, 8 were designated as race 0, 21 as race 1, and 12 as race 2. Of the isolates in VCG 0082, 6 were designated as race 0, 11 as race 1, and 10 as race 2. All isolates in VCG 0083 were designated as race 2. Isolates from more than one race within the same VCG or isolates from more than one VCG were recovered from single plants and fields. No differences in aggressiveness on differential watermelon cultivars were observed among isolates from different VCGs of the same race. A diverse association between virulence and VCG throughout the Mid-Atlantic region suggests that the pathotypes of F. oxysporum f. sp. niveum may be of local origin or at least long existent in the region.     

Cloning of DNA fragments specific to the pathotype and race of <Emphasis Type="Italic">Verticillium dahliae</Emphasis>

Japanese isolates of Verticillium dahliae, a causal agent of wilt disease in many plants, are classifiable into pathotypes based on their pathogenicity. Because these pathotypes are morphologically indistinguishable, establishing a rapid identification method is very important for the control of this pathogen in Japan. For cloning DNA fragments that are useful for identification and specific detection of V. dahliae pathotypes, we performed random amplified polymorphic DNA (RAPD) analyses using various isolates. One polymerase chain reaction (PCR) product, E10-U48, was specific to isolates pathogenic to sweet pepper. The other product, B68-TV, was specific to race 1 of isolates pathogenic to tomato. The specificity of these sequences was confirmed by genomic Southern hybridization. Further analyses revealed that the region peripheral to B68-TV obtained from the genomic DNA library includes the sequence specific to all isolates pathogenic to tomato (races 1 and 2). Moreover, sequence tagged site (STS) primers designed from B68-TV and its peripheral region showed race-specific and pathotype-specific amplification in a PCR assay. The probes and primers obtained in this study are likely to be useful tools for the identification and specific detection of pathotypes and races of V. dahliae. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession number AB095266.     

Electrophoretic karyotyping and mapping of pathotype-specific DNA sequences in Japanese isolates of <Emphasis Type="Italic">Verticillium dahliae</Emphasis>

The chromosome number and electrophoretic karyotype of Japanese isolates of Verticillium dahliae were investigated. In a genomic Southern blot analysis of seven isolates probed with a telomere consensus sequence (TTAGGG)₅, 12 or 14 bands were observed. Furthermore, pulsed-field gel electrophoresis (PFGE) of these isolates revealed five or six chromosomal bands. A band (approx. 3.5 Mbp) common to all isolates apparently contained more than two chromosomes. From these results, we concluded that each isolate’s chromosome number is six (an eggplant pathotype isolate) or seven (all isolates of tomato and sweet pepper pathotypes). Although the chromosome sizes differed among isolates, karyotypes were similar within tomato and sweet pepper pathotypes. A small chromosome (approx. 1.8 Mbp) was observed only in the sweet pepper pathotype. Subsequent PFGE-Southern hybridization analyses revealed that the three DNA fragments specific to tomato pathotype are located on the same chromosome. These results suggest that the tomato-pathotype-specific DNA sequences might coexist on one chromosome.     

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.