Physiological Races and Vegetative Compatibility Groups of Fusarium oxysporum f. sp. lactucae Isolated from Crisphead Lettuce in Japan

One hundred and sixteen isolates of Fusarium oxysporum f. sp. lactucae obtained from 85 fields in three crisphead lettuce-producing areas in Nagano Prefecture, Japan were typed for races using differential cultivars Patriot, Banchu Red Fire and Costa Rica No. 4. They were also grouped into vegetative compatibility groups (VCGs) using complementation tests with nitrate non-utilizing (nit) mutants. Two California strains reported as F. oxysporum f. sp. lactucum, a type culture of F. oxysporum f. sp. lactucae, and 28 avirulent isolates of F. oxysporum obtained from crisphead lettuce were included for comparison. Among Nagano isolates, 66 isolates were identified as race 1, and 50 as race 2. Race 1 strains derived from Shiojiri and Komoro cities and race 2 from Kawakami village and Komoro city. All isolates of race 2 were biotin auxotrophs, and the race could be distinguished based on its requirement for biotin on minimal nitrate agar medium (MM). Pathogenic isolates were classified into two VCGs and three heterokaryon self-incompatible isolates. Strong correlations were found between race and VCG. All the race 1 strains were assigned to VCG 1 except self-incompatible isolates, and all the race 2 strains to VCG 2. The 28 avirulent isolates of F. oxysporum were incompatible with VCG 1 and VCG 2. California strains was vegetatively compatible with VCG 1, and they were assigned to race 1. Based on vegetative compatibility, these two races of F. oxysporum f. sp. lactucae may be genetically distinct, and F. oxysporum f. sp. lactucae race 1 is identical to F. oxysporum f. sp. lactucum. Received 7 May 2002/ Accepted in revised form 6 September 2002     

Sporulation of Fusarium oxysporum f. sp. lycopersici on Stem Surfaces of Tomato Plants and Aerial Dissemination of Inoculum

ABSTRACT Plants exhibiting symptoms of wilt and xylem discoloration typical of Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici were observed in greenhouses of cherry tomatoes at various sites in Israel. However, the lower stems of some of these plants were covered with a pink layer of macroconidia of F. oxysporum. This sign resembles the sporulating layer on stems of tomato plants infected with F. oxysporum f. sp. radicis-lycopersici, which causes the crown and root rot disease. Monoconidial isolates of F. oxysporum from diseased plants were assigned to vegetative compatibility group 0030 of F. oxysporum f. sp. lycopersici and identified as belonging to race 1 of F. oxysporum f. sp. lycopersici. The possibility of coinfection with F. oxysporum f. sp. lycopersici and F. oxysporum f. sp. radicis-lycopersici was excluded by testing several macroconidia from each plant. Airborne propagules of F. oxysporum f. sp. lycopersici were trapped on selective medium in greenhouses in which plants with a sporulating layer had been growing. Sporulation on stems was reproduced by inoculating tomato plants with races 1 and 2 of F. oxysporum f. sp. lycopersici. This phenomenon has not been reported previously with F. oxysporum f. sp. lycopersici and might be connected to specific environmental conditions, e.g., high humidity. The sporulation of F. oxysporum f. sp. lycopersici on plant stems and the resultant aerial dissemination of macroconidia may have serious epidemiological consequences. Sanitation of the greenhouse structure, as part of a holistic disease management approach, is necessary to ensure effective disease control.     

Biological and Molecular Characterization of Fusarium oxysporum f. sp. lycopersici Divides Race 1 Isolates into Separate Virulence Groups

ABSTRACT A collection of race 1 and race 2 isolates of Fusarium oxysporum f. sp. lycopersici was screened for vegetative compatibility and characterized by random amplified polymorphic DNA (RAPD) analysis to establish the identity and genetic diversity of the isolates. Comparison of RAPD profiles revealed two main groups that coincide with vegetative compatibility groups (VCGs). In addition, several single-member VCGs were identified that could not be grouped in one of the two main RAPD clusters. This suggests that F. oxysporum f. sp. lycopersici is a polyphyletic taxon. To assign avirulence genotypes to race 1 isolates, they were tested for their virulence on a small set of tomato lines (Lycopersicon esculentum), including line OT364. This line was selected because it shows resistance to race 2 isolates but, unlike most other race 2-resistant lines, susceptibility to race 1 isolates. To exclude the influence of other components than those related to the race-specific resistance response, we tested the virulence of race 1 isolates on a susceptible tomato that has become race 2 resistant by introduction of an I-2 transgene. The results show that both line OT364 and the transgenic line were significantly affected by four race 1 isolates, but not by seven other race 1 isolates nor by any race 2 isolates. This allowed a subdivision of race 1 isolates based on the presence or absence of an avirulence gene corresponding to the I-2 resistance gene. The data presented here support a gene-for-gene relationship for the interaction between F. oxysporum f. sp. lycopersici and its host tomato.     

Pathogenic, Genetic and Molecular Characterisation of Fusarium oxysporum f.sp. lilii

Isolates of Fusarium oxysporum from lily were screened for pathogenicity, vegetative compatibility and DNA restriction fragment length polymorphisms, and compared to reference isolates of F. oxysporum f.sp. gladioli and F. oxysporum f.sp. tulipae to justify the distinction of F. oxysporum f.sp. lilii. Twenty-four isolates from different locations in The Netherlands (18 isolates), Italy (4 isolates), Poland and the United States (1 isolate each) shared unique RFLP patterns with probes D4 and pFOM7, while hybridization did not occur with a third probe (F9). Except for a self-incompatible isolate, these 24 isolates all belonged to a single vegetative compatibility group (VCG 0190). Isolates belonging to VCG 0190 were highly pathogenic to lily, but not to gladiolus or tulip, except for a single nonpathogenic isolate. Six saprophytic isolates of F. oxysporum from lily were nonpathogenic or only slightly aggressive to lily, gladiolus and tulip, belonged to unique VCGs and had distinct RFLP patterns. Three pathogenic isolates previously considered to belong to F. oxysporum f.sp. lilii were identified as F. proliferatum var. minus; all three belonged to the same VCG and shared unique RFLP patterns. These three isolates were moderately pathogenic to lily and nonpathogenic to gladiolus and tulip. The reference isolates of F. oxysporum f.sp. tulipae were pathogenic to tulip, but not to lily and gladiolus; they shared a distinct RFLP pattern, different from those encountered among pathogenic and saprophytic isolates from lily, and formed a separate new VCG (VCG 0230). Reference isolates of F. oxysporum f.sp. gladioli belonging to VCG 0340 proved pathogenic to both gladiolus and lily, but not to tulip. These isolates, as well as isolates belonging to VCGs 0341, 0342 and 0343 of F. oxysporum f.sp. gladioli, had RFLP patterns different from those encountered among the isolates from lily or tulip. These findings identify F. oxysporum f.sp. lilii as a single clonal lineage, distinct from F. oxysporum f.sp. gladioli and f.sp. tulipae.     

Genetic Diversity of Pathogenic and Nonpathogenic Populations of Fusarium oxysporum Isolated from Carnation Fields in Argentina

ABSTRACT In order to elucidate the origin of Fusarium oxysporum f. sp. dianthi in Argentina, the genetic diversity among pathogenic isolates together with co-occurring nonpathogenic isolates on carnation was investigated. In all, 151 isolates of F. oxysporum were obtained from soils and carnation plants from several horticultural farms in Argentina. The isolates were characterized using vegetative compatibility group (VCG), intergenic spacer (IGS) typing, and pathogenicity tests on carnation. Seven reference strains of F. oxysporum f. sp. dianthi also were analyzed and assigned to six different IGS types and six VCGs. Twenty-two Argentinean isolates were pathogenic on carnation, had the same IGS type (50), and belonged to a single VCG (0021). The 129 remaining isolates were nonpathogenic on carnation and sorted into 23 IGS types and 97 VCGs. The same VCG never occurred in different IGS types. Our results suggest that the pathogen did not originate in the local populations of F. oxysporum but, rather, that it was introduced into Argentina. Given the genetic homogeneity within Argentinean isolates of F. oxysporum f. sp. dianthi, either IGS type or VCG can be used for the identification of the forma specialis dianthi currently in Argentina.     

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.     

Examination of the relationships between vegetative compatibility groups and races in Fusarium oxysporum f.sp. dianthi

The feasibility of identifying races of Fusarium oxysporum f.sp. dianthi by tests for vegetative compatibility type was investigated. Nitrate non-utilizing nitl and NitM mutants were generated from 51 isolates of F. oxysporum f.sp. dianthi , 18 isolates of f. oxysporum from Dianthus spp. not belonging to f.sp. dianthi and, for comparison, 11 isolates of F. proliferatum from Dianthus spp. Vegetative compatibility groups (VCGs) among the isolates were identified by pairing all nitl with all NitM mutants.
Vegetative compatibility was found between isolates of F. oxysporum f.sp. dianthi races 1 and 8 (VCG 0022), races 2, 5 and 6 (VCG 0021) and race 4 (VCG 0020), and wilt-causing isolates previously classified as F. redolens from D. caryophyllus (VCG 0023) and D. barbatus (VCG 0024), Three self-compatible wilt-causing isolates were vegetatively incompatible with all other isolates (VCGs 0025,0026 and 0027), Two VCGs were found among isolates of F. oxysporum from D. caryophyllus not belonging to f.sp. dianthi ; six non-pathogenic isolates were self-compatible but vegetatively incompatible with all other isolates. The foot-rot-associated isolates of F. proliferatum from D. caryophyllus constituted a separate VCG.
Virulence analyses revealed at least four new races among VCGs 0023 to 0027, New Isolates could be categorized as races as a result of VCG analysis and VCG classification correctly indicated that the race identities previously ascribed to two old isolates had been incorrect. Vegetative compatibility tests offer the prospect for rapid identification of races, although inoculation tests continue to be necessary to differentiate races that belong to a single VCG.     

Three evolutionary lineages of tomato wilt pathogen, Fusarium oxysporum f. sp. lycopersici, based on sequences of IGS, MAT1, and pg1, are each composed of isolates of a single mating type and a single or closely related vegetative compatibility group

Three evolutionary lineages of the tomato wilt pathogen Fusarium oxysporum f. sp. lycopersici were found among a worldwide sample of isolates based on phylogenetic analysis of the ribosomal DNA intergenic spacer region. Each lineage consisted of isolates mainly belonging to a single or closely related vegetative compatibility group (VCG) and a single mating type (MAT). The first lineage (A1) was composed of isolates VCG 0031 and MAT1-1; the second (A2) included VCG 0030 and/or 0032 and MAT1-1; and the third (A3) included VCG 0033 and MAT1-2. Race 1 and race 2 isolates belonged to the A1 or A2 lineages, and race 3 belonged to A2 or A3 lineages, suggesting that there is no correlation between race and lineage. However, for the isolates from Japan, race 1 (with one exception), race 2, and race 3 isolates belonged to A2, A1, and A3 lineages, respectively. These results suggest that the races could have evolved independently in each lineage; and in Japan the present races were likely to have been introduced independently after they had evolved in other locations.     

Population Genetic Analysis Corroborates Dispersal of Fusarium oxysporum f. sp. radicis-lycopersici from Florida to Europe

ABSTRACT Fusarium oxysporum isolates from tomato plants displaying crown and root rot symptoms were collected in central and southern Florida and analyzed using vegetative compatibility grouping (VCG) and nuclear restriction fragment length polymorphism (RFLP) data. VCG 0094 of F. oxysporum f. sp. radicis-lycopersici, previously known only from northwestern Europe, was predominant among 387 isolates assessed. In addition, two newly described VCGs (0098 and 0099) were detected at low frequencies. Floridian VCG 0094 isolates displayed a continuum of compatibilities, which is in contrast to the three distinct subgroups previously identified among European VCG 0094 isolates. RFLP haplotypes were constructed using one repetitive and three low-copy probes. Population subdivision of VCG 0094 from various Floridian counties and from northwestern Europe (Belgium, the Netherlands, and the United Kingdom) was evaluated by analysis of molecular variance. A "natural" population structure was revealed, differentiating populations from the east and west coasts of Florida. In addition, isolates from Europe were statistically indistinguishable from the Palm Beach County, FL, population. Furthermore, gene diversity among Palm Beach County VCG 0094 isolates was more than five times greater than among European isolates. Results from both VCG and RFLP analyses strongly support the inference that the European VCG 0094 constitutes a founder population that resulted from intercontinental migration of a few isolates from Palm Beach County, FL.     

Genetic diversity among isolates of Fusariumoxysporum f.sp. canariensis

Fusarium oxysporum f.sp. canariensis causes vascular wilt disease of Phoenix canariensis , the Canary Island date palm. Seventy-two isolates of this fungus were obtained from diverse geographic locations including France, Japan, Italy, the Canary Islands, and California, Florida and Nevada, USA. The isolates were tested for vegetative compatibility and for similarities based on mitochondrial DNA (mtDNA), single-copy sequences and repetitive DNA (pEY10) polymorphisms. Seventy-one percent of the isolates belonged to a single vegetative compatibility group (VCG 0240), and four closely related mitochondrial RFLP patterns were found. A subset of the isolates was further tested for single-copy RFLPs and repetitive DNA fingerprints. Only four single-copy RFLP haplotypes were found among 25 representative isolates of F. oxysporum f.sp. canariensis tested, using nine polymorphic single-locus probe/enzyme combinations. Finally, 32 different pEY10 DNA fingerprints were found out of 57 isolates examined. Overall the results indicate that F. oxysporum f.sp. canariensis is a single lineage with a low to moderate level of genetic diversity.     

Molecular characterisation of vegetative compatibility groups in Fusarium oxysporum f. sp. radicis-lycopersici and f. sp. lycopersici by random amplification of polymorphic DNA and microsatellite-primed PCR

Random amplification of polymorphic DNA (RAPD-PCR) analysis was conducted on 48 isolates of Fusarium oxysporum f. sp. radicis-lycopersici (F.o.r.l.) from different geographic regions, representing all known vegetative compatibility groups (VCGs) except VCG 0097 and VCG 0099 and on eight isolates of F.oxysporum f. sp. lycopersici (F.o.l.), representing VCGs 0030, 0031, 0032 and 0033. Upon UPGMA (unweighted pair-group method with arithmetic averages) analysis of 86 RAPD-PCR markers generated by 16 informative primers and 44 markers obtained with eight microsatellite primers, a close relatedness was evident for F.o.r.l. isolates in VCGs 0090, 0092, 0096, and, to a lesser extent, for those in VCG 0093. Representatives of VCG 0091 formed a distinct group, while F.o.r.l. isolates in VCGs 0094 and 0098 were not distinguishable by the tested markers, most of which were also shared by F.o.l. isolates belonging to VCGs 0031 and 0033. F.o.l. isolates in VCGs 0030 and 0032 shared most of the molecular markers. The correlation between RAPD-PCR and microsatellite genetic distance was highly significant (R² = 0.77; P by Mantel test < 0.001). The molecular variability observed in both formae speciales is discussed in relation to the development of F.o.r.l.- and F.o.l.-specific diagnostic tools.     

Genetic diversity in Fusarium oxysporum f.sp. dianthi and Fusarium redolens f.sp. dianthi

Pathogenic isolates were selected representing all known vegetative compatibility groups (VCGs) and races of Fusarium oxysporum sensu lato from Dianthus spp. On basis of differences in the internal transcribed spacer region of the ribosomal DNA, six VCGs were classified as F. oxysporum f.sp. dianthi and four as F. redolens f.sp. dianthi. All VCGs of F. oxysporum f.sp. dianthi were characterized by unique restriction fragment length polymorphisms (RFLPs), unique overall esterase profiles, and unique virulence spectra, supporting a clonal lineage concept. Two VCGs of F. oxysporum f.sp. dianthi nevertheless comprised more than one race, but races within the same VCG shared the same distinct overall virulence spectrum. VCGs belonging to F. redolens f.sp. dianthi also had unique RFLPs and unique virulence spectra, but had grossly identical esterase profiles. Three new races (9, 10 and 11) are described for F. oxysporum f.sp. dianthi, and four for F. redolens f.sp. dianthi. Two races previously considered lost were recovered; race 7 was identified as a member of VCG 0021 of F. oxysporum f.sp. dianthi while race 3 was identified as a distinct VCG and race of F. redolens f.sp. dianthi. A summary of races and VCGs in F. oxysporum f.sp. dianthi and F. redolens f.sp. dianthi is presented.     

Vegetative compatibility of Fusarium oxysporum from sweet basil in Israel

Fusarium wilt and crown rot of sweet basil, caused by Fusarium oxysporum f.sp. basilici (F.o.ba.), is widespread in Israel. Affected plants show a variety of symptoms, including vascular wilt as well as crown rot, and masses of macroconidia on stem surfaces. We used vegetative compatibility to determine whether F.o.ba. isolates associated with various symptoms and sources are genetically related. All 119 isolates previously described as F.o.ba., and 42 additional F. oxysporum isolates which had not been tested for pathogenicity, belonged to a single vegetative compatibility group (VCG). The various symptoms are therefore induced by a single pathogenic form which appears to be a specific clone of F. oxysporum. The isolates of F.o.ba. from Israel were vegetatively compatible with eight isolates of F.o.ba. from Italy and the USA, but not with nonpathogenic isolates of F. oxysporum from basil, or with F.o. lycopersici or F.o. radicis-lycopersici from tomato. We conclude that the population of F.o.ba. in Israel belongs to the common VCG of this pathogen described in the USA, and which includes American and Italian isolates.     

Phylogeny of Fusarium oxysporum f. sp. lactucae Inferred from Mitochondrial Small Subunit, Elongation Factor 1-alpha, and Nuclear Ribosomal Intergenic Spacer Sequence Data

ABSTRACT Fusarium oxysporum f. sp. lactucae, causal agent of Fusarium wilt of lettuce, is a serious pathogen recently reported in Arizona. Sequence analysis of the mitochondrial small subunit (mtSSU), translation elongation factor 1-alpha (EF-1alpha) gene, and the nuclear ribosomal DNA intergenic spacer (IGS) region was conducted to resolve relationships among f. sp. lactucae isolates, F. oxysporum isolates from other hosts, and local non-pathogenic isolates. Analysis of mtSSU sequences provided limited phylogenetic resolution and did not differentiate the lactucae isolates from 13 other F. oxysporum isolates. Analysis of EF-1alpha sequences resulted in moderate resolution, grouping seven formae speciales with the lactucae isolates. Analysis of the IGS region revealed numerous sequence polymorphisms among F. oxysporum formae speciales consisting of insertions, deletions, and single nucleotide transitions and substitutions. Repeat sequence analysis revealed several duplicated subrepeat units that were distributed across much of the region. Based on analysis of the IGS sequence data, lactucae race 1 isolates resolved as a monophyletic group with three other formae speciales of F. oxysporum. In all analyses, lactucae race 2 isolates composed a separate lineage that was phylo-genetically distinct and distantly related to the lactucae race 1 isolates.     

Loss of Avirulence and Reduced Pathogenicity of a Gamma-Irradiated Mutant of Fusarium oxysporum f. sp. lycopersici

ABSTRACT The tomato Fusarium resistance gene I-2 confers resistance to F. oxy-sporum f. sp. lycopersici race 2, which expresses the corresponding aviru-lence gene avrI-2. To elucidate the molecular basis of this gene-for-gene interaction, we initiated a search for the avrI-2 gene. Gamma irradiation mutagenesis, using (137)Cs, was performed to generate an avrI-2 mutant of F. oxysporum f. sp. lycopersici. To this end, a race 2 isolate was first transformed with a phleomycine resistance gene and a GUS marker gene in order to distinguish mutants from contaminating isolates. A total of 21,712 mutagenized colonies was tested for loss of avirulence on I-2-containing tomato seedlings. One mutant was selected that showed the expected loss of avirulence but, surprisingly, also showed reduced pathogenicity toward susceptible tomato plants. DNA analysis was subsequently used to visualize genomic changes in the mutant. Southern analysis on contour-clamped homogeneous electrophoretic field blots demonstrated a translocation of a 3.75-Mb chromosome in the mutant. Random amplified polymorphic DNA and amplified fragment length polymorphism analysis identified at least nine polymorphisms between the wild-type and mutant isolates. Most of these polymorphisms appeared as extra fragments in the mutant and contained repetitive DNA sequences.     

Electrophoretic karyotype variation among pathotypes of Fusarium oxysporum f.sp. dianthi

Karyotype analysis by pulsed-field gel electrophoresis was applied to characterize isolates of Fusarium oxysporum f.sp. dianthi , the causal agent of Fusarium wilt on carnation. Eleven distinct chromosomal DNA patterns were detected among 38 pathogenic isolates, and the total genome size was estimated to range from 23·7 to 36·4 Mb. Except for isolates belonging to pathotypes 2 and 4 , all members of the same pathotype shared overlapping electrophoretic karyotypes. Karyotypes of isolates assigned to pathotypes 1 and 8 showed a high degree of similarity, in accordance with VCG and RFLP analysis. The same electrophoretic karyotype was also shared by members of pathotypes 2 and 5, thus confirming results obtained by both VCG and RFLP grouping, A single representative of pathotype 6, previously confined to the same VCG and RFLP group as pathotypes 2 and 5, had a slightly different chromosomal pattern. Isolates assigned to pathotype 4 showed four related karyotypes which partially differed in both the number and size of chromosomal bands. However, all strains assigned to this pathotype shared a basic profile of nine chromosomal bands, while two low-molecular-weight bands were present or absent. The findings are discussed with regard both to the suitability of race distinction in the case of the special form dianthi of F. oxysporum and to the use of karyotype analysis by PFGE as a tool for the study of the population genetics of this fungus.     

Molecular identification of two vegetative compatibility groups of Fusarium oxysporum f. sp. cepae

Fusarium oxysporum f. sp. cepae, which causes basal rot of onion, consists of seven vegetative compatibility groups (VCGs 0420 to 0426) and several single-member VCGs (SMVs). F. oxysporum f. sp. cepae populations in South Africa and Colorado each consist of one main VCG (namely, VCG 0425 and 0421, respectively). The aim of this study was to develop sequence-characterized amplified region (SCAR) markers for the identification of VCGs 0425 and 0421, using 79 previously characterized F. oxysporum isolates. A second aim was to investigate the prevalence of VCG 0425 among 88 uncharacterized South African onion F. oxysporum isolates using (i) the developed SCAR markers and (ii) inter-retrotransposon (IR)- and random amplified polymorphic DNA (RAPD) fingerprinting. Only two RAPD primers provided informative fingerprints for VCG 0425 isolates but these could not be developed into SCAR markers, although they provided diagnostic fragments for differentiation of VCG 0425 from VCG 0421. IR fingerprinting data were used to develop a multiplex IR-SCAR polymerase chain reaction method for the identification of VCG 0421, VCG 0425, and SMV 4 isolates as a group. Molecular identification of the uncharacterized collection of 88 F. oxysporum isolates (65 F. oxysporum f. sp. cepae and 23 F. oxysporum isolates nonpathogenic to onion) confirmed that VCG 0425 is the main VCG in South Africa, with all but 3 of the 65 F. oxysporum f. sp. cepae isolates having the molecular characteristics of this VCG. Genotyping and VCG testing showed that two of the three aforementioned isolates were new SMVs (SMV 6 and SMV 7), whereas the third (previously known as SMV 3) now belongs to VGC 0247.     

Restriction fragment length polymorphisms in Fusarium oxysporum f.sp. dianthi and other fusaria from Dianthus species

DNA restriction fragment length polymorphisms (RFLPs) among 46 isolates of Fusarium oxysporum from Dianthus spp., representing the known range of pathogenicity in carnation, were determined using total DNA digested with the restriction enzyme Hind III and a previously described probe, D4. Distinct multiple band RFLP patterns were found, which delineated RFLP groups as follows: (i) F. oxysporum f.sp. dianthi races I and 8; (ii) F. oxysporum f.sp. dianthi races 2, 5 and 6; (iii) F. oxysporum f.sp. dianthi race 4; (iv) a recently described race of F. oxysporum f.sp. dianthi (wilt-causing isolates from D. caryophyllus formerly classified as F. redolens); (v) wilt-causing isolates from D. barbatus formerly classified as F. redolens and (vi), (vii) and (viii), three further recently described races of F. oxysporum f.sp. dianthi. Isolate groups derived from analysis of RFLPs were consistent with existing and recently described vegetative compatibility groups (VCGs) in F. oxysporum f.sp. dianthi , but not in all cases with races. Isolates of F. oxysporum and F. proliferatum not associated with wilt disease had simpler RFLP patterns (with one exception) that were not associated with VCGs.     

Genetic Diversity of Fusarium oxysporum Isolates from Cucumber: Differentiation by Pathogenicity, Vegetative Compatibility, and RAPD Fingerprinting

ABSTRACT A total of 106 isolates of Fusarium oxysporum obtained from diseased cucumber plants showing typical root and stem rot or Fusarium wilt symptoms were characterized by pathogenicity, vegetative compatibility, and random amplified polymorphic DNA (RAPD). Twelve isolates of other formae speciales and races of F. oxysporum from cucurbit hosts, three avirulent isolates of F. oxysporum, and four isolates of Fusarium spp. obtained from cucumber were included for comparison. Of the 106 isolates of F. oxysporum from cucumber, 68 were identified by pathogenicity as F. oxysporum f. sp. radicis-cucumerinum, 32 as F. oxysporum f. sp. cucumerinum, and 6 were avirulent on cucumber. Isolates of F. oxysporum f. sp. radicis-cucumerinum were vegetatively incompatible with F. oxysporum f. sp. cucumerinum and the other Fusarium isolates tested. A total of 60 isolates of F. oxysporum f. sp. radicis-cucumerinum was assigned to vegetative compatibility group (VCG) 0260 and 5 to VCG 0261, while 3 were vegetatively compatible with isolates in both VCGs 0260 and 0261 (bridging isolates). All 68 isolates of F. oxysporum f. sp. radicis-cucumerinum belonged to a single RAPD group. A total of 32 isolates of F. oxysporum f. sp. cucumerinum was assigned to eight different VCGs and two different RAPD groups, while 2 isolates were vegetatively self-incompatible. Pathogenicity, vegetative compatibility, and RAPD were effective in distinguishing isolates of F. oxysporum f. sp. radicis-cucumerinum from those of F. oxysporum f. sp. cucumerinum. Parsimony and bootstrap analysis of the RAPD data placed each of the two formae speciales into a different phylogenetic branch.     

Characterization of Fusarium oxysporum f. sp. radicis-cucumerinum attacking melon under natural conditions in Greece

A severe root and stem rot disease of melon was observed during the 2001 growing season on four glasshouse crops in Heraklio, Greece. A total of 43 isolates of F. oxysporum , obtained in Crete from glasshouse-grown melon and showing fusarium wilt or root and stem rot symptoms, were characterized by pathogenicity and vegetative compatibility. The majority of these isolates was also fingerprinted via amplified fragment length polymorphic (AFLP) analysis. Of the total number of isolates, 22 were identified by pathogenicity tests as F. oxysporum f. sp. melonis , 20 as F. oxysporum f. sp. radicis-cucumerinum , while one isolate was nonpathogenic on cucumber, melon, sponge gourd and pumpkin. All 22 isolates of F. oxysporum f. sp. melonis were assigned to vegetative compatibility group (VCG) 0134, and all 20 isolates of F. oxysporum f. sp. radicis-cucumerinum to VCG 0260. Isolates of F. oxysporum f. sp. radicis-cucumerinum were incompatible with isolates of F. oxysporum f. sp. melonis. AFLP fingerprinting allowed for the clustering of the isolates of the two formae speciales of F. oxysporum along two separate phenetic groups: f. sp. melonis to AFLP major haplotype I, and f. sp. radicis-cucumerinum to AFLP major haplotype II. Overall, pathogenicity, vegetative compatibility grouping and AFLP analysis were correlated and effectively distinguished isolates of F. oxysporum from melon. This appears to be the first report of natural infection of melon by F. oxysporum f. sp. radicis-cucumerinum worldwide.