Genetic Constitution and Pathogenicity of Lolium Isolates of Magnaporthe oryzae in Comparison with Host Species-Specific Pathotypes of the Blast Fungus

ABSTRACT Fungal isolates from gray leaf spot on perennial ryegrass (prg isolates) were characterized by DNA analyses, mating tests, and pathogenicity assays. All of the prg isolates were interfertile with Triticum isolates and clustered into the crop isolate group (CC group) on a dendrogram constructed from rDNA-internal transcribed spacer 2 sequences. Since the CC group corresponded to a newly proposed species, Magnaporthe oryzae, all of the prg isolates were designated M. oryzae. However, DNA fingerprinting with MGR586, MGR583, and Pot2 showed that the prg isolates are divided into two distinct populations, i.e., TALF isolates and WK isolates. The TALF isolates were virulent only on Lolium species, whereas the WK isolates were less specific, suggesting that gray leaf spot can be caused not only by Lolium-specific isolates but also by less specific isolates. We designated the TALF isolates as Lolium pathotype. The TALF isolates showed diverse karyotypes in spite of being uniform in DNA fingerprints, suggesting that theyare unstable in genome organization.     

Studies on thiabendazole resistance of Penicillium expansum of pears: pathogenic fitness and genetic characterization

Isolates of Penicillium expansum recovered from stored pears were scored for resistance to the fungicide thiabendazole (TBZ) and for pathogenic fitness. Out of 50 isolates, nine were sensitive (S) and 41 resistant (R or RR). Seven of these resistant isolates (RR) germinated with a higher percentage on TBZ-amended medium than on unamended medium. Six S isolates and six RR isolates were chosen at random for further analysis. S and RR isolates had similar in vitro growth fitness, although RR isolates were characterized by higher infection severity on fruits. Laboratory-induced resistant isolates were generated by UV-irradiating S strains, and a similar correlation between the induced TBZ resistance and pathogenic fitness was observed. The β-tubulin gene of RR and S isolates was amplified and sequenced; mutations correlating with TBZ resistance were identified at residues Phe 167 and Glu 198. Analogous mutations were detected in the laboratory-induced resistant isolates.     

Morphology, pathogenicity and isozyme variation amongst French isolatesof Leptosphaeria maculans recovered from Brassica juncea cv. Picra

The characteristics of 36 isolates of Leptosphaeria maculans originating from cv. Picra were investigated using cultural, pathogenicity and isozyme analyses in comparison with six known isolates of A- and B-groups. Picra-related isolates were similar to the three known B-group isolates from Brassica napus using a cultural test. Two known B-group isolates and 29 of the 36 Picra-related isolates tested were aggressive on cv. Picra, whereas all the three known A-group isolates were not. All the 42 isolates tested were aggressive on the B. napus – B. juncea recombinant line MX and on B. napus cv. Westar. Phosphoglucose isomerase analysis showed two different patterns, separating A-group known (fast band) from B-group known isolates (slow band). All cv. Picra isolates displayed the slow band. Considerable differences in isoesterase patterns were found between known A- and B-group isolates. Isolates recovered from cv. Picra displayed six different electrophoretic patterns, including that of the known B-group isolates. Clusters of the 42 isolates, generated by UPGMA analysis based on similarity coefficients of electrophoretic types, matched the previous classification into A- and B-groups, although two atypical Picra-related isolates with a singular pattern clustered with the A-group. The importance of these isolates for blackleg epidemiology and resistance breeding is discussed.     

Comparison of Pathogenicity and Nucleotide Sequences of 3′-terminal Regions of Bean yellow mosaic virus Isolates from Gladiolus

Sixty-four isolates of Bean yellow mosaic virus (BYMV) from cultivated and naturalized gladioli were divided into two pathogenic groups, necrotic spot (NS) and chlorotic spot (CS) groups on Chenopodium quinoa. NS-type isolates (S-22N and E-24N), CS-type isolates (S-22C and E-92C), and broad bean isolates (Sb-50C and Sb-12C) differed in their pathogenicity on Antirrhinum majus, Nicotiana benthamiana, Phaseolus vulgaris, Spinacia oleracea and Vigna unguiculata. The four gladiolus isolates were different from BYMV-B, -P, -O and C1YVV-N in their pathogenicity on these plants, while the two broad bean isolates were similar to BYMV-B, originally from broad bean. The nucleotide (nt) sequences of the 3′-terminal region of the BYMV RNA genome of the two NS-type isolates, the two CS-type isolates, the two broad bean isolates and BYMV-B, -P and -O were determined. In a phylogenetic tree based on the CP amino acid (aa) sequences, the two NS-type isolates clustered together (identity 98.4% and 98.2% at the nt and aa level, respectively). The two CS-type isolates clustered with BYMV-O (93.2 to 99.3% nt identity and 95.6 to 98.5% aa identity). The two broad bean isolates clustered with BYMV-B (99.0 to 99.5% nt identity and 98.9 to 99.6% aa identity). BYMV-P clustered with BYMV-CS (identity 97.7% and 99.3% at the nt and aa level, respectively). The obtained sequences were compared with those of the 3′-terminal regions of seven published BYMV isolates. In a phylogenetic tree based on deduced aa sequences, BYMV isolates were divided into four clusters. Received 1 July 1999/ Accepted in revised form 22 May 2000     

Vegetative Compatibility Groups in Cercospora kikuchii, the Causal Agent of Cercospora Leaf Blight and Purple Seed Stain in Soybean

ABSTRACT Nitrogen nonutilizing (Nit) mutants were used to assess vegetative compatibility of 58 isolates of Cercospora kikuchii, 55 of which were isolated from soybean plants in Louisiana. Two isolates were vegetatively self-incompatible. Of 56 self-compatible isolates, 16 were assigned to six multimember vegetative compatibility groups (VCGs), 01 to 06, with 2 or 3 isolates in each VCG. The other 40 isolates each belonged to a distinct VCG. All six multimember VCGs contained isolates from different soy bean cultivars, and three included isolates from different locations. Only one of six multimember VCGs included isolates both from soybean leaves and seed, while the other five included isolates from only leaves or seed. The likelihood of tissue specificity or preference was discussed. All isolates and tested Nit mutants produced cercosporin on potato dextrose agar under light. Significantly different amounts of cercosporin were produced among wild-type isolates, and two Nit mutants produced significantly more cercosporin than their wild-type counterparts. All isolates produced typical Cercospora leaf blight symptoms on soybean plants in greenhouse pathogenicity tests.     

RAPD Analysis Provides Insight into the Biology and Epidemiology of Uncinula necator

ABSTRACT Ninety isolates of grape powdery mildew (Uncinula necator) from Europe (sixty-two) and India (twenty-eight) were collected. Ten of the sixty-two European isolates originated from mycelium overwintering in dormant buds ("flagshoots"). Mating types were determined, and genetic variation was assessed by random amplified polymorphic DNA (RAPD). Forty-one European isolates, including all "flagshoot" isolates, were mating type +, and twenty-one were mating type -. All Indian isolates were mating type -. Phenetic analysis based on 414 amplicons revealed three main groups. Most European isolates (53) clustered together. Nine flagshoot isolates clustered in a second distinct group. These isolates, which coexisted with other isolates in the field, may represent a genetically isolated biotype of U. necator. Indian isolates clustered into two groups. The first group (15 isolates) was a subgroup of the group containing European nonflagshoot isolates. The second group (12 isolates) was distinct from the other groups. These two groups of Indian isolates may represent genetically isolated populations with different climatic tolerances. A polymerase chain reaction primer pair, derived from a RAPD fragment specific to the Indian isolates, proved to be suitable for field studies.     

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.     

Reassessment of vegetative compatibility of Sclerotinia homoeocarpa using nitrate-nonutilizing mutants

Nitrate-nonutilizing (nit) mutants were recovered for the first time from 21 isolates of Sclerotinia homoeocarpa collected in the United States. Mutants were selected from shredded mycelium of each isolate when cultured on water agar medium amended with 4% (wt/vol) potassium chlorate. The mutants could be classified into three phenotypes: nit1, nit3, and NitM, based on their growth on minimal medium (Czapek solution agar) supplemented with NaNO(2) or hypoxanthine. Complementary heterokaryons were observed in pairings between different phenotypes of nit mutants derived from compatible isolates, but not in self-fusions or pairings between incompatible isolates. The vigor of prototrophic growth varied with isolates and mutant phenotypes. Strong and continuous heterokaryons, as well as weak and spontaneous ones, formed depending on pairings of nit mutants. Stable heterokaryons between compatible isolates, but apoptotic reactions between incompatible isolates, were observed immediately after hyphal fusion under the epifluorescence microscope. The 21 isolates used in this study, which were previously assigned into 11 different vegetative compatibility groups (VCGs) based on the formation of a barrage zone at the contact site of paired isolates on complete medium (potato dextrose agar), were regrouped into five VCGs based on heterokaryon formation between nit mutants on minimal medium.     

Carbendazim resistance in the eyespot pathogen Pseudocercosporella herpotrichoides

Mycelial isolates (115) of Pseudocercosporella herpotrichoides were obtained from five field sites in England. Carbendazim-resistant isolates were detected by their mycelial growth on agar containing 1 μg/ml carbendazim. Resistant isolates were found at two of the five sites examined and one of these had never been treated with benzimidazole fungicides. Amongst the carbendazim- resistant isolates there was a predominance of isolates with pale mycelium, an irregular colony margin and a relatively slow growth rate; however, this association was not absolute. Large differences in the effects of carbendazim on mycelial growth of sensitive and resistant isolates were demonstrated; growth of sensitive isolates was completely inhibited at 0.5 μg /ml carbendazim whilst five of the six resistant isolates examined grew on agar containing 1000 μg/ml fungicide. The carbendazim-resistant isolates were cross-resistant to benomyl, thiophanate-methyl and to a Icsser degree thiabendazole, but not to prochloraz. Conidia of carbendazim-resistant isolates were as resistant. Carbendazim-resistant isolates were just as pathogenic to wheat as sensitive isolates. The implications of these results and other reports of benzimidazole resistance in P. herpotrichoides are discussed in relation to disease control.     

Characterization of Verticillium dahliae Isolates from Potato on Hokkaido by Random Amplified Polymorphic DNA (RAPD) and REP-PCR Analyses

Verticillium dahliae isolates from potato on the island of Hokkaido (potato isolates) and those belonging to pathotypes A (eggplant pathotype), B (tomato pathotype) and C (sweet pepper pathotype) were divided into three distinct groups by RAPD and REP-PCR. The three DNA groups I, II, III consisted of pathotypes A and C, pathotype B and potato isolates, respectively. The potato isolates were assigned to pathotype A on the basis of pathogenicity. Another set of potato isolates was further collected from eight potato cropping regions on Hokkaido to further examine the relationships among them in detail. Only one of these isolates was identified as DNA group II, but all the others were classified as DNA group III. Isolates from daikon, eggplant, and melon on Hokkaido also belonged to DNA group III. These results suggest that V. dahliae isolates from Hokkaido are unique at the DNA level and different from other pathotype A isolates in Japan. Received 28 February 2000/ Accepted in revised form 6 November 2000     

Population Genetic Structure and Host Specificity of Alternaria spp. Causing Brown Spot of Minneola Tangelo and Rough Lemon in Florida

ABSTRACT Alternaria spp. were sampled from two rough lemon (RL) and two Minneola tangelo (MIN) groves in a limited geographic area in central Florida to test for host-specialized forms of the pathogen. Isolates of Alternaria spp. were scored for variation at 16 putative random amplified polymorphic DNA (RAPD) loci and for pathogenicity on both hosts. Subpopulations on each host were differentiated genetically and pathogenically, which was consistent with the hypothesis of host specialization. Highly significant genetic differentiation was detected among all four subpopulations (Nei's coefficient of gene differentiation [G(ST)] = 0.292, P = 0.000); most of the differentiation occurred between hosts (G(ST) = 0.278, P = 0.000). Phenograms of qualitative similarities among isolates within subpopulations revealed two or three distinct clusters of isolates within each subpopulation. The majority of isolates sampled from RL were pathogenic on RL and not on MIN, although a few RL isolates were able to induce disease on MIN, and 44% were nonpathogenic on either host. In contrast, isolates from MIN were pathogenic only on MIN, never on RL, and only 3% of the isolates were nonpathogenic. Overall, three genetically distinct clusters of isolates were detected on both hosts. One of the clusters (cluster A) sampled from RL was pathogenic on RL and not on MIN and consisted almost entirely of one RAPD genotype. This cluster also contained two isolates that were 93% similar to the majority genotype but were pathogenic on MIN and not RL. In isolates from MIN, two distinct clusters of isolates were found in one subpopulation (clusters B and C), and three distinct clusters were found in another subpopulation (clusters A, B, and C). Clusters A and B were found on both hosts, while cluster C was limited to MIN. Populations of Alternaria spp. sampled from RL and MIN showed a high degree of host specificity; however, the specificity obscured a high level of genetic variation within subpopulations.     

The first report of tomato foot rot caused by <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> AG-3 PT and AG-2-Nt and its host range and molecular characterization

Foot rot of mature tomato plants was found in four cities of Hokkaido, Japan, from 2004 to 2007. Six of eight isolates obtained from damaged tissues were identified as Rhizoctonia solani anastomosis group (AG)-3, and the remaining two isolates belonged to AG-2-1. We compared these isolates with nine reference isolates including the different subgroups in AG-3 (PT, TB and TM) and AG-2-Nt (pathogen of tobacco leaf spot) within AG-2-1 in terms of pathogenicity to tomato, tobacco and potato. All eight isolates caused foot rot on tomato. The six AG-3 isolates caused stem rot on young potato plants. While, all reference isolates of AG-3 PT causing stem rot of young potato plants incited foot rot on tomato. The two AG-2-1 isolates and an AG-2-Nt reference isolate caused severe leaf spot on tobacco leaves. The sequences of rDNA- ITS region and rDNA-IGS1 region of the AG-3 isolates showed high similarity to that of AG-3 PT isolates. Phylogenetic tree based on ITS and IGS1 regions of rDNA indicated that the AG-2-1 isolates from tomato formed a single clade with AG-2-Nt isolates and that they were separate from Japanese AG-2-1 isolates (culture type II). Pathogenicity tests and DNA sequence evaluation of the causal fungi revealed that the present isolates of AG-3 and AG-2-1 belonged to AG-3 PT and AG-2-Nt, respectively. This is the first report of tomato foot rot caused by R. solani in Japan.     

Characterization of Botryosphaeria dothidea Isolates Collected from Pistachio and Other Plant Hosts in California

ABSTRACT Eighty-six isolates of Botryosphaeria dothidea, the causal agent of Botryosphaeria panicle and shoot blight of pistachio, were collected from pistachio and other plant hosts in California. The isolates were characterized by microsatellite-primed polymerase chain reaction (MP-PCR), sequences of the nuclear ribosomal DNA internal transcribed spacer region (ITS1, 5.8S gene, and ITS2), morphological and cultural characters, osmotic and fungicide sensitivity, and pathogenicity on pistachio. Three groups of these isolates were identified based upon analysis of MP-PCR data and ITS sequences. Group I contained 43 pycnidiospore-derived isolates collected from pistachio and other hosts. Group II consisted of 20 ascosporic isolates obtained from a single sequoia plant. Group III consisted of 20 ascosporic isolates from three shoots on a single blackberry plant, two pycnidiospore-derived isolates from incense cedar, and one from pistachio. Group I predominated over the other two groups in California pistachio orchards. B. dothidea isolates of group III grew faster on acidified potato dextrose agar (APDA) than the isolates of groups I and II. Isolates of group III produced pycnidia on both APDA and autoclaved pistachio shoots, but the isolates of the other two groups produced pycnidia on only autoclaved pistachio shoots. Additionally, significant differences in osmotic and fungicide sensitivities were observed among these three groups. Results from lathhouse inoculations demonstrated that the representative isolates for each of the three groups were all capable of infecting pistachio and producing characteristic disease symptoms of Botryosphaeria blight. The virulence of group II isolates on pistachio was, however, significantly lower than that of group I isolates.     

Biochemical and pathogenic differences between Kenyan and Brazilian isolates of pseudomonas syringae pv. garcae

Isolates of Pseudomonas syringae pv. garcae from Kenya and Brazil differed in pathogenic and biochemical characters. In inoculations on Coffea arabica var. SL28 from Kenya, only the Kenyan isolates were virulent. The Kenyan isolates were not bacteriocin producers while the Brazilian isolates were active producers comparable to P. s. syringae from lilac ( Syringa vulgaris ). Pigment production separated the two types of P. s. garcae isolates distinctly. The Kenyan isolates produced the UV fluorescent yellow-green siderophore while the Brazilian isolates produced a nonfluorescent brown diffusible pigment on King's B medium. API-20NE diagnostic kits were largely ineffective in distinguishing between biochemical reactions of P. s. garcae isolates from Kenya and Brazil or between these and P. s. syringae . Syringomycin activity on lemon and Geotrichum candidum distinguished P. s. syringae from P. s. garcae isolates. It is concluded that P. s. garcae (as represented by the seven cultures from the National Collection of Plant Pathogenic Bacteria, Harpenden, UK) exists in at least two strains, the Kenyan isolates comprising one strain while the Brazilian isolates comprise one or more distinct strains.     

Pathogenic characteristics of isolates of Aphanomyces euteiches from pea in France

Aphanomyces root rot ( Aphanomyces euteiches ) has become a very destructive disease in French pea crops since 1993. The host specificity of the French pea-infecting populations of this pathogen was investigated by inoculating pea, common vetch, alfalfa, broad bean and green bean with 91 pea-infecting A. euteiches isolates, originating from the main areas of infestation in France. These isolates were compared to 13 isolates from various countries and hosts (pea, green bean, alfalfa). Virulence phenotypes were defined according to the pathogenicity data on the different hosts: all isolates from France infected two to five legume species, with most infecting pea, vetch, alfalfa and broad bean. Four pathotypes were characterized within the French isolates: one type corresponded to broad host range isolates, the second was composed of isolates preferentially agressive on pea/vetch/alfalfa and weakly aggressive on broad bean, and two others corresponding to more specialized isolates that preferentially infected pea/vetch or pea/vetch/alfalfa. Most isolates from France were preferentially pathogenic on pea, like the pea-infecting isolates from other countries, but were less specialized than the alfalfa- and green bean-infecting isolates from other countries. These results suggest that A. euteiches isolates may be maintained on wild or cultivated legumes other than pea in France.     

Strains of Botrytis cinerea resistant to dicarboximide and benzimidazole fungicides in New Zealand vineyards

In a survey of New Zealand vineyards at harvest 1985, isolates of Botrytis cinerea resistant to benzimidazole and to dicarboximide fungicides were common. The mean frequency of resistance in the major vine-growing districts ranged from 8 to 41% for benzimidazoles, and from 51 to 59% for dicarboximides. All benzimidazole-resistant isolates showed high levels of resistance (EC50 greater than 100 mg/l carbendazim based on radial growth response), and all dicarboximide-resistant isolates showed low levels of resistance. Two subgroups of dicarboximide-resistant isolates were recognized, distinguished in the first instance by their osmotic response. Low-level resistant isolates, which formed a dense margin on osmotically amended medium, exhibited an EC50 for mycelial growth on iprodione of c. 3-2 mg/l; ultra-low-level resistant isolates, which formed a fibrillose margin on osmotically amended medium identical to that of sensitive isolates, exhibited an EC50 of c. 1-3 mg/1. In agar culture, radial growth rate, and conidial and sclerotial production of both subgroups were similar to those of sensitive isolates. Virulence (lesion size) and conidial production on grape berries were highest in sensitive isolates, intermediate in ultra-low-level dicarboximide-resistant isolates, and lowest in low-level dicarboximide-resistant isolates. Evidence is presented indicating that ultra-low-level dicarboximide-resistant strains have progressively replaced low-level dicarboximide-resistant strains in the vineyard population. The presence of dicarboximide-resistant strains was linked with a partial loss of fungicide efficacy.     

Differential Inhibition of Sphaeropsis sapinea Morphotypes by a Phenolic Compound and Several Monoterpenes of Red Pine

ABSTRACT The in vitro effects of a red pine phenolic compound (pinosylvin), a phenolic compound common to other species (tannic acid), and the major red pine monoterpenes (alpha-pinene, beta-pinene, and delta-3-carene) on spore germination and mycelial growth of Sphaeropsis sapinea were examined. Two A and two B morphotype isolates were used. At 88 mug/mm(2), pinosylvin inhibited spore germination of all four isolates (98 to 100%). At 8.8mug/mm(2), spore germination of B isolates was inhibited more than that of A isolates (73 versus 30%). Pinosylvin also inhibited mycelial growth of B isolates more than that of A isolates (84 versus 13% at 88 mug/mm(2)). Tannic acid stimulated or had little affect on spore germination and had little affect on mycelial growth of either morphotype. Spore germination of B isolates was inhibited more than that of A isolates by beta-pinene at saturation (79 versus 37%). Spore germination of B isolates was inhibited and germination of A isolates was stimulated by delta-3-carene below saturation (49 versus -7%). Mycelial growth of B isolates was inhibited more than that of A isolates by all monoterpenes at saturation. Differences observed between morphotypes below saturation were significant only for beta-pinene. These results demonstrate the biological activity of a phenolic compound and monoterpenes that occur in red pine. The differential responses might provide means of distinguishing morphotypes and offer a potential explanation for ecological specialization.     

Genetic differentiation of Puccinia triticina populations in the Middle East and genetic similarity with populations in Central Asia

Leaf rust of wheat, caused by Puccinia triticina, is a common and widespread disease in the Middle East. The objective of this study was to determine whether genetically differentiated groups of P. triticina are present in the Middle East region and to compare the population from the Middle East with the previously characterized population from Central Asia to determine whether genetically similar groups of isolates are found in the two regions. In total, 118 isolates of P. triticina collected from common wheat and durum wheat in Egypt, Israel, Turkey, Ethiopia, and Kenya were tested for virulence on 20 lines of wheat with single genes for leaf rust resistance and for molecular genotypes with 23 simple-sequence repeat (SSR) markers. After removal of isolates with identical virulence and SSR genotype in each country, 103 isolates were retained for further analysis. Clustering of SSR genotypes based on two-dimensional principal coordinates and virulence to wheat differential lines grouped the isolates into four Middle East (ME) groups. The two largest ME groups had virulence phenotypes typical of isolates collected from common wheat and two smaller ME groups had virulence typical of isolates collected from durum wheat. All pairs of ME groups were significantly differentiated for SSR genotype based on R(ST) and F(ST) statistics, and for virulence phenotype based on Φ(PT). All ME groups had observed values of heterozygosity greater than expected and significant fixation indices that indicated the clonal reproduction of urediniospores in the overall population. Linkage disequilibria for SSR genotypes was high across the entire population. The overall values of R(ST) and F(ST) were lower when isolates were grouped by country of origin that indicated the likely migration of isolates within the region. Although the two ME groups with virulence typical of isolates from common wheat were not differentiated for SSR genotype from groups of isolates from Central Asia based on R(ST), there was no direct evidence for migration between the two regions because all ME isolates differed from the Central Asia isolates for SSR genotypes.     

Distinguishing characteristics and vegetative compatibility of Colletotrichum kahawe in comparison with other related species from coffee

On the basis of pathogenicity tests on green berries or hypocotyls of coffee and by morphological and biochemical characteristics in culture, 31 isolates of Colletotrichum were classified into C. kahawe (24 isolates), C. gloeosporioides (six isolates) or C. acutatum (one isolate). Within these groups of isolates, vegetative compatibility groups (VCGs) were determined by complementation tests with mutants in the nitrate assimilation pathway. There were distinct incompatibility barriers between the three species. Among the C. gloeosporioides group, the three isolates tested were self-compatible but incompatible with each other. Within C. kahawe , 18 isolates were self-compatible and only one main VCG was detected. However, partial compatibility in C. kahawe was also indicated by variation in the intensity of heterokaryon formation between different pairs of isolates and between different types of mutant. The existence of only one VCG in C. kahawe is consistent with the low level of variation found in previous work on DNA polymorphism.     

Molecular variation within some Japanese isolates of Verticillium dahliae

Eight isolates of Verticillium dahliae from Japan, classified into four groups based on pathogenicity to differential hosts, were compared with isolates in previously defined RFLP groups. Within each of two of the pathogenicity groups (JB and JC) the pairs of haploid isolates were closely related but those in a third group (JA; isolates not pathogenic to sweet pepper or tomato) were not. Only one of the six haploid isolates (one of the two in the JA group) could be placed in an existing RFLP group. The two diploid isolates (the JD pathogenicity group) were similar to RFLP group D and only distantly related to the six haploid isolates. Of the Japanese pathogenicity groups, only JD corresponded to an existing RFLP group.