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Louis Bernier - One of the best experts on this subject based on the ideXlab platform.
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Ophiostoma Ulmi dna naturally introgressed into an isolate of Ophiostoma novo Ulmi is clustered around pathogenicity and mating type loci
Phytoprotection, 2019Co-Authors: Abdelali Ettouil, C M Brasier, Mathieu Dusabenyagasani, Guillaume F Bouvet, Louis BernierAbstract:The invasive fungal pathogens Ophiostoma Ulmi and O. novo-Ulmi have caused two successive pandemics of Dutch elm disease since the beginning of the 20th century. In nature, the highly aggressive O. novo-Ulmi may hybridize with the less aggressive O. Ulmi. Growth rate and molecular analyses were conducted on an unusual, moderately aggressive O. novo-Ulmi isolate, AST27, carrying an introgressed pathogenicity gene, Pat1-m; on highly aggressive O. novo-Ulmi isolate H327; on O. Ulmi isolates Q412T and W9; and on progeny from laboratory crosses between H327 and AST27. Genetic analysis indicated that the Pat1 and Mat1 (mating type) loci were in different linkage groups corresponding to O. novo-Ulmi H327 chromosomes 1 and 2, respectively. Most of the molecular differences between the nuclear genomes of H327 and AST27 occurred in the vicinity of Pat1 and Mat1. In addition, two putative quanti-tative trait loci, Mgr1 and Mgr2, which influence mycelial growth rate at 21°C and 28°C, the optima for O. novo-Ulmi and O. Ulmi, were linked to Mat1 and Pat1, respectively.
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Characterization of three DNA transposons in the Dutch elm disease fungi and evidence of repeat-induced point (RIP) mutations.
Fungal genetics and biology : FG & B, 2006Co-Authors: Guillaume F Bouvet, Volker Jacobi, Louis BernierAbstract:Transposable elements (TEs) are fundamental components of eukaryotic genomes and can contribute in various ways to genome plasticity and evolution. We describe here the first three DNA transposons in the Dutch elm disease (DED) pathogens Ophiostoma Ulmi and O. novo-Ulmi, named OPHIO1, OPHIO2 and OPHIO3. We demonstrate that OPHIO transposons, which show high homology to Fot1/pogo TEs within the Tc1/mariner superfamily, have different distribution patterns and specificity in the DED fungi and that interspecific hybrids could act as genetic bridges for transmission of TEs between closely related fungal species. OPHIO3 was found to have undergone repeat-induced point mutations (RIP). We have also developed a complementary method to Margolin’s ratios based on the computation of cumulative transition scores (CTS) in order to visualize rapidly RIP signatures on individual DNA strands of OPHIO transposons and TEs found in other ascomycete fungi.
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assessment of phaeotheca dimorphospora for biological control of the dutch elm disease pathogens Ophiostoma Ulmi and o novo Ulmi
Plant Pathology, 1996Co-Authors: Louis Bernier, G. B. Ouellette, D Yang, M DessureaultAbstract:The antagonistic fungus Phaeotheca dimorphospora was tested as a biocontrol agent against the Dutch elm disease pathogens, Ophiostoma Ulmi and 0. novo-Ulmi, on Ulmus americana seedlings in the glasshouse. Curative inoculation of seedlings with P. dimorphospora had no significant effect on disease development. Conditioning inoculation of seedlings with the antagonist protected them against 0. Ulmi but not against the more aggressive 0. novo-Ulmi. In seedlings challenged with both the antagonist and either one of the pathogens, P. dimorphospora only spread locally around the inoculation point; however, the pathogens spread systemically throughout the whole plant. O. novo-Ulmi survived in the region colonized by P. dimorphospora, whereas 0. Ulmi did not.
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Assessment of Phaeotheca dimorphospora for biological control of the Dutch elm disease pathogens, Ophiostoma Ulmi and O. novo‐Ulmi
Plant Pathology, 1996Co-Authors: Louis Bernier, G. B. Ouellette, D Yang, M DessureaultAbstract:The antagonistic fungus Phaeotheca dimorphospora was tested as a biocontrol agent against the Dutch elm disease pathogens, Ophiostoma Ulmi and 0. novo-Ulmi, on Ulmus americana seedlings in the glasshouse. Curative inoculation of seedlings with P. dimorphospora had no significant effect on disease development. Conditioning inoculation of seedlings with the antagonist protected them against 0. Ulmi but not against the more aggressive 0. novo-Ulmi. In seedlings challenged with both the antagonist and either one of the pathogens, P. dimorphospora only spread locally around the inoculation point; however, the pathogens spread systemically throughout the whole plant. O. novo-Ulmi survived in the region colonized by P. dimorphospora, whereas 0. Ulmi did not.
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Inheritance of chromosome-length polymorphisms in Ophiostoma Ulmi (sensu lato).
Current genetics, 1995Co-Authors: Ken Dewar, Louis BernierAbstract:We have investigated the mitotic and meiotic transmission of chromosome-length polymorphisms in Ophiostoma Ulmi s.l., the causal agent of Dutch elm disease. The North-American aggressive (NAN) strain CESS16K has an atypical electrophoretic karyotype, carrying two chromosome-sized DNAs (chDNAs) that have not been observed in other members of the NAN biotype. Independent CESS16K chDNA preparations, even after repeated inoculation and recovery from the elm host, and analysis of 16 progeny strains after a cross between the NAN strains FG245Br-O and CESS16K, demonstrated that these unique chDNAs are integral components of the CESS16K genome. Analysis of the progeny, by electrophoretic karyotyping and hybridizations with probes specific to individual chDNAs, presented evidence that genome rearrangements can occur as a consequence of meiosis. Even though novel electrophoretic karyotypes and a novel-sized chromosome were observed in the karyotypes of the progeny strains, the low level of reassortment between the chromosomes carrying length polymorphisms presented evidence that there are constraints to genome plasticity for this fungus.
Martin Hubbes - One of the best experts on this subject based on the ideXlab platform.
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Rapid differentiation of Ophiostoma Ulmi and Ophiostoma novo‐Ulmi isolates by matrix‐assisted‐laser‐desorption/ionization time‐of‐flight/time‐of‐flight mass spectrometry
Forest Pathology, 2010Co-Authors: C Huang, Martin Hubbes, Mohini Sain, Robert Jeng, M T DumasAbstract:Summary The intact yeast phase spores of Ophiostoma Ulmi and O. novo-Ulmi isolates were analysed by matrix-assisted-laser-desorption/ionization time-of-flight/time-of-flight mass spectrometry. The results clearly showed that isolates of O. Ulmi and O. novo-Ulmi have different mass peak profiles. The specific mass in m/z may vary slightly. One of the peaks from m/z 7623 to 7630 dominated (in high intensity) mass spectra for all isolates of O. novo-Ulmi tested in this study. This specific peak is believed to be CU (cerato-Ulmi) protein. However, no specific m/z peak can be found to distinguish between the isolates of ssp. novo-Ulmi and ssp. americana. On the contrary, all isolates of O. Ulmi tested possessed one of a dominate peak at m/z 7337 to 7342, but none around m/z 7626 as shown in O. novo-Ulmi isolates.
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isolation and characterization of the cerato Ulmin toxin gene of the dutch elm disease pathogen Ophiostoma Ulmi
Current Genetics, 1994Co-Authors: Christine G Bowden, Martin Hubbes, William E Hintz, Robert Jeng, Paul A HorgenAbstract:The hydrophobic protein cerato-Ulmin (CU), produced by Ophiostoma Ulmi, has been implicated in the pathogencity of this fungus on elm. Primers were designed based on the nucleotide sequence deduced from the published CU amino-acid sequence, and a DNA fragment of the cu gene was amplified using the polymerase chain reaction. The amplified cu fragment was used as a hybridization probe to identify and isolate the cu gene from a genomic DNA library of an aggressive isolate of O. Ulmi (= O. novo-Ulmi). The cu coding region is interrupted by two introns and encodes a 100 amino-acid prepro-CU polypeptide that is processed to a 75 amino-acid mature protein upon secretion. CU shows significant sequence similarity to hydrophobins secreted by certain other fungi.
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A glycoprotein isolated from culture filtrates of Ophiostoma Ulmi as a mansonone-inducing elicitor on elm callus
Mycological Research, 1994Co-Authors: D Yang, Martin Hubbes, R. S. JengAbstract:A 21 kDa glycoprotein, identified as a mansonone-inducing elicitor on elm callus, was purified from culture filtrates of Ophiostoma Ulmi using HPLC ion-exchange chromatography. Both aggressive and non-aggressive isolates of O. Ulmi yielded this elicitor. The glycoprotein is composed of 19 different amino acids and has a 17–20% carbohydrate content, namely α-glucose, β-glucose, galactose and some other unidentified sugars. Polyclonal antiserum against this elicitor was raised in a New Zealand white rabbit. Western blotting of a fungal filtrate revealed that the antiserum reacted only with the 21 kDa glycoprotein.
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Induction and genetic characterization of ultraviolet-sensitive mutants in the elm tree pathogen Ophiostoma Ulmi (sensu lato)
Mycological Research, 1994Co-Authors: Louis Bernier, Martin HubbesAbstract:The lethal and mutagenic effects of ultraviolet (uv) irradiation on Ophiostoma Ulmi sensu lato were tested. Exposure to uv rays increased the frequency at which benomyl-resistant mutants were recovered in five wild-type strains representing the non-aggressive species O. Ulmi and both Eurasian and North American races of the aggressive O. novo-Ulmi . Treatment of yeast-like cells from wild-type strain MH 75 and laboratory strain LB 44-R-2 with the alkylating agent N -methyl- N' -nitro- N -nitrosoguanidine allowed the recovery of four uv-sensitive mutants. All mutants were photoreactivable, whereas one strain was resistant to caffeine. Meiotic analysis provided evidence that the four strains carried non-allelic mutations. The uvs1 and uvs3 loci were linked and found to occur on linkage group I. The uvs2 and uvs4 loci were assigned to linkage groups III and IV, respectively. Two of the uv-sensitive strains also appeared to be hypermutable and might therefore be useful for the induction of additional types of mutants in O. Ulmi sensu lato .
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A genetic survey of the pathogenic fungus Ophiostoma Ulmi across a Dutch elm disease front in western Canada.
Genome, 1993Co-Authors: William E Hintz, Martin Hubbes, Robert Jeng, D. Q. Yang, Paul A HorgenAbstract:The natural population structure of the Dutch elm pathogen Ophiostoma Ulmi was determined from isolated collected from across a Western Canadian disease front through an analysis of restriction-site polymorphisms in the ribosomal DNA repeat, length mutations in the mitochondrial genomes, and through DNA fingerprinting of the nuclear genomes using a minisatellite DNA probe. The 8.8-kbp rDNA repeat was selected from a genomic library, and restriction-site and genic maps were constructed for the nonaggressive and aggressive subgroups of O. Ulmi. There were only three restriction-site differences that distinguished these two subgroups and no intrasubgroup variation was detected. All of the isolates collected from the disease front were of the aggressive subgroup and were represented by two distinct nuclear and four mitochondrial genotypes. The minority of the isolates were of a single genotype (type A nuclear DNA; type I mtDNA), indicating the presence of a single very large clone extending across much of Manitoba and into Saskatchewan.
Robert Jeng - One of the best experts on this subject based on the ideXlab platform.
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rapid differentiation of Ophiostoma Ulmi and Ophiostoma novo Ulmi isolates by matrix assisted laser desorption ionization time of flight time of flight mass spectrometry
Forest Pathology, 2010Co-Authors: C Huang, Mohini Sain, Robert Jeng, M Hubbes, M T DumasAbstract:Summary The intact yeast phase spores of Ophiostoma Ulmi and O. novo-Ulmi isolates were analysed by matrix-assisted-laser-desorption/ionization time-of-flight/time-of-flight mass spectrometry. The results clearly showed that isolates of O. Ulmi and O. novo-Ulmi have different mass peak profiles. The specific mass in m/z may vary slightly. One of the peaks from m/z 7623 to 7630 dominated (in high intensity) mass spectra for all isolates of O. novo-Ulmi tested in this study. This specific peak is believed to be CU (cerato-Ulmi) protein. However, no specific m/z peak can be found to distinguish between the isolates of ssp. novo-Ulmi and ssp. americana. On the contrary, all isolates of O. Ulmi tested possessed one of a dominate peak at m/z 7337 to 7342, but none around m/z 7626 as shown in O. novo-Ulmi isolates.
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Rapid differentiation of Ophiostoma Ulmi and Ophiostoma novo‐Ulmi isolates by matrix‐assisted‐laser‐desorption/ionization time‐of‐flight/time‐of‐flight mass spectrometry
Forest Pathology, 2010Co-Authors: C Huang, Martin Hubbes, Mohini Sain, Robert Jeng, M T DumasAbstract:Summary The intact yeast phase spores of Ophiostoma Ulmi and O. novo-Ulmi isolates were analysed by matrix-assisted-laser-desorption/ionization time-of-flight/time-of-flight mass spectrometry. The results clearly showed that isolates of O. Ulmi and O. novo-Ulmi have different mass peak profiles. The specific mass in m/z may vary slightly. One of the peaks from m/z 7623 to 7630 dominated (in high intensity) mass spectra for all isolates of O. novo-Ulmi tested in this study. This specific peak is believed to be CU (cerato-Ulmi) protein. However, no specific m/z peak can be found to distinguish between the isolates of ssp. novo-Ulmi and ssp. americana. On the contrary, all isolates of O. Ulmi tested possessed one of a dominate peak at m/z 7337 to 7342, but none around m/z 7626 as shown in O. novo-Ulmi isolates.
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starch like exopolysaccharide produced by the filamentous fungi Ophiostoma Ulmi and o novo Ulmi
Forest Pathology, 2007Co-Authors: Robert Jeng, Mohini Sain, C Huang, M Hubbes, Arturo Rodriguez, Bradley A SavilleAbstract:Summary This paper describes the chemical and biochemical properties of exopolysaccharides (EPS) produced by Ophiostoma Ulmi and O. novo-Ulmi isolates, the Dutch elm disease (DED) fungi. Some of EPS have been considered as pathogenicity factor in the DED complex. The selected isolates grow well and produce EPS in a medium containing various types of carbon and nitrogen sources. EPS obtained from potato dextrose broth (PDB) medium appeared to be opaque, firm and stained purple blue with iodine-potassium iodide solution, whereas those from yeast extract (YE) medium were less opaque, jelly-like and remained unchanged in iodine solution. The selected fungal isolates produced much higher molecular weight EPS from the medium containing YE than from PDB. The results of this study suggest that high molecular weight compounds produced by O. Ulmi (W9) and O. novo-Ulmi (R136) are not involved in DED pathogenesis. Spectrometric analysis of acid-digested EPS obtained from PDB and YE revealed the presence of a monomer similar to glucose used as a standard. Thin layer chromatography indicated that glucan-1,4-α-glucosidase (glucoamylase) only hydrolyses EPS from PDB media and releases glucose. The results strongly indicate that isolates of O. Ulmi and O. novo-Ulmi produce starch-like EPS from PDB medium. The EPS obtained from YE medium lacked this characteristic. The biological significance and the potential use of these EPS are discussed.
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a comparison of the nucleotide sequence of the cerato Ulmin gene and the rdna its between aggressive and non aggressive isolates of Ophiostoma Ulmi sensu lato the causal agent of dutch elm disease
Current Genetics, 1996Co-Authors: Robert Jeng, Christine G Bowden, William E Hintz, Paul A Horgen, M HubbesAbstract:Little genetic information exists comparing aggressive and non-aggressive isolates of the causal agent of Dutch elm disease,Ophiostoma Ulmi. Two genetic elements were compared between the subgroups. The ceratoUlmincu gene product has been associated with disease symptoms. Nucleotide-sequence analysis ofcu and the internal transcribed spacer (ITS) region of the rDNA were made from three aggressive and three non-aggressive isolates of the pathogen. Our results suggested uniformity within, and unique differences between, subgroups. Differences were detected forcu in the promoter, coding, and transcription termination regions. Sequence data for the ITS clearly distinguish the subgroups.
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isolation and characterization of the cerato Ulmin toxin gene of the dutch elm disease pathogen Ophiostoma Ulmi
Current Genetics, 1994Co-Authors: Christine G Bowden, Martin Hubbes, William E Hintz, Robert Jeng, Paul A HorgenAbstract:The hydrophobic protein cerato-Ulmin (CU), produced by Ophiostoma Ulmi, has been implicated in the pathogencity of this fungus on elm. Primers were designed based on the nucleotide sequence deduced from the published CU amino-acid sequence, and a DNA fragment of the cu gene was amplified using the polymerase chain reaction. The amplified cu fragment was used as a hybridization probe to identify and isolate the cu gene from a genomic DNA library of an aggressive isolate of O. Ulmi (= O. novo-Ulmi). The cu coding region is interrupted by two introns and encodes a 100 amino-acid prepro-CU polypeptide that is processed to a 75 amino-acid mature protein upon secretion. CU shows significant sequence similarity to hydrophobins secreted by certain other fungi.
Subhash C. Domir - One of the best experts on this subject based on the ideXlab platform.
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Host-Parasite Relationships of Susceptible and Resistant Elm Callus Cultures Challenged with Ophiostoma Ulmi (Buisman) Nannf.
Journal of Environmental Horticulture, 1996Co-Authors: Charles R. Krause, L. R. Schreiber, J. M. Ichida, Subhash C. DomirAbstract:Abstract Ultrastructural effects of Ophiostoma Ulmi (Buisman) Nannf..(= Ceratocystis Ulmi Buisman C. Moreau) on susceptible American elm (Ulmus americana L.) callus tissue consisted of extensive vacuolation, accumulation of cytolytic substances, and plasmolysis when viewed with electron and light microscopy. Infected resistant American elm callus tissue revealed slight cell wall damage with some phenolic-like deposits but adjacent cells, membranes, mitochondria and nuclei were intact. Fungal hyphae that adhered to callus grown from susceptible American elm plants were regularly observed. Sparse hyphal growth was not suspended above resistant American elm callus cells. Callus from nonhost and resistant elms showed reduced hyphal growth between host cells compared to susceptible elm with increased accumulation of extracellular, phenolic-like deposits than in callus of American elm. The fungal structures on resistant tissue showed evidence of irregular growth and morphology. The latter suggest a phytoalexin-like response by the resistant American elm callus tissue.
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INFLUENCE OF COCONUT MILK SOURCE ON HOST-PATHOGEN INTERACTIONS BETWEEN Ophiostoma Ulmi AND ULMUS SELECTIONS
1994Co-Authors: Subhash C. Domir, Lawrence R. Schreiber, Steven M. EshitaAbstract:This study compared the effects of two sources of coconut milk in modified Murashige and Skoog medium on growth of Ophiostoma Ulmi on five selections of elm callus cultures. One medium (CMC) contained coconut milk from fresh coconuts; the other medium, (CMS), coconut milk ob- tained from Sigma Chemical Co. These studies showed that the coconut milk source affected fungal growth significantly, varying with elm selection and aggressiveness of the Ophiostoma Ulmi isolate. An evaluation was made on produc- tion of secondary metabolites in callus cultures with each source of coconut milk. High performance liquid chromatogra- phy from Ulmus americana showed a higher level of those secondary metabolites using CMS medium when callus was from mature, DED-susceptible trees, but higher levels with CMC when callus was from DED-resistant trees.
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Efficacy of criteria to identify aggressiveness in Ophiostoma Ulmi and resistance in American elm germ plasm
Plant Disease, 1994Co-Authors: L. R. Schreiber, Subhash C. DomirAbstract:Criteria were evaluated to identify levels of aggressiveness of the Dutch elm disease pathogen, Ophiostoma Ulmi, and resistance in American elms. Twenty-year-old American elms were inoculated with putative nonaggressive strains PG442 and TN and aggressive strains PMP1, H961, and 16K. Strains PMP1 and H961 were confirmed to be aggressive and strains TN, PG442, and 16K to be nonaggressive. Six-month-old American elm seedlings were inoculated with the five O. Ulmi strains, and aggressiveness was judged by disease symptoms and fungus multiplication. Vascular discoloration and numbers of colony-forming units most closely correlated with in vivo results. By most in vitro criteria, PG442 was categorized as aggressive
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Development of Model Systems to Screen Elms Resistant to Dutch Elm Disease
Dutch Elm Disease Research, 1993Co-Authors: Subhash C. Domir, Lawrence R. Schreiber, Paula M. PijutAbstract:Dutch elm disease (DED), a serious vascular wilt disease caused by Ophiostoma Ulmi (Buisman) Nannf., has been responsible for destruction of elm trees in Europe and North America (Went 1954). The principal host in North America is the American elm, Ulmus americana L. The most practical means for suppressing this disease is the exploitation of polygenetically controlled host resistance (Heybroek 1970). Conventional breeding programs for improving disease resistance of elms require a long term commitment and resources to develop and evaluate germplasm. In various studies on host-parasite interactions to determine the nature of infection and mechanisms of resistance, tyloses formation, pit membrane alterations, cell wall breakdown, direct penetration of vessel cell walls and invasion of U. americana L. by O. Ulmi have been reported to occur (Krause and Wilson 1972; MacDonald and McNabb 1974; Ouellette 1978a; Ouellette 1978b).
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Effect of Elm Selection, Explant Source and Medium Composition on Growth of Ophiostoma Ulmi on Callus Cultures
Journal of Environmental Horticulture, 1992Co-Authors: Subhash C. Domir, Lawrence R. Schreiber, Jann M Ichida, Steven M. EshitaAbstract:Abstract We examined the effects of elm selection, explant source and media composition on growth of the Dutch elm disease (DED) fungus Ophiostoma Ulmi on callus cultures. Calluses were generated from leaf and stem tissue of an American elm (Ulmus Americana L.) seedling (A), susceptible to the disease; an American elm selection 8630, resistant to the disease; and a Siberian elm (U. pumila L.) seedling, also resistant to DED. Calluses were generated on modified Murashige-Skoog (MMS) medium, either with (MMSC) or without coconut milk. Explant source did not affect the fungal growth rate on the callus. Rate of O. Ulmi growth on American elm A callus was similar on both media; on Siberian and 8630, fungal growth rate was more rapid on callus cultured on MMS than on MMSC. However, in the absence of callus tissue, O. Ulmi growth on MMSC medium was more than five times as rapid as it was on MMS. We observed significant interactions between explant source and selection, and between medium and selection. Fungal gr...
C M Brasier - One of the best experts on this subject based on the ideXlab platform.
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Ophiostoma Ulmi dna naturally introgressed into an isolate of Ophiostoma novo Ulmi is clustered around pathogenicity and mating type loci
Phytoprotection, 2019Co-Authors: Abdelali Ettouil, C M Brasier, Mathieu Dusabenyagasani, Guillaume F Bouvet, Louis BernierAbstract:The invasive fungal pathogens Ophiostoma Ulmi and O. novo-Ulmi have caused two successive pandemics of Dutch elm disease since the beginning of the 20th century. In nature, the highly aggressive O. novo-Ulmi may hybridize with the less aggressive O. Ulmi. Growth rate and molecular analyses were conducted on an unusual, moderately aggressive O. novo-Ulmi isolate, AST27, carrying an introgressed pathogenicity gene, Pat1-m; on highly aggressive O. novo-Ulmi isolate H327; on O. Ulmi isolates Q412T and W9; and on progeny from laboratory crosses between H327 and AST27. Genetic analysis indicated that the Pat1 and Mat1 (mating type) loci were in different linkage groups corresponding to O. novo-Ulmi H327 chromosomes 1 and 2, respectively. Most of the molecular differences between the nuclear genomes of H327 and AST27 occurred in the vicinity of Pat1 and Mat1. In addition, two putative quanti-tative trait loci, Mgr1 and Mgr2, which influence mycelial growth rate at 21°C and 28°C, the optima for O. novo-Ulmi and O. Ulmi, were linked to Mat1 and Pat1, respectively.
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rare interspecific hybrids in natural populations of the dutch elm disease pathogens Ophiostoma Ulmi and o novo Ulmi
Fungal Biology, 1998Co-Authors: C M Brasier, Susan Kirk, N D Pipe, K W BuckAbstract:Ophiostoma Ulmi and O. novo-Ulmi are partly reproductively isolated, morphologically, behaviourally and molecularly distinct species responsible for the first and current pandemics of Dutch elm disease, respectively. Among >11000 isolates sampled from Dutch elm disease sites across Eurasia and North America since 1973, nine could not be assigned to O. Ulmi or O. novo-Ulmi . Of these isolates one (P129) was from Poland and eight (d10, d11, e12, e27, e28, e37, f30 and g3) were from a single bark sample in Portugal. These nine isolates were termed ‘fast-waxy’ isolates because of their unusual cultural characteristics. The possibility that they were interspecific hybrids was investigated. When compared with O. Ulmi and O. novo-Ulmi for colony pattern, growth-rate, optimum temperature for growth, vascular wilt ability, elm bark colonizing ability, cerato-Ulmin toxin production, ability to fertilize (as ♂) O. novo-Ulmi , and ability to be fertilized (as ♀) by O. Ulmi , they exhibited a combination of O. Ulmi -like, O. novo-Ulmi -like, intermediate or novel characters (female sterility) consistent with their being hybrids. P129 and representative Portuguese isolates d10 and e27 each exhibited a different combination of characters, indicating each was a different hybrid genotype. When d10 and e27 were independently crossed to the same O. novo-Ulmi isolate, differences in their F 1 progeny sets for growth-rate and pathogenicity distributions were consistent with their being different recombinant genotypes. A molecular analysis of P129, d10 and e27 using RAPDs of genomic DNA, rDNA RFLPs and cerato-Ulmin gene sequences confirmed that each was a unique interspecific hybrid. The mechanism of origin of these hybrids and their evolutionary significance are discussed. Combined experimental and circumstantial evidence indicates that they are relatively unfit, rare and probably transient, and that they arise when O. novo-Ulmi invades territory occupied by O. Ulmi and replaces it. Nonetheless, the possibility that the hybrids act as a genetic bridge, facilitating transfer of novel vegetative compatibility loci and other loci form O. Ulmi to O. novo-Ulmi at recent epidemic fronts, requires investigation.
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molecular relationships between Ophiostoma Ulmi and the nan and ean races of o novo Ulmi determined by rapd markers
Fungal Biology, 1995Co-Authors: N D Pipe, K W Buck, C M BrasierAbstract:Thirty-six isolates of Ophiostoma Ulmi and O. novo-Ulmi (EAN and NAN races) were compared using randomly amplified polymorphic DNA (RAPD) markers. The separation of three distinct clusters, and the quantitative relationships between them, is in good agreement with the designation of 0. Ulmi and O. novo-Ulmi as distinct species and the designation of the EAN and NAN races of 0. novo-Ulmi as closely related but distinct biological entities. The RAPD analysis was found to be more sensitive than restriction fragment polymorphism (RFLP) analysis of the same isolates, and allowed variation within each of the three taxa to be detected. Some isolates from widely separated geographical locations had identical RAPD and RFLP profiles indicating the likely route of spread of individual genotypes of the fungus. Occasionally isolates with identical RAPD and RFLP profiles differed in their vegetative compatibility (vc) group, suggesting positive selection of vc mutants, possibly as a result of their remaining free from deleterious virus-like cytoplasmic agents (d-factors). The results are discussed in terms of hypotheses regarding the evolution of the EAN and NAN races.
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Contrasting structure of European and North American populations of Ophiostoma Ulmi
Mycological Research, 1994Co-Authors: A.g. Mitchell, C M BrasierAbstract:The structures of European and North American populations of Ophiostoma Ulmi , responsible for the first pandemic of Dutch elm disease, were compared by assessing the diversity of vegetative compatibility (vc) types and sexual mating types. All six European samples examined were highly diverse for vc-types whether the samples were continental, regional, or very local in origin. Overall, the A and B sexual mating types occurred in roughly equal frequency in Europe. In contrast, a single vc-type predominated in both a part-continental and a regional sample from North America ( ca 74 and 94% respectively). This was termed the O. Ulmi North American vc supergroup. In this vc-type the A sexual compatibility type was dominant ( ca 65 and 82% respectively). The small remainder of North American isolates mainly comprised diverse vc-types, most of which were B-types. The North American vc supergroup was also the largest single vc group found locally in Europe. Circumstantial evidence suggests that the O. Ulmi vc supergroup may have been present in North America since at least the 1940s. Its existence may provide a clue to the time and place of the first appearance on the North American continent of O. novoUlmi , responsible for the current second pandemic of the disease. Possible reasons for the differences between present day North American and European O. Ulmi populations are discussed. It is suggested that the O. Ulmi North American vc supergroup may once have been the dominant vc-type in Europe as well as in North America, and that the European O. Ulmi population may have become diversified in vc-types when the first epidemic in Europe declined during the 1940s.
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Molecular relationships between Ophiostoma Ulmi and the NAN and EAN races of O. novo-Ulmi determined by restriction fragment length polymorphisms of nuclear DNA
Mycological Research, 1993Co-Authors: M. R. Bates, Kenneth W. Buck, C M BrasierAbstract:Southern blots of restriction endonuclease-digested nuclear DNA from 37 isolates of Ophiostoma Ulmi and O. novo-Ulmi (EAN and NAN races) were hybridised with probes from a library of cloned fragments of O. Ulmi nuclear DNA to search for restriction fragment length polymorphisms (RFLPs). About 40% of enzyme-probe combinations tested were unable to distinguish between O. Ulmi and O. novo-Ulmi isolates. Another 40% were able to distinguish all O. Ulmi isolates from all O. novo-Ulmi isolates, though not between the EAN and NAN races. 2·3% of enzyme-clone combinations were able to distinguish all EAN from all NAN isolates, and these were also able to distinguish all the O. Ulmi isolates. A number of clones detected variability within O. Ulmi and within the EAN and NAN races. Overall, 16 distinct nuclear RFLP types were identified, five in O. Ulmi , three in the EAN race and six in the NAN race. Isolates within a vegetative compatibility group had the same, or a closely similar, nuclear RFLP type. The RFLP profiles were consistent with an evolutionary direction O. Ulmi → O. novo-Ulmi EAN → O. novo-Ulmi NAN.