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Mycologia, 96(6), 2004, pp. 1306-1315.
© 2004 by The Mycological Society of America

Epitypification of Ophiostoma galeiforme and phylogeny of species in the O. galeiforme complex


XuDong Zhou 1

     Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, 0002, South Africa

Z. Wilhelm de Beer

     Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, 0002, South Africa

Thomas C. Harrington
Doug McNew

     Department of Plant Pathology, Iowa State University, Ames, Iowa 50011

Thomas Kirisits

     Institute of Forest Entomology, Forest Pathology and Forest Protection (IFFF), Department of Forest and Soil Sciences, BOKU—University of Natural Resources and Applied Life Sciences, Hasenauerstrasse 38, A-1190 Vienna, Austria

Michael J. Wingfield 2

     Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, 0002, South Africa


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 TAXONOMY
 DISCUSSION
 LITERATURE CITED
 

Ophiostoma galeiforme was described first in 1951 from Larix kaempferi in Scotland, where it was found to be associated with the bark beetles Hy-lurgops palliatus, Dryocoetes autographus, and the ambrosia beetle Trypodendron lineatum. The taxonomy of this fungus has been uncertain because of a lack of sexual structures on the type specimen and contamination of a preserved ex-type culture. The aim of this study was to clarify application of the species name, O. galeiforme, by designating an epitype and to consider phylogenetic relationships of the species. Nineteen isolates resembling O. galeiforme from different parts of the world were used, including collections from Pinus sylvestris infested with Tomicus pi-niperda in Scotland and the contaminated ex-type culture. Morphological characteristics of isolates from Sweden, South Africa, Scotland, Chile and Aus-tria corresponded well with those originally described for O. galeiforme, and an isolate from Scotland is designated as the epitype. A detailed description is provided. Results of interfertility tests showed that O. galeiforme is heterothallic. Analysis of ITS rDNA sequences showed that the isolates representing O. galeiforme were distinct from three morphologically similar isolates from the USA and Mexico, which probably represent an undescribed taxon.

Key words: bark beetles, bluestain fungi, ITS, sapstain, Tomicus piniperda


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 TAXONOMY
 DISCUSSION
 LITERATURE CITED
 
Bark beetles (Coleoptera: Scolytidae) commonly occur in most coniferous forest ecosystems, and several species are regarded as important forest pests (Wood and Bright 1992Go). Most coniferous bark beetle species act as vectors of fungi, specifically Ophiostoma species (Beaver 1989Go, Paine et al 1997Go, Whitney 1982Go, Wingfield et al 1993Go). The genus Ophiostoma includes a few primary tree pathogens as well as many agents of sapstain (Brasier 1979Go, 1991Go; Brasier and Mehrotra 1995Go; Harrington 1993Go; Lagerberg et al 1927Go; Seifert 1993Go).

The sapstain fungus Ophiostoma galeiforme (Bakshi) Mathiesen-Käärik originally was described from Scot-land as Ceratocystis galeiforme Bakshi (Bakshi 1951Go, Mathiesen-Käärik 1953Go). This fungus was isolated from the bark of Larix kaempferi infested with the bark beetles Hylurgops palliatus (Gyllenhal), Dryocoe-tes autographus (Ratzeburg), and the ambrosia beetle Trypodendron lineatum (Olivier) (Bakshi 1951Go). Later the fungus was found on Picea abies infested with Hy-lastes cunicularius (Errichson) in Sweden (Mathie-sen-Käärik 1953Go, 1960Go). Ophiostoma galeiforme also is associated with exotic pine-infesting bark beetles in Chile and South Africa (Zhou et al 2001Go, 2004aGo). In addition, an O. galeiforme-like isolate recently has been isolated from Dendroctonus mexicanus (Hop-kins) infesting Pinus pseudostrobus in Mexico (Zhou et al 2004bGo).

The taxonomic status of O. galeiforme is uncertain because the type specimen lacks perithecia (Hunt 1956Go, Upadhyay 1981Go). Although Hunt (1956)Go accepted the species in his study of the genus Cerato-cystis, Upadhyay (1981)Go and Seifert et al (1993)Go considered it a species of uncertain status. Article 9.7 of the International Code of Botanical Nomenclature(Greuter et al 2000Go) allows the designation of a specimen and/or a culture as an epitype where the ho-lotype does not show the necessary distinguishing characters. The aim of this study was to reconsider the taxonomic status of O. galeiforme and designate an epitype for the species. Light microscopy was employed to examine isolates, and sequences of the ITS (internal transcribed spacer) region of the ribosomal RNA operon were used to assess phylogenetic relationships.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 TAXONOMY
 DISCUSSION
 LITERATURE CITED
 
Fungal isolates and morphological investigation. – The available morphological structures on the holotype of O. galei-forme (IMI20168 were examined. A culture from the type (CBS137.51) was found to be contaminated with a Cado-phora sp., and repeated attempts to purify it failed. Eighteen other isolates, morphologically and ecologically similar to O. galeiforme, were included in the study (TABLE IGo). Single-conidial cultures were prepared for all these isolates and were grown on 2% MEA (20 g Biolab malt extract, 20 g Biolab agar and 1000 mL de-ionized water). One isolate from Scotland (CMW5290), originating from ascospore masses taken from a perithecium occurring in the galleries of the bark beetle Tomicus piniperda on Pinus sylvestris produced perithecia in culture. This isolate was grown on malt agar (2% malt, 1.6% agar) supplemented with pieces of Norway spruce sapwood and on oatmeal agar (Gams et al 1998Go) at room temperature and diffuse daylight. After onset of sporulation, fungal structures were mounted on slides in lactophenol. Forty perithecia, ascospores, conidiophores and conidia were measured using a light microscope. Ranges and averages were computed for all fungal cultures, which are maintained in the culture collection (CMW) of the Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, South Africa, and/or the culture collection of TC Harrington (C), Department of Plant Pathology, Iowa State University, Iowa.


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  		TABLE I. Fungal isolates included in this study
 
Mating experiments. – Four isolates (CMW578 and CMW580 from South Africa, CMW4441 and CMW4443 from Scot-land) (TABLE IGo) resembling O. galeiforme were chosen to determine thallism and to obtain perithecia. Two crosses, one (DM270) between the two South African isolates and a second (DM269) between the two isolates from Scotland, produced perithecia; 20 single ascospore cultures each (DM270-1 to DM270-20, and DM269-1 to DM269-20) were prepared from perithecia obtained from each of the two crosses, and eight progeny from each set were selected and paired in every possible combination. Four tester strains each (two of each mating type) of each progeny set were paired in every possible combination and with a culture derived from the epitype (CMW5290). All pairings were conducted on MEA with pine twigs as described by Harrington et al (2001)Go and monitored for the appearance of perithecia.

DNA sequencing and phylogenetic analysis. – Hyphal-tip cultures of selected isolates were prepared for DNA extraction and sequencing (TABLE IGo). DNA was extracted using a mod-ified version of the extraction method developed by Raeder and Broda (1985)Go. The ITS1 and ITS2 (internal transcribed spacer) regions, including the 5.8S gene of the ribosomal RNA operon, were amplified using primers ITS1-F (Gardes and Bruns 1993Go) and ITS4 (White et al 1990Go). PCR products were sequenced with the same primers used for PCR, as well as two additional internal primers, CS2 (Wingfield et al 1996Go) and ITS3 (White et al 1990Go). Conditions for PCR amplification and sequencing reactions were as described by Zhou et al (2004a)Go. A search of similar ITS sequences using BLAST (National Center for Biotechnology Information, USA), indicated that the sequence of Leptogra-phium guttulatum MJ Wingfield & K Jacobs was closest to O. galeiforme. Two isolates (CMW1310 and CMW742) (TABLE IGo) of L. guttulatum then were sequenced and included in this study because only part of the ITS sequence of the species is available from GenBank. The resulting sequences first were aligned using Clustal X (1.81) and further manually aligned using Sequence Navigator version 1.01 (ABI PRISM, PerkinElmer). Phylogenetic relationships among the isolates were determined using distance analyses in PAUP* version 4.0b10 (Phylogenetic Analysis Using Parsimony) (Swofford 1998Go). Trees were constructed using the neighbor-joining tree-building algorithm (Saitou and Nei 1987Go). An isolate of O. cucullatum Solheim was used as out-group taxon. Bootstrap analysis (1000 replicates) was run to determine confidence of the branching points (Felsenstein 1985Go).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
TAXONOMY
 DISCUSSION
 LITERATURE CITED
 
Morphology. – All O. galeiforme isolates produced co-nidiophores in culture. A continuum of conidio-phores existed from mononematous to synnematous, although the synnemata dominated in all cultures. Morphological comparisons showed no differences among the conidiophores and conidia of the isolates from Sweden, South Africa, Scotland, Chile and Aus-tria and those present on the holotype specimen (IMI20168. Only one of the isolates (CMW5290) derived from an ascospore mass, produced perithecia in culture, and it probably consisted of both mating types or it was a heterokaryon. Measurements of the teleomorph and anamorph corresponded well with those described previously (TABLE IIGo). Three O. gal-eiforme-like isolates from Mexico (CMW9490), Geor-gia, USA (C527), and California, USA (C1293), morphologically were similar to the O. galeiforme isolates from Sweden, South Africa, Scotland, Chile and Aus-tria, but colony color of the isolates from Mexico and the USA was distinctly lighter than that of other isolates.


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  		TABLE II. Comparison of the morphology of the epitype specimen and previous descriptions of O. galeiforme (all measurements in µm)
 
Mating experiments. – Perithecia with fertile asco-spores were formed in pairings between two South African isolates (CMW578 and CMW580) and between two Scottish isolates (CMW4441 and CMW4443). None of the 20 single-ascospore cultures derived from either of these crosses gave rise to peri-thecia, but pairings among the single ascospore progeny indicated that the fungus is heterothallic and has two mating types. Pairings between the tester strains selected from the above crosses showed that the South African isolates were sexually compatible with the Scottish isolates (TABLE IIIGo). A self-sterile culture, CMW5290, which was used to generate the epitype specimen, also was compatible with some tester strains (TABLE IIIGo). Compatible crosses resulted in perithecia with viable ascospores 4–8 wk after being crossed.


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  		TABLE III. Mating experiments of O. galeiforme tester strains and the epitype strain (CMW5290)
 
DNA Sequence analysis. – Fragments approximately 510 bp in size were amplified from the DNA of all isolates (TABLE IGo), except from two isolates of L. gut-tulatum (580 bp) and the culture (CBS137.51) labeled as ex-type (463 bp). This latter fragment was sequenced, and a BLAST search revealed that it was similar to a species of Cadophora and, thus, was a contaminant. Manual alignment of the remaining sequences resulted in a total of 592 characters that were used in a distance analyses. Three main clusters were evident in the phylogram (FIG. 1Go) obtained with the neighbor-joining, tree-building algorithm. The first cluster, including three similar ITS sequence, represented the O. galeiforme group and had a bootstrap support of 98%. Isolates from Chile, South Af-rica and Sweden shared one ITS sequence, five isolates from Scotland had a second sequence and the Austrian isolate had a third sequence. The second cluster, with a bootstrap support of 59%, included the three isolates from Mexico and the USA. The third cluster consisted of two isolates of L. guttula-tum, with 100% support.



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  		FIG. 1. Phylogram of the Ophiostoma galeiforme complex based on ITS sequences (ITS1 and ITS2 regions, as well as 5.8S rRNA gene) generated with the neighbor-joining, tree-building algorithm in PAUP*. Bar = total nucleotide differences between taxa. Bootstrap values (%) are indicated above the branches.

 

   TAXONOMY
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 TAXONOMY
DISCUSSION
 LITERATURE CITED
 
The five O. galeiforme isolates from Scotland morphologically are indistinguishable, and the anamorph characteristics also are indistinguishable from those on the holotype specimen originating from Scotland. These isolates had identical ITS sequences, differed only by one base pair from the Austrian isolate and differed by two base pairs from the isolates from Chile, South Africa and Sweden. Furthermore, prog eny from crossings of Scottish and South African isolates were fully interfertile. These isolates, therefore, are considered to represent a single species whose morphological characteristics agree well with the original description of O. galeiforme (Bakshi 1951Go). A dried culture (2% malt and 1.6% agar with pieces of Norway spruce sapwood), bearing perithecia and mononematous and synnematous anamorphs of a Scottish isolate (CMW5290), is designated as the ep-itype of O. galeiforme because it originated from the same geographical region as the holotype specimen. The epitype specimen has been deposited in the National Collection of Fungal Specimens of South Af-rica (PREM57491), and the culture is maintained in the collection of the Forestry and Agricultural Bio-technology Institute (FABI), University of Pretoria, Pretoria, South Africa (CMW5290), as well as with the Centraalbureau voor Schimmelcultures, Utrecht, Netherlands (CBS115711). The species description provided below is based on the epitype specimen and culture of O. galeiforme.

Ophiostoma galeiforme (Bakshi) Mathiesen-Käärik, Meddel. Statens Skogs-Forskningsinst. 43:47. 1953 {equiv}Ceratocystis galeiforme Bakshi, Mycol. Pap. 35:13. 1951. Colonies reaching 30 mm diam in 10 d on 2% MEA at 25 C. Colonies light grey (19''d, Rayner 1970Go) to dark brown (13'''''k) with age, appressed with yeasty appearance. Perithecia rarely and sparsely produced in culture but readily formed in pairings between sexually compatible strains after 4–8 wk incubation. Peri-thecial bases globose, dark brown to black, 60–240(–550) µm diam (FIG. 2CGo), with few ornamental hyphae. Perithecial necks dark brown to black, 260–585(–840) µm long, 20–52(–93) µm wide at the base, 8–25(–54) µm wide at the apex. Ostiolar hyphae absent (FIG. 2BGo). Asci not observed. Ascospores hyaline, aseptate, with brim, bean shaped in side view, 2.0–3.5(–5.0) x 1.0–1.5(–3.0) µm (FIG. 2AGo).



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  		FIG. 2A–I. Ophiostoma galeiforme (CMW 5290) on malt agar with pieces of Norway spruce sapwood. A. Bean-shaped ascospores (Bar = 2.5 µm). B. Apex of the neck lacking ostiolar hyphae (Bar = 10 µm). C. Perithecium with long neck (Bar = 85 µm). D. Conidia of synnematous anamorph (Bar = 5 µm). E. Conidiogenous apparatus of synnematous anamorph (Bar = 8 µm). F. Synnematous anamorph (Bar = 80 µm). G. Conidia of mononematous anamorph (Bar = 5 µm). H. Conidiogenous apparatus of mononematous anamorph (Bar = 8 µm). I. Mononematous anamorph (Bar = 20 µm).

 
Synnematous anamorph predominant in culture. Conidiophores with apex hyaline to light grey, stalk brown, 50–260(–740) µm long, 7–29(–97) µm wide at base, 10–48(–190) µm wide at head (FIG. 2FGo). Con-idiogenous cells, 8–12(–15) x 1.0–1.5(–2.0) µm (FIG. 2EGo). Conidia hyaline, cylindrical, 2.0–4.0(–6.0) x 1.0–2.0(–3.0) µm (FIG. 2DGo).

Mononematous anamorph rarely produced in culture. Conidiophores with up to 10 septa, 60–92(–130) µm long (FIG. 2IGo). Primary branches, cylindrical, 10–20(–25) µm long. Secondary branches, 8–15(–20) µm long. Conidiogenous cells, cylindrical, 5.5–10(–16) x 1.0–1.5(–2.0) µm (FIG. 2HGo). Conidia hyaline, cylindrical to ellipsoid, with a truncate base, 2.0–3.5(–4.5) x 1.0–1.5(–2.0) µm (FIG. 2GGo).

Specimens examined. – SCOTLAND: Perthshire, Blair Ath-oll. Bark of Larix kaempferi ( Japanese larch), associated with bark beetles Hylurgops palliatus and Dryocoetes autogra-phus, 1951, BK Bakshi (HOLOTY PE. IMI20168. SCOT-LAND: Elgin. Pinus sylvestris (Scotch pine) infested with the bark beetle Tomicus piniperda, 29 Aug 1997, T Kirisits and MJ Wingfield (EPITY PE: PREM57491; CMW5290 = CBS115711). SCOTLAND: Elgin. P. sylvestris infested with T. piniperda, 29 Aug 1997, MJ Wingfield and T Kirisits PREM57492 (CMW4426). SCOTLAND: Elgin. P. sylvestris infested with T. piniperda, 29 Aug 1997, MJ Wingfield and T Kirisits PREM57493 (CMW4447).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 TAXONOMY
 DISCUSSION
LITERATURE CITED
 
We have confirmed previous reports that the holo-type of O. galeiforme contains only the anamorph of the fungus and that the ex-type culture deposited at CBS is contaminated. An epitype thus has been designated based on a collection from the same geographical area where O. galeiforme was first collected. The results of this study have also confirmed that O. galeiforme occurs in Chile, South Africa and Sweden and provide the first report of the fungus from Aus-tria and Central Europe. This is also the first report of the association between this fungus and Tomicus piniperda. Three isolates from the USA and Mexico thought to represent this species are different and probably represent an undescribed taxon.

Results of interfertility tests showed that O. galei-forme is heterothallic. Pairings between isolates of opposite mating types produced perithecia and those between isolates of the same mating type were negative. However, the field-collected epitype strain (CMW5290) used in this study produced perithecia and ascospores, which probably accounts for the fact that Bakshi (1951)Go reported that O. galeiforme is ho-mothallic. We believe that field isolates with perithe-cia represent either heterokaryons or are mixtures of hyphae of opposite mating type.

In the descriptions of O. galeiforme by Bakshi (1951)Go and Hunt (1956)Go, the conidial states were assigned to three genera: Graphium, Leptographium and Cephalosporium. Both Mathiesen-Käärik (1953)Go and Hunt (1956)Go mentioned that the fungus formed a continuum of conidiophore structures varying from single, simple conidiophores to true synnemata, typical of the genus Graphium, now referred to Pe-sotum (Harrington et al 2001Go). Wingfield (1993)Go stated that it was difficult to assign a generic name to the anamorph of O. galeiforme because the species has both synnematous and mononematous states. Scanning electron microscopy studies further showed a continuum in patterns of conidium development including those typical for Sporothrix, Hyalorhinocla-diella and Graphium (now Pesotum) (Benade et al 1997Go). Harrington et al (2001)Go restricted Pesotum to those species forming both synnemata and Sporothrix conidiophores with prominent denticles on the con-idiogenous cells, which are members of the O. piceae complex. They proposed that the synnemata of O. galeiforme are loosely to tightly fused Leptographium-like conidiophores and that the anamorph would be better placed in Leptographium than in Pesotum. The anamorph of the closely related O. cucullatum was transferred to Phialographium (as P. erubescens (Ma-thiesen-Käärik) Harrington et McNew) based on its phialidic conidial ontogeny (Harrington et al 2001Go). In this study, both the synnematal and mononematal forms of the anamorph of O. galeiforme were observed, although the synnematal form was predominant, and the conidiogenous cells are sympodial and phialidic. We do not believe that it is necessary to provide a formal name for the anamorph, but if necessary we preferentially would refer to it as Leptogra-phium.

Analysis of sequence data for O. galeiforme isolates from Chile and South Africa presented in this study has shown that these isolates phylogenetically are re lated closely to those from Sweden, Scotland and Austria. Occurrence of mating between the isolates from South Africa and Scotland affirmed that these isolates represent a single biological species. Some of the Ophiostoma species on Pinaceae in countries such as South Africa and Chile are carried by bark beetles that accidentally were introduced into these countries from Europe (Ciesla 1988Go, Tribe 1992Go). Ophios-toma galeiforme apparently is associated commonly with a wide range of bark beetles in Europe, and it was likely introduced into South Africa and Chile with one or more of these European insects. In South Africa, O. galeiforme is associated with Hylurgus lig-niperda (Fabricius) (Zhou et al 2001Go), and in Chile we commonly have isolated it from both Hylastes ater and Hylurgus ligniperda (Zhou et al 2004aGo). None of these Eurasian insects has been connected with O. galeiforme in their natural habitat, but this is probably due only to the lack of studies of fungi associated with these insects.


   ACKNOWLEDGMENTS
 
We thank the National Research Foundation (NRF) and members of the Tree Protection Co-operative Programme (TPCP) and the THRIP initiative of the Department of Trade and Industry, South Africa, for financial support. We also thank Dr Derek Redfern of the Forestry Commission, UK, for making it possible for MJ Wingfield and T Kirisits to collect isolates of O. galeiforme from Scotland.


   FOOTNOTES
 
Accepted for publication June 28, 2004.

1 Current address: University of Tibet, Lhasa, 850000, P.R. China. Back

2 Corresponding author. E-mail: Mike.Wingfield{at}fabi.up.ac.za


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 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 TAXONOMY
 DISCUSSION
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Q. Lu, C. Decock, X. Y. Zhang, and H. Maraite
Leptographium sinoprocerum sp. nov., an undescribed species associated with Pinus tabuliformis-Dendroctonus valens in northern China.
Mycologia, March 1, 2008; 100(2): 275 - 290.
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R. D. Zipfel, Z. W. de Beer, K. Jacobs, B. D. Wingfield, and M. J. Wingfield
Multi-gene phylogenies define Ceratocystiopsis and Grosmannia distinct from Ophiostoma.
Stud Mycol, January 1, 2006; 55: 75 - 97.
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X. Zhou, Z. W. de Beer, and M. J. Wingfield
DNA sequence comparisons of Ophiostoma spp., including Ophiostoma aurorae sp. nov., associated with pine bark beetles in South Africa.
Stud Mycol, January 1, 2006; 55: 269 - 277.
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