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Utriascus, a new ascomycetous genus in the Sordariales

     Institute of Botany, Dept. Plant Taxonomy and Biosystematics, Academy of Sciences, CZ-252 43 Prhonice, Czech Republic

	ABSTRACT

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The new monotypic genus Utriascus is described from wood of Ulmus glabra in the umava Mts. National Park, Czech Republic. It is characterized by superficial, setose ascomata, unitunicate, saccate, and long-pedunculate asci that lack any discharge mechanism in the apex and one-celled, dark pigmented ascospores enclosed in a hyaline ornamented sheath. Utriascus is classified in the Sordariales.

Key words: gelatinous equipment, one-celled ascospores, ornamentation, saprobic, systematics

	INTRODUCTION

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During a mycological survey of the umava Mts. National Park, Czech Republic, a new ascomycete on rotten wood of Ulmus glabra was found. The unique morphological characteristics of the perithecia, asci, and ascospores indicate that it represents a new species in a new monotypic genus Utriascus, therefore a new genus in the Sordariales is proposed. Several attempts to cultivate ascospores of this fungus on cornmeal (CMA, Difco), potato-carrot (PCA, Gams et al 1998) and oatmeal agar (OA, Gams et al 1998) have proved unsuccessful. The anamorph remains unknown.

	MATERIALS AND METHODS

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Perithecia were rehydrated in distilled water and subsequently studied in water, Melzer's reagent, cotton blue in lactic acid, and Congo red. Measurements were made from preparations mounted in water. Images were captured in Melzer's reagents using differential interference microscopy (DIC) and processed using Adobe Photoshop 6.0 CE.

	TAXONOMY

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Utriascus Réblová, gen. nov.

Ascomata superficialia, subglobosa usque conica, minute papilla, ostiolata, setose. Setis acutis usque obtusis, simplicibus, obscure fuscis vel opacis. Pariete perithecii fragili, dilute brunneo, bistratoso. Filamenta hamathecii deliquescentia. Asci octospori, unitunicati, uteriformes, pedunculati, apice non amyloideo, annulo nullo. Ascosporae bilateraliter applanatae, e fronte visae rotundatae vel subellipsoideae, unicellulares, juvenes olivaceae vel dilute brunneae, maturitate brunnescentes, strato hyalino verruculoso persistente circumdatae. Pori vel fissurae germinationis absentes.

Anamorph. Unknown.

Etymology. Latin, uter = referring to saccate shape of asci.

Type species. Utriascus gabretae Réblová.

Utriascus gabretae Réblová, spec. nov. Figs. 1–16 .

View larger version (161K): [in this window] [in a new window]    FIGS. 1–7. Utriascus gabretae. 1. Young asci containing immature ascospores. 2–6. Asci with ascospores. 7. Part of the perithecial wall: longitudinal section. Bars: 1–3, 5, 7 = 10 µm; 4, 6 = 20 µm. 1–7 from PRM 896154 (HOLOTYPE)

View larger version (154K): [in this window] [in a new window]    FIGS. 8–14. Utriascus gabretae. 8–10. Mature asci containing ascospores. 11. Hyaline, finely verruculose sheath, ornamentation well visible in immature ascospores. 12. Young ascospores. 13. Mature ascospores. 14. Young and mature asci. Bar: 8–14 = 10 µm. 8–14 from PRM 896154 (HOLOTYPE)

View larger version (59K): [in this window] [in a new window]    FIG. 16. Utriascus gabretae. Median, longitudinal section of perithecium seated on the natural substratum. Bar: 100 µm. From PRM 896154 (HOLOTYPE)

Ascomata superficial, solitary or in small groups, subglobose to conical, 330–450 µm wide, 320–450 µm high, papillate, setose, when old pierced with a pore at the top. Ascomata attached to the substratum with long, brown, flexuous, unbranched hyphae ca 2.5–3 µm wide. Setae short, apically pointed to blunt, 0–1-septate, dark brown, opaque, 10–25 µm long, 2.5–3.5 µm wide near the base, covering whole perithecium. Perithecial wall hard, fragile, two-layered, 20–30 µm thick; outer wall of thick-walled, dark brown, polyhedral cells with opaque walls, externally heavily pigmented; inner layer of thin-walled, polyhedral to compressed hyaline cells. Interthecial filaments difficult to observe or rarely seen as septate, filiform, hyaline fragments among asci, deliquescing. Periphyses not observed. Asci unitunicate, thin-walled, saccate, formed in a basal fascicle; the spore bearing part (45–)54–72 µm long and (22–)31–34(–38) µm wide, long-stipitate, stipe 25–45(–52) µm long, apically narrowly to broadly rounded depending on the arrangement of ascospores within the ascus, 8-spored, persistent at maturity. Ascal apex non-amyloid, lacking apical ring or any discharge mechanism. Ascospores apparently bilaterally flattened with an elliptical outline, ca 7–9 µm thick, ± circular in front view, 15–18 x 15–18 µm, 1-celled, olivaceous to pale brown when young, mid brown at maturity, enclosed in a firm, hyaline, finely verruculose sheath (1–)1.5–2.5(–3) µm thick. Sheath present and ornamented in the earliest stages of ascospore development. Ascospores filled with many droplets. Germ pores and germ slit lacking.

Anamorph. Unknown.

Etymology. Latin, Silva Gabreta' = umava Mts., National Park, referring to the area where the fungus was collected.

Habitat. Saprobe on soft decayed wood of Ulmus glabra.

Specimen examined. CZECH REPUBLIC. SOUTHERN BOHEMIA: umava Mts. National Park, Volary, Medvdice Nature reserve, decayed wood of a trunk of Ulmus glabra, 31 Aug 1998, M. Réblová MR 1297/98 (HOLOTYPE, PRM 896154).

Distribution. Known only from type collection.

Commentary. All cultivation attempts were unsuccessful. The dematiaceous hyphomycete Virgariella atra S. Hughes grew abundantly on the wood surface around perithecia. It is unlikely that V. atra is the anamorph of U. gabretae because species of Virgariella S. Hughes (Hughes 1953, Sutton 1992) have been associated with the following teleomorph genera, mostly in the Xylariales, e.g. Hypoxylon Bull. (Ju and Rogers 1996), Anthostomella Sacc. (Francis et al 1980), Biscogniauxia Kuntze (Ju et al 1998) or with a loculoascomycete Gibbera Sacc. (Sivanesan 1984). However, Virgariella-like anamorphs have been also associated with Effetia Bartoli et al, a perithecial ascomycete genus isolated from tropical forest soil and classified as an atypical member of the Sordariales (Bartoli et al 1984). Effetia differs from Utriascus in having membranaceous perithecial wall, cylindrical asci and olivaceous-brown, elliptical, smooth-walled ascospores that lack any gelatinous sheath and have a distinct germ pore.

When ascomata of U. gabretae are squashed in a drop of water on a slide, mature asci remain attached in a basal fascicle. The ascal apex is broad and uniformly thin-walled, lacking any discharge mechanism. No pore, refractive membrane, or ring was observed with any dye tried.

	DISCUSSION

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Utriascus is characterized by superficial ascomata, saccate long-pedunculate asci that form in a basal fascicle, persist at maturity and lack any discharge mechanism, and globose, one-celled, dark pigmented ascospores enclosed in a hyaline, firm, ornamented sheath. The sheath did not stain either in Congo red or cotton blue in lactic acid. The ascospores collapse upon drying. Interthecial filaments deliquesce early. They were observed as fragments among asci and thus it is not possible to say whether they are apically free or not. The combination of these morphological features suggests that Utriascus should be accommodated in the Sordariales.

Most taxa of the Sordariales are characterized by one-celled pigmented ascospores with a variety of sheaths or appendages, e.g., Apodospora Cain & J.H. Mirza, Arnium Nitschke ex G. Winter, Bombardioidea C. Moreau ex N. Lundq., Fimetariella Griffiths & Seaver and Sordaria Ces. & De Not. Typically the sheaths are described as gelatinous, lacking any microstructure and ornamentation, and tending to swell in water and sometimes dissolving. However, Lundqvist (1972) observed that some variation in structure and consistency might occur even in the same species and in the same gelatinous equipment. The sheath in U. gabretae is apparently firm, finely verruculose, of constant thickness, and neither swells in water nor dissolves later. In the Sordariales bilaterally flattened dark pigmented ascospores occur only in Coniochaeta (Sacc.) Cooke. It differs from Utriascus in ascus morphology, presence of a germ slit in ascospores, and a dissolving ascospore sheath in some species. A similar ascus shape occurs in the Sordariales in both perithecial and cleistothecial members, e.g., polysporous species of Podospora Ces. emend. Lundq. or Tripterospora Cain and Thielavia Zopf, respectively (Lundqvist 1972). In all three genera, asci lack any apical ring or apical light-refractive membranes and ascospores differ significantly from those of Utriascus. The asci developing in a basal fascicle are typical of some other sordariaceous fungi, e.g., Chaetomium Kunze (Corlett 1966), Podospora (Mai 1976), Gelasinospora Dowding, Sordaria (Mai 1977), and Triangularia Boedijn (Huang 1975, 1976).

Saccate and long-pedicellate asci in combination with one-celled subglobose ascospores are also typical of Thalassogena Kohlm. & Volkm.-Kohlm., a member of the Halosphaeriales. However, this genus clearly differs from Utriascus in smooth hyaline ascospores lacking gelatinous equipment, asci containing an apical pore, presence of catenophyses, and marine habitat (Kohlmeyer and Volkman-Kohlmeyer 1987). Similar asci also occur e.g., in Nais Kohlm. or Aniptodera Shearer & M.A. Mill. of the Halosphaeriales, although both possess hyaline, bicellular ascospores having gelatinous appendages.

Outside the Sordariales, globose, dark pigmented ascospores occur, for example in Reticulosphaeria Sivan. & Bahekar (Cainiaceae, Amphisphaeriales, Sivanesan and Bahekar 1982, Kang et al 1999). Reticulosphaeria has typically reticulate ascospores that lack any sheath or gelatinous equipment, cylindrical short-pedicellate asci with amyloidal apical ring, and conical glabrous perithecia immersed in the bark with a tendency to form a clypeus. These characteristics clearly distinguish it from Utriascus.

View larger version (61K): [in this window] [in a new window]    FIG. 15. Utriascus gabretae. A. Mature asci containing ascospores. B. Young ascus containing immature ascospores. C. Ascospores. D. Fragments of interthecial filaments. Bar: 10 µm. From PRM 896154 (HOLOTYPE)

	ACKNOWLEDGMENTS

	FOOTNOTES

 
¹ Corresponding author, reblova{at}ibot.cas.cz

Accepted for publication June 15, 2002.

	LITERATURE CITED

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS TAXONOMY DISCUSSION LITERATURE CITED

 
Bartoli A, Maggi O, Persiani AM., 1984 Effetia, a new genus of Ascomycetes from tropical forest soil. Mycotaxon 19:515-522

Corlett M., 1966 Perithecium development in Chaetomium trigonosporum. Can J Bot 44:155-162

Francis SM, Minter DW, Caine TS., 1980 Three new species of Anthostomella. Trans Br Mycol Soc 75:201-206

Gams W, Hoekstra ES, Aptroot A., 1998 CBS Course of Mycology, CBS. Baarn. 165 p

Huang LH., 1975 A new species of Triangularia from Ohio soil. Can J Bot 53:560-564

———. 1976 Developmental morphology of Triangularia backusii (Sordariaceae). Can J Bot 54:250-267

Hughes SJ., 1953 Conidiophores, conidia, and classification. Can J Bot 31:577-659

Ju MY, Rogers JD., 1996 A revision of the genus Hypoxylon. Mycol Mem 20:1-365

———, ———, San Martin F, Granmo A., 1998 The genus Biscogniauxia. Mycotaxon 66:1-98

Kang JIC, Hyde KD, Kong RYC., 1999 Studies on Amphisphaeriales: The Cainiaceae. Mycol Res 103:1621-1627

Kohlmeyer J, Volkman-Kohlmeyer B., 1987 Thalassogena, a new ascomycetous genus in the Halosphaeriaceae. Syst Ascom 6:223-228

Lundqvist N., 1972 Nordic Sordariaceae s. lat. Symb Bot Upsal 20:1-360

Mai SH., 1976 Morphological studies in Podospora anserine. Amer J Bot 63:821-825

———. 1977 Morphological studies in Sordaria fimicola and Gelasinospora longispora. Amer J Bot 64:489-495

Sivanesan A., 1984 Acantharia, Gibbera and their anamorphs. Trans Br Mycol Soc 82:507-529

———, Bahekar V., 1982 Reticulosphaeria indica gen. et sp. nov. from India. Trans Br Mycol Soc 78:547-551

Sutton BC., 1992 The relationships of Virgariella verrucosa sp. nov. on Aloe leaves from Turkey. Sydowia 44:321-331

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