Hypoxylon petriniae

              

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Hypoxylon petriniae Stadler & Fournier

Stromata elongate to irregularly effused on wood or bark of Fraxinus, plane, with inconspicuous perithecial mounds, usually finely wrinkled, 6-60 (-120) mm long x 3-22 (-25) mm broad x 0.3-0.8 mm thick; margins black and linear, surface pale purplish grey (127), vinaceous grey (116), vinaceous purple (101), dark vinaceous (82) to brown vinaceous (84); yellowish brown, orange (7) to rust (39) granules beneath surface and between perithecia with KOH-extractable pigments orange (7) or rust (39); the tissue below the perithecial layer inconspicuous, up to 0.4 mm, dark brown to blackish.

Perithecia spherical to obovoid, 250-380 m diam x 250-500 m high.

Ostioles umbilicate, on mature stromata frequently surrounded by a ring of white material 50-70 m diam.

Asci 115-145 m total length x 7-10 m broad, the spore-bearing parts 65-85 m long, the stipes 37-64 (-72) m long, with apical ring amyloid, discoid, 0.8-1 m high x 2.7-3.4 m broad.

Ascospores brown, ellipsoid-inequilateral to slightly falcate, 8.8-11.5 (-13) x 4.8-6 m, M = 10.7 x 5.1 m, with straight germ slit spore-length; perispore dehiscent in 10% KOH, appearing smooth by L. M., but showing conspicuous transverse striations by SEM (Stadler et al., 2004b).

Anamorph in nature: at margins of young stromata or on old stromata, velvety, buff (45) to honey (65). Conidiogenous cells yellowish to light brown, smooth, 10-30 x 2-3 m; conidia ellipsoid, 7-8 x 3-4 m. The conidiogenous structure is Virgariella-like, as confirmed by culturing on OA (Stadler et al., 2004b) .

Habitat: frequently on bark, more rarely on wood of dead branches still attached to the trunk or lying on the ground. A common saprophyte of Fraxinus excelsior, but also occasionally found on Acer monspessulanus, Populus tremula, Salix sp.

Known distribution: Probably widespread in Europe. Known from France, Germany, Norway (Granmo 1999, as H. cercidicola), Switzerland and U. K. (Petrini & Mller, 1986, as H. rubiginosum var. cercidicola).

Specimens examined: FRANCE. Arige (09): Rimont, Las Muros, 10 Sept. 1996, JF-96094, on Fraxinus excelsior; Rimont, Binette, 26 Apr. 2000, JF-00044, on Fraxinus excelsior; Rimont, Las Muros, 02 Aug. 2000, JF-00140, on Fraxinus excelsior; Rimont, Las Muros, 02 Sept 2000, JF- 00180, on Fraxinus excelsior, associated with H. rubiginosum; Rimont, Las Muros, 19 May 2001, JF-01096, on Fraxinus excelsior (isotype); Rimont, Grillou, 19 May 2001, JF-01097, on Fraxinus excelsior; Rimont, Las Muros, 16 Aug. 2003, JF-03139, on Populus tremula, associated with H. perforatum, H. rubiginosum and Eutypa sparsa. Prat Communal, Loumet, 1000m, 03 Sept. 2004, JF-04215, on Salix sp.Saint Jean de Verges, Villeneuve du Bosc, 13 Dec. 1998, JF-98210, on Fraxinus excelsior. Deux Svres (79): Virollet , Fort de Chiz, 27 Apr. 2004, JF-04046, on bark of Acer monspessulanus. Finistre (29): Plohars, Pont Douar, Fort de Carnot, 26 Oct. 2002, leg P. Leroy, JF-02204, on Fraxinus excelsior. Loir et Cher (41): St Georges du Cher, Camping, 17 Nov. 2003, PL-2467A, leg. P. Leroy, on Fraxinus excelsior. Pyrnes Atlantiques (64): Auterrive, Ile du Gave d'Oloron, 06 Nov. 2003, JF-03225, on Fraxinus excelsior. Vende (85): Avrill, Bois de la Garde, 05 Jun. 2003, JF603091, on Fraxinus excelsior.

Notes: Hypoxylon petriniae is a new name given to a common and widespread fungus previously known as H. rubiginosum var. cercidicola (Petrini & Mller, 1986) and H. cercidicola (Granmo, 1999). Both species concepts referred to Diatrype cercidicola Berk. & Curtis ex Peck and H. suborbiculare Peck, a later name given by Peck, based on better material, to the fungus he first identified to D. cercidicola.

On the other hand, Ju & Rogers (1996), refering to the same type collections, erected H. cercidicolum to replace H. moravicum Pouzar (Pouzar, 1972), and included the fungus corresponding to H. rubiginosum var. cercidicola sensu Petrini & Mller within their concept of H. rubiginosum. The epithet cercidicola became therefore ambiguous, while the morphological differences of the variety cercidicola with H. rubiginosum pointed out by Petrini & Mller and Granmo were sound enough to consider H. rubiginosum sensu Ju & Rogers as an assemblage of two different species, one with vinaceous stromatal surface, the other one with rust stromatal surface.

HPLC profiling of material of Hypoxylon species from France, Germany, Switzerland and United Kingdom, along with the type of H. suborbiculare Peck., allowed for a better understanding of this nomenclatural situation which is much confused from the beginning (Stadler et al., 2004b).

The species with thin, vinaceous stromata called H. rubiginosum var. cercidicola or H. cercidicola proved to differ from the typical H. rubiginosum in lacking mitorubrin and in containig BNT, while they both contain rubiginosins A and C. H. petriniae appears to be the only temperate species with both BNT and rubiginosins. This striking difference of secondary metabolites, along with morphological differences reporded by Petrini & Mller (1986) and Granmo (1999), and evidence of a Virgariella-like anamorph (Stadler et al., 2004b) versus a Nodulisporium-like in H. rubiginosum (Ju & Rogers, 1996) confirmed this species was different from H. rubiginosum. In order to avoid further confusions related to the epithet cercidicola, this species was named H. petriniae in honour of Liliane Petrini who first recognized the peculiarities of this taxon (Stadler et al., 2004b).

HPLC analyses also proved H. suborbiculare lacks BNT, a very stable metabolite which can be detected from very aged material, and therefore cannot be a synonym of H. petriniae. However, the results of HPLC analyses of Peck's material are not fully conclusive, for they revealed the presence of prevailing unknown metabolites that could be artefacts due to a preservative treatment, along with rubiginosin C and traces of mitorubrin and orsellinic acid. These results are slightly deviating from those obtained from fresh material of H. cercidicolum sensu Ju & Rogers (1996) (= H. moravicum Pouzar) in which mitorubrin is the prevailing metabolite along with rubiginosin A. The question of the identity of H. cercidicolum is still pending until fresh material corresponding to H. suborbiculare is found in North America and submitted to HPLC (Stadler et al., 2004b).

Hypoxylon petriniae is readily distinguished from other Hypoxylon species with effused vinaceous brown stromata in having orange KOH-extractable pigments. Moreover, its thin stromata with usually black margins and a marked host preference for Fraxinus make it a rather distinctive taxon. These subtle morphological differences are more obvious when it is found growing close to H. rubiginosum or H. perforatum on a same branch, which occurs sometimes and provides a good training to the field mycologist..