Stegonsporiicola aurantiaca Voglmayr, sp. nov.

Index Fungorum number: IF 902413; Mycobank number: MB 902413; Facesoffungi number: FoF 16072; Fig. 1

Etymology – With reference to the orange conidiomata and conidia.

Holotype – WU-MYC 0049454

Fungicolous on effete conidiomata and stromata of Stegonsporium. Sexual morph: Not observed. Asexual morph: Conidiomata 0.5–1.5 mm diam, 200–350 µm high, sporodochial, immersed to erumpent, oval, polyangular to circular, surrounded by bark flaps. Conidiophores hyaline, branched, with clamps at septa, 2.5–6.5 µm wide, wall distinctly swelling to 2.5 µm with age. Conidiogenous cells holoblastic, monoblastic, terminal, hyaline, without scars or denticles. Conidia (13–)16–21(–27)×(11–)13.8–17.6(–21.6) μm (x̅=18.6×15.7 μm, n=162), subglobose to globose, young subhyaline, pale yellow to orange with age, dictyosporous, bulbil-like, composed of 5–10 swollen cells of 5–12 µm diam., with a hyaline, smooth wall and fine pale orange granular contents, which sometimes fuse to an orange guttule of 1.3–4 μm diam.

Culture characteristics – Colonies on CMD cottony, first cream, soon becoming bright orange, reverse bright orange, becoming orange brown in the centre, reaching 55–60 mm diam. in 28 days at 22 °C. Mycelia are immersed at margins, superficial in the centre, effuse with diffuse regular edge. No sporulation observed in pure culture.

Material examined – (all on effete conidiomata or stromata of Stegonsporium sp., Stilbosporaceae, on Acer pseudoplatanus, Aceraceae)—AUSTRIA, Oberösterreich, Raab, Wetzlbach, 24 Dec. 2017, H. Voglmayr, BOS (WU-MYC 0049454, holotype), ex-type, CBS 149659; Niederösterreich, Gießhübl, Wassergspreng, 11 February 2009, H. Voglmayr (WU-MYC 0049455, paratype); Niederösterreich, Hardegg, Hammerschmiede, 8 May 2008, H. Voglmayr (WU-MYC 0049456, paratype); Niederösterreich, Lahnsattel, Donaudörfl, 23 April 2008, H. Voglmayr, LO (WU-MYC 0049457, paratype); Niederösterreich, Mariensee, 24 May 2010, H. Voglmayr (WU-MYC 0049458, paratype); Oberösterreich, Raab, Rotes Kreuz, Rothmayrberg, 15 May 2021, H. Voglmayr (WU-MYC 0049459, paratype); Oberösterreich, St. Willibald, Große Sallet, 30 April 2022, H. Voglmayr (WU-MYC 0049460, paratype); Steiermark, Gröbming, Öfen, 31 May 2009, H. Voglmayr (WU-MYC 0049461, paratype); Steiermark, Kleines Sölktal, Schwarzensee, 1 June 2009, H. Voglmayr (WU-MYC
0049462, paratype).

GenBank numbers – SSU-ITS-LSU: OQ102368 (WUMYC 0049454, ex holotype), OQ102369 (WU-MYC 0049457, ex paratype).

Notes – The bright orange sporodochial conidiomata producing bulbil-like dictyoconidia with hyaline walls and orange granular content are characteristic for the species. Upon closer examination, S. aurantiaca was constantly found growing on effete conidiomata and stromata of Stegonsporium sp. (Stilbosporaceae, Diaporthales), indicating a mycoparasitic habit. In suitable habitats, it seems to be rather common but easily overlooked on dead corticated branches of Acer pseudoplatanus in spring, following the development of its Stegonsporium host which mostly occurs during the winter months, and it is apparently host-specific on Stegonsporium.

Figure 1 – Stegonsporiicola aurantiaca (a–c, g, n, o WUMYC 0049454, holotype; d WU-MYC 0049460; e, f CBS 149659, ex holotype; h WUMYC 0049457; i–m WU-MYC 0049461). a, b Frontal view of the sporodochial conidiomata. c Conidioma in section, growing on an effete conidioma of Stegonsporium (arrows). d Conidioma in section, growing on effete stroma of Stegonsporium; arrows denoting perithecia of the host. e Frontal view of the culture. f Reverse view of the culture. g Conidioma in section with conidia on top and dead dark brown conidia of Stegonsporium mostly at the base. h, o Conidia. i, j Clamps on hyphae. k–n Developing conidia on conidiophores with clamps (arrows). All microscope mounts in water. Scale bars: a=1 cm, b–d=200 µm, g=50 µm, h=20 µm, i, j=5 µm, k–o=10 µm