Helicosporium sexuale Boonmee, Promputtha & K.D. Hyde, sp. nov.

Index Fungorum number: IF 558542; MycoBank number: MB 558542; Facesoffungi number: FoF 09194; Fig. 1

Etymology – ‘sexuale’ referring to sexual morph.

Holotype – MFLU 21-0104

Saprobic on decaying wood. Sexual morph Ascomata 185–235 × 116–214 µm, superficial, solitary, scattered, globose to subglobose, yellowish brown, shiny when fresh, with sparsely setae, minutely papilla, ostiolate. Setae 73–88 × 4–8 µm, stiff, tapering to an acute tip, septate, dark brown. Peridium 8–12 wide µm, composed of 2–3- layer cells of textura angularis, yellowish brown to hyaline cells, lacking pseudoparaphyses. Asci 54.5–76×11–20 µm, 8-spored, bitunicate, cylindric-clavate, rounded at apex, sessile. Ascospores 51.5–71×3–4 µm, fasciculate, cylindrical, narrowly fusiform, subacute ends, straight to slightly curved, 9–11-spetate, not constricted at septa, hyaline, smoothwalled. Asexual morph Undetermined.

Culture characteristics – Ascospores germinating on MEA within 24 h and many germ tubes produced from ascospore cells. Colonies growing on MEA slowly, less than 5 mm diam. in 7 days at room temperature, slightly raised-radially with entire edge, brown to dark brown, asexual conidia not formed at 60 days.

Material examined – THAILAND, Chanthaburi Province, Laem Sing, Ban Phlio, on decaying wood in a terrestrial habitat, 7 July 2016, S. Boonmee, NTP15 (MFLU 21-0104, holotype), ex-type living culture, MFLUCC 16-1244.

GenBank numbers – ITS=MZ538503, LSU=MZ538537, RPB2=MZ567111, TEF1-α=MZ567082.

Notes – Phylogenetic analysis indicates that Helicosporium sexuale (MFLUCC 16-1244) is basal to H. vegetum strains (CBS 254.75, CBS 269.52, CBS 941.72, NBRC 303045 and NBRC 9014) with 96% MLBS, 1.00 BYPP support (Fig. 2); the phylogeny also shows that it is a distinct species (Fig. 2). Helicosporium sexuale differed from H. vegetum and other species by the capacity to form its sexual morphs (Fig. 1). We therefore, introduce H. sexuale as a new sexual species in Helicosporium.

Figure 1 – Helicosporium sexuale (MFLU 21-0104, holotype). a Superficial ascomata on decaying wood substrate. b Squash mount of ascoma showing peridium. c Setae. d–f Asci. g–j Ascospores. k Germinated conidium. l, m Culture on MEA from surface and reverse after 1 month. Scale bars: a=200 µm, b=100 µm, c–f=40 µm, g–k=20 µm

Figure 2 – Maximum likelihood phylogenetic tree based on a combined ITS, LSU and TEF1-α sequence data of Helicosporium taxa and related genera in Tubeufiaceae. Thirty-two taxa are included in the combined analyses which comprise a total of 2367 characters. Berkleasmium thailandicum (MFLUCC 15-1248 and MFLUCC 17-1984) are selected as the outgroup taxa. The best RAxML tree with a final likelihood value of − 8690.594891 is presented. RAxML analysis yielded 609 distinct alignment patterns and 25.02% of undetermined characters or gaps. Estimated base frequencies were as follows: A=0.231326, C=0.266395, G=0.273200, T=0.229079, with substitution rates AC=1.159455, AG=2.641204, AT=1.962575, CG=0.673701, CT=9.846706, GT=1.000000; gamma distribution shape parameter alpha=0.182397. Bootstrap support values for maximum likelihood (MLBS, left) equal to or greater than 70% is given above the nodes. Bayesian posterior probabilities (BYPP, right) equal to or greater than 0.95 are given above the nodes. Ex-type strains are in bold and newly generated sequences are in blue