Halobyssothecium sichuanense Y. Qing & H. Zhang, sp. nov.

Index Fungorum number: IF 559791; MycoBank number: MB 559791; Facesoffungi number: FoF 12672; Fig. 1

Etymology – Referring to this species collected from Sichuan.

Holotype – CN12 (IFRD).

Saprobic on decaying wood in freshwater habitats. Sexual morph: Undetermined. Asexual morph: Conidiomata 90–180 µm high, 180–310 µm in diam, pycnidial, scattered, semi-immersed to superficial, ellipsoidal, dark brown to black, unilocular, sometimes white at the top, ostiolate. Conidiomatal wall 19–35 μm, composed of thick-walled, dark brown cells of textura angularis. Conidiophores reduced to conidiogenous cells. Conidiogenous cells 3–7×2–4 μm, holoblastic, determinate, cylindrical to subcylindrical, aseptate, hyaline, smooth-walled. Conidia 8–15 × 6–8 µm (x̅= 12.4 × 6.7 μm, n = 20), ellipsoidal to
ovoidal, aseptate, rarely 1-septate, hyaline, thin-walled, smooth, with one large guttule or several smaller ones in each cell.

Culture characteristics – On PDA, colony circular, conidia germinated within 24 h, reaching 23 mm in 1 month at room temperature (25 °C), grey to brown from above, dark brown from below, surface rough and dry, umbonate, with dense white mycelium in the middle, regular edge.

Material examined – China, Sichuan Province, Yibin, Changning River, on submerged wood, 29 March 2021, Y. Qing, CN12 (IFRD, holotype).

GenBank numbers – ITS=ON124829, LSU=ON124829.

Notes – Halobyssothecium sichuanense is a distinct species and close to the sexual species H. thailandica (Fig. 2). Halobyssothecium bambusicola, H. kunmingense, H. phragmitis and H. unicellulare are also known from their asexual morphs. Halobyssothecium sichuanense morphologically differs from H. bambusicola and H. phragmitis in conidial shape (ellipsoidal to ovoidal in H. sichuanense vs. globose to obovate in H. bambusicola vs. ovoid to fusoid-ellipsoidal in H. phragmitis, Calabon et al. 2021); from H. kunmingense in having smaller conidiomata (210–250 μm high vs. 90–180 μm high, Dong et al. 2020); and from H. unicellulare in having larger conidia (8–15×6–8 μm vs. 6–9×4–5 μm) and cylindrical to subcylindrical conidiogenous cells as compared to globose, subglobose to pear-shaped ones in H. unicellulare (Hyde et al. 2016). All of the four known asexual species are phylogenetically distinguished from our new isolate. Therefore, it is introduced as a new species H. sichuanense.

Figure 1 – Halobyssothecium sichuanense (CN12, holotype). a, b Colonies on substrate. c Developing conidia attach to conidiogenous cell. d–h Conidia. i Germinating conidia on PDA. j Surface view of culture on PDA. k Reverse view of culture on PDA. Scale bar: c=35 µm, i=20 µm, d–h=5 µm

Figure 2 – The best scoring Maximum Likelihood (RAxML) tree of family Lentitheciaceae, based on LSU, SSU, ITS and TEF1-α sequence dataset. The tree is rooted with Corynespora smithii (CABI5649b) and Corynespora cassiicola (CBS 100822). Maximum likelihood support values greater than 70% and Bayesian posterior probabilities greater than 0.95 are shown near the nodes. Newly strain in this study is shown in red, and new species is shown in blue. Ex-type strains are shown in bold. The optimal score of RAxML analysis results ln L=− 36,913.321704. Estimated base frequencies are as follows: A=0.238921, C=0.248704, G=0.273797, T=0.238578; substitution rates AC=1.113695, AG=2.495521, AT=1.345905, CG=1.136632, CT=5.923529, GT=1.000000; gamma distribution shape parameter a=0.220373