Setoseptoria bambusae Senan., J.Z. Fu & K.D. Hyde, sp.nov.

Index Fungorum number: IF 900416; MycoBank number: MB 900416; Facesoffungi number: FoF 12786; Fig. 1

Etymology – based on the host genus Bambusa.

Saprobic on dead stem of Bambusa sp. Sexual morph: Clypeus spread over ascomata, lenticular, comprise of small, highly melanized, black, compressed cells. Ascomata 180–210 µm high, 150–190 µm diam. (x=200 × 160 µm, n=10), superficial to erumpent, solitary to rarely gregarious, scattered, globose, uni to multiloculate, black, short papillate, ostiolate. Ostiole canal comprises filiform, hyaline pseudoparaphyses. Peridium 8–10 µm wide at the base, 15–20 µm wide at the sides, thick, comprised of heavily pigmented, thick-walled, dark brown, tightly packed cells of textura angularis. Hamathecium comprising numerous, 1.5–2.5 µm wide (x=2 µm), filamentous, branched, septate, pseudoparaphyses. Asci 85–100 × 12–15 µm (x = 96 × 13 µm, n = 20), 8-spored, bitunicate, fissitunicate, clavate to cylindric-clavate, pedicellate, apex rounded with a minute ocular chamber. Ascospores 20–25 × 3–4.5 µm (x = 23 × 4 µm, n = 20), overlapping uniseriate to biseriate, narrowly fusiform, 1–3-septate, deeply constricted at the middle septum, slightly constricted at the other septa, hyaline, asymmetric, narrowly rounded at the ends, one large guttule in each cell or multi-guttulate, surrounded by a thin (1.5–3 µm wide) mucilaginous sheath. Asexual morph: Undetermined.

Culture characteristics – Colonies on PDA reaching 5 cm diam. after 14 days in dark at 25 °C, flat, circular, filamentous margin, zonate, greenish grey, wooly aerial mycelial clots crowed on surface, margin with white filamentous hyphae, reverse dark grey with white margin, no sporulate, no pigments produced.

Material examined – China, Guangdong Province, Guangzhou City, a freshwater stream near Baiyun Mountain (23° 09′ 35″ N 113° 17′ 40″ E), stem of Bambusa sp., 23 September 2021, Jizhen Fu, SHB 1 (MHZU 22-0133, holotype), ex-type culture ZHKUCC 22-0228.

GenBank numbers – ITS: OR164941, LSU: OR164969, SSU: OR150418.

Notes – The combined gene analysis of ITS, LSU, SSU and tef1-α sequences (Fig. 2) showed that our isolate (ZHKUCC 22-0228) grouped with Setoseptoria species and they formed a distinct sub-clade between S. phragmitis and S. magniarundinacea with ML/BI=81%/0.95 support. The base pair differences of ITS, LSU, and SSU loci of our isolate with S. phragmitis were 3.32%, 1.4%, 0.29% while these differences for S. magniarundinacea are 9.98%, 1.63%, 0.19% respectively.

Figure 1 – Setoseptoria bambusae (MHZU 22-0133, holotype). a Ascomata on substrate. b Close-up view of ascoma. c Vertical cross section of ascoma. d Peridium. e Pseudoparaphyses. f–h Asci. i–o Ascospores. p Germinating ascospores. q Surface view of colony on PDA. r Reverse view of colony on PDA. Scale bars: c=100 µm, f–h=50 µm, i–o=12.5 µm, d, p=25 µm

Figure 2 – Phylogram generated from maximum likelihood analysis based on combined ITS, LSU, SSU and tef1-α sequence data which comprised 3408 characters (ITS=601, LSU=856, SSU=1,022, tef1-α=929). The best scoring RAxML tree with a final likelihood value of − 10,069.029510 is presented. The matrix had 646 distinct alignment patterns, with 28.8% of undetermined characters or gaps. Estimated base frequencies were as follows: A=0.237780, C=0.274787, G=0.244558, T=0.242875; substitution rates: AC=1.519491, AG=2.922803, AT=1.750316, CG=1.738507, CT=9.995833, GT=1.0; gamma distribution shape parameter α=0.334816. Bootstrap support for maximum likelihood (ML) equal to or greater than 50% and clade credibility values greater than 0.90 (the rounding of values to 2 decimal proportions) from Bayesian inference analysis are labelled at each node. Ex-type strains are in bold, while the new isolate is indicated in blue bold. The tree is rooted to Massarina arundiaaceae (H3953) and M. cisti (CBS 266.62)