Mucispora maesotensis Chuaseehar., Nuankaew, Somrith. & Boonyuen, sp. nov.

Index Fungorum number: IF 900199; Mycobank number: MB 900199; Facesoffungi number: FoF 15105; Fig. 1

Etymology – The specific epithet “maesotensis” refers to the Mae Sot District, Tak Province, Thailand where is the type locality of this fungus.

Holotype – BBH 49600

Saprobic on submerged wood in freshwater habitat. Sexual morph: not observed. Asexual morph: Colonies on natural substratum sparse, scattered, hairy, black. Mycelium 2–2.5 μm diam, mostly immersed, composed of branched, septate, smooth-walled, pale brown to brown hyphae. Conidiophores 46–107.7 × 5–6.4 μm ( x̄= 73.3 × 5.6 μm, n = 15), macronematous, mononematous, solitary or in small groups on compactly aggregated cells, simple, cylindrical, erect, straight, 2–6-septate, smooth-walled, brown below, paler towards the apex, with up to 3 or more percurrent extensions. Conidiogenous cells holoblastic, monoblastic, integrated, terminal, cylindrical, pale brown. Conidia 24.5–37 × 14.2–22.5 μm (x̄= 30.8 × 17.7 μm, n = 25), acrogenous, solitary, ellipsoidal to obovoid, apex rounded and base truncate, 3-septate, smooth-walled, dark brown to black, often paler at the basal cell, with unobservable septa at maturity. Conidial secession schizolytic.

Culture characteristics – Colonies on PDA reaching 12–15 mm diam., after 27 days at 25 °C, glabrous, white, round, margins mostly entire, soluble pigment absent, exudates absent, reverse white with dark grey at center. Vegetative hyphae on PDA medium 1.5–4 μm diam., composed of branched, septate, smooth-walled, subhyaline to pale brown. Conidiophores 16.1–111.5 × 4.6–6.2 μm (x̅=54.2 × 5.4 μm, n=15), macronematous, mononematous, solitary, simple, cylindrical, erect, straight, 1–5-septate, smooth-walled, brown, paler towards the apex, with up to 5 or more percurrent extensions. Conidiogenous cells holoblastic, monoblastic, integrated, terminal, cylindrical, pale brown. Conidia 27.3–33.5 × 14.5–19 μm (x̅=29.6 × 17 μm, n=30), acrogenous, solitary, ellipsoidal to obovoid, apex rounded and base truncate, 3-septate, smooth-walled, dark brown to black, basal cell paler. Conidial secession schizolytic.

Material examined – Thailand, Tak Province, Mae Sot District, Pha Daeng Waterfall Nature Trail, on submerged wood of an unidentified plant in a small freshwater stream, 24 May 2022, N. Boonyuen, isolate FF01097 (BBH 49600, holotype), ex-type, TBRC-BCC 95165; isolate FF01097.01 (BBH 49601, isotype), living culture, TBRC-BCC 95166.

GenBank numbers – TBRC-BCC 95165: ITS=OQ121935, LSU = OQ121953, rpb2= OQ116758, SSU: OQ121944, tef1-α=OQ116766; TBRC-BCC 95166: ITS=OQ121936, LSU = OQ121954, rpb2= OQ116759, SSU: OQ121945, tef1-α=OQ116767.

Notes – In the phylogenetic analysis of Mucispora, isolates from the present study, developed a particular phylogenetic relationship to M. obscuriseptata with 100% ML bootstrap and 1.00 BYPP values (Fig. 2). Our isolates share some morphological characteristics with M. obscuriseptata including mononematous, simple conidiophores, cylindrical conidiogenous cells with ellipsoidal to obovoid, dark brown, 3-septate conidia (Fig. 1). However, M. obscuriseptata differs from M. maesotensis because its conidia are predominantly surrounded by a hyaline mucilaginous sheath and have longer conidiophores (80–170×5–7.5 μm; Yang et al. 2016). In culture, these two species mainly differ in the size of conidiophore and conidial septation. Mucispora maesotensis has unbranched, smaller conidiophores and 3-septate conidia, while M. obscuriseptata has branched, longer (up to 367×4.5–9 μm) conidiophores and 2−3-septate with rarely uniseptate conidia (Yang et al. 2016). Thus, we propose Mucispora maesotensis as new to science.

Figure 1 – Mucispora maesotensis (BBH 49600, holotype). a, b Colonies on natural substrate. c–e Conidiophores with conidia. f Conidiophore. g–i Conidia. j–n Hyphae and conidiophores with conidia on PDA. o–r Conidia. Upper and reverse views of culture on PDA after 27 days at 25 °C. Scale bars: a, b=100 μm, c–r=20 μm

Figure 2 – Phylogram generated from maximum likelihood analysis (RAxML) of the Fuscosporellaceae based on the combined ITS, LSU and rpb2 sequence data. Twenty-eight taxa are included in the combined analyses, which comprise 2515 characters with gaps. Canalisporium caribense (SS 03839) and Pleurothecium semifecundum (CBS 131271) were used as the outgroup. The best scoring RAxML tree with a final likelihood value of − 14,326.553200 is presented. The matrix had 1,199 distinct alignment patterns, with 34.92% of undetermined characters or gaps. The proportion of invariable sites was 0.224117. Estimated base frequencies were as follows: A=0.225509, C=0.298033, G=0.295650, T=0.180808; substitution rates: AC=1.094752, AG=2.429464, AT=1.688220, CG=0.843807, CT=6.850439, GT=1.00000; gamma distribution shape parameter α=0.516382. Bootstrap support values for ML equal to or greater than 70% and BYPP equal to or greater than 0.95
are given near the nodes. T=ex-type strain. The newly generated sequences are indicated in blue bold