Parahelicomyces dictyosporus M.S. Calabon, E.B.G. Jones & K.D. Hyde, sp. nov.

Index Fungorum number: IF 559841; Mycobank number:  MB 559841; Facesofungi number: FoF 12738; Fig. 1

Etymology – “dictyosporus” referring to dictyospores of this fungus.

Holotype–  MFLU 22-0119.

Saprobic on submerged decaying wood in a freshwater stream. Sexual morph: Undetermined. Asexual morph: Hyphomycetous, dictyosporous. Conidiophores lacking. Conidiogenous cells holoblastic, monoblastic, integrated, cylindric, apical, hyaline to pale brown. Dictyospores 40–70×25–70 μm (x̄=52.3×43.1 μm, n=20) acrogenous, carbonaceous, friable, solitary, mostly globose, subglobose to ovoid indistinctly dictyoseptate, verrucose, brown when young, dark brown to black when matured.

Culture characteristics: – Conidia germinating on malt extract agar (MEA) and producing germ tubes within 24 h. Colonies growing on MEA, circular, with flat surface, edge entire to filiform, reaching 30–35 mm in 4 weeks at 25 °C, from above brown to dark brown, from below dark brown. Mycelia superficial and partially immersed, branched, septate, hyaline to pale brown. Sporulation in culture. Conidiophores lacking. Conidiogenous cells holoblastic, monoblastic, integrated, cylindric, apical, hyaline to pale brown. Dictyospores 35–70×25–70 μm (x̄=53.1×45.2 μm, n=50) acrogenous, carbonaceous, friable, solitary, variable in shape, broadly oval to ellipsoidal when young, mostly globose when mature, indistinctly dictyoseptate, verrucose, hyaline to pale brown when young, dark brown to black when matured.

Habitat and distribution: – Parahelicomyces dictyosporus was observed from submerged decaying culms of Spartina sp. in tropical saltmarsh area, and is currently only found in Thailand.

Material examined: – Thailand, Prachuap Khiri Khan, Pran Buri, 12°23′43.0″N 99°58′28.3″E, on submerged decaying culms of Spartina sp. (Poaceae), 20 July 2019, M.S. Calabon, MCFWBB (MFLU 22-0119, holotype), ex-type living culture, MFLUCC 22-0080.

GenBank numbers – ITS=OP216409, LSU=OP216404, TEF1-α=OP251194, RPB2=OP251198.

Notes – The isolate MFLU 22-0119 is morphologically similar with Tubeufia dictyospora (MFLU 17–1173) with globose to subglobose dictyospores but the latter has a larger dictyospores [60–100 × 60–70(–80) μm vs. 40–70 × 25–70 μm] (Lu et al. 2018). NCBI BLASTn of the sequences of isolate MFLUCC 22-0119 showed the this is closely related to Parahelicomyces: LSU (P. hyalosporus CBS 283.51, 99.51%), ITS (P. aquaticus MFLUCC 16-0234, 92.20%), TEF1-α (P. aquaticus MFLUCC 16-0234, 98.46%; P. quercus MFUCC 17-0895, 98.02%), and RPB2 (P. hyalosporus AFTOL-ID, 94.30%). The multi-locus phylogenetic analysis placed the isolate within Parahelicomyces in a subclade with a terrestrial species P. chiangmaiensis and the freshwater species P. aquaticus (Fig. 2). In pairwise nucleotide comparisons of P. dictyosporus with the sister taxon P. chiangmaiensis (MFUCC 21-0159), there is a nucleotide differences of 3.36% (13 bp) in ITS (of 387 nucleotides altogether), 1.86% (16 bp) in TEF1-α (of 861 nucleotides altogether), and 3.26% (26 bp) in RPB2 (of 797 nucleotides altogether). Parahelicomyces dictyosporus is a dictyosporous species and this morphological character is unique compared to other Parahelicomyces species with cylindrical, branched conidiophores, and acropleurogenous, helicoid conidia. Parahelicomyces dictyosporus is the first species of Parahelicomyces reported from marine habitats, and the third species recorded from aquatic environments in Thailand, wherein Para. aquaticus and Para. talbotii were earlier recorded by Lu et al. (2018).

Figure 1 – Parahelicomyces dictyosporus (MFLU 22-0119, holotype). a Colonies in natural substrates. b–f Dictyochlamydospores. g Germinated conidium. h, i Colonies on MEA from surface and in reverse. j Dictyochlamydospores in culture. k–q Development of dictyochlamydospores. r–u Dictyochlamydospores Scale bars: a, j=100 µm, b–g, k–u=20 µm

Figure 2 – Phylogram generated from maximum likelihood analysis based on combined LSU, ITS, TEF1-α, and RPB2 sequence data representing Tubeufiaceae (Tubeufiales). One hundred strains are included in the combined analyses which comprised 3726 characters (806 characters for LSU, 967 characters for ITS, 910 characters for TEF1-α, and 1043 characters for RPB2) after alignment. Bezerromyces pernambucoensis (URM7412) and Bezerromyces pseudobrasiliensis (URM7414) in Tubeufiaceae (Tubeufiales) were used as the outgroup taxa. The best scoring RAxML tree with a final likelihood value of−44,231.079169 is presented. The matrix had 1741 distinct alignment patterns, with 33.38% of undetermined characters or gaps. Estimated base frequencies were as follows: A=0.242684, C=0.256704, G=0.264190, T=0.236422; substitution rates: AC=1.008141, AG=3.810958, AT=1.774984, CG=0.705605, CT=6.978420, GT=1.000000; gamma distribution shape parameter α=0.240917. Bootstrap support values for ML equal to or greater than 70% are given above the nodes (left side). Bayesian posterior probabilities (BYPP) equal to or greater than 0.95 are given above the nodes (right side). Ex-type strains are in bold and newly generated sequences are in blue