Phaeocytostroma yomense Boonmee, Chandrasiri & K.D. Hyde, sp. nov.

Index Fungorum number: IF 558544; MycoBank number: MB 558544; Facesoffungi number: FoF 09958; Fig. 1

Etymology – In reference to the Yom River where the holotype was collected.

Holotype – MFLU 21-0070

Saprobic on decaying submerged wood in the river. Sexual morph Undetermined. Asexual morph Coelomycetous. Conidiomata 337–452 μm high, 246–393 μm diam., pycnidial, white cream, superficial, scattered, gregarious, covered by massy brown hyphal mats, subglobose, uniloculate, transparent when fresh, simply fragile when dry, ostiole, dehiscence by breakdown of upper wall of conidiomata. Conidiomata walls easily fragile, difficult to observe, conidiophores and conidiogenous cells not seen. Conidia 14–23×3–6 μm (x̅=18×4.5 μm, n=20), cylindrical-ellipsoid, oblong allantoid, asymmetrical with obtuse ends, aseptate, pale brown, smooth-walled.

Culture characteristics – Conidium germinating on water agar within 12 h at room temperature. Colonies on PDA, fast growing, reaching 5 cm diam., in 2 weeks, slightly effuse, entire edge, brown to dark brown in surface, dark brown in reverse, mycelium superficial, partially immersed, brown, radiating outwards.

Material examined – THAILAND, Phayao Province, Pong, Yom River, on decaying submerged wood in the river shore, 18 December 2019, S. Boonmee and K.S.U. Chandrasiri, YR2 (MFLU 21-0070, holotype), ex-type living culture, MFLUCC 21-0093.

GenBank numbers – ITS=MZ538521, LSU=MZ538555.

Notes – Phaeocytostroma yomense shares similar conidial features such as cylindrical-ellipsoid to oblong shapes and pale brown colour to species Ph. sacchari (Sutton 1964, 1980), but Ph. yomense differs from Ph. sacchari in conidiomatal features such as superficial, bright pigmented and covered by hyphal mats. Phylogenetically, Ph. yomense is position in a distinct lineage basal to the strain of Ph. plurivorum (CBS 113835) with 98% MLBS, 1.00 BYPP support (Fig. 2). A comparison of the ITS sequence between Ph. yomense (MFLUCC 21-0093) and Ph. plurivorum (CBS 113835) showed 1.54% (9/581 bp with 7 gabs difference). However, Ph. yomense differs from Ph. plurivorum (Sutton 1980) in having white cream and smaller conidiomata (337–452 × 246–393 μm vs. up to 700 × 300–400 μm). Phaeocytostroma yomense differs from other species by its current occurrence as an aquatic taxon in a freshwater habitat and having superficial, white cream pigmented, covered by massy hyphal mat conidiomata and pale brown conidia (Fig. 1). We therefore, introduce a new species Ph. yomense based on its morphological distinctness and phylogenetic affinity.

Figure 1 – Phaeocytostroma yomense (MFLU 21-0070, holotype). a, b Appearance of white conidiomata on decaying submersed wood substrate. c–e Conidia. f Germinated conidium. g, h Culture on PDA from surface and reverse. Scale bars: a=100 μm, b=50 μm, c, e, f=20 μm, d=10 μm

Figure 2 – Maximum likelihood phylogenetic tree based on a combined ITS, LSU and TEF1-α sequence data of Phaeocytostroma taxa and some related genera in Diaporthaceae. The tree is rooted with Phomopsis viticola (UCD2009SB). 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. The newly generated sequence is in blue bold