Rhexoacrodictys nigrospora Boonmee, D.F. Bao & K.D. Hyde, sp. nov.
Index Fungorum number: IF 558545; MycoBank number: MB 558545; Facesoffungi number: FoF 09200; Fig. 1
Etymology – The specific epithet “nigrospora” refers to the black conidia.
Holotype – MFLU 21-0073
Saprobic on decaying bark. Sexual morph Undetermined. Asexual morph Hyphomycetous. Colonies superficial, dark brown to black. Mycelium superficial and immersed, composed of branched, septate, pale brown to brown hyphae, 1–2 µm wide, verruculose or finely echinulate-walled. Conidiophores micronematous or semi-macronematous, mononematous, cylindrical filamentous, flexuous, scattered to grouped, simple, single or a loose cluster brown to dark brown, smooth-walled. Conidiogenous cells monoblastic, polyblastic, integrated, terminal and intercalary or discrete, determinate. Conidia 15–31×16–33 µm (x̅=22×23 µm, n=20), holoblastic, solitary, dry, acrogenous, simple, globose to subglobose, truncate at the base, multi-septate, dark brown when immature, becoming black and faintly septate at maturity, thick and smooth-walled.
Culture characteristics – Conidia germinating on PDA within 24 h and germ tubes arising from terminal end cell. Colonies on malt extract agar (MEA), reaching 3.5 cm diam. after 2 weeks at room temperature, colonies circular, low convex, surface slightly rough with entire edge, around the white to greyish brown, dark green to black at the reverse.
Material examined – THAILAND, Phetchabun Province, Lom Sak, on decaying bark, 25 July 2019, S. Boonmee, LSP03 (MFLU 21-0073, holotype), ex-type living culture, MFLUCC 21-0096; Mukdahan Province, on decaying wood, 24 July 2019, S. Boonmee, WD09 (MFLU 21-0074), living
culture MFLUCC 21-0097.
GenBank number – LSP03: ITS = MZ538524, LSU = MZ538558, TEF1-α = MZ567100; WD09: ITS= MZ538525, LSU = MZ538559, SSU = MZ538574, RPB2=MZ567113, TEF1-α=MZ567101.
Notes – Rhexoacrodictys nigrospora differs from the type Rh. erecta and other species in having cylindrical filamentous, flexuous conidiophores and globose to subglobose, faintly septate, dark brown to black conidia (Baker et al. 2002; Xiao et al. 2018). Phylogenetically, Rh. nigrospora forms a distinct lineage basal to Rhexoacrodictys species with 100% MSBS, 1.00 BYPP support (Fig. 2). Currently, only four species listed in this genus (Species Fungorum 2021). We, therefore introduce Rh. nigrospora (Fig. 1) as the fifth species in Rhexoacrodictys based on morphological and phylogenetic analyses.
Figure 1 – Rhexoacrodictys nigrospora (MFLU 21-0073, holotype). a, b Conidiomata on the substrate. c Squash of mount of conidia. d Conidiophores with minutely conidiogenous cells. e–g Conidia. h Germinated conidium. i, j Culture on PDA from surface and reverse. Scale bars: c, e, f=10 µm, d, g=20 µm
Figure 2 – Maximum likelihood phylogenetic tree based on a combined LSU, ITS, SSU, TEF1-α and RPB2 sequence data of genera in Savoryellaceae. Conioscypha aquatica MFLUCC 18-1333 and C. submersa MFLU 18-1639 are selected as the outgroup taxa. 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. Ex-type strains are in bold and newly generated sequences are in blue