Xenoastrosphaeriella trochus (D. Hawksw.) Phookamsak, H.B. Jiang, & K.D. Hyde, comb. nov. Fig. 54
≡ Astrosphaeriella trochus (Penz. & Sacc.) D. Hawksw., Bot. J. Linn. Soc. 82: 46 (1981).
≡ Melanomma trochus Penz. & Sacc., Malpighia 11(9-10): 401 (1897).
MycoBank number: MB 111138; Index Fungorum number: IF 111138; Facesoffungi number: FoF 08164;
Saprobic on Thysanolaena maxima (Poaceae), visible as black, opaque, cone-like, on the host surface. Sexual morph: Ascomata 570–810 μm high, 590–760 μm diam., carbonaceous, dark brown to black, opaque, solitary to gregarious, erumpent through the outer layers of the host tissue, becoming superficial, easily broken, conical to mammiform, with host cortex persisting as ruptured, reflexed, stellate, host remnants, around the base, uni-loculate, rarely bi-loculate, glabrous, ostiolate, with a minute papilla. Peridium 40–110 μm wide, of unequal thickness, poorly developed at the base, thicker at sides towards the apex, composed of small, dark opaque, melanized cells of textura prismatica or palisade-like. Hamathecium comprising dense, 0.5–1.5 μm wide, filiform, trabeculate, anastomosing at the apex, pseudoparaphyses, embedded in a hyaline gelatinous matrix. Asci (125–)160–190(–215) × 10–12(–14) μm (x̅ = 172.5 × 11.9 μm, n = 30), 8-spored, bitunicate, fissitunicate, subcylindrical to cylindric-clavate, short pedicellate, apically rounded, with well- developed ocular chamber. Ascospores (40–)45–55(–57) × 4.5–6 μm (x̅ = 48.2 × 5.6 μm, n = 30), overlapping 1–2-seriate, narrowly elongate fusiform with acute ends, brown to reddish brown, paler at the end cells, (3–)5-septate, slightly constricted at the septa, smooth-walled, with conspicuous mucilaginous sheath surrounded ascospores. Asexual morph: Undetermined.
Culture characteristics – Ascospores germinated on WA after 8 hours at 25°C under a dark condition. Colonies on PDA reaching 35–40 mm diam. after 4 weeks at 25–30°C, colonies circular, dense, slightly raised to convex, or dome-shaped, dull, surface slightly rough with small turfs and brown droplets, edge entire, velvety to floccose; colony from above, drak-green at the margin, grey-greenish at the center; from below, dark brown to black at the margin, paler at the center; not producing pigmentation in agar.
Material examined – China, Yunnan Province, Xishuangbanna, Mengla County, Xishuangbanna tropical botanical garden, on dead stem of Thysanolaena maxima, 27 April 2017, Phookamsak, IS001 (KUN-HKAS 107533), living culture, KUMCC 18-0194.
GenBank number – LSU: MT659668, SSU: MT659669, tef: MT653597, rpb-2: MT653598
Hosts – Various unidentified bamboo and stout grasses; Chusquea sp., Phragmites sp., Phyllostachys bambusoides, Thysanolaena maxima (Hawksworth 1981, Hawksworth & Boise 1985, Hyde & Fröhlich 1998).
Distributions – Chile, China (Xishuangbanna, Yunnan), Colombia, Ecuador, French Guiana, Japan, Indonesia, South Africa, Taiwan, Uganda (Hawksworth 1981, Hawksworth & Boise 1985, Hyde & Fröhlich 1998).
Notes – Astrosphaeriella trochus was designated for Melanomma trochus by Hawksworth (1981). However, the species should be transferred to Xenoastrosphaeriella based on multi-gene phylogeny and morphology. Xenoastrosphaeriella trochus is similar to X. tornata in having conical to mammiform, carbonaceous ascomata, cylindric-clavate asci and broadly fusiform, reddish brown ascospores, but differs in septa number and with or without a sheath (Phookamsak et al. 2015b, this study). Based on the present phylogeny (Fig. 53), X. tornata and X. trochus grouped together with high statistic support (100 % MLBS, 1.0 PP).
Xenoastrosphaeriella trochus is mostly similar to Astrosphaeriella exorrhiza in having (3–)5- septate, elongate-fusiform ascospores (Hawksworth & Boise 1985, Hyde & Fröhlich 1998). However, the species differs from A. exorrhiza in having smaller asci and ascospores [A. trochus: (44–)48–65(–72) × (5–)6–8(–9) μm vs. (68–)74–88 × 8–10 μm: A. exorrhiza] (Hawksworth & Boise 1985, Hyde & Fröhlich 1998). Astrosphaeriella exorrhiza was found on Thysanolaena maxima in Thailand (Phookamsak et al. 2015b) which is the same host of our new collection from Xishuangbanna, China. These two species maybe conspecific, however, this conspecific status will eventually need to be confirmed by molecular data.
Figure 53 – Phylogram generated from maximum likelihood analysis (RAxML) of genera in Astrosphaeriellaceae based on LSU, rpb-2, SSU and tef1 sequence data. Maximum likelihood bootstrap values equal or above 70 %, Bayesian posterior probabilities equal or above 0.90 (MLBS/PP) are given at the nodes. An original isolate number is noted after the species name. The tree is rooted to Delitschia chaetomioides (SHM 3253.2) and D. winteri (AFTOL-ID 1599). The ex-type strains are indicated in bold. Newly sequence is in blue. Hyphen (-) represents support values below 70 % MLBS and 0.90 PP.
Figure 54 – Xenoastrosphaeriella trochus (KUN-HKAS 107533). a Appearance of ascomata on host surface. b, c Section through ascoma. d, e Section through peridial structures. f Asci with trabeculate pseudoparaphyses embedded in a mucilaginous matrix. g, j Asci. h Ascus stained by congo red. i Ascus stained by India ink. k–o Ascospores. p Ascospore stained by India ink. q Germinated ascospore. r, s Culture characteristic on PDA after 4 weeks (r = from above, s = from below). Scale bars: b, c = 200 μm, e, f = 50 μm, d, g–j, q = 20 μm, k–p = 10 μm.