Rhytidhysteron subrufulum X.L. Xu & C.L. Yang

Senwanna, Chanokned, Suwannarach, Nakarin, Phookamsak, Rungtiwa, Kumla, Jaturong & Hongsanan, Sinang, 2023, New host and geographical records of Rhytidhysteron in northern Thailand, and species synonymization, Phytotaxa 601 (2), pp. 157-173 : 165-168

Rhytidhysteron subrufulum X.L. Xu & C.L. Yang , in Xu et al., Cryptog. Mycol. 43(3): 72 (2022) FIGURE 4

Saprobic on dead twig of Prunus sp. Sexual morph: Ascomata 850–1360 µm long, 200–630 µm wide, 335–515 µm high (x = 1086 × 445 × 465 µm, n = 7), hysterothecial when young, slightly opened when mature, superficial, coriaceous, scattered, elongate, elliptic, to Y-shaped, or irregular in shape, opening by a longitudinal slit, closed at first and opening at maturity, with perpendicularly striate along the axis, dark brown to black with dark brown at the center. Exciple (25–)30–91(–127) µm wide, composed of cells of textura globulosa to textura angularis, an outer layer dark brown to black, thick-walled, an inner layer hyaline to pale brown, thin-walled, small cell of textura angularis to textura prismatica, continuous to the base (hypothecium). Hamathecium comprising 1.5–3.5 µm wide, numerous, cylindrical to filiform, septate, branching pseudoparaphyses, fused and slightly swollen at the apex, enclosed in a gelatinous matrix, forming brown to dark brown epithecium above the asci. Asci 161–197 × 14–17(–20.5) µm (x = 180.7 × 16 µm, n = 15), 4–8-spored, bitunicate, cylindrical, straight or slightly curved, with a short pedicel, rounded at the apex, with an ocular chamber. Ascospores 24–32 × 9.5–14 µm (x = 28 × 11.7 µm, n = 50), uniseriate, slightly overlapping, hyaline to pale brown when immature, becoming reddish-brown to dark brown when mature, ellipsoidal to broadly fusiform, rounded to slightly pointed at both ends, 1–3-septate, thick septate, constricted at the septum, rough-walled, with small guttules. Asexual morph: Undetermined.

Culture characteristics:— Ascospores germinating on PDA within 24 hours at room temperature and produced germ tubes from the end of ascospores. Colonies on PDA circular, medium dense, slightly raised, edge entire, velvety to fluffy, white at the margin, greyish green at the surface; not producing pigment on agar.

Material examined:— THAILAND, Chiang Mai Province, Chai Prakan District, Nong Bua Subdistrict, Sinchai Village, on a dead twig of Prunus sp. (Rosaceae) , 3 March 2023, S. Hongsanan, CR03.3 ( CMUB 4003), living culture SDBR-CMU475.

Host and distribution:— Broussonetia papyrifera ( Moraceae , China; Xu et al. 2022), Carya illinoinensis ( Juglandaceae , China; Xu et al. 2022), Chimonanthus praecox ( Calycanthaceae , China; Xu et al. 2022), Citrus reticulata ( Rutaceae , China; Xu et al. 2022), Osmanthus fragrans ( Oleaceae , China; Xu et al. 2022), Prunus sp. ( Rosaceae , Thailand; this study), Robinia pseudoacacia ( Fabaceae , China; Xu et al. 2022).

Notes:— In a BLASTn search, the ITS sequence showed 100% similarity to Rhytidhysteron subrufulum (SICAUCC 22-0001; OM333896). Phylogenetic analyses indicated that our strain SDBR-CMU475 grouped with R. subrufulum in a well-supported clade ( FIGURE 1 ). A comparison of LSU, ITS and TEF1 nucleotide base pairs showed that SDBR-CMU475 is identical (0/833 bp in LSU, 0/585 bp in ITS and 2/937 bp in TEF1) to the type strain of R. subrufulum . Xu et al. (2022) introduced R. subrufulum based on morphology and molecular data. The morphology of our collection (CMUB4003) is similar to R. subrufulum described by Xu et al. (2022) in having hysterothecia with perpendicular striated, and ellipsoidal to broadly fusiform ascospores with 1–3-septate. The size and shape of asci and ascospores of CMUB4003 (asci 161–197 × 14–17(–20.5) μm, ascospores 24–32 × 9.5–14) are partially overlapping in the range of SICAU 19-0010 (holotype) (asci 183–214 × 13–20 μm, ascospores 29–41 × 10–15 μm). Therefore, we identify our collection as R. subrufulum and this is a new host record for R. subrufulum on Prunus sp. in Thailand. Similarly, this is the first graphical record of R. subrufulum from Thailand.

Figures

FIGURE 1. Phylogenetic tree conducted by maximum likelihood (RAxML) based on analysis of a combined LSU, ITS, SSU, and TEF1 sequence data of Rhytidhysteron species. Bootstrap values for ML equal to or greater than 60% and Bayesian posterior probabilities (PP) equal to or greater than 0.90 are defined as ML/PP above the nodes. The tree is rooted to Gloniopsis calami (MFLUCC 15-0739) and G. praelonga (CBS 112415). The newly generated strains are indicated in blue and the type strains are in black bold.

FIGURE 4. Rhytidhysteron subrufulum (CMUB4003, new host and geographical record). a–c Appearance of ascomata on the substrate. d Section through ascoma. e, f Exciple. g, h Psudoparaphyses. i–n Asci from different stages. o, p Ocular chamber. qAscospores. Scale bars: b, c = 1000 µm, d = 200 µm, i–n = 50 µm, e–h, o–q = 20 µm.