Pseudobactrodesmium stilboideum (R. F. Castañeda & G.R.W. Arnold) M.S. Calabon, Boonmee, E.B.G. Jones, K.D. Hyde, comb. nov.
Index Fungorum number: IF 558643; MycoBank number: MB 558643; Facesoffungi number: FoF 09154; Fig. 1
≡ Bactrodesmium stilboideum R. F. Castañeda & G. R. W. Arnold, Revta Jardín bot. Nac., Univ. Habana 6(1): 48 (1985)
=Stigmina longispora var. stilboidea (R.F. Castañeda & G.R.W. Arnold) J. Mena & Mercado, Reporte de Investigacion del Instituto de Ecología y Sistemática 17: 10(1987).
Saprobic on submerged decaying wood in a freshwater habitat. Sexual morph Undetermined. Asexual morph Hyphomycetous. Colonies on natural substrate 415–635 × 14–40.5 μm (x̅= 494.5 × 28 μm, n = 15), synnematous, superficial, effuse, scattered, dark brown to dark olivaceous brown. Mycelium mostly immersed, composed of white, septate, branched and guttulate hyphae. Conidiophores 15–30 × 2–4 μm (x̅= 25 × 3 μm, n = 15) macronematous, fasciculate, synnematous, compact, erect, subcylindrical, septate, slightly constricted at the septa, unbranched or branched, brown, smooth. Conidiogenous cells monoblastic, terminal, discrete, subcylindrical, pale brown, elongating percurrently. Conidia 48–65×7–8 μm (x̅=55×7.5 μm, n=50), solitary, dry, subcylindrical to narrowly fusiform, usually straight or slightly curved, euseptate, 9–13-phragmoseptate, thin and smooth-walled, slightly constricted and darker at septa, brown, paler towards both ends, obscurely guttulate, wedge-shaped at basal cell, with tapering apical cells, often enveloped by a hyaline, spherical, thin, mucilaginous cap at the apex, 8–10 μm diam. Apical cells elongated, up to 12 μm long, tapering gradually toward apex, hyaline to subhyaline, with subglobose tuberculate ends, secession schizolytic.
Culture characteristics – Conidia germinating on malt extract agar (MEA) within 24 h. Germ tubes produced from the basal and apical cell of conidia. Colonies growing on MEA, reaching 20–25 mm in 2 weeks at 25 °C. Mycelia superficial, circular, with entire margin, flat, smooth, from above white, from below smoke grey.
Material examined – THAILAND, Tak Province, Tha Sing Yang, Ban Mae Ja Wang, on submerged decaying wood in a freshwater river, 17 October 2019, N. Padaruth, CC44 (MFLU 21-0120), living culture, MFLUCC 21-0101.
GenBank numbers – ITS=MT864357, LSU=MT860435.
Notes – Dong et al. (2020a) synonymized Pseudobactrodesmium stilboideum under P. longisporum but based on the phylogenetic analysis of LSU and ITS sequence dataset (Fig. 2), it did not group with strains of P. longisporum but clustered with P. stilboideum MHR 18017. The aggregation of conidiophores distinguished the two species wherein P. stilboideum has synnematous formation but in P. longisporum, it is sporodochial with mononematous, fasciculate conidiophores (Ellis 1976; Castañeda-Ruiz and Arnold 1985; Dong et al. 2020a). Moreover, P. stilboideum has shorter and narrower (48–65×7–8 μm) and 9–13-septate conidia (Fig. 1), while P. longisporum has longer and wider (85–119×8–9.5 μm) and 16–21-septate conidia (Ellis 1976). Pseudobactrodesmium stilboideum was isolated on decaying unidentified wood and dead leaves of Calyptronoma plumeriana and is distributed in Cuba, Puerto Rico, South Africa, Taiwan, Thailand and UK (Ellis 1976; Castañeda-Ruiz and Arnold 1985; Hu et al. 2010a).
Figure 1 – Pseudobactrodesmium stilboideum (MFLU 21-0120). a Substrate. b–e Synnemata on submerged wood. f–h Synnemata and densely branched conidiophores, conidiogenous cells and attached conidia. i–l Conidia and mucilaginous cap at the apex. m Germinated conidium. n Culture on MEA from surface and reverse. Scale bars: b, c=500 μm, d–f=200 μm, g–m=50 μm
Figure 2 – Phylogenetic tree generated from maximum likelihood (ML) analysis based on combined LSU and ITS sequence data for the species from Dactylosporaceae. Five species of Sporidesmium aquaticum, S. bambusicola, S. fluminicola, S. submersum and S. thailandense (Sporidesmiaceae) are used as outgroup taxa. The dataset comprised and 1222 characters after alignment including gaps (LSU=793 bp, ITS=429 bp). The RAxML analysis of the combined dataset yielded a best scoring tree with a final ML optimization likelihood value of − 3662.794208. The matrix had 1053 distinct alignment patterns, with 51.86% undetermined characters or gaps. Estimated base frequencies were as follows: A=0.266384, C=0.211364, G=0.273019, T=0.249233; substitution rates AC=1.261100,
AG=2.304874, AT=1.337644, CG=1.220148, CT=5.907736, GT=1.000000; gamma distribution shape parameter α=0.284689. Support values for maximum likelihood (MLBS) above than 75% and Bayesian posterior probabilities (BYPP) greater than 0.95 are given at the nodes. Ex-type species are in bold and newly generated sequence is in blue