Byssothecium
Citation: Pem D et al. (2019) Mycosphere Notes 275-324: A morphotaxonomic revision and typification of obscure Dothideomycetes genera (incertae sedis). Mycosphere 10(1), 1115–1246
Byssothecium Fuckel, Bot. Ztg. 19(no. 35): 251 (1861)
Index Fungorum number: IF 06498; Facesoffungi number: FoF 714
Saprobic or parasitic on Medicaginis sativae. Sexual morph: Ascomata pseudothecioid solitary, scattered, or in groups, immersed, semi-immersed to erumpent, globose to subglobose, black, apex with a short papilla. Peridium coriaceous, consisting of thick-walled, brown cells of textura angularis. Hamathecium composed of pseudoparaphyses, embedded in mucilage, branching, septate and anastomosing between and above the asci. Asci 8-spored, bitunicate, fissitunicate, cylindro-clavate, slightly curved when immature, pedicellate. Ascospores biseriate to uniseriate, fusiform, hyaline when immature, dark brown at maturity, 3- trans-septate, and variously ornamented. Asexual morph: Undetermined.
Type species – Byssothecium circinans Fuckel
Notes – The genus Byssothecium was introduced by Fuckel (1861) with the type species B. circinans. The latter was described as a saprobe or parasite of Medicago sativa (Semeniuk 1983) and a Pleospora-type centrum was observed (Boise 1983). A chaetophoma-like anamorph is reported in culture, however, no culture or herbarium specimen is listed (Boise 1983). Byssothecium was considered as closely related to Teichospora (Boise 1983). Later, it was accepted as a genus in Massarinaceae by Zhang et al. (2009). Some studies showed that Byssothecium was distinct from Massarinaceae and was placed in Dothideomycetes genera incertae sedis (Lumbsch & Huhndorf 2010, Wijayawardene et al. 2014). However, in the phylogenetic analysis done by Chethana et al. (2015) and Thambugala et al. (2015), Byssothecium clustered in Massarinaceae. Currently, the genus consists of eight species (Index fungorum 2019). The asexual morph is coelomycetous (Wijayawardene et al. 2017). Cultures and sequences are available for B. circinans however, it could not be accommodated in any family so far (Wijayawardene et al. 2018). We examined the isotype specimen of B. circinans and according to morphological characters, B. circinans share morphological similarities to species in Trematosphaeriaceae such as subglobose, black, coriaceous ascomata, thick-walled cells of textura angularis, septate, cellular pseudoparaphyses, embedded in mucilage, branching and anastomosing between and above the asci, cylindric-clavate bitunicate asci and brown fusiform ascospores. But, based on a megablast search using the LSU sequence of Byssothecium circinans, the closest matches in NCBI’s GenBank nucleotide database were Helminthosporium juglandinum (L97), Helminthosporium juglandinum (L118), Helminthosporium juglandinum (L101) with 100%, 99%, 99% similarities respectively with 0% gaps. Phylogenetic analyses of the putative strain of Byssothecium circinans (CBS 675.92) available in GenBank shows that Byssothecium forms a lineage basal to Pseudodidymosphaeria spartii (CBS 183.58) (Fig. 8). Byssothecium resembles Pseudodidymosphaeria in having semi-immersed ascomata, however, it differs from other morphological characters. The genus Byssothecium rather resembles species of Pseudosplanchonema in having pseudothecioid ascomata and cylindro-clavate asci but differs in ascospores characters (3- trans-septate vs 1-sub-median septate, pseudosepta between the guttules). We therefore, place Byssothecium in Massarinaceae.
Figure 1 – Phylogram generated from maximum likelihood analysis based on combined LSU, SSU and BTUB sequence data. Related sequences were retrived from Liu et al. (2017). Twenty-one strains are included in the combined gene analyses comprising 2327 characters after alignment (856 characters for LSU, 1058 characters for SSU and 411 characters for BTUB). Paracamarosporium hawaiiense (CBS 120025) and Paraconiothyrium fungicola (CBS 113269) are used as the outgroup taxon. The tree topology of the Bayesian analysis was similar to the maximum likelihood analysis. The best RaxML tree with a final likelihood value of -7593.818950 is presented. The matrix had 535 distinct alignment patterns, with 30.91% undetermined characters or gaps. Estimated base frequencies were as follows: A = 0.254460, C = 0.214516, G = 0.284400, T = 0.246625; substitution rates AC = 1.248767, AG = 2.513663, AT = 1.269748, CG = 0.839642, CT = 4.977442, GT = 1.000000; gamma distribution shape parameter α = 0.917153. Bootstrap values for maximum likelihood equal to or greater than 50 and Bayesian posterior probabilities equal or greater than 0.95 are placed above or below the branches, respectively. Ex-type strains are in bold and black. The newly generated sequences are indicated in blue.
References
Boise J. 1983 – On Trematosphaeria circinans and Reinstatement of the Genus Byssothecium. Mycologia 75 (4), 666–669.
Chethana T, Liu M, Ariyawansa HA, Konta S, Wanasinghe DN, Zhou Y et al. 2015 – Splanchnonema-like species in Pleosporales: introducing Pseudosplanchnonema gen. nov. in Massarinaceae. Phytotaxa 231(2), 133–144.
Fuckel L. 1861– Mykologisches. Botanische Zeitung 19 (35), 249–252.
Index Fungorum. 2019 – http://www.indexfungorum.org/Names/Names.asp (Accessed 17 May 2019).
Lumbsch HT, Huhndorf SM. 2010 – Outline of Ascomycota 2009. Myconet 14, 1–64.
Thambugala KM, Chunfang Y, Camporesi E, Bahkali AH, Liu ZY, Hyde KD. 2015b – Pseudodidymosphaeria gen. nov. in Massarinaceae. Phytotaxa 231, 271–282.
Wijayawardene NN, Crous PW, Kirk PM, Hawksworth DL et al. 2014b – Naming and outline of Dothideomycetes–2014 including proposals for the protection or suppression of generic names. Fungal Diversity 69, 1–5.
Wijayawardene NN, Hyde KD, Lumbsch HT, Liu JK et al. 2018 – Outline of Ascomycota: 2017. Fungal Diversity 88, 167–263.
Wijayawardene NN, Hyde KD, Rajeshkumar KC, Hawksworth DL et al. 2017 – Notes for genera: Ascomycota. Fungal Diversity 86, 1–594.
Zhang Y, Wang HK, Fournier J, Crous PW et al. 2009 – Towards a phylogenetic clarification of Lophiostoma/Massarina and morphologically similar genera in the Pleosporaceae. Fungal Diversity 38, 225–251.
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