Thyrostroma Höhn., Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften Math.-naturw. Klasse Abt. I 120: 472 (1911)


Thyrostroma belongs to Dothidotthiaceae of Pleosporales in Dothideomycetes, Ascomycota (Hongsanan et al. 2020). Thyrostroma was established by Höhnel (1911) and is typified by T. compactum. Thyrostroma had been treated as a synonym of Coryneum, Stegonsporium, Stigmina, and Thyrococcum, Thyrostromella and Wilsonomyces (Höhnel 1911; Morgan-Jones 1971; Sutton and Pascoe 1989; Sutton 1997; Index Fungorum 2020). Thyrostroma has been reported as the asexual morph of Dothidotthia based on the production of a hyphomycete state in culture (Ramaley 2005), however, there is no phylogenetic evidence to support this link. With new morphological information and phylogenetic analyses, Thyrostroma and Dothidotthia species were retained in separate genera (Crous et al. 2016; Marin-Felix et al. 2017; Senwanna et al. 2019). Thyrostroma species are pathogens, saprobes or endophytes associated with canker, dieback and leaf spots in terrestrial habitats (Yuan and Old 1990; Marin-Felix et al. 2017; Senwanna et al. 2019). Species of Thyrostroma have been recorded from various plants, however, host-specificity and pathogenic capacity of Thyrostroma has not yet been clarified.

Classification – Ascomycota, Pezizomycota, Dothideomycetes, Pleosporomycetidae, Pleosporales, Dothidotthiaceae

Type species Thyrostroma compactum (Sacc.) Höhn

Distribution – Australia, Iran, Korea, Russia, USA, Uzbekistan

Disease Symptoms – Thyrostroma canker, dieback and leaf spots (Fig. 1a, b)

Hosts – Pathogens of Acanthophyllum sp., Astragalus sp., Capparis parvifiora, Celtis occidentalis, Cornus officinalis, Echinops sp., Elaeagnus angustifolia, Ephedra equisetina, Eucalyptus mannifera subsp. maculosa, Franseria sp., Halimodendron halodendron, Lycium barbarum, Morus alba, Robinia pseudoacacia, Sambucus caerulea, Styphnolobium japonicum, Tilia cordata, Ulmus pumila (Farr and Rossman 2020).

Morphological based identification and diversity

Thyrostroma species can be differentiated using conidial dimensions and septation in aged conidia and molecular phylogeny (Crous et al. 2016; Marin-Felix et al. 2017; Senwanna et al. 2019; Fig. 1). Senwanna et al. (2019) reported the sexual morph of Thyrostroma in T. ulmicola for the first time. The sexual morph is characterized by pseudothecial, immersed, erumpent or superficial, uniloculate or multiloculate ascostromata, globose to subglobose ascomata, a two-layered peridium, bitunicate, clavate asci, fusiform to ellipsoidal, 1-septate, ascospores.

Fig. 1 a, b. Symptoms on Ulmus pumila caused by Thyrostroma ulmicola (MFLU 16-1622); c, d Sporodochia on the host surface. e Section of sporodochium. f Conidiogenesis and conidiogenous cells. g–l Conidia. m Germinated conidium. Scale bars: d = 1000 µm, e = 200 µm, f–m = 30 µm.

Molecular based identification and diversity

In the past, there has been no comprehensive phylogenetic study in Thyrostroma and consequently, its taxonomy was and still is mostly based on morphological characters. Based on LSU sequence data, Thyrostroma clustered in a well-supported clade within the Dothidotthiaceae (Marin-Felix et al. 2017; Crous et al. 2019). The asexual morph and sexual morph relationship were resolved by Senwanna et al. (2019) by molecular evidence. To achieve correct generic and species identification and taxonomic placement, phylogenetic studies using LSU, SSU, ITS, and tef1 were performed (Senwanna et al. 2019). This study reconstructs the phylogeny using a combined LSU, SSU, ITS, and tef1 sequence dataset (Fig. 2). The topology is in accordance with Marin-Felix et al. (2017), Senwanna et al. (2019) and Hyde et al. (2020b).

Recommended genetic marker (genus level) – LSU

Recommended genetic markers (species level) – ITS, tef1, rpb2 and tub2

LSU, ITS and tef1 are the common genetic markers used in the identification of Thyrostroma species. Combined LSU, SSU, ITS and tef1 genes provide a satisfactory resolution for resolving species. Based on the comparison of ITS and tef1gene regions, most species in Thyrostroma are not significantly different from one another, therefore, Senwanna et al. (2019) suggested that rpb2, tub2 are reliable genes for distinguishing species within Thyrostroma.

Accepted number of species – There are 27 epithets in Index Fungorum (2020), however only 13 species have DNA sequence data (Table 1).

References – Höhnel 1911, Yuan and Old 1990, Ramaley 2005 (morphology); Marin-Felix et al. 2017, Crous et al. 2016, 2019, Senwanna et al. 2019 (morphology and phylogeny).



Table 1 DNA barcodes available for Thyrostroma. Ex-type/ex-epitype/ex-neotype/ex-lectotype strains are in bold and marked with an asterisk (*). Voucher strains are also in bold.

Species Isolate/Voucher no LSU SSU ITS tef1
Thyrostroma compactum CBS 335.37 KY905664 _ KY905670 KY905681
T. cornicola CBS 141280* KX228300 _ KX228248 KX228372
T. ephedricola MFLUCC 18-1125* MK765854 MK765853 MK765855 _
T. franseriae CBS 487.71* KX228301 _ KX228249 KY905680
  CBS 700.70 KX228302 _ KX228250 KY905682
T. jaczewskii MFLUCC 18-0787 MK765857 MK765858 MK765856 _
T. celtidis MFLUCC 16-1186* MK751822 MK751767 MK751732 MK908022
T. moricola MFLU 16-1795* MK751823 MK751768 MK751733 MK908023
T. lycii MFLUCC 16-1170* MK751824 MK751769 MK751734 MK908024
T. robiniae MFLUCC 18-1191* MK751825 MK751770 MK751735 MK908025
T. styphnolobii MFLUCC 16-1160* MK751826 MK751771 MK751736 MK908026
T. tiliae MFLUCC 16-1176 MK751827 MK751772 MK751737 MK908027
  MFLUCC 16-1178* MK751828 MK751773 MK751738 MK908028
  MFLUCC 16-1180 MK751829 MK751774 MK751739 MK908029
  MFLUCC 16-1188 MK751830 MK751775 MK751740 MK908030
T. ulmicola MFLUCC 16-1172* MK751840 MK751785 MK751750 MK908040
  MFLUCC 16-1173 MK751841 MK751786 MK751751 MK908041
  MFLUCC 16-1163 MK751834 MK751779 MK751744 MK908034
  MFLUCC 16-1711 MK751839 MK751784 MK751749 MK908039
T. ulmigenum MFLUCC 16-1166* MK751846 MK751791 MK751756 MK908046
  MFLUCC 16-1164 MK751845 MK751790 MK751755 MK908045

Fig. 2 Phylogenetic tree generated by maximum likelihood analysis of LSU, SSU, ITS and tef1 sequence data of Thyrostroma species. Related sequences were obtained from GenBank. The tree was rooted with Dothidotthia robiniae (MFLUCC 16-1175), D. symphoricarpi (CPC 12929) and Wilsonomyces carpophilus CBS 147.36). Tree topology of the ML analysis was similar to the Bayesian analysis. The best scoring RAxML tree with a final likelihood value of -5556.187049 is presented. The matrix had 170 distinct alignment patterns, with 18.30% of undetermined characters or gaps. Estimated base frequencies were as follows: A = 0.243922, C = 0.240705, G = 0.270231, T = 0.245142; substitution rates AC = 3.570314, AG = 6.771467, AT 4.177691, CG = 1.603201, CT = 31.935571, GT = 1.000000; gamma distribution shape parameter α = 0.602378. Maximum likelihood bootstrap support values greater than 60% and Bayesian posterior probabilities ≥ 0.95 (BYPP) are indicated above the nodes. Ex-type (ex-epitype) and voucher strains are in bold.

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