16 Oct Cytospora

Cytospora Ehrenb., Sylv. mycol. berol.: 28 (1818)

Cytospora was introduced by Ehrenberg (1818) as the type genus of the family Cytosporaceae in Diaporthales (Wehmeyer 1975; Barr 1978; Eriksson 2001; Castlebury et al. 2002). The genus is an important pathogenic fungus, causing canker and dieback on branches of a wide range of hosts with a wide distribution (Adams et al. 2005, 2006; Hyde et al. 2017, 2018; Norphanphoun et al. 2017, 2018).

Classification –Sordariomycetes, Diaporthomycetidae, Diaporthales, Valsaceae

Type species – Cytospora chrysosperma (Pers.) Fr. 1823

Distribution – Worldwide

Disease symptoms – Canker and dieback disease on branches

Hosts – Species of Abies, Acer, Berberis, Betula, Ceratonia, Cornus, Cotinus, Crataegus, Elaeagnus, Eriobotrya, Eucalyptus, Juniperus, Lumnitzera, Malus, Picea, Pinus, Platanus, Platycladus, Populus, Prunus, Pyrus, Quercus, Rosa, Salix, Sequoia, Sibiraea, Sorbaronia, Sorbus, Spiraea, Styphnolobium, Syringa, Syzygium, Tibouchina, Ulmus, Vitis and Xylocarpus (Norphanphoun et al. 2018).

Morphological based identification and diversity

Cytospora is characterized by multi-loculate conidiomata with ostiolar necks and unicellular, elongate-allantoid to subcylindrical, hyaline conidia (Fan et al. 2015a, b; Norphanphoun et al. 2017, 2018; Fig. 7). The genus which was reported as causing canker diseases in many woody plants was established in 1818 and studied in detail by taxonomists (Fries 1823; Saccardo 1884). Valsa Fr. was reported as the sexual stage of this genus and therefore, Valsa was treated as a synonym of Cytospora (1818) based on the International Code of Nomenclature for Algae, Fungi, and Plants (ICN, McNeill et al. 2012), with Cytospora being the oldest and most widely used name (Adams et al. 2005; Fotouhifar et al. 2010; Fan et al. 2014; Rossman et al. 2015). Previously, the conventional identification of species in Cytospora was based on their host association, often with vague morphological descriptions. Mycologists began to elucidate the relationships between Cytospora species and their hosts, with morphological observations combined with phylogenetic analyses using internal transcribed spacer (ITS) regions as an effective fungal DNA barcode (Adams et al. 2005, 2006; Fotouhifar et al. 2010; Schoch et al. 2012). The establishment of multi-gene analyses using ITS, LSU, ACT, RPB2, TUB2 has proved comprehensive for the species level (Fan et al. 2015a, b, 2020; Liu et al. 2015; Yang et al. 2015; Hyde et al. 2016; Li et al. 2016; Norphanphoun 2017, 2018; Phookamsak et al. 2019).

Fig. Cytospora ampulliformis a stromatal habit in wood. b fruiting bodies on the substrate. c surface of fruiting bodies. d cross-section of the stroma showing conidiomata. e peridium. f ostiolar neck. g–i Conidiogenous cells with attached conidia. j Mature conidia. k, l Colonies on MEA (k-from above, l-from below). Scale bars: a = 2 mm, b = 1 mm, c= 500 µm, d, f = 200 µm, e = 50 µm, g, h = 10 µm, i, j = 5 µm.

Molecular based identification and diversity

        Comprehensive multigene phylogenetic analyses for this genus were performed by Fan et al. (2015a, b, 2020) and Norphanphoun et al. (2017, 2018).

This study reconstructs the phylogeny of Cytospora based on analyses of a combined ITS, LSU, ACT and RPB2 sequence data (Table 3, Fig 8). The phylogenetic tree is updated with recently introduced Cytospora species and corresponds to previous studies (Norphanphoun et al. 2018).

Recommended genetic markers (genus level) – LSU, ITS

Recommended genetic markers (species level) – ITS, ACT and RPB2

The accepted number of species: There are 630 species in Index Fungorum (2019) with an estimated 110 species in Kirk et al. (2008), 85 species have molecular data.

References: Fan et al. 2015a, b, Lawrence et al. 2017, Senanayake et al. 2017, 2018 (morphology), Norphanphoun et al. 2017, 2018 (morphology, phylogeny).

Table Details of Cytospora isolates used in the phylogenetic analyses. Ex-type (or ex-epitype) strains are in bold and marked with an asterisk* and voucher strains are in bold.

Fig Phylogenetic tree generated by maximum likelihood analysis of combined ITS, LSU, ACT and RPB2 sequence data of Cytospora species. Related sequences were obtained from GenBank. Eighty-five isolates are included in the analyses, which comprise 2756 characters including gaps. Single gene analyses were carried out and compared with each species, to compare the topology of the tree and clade stability. The tree was rooted with Diaporthe eres (AFTOL-ID 935). The tree topology of the ML analysis was similar to the MP. The best scoring RAxML tree with a final likelihood value of -8386.622374 is presented. The matrix had 388 distinct alignment patterns, with 11.83% of undetermined characters or gaps. Estimated base frequencies were as follows; A = 0.245798, C = 0.237676, G = 0.273178, T = 0.243348; substitution rates AC = 1.882600, AG = 4.123164, AT = 2.015920, CG = 0.907833, CT = 12.626910, GT = 1.000000; gamma distribution shape parameter α = 1.105097. RAxML bootstrap support values ≥70% (BT) and bayesian posterior probabilities ≥0.95 (PP) are shown respectively near the nodes. Ex-type strains are in bold.