Phaeoacremonium
W. Gams, et al., Mycologia 88: 789. 1996. Fig. 43.
Fig. 43. Morphological structures of Phaeoacremonium spp. A–K. Asexual morphs. A. Conidiophores branched. B. Conidiophores unbranched. C. Percurrent rejuvenation of conidiophore. D. Mycelium showing prominent exudate droplets observed as warts. E. Conidiophore with polyphialides. F. Type III phialides. G. Type II phialide. H. Type I phialide. I. Conidia. J. Conidiophore. K. Type II phialide. L–S. Sexual morph. L, M. Ascomata on canes of Vitis vinifera. N. Longitudinal section through ascoma. O. One paraphyses. P, Q. Asci attached to ascogenous hyphae. R. Asci. S. Ascospores. A, B, D, F, G, I. Phaeoacremonium parasiticum (ex-type CBS 860.73). C. Phaeoacremonium hispanicum (ex-type CBS 123910). E. Phaeoacremonium amygdalinum (ex-type CBS 128570). H. Phaeoacremonium minimum (ex-type CBS 246.91). L–S. Phaeoacremonium minimum (holotype CBS 17463). Scale bars: A, C, J, K, O, P = 10 μm; L, M = 200 μm; N = 100 μm; A applies to A, B, D, F–I; C applies to C, E; P applies to P–S.
Synonym: Togninia Berl., Icon. fung. (Abellini) 3: 9. 1900.
Classification: Sordariomycetes, Sordariomycetidae, Togniniales, Togniniaceae.
Type species: Phaeoacremonium parasiticum (Ajello, et al.) W. Gams, et al., basionym: Phialophora parasitica Ajello, et al. Holotype and ex-type strain: CBS H-17463, CBS 860.73.
DNA barcodes (genus): SSU, LSU.
DNA barcodes (species): act, tub2. Table 14. Fig. 44.
Table 14. DNA barcodes of accepted Phaeoacremonium spp.
- 1
-
CBS: Westerdijk Fungal Biodiversity Institute, Utrecht, The Netherlands; IFRDCC: International Fungal Research and Development Center, Bailongsi, China; ICMP: International Collection of Microorganisms from Plants, Auckland, New Zealand; PARC: Pacific Agri-Food Research Centre in Summerland, British Columbia, Canada; CMM: Culture Collection of Phytopathogenic Fungi “Prof. Maria Menezes”, Universidade Federal Rural de Pernambuco, Recife, Brazil; STE-U: Department of Plant Pathology, Stellenbosch University, South Africa; MFLUCC: Mae Fah Luang Culture Collection, Chiang Rai, Thailand. T indicates ex-type strains. ∗Ex-type of Pha. novae-zealandiae, synonymised with Pha. leptorrhynchum by Réblová (2011).
- 2
-
act: partial actin gene; tub2: partial β-tubulin gene.
- 3
-
Not available. Only ITS sequence available: NR136032.
Fig. 44. Bayesian consensus tree of the genus Phaeoacremonium as estimated from the combined act (∼260 bp) and tub2 (∼680 bp) regions. Bayesian posterior probability values and bootstrap support percentages are shown at the nodes. Support values of less than 0.7 posterior probability and 70 % bootstrap are not shown. Jattaea algeriensis, Calosphearia africana and Pleurostoma richardsiae were used as outgroups. GenBank accession numbers are listed in Spies et al. (2018). T indicates ex-type strains. TreeBASE: S22407.
Ascomata perithecial, aggregated or solitary, superficial to immersed, non-stromatic, globose to subglobose, dark, opaque, long-necked; necks straight or flexuous; ascomatal wall fragile to leathery, comprising two layers of textura angularis: outer layer brown to dark brown, with cells smaller and more rounded than those of inner layer; inner layer hyaline to pale brown, cells flattened. Paraphyses abundant, broadly cellular, slightly constricted at septa, branching, hyaline, slightly tapering apically or thread-like towards apex. Ascogenous hyphae hyaline, sometimes branched in basal region, elongating during ascal formation with remnant tissue from which single asci arise. Asci arising in acropetal succession, appearing spicate when mature, unitunicate, 8-spored, ascal apex thickened with a nonamyloid apical ring, basally bluntly obtuse, sessile. Ascospores hyaline, aseptate, allantoid, reniform, cylindrical or oblong-ellipsoidal, mostly biseriate or in a single row. Conidiophores branched in basal region or unbranched, arising from aerial or submerged hyphae, erect, nearly cylindrical when unbranched, slightly tapering, straight or flexuous, variable in length, up to 7-septate, mostly pale brown, paler towards tip, percurrent rejuvenation observed, small warts or verruculose ornamentation mostly at base, usually with one integrated terminal phialide and one or two additional, discrete phialides at uppermost septum. Conidiogenous cells phialidic, discrete or integrated, terminal or lateral, mostly monophialidic, sometimes polyphialidic, sparsely warted, verruculose or smooth, pale brown to hyaline, with an inconspicuous funnel-shaped collarette. Three distinct classes of phialides (Types I–III) can be observed. Conidia aggregated into round, slimy heads at apices of phialides, hyaline, aseptate, smooth-walled, oblong-ellipsoidal to obovate, cylindrical, allantoid or reniform, uncommonly fusiform-ellipsoidal or globose, becoming biguttulate with age.
Culture characteristics: Colonies on MEA flat with entire margins, mostly moderately dense, predominantly felty, and sometimes woolly; brown, olive-grey, pale yellow to beige or pink to dark pink.
Optimal media and cultivation conditions: 2 % MEA to induce sporulation of asexual morph. Cultural characters that are useful to distinguish Phaeoacremonium species include colour of colonies on MEA, and yellow pigment production on PDA and OA. For the sexual morph 2 % WA is used with twice-autoclaved pieces of 3–4 cm of grapevine cane at 22 °C (GWA).
Distribution: Worldwide.
Hosts: Frequently isolated from both diseased woody plants with brown wood streaking, and humans with phaeohyphomycotic infections. Other hosts include larvae of bark beetles, arthropods, and soil. Because of the involvement of members of this genus in Petri disease and esca of grapevines (Vitis spp.), isolates from this host have been intensively studied (Mostert et al., 2006, Gramaje et al., 2015, Spies et al., 2018). Even though Phaeoacremonium species can infect a wide range of woody hosts (more than 40 host plants), recent publications have shown the importance of Phaeoacremonium species in causing brown wood streaking of Olea europaea (Oleaceae) and Prunus spp. (Rosaceae) (Damm et al., 2008, Carlucci et al., 2015).
Notes: Species delimitation based on morphology alone has little value since many species have overlapping characters. Moreover, the morphology of the sexual morph cannot be used because only 15 taxa are known. The two gene regions used most frequently for phylogenetic analyses are actin (act) and partial beta-tubulin (tub2) genes (Mostert et al. 2006). Phylogenetic analyses combining these two regions allow for the resolution of almost all currently known Phaeoacremonium species with good support (≥0.97 PP, ≥96 % BS) (Fig. 44). The three exceptions to this are Pha. griseorubrum (paraphyletic), Pha. roseum (0.72 PP, 100 % BS) and Pha. viticola (0.87 PP, 62 % BS) (Fig. 44, also see Gramaje et al. 2015 and Spies et al. 2018). Other gene regions that have been used include the ITS, tef1 and cal (Groenewald et al., 2001, Mostert et al., 2005, Úrbez-Torres et al., 2014). Úrbez-Torres et al. (2014) included ITS and tef1 data along with act and tub in their phylogeny, which resolved all included species with more than 97 % or 96 % bootstrap support in maximum parsimony and neighbour joining analyses respectively. The ITS region is considered insufficiently variable to distinguish between several of the species and is not recommended as a barcode (Mostert et al. 2005); however, considering the resolution and support in the phylogeny of Úrbez-Torres et al. (2014), the tef1 region is valuable in resolving issues with support and resolution in the act-tub2 phylogeny. The cal region was sequenced for a limited number of species by Mostert et al. (2005) to resolve taxa related to Pha. rubrigenum. Unfortunately, sequence data for this region are available for a limited number of species and its usefulness in distinguishing between Phaeoacremonium species remains uncertain.
References: Crous et al. 1996 (taxonomy); Eskalen et al., 2005, Rooney-Latham et al., 2005 (sexual morph); Mostert et al., 2006, Gramaje et al., 2015 (taxonomy, distribution, host range, detection, identification, pathogenesis and epidemiology); Aroca and Raposo, 2007, Pouzoulet et al., 2013, Úrbez-Torres et al., 2015 (detection and identification); Halleen et al., 2007, Damm et al., 2008, Aroca and Raposo, 2009, Gramaje et al., 2010 (pathogenicity); Blanco-Ulate et al. 2013 (genome sequence); Moyo et al., 2014, Agustí-Brisach et al., 2015 (epidemiology); Réblová et al. 2015 (systematics).
Phaeoacremonium pravum
C.F.J. Spies, L. Mostert & Halleen, sp. nov. MycoBank MB821019. Fig. 45.
Fig. 45. Phaeoacremonium pravum (ex-type CBS 142686). A–C. Eight-d-old colonies on MEA (A), PDA (B) and OA (C). D. Subcylindrical type I phialides with funnel-shaped collarettes. E, F. Type III phialides. G, J. Branched conidiophores with crooked type II phialides. H. Elongate ampulliform type I phialide. I. Type I phialide with conidia borne in a slimy head. K. Crooked elongate ampulliform type I phialide with a funnel-shaped collarette showing lateral vegetative proliferation. Scale bar: K = 10 μm, K applies to D–K.
Etymology: Latin, pravum meaning crooked, in reference to the crooked shape of some phialides.
Mycelium of branched, prominently septate, hyaline to pale brown, smooth to finely verruculose (1–)1.5–2.5 (av. 2) μm diam hyphae, forming bundles of up to 5 strands, individual strands in bundles often forming direct hyphal connections. Conidiophores (14.5–)16–61(–77) × 1.5–2.5 (av. 28.5 × 2) μm, smooth to finely verruculose, usually branched, hyaline, up to 9 septa. Phialides terminal or lateral, monophialidic, sometimes proliferating vegetatively behind collarette, types I and II dominant, collarettes funnel-shaped, 0.5–1.5 × 0.5–2 (av. 1 × 1.5) μm, smooth, hyaline; type I mainly subcylindrical, sometimes elongate ampulliform, (2–)2.5–10.5(–11) × 1–2 (av. 6 × 1.5) μm; type II subcylindrical with tapering apex to elongate ampulliform, sometimes curved or bent especially at apex, (8–)8.5–14(–14.5) × 1.5–2(–2.5) (av. 11.5 × 2) μm; type III subcylindrical with tapering apex to subulate, sometimes slender navicular, (14–)14.5–26.5(–31.5) × 1.5–2 (av. 19 × 1.5) μm. Conidia 3–4(–4.5) × 1.5(–2) (av. 3.5 × 1.5) μm, borne in slimy heads, oblong-ovoid to ellipsoidal to allantoid.
Culture characteristics: Colonies reaching a radius of 8–10 mm after 8 d at 25 °C. Minimum temperature for growth 10 °C, optimum 20 °C, maximum 35 °C. Colonies on MEA smooth, submerged with entire edge, after 16 d white to pale buff above and in reverse. Colonies on PDA smooth, submerged, with central folds, with entire margin, after 16 d white to pale buff above and in reverse. Colonies on OA felty, folded, with submerged margins, with entire edge, after 16 d white to pale smoke grey with darker margins.
Materials examined: South Africa, from wood of Vitis berlandieri × V. rupestris (rootstock cv. Richter 110) (Vitaceae), 18 Sep. 2014, A. Vermeulen (holotype CBS-H 23158, culture ex-type CBS 142686 = STE-U 8363 = CSN3); ibid., on Vitis vinifera cv. Early Sweet cordon (Vitaceae), 18 Sep. 2014, A. Vermeulen, CBS 142687 = STE-U 8364 = CSN11.
Notes: There are several differences between the ex-type strain (CBS 142686) and strain CBS 142687. Strain CBS 142687 had a higher optimum and maximum temperatures for growth (25 °C and 37 °C, respectively) than strain CBS 142686 and reached a radius of 11–12 mm after 8 d at 25 °C. After 16 d, colonies of strain CBS 142687 also had pronounced pigmentation on MEA i.e. rosy vinaceous with dark purple patches with central white tufts of aerial mycelium, and on PDA i.e. livid red to dark vinaceous with white to smoke grey woolly aerial mycelium, and on OA i.e. mouse grey to olivaceous grey with white margins. The act sequence of strain CBS 142687 differs from that of the ex-type (CBS 142686) at six positions over a length of 210 bases, resulting in paraphyly of this species in an act-only phylogeny (Spies et al. 2018). Considering the high similarity of tub2 sequences (598/599 identical bases), strong support for the monophyly of Pha. pravum in the combined act-tub2 phylogeny, and the fact that both strains produced curved phialides, CBS 142687 is regarded as Pha. pravum until additional strains and data become available to indicate differently.
Authors: D. Gramaje, L. Mostert, C.F.J. Spies & F. Halleen