Microdochium
Syd. & P. Syd., Ann. Mycol. 22: 267. 1924. Fig. 36.
Fig. 36. Microdochium spp. A–F. Sexual morph of Microdochium seminicola (ex-type CBS 139951). A. Colony overview. B. Ascomata. C–E. Asci. F. Ascospores. G–U. Asexual morphs. G, H. Sporodochium. G. Microdochium phragmites (CBS 423.78). H. Microdochium lycopodinum (CBS 109399). I–N. Conidiophores and conidiogenous cells. I. Microdochium neoqueenslandicum (ex-type CBS 108926). J. Microdochium citrinidiscum (ex-type CBS 109067). K. Microdochium seminicola (ex-type CBS 139951). L. Microdochium phragmites (ex-epitype CBS 285.71). M. Microdochium phragmites (CBS 423.78). N. Microdochium fisheri (ex-type CBS 242.91). O–U. Conidia. O. Microdochium seminicola (ex-type CBS 139951). P. Microdochium lycopodinum (CBS 109399). Q. Microdochium fisheri (ex-type CBS 242.91). R. Microdochium neoqueenslandicum (ex-type CBS 108926). S. Microdochium phragmites (CBS 423.78). T. Microdochium phragmites (ex-epitype CBS 285.71). U. Microdochium citrinidiscum (ex-type CBS 109067). V, W. Chlamydospores. V. Microdochium bolleyi (CPC 29379). W. Microdochium trichocladiopsis (ex-type CBS 623.77). Scale bars: H = 100 μm; G = 50 μm; others = 10 μm.
Synonyms: Monographella Petr., Ann. Mycol. 22: 144. 1924.
Griphosphaerella Petr., Ann. Mycol. 25: 209. 1927.
Gloeocercospora D.C. Bain & Edgerton, Phytopathology 33: 225. 1943. (nom. inval., Art. 39.1, Melbourne).
Gloeocercospora D.C. Bain & Edgerton ex Deighton, Trans. Brit. Mycol. Soc. 57: 358. 1971.
Gerlachia W. Gams & E. Müll., Neth. J. Pl. Path. 86: 49. 1980.
Classification: Sordariomycetes, Xylariomycetidae, Xylariales, Microdochiaceae.
Type species: Microdochium phragmitis Syd. Holotype: K-IMI 193888. Epitype and ex-epitype strain designated by Hernández-Restrepo et al. (2016a): CBS H-22135, CBS 285.71.
DNA barcode (genus): LSU.
DNA barcodes (species): ITS, rpb2, tub2. Table 11. Fig. 37.
Table 11. DNA barcodes of accepted Microdochium spp.
- 1
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CBS: Westerdijk Fungal Biodiversity Institute, Utrecht, the Netherlands; CPC: Personal collection of Pedro Crous housed at the Westerdijk Fungal Biodiversity Institute; CGMCC: China General Microbiological Culture Collection Center. T and ET indicate ex-type and ex-epitype strains.
- 2
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ITS: internal transcribed spacers and intervening 5.8S nrDNA; rpb2: partial RNA polymerase II second largest subunit gene; tub2: partial β-tubulin gene.
Fig. 37. RAxML phylogram obtained from the combined ITS (618 bp), LSU (838 bp), tub2 (689 bp) and rpb2 (858 bp) sequence alignment of all the accepted species of Microdochium. The tree was rooted to Thamnomyces dendroidea CBS 123578 and Xylaria polymorpha MUCL 49884. The novel species described in this study is shown in bold. RAxML bootstrap support (BS) values above 70 % are shown in the nodes. GenBank accession numbers are indicated in Table 11. T and ET indicate ex-type and ex-epitype strains, respectively. TreeBASE: S21899.
Ascomata perithecial, immersed, subepidermal, solitary or in groups, pale brown to black, globose, subglobose to oval; ostiole central, neck papillate and often acute, usually more distinctly pigmented than ascomatal body, filled with slightly clavate periphyses; ascomatal wall brown, thin-walled, thickened and darker around ostiole, in face view textura angularis-epidermoidea. Hamathecium comprising septate, filamentous, apically free, thin-walled paraphyses. Asci unitunicate, oblong to clavate, with 8 bi- to multiseriate ascospores, apex with an amyloid, refractive, flat, funnel-shaped ring. Ascospores clavate, fusoid or oblong, hyaline to brownish, straight or curved, smooth, septate. Conidiomata absent or present, sporodochial, epidermal or subepidermal, erumpent through stomata, or rupture of outer epidermal wall and cuticle, or by specialised egression hyphae through outer epidermal wall, hyaline, pseudoparenchymatic, spreading after egress. Conidiophores more or less verticillate, often slightly differentiated, reduced to conidiogenous cells, hyaline, smooth. Conidiogenous cells holoblastic, discrete, hyaline, smooth, solitary or aggregated in small sporodochia. Two kinds: with sympodial proliferation, cylindrical or slightly tapering to clavate, denticulate with one or more apical denticles; or with percurrent proliferation (annellidic), subcylindrical, obpyriform, ampulliform to lageniform. Conidia dry or in slimy mass, unicellular or multiseptate, hyaline, smooth, lunate, falcate, fusiform, filiform, obovoid or subpyriform, straight or curved, apex rounded, base flattened. Sometimes conidia originate directly from hyphae. Chlamydospores terminal or intercalary, solitary, in chains or grouped in clusters, brown (adapted from Hernández-Restrepo et al. 2016a).
Culture characteristics: Colonies on OA saffron, salmon, peach or white when young, some species grey or dark grey when mature, glabrous or with moderate amount of mycelium, cottony to floccose, margin effuse.
Optimal media and cultivation conditions: OA at 25 °C under dark conditions.
Distribution: Worldwide.
Hosts: Mainly pathogens of grasses and cereals, but some also occur on non-grass hosts as Opuntia (Cactaceae) and Lycopodium (Lycopodiaceae), may cause losses to crops including rice, maize, wheat, barley and sorghum. Other species can be found in harvested grains.
Disease symptoms: Microdochium patch or pink snow patch, leaf scald disease, tar spot disease, root necrosis and decay of grasses, leaf spots, among others.
Notes: Microdochium includes plant pathogenic as well as saprobic and soil fungi (Sydow, 1924, De Hoog and Hermanides-Nijhof, 1977, Parkinson et al., 1981, Jaklitsch and Voglmayr, 2012, Zhang et al., 2015, Hernández-Restrepo et al., 2016a, Crous et al., 2018). For many years, species of Microdochium were recognised as fusarium-like fungi; however, morphological and molecular data separate these genera. Conidiogenesis in Microdochium is not phialidic as in true Fusarium species and the conidia have truncate basal cells rather than “foot-cells”. The sexual morphs of Microdochium are monographella-like, and it belongs in the Microdochiaceae (Xylariales) phylogenetically distant from true Fusarium in Nectriaceae (Hypocreales).
For an accurate species identification of Microdochium species, DNA sequence analyses are required. Among the four loci studied (i.e. LSU, ITS, rpb2 and tub2), LSU is useful only for generic placement. Phylogenies based on individual gene regions of ITS, rpb2 and tub2, can be used to distinguish 14 species in Microdochium; those phylogenies generated from tub2 show longer distances between species and higher support values. This is more informative than ITS and rpb2 (Hernández-Restrepo et al. 2016a).
References: Parkinson et al., 1981, Müller and Samuels, 1984, Zhang et al., 2015 (morphology and pathogenicity); von Arx, 1981, von Arx, 1984, Braun, 1995 (taxonomy); Hong et al. 2008 (pathogenicity); Hernández-Restrepo et al. 2016a (morphology and phylogeny).
Etymology: Name is derived from New Zealand, the country where this fungus was collected.
Mycelium superficial and immersed, composed of septate, branched, hyaline, smooth, 1–2.5 wide hyphae. Conidiomata sporodochium-like, formed in aerial mycelium or on agar surface, hyaline to pink. Conidiophores often reduced to conidiogenous cells. Conidiogenous cells 4–10 × 2–3 μm, integrated, terminal, polyblastic, proliferation sympodial, cylindrical to lageniform, hyaline, smooth; sometimes conidia formed directly on mycelium. Conidia 5.5–10 × 2–2.5 μm, solitary, fusoid, allantoid, lunate or slightly sigmoid, straight or curved, hyaline, smooth, 0(–1)-septate, base truncate. Chlamydospores not observed.
Culture characteristics: Colonies on OA reaching 45 mm diam after 1 wk at 25 °C, centre flat and rosy buff, periphery cottony and white, margins effuse; reverse rosy buff in centre.
Materials examined: New Zealand, Christchurch, from turf leaves (Poaceae), 2015, R. Thangavel (holotype CBS H-23384, culture ex-type CBS 143847 = CPC 29376 = ICMP 21872 = MPI T15_05208H); ibid., Richmond, Nelson, on spruce (Pinaceae), 2014, R. Thangavel (CPC 29693 = MPI T14_00277D).
Notes: Microdochium novae-zelandiae is known from two isolates, both of which were collected in New Zealand from different hosts belonging to the families Pinaceae and Poaceae. Based on a four-gene analysis, the new species was placed in a clade distinct from M. bolleyi, M. colombiense, M. majus and M. nivale (Fig. 37). Morphologically, M. novae-zelandiae has conidia similar in size to M. bolleyi and M. colombiense. However, subtle morphological differences exist in the conidial shapes of these taxa with M. novae-zelandiae having sigmoidal conidia. Compared with M. phragmitis, conidia of M. novae-zelandiae are smaller, mainly aseptate with variable shape [5.5–10 × 2–2.5 μm, 0(–1)-septate, fusiform, allantoid, lunate or slightly sigmoid in M. novae-zelandiae vs. 10–14.5 × 2–3 μm, 0–1-sepate, fusiform to navicular in M. phragmitis].
Authors: M. Hernández-Restrepo, R. Thangavel & P.W. Crous