Gaeumannomyces

Arx & D.L. Olivier, Trans. Brit. Mycol. Soc. 35: 32. 1952. Fig. 16.

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Fig. 16. Gaeumannomyces spp. A–F. Sexual morph. A. Ascoma of Gaeumannomyces oryzicola (ex-type CBS 141390). B. Asci and paraphyses of Gaeumannomyces oryzinus (CPC 26065). C–E. Asci. C, D. Gaeumannomyces oryzinus (CPC 26043). E. Gaeumannomyces oryzicola (ex-type CBS 141390). F. Ascospores of Gaeumannomyces oryzinus (CBS 235.32). G–AH. Asexual morph. G–P. Conidiophores and conidiogenous cells. G. Gaeumannomyces californicus (ex-type CBS 141377). H. Gaeumannomyces fusiformis (ex-type CBS 141379). I. Gaeumannomyces arxii (CBS 903.73). J, N. Gaeumannomyces walkeri (ex-type CBS 141400). K. Gaeumannomyces graminis (CBS 141386). L. Gaeumannomyces graminicola (CBS 352.93). M. Gaeumannomyces oryzicola (ex-type CBS 141390). O. Gaeumannomyces oryzinus (CPC 26032). P. Gaeumannomyces radicicola (ex-type CBS 296.53). Q–Y. Conidia. Q. Gaeumannomyces radicicola (ex-type CBS 296.53). R. Gaeumannomyces oryzicola (ex-type CBS 141390). S, T. Gaeumannomyces walkeri (ex-type CBS 141400). U. Gaeumannomyces oryzinus (CPC 26067). V. Gaeumannomyces ellisiorum (ex-type CBS 387.81). W. Gaeumannomyces floridanus (ex-type CBS 141378). X. Gaeumannomyces graminicola (CPC 26036). Y. Gaeumannomyces arxii (CBS 903.73). Z–AH. Hyphopodia. Z. Gaeumannomyces ellisiorum (ex-type CBS 387.81). AA, AC. Gaeumannomyces glycinicola (CBS 141380). AB. Gaeumannomyces floridanus (ex-type CBS 141378). AD. Gaeumannomyces graminicola (CPC 26025). AE. Gaeumannomyces californicus (ex-type CBS 141377). AG. Gaeumannomyces oryzinus (CPC 26032). AF. Gaeumannomyces hyphopodioides (CPC 26267). AH. Gaeumannomyces walkeri (ex-type CBS 141400). Scale bars: A, B = 50 μm; C–F = 20 μm; others = 10 μm. Pictures taken from Hernández-Restrepo et al. (2016b).

Synonyms: Rhaphidospora Fr., Summa veg. Scand. 2: 401. 1849.

Rhaphidophora Ces. & De Not., Sfer. Ital.: 79. 1863.

Classification: Sordariomycetes, Sordariomycetidae, Magnaporthales, Magnaporthaceae.

Type species: Gaeumannomyces graminis (Sacc.) Arx & D.L. Olivier, basionym: Rhaphidophora graminis Sacc. Representative strain: CPC 26020 = CBS 141384.

DNA barcode (genus): LSU.

DNA barcodes (species): ITS, tef1, rpb1. Table 6. Fig. 17.

Table 6. DNA barcodes of accepted Gaeumannomyces spp.

Species	Isolates1	GenBank accession numbers2			References
		ITS	rpb1	tef1
Gaeumannomyces amomi	CBS 109354T	AY265318	–	KX306679	Bussaban et al., 2005, Hernández-Restrepo et al., 2016b
G. arxii	CBS 903.73T	KM484837	KM485053	KX306681	Klaubauf et al., 2014, Hernández-Restrepo et al., 2016b
G. australiensis	CBS 141387T	KX306480	KX306619	KX306683	Hernández-Restrepo et al. (2016b)
G. avenae	CPC 26258ET	KX306486	KX306622	KX306688	Hernández-Restrepo et al. (2016b)
G. californicus	CBS 141377T	KX306490	KX306625	KX306691	Hernández-Restrepo et al. (2016b)
G. ellisiorum	CBS 387.81T	KM484835	KM485051	KX306692	Klaubauf et al., 2014, Hernández-Restrepo et al., 2016b
G. floridanus	CBS 141378T	KX306491	KX306626	KX306693	Hernández-Restrepo et al. (2016b)
G. fusiformis	CBS 141379T	KX306492	KX306627	KX306694	Hernández-Restrepo et al. (2016b)
G. glycinicola	CPC 26057T	KX306493	KX306628	KX306695	Hernández-Restrepo et al. (2016b)
G. graminicola	CBS 352.93T	KM484834	KM485050	KX306697	Klaubauf et al., 2014, Hernández-Restrepo et al., 2016b
G. graminis	CPC 26020	KX306498	KX306633	KX306701	Hernández-Restrepo et al. (2016b)
G. hyphopodioides	CBS 350.77T	KX306506	KM009192	KM009204	Hernández-Restrepo et al., 2016b, Luo et al., 2014
G. oryzicola	CBS 141390T	KX306516	KX306646	KX306717	Hernández-Restrepo et al. (2016b)
G. oryzinus	CBS 235.32	JX134669	KM485049	JX134695	Klaubauf et al., 2014, Luo and Zhang, 2013
G. radicicola	CBS 296.53T	KM484845	KM485061	KM009206	Klaubauf et al. (2014)
G. setariicola	CBS 141394T	KX306524	KX306654	KX306725	Hernández-Restrepo et al. (2016b)
G. tritici	CBS 905.73	KM484841	KM485057	KX306731	Klaubauf et al., 2014, Hernández-Restrepo et al., 2016b
G. walkeri	CBS 141400T	KX306543	KX306670	KX306746	Hernández-Restrepo et al. (2016b)
G. wongoonoo	BRIP 60376A	KP162137	–	–	Wong (2002)

1

BRIP: Queensland Plant Pathology Herbarium, Brisbane, Australia; CBS: Westerdijk Fungal Biodiversity Institute, Utrecht, the Netherlands; CPC: Culture collection of Pedro Crous, housed at the Westerdijk Fungal Biodiversity Institute. ^{T, ET} and ^A indicate ex-type, ex-epitype and authentic strains, respectively.

2

ITS: internal transcribed spacers and intervening 5.8S nrDNA; rpb1: partial RNA polymerase II largest subunit gene; tef1: partial elongation factor gene.

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Fig. 17. RAxML phylogram obtained from the combined ITS (715 bp), LSU (881 bp), rpb1 (617 bp) and tef1 (427 bp) sequence alignment of all the accepted species of Gaeumannomyces. The tree was rooted to Pseudophialophora eragrostis CM12m9 and Falciphora oryzae CBS 125863. RAxML bootstrap support (BS) values above 70 % are shown in the nodes. GenBank accession numbers are indicated in Table 6. ^{T, ET} and ^A indicate ex-type, ex-epitype and authentic strains, respectively. TreeBASE: S21899.

Ascomata perithecial, superficial, submerged, globose, subglobose to elliptical, with a central, ostiolate, cylindrical neck, dark brown to black; ascomatal wall comprised of pseudoparenchymatous cells, light or brown. Hamathecium comprised of septate, often constricted at septa, hyaline paraphyses, widest at base and gradually narrow at apex, exceeding asci, dissolving at maturity. Asci numerous, unitunicate, cylindrical to elongated clavate, short stalked, with apical refractile ring, 8-spored. Ascospores cylindrical, slightly curved to sinuate, widest in middle, ends rounded, vacuolated, septate, septa often indistinct, hyaline to pale brown, faintly tinted yellowish in mass. Conidiophores branched, verticillate, indeterminate, brown, often reduced to conidiogenous cells, hyaline to brown. Conidiogenous cells phialidic, solitary or in dense clusters, lageniform, cylindrical, straight or slightly curved tapering to a short cylindrical to funnel-shaped or hardly visible collarette. Conidia dimorphic (A) according to Wong & Walker (1975) “germinating phialidic conidia”: solitary, grouped in slimy heads, ovoid to cylindrical, straight or slightly curved, tapering to an often acute base, hyaline, and/or (B) according to Wong & Walker (1975) “non-germinating phialidic conidia”: solitary, arranged in heads, hyaline, falcate to lunate, usually strongly curved in a semicircle with varying degrees of curvature. Hyphopodia when present hyaline becoming brown when mature, simple or lobed. Sclerotia present or absent (adapted from Hernández-Restrepo et al. 2016b).

Culture characteristics: Colonies on PDA mycelium mostly submerged, dark (grey olivaceous, greyish sepia, isabelline) aerial mycelium scarce, or sometimes cottony, white; margin effuse, irregular to rhizoid. On MEA elevated, cottony to funiculose, aerial mycelium white or pale i.e. pale greenish grey, smoke grey, submerged mycelium black, margin effuse to rhizoid. Cultures of Gaeumannomyces vary in colour, growth rate and amount of aerial mycelium, dark hyphal strands and black sclerotia.

Optimal media and cultivation conditions: MEA and PDA incubated at 15–30 °C depending of species. Other methods described for production of perithecia include PDA with wheat seedlings (Speakman 1982) and flooded cultures in MPA (Speakman 1984).

Distribution: Worldwide.

Hosts: Mainly pathogens on grasses (Poaceae on Avena, Hordeum, Oryza & Leersia, Secale, Sorghum, Triticum, xTriticale, Zea, turf grasses, buffalo grass and other grasses) and Cyperaceae, but some occur on non-grass hosts as saprobes or endophytes.

Disease symptoms: Take-all, crown black sheath rot, dieback, root decline, patches of white heads after flowering, stem- and root rot.

Notes: Gaeumannomyces comprises about 20 species (Hernández-Restrepo et al. 2016b) that are mainly pathogenic to grasses, but some species are also regarded as saprobic or endophytic. The generic type Gaeumannomyces graminis included four varieties based on ascospore size, hyphopodial morphology and host preferences i.e. G. graminis var. graminis, G. graminis var. avenae, G. graminis var. tritici and G. graminis var. maydis (Turner, 1940, Dennis, 1960, Walker, 1972, Yao et al., 1992). After a wide range of isolates were subjected to DNA sequence analyses, it was demonstrated that these established varieties and cryptic species represent different, phylogenetically supported species (Ward and Bateman, 1999, Ulrich et al., 2000, Freeman and Ward, 2004, Hernández-Restrepo et al., 2016b). Gaeumannomyces tritici and G. avenae, the causal agents of take-all of wheat and oat respectively, are more aggressive pathogens than G. graminis and other species in the genus. Species of Gaeumannomyces are morphologically difficult to distinguish because of their simple morphology, overlapping morphological features and considerable intraspecific variation.

References: von Arx and Olivier, 1952, Deacon, 1973, Deacon, 1974 (taxonomy); Walker, 1972, Walker, 1975, Walker, 1980, Walker, 1981 (taxonomy, morphology, pathogenicity); Asher & Shipton 1981 (biology and control); Elliott, 1991, Elliott et al., 1993 (pathogenicity); Bateman et al., 1992, Augustin et al., 1999, Ulrich et al., 2000, Rachdawong et al., 2002 (molecular data); Freeman & Ward 2004 (review); Hernández-Restrepo et al. 2016b (morphology and phylogeny).

Authors: M. Hernández-Restrepo & P.W. Crous