Arx & D.L. Olivier, Trans. Brit. Mycol. Soc. 35: 32. 1952. Fig. 16.
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.
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.
ITS: internal transcribed spacers and intervening 5.8S nrDNA; rpb1: partial RNA polymerase II largest subunit gene; tef1: partial elongation factor gene.
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).
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.
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