Dark Septate Endophytes (DSE) in Polluted Areas 133TAXONOMY OF DSE
These fungi belong to a wide range of ascomycete taxa, but are often
members of the order Helotiales, such as Phialocephala fortinii,
Leptodontidium orchidicola or Meliniomyces bicolor (Jumpponen & Trappe,
1998; Addy et al., 2005; Vrålstad et al., 2002a). Belonging to this order we can
find an ecologically diverse and complex group of pathogenic fungi,
saprophytes, DSE, parasites of others fungi and ectomycorrhizal and ericoid
mycorrhizal fungi (Vrålstad et al., 2002a; Tedersoo et al., 2009).
Teleomorphic species of the Helotiales are characterised by inoperculate asci
and discoid, turbinate or clavate ascocarps ranging in size from the hardly
visible members of the Hyaloscyphaceae to more prominent members of the
Geoglossaceae and Sclerotiniaceae. The Helotiales was erected by Nannfeldt
(1932), and was replaced with Leotiales (Carpenter, 1988). However, the
Helotiales sensu str. and Leotiales sensu str. are currently recognised as two
separate orders, the latter only comprising the Leotiaceae sensu str. (Korf &
Lizon, 2001).
As shown in Figure 2 (Fernández-Miranda, 2014), the position of many
species within the order Helotiales is very complex, and there are species with
an uncertain position as seen in the last reorganization of the
Hyaloscypaheceae family (Han et al., 2014).
Based on rDNA ITS sequence analysis, Tedersoo et al., (2009)
differentiated 6 complexes. Several Helotiales subgroups such as the
Phialocephala–Acephala and Rhizoscyphus–Meliniomyces complexes and
Lachnum spp.
FORM INDICATES FUNCTION?
But DSE not only forms microsclerotia. Several studies demonstrated
(Fernández-Miranda, 2014; Hrynkiewick et al., 2009; Vrålstad et al., 2002a)
that these fungi are able to generate layers of fungal hyphae covering the root
surface (Figure 3 A), which could be defined as mantle, and a labyrinthine
network of hyphae among root cells that could be a Hartig net (Figure 3 B).
Therefore, these organisms are capable of generating structures that could fit
into the definition of ectomycorrhizas, at least from a structural point of view.
Moreover, in the same root system of Salix glauca, Fernando & Currah
(1996) observed that the fungi Phialocephala fortinii is capable of forming