Highlights of the Didymellaceae - Studies in Mycology

AveSkAMp et al.
also hosts the setae-lacking species Ph. pratorum, which was
classified in section Phoma. Several other coelomycete fungi are
accommodated here as well, including Phialophorophoma litoralis,
Pleurophoma cava, a sterile strain that once has been identified
as Coniothyrium sp. and various Pyrenochaeta species. The
close morphological relation between the genera Pyrenochaeta,
Pleurophoma and Phoma section Paraphoma was already
noted by Boerema et al. (1996) and Grondona et al. (1997). Like
Phialophorophoma litoralis and Pleurophoma cava, Pyrenochaeta
is characterised by the formation of elongated, filiform, multiseptate
conidiophores, a character that is however not found in the
various Phoma species embedded in this clade (De Gruyter et
al. 2009). A further delineation of the species associated with the
genera Pyrenochaeta and Pleurophoma and the Phoma section
Paraphoma will be provided in a follow-up paper by De Gruyter et
al. (2010).
Section Peyronellaea
The chlamydospore-producing species have been treated before
by Aveskamp et al. (2009a), who revealed that also Phoma section
Peyronellaea is artificial from an evolutionary point of view. Most
species, including the type Ph. glomerata, cluster in group K of Fig.
2, along with many other (uni- and multicellular) chlamydospore
producing species. To be in accordance with the phylogenetic
results, this cluster is elevated to generic level, which is named after
the section Peyronellaea. A second group of species belonging to
this section is recovered in clade L, which groups species that
produce botryoid or epicoccoid dictyochlamydospores, including
Epicoccum nigrum. Two species, Ph. pimprina and Ph. sorghina
are recombined into Epicoccum here. Species that produce
pseudoscleroid chlamydospores, such as Ph. violicicola and Ph.
chrysanthemicola were found to cluster outside the Didymellaceae.
Section Phoma
Species ascribed to Phoma section Phoma are retrieved in
practically all clades of the trees produced in the present study.
This supports the general idea that this section has been used as
a “waste-bin” for phomoid taxa that could not be placed in other
sections or genera due to the lack or presence of typical sectional
characters.
The type species of this section, and also of the genus as a
whole, is Ph. herbarum (Boerema 1964). The reference strains of
this species are accommodated amongst the basal polytomous
species of the Didymellaceae. This suggests that it has branched
off from most other members of this family in an early phase of the
development of the Didymellaceae and probably evolved further
without recombining with other taxa.
Although the description of Ph. crinicola is highly similar to
that of other species in the B. exigua clade presented in Fig. 2, it
has never been recognised as such due to the absence of septate
conidia. Nevertheless, the remaining characters do not contradict
with the description given for Ph. exigua (Van der Aa et al. 2000).
The pycnidia of Ph. crinicola usually carry a single ostiole, but
pycnidia are regularly observed lacking an apparent ostiole. This
may correspond with the ostiolar openings of many species found
within the exigua clade, which are often lined or filled with papillate,
hyaline cells.
Similar findings are Ph. aurea and Ph. nigricans in clade K,
which is mainly filled with chlamydospore-forming species that were
previously associated with the section Peyronellaea. Both species
were originally described from New Zealand (Johnston & Boerema
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1981, De Gruyter et al. 1993), but may be commonly present on
the whole Australasian continent (De Gruyter et al. 1993, 1998).
Two other species, belonging to section Phoma, but found in this
clade are Ph. anserina and Ph. eucalyptica. Both species produce
swollen cells in older cultures (De Gruyter & Noordeloos 1992),
which may be an initial phase of chlamydospore formation.
Fifteen species are phylogenetically only distantly related to the
Didymellaceae, and should therefore be excluded from the genus.
These species include the current Ph. apiicola, Ph. capitulum, Ph.
fallens, Ph. fimeti, Ph. flavescens, Ph. flavigena, Ph. glaucispora,
Ph. haematocycla, Ph. lini, Ph. minutispora, Ph. multipora, Ph.
opuntiae, Ph. pratorum, Ph. valerianae, and Ph. vasinfecta. The
problem in recombining these species is, however, the absence
of characters that could link these taxa to a specific genus. No
teleomorphs are known in this group.
Section Phyllostictoides
All taxa belonging to Phoma section Phyllostictoides are retrieved
in the Didymellaceae clade of Fig. 1 (Clade 8). This is remarkable
as this large section has been regarded, just like section Phoma,
to be a repository for all species that could not be accommodated
elsewhere. Nevertheless, within the Didymellaceae this section
falls apart as species occur in many distinct clades.
The major body of the Phyllostictoides species is retrieved in
group N, in which all Ph. exigua-related species and varieties are
found (Aveskamp et al. 2009b), as well as Ph. crinicola and Ph.
hedericola, which were associated with Phoma section Phoma.
A second group in which many Phyllostictoides taxa cluster is
clade R. This clade comprises many species of the former section
Heterospora, and several species that were excluded from this
section and transferred to Phyllostictoides by Boerema et al.
(1997), such as Ph. cucurbitacearum and Ph. ligulicola.
Section Pilosa
Only one of both members of the section Pilosa was included in
the present study. The type of this section, Ph. betae, produces a
teleomorph in Pleospora, a genus that is typified by Pl. herbarum.
Both species are related and are found in the Pleosporaceae and
Leptosphaeriaceae clade, although the genetic distance between
these species is significant. This finding illustrates the difficulties
that are experienced when delineating the Pleosporaceae (Dong
et al. 1998).
Section Plenodomus
Thus far the only section created by Boerema that still may
be monophyletic is the section Plenodomus, of which all the
members are found in the Leptosphaeriaceae. However, some
species associated with other sections, such as Ph. apiicola,
Ph. valerianae, Ph. vasinfecta (section Phoma) and Ph. violicola
(section Peyronellaea) are also linked to this clade and are found
to be closely related to the Plenodomus species. The section
Plenodomus is associated with a Leptosphaeria teleomorph, but
for the aberrant Phoma states found in this clade, no teleomorphs
are known. Boerema et al. (2004) mentioned five Leptosphaeria
species that produce Phoma anamorphs, but that do not fit within
the Plenodomus concept. These species, including L. sacchari, L.
haematitis, L. libanotis, L. purpurea and L. weimeri were however
not to our disposal, and were therefore not studied. Apparently the
genus Leptosphaeria produces multiple anamorphs.
Most taxonomic studies on the Leptosphaeriaceae reveal
a monophyletic group, although in these studies, only a limited