True Fungi (Eumycophyta) 1
Deuteromycota – Fungi
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This group of fungi comprises over
20,000 species and is very important in breaking down organic matter, as
plant and animal pathogens and for industrial importance. They are all higher true fungi, which lack
a known perfect stage. Their mycelium
is like that in the Ascomycota and vegetative reproduction structures are
common to both groups. Over 90
percent of the important fungi that have been shown to possess a perfect, or
sexual, stage have been Ascomycota.
Most of the Deuteromycota produce conidia of one kind or another. There is substantial evidence that at
least the majority of these fungi are of Ascomycetous affinities. Indeed, it is probable that a great many
of them are Ascomycota whose perfect stages have simply escaped
discovery. Mycologists continue to
report finding ascigerous stages of several fungi previously included in this
group. Thereafter these drop out of
the Fungi Imperfecti and are renamed and reclassified on the basis of the
newly acquired information. How many
other members of the Fungi Imperfecti will in a similar way ultimately be
eliminated from the group can only be conjectured. However, it seems likely that among the large number of species
at present catalogued as Deuteromycota, there are some that never do produce
a perfect stage, perhaps having lost the ability in the course of evolution,
reproduction by conidia or other vegetative means having proved adequate for
survival. Four orders that will be
discussed here are Sphaeropsidales, Melanconiales, Moniliales and Mycelia Sterilia.
In 1952 Alexopoulos gave a
detailed narrative of the Deuteromycota, and the following description is
derived therefrom [Alexopoulos, C. J. 1952.
John Wiley & Sons, NY. 482
A great many
fungi are known which have septate mycelium and which, so far as anyone has
been able to discover, reproduce only by means of conidia. Since these fungi
apparently lack a sexual phase (perfect stage), we call them commonly
"imperfect fungi," and technically "Fungi Imperfecti."
Many of these are saprobic, but many are of great importance to us because
they are parasites that cause diseases of plants, animals, and human beings.
The conidial stages of most
of these fungi are very similar to conidial stages of some well-known
Ascomycota, and we presume that, with relatively few exceptions, the
imperfect fungi represent conidial stages of Ascomycota whose ascigerous
stages are either rarely formed in nature and have .not been found, or have
been dropped from the life cycle in the evolution of these organisms. Indeed,
in some cases we have found the sexual stages in nature or have produced them
in culture many years after the fungi were first described as imperfect
fungi. In such cases, the organisms can be classified in the ascomycete
genera in which the characters of the ascigerous stage place them.
In a few cases, the perfect
stages, which have been discovered, have proved to be Basidiomycota. The
Fungi Imperfecti are, therefore, conidial stages of Ascomycota, or, more
rarely, Basidiomycota, whose sexual stages have not been discovered or no
Because there are thousands
of such fungi which do not fit our classification system, because it is based
on the characters of the sexual stage, a practical need has arisen for a
convenient system, artificial though it be, the chief purpose of which is to
'provide a method of identifying and naming these organisms. Accordingly, we
group all these fungi into the form-class Deuteromycota, which we subdivide
into a number of form-orders, form-families, form-genera, and form- species.
In each of these categories we group fungi which have in common some
morphological characteristics of their conidial stages, and which we can,
therefore, conveniently identify and catalog. By such groupings, however, in
no way do we imply that the organisms we place in anyone group are related,
for we cannot surmise relation- ships in fungi unless we know the sexual
stages. Two fungi whose conidial stages are almost exactly alike, and which,
therefore, we would classify in the same form-genus, might have sexual
stages, which are sufficiently different to place them in different ascomycetous
genera. For example, Septoria rubi and Septoria avenae, two "imperfect
fungi" which we had classified in the form-genus Septoria on the basis
of their conidial stages, were found to have perfect stages, one of which
belongs to the ascomycetous genus Mycosphaerella (MycosPhaerella rubi), and
the other to the ascomycetous genus Leptosphaeria (Lepto- sphaeria avenaria).
Similarly, two Ascomycota belonging to the same ascomycetous genus may have
vastly different conidial stages. For example, Mycos Phaerella fragariae
on strawberry forms its conidia at the tips of long, loosely produced,
unorganized conidiophores, whereas the aforementioned Mycosphaerella rubi on
raspberry, bears its conidia on very short conidiophores inside a pycnidium.
In accordance with our artificial system of classification of the
Deuteromycota, we would place the conidia of Mycosphaerella fragariae in the
form-genus Ramularia that belongs in the form-order Moniliales, but those of
Mycsphaerella rubi in the form-genus Septoria that belongs to the form- order
Sphaeropsidales. Because of these facts, it is clearly impossible to devise a
system of Classification of the Deuteromycota, which will indicate
relationships. Once you understand this situation you will have no difficulty
in grasping and accepting the seemingly complicated and confused state of
affairs arising from the existence of this large group of fungi.
The convenience of such a
system of classification for the imperfect fungi has been carried further to
include the conidial stages of known Ascomycota. Since many Ascomycota,
particularly the parasitic ones form their ascocarps but once a year, we are
much more likely to en- counter these fungi in their conidial stages. By
including these stages in the general scheme of classification of the
Deuteromycota, we can identify a fungus by its conidial stage without having
to wait for it to develop its ascus stage. This, of course, results in two
names for each Ascomycete whose conidial stage was discovered before its
perfect stage: one name-the valid one-which we give to the ascigerous stage
to indicate its relationships, and one name-a synonym-which indicates the
type of conidia the fungus produces. For example Venturia inaequalis,
the cause of apple scab,
produces one- or two-celled, brown conidia on short conidiophores. As these
are the characters of the form-genus Fusicladium, we often refer to
the imperfect stage of Venturia inaequalis as Fusicladium
dendriticum, which name was given to the fungus before the perfect stage
was discovered. Since, according to the International Rules of Botanical
Nomenclature, a member of the Plant Kingdom may have but one valid name, Venturia
inaequalis is the valid name of the fungus. But, since the name Fusicladium
indicates to the mycologist the precise type of conidial stage produced,
mycologists find it more convenient to say that Venturia inaequalis has
a Fusicladium imperfect stage than to describe the conidia and
conidiophores in many words. For this reason we often write the name of the
imperfect stage of an ascomycete in parenthesis after the valid name thus: Venturia
in- aequalis (= Fusicladium dendriticum); or still more properly: Venturia
inaequalis (Cke.) Wint. [= Fusicladium dendriticum (Wal.) Fcl.].
The naming of the conidial stages is so convenient and has been adopted so
widely that the International Botanical Congress decided at its Stockholm
meeting in 1950 to legalize the use of form-names for conidial stages, still
recognizing, of course, the name of the perfect stage as the official name
for the entire organism. Thus, when we speak or write about the apple scab
fungus as a whole, or of its ascus stage in particular, we use the
name Venturia inaequalis, but when we are dealing with the conidial
stage of this fungus it is convenient- and now legal and proper-to refer to
it as Fusicladium dendriticum.
Before discussing the classification of the Deuteromycota, it is well to
review the various methods of conidial production and to say something about the
morphology of the structures concerned.
The Conidiophor: Conidia
are generally borne on conidiophores, which may be produced loosely and
indiscriminately by the somatic hyphae or grouped in various types of asexual
fruiting bodies. Fungi that produce conidia on more or less loose, cottony
hyphae we often term Hyphomycetes. Such cnidiiferous hyphae may be simple or
variously branched. They may be little different from the somatic hyphae and
indistinguishable from them, or they may be characteristically marked and
provided with sterigmata or specialized branches on which they bear the
conidia. Some conidiophores are inflated at the tips, as we have seen in Aspergillus;
others are inflated at intervals, forming knee-like structures in which
the conidia are grouped (Gonatobotrys); still others have many
branches that are characteristically arranged in whorls (Verticillium), in
a sympodium (Monopodium), or in various other ways (Plate 102). In fact, we can find
almost every conceivable variation in the branching or marking of
reproductive hyphae among the more than 10,000 species that produce their
conidia in this fashion.
A group of conidiophores
often unite at the base and part way up toward the tip, and form a structure
we call a synnema (Plate 103d). The top of the synnema
is often much branched, the conidia arising at the tips of the numerous
branches. In some synnemata the stalk of the fructification is longer in
comparison to the branched top, and the fruiting body resembles a
long-handled feather- duster. When a large number of conidiophores arise from
the surface of a cushion-shaped stroma, the resulting structure is a
Besides true conidia, some
fungi, especially animal and human pathogens, produce other types of asexual
spores such as microconidia, blastospores, and arthrospores. Microconidia are
very small conidia. Blastospores (Gr. blastos = bud, shoot + sporos = seed, spore) are asexual spores
formed by budding either directly from a hypha, or from any other cell.
Arthrospores (Gr. arthron = joint + sporos = seed, spore) are formed
by the breaking up of the hyphae into their component cells. They are no different
from oidia. All three of these germinate to form mycelium and function the
same as conidia.
The Pycnidium: In
a certain group of imperfect fungi, the conidia arise in globose or
flask-shaped bodies known as pycnidia. The conidiophores in the pycnidia are
generally very short (Phyllosticta) in some cases almost absent (Plenodomus).
In the pycnidia of other fungi, on the contrary, the conidiophores are
quite long and distinctly branched (Dendrophoma) (Plate 102b). In all cases, they
arise from the internal cells of the pycnidial wall. In external appearance,
some pycnidia resemble perithecia of some of the Pyrenomycetes, and the only
way you can be certain of their nature is to crush them and examine their
contents under the microscope. The perithecia, of course, contain asci,
whereas the pycnidia contain conidia.
The pycnidial wall is pseudoparenchymatous. Approximately
the same variations in configuration can be found in pycnidia as have been
described for perithecia. Pycnidia may be completely closed or may have an
opening (ostiole); they may be provided with a small papilla or with a long
neck leading to the opening; they vary greatly in size, shape, color, and
consistency of wall; they may be superficial or sunk in the substratum; they
may be uniloculate, simple or labyrinthiform; they may be formed directly by
the loose mycelium or may be definitely stromatic. This great variation in
pycnidial structure serves to delimit the various genera of the pycnidial
Deuteromycota (Plate 150).
Kempton (1919) found that
this group of fungi utilizes three methods of pycnidial production. According
to the first of these, which Kempton calls simple meristogenous, the
pycnidium originates from the division of a single cell or a number of
adjacent cells in the same hypha (Plate 151a). In the compound meristogenous
type the pycnidial origin is traced to the division and merging of several
cells from several closely appressed hyphae (Plate 151b). Finally, in the
symphogenous type of development, a number of hyphal branches from different
hyphae grow toward a common point and interweave to form the pycnidial
initial (Plate 151c).
From this the pycnidial wall develops, a cavity is formed in the center, and
the conidiophores grow out of the inner wall cells lining the cavity. The
conidia, also called pycnidiospores when they are borne in pycnidia, are
produced at the tips of the conidiophores.
The Acervulus: The acervulus is typically a flat, open bed
of generally short conidiophores growing side-by-side and arising from a more
or less stromatic mass of hyphae. Conidia are borne at the tips of the
conidiophores. Some authors do not consider any such structure an acervulus
unless it is formed underneath the cuticle or epidermis of a host plant and
eventually becomes erumpent. Such a concept, which would define a fungal
structure not in terms of its own morphology but rather in terms of its
relation to the host, should probably be avoided.
In addition to the
conidiophores and interspersed with them, some acervuli produce long, stiff,
pointed, dark structures that look like bristles; these are the setae (sing.
seta; L. seta = bristle). Setae
may be abundantly formed by certain form-species or may be very sparse. As a
matter of fact, it appears that the type of substratum and environmental
factors influence this characteristic considerably.
methods employed for the formation of pycnidia also serve for the formation
of. acervuli, the origin of which may be simple meristogenous, compound
meristogenous, or symphogenous. This undoubtedly explains the fact that
intermediate forms, between pycnidia and acervuli are produced by some fungi
which ~re, therefore, difficult to classify.
Characteristics Used In Classification: The
characteristics we use for the classification of the Deuteromycota are the
type of fructification and the shape, color, 'and septation of the conidia.
Types of fructification form the basis for separation of form-orders. We
place those fungi which produce their conidia in pycnidia in the form- order
Sphaeropsidales; all those which form acervuli, in the Melanconiales; and.
those which reproduce in any other way (budding, fragmentation of hyphae into
oidia, loose conidiophores, sporodochia, or synnemata), in the Moniliales. A
group of fungi also exists in which no conidia or other reproductive cells
are known. These we place in the form-order Mycelia Sterilia. Many of the
Mycelia Sterilia, when their perfect stages were discovered, proved to be
The Sphaeropsidales and
Moniliales are subdivided into a number of form-families, the first on the
basis of pycnidial characters such as shape, color, and consistency of wall,
the second on the basis of conidiophore grouping and color. The Melanconiales
comprise only one form-family, the Melanconiaceae, and the Mycelia Sterilia
are an assemblage of form-genera so heterogeneous that we make no attempt
whatever to organize them into form-families.
Form-genera of the Deuteromycota
are based on such characters as type of conidiophores, and color, shape, and
septation of conidia. Form-species are based almost entirely upon the host on
which they are found and the size of their conidia.
Because of the great number of form-genera in the Deuteromycota (Bender
listed 1335 in 1931), Saccardo (1899) proposed a breakdown of the
classification into groupings (sections) of form-genera in accordance with
conidial characters. This is a very convenient system and one that
mycologists the world over have adopted.
The "section" is
not an official category in the classification system, but rather a
convenient group of form-genera under each form-family, which exhibit the
same conidial characters as far as shape, color, and septation are concerned.
this order the spores are borne in a flask-shaped pycnidium on the inside of
which are conidiophores bearing conidia (pycnospores).
form-families have been distinguished as follows: (1) Sphaeropsidaceae
(pycnidia dark colored,
leathery to carbonous, stromatic or non-stromatic generally provided with a
circular opening). (2) Zythiaceae (pycnidia
as in the Sphaeropsidaceae but light colored instead of dark, and soft or
waxy instead of leathery). (3) Leptostromataceae (pycnidia
shield-shaped or elongated, flattened).
(4) Excipulaceae (mature pycnidia
somewhat deeply cup-shaped).
In the family Sphaeropsidaceae species of the genus Darluca are
hyperparasitic on rusts. Species of Cicinnobolus
are hyperparasites of powdery mildew.
Their mycelium is grown longitudinally in the mycelium of their hosts.
refer to the following plates for characteristic structures in the
150 = Pycnidia types: Zythis fragariae, Dendrophoma
abscurans, Chaetomella atra, Diplodia zeae,
Fusicoccum viticolum & Endothia parasitica.
Plate 151 = Pycnidial
development: Phoma herbarum, P.
pirina & Zythia fragariae.
Plate 153 = Sphaeropsidales: Pycnidiospore types.
240 = Example Structures:
Deuteromycota: Sphaeropsidales: Sphaerioidaceae
Melanconiales Spores are borne on an
acervulus in this order (as in the genus Higginsia of the Ascomycota)
form-family has been designated: Melanconiaceae. Many species are parasitic on plants and
cause a group of diseases called anthracnoses. The acervuli that are the characteristic
structures of this family usually develop below the cuticle or below the
epidermis of the host plant. They
release their conidia in characteristic droplets, which may be white,
cream-colored, pink, orange or black depending on the pigmentation of the
In the family
has setae, the genus Colletotrichum does not have setae and Cylindrosporium
is lit the genus Higginsia of the Ascomycota: Helotiales.
Please refer to the
following plates for characteristic structures in the Melanconiales:
Deuteromycota (Fungi Imperfecti): Melanconiales
= Acervuli: Gloeosporium sp.
& Colletotrichum lindemuthianum.
= Melanconiales: Conidia types.
Plate 241 = Example
Structures: Deuteromycota: Melanconiales & Mycelia Sterilia
order includes all the other spore-producing forms and contains the greatest
number of species. Many species are
of great importance and the group contains most of the fungal
pathogens of humans. It is also the group that has many of the
fungi that or of industrial importance.
Species of Penicillium and Aspergillus that are not
known to form cleistothecia are included.
The so-named "false yeasts" that are not known to produce
ascospores are grouped here. There
are a number of serious plant pathogens as well and some common contaminants
of the biological laboratory and many soil fungi what are saprobic and may
play a significant role in the soil economy.
Eight family are included here.
The family Stilbaceae has
a coremium or synnema. The majority
of species are saprobic. The
is economically important because several species are
responsible for blue stain of lumber
that reduces market value. The
imperfect stage of Ophiostoma ulmi (= Graphium ulmi) belongs here
The family Tuberculariaceae has
a sporodochium, which is a cushion-like mass of hyphae. The genera Tubercularia, Volutella
and Fusarium are well known.
In Tubercularia the sporodochium is usually shaped like a
mushroom, with a very short stalk and a smooth surface. In Volutella the sporodochium produces
setae that arise here and there over the entire fructification. Volutella fructi causes Dry Rot
of Apples. The form-genus Fusarium is the largest in this family and taxonomically one of the
most difficult of all fungal groups. Fusarium
produces long, crescent-shaped, multiseptate macroconidia usually borne on
sporodochia, and very small spherical, oval elongated or crescent shaped
microconidia on simple or branched single hyphae. Chlamydospores are also regularly produced by the mycelium, and
sclerotia are often formed. Parasitic
species are generally vascular parasites that cause wilts of plants by
plugging the conducting tissues and by toxin secretions. Among the most destructive species are Fusarium
solani on potato, Fusarium cubense on banana and Fusarium
lini on flax (Plate 159).
The families Moniliaceae and Dermatiaceae have
spores scattered over the mycelium.
The Moniliaceae have hyaline spores whereas the Dermatiaceae have dark
pigmented spores. The genus Thielaviopsis
has endoconidia, but they may also produce macroconidia or chlamydospores in
Moniliaceae is the larges of all the form-families. It includes all imperfect fungi that produce conidia on
unorganized, hyaline conidiophores or directly on the somatic hyphae. Most species are saprobic, but many are
important plant parasites
and others are human pathogens. The imperfect stages of Aspergillus and
Penicillium belong here (Plate 102,f).
The family Dermophyta is
related to Gymnoascaceae of the Ascomycota.
In the family Cryptococcaceae there
are asporagenous yeasts, which are related to Saccharomyces of the
Ascomycota. The Genus Candida incites a human disease
called "Thrush." The Genus Cryptococcus
includes animal pathogens and Torulopsis is
a food yeast that is used for animal food.
The family Rhodotorulaceae is asporagenous yeasts
that are possibly related to the Basidiomycota: Dacryomycetales.
The family Sporobolomycetaceae is
also asporagenous yeasts that are possibly related to the Basidiomycota: Dacryomycetales. Sporobolomyces species have pink or orange-pigmented
forms. They may reproduce by simple
budding or they may produce sterigmata with spores that are shot off forcibly
Please refer to the
following plates for characteristic structures in the Moniliales:
Deuteromycota (Fungi Imperfecti): Moniliales
= Capsules of Cryptococcus neoformans.
= Structures of Candida albicans & Geotrichum sp.
= Budding & spore production: Nectaromyces
spp. & Sporobolomyces spp.
= Moniliales: Conidia types.
= Sporodochium of Fusarium lini & Fusarium sp.
242 = Example Structures:
Mycelia Sterilia includes a group of fungi in which no
conidia or other reproductive cells are known. Sclerotia are formed, but there are no fruiting bodies (=
spores). Many of the Mycelia Sterilia
proved to be Basidiomycota when their perfect stages were discovered. Of the over two form-genera in this group,
and Sclerotium are the best known and most
widely distributed. Rhizoctonia
is usually found in soils causing damping-off and
root rot of their host
filamentosa, a basidiomycete, has Rhizoctonia solani as
its imperfect stage. It causes Black
Scurf of potatoes
and attacks other plants as well. Sclerotium cepivorum known in the form of small black
slcerotia produced on white, cottony hyphae, causes white rot of onions and
garlic. Sclerotium rolfsii is
omnivorous and can be very destructive on plants.
refer to the following plates for characteristic structures in the Mycelia
Deuteromycota (Fungi Imperfecti): Mycelia
Plate 241 = Example
Structures: Deuteromycota: Melanconiales & Mycelia Sterilia
Recognition of Tribes And Sub-Tribes
The final subdivision of most of
the families into the equivalent of tribes and sub-tribes is done on the basis
of spore form, structure and color, and utilizing the "Saccardo
Spore Sections" (= Italian mycologist: 1880-1925) with the
Amerosporae = spores 1-celled but not long, notstellate, spiral, or
Hyalosporae = spores hyaline
Phaeosporae = spores dark
Didymosporae = spores 2-celled, not stellate, spiral, or filiform
Hylodidymae = spores hyaline
Phaeodidymae = spores dark
Phragmosporae = spores more than 2-celled (variable), not stellate,
spiral, or filiform
Hyalophragmiae = spores hyaline
Phaeophragmiae = spores dark
Scoloecosporae = spores long and slender (scolecospores) septate or
Dictyosporae = spores muriform
Hyalodictyae = spores hyaline
Phaeodictyae = spores dark
Helicosporae = spores spirally coiled, continuous or septate
Staurosporae = spores
stellate (star-shaped) or radiate, continuous or septate