L.12-G.Biology
Mycology
D.Ebtihal Muiz
Division:Deuteromycota
The division Deuteromycota is also called the Fungi Imperfecti or
Imperfect Fungi referring to our "imperfect" knowledge of their complete
life cycles. The Deuteromycota are characterized by production of septate
mycelium and/or yeasts, and a sexual life cycle that is either unknown or
absent. Asexual reproduction is by means of conidia (sing.=conidium) or
may be lacking. A conidium may be defined as an asexual spore that is
not produced in a sporangium. Where sexual reproduction has been
determined for species in this taxon, the sexual stage is usually referrable
to the Ascomycota or Basidiomycota. Ideally, once the sexual stage has
been determined, that species should be reclassified and placed in the
appropriate subdivision. However, this did not prove to be practical since
many species are known best by their asexual stage. Thus, a compromise
was reached and both the asexual and sexual stage are recognized. As
previously discussed in the Ascomycota, when both sexual and asexual
stages are known to occur in a life cycle, they are referred to as
telomorph and anamorph, respectively. The Deuteromycota is a
heterogeneous group of unrelated species in which sexual reproduction
has never been observed. Since mycologists refer to the "perfect phase"
of a life cycle as the phase in which sexual reproduction occurs, these
fungi are often referred to as imperfect fungi. These fungi may have lost
their sexual phase through the course of evolution. Alternatively,
biologists simply may not have found the appropriate environmental
conditions to observe development of the sexual phase of their life cycle.
The Deuteromycota are classified as fungi for two main reasons. First,
their multicellular tissue is similar to the hyphae of sac fungi and club
fungi. Second, they have erect hyphae with asexual spores, called
conidiophores, which are similar to those of the sac fungi and club fungi.
Most imperfect fungi are believed to be related to the sac fungi because
their conidiophores closely resemble those produced by the sac fungi
during their sexual phase. The imperfect fungi are not placed in the
Ascomycota phylum because classification of that group is based on the
morphology of sexual structures which the Deuteromycota do not have.
The best known fungus in this phylum is Penicillium. Some species in
this genus appear as pathogenic, blue-green molds on fruits, vegetables,
and cheeses. Several other species are important for the making of
cheeses, such as blue cheese, Roquefort, and Camembert. Certainly the
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best known product from this genus is penicillin, the first widely-used
antibiotic. Penicillin was first discovered in Penicillium notatum over 50
years ago, but is now known to be produced by many other species in this
genus. There are a number of different classification schemes for this
group of fungi. However, keep in mind that since we are not working
with sexual stages here that the classification schemes used to classify the
Deuteromycota is artificial and is not intended to show relationship
between the taxa.
These groups are no longer formally accepted because they do not
adhere to the principle of monophyly. The taxon names are sometimes
used informally. In particular, the term 'hyphomycetes' is often used to
refer to molds, and the term 'coelomycetes' is used to refer to many
asexually reproducing plant pathogens that form discrete fruiting bodies.
Other systems of classification are reviewed by Kendrick (1981).

Class Hyphomycetes lacking fruiting bodies
o Order Moniliales (producing spores on simple
conidiophores)
o Order Stilbellales (producing spores on synnemata)
o Order Tuberculariales (producing spores in sporodochia)

Class Coelomycetes spores produced in fruiting bodies
o Order Melanconiales (producing spores in acervuli)
o Order Sphaeropsidales (producing spores in pycnidia)

Class Agonomycetales lacking spoes
. Some example of orders:
1-Order: Moniliales
Conidia and conidiophore produced on mycelium (Fig. 1-2)
Figure 1: Conidiophores of Ulocladium and a single
conidium. Conidia in this order are produced directly
on hyhal cell or specialized hyphal cells called
conidiophores.
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Figure 2: Conidia of Alternaria tenuis are borne in
chains
2- Order: Sphaeropsidales
Conidia and conidiophore produced in pycnidia (sing.=pycnidium): A
fruiting body of variable shape and size, e.g., globose, flask-shaped, diskshaped, etc., in which conidia and conidiophore are borne.
Figure 4: Pycnidium of Chaetomella. Unlike most
pycnidium, this genus does not have a closed, flaskedshaped pycnidium. It is a bowl-shaped structure with many
setae: dark, thick-walled hairs.
Figure 5: Conidia of Chaetomella are bean-shaped.
3- Order: Melanconiales
Conidia and conidiohore produced in acervuli (sing.=acervulus): A platelike stroma on which conidia and conidiophore are borne (Figs. 6-8).
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Figure 6: Acervulus of Pestalotia sp. The
acervulus is covered by dark conidia
Figure 7: Acervulus at a slightly higher
magnification, with fewer conidia. The acervulus
appears to be almost cellular because of its
tightly interwoven hyphae.
Figure 8: Conidia of Pestalotia are very
distinctive.The end cells with the single
appendage is where the conidia were attached
and the other end of the conidium has two to
three appendages. Micrographs were taken under
phase optics.
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4-Order: Mycelia Sterlia
Mycelium sterile, conidia not produced. Thus, in order to identify these
fungi, other characteristics must be utilized. For example, sclerotia
(sing.= sclerotium) may be produced (Fig. 9). A sclerotium is a usually
rounded structure composed of mass of hyphae, which is normally sterile.
Such a structure serves as a "resistant" stage which may give rise to
mycelium, fruitbodies or stromata. Some genera may also have
distinctive mycelia characteristics that allow them to be identified (Fig.
10).
Figure 9: A sclerotium of the genus Sclerotium the
genus Sclerotium sp. is pictured. Taxa producing
sclerotia differ in their apperance and the differences
in their morphology is the basis by which their
genera are defined.
Figure 10: The mycelium pictured at the left is
typical of the genus Rhizoctonia. The hypha is
relatively broad and has a characteristic branching
pattern. Hyphal branches are oriented perpendicular
from their point of origin and are noticeably
constricted at their
base. Immediately above the constriction, a septum is formed.
Once again, keep in mind that the classification schemes used to
categorize the Deuteromycota is artificial and has no meaning, with
respect to phylogeny.
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