Ascomycetes: Phylum Ascomycota
Ascomycetes
• Group of fungi
characterized
by their
production of
sexual spores
in a sac-like
structure called
an ascus.
“Cup fungus”
Types of Ascomycete
• yeast
• powdery mildew
• cup fungi
– many of these produce spores suited
for airborne dispersion.
The Ascomycota
•Most are blue-green, red and brown molds
that cause food spoilage
• Non motile
•Penicillin
•Form ascospores Internally in Asci
Ascomycetes Eyelash cup, Scutellinia scutellata
Ascomycetes can cause plant
disease
• Brown rot of stone
fruits (Monilinia
fructicola)
•chestnut blight
(Cryphonectria
parasitica)
Dutch elm disease
( Ophiostoma ulmi)
Beneficial Ascomycete
• Many Yeast are also ascomycetes
•Edible Morels and truffles
Edible black truffle,
Tuber melanosporum
spore-bearing structure is
produced below ground
mainly on oaks and
hazelnuts
Edible Ascomycete
Ascomycetes growth
• Most have either unicellular or
filamentous growth forms
• Hyphae have perforated septa
• Hyphal cells of Vegetative
mycelim may be either
uninucleated or multinucleated
• Some are homothallic others
heterothallic
Life cycle of an Ascomycete
• Most species undergo asexual reproduction
by the formation of multinucleated conidia
• Conidia formed from the conidiogenous
cells
• Conidiogeneous cells are borne at the tips of
modified hyphae called conidiophores
“conidia bearers”
Conidia- the characteristic
asexual spores of
ascomycetes shows the
stages in the formation of
conidia which infects the
velvetbean caterpillar
TEM of Various
stages of
developments of
conidida
Ascomycetes spore development vs.
Zygomycetes spore development
• Unlike zygomycetes which produce spores
internally within a sporangium,
ascomycetes produce their asexual spores
externally as conidia.
Sexual reproduction in
Ascomycetes
• Always involves the formation of an ascus (pl.
asci)- saclike structure within which a haploid
ascospores are formed following meiosis.
• Because the ascus resembles as sac, commonly
referred to as “sac fungi”
• Both the asci and ascospores are unique structures
that distinguish the ascomycetes from all other
fungi
• Ascus formation usually occurs within a complex
structure composed of tightly interwoven hyphaethe ascoma (pl. ascomata) or ascocarp.
Maturing ascospores in
Asci of Ascodesmis
nigricans
Enclosed asci and
ascospores of Ascoma
called a cleistrothecium
An ascoma of Coniochaeta
showing the enclosed asci
and ascospores
Perithecium- fruiting body
contains ascospores
Xylaria fungus
Perithecium with ascospores
“Dead mans fingers”
Finger Xsec
Hymenial layer
• Asci usually develop on an inner surface of
the asoma, a layer called the hymenium or
hymenial layer
Hymenium of an ascomycete showing asci with
ascospores section thru the hymenial layer of Morela
Life cycle of Ascomycete
• The mycelium grows out from a
germinating ascospore
• Mycelium begins to reproduce asexually by
forming conidia
• Many conidia are produced
• Conidia are responsible for propagating and
disseminating the fungus
Ascomycete life cycle
Sexual Reproduction
• Occurs on the same mycelium that produces
conidia
• The formation of multinucleate gametangia called
antheridia (male) and ascogonia (female) precedes
sexual reproduction
• Male nuclei pass into the ascogonium via the
trichogyne which is an outgrowth of the
ascogonium
• Genetically different nuclei pair but do not fuse
• Ascogenous hyphae now begin to grow
• Compatible pairs of nuclei migrate and cell
division occurs and creates dikaryotic cells- two
compatible haploid nuclei
• Crozier- the apical cell of the ascogenous hypha
which allows the paired nuclei to divide
simultaneously
• Compatible pair of nuclei fuse (karyogamy) to
form a zygote
• Zygote undergoes meiosis producing ascus with 8
nuclei
• Haploid nuclei cut off to form ascospores
• Ascus as it matures becomes turgid, and finally
burst to release its ascospores