Ascomycetes are a large phylum of fungi characterized by producing sexual spores called ascospores within a sac-like structure called an ascus. Common types of ascomycetes include yeasts, powdery mildews, and cup fungi. Ascomycetes can cause food spoilage and plant diseases but also include many edible mushrooms and fungi used to produce antibiotics. The lifecycle of ascomycetes involves both asexual reproduction via conidia and sexual reproduction involving the formation of ascospores within asci.
12. 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
13. 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”
14. Conidia- the characteristic
asexual spores of
ascomycetes shows the
stages in the formation of
conidia which infects the
velvetbean caterpillar
16. Ascomycetes spore development vs.
Zygomycetes spore development
• Unlike zygomycetes which produce spores
internally within a sporangium,
ascomycetes produce their asexual spores
externally as conidia.
17. 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 hyphae-
the ascoma (pl. ascomata) or ascocarp.
22. Hymenial layer
• Asci usually develop on an inner surface of
the asoma, a layer called the hymenium or
hymenial layer
23. Hymenium of an ascomycete showing asci with
ascospores section thru the hymenial layer of Morela
24. 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
26. 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
27.
28. • 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