ascomycetes: phylum ascomycota
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Ascomycetes: Phylum Ascomycota
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Ascomycetes
• Group of fungi characterized by their production of sexual spores in a sac-like structure called an ascus.
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“Cup fungus”
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Types of Ascomycete
• yeast• powdery mildew
• cup fungi–many of these produce spores suited
for airborne dispersion.
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The Ascomycota
• Non motile
•Form ascospores Internally in Asci
•Most are blue-green, red and brown molds that cause food spoilage
•Penicillin
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Ascomycetes Eyelash cup, Scutellinia scutellata
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Ascomycetes can cause plant disease
• Brown rot of stone fruits (Monilinia fructicola)
•chestnut blight (Cryphonectria parasitica)
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Dutch elm disease ( Ophiostoma ulmi)
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Beneficial Ascomycete• Many Yeast are also ascomycetes
•Edible Morels and truffles
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Edible black truffle, Tuber melanosporum spore-bearing structure is produced below ground mainly on oaks and hazelnuts
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Edible Ascomycete
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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
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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”
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Conidia- the characteristic asexual spores of ascomycetes shows the stages in the formation of conidia which infects the velvetbean caterpillar
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TEM of Various stages of developments of conidida
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Ascomycetes spore development vs. Zygomycetes spore development
• Unlike zygomycetes which produce spores internally within a sporangium, ascomycetes produce their asexual spores externally as conidia.
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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.
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Maturing ascospores in Asci of Ascodesmis nigricans
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Enclosed asci and ascospores of Ascoma called a cleistrothecium
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An ascoma of Coniochaeta showing the enclosed asci and ascospores
Perithecium- fruiting body contains ascospores
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Xylaria fungus
“Dead mans fingers”
Perithecium with ascospores
Finger Xsec
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Hymenial layer
• Asci usually develop on an inner surface of the asoma, a layer called the hymenium or hymenial layer
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Hymenium of an ascomycete showing asci with ascospores section thru the hymenial layer of Morela
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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
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Ascomycete life cycle
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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
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• 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
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