Ascomycota Flashcards
Phylum Ascomycota
Class Ascomycetes
Morphology
-filamentous when growing (except unicellular yeasts)
-hyphae are septate
-hyphae cells of vegetative mycelium may be uninucleate or multinucleate
-some species are homothallic (self-fertile) = produce sexual structures from single genetic strain
Most of the blue-green, red and brown molds that cause food to spoil are _______
Ascomycetes
Ascomycetes cause what plant diseases
Powdery mildews that attack fruit, chestnut blight and Dutch elm disease
Yeasts belong to which fungal group
Ascomycetes
Asexual reproduction of Ascomycetes
-Form specialized spores “conidia”
-Conidia cut off from tips of modified hyphae “conidiophores”
-Conidia usually are multinucleate
Sexual reproduction of Ascomycetes
-Formation of “ascus” (asci-plural) = a sac like structure
-characteristic if phylum ascomycota
The Ascomycetes can be divided into two main groups based on Ascus morphology…..
- Unitunicate asci-thin wall
- Bitunucate asci-double wall Ascus
Ascus formation and types of asci
-complex studies composed of tightly interwoven hyphae called the ascoma also known as an ascocarp
-an ascoma may be open and more or less cup-shaped (apothecium) or closed and spherical (cleistothecium) or flask shaped with a small pore through which ascospores escape (perithecium)
The layer of asci is called the ______ or ________ layer.
In one other group, the “ascostomal” fungi, the asci are formed inside a chamber called a _______ within a mass of tissue called a ____. Such chambers differ from perithecia in that they have no….
Hymenium or hymeneal layer
Ascostroma
Strike
Wall or hymenium, and therefore are called pseudothecia
Life cycle of Ascomycetes
-Mycelium initiated with germination of an ascocarp.
-After vegetative growth, the mycelium begin to form conidiophores that bear Conidia.
-Ascus formation occurs on same mycelium that produced Conidia and is preceded by the formation of generally multinucleate gametangia called antheridia and ascogonia
-Male nuclei of the antheridium pass into the ascogonium via a Trichogyne which grows from the ascogonium
-plasmogamy, make then pair with the genetically different female nuclei within common cytoplasm but do not fuse.
-hyphal filaments now begin to grow out of the ascogonium and elongate into ascogonous hyphae
-as they grow, pairs of nuclei migrate into them and simultaneous mitotic division occurs in the hypahe and ascogonium.
-cell division in developing as igneous hypahe occurs and result in dikaryotic cells (2 haploid nuclei)
-the Ascus forms from tips of the developing dikaryotic, ascogenous hypahe
-one binucleate cells of the dikaryotic hypaha grows over to form a crozier, here the two nuclei divide, two septa are formed dividing hook into 3 cells, the middle becomes the Ascus and Karyogamy occurs here.
-the young Ascus begins to elongate
-haploid nuclei are then cut off in segments of the cytoplasm to form ascospores-burst off into air
Sexual sporulation in the ascomycota
-apical compartment of a dikaryotic ascogenous hypha Elgin’s yes and bends over to form a hook (crozier)
-two compatible nuclei in the apical compartment undergo mitosis
-septa develop to divide crosier into 3 compartments (the tip and Basal compare tins are uninucleate; middle is binucleate and is called the Ascus mother cell)
-nuclei in apical mother cell fuse to form a diploid nucleus, that undergoes meiosis to form four haploid nuclei
-each haploid nucleus divided mitotically resulting in 8 haploid nuclei
-portion of protoplasm envelopes each nucleus, forms a wall and matured into an Ascus
-another Ascus mother cell will have been developing alongside the first
-in most ascomycota, form in groups, surrounded by hypahe
3 cells of crozier
Apical- uninucleate
Penultimate cell “Ascus mother cells” -binucleate
Stalk cell (uninucleate)
Types of ascomycota
-Cleistothecium = closed
-perithecium = flask
-apothecium = cup
Cleistothesium characteristics
Closed Ascomata
-round, completely closed ascocarps; asci are arranged irregularly
-cleistothecia burst open to release their asci and ascocarps
Perithecium characterisitcs
-flask shaped ascocarps; open via a neck like ostiole with a terminal pore through which the ascocarps are liberated
-asci are arranged in orderly layer at the base of the cavity
Apothecium characteristics
-open or cup shaped ascocarp; asci are arranged on the exposed surface
-layer of asci is called the “hymenium” or hymeneal layer
Ascostroma
Pl: ascostromsta
Fruiting bodies containing bitunicate (double walled) asci in locules (cavities) usually dark with multiple locules, but sometimes single (pseudothecium)
How does a pseudothecium differ from a perithecium that is formed within a stroma
Peritehcial wall is formed by the perithecium that delimits it from the stroma. Such a wall layer is absent in the pseudothecium of the Dothideomycetes
As well, in the pseudothecium, the asci are not regularly organized into a hymenium and they are bitunucate, having a double wall which expands when it takes up water and shoots the enclosed spores out suddenly to disperse them.
Unicellular ascomycota lack _______
Ascomata
Order Endomycetales
Order Taphrinales
Order Endomycetales (yeasts)
-asexual reproduction
-fission or by pinching off of small buds
-no spore formation
Order Endomycetales (yeasts)
-sexual reproduction
- Two cells or two ascocarps unite to form a diploid zygote.
-single cell acts as an Ascus = Holocarpic (whole organism becomes the reproductive structure)
-zygote produces asexual buds or undergoes meiosis to produce four haploid nuclei (mitotic division)
Ascospores either bud asexually or fuse with another cell to repeat sexual process
Order Taphrinales
-life history
-primarily parasitic on higher plants
-cause deformities of leaves, stems and fruit
-excess growth of hyphae between host cells causes the leaves to curl
Asci of Taphrina deformans
-hypahe produce baked asci (not surrounded by ascoma) on surface of infected tissue
-asci develop to form dikaryotic hypahe, formed by sexual fusion of compatible hyphal strains within host tissue
Remaining orders of Ascomycota are separated based on……
Differences in the types of asci, the form of release of Ascospores, the types of ascoma surrounding the asci
A=unitunicate: thin walls, some release spores through small pore (operculum) while some possess a structure called an apical ring apparatus. In both spores are forcibly expelled into the air.
B=bitunicate : double wall, spores expelled theough apical pore
Order Eurotiales
-life history
-asci organization
-ascoma structure
-release of Ascospores
-reproduction method
-short lived
-asci scattered within cleistothecal ascoma and are arranged irregularly, no asci arranged on hymenium
-ascoma is completely enclosed sphere, the walls of which are made of dikaryotic hypahe
-requires degradation of breaking of the wall of the cleistothecium (no force discharge)
-primarily reproduce by formation of Conidia which are pinched off conidiophores
Order Eurotiales
Penicillium sp. importance
Blue and green molds
-repressed bacterial growth without being toxic to animal tissues. Led to antibiotics
-also used to give certain cheese their flavour, odour and character
Order Eurotiales
Aspergillus sp.
-appearance
-danger
-economic important
-conidiophores are erect and unbranched and it’s apex swells into a globular head, from which a large number of projections (phialides) bud out, each of which produce a growing chain of Conidia with youngest at the bottom. Produce black Conidia
-if inhaled, fungus can colonize lungs, causing spergillosis, and can be fatal
-production of citric acid
Order Erysiphales
-life history
-obligate plant parasites
-attack leaves and aerial parts of flowering plants
-appear as powdery mildew
Erysiphales
Infection stages/ life cycle
-begins with sexual Ascospores, or the asexual Conidia germinating on the surface of the host plants lead or stem.
-the result of germination is a branched, septate mycelium of uninucleate cells on the surface of the leaf, which feeds by putting haustoria into the epidermal cells
-in most powdery mildews, only the epidermal cells are attacked
-external mycelium gives rise to short, erect conidiophores, each of which cuts off a single row of barrel-shaped spores, the youngest being at the base.
-the diseased parts become covered with a “forest” of these conidiophores which, with their spore chains, give the white powdery appearance.
-ripe spores become detached and are readily dispersed by the wind, causing new infection
-by late august, the sexual cleistothecia are produced, from the walls specialized hypahe grow out.The cleistothecia represent the hibernating stage (black dots)
-Ascospores are dormant all winter and in late spring they resume.
-when Asci expand they rupture the cleistothecial wall and protrude beyond it. They bust and send Ascospores into the air causing new infection
How are Cleistothcia of Erysiphales unique
Asci arranged in a hymenial layer
Order Sordariales
-habitat/ life history
-morphology
-saprotrophs on dung, rotting wood and soil
-Ascomata are dark perithecia
Order Claviciptales
-what do they produce
Production of Schlerotia or ergots
-hyphae continue to grow in the ovary and produce a hard, purplish sclerotic
-sclerotium drops to the found to overwinter
Order Claviciptales
-habitat/ life history
-causes of ergot of eye and other grasses in temperature regions
-spores infect the ovaries if grasses-> mycelium produced numerous Conidia
-Conidia are excluded from the infected flowers in a sticky fluid called honeydew-> attracts insects to spore mass= Conidia dispersed by insects and dispersal by splashing rain
Upon germination, each sclerotium produces…..
One or more stalked “stromata” within which are embedded numerous perithecia
-asci within perithecia are arranged in a humenal layer
-Ascospores are released through the small “ostiole” at the narrow end
Ergot danger
Although, seldom causes serious damage to the crop of rye, it is dangerous because a small amount mixed with the rye grains is enough to cause severe illness among domestic animals or people who eat bread containing flour from such grains
-sclerotia contain powerful alkaloids like the hallucinogen lysergic acid
Erogotism-toxic condition caused by eating grain infected with ergot is often accompanied by gangrene, nervous spasm, psychotic delusions and convulsions
Ergot economic importance
Causes muscles to contract and blood vessels to constrict
-used to treat high blood pressure and stopping maternal bleeding after childbirth.
-also used to treat headaches
Apothecial Ascomycota
Produce apothecia with the asci arranged in an exposed, palisade-like layer called the hymenium.
Many are disc of cup shaped, other forms exist and can range in size from microscopic to large morels
Includes order Pezizales
Order Pezizales
-ascocarp appearance
-habitat
-lifestyle
-reproduction style
-relatively large and fleshy
-grow on dung or soil but occasionally in plant tissue
-most are saprobic
-sexually by Ascus formation
No condia!!!!
Peziza sp.
-apothecia size and appearance
-apothecia structure
-exceeds 10cm in diameter
-bowl shaped when young and became flattened and distorted with age.
-pale, dawn colour, other species have bright orange colour
-apothecium consists of a thick supporting layer of pseudo parenchyma and a hymenal layer
Peziza sp.
-at maturity, the ______ and _______ are positively ______
-at maturity, asci tips and the sterile paraphrases are positively phototropic (bending towards light)
Peziza sp.
-Asci burst
When Asci burst, the Ascospores are ejected up to 3 cm.
-in many cup fungi, the phenomenon of “puffing” occurs. During this time when thousands of asci have reached this super stretched condition, the asci burst simultaneously throwing into the air a cloud of Ascospores which drift away like smoke.
What would happen if Pezizales has non phototropic asci
-a portion of the discharged spores would be wasted through striking the opposing hymenal surface
Morchella sp. (Morels)
-appearance
-importance
-the apothecia have stalks or stipes, the fertile portion is called the pileus
-piles is essentially discoid, but it is folded over the stipe apex and is highly contorted. These distortion greatly increase the surface area of the pileus.
-the hymenium lines the large pits which are separated by sterile ridges
-highly prized edible fungi
Class Dothideomycetes are also called what
Loculoascomycetes
Class Dothideomycetes
Pathogens in this class are…
Black knot on fruit trees
Leaf and flume blotch on wheat and rye
Apple scab
The Dothideomycetes are Ascomycetes that are characterized by producing their asci in _________
Ascostroma - a locule that forms in a stroma where the asci are borne. This differed from a perithecium that is formed within a storma in that a perithecia wall is formed by the perithecium that delimits it from the stroma. Such a wall is absent in the pseudothecia of the Dothideomycetes
Ascostroma
A fruiting body containing bitunicate asci in locules; usually dark with multiple locules, but sometimes single (pseudothecium)
Black Knot Fungus appearance and causes of disease
-affects plum, damson, cherry, peach and apricots
-disease produces rough, back areas that encircle and kill infected parts, and provide habitat for insects
-pathogen cusses the formation of elongated black hypertrophied host tissue on the current year’s branches or on trunks. Generally confined to one side and are several times the normal diameter of the stem.
-Olive green swellings from the disease are visible in the late spring, but as it spreads and matures typically by automobile flight black knots circle and kill affected parts. The knots vary in size from one inch to one foot.
-older trees can kill trees by promoting insect infestations
Black knot fungus
Through the seasons
Overwinters fruiting structures on the surface of knots. Spores may be released during wet weather from the time of bud break until terminal shoot growth stops, but mostly between white bud and fruit set stages.
-infection follows on succulent shoots or wound sites. Swelling does not appear until the summer or fall after infection.
-cankers continue perennial development on the stem, and two years after initial infection the knot had its first fruiting structure at the edges of the swellings.
-spores are released and initiate new infections.
Is Black knot disease fatal
Rarely, but infected trees become stunted and dwarfed
Lichens
How are they made?
They are a symbiotic relationship between two completely different organisms- a fungus will provide protection, moisture retention, mineral salts and organic materials from the substrate to the algae. The alga in return, either through diffusion or fungal haustoria, provide carbohydrates, or guan nitrogen and vitamins to the fungi.
What organism is dominant in the lichen relationship
Fungi
Crustose Lichens
-entire thallus attached to the substrate
-grow on rock, soil, wood or tree bark
-Endolithic and endophloic lichens grow just breathe the surface of rocks and bark
Crustose lichens 3 distinct layers
Upper cortex- tightly woven fungal cells
Algal layer- loosely woven fungal hypahe with algal cells
Medulla of fungal hyphae: water and nutrient storage
Do Crustose lichens have a lower cortex
No
Crustose lichens growth
Growth occurs around the rim and sometimes the older portions dry and crack (rimose)
Often the soil crutose lichens break away from the substrate at the edges (squamulose)
Foliose Lichens appearance
-appear thalloid but have a more leafy appearance than crustose lichens
-usually attached to substrate by rhizines
-larger than crustose lichens.
-upper thallus is different from lower thallus in colour and texture.
-thallus is separated into lobes and extremities
-most of the thallus is not attached to the substrate
Foliose lichens are anatomically separated into what distinct layers
-upper cortext: secreted gelatinous layer to provide further protection from water loss.
-algal and medulla layer are similar to crutose lichens
-lower cortex: compact, protective layer of fungal hyphae that produces rhizines
Rhizines function
Primarily as anchoring structures but also have a limited role in water and mineral absorption
Fruticose Lichens appearance and habitat
-simple or divided branches: erect or pendent
-base may be more thalloid in appearance (podetium) than erect branches in soil or rock growing organisms
-cylindrical thallus
May rise erect from substrate or hang from tree branches
Fruticose lichens layers
Outer cortex: similar to upper cortex, but is around cylindrical thallus
Algae layer
Medulla
In some forms the very center of each strand is hollow
Two components to lichen reproduction are ….
- reproduction of the symbiont (fungus and partners)
- Reproduction of algae or fungi components
Fragmentation of lichens
Lichen breaks into small pieces-> carried by animal or wind
Soredia of lichens
-strucures of algal cells surrounded by fungal hyphae
-arise in algal layer and break through upper cortex as dividing units (powdery) or as small clusters (soralia)
30% of lichens
Isidia of lichens
-outgrowth on the upper or outer cortex of foliose and fruticose lichens
-contain cortical, algal and medullary layers and apples as cylindrical finger-like growth or flattened pads
15% of lichens
Reproduction of the symbiont (fungus and partners) involves what?
Asexual reproduction of portions of the fungus and the Alga. The lichen itself (symbiont) can only be reproduce asexually. Small units (propagules or fragments) containing portions of both the Alga and fungus, break off from the main organism and begin to develop on their own. There are three methods this reproduction can occur:
-fragmentation
-soredia
-isidia
Reproduction of fungal components involved what?
-involves only the fungus
-asexual or sexual
-The ascocarp or fruiting body is an apothercium, cup-shaped structure bearing hundreds of asci. A few have the more enclosed perithecia. The fungus may also produce asexual spores and the algae reproduce by cell division or sporulation.
