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Ascomycetes II in lab tomorrowAscomycetes II in lab tomorrow• Quiz (Lab manual pages 35 -50 ‘Ascos I’ & ‘Ascos
II’ and intro pages for Ascos III (pp. 51-52) intro pages for Isolation of fungal pathogens (pp. 7-8).
• Look at Ascomycete diseases – signs and symptoms – emphasis is on asexual reproductive structures
• Attempt to isolate fungal pathogens into culture
Ascomycetes II• Diseases caused by Ascomycete
pathogens where the asexual spore stage(s) plays a prominent role
• This group has the largest number of pathogen species relative to other groups we will look at
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Other names for this group:Fungi ImperfectiDeuteromycetes
Artificial taxonomic names created to solve a practical problem:
• Ascomycetes for which the ability to produce sexual spores has been lost
or• Sexual spores are only very rarely involved
with the primary disease cycle
Names given to fungal species are based on the Names given to fungal species are based on the morphology (size and shape) of the spores and morphology (size and shape) of the spores and
sporocarpssporocarps (e.g., ascocarps)(e.g., ascocarps)
Owing to the rarity of observation of sexual Owing to the rarity of observation of sexual stages in many Ascomycetes, potentially two stages in many Ascomycetes, potentially two Latin binomial names can be assigned to one Latin binomial names can be assigned to one
organismorganism
One name is based on the sexual spore (if it One name is based on the sexual spore (if it exists) and the other name is based on asexual exists) and the other name is based on asexual
spore (it usually exists)spore (it usually exists)
Practical problem:
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Teleomorphic name Anamorphic name
Anamorph“imperfect stage”
Preferred terminology:Teleomorph
“perfect stage”
Spilocaea pomiSpilocaea pomiBotrytis spp.Fusarium spp.Verticillium dahliaedoes not existdoes not exist
Examples:Venturia inequalisBotryotiniaBotryotinia spp.spp.Giberella spp.does not existdoes not existSclerotinia sclerotiorum
Spores formed by mitosis (conidia)
Spores formed by meiosis (ascospores)
Based on asexual stageBased on sexual stage
Asexual fruiting bodiesTrees -- conidiophores
Disks -- acervulus
Flasks -- pycnidia
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Conidial life cycle
Anamorphic genera that cause important plant diseases
• Septoria (pycnidium)• Colletotrichum (acervulus)• Alternaria (coniophore)• Botrytis (conidiophore)• Verticillium (conidiophore & microsclerotia)
• Fusarium (conidiophore & clamydospore)
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PycnidiumFlask-shapedstructure bearing conidia –
Typically, duringrain, spores oozeout, and are Splash dispersed
PycnidiaSimilar to a perithecium but with conidia instead of asci
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Seportia leaf spots – necrotrophic
Pycnidia
Needle-shaped conidia
Acervulus
Flat or disk-shaped fruiting bodyimbedded in plant tissue
Frequently, fungi that produce this type of structure cause “antracnose” diseases
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Anthracnose of bean
Anthracnoseof turf
33rdrd Type:Type: Conidia on conidiophoresIn this group of anamorphs, theconidiophore isstalk- or tree-like
typical pathogen:facultative saprophyte
typical diseases:molds, vascular wiltsroot & crown rotsleaf spots
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Gray Mold - Botrytis
Gray mold –common rot of many fruits, flowers andvegetables
Neck rot of onion
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Botrytis conidiophore
Botryotiniateleomorph(apothecium) – veryrare in nature
Conidiophore with masses of conidiaTeleomorph has not been observed
Verticillium – vascular wilts
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Microsclerotia of Verticillium dahliae
Dutch Elm Disease –another vascular wilt
Bark Beetle vectors fungus from dead elms to healthy elms
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Synnema(agregatedconidiophore)
The synnemaform in beetle galleries in dead elm logs
Dutch Elm Disease
FusariumThree types of asexual spores:•macroconidia•microconidia•clamydospores