Oomycetes & Ascomycetes Flashcards
mycelium
The mass of hyphae that make up the vegetative body of a fungus
forma specialis
A fungal biotype that can only infect certain species of plants; analogous to pathovar
teleomorph, perfect stage
The sexual form in the life cycle of a fungus
anamorph, imperfect stage
The asexual form in the life cycle of a fungus, when asexual spores (such a conidia) or no spores are produced
pathogenicity VS virulence
P= The qualitative ability of an organism to cause disease
V=The quantitative ability of a strain of an organism to cause disease
germ tube
The first structure that emerges from a germinating fungal spore is called a germ tube.
appressorium
Swollen structure on the end of a fungal germ tube; a penetration peg emerges from it
vertical resistance VS horizontal resistance
Type of host resistance where essentially no disease develops on inoculated plants; race-specific (vertical resistance, specific resistance, complete resistance)
Type of host resistance where inoculated plants develop disease but less than fully susceptible plants; no races occur (horizontal resistance, general resistance, partial resistance)
Zoospore
A spore bearing flagella and capable of moving in water
Sporangium
A container or case of asexual spores. In some cases it functions as a single spore.
oospore
A thick-walled, sexual spore of an oomycete
Chlamydospore
A thick walled asexual spore formed by the modification of a cell of a fungus hypha.
Ascomycete
A group of fungi producing their sexual spores, ascospores, within asci.
Conidium
An asexual fungus spore formed from the end of a conidiophore.
Ascospore
A sexually produced spore borne in an ascus. (
ascocarp
A fruiting body of an ascomycete.
Acervulus (acervuli pl)
A subepidermal, saucer-shaped, asexual fruiting body producing conidia on short conidiophores.
Cleistothecium/chasmothecium
An entirely closed ascocarp (fruiting body of ascomyetes).
Sclerotium
A compact mass of hyphae with or without host tissue, usually with a darkened rind, and capable of surviving under unfavorable conditions.
Pycnidium
An asexual, spherical or flask-shaped fruiting body lined inside with conidiophores and producing conidia
Conidiophore
A specialize hypha on which one or more conidia are produced.
Perethecium
The flask-shaped ascocarp, having an opening or pore.
Apothecium
An open cup- or saucer-shaped ascocarp of some Ascomycetes.
race
A pathogen population that attacks a given set of plant varieties
induced
Host defenses can be preformed or induced
defense elicitors
Pathogen biochemicals that trigger host resistance are called ___.
papilla
A plant cell wall deposition produced as a resistance response to fungal penetration is called papilla
phytoalexin
Antimicrobial substance produced in plants in response to infection
gene for gene theory
Theory that postulates that, for every host gene for resistance, there is a corresponding pathogen gene for avirulence; resulting from co-evolution of pathogen and host
hypersensitive reaction
Rapid, localized cell death at the site of infection in resistant interactions between plants and pathogens
toxins
Class of chemical weapons produced by necrotrophic pathogens that kill host tissue
enzymes
Class of chemical weapons produced by necrotrophic pathogens that digest host tissue
gums
Class of chemical weapons produced by pathogens that plug vascular tissue
Systemic acquired resistance
Host plant resistance that is induced nonspecifically, is effective against a variety of pathogens, and is systemic. Can be induced by synthetic chemicals such as acibenzolar-S-methyl.
gene silencing, RNAi/RNA interference/RNA silencing
Resistance to viruses whereby RNA viruses are destroyed or inactivated in the host cell… Eukaryotic mechanism by which specific RNA targets are destroyed or inactivated
ceonocytic
Having multiple nuclei embedded in cytoplasm without cross walls; nonseptate (oomycetes)
Downy mildew
A plant disease in which the fungus appears as a downy growth on the host surface; caused by a member of the oomycetes
Flagellum
Hairlike, whiplike, or tinsel-like appendage of a motile cell, bacterium or zoospore that provides locomotion
Fruiting body
Any of various complex, spore-bearing fungal structures fungus a eukaryotic organism that is usually filamentous (forming a mycelium) and heterotrophic, has cell walls composed of chitin, and reproduces by sexual and/or asexual spores
sporangiophore
Sporangium-bearing stalk of a fungus
sporangium
A container or case of asexual spores. In some cases it functions as a spore by germinating to form a germ tube
zoospore
A spore bearing flagella and capable of moving in water (oomycetes)
oomycete examples
Pythium and Phytophthora are members of this group of fungal-like organisms
oospore
A thick walled, sexual spore produced by oomycetes; adapted for survival … can germinate to producte either a germ tube, sporangium, or zoospore
Pythium symptoms and disease cycle
facultative parasites. Genus of fungal-like organism commonly causing seed rot and damping off … Source (=location) of primary inoculum of Pythium is from the soil, organic matter, including thatch… over winters as oospore or mycelium… disseminated by surface water, movement of soil/OM,
pythium control
A systemic fungicide commonly used against Pythium seedling diseases (Metalaxyl/Mefanoxam) A contact fungicide commonly used against Pythium seedling disease (captan) Which event in the disease cycle for Pythium seed rot do contact seed treatment fungicides target? (infection) Which event in the disease cycle for Pythium seed rot does soil sterilization target? (survival) Which event(s) in the disease cycle for Pythium blight of turfgrass does water management target? (PPI, DPI, infection, colonization, PSI, DSI)
Which event in the disease cycle for Pythium blight of turfgrass does N management target? (infection, colonization, product of secondary inoculum) … Name a factor that can enhance Pythium diseases (soil wetness, high N, suboptimal or supraoptimal temperature)
black shank of tobacco and disease cycle
P. nicotianae. facultative saprophyte. primary inoculum: soil, overwintering structure: chlamydospore. host range: tobacco. control: fungicides (mefanoxam/metalaxyl) , sanitation, resistance, rotation, soil drainage. symptom:stunting, wilting, foliar chlorosis, stem rot. dissemination: soil runoff, movement of sod, creeks, irrigation from ponds. infect: emergence sites for secondary roots, root apices. Sporangia of Phytophthora often can germinate directly (germ tube) or indirectly (zoospores). What environmental condition determines which will occur? (temperature)
conidium
An asexual fungal spore formed from the end of a conidiophore
ascus
saclike structure containing ascospores (typically eight) and usually borne in a fungal fruiting body
downy mildew of grape and disease cycle
P. viticola. primary inoculum: dead leaves, live infected shoots. infects leaves, young shoots, berries by entering through stomata with haustorium. symptoms: leaf spot/blight, shoot blight, berry rot. secondary inoculum: sporangium, zoospore. control: contact fungicides (Bordeaux mix, mancozeb, which interupt infection) favorable conditions: cool & wet conditions; succulent growth, low light
haustorium
A hyphal projection into live host cells which acts as an absorbing organ
blue mold of tobacco and disease cycle
P. tabacina. overwinters: wild tobacco relatives in TX and Mexico. control: cultural- wider row spacing to increase air circulation, reducing leaf wetness (effecting infection, and production of secondary inoculum).
powdery mildew of rose and disease cycle
Sphaerotheca pannosa f. sp. rosae. primary inoculum source: buds w/mycelium, cleistothecia on fallen leaves. product ascopores. dispersal of conidia and ascopores: wind. colonizes on plant surface. symptoms: leaf distortion, chlorosis, leaf necrosis, defoliation. sign: conidia and mycelium. secondary inoculum: conidia. control: contact fungicides like sulfur, systemic like propiconazole. oils, detergents, or baking soda also kills mycelium.
prefers soils high in N and infects juvenile tissue.
