Oomycetes & Ascomycetes

Question 1

mycelium

Answer 1

The mass of hyphae that make up the vegetative body of a fungus

Question 2

forma specialis

Answer 2

A fungal biotype that can only infect certain species of plants; analogous to pathovar

Question 3

teleomorph, perfect stage

Answer 3

The sexual form in the life cycle of a fungus

Question 4

anamorph, imperfect stage

Answer 4

The asexual form in the life cycle of a fungus, when asexual spores (such a conidia) or no spores are produced

Question 5

pathogenicity VS virulence

Answer 5

P= The qualitative ability of an organism to cause disease

V=The quantitative ability of a strain of an organism to cause disease

Question 6

germ tube

Answer 6

The first structure that emerges from a germinating fungal spore is called a germ tube.

Question 7

appressorium

Answer 7

Swollen structure on the end of a fungal germ tube; a penetration peg emerges from it

Question 8

vertical resistance VS horizontal resistance

Answer 8

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)

Question 9

Zoospore

Answer 9

A spore bearing flagella and capable of moving in water

Question 10

Sporangium

Answer 10

A container or case of asexual spores. In some cases it functions as a single spore.

Question 11

oospore

Answer 11

A thick-walled, sexual spore of an oomycete

Question 12

Chlamydospore

Answer 12

A thick walled asexual spore formed by the modification of a cell of a fungus hypha.

Question 13

Ascomycete

Answer 13

A group of fungi producing their sexual spores, ascospores, within asci.

Question 14

Conidium

Answer 14

An asexual fungus spore formed from the end of a conidiophore.

Question 15

Ascospore

Answer 15

A sexually produced spore borne in an ascus. (

Question 16

ascocarp

Answer 16

A fruiting body of an ascomycete.

Question 17

Acervulus (acervuli pl)

Answer 17

A subepidermal, saucer-shaped, asexual fruiting body producing conidia on short conidiophores.

Question 18

Cleistothecium/chasmothecium

Answer 18

An entirely closed ascocarp (fruiting body of ascomyetes).

Question 19

Sclerotium

Answer 19

A compact mass of hyphae with or without host tissue, usually with a darkened rind, and capable of surviving under unfavorable conditions.

Question 20

Pycnidium

Answer 20

An asexual, spherical or flask-shaped fruiting body lined inside with conidiophores and producing conidia

Question 21

Conidiophore

Answer 21

A specialize hypha on which one or more conidia are produced.

Question 22

Perethecium

Answer 22

The flask-shaped ascocarp, having an opening or pore.

Question 23

Apothecium

Answer 23

An open cup- or saucer-shaped ascocarp of some Ascomycetes.

Question 24

race

Answer 24

A pathogen population that attacks a given set of plant varieties

Question 25

induced

Answer 25

Host defenses can be preformed or induced

Question 26

defense elicitors

Answer 26

Pathogen biochemicals that trigger host resistance are called ___.

Question 27

papilla

Answer 27

A plant cell wall deposition produced as a resistance response to fungal penetration is called papilla

Question 28

phytoalexin

Answer 28

Antimicrobial substance produced in plants in response to infection

Question 29

gene for gene theory

Answer 29

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

Question 30

hypersensitive reaction

Answer 30

Rapid, localized cell death at the site of infection in resistant interactions between plants and pathogens

Question 31

toxins

Answer 31

Class of chemical weapons produced by necrotrophic pathogens that kill host tissue

Question 32

enzymes

Answer 32

Class of chemical weapons produced by necrotrophic pathogens that digest host tissue

Question 33

gums

Answer 33

Class of chemical weapons produced by pathogens that plug vascular tissue

Question 34

Systemic acquired resistance

Answer 34

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.

Question 35

gene silencing, RNAi/RNA interference/RNA silencing

Answer 35

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

Question 36

ceonocytic

Answer 36

Having multiple nuclei embedded in cytoplasm without cross walls; nonseptate (oomycetes)

Question 37

Downy mildew

Answer 37

A plant disease in which the fungus appears as a downy growth on the host surface; caused by a member of the oomycetes

Question 38

Flagellum

Answer 38

Hairlike, whiplike, or tinsel-like appendage of a motile cell, bacterium or zoospore that provides locomotion

Question 39

Fruiting body

Answer 39

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

Question 40

sporangiophore

Answer 40

Sporangium-bearing stalk of a fungus

Question 41

sporangium

Answer 41

A container or case of asexual spores. In some cases it functions as a spore by germinating to form a germ tube

Question 42

zoospore

Answer 42

A spore bearing flagella and capable of moving in water (oomycetes)

Question 43

oomycete examples

Answer 43

Pythium and Phytophthora are members of this group of fungal-like organisms

Question 44

oospore

Answer 44

A thick walled, sexual spore produced by oomycetes; adapted for survival ... can germinate to producte either a germ tube, sporangium, or zoospore

Question 45

Pythium symptoms and disease cycle

Answer 45

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,

Question 46

pythium control

Answer 46

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)

Question 47

black shank of tobacco and disease cycle

Answer 47

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)

Question 48

conidium

Answer 48

An asexual fungal spore formed from the end of a conidiophore

Question 49

ascus

Answer 49

saclike structure containing ascospores (typically eight) and usually borne in a fungal fruiting body

Question 50

downy mildew of grape and disease cycle

Answer 50

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

Question 51

haustorium

Answer 51

A hyphal projection into live host cells which acts as an absorbing organ

Question 52

blue mold of tobacco and disease cycle

Answer 52

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).

Question 53

powdery mildew of rose and disease cycle

Answer 53

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.