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APS 137 Plant Physiology, Reproduction and Growth > Lecture 12: Fungi as parasites and pathogens > Flashcards

Lecture 12: Fungi as parasites and pathogens Flashcards

1
Q

Parasite:

A

an organisms which lives in or on another organism (its host) and benefits by deriving nutrients at the other’s expense (negative effect but can be very small)

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2
Q

pathogen:

A

causes disease in its host (definite negative effect on host)

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3
Q

what makes fungi such good parasites?

A

Asexual reproduction

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4
Q

how does asexual reproduction aid parasites?

A
  • allows more rapid dispersal than sexual reproduction, great when conditions are ideal
  • Adverse environmental conditions often cause sexual reproduction in fungi
  • Asexual achieved through different methods
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5
Q

Asexual reproduction methods in fungi

A
  • asexual spores
  • hyphal fragmentation
  • cell vision/budding (unicellular fungi)
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6
Q

asexual reproduction via vegetative spores:

A

Asexual spores are genetically identical to the parent and may be released either outside or within sporangium

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7
Q

asexual reproduction via cell fission or budding (unicellular fungi)

A

1) cell replicates its DNA
2) The cytoplasmic membrane elongates, separating DNA molecules
3) Cross wall forms; membrane invaginate
4) cross wall forms completely
5) daughter cells

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8
Q

Asexual reproduction via hypha fragmentation

A

hypha simply fragments into single cells

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9
Q

2 types of fungal plant parasites:

A
  • Necrotrophic

- Biotrophic

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10
Q

necrotrophic:

A
  • host plants cells are destroyed, and the fungal pathogen feeds off this material
  • sometimes the damage is discrete, sometimes it causes whole plant death
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11
Q

biotrophic:

A

-tissues are invaded but are not killed

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12
Q

necrotrophic/biotrophic or both?

A

some fungal species undergo both a biotrophic stage and a necrotrophic

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13
Q

airborne Biographic infection (Uromyces fabae)

A

1) spore arrives on plant surface
2) spore germination
3) spore swells and germ-tube emerges
4) Appressorium develops if a leaf/stem infecting fungus
5) infection peg exerts pressure against cell wall
6) cell wall penetration and a haustorium is formed

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14
Q

haustorium:

A

hyphae specialised for extracting nutrients from living cells

  • 2 parts: haustorial mother cell and large SA bit inside the cell.
  • transport of H+ and metabolites
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15
Q

haustorium membrane and wall

A
  • haustorial plasma membrane
  • haustorial wall
  • extrahaustorial matrix
  • extrahaustorial membrane
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16
Q

what links haustorial mother cell to main bit

A

neckband

17
Q

sugar deposition in healthy leaf

A
  • sugars are produced in the leaf via photosynthesis (SOURCE)
  • sugares are transported to the centres of growth or storage (SINK)
18
Q

sugar deposition in unhealthy leaf (biotrophic infection e.g Rhytisma acerinum)

A
  • MOST sugar transported towards the fungal mycelium

- LITTLE sugar transported to the centres of growth or storage (SINK)

19
Q

2 examples of biotroophic infections:

A

-stem rust –>(Basidiomycete: Puccinia graminis)
-Powdery mildew –> (Ascomycete:
Podosphaera fuliginea)

20
Q

Necrotrophic infection example

A
  • (Phytophthora infestans)
  • The Irish Famine of 1846-50
  • potato blight causes black rot on potatoes
  • peasants who ate the rotten potatoes became unwell and many got cholera and typhus. Wages to landlords couldn’t be paid
  • many died (1mill), or emigrated (2mill). Population went from 8 to 5 million
21
Q

sporangia

A

encolure in which spored are formed

22
Q

Zoospore:

A

spore with flagella

23
Q

potato blight lifecycle:

A
  • sporangia formed on diseased seedling and leaves are dispersed to healthy leaves
    -zoospores are produced and released form sporgania
    -Zoospores infect leaves
    -THEN EITHER
    – lesions and fungus develop on leaves
    OR
    –zoospores infect tubers
    -seedlings produced by infected tubers come diseased
    BACK TO BEGINNING
24
Q

New P. infestans strains

A
  • new very virulent strain called P. infestans US-8
  • no known fungicide can harm it
  • rapidly mutates to form resistance against new potato resistance genes or fungicides
25
Q

Dutch elm disease:

A
  • caused by an Ascomycete fungi species and spread bu the Elm bark beetle
  • Ophiostoma ilmi(1930’s attack) pathogen has newer, very aggressive subgroup Ophiostoma Novo-ulmi (1970’s attack)
  • ~90% of UK’s Elms have died (>25 million trees), and is still spreading northwards
26
Q

Dutch Elm disease cycle:

A

-Adult beetles emerge in spring & summer from bark of dead/decaying elms carrying fungal spores
-They feed on the twig crotches of healthy elms and introduces spores into wood
-Infected parts wilt and diseased twigs show dark streaks/ spots
-Trees weakened by disease become breeding sites for beetles
-Larvae develop galleries with in the bark
-Fungus fruits in the pupal chambers
AND REPEAT

27
Q

The actual cause of death for dutch elm disease is:

A

DEHYDRATION/STARVATION

  • in an attempt to block the fungus from spreading farther, the tree reacts by plugging its own xylem tissue with gum
  • as the xylem delivers water and nutrients to the rest of the plant, these plugs prevent them from travelling up the trunk of the tree, eventually killing it
28
Q

fungi can also be the solution ( to other fungi)

A

Biocontrol: plant pathogenic gun can be infected by mycoparasitic fungi
e.g. ~30 genera of fungi can be hyperparasitic on rust fungi

29
Q

fungi parasitic on insects:

A
  • Ability to attack and invade insects has evolved repeatedly; most fungi taxonomic groups have insect parasites
  • Most species specialised on one stage (larval/pupal/adult)
30
Q

cordyceps:

A

genus of ascomycete fungi. all are endoparasitoids, parasitic mainly on insects and other arthropods

31
Q

Anti-zombie-fungus fungus: Hyperparasitic control of ant parasite

A

-Ophiocordyceps infection in ants
-Only ~ 6.5% of all fruiting bodies
are viable spore-producers.
-This is caused by the castration of the fungus by an unknown hyperparasite, which may cause the limiting of the viable infectious spores.
-Ant colonies might not be in as much danger as previously thought

32
Q

Nematophagous fungus

A
  • loops and snares (can be inflated in 1/10th second)

- sticky hyphae

33
Q

Chytridiomycosis

A
  • infectious disease affects amphibians worldwide.
  • caused by chytrid fungus: Batrachochytrium dendrobatidis
  • the fungus invades the surface layers of the frogs skin. Infected skin cannot breathe, hydrate, osmorefulate, or thermoregulate correctly
34
Q

Chytridiomycosis in frogs example cycle

A

-Motile zoospores: swim in water, penetrate skin & form zoosporangium
-growth in diameter and complexity
-dischage papilla forms
-mortaliy ~2 weeks
-cap lost, zoospores escape through skin
(23 degrees critical temp)

35
Q

Chytrid fungus associated with how many species

A
  • Associated with >200 species extinctions of amphibians; 30% of the amphibian species of the world affected
  • -the mechanism behind the ra[id global emergence of the disease is poorly understood
  • no control method has proved to be feasible on a large scale
36
Q

enhanced call effort in Japanese tree frogs infects by amphibian chytrid fungus paper:

A
  • infected male Japanese tree frogs called more rapidly and produces longer calls than uninfected males
  • this enhanced call effort may reflect pathogen manipulation of host behaviour to foster disease transmission
37
Q

white nose syndrome:

A
  • emerging disease in North American bats caused by the fungus Pseudogymnoascus destructans, a psychrophilis (cold-loving) ascomycete fungus
  • disease is characterised by invasive growth of P.destructans on the muzzle and wings of hibernating bates
  • Death from expending the fat reserves for winter survival? Associated with unusual winter behavior like abnormally frequent or long arousal from hibernation
38
Q

when was white nose syndrome first identified

A
  • 2006
  • By 2012 was associated with at least 5.7 million bat deaths; some species have declined >90% within five years of the disease reaching a site
  • No obvious treatment or means of preventing transmission is known
39
Q

examples of human fungal diseases:

A
  • dandruff
  • ring worm, barbers itch, athletes foot
  • mucorosis
  • aspergillosis

APS 137 Plant Physiology, Reproduction and Growth (18 decks)

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