Lecture 12: Fungi as parasites and pathogens

Question 1

Parasite:

Answer 1

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)

Question 2

pathogen:

Answer 2

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

Question 3

what makes fungi such good parasites?

Answer 3

Asexual reproduction

Question 4

how does asexual reproduction aid parasites?

Answer 4

• 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

Question 5

Asexual reproduction methods in fungi

Answer 5

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

Question 6

asexual reproduction via vegetative spores:

Answer 6

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

Question 7

asexual reproduction via cell fission or budding (unicellular fungi)

Answer 7

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

Question 8

Asexual reproduction via hypha fragmentation

Answer 8

hypha simply fragments into single cells

Question 9

2 types of fungal plant parasites:

Answer 9

• Necrotrophic

- Biotrophic

Question 10

necrotrophic:

Answer 10

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

Question 11

biotrophic:

Answer 11

-tissues are invaded but are not killed

Question 12

necrotrophic/biotrophic or both?

Answer 12

some fungal species undergo both a biotrophic stage and a necrotrophic

Question 13

airborne Biographic infection (Uromyces fabae)

Answer 13

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

Question 14

haustorium:

Answer 14

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

Question 15

haustorium membrane and wall

Answer 15

• haustorial plasma membrane
• haustorial wall
• extrahaustorial matrix
• extrahaustorial membrane

Question 16

what links haustorial mother cell to main bit

Answer 16

neckband

Question 17

sugar deposition in healthy leaf

Answer 17

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

Question 18

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

Answer 18

• MOST sugar transported towards the fungal mycelium

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

Question 19

2 examples of biotroophic infections:

Answer 19

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

Question 20

Necrotrophic infection example

Answer 20

• (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

Question 21

sporangia

Answer 21

encolure in which spored are formed

Question 22

Zoospore:

Answer 22

spore with flagella

Question 23

potato blight lifecycle:

Answer 23

• 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

Question 24

New P. infestans strains

Answer 24

• 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

Question 25

Dutch elm disease:

Answer 25

- 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

Question 26

Dutch Elm disease cycle:

Answer 26

-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

Question 27

The actual cause of death for dutch elm disease is:

Answer 27

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

Question 28

fungi can also be the solution ( to other fungi)

Answer 28

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

Question 29

fungi parasitic on insects:

Answer 29

- 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)

Question 30

cordyceps:

Answer 30

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

Question 31

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

Answer 31

-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

Question 32

Nematophagous fungus

Answer 32

- loops and snares (can be inflated in 1/10th second) | - sticky hyphae

Question 33

Chytridiomycosis

Answer 33

- 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

Question 34

Chytridiomycosis in frogs example cycle

Answer 34

-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)

Question 35

Chytrid fungus associated with how many species

Answer 35

- 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

Question 36

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

Answer 36

- 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

Question 37

white nose syndrome:

Answer 37

- 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

Question 38

when was white nose syndrome first identified

Answer 38

- 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

Question 39

examples of human fungal diseases:

Answer 39

- dandruff - ring worm, barbers itch, athletes foot - mucorosis - aspergillosis