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EcologyA > Fungi-plant Interactions > Flashcards

Fungi-plant Interactions Flashcards

1
Q

The factors that influence disease susceptibility

A

Severity of environment
Pathogen: virulence, abundance
Host susceptibility

If any of these are 0, disease wont develop

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2
Q

Method of fungal arrival and entry into plant

A

Spores

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3
Q

Types of spores

A

Thin walled
Resting spores
Sclerotia
Zoospores

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4
Q

Different methods of spore travel

A

Wind
Rain splash
Animal vectors

May need certain stimulants or conditions to then germinate

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5
Q

Describe use of mycelium when spreading fungi

A

Some fungi can arrive as spores
Colonise wood
Then spread between other hosts via a root graft

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6
Q

Describe infection courts

A

Wounds
Natural openings e.g. stomata (common with obligate parasites)
Intact surfaces (common with pathogens and facultative parasites)

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7
Q

Methods of plant tissue penetration

A

Appressorium
Vectors
Natural openings

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8
Q

Describe fungal appressorium for penetrating plant tissue

A
  • hyphae grows along plant cuticle out of spore
  • produces appressorium and penetration peg = mechanical pressure (and may release enzymes)
  • haustoria grows within cell to extract plant nutrients (central body with extending lobes)
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9
Q

Describe vectors penetrating plant tissue

A

Can occur via animal vectors feeding/oviposition
- create infectious courts fungus can enter through

E.g. bark beetles, twig crotches that open the xylem and o.ulmi = Dutch elm disease

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10
Q

Describe natural openings and plant tissue penetration

A
  • spore on leaf surface releases hyphae
  • hyphae dont grow with leaf grooves but across them = figmatropic response
  • increases chance of finding stoma
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11
Q

What are the two categories of host resistance

A

Preformed defence

Induced defence

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12
Q

Forms of plant preformed defence

A

Thick cell walls
Cutin = Suberin or waxes covering plant exterior
Bark = physical and chemical defence
Phytoanticipins = inhibitory compounds against pathogens

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13
Q

What are the 2 forms of induced defence

A

Rapid

Slower

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14
Q

Forms of rapid induced defence

A
  • oxidative outburst
  • nitrous oxide production
  • cross linking of cell wall proteins
  • production of callose
  • hypersensitive response
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15
Q

Affect of nitrous oxide production on plant defence

A

Signalling molecule

Initiate programmed cell death of infected cells

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16
Q

Affect of production of callose of plant defence

A

A polysaccharide that sits between plasma membrane and cell wall to prevent fungal entry

17
Q

What is the hypersensitive response for plant defence

A

Increased production of antagonistic chemicals
Will also cause plant cells to die
Defence mostly against biotrophic pathogens as they depend on living cells

18
Q

Forms of slow induced defence in plants

A
  • phytoalexins
  • lignification
  • suberization
  • hydroxyproline-rich glycoproteins (HGRPs)
  • pathogenesis related proteins (PRPs)
  • system resistance
19
Q

Describe role of phytoalexins in slow plant induced defence

A

Provide future resistance to pathogen that has previously infected plant

20
Q

Describe role of suberization in slow induced plant defence

A

Turning cell walls into cork metrical by producing Suberin

21
Q

What is innoculum potential?

A

Whether disease develops

  • increasing the number of spores increases the chance it will reach a plant and that the plant wont be able to defend itself
  • varies between disease and multiple factors can affect
22
Q

What is a necrotroph

A

Lives inside dead plant cells

23
Q

What is a biotrophs

A

Found within living cells

Relies on a balanced relationship

24
Q

Methods of necrotroph establishment and exploitation

A

Enzymes: damping off
Toxins
Vascular wilts

Provides fungus with nutrients
Cell death can be extensive or localised

25
Q

What is enzymatic damping off

A

Often with oomycetes

Pectin is broke down (middle lamellae) = cells become soft water tissue and fruit has soft rot

26
Q

Role of toxins in necrotrophic establishment and exploitation.

A

Cause tiny lesions on the leaves that spread
Often slow but can have fast action
Tissue remains dry but discoloured

27
Q

Describe the role of vascular wilting on necrotrophic establishment and exploitation

A
  • Vascular wilt caused by damage to vascular tissue
  • Produce toxins in xylem..spreads to leaves = loss of transport control
  • results in death
28
Q

E.g. of necrotrophic fungus

A

Dutch elm disease = wilt disease

  1. Ophiostoma ulmi 1910-1940
    - killed 10-40%
  2. O.novo-ulmi replaced O.ulmi in 1940s
    - more aggressive = most elms in Britain dead

Spread via elm bark beetles
= xylem blocked by gums, tyloses and fungal material

29
Q

Whats tyloses?

A

Outgrowths of parenchyma cells in xylem

Occurs when stressed

30
Q

How biotrophs cause establishment and exploitation in plant tissue

A

Abstract nutrients by ‘switching on’ enzymes

Later functioning of host

31
Q

E..g of biotroph altering plant functioning

A

Green islands = increase of chlorophyll

Longer photosynthesis than there should be to feed the fungus

32
Q

E.g. of biotrophic parasites

A

Rusts
Smuts
Downy mildew
Powdery mildew

33
Q

Hemibiotroph

A

Pathogenic fungi with biotrophic life phase whilst it establishes itself in host

34
Q

E.g. of hemibiotroph

A

Rice blast, magnaporthe oryzae

  • spore produces appressorium and peg
  • haustoria produced: causes lesions
  • spreads via pants plasmodesmata

Initially feeds on living cells then causes death

  • week to germinate
  • 20,000 spores within one leaf lesion
35
Q

Polycyclic disease

A

Multiple infection cycles per year

36
Q

Exit/survival strategy of necrotroph

A

Free from competition initially = slow growing in passive occupation
Combat fungi arrive = colonisation rate decreases
- if fungus has enough territory and resistant spores will win

Saprotrophic = grow out into soil and are combative
OR
Avoid combat and extend though soil as mycelial cord or rhizomorph

37
Q

Difference in life strategies in necrotrophic and biotrophic

A

Biotroph more K selected than necrotroph

Parasites stress tolerant

38
Q

Emerging infectious diseases emergence

A

Pathogenic fungi often little threat in local region where they co-evolve with hosts
Emerge when:
- increase in incidence, host range or geographical range
- altered pathogenesis
- newly evolved
- newly discovered

39
Q

E.g. if emerging infectious disease

A

Potato blight
From South America to Europe
1million people dead
1 million emigrated

EcologyA (18 decks)

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