Fungi-plant Interactions

Question 1

The factors that influence disease susceptibility

Answer 1

Severity of environment
Pathogen: virulence, abundance
Host susceptibility

If any of these are 0, disease wont develop

Question 2

Method of fungal arrival and entry into plant

Answer 2

Spores

Question 3

Types of spores

Answer 3

Thin walled
Resting spores
Sclerotia
Zoospores

Question 4

Different methods of spore travel

Answer 4

Wind
Rain splash
Animal vectors

May need certain stimulants or conditions to then germinate

Question 5

Describe use of mycelium when spreading fungi

Answer 5

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

Question 6

Describe infection courts

Answer 6

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

Question 7

Methods of plant tissue penetration

Answer 7

Appressorium
Vectors
Natural openings

Question 8

Describe fungal appressorium for penetrating plant tissue

Answer 8

• 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)

Question 9

Describe vectors penetrating plant tissue

Answer 9

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

Question 10

Describe natural openings and plant tissue penetration

Answer 10

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

Question 11

What are the two categories of host resistance

Answer 11

Preformed defence

Induced defence

Question 12

Forms of plant preformed defence

Answer 12

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

Question 13

What are the 2 forms of induced defence

Answer 13

Rapid

Slower

Question 14

Forms of rapid induced defence

Answer 14

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

Question 15

Affect of nitrous oxide production on plant defence

Answer 15

Signalling molecule

Initiate programmed cell death of infected cells

Question 16

Affect of production of callose of plant defence

Answer 16

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

Question 17

What is the hypersensitive response for plant defence

Answer 17

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

Question 18

Forms of slow induced defence in plants

Answer 18

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

Question 19

Describe role of phytoalexins in slow plant induced defence

Answer 19

Provide future resistance to pathogen that has previously infected plant

Question 20

Describe role of suberization in slow induced plant defence

Answer 20

Turning cell walls into cork metrical by producing Suberin

Question 21

What is innoculum potential?

Answer 21

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

Question 22

What is a necrotroph

Answer 22

Lives inside dead plant cells

Question 23

What is a biotrophs

Answer 23

Found within living cells

Relies on a balanced relationship

Question 24

Methods of necrotroph establishment and exploitation

Answer 24

Enzymes: damping off
Toxins
Vascular wilts

Provides fungus with nutrients
Cell death can be extensive or localised

Question 25

What is enzymatic damping off

Answer 25

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

Question 26

Role of toxins in necrotrophic establishment and exploitation.

Answer 26

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

Question 27

Describe the role of vascular wilting on necrotrophic establishment and exploitation

Answer 27

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

Question 28

E.g. of necrotrophic fungus

Answer 28

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

Question 29

Whats tyloses?

Answer 29

Outgrowths of parenchyma cells in xylem | Occurs when stressed

Question 30

How biotrophs cause establishment and exploitation in plant tissue

Answer 30

Abstract nutrients by ‘switching on’ enzymes | Later functioning of host

Question 31

E..g of biotroph altering plant functioning

Answer 31

Green islands = increase of chlorophyll | Longer photosynthesis than there should be to feed the fungus

Question 32

E.g. of biotrophic parasites

Answer 32

Rusts Smuts Downy mildew Powdery mildew

Question 33

Hemibiotroph

Answer 33

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

Question 34

E.g. of hemibiotroph

Answer 34

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

Question 35

Polycyclic disease

Answer 35

Multiple infection cycles per year

Question 36

Exit/survival strategy of necrotroph

Answer 36

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

Question 37

Difference in life strategies in necrotrophic and biotrophic

Answer 37

Biotroph more K selected than necrotroph Parasites stress tolerant

Question 38

Emerging infectious diseases emergence

Answer 38

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

Question 39

E.g. if emerging infectious disease

Answer 39

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