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26 Cards in this Set

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What is the most common disease causing fungal phyla?

The ascomycota




but disease causing fungus can be found in all phyla

Describe the types of parasitism.


Give a fungal example which falls within each type.

1. Obligate parisites - Highly host specific & live entirely on the host - powdery mildew funghi


2. Facultative Parasites - opportunistic - lead predominantly saprophytic lives in soil or plant debris

What are the main types of nutrition of a fungus?

1. Biotrophic - feed on living plant tissue


2. Necrotrophic - feed on dead tissue

How can a fungus gain entry to a host?

1. Wounds


2. Direct penetration


3. Natural openings

How do wounds in a plant facilitate fungal infection?

Lacerated cells provide an accessible source of nutrients which fungus can detect and move towards (chemotaxis) which are utilised by funghi and enable invasion of adjacent cells.

How do fungus directly penetrate a plant cell?

1. Enlarged, flattened body which tightly adheres to the cell wall called the appressorium 
2. The appressorium eventually forms a slender outgrowth from the bottom of its body - the infection peg. 
3. The infection peg forces its way into the cel...

1. Enlarged, flattened body which tightly adheres to the cell wall called the appressorium


2. The appressorium eventually forms a slender outgrowth from the bottom of its body - the infection peg.


3. The infection peg forces its way into the cell mechanically


4. The infection peg grows off cropping haustorium which directly penetrate cells

How do some fungi weaken the cell wall?

The secretion of the enzyme cutinase

What natural openings leave the plant open to fungal infection?

1. Stomata


2. Lenticels


3. Nectarthodes


4. Hydrathodes

What is the most common natural opening entry?


How does infection occur through this opening

The stomata on the underside of the leaf are a detectable nutrient source by funghi germ tubes.


The germ tubes move towards the nutrient source and form a tight appressorium over the stomata and then extend a fine hyphae down the stomata into the stomatal cavity

How does a fungus establish itself within the host after penetration?

Hyphae extend into the plant and then can grown intercellularly (between host cells) or intracellularly (between plant cells)

What are haustoria?

The outgrowths from the infection peg / infection hyphae which serve as the mechanism by which INTERCELLULAR hyphae absorb nutrients from living plant cells

What are the causes of the pathological effects observed from fungal infection of plants?

Production of enzymes and toxins which results in destruction of host tissue

What disease affects many fruit and vegetables which makes tissue soft?


Name a causative bacteria.

Soft rot disease


1. Apples - Sclerotinia fructigena


2. Rhizopus - sweet potato

What toxins are produced by the Helminthosproium species?


What is the general effect of each?


What diseases are caused by them?

1. Victorin - H.victoriae


- inhibits protein synthesis - destruction of plasmalemma


-- Oat blight




2. T-Toxin - H.maydis


-ruptures tonoplast, impairs mitochondria


-- Corn Blight

What is the difference between a typical 'rot' and a 'soft rot'?

A soft rot causes extensive tissue damange and cell death - it shows necrotic symptoms in leaves, stems and roots.




A 'rot' does not cause extensive tissue breakdown / necrotic symptoms.

What is a major fungus genus which infects field crops?

Fusarium

What is a symptom which is a large necrotic area termed?

Blight

In what ways can fungus exploit the growth mechanisms of a plant?


What is the classic example?

Interfere with plant hormonal control to cause abnormal growth responses which can affect water movement and reproduction.


Crown gall disease - Agrobacterium tumefaciens

What is plant tissue overgrowth also known as?

Hyperplasia

What causes wilt?

Water movement disruption.

What is the causative agent of Ash Dieback?

Chalara fraxinea - an ascomycete

What is the life cycle of the Ash Dieback causative agent?

1. Begins in leaf litter


2. Sporulation occurs - spread by wind


3. Spores stick to new leaves by mucus secretion


4. Gains entry via an appressorium


5. necrotic lesions on dead leaves, twigs, and stems


6. Leads to wilting and dieback

What kinds of host resistance to fungus are there?



1. Preformed fungitoxin compounds - Phytoanticipins


2. Induced fungitoxin compounds - Phytoalexins


3. Structural responses - formation of papilla

Give an example of a preformed fungitoxin compound.

Saporins of oats and tomatoes

Give an example of an induced phytotoxic compound.

Pisatin from peas

What is a 'papilla'?


What is a proposed purpose?

A structural defence response to fungi. A localised thickening of cell walls where the hyphae enters the cell.




Delays fungal entry to allow activation of other defences