Week 20: (B) Plant Associations (disease)

Question 1

What organisms cause disease intracellularly?

Answer 1

viruses & prokaryotes

Question 2

What organisms cause disease extracellularly?

Answer 2

Prokaryotes

Eukaryotes: fungi, oomycetes, nematodes, insects and plants

Question 3

What strategies do pathogens needs to do to be successful ?

Answer 3

Find the host and attach to it

Gain entry through the plant’s impermeable defenses

Avoid the plant’s defense responses

Grow and reproduce

Spread to other plants

Question 4

How many microbes actually cause disease in plants?

Answer 4

ver vey few interactions lead to disease

Question 5

What 3 factors must occur for a plant to be exposed to a disease? ( disease triangle)

Answer 5

~Pathogen- Must be able to overcome the plant defences
~Host - must be susceptible to the pathogen
~Environment - must tip in the balance in favour of pathogen

Question 6

What are 5 types of pathogen lifestyle?

Answer 6

Faculative 
Obligate 
Biotrophic 
Necrotrophic 
Hemibiotrophic

Question 7

What 2 lifestyles of a pathogens arose one another?

Answer 7

Biotrophs and necrotrophs

Question 8

What are the features of biotrophs?

Answer 8

‘Pretend harmony”
Fewer cell wall-degrading enzymes than non-biotrophs
Evade detection and avoid elicitation of defence responses

Question 9

What are the features of necrotrophs?

Answer 9

‘Smash and grab”

Produce toxins and cell wall-degrading enzymes

Question 10

What are the problems of a virus?

Answer 10

They are difficult to control. Can mute very quickly, overcome resistances.
The more we know about them the more possibilities we will have to control them.

Question 11

What are the key features of viruses?

Answer 11

ds DNA/RNA
ss DNA/RNA
-Most plant viruses have RNA genomes
-Viruses replicate using plant cell materials and machinery

Question 12

How do insects transmit transmit viruses?

Answer 12

Aphids (vectors) feed on phloem sap using a stylet that they inject virus into the plant’s veins
So if there are virus particles in the phloem they will be sucked up.

Question 13

What are the types of Bacterial pathogens (virulence strategies)?

Answer 13

Hemibiotroph
biotroph
Nectrotrophs

Question 14

How does hemibiotroph inject pathogen to plant?

Answer 14

using a type 3 secretion system (pseudomonas)

secretes type 3 effector proteins

Question 15

How does the Biotroph inject pathogen to plant?

Answer 15

Using a type 4 secretion system (agrobacterium) injects tDNA to Ti plasmid

Question 16

How does Nectrotrophs inject pathogen to plant?

Answer 16

Using a type 2 secretion system (Erwinia) uses cell wall degrading enzymes

Question 17

How to nematodes infect plant with pathogen?

Answer 17

Some are plant pests, some eat plant pests, and some are human pathogens

Question 18

What are 2 types of pathogenic nematodes?

Answer 18

Rook-knot nematode- induce expansion in 5-7 neighbouring cells to produce giant cells
Cyst nematode- Cyst nematodes partially dissolve cell walls between cells to produce a syncytium

Question 19

What is an example of a fungal pathogen?

Answer 19

Rice blast fungus –
Rice blast fungus

Magnaporthe oryzae

Question 20

What are the key features of the rice blast fungus?

Answer 20

• Major disease of rice
• Air-borne disease
• Infects foliar (leaf) tissue
• Biotrophic

Question 21

How does Rice blast fungus infect a plant?

Answer 21

Once conidia reaches leaf surface, a germ tube and a melanized appressorium
Really high pressure builds up in the appressorium
This allows penetration of the leaf surface
Fungus all grow intracellularly

Question 22

What is a type of Oomycetes?

Answer 22

Late Blight - Phytophthora infestans

Question 23

What is the effect of the Oomycetes?

Answer 23

responsible for the Irish potato famin
Hard to control
Genetic resistance readily defeated