L20- Microbial pathogens of plants and insects Flashcards
To cause disease what 5 things must a pathogen do?
- Recognize the host,
- penetrate host barriers
- move through host tissue
- utilize host components (nutrition for growth and reproduction
- suppress host defence systems
What caused the potato famine?
Phytophtora infestans
What do the enzymes produced by the pathogen do?
- gain access to the host, disintegrate plant structure
- movement of microbe in host tissue
- impair cell function
- breakdown host molecules to absorb them
What do toxins made by pathogens do?
- disrupt host metabolism and kill cells
2. interfere with host cell functions
What do growth regulators made by the pathogen do?
alter the amount and activities of growth regulatory substances in plants to favour pathogen invasion
What are mos plant viruses transmitted through?
Insects (carried through grafting)
What is tristeza of citrus fruits?
Virus- caused. Causes declin in growth and lower yields. Severe outbreaks can kill citrus trees. loss of chlorophyll i think.
Give 5 plant bacterial diseases?
- soft rots- erwinia on vegetables
- wilts- clog vascular tissue- pierc’es disease of grapes
- blights- rapid destriction of plant tissue. Erwinia of apples and pears.
- Cankers (sores)- citrus canker
- Plant tumours- crown gall (transfer plasmid)
What are nectotrophs?
Fungal pathogens. Invade and kill plant tissue rapidly. Then live saprophytically on dead remains
How do nectotrophs penetrate the plant?
They penetrate directly by clinging on and puncturing the cell. End of germ tube anchors to leaf surface.
2. Germ tube swells, increase in internal turgor pressure.
3. thin infection peg “punches” through plant cell wall, using enzymes too,
This is called appressoria formation
What are biotrophs?
Fungal pathogens. Found on living plants. Have very complex nutrient requirements and do not kill host cells rapidly.
Give an example of a biotroph?
Powdery mildews and rusts. (pathogens are specialized for each plant)
What do necrotrophs and biotrophs form to invade plants?
Necrotrophs- appressoria
Biotrophs- haustoria
How do biotrophs invade plant hosts?
Produce haustoria. Punches into plant cell but doesn’t penetrate the cytoplasm so the plant can;t detect that it’s being penetrated.
Why does a plant carry on photosynthesising when its invaded by a biotroph?
It causes patches on the leaf but the rest of the leaf can carry on photosynthesising and providing sugars for the biotroph. The plant can;t detect the invasion so isn;t defending itself against the pathogen.
