Lecture 3 Flashcards
Parasite
an organism that lives on or in some other organism for its food requirements
Pathogen
an organism that causes disease in another organism
Pathogenicity
ability of a pathogen to cause disease
whats the relationship between pathgoens and parasites
Every pathogen is a parasite but not every parasite is a pathogen
What do we need for a disease to occur?
3 items and what is the image called
Disease triangle
- A virulent pathogen
- A susceptible host
- Conducive environment for pathogen infection and disease development
diff between disease cycle vs life cycle
Disease cycle : series of events that lead to development of disease from beginning of infection to perpetuation to again beginning of infection.
Life cycle: series of events for a pathogen’s life from spore production to production of fruiting bodies and spores again
Inoculation
Initial contact of a pathogen with a plant site where infection begins
Inoculum
definition & Primary vs secondary
= The pathogen entity (spores or mycelium) that comes in contact with plant host
primary inoculum = very first infection in a season on healthy crop or plant
Secondary inoculum = results in secondary infections
inoculum produced from the primary inoculum is called secondary inoculum
Propagule
single unit of inoculum
Ex. single spore of rust/sclerotium of a
fungus/single hypha
Forms of inoculum
4 types & examples of them
- Fungi : spores, fruiting bodies or fruiting body parts, ascospores, basidiospores, sclerotia, conidia, mycelium.
- Bacteria, phytoplasmas : whole cells
- Viruses/viroids: particles or nucleic acids
- Nematodes: eggs, larvae, or adults
Sources of inoculum
- Plant debri
- spropagules in the soil (fungi, bacteria, and nematodes)
- seed or plant parts, weeds, volunteer plants, alternate hosts
- Insect-vectors or other abiotic vectors (survival is not long and rare on abiotic
vectors such as tools, machinery) for viruses
How do inoculum travel
Passive & active
Mostly passive
- wind (e.g. rusts, mildews)
- water (many pathogens)
- insects (most virus diseases)
- soil (e.g. zoospores, nematodes, oospores),
- plant residue (e.g. most necrotrophs or hemi-biotrophs).
Active arrival
* examples of certain nematodes,zoospores, bacteria, or fungi that moves/grows towards plants in response to chemicals/signals released by plant roots.
How do pathogens that need to penetrate into the plant attach to the surface
- The propagules of these pathogens have mucilaginous surfaces that have mixtures of water-soluble polysaccharides, glycoproteins, lipids and fibrillar materials, which upon coming in contact with moist surface become sticky and help pathogen propagules adhere to the surface
How does Fungi Mildew attach themself to the plants? Whats the main difference from the main pathogen methods
- fungi (mildews), do not need free water/moisture on plant surface as the spores release cutinase enzyme from their spores which makes plant surface hydrophilic and helps stick the spores.
- mildew spores have good moisture content relative to other fungi
How does pathoden and plants recognize eachother
- through biochemical signals
- pathogens can easily infect if the host fails to recognize or defend itself
3 types of penetration used by pathogens
- Direct penetration
- penetration through natural openings
- penetration through natural wounds
Describe Direct penetration
Describe penetrathough through natural openings
Describe penetration through natural wounds
When is it a good time for spores to germinate?
- no competition from other spores in the vicinity
- host surface and conditions (water
availability etc) are ideal for the germination
How does germination happen and what structure does it form?
- Stored food reserves of the spore (lipids, carbohydrates, polyols) are mobilized for rapid formation of cell wall and germ tube formation
What is the Germ Tube
how does it differ from mycelium
- Formed during germination
- specialized structure that perceives host surface
- Differs from mycelium as it grows on the outside of the host’s surface. Dosent grow very far before forming appressorium
What is the appressoria and what does it do to the plant?
- adhere tightly to the host surface and secrete extracellular enzymes, generate physical force to penetrate the plant cuticle
How much pressure is inside the appressorium
40 times greater than the pressure of a typical car tire
How does the appressorium create so much pressure to physically penetrate the plant surface
- Turgor pressure is result of enormous accumulation of ‘glycerol’ in the appressorium & due to high osmotic pressure drawing water into the call and pushing the thin hypha through the host cuticle
What is the hypha
the appressorial penetration peg that gets pushed into the host cuticle
Definition of Infection
what are the results of infections
- process by which pathogens get established with the host and start obtaining food and nutrition
- appearance of symptoms and sometimes both symptoms and signs
What can halt and infection?
And what is it called
- adverse environmental or host developmental conditions
- quiescent infections
What phase comes after infection
- Incubation / latent period
How does Fungi, nematodes, bacteria, viruses, viroids, phytoplasmas invade the plant
- Fungi and nematodes : grow inter- and intra-cellularly.
- Bacteria: invades intercellularly.
- Viruses, viroids, phytoplasmas: invade intracellularly
How does Fungi, nematodes, bacteria, viruses, viroids, phytoplasmas colonize and reproduce
- Fungi: mostly reproduce on plant surface
- bacteria : between cells and comes to the surface through wounds and cracks
- nematodes : lay eggs near root surface.
- Viruses, viroids, and phytoplasmas : reproduce inside cells
Dissemination
= spread of the pathogen. (short thorugh nematodes, passivly though vectors)
when does Overwintering happen, and what do the pathogens do?
= When the environment is not conducive and crop season is coming to an end, the pathogen pushes itself to start producing overwintering structures or ways to overwinter
- Fungi : eg. formation of resting spores, dormant mycelium, sclerotia, and in association with wild grasses or other hosts.
- Nematodes overwinter as eggs or even larvae.
- Bacteria : similar strategies as fungi but they do not survive well in soil except debris, seeds or weed plants.
Monocyclic vs polycyclic diseases
their examples & inoculum type
Monocyclicdiseases
- pathogens complete only one cycle of disease in one year or one season
- smuts, root rots, vascular wilts
- primary inoculum is the only inoculum available
polycyclic diseases
- diseases can complete more than one generation of infection
- rusts, airborne pathogens, insect-borne viruses
