Topics 1 & 2 Flashcards
What is disease?
“Any malfunctioning of host cells and tissues that results from continuous irritation by a pathogenic agent or environmental factor and leads to development of symptoms.”
(Agrios)
How does disease differ from injury?
Disease results from the interaction of the host organism and the causal agent of disease, a disease is progressive and can acute harm or is injurious. Disease itself is not an injury.
How do plant diseases cause economic loss?
- Reduced yield
- Reduced quality
- Management costs
- Regulatory costs
- quarantines
- phytosanitary actions
How can plant diseases impact natural and agronomic ecosystems and food production?
- Can prevent the growth or establishment of a plant species
- Can eliminate or greatly reduce the presence of of a plant species
- Can change production practices or which plant species or varieties can be grown.
What are the three parts of the disease triangle?
PDT
Why are all three parts of the disease triangle essential for disease development?
A disease is the manifestation of the interaction between a host and a pathogen or abiotic pressure. The pathogen or abiotic pressure’s presence is dependant on the enviornment.
What are signs?
Visible pathogen structures
What are symptoms?
Physical manifestation or appearance of disease
- appearance results from the interaction of host and disease causing agent.
How can signs and symptoms be used in diagnosing a disease?
Knowing symptoms of a given disease can be a base line for diagnosing the causal agent, and knowing signs can be critical in this determination.
What are the major causes of plant disease?
- Fungi
- Oomycetes
- Bacteria
- Viruses and viroids
- Nematodes
- Abiotic factors
How do biotic causes of disease differ from abiotic diseases?
Biotic causes of disease will usually have a visible origin of infection, and symptoms won’t be as wide spread as abiotic disease causal agents.
What is an infectious disease?
A disease caused by a pathogen (biotic)
How does an infectious disease differ from those that are non-infectious?
Infectious disease is caused from biotic causal agents, non-infectious is from abiotic agents.
What are parasites?
Organisms that live in or on another organism (its host) and benefits by deriving nutrients at the host’s expense.
What are saprophytes?
a plant, fungus, or microorganism that lives on dead or decaying organic matter.
Can a plant pathogen be a parasite and a saprophyte?
yes, theres species that can be parasitic at one point of their life and saprophytic at another.
Are there plant pathogens that are not saprophytes?
yes, biotrophs for example
Is there a term for plant pathogens that are not saprophytic?
Biotroph/ biotrophic
What is the term for pathogens that must keep their host alive in order to obtain food and reproduce?
Biotroph
What term describes pathogens that kill tissue and then feed off of the dead tissue?
Necrotroph
What is a hemibiotroph?
An organism that is parasitic in living tissue for some time and then continues to live in dead tissue
What is a disease cycle?
The chain of events that leads to the development of a disease- may be different to the pathogen’s life cycle.
What are the different parts of a disease cycle?
The incidence and severity of the majority of plant diseases vary on a distinct cyclic basis. Each cycle includes two alternating phases; the parasitic phase and the survival or oversummering phase. The seasonal nature of the production of annual crops and the seasonal nature of climate are the main factors contributing to the cyclical nature of plant diseases.
How does a disease cycle relate to the life cycle of a pathogen?
The disease cycle will interact with the pathogen’s life cycle, but won’t always be identical. Either cycles may contain steps the other does not.
What is the difference between a monocyclic and a poly cyclic disease?
Monocyclic diseases only have a primary inoculm, poly have two or more inoculm.
Why is understanding a disease cycle and the disease triangle useful in developing management strategies for a disease?
Knowing when a host is susceptible is important to timing applications of preventatives. Knowing when a pathogen is reproducing and what signs look like will help to avoid contact.
How is disease diagnosed?
…
What are Koch’s postulates?
- The suspected pathogen must be consistently associated with diseased plants. - record symptoms, signs, host species and variety. 2. The suspected pathogen must be isolated in a pure culture and its characteristics noted. 3. The disease must be reproduced in a healthy plant inoculated with the isolated organism. 4. The same pathogen characterized in step 2 must be isolated from the inoculated plant.
How are Koch’s postulates used in diagnosis?
…
Why is it difficult to satisfy Koch’s postulates with an obligate parasite?
They cannot be separated/ isolated from their hosts.
What is an obligate parasite?
…
What are the four principles of plant disease management?
- Avoidance 2. Exclusion 3. Eradication 4. Protection
What is Avirulence?
not virulent; unable to produce disease
What is a Biotroph?
Any parasite that cannot survive in a dead host and therefore keeps it alive
What is a compatible interaction?
…
What is a facultative parasite?
…
What is a facultative saprophyte?
an organism, usually parasitic, that occasionally may live and grow as a saprophyte