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."
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
- phytosanitary actions
- 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?
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?
- Viruses and viroids
- 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?
What is the term for pathogens that must keep their host alive in order to obtain food and reproduce?
What term describes pathogens that kill tissue and then feed off of the dead tissue?
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?
1. 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?
1. 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
What is a host?
A susceptible plant.
What is an infection?
Infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to the infectious agents
What is an infection court?
A site in or on a host plant where infection can occur.
What is an incompatible interaction?
When a plant pathogen cannot feed off of the host.
What is an inoculation?
The act of inoculating; the placement of microorganisms or viruses at a site where infection is possible (the infection court).
What is an inoculum?
The population of microorganisms introduced in an inoculation; the units of a parasite capable of initiating an infection.
What is a monocylic disease cycle?
A disease cycle that confines to the steps of the following in a cycle: -infection and colonization -survival -primary inoculum -dispersal of inoculum -infection court
What are polycyclic diseases?
A disease that follows: -infection and colonization -survival -primary inoculum -dispersal of primary inoculum -infection court or -infection and colonizaiton -secondary inoculum -infection court
What is a necroptroph?
1. An organism that kills part or all of another organism before deriving nutrients from it (usually applied to plant pathogens). 2. An organism that derives nutrients from dead plant or animal tissues, whether or not it is responsible for the death of those tissues.
What is an obligate parasite?
An organism that is incapable of living as a saprophyte and must live as a parasite.
What is a parasite?
An organism living in or on another living organism (host) from which it extracts nutrients.
What is parasitism?
the practice of living as a parasite in or on another organism.
What is a pathogen?
An agent (biotic or abiotic) that causes plant disease.
What is pathogenicity?
The capability of a pathogen to cause disease.
What is a primary inoculum?
The overwintering or oversummering pathogen or its propagules that cause primary infection.
What is a secondary inolulum?
secondary inoculum. Inoculum produced by infections that took place during the same growing season.
What is it to be resistance/resistant?
The ability of an organism to exclude or overcome, completely or in some degree, the effect of a pathogen or other damaging factor/ possessing resitance.
what is a saprophyte?
An organism that obtains its nutrients from non-living organic matter (commonly dead and decaying plant or animal matter) by absorbing soluble organic compounds. (Also saprotroph, and saprobe.)
What is it to be susceptible or to have susceptibility?
Lacking the inherent ability to resist disease or attack by a given pathogen; not immune; the inability of a plant to resist the effect of a pathogen or other damaging factor.
What is virulence?
What are the three components of the disease triangle?
What is an example of a disease triangle for apple scab?
What is an example of a disease triangle for late blight of tomato?
What is an example of a disease triangle for late blight of potato?
Why is it often recommended that a diagnosis should be made using plants or plant parts with a range of symptoms from early stages to late stages of disease-but not completely dead plants?
What are Koch's four postulates for establishing pathogenicity?
Why is it not sufficient to simply isolate an organism from infected tissue and assert that it is the pathogen?
Koch originally stated three postulates; the fourth was added later. Why might it have been added?
What are some advantages annual plants have over perrenial plants when it comes to disease management?
If you were able to manage a disease with a fungicide, when should plants be protected if the disease is monocyclic?
If you were able to manage a disease with a fungicide, when would the plants be protected if the disease is polycyclic?
What are the important points of the life cycle of a new pathogen that need to be known in order to create an appropriate management program?
What are some advantages and disadvantages of the biotrophic and necrotrophic forms of parasitism?
How would a disease caused by a biotroph differ from a disease caused by a necrotroph in terms of symptoms and continued survival of the host plant?
You have just joined the peace corps, and your assignment is to establish a plant disease diagnostic laboratory. Electricity will be unreliable. What basic equipment and materials will you request, and what kinds of diseases (e.g., pathogen identification) will you be able to diagnose?
What are biotic causes of disease?
Pathogen: -an organism capable of causing disease. -pathogens are infectious. Types of pathogens: -Bacteria -Prokaryotes -Fungi -Oomyctes -Viruses -Nematodes -Protozoa -Parasitic seed plants
What are abiotic causes of disease?
Non infectious. Continuous environmental stresses: -air pollution - nutrient stress -water stress -temperature stress
What is a pathogen?
A biotic agent causing disease. Always a parasite. Sometimes a saprophyte. Infectious.
Genetic factors associated with pathogens-
Pathogenicity. Virulence. Sensitivity to fungicides and antibiotics.
Terms associated with pathogens-
Feeding associations: -Biotroph (obligate parasite- never saprophyte) -Hemibiotroph -Necrotroph -saprophytes and obligate saprophytes.
What determines if a plant is a host?
Host v non host. Host range -genotypes of host and pathogen Age of tissue Host organs and tissues physiological state of the host
What are some means for diagnosis for a known disease?
Symptoms. Signs- present before or after incubation (e.g. fungal spores, bacterial streaming) Isolate pathogen in pure culture (not always possible). Microscopy. Use of serological and molecular tools. Literatre and web resource : e.g., APS, Compendia, Extension, USDA.
Is Sclerotinia sclerotiorum polycyclic or monocyclic?
What is the disease cycle of white mold Sclerotinia sclerotiorum?
-Apothecia emerge from sclerotia located near the soil surface. -Ascospores are released and blown by wind. -Ascospores infect aerial plant parts, aided by food energy obtained from flower petals. -Lesion development and expansion. -Maturation of sclerotia on and in diseased tissue. -Sclerotia accumulate on soil as plant material decays. -Sclerotium overwinterig in soil. or -Sclerotium overwinterig in soil. -Hyphae produced by sclerotia infect crowns and basal stems of nearby plants. -maturation of sclerotia on and in diseased tissue. -Sclerotia accumulate in soil as plant material decays.
What is the disease cycle of Apple scab Venturia inaequalis
-Ascus containing Ascospores release their ascospores which travel by wind to a host plant. -Ascospores infect the host forming scabs on leaves and fruit. -Infected plant parts fall to the ground. -Pseudothecia form in fallen leaves. or -conidia infect host plant from fallen leaves
Is Venturia inaequalis mono or polycyclic?
What is a conidia?
What is an ascospore?
What is an ascus?
What is a pseudothecia?
What is a sclerotia?
What is a powdery mildew?
fungi that are obligate, biotrophic parasites of the phylum Ascomycota of Kingdom Fungi.
How do powdery mildews typically grow?
Superficially, or epiphytically on plant surfaces.
What are the favorable conditions of infection by a powdery mildew?
High humidity, but not by free water. Typically powdery mmildew species have a narrow host range.
Where on a leaf are hyphae of powdery mildew produced during the growing season?
On both the abaxial (bottom) and adaxial (top) sides for PM although some species can be restricted to one side.