Lecture 3 Flashcards
Repeated disease assessments produce a…
Disease progress curve
What is AUDPC?
Area Under Disease Progress Curve
Describe the disease cycle for a monocyclic disease, each of the seven parts and what type of infection
- Inoculation
- Penetration
- Invasion
- Sporulation
- Over-seasoning
- Primary Inoculum
- Dispersal
1-4 are the Primary inoculation
Describe the difference between a monocyclic disease and a polycyclic?
They differ in that after the dispersal of the first cycle of the disease we can then have a secondary infection with the sporulation of secondary inoculum on the same plant. Thus we have the same disease on the same plant but at different stages and affecting the plant in many different ways
What does disease severity for a monocyclic disease look like on a graph?
It looks like a negative exponential curve. For the first half the disease increase in time depends on the production dynamic of the primary inoculum. The latter half or final disease severity is proportional to the initial inoculum
What does disease severity for a polycyclic disease look like on a graph?
It looks like an S curve (logistic function). There are three phases. Lag, Log, asymtotic. The lag phase has a slow increase. The log phase shows a fast increase caused by high inoculum dose and high amounts of host sites that are free from disease. The slow decrease in the asymtotic phase is due to a lack of host sites free from infection.
The Reduction of Y0 Causes …. in a logistical function graph for a polycyclic disease
A shift of the disease progress where Y0 is time
The reduction of r causes… in a logistical function graph for a polycyclic disease. Also what is r
a slow down in the disease progress because r is the variable for the infection rate
Describe 5 categories of host tissue during the epidemic
- Healthy
- Affected (with latent infection)
- Affected (with visible lesion)
- Affected (with fertile lesion)
- Affected (with infertile lesion)
What are the seven drivers of epidemics?
- y0: initial disease
- IE: Infection efficiency
- D: Dispersal efficiency
- S: Sporulation Rate
- p: latent period
- i: infectious period
- H: Host tissue available for infection
2-6 are what make up R
dyt/dt = Rt * (yt-(p-l) - yt-(p-l)-i)*(1-yt+l) is the equation for a disease taking into account all factors of an epidemic, describe each variable and what it accounts for
- Rt: St x Dt x IEt
- (yt-(p-l) - yt-(p-l)-i): is sporulating
- (1-yt+l): is Healthy tissue
What is a plant disease model?
A simplification of the relationships between a pathogen and host plant, and the environment that determine whether and how an epidemic develops over time and space
What are two types of models that we can use?
- Empirical models (data-based models)
- Fundamental models (Process-based models)
Describe the life cycles of plasmopara viticola and the 13 parts of its life
- Oogonium and anteridium (from previously infected leaves)
- Become oospores on dead leaf material
- We have overwinter ospore dormancy
- Then ospore germination
- They become microsporangia
- From them we get zoospores
- They are splash dispersed
- And inoculate on the plant
- Where they then penetrate the plant
- and invade the plant
- From here they can remain in the leaf tissue to become oogonium, or can sporulate
- Producing zoosporangia
- That are air dispersed onto the same plant or one near by.
How do empirical models work and what are the four steps for developing them?
Empirical models analyze quantitative relations
1. Collect real data
2. Analyze the quantitative relationships
3. Elaborate the models
4. Evaluate the model
What is the 3 10 rule and what are its parameters?
The 3 10 rule is for predicting first seasonal infection of grape downey mildew
- Rain that is greater or equal to 10 mm in 24-48 hours
- Air temperature greater or equal to 10 C
- Shoots at a minimum of 10 cm in length
Finish the sentence: More sophisticated methods of data analysis…
improve the capability of searching the relationships in the data set but they do not change the modeling approach
What are some pros and cons of empirical models (2 pros, 5 cons)
Pros:
1. Easy to develop
2. incomplete biological knowledge
Cons:
1. Wide data set necessary
2. No information on biological processes
3. Generalization impossible
4. No prediction outside of data range
5. Validation and calibration necessary
Main ways for the development of process-based models (8 steps)
- Define relevant stages of disease/infection cycle
- Define the variables that influence processes
- Design the logical model
- Search for data or plan specific experiments
- Develop mathematical relationships
- Validation
- Evaluation
- Piloting
Systems analysis
What does this mean in systems analysis?
State variables: represent states of the system (e.g., the number of spores, the amount of infected host tissue)
What does this mean in systems analysis?
Flows: connect state variables
What does this mean in systems analysis?
Rate variables (or rates): indicate the rate at which a state variable changes; a rate depends on state and driving variables according to rules based on the knowledge of processes in the system.
What does this mean in systems analysis?
Driving (external) variables: external factors that influence the system but are not influenced by the processes within the system (e.g., the weather variables)
or
Constants: entities that do not vary within the system; they represent known and unchanging physical, biological, or ecological values
or
Parameters: values that are constant in a particular case but may vary from case to case (different model run or a different situation
What does this mean in systems analysis?
Flows: connect driving variables to rates
What does this mean in systems analysis?
Auxiliary variables: intermediate variables
What does this mean in systems analysis?
Interrupted flows
What does this mean in systems analysis?
State variables which enter or exit from the system, which are not quantified
What does this mean in systems analysis?
Switches: account for logical operators with the following syntax: if ‘condition’ then ‘go to’, else ‘go to’.
What are the 7 influences on the disease from the environment?
- Temperature (T)
- Relative Humidity (RH)
- Leaf wetness (LW)
- Rain (R)
- Water activity (Aw)
- U
- Lt
Discuss the inner vairables
- True Negative
- False negative
- False positive
- True positive
Describe the four strengths of mechanistic models
- High level of detail on process
- Accuracy of robustness
- Prediction possible
- Flexibility
Describe the four weakness of the mechanistic models
- High complexity
- Multidisciplinarity
- Development time consuming
- Development costs
What is the Etat Potentiel d’Infection
A French empirical approach model
What is IPM?
“a pest control system that uses a set of methods that satisfy economic, ecological and toxicological requirements by giving priority to natural control and by respecting tolerance thresholds”
