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wsucoug12
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Define Epidemiology
- upon the population
- science of disease in populations
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Define Epidemic
- change in disease intensity in
- a host population over time and space
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what makes up the epidemic pyramid
- With epidemic in the center:
- Host
- Time and space
- pathogen
- environment
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What is an Incidence?
Proportion of infected or diseased plants
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What is the severity of a disease?
- Proportion of symptomatic tissues in
- infected plants
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What do we do with disease intensity data?
- Describe, compare and predict epidemics:
- over time & space
- estimate impacts on yield
- under different management regimes
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What does AUDPC stand for?
- Area under the disease
- progress curve
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How can we use disease curves
- Describe diseases over time and space
- • Monitor response of disease to control
- measures
- • Use data to build models to estimate
- parameters, trends, & predict epidemics
- • Use data to test hypotheses about
- effects of management on disease
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What factors influence disease?
- Initial inoculum = X0
- Rate constant =R
- Time = T
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Why use disease progress curves?
- • Compare control measures
- • Compare effect of environment on disease development
- • Predict future disease development
- • Disease forecasting for improved control
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What causes Mummyberry on blueberry
Monilinia vaccinii-corymbosi
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Modeling Polycyclic Epidemics
- X = X0e^rt
- Modeling Polycyclic Epidemics
- • X = disease at time t
- • X0= initial inoculum
- • r = rate of disease increase
- • t = time
- • e = base of natural log
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Compare the equations for the two types of disease cycles
- Monocyclic Model X = XORt
- Polycyclic Model: X = XOe^rt
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What are 3 ways in which we
can reduce X at any point in the
epidemic:
- 1) Reduce the initial inoculum XO
- 2) Reduce the rate of infection (R in the monocyclic model and r in
- the polycyclic model)
- 3) Reduce the duration of the epidemic (the time, t, at the end of
- the epidemic)
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What is X0 composed of?
- X0 depends upon:
- • inoculum from previous crops within a field
- • inoculum from crops in adjacent fields
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How is the initial inoculum (XO) reduced?
- destroying infested plant debris
- • removing diseased plants
- • chemical seed treatments
- • protective fungicides
- • race-specific disease resistance
- • biological control agents targeted
- at initial inoculum
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What causes Mummyberry on blueberry?
Monilinia vaccinii-corymbosi
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How to manage Monilinia vaccinii-corymbosi
- Bury mummified berries
- Mulching to cover mummies
- Disruption of apothecia development in spring bycultivation or raking
- Use resistant cultivars
- Manual removal
- Application of fungicide to developing apothecia
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What is R composed of?
- r depends upon
- reproductive potential of the pathogen
- virulence of the pathogen
- susceptibility of the host
- conduciveness of environment
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WHat do you need to get Mummyberry disease?
- susceptible flower buds and leaves
- rain and fog
- mummyberry apothecia producing spores
- higher temps cause the spores to germinate faster
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what reduces r?
- r is affected by:
- non-specific disease resistance or “ratereducingresistance”
- systemic fungicides
- cultural practices that alter environment
- removal of diseased plants
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Disease Control Effect of Reduction in Primary Inoculum and Rate of Disease Increase
Conclusion: Reducing initial inoculum forpolycyclic epidemics only effective whenrate of disease increase is low
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How do humans affect the susceptibility of plants to disease?
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How do humans affect the susceptibility of plants to disease?
- Introduced Plants
- many crop plants are grown far from their native range
- pathogens in area of introduction may jump to new host that lacks resistance
- Genetic Uniformity- large populations of genetically identical plants
- uniform ripening times, uniform processing qualities,facilitate single harvesting operation
- creates conditions for large-scale epidemics (eg. potatolate blight, Southern corn leaf blight).
- Monoculture
- planting pure stands of a crop plant higher density plantings = more disease
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How do humans affect the environment to favor plant disease?
- Water Management
- timing of irrigation – morning versus evening?
- overhead versus under-canopy irrigation
- Cultural practices reduced tillage or “no-till” can increase severity ofcertain pathogens due to increased primary inoculum survival
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How do humans affect the ability of pathogens to cause disease?
- Introduced Pathogens- moving plants around the world has also movedpathogens with the plants- eg. chestnut blight fungus moved from Japan to theUS on imported Japanese chestnut trees
- Seedborne Pathogens- eg. Ascochyta blight fungus introduced to US PNWon chickpea seeds imported from Syria to evaluate chickpea germplasm for adaptation
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