PCA - PLANT PATHOGENS FINAL EXAM QUESTIONS AND ANSWERS
(VERIFIED AND WELL DETAILED ANSWERS) LATEST UPDATE
2025/2026
Plant Disease Definition -CORREC ANSWER- Abnormal physiological
processes caused by a causal pathogen
Economic significance of plant diseases -CORREC ANSWER- Losses of yield,
crops, inputs, land
Pathogen -CORREC ANSWER- Causal agent of disease
Signs of disease -CORREC ANSWER- Structures of the pathogen
Symptoms of disease -CORREC ANSWER- Plant response to pathogen infection
Abiotic factors of plant disease -CORREC ANSWER- Air pollution, temperature,
nutrients
Biotic factors of plant disease -CORREC ANSWER- Living organisms (fungi,
bacteria, viruses)
Obligate parasite -CORREC ANSWER- unable to grow outside of a living host
,Facultative saprophyte -CORREC ANSWER- prefers living organic matter as a
source of nutrition but can adapt to the use of dead organic matter under certain
conditions
Facultative parasite -CORREC ANSWER- A pathogen that prefers dead inorganic
material, but can also obtain nourishment from living organic material
Biotroph -CORREC ANSWER- Any parasite that cannot survive in a dead host
and therefore keeps it alive
Necrotroph -CORREC ANSWER- Parasite that kills host cells
Koch's Postulates -CORREC ANSWER- series of guidelines used to identify the
microorganism that causes a specific disease
Three components of disease triangle -CORREC ANSWER- Causal agent,
environment, host
Role of each component of disease triangle -CORREC ANSWER- All three must
be present for disease to occur. Environment must favor causal agent. Host must
favor causal agent.
How humans impact each component of disease triangle -CORREC ANSWER-
Manipulate the environment, host-plant resistance,
preventative/suppressive/erradicative pesticides
,Impact of epidemic when one component of disease triangle does not come into
contact with the other two components -CORREC ANSWER- Slows epidemic to
a halt. Disease spread needs all three components interacting
Management strategy to break environment component -CORREC ANSWER-
Alter planting dates, remove alternative hosts, alter harvest
Management strategy to break host component -CORREC ANSWER- Alternate
crop, host-plant resistance
Management strategy to break causal agent component -CORREC ANSWER-
Pesticide applications
How can knowledge of plant disease triangle be used in diagnosis? -CORREC
ANSWER- Can rule out different pathogens based on host and environment.
Epidemiology -CORREC ANSWER- Branch of medical science concerned with
the incidence, distribution, and control of diseases that affect large numbers of
people.
Environmental factors that affect epidemics -CORREC ANSWER- Temperature,
humidity, moisture, soil pH, nutrient availability, air movement
Importance of time in the development of an epidemic -CORREC ANSWER-
Epidemics develop very quickly if conditions are favorable. It is critical to reduce
the rate of infection during susceptible life stages of the plant
, How does type of reproduction cycle affect development of an epidemic -
CORREC ANSWER- Polycyclic epidemics can develop much more rapidly than
monocyclic epidemics because of secondary inoculum production.
How does dissemination affect development of an epidemic -CORREC
ANSWER- Conditions that increase dissemination will accelerate development of
epidemics
Monocyclic disease -CORREC ANSWER- Disease that only has a primary
infection cycle
Polycyclic disease -CORREC ANSWER- Disease that produces a secondary
inoculum, and has a secondary infection cycle in addition to a primary infection
cycle
Why are monocyclic diseases less likely to result in serious epidemics? -CORREC
ANSWER- Controlling primary inoculum is much easier than controlling primary
and secondary inoculum. Once primary inoculum is controlled and dissemination
is controlled, the disease essentially stops developing.
How do sanitation practices impact monocyclic diseases? -CORREC ANSWER-
Epidemic may be delayed, but severe epidemic can still occur if environmental
conditions are favorable for disease development
How do sanitation practices impact polycyclic diseases? -CORREC ANSWER-
Reducing primary inoculum may reduce the amount of secondary inoculum
produced. If rate of infection is high, there is little effect. But if rate of infection is
low, it may reduce an epidemic
(VERIFIED AND WELL DETAILED ANSWERS) LATEST UPDATE
2025/2026
Plant Disease Definition -CORREC ANSWER- Abnormal physiological
processes caused by a causal pathogen
Economic significance of plant diseases -CORREC ANSWER- Losses of yield,
crops, inputs, land
Pathogen -CORREC ANSWER- Causal agent of disease
Signs of disease -CORREC ANSWER- Structures of the pathogen
Symptoms of disease -CORREC ANSWER- Plant response to pathogen infection
Abiotic factors of plant disease -CORREC ANSWER- Air pollution, temperature,
nutrients
Biotic factors of plant disease -CORREC ANSWER- Living organisms (fungi,
bacteria, viruses)
Obligate parasite -CORREC ANSWER- unable to grow outside of a living host
,Facultative saprophyte -CORREC ANSWER- prefers living organic matter as a
source of nutrition but can adapt to the use of dead organic matter under certain
conditions
Facultative parasite -CORREC ANSWER- A pathogen that prefers dead inorganic
material, but can also obtain nourishment from living organic material
Biotroph -CORREC ANSWER- Any parasite that cannot survive in a dead host
and therefore keeps it alive
Necrotroph -CORREC ANSWER- Parasite that kills host cells
Koch's Postulates -CORREC ANSWER- series of guidelines used to identify the
microorganism that causes a specific disease
Three components of disease triangle -CORREC ANSWER- Causal agent,
environment, host
Role of each component of disease triangle -CORREC ANSWER- All three must
be present for disease to occur. Environment must favor causal agent. Host must
favor causal agent.
How humans impact each component of disease triangle -CORREC ANSWER-
Manipulate the environment, host-plant resistance,
preventative/suppressive/erradicative pesticides
,Impact of epidemic when one component of disease triangle does not come into
contact with the other two components -CORREC ANSWER- Slows epidemic to
a halt. Disease spread needs all three components interacting
Management strategy to break environment component -CORREC ANSWER-
Alter planting dates, remove alternative hosts, alter harvest
Management strategy to break host component -CORREC ANSWER- Alternate
crop, host-plant resistance
Management strategy to break causal agent component -CORREC ANSWER-
Pesticide applications
How can knowledge of plant disease triangle be used in diagnosis? -CORREC
ANSWER- Can rule out different pathogens based on host and environment.
Epidemiology -CORREC ANSWER- Branch of medical science concerned with
the incidence, distribution, and control of diseases that affect large numbers of
people.
Environmental factors that affect epidemics -CORREC ANSWER- Temperature,
humidity, moisture, soil pH, nutrient availability, air movement
Importance of time in the development of an epidemic -CORREC ANSWER-
Epidemics develop very quickly if conditions are favorable. It is critical to reduce
the rate of infection during susceptible life stages of the plant
, How does type of reproduction cycle affect development of an epidemic -
CORREC ANSWER- Polycyclic epidemics can develop much more rapidly than
monocyclic epidemics because of secondary inoculum production.
How does dissemination affect development of an epidemic -CORREC
ANSWER- Conditions that increase dissemination will accelerate development of
epidemics
Monocyclic disease -CORREC ANSWER- Disease that only has a primary
infection cycle
Polycyclic disease -CORREC ANSWER- Disease that produces a secondary
inoculum, and has a secondary infection cycle in addition to a primary infection
cycle
Why are monocyclic diseases less likely to result in serious epidemics? -CORREC
ANSWER- Controlling primary inoculum is much easier than controlling primary
and secondary inoculum. Once primary inoculum is controlled and dissemination
is controlled, the disease essentially stops developing.
How do sanitation practices impact monocyclic diseases? -CORREC ANSWER-
Epidemic may be delayed, but severe epidemic can still occur if environmental
conditions are favorable for disease development
How do sanitation practices impact polycyclic diseases? -CORREC ANSWER-
Reducing primary inoculum may reduce the amount of secondary inoculum
produced. If rate of infection is high, there is little effect. But if rate of infection is
low, it may reduce an epidemic
