PCA - Plant Pathogens [2026/2027] | UPDATED
ACTUAL Exam Question and Answer with Rationales |
Ultimate Exam Prep
• What is the economical significance of plant disease -✓✓ Losses of yields, crops,
inputs, and land
• Pathogen -✓✓ a causal agent of the disease
• Disease -✓✓ an abnormal condition that causes issues like declined health or
death of a plant
• Sign -✓✓ the presence of a structure of a pathogen (spore, mycelium, or even
mold growth)
• Symptom -✓✓ a plant response to a pathogen infection (decline of growth, vigor,
or even death)
• What are some abiotic factors that cause plant diseases -✓✓
• What are some biotic factors that cause plant diseases -✓✓
• Obligate parasite -✓✓ Unable to grow outside of a living host (viruses)
• Facultative saprophytes -✓✓ prefers living organic matter as a source of nutrition
but can adapt to the use of dead organic matter under certain conditions
(phytophthora)
,• Facultative parasites -✓✓ a pathogen that prefers dead inorganic material, but can
also obtain nourishment from living organic material (bacteria)
• Biotrophic -✓✓ Any parasite that cannot survive in a dead host and therefore
keeps it alive
• Necrotrophic -✓✓ parasites that kill the host cells
• Kotch postulates -✓✓ A series or guidelines used to identify the microorganism
that causes a specific disease
• What are the three components of plant disease triangle -✓✓ the environment, the
host, and the causal agent
• What is the role of each of the component of the disease triangle -✓✓ All three
must be present in order for infection to take place, the environment must favor the
causal agent and the host must be susceptible to the causal agent
• How do humans impact the disease triangle -✓✓ Humans can manipulate the
environment, plant host resistant varieties, and use
preventative/suppressive/eradicative pesticides all to change a piece of the disease
triangle
• How does one component of the triangle impact a epidemic if it does not come
into contact with the other two -✓✓ If one component of the plant disease triangle
is missing the epidemic will slow to a halt, in order for the disease to spread it must
have all three parts of the triangle
, • How can you break the environment portion of the disease triangle -✓✓ alter
planting dates, remove alternative host, alter harvest dates
• How can you break the host portion of the disease triangle -✓✓ alternate crop,
plant host resistance species
• How can you break the causal agent portion of the disease triangle -✓✓ Pesticide
application
• How does the disease triangle help in diagnosis -✓✓ If you understand the plant
disease triangle you can use the host species and environment of a area where the
crop is planted to rule out different pathogens
• Epidemiology -✓✓ Branch of medical science concerned with the incidence,
distribution, and control of disease that affect large numbers of people or hosts
• List the environmental factors that affect epidemics and explain how they do so -
✓✓ Temperature, humidity, moisture, soil pH, nutrient availability, and air
movement
• Describe the importance of time in the development of an epidemic -✓✓
Epidemics develop quickly if conditions are favorable. It is critical to reduce the
rate of infection during susceptible life stages of the plant
• How does type reproduction affect the development of an epidemic -✓✓
polycyclic epidemics can develop much more rapidly than monocyclic epidemics
because of secondary inoculum production
ACTUAL Exam Question and Answer with Rationales |
Ultimate Exam Prep
• What is the economical significance of plant disease -✓✓ Losses of yields, crops,
inputs, and land
• Pathogen -✓✓ a causal agent of the disease
• Disease -✓✓ an abnormal condition that causes issues like declined health or
death of a plant
• Sign -✓✓ the presence of a structure of a pathogen (spore, mycelium, or even
mold growth)
• Symptom -✓✓ a plant response to a pathogen infection (decline of growth, vigor,
or even death)
• What are some abiotic factors that cause plant diseases -✓✓
• What are some biotic factors that cause plant diseases -✓✓
• Obligate parasite -✓✓ Unable to grow outside of a living host (viruses)
• Facultative saprophytes -✓✓ prefers living organic matter as a source of nutrition
but can adapt to the use of dead organic matter under certain conditions
(phytophthora)
,• Facultative parasites -✓✓ a pathogen that prefers dead inorganic material, but can
also obtain nourishment from living organic material (bacteria)
• Biotrophic -✓✓ Any parasite that cannot survive in a dead host and therefore
keeps it alive
• Necrotrophic -✓✓ parasites that kill the host cells
• Kotch postulates -✓✓ A series or guidelines used to identify the microorganism
that causes a specific disease
• What are the three components of plant disease triangle -✓✓ the environment, the
host, and the causal agent
• What is the role of each of the component of the disease triangle -✓✓ All three
must be present in order for infection to take place, the environment must favor the
causal agent and the host must be susceptible to the causal agent
• How do humans impact the disease triangle -✓✓ Humans can manipulate the
environment, plant host resistant varieties, and use
preventative/suppressive/eradicative pesticides all to change a piece of the disease
triangle
• How does one component of the triangle impact a epidemic if it does not come
into contact with the other two -✓✓ If one component of the plant disease triangle
is missing the epidemic will slow to a halt, in order for the disease to spread it must
have all three parts of the triangle
, • How can you break the environment portion of the disease triangle -✓✓ alter
planting dates, remove alternative host, alter harvest dates
• How can you break the host portion of the disease triangle -✓✓ alternate crop,
plant host resistance species
• How can you break the causal agent portion of the disease triangle -✓✓ Pesticide
application
• How does the disease triangle help in diagnosis -✓✓ If you understand the plant
disease triangle you can use the host species and environment of a area where the
crop is planted to rule out different pathogens
• Epidemiology -✓✓ Branch of medical science concerned with the incidence,
distribution, and control of disease that affect large numbers of people or hosts
• List the environmental factors that affect epidemics and explain how they do so -
✓✓ Temperature, humidity, moisture, soil pH, nutrient availability, and air
movement
• Describe the importance of time in the development of an epidemic -✓✓
Epidemics develop quickly if conditions are favorable. It is critical to reduce the
rate of infection during susceptible life stages of the plant
• How does type reproduction affect the development of an epidemic -✓✓
polycyclic epidemics can develop much more rapidly than monocyclic epidemics
because of secondary inoculum production
