1
PCA EXAM 2026: PLANT PATHOGENS
QUESTIONS WITH CORRECT
SOLUTIONS
Plant disease - correct-answer -Abnormal physiological processes caused by a
causal pathogen
What is the economical significance of plant disease - correct-answer -Losses of
yields, crops, inputs, and land
Pathogen - correct-answer -a causal agent of the disease
Disease - correct-answer -an abnormal condition that causes issues like declined
health or death of a plant
Sign - correct-answer -the presence of a structure of a pathogen (spore,
mycelium, or even mold growth)
, 2
Symptom - correct-answer -a plant response to a pathogen infection (decline of
growth, vigor, or even death)
What are some abiotic factors that cause plant diseases - correct-answer -
What are some biotic factors that cause plant diseases - correct-answer -
Obligate parasite - correct-answer -Unable to grow outside of a living host
(viruses)
Facultative saprophytes - correct-answer -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 - correct-answer -a pathogen that prefers dead inorganic
material, but can also obtain nourishment from living organic material (bacteria)
, 3
Biotrophic - correct-answer -Any parasite that cannot survive in a dead host and
therefore keeps it alive
Necrotrophic - correct-answer -parasites that kill the host cells
Kotch postulates - correct-answer -A series or guidelines used to identify the
microorganism that causes a specific disease
What are the three components of plant disease triangle - correct-answer -the
environment, the host, and the causal agent
What is the role of each of the component of the disease triangle - correct-answer
-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 - correct-answer -Humans can
manipulate the environment, plant host resistant varieties, and use
preventative/suppressive/eradicative pesticides all to change a piece of the
disease triangle
, 4
How does one component of the triangle impact a epidemic if it does not come
into contact with the other two - correct-answer -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 - correct-
answer -alter planting dates, remove alternative host, alter harvest dates
How can you break the host portion of the disease triangle - correct-answer -
alternate crop, plant host resistance species
How can you break the causal agent portion of the disease triangle - correct-
answer -Pesticide application
How does the disease triangle help in diagnosis - correct-answer -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 - correct-answer -Branch of medical science concerned with the
incidence, distribution, and control of disease that affect large numbers of people
or hosts
PCA EXAM 2026: PLANT PATHOGENS
QUESTIONS WITH CORRECT
SOLUTIONS
Plant disease - correct-answer -Abnormal physiological processes caused by a
causal pathogen
What is the economical significance of plant disease - correct-answer -Losses of
yields, crops, inputs, and land
Pathogen - correct-answer -a causal agent of the disease
Disease - correct-answer -an abnormal condition that causes issues like declined
health or death of a plant
Sign - correct-answer -the presence of a structure of a pathogen (spore,
mycelium, or even mold growth)
, 2
Symptom - correct-answer -a plant response to a pathogen infection (decline of
growth, vigor, or even death)
What are some abiotic factors that cause plant diseases - correct-answer -
What are some biotic factors that cause plant diseases - correct-answer -
Obligate parasite - correct-answer -Unable to grow outside of a living host
(viruses)
Facultative saprophytes - correct-answer -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 - correct-answer -a pathogen that prefers dead inorganic
material, but can also obtain nourishment from living organic material (bacteria)
, 3
Biotrophic - correct-answer -Any parasite that cannot survive in a dead host and
therefore keeps it alive
Necrotrophic - correct-answer -parasites that kill the host cells
Kotch postulates - correct-answer -A series or guidelines used to identify the
microorganism that causes a specific disease
What are the three components of plant disease triangle - correct-answer -the
environment, the host, and the causal agent
What is the role of each of the component of the disease triangle - correct-answer
-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 - correct-answer -Humans can
manipulate the environment, plant host resistant varieties, and use
preventative/suppressive/eradicative pesticides all to change a piece of the
disease triangle
, 4
How does one component of the triangle impact a epidemic if it does not come
into contact with the other two - correct-answer -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 - correct-
answer -alter planting dates, remove alternative host, alter harvest dates
How can you break the host portion of the disease triangle - correct-answer -
alternate crop, plant host resistance species
How can you break the causal agent portion of the disease triangle - correct-
answer -Pesticide application
How does the disease triangle help in diagnosis - correct-answer -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 - correct-answer -Branch of medical science concerned with the
incidence, distribution, and control of disease that affect large numbers of people
or hosts
