Question

Which of the following is an example of polycyclic pathogen? A. Pythium species, B. Phytophthora infestans, C. Ustilago hordei, D. Ustilago segetum tritici.

• A. A Only
• B. B Only
• C. A and B Only
• D. C and D Only

Hint:

Polycyclic pathogens produce repeated disease cycles in one season. Late blight pathogen Phytophthora infestans is a common example.

Answer 1

The Correct Option is B

Concept:
Plant pathogens may be monocyclic or polycyclic. A polycyclic pathogen produces repeated infection cycles during the same growing season.

Step 1: Understand polycyclic pathogen.
A polycyclic pathogen produces secondary inoculum many times in one crop season. \[ \text{Primary infection} \rightarrow \text{Secondary infection} \rightarrow \text{Repeated disease spread} \]

Step 2: Check Phytophthora infestans.
Phytophthora infestans causes late blight of potato. It produces repeated infection cycles under favourable conditions. \[ B \text{ is correct} \]

Step 3: Check smut pathogens.
Ustilago hordei and Ustilago segetum tritici are smut pathogens. Smut diseases are generally not treated as typical polycyclic diseases.

Step 4: Final selection.
Among the given options, the best example of a polycyclic pathogen is: \[ \textit{Phytophthora infestans} \] \[ \therefore \text{Correct Answer is (B)} \]