Question

Polycyclic diseases are characterized by __________.
(A) Air borne nature
(B) Foliar infection
(C) Multiplicity of infection
(D) Short generation time
Choose the correct answer from the options given below :

• A. (A), (B) and (D) only.
• B. (A), (B) and (C) only.
• C. (A), (B), (C) and (D).
• D. (B), (C) and (D) only.

Hint:

Classic examples of polycyclic diseases include late blight of potato (Phytophthora infestans), wheat rusts (Puccinia spp.), and powdery mildews.
These diseases require continuous monitoring and protective fungicide applications because their short generation times allow them to spread exponentially.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Plant diseases are classified as monocyclic or polycyclic based on the number of infection cycles the pathogen completes during a single cropping season.
Polycyclic diseases are caused by pathogens that complete several generations within one growing season, leading to rapid disease spread and explosive epidemics.

Step 2: Detailed Explanation:
Let us analyze each of the biological characteristics associated with polycyclic diseases:
(A) Air-borne nature:
Most polycyclic pathogens rely on wind or air currents to disperse their asexual spores (such as conidia, sporangia, or urediniospores) rapidly over large areas, allowing new infections to establish quickly.
Thus, (A) is a characteristic.
(B) Foliar infection:
Many polycyclic diseases infect above-ground tissues, primarily leaves and stems, where environmental factors like wind and rain-splash facilitate rapid spore dispersal.
Thus, (B) is a characteristic.
(C) Multiplicity of infection:
Because these pathogens produce multiple generations per season, a single plant or crop can be infected repeatedly by successive waves of spores, creating a compounding effect on disease severity.
Thus, (C) is a characteristic.
(D) Short generation time:
To complete multiple cycles within a single crop growing season, these pathogens must have very short generation times (often completing a cycle in just 7 to 14 days under optimal conditions).
This rapid reproduction drives exponential disease development.
Therefore, all four characteristics (A, B, C, and D) are features of polycyclic diseases.

Step 3: Final Answer:
Polycyclic diseases are characterized by all the listed features (A, B, C, and D).
This corresponds to Option (C).