Question

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Plant disease symptoms need not harbor the pathogen propagules always
Reason R: Crown gall harbors Agrobacterium tumefaciens
In light of the above statements, choose the correct answer from the options given below

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true but R is NOT the correct explanation of A
• C. A is true but R is false
• D. A is false but R is true

Hint:

Symptoms = Plant's reaction (e.g., Wilt, Gall).
Signs = Pathogen itself (e.g., Ooze, Mycelium).
Symptoms can be systemic even if the infection is localized.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
This question discusses the difference between disease symptoms (outward expressions of disease) and the physical presence of the pathogen (signs).

Step 2: Detailed Explanation:

• Assertion Analysis: Symptoms are the result of the plant's physiological response to infection.
In many cases, symptoms like wilting, chlorosis, or necrosis are caused by toxins or hormonal imbalances produced by a pathogen located elsewhere.
For example, in vascular wilts, the pathogen is in the xylem, but the symptom (wilting) is seen in the leaves where no pathogen might be present.
Therefore, a symptomatic tissue does not always contain the pathogen. Assertion A is True.

• Reason Analysis: Crown gall is a disease where the bacterium Agrobacterium tumefaciens transfers T-DNA into the plant genome, causing uncontrolled cell division (tumors).
The bacterium itself typically resides in the intercellular spaces of the gall tissue or on the surface of the roots.
Thus, the gall symptom indeed harbors the pathogen. Reason R is True.

• Relationship: While both statements are true, the fact that Crown gall harbors its pathogen (Reason R) does not explain why other symptoms might not harbor pathogens (Assertion A).
In fact, Reason R is an example of a symptom that does harbor the pathogen, which is the opposite of the scenario described in the assertion.
Final Answer:
Both statements are scientifically correct, but they do not share a logical cause-and-effect relationship.