Question

Given below are two statements, one is labelled as Assertion (A) and other labelled as Reason (R). 
• [Assertion (A):] Rust is incited not only by fungi but also by other organisms. 
• [Reason (R):] Colour of rust pustule reveal its causal agent.
 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:

Remember that Red rust of tea is a classic exam question: it is caused by the green alga Cephaleuros virescens, making it a rare example of an algal plant pathogen.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
"Rust" is a common term used to describe plant diseases characterized by rust-colored, powdery pustules on host leaves, stems, or fruits.
While true rusts are caused by specialized biotrophic fungi, other pathogens can produce similar symptoms.

Step 3: Detailed Explanation:
Let us analyze the Assertion and Reason statements:
- Assertion (A) is true: True rust diseases are caused exclusively by fungi of the order Uredinales (Basidiomycota).
However, other organisms can cause diseases commonly referred to as "rusts" due to their similar symptoms.
For example, "Red rust of tea" is caused by Cephaleuros virescens, which is a parasitic green alga, not a fungus.
Additionally, "White rust" of crucifers is caused by Albugo candida, which is an oomycete.
This confirms that diseases described as rust are incited by organisms other than true fungi.
- Reason (R) is true: The color of rust pustules is a useful diagnostic feature for identifying the causal pathogen.
For example, in wheat rusts:
1. Puccinia graminis f. sp. tritici produces dark brown to black pustules (black rust).
2. Puccinia triticina produces orange-brown pustules (brown rust).
3. Puccinia striiformis produces bright yellow pustules arranged in stripes (yellow rust).
Thus, the color of the pustules helps identify the specific pathogen.
- Evaluating the connection: The Reason describes a diagnostic method based on pustule color.
It does not explain why rust symptoms can be caused by different groups of organisms.
Therefore, both statements are true, but (R) is not the correct explanation of (A).

Step 4: Final Answer:
Both (A) and (R) are true, but (R) is not the correct explanation of (A), matching Option (B).