Question

Given below are two statements, one is labelled as Assertion (A) and other labelled as Reason (R). 
• [Assertion (A):] Biotrophs can be easily cultured in artificial medium. 
• [Reason (R):] Biotrophs lost their independent growth due to co-evolution with the host. 
In light of the above statements, choose the most appropriate answer from the options given below: 
 

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A).
• B. Both (A) and (R) are correct but (R) is NOT the correct explanation of (A).
• C. (A) is correct but (R) is not correct.
• D. (A) is not correct but (R) is correct.

Hint:

To remember pathogen nutrition styles:
- Biotrophs: Require living cells (e.g., rusts, powdery mildews). Cannot be grown on artificial media.
- Necrotrophs: Kill cells and feed on dead tissue (e.g., Alternaria). Easy to culture.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Plant pathogens are classified into different groups based on how they obtain nutrients from host tissues: biotrophs, necrotrophs, and hemibiotrophs.
Biotrophs are obligate parasites that can only grow, develop, and reproduce on living host tissues.

Step 3: Detailed Explanation:
Let us analyze the Assertion and Reason statements to evaluate their accuracy:
- Assertion (A) is not correct: Because biotrophs are obligate parasites, they cannot be cultured on standard, non-living artificial nutrient media (such as agar plates).
They rely entirely on the living cells of their hosts to complete their life cycles.
Examples of biotrophs include rust fungi (Puccinia spp.), powdery mildew fungi (Erysiphe spp.), and downy mildew oomycetes.
- Reason (R) is correct: During evolutionary history, biotrophs co-evolved closely with their specific plant hosts.
Through this co-evolution, they lost many essential metabolic pathways and genes required for independent synthesis of nutrients.
Instead, they rely on specialized feeding structures called haustoria to absorb nutrients directly from living host cells.
Since they lack these metabolic genes, they cannot grow independently of their hosts.
Therefore, the Assertion is false, but the Reason is true.

Step 4: Final Answer:
The correct option is (A) is not correct but (R) is correct, matching Option (D).