Question

Powdery mildew diseases of crop plants are incited by
(A) Fungal Biotrophs

• A. Bacterial Biotrophs
• B. Fungal Hemibiotrophs
• C. Fungal Necrotrophs
• D.

Hint:

Powdery mildew = Fungal Obligate Biotroph.
They are easy to identify by the white, "powdery" superficial growth (mycelia and conidia) on leaf surfaces.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the biological nature and nutritional strategy of the pathogens responsible for powdery mildew diseases.

Step 2: Detailed Explanation:

• Causal Organisms: Powdery mildews are caused by a specific group of fungi belonging to the Order Erysiphales (Phylum Ascomycota).

• Nutritional Strategy: These fungi are obligate biotrophs. This means they can only obtain nutrients from living host cells. They do not kill the host tissue immediately; instead, they establish a specialized feeding structure called a haustorium inside the epidermal cells to divert nutrients for their own growth.

• Analysis of Options:
- Biotrophs (A): Correct. They grow on living tissue and cannot be cultured on artificial lab media.
- Hemibiotrophs (C): Incorrect. These start as biotrophs but later kill the tissue and live as saprophytes (e.g., Phytophthora).
- Necrotrophs (D): Incorrect. These kill the host cells using toxins and enzymes and then feed on the dead remains (e.g., Alternaria).
- Bacteria (B): Incorrect. Powdery mildews are strictly fungal diseases.
Final Answer:
Powdery mildews are classic examples of obligate fungal biotrophs.
The correct option is (A).