Question

What is the causal organism of the downy mildew of bajra ?

• A. S. graminicola (Sclerospora)
• B. C. fusiformis
• C. Agrobacterium tumefaciens
• D. Erwinia amylovora

Hint:

The "Green Ear" symptom is the post-flowering stage of downy mildew in Pearl Millet caused by Sclerospora graminicola.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Downy mildew (also known as green ear disease) is a destructive disease affecting Pearl Millet (Bajra, Pennisetum glaucum).
Correctly identifying the pathogen classification is essential for selecting targeted chemical and biological control strategies.

Step 2: Detailed Explanation:
The downy mildew of bajra is caused by the oomycete pathogen Sclerospora graminicola.
This biotrophic oomycete causes systemic infection in the plant.
The diagnostic symptoms of the disease are divided into two phases:
1. Downy Mildew Phase: White, downy fungal growth appears on the lower surface of infected leaves under humid conditions, followed by chlorosis.
2. Green Ear Phase: The floral parts (panicle) are transformed into green, leafy structures, making the ear completely sterile.
Let us examine the other pathogens for context:
- Claviceps fusiformis causes ergot disease in bajra.
- Agrobacterium tumefaciens is a bacterium that causes crown gall disease in dicots.
- Erwinia amylovora is a bacterium responsible for fire blight in rosaceous plants.

Step 3: Final Answer:
The causal organism of the downy mildew of bajra is Sclerospora graminicola.