Name two plant diseases which are caused by the action of microorganism.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for two plant diseases caused by microorganisms. Microorganisms include bacteria, fungi, viruses, and protozoa.

2. **Identifying Plant Diseases**: We need to identify specific diseases that affect plants and are caused by microorganisms.

3. **First Disease - Rust of Wheat**:
- **Description**: Rust of wheat is a disease characterized by the appearance of reddish-brown powdery spots on the leaves and grains of wheat plants.
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