Select the incorrect statement.

Options

A. Anthrax is a bacterial disease that affects both humans and cattle.
B. Rust of wheat is a fungal disease that spreads by air.
C. Citrus canker is a viral disease that affects citrus fruits.
D. Yellow vein mosaic is a viral disease that affects ladyfinger.

Explanation

To solve the question of selecting the incorrect statement, we will analyze each of the provided statements step by step.

### Step-by-Step Solution:

1. **Statement 1: Anthrax is a bacterial disease that affects both humans and cattle.**
- **Analysis:** This statement is true. Anthrax is indeed caused by the bacterium Bacillus anthracis and can infect both humans and animals, particularly cattle.

2. **Statement 2: Ergot of wheat is a fungal disease that is spread by air.**
- **Analysis:** This statement is also true. Ergot is caused by the fungus Claviceps purpurea, which produces spores that can be spread through the air, affecting wheat and other grasses.

3. **Statement 3: Citrus canker is a viral disease that affects citrus fruits.**
- **Analysis:** This statement is incorrect. Citrus canker is not a viral disease; it is caused by the bacterium Xanthomonas citri. Therefore, this statement is the false one.

4. **Statement 4: Yellow vein mosaic is a viral disease that affects ladies' finger.**
- **Analysis:** This statement is true. Yellow vein mosaic is indeed caused by a virus and affects the leaves of the ladies' finger (okra) plants, causing discoloration and stunted growth.

### Conclusion:
The incorrect statement is **Statement 3: Citrus canker is a viral disease that affects citrus fruits.**

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