Potato spindle tuber disease is caused by

Options

A. A nematode
B. A virus
C. A bacterium
D. A viroid

Answer

### Step-by-Step Solution:

1. **Understanding the Disease**: The question asks about the causative agent of Potato spindle tuber disease. It is essential to know what this disease is and its effects on potatoes.

2. **Identifying the Options**: The options provided are Nematode, Virus, Bacterium, and Viroid. We need to analyze each option to determine which one is responsible for causing the disease.

3. **Evaluating Each Option**:
- **Nematode**: This is a type of worm that can affect plants, but it is not the cause of Potato spindle tuber disease. Therefore, this option is incorrect.
- **Virus**: While viruses can cause various plant diseases, Potato spindle tuber disease is not caused by a virus. Thus, this option is also incorrect.
- **Bacterium**: Bacteria can cause diseases in plants, but they are not responsible for Potato spindle tuber disease. This option is incorrect as well.
- **Viroid**: Viroids are small, circular RNA molecules that can cause diseases in plants. Potato spindle tuber disease is indeed caused by a viroid. This option is correct.

4. **Conclusion**: After evaluating all the options, the correct answer is that Potato spindle tuber disease is caused by a Viroid.

### Final Answer:
Potato spindle tuber disease is caused by **Viroid**.

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