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. **Understand the Disease**: Begin by identifying what Potato Spindle Tuber Disease (PSTD) is. It is a disease that affects potato plants and is characterized by the formation of spindle-shaped tubers.

2. **Identify the Causative Agent**: To determine what causes PSTD, we need to look into the biological classification of pathogens. The options provided are nematodes, viruses, bacteria, and viroids.

3. **Research on PSTD**: Studies have shown that Potato Spindle Tuber Disease is caused by a specific type of pathogen. It is important to note that this disease is not caused by a nematode, virus, or bacterium.

4. **Determine the Correct Answer**: The causative agent of Potato Spindle Tuber Disease is a viroid, which is a small, circular piece of RNA that does not code for proteins and is known to cause diseases in plants.

5. **Final Conclusion**: Based on the information gathered, the answer to the question "Potato spindle tuber disease is caused by" is a viroid.

**Final Answer**: Potato spindle tuber disease is caused by a viroid.

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