A disease caused by a viroid is :

Options

A. Potato blight
B. Bunchy top of papaya
C. Leaf curl of papaya
D. Potato spindle tuber

Answer

To solve the question about which disease is caused by a viroid, we will analyze the options provided in the video transcript step by step.

### Step-by-Step Solution:

1. **Understanding Viroids**:
- Viroids are infectious agents that are smaller than viruses. They consist solely of a short strand of circular RNA and do not have a protein coat. This distinguishes them from viruses, which typically have both RNA or DNA and a protein coat.

2. **Identifying the Diseases**:
- The transcript mentions several diseases:
- **Potato Blight**: Caused by the fungus Phytophthora infestans, which is not a viroid.
- **Bunchy Top of Papaya**: Caused by a leafhopper, not a viroid.
- **Leaf Curl of Papaya**: Caused by a DNA virus from the Begomovirus genus, so this is also not a viroid.
- **Potato Spindle Tuber Disease**: This is a disease associated with a viroid known as Potato Spindle Tuber Viroid (PSTVD). It affects potatoes and causes deformities in the tubers.

3. **Conclusion**:
- Based on the analysis, the disease caused by a viroid is **Potato Spindle Tuber Disease**.

### Final Answer:
The disease caused by a viroid is **Potato Spindle Tuber Disease**.