The following were the observations made for an infectious agent.
(i) smaller than a virus,
(ii) its nucleic acid had ribose as sugar
(iii) lacks a Protein coat.
Select the disease /s it is most likely to cause.

Options

A. Potato spindle tuber disease
B. Potato leaf roll
C. Potato leaf curl
D. Both (a) and (b)

Answer

To solve the question regarding the infectious agent with the given observations, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Characteristics of the Infectious Agent**:
- The agent is smaller than a virus.
- Its nucleic acid contains ribose as sugar.
- It lacks a protein coat.

2. **Determine the Type of Infectious Agent**:
- Based on the characteristics, we can deduce that the infectious agent is likely a **viroid**. Viroids are known to be smaller than viruses, consist of RNA (which contains ribose), and do not have a protein coat.

3. **Research Diseases Caused by Viroids**:
- Viroids are known to cause specific plant diseases. One notable disease caused by viroids is **Potato Spindle Tuber Disease**. Other diseases associated with viroids include **Potato Leaf Roll Disease** and **Potato Leaf Curl Disease**.

4. **Select the Most Likely Disease**:
- Given the observations and the identification of the infectious agent as a viroid, the disease it is most likely to cause is **Potato Spindle Tuber Disease**.

5. **Final Answer**:
- The infectious agent described is most likely to cause **Potato Spindle Tuber Disease**.