Viroid causes
(a) Cauliflower mosaic
(b) Potato spindle mosaic
(c) Tobacco mosaic
(d) Tulip yellow mosaic.

Options

A. Caulflower mosaic
B. Potato spindle mosaic
C. Tobacco mosaic
D. Tulip yellw mosaic.

Answer

To solve the question "Viroid causes," we need to analyze the options provided and identify which condition is caused by a viroid. Here’s a step-by-step solution:

### Step 1: Understand what a viroid is
A viroid is a small, circular piece of RNA that is capable of causing disease in plants. Unlike viruses, viroids do not have a protein coat; they are composed solely of RNA.

### Step 2: Identify the first known viroid
The first viroid that was identified is the Potato Spindle Tuber Viroid (PSTVD), which is responsible for causing the Potato Spindle Mosaic disease.

### Step 3: Analyze the options
- **(a) Cauliflower mosaic**: This disease is caused by a virus, specifically the Cauliflower Mosaic Virus (CaMV).
- **(b) Potato spindle mosaic**: This is caused by the Potato Spindle Tuber Viroid, which we have identified as a viroid.
- **(c) Tobacco mosaic**: This disease is caused by the Tobacco Mosaic Virus (TMV).
- **(d) Tulip yellow mosaic**: This is caused by the Tulip Breaking Virus, which is also a virus.

### Step 4: Determine the correct answer
From the analysis, we see that only option (b) Potato spindle mosaic is caused by a viroid. The other options are caused by viruses.

### Final Answer
The correct answer is **(b) Potato spindle mosaic**.

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