The disease crown gall is caused by

Options

A. Algae
B. Fungi
C. Virus
D. Bacteria

Answer

### Step-by-Step Solution:

1. **Identify the Disease**: The question asks about the disease known as crown gall. It is important to recognize that this disease affects plants.

2. **Understand the Cause**: Crown gall is specifically caused by a bacterium. The name of this bacterium is crucial to answering the question correctly.

3. **Name the Bacterium**: The bacterium responsible for causing crown gall is called *Agrobacterium tumefaciens*. This bacterium is known for inducing tumor formation in plants.

4. **Effects on Plants**: When *Agrobacterium tumefaciens* infects a plant, it leads to the formation of tumors, particularly at the root or stem, which is characteristic of the crown gall disease.

5. **Select the Correct Option**: Based on the information gathered, the correct answer to the question is the option that mentions *Agrobacterium tumefaciens*.

### Final Answer:
The disease crown gall is caused by *Agrobacterium tumefaciens*.

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