What is the cause of Crown Gall disease in plants ?

Explanation

**Step-by-Step Solution:**

1. **Understanding Crown Gall Disease**: Crown gall disease is characterized by the formation of tumors on the plant body. These tumors typically appear at the crown of the plant, which is the area where the stem meets the roots.

2. **Identifying the Pathogen**: The primary cause of crown gall disease is a specific bacterium known as *Agrobacterium tumefaciens*. This bacterium is classified as a bacterial plant pathogen.

3. **Entry Mechanism**: The bacterium enters the plant through root wounds. These wounds can occur due to various forms of physical damage to the roots.

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