Crown galls in plants is caused by bacterium which is most widely used in genetic engineering is:-

Options

A. E.coli
B. Agrobacterium
C. Pseudomonas
D. Nitrosomonas

Answer

To answer the question, "Crown galls in plants is caused by bacterium which is most widely used in genetic engineering is:", we can follow these steps:

### Step 1: Identify the Cause of Crown Galls
Crown galls are tumors that form on the plant tissues, particularly in dicot plants. These galls are caused by a specific bacterium.

**Hint:** Think about which bacteria are known to induce tumor formation in plants.

### Step 2: Recognize the Bacterium Responsible
The bacterium responsible for causing crown galls is **Agrobacterium tumefaciens**. This bacterium is known for its ability to transfer a piece of DNA (T-DNA) into the plant cells.

**Hint:** Recall the name of the bacterium that is often associated with genetic engineering and plant pathology.

### Step 3: Understand the Mechanism
Agrobacterium tumefaciens carries a plasmid known as the **T.I. plasmid** (tumor-inducing plasmid). When it infects a plant, it transfers the T-DNA from this plasmid into the plant's genome, leading to the formation of crown galls.

**Hint:** Consider what type of genetic material is transferred by the bacterium to induce tumor formation.

### Step 4: Link to Genetic Engineering
Due to its ability to transfer DNA into plant cells naturally, Agrobacterium tumefaciens is widely used in genetic engineering to introduce new genes into plants.

**Hint:** Think about which bacterium is often referred to as a "natural genetic engineer" because of its ability to integrate DNA into plant genomes.

### Conclusion
Based on the above steps, the bacterium that causes crown galls in plants and is most widely used in genetic engineering is **Agrobacterium tumefaciens**.

**Final Answer:** Agrobacterium tumefaciens