Ti-plasmids used in genetic engineering is obtained from :

Options

A. Bacillus thuringiensis
B. Agrobacterium rhizogenes
C. Agrobcterium tumefaciens
D. Pseudomonas syringae

Answer

To answer the question regarding the source of Ti-plasmids used in genetic engineering, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Ti-plasmids**: Ti-plasmids, or tumor-inducing plasmids, are a type of plasmid that can induce tumors in plants. They are crucial in genetic engineering, particularly for creating transgenic plants.

2. **Identify the Options**: The options provided are:
- Bacillus thuringiensis
- Agrobacterium rhizogenes
- Agrobacterium tumefaciens
- Pseudomonas syringae

3. **Evaluate Each Option**:
- **Bacillus thuringiensis (Bt)**: This bacterium is known for its role in producing insecticidal proteins and is used in creating Bt crops. However, it does not produce Ti-plasmids.
- **Agrobacterium rhizogenes**: This bacterium is associated with root-inducing plasmids (Ri-plasmids) but is not the source of Ti-plasmids.
- **Agrobacterium tumefaciens**: This is the key bacterium that contains Ti-plasmids. It is widely used in genetic engineering to transfer genes into plant cells.
- **Pseudomonas syringae**: This is known for its role in plant pathology and is not related to Ti-plasmids.

4. **Conclusion**: Based on the evaluation, the correct answer is **Agrobacterium tumefaciens**, as it is the source of Ti-plasmids used in genetic engineering.

### Final Answer:
Ti-plasmids used in genetic engineering are obtained from **Agrobacterium tumefaciens**.