Which one of the following is commonly used in transfer of foreign DNA into crop plants?

Options

A. Trichoderma harzianum
B. Meloidogyne incognita
C. Agrobacterium tumefaciens
D. Penicillium expansum

Answer

To answer the question "Which one of the following is commonly used in the transfer of foreign DNA into crop plants?", we will analyze each option provided.

### Step-by-Step Solution:

1. **Identify the Options**: The options given are:
- A) Trichoderma harrisianum
- B) Mellitogaine incognita
- C) Agrobacterium tumefaciens
- D) Penicillium expansum

2. **Analyze Trichoderma harrisianum**:
- This is a type of fungus. It does not have an external plasmid in its cytoplasm, which means it cannot be used as a vector for gene transfer.

3. **Analyze Mellitogaine incognita**:
- This is a nematode. Similar to Trichoderma, it also lacks plasmids, making it unsuitable for transferring foreign DNA into plants.

4. **Analyze Penicillium expansum**:
- This is another type of fungus. Like the previous two, it does not possess plasmids and therefore cannot be used for gene transfer methods.

5. **Analyze Agrobacterium tumefaciens**:
- This is a bacterium that contains an external plasmid, known as the Ti-plasmid (tumor-inducing plasmid). Agrobacterium tumefaciens is a soil-borne pathogen that has the natural ability to transfer DNA into plant cells. It induces crown gall disease in plants by transferring its T-DNA into the host plant cells.

6. **Conclusion**: Since Agrobacterium tumefaciens can naturally transfer foreign DNA into crop plants by utilizing its Ti-plasmid, it is the correct answer. Therefore, the answer to the question is:
- **C) Agrobacterium tumefaciens**