A dicotyledonous plant forms crown gall when

Options

A. Agrobacterium tumefaciens comes in contact with the plant
B. Agrobacterium rhizogenes comes in contact with the plant
C. A specific part of DNA from the Ti plasmid gets integrated with the plant chromosome
D. A specific part from the Ri plasmid gets integrated with the plant chromosome

Answer

To solve the question "A dicotyledonous plant forms crown gall when," we need to analyze the options provided and understand the process involved in crown gall formation.

### Step-by-Step Solution:

1. **Understanding Crown Gall Disease**: Crown gall is a plant disease characterized by the formation of tumors, primarily caused by the bacterium *Agrobacterium tumefaciens*. This bacterium is known for its ability to transfer genetic material to plant cells.

2. **Identifying the Bacterium**: Among the options, we need to identify which bacterium is responsible for crown gall disease. The correct bacterium is *Agrobacterium tumefaciens*, which contains a specific plasmid known as the Ti plasmid (tumor-inducing plasmid).

3. **Role of Ti Plasmid**: The Ti plasmid carries genes that are responsible for the formation of tumors in plants. When *Agrobacterium tumefaciens* comes into contact with a plant, a specific part of the Ti plasmid's DNA (known as T-DNA) is transferred and integrated into the plant's genome.

4. **Integration into Plant Genome**: The integration of T-DNA into the plant chromosomes is crucial for the development of crown gall. This integration leads to the expression of genes that promote uncontrolled cell division, resulting in tumor formation.

5. **Evaluating the Options**:
- **Option A**: "Agrobacterium tumefaciens comes in contact with the plant" - This is partially correct, but it is the integration of the Ti plasmid that is essential.
- **Option B**: "Agrobacterium rhizocenes comes in contact with the plant" - This is incorrect as *Agrobacterium rhizocenes* is not involved in crown gall formation.
- **Option C**: "A specific part of DNA from Ti plasmids gets integrated with the plant chromosomes" - This is correct as it describes the mechanism of crown gall formation accurately.
- **Option D**: "A specific part from Ri plasmids get integrated with the plant chromosomes" - This is incorrect as Ri plasmids are not involved in crown gall disease.

6. **Conclusion**: The correct answer is **Option C**: "A specific part of DNA from Ti plasmids gets integrated with the plant chromosomes."