Which of the following bacterium is associated with the roots of legumes?

Options

A. Rhizobium
B. Nostoc
C. Spirogyra
D. Clostridium

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which bacterium is associated with the roots of legumes. Legumes are a family of plants that include beans, peas, and lentils.

2. **Identifying the Role of Bacteria**: Certain bacteria have a symbiotic relationship with leguminous plants. These bacteria are known for their ability to fix nitrogen from the atmosphere, which is essential for plant growth.

3. **Evaluating the Options**:
- **Rhizobium**: This bacterium is well-known for its symbiotic relationship with the roots of legumes. It fixes atmospheric nitrogen and enhances soil fertility.
- **Nostoc**: This is a free-living nitrogen-fixing bacterium but is not specifically associated with legume roots.
- **Spirogyra**: This is actually an algae, not a bacterium, and does not fix nitrogen in the same way.
- **Clostridium**: While this is a type of bacterium, it is primarily known for its role in medicine and not specifically for a symbiotic relationship with legumes.

4. **Conclusion**: Based on the evaluation, the bacterium associated with the roots of legumes is **Rhizobium**.

5. **Final Answer**: The correct answer is **Rhizobium**.

---