A nitrogen fixing microbe associated with Azolla in rice fields is

Options

A. Anabaena
B. Frankia
C. Tolypothrix
D. Spirulina

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Question**: The question asks for a nitrogen-fixing microbe that is associated with Azolla in rice fields.

2. **Identifying Nitrogen-Fixing Microbes**: Nitrogen-fixing microbes are organisms that can convert atmospheric nitrogen (N2) into ammonia (NH3), which is a form that plants can use for growth.

3. **Recognizing Azolla**: Azolla is an aquatic fern that grows in rice fields and has a symbiotic relationship with certain nitrogen-fixing microbes.

4. **Identifying the Correct Microbe**: Among the options given (Anabena, Francia, Tolipothorax, Spirulina), we need to identify which one is known to associate with Azolla.

5. **Analyzing Each Option**:
- **Anabena**: This is a cyanobacterium that is known to form a symbiotic relationship with Azolla, aiding in nitrogen fixation.
- **Francia**: This is also a nitrogen-fixing bacterium but is associated with actinorhizal plants, not Azolla.
- **Tolipothorax**: This is another cyanobacterium but does not associate with Azolla.
- **Spirulina**: This is a single-celled organism known for its protein content and does not fix nitrogen in association with Azolla.

6. **Conclusion**: The nitrogen-fixing microbe associated with Azolla in rice fields is **Anabena**.

**Final Answer**: Anabena

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