Which of the following shows symbiotic association with root nodules of Casuarina?

Options

A. Frankia
B. Aulosira
C. Anabaena
D. Cyanobacteria

Answer

To solve the question regarding which organism shows a symbiotic association with the root nodules of Casuarina, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Symbiotic Association**:
- Symbiotic association refers to a close and often long-term interaction between two different biological species. In this context, we are looking for an organism that forms a mutualistic relationship with the root nodules of Casuarina.

2. **Identifying the Options**:
- The options provided are Francia, Allocera, Anabena, and possibly others not mentioned in the transcript.

3. **Analyzing Francia**:
- Francia is identified as a nitrogen-fixing bacteria. It has the ability to convert atmospheric nitrogen into a form that plants can use. This process occurs in the root nodules of plants like Casuarina, indicating a symbiotic relationship.

4. **Examining Allocera and Anabena**:
- Allocera and Anabena are also mentioned. However, it is noted that these bacteria fix nitrogen independently and do not form a symbiotic relationship with Casuarina. They possess a specialized cell called heterocyst for nitrogen fixation but do not reside in root nodules.

5. **Conclusion**:
- Based on the analysis, the only organism that shows a symbiotic association with the root nodules of Casuarina is Francia.

6. **Final Answer**:
- Therefore, the correct answer to the question is **Francia**.