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. **Understand the Question**: The question asks about the organism that forms a symbiotic relationship with the root nodules of Casuarina.

2. **Identify the Options**: The options provided are:
- Francia
- Allocera
- Anabina
- Cyanobacteria

3. **Define 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 a nitrogen-fixing bacterium that forms such an association with Casuarina.

4. **Research the Organisms**:
- **Francia**: This is a gram-positive nitrogen-fixing actinobacterium known to form symbiotic relationships with actinorhizal plants, including Casuarina.
- **Allocera**: There is limited information on this organism in relation to Casuarina.
- **Anabina**: This is a free-living cyanobacterium that does not form symbiotic relationships with Casuarina.
- **Cyanobacteria**: While they can fix nitrogen, they are generally free-living and do not form symbiotic associations with Casuarina.

5. **Conclusion**: Based on the definitions and associations, the organism that shows a symbiotic association with the root nodules of Casuarina is **Francia**.

### Final Answer:
**Francia**

---