Which of these forms a symbiotic association with roots and helps to improve phosphorus uptake?

Options

A. Glomus
B. Rhizobium
C. Azoosprillum
D. More than one option is correct

Answer

To solve the question, "Which of these forms a symbiotic association with roots and helps to improve phosphorus uptake?" we will analyze the options provided: Glomus, Rhizobium, Azospirillum, and more than one option is correct.

### Step-by-Step Solution:

1. **Understanding Symbiotic Associations**:
- Symbiotic associations are interactions between two different organisms where both benefit from the relationship. In plants, these associations often occur with fungi or bacteria.

2. **Identifying the Role of Fungi**:
- Fungi, particularly those in the Glomus genus, form a symbiotic relationship with the roots of higher plants. This relationship is known as mycorrhizae.

3. **Function of Mycorrhizae**:
- Mycorrhizae enhance the plant's ability to absorb nutrients, especially phosphorus, from the soil. The fungal partner absorbs phosphorus and transfers it to the plant, improving its nutrient uptake.

4. **Analyzing the Options**:
- **Glomus**: This is the correct answer as it forms mycorrhizal associations with plant roots and aids in phosphorus uptake.
- **Rhizobium**: This is a nitrogen-fixing bacterium that forms symbiotic relationships with legumes, primarily aiding in nitrogen uptake, not phosphorus.
- **Azospirillum**: This is a free-living nitrogen-fixing bacterium that also does not contribute significantly to phosphorus uptake.
- **More than one option is correct**: This option is incorrect as only Glomus is relevant to phosphorus uptake.

5. **Conclusion**:
- The correct answer is **Glomus**, as it forms a symbiotic association with roots and helps improve phosphorus uptake.

### Final Answer:
**Glomus**