Which one of the following is not a biofertilizer?

Options

A. mycorrhiza
B. Agrobacterium
C. Rhizobium
D. Nostoc

Answer

To determine which of the following is not a biofertilizer, we will analyze each option provided.

### Step-by-Step Solution:

1. **Understand the Definition of Biofertilizers**:
Biofertilizers are living microorganisms that enhance the availability of nutrients to plants. They can improve soil fertility and promote plant growth.

2. **Analyze Mycorrhizae**:
- Mycorrhizae are symbiotic associations between fungi and plant roots.
- They help in the absorption of nutrients, particularly phosphorus, from the soil.
- **Conclusion**: Mycorrhizae are considered biofertilizers.

3. **Analyze Agrobacterium**:
- Agrobacterium is a genus of bacteria known for its ability to transfer genes to plants, particularly in genetic engineering.
- It does not enhance nutrient availability in the soil or promote plant growth directly.
- **Conclusion**: Agrobacterium is not a biofertilizer.

4. **Analyze Rhizobium**:
- Rhizobium are bacteria that form symbiotic relationships with legumes, fixing atmospheric nitrogen into a form that plants can use.
- This process enriches the soil with nitrogen, making Rhizobium a biofertilizer.
- **Conclusion**: Rhizobium is a biofertilizer.

5. **Analyze Blue-Green Algae (Cyanobacteria)**:
- Blue-green algae are capable of fixing atmospheric nitrogen and can improve soil fertility.
- They are often used as biofertilizers in paddy fields.
- **Conclusion**: Blue-green algae are biofertilizers.

6. **Final Conclusion**:
- Based on the analysis, the only option that is not a biofertilizer is **Agrobacterium**.

### Final Answer:
Agrobacterium is not a biofertilizer.

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