Major sources of biofertilizers are

Options

A. Selected symbiotic micro-organisms
B. Only nitrogen fixing bacteria
C. Only nitrogen fixing cyanobacteria
D. Bacteria, cyanobacteria and fungi

Answer

### Step-by-Step Solution:

1. **Understanding Biofertilizers**:
- Biofertilizers are defined as living microorganisms that enhance plant nutrition by increasing the availability of nutrients in the soil.

2. **Types of Microorganisms in Biofertilizers**:
- Various types of microorganisms are utilized as biofertilizers, including beneficial bacteria, fungi, and cyanobacteria.

3. **Role of Microorganisms**:
- These microorganisms colonize the root interior and rhizosphere of plants, establishing a symbiotic relationship that benefits both the plant and the microbes.

4. **Identifying Major Sources**:
- The major sources of biofertilizers include:
- **Bacteria**: Particularly nitrogen-fixing bacteria that convert atmospheric nitrogen into a form usable by plants.
- **Cyanobacteria**: These are also nitrogen-fixing organisms that contribute to soil fertility.
- **Fungi**: Mycorrhizal fungi, for example, enhance nutrient uptake for plants.

5. **Conclusion**:
- Given that biofertilizers can include bacteria, cyanobacteria, and fungi, the most comprehensive answer to the question is that the major sources of biofertilizers are bacteria, cyanobacteria, and fungi.

### Final Answer:
The major sources of biofertilizers are bacteria, cyanobacteria, and fungi.

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