Aquatic fern which supports the growth of blue green algae, Anabaena, and used to increase the yield of paddy crop is

Options

A. Salvinia
B. Marsilea
C. lsoetes
D. Azolla

Answer

To solve the question about the aquatic fern that supports the growth of blue-green algae (Anabaena) and is used to increase the yield of paddy crops, we can follow these steps:

### Step 1: Understand the Question
The question asks for an aquatic fern that has two specific characteristics: it supports the growth of blue-green algae (Anabaena) and is used to enhance the yield of paddy crops.

### Step 2: Identify the Options
The options provided are:
1. Salvinia
2. Marsilea
3. Isoetes
4. Azolla

### Step 3: Analyze Each Option
- **Salvinia**: This is an aquatic fern, but it is not primarily known for its role in supporting Anabaena or enhancing paddy crop yields.
- **Marsilea**: This is another type of aquatic fern, but it does not have a significant association with Anabaena or paddy crop yield enhancement.
- **Isoetes**: This is a genus of aquatic plants, but it is not commonly linked to the growth of Anabaena or used in paddy cultivation.
- **Azolla**: This is a well-known aquatic fern that is specifically recognized for its ability to support the growth of blue-green algae (Anabaena) and is widely used as a bio-fertilizer to increase the yield of paddy crops.

### Step 4: Conclusion
Based on the analysis, the correct answer is **Azolla**. It is the aquatic fern that supports the growth of Anabaena and is used to enhance paddy crop yields.

### Final Answer
**Azolla**

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