Why are cyanobacteria considered useful in paddy fields?

Explanation

**Step-by-Step Solution:**

1. **Introduction to Cyanobacteria**:
- Cyanobacteria are a group of photosynthetic bacteria that are commonly found in various environments, including paddy fields. They are also known as blue-green algae.

2. **Common Types in Paddy Fields**:
- Two well-known genera of cyanobacteria that are often found in paddy fields are *Joannabena* and *Nostoc*.

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