An associated symbiotic bacterium responsible for nitrogen fixation and secretion of growth promoting substances is

Options

A. Klebsiella
B. Azotobacter
C. Clostridium
D. Azospirillum

Answer

To solve the question regarding the associated symbiotic bacterium responsible for nitrogen fixation and secretion of growth-promoting substances, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Characteristics of the Bacteria**:
- The question specifies that we are looking for a symbiotic bacterium.
- It must be capable of nitrogen fixation.
- It should also secrete growth-promoting substances.

2. **Analyze the Given Options**:
- The options provided are:
- A) Lipcella
- B) Azotobacter
- C) Clostridium
- D) Azospirilla

3. **Evaluate Each Option**:
- **Lipcella**: Not widely recognized in the context of nitrogen fixation or growth promotion.
- **Azotobacter**: This is a free-living nitrogen-fixing bacterium but not typically classified as symbiotic.
- **Clostridium**: While some species can fix nitrogen, they are not known for symbiotic relationships or growth promotion.
- **Azospirilla**: This is a symbiotic, nitrogen-fixing bacterium that is known to promote plant growth by secreting growth-promoting substances.

4. **Select the Correct Answer**:
- Based on the analysis, the bacterium that fits all the criteria (symbiotic, nitrogen-fixing, and growth-promoting) is **Azospirilla**.

5. **Conclusion**:
- Therefore, the correct answer to the question is **D) Azospirilla**.