The microbe associated with root nodule formation is

Options

A. Trichoderma
B. Rhizobium
C. Azotobacter
D. Monascus

Answer

To solve the question regarding the microbe associated with root nodule formation, we can follow these steps:

### Step 1: Understand the Question
The question asks for the specific microbe that is associated with the formation of root nodules in plants. Root nodules are specialized structures that form on the roots of certain plants, particularly legumes, and are involved in nitrogen fixation.

### Step 2: Analyze the Options
The options provided are:
1. Trichoderma
2. Rhizobium
3. Azotobacter
4. Monascus

### Step 3: Evaluate Each Option
- **Trichoderma**: This is a genus of fungi that is known for its role as a biocontrol agent and biofungicide. It does not participate in root nodule formation or nitrogen fixation in legumes. Therefore, this option is incorrect.

- **Rhizobium**: This is a genus of bacteria that forms symbiotic relationships with leguminous plants. It is well-known for its role in root nodule formation and nitrogen fixation. This option is correct.

- **Azotobacter**: This is a free-living nitrogen-fixing bacterium, but it does not form root nodules with plants. It is not involved in the symbiotic relationship that leads to root nodule formation. Thus, this option is incorrect.

- **Monascus**: This is a genus of fungi that is primarily used in the commercial production of statins. It does not play a role in root nodule formation. Therefore, this option is also incorrect.

### Step 4: Conclusion
Based on the analysis of the options, the microbe associated with root nodule formation is **Rhizobium**.

### Final Answer
The correct answer is **Rhizobium**.

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