Root nodules in Alnus is formed by

Options

A. Rhizobium
B. Azospirillum
C. Frankia
D. Clostridium

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the organism responsible for the formation of root nodules in the plant Alnus.

2. **Identifying Alnus**: Alnus is a genus of trees commonly known as alder. It is important to note that Alnus is not a leguminous plant, which typically forms root nodules with specific nitrogen-fixing bacteria.

3. **Nitrogen Requirement in Plants**: Plants require nitrogen for their growth and metabolism. However, they cannot directly absorb atmospheric nitrogen (N2). Instead, they need nitrogen in the form of nitrates (NO3-) or nitrites (NO2-).

4. **Symbiotic Relationships**: In many plants, especially legumes, nitrogen-fixing bacteria (like Rhizobium) form symbiotic relationships with the roots, leading to the formation of root nodules. These bacteria convert atmospheric nitrogen into a form that plants can use.

5. **Identifying the Correct Bacteria for Alnus**: For non-leguminous plants like Alnus, the nitrogen-fixing bacteria responsible for forming root nodules is not Rhizobium but rather Frankia. Frankia is a genus of actinobacteria that forms symbiotic relationships with non-leguminous plants.

6. **Conclusion**: Therefore, the organism responsible for the formation of root nodules in Alnus is Frankia.

**Final Answer**: Root nodules in Alnus are formed by Frankia.

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