Which of the following statement is incorrect?

Options

A. Rhizobium and Frankia are free living bacteria of soil
B. Symbiotic Rhizobium is rod shaped (Bacillus)
C. Root nodule of pulse are pink due to the presence of leghaemoglobin
D. Frankia can fix nitrogen on Alnus

Answer

To determine which statement is incorrect, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Analyze Option A**:
- The statement mentions that "Rhizobium and Frankia are free-living bacteria of soil."
- **Evaluation**: This statement is correct. Rhizobium and Frankia are indeed free-living nitrogen-fixing bacteria found in the soil.

2. **Analyze Option B**:
- The statement claims that "Symbiotic Rhizobium is rod-shaped bacillus."
- **Evaluation**: This statement is incorrect because while Rhizobium is rod-shaped, it is primarily known for its symbiotic relationship with legumes, not as a free-living bacterium. The confusion arises from the term "symbiotic" being used incorrectly in this context.

3. **Analyze Option C**:
- The statement states that "The root nodules of pulses are pink because they have a pigment of leghemoglobin."
- **Evaluation**: This statement is correct. The pink color of root nodules in legumes is indeed due to the presence of leghemoglobin, which helps in the regulation of oxygen for nitrogen-fixing bacteria.

4. **Analyze Option D**:
- The statement says "Frankia can fix nitrogen in actinorhizal plants."
- **Evaluation**: This statement is also correct. Frankia is known to form symbiotic relationships with actinorhizal plants and can fix nitrogen.

### Conclusion:
After evaluating all the options, the incorrect statement is **Option B**.

### Final Answer:
**Option B** is the incorrect statement.

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