Question

Which nitrogen fixing symbiont is associated with sugarcane as a host plant?

• A. Frankia
• B. Acetobacter
• C. Anabaena
• D. Nostoc

Hint:

Remember key symbiotic pairs: {Rhizobium}-legumes, {Frankia}-actinorhizal plants, {Anabaena}-{Azolla}, and {Acetobacter}-sugarcane. These are classic examples frequently asked in exams.

Answer 1

The Correct Option is B

Step 1: Concept Summary:
The question requires identifying a nitrogen-fixing bacterium forming a symbiotic, endophytic (internal, non-disease-causing) relationship with sugarcane.
Step 2: Option Analysis:
Detailed examination of each option:

Frankia: Nitrogen-fixing actinomycetes forming root nodules on actinorhizal plants like alder ({Alnus}) and casuarina, but not sugarcane.

Acetobacter: Specifically, {Gluconacetobacter diazotrophicus}, a known endophytic bacterium within sugarcane tissues. It significantly fixes atmospheric nitrogen, benefiting the plant.

Anabaena: A cyanobacteria genus known for its symbiotic nitrogen fixation within the aquatic fern {Azolla}. Not associated with sugarcane.

Nostoc: A cyanobacteria genus forming symbiotic relationships with fungi, bryophytes, and cycads (in coralloid roots), but not primarily with sugarcane.

Step 3: Conclusion:
{Acetobacter} (specifically {Gluconacetobacter}) is the nitrogen-fixing symbiont associated with sugarcane, based on established symbiotic relationships.