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: Understanding the Concept:
The question asks to identify a nitrogen-fixing bacterium that lives in a symbiotic relationship with sugarcane. This type of symbiosis, where the microbe lives inside the plant tissues without causing disease, is called an endophytic relationship.
Step 2: Detailed Explanation:
Let's analyze the options:

Frankia: This is a genus of nitrogen-fixing, filamentous bacteria (actinomycetes) that forms root nodules on actinorhizal plants, such as alder ({Alnus}) and casuarina. It is not associated with sugarcane.

Acetobacter: A specific species, {Gluconacetobacter diazotrophicus} (formerly in the {Acetobacter} genus), is a well-known endophytic bacterium that lives within the tissues of sugarcane. It can fix significant amounts of atmospheric nitrogen, contributing to the plant's nitrogen needs.

Anabaena: This is a genus of filamentous cyanobacteria. It is famous for its symbiotic relationship with the aquatic fern {Azolla}, where it fixes nitrogen within the fern's leaves. It is not associated with sugarcane.

Nostoc: This is another genus of cyanobacteria that can be free-living or form symbiotic relationships with fungi (to form lichens), bryophytes, and some vascular plants like cycads (in their coralloid roots). It is not the primary symbiont of sugarcane.

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