Question

Which of the following is not a biofertilizer?

• A. Salmonella
• B. Rhizobium
• C. Nostoc
• D. Azolla

Hint:

Remember that biofertilizers contain beneficial, nitrogen-fixing, or phosphorus-solubilizing microbes (like Rhizobium, Nostoc, and Azolla). Salmonella is a pathogenic bacterium and does not fit this category.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Biofertilizers are preparations containing living microorganisms that, when applied to seed, plant surfaces, or soil, colonize the interior of the plant or the rhizosphere.
They promote plant growth by increasing the availability or supply of primary nutrients, such as nitrogen and phosphorus, to the host plant.

Step 2: Detailed Explanation:
Let us review the properties of each organism listed:
- Salmonella:
A genus of Gram-negative, rod-shaped enterobacteria.
They are pathogenic bacteria responsible for food poisoning, typhoid, and enteric fever in humans and animals.
They have no agricultural benefits and are not biofertilizers.
Thus, Salmonella is the correct answer.
- Rhizobium:
A genus of soil bacteria that fix nitrogen after establishing a symbiotic relationship inside the root nodules of legumes.
They are widely used as biofertilizers in legume crops.
- Nostoc:
A genus of blue-green algae (cyanobacteria) that can fix atmospheric nitrogen in specialized cells called heterocysts.
They are used as biofertilizers, particularly in flooded rice fields.
- Azolla:
A genus of small, floating freshwater ferns.
They have a symbiotic relationship with the nitrogen-fixing cyanobacterium Anabaena azollae.
Because of this symbiosis, Azolla grows rapidly and is used as a green manure and biofertilizer in rice paddies.

Step 3: Final Answer:
Salmonella is a pathogen, not a biofertilizer.
Thus, the correct choice is (A).