Question:
Which of the following are \( \text{N}_2 \) fixing biofertilizers?
(A). Rhizobium spp.
(B). Mycorrhizae
(C). Azospirillum spp.
(D). Penicillium bilaii
Choose the correct answer from the options given below:
Which of the following are \( \text{N}_2 \) fixing biofertilizers?
(A). Rhizobium spp.
(B). Mycorrhizae
(C). Azospirillum spp.
(D). Penicillium bilaii
Choose the correct answer from the options given below:
(A). Rhizobium spp.
(B). Mycorrhizae
(C). Azospirillum spp.
(D). Penicillium bilaii
Choose the correct answer from the options given below:
Show Hint
Categorize biofertilizers into three main functional groups:
1. Nitrogen Fixers: Rhizobium, Azotobacter, Azospirillum, Blue-Green Algae, Azolla.
2. Phosphorus Solubilizers: Bacillus polymyxa, Pseudomonas striata, Penicillium bilaii.
3. Phosphorus Mobilizers: Mycorrhizae (VAM).
1. Nitrogen Fixers: Rhizobium, Azotobacter, Azospirillum, Blue-Green Algae, Azolla.
2. Phosphorus Solubilizers: Bacillus polymyxa, Pseudomonas striata, Penicillium bilaii.
3. Phosphorus Mobilizers: Mycorrhizae (VAM).
Updated On: Jul 29, 2026
- (A) and (D) only.
- (B) and (D) only.
- (A) and (C) only.
- (B) and (C) only.
Show Solution
Verified By Collegedunia
The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
Biofertilizers are preparations containing living microorganisms that, when applied to seeds, plant surfaces, or soil, colonize the rhizosphere and promote plant growth by increasing the availability or supply of primary nutrients to the host plant.
Step 2: Detailed Explanation:
Let us analyze the microbiological function of each biofertilizer listed:
- (A). Rhizobium spp.: This is a symbiotic bacterium that colonizes the root nodules of leguminous crops (like chickpea, soybean, and pea).
It is highly effective in fixing atmospheric dinitrogen (\(\text{N}_2\)) into ammonia, making it a classic nitrogen-fixing biofertilizer.
- (B). Mycorrhizae: These are symbiotic fungal associations with plant roots (such as VAM - Vesicular Arbuscular Mycorrhizae).
They assist the plant primarily in absorbing phosphorus (P) and water from deep soil layers, not in nitrogen fixation.
- (C). Azospirillum spp.: This is a free-living or associative symbiotic nitrogen-fixing bacterium that colonizes the roots of cereal crops (such as maize, sorghum, and millet).
It fixes atmospheric nitrogen and produces plant growth-promoting substances (auxins), making it a nitrogen-fixing biofertilizer.
- (D). Penicillium bilaii: This is a soil fungus used as a phosphorus-solubilizing biofertilizer.
It releases organic acids that solubilize insoluble inorganic phosphates in the soil, making them available to the plant.
Therefore, only (A) and (C) are nitrogen-fixing biofertilizers.
Step 3: Final Answer:
The correct combination is (A) and (C) only.
Biofertilizers are preparations containing living microorganisms that, when applied to seeds, plant surfaces, or soil, colonize the rhizosphere and promote plant growth by increasing the availability or supply of primary nutrients to the host plant.
Step 2: Detailed Explanation:
Let us analyze the microbiological function of each biofertilizer listed:
- (A). Rhizobium spp.: This is a symbiotic bacterium that colonizes the root nodules of leguminous crops (like chickpea, soybean, and pea).
It is highly effective in fixing atmospheric dinitrogen (\(\text{N}_2\)) into ammonia, making it a classic nitrogen-fixing biofertilizer.
- (B). Mycorrhizae: These are symbiotic fungal associations with plant roots (such as VAM - Vesicular Arbuscular Mycorrhizae).
They assist the plant primarily in absorbing phosphorus (P) and water from deep soil layers, not in nitrogen fixation.
- (C). Azospirillum spp.: This is a free-living or associative symbiotic nitrogen-fixing bacterium that colonizes the roots of cereal crops (such as maize, sorghum, and millet).
It fixes atmospheric nitrogen and produces plant growth-promoting substances (auxins), making it a nitrogen-fixing biofertilizer.
- (D). Penicillium bilaii: This is a soil fungus used as a phosphorus-solubilizing biofertilizer.
It releases organic acids that solubilize insoluble inorganic phosphates in the soil, making them available to the plant.
Therefore, only (A) and (C) are nitrogen-fixing biofertilizers.
Step 3: Final Answer:
The correct combination is (A) and (C) only.
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