The correct answer is Option (1) - Azolla and BGA (Blue-Green Algae).
Explanation:
- Azolla is an aquatic fern that forms a symbiotic relationship with the nitrogen-fixing cyanobacterium Anabaena azollae. This association enables Azolla to fix atmospheric nitrogen, enriching the soil, particularly in paddy fields. Its rapid growth and decomposition make it an effective green manure.
- Blue-Green Algae (BGA), also known as cyanobacteria, are photosynthetic microorganisms capable of fixing atmospheric nitrogen. Genera such as Nostoc, Anabaena, and Oscillatoria are commonly used as biofertilizers to enhance soil fertility, especially in rice cultivation.
Regarding the other options:
- Salmonella and E. coli: These are pathogenic bacteria associated with foodborne illnesses and are not used as biofertilizers.
- Nostoc and legumes: While Nostoc is a nitrogen-fixing cyanobacterium, it does not form a symbiotic relationship with legumes. Legumes typically associate with Rhizobium species for nitrogen fixation.
- Rhizobium and grasses: Rhizobium forms symbiotic relationships primarily with leguminous plants, not grasses.
- Therefore, Azolla and BGA constitute a pair of biofertilizers.
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