Correct Option
The correct option isLegumes
Explanation
Biological Nitrogen Fixation is the metabolic process by which atmospheric nitrogen is converted into ammonia by microorganisms. Rhizobium is a soil bacterium that establishes a symbiotic relationship with specific plants to facilitate this process.Analysis:
- Legumes (Correct): The symbiotic relationship of Rhizobium is host-specific to the family Fabaceae (legumes), which includes plants like peas, beans, lentils, and soybeans. The bacteria colonize the roots of these plants, inducing the division of cortical and pericycle cells to form specialized structures called root nodules. Inside these nodules, the bacteria fix atmospheric nitrogen.
- Graminoids: Grasses and cereals (e.g., wheat, maize) typically rely on free-living nitrogen fixers (like Azotobacter) or associative symbionts (like Azospirillum), but they do not form nodules with Rhizobium.
- Other Groups: Citrus species and Hydrophytes do not host Rhizobium. While some non-leguminous plants (e.g., Alnus) do form nitrogen-fixing nodules, the symbiont involved is usually the actinobacterium Frankia, not Rhizobium.
Key Takeaway: The symbiotic association of Rhizobium involving root nodule formation is restricted to leguminous plants.