Correct Option (D):
Mycorrhiza represents a symbiotic association between fungi and the roots of higher plants. In this mutualistic relationship, the fungus colonizes the plant's root system, significantly enhancing its ability to absorb water and essential nutrients, particularly phosphorus, from the soil. In return, the plant provides the fungus with carbohydrates produced through photosynthesis. This interaction is vital for the growth and survival of many plant species, especially in nutrient-poor environments, making it a crucial functional association.
Incorrect Options:
1) Bio fertilizer:
Bio fertilizers are preparations containing living microorganisms that enhance soil fertility or promote plant growth by increasing nutrient availability. While mycorrhizal fungi can act as bio fertilizers, the term 'bio fertilizer' is a broad category encompassing various microbial interactions (e.g., nitrogen-fixing bacteria, phosphate-solubilizing bacteria, along with mycorrhizal fungi). It does not specifically name the functional association between fungi and the roots of higher plants; Mycorrhiza is the precise term for this specific association.
2) Coralloid root:
Coralloid roots are specialized roots found in cycads. These roots grow upwards, often branching dichotomously, and contain a symbiotic association with nitrogen-fixing cyanobacteria (e.g., Nostoc). This association is with cyanobacteria, not fungi, and therefore does not fit the description of a functional association between fungi and the roots of higher plants.
3) Lichen:
Lichens are composite organisms that arise from algae or cyanobacteria living among filaments of a fungus in a mutualistic relationship. This association occurs between fungi and photosynthetic partners (algae or cyanobacteria), typically on surfaces like rocks, trees, or soil, and not directly with the roots of higher plants.