Mycorrhiza is a symbiotic association of roots of higher plants with
A.Actinomycetes fungi mainly
B.Basidiomycetes fungi mainly
C.Bacteria
D.Cyanobacteria

Hint: Symbiosis is the living of one or more organisms together. Symbiotic association is the general term for partnerships for benefits. In simple words, organisms benefit from each other.

Complete answer:
Mycorrhiza is a symbiotic relationship of higher plants with basidiomycetes fungi. Mycorrhiza is a strong relationship between the roots of a plant and a mycorrhizal fungus. In this association, both the plant and the fungus get benefited. The fungus gains nutrients from the plant root. Mycorrhiza increases the surface area of the root system of plants because of hyphae, which expands beyond the nutrition depletion zone. Plant provides fungi with the carbohydrates that are formed from photosynthesis. Fungi colonize the roots system of plants.
Hence, option B: Basidiomycetes fungi mainly is the correct answer.

Note: Since most of the time, nutrients are depleted into the soil, the plants form a symbiotic relationship with fungi. It is called symbiotic because plants gain phosphate and other minerals through the fungus, while the fungus obtains its sugar from plants.