Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Plants having mycorrhizal associations show resistance to root-borne pathogens and tolerance to salinity and drought.
Reason (R): In mycorrhiza, the fungal symbiont absorbs phosphorus from the soil and passes it to the plant.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are true but (R) is not the correct explanation of (A).
Assertion (A): Plants having mycorrhizal associations show resistance to root-borne pathogens and tolerance to salinity and drought. — True. NCERT lists resistance to root-borne pathogens, tolerance to salinity and drought, and better plant growth as benefits seen in plants with mycorrhiza.
Reason (R): In mycorrhiza, the fungal symbiont absorbs phosphorus from the soil and passes it to the plant. — True. Mycorrhiza is a symbiotic association of a fungus (for example, many members of the genus Glomus) with plant roots, and the fungus supplies the plant with phosphorus.
A is about protection and stress tolerance: resistance to pathogens and tolerance of salt and drought. R is about nutrition: the supply of phosphorus to the plant.
Why R does not explain A? NCERT gives the phosphorus supply first and then says such plants “show other benefits also”, listing pathogen resistance and salinity and drought tolerance. These are additional benefits, not results of phosphorus uptake, so R explains why the plant is better fed but not why it resists pathogens or tolerates salt and drought. Both statements are true, but R is not the correct explanation of A.
NCERT Extract:
Microbes as Biofertilisers – “Fungi are also known to form symbiotic associations with plants (mycorrhiza). Many members of the genus Glomus form mycorrhiza. The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant. Plants having such associations show other benefits also, such as resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in plant growth and development.”