What is the purpose of bagging in artificial hybridisation?

The correct answer is Option (4) → To prevent contamination of the stigma with unwanted pollen

In artificial hybridisation, a plant breeder crosses two chosen parents. Only the desired pollen must reach the stigma. So, after emasculation (removal of the anthers), the flower is covered with a bag, usually of butter paper. This step is called bagging.

Option (1) To prevent the stigma from drying out — Incorrect. Bagging is not done to keep the stigma moist. Its job is to keep unwanted pollen out.

Option (2) To ensure proper pollination between flowers — Incorrect. Bagging does not bring about pollination. The breeder later dusts the chosen pollen on the stigma by hand.

Option (3) To protect the flowers from insect damage — Incorrect. The bag is not meant to guard against insect damage. It stops insects and wind from carrying unwanted pollen to the stigma.

Option (4) To prevent contamination of the stigma with unwanted pollen — Correct. The bag prevents contamination of the stigma with unwanted pollen, so only the desired pollen fertilises the flower.

NCERT Extract:
Pollination – “… Artificial hybridisation is one of the major approaches of crop improvement programme. In such crossing experiments it is important to make sure that only the desired pollen grains are used for pollination and the stigma is protected from contamination (from unwanted pollen). … Emasculated flowers have to be covered with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollen. This process is called bagging.”