Assertion: The process of plant tissue culture can be used for faster vegetative propagation of new crop varieties.

Reason: Cells in a callus are totipotent in nature.

The correct option is A Both assertion and reason are true and the reason is the correct explanation for the assertion
Tissue culture is the technique of growing plant cells, tissues or organs in a sterile culture medium under controlled environmental conditions. It is used for the faster vegetative multiplication (micropropagation) of new varieties of plants developed through plant breeding.

This is possible because the explant grows into a mass of undifferentiated totipotent cells called callus, when grown in the artificial growth medium. Each cell generated like this can grow into new plantlets.

Totipotency refers to the ability of a cell to divide and differentiate into any cell type, such that it can give rise to an entire organism.

The culture media used for growing the explant has all necessary nutrients such as inorganic salts (for proper growth), sugars (as energy source), amino acids (for production of proteins), vitamins (for proper growth) and growth hormones (for differentiation of tissues).

This entire process can be carried out in a few weeks time. Whereas, traditional breeding techniques might take up several months to grow a new plant from seeds of the new varieties and the number of new plants generated will be less in number compared to tissue culture.