Virus-free plants can be obtained by shoot tip culture because the shoot meristem is full of the meristematic cell which has the immense potential to divide and the damaged cells are replaced quickly. The steps of shoot tip culture are as follows:
1) The shoot tip is cut with the sterilized knife and used as explant.
2) The explant is surface sterilized.
3) Culture the explant on a nutrient media.
4) The explant turns to callus.
5) Callus is transferred to the media with the high concentration of cytokinin and low concentration of auxin for development of shoot.
6) After the development of shoots, it is transferred to rooting media which contains the high concentration of auxin and low concentration of cytokinin for rooting.
4) After growth of root and shoot, it undergoes hardening treatment where it is grown under temperature available on fields to prepare them for growth.
5) The plantlets are removed from the plant media and transferred to the soil.
So, the correct answer is option D.