Describe the tissue culture technique and what are the advantages of tissue culture over conventional method of plant breeding in crop improvement programmes.

Tissue culture is a method of biological research in which fragments of tissue from an animal or plant are transferred to an artificial environment in which they can continue to survive and function. Plant tissue culture is performed under aseptic conditions. Living plant materials are obtained as explants. Surface sterilisation of starting material (explants) in chemical solutions (alcohol and sodium hypochlorite) is required. Explants are then usually placed on the surface of a solid culture medium or in a liquid medium. Solid and liquid media are generally composed of inorganic salts and organic nutrients, vitamins and plant hormones.

As the cultures grow, there is the formation of callus which is an undifferentiated mass of cells. The callus divides and the cells are transferred to new media to allow growth of the cells. The plant hormones can be added which can promote shoot and root formation. These plants are cultured in nurseries and greenhouses. Later, the plants are transferred to the fields.

Advantages of tissue culture:

• Selection of superior recombinants can be done by tissue culture which is not possible in conventional breeding.
• The fruiting and flowering can be regulated in case of tissue culture.
  
• The problem related to seed dormancy can be easily eliminated.
• Virus-free plants can be easily produced by tissue culture.