CBSE Class 12-science Answered

Virus-free plants are generated using tissue culture techniques. The apical meristem consisting of a dome of undifferentiated, rapidly dividing cells are dissected and cultured on a suitable nutrient medium to obtain callus and subsequently regenerate whole virus-free plants. Once virus-free plants are obtained, their number can be increased by micropropagation and maintained free from virus infection.

On the other hand, virus-resistant transgenic plants (VRTPs) have been developed by the transfer of transgenes from viruses, plants or other origin. The transgenes of viral origin include replicase protein, movement protein, proteases, antisense sequences and plantibodies that are useful for developing VRTPs. There now exists a wide variety of methods of plant transformation that can be used to produce virus-resistant plants.  Agrobacterium-mediated transformation and microprojectile bombardment have been used to produce virus resistant plants that have been field-tested or even been commercialized.

Virus-free plants are raised to maintain the plant population free from the attack of viruses. However, virus-resistant plants have been developed commercially through genetic engineering to combat infection caused by viruses. Therefore, although the plants are virus-free, they need to be transformed through genetic engineering to make them virus-resistant.