Maintenance of Virus Free Stocks- Plants freed from viruses are maintained in insect free glass houses or cages. This is necessary to prevent reinfection by the viruses since such plants are as susceptible to virus infection as the parent variety from which they were obtained.

A large scale multiplication of such plants can be done in areas where and during seasons when the chances of infection by the virus are minimal. However, the best and cheapest means of maintaining virus-free plants is in in vitro cultures.