The virus infected plants only the meristematic cells of the apical dome are devoid of virus. Therefore, by using shoot apical meristem culture, virus free plants can be raised.
Related Theory
In the meristem there is no cells differentiation. Virus can't move from cell to cell through plasmodesmesta using their Movement protein.
Meristematic cells are considered as virus free because:
(1) Meristematic cells have high multiplication rate than viral cell multiplication rates.
(2) Viruses generally move in plant body through vascular bundles. There is the absence of vascular bundles in meristematic regions.
(3) High auxin concentration and cytokinin concentration and low pH value at which viruses could not survive.
(4) High metabolic activity.
(5) RNA silencing mechanism. According to some findings, it has been hypothesized that the defense systems in meristematic regions treat viruses as foreign particles thus prevent the viruses into the meristematic regions.