The other is micropropagation. As I understand it, the growing points extend faster than the virus can advance through the plant. So growing new plants from these should clean the stock.
(I worked on a micro propagation nursery, which specialised in virus free, back in the '70s)
We put stock plants in a heated greenhouse, hot enough that the virus replication shut down, such that any new growth / cell division was virus free, and then cut off the tip of the meristem, under a microscope, and grew that on in test-tube etc.
Can't remember what temperature the virus-shut-down greenhouse was, but I remember it was sweltering - couldn't spend more than a few minutes in there. Also can;t remember what happened in winter - although oil was cheap back then, so the boss probably just continued to run it at absurd temperatures!
Either way, the plants didn't like the temperature either and getting them to make ANY new growth, so we could cut off their meristems! was a challenge in itself.
