'zyme = commercial enzyme product (eg hygrozyme, cannazyme,sensizyme) that will hasten the decomposition of cellulosic tissue in the media. I've fallen into the habit of referring to that whole class of products as " 'zymes"- they're all pretty similar in action. As I remember, Sensizyme claims 80 or so specific enzymes in their product, or 57 herbs and spices, or some-such. Yadda Yadda Yadda.

Over the course of time, some root mortality is normal and healthy. Out in the world, this isn't too much of a problem- but any digestive process ( well, not any...but let's not go there) that stalls for whatever reason results in the buildup of intermediary metabolites, which may or may not be problematic.

It's not so much tobacco smoke that's a vector for TVM as tobacco handling and partially burnt tobbacco particles which become airborne- but where there's smokers, there's smokes. Fire, luckily, is somewhat effective against mosaic.

What concerns me is that you seem to be saying that this plant has never thrived- classic MV. Pokey pokey pokey and then all of the sudden dead. But there are a lot of things that can do this- metal toxicities, fungal wilts.

If this is commercial seed or cutting, Ya might want to think about just replacing it- general "Failure to thrive" is very difficult to diagnose.

Basically you've got, as possibilities

-Pathogen ( Infective diseases are rarely treated, it is almost always more practical to destroy the host)
-Genetic disorder ( non-pathogenic - ie bad RNA from a parent that is not viral)
-Incompatible environmental conditions ( which means you can't actually grow it, anyway...)
-Media Problems

As we've got no more specific diagnosis, and only one possibility is treatable, it makes sense to treat for that possibility and hope for response. Only way to play the hand- everything else is a fold.

At the same time, you've got a plant which is more likely to harbor pathogens, primary or secondary, as it's immune system is comprimised. Unhealthy plants, like unhealthy people, get sick easier. AIDS doesn't kill- the secondaries do. End result is the same.

So you want to put it aside, to protect the rest of your plants, until you see a good response to a media change.