I have found variegated V. riviniana several times, usually self-sown beneath variegated plants (Vina minor or Sambucus nigra), but the variegation is usally not very good (not as good as Natha's in http://forums.gardenweb.com/forums/load/violet/msg080452544219.html). But I have not thought there might be any effect of temperature on virus virility, but would be interested to hear if you find some evidence to support your hypothesis.

Interesting - not virus virility, but rather a virus' ability to spread fully into the youngest meristematic tissue, is known to be affected by surplus heat. This is the basis for heat-treatment to eliminate viruses from plant stocks, although it is certainly not 100% and plenty of cases exist where the virus has made a slow return to previously "cleaned" stock. I have not heard of viruses being prevented by cold, but there is always that possibility. More reading to be done ;-)

Stefan

You're right Stefan. Denis gave me a link to a very interesting article talking about heat-treatment on virus in plants: sorry, it's in French ;-) for once lol.
I pray the one I don't believe in (God) not to see my viola cured ! I'm sure it can't anyway: Nat' has a green house where it's very hot during summer (more than 40°)and her riviniana is still variegated.
Mike, I'll never find any evidence, I'm definitively not a scientist, just an impassioned amateur trying to understand and wanting shared experiences for a better understanding.

I guess the point is: heat helps the virus but if it's too much, it obstructs it. The cold just make it sleep. Maybe without the falls and the winter, that viola would die.

Take care :-)
Thierry.

Here is a link that might be useful: heat-treatment

I'd just add the comment that I noticed light seasonal variations in the variegation of this violet...Foliage being a bit greener ( more green? lol) during winter...

Take care of your babies etii! ;-))