I kept seeing somewhere for a while that Ohio based grape varieties are used for the root stock now used, but I can't find this anywhere now. Perhaps it isn't accurate.
Interestingly enough, a few weeks ago I had a Riesling from Washington that had "100% vinifera rootstock" prominently printed on the label. Not every part of the world got hit by phylloxera. I understand that some parts of South America (either Argentina or Chile, I can't remember) were spared as well.