Originally Posted by Bigjim68
I seem to remember from years and years ago a disease wiped out the French cab crop and the vines were replanted with California stock.
Close, but not exactly.
In the late 1800s, an American pest, the tiny phylloxera aphid, made its way across the Atlantic to France, by hitchhiking on some grapevine cuttings. Phylloxera will eat the roots of vines and cause the plant to slowly die. American vines, which are tougher, are impervious to the effects of the pest, but European vines (Cabernet, Merlot, Pinot Noir, etc.) don't have this defense.
When the American cuttings were planted, the phylloxera spread unimpeded across much of Europe and devastated countless vineyards. Since the pest lives within the soil, they were unable to eradicate it using traditional methods.
So someone came up with the idea of grafting European grape varieties onto the hardier American rootstock. To this day, with the exception of few places where the pest hasn't migrated, almost all wine grape varieties are grafted onto American vine roots.