First, a little background on the difference between European and American grapes: Both European and (most) American grapevines share the same genus: Vitis. However, European grapes are of the species vinifera, whereas American grapes are of different species such as V. labrusca, V. rupestris, V. riparia and many more.
(Sorry for all the technical botany stuff- it’ll come in handy later, I promise. There will be no exam!)
Phylloxera, a tiny root louse, was introduced when American grapes were taken back to France for experimental planting. It is native to many eastern regions of the US so many American vines have developed enough resistance to keep living and producing fruit (though not truly an immunity as some will suggest.) However, V. vinifera, having evolved in Europe, had no such defenses. So when phylloxera was introduced to France in soil surrounding American vines, the destruction was brutal. By 1900, close to 75% of French vineyards had been severely affected and it had also spread to the rest of Europe, causing a major economic disaster
So, what to do?
Because European wines had come to depend on specific varieties (Cabernet Sauvignon, Chardonnay, Pinot Noir, etc) it wouldn’t really do to just start making wine out of American grapes. They have some significant taste differences (think of the specific flavor of Concords) and much tradition would be lost…
Due to the way grapevines reproduce (I actually won’t go into detail here,) cross breeding between American and European grapes wouldn’t be ideal either- you’d lose the traditional varietal color and flavor characteristics and there’s no way to guarantee that the phylloxera resistance would actually be passed on.
So, that’s where grafting came into play (this totally blew my mind when I first learned of it- and seeing it done in person was awesome.) It is now commonplace to take the roots and below soil portion of an American grapevine and graft it to the upper, fruiting portion of a European variety. Voila! You have a plant that produces yummy, traditional wine grapes on the top, yet has roots that won’t get destroyed by lice! The vast majority of grapevines in Europe (and many in the US) are now rooted on American rootstock! Pretty neat, huh?
Did you know?
Due to the phylloxera epidemic, most states with significant viticulture observe strict quarantine rules and participate in clean breeding programs led by UC Davis. Though many vineyards are not legally required to participate, they are strongly encouraged by state agencies. Washington State has yet to see any significant phylloxera infestation thanks to these efforts. Similarly, Australia has seen little to no infestation and is the only place in the world where Vitis vinifera is commonly grown on its own roots.