Grapes or rootstocks

One item of agricultural biodiversity interest from my visit to Bologna last weekend, this rather charming 1926 poster. ¹ It offers, as you can see, American vines. And here’s my question: varieties, or Phylloxera-resistant rootstocks?

1. Apologies for the quality. I took it after a rather wonderful lunch at Il Tinello, and alcoholic beverages had been involved.