rootstock
The lower portion of a root and its corresponding growth buds, used for plant propagation. In grape growing, the rootstock should be resistant to pests like phylloxera and nematodes. In addition, rootstock is chosen based on environmental factors like soil salinity or potential drought conditions. American rootstock often has European (Vitis vinifera) vines grafted to it.
The New Wine Lovers Companion, 2nd Edition, by Ron Herbst and Sharon Tyler Herbst. Copyright © (1) 2003, 1995 by Ron Herbst and Sharon Tyler Herbst. Reprinted by arrangement with Barron's Educational Series, Inc.