The root system and lower trunk of a grafted plant, chosen for traits like disease resistance, vigor control, or environmental adaptation.
In plain terms
When you graft a desirable variety (scion) onto another plant (rootstock), you're getting two plants' traits. The rootstock provides roots, disease resistance, or vigor control. A dwarfing rootstock keeps trees compact; a disease-resistant rootstock avoids soil diseases. Rootstocks are chosen strategically for specific goals.
Why this matters
Understanding rootstocks explains why fruit tree varieties matter. A desirable apple variety on a dwarfing rootstock creates a compact tree; on a vigorous rootstock, it's large.
In practice
Examples
Apple grafted onto dwarfing rootstock; compact tree suitable for small yards.
Apple grafted onto vigorous rootstock; large tree for standard orchard.