crown gall

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A widespread plant disease caused by Agrobacterium tumefaciens and characterized by the formation of tumorous galls, especially at the junction of root and stem.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A disease of plants caused by infection of soil bacteria of the genus Agrobacterium

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a bacterial disease of plants (especially pome and stone fruits and grapes and roses) which forms excrescences on the stem near the ground