Crown gall disease Affects woody and herbaceous plants belonging to 140 genera and more than 60 families. In nature, mostly on pome and stone fruit trees, brambles and grapes . Agrobacterium tumefaciens Crown gall tumors on rose stems A. tum . The superficial similarity between plant tumors and animal tumors was a strong impetus, in the 1970's, for the study of crown gall disease. Small overgrowths in stem and roots, particularly near the soil line .
Tumors usually originate in a wound .
Tumors initially spherical, but outer tissues become convoluted and black or brown . Tumors are often connected to plant by a narrow neck of tissue. Bacteria are absent from the center of the tumors but can be found intercellularly in their periphery. Since tumor has no significant vascular connection to plant, tissue will rot and slough off. New tumors can re-form at same site in following year.