Agrobacterium tumefaciens causes crown gall disease of a wide range of dicotyledonous broadleaved plants, especially members of the rose family such as apple, pear, peach, cherry, almond, raspberry and roses. A separate strain, termed biovar 3, causes crown gall of grapevine. The disease gains its name from the large tumourlike swellings galls that typically occur at the crown of the plant, just above soil level. Although it reduces the marketability of nursery stock, it usually does not cause serious damage to older plants. Nevertheless, this disease is one of the most widely known, because of its remarkable biology. Basically, the bacterium transfers part of its DNA to the plant, and this DNA integrates into the plant’s genome, causing the production of tumours and associated changes in plant metabolism.

Website: http://www.biology.ed.ac.uk/research/groups/jdeacon/microbes/crown.htm