Symptoms and signs

Crown gall is identified by overgrowths appearing as galls on roots and at the base or "crown" of woody plants such as pome (e.g., apple, pear) and stone (e.g., cherry, apricot) fruit and nut (e.g., almond, walnut) trees (Figure 1). Crown galls are also formed on ornamental woody crops such as roses, Marguerite daisies, and Chrysanthemum spp. as well as on vines and canes such as grapevines (Figure 2) and raspberries. Marguerite daisies, chrysanthemums and grapevines can become infected systemically. Occasionally, galls have been observed on field crops such as cotton, sugar beets, tomatoes, beans (Figure 3) and alfalfa (Figure 4), but the disease does not impact such crops economically. Crown gall is caused by Agrobacterium tumefaciens, a Gram-negative, bacilliform bacterium that is normally associated with the roots of many different plants in the field. This bacterium can survive in the free-living state in many soils with good aeration such as sandy loams where crown gall diseased plants have grown. The bacterium can also survive on the surface of roots (rhizoplane) of many orchard weeds.

Figure 1.	Figure 2.
Figure 3.	Figure 4.

Plants representing over 93 plant families are susceptible to crown gall as judged by experimental inoculations. Owing to their high susceptibility to crown gall, plants such as Jimson weed (Datura stramonium) and sunflower (Helianthus annuus) are used as assay hosts for testing the degree of virulence of A. tumefaciens. Also, Kalanchoë daigmontiana (also known as Bryophyllum) is used for assaying A. tumefaciens, but the plant is less sensitive than Datura.

Copyright © 2002
by The American Phytopathological Society