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. 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 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 and alfalfa, 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.
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