Field Guide     Crop Diseases     Crown Gall

Crown Gall

CROPS IMPACTED: apple, pear, cherry, walnut, almond, cotton, tomatoes, alfalfa, beans, grapevine

Crown Gall

Family: Rhizobiaceae

Crown Gall Crown Gall

About Crown Gall

Life Cycle

Crown gall disease is caused by the soil bacteria Agrobacterium tumefaciens, which is a gram-negative bacterium. When crown galls initially form on a plant, they are fairly hard and robust. The growth can be seen approximately 14 days after initial infection. After about a year; however, they become more complex with several cavities and can be easily crumbled as the cells continue to die. There are many different pests that use these cavities as a home, such as earwigs. When a crown gall is aged like this, they can be detached with ease from the plants root. The younger galls contain much more of the bacteria that causes this disease. Crown gall bacteria can overwinter in the soil and on surface roots of weeds close to host plants. Infection is likely to occur after plant injury, such as a wound caused from cultivating practices, frost, or weed removal. Infection is also caused by contaminated equipment. If galls form on subterranean parts, this means the initial stock used in planting was infected. The bacterium can persist in the soil for several years.

Crown Gall Identification and Habitat

Identification

This disease is easy to recognize by the overgrowths that appear on a plants roots and crown. The galls typically start off white and spherical in shape, but will darken as it ages and the outer cells begin to die. It most commonly occurs on woody plants and broad leaved plants. While it can also infect other crops such as alfalfa, cotton, and beans, it does not often cause a significant amount of economic harm to them. When crown galls do seriously affect a plant, symptoms include yield loss, stunted growth, less plant vigor, foliage reduction, and overall plant stress. On infected mature trees, sometimes new growths appear close to the trunk, which is a good indicator of an infected root system. The severity of the infection depends on the number of Agrobacterium tumefaciens cells that have entered the plant; the more cells, the larger the gall and the faster the growth rate. If a plant is infected via frost, especially in the case of a grapevine, this is a tissue injury and will cause galls to form all along the host’s vascular system.

Habitat

Agrobacterium tumefaciens is quite capable of independent survival in different soil types as long as it has good air circulation; however, they tend to occur most often in sandy loam soil. There are many different species susceptible to this disease, covering more than 92 plant families. The bacterium is not particular about nutritional requirements. This disease is often more prevalent following a harsh winter after plants experience injury, especially when the host is younger.

Crown Gall Management and Control Methods

Cultural Control

To manage crown gall disease, practice crop rotation. Use cereal crops and follow-up with green manuring, which can help lessen the presence of A. tumefaciens. Practice handling plants with care to avoid injury. Whenever possible, select sites to plant with good water drainage and air circulation. Always select varieties that are least susceptible to A. tumefaciens. When orchard trees are infected at maturity, they are still able to live for a long period of time after with proper maintenance, including fertilizer, irrigation, and other care methods necessary. They will be able to produce; however, gradually as the infection becomes more severe, the plant will become dehydrated to a significant extent.

Chemical Control

There are chemical control methods available to assist in the management of crown gall disease. Using compounds that are creosote-based, copper based, or strong oxidants (e.g., sodium hypochlorite) are effective treatments. Always be sure to carefully read the label for cautions and proper application before use. However, it is important to note that the application procedure is costly and should only be used when the infection is economically significant. If the disease has infected a large portion of the root system, this treatment is unlikely to have noticeable results. Due to this, chemicals are not often used for the management of this disease.

Alternative Crown Gall Names

  • • Agrobacterium tumefaciens

Sources

http://www.apsnet.org/edcenter/intropp/lessons/prokaryotes/Pages/CrownGall.aspx

http://www.ipm.ucdavis.edu/PMG/r5100411.html