Crown Gall of Plants

Question 1

Cause

Answer 1

Name of bacteria : Agrobacterium tumefaciens

Question 2

Distribution

Answer 2

Found worldwide and can infect more than 600 species of plants

Question 3

Transmission

Answer 3

*The Agrobacterium tumefaciens can be transmitted from one host to another directly (via infected plant root to susceptible plant root contact) or indirectly (via grafting tools, car tires, infested soil reservoirs, or movement of infested soil by boots or rain).

*The bacteria require a wound as a portal of entry.

Question 4

Impact on host

Answer 4

Galls form on stems, roots, trunks or branches, which can lead to stunted growth and wilting (because the gall formation interferes with water and food transport). Initially, galls form on the ‘crown’ of the plant, which refers to where the main roots join the stem, just above soil level.

Symptoms include roundish rough-surfaced galls (woody tumor like growths), several centimeters or more in diameter, usually at or near the soil line, on a graft site or bud union, or on roots and lower stems. The galls are at first cream-colored or greenish and later turn brown or black. As the disease progresses, plants lose vigor and may eventually die.

Question 5

Treatment

Answer 5

There is no cure for crown gall once galls begin to form. Galls can be pruned away, but new galls may reform elsewhere on the plant.

Question 6

Prevention/control

Answer 6

Remove and destroy the infected plant. The bacteria can persist in the soil for two years after the plant is gone, so avoid planting any other susceptible plants in the area until the bacteria die out for lack of a host plant.

If crown gall is found after planting, the plant should be dug up along with all the soil immediately around the plant. Dispose of the plant via burning or burying it in a landfill. All tools should be thoroughly cleaned and sterilized with rubbing alcohol.

Question 7

Life Cycle

Answer 7

Bacterial spores released from infected plant galls. Direct or indirect modes of transmission occur, where spores are transmitted by contact or by vehicle into wounded roots in a susceptible plant (the portal entry is through a wound).

Bacterium attaches to a wounded plant cell, multiplies, and then transfers a plasmid into plant cells. The plasmid contains genes for uncontrolled cell growth. The plant cell genome transforms and starts to divide, rapidly forming galls. Galls grow around the crown of the plant and stunted plant growth results. Spores can be released to continue the cycle.