Beginner

Scientific Name: Agrobacterium tumefaciens and Agrobacterium rubi

Identification

• Soil-borne bacteria infect raspberry roots, crowns and lower stems through wounds.
• Plant tissue grows abnormally, producing spongy wart-like galls on infected crowns and roots.
• Galls become hard and woody as they age.
• In severe cases plant becomes weak, stunted and unproductive.
• Leaves turn yellow and dry up at the edges.
• Infected canes split open and dry out at the site of the gall.

Often Confused With
Nematodes

Period of Activity
Galls appear as the weather warms and soil temperatures increase in spring and early summer.

Scouting Notes
Look for deformed plant tissue near the crown of plants.  If plants are weak and unthrifty, dig up the entire crown and root system to look for galls.  

Thresholds
None established.  

Advanced

Scientific Name:Agrobacterium tumefaciens and Agrobacterium rubi

Identification
This disease is caused by soil-borne bacteria that infect raspberry roots, crowns and lower stems through wounds. The bacteria induce plant tissue to grow abnormally, causing spongy wart-like galls on infected crowns and roots. The galls become hard and woody as they age. As galls develop, water and nutrient uptake is compromised and the plant becomes weak, stunted and unproductive. The leaves turn yellow and dry up at the edges.

Often Confused With

Nematodes
Both crown gall and nematodes cause stunted growth and low vigour, increasing with time. The problem is easy to distinguish if plants are dug up and the root and crown tissue is examined for the presence of galls.

Biology
The bacteria that cause crown gall live in the soil and infect plants through wounds.  These bacteria are already present in some fields, especially ones where tree fruit or raspberries have been grown. Crown gall can also be introduced to new fields on planting stock. Once present, the bacteria survive for many years in decaying root galls or alternate hosts. Wounds that result from winter injury, insect damage or cultivation encourage new crown gall infections.

The galls disintegrate over the winter and release the disease-causing bacteria into the soil. New galls often form the following spring in the area of the old galls. As infected cells continue to divide and grow, the cane may split open and dry out. The resulting wound can serve as a new entry site for crown gall bacteria.

Two different bacteria can cause gall formation on infected plants. Agrobacterium rubi is mainly responsible for the formation of galls on fruiting canes. Agrobacterium tumefaciens causes infections on roots and crowns. A tumefaciens includes a piece of DNA, called a Ti-plasmid,  that induces plant host cells to produce excessive quantities of growth hormones and amino acids, leading to the formation of galls.

Because the T-DNA is inserted into the genome of infected cells, existing galls will continue to grow and new galls may form as the infected cells divide, even in the absence of the bacteria. Over the winter, existing galls turn black and die, but new galls will appear near the old ones in the spring .  Galls can also form on plants propagated from these infected plants. 

Period of Activity
Galls appear as the weather warms and soil temperatures increase in spring and early summer.

Scouting Notes
Look for deformed plant tissue near the crown of plants as well as cracked, swollen canes as they can indicate old gall sites. If plants are weak and unthrifty, dig up the entire crown and root system to look for galls.  

Thresholds
None established.  

Management Notes

• Do not plant canes infected with crown gall. Purchase disease-free plants from an accredited nursery, and inspect roots before planting.
• Do not plant new canes in fields where there is a history of crown gall.
• Maintain good soil fertility.
• Avoid injury to crown and roots.
• The cultivars Boyne and Meeker have shown tolerance to crown and cane gall, while Royalty and Qualicum are very susceptible to this disease.