Bacterial ring rot of potato is caused by the bacterium Clavibacter sepedonicus. Bacteria play a vital role in ecosystems by breaking down organic matter and returning nutrients to the soil. While most are beneficial, a small number are pathogenic and can cause significant damage to crops like potatoes, especially under favorable conditions. Although Bacterial ring rot does not pose a human health risk, it is of considerable economic importance due to its potential to reduce yield and quality.
Where it is
Bacterial ring rot is present in localized areas in several countries in Asia, Europe and North America.
How to spot it
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Infected stems and foliage -
Creamy yellow to light brown decay in vascular ring -
Cavities surrounded by cork tissue -
External tuber cracks
Shoots and foliage
- Symptoms will appear after mid-season, if at all.
- Even under high levels of infection, some stems and leaves may show signs of wilting during the day, but will recover at night.
- On infected stems, the lower leaves will turn yellow and wilt first, and the others will follow as the disease progresses up the stem.
- The leaves may take on a mottled appearance with rolled margins. The vascular tissue of infected stems (when cut) will appear brown and a creamy bacterial exudate can be squeezed from the cut end.
Tubers
Under field conditions, symptoms are very difficult to see. Even in storage, the tubers may sit for 2-3 months without any visible symptoms. Some infected tubers never show symptoms and can give rise to symptomless plants and tubers.
- with mild infection, there may be no visible external signs of the disease, and internally there may be a broken dark line in the vascular ring or a continuous yellowish discolouration.
- under severe infection, symptoms may include red areas around the eyes and slightly sunken and cracked surfaces.
- heavily infected tubers will also have a secondary infection, which will completely break down the tuber into a rotting brown mush extruding bacterial slime.
Bacterial ring rot resembles early blight, late blight, blackleg, brown rot, freezing injury and water damage. Therefore, laboratory diagnosis is required to confirm the presence of the bacteria.
How it spreads
Unlike many plant-pathogenic bacteria that survive in soil and develop in host plants, bacterial ring rot is transmitted exclusively through infected potato tissues. Infected tubers are the primary means of disease spread, especially in seed potatoes.
Clavibacter sepedonicus is a Gram-positive bacterium that persists in potato tubers and stems. Under field conditions, the disease is spread by cutting seed potatoes for planting and then by cultivating, where plant to plant infection is achieved by wounds inflicted by machinery. Once infected, the bacteria will move slowly through the vascular tissue to infect the tubers and all the lower portions of the growing plant.
Late in the growing season, the bacteria move down from the stems to infect new tubers. This disease derives its name from the breaking down and rotting of the vascular ring within the tuber. This ring is located about 6.5 mm below the skin surface. The bacterium can survive for up to 2 years in the dried slime leaked out of tubers and stems that may be found on crates, sacks, farm machinery and other surfaces. Spread of the disease is possible via the dried slime. Survival of the bacterium is best under cool dry conditions.
The pathogen can also be spread through contaminated surfaces, including equipment, storage facilities and vehicles used during production, storage, and transport. This makes on farm biosecurity program, including cleaning and disinfection of equipment entering the farm, a critical control measure.
Potato (Solanum tuberosum) is the only plant where natural infection has been found to cause disease. Tomato (Solanum lycopersicum) and eggplant (Solanum melongena) have been shown to be susceptible only in inoculated plants under experimental conditions. Sugarbeet (Beta vulgaris var. saccharifera) has been described as a natural symptomless host.
What you can do
Bacterial ring rot is one of the most serious regulated non-quarantine diseases of potatoes in Canada. There is a zero tolerance for bacterial ring rot on all Canadian seed potato farms.
To prevent the spread of bacterial ring rot:
- use only certified seed potatoes
- thoroughly clean and disinfect all equipment and containers before entering the seed potato farm unit
- ensure strict separation between seed potato farm units and any other potato farms or packing operations
- practice good record-keeping and traceability – they are critical for effective disease management
If you are a certified seed potato grower and think you have found bacterial ring rot on your farm unit, contact your local CFIA office. All other potato producers and the general public should contact their provincial department of agriculture.
What we are doing
It was first detected in Canada in the 1930s, where the planting of infected seed tubers helped it spread quickly. Seed certification standards we're introduced and enforced, which improved sanitary methods and brought this highly destructive disease under control.
The Canadian Food Inspection Agency (CFIA) classifies bacterial ring rot as a regulated non-quarantine pest with zero tolerance in seed potatoes under the Canadian Seed Potato Certification Program. To protect the integrity of Canada's seed potato industry, we enforce strict testing and inspection protocols to prevent the introduction and spread of bacterial ring rot and other bacterial diseases.
- D-97-12: Seed Potato Certification Program – Bacterial Ring Rot Testing Program for Field Grown Seed Potatoes
- D-95-18: Seed Potato Certification Program – Investigation Procedure after Clavibacter michiganensis Subsp. sepedonicus Has Been Detected on a Seed Potato Farming Unit