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Identify Clubroot

Information adapted from Agri-Facts, Clubroot Disease of Canola and Mustard, Alberta Agriculture and Rural Development, May 2007 Revision.

Identification

Fig 1. Patches premature ripening

Photo courtesy of S.E. Strelkov, University of Alberta

Fig 2. Clubroot causes drought-stress

© Monsanto Canada Inc. Used with permission

Roots of infected plants become malformed due to increased cell division and growth, which leads to the development of galls. Clubroot galls tie up nutrients, and severely infected roots can’t transport adequate water and nutrients to aboveground plant tissues.

Depending on local conditions and timing of infection, clubroot infected canola may look very similar to canola suffering from other diseases or environmental stresses. Patches of prematurely ripening canola due to clubroot infection (see Figure 1) could be confused with other diseases such as sclerotinia, blackleg or fusarium wilt, or moisture stress (drought, waterlogging) if only viewed from a distance.

Symptoms in the field will vary depending on the growth stage of the crop when infection occurs, the level of infection and conditions after infection takes place. Early infection at the seedling stage can result in wilting, stunting, yellowing and even death of canola plants in the late rosette to early podding stage.

Infection that occurs at later crop stages may not show plant wilting, stunting or yellowing. However, infected plants may ripen prematurely, resulting in shriveled seeds, negatively impacting both yield and quality (oil content). This is a common symptom in any canola crop that ripens prematurely. Lack of moisture and high temperatures later in the season can have the same results.

Since above-ground symptoms of clubroot may be incorrectly attributed to moisture stress or to diseases such as blackleg, fusarium wilt or sclerotinia, proper diagnosis of clubroot should always include digging up plants to check for gall formation on roots (see Figure 3).

Typically, it takes six to eight weeks from initial infection to gall formation, but this depends on when the field receives rain. The best time to scout for clubroot symptoms on roots is late in the season, approximately two weeks before swathing, since root galls should be easy to identify at this time (see Figures 4 to 8).

Another good option is to identify patches of concern while swathing and sample afterwards. Since the entire field is traversed during swathing, this will give the most detailed indication of the incidence in the field. If suspicious plants are not sampled until several weeks after swathing, the root galls may have decayed already, and typical whitish galls will no longer be present. Instead, the decayed galls give roots a brown, peaty appearance (See Figures 8 and 9) rather than the healthy white colour associated with normal roots.

Fig 3. Always dig up roots when scouting for clubroot

Photo courtesy of Parkland County Agricultural Services,
Alberta Canada

Fig 4. Initial infection, small gall

© Monsanto Canada Inc. Used with permission

 

Fig 5. Small galls begin to expand

© Monsanto Canada Inc. Used with permission

 

Fig 6. Moderately infected canola root

© Monsanto Canada Inc. Used with permission

 

Fig 7. Plant begins to die, galls appear 'woody'

© Monsanto Canada Inc. Used with permission

Fig 8. Decaying galls appear 'peaty'

© Monsanto Canada Inc. Used with permission

 

Fig 9. Decayed clubroot galls and whitish stem appearance

Photo courtesy of T.K. Turkington, AAFC Lacombe

 

Fig 10. Shepherd's purse is a host for clubroot

© Monsanto Canada Inc. Used with permission

 

Clubroot infects all species of plants in the Crucifer (Brassicaecea) family. Weeds such as Shepherd’s purse, stinkweed, flixweed, wild mustard and many others in this family will carry and increase this disease (see Figure 10).

Hybridization nodules on canola roots (see Figures 11 and 12), although rare, could be confused with clubroot galls although these appear as small, round nodules located at root nodes. The interior texture of a clubroot gall is spongy or marbled, while hybridization nodules are uniformly dense inside, like healthy roots. Also, hybridization nodules will not decay rapidly to a peaty appearance like clubroot galls.

 

Fig 11. Hybridization nodules on canola root

Photo courtesy of Rob Dunn

 

Fig 12. Hybridization nodules on canola root

Photo courtesy of Alvin Eyolfson, Battle River Research Group

 

 

Testing

Soil and plant testing for clubroot is conducted by commercial laboratories, but fields should be scouted and identification of other potential problems considered first.

Soil and plant samples can be tested for the presence of clubroot DNA via PCR (Polymerase Chain Reaction) methodology. The labs in Canada that currently provide this service are listed below:

  • 20/20 Seed Labs
    507 11th Ave
    Nisku, AB T9E 7N5
    (780) 955-3435

  • Exova
    7217 Roper Road NW
    Edmonton, AB T6B 3J4
    (780) 438-5522
     
  • BioVision Seed Labs
    #310 - 280 Portage Close
    Sherwood Park, AB T8H 2R6
    1-800-952-5407
     
  • Discovery Seed Labs
    450 Melville Street
    Saskatoon, SK S7J 4M2
    (306) 249-4484
     
  • Pest Surveillance Initiative (PSI)
    5A 1325 Markham Road
    Winnipeg, MB R3T 4J6
    (204) 813-2171
     
  • A&L Canada Laboratories Inc.
    2136 Jetstream Road
    London, ON N5V 3P5
    (519) 457-2575 


For soil sampling
: Obtain approximately 500 grams (2.5 cups) of soil for this test. This should be a composite sample taken in a “W” pattern near the major approach or entrance to the field or in the plot area. Sample soil from the top 5 cm (A horizon), excluding as much surface organic matter as possible.

For plant sampling: Obtain roots from suspected plants and place in a zip-lock bag. These can be fresh or dry roots. If available, plant tissue samples are preferable to soil samples to test for the presence of the clubroot pathogen.

The PCR test is a reliable method for molecular detection of the clubroot pathogen and will give either a positive or negative result for the presence of clubroot in the sample. However, there is currently no mechanism in place to correlate this test result to the potential for infection in the field. Research is underway in this area.

If a sample tests positive for the presence of the clubroot pathogen, use caution when extrapolating the results obtained for a particular sample to an entire field.

In Alberta:

Producers finding suspicious roots can contact and send samples to one of four commercial labs (20/20 Seed Labs, Biovision Seed Labs, Discovery Seed Labs or Exova Edmonton) for testing.

In Manitoba:

For visual diagnosis, submit suspicious samples to the Manitoba Crop Diagnostic Centre. Send a complete sample (the entire fresh plant in a plastic bag) along with the proper form, with as much information filled out as possible, to the Crop Diagnostic Centre. General guidelines for submitting a sample can be found at:

Submitting Samples for Diagnosis to the Crop Diagnostic Centre (PDF)

This submission form is available directly from the Diagnostic Centre, through Manitoba Agriculture, Food and Rural Initiatives offices, or can be accessed at the following link.

Diagnostics Form for Crops, Insects and Weeds (PDF)

There is currently no charge for crop related samples. For more information or to submit a sample:

Crop Diagnostic Centre, Crops Knowledge Centre
Agricultural Services Complex
204 – 545 University Crescent
Winnipeg, Manitoba
R3T 5S6
(204) 945-7707

For PCR diagnosis, farmers finding suspicious roots can also contact and send samples to one of three commercial labs (20/20 Seed Labs, Biovision Seed Labs or Pest Surveillance Initiative) for testing.

In Saskatchewan:

For visual diagnosis of plants, submit suspicious samples to the Crop Protection Laboratory. To submit, send a complete sample (the entire plant, preferably more than one) along with the proper form with as much information filled out as possible to the Crop Protection Laboratory. This form is available directly from the laboratory, through Saskatchewan Agriculture, or can be found online. Note: when downloading and using the Internet version of the form, four copies of the fully completed form are required, along with the sample, for submission to the laboratory. For more information or to submit a complete sample:

Crop Protection Laboratory
125 - 3085 Albert Street
Regina, Saskatchewan
S4N 6P6
(306) 787-8130

For PCR diagnosis, farmers finding suspicious roots can contact and send samples to one of three commercial labs (20/20 Seed Labs, Biovision Seed Labs or Discovery Seed Labs) for testing.