Identify Clubroot
Information adapted from Agri-Facts, Clubroot Disease of Canola and Mustard, Alberta Agriculture and Rural Development, May 2007 Revision.
Roots of infected plants become malformed due to increased cell division and growth, which leads to the development of gall formations. 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 6) could be confused with other diseases such as sclerotinia, blackleg or fusarium wilt.
Symptoms in the field will vary depending on the growth stage of the crop when infection occurs. Early infection at the seedling stage can result in wilting, stunting, and yellowing 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 will 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. Clubroot is not a phytosanitary issue for trade.
Because of the potential for visual symptoms of clubroot to be incorrectly attributed to heat 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 5).
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.
Another option is to identify patches of concern while swathing and sample afterwards. If suspicious plants are not sampled until 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 Figure 7) rather than the healthy white colour associated with normal roots.
Hybridization nodules on canola roots (see Figures 8 and 9), although rare, could be confused with clubroot galls but 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.
Yield Loss
A rule of thumb is that yield losses due to clubroot are about half of the percentage of infected stems. For example, if almost 100% of plants in a field are infected, expect about 50% yield loss, while infestations of 10-20% of plants should lead to 5-10% yield loss. This pattern of yield loss is very similar to sclerotinia stem rot in canola. Both clubroot and sclerotinia restrict the flow of water and nutrients from roots to aboveground plant tissues. Severe field infestations in Alberta have caused total yield loss (not worth harvesting) in a few cases.
Clubroot is a disease that affects crucifers worldwide. In the United States, there have been a number of reports of clubroot on Brassica crops from several states, varying in degree of severity and incidence.
In Canada, clubroot is primarily established in the vegetable growing regions of British Columbia, Quebec, Ontario, and the Atlantic provinces. It has also been detected in vegetable crops in both Alberta and Manitoba. Identification of clubroot in commercial canola fields in western Canada is a relatively recent occurrence.
Alberta
In 2003, clubroot was identified in canola near Edmonton, AB. This was the first report of clubroot in a commercial canola field in Canada. Since 2003, clubroot has been found in an increasing number of canola crops in this region. According to information provided by the Alberta Clubroot Management Committee, clubroot has been detected in approximately 405 fields, with incidence levels ranging from below 30% (low) to above 70% (high). The disease distribution in infested fields has generally been patchy but in the 10 to 15% of canola crops with high levels of clubroot infestation, the disease has occurred fairly evenly throughout the field. In 2008, approximately 160 new fields were confirmed through survey work by the University of Alberta, Alberta Agriculture and Rural Development, and Agricultural Service Boards. Fifiteen counties and the City of Edmonton have been affected in Alberta (see Figure 10). These counties include Sturgeon, Leduc, Parkland, Wetaskiwin, Strathcona, Westlock, Camrose, Flagstaff, Barrhead, Lac Ste. Anne, Newell, Ponoka, Lacombe, Yellowhead, and Cypress. The number of fields wiith positive detections in these counties is extremely variable. Sturgeon and Leduc each have over 100 fields with positive detections, while Parkland has over 40 fields and Westlock has ten fields. The City of Edmonton has 15 fields with positive detections while Wetaskiwin, Strathcona, Barrhead, Camrose, Flagstaff, Ponoka, and Newell each have between 3 and 9 fields with positive detections. Lacombe, Lac Ste. Anne, Yellowhead, and Cypress each have 1 to 2 fields with positive detections.
For information about specific fields, please contact local county offices.
Manitoba
According to information provided by Manitoba Agriculture, Food and Rural Initiatives, the presence of the pathogen (Plasmodiophora brassicae) responsible for clubroot has been reported in Manitoba on symptomatic cruciferous vegetables. Reports have been very sparse, with the first note dating back to an unconfirmed report on rutabaga in 1925. In the 1980’s, clubroot was found on market garden cruciferous vegetables. The most recently known detection of clubroot in Manitoba occurred in 2005, on canola. This occurrence was of very low incidence, and the symptoms were of very low severity. Reports from disease surveys of canola in Manitoba, which were not targeted at clubroot, have detected no plants with symptoms of clubroot in canola production areas.
Saskatchewan
According the Saskatchewan Ministry of Agriculture, clubroot symptoms have not been observed on any of the canola crops surveyed in Saskatchwan disease surveys; however in 2008 the clubroot pathogen's DNA was detected in a soil sample collected from one field in the survey. Further testing is being conducted to confirm the results and determine whether or not the pathogen is viable; results are expected by the end of June 2009. Confirmation of clubroot requires observation of disease symptoms in a susceptible crop in addition to detection of the pathogen's DNA in a plant or soil sample.
This incidence emphasizes the importance of equipment cleaning, especially when moving from affected or suspected areas to clubroot-free areas. Farmers and agronomists must be aware of this disease and be proactive in helping prevent its wide-spread establishment and spread.
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 two labs in Canada that currently provide this service are listed below:
1. 20/20 Seed Labs
201- 509 11th Ave
Nisku, AB T9E 7N5
(780) 955-3435
2. BioVision Seed Labs
7225 B Roper Road
Edmonton, AB T6B 3J4
1-800-952-5407
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.
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 two commercial labs (20/20 Seed Labs or Biovision Seed Labs) 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:
www.clubroot.ca/docs/Manitoba1.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.
www.clubroot.ca/docs/Manitoba2.pdf
There is currently no charge for crop related samples. For more information or to submit a sample:
1. 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 two commercial labs (20/20 Seed Labs or Biovision Seed Labs) for testing.
In Saskatchewan:
For visual diagnosis, 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 at http://www.agriculture.gov.sk.ca/Forms under 'crop forms'. 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:
1. 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 two commercial labs (20/20 Seed Labs or Biovision Seed Labs) for testing.