Gossen, McDonald & Hwang: Extent of Infestation and Potential Eradication of Clubroot at Sites in Saskatchewan
Date: May 2016
Term: 3 years
Status: Completed
Researcher(s): Bruce Gossen, Agriculture and Agri-Food Canada, Saskatoon SK; M.R. McDonald, University of Guelph; S.F. Hwang, Alberta Agriculture and Forestry
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: ADF, WGRF
Project Summary
Clubroot is a destructive soil-borne disease that represents a potentially serious threat to canola production in Saskatchewan. In a recent three-year study, researchers investigated the possibility of eradicating small areas of infestation if they were identified early enough, assessed different actives and determined the distribution of the pathogen in soils. As a result of the study, several fumigants with efficacy against the resting spores of P. brassicae were identified and confirmed. Based on these results, a recipe that producers could use to manage small areas of clubroot infestation has been proposed and testing is planned in one or more commercial field situations.
Clubroot (Plasmodiophora brassicae) was identified on canola in western Canada for the first time near Edmonton AB in 2003, and has subsequently been identified from more than 2000 fields across Alberta. Studies on factors affecting the development of clubroot on canola demonstrated that the pathogen was difficult to control using conventional approaches (seed treatments, soil amendments), that canola production in most regions of the Canadian prairies was at risk of clubroot spread, that the pathogen moves readily on farm machinery and in wind and water, and that a breakdown in the resistance of resistant cultivars was already occurring. Therefore, clubroot represents a potentially serious threat to canola production in Saskatchewan.
Researchers from Agriculture and Agri-Food Canada in Saskatoon in collaboration with the University of Guelph and Alberta Agriculture and Forestry conducted a three-year study from 2013 to 2015 to help determine if it might be possible to contain or even eliminate small areas of infestation if they were identified early enough. The objectives of this study were to 1) investigate the feasibility of eradicating clubroot from small-scale clubroot infestations to prevent establishment of the disease in new locations, 2) to assess selected actives on a range of soil types, and 3) to assess the horizontal and vertical distribution of resting spores in the soil profile at infested sites. Also, industries involved in large scale movement of soil (oil and gas, road construction) need to know if the soil that they are moving is contaminated with resting spores of clubroot.
Laboratory and field trials to assess the efficacy of fumigants were conducted in Ontario and Alberta from 2013-2015. At the University of Guelph trials in the laboratory, field plots and commercial fields tested several fumigants including metam sodium (41% sodium methyldithiocarbamat, trade name Busan 1236), chloropicrin (85%, trade name Pic Plus), and the biofumigant MustGrow (100% Brasssica juncea). In Alberta, testing with the fumigants metam sodium and dazomet was conducted on a heavy clay-loam soil at the clubroot nursery site, Crop Diversification Centre North near Edmonton in small plots. For all trials, clubroot severity was examined at about 6 wk after seeding. Plants were removed from the soil and assessed for clubroot symptoms. Clubroot incidence and severity were assessed using a 03 scaling system, where 0 = no clubbing, 1 < 1/3 of tap root with clubbing symptoms, 2 = 1/3 to 2/3 of root area with clubs, and 3 > 2/3 clubbing of roots. Resting spore concentration samples were collected from three sites infested with P. brassicae in Ontario and three in Alberta and estimated using an improved qPCR technique developed in this project.
Overall, the results of the initial studies under controlled conditions demonstrated that several actives had excellent activity against resting spores. However, efficacy in field trials was consistently low, even when the fumigants were applied using professional-grade application equipment. One factor that increased efficacy was the quality of the cover applied after fumigation. A totally impermeable film (TIF) cover produced much higher efficacy than construction-grade plastics, but at a higher cost. No treatment totally eradicated the pathogen on any soil or in any year.
The study also showed that pathogen distribution was highly variable, both horizontally and vertically – samples only 0.5 m apart often contained very different levels of spores. This indicates that spores can move downward slowly over time, likely in ground water. Resting spores present deep in the soil profile will have little effect on producers because any resulting infection will occur late and have little impact on crop development. However, they could impact companies involved in large-scale movement of soil, such as oil and gas companies and some construction activities (e.g., highways, housing). These industries in Saskatchewan have already been informed via their representatives in the Saskatchewan Clubroot Initiative.
Researchers were also able to improve estimates of resting spore concentration and successfully developed a technique for distinguishing between viable and dead resting spores using qPCR with a pre-treatment of propidium monoazide. These improvements represent a substantial contribution to knowledge of the biology and assessment of clubroot. However, the study demonstrated that resting spore numbers can only be reduced, but not totally eliminated, by application of fumigants. The success of the development of a rapid and accurate assessment of resting spore viability will improve assessments of treatment efficacy against resting spores, which may eventually be used to identify effective treatments for soil amendments, sanitation and fumigation, where progress has been hampered by the need to conduct resource-intensive bioassays.
The study indentified and confirmed several fumigants with efficacy against the resting spores of P. brassicae. However, most producers on the prairies do not have access to the specialized application equipment and covers required to allow fumigants to work effectively, but fumigation may represent a viable option for some companies (e.g., oil and gas pipelines). Based on these results, a recipe that producers could use to manage small areas of clubroot infestation has been proposed and testing is planned in one or more commercial field situations.
Scientific publications.
Hwang, S.F., Ahmed, H.U., Zhou, Q., Strelkov, S.E., Gossen, B.D., Peng, G., and Turnbull, G.D. 2014. Efficacy of Vapam fumigant against clubroot (Plasmodiophora brassicae) of canola. Plant Pathol. 63: 1374–1383. Doi: 10.1111/ppa.12207.
Deora, A., Gossen, B.D., Amirsadeghi, S., and McDonald, M.R. 2015. A multiplex qPCR assay for detection and quantification of Plasmodiophora brassicae in soil. Plant Dis. 99: 1002–1009. http://dx.doi.org/10.1094/PDIS-06-14-0608-RE.
Al-Daoud, F., Gossen, B.D., and McDonald, M.R. 2016. Propidium monoazide improves quantification of viable resting spores of Plasmodiophora brassicae with qPCR. Plant Dis. xx: xxx–xxx. (Accepted)
Cranmer T.J.., Gossen, B.D., Al-Daoud, F., Deora, A., and McDonald, M.R. 2016. Vertical distribution of resting spores of Plasmodiophora brassicae in soil. Eur. J Plant Pathol. xx: xxx–xxx. (Submitted).
Hwang, S.F., Ahmed, H.U., Strelkov, S.E., Zhou, Q., Gossen, B.D., McDonald, M.R., and Turnbull, G.D. 2016. Suppression of clubroot by dazomet fumigant. Plant Pathol. xx: xxx-xxx (Submitted).