Clubroot of Canola: Overview of an Emerging Problem Stephen Strelkov 2011 Manitoba Agronomists Conference 13 th Dec. 2011, Winnipeg MB Department of Agricultural, Food and Nutritional Science 410 Agriculture/Forestry Centre University of Alberta Edmonton AB T6G 2P5
Outline of Presentation Introduction to clubroot Current disease situation Pathogen dispersal mechanisms Clubroot resistant canola and resistance stewardship Integrated management of clubroot Conclusions
Clubroot Pathogen: Plasmodiophora brassicae Hosts: Canola, mustard, cruciferous vegetables and weeds Soilborne pathogen: Long-lived resting spores Occurrence: Traditionally BC & eastern Canada Cruciferous vegetables
Symptoms Below ground: Root galls (club-shaped swellings) White at first, turn grayish-brown to dark brown Above ground: Stunting, wilting, yellowing, shriveled seed
Healthy Plants Clubroot Patch
Disease Cycle S.E. Strelkov
Resting Spores in Host Roots J.P. Tewari
Clubroot on Canola in Alberta Discovery of clubroot in 2003 was a cause for concern 12 fields near Edmonton, AB Strelkov et al. (2005) Britannica Encycl.
Strelkov et al. Clubroot Situation (Fall 2011) 831fields with confirmed P. brassicae infestations Mostly in central Alberta Few cases in southern Alberta and Saskatchewan A few infected plants in experimental plots in Elm Creek, MB (2005)
Characteristics of Infested Fields ph from 4.8 to 7.6 (average = 6.2) Significant negative correlation between severity and soil ph Most heavily infested fields generally in canola-cereal-canolacereal rotation canola-canola rotation Strelkov et al. 2007
Clubroot Spread Principal mechanism of spread is on machinery Other dispersal mechanisms have also been implicated 6 0.296 150 m 7 8 0.169 0.155 3 4 2 0.324 0.310 5 0.394 0.479 150 m 150 m 9 0.225 150 m 1 Field Entrance 0.901 Cao et al. 2009
Seedborne Dispersal Clubroot cannot directly infect seeds or potato tubers Can only occur as an external contaminant Developed and validated a qpcr-based protocol to quantify inoculum loads on seeds/tubers Combined with Evan s blue viability staining Greenhouse bioassays
Seedborne Dispersal Assessed 46 seed or tuber lots harvested from regions in AB where clubroot is prevalent Quantifiable levels of infestation on: 6 of 16 non-cleaned samples 1 of 30 commercially cleaned samples
Crop Resting Spore Loads Spore Load per 10 g Seed (qpcr) Viability (Evan s Blue Staining) Commercially Cleaned? Wheat 3.43 10 4 80% No Canola 4.04 10 3 90% No Pea <1,000 98% Yes Potato 1.40 10 4 90% No Pea ( 3) <1,000 97 100% No Spore loads as determined by qpcr on samples testing positive by conventional PCR (Rennie et al. 2011)
Seedborne Dispersal Levels of infestation in some non-cleaned samples greater than that required to cause clubroot in greenhouse bioassays Seedborne dissemination could serve as secondary mechanism of spread Seed cleaning seemed to be effective in reducing the risk Common seed treatments also effective in reducing the risk Farmers should avoid planting of common, untreated seeds harvested from clubroot-infested fields
Dispersal in Dust & Water Clubroot dispersal in dust and water may also occur Extent of problem not well defined Epidemiological studies to track and quantify spread Conventional PCR M C Dust Rennie et al.
Research Sites
BSNE (Dust) Samplers 105cm - 5 80cm - 4 60cm - 3 35cm - 2 10cm - 1
Sampling Wind direction Commercial Fields Research Plots
Wind direction A E B C D Sampler Conventional Detection Quantification A No Resting Spores No Resting Spores B No Resting Spores No Resting Spores C Resting Spores Detected Marginal in C1 D Resting Spores Detected Highest in D5 E Resting Spores Detected Highest in E5
Management of Clubroot Initial focus was on exclusion of the pathogen and long rotations out of susceptible crops Work underway to evaluate efficacy of fungicides, soil amendments and biological control agents Intensive resistance-breeding efforts Public institutions and private industry
Genetic Resistance Widespread release of resistant cultivars in 2010 All have good resistance to predominant pathotypes Represent most important tool for clubroot management
Resistance Stewardship Resistance will have to be well-managed: Pathogen populations can adapt in response to selection pressure Continuous cropping of a resistance source
Variability in Virulence Pathotype 5 (3%) Pathotype 2 (7%) Pathotype 8 (14%) Pathotype 2 (7%) Pathotype 6 (7%) Pathotype 3 (90%) Pathotype 3 (72%) Field Populations Single-Spore Isolates Classification on the differentials of Williams (1966) Howard et al. 2010
Pathogen Cycling Experiment Objective: To assess the effect of multiple infection cycles on the virulence of P. brassicae Methodology: Population and single-spore isolate representing pathotype 3 Cycled 5 on a selection of R, MR and S host genotypes
Methodology 6 weeks 6 weeks X 5 Inoculate with spores Rate disease & harvest spores Re-inoculate
Pathogen Cycling Repeated cropping of a resistance source can erode the effectiveness of that resistance Resistance stewardship is important! CV-R BL CV-S LeBoldus et al. (In Press)
Field Situation - 2011 Extensive surveillance revealed that all canola products with genetic resistance to clubroot were still fully effective against this disease in 2011 Disease severity on resistant canola crops was low (0.2 10.2%) Severe clubroot found in many of the canola crops sown to susceptible cultivars (severity >60% in some)
Continued Monitoring We plan continued surveys for clubroot in 2012; this will include monitoring and field sampling in clubroot affected regions to follow the performance of clubroot-resistant canola genotypes
Cross-Infectivity Experiments Objective: To assess whether various commercial canola cultivars carry the same or different sources of resistance Methodology: Cross-inoculate canola cultivars with P. brassicae populations cycled on other Brassica hosts Rationale: If same source of resistance, then pathogen populations cycled on one cultivar should show increased infectivity on other cultivars
Cross-Infectivity Experiments Pathogen populations cycled on one host did not show equivalent increases in virulence on other hosts Canola host Cycled populations CV-R BL ECD 05 ECD 15 W 5.5±9.4 1.9±7.7 4.6±8.9 5.5±9.4 X 8.6±2.9 0.0±0.0 0.0±0.0 0.0±0.0 Y 1.9±7.7 0.0±0.0 0.0±0.0 0.0±0.0 Z 11.1±9.5 0.0±0.0 0.0±0.0 0.0±0.0 LeBoldus et al. (In Press)
Rotation of Resistance Sources Cross-infectivity experiments suggest that some cultivars may be carrying different clubroot resistance sources Potential for rotation of resistance sources Further work is ongoing
Resistance Stewardship Genetic resistance represents most effective and economical clubroot management tool Sources of resistance will have to be well managed 1 in 4 rotation with clubroot resistant canola is recommended Rotation of cultivars Use resistance as part of an integrated strategy
Integrated Clubroot Management Based on deployment of resistant cultivars in combination with other strategies: Continued surveillance Proper sanitation Crop rotation Fungicides and soil amendments for spot treatments?
Conclusions Clubroot now endemic to canola in central Alberta Disease appears to be spreading by a variety of mechanisms Management can be difficult Resistant cultivars represent an important new clubroot management tool Will have to be used as part of an integrated approach
Acknowledgments Collaborators: S.F. Hwang, T.K. Turkington, G. Peng, R.J. Howard & others Students & other research personnel: D. Rennie, V.P. Manolii, T. Cao, J. LeBoldus & others Funders: Canola Council of Canada through AAFC Clubroot Risk Mitigation Initiative, Alberta Crop Industry Development Fund, Agriculture & Food Council, ACPC, Canadian Seed Growers Association, SaskCanola, MCGA and other industry partners