Clubroot of Canola: Overview of an Emerging Problem · 2020. 3. 2. · Clubroot of Canola: Overview...
Transcript of Clubroot of Canola: Overview of an Emerging Problem · 2020. 3. 2. · Clubroot of Canola: Overview...
Clubroot of Canola: Overview of
an Emerging Problem
Stephen Strelkov
2011 Manitoba Agronomists Conference
13th 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.
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)
Strelkov et al.
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-canola-
cereal rotation
– canola-canola rotation
Strelkov et al. 2007
Clubroot Spread
• Principal
mechanism of
spread is on
machinery
• Other dispersal
mechanisms
have also been
implicated
8 7
6
5 4 3
2
9
1 Field Entrance
150 m
150 m
150 m
150 m
0.901
0.479
0.225
0.155 0.169
0.296
0.394
0.324 0.310
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
Resting Spore Loads
Spore loads as determined by qPCR on samples testing positive by conventional PCR
(Rennie et al. 2011)
Crop Spore Load
per 10 g Seed
(qPCR)
Viability
(Evan’s Blue
Staining)
Commercially
Cleaned?
Wheat 3.43 × 104 80% No
Canola 4.04 × 103 90% No
Pea <1,000 98% Yes
Potato 1.40 × 104 90% No
Pea (× 3) <1,000 97 – 100% No
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
Commercial Fields Research Plots
Wind direction
E
A
B
C
D
E
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
Wind direction
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 3
(90%)
Pathotype 5
(3%)
Pathotype 2
(7%)
Pathotype 3
(72%)
Pathotype 6
(7%)
Pathotype 8
(14%)
Pathotype 2
(7%)
“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
Inoculate
with spores
6 weeks
Rate disease &
harvest spores Re-inoculate
6 weeks X 5
Pathogen Cycling
LeBoldus et al. (In Press)
Repeated cropping of a
resistance source can erode
the effectiveness of that
resistance
Resistance stewardship is
important!
CV-R CV-S BL
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
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)
Pathogen
populations
cycled on one host
did not show
equivalent
increases in
virulence on other
hosts
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