Clubroot Update
Jan 19/2016
Red Deer
Photo courtesy of Dr. Ron Howard
J.P. Tewari
Lifecycle of Clubroot
• Strains of clubroot can overcome
resistance. Over-reliance on
resistant varieties in short rotations
will increase the risk of build up of
various strains and should be
avoided.
History teaches us but do we listen?
• Clubroot resistant cabbage in USA becomes
susceptible (Seaman, U of Wisconsin,1960)
• Chinese cabbage clubroot resistance
overcome in Australia (Donald et al., 2006)
• CR Chinese cabbage in Japan overcome
about 10 years after introduction (Tanaka
and Ito, 2013).
Canola Clubroot Resistance
• Most likely all western Canada current
resistance in canola is from the European
winter oilseed variety ‘Mendel’
Alberta Situation
Clubroot in Alberta 2003 to
2015
• First canola field reported in
AB in 2003
• Over 2000 known fields
infested in AB
• Fields in AB have been
reported to have > 10m
spores/gram in soil
2013 Situation
• New strain of clubroot
• 5x….
• This new strain was tested
against all existing CR
varieties
• Most cases severity > 90%
2014 Situation
• Target survey on CR
cultivars
• 16 fields of pathogen
shift
• In addition to 5x, 9
distinct pathotype
variants
Strelkov & Cao, unpublished
2015 Survey
• Survey
conducted on CR
fields
• Found 32 new
‘suspicious’ fields
in Central AB
• Samples to be
pathotyped at
UofA
Classification of New Strains of
Plasmodiophora brassicae:
A Preliminary Assessment
S.E. Strelkov, S.F. Hwang, V.P. Manolii,
and T. Cao
Pathogen
S
S
S
R
S
Pathogen isolates are grouped into
strains based on the symptoms they
cause on a defined group of hosts
‘Pathotype 5x’
Host variety
Jersey Queen (cabbage)
Badger Shipper (cabbage)
Laurentian (rutabaga)
Wilhemsburger (rutabaga)
Canadian ‘clubroot
resistant’ canola
Pathotype
3
5
5x
+
+
-
-
+
Pathotype designations as defined on system of Williams (1966)
Nine distinct virulence phenotypes detected
Field population
Genotype
CDCN#2
CDCN#
4
CDCN#6
ECD 02
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
ECD 05
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
ECD 06
+
+
‐
‐
+
+
+
+
+
+
+
+
+
+
+
+
ECD 08
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
ECD 09
+
+
‐
‐
+
+
+
+
+
+
+
+
+
+
+
+
ECD 10
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
ECD 11
‐
‐
‐
‐
‐
‐
‐
+
‐
‐
‐
‐
‐
‐
‐
‐
ECD 13
‐
+
‐
+
+
+
+
+
+
+
+
‐
‐
+
+
+
Brutor
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Laurentian
‐
+
‐
‐
+
‐
+
+
+
+
+
+
+
+
+
+
Mendel
‐
‐
‐
‐
‐
+
+
+
+
+
+
‐
‐
+
+
‐
Westar
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
45H29
‐
‐
+
+
+
+
+
+
+
+
+
+
+
+
+
‐
Pathotype designation:
CCD (temporary)
A
B
C
D
E
F
G
H
G
G
G
I
I
G
G
B
Williams, 1966
5
3
5
6
3
6
3
2
3
3
3
8
8
3
3
3
Some et al., 1996
P2
P2
P3
P3
P2
P2
P2
P2
P2
P2
P2
P2
P2
P2
P2
P2
CDCS
F1‐14
F175‐14
F3‐14
F183‐
14
F184‐
14
F185‐
14
F186‐
14
F187‐
14
F188‐
14
F189‐
14
F331‐14
F41‐14
•
•
One variant of pathotype 3 was most common: 6 of 16 populations
One variant of pathotype 2 also highly virulent (11 of 13 differentials)
Words of Caution
• Novel strains tested are
‘field’ populations
• May represent mixture of
pathotypes
– Masking of rarer strains
– Antagonistic/synergistic
interactions
• Analysis of single-spore will
be important
Characterizing P5x populations with B. napus lines at
AAFC, Saskatoon
B. napus
LG-01
LG-02
LG-03
BN-E-06
R
S
R
BN-E-08
S
S
S
BN-E-09
R
R
R
BN-I-01
R
S
S
 Differential reactions were found in a set of B. napus lines at AAFC.
 There are at least 3 races in P5x populations.
 LG-2 is the most aggressive one.
 BN-E-09 is resistant to all.
Clubroot Severity in B-Tolerant
Lines
100
90
Severity (DSI)
80
70
60
50
40
30
20
10
0
Untreated
Treated
A fungal endophyte that induces resistance
to clubroot in canola
Clubroot severity (%)
60
qPCR
50
y = 24.3x2 - 66.8x + 52
R2 = 0.86
40
30
20
10
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Colonization of canola roots by Hc (ng/g)
2