Virulence and pathotype classification of Plasmodiophora brassicae populations collected from clubroot resistant canola (Brassica napus) in Canada

Figures & data

Table 1. Pathotype classification scheme on the hosts of the Canadian Clubroot Differential Set.

Pathotype designation^a,b
CCD	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	P	X
Williams	3	2	5	3	8	2	5	3	5	8	5	5	6	8	3	8	5
Somé et al.	P2	P2	P2	P2	P2	P2	P3	P2	P2	P3	P3	P3	P2	P2	P3	P2	P3
Differential Host^c	Reaction^d
ECD 02	−	−	−	−	−	−	−	−	−	−	−	−	−	−	−	−	−
ECD 05	+	+	+	+	+	+	+	+	+	+	+	+	+	+	+	+	+
ECD 06	+	+	+	+	+	+	−	+	+	−	−	−	+	+	−	+	−
ECD 08	+	+	+	+	+	+	+	+	+	+	−	+	+	+	+	+	+
ECD 09	+	+	+	+	+	+	−	+	+	−	−	−	+	+	+	+	−
ECD 10	−	−	−	−	−	−	−	−	−	−	−	−	−	−	−	−	−
ECD 11	−	+	−	−	−	+	−	−	−	−	−	−	−	−	−	−	−
ECD 13	+	+	−	+	−	+	−	+	−	−	−	−	+	−	−	−	−
Brutor	+	+	+	+	+	+	+	+	+	+	+	+	+	+	+	+	+
Laurentian	+	+	−	+	+	+	−	+	−	+	−	−	−	+	+	+	−
Mendel	+	+	−	−	−	−	−	−	−	−	−	−	−	−	−	+	+
Westar	+	+	+	+	+	+	+	+	+	+	+	+	+	+	+	+	+
45H29	+	+	+	+	+	−	+	−	−	+	+	−	−	−	+	+	+

^a Pathotype designations are based on the systems of the Canadian Clubroot Differential (CCD) Set, Williams (1966) and Somé et al. (1996); ECD 10, 11 and 13 are included in the differentials of Williams (1966), along with ‘Laurentian’, while the differentials of Somé et al. (1996) consist of ECD 06, ‘Laurentian’ and ‘Brutor’. All hosts designated ECD are also members of the European Clubroot Differential Set (Buczacki et al., 1975), but ECD pathotype designations could not be obtained since not all ECD differentials were included in the test.

^b CCD pathotypes F, H, I, M and N correspond to the original pathotypes 2, 3, 5, 6 and 8, as defined on the differentials of Williams (1966), which cannot overcome resistance in any clubroot resistant B. napus host; CCD pathotype L corresponds to the P. brassicae population D-G3 reported by Strelkov et al. (2016a), while CCD pathotype X corresponds to the populations L-G1, L-G2 and L-G3 reported by Strelkov et al. (2016a).

^c European Clubroot Differential (ECD) 02 = Brassica rapa ssp. rapifera line AAbbCC; ECD 05 = B. rapa var. pekinensis ‘Granaat’; ECD 06 = Brassica napus ‘Nevin’; ECD 08 = B. napus ‘Giant Rape’ selection; ECD 09 = B. napus New Zealand resistant rape; ECD 10 = B. napus var. napobrassica ‘Wilhemsburger’; ECD 11 = Brassica oleracea var. capitata ‘Badger Shipper’; ECD 13 = ‘Jersey Queen’; Brutor = B. napus ‘Brutor’; Laur. = B. napus var. napobrassica ‘Laurentian’; Westar = B. napus ‘Westar’; and 45H29 = B. napus ‘45H29’.

^d A plus (+) sign denotes a susceptible host reaction, while a minus (−) sign denotes a resistant reaction. Host reactions were classified as + or − based on the index of disease (ID) that developed 6 weeks following inoculation; for a reaction to be considered resistant, the mean ID must be <50% and the 95% confidence interval must not exceed 50%.

Table 2. Clubroot disease severity on clubroot-resistant canola cultivars and the universally susceptible Chinese cabbage ‘Granaat’ (European Clubroot Differential (ECD 05)) after inoculation with populations of Plasmodiophora brassicae representing different pathotypes, as defined on the Canadian Clubroot Differential Set, and collected in Alberta, Canada, from 2014–2016.

	Host Genotype^b
Pathotype^a	ECD 05	9558C	1960	45H29	6056CR	74-54RR	D3152	L135C	D3155C
2014
A (5)	97.3 (93.8–100)	63.5 (58.1–70.4)	95.8 (92.0–99.3)	97.8 (97.2–98.6)	96.9 (90.3–100)	95.3 (85.4–98.6)	97.3 (94.9–100)	93.2 (87.5–96.5)
B (1)	100	61.1	97.2	95.0	99.3	95.1	98.6	94.4
C (1)	97.9	75.0	97.9	99.3	93.8	98.6	92.0	98.6
D (1)	96.5	58.3	95.8	97.2	98.6	98.6	97.2	97.9
E (2)	98.6 (98.5–98.6)	75.8 (69.6–81.9)	99.3 (98.5–100)	99.0 (97.9–100)	99.3 (98.6–100)	98.3 (97.9–98.6)	97.9 (97.9–97.9)	98.3 (96.5–100)
G (2)	95.4 (91.4–99.3)	27.9 (9.7–46.0*)	72.9 (45.7*-100)	76.6 (58.1–95.1)	77.8 (58.3–97.2)	74.7 (52.3–97.1)	71.7 (46.8*-96.5)	83.7 (71.5–95.8)
H (2)	93.7 (93.5–93.8)	18.6 (16.4–20.8)	40.2 (36.8–43.5*)	38.6 (34.7–42.4)	46.0 (39.0–52.9)	38.9 (22.2–55.6)	45.2 (36.8–53.5)	48.6 (34.0–63.2)
I (1)	91.0	5.7	15.4	17.4	35.4	19.9	18.1	47.4*
P (1)	93.8	41.7	87.5	93.8	91.7	93.8	93.7	91.7
2015
A (15)	96.4 (84.7–100)	80.6 (24.3–100)	89.4 (42.2*–100)	89.8 (50.6–100)	91.2 (45.9*–100)	89.7 (23.6–100)	91.9 (65.4–100)	93.6 (69.3–100)
D (5)	97.2 (88.9–100)	33.5 (16.0–60.7)	39.7 (10.8–83.6)	62.0 (54.2–73.9)	48.6 (24.0–77.5)	36.0 (7.6–79.2)	53.3 (20.8–93.1)	40.0 (7.3–94.4)
G (2)	96.9 (94.4–99.3)	29.8 (13.7–45.8*)	37.5 (12.5–62.5)	57.0 (49.4*–64.6)	40.0 (27.1–52.8)	43.1 (31.3–54.9)	57.1 (41.3–72.9)	57.4 (39.1–75.7)
J (1)	93.8	45.8	45.1*	66.2	38.2	39.6	43.8*	54.2
K (1)	93.1	25.6	13.9	57.8	34.7	30.6	39.6	53.5
2016
A (19)	99.9 (98.6–100)	68.0 (50.7–100)	98.0 (93.8–100)	98.9 (96.5–100)	98.8 (93.1–100)	98.1 (93.1–100)		98.6 (94.4–100)	98.3 (91.0–100)
O (2)	100 (100–100)	92.4 (90.3–94.4)	100 (100–100)	100 (100–100)	100 (100–100)	100 (100–100)		100 (100–100)	100 (100–100)
P (1)	100	74.3	100	100	100	100		100	100

^a Pathotype designations are as defined on the Canadian Clubroot Differential Set (Table 1); the numbers in parentheses indicate the number of P. brassicae populations classified as a particular pathotype each year.

^b Indices of disease (ID, %) are shown, representing the mean of all populations classified as a particular pathotype each year (the range of values is indicated in parentheses). The mean ID values (± standard error) for individual populations are included in Supplementary Table 2. A host was considered resistant if the mean ID was <50% and the 95% confidence interval (CI) did not overlap 50%. The numbers in bold indicate susceptible reactions; those reactions in which the mean ID was <50% but the 95% CI overlapped 50% are denoted with an asterisk (*).

Table 3. Reaction of the hosts of the Canadian Clubroot Differential Set to inoculation with populations of Plasmodiophora brassicae representing each of the different pathotypes and collected in Alberta, Canada, from 2014–2016.

	Host Genotype^b,c
Pathotype^a	ECD 02	ECD 05	ECD 06	ECD 08	ECD 09	ECD 10	ECD 11	ECD 13	Brutor	Laur.	Mendel	Westar	45H29
2014
A (5)	0.1 (0–0.7)	97.9 (93.8–100)	84.7 (76.4–91.0)	83.2 (62.5–96.5)	82.6 (54.9–96.5)	9.9 (4.2–19.8)	13.2 (7.6–27.8)	52.6 (45.1*–56.9)	97.5 (91.0–100)	84.0 (70.8–96.3)	53.4 (45.1*–58.3)	91.0 (83.3–95.8)	97.1 (94.4–98.6)
B (1)	0	93.1	79.2	77.1	72.2	12.5	50.0	68.1	90.3	90.2	71.5	90.3	93.6
C (1)	0	91.7	68.8	61.1	57.6	4.4	0	29.3	85.4	29.0	18.1	65.3	98.6
D (1)	2.1	100	85.0	93.1	92.6	13.9	27.8	59.7	100	80.6	30.4	73.5	98.6
E (2)	1.1 (0–2.1)	93.8 (93.1–94.4)	78.1 (61.8–94.4)	60.9 (57.9–63.9)	58.4 (52.8–64.0)	5.6 (3.5–7.6)	4.2 (0.7–7.6)	13.6 (8.3–18.8)	79.9 (74.3–85.4)	57.0 (54.9–59.1)	29.5 (26.4–32.6)	88.6 (85.4–91.7)	95.1 (94.4–95.8)
G (2)	1.1 (0–2.1)	90.6 (86.8–94.4)	18.1 (5.6–30.6)	77.8 (61.8–93.8)	15.7 (4.2–27.1)	2.8 (0–5.6)	0	9.8 (3.5–16.0)	74.7 (54.9–94.4)	19.8 (15.3–24.3)	6.6 (4.2–9.0)	73.3 (52.1–94.4)	74.7 (55.6–93.8)
H (2)	0.4 (0–0.7)	97.9 (95.8–100)	86.1 (81.9–90.3)	89.3 (88.9–89.6)	83.0 (78.5–87.5)	6.3 (5.6–6.9)	11.8 (0–23.6)	65.6 (61.1–70.1)	96.6 (93.1–100)	87.2 (74.3–100)	7.7 (5.6–9.7)	95.9 (91.7–100)	35.4 (32.6–38.2)
I (1)	4.9	97.2	86.8	88.2	88.9	7.6	2.1	25.8	78.5	28.7	5.7	70.8	19.4
P (1)	4.2	97.2	71.5	75.0	76.4	6.9	2.8	41.7	99.3	75.4	46.7*	87.5	93.8
2015
A (15)	5.0 (0–15.3)	99.4 (97.9–100)	96.7 (88.9–100)	99.1 (95.1–100)	96.2 (80.6–100)	19.0 (3.1–34.7)	11.3 (1.4–29.9)	76.9 (59.7–98.6)	99.5 (97.9–100)	94.3 (69.5–100)	91.0 (79.2–100)	99.5 (97.2–100)	96.3 (66.7–100)
D (5)	0.3 (0–1.4)	97.5 (92.4–100)	82.9 (68.8–100)	94.2 (82.6–100)	91.5 (84.0–100)	13.1 (1.4–30.6)	5.8 (1.4–10.4)	64.6 (48.6–81.9)	96.4 (91.0–100)	81.2 (56.9–100)	30.2 (10.4–43.8)	95.6 (92.9–100)	65.1 (52.1–95.1)
G (2)	0	98.6 (97.2–100)	8.4 (6.3–10.4)	80.9 (66.6–95.1)	20.5 (11.8–29.2)	0	0	27.5 (15.3–39.6)	98.6 (97.2–100)	7.0 (5.6–8.3)	6.6 (5.6–7.6)	94.8 (93.1–96.5)	57.7 (50.7–64.6)
J (1)	0	98.6	31.9	70.1	43.1	0	0	29.9	100	69.4	1.4	100	52.1
K (1)	1.4	96.5	2.1	33.9	5.6	0	0	27.1	99.3	29.9	11.1	97.2	53.5
2016
A (19)	3.6 (0–13.9)	99.8 (97.2–100)	69.0 (58.2–82.3)	99.2 (93.8–100)	91.4 (54.9–100)	18.6 (5.7–33.3)	16.9 (0.7–38.2)	78.2 (52.1–95.7)	98.8 (90.8–100)	95.1 (85.2–100)	67.7 (47.2*–95.1)	99.5 (94.9–100)	99.1 (91.5–100)
O (2)	0.4 (0–0.7)	99.0 (97.9–100)	39.0 (34.2–43.8)	93.4 (92.9–93.8)	71.7 (69.6–73.7)	2.6 (1.4–3.7)	2.8 (2.1–3.5)	61.2 (56.3–66.0)	93.7 (92.3–95.1)	89.6 (81.3–97.9)	40.0 (38.2–41.7)	92.4 (92.4–92.4)	91.4 (91.0–91.7)
P (1)	0.7	95.8	41.7*	90.0	81.0	5.0	4.9	43.2	95.7	68.8	53.5	92.6	90.8

^a Pathotype designations are as defined on the Canadian Clubroot Differential Set (Table 1); the numbers in parentheses indicate the number of P. brassicae populations classified as a particular pathotype each year.

^b European Clubroot Differential (ECD) 02 = Brassica rapa ssp. rapifera line AAbbCC; ECD 05 = B. rapa var. pekinensis ‘Granaat’; ECD 06 = Brassica napus ‘Nevin’; ECD 08 = B. napus ‘Giant Rape’ selection; ECD 09 = B. napus New Zealand resistant rape; ECD 10 = B. napus var. napobrassica ‘Wilhemsburger’; ECD 11 = Brassica oleracea var. capitata ‘Badger Shipper’; ECD 13 = ‘Jersey Queen’; Brutor = B. napus ‘Brutor’; Laur. = B. napus var. napobrassica ‘Laurentian’; Westar = B. napus ‘Westar’; and 45H29 = B. napus ‘45H29’.

^c Indices of disease (ID, %) are shown, representing the mean of all populations classified as a particular pathotype each year (the range of values is indicated in parentheses). The mean ID values (± standard error) for individual populations are included in Supplementary Table 3. A host was considered resistant if the mean ID was <50% and the 95% confidence interval (CI) did not overlap 50%. The numbers in bold indicate susceptible reactions; those reactions in which the mean ID <50% but the 95% CI overlapped 50% are denoted with an asterisk (*).

Fig. 1 (Colour online) Distribution of the Plasmodiophora brassicae populations characterized in this study. The pathotype designations of each population are indicated according to the systems of Williams (1966) (numbers) or the Canadian Clubroot Differential (CCD) Set (letters).

Table 4. Reaction of the putative Canadian Clubroot Differential (CCD) hosts to Plasmodiophora brassicae single-spore isolates representing the original pathotypes (as per Williams (1966)) identified in Canada prior to the emergence of pathogen populations able to overcome clubroot resistance in canola.

	Host Genotype^b,c
Isolate^a	ECD 02	ECD 05	ECD 06	ECD 08	ECD 09	ECD 10	ECD 11	ECD 13	Brutor	Laur.	Mendel	Westar	45H29	CCD Code^d
SACANss3 Pathotype 2	0	99.3 ± 0.7	69.5 ± 2.5	97.2 ± 1.1	77.8 ± 2.0	10.4 ± 1.3	59.1 ± 3.8	63.9 ± 3.0	94.9 ± 3.0	75.9 ± 1.7	11.8 ± 2.1	98.6 ± 1.4	7.7 ± 3.5	F
SACANss1 Pathotype 3	0	100 ± 0.0	91.4 ± 2.6	100 ± 0.0	94.5 ± 2.5	16.0 ± 3.5	28.2 ± 2.6	60.2 ± 1.4	100 ± 0.0	91.0 ± 1.3	11.8 ± 2.1	100 ± 0.0	6.3 ± 4.0	H
ORCAss4 Pathotype 5	0	87.5 ± 1.8	47.8* ± 8.8	84.0 ± 0.7	61.1 ± 4.1	15.3 ± 1.8	3.5 ± 1.7	25.7 ± 2.9	84.0 ± 1.7	29.9 ± 2.6	5.6 ± 2.0	82.7 ± 2.4	4.2 ± 2.4	I
AbotJEss1 Pathotype 6	0	90.3 ± 0.8	47.2* ± 2.0	90.1 ± 1.0	62.5 ± 4.0	8.3 ± 1.1	4.9 ± 2.4	85.2 ± 2.0	73.6 ± 2.4	32.7 ± 1.3	4.9 ± 2.1	90.1 ± 0.7	8.3 ± 1.1	M
ORCAss2 Pathotype 8	0	96.5 ± 1.7	82.6 ± 1.7	92.7 ± 0.8	89.6 ± 1.3	10.4 ± 1.3	7.0 ± 1.7	23.6 ± 2.9	93.8 ± 1.3	78.5 ± 1.7	6.9 ± 1.4	93.5 ± 0.6	9.7 ± 0.8	N

^a Plasmodiophora brassicae single-spore isolates were originally purified and characterized by Xue et al. (2008); these were obtained from pathogen populations collected prior to 2007. The pathotype classifications indicated in this column are as per Williams (1966).

^b European Clubroot Differential (ECD) 02 = Brassica rapa ssp. rapifera line AAbbCC; ECD 05 = B. rapa var. pekinensis ‘Granaat’; ECD 06 = Brassica napus ‘Nevin’; ECD 08 = B. napus ‘Giant Rape’ selection; ECD 09 = B. napus New Zealand resistant rape; ECD 10 = B. napus var. napobrassica ‘Wilhemsburger’; ECD 11 = Brassica oleracea var. capitata ‘Badger Shipper’; ECD 13 = ‘Jersey Queen’; Brutor = B. napus ‘Brutor’; Laur. = B. napus var. napobrassica ‘Laurentian’; Westar = B. napus ‘Westar’; and 45H29 = B. napus ‘45H29’.

^c The mean index of disease (ID, %) ± standard error is shown for each host genotype/pathogen combination. A host was considered resistant if the mean ID was <50% and the 95% confidence interval (CI) did not overlap 50%. The numbers in bold indicate susceptible reactions; those reactions in which the mean ID <50% but the 95% CI overlapped 50% are denoted with an asterisk (*).

^d CCD code refers to pathotype classification on the CCD Set as per Table 1.

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