Table 3.

Disease severity index (DSI_b) and disease incidence (DI_b, percentage of diseased plants) of clubroot in bioassays performed in a growth chamber with soil from field trials 2017/2018 with the susceptible Cultivar mix and clubroot-resistant cultivars cv. Mentor, cv. Alister, and cv. Archimedes, and number of gene copies (logarithm at calculation) of Plasmodiophora brassicae. Values are mean for soil samples from each plot (n = 4). Sites were selected based on field abundance (gene copies g⁻¹ soil) of Plasmodiophora brassicae DNA (Simrishamn 1,100,000; Tomelilla 2,500,000; Kumla 15,000; Hallsberg 2500).

Treatment	DSIb (0–100)		DSIb (%)		Gene Copies (No. g soil−1)		DSIb × Gene Copies	DIb × Gene Copies
Gene copies P. brassicae, average:
Simrishamn					419,200	b *
Tomelilla					1,187,100	a
Kumla					55,600	c
Hallsberg					2800	c
p-value					<0.001
Coeff. of var. †					119
Field-wise:
Simrishamn
Cultivar mix	77.5	a *	94.5	a	562,300		p = 0.035	ns
cv. Mentor	21.9	bcd	30.5	bcd	435,700		p < 0.001	p < 0.001
cv. Alister	38.6	b	49.2	b	204,100		p = 0.012	p = 0.027
cv. Archimedes	34.4	b	46.6	b	474,700		ns	ns
p-value	0.020		0.020		ns
Coeff. of var.	141		134		103
Tomelilla
Cultivar mix	75.2	a	86.4	a	784,300		ns	ns
cv. Mentor	31.6	b	40.2	bc	1,129,800		ns	ns
cv. Alister	32.8	b	42.9	b	1,603,200		ns	ns
cv. Archimedes	7.0	de	16.5	cde	1,231,000		ns	ns
p-value	<0.001		ns		ns
Coeff. of var.	71		66		72
Kumla
Cultivar mix	29.9	bc	42.0	bc	68,300		ns	ns
cv. Mentor	9.0	cde	14.8	de	49,500		p = 0.011	p = 0.009
cv. Alister	7.5	cde	9.5	de	38,800		ns	ns
cv. Archimedes	4.4	de	8.2	de	65,800		p = 0.017	p = 0.009
p-value	ns		ns		ns
Coeff. of var.	323		323		76
Hallsberg
Cultivar mix	1.3	de	2.8	e	3800		ns	ns
cv. Mentor	0.5	e	1.2	e	1700		ns	ns
cv. Alister	0.8	e	1.8	e	2800		ns	ns
cv. Archimedes	0.0	e	0.0	e	3020		ns	ns
p-value	ns		ns		ns
Coeff. of var.	323		323		77

^† Coefficient of variation. * Different letters indicate significant differences according to Tukey’s HSD-test (p < 0.05).