Table 3.

Severity of black scurf in selected potato cv. Russet Burbank variants in glasshouse (GH1—2010; GH2 and GH3—2011) trials. Rhizoctonia solani AG3 isolates R299, R422, and TAS1 were tested separately in each trial.

Variants	Relative tuber disease severitya			Disease severity (surface cover score 0–6 (%))b
				GH1			GH2			GH3
	Common scab	Powdery scab	Black scurf	R299	R422	TAS1 c	R299	R422	TAS1	R299	R422	TAS1
A380	0.19	0.44	0.35	2.17 (19.5)	1.90 (9.8)	0.5b (1.22)	0.47 (0.97)	0.58 (1.64)	0.33b (.33)	0.56 (1.22)	0.33 (0.78)	0.18b (0.18)
A168a	0.21	0.36	0.67	3.42 (34.2)	1.45 (6.3)	0.71b (2.48)	—	—	—	—	—	—
TC-RB8	0.57	0.98	0.54	3.25 (27.9)	1.42 (7.2)	0.99b (5.05)	1.01 (3.80)	0.44 (0.83)	0.53b (1.19)	0.85 (2.18)	1.10 (3.99)	0.50b (0.77)
A362	0.66	0.8	0.66	2.93 (22.3)	1.27 (5.8)	0.97b (4.41)	—	—	—	—	—	—
Russet Burbank (parent)	1	1	1	3.15 (26.4)	2.35 (16.8)	2.17a (14.18)	2.17 (12.67)	1.76 (13.07)	1.66a (7.18)	1.77 (9.63)	1.17 (3.75)	1.67a (7.33)
P				0.39	0.22	0.04	0.12	0.25	0.01	0.14	0.16	0.01
LSD (0.05)				ns	ns	1.11	ns	ns	0.75	ns	ns	0.76

—: lines not tested within the specified trial.

^aMean relative disease severity score for common scab, powdery scab, and black scurf was generated for each variant by dividing the mean disease score of each variant by the mean disease score of the parent cultivar in each trial in which they appeared and averaging the result. Common scab data are from [3] and powdery scab data are from [2].

^bTuber disease surface cover score—0: no disease, 0.5 ≤ 1%, 1: 2–5%, 2: 6–10%, 3: 11–30%, 4: 31–50%, 5: 51–70%, and 6 > 70%. In brackets: estimated tuber surface coverage is calculated from disease cover score using median percentile scores within the allocated range.

^cMeans followed by the same letter within the same column are not significantly different at P = 0.05 using Fisher's LSD test; ns: non-significant.