Screening Potato Selections for Resistance to Corky Ringspot Disease
K.A. Rykbost and J. Maxwell s
Introduction
Corky ringspot disease (CRS) in
potatoes occurs in isolated locations, scattered
around the potato production areas of the
Pacific Northwest. Since Temik use on potato
crops was suspended in 1990, CRS is occurring
in new locations in the northwest. Several
samples of CRS infected tubers are submitted
to KES personnel for evaluation each year. The
reinstatement of Temik for use on potatoes in
the Pacific Northwest will allow control of this
disease in late maturing varieties in long-season
environments. A restriction of 150 days-toharvest will preclude the use of Temik in many
areas, including most crops in the Klamath
Basin. With no other reliable options for
control of the vector of CRS, the stubby-root
nematode (Trichodorus spp.), variety resistance
or tolerance is an increasingly important
approach to management of this disease.
Varietal response to the causal pathogen
of CRS, tobacco rattle virus, varies widely.
The Aberdeen, Idaho USDA-ARS potato
breeding program has directed a small portion
of the effort toward development of selections
resistant to or tolerant of CRS. The Aberdeen
breeding and selection team has screened
varieties for response to CRS but they do not
have sufficient populations of virus infected
stubby-root
1 /
nematodes to produce consistent infections in
susceptible standard varieties. A KES field
with a history of CRS infections and root-knot
nematode blemish was offered to supplement
the Aberdeen program in 1994 and 1996.
Procedures
The site for the study is a Poe fine sandy
loam soil type. No fumigants or nematicides
have been applied at this site since 1988.
Composite soil samples were collected from
each half of the trial site at depths of 0 to 8 and
8 to 16 inches on April 4, and 0 to 12 inches on
October 7, 1996, to determine nematode
population density. Twenty-seven varieties or
selections were screened in three replications of
20 hills each, arranged in a modified
randomized complete block design. Each plot
was paired with a Russet Burbank standard in
an adjacent row. Seed was planted at 8.7-inch
spacing in 32-inch rows on May 23. Standard
cultural practices were followed as described
for other experiments (page 41), except that no
nematode control measures were applied.
Vines were desiccated with Diquat applied at
1.0 pint/acre on September 12 and all tubers
from each plot were harvested with a one-row
digger-bagger on October 3 and stored until
grading on October 29.
Superintendent/Professor and Biological Sciences Research Technician III, respectively,
Klamath Experiment Station, Klamath Falls, OR.
Acknowledgments: OSU Nematology Program personnel in the Department of Botany and Plant
Pathology provided analysis of soil samples for nematode identification and counts, Dr. Stephen Love,
University of Idaho, provided selections for evaluation, and the Oregon Potato Commission, USDAARS, and USDA-CREES provided funding for the study.
Klamath Experiment Station 81
Intact tubers were visually inspected for
root-knot nematode (Meloidogyne chitwoodi)
blemish symptoms. Samples ranged from no
visible symptoms to severe blemish on all
tubers. Tubers from each individual plot were
scored as 0, 25, 50, 75, or 100 percent root-knot
nematode blemished. Twenty-five tubers from
each plot were cut into quarters and exposed
surfaces were inspected for CRS symptoms.
Each tuber was scored as follows:
1) no symptoms observed - no damage;
2) 1 to 5 percent damage (slight) - not
more than one 1/8-inch diameter or
larger diffuse brown spot per 1/2-inch
tuber length;
3) 6 to 10 percent damage (moderate) not more than two 1/8-inch diameter
or larger diffuse brown spots per 1/2inch tuber length;
4) >10 percent damage (severe) - more
than two 1/8-inch diameter or larger
spots per 1/2-inch tuber length.
A CRS Rating Index (RI) was
calculated as: RI = (1.0 X number of tubers
with no damage + 2.0 X number of tubers with
slight damage + 3.0 X number of tubers with
moderate damage + 4.0 X number of tubers
with severe damage)/25 (total number of
tubers). On this basis, scores range from 1.0
for a clean sample with no CRS symptoms, to
4.0 for a sample with all tubers having severe
symptoms.
Results and Discussion
April soil samples indicated populations
of root-knot nematodes were 40 to 60/250 g dry
soil, and stubby-root populations ranged from
30 to 80/250 g dry soil. Two composite
samples collected after harvest measured rootknot populations at 30 and 193/250 g, and
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stubby-root populations at 4 and 7/250 g dry
soil. Compared with populations measured in
several plots of the nematode control study
described in the previous section of this report,
these were moderate populations for both
nematode species.
Stubby-root nematode populations were
apparently quite uniform throughout the study
area. CRS symptoms were observed in each of
the 54 Russet Burbank control samples.
Severity ratings for Russet Burbank were
consistently in the slight to moderate range, a
level that would be unacceptable for processing
or fresh market use (Table 1). No CRS
symptoms were observed in any tubers in
Brador, Gemchip, A8793-6, TX1385-12 Ru, or
NZA8904-2. Several other selections with RI
less than 1.3 appear to be only mildly
susceptible to CRS damage. Previous
experience has shown that Russet Norkotah has
a lower incidence and very mild CRS
symptoms in situations where Russet Burbank
and Century Russet express much greater
damage. Results in this study indicate a similar
low incidence in TXNS112, which is a Texas
line selection of Russet Norkotah.
Root-knot nematode populations were
not uniform in the study area. Blemish was
observed in about one-third of the Russet
Burbank control plots, and two-thirds of
samples from selections. Interpretations of
tuber blemish data must be made with care.
For example, the data show no infection in
A8787-2, but little infection in the adjacent
Russet Burbank either. On the other extreme,
Russet Burbank adjacent to TXAV657-27 had
100 percent blemish, while no blemish was
observed in TXAV657-27. Several other
selections had considerably less tuber blemish
than adjacent Russet Burbank samples,
including the two Russet Norkotah selections,
TXNS112 and TXNS278.
Klamath Experiment Station
Table 1.
Variety /
Selection
Corky ringspot (CRS) infection by severity classification, CRS rating index (RI), and root-knot
nematode blemish for potato selections and adjacent Russet Burbank controls grown at
Klamath Falls, OR, 1996.
none
CRS Severity
slight
moderate
--------
severe
CRS RI
Selection Burbank
Nematode blemish
Selection Burbank
-------------
Brador
Chipeta
Gemchip
White Rose
A82360-7
100
91
100
58
45
0
7
0
42
47
0
0
0
0
8
0
2
0
0
0
1.0
1.2
1.0
1.4
1.7
2.6
2.8
2.6
2.1
2.4
33
33
33
33
17
58
67
25
50
75
A8495-1
A84118-3
A86102-6
A8787-2
A8787-26
40
55
45
73
33
30
43
52
27
39
27
2
3
0
15
3
0
0
0
13
2.0
1.5
1.5
1.3
2.1
2.6
2.4
2.2
2.1
2.7
67
33
58
0
42
33
33
58
25
33
A8792-1
A8793-6
A87295-3
A89241-6
A89244-3
28
100
85
40
72
40
0
13
30
28
19
0
2
30
0
13
0
0
0
0
2.2
1.0
1.2
1.9
1.3
2.6
2.1
2.6
2.5
2.4
25
58
33
17
67
100
58
33
83
50
80
42
85
20
25
17
35
13
30
48
3
18
2
38
15
0
5
0
12
12
1.3
1.9
1.2
2.4
2.2
2.3
2.3
2.2
2.5
2.8
0
0
17
0
33
58
17
25
42
58
57
47
100
75
83
57
100
43
43
0
23
10
25
0
0
10
0
2
7
15
0
0
0
0
0
0
3
0
1.4
1.6
1.0
1.3
1.2
1.7
1.0
2.7
2.7
2.3
2.5
2.6
2.7
2.6
67
50
33
0
0
8
0
67
67
50
100
67
92
42
65
25
8
2
1.5
2.5
28
54
A90550-3
A91164-5
A91319-1
A91550-1
A085165-1
C085026-4
TX1229-2RU
TX1385-12RU
TXAV657-27
TXNS112
TXNS278
NZA8904-2
Mean
Klamath Experiment Station
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