Klamath Experiment Station
Effect of Seedborne Potato Virus Y on the Performance of Russet Norkotah at
Hermiston and Klamath Falls, OR, and Tulelake, CA, 1997
K.A. Rvkbostl, D. }lane', P. Hamm', R. Voss 3 , and D. Kirby'
lib
,ract
Russet Norkotah and Shepody have
become very important varieties in the
Pacific Northwest for fresh market use and
French fry processing, respectively. Both
varieties are very susceptible to Potato Virus
Y (PVY) but express little, if any PVY symptoms. As a result, seed producers have experienced relatively high incidences of PVY in
lots passing field certification inspections. In
1996, greenhouse and laboratory tests of
commercial seed lots of Russet Norkotah
found PVY infection levels up to 50 percent in
lots that passed field inspections within
tolerances for Generation II and III seed
classifications.
Research plots were established in
1996 at Klamath Falls and Hermiston, Oregon,
and Tulelake, California, to determine 1) the
effects of seedborne PVY infections on virus
spread during the growing season, 2) the
effects of seedborne PVY on yield and grade
of Russet Norkotah, and 3) the economic
consequences of varying levels of seedborne
PVY infections. Studies were repeated at the
three locations in 1997. Virus spread occurred
earlier and was more extensive at Hermiston
y
than at Klamath Falls or Tulelake in both
years. Plants derived from PVY-free seed
were nearly 100 percent PVY-infected at
Hermiston-at early senescence. Comparisons
of plots with PVY-free seed versus plots
where initial PVY infection levels were about
50 percent in 1996 and 100 percent in 1997
showed seedborne PVY at these levels reduced No. 1 yields by about 40 percent at
Hermiston, 20 percent at Tulelake, and 12
percent at Klamath Falls. Related reductions
in gross crop value were estimated at 39, 26,
and 14 percent, respectively. Conditions in the
Columbia Basin produce greater stress in
PVY- infected plants than occurs in the cooler,
short-season production area of the Klamath
Basin.
Introduction
Preliminary research was conducted in
growers' fields in the Columbia Basin of
Oregon in 1994 and 1995. Results showed
seedborne PVY-infected Russet Norkotah
plants had significantly lower total yield and
yield of large tubers, fewer tubers per plant,
and lower specific gravity than adjacent plants
V Superintendent/Professor, Klamath Experiment Station (KES), Klamath Falls, OR.
2 / Instructor and Extension Plant Pathologist, respectively, Hermiston Agricultural Research and
Extension Center (HAREC), Hermiston, OR.
3 / Extension Specialist, Department of Vegetable Crops, UC Davis, Davis, CA.
4 / Acting Superintendent/Research Associate, UC Intermountain Research and Extension Center
(IREC). Tulelake. CA.
Acknowledgments: Funding support provided by the Oregon Potato Commission and the Klamath
Basin Potato Growers Association is gratefully recognized.
Klamath Experiment Station 1997 53
Klamath Experiment Station
Effect of Seedborne Potato Virus Y on the Performance of Russet Norkotah at
Hermiston and Klamath Falls, OR, and Tulelake, CA, 1997
that were initially PVY-free. In 1996,
several Norkotah seed lots in Klamath
County and central Oregon were found to
have over 20 percent PVY- infection based
on greenhouse tests. Local commercial
growers were faced with the choice of
accepting seed lots with high virus readings or seeking seed from other regions at
higher costs and with greater risk of
infection with other diseases, including
late blight.
The 1996 study evaluated seed lots
with 0 percent and 49 percent PVY infection, based on greenhouse tests. In 1997,
seed lots with 0 percent and nearly 100
percent PVY were obtained for evaluation.
While 1996 data showed greater virus
spread at Hermiston, the timing of spread
was not known as samples were only
obtained at early and late dates. Sampling
for PVY infection was expanded to include a mid-season date in 1997 to assist
in identifying the timing of virus spread.
This information might help to explain the
areater effect of PVY at Hermiston.
Procedures
Seed lots of Russet Norkotah used
included Generation III lots from Klamath
County that tested 0.0 and 48.9 percent
PVY in greenhouse tests for the 1996
study, and a Klamath County Generation
III lot testing 0.0 and a Central Oregon lot
testing nearly 100 percent PVY for the
1997 trial. Sufficient seed of each lot was
obtained for all trial sites. Tubers were
hand-cut to approximately 1.5 to 2.0
ounces/seedpiece about 10 days before
54 Klamath Experiment Station 1997
planting. Cut seed from the two lots were maintained separately and allowed to suberize until
just before planting to avoid contact and potential
spread of virus before suberization.
The experimental design at each site
included two-row plots with 60 hills/plot, two
border rows between plots planted with PVY-free
seed, five replications, and five treatments with
the following blend of seed lots: 1) 60 seedpieces
from the clean lot (Lot #1); 2) 45 seedpieces from
Lot #1 and 15 seedpieces from the PVY infected
seed lot (Lot #2); 3) 30 seedpieces from each lot;
4) 15 seedpieces from Lot #1 and 45 seedpieces
from Lot #2; 5) 60 seedpieces from Lot #2.
Planting dates in 1996 were Hermiston
(HAREC), April 5; Tulelake (IREC). May 8; and
Klamath Falls (KES), May 24; and in 1997 were
HAREC, April 25; IREC, May 14; and KES, May
20. Standard cultural practices, including standard
insect control measures, were followed at all sites
each year. When plants were 6 to 8 inches high,
30 plants from each plot were individually
sampled and tested serologically for PVY infection. All samples were assayed at HAREC.
Sampling dates in 1996 were May 29 and July 23
at HAREC, June 24 and August 26 at IREC, and
July 8 and September 3 at KES. In 1997, samples
were taken on June 3, July 7, and August 4 at
HAREC; June 26, July 21, and August 11 at
IREC; and June 30, July 28, and August 18 at
KES.
At HAREC, all plants sampled were
individually labelled initially and only plants
testing negative at the first sampling were subsequently sampled. Mid-season sampling was done
on all plots at HAREC. At IREC and KES, 1997
mid-season samples were obtained only on treatments 1, 2, and 3.
Klamath Experiment Station
Effect of Seedborne Potato Virus Y on the Performance of Russet Norkotah at
Hermiston and Klamath Falls, OR, and Tulelake, CA, 1997
Tubers were harvested on August 20,
September 23, and September 24 in 1996 and
on August 27, September 22, and September
29 in 1997 at HAREC, IREC, and KES,
respectively. All tubers from each plot at all
sites were graded to USDA standards. Specific
gravity was measured by the weight-in-air,
weight-in-water method at HAREC and KES.
Gross crop values were calculated for treatment means only, using the following prices
for yield components: U.S. No. ls 4- to 8-oz at
S3.75/cwt; U.S. No. ls 8- to 12-oz at $9.00/
cwt; U.S. No. is > 12 oz at $10.00/cwt; Bs,
No. 2s, and culls at $1.00/cwt. These prices
are approximate November 1997 fresh market
values for Russet Norkotah in the Klamath
Basin. Grower returns at these prices were
about $4.00/cwt.
Yield and grade data were subjected to
statistical analyses using MSUSTAT software.
Effects of PVY-infection levels on total yield
of No. I s and total yield were analyzed by
linear regression analysis using MSTATC
software.
Results and Discussion
Emergence data from HAREC and
KES showed seedborne PVY had no effect on
rate of emergence or final stands in either year.
Stands were 94 percent or higher in all treatments in both years. The PVY-infection level
had no effect on internal defects, based on
inspection of 10 large tubers from each plot in
both years at KES. Specific gravity was not
affected by PVY-infection levels.
In both years. the seed lot found to be
PVY-free in greenhouse tests exhibited nearly
zero virus infection in initial field samples
(Table 1). The infected seed lot in 1996 had
initial field infection readings of about 65
percent compared to a greenhouse test of 49
percent. The infected seed lot in 1997 had
initial field infection levels of nearly 100
percent at each site. Virus spread was greater
at Hermiston than at Klamath Basin sites. The
clean seed lot reached 79 percent infection at
Hermiston but only 21 percent at IREC and
KES in 1996. In 1997, virus infection in the
clean seed lot reached 87 percent in early
August at HAREC, 45 percent in late August
at KES, and only 7 percent at IREC in midAugust. Mid-season virus sampling demonstrated an earlier virus spread at HAREC than
at KES. Very little virus spread occurred at
IREC in the 1997 study. The greater spread of
infection at Hermiston may be due to higher
insect populations and frequent windy conditions which encourage plant-to-plant mechanical spread. The occurrence of high infection
levels in the treatment which was solely
derived from PVY-free seed, in spite of two
border rows planted with PVY-free seed
between plot rows, probably suggests an
important role for aphids or other insects as a
vector, at least in these plots.
Effects of tuber-perpetuated virus on
yield, grade, and tuber size distribution are
presented in Tables 2 and 3. In both years,
virus infection significantly reduced No. 1 and
total yield at HAREC. The No. 1 yield reduction from treatment 1 to treatment 5 was 40
and 37 percent in 1996 and 1997, respectively,
even though treatment 1 had a high infection
level by late season. The intermediate treatments, derived by blending seed lots, exhibited intermediate yields. The yield reductions
Klamath Experiment Station 1997 55
Klamath Experiment Station
Effect of Seedborne Potato Virus Y on the Performance of Russet Norkotah at
Hermiston and Klamath Falls, OR, and Tulelake, CA, 1997
experienced at HAREC were similar to results
observed in studies conducted in commercial
fields in 1995. Yield reductions at HAREC
were due to reduced yield in all No. 1 size
fractions.
Effects of virus infection levels on
yields at IREC and KES were less than at
HAREC and were not as consistent between
years at KES (Tables 2 and 3). At IREC, the
reduction in total No. 1 yields between treatments I and 5 was 20 percent in both years;
one-half of the HAREC response. At KES,
nonsignificant reductions in total No. 1 yields
were 7 and 16 percent for 1996 and 1997,
respectively. As PVY-infection levels had
little effect on yield of smalls, No. 2s, or culls,
the response to PVY in total yield was very
similar to the response in total No. 1 yield for
all locations and both years.
The effects of seedborne PVY infection on yield were evaluated statistically by
regression analyses (Table 4). Linear and
quadratic regression equations were compared
for total and total No. 1 yields for the HAREC
site. The quadratic component did not significantly improve the fit of the model over the
linear model. Therefore, quadratic equations
were not evaluated for the less responsive
IREC and KES sites. In both years, regression
analyses found significant differences in the
slope of the equations, indicating a greater
effect of PVY at HAREC, less at IREC, and
the least effect at KES. An over-years analysis
found significant differences between years in
yield levels, but not in the slope of the regression equations. This indicates that effects of
seed-borne PVY on yields were consistent
from year to year within a given location. The
56 Klamath Experiment Station 1997
regression lines are shown for total No. 1 yield
for all locations and both years in Figure 1.
Effects of PVY-infection levels on
economic returns were evaluated based on
treatment averages; they were, therefore, not
statistically analyzed (Table 5). Crop prices
will have a large effect on the economic
consequences of yield losses. Prices selected
for the comparison were November 1997
fresh-market prices common in the Klamath
Basin for Russet Norkotah. These prices were
typically returning about $4.00/cwt to growers
for bin-run crops. U.S. No. 2s were returning
about $2.50/cwt under these conditions, but
they represented a very small fraction of the
yield in these trials and were valued at the
price for smalls and culls. In general, the
observed yield reductions were due to lower
yields of the large No.1 fraction, the most
valuable component of fresh-market crops.
The loss in crop value is therefore likely to be
greater on a percentage basis, than the loss in
No. 1 or total yield.
Conclusions
Tuber-perpetuated PVY-infections
produced site-specific yield reductions at
Hermiston and Klamath Falls, Oregon, and Tulelake, California. Virus spread was more
extensive in the warm-season conditions of
the Columbia Basin than in the cool-season
region of the Klamath Basin. Data from 1997
indicated that the spread also occurred earlier
at Hermiston. Plots that initially had nearly
PVY-free plants were 80 percent PVY-infected by time of senescence at Hermiston.
Total and total No. I yield reductions
for highly infected seed versus initially PVY-
Klamath Experiment Station
Effect of Seedborne Potato Virus Y on the Performance of Russet Norkotah at
Hermiston and Klamath Falls, OR, and Tulelake, CA, 1997
free seed ranged from about 40 percent at
Hermiston, to 20 percent at Tulelake, and 10
percent at Klamath Falls. These were quite
consistent over years in spite of a difference in
initial PVY-infection levels between years.
The yield reduction was generally observed in
all size fractions of U.S. No. I s. PVY infection did not affect emergence, final stands,
internal defects, or specific gravity. Reductions in gross value were similar to losses in
U.S. No. ls.
The greater response to PVY infection
at Hermiston than at either Klamath Basin site
is believed to be related to climatic differences. Greater insect populations in the warm
environment and frequent windy conditions in
the Hermiston area probably account for more
virus spread. High temperatures common in
the warm, long-season, environment of the
Columbia Basin likely resulted in greater
environmental stress on plants infected with
PVY.
Klamath Experiment Station 1997 57
Klamath Experiment Station
Table 1. PVY infection levels for Russet Norkotah seed-lot treatments grown at three locations,
1996 and 1997.
PVY Infection Level
1997
1996
Treatment
Early
season
Late
season
Early
season
Mid
season
Late
season
2
27
50
73
98
26
58
85
92
99
87
98
100
100
100
1
24
48
74
99
2
23
42
NS
NS
7
34
56
72
100
0
23
51
73
97
14
45
69
NS
NS
45
59
80
93
100
1
25
50
73
98
14
42
65
NS
NS
46
64
79
88
100
Hermiston, OR
1
2
3
4
5
0
20
38
53
60
79
97
98
100
99
Tulelake, CA
1
2
3
4
5
3
16
30
62
56
21
52
67
81
85
1
2
3
4
5
1
21
39
51
79
21
45
65
NS
NS
1
2
3
4
5
1
19
36
55
65
40
65
77
NS
NS
Klamath Falls, OR
Mean
NS: Not sampled.
58 Klamath Experiment Station 1997
Klamath Experiment Station
Table 2. Yield, grade, and tuber size distribution response to seedborne PVY infection in Russet
Norkotah potatoes grown at three locations, 1996.
Treatment PVY (%)
Yield
Yield U.S. No. ls
Initial
4-8 oz
8-12 oz
> 12 oz total
Bs
No. 2s & culls total
cwt/A
Hermiston, OR
1
2
3
4
5
0
20
38
53
60
LSD (P = 0.05)
CV (%)
143
137
115
125
94
165
128
122
106
84
124
103
87
90
78
433369
324
322
255
64
75
69
70
66
12
11
8
8
7
515
449
400
400
328
25
15
27
17
23
18
50
11
NS
12
NS
77
56
10
Tulelake, CA
1
2
3
4
5
3
16
30
62
56
LSD (P. 0.05)
CV(Vc )
100
114
94
108
112
145
134
133
149
118
171
147
143
125
105
416
395
369
381
334
47
45
47
40
47
53
33
29
25
39
518
473
445
446
420
NS
12
NS
16
31
17
49
10
NS
17
NS
51
45
7
Klamath Falls. OR
1
2
3
4
5
LSD (P= 0.05)
CV ( %)
1
21
39
51
79
121
128
127
118
118
112
125
132
121
121
154
150
135
135
122
387
402
394
375
361
34
30
30
27
25
40
46
50
34
30
462
478
473
436
417
NS
22
NS
16
NS
24
NS
11
NS
25
NS
29
NS
10
Klamath Experiment Station 1997 59
Klamath Experiment Station
Table 3. Yield, grade, and tuber size distribution response to seedborne PVY infection in Russet
Norkotah potatoes grown at three locations, 1997.
Initial
Treatment
PVY (%)
Yield U.S. No. is
4-8 oz
8-12 oz
Yield
> 12 oz total
Bs
No. 2s & culls total
cwt/A
Hermiston, OR
1
2
3
4
5
LSD (P= 0.05)
CV (%)
97
96
107
87
75
11
5
6
8
13
610
512
470
422
403
56
11
20
16
NS
65
47
7
2
27
50
73
98
266
2/2
201
188
167
180
140
123
103
116
57
48
32
36
32
502
411
356
327
316
8
12
35
12
34
19
NS
41
-
Tulelake, CA
1
2
3
4
5
LSD (P = 0.05)
CV( 9c)
1
24
48
74
99
159
142
155
144
168
161
128
122
122
110
62
80
56
64
28
382
351
333
331
307
34
28
32
31
29
13
12
11
10
10
430
390
376
372
346
9
13
NS
14
28
16
24
31
21
5
NS
24
NS
41
18
3
Klamath Falls, OR
1
2
3
4
5
LSD (P= 0.05)
CV (%)
0
23
51
73
97
135
145
117
122
112
189
197
161
155
157
199
183
197
186
172
523
526
475
463
441
25
24
20
24
18
44
30
40
27
31
591
580
535
514
490
6
9
NS
18
34
15
NS
20
NS
10
NS
30
NS
40
56
8
60 Klamath Experiment Station 1997
Klamath Experiment Station
Table 4. Summary of regression analyses relating initial field PVY infection levels to total yield
of U.S. No. ls and total yield of Russet Norkotah grown at three locations, 1996 and 1997.
Parameters
X
Y
Year
Location
%PVY
%PVY
%PVY
Yield No. ls
Yield No. ls
Yield No. ls
1996
1996
1996
Hermiston, OR
Tulelake, CA
Klamath Falls, OR
Y = 417 - 2.216X
Y = 410 - 0.852X
Y = 401 - 0.452X
%PVY
%PVY
%PVY
Total Yield
Total Yield
Total Yield
1996
1996
1996
Hermiston, OR
Tulelake, CA
Klamath Falls, OR
Y = 500 - 2.361X
Y = 501 - 1.106X
Y = 481 - 0.728X
0.76
0.51
0.43
%PVY
%PVY
%PVY
Yield No. ls
Yield No. ls
Yield No. is
1997
1997
1997
Hermiston, OR
Tulelake, CA
Klamath Falls, OR
Y = 475 - 1.846X
Y = 374 - 0.675X
Y = 531 - 0.928X
0.72
0.72
0.58
%PVY
%PVY
%PVY
Total Yield
Total Yield
Total Yield
1997
1997
1997
Hermiston, OR
Tulelake, CA
Klamath Falls, OR
Y = 587 - 2.065X
Y = 419 - 0.733X
Y = 595 - 1.091X
0.81
0.78
0.70
%PVY
%PVY
%PVY
Yield No. 1 s
Yield No. ls
Yield No. ls
2-Year
2-Year
2-Year
Hermiston, OR
Tulelake, CA
Klamath Falls, OR
Y = 432 - 1.655X
Y = 395 - 0.828X
Y = 454 - 0.456X
0.62
0.57
0.21
%PVY
%PVY
%PVY
Total Yield
Total Yield
Total Yield
2-Year
2-Year
2-Year
Hermiston, OR
Tulelake, CA
Klamath Falls, OR
Y = 524 - 1.738X
Y = 467 - 1.074X
Y = 528 - 0.692X
0.61
0.57
0.33
Regression Equation
.
0.77
0.44
0.30
Klamath Experiment Station 1997 61
Klamath Experiment Station
Table 5. Effect of seedborne PVY infection on gross crop value of Russet Norkotah potatoes grown
at three locations. 1996 and 1997.
Gross crop value
Treatment
Year
HAREC
IREC
I
KES
Mean
$/acre
1
1
2
3
4
5
1996
3340
2780
2480
2400
1960
3490
3180
3060
3060
2620
3080
3180
3090
2940
2810
3300
3050
2880
2800
2460
1
2
3
4
5
1997
3300
2670
2290
2090
2080
2710
2520
2280
2320
1940
4270
4200
3920
3760
3480
3430
3130
2830
2720
2500
l
2
3
4
5
Mean
3320
2730
2390
2250
2020
3100
2850
2670
2690
2280
3680
3690
3510
3350
3150
3370
3090
2860
2760
2480
/ Based on prices as follows:
U.S. No. ls 4-8 oz at $3.75/cwt
U.S. No. is 8-12 oz at $9.00/cwt
U.S. No. ls > 12 oz at $10.00/cwt
Bs, No. 2s & culls at $1.00/cwt
HAREC: Hermiston Agricultural Research and Extension Center, Hermiston, OR.
IREC:
Intermountain Research and Extension Center, Tulelake, CA.
KES:
Klamath Experiment Station, Klamath Falls, OR.
62 Klamath Experiment Station 1997
ti
•
Klamath Experiment Station
4 's 550 Hermiston, OR
500
(1)
3 450 •E% 400 -
• 350 a
ird
3
300 250
12 200 0
20
40
60
80
100
Initial PVY Infection (%)
Tulelake, CA
550 O 500 ca
450
2. 400
. ... ..
cn
x350
2
Ti
. ..........
300
-
250
1- 200 0
20
40
60
80
100
Initial PVY Infection (%)
550 Klamath Falls, OR
4...
'(.7) 500 450 -E- 400
cn
;- 350 )
Z
300 250 1- 200 0
20
40
60
80
100
Initial PVY Infection (%)
1996 - - 1997
Figure 1. Effect of seed-borne PVY infection on total No. 1 yield of Russet Norkotah, 1996 and 1997.
Klamath Experiment Station 1997 63