AN ABSTRACT OF THE THESIS OF
Heather M. Partipilo for the degree of Master of Science in Botany and Plant
Pathology presented on March 11, 2002. Title: Seedborne Phytophthora infestans:
Effect of Pathogen Clonal Lineage and Potato Cultivar on Seed Transmission of
Late Blight and Plant Growth Responses.
Abstract approved:
Redacted for Privacy
Seed piece to plant transmission of the potato late blight pathogen,
Phytophthora infestans, occurred with isolates of the clonal lineages US-8 in
Oregon and US-li in Washington in field trials. Average transmission rate across
potato cultivars was 0.5 and 2.4% with US-8, and 0.8 and 1.0% with US-il in 1999
and 2000, respectively. Transmission rate with US-8 was 2.3% for Russet Burbank
(RB) in 1999 and 1.7, 0.7, 4.3, 7.6 and 0.5% for Baimock, Bzura, Ranger, Russet
Norkotah (RN), and Umatilla, respectively, in 2000. Transmission rate with US-i 1
in 1999 was 0.5, 4.9 and 1.4% for RB, RN, and Shepody, respectively, and 1.7%
for RB in 2000. Seedborne inoculum of both clonal lineages significantly affected
stand establishment and plant vigor. With US-8, final emergence, emergence rate,
and aerial biomass of cvs Kennebec, RB, RN, and Shepody were significantly
lower than Bzura in 1999, whereas in 2000, these same responses in Chieftain,
Bannock, Ranger, and Shepody were significantly lower than Bzura, Umatilla and
RN. With US-il, these same response variables were significantly lower in
Kennebec, RN and Shepody compared to Bzura and RB in 1999, and were
significantly lower in Bannock, Chieftain, Ranger and Shepody compared to RB
and Umatilla in 2000.
Plant growth responses of cvs RB and RN grown from seed pieces infected
with US-8 or US-il were evaluated in greenhouse trials. RN was equally
susceptible to both cional lineages whereas RB was more resistant than RN to
seedborne inoculum of US-il. Compared to RN its final emergence was higher,
emergence rate was faster, aerial biomass was greater, and seed piece decay was
lower. US-8 was more aggressive than US-i 1 on RB. US-8 caused a greater
reduction in final emergence, emergence rate, and aerial biomass, and a greater
increase in seed piece decay. The two clonal lineages were similar in their
aggressiveness on RN. This is the first report of cultivar*clonal lineage*inoculum
density interactions for plant growth responses of potato grown from seed pieces
infected with P.
infestans.
© HEATHER M. PARTIPILO
March 11,2002
All rights reserved.
Seedborne Phytophthora infestans: Effect of Pathogen Clonal Lineage and Potato
Cultivar on Seed Transmission of Late Blight and Plant Growth Responses
by
Heather M. Partipilo
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
Presented March 11, 2002
Commencement June, 2002
Master of Science thesis of Heather M. Partipilo presented on March 11, 2002.
Redacted for Privacy
Major çfrofesr, representing Botany and Plant Pathology
Redacted for Privacy
Chair of Department of B
and Plant Patholo
Redacted for Privacy
Dean of Gthdtiâte School
I understand that my thesis will become part of the permanent collection of Oregon
State University libraries. My signature below authorizes release of my thesis to
any reader upon request.
Redacted for Privacy
Author
ACKNOWLEDGEMENTS
This thesis could not have been accomplished without the tremendous
support provided by Dr. Mary Powelson and Dr. Debra Inglis. I would also like to
acknowledge the invaluable laboratory, field, greenhouse, and statistical assistance
provided by Robin Ludy, Dale Bargsten, Babette Gundersen, Dr. Ken Johnson, Dr.
Fred Ramsey, Cliff Pereira, Beth Hoinacki, Ingrid Berlanger, Justin Misner, Tim
Nam, Erin Bastian, and Christina Nelson, as well as Aaron Henderson and Jim Fell
at the OSU Botany Field Lab.
11
TABLE OF CONTENTS
Page
CHAPTER 1. INTRODUCTION
. 1
CHAPTER 2. LITERATURE REVIEW
DISEASE SIGNIFICANCE
PATHOGEN BIOLOGY
.................................................. 3
....................................................... 3
............................................................ 4
SEED TO PLANT TRANSMISSION
PATHOGEN CLONAL LINEAGE
............................................ 5
................................................
9
SEED PIECE DECAY ..............................................................
11
CULTIVARS
.......................................................................
12
OBJECTIVES
......................................................................
14
CHAPTER 3. GROWTH RESPONSES OF POTATO TO SEEDBORNE
INOCULUM OF PHYTOPHTHORA INFESTANS ..................................... 15
ABSTRACT........................................................................ 16
INTRODUCTION
....................................................................
17
MATERIALS AND METHODS ................................................. 19
RESULTS........................................................................... 21
DISCUSSION
...................................................................... 36
CHAPTER 4. SEEDBORNE PHYTOPHTHORA INFESTANS: SEED TO
PLANT TRANSMISSION AND GROWTH RESPONSES OF DIFFERENT
POTATO CULTIVARS .................................................................... 41
ABSTRACT........................................................................ 42
INTRODUCTION
.................................................................. 43
111
TABLE OF CONTENTS (Continued)
Page
MATERIALS AND METHODS
.45
RESULTS........................................................................... 49
DISCUSSION
...................................................................... 63
CHAPTER 5. SUMMARY ................................................................ 72
LITERATURE CITED
.................................................................... 74
APPENDICES............................................................................... 80
APPENDIX A. SUPPLEMENTAL ANALYSES OF CHAPTER 3 ....... 81
APPENDIX B. SUPPLEMENTAL ANALYSES OF CHAPTER 4 ...... 101
lv
LIST OF FIGURES
Figure
3.1
Seed piece to plant transmission of late blight (Phytophthora
infestans, isolate of US-8 clonal lineage) in potato cv Russet
Burbank.............................................................................. 22
3.2
Relationship between inoculum density of clonal lineages US-8
and US-i 1 of Phytophthora infestans and emergence of potato
cvs Russet Burbank (RB) and Russet Norkotah (RN) in A) Trial 1,
B) Trial 2, and C) Trial 3 .......................................................... 24
3.3
Relationship between inoculum density of clonal lineages US-8
and US-il of Phytophthora infestans and emergence rate of potato
cvs Russet Burbank (RB) and Russet Norkotah (RN) in A) Trial 1,
B) Trial 2, and C) Trial 3 ......................................................... 27
3.4
Relationship between inoculum density of clonal lineages US-8
and US-i 1 of Phytophthora infestans and aerial biomass of potato
cvs Russet Burbank (RB) and Russet Norkotah (RN) in A) Trial 1,
B) Trial 2, and C) Trial 3 ......................................................... 31
3.5
Relationship between inoculum density of clonal lineages US-8
and US-i 1 of Phytophthora infestans and seed piece decay of potato
cvs Russet Burbank (RB) and Russet Norkotah (RN) in A) Trial 1,
B) Trial 2, and C) Trial 3 .......................................................... 34
4.1
Relationship between inoculum density of clonal lineages US-8
and US-i 1 of Phytophthora infestans and emergence of potato
seed pieces of cultivars Bzura (BZ), Chieftain (CH), Kennebec
(KE), Ranger Russet (RR), Russet Burbank (RB), Russet
Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
inoculated with A) zoospores of US-8 in Oregon in 1999; B)
sporangia of US-8 in Oregon in 1999; C) sporangia of US-8 in
Oregon in 2000; D) zoospores of US-li in Washington in 1999;
E) sporangia of US-li in Washington in 1999; and F) sporangia
of US-il in Washington in 2000 .................................................. 51
V
LIST OF FIGURES (Continued)
Figure
4.2
Relationship between inoculum density of clonal lineages US-8
and US-li of Phytophthora infestans and emergence rate of potato
seed pieces of cultivars Bzura (BZ), Chieftain (CH), Kennebec
(KE), Ranger Russet (RR), Russet Burbank (RB), Russet
Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
inoculated with A) zoospores of US-8 in Oregon in 1999; B)
sporangia of US-8 in Oregon in 1999; C) sporangia of US-8 in
Oregon in 2000; D) zoospores of US-li in Washington in 1999;
E) sporangia of US-il in Washington in 1999; and F) sporangia
of US-il in Washington in 2000 ................................................. 56
4.3
Relationship between inoculum density of cional lineages US-8
and US-i 1 of Phytophthora infestans and aerial biomass per plant
of potato cultivars Bzura (BZ), Chieftain (CH), Kennebec (KE),
Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN),
Shepody (SH), and Umatilla Russet (UR) inoculated with A)
zoospores of US-8 in Oregon in 1999; B) sporangia of US-8 in
Oregon in i 999; C) sporangia of US-8 in Oregon in 2000; D)
zoospores of US-i 1 in Washington in 1999; E) sporangia of US-i I
in Washington in i999; and F) sporangia of US-il in Washington
in2000
4.4
................................................................................ 60
Relationship between inoculum density of clonal lineages US-8
and US-i 1 of Phytophthora infestans and seed piece decay of
potato seed pieces of cultivars Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB),
Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
inoculated with A) zoospores of US-8 in Oregon in 1999; B)
sporangia of US-8 in Oregon in 1999; C) sporangia of US-8 in
Oregon in 2000; D) zoospores of US-i 1 in Washington in 1999;
E) sporangia of US-li in Washington in 1999; and F) sporangia
of US-i 1 in Washington in 2000 .................................................
65
vi
LIST OF TABLES
Table
Page
3.1
General linear model summaries for emergence of seed pieces of
potato cvs Russet Burbank and Russet Norkotah inoculated with
a range of inoculum densities of isolates of clonal lineages US-8
and US-il of Phytophthora infestans ........................................... 23
3.2
General linear model summaries for emergence rates of seed pieces
of potato cultivars Russet Burbank and Russet Norkotah inoculated
with a range of inoculum densities of isolates of clonal lineages
US-8 and US-i 1 of Phytophthora infestans .................................... 26
3.3
General linear model summaries for aerial biomass of plants grown
from potato seed pieces of cultivars Russet Burbank and Russet
Norkotah inoculated with a range of inoculum densities of isolates
of clonal lineages US-S and US-li of Phytophthora infestans .............. 30
3.4
General linear model summaries for seed piece decay of potato
cultivars Russet Burbank and Russet Norkotah seed pieces
inoculated with a range of inoculum densities of isolates of clonal
lineages US-8 and US-i 1 of Phytophthora infestans .......................... 33
4.1
General linear model summaries for emergence failure, i.e.
ln( 1/(1 -( i -% emergence))), of seed pieces of different potato
cultivars inoculated with a range of inoculum densities of isolates
of clonal lineages US-8 and US-i 1 of Phytophthora infestans .............. 50
4.2
General linear model summaries for rate of plant emergence of
different potato cultivars inoculated with a range of inoculum
densities of Phytophthora infestans .............................................. 54
4.3
Mean emergence rate (% emergence/day) of seed pieces of
different cultivars inoculated with a range of inoculum densities
(2.5, 25, and 250 or 50, 100, 400, and 800) of sporangia or
zoospores of Phytophthora infestans US-8 in Oregon and US-i 1
inWashington ....................................................................... 58
4.4
General linear model summaries for aerial biomass per plant (dry, g)
of potato seed pieces of different cultivars inoculated with a range
of inoculum densities of Phytophthora infestans ................................ 59
vii
LIST OF TABLES (Continued)
Table
4.5
Page
General linear model summaries for seed piece decay (transformed
into ln(1/(1-%seed piece decay))) of potato seed pieces of different
cultivars inoculated with a range of inoculum densities of
Phytophthora infestans ............................................................. 64
vii'
LIST OF APPENDIX FIGURES
Page
Figure
A. 1
Percent final emergence of potato cultivars Russet Burbank (RB)
and Russet Norkotah (RN) as affected by isolates of the clonal
lineages US-8 and US-i i of Phytophihora infestans averaged
over inoculum density applied to seed pieces .................................. 82
A.2
Effect of inoculum density of isolates of the clonal lineages US-8
or US-i 1 of Phytophthora infestans on emergence rate (r), %
emergence/day, of potato cvs Russet Burbank (RB) and Russet
Norkotah (RN) in A-D, Trial 1; E-H, Trial 2; and I-L, Trial 3 .............. 83
A.3
Percent emergence/day, r, of potato cultivars Russet Burbank (RB)
and Russet Norkotah (RN) as affected by isolates of the clonal
lineages US-8 and US-il of Phytophthora infestans averaged over
inoculum density applied to seed pieces ......................................... 85
A.4
Plant aerial biomass of potato cultivars Russet Burbank (RB) and
Russet Norkotah (RN) as affected by isolates of the clonal lineages
of Phytophthora infestans averaged over inoculum density applied
to seed pieces ....................................................................... 86
A.5
Seed piece decay of potato cultivars Russet Burbank (RB) and
Russet Norkotah (RN) as affected by isolates of the clonal lineages
of Phytophthora infestans averaged over inoculum density applied
to seed pieces ....................................................................... 87
B. I
Final percent emergence failure of potato cultivars Bannock Russet
(BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet
(RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH),
and Umatilla Russet (UR) inoculated with a range of inoculum
densities of Phytophthora infestans with A) zoospores of US-8 in
Oregon in 1999; B) sporangia of US-8 in OR in 1999; C) sporangia
of US-8 in OR in 2000; D) zoospores of US-i 1 in Washington in
1999; E) sporangia of US-li in WA in 1999; and F) sporangia of
US-li in WA in 2000 ............................................................ 102
lx
LIST OF APPENDIX FIGURES (Continued)
Figure
Page
B.2
Emergence rate (% emergence/day) of potato cultivars Bannock
Russet (BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger
Russet (RR), Russet Burbank (RB), Russet Norkotah (RN),
Shepody (SH), and Umatilla Russet (UR) inoculated with
increasing zoospore or sporangial densities of Phytophthora
infestans clonal lineages US-8 in Oregon (A-M and AA-AD) and
US-li in Washington (N-Z and AE-AG) in 1999 and 2000 ............... 104
B .3
Mean emergence rate (% emergence/day) of potato cultivars
Bannock Russet (BR), Bzura (BZ), Chieftain (CH), Kennebec
(KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah
(RN), Shepody (SH), and Umatilla Russet (UR) inoculated with a
range of inoculum densities of Phytophthora infestans with A)
zoospores of clonal lineage US-8 in Oregon in 1999; B) sporangia
of US-8 in OR in 1999; C) sporangia of US-8 in OR in 2000; D)
zoospores of US-i 1 in Washington in 1999; E) sporangia of US-i 1
in WA in 1999; and F) sporangia of US-il in WA in 2000 ................
108
B .4
Mean aerial biomass per plant of potato cultivars Bannock Russet
(BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet
(RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH),
and Umatilla Russet (UR) inoculated with a range of inoculum
densities of Phytophthora infestans with A) zoospores of clonal
lineage US-8 in Oregon in 1999; B) sporangia of US-8 in Oregon in
1999; C) sporangia of US-8 in Oregon in 2000; D) zoospores of
US-il in Washington in 1999; E) sporangia of US-li inWashington
in 1999; and F) sporangia of US-il in Washington in 2000 ............... 110
B.5
Mean seed piece decay of potato cultivars Bannock Russet (BR),
Bzura (BZ), Chieftain (Cl-i), Kennebec (KE), Ranger Russet (RR),
Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and
Umatilla Russet (UR) inoculated with a range of inoculum
densities of Phytophthora infestans with A) zoospores of clonal
lineage US-8 in Oregon in 1999; B) sporangia of US-8 in Oregon
in 1999; C) sporangia of US-8 in Oregon in 2000; D) zoospores
of US-Il in Washington in 1999; E) sporangia of US-il in
Washington in 1999; and F) sporangia of US-il in Washington in
2000 ................................................................................ 112
x
LIST OF APPENDIX TABLES
Table
Page
A. 1.
Comparison of significant differences between estimated
intercept and slope parameters for regression of emergence,
emergence rate, aerial biomass and seed piece decay responses
of potato cvs Russet Norkotah and Russet Burbank on increasing
inoculum concentrations of isolates of clonal lineages US-8 and
US-li of Phytophthora infestans ................................................. 88
A.2
Emergence of seed pieces of potato cultivars Russet Burbank and
Russet Norkotah inoculated with sporangia of isolates of clonal
lineages US-8 and US-i 1 of Phytophthora infestans ......................... 89
A.3
General linear model significance values for emergence,
emergence rate, aerial biomass, and seed piece decay interactions
and main effects of cultivars Russet Burbank (RB) and Russet
Norkotah (RN) inoculated with a range of sporangia of isolates
of clonal lineages US-8 and US-i 1 of Phytophthora infestans in
threetrials
A.4
............................................................................ 90
Comparison of percent emergence of potato cvs Russet Burbank
(RB) and Russet Norkotah (RN) seed pieces inoculated with
increasing sporangial densities of Phytophthora infestans
clonal lineages US-8 or US-i 1 (left), and the percent change in
emergence compared to the control (right) ..................................... 92
A.5
Comparison of percent final emergence for Russet Burbank (RB)
and Russet Norkotah (RN) inoculated with sporangia of
Phytophthora infestans clonal lineages US-8 or US-i 1 ........................ 93
A.6
Comparison of emergence rates (% emergence/day) of potato
cultivars Russet Burbank (RB) and Russet Norkotah (RN)
inoculated with increasing sporangial densities of Phytophthora
infestans clonal lineages US-8 or US-li (left), and percent change
in emergence rate compared to the control (right) ............................. 94
A.7
Comparison of emergence rates (% emergence/day) for Russet
Burbank (RB) and Russet Norkotah (RN) inoculated with
sporangia of Phytophthora infestans clonal lineages US-8 or US-i 1 ...... 95
xl
LIST OF APPENDIX TABLES (Continued)
Table
Page
A.8
Comparison of mean emergence rates (% emergence/day),
regardless of inoculum density (not including controls), for Russet
Burbank (RB) and Russet Norkotah (RN) inoculated with isolates
of clonal lineages US-8 or US-i 1 in 3 greenhouse trials ..................... 96
A. 9
Comparison of average aerial biomass per plant (dry, g) for Russet
Burbank (RB) and Russet Norkotah (RN) inoculated with
increasing sporangial densities of Phytophthora infestans
clonal lineages US-8 or US-i 1 (left), and the percent change in
aerial biomass compared to the control (right) ................................. 97
A. 10
Comparison of average aerial biomass per plant (dry, g) of Russet
Burbank (RB) and Russet Norkotah (RN) inoculated with
increasing sporangial densities of Phytophthora infestans clonal
lineages US-8 or US-li ............................................................
98
A. 11
Comparison of percent seed piece decay of Russet Burbank (RB)
and Russet Norkotah (RN) inoculated with increasing sporangial
densities of Phytophthora infestans clonal lineages US-8 or US-i 1
(left), and percent change in seed piece decay compared to the
controls (right) ...................................................................... 99
A. 12
Comparison of percent seed piece decay of Russet Burbank (RB)
and Russet Norkotah (RN) inoculated with increasing sporangial
densities of Phytophthora infestans clonal lineages US-8 or US-li ...... 100
B. 1
Reference information for the six seedborne Phytophthora
infestans field trials conducted in Oregon and Washington ................. 114
B.2
Cumulative totals of seed piece to plant transmission of late blight
across a range of sporangia and zoo spore inoculum densities
(spores per seed piece) in six field studies ....................................
B.3
115
Number of days after planting and emergence (dap and dae) that
seed piece to plant transmission occurred, and the transmission
rates (%) in field trials in Oregon (US-8) and Washington (US-i 1)
in1999 and2000
.................................................................
116
xii
LIST OF APPENDIX TABLES (Continued)
Table
B.4
Emergence of seed pieces of potato cultivars Bannock Russet
(BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet
(RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody
(SH), and Umatilla Russet (UR) inoculated with sporangia or
zoospores of Phytophthora infestans in Oregon (US-8) and
Washington (US-Il) ............................................................. 117
B.5
Significance of effect of increasing inoculum density on
emergence failure, emergence rate, aerial biomass, and seed piece
decay of different potato cultivars inoculated with 2.5, 25, or 250
sporangia or zoospores per seed piece (1999 trials), or with 50,
100, 400 or 800 sporangia per seed piece (2000 trials) of
Phytophthora infestans clonal lineages US-8 in Oregon or US-il
inWashington .................................................................... 118
B.6
Comparison of percent final emergence of potato cultivars Bannock
Russet (BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger
Russet (RR), Russet Burbank (RB), Russet Norkotah (RN),
Shepody (SH), and Umatilla Russet (UR) at each inoculum density
of zoospore or sporangial Phytophthora infestans US-8 (left), and
the percent change in emergence compared to the controls (right) ........ 119
B.7
Comparison of percent final emergence of potato cultivars Bannock
Russet (BR), Bzura (BZ), Chieftain (CII), Kennebec (KE), Ranger
Russet (RR), Russet Burbank (RB), Russet Norkotah (RN),
Shepody (SH), and Umatilla Russet (UR) at each inoculum density
of zoospore or sporangial Phytophthora infestans US-i 1 (left), and
the percent change in emergence compared to the controls (right) ........ 120
B.8
Percent final emergence and comparison of potato cultivars Bannock
Russet (BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger
Russet (RR), Russet Burbank (RB), Russet Norkotah (RN),
Shepody (SH), and Umatilla Russet (UR) inoculated with a range of
inoculum densities of zoospore or sporangial Phytophthora infestans
clonal lineage US-8 in Oregon in 1999 and 2000 ............................ 121
xlii
LIST OF APPENDIX TABLES (Continued)
Table
Page
B.9
Percent final emergence and comparison of potato cultivars Bannock
Russet (BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger
Russet (RR), Russet Burbank (RB), Russet Norkotah (RN),
Shepody (SH), and Umatilla Russet (UR) inoculated with a range of
inoculum densities of zoospore or sporangial Phytophthora infestans
clonal lineage US-li in Washington in 1999 and 2000 ..................... 122
B. 10
Comparison of estimated regression slope parameters for
emergence failure of potato cultivars Bannock Russet (BR),
Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR),
Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH) and
Umatilla Russet (UR) on increasing inoculum densities of clonal
lineages US-8 (Oregon) and US-li (Washington) of Phytophthora
infestans............................................................................ 123
B. ii
Comparison of emergence rates (% emergence/day) for potato
cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB),
Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
at each inoculum density of zoo spore or sporangial Phytophthora
infestans clonal lineage US-8 (left), and the percent change in
emergence rate compared to the controls (right) .............................. 124
B. 12
Comparison of emergence rates (% emergence/day) for potato
cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB),
Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
at each inoculum density of zoospore or sporangial Phytophthora
infestans clonal lineage US-li (left), and the percent change in
emergence rate compared to controls (right) .................................. 125
B. 13
Emergence rates (% emergence/day) and comparison of potato
cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB),
Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
inoculated with increasing zoospore or sporangial inoculum
densities of Phytophthora infestans clonal lineages US-8 in OR
and US-il in WA during 1999 and 2000 ...................................... 126
xiv
LIST OF APPENDIX TABLES (Continued)
Table
B.14
Comparison of estimated regression slope parameters for
emergence rate of potato cultivars Bannock Russet (BR), Bzura
(BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR),
Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH) and
Umatilla Russet (UR) on increasing inoculum densities of
Phytophthora infestans clonal lineages US-8 in OR and US-li
inWA............................................................................... 127
B. 15
Comparison of average plant aerial biomass (dry, g/plant) for
potato cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet
Norkotah (RN), Shepody (SH), and Umatilla Russet (UR) at each
inoculum density of zoo spore or sporangial Phytophthora infestans
clonal lineage US-8 (left), and the percent change in average aerial
biomass per plant compared to the controls (right) .......................... 128
B. 16
Comparison of average plant aerial biomass (dry, g/plant) for
potato cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB),
Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
at each inoculum density of zoospore or sporangial Phytophthora
infestans clonal lineage US-il (left), and the percent change in
average aerial biomass per plant compared to the controls (right) ........ 129
B. 17
Average plant aerial biomass (dry, g/plant) and comparison of
potato cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet
Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
inoculated with a range of inoculum densities of zoo spore or
sporangial Phytophthora infestans clonal lineage US-8 in Oregon
in 1999 and 2000 ................................................................. 130
xv
LIST OF APPENDIX TABLES (Continued)
Table
Page
B. 18
Average plant aerial biomass (dry, g/plant) and comparison of
potato cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet
Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
inoculated with a range of inoculum densities of zoospore or
sporangial Phytophthora infestans clonal lineage US-li in
Washington in 1999 and 2000 .................................................. 131
B. 19
Comparison of estimated intercept and slope parameters for
regression of aerial biomass of potato cultivars Bannock Russet
(BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet
(RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH)
and Umatilla Russet (UR) on increasing inoculum densities of
Phytophthora infestans clonal lineages US-8 in Oregon and US-il
in Washington in 1999 and 2000 ................................................ 132
B.20
Comparison of percent seed piece decay at harvest for potato
cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB),
Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
at each inoculum density of zoospore or sporangial Phytophthora
infestans clonal lineage US-8 (left), and the percent change in seed
piece decay compared to the controls (right) ................................. 133
B.21
Comparison of percent seed piece decay at harvest for potato
cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB),
Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
at each inoculum density of zoo spore or sporangial Phytophthora
infestans clonal lineage US-i 1 (left), and the percent change in seed
piece decay compared to the controls (right) ................................. 134
xvi
LIST OF APPENDIX TABLES (Continued)
Table
Page
B.22
Percent seed piece decay at harvest and comparison of potato
cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB),
Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
inoculated with a range of inoculum densities of zoospore or
sporangial Phytophthora infestans clonal lineage US-8 in Oregon
in 1999 and 2000 ................................................................. 135
B.23
Percent seed piece decay at harvest and comparison of potato
cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB),
Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
inoculated with a range of inoculum densities of zoospore or
sporangial Phytophthora infestans clonal lineage US-il in
Washington in 1999 and 2000 .................................................. 136
B.24
Comparison of estimated intercept and slope parameters for
regression of seed piece decay of potato cultivars Bannock Russet
(BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet
(RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH)
and Umatilla Russet (UR) on increasing inoculum densities of
Phytophthora infestans zoospores or sporangia of clonal lineages
US-8 in Oregon and US-il in Washington in 1999 and 2000 .............. 137
B.25
Average environmental conditions for six experimental field trials
in Oregon and Washington in 1999 and 2000 ................................ 138
xvii
DEDICATION
I dedicate this work to my parents, Roger D. and Carol L. Partipilo, whom I love
dearly.
Seedborne Phytophthora infestans: Effect of Pathogen Clonal Lineage and Potato
Cultivar on Seed Transmission of Late Blight and Plant Growth Responses
CHAPTER 1
INTRODUCTION
Late blight of potato, caused by Phytophthora infestans (Mont.) de Bary,
was found in the Columbia Basin of north-central Oregon and south-central
Washington as early as 1947 (Anonymous, 1947). Since 1990 it has reemerged as a
serious disease of potatoes throughout the Columbia Basin and the United States.
Sources of inoculum for initiating late blight epidemics are cull piles, volunteer
potatoes, and seed tubers. Blighted seed tubers are not regarded as an important
within field source of inoculum because they decay before the plant has the chance
to emerge. Blighted seed pieces, however, are a source of inoculum for
contamination and subsequent infection of healthy seed pieces (Lambert et al.,
1998). Spread of P. infestans from blighted to healthy seed pieces occurs during
seed cutting, handling, and planting operations. When infected seed pieces are
planted the pathogen can be transmitted up the growing tissues to the foliage
(Appel, 2001; de Bary, 1861; Massee, 1910; Melhus, 1915; van der Zaag, 1956)
where cool, moist conditions can trigger sporulation and the spread of the disease.
Planting of infected seed pieces contributes to risk of seed to plant transmission
(Marshall and Stevenson, 1996; van der Zaag, 1956), seed piece decay (Lambert et
al., 1998; Marshall and Stevenson, 1996), and a decrease in stand (Deahl, 1995;
Platt et al., 1999).
All commercial potato cultivars currently grown in the United States are
susceptible to the tuber and foliar phase of the disease, but cultivars differ in their
degree of susceptibility. The two clonal lineages of P. infestans that predominate in
the Pacific Northwest, US-8 and US-il, differ in their aggressiveness on potato
2
foliage, in mating type, and their average number of virulence factors. Both,
however, are insensitive to the fungicide metalaxyl (Inglis et
al., 1996).
The overall objective of this research was to assess the effect of seedborne
inoculum of two clonal lineages of P.
infestans
on (i) seed piece to plant
transmission and (ii) stand establishment, plant vigor, and seed piece decay in
different potato cultivars.
3
CHAPTER 2
LITERATURE REVIEW
DISEASE SIGNIFICANCE
Late blight, caused by Phytophthora infestans (Mont.) de Bary, affects
many solanaceous crops including cultivated potato (Solanum tuberosum L.). The
disease has reemerged as a significant disease in most major potato growing
regions around the world (Fry and Goodwin, 1997a, 1997b; Hamm etal., 1994;
Kadish and Cohen, 1992). The disease has increased in economic significance in
the past decade because of the appearance of new, more aggressive populations that
are also insensitive to the fungicide metalaxyl (Joimson et al., 1996, 1997). In
1995, the Columbia Basin of Oregon and Washington, which produces 20% of the
U.S. potato crop, had greater than 65,000 ha (160,000 acres) affected by late blight,
costing an estimated $30 million to control (Johnson et al., 1997). In contrast, in
1990 when the older, metalaxyl-sensitive clonal lineage predominated, only 250 ha
(618 acres) in the Columbia Basin were affected (Johnson et al., 1997).
ru
PATHOGEN BIOLOGY
Phytophthora infestans is a truly unique plant pathogen. When the genus
Phytophthora was first described by Anton de Bary in 1876, he used the words
"plant destroyer" to characterize it. Although sometimes termed a fungal pathogen,
it is actually not one of the true fungi. P. infestans is currently classified as an
oomycete in the Kingdom Chromista (Agrios, 1997; Fry and Goodwin, I 997a),
Protoctista (Fry and Goodwin, 1 997a), or Stramenopila (Alexopoulos, 1996),
kingdoms distinctly apart from the true fungi, plants, or animals. It is a
heterothallic, hemibiotroph capable of both sexual and asexual reproduction,
although the predominant reproductive mode is asexual. The coenocytic vegetative
mycelium produces branched sporangiophores that bear several lemon-shaped
sporangia. The sporangia germinate by releasing 3 to 8 zoospores at temperatures
up to 12-15 °C (Agrios, 1997; Crosier, 1934). At warmer temperatures (>15 °C) the
sporangium may germinate directly by producing a germ tube. In pure culture,
temperatures between 18 and 22 °C are optimum for rapid and profuse sporulation,
and a range of 21 to 24 °C is optimum for producing the most sporangia per
sporangiophore (Crosier, 1934). Less hospitable environmental conditions induce a
quasi-dormant state where the pathogen survives only within susceptible plant
tissues.
Foliage and tubers of all commercially grown potatoes are susceptible to the
disease. Foliar lesions typically start as dark water-soaked spots that enlarge
quickly and are surrounded by a chlorotic green to yellow halo that is encompassed
by fluffy white mycelium bearing sporangiophores. Lesion expansion and
sporulation occur under cool, moist conditions.
Tuber infection, unlike foliar infection, begins as brown-to-purplish sunken
areas (Pethybridge and Murphy, 1913). Disease development below the periderm is
characterized by tan to reddish-brown, dry, granular rot and brown finger-like
extensions protruding about 1.3 cm into healthy tissues. The margin between
healthy and diseased tissue is often indistinct.
The pathogen survives from year to year in association with the tuber.
Infected tubers may remain dormant during storage with few visible signs of the
disease (Massee, 1910). The following year, cutting of blighted or infected seed
pieces in preparation for planting can induce sporulation. During the seed handling
operation spores are spread to healthy seed pieces (Dowley and O'Sullivan, 1991;
Lambert etal., 1998). Piles of discarded cull potatoes also can produce copious
amounts of inoculum (Bonde and Schultz, 1943). And lastly, volunteer potatoes
emerging from infected daughter tubers not harvested from a field the previous year
can be a further source of initial inoculum.
SEED TO PLANT TRANSMISSION
Transmission of P.
infestans
from diseased tubers was postulated as early as
1861 (Anton de Bary, 1861). Estimates have been made as to the number of
blighted seed tubers needed to produce one transmission event. Van der Zaag
(1956) estimated one transmission event for every 100 diseased tubers planted.
Estimates by Hirst and Stedman (1960) take several factors into account, including
(i) failure of diseased tubers to sprout; (ii) failure of weakened sprouts to reach
above soil level; (iii) death of mycelium; and, (iv) failure of mycelium to move up
the stem. These factors and their experimental evidence led to an estimate of one
invaded stem for every 150 blighted tubers planted (Hirst and Stedman, 1960). In a
study conducted between 1954 and 1958, 3260 blighted tubers of several potato
varieties were planted, of which 21(0.64%) produced invaded stems (Hirst and
Stedman, 1960). A higher transmission rate of 20% blighted plants have been seen
in glasshouse experiments, when infected, not blighted tubers, were planted (Singh
and Bhattacharyya, 1990).
In 1876, de Bary stated that mycelium could survive perennially within
tubers (de Bary, 1876). He noted healthy and diseased shoots from blighted tubers
and that sickly shoots were killed after a slow period of disease development. In the
years following de Bary, a few researchers began to debate whether mycelium
could hibernate within diseased tubers (Massee, 1910; Pethybridge, 1911). Massee
(1910) stated that hibernating mycelium of infected tubers invaded stems and
leaves when the environment was damp. Doubting Massee's theory of infection
from dormant mycelium, Pethybridge (1911) planted blighted seed tubers in a
greenhouse and found that they either rotted or produced healthy, although
somewhat less robust, plants. The one diseased shoot that emerged from the 12
7
blighted tubers that were planted soon died, apparently infected from mycelium
that entered the shoot from the parent seed. Despite this observation, and the
admission that the occasional diseased plant could be produced from diseased
tubers, Pethybridge still believed that the only way late blight spread was by aerial
spores, and not infected seed. More recent research reveals that dormant nonvisible sprout infections from diseased tubers do exist (Appel, 2001) and are able to
produce primary infections on foliage months after stem elongation if moisture is
provided (Deahi, 1995).
Many early seed piece transmission studies were conducted only under
laboratory conditions, but this soon changed when a single infected plant (arising
from an blighted seed piece) was found in field trials in Maine (Meihus, 1915).
When this diseased plant was first observed there was no evidence of sporulation,
but stem discoloration extended 1.5 cm above soil level and 15 cm down to the
seed piece. Melhus (1915) observed that field grown plants behaved just as those
grown in the laboratory; shoots were infected before reaching the soil surface, and
some infected shoots became infection foci. Not only did he make the assumption
that infection centers originate from plantings of infected seed potatoes, but he
reasoned that only mildly infected seed tubers produce infected progeny due to
rotting of the more diseased tubers.
Credit for making the connection between diseased tubers and symptomatic
plants is also given to D.E. Van der Zaag (1956). He linked the incidence of
diseased seed tubers with the first manifestations of late blight in the field. In
8
experiments with blighted tubers, diseased plants from sporulating parent tubers
developed small brown-colored shoots. He therefore reasoned that tubers attacked
by P. infestans produce diseased plants and that Phytophthora grows up the stem
from the tuber to infect the foliage (Van der Zaag, 1956). A recent study (Appel,
2001) using PCR has confirmed that mycelium of P. infestans grows systemically
to stems from infected seed tubers, supporting this earlier hypothesis.
The low transmission rates seen by de Bary, Melhus, and Pethybridge make
it easy to understand why, in later experiments, lesions extending from the seed
tuber to the sprout were sometimes never found. In Maine, the transmission
frequency averaged 0.003% over a six-year period (Bonde and Shultze, 1943). On
Long Island, a 10% transmission rate was reported from a planting of 90 infected
tubers, but this represented nine symptomatic plants in a field with only 44%
emergence (Peterson, 1947). This transmission frequency, while high, would have
been higher (9/40 or 22.5%) if alternatively reported as the number of transmission
events per emerged plants.
Seed piece transmission frequencies also have been related to potato
cultivar. Cultivars are known to vary widely in their foliar and tuber susceptibility
to late blight (Inglis and Johnson, 1994; Inglis et al., 1996; Pethybridge and
Murphy, 1913). These susceptibilities do not always match, i.e., a cultivar with a
low foliar susceptibility may possess high tuber susceptibility or vice versa.
Furthermore, Van der Zaag (1956) reported the highest transmission frequencies in
cultivars that were susceptible to both the tuber and foliar phases of the disease and
the lowest transmission frequencies in cultivars susceptible to either the tuber or the
foliar phases. Whether or not he believed that the susceptibilities of the foliage and
tubers were or were not linked is not clear. In another study by Doster et al. (1989),
inoculated seed pieces of susceptible and moderately resistant cultivars were
planted and foliar late blight lesions tended to appear, first on plants of susceptible
cultivars before they appeared on the plants of moderately resistant cultivars.
Therefore, the overall susceptibility of the cultivar may in fact relate to the
transmission frequencies that occur within specific plantings.
Transmission rate is also affected by pathogen genotype. Marshall and
Stevenson (1996) found distinct variation in seed transmission between P. infestans
genotypes. Seed to plant transmission in Russet Norkotah generated 19.4%
diseased sprouts with the US-8 lineage compared to 1.9% diseased sprouts with
the US-i lineage.
PATHOGEN CLONAL LINEAGE
In the Pacific Northwest, two clonal lineages of P. infestans currently
predominate, US-8 (A2 mating type, metalaxyl insensitive) and US-i 1 (Al mating
type, metalaxyl insensitive). US-8 was first detected in New York in 1992 and then
in Maine in 1993 (Goodwin etal., 1995). By 1994, it had spread to the southeast,
northeast, and midwest potato growing regions of the United States, and by 1995,
was found in the western states (Fry and Goodwin, 1 997a). US-il was isolated in
10
the Columbia Basin in 1993 (Gavino et
1994 (Inglis
etal.,
al.,
2000), in northwestern Washington in
1996), and in New York in 1995 (Goodwin etal., 1998). The
most commonly detected clonal lineage found in the United States and Canada in
1994, 1995, and 1996 was US-8 at 77.2, 47.7, and 69.2%, respectively (Goodwin
al.,
et
1998), and US-i 1 was the third most common lineage occurring at 6.7 and
6.2% in 1994 and 1995, respectively (Goodwin
et al.,
1998). In western
Washington in 1996, all 160 isolations were US-il, and of the 120 isolations made
in 1997, 69% were US-il and 21% were US-8 (Dorrance etal., 1999). US-li also
was found in 24 counties in California in 1998 (Gavino, 2000).
Genotypic similarities between US-8 and US-il have been proposed.
Goodwin et
al.
(1998) suggested that US-i 1 originated from a sexual
recombination event between US-8 (A2) and US-6 (Al), because both US-8 and
US-il possess three copies of the chromosomes that carry the Gpi locus (Goodwin
etal.,
1995, 1998). Based on polymorphism patterns, mating type, and mtDNA
haplotypes, Gavino
et al.
(2000) stated that US-il was the result of a sexual
recombination event in the Columbia Basin population, but hypothesized a US-6 x
US-7 parentage.
Lineage comparisons go beyond migratory history and genetic origins. The
host range of US-8 includes potato and hairy nightshade (Dorrance et
Goodwin
etal.,
al.,
1999;
1998). US-li, on the other hand, may have a much broader host
range that includes potato, tomato, bittersweet, and hairy nightshade (Dorrance et
al.,
1999).
11
Aggressiveness may be one factor in the replacement of older clonal
lineages with newer ones (Kato and Fry, 1995; Lambert and Currier, 1997; Miller
etal., 1998). On foliage, US-8's latent period is shorter, spore production per lesion
is higher, and tissue colonization is more aggressive on detached leaflets compared
to metalaxyl-sensitive isolates (US-7, US-6, and US-i) (Miller etal., 1995, 1997).
Slightly different findings arose in a comparison of the competitive fitness of US-i
to US-8 under laboratory conditions; US-i was found to have a higher leaflet
infection frequency than US-8, but US-8 had higher sporulation levels and a shorter
latent period (Kato and Fry, 1995). US-8 isolates also are more aggressive than US1 (Al, metalaxyl sensitive) isolates on tuber tissues. Three weeks after an injection
of inoculum, surface areas of tubers treated with US-8 isolates were 70-90%
blighted, whereas tubers treated with US-i isolates were only 40-60% blighted
(Deahi, 1995). Similarly, when the clonal lineages US-i, US-6, US-7, and US-8
were inoculated onto four different potato cultivars, the US-8 clonal lineage caused
the fastest and most extensive tuber rot (Lambert and Currier, 1997).
SEED PIECE DECAY
Seed piece decay is the partial or total decomposition of the seed piece
caused primarily by soft rot bacteria. Entry points for these bacteria are provided by
P. infestans infections (Fry and Goodwin, 1997a). Doster et al. (1989) noted that
infected tubers regularly rotted before emergence. Furthermore, tubers with greater
12
than 25% of their surface areas blighted, failed to germinate (Singh and
Bhattacharyya, 1990). Weihing and O'Keefe (1962) reasoned that two factors, in
addition to environment, susceptibility inherent to the tuber and inoculum volume,
influence the likelihood of seed piece decay.
Clonal lineage also contributes to the amount and severity of seed piece
decay. In one experiment, inoculation with a US-8 isolate led to 52% seed piece
decay before emergence (83/159) compared to 0% (0/160) with a US-i isolate
(Marshall and Stevenson, 1996). In another study, tubers were inoculated with the
older (US-i) or newer clones (US-6, US-7, US-8) and incubated for several weeks.
The lateral spread of rot was greater for the newer clones, particularly US-8,
compared to the older US-i lineage (Lambert and Currier, 1997).
CULTIVARS
Few potato cultivars today are grown based on their reaction to late blight;
rather, they are grown because of their fresh-market or processing qualities. In
1994, over 60% of the potatoes grown in the United States were Russet Burbank,
Russet Norkotah, and Shepody, and in Washington alone these cultivars comprised
80% of this state's potato acreage (Inglis etal., 1996; National Agriculture
Statistics Service Potato Objective Yield Surveys, 1994). By 2000, about 70% of
the acreage in Oregon and Washington were planted to these three cultivars. Today,
the predominant cultivars grown in Oregon are Russet Burbank (32.7%), Russet
13
Norkotah (27.8%), Shepody (9.8%), Ranger Russet (11.2%) and Umatilla Russet
(3.1%); and similarly, Washington grows 33.7% Russet Burbank, 17.2% Russet
Norkotah, 10.8% Shepody, 20.2% Ranger Russet, and 12.3% Umatilla (Potato
Progress, 2001). In western Oregon and western Washington, mostly red and white
fresh-market potatoes are grown, with some acreage in russet and chipping varieties
(Dorrance et
al.,
1999).
Tubers and foliage of cultivars differ in their susceptibilities to late blight,
e.g., high susceptibility of the foliage does not necessarily mean high susceptibility
in the tuber, and vice versa (Kirk et al., 2001; Inglis
Murphy, 1913; Thurston
et al.,
et al.,
1996; Pethybridge and
1985). Based on foliar area under disease progress
curve (AUDPC) values, the rank order from least to most susceptible of some of
the common cultivars grown in Washington was: Kennebec <Russet Burbank <
Ranger Russet < Shepody < Russet Norkotah (inglis and Johnson, 1994; Inglis et
al.,
1996). Platt and McRae (1990) in eastern Canada also used AUDPC values to
rank 66 cultivars from most resistant to most susceptible. Kennebec ranked 6th
Russet Burbank ranked
and Shepody ranked 38th AUDPC values also were
used to rank several cultivars from least to most susceptible in New York against
US-8 in 1994. Russet Norkotah and Shepody were the most susceptible, followed
by Russet Burbank and Ranger Russet; Kermebec was the least susceptible (Inglis
et al.,
1996). The two cultivars with the highest percentage of visibly blighted
tubers in western Washington in 1993 (US-6) and 1994 (US-li) were Russet
Norkotah and Shepody. Ranger Russet (2.3 and 2.8%), Russet Burbank (3.7 and
14
2.7%), and Kennebec (2.3, 4.7%) had significantly less tuber blight at harvest with
US-6 and US-il, respectively (Inglis
et al.,
1996). Inoculation of tubers of Russet
Burbank, Russet Norkotah, Ranger Russet, and Shepody with US-8 resulted in 90,
80, 75, and 70%, respectively, of the tuber surface area blighted (Deahl, 1995).
OBJECTIVES
The objective of this research was to assess the effect of seedborne
inoculum of two clonal lineages of P.
infestans
in different potato cultivars on (i)
seed piece to plant transmission and (ii) stand establishment, plant vigor, and seed
piece decay.
15
CHAPTER 3
GROWTH RESPONSES OF POTATO TO SEEDBORNE INOCULUM OF
PHYTOPHTHORA INFESTANS
Heather M. Partipilo and Mary L. Powelson
16
ABSTRACT
Plant growth responses of potato cvs Russet Burbank and Russet Norkotah
grown from seed pieces infected with isolates representing the US-8 or US-li
clonal lineages of Phytophthora infestans were evaluated in the greenhouse.
Cultivar*clonal lineage*inoculum density interactions were significant in three
trials for plant responses of final emergence, emergence rate, aerial biomass and
seed piece decay. Russet Norkotah was equally susceptible to both clonal lineages.
Russet Burbank was more resistant than Russet Norkotah to seedborne inoculum of
US-i 1. Compared to Russet Norkotah, Russet Burbank's final percent emergence
was higher, emergence rate was faster, aerial biomass was greater, and amount of
seed piece decay was lower when inoculated with US-i 1. US-8 was more
aggressive than US-li on Russet Burbank. US-8 caused a greater reduction in final
emergence, emergence rate, and aerial biomass, and a greater increase in seed piece
decay. The two lineages were similar in their aggressiveness on Russet Norkotah.
This is the first report of a cultivar*pathogen clonal lineage*inoculum density
interaction for stand establishment and plant vigor responses of potato grown from
seed pieces infected with P. infestans.
17
INTRODUCTION
In recent years, late blight, caused by Phytophthora infestans (Mont.) de
Bary, has reemerged as a significant disease of potato (Solanum tuberosum L.) (Fry
and Goodwin, 1997a; Johnson et al., 1997). North American populations of P.
infestans, once predominated by US-i (metalaxyl sensitive, Al mating type) have
been eclipsed by newer, more aggressive clonal lineages (Fry et al., 1993; Goodwin
et al., 1994; Hamm et al., 1994). Over the past decade, late blight has caused
greater yield losses and frequently higher expenditures for chemical protection
(Johnson et al., 1997).
In the Pacific Northwest the two predominant clonal lineages are US-8 (A2)
and Us-i 1 (Al) (Dorrance etal., 1999). These lineages differ slightly in their
virulence complexity. For example, isolates collected in Washington in 1999 had
an average of 9.3 and 6.3 virulence factors for US-8 and US-li, respectively (Derie
and Inglis, 2001). While not a definitive measure of comparison, other very
aggressive P. infestans races found throughout Europe also have been shown to
carry as many as nine virulence factors (Turkenstein, 1993).
These newer clonal lineages, whether immigrants or newly developed
lineages, are more aggressive than the US-i lineage in terms of colonization of
foliar and tuber tissues (Deahl, 1995; Fry and Goodwin, 1 997a; Goodwin et al.,
1998; Inglis et al., 1996; Miller et al., 1995, 1997; Lambert and Currier, 1997;
Marshall and Stevenson, 1996; Salas etal., 1999).
18
The reaction of potato foliage and tubers to the old and new lineages of P.
infestans
has been documented many times (Boyd, 1980; Deahi, 1995; Dorrance
and Inglis, 1998; Lambert and Currier, 1997). The effect of seedbome inoculum of
these new clonal lineages on seed piece decay, stand establishment, and plant vigor
has received less attention.
Clonal lineage contributes to the amount of seed piece decay and final
emergence. Platt
et al.
(1999) reported lower emergence and higher incidences of
seed piece decay when seed pieces of eight different cultivars were inoculated with
US-8 compared to US-i. Additionally, when both inoculum density and incubation
period were increased emergence decreased and seed piece decay increased (Platt
et al., 1999). Marshall and Stevenson (1996) also reported that seed pieces
inoculated with US-8 resulted in a significantly greater incidence of seed piece
decay before emergence compared to US-i (Marshall and Stevenson, 1996). The
only descriptions of visibly diseased plant responses to seedborne inoculum in the
literature are 'small', 'puny', 'passably vigorous', and 'less robust' (Pethybridge,
1911; Salmon and Ware, 1926). Non-symptomatic plants simply lack description.
Differences in tuber resistance to late blight and seed piece decay vary
among cultivars, and often do not correlate with foliar resistance (Davila, 1964;
Dorrance and Inglis, 1998; Doster; 1989; Inglis et
Stewart et
al.,
al.,
1996; Lapwood, 1967;
1994; Wastie, 1991; Weihing and O'Keefe, 1962). For example,
when the seed pieces of several cultivars differing in tuber resistance to late blight
were inoculated with US-i or US-8, the less susceptible cultivars had less seed
19
piece decay and greater emergence than the more susceptible ones (Platt et al.,
1999).
The objective of this study was to directly compare the effect of seedborne
inoculum of US-8 and US-il on plant growth responses and seed piece decay in
potato cvs Russet Burbank and Russet Norkotah.
MATERIALS AND METHODS
Treatments and experimental design. Five inoculum densities of two clonal
lineages of P. infestans were combined factorially with two potato cultivars for a
total of 18 treatments. Inoculum densities were established at 0, 25, 50, 100, or 400
sporangia per seed piece in trial 1, and 0, 50, 100, 400 or 800 sporangia per seed
piece in trials 2 and 3. Greenhouse space was divided into five blocked areas where
each inoculum density*clonal lineage*cultivar treatment was replicated twice per
block. Each replication had five seed pieces.
Inoculum and cultivars. Isolates of P. infestans clonal lineages US-8 and US-i 1
were collected from naturally infected potato plants in Oregon in 1999 and 2000.
Isolates were cultured on modified (Appendix A) rye B agar (Caten and Jinks,
1968) at approximately 17 °C for 12-14 days. Plates were flooded with sterile water
(4.5 ml), and the sporangia were gently dislodged with an angled stir rod. The
sporangial suspensions within each genotype were combined, filtered through
cotton cheesecloth, and adjusted to the desired inoculum density with the aide of a
20
hemacytometer. Certified seed potatoes (Solanum
tuberosum L.)
of cvs Russet
Burbank and Russet Norkotah were cut with a melon ball scoop into single eye
seed pieces (-25.4 mm in diameter) weighing approximately 15 g. Seed pieces
were healed for 18 hr at room temperature prior to inoculation. Approximately 15
ml of the sporangial suspension or distilled water was delivered per 50 seed pieces.
Within 1 hr after inoculation, seed pieces were planted 5 cm deep in a steampasteurized greenhouse potting mix (trials 1 and 2) or a commercially bagged
soilless mix (trail 3) in 10 cm diameter x 13 cm deep plastic pots. The pots were
kept on greenhouse benches and were not given supplemental lighting.
Response variables. Data on plant emergence were collected daily. After 4-5 wk,
plants were removed from the pots and the stem and below ground stem were
examined for late blight lesions. The foliage (leaves and stems) of each plant was
cut at the soil line, dried at 43 °C for several days and weighed. Seed pieces were
evaluated for symptoms of bacterial soft rot.
Data analysis. Emergence and seed piece decay, expressed as percentages, were
based on the final number of emerged plants or decayed seed pieces, respectively,
divided by number of seed pieces planted. Emergence rate, r (slope), expressed as
percent emergence/day, was based on a 5-day window starting the day of first
emergence of each cultivar's water-inoculated control. SAS® version 8.1
(Statistical Analysis Systems, SAS Institute, Cary, NC) was used for all ANOVA
and regression (GLM) analyses, and for the determination of interactions among
main effects. Means were separated by Fisher's least significant difference (LSD)
21
test. Data were transformed using logarithms, arcsine square roots, logits, or the
multiple infection transformation (Gregory, 1948) with little success in linearizing
the most curvilinear responses, therefore, raw data were judged the most
appropriate for the analyses and figures. The water control was not included in any
of the primary analyses. The 800-sporangialseed piece inoculum density in the
third trial was dropped from the respective analyses due to response saturation.
Overall experimental error was compared to error associated with
replications within blocks. These errors were similar for all response variables in all
experiments, and therefore, individual replication observations values were used
rather than an averaged observation per block.
RESULTS
Transmission. Seed piece to plant transmission of P. infestans was observed in one
plant of Russet Burbank grown from a seed piece inoculated with 400 sporangia of
US-8 (Fig. 3.1). The plant emerged normally, developed two separate shoots, and
appeared healthy until 10 days after emergence when a stem lesion and foliar
wilting were noted on one of the two stems. Microscopic examination of the sprout
confirmed the presence of mycelium and sporangia of P. infestans.
Plant emergence. Final emergence of inoculated seed pieces, averaged across
treatments, was 78, 71, and 28% for trials 1, 2, and 3, respectively. The three-way
interaction of cultivar, clonal lineage, and inoculum density was significant
22
Fig. 3.1. Seed piece to plant transmission of late blight (Phytophthora infestans,
isolate of US-8 clonal lineage) in potato cv Russet Burbank.
(P1<O.0001,
P2=O.0001, P3=O.0365) for final percent emergence in all trials (Table
3.1). Final emergence responses differed significantly by treatment both in
magnitude (cultivar*clonal lineage) and shape (cultivar*clonal lineage*inoculum
density) (Table 3.1). Emergence responses were greater for Russet Burbank than
Russet Norkotah (Fig. 3.2). The clonal lineage*inoculum density interaction for
emergence was significant
(P1<O.0001; P2<O.000l;
P3=O.0031) for Russet Burbank
in all three trials, but not for Russet Norkotah. With an increase in inoculum
density of either US-8 or US-il, the decrease in emergence of Russet Norkotah
was significant (P1,2,3<O.0001), and in trials 1 and 3 these responses were nearly
identical (Fig. 3.2). In contrast, emergence of Russet Burbank significantly
23
Table 3.1. General linear model summaries for emergence of seed pieces of potato
cvs Russet Burbank and Russet Norkotah inoculated with a range of inoculum
of isolates of the clonal lineages US-8 and US-li of Phytophthora
infestans.
densitiesa
Type I
Source DF
SS
Mean
Square
F Value
Pr>F
Trial 1
Block
Cultivar*Clonal lineage
Inoculum density
4
Cultivar*ClonaI lineage*Inoculum density
9
3
3
1940
30610
32990
14950
485
10203
10997
1661
0.1415
36.9 <0.0001
39.8 <0.0001
6.0 <0.0001
1.8
Trial 2
Block
Cultivar*Clonal lineage
Inoculum density
4
1240
3
Cultivar*Clonal lineage*Inoculum density
9
48980
45980
21160
310
16327
15327
2351
49.8
7.6
0.4059
<0.0001
<0.0001
<0.0001
4
53
13
0.1
0.9949
3
1.0
53.1
Trial 3
Block
Cultivar*Clonal lineage
Clonal lineage*Inoculum density
83013 27671
107.9 <0.000 1
24047 12023
46.9 <0.0001
Cultivar*Clonal lineage*Inoculum density
2.3
0.0365
3607
601
aSeed pieces were inoculated with 25, 50, 100 or 400 (Trial 1), or with 50, 100,
400, or 800 sporangia per seed piece (Trials 2 and 3).
3
2
6
(P<0.0001) decreased as inoculum density of US-8 increased (P<0.0001), but
emergence did not significantly decrease with US-i 1 in two of three trials (Fig.
3.2). At inoculum densities ranging from 25 to 400 (Trial 1) or 50 to 800 (Trials 2
and 3) sporangia per seed piece, mean emergence failure of US-8 inoculated seed
pieces of Russet Burbank was significantly (P0.05) greater (27 to 63%) than those
inoculated with US-i 1.
Emergence rate. Cultivar*clonal lineage*inoculum density interactions for
emergence rate were significant (P10.0257; P20.0062; P3=0.0004) in all three
24
Fig. 3.2. Relationship between inoculum density of clonal lineages US-8 and USii of Phytophthora infestans and emergence of potato cvs Russet Burbank (RB)
and Russet Norkotah (RN) in A) Trial 1, B) Trial 2, and C) Trial 3. Seed pieces
were inoculated with a sporangial suspension of US-8 or US-i 1 and immediately
planted. Russet Burbank/US-8: open circles (0); Russet Burbank/US-i 1: solid
black circles (); Russet NorkotahfUS-8: open squares (LII); Russet Norkotah/US11: solid black squares 4. A) RB/8: y = -0.1 807x + 79.979, R = 0.9304; RB/i 1: y
= -0.022x + 91.658, R2 = 0.441; RN/8: y = -0.081x + 96.639, R2 = 0.9951; RN/il:
y = -0.0946x + 97.105, R2 = 0.878. B) RB/8: y = -0.0648x + 93.37, R = 0.9891;
RB/li: y = -0.0039x + 99.324, R2 0.6865; RN/8: y = -0.0954x + 81.201, R2 =
0.7924; RN/i 1: y -0.0547x + 85.965, R2 0.9791. C) RB/8: y = -0.067 lx +
47.65, R2 = 0.6776; RB/il: y = -0.0626x + 88.613, R2 0.9367; RN/8: y =
0.0282x + 18.504, R2 = 0.4624; RN/il: y = -0.0337x + 22.872, R2 = 0.5543.
25
100
80
R8
60
/ 11
0
40
20
0
100
80
"p
0"
1F
100
80
.
.
60
RB/il
40
N
0
20
0
0
Fig. 3.2.
200
400
Sporangialseed piece
600
26
Table 3.2. General linear model summaries for emergence rates of seed pieces of
potato cultivars Russet Burbank and Russet Norkotah inoculated with a range of
inoculum densitiesa of isolates of the clonal lineages US-8 and US-li of
Phytophthora infestans.
Type I
Source DF
SS
Mean
Square
F Value
54
1.4
969
646
24.8
Pr>F
Trial 1
Block
Cultivar*Clonal lineage
Inoculum density
4
Cultivar*Clonal lineage*Inoculum density
9
3
3
217
2908
1939
773
86
16.5
2.2
0.2411
<0.0001
<0.0001
0.0257
Trial 2
Block
Cultivar*Clonal lineage
Inoculum density
4
Cultivar*Clonal lineage*Inoculum density
9
3
3
253
1779
2434
1039
63
593
811
115
0.2118
<0.0001
<0.0001
2.7
0.0062
1.5
13.9
19.0
Trial 3
0.9384
1826
<0.0001
3
5478
<0.0001
580
2
1161
Cultivar*Clonal lineage*Inoculum density 6
67
0.0004
400
aSeed pieces were inoculated with 25, 50, 100 or 400 (Trial 1), or with 50, 100, 400
or 800 sporangia per seed piece (Trials 2 and 3).
Block
Cultivar*Clonal lineage
Inoculumdensity
4
12
3
0.2
126.0
40.0
4.6
trials (Table 3.2). The clonal lineage*inoculum density interaction for emergence
rate was significant for Russet Burbank in all three trials (Pir=0.0073; P2=0.0536;
P3=0.0108), but not for Russet Norkotah. Emergence rate responses differed
significantly over the range of inoculum densities both in magnitude (cultivar*
clonal lineage) and linear/curvilinear shape (cultivar*clonal lineage*inoculum
density) (Fig. 3.3; Table 3.2). Similar to emergence, the overall emergence rate
response for Russet Burbank was greater than Russet Norkotah (Fig. 3.3). As
inoculum density increased, the rate of emergence of seed pieces decreased
27
Fig. 3.3. Relationship between inoculum density of clonal lineages US-8 and US11 of Phytophthora infestans and emergence rate of potato cvs Russet Burbank
(RB) and Russet Norkotah (RN) in A) Trial 1, B) Trial 2, and C) Trial 3. Seed
pieces were inoculated with a sporangial suspension of US-8 or US-li and
immediately planted. Russet Burbank!US-8: open circles (0); Russet Burbank/US11: solid black circles (); Russet NorkotahlUS-8: open squares (CI); Russet
Norkotah/LJS-1 1: solid black squares 4. A) RB/8: y = -0.037x + 16.475, R2 =
0.9046; RB/il: y -0.0026x + 23.173, R2 = 0.0557; RN/8: y = -0.0273x + 23.581,
0.985; RN/li: y -0.0236x +21.544, R2 = 0.9268. B) RBI8: y = -0.0153x +
19.659, R2 = 0.8512; RB/li: y= -0.0028x +19.393, R2 0.4883; RN/8: y =
0.0208x + 16.931, R2 = 0.767; RN/il: y= -0.OiO2x + 14.49, R2 = 0.8889. C) RB/8:
y-0.0158x+ 10.93,R2=0.5708;RB/li:y-0.0155x+21.06,R2O.9i73;
RN/8: y
0.5234.
-0.0032x + 2.068, R2
=
0.3923; RN/li: y = -0.0046x + 3.15, R2
=
28
B/11,
25
r
20
U
15
10
5
0
25
B/il
10
25
20
15
10
5
0
0
200
400
Sporangialseed piece
Fig. 3.3.
600
800
29
significantly (P<0.05) for all treatments except Russet Burbank inoculated with
US-li in trials 1 and 2 (Fig. 3.3). In trial 3, the emergence rate of Russet Burbank
seed pieces inoculated with US-i i decreased significantly with increasing
inoculum density, but were not as affected as the other three treatments (Fig. 3.3
C). Russet Norkotah seed pieces had similar significant (P<0.05) reductions in
emergence rates with increasing inoculum density whether inoculated with US-8 or
US-i 1 (Fig. 3.3). In trial 3, the water-inoculated control of Russet Norkotah did not
have a similar emergence rate to Russet Burbank, as had occurred in trials 1 and 2
(Fig. 3.3). Cultivar*clonal lineage interactions were significant at inoculum
densities of 100 and 400 sporangialseed piece in trials 1 and 3 (P0.05).
Aerial biomass. The cultivar*clonal lineage*inoculum density interaction for
aerial biomass was significant (Pi=0.02O9; P20.0002; P30.0007) in all three trials
(Table 3.3). The cional lineage*inoculum density interaction for aerial biomass was
significant for Russet Burbank in two of three trials (Piz=0.0296; P2=0.i704;
P30.0046), but not for Russet Norkotah. Russet Burbank inoculated with US-i 1
was the only treatment to consistently maintain normal biomass at increasingly
high inoculum densities (Fig. 3.4). Plant biomass was not significantly different
than the water control at low inoculum densities for all treatments in all trials, but
when inoculum densities reached 400 and 800 sporangialseed piece the values
dropped significantly (P0.05). Cultivar*clonal lineage interactions were limited to
the highest inoculum densities in two of three trials (P<0.0 1).
30
Table 3.3. General linear model summaries for aerial biomass of plants grown from
potato seed pieces of cultivars Russet Burbank and Russet Norkotah inoculated
with a range of inoculum densitiesa of isolates of the clonal lineages US-8 and US11 of Phytophthora infestans.
Type I
Mean
SS
SQuare
F Value
0.00
0.03
0.04
0.03
0.24
2.40
4.03
2.27
0.9165
0.0708
0.0087
0.0209
0.02
0.10
0.10
0.04
1.67
9.95
9.55
3.86
0.1605
<0.0001
<0.0001
0.0002
0.00
0.28
0.04
1.61
0.1765
90.91
14.07
<0.000 1
<0.000 1
Source DF
Pr>F
Trial 1
Block
Cultivar*Clonal lineage
Inoculum density
4
0.01
3
3
Cultivar*Clonal lineage*Inoculum density
9
0.08
0.13
0.23
Block
Cultivar*Clonal lineage
Inoculum density
4
0.07
3
0.31
3
Cultivar*Clonal lineage*Inoculum density
9
0.30
0.36
Trial 2
Trial 3
Block
Cultivar*Clonal lineage
Inoculum density
4
3
0.02
0.83
0.09
0.08
2
Cultivar*Clonal lineage*Inoculum density 6
4.26
0.01
0.0007
aSeed pieces were inoculated with 25, 50, 100 or 400 (trial 1), or with 50, 100, 400
and 800 sporangia per seed piece (trials 2 and 3).
Seed piece decay. The cultivar*clonal lineage*inoculum density interaction for
seed piece decay was significant (Pi<0.0001; P2=0.0001; P30.0774) in two of
three trials (Table 3.4). In all trials, incidence of seed piece decay increased
significantly (P<0.000l) with increasing inoculum density for all treatments except
Russet Burbank inoculated with US-li (Fig. 3.5). In trial 1, decay of seed pieces of
Russet Burbank with US-i 1 fluctuated, but the response was relatively flat. In trials
2 and 3, the decay response of Russet Burbank inoculated with US-li was clearly
separated from that of Russet Norkotah with either lineage and from Russet
31
Fig. 3.4. Relationship between inoculum density of clonal lineages US-8 and USii of Phytophthora infestans and aerial biomass of potato cvs Russet Burbank (B)
and Russet Norkotah (N) in A) Trial 1, B) Trial 2, and C) Trial 3. Seed pieces were
inoculated with a sporangial suspension of US-8 or US-li and immediately
planted. Russet Burbank/US-8: open circles (0); Russet Burbank/US-i 1: solid
black circles (); Russet NorkotahlUS-8: open squares (LI); Russet NorkotahlUS11: solid black squares 4. A) B/8: y = -0.0006x + 0.4468, R2 = 0.9919; B/il: y =
0.00002x + 0.3973, R2 0.1394; N/8: y = -0.00002x + 0.4253, R2 = 0.014; N/li: y
= -0.0002x + 0.4362, R2 = 0.9924. B) B/8: y -0.000006x + 0.3572, R2 = 0.8366;
B/i 1: y = -0.00003x + 0.355, R2 = 0.2866; N/8: y = -0.0002x + 0.3404, R2
0.5286; N/il: y -0.0003x + 0.3607, R2 0.9857. C) B/8: y = -O.0003x + 0.1951,
R2 = 0.9085; B/il: y -0.00007x + 0.2327, R2 = 0.8928; N/8: y = -0.00005x +
0.0328, R2 = 0.4867; N/li: y = -0.00006x + 0.0401, R2 = 0.7632.
32
0.5
0.4
0.3
0.2
0.1
0
0.5
B
B/li
0.3
C
0.1
0
I
I
I
0.5
0.4
0.3
0.2
0.1
0
0
Fig. 3.4.
200
400
Sporangialseed piece
600
800
33
Table 3.4. General linear model summaries for seed piece decay of potato cultivars
Russet Burbank and Russet Norkotah seed pieces inoculated with a range of
inoculum densitiesa of isolates of the clonal lineages US-8 and US-il of
Phytophthora infestans.
Type I
Source DF
SS
Mean
Square
F Value
Pr>F
Trial 1
Block
Cultivar*Clonallineage
Inoculum density
4
Cultivar*Clonal lineage*Inoculum density
9
3
3
603
47852
25902
27836
151
15961
8634
3093
0.8467
0.4
36.6 <0.0001
19.8 <0.0001
7.1
<0.000 1
2.5
30.7
39.1
4.1
0.0481
Trial 2
Block
Cultivar*Clonal lineage
Inoculum density
4
Cultivar*Clonal lineage*Inoculum density
9
3
3
4375
40922
52159
16220
1094
13641
17386
1802
<0.000 1
<0.0001
0.0001
Trial3
0.7735
487
122
0.5
20880
6960
25.6 <0.0001
9920
4960
18.3 <0.0001
2
Cultivar*Clonal lineage*Inoculum density
0.0774
3200
533
2.0
6
aSeed pieces were inoculated with 25, 50, 100 or 400 (trial 1), or with 50, 100, 400
and 800 sporangia per seed piece (trials 2 and 3).
Block
Cultivar*Clonal lineage
Inoculum density
4
3
Burbank with US-8 (Fig. 3.5). Mean decay of all inoculated Russet Norkotah seed
pieces together was statistically similar regardless of clonal lineage. In contrast, the
mean decay of Russet Burbank increased significantly (P<0.05) with US-8
compared to US-li. Significant cultivar*clonal lineage interactions occurred at 50
sporangia/seed piece in trials 2 and 3, and at 400 sporangialseed piece in trials I
and 3 (P<0.05).
34
Fig. 3.5. Relationship between inoculum density of clonal lineages US-8 and US11 of Phytophthora infestans and seed piece decay of potato cvs Russet Burbank
(B) and Russet Norkotah (N) in A) Trial 1, B) Trial 2, and C) Trial 3. Seed pieces
were inoculated with a sporangial suspension of US-8 or US-li and immediately
planted. Russet BurbanklUS-8: open circles (0); Russet Burbank/US-i 1: solid
black circles (); Russet Norkotah/US-8: open squares (111); Russet NorkotahlUS11: solid black squares (I. A) B/8: y = 0.1032x + 54.663, R2 = 0.8521; B/il: y =
0.0367x + 62.523, R2 0.4779; N/8: y 0.0984x + 11.858, R2 = 0.9685; N/i i: y =
0.1716x+ l0.332,R2=O.8639.B)B/8:y0.0375x+40.851,R20.9733;B/ii:y
= 0.03 i8x + 10.266, R2 = 0.9704; N/8: y 0.0945x + 20.606, R2 = 0.754; N/il: y =
0.0663x + 42.634, R2 0.9133. C) B/8: y 0.0436x + 70.29, R2 = 0.7147; B/il: y
= 0.0628x + 49.29, R2 = 0.9875; N/8: y = 0.0201x + 86.71, R2 = 0.5403; N/il: y
=0.0102x + 93.07, R2 0.722.
35
100
80
60
40
20
N
0
100
80
N/li
B/8
V
V
0
V
40
20
8B/8T
0
100
80
60
40
20
0
I
0
Fig. 3.5.
200
I
400
Sporangialseed piece
I
600
I
800
36
DISCUSSION
Seed piece health and overall plant growth and vigor was compromised by
seedborne inoculum of P. infestans. The two clonal lineages of P. infestans
interacted differentially to affect the growth responses of both Russet Burbank and
Russet Norkotah. Based on final emergence, emergence rate, aerial biomass, and
seed piece decay, Russet Norkotah was equally susceptible to both genotypes,
whereas Russet Burbank was more resistant than Russet Norkotah to seedborne
inoculum of US-il. Regression of inoculum density of US-8 and US-li on final
emergence, rate of emergence, aerial biomass, and seed piece decay of Russet
Burbank indicated that US-8 had a greater effect than US-i 1 on seed health, stand
establishment and plant vigor. Both clonal lineages were equally aggressive on
Russet Norkotah.
Aggressiveness of US-8 and US-il have been compared to each other and
to the older lineages of P. infestans in both foliage and tuber assays. US-8 has a
shorter latent period than the older US-i lineage (Kato and Fry, 1995) and is a
more aggressive tissue colonizer and spore producer than other newer lineages
(Deahl, 1995; Miller et al., 1995 and 1997). In a recent study, Miller et al. (1998)
compared aggressiveness characteristics of US-8 and US-li to US-i, US-6, and
US-7 in a detached leaflet assay with Russet Burbank. US-8 had a significantly
higher area under lesion expansion curve (AULEC) value and a shorter latent
period than US-i, US-6, and US-7 but was statistically similar to US-il (Miller et
37
al., 1998). When detached leaflets of Russet Norkotah were inoculated with US-8
or US-il, AULEC and latent period values were similar for both lineages, and both
had larger AULEC values and shorter latent periods than US-i (Miller et al., 1995,
1997 and 1998).
In tuber assays, tuber rot was significantly deeper and wider, and progressed
faster into tissues with US-6, US-7, and US-8 compared to US-i during the 4 wk
incubation period. Of the four isolates US-8 was the most rapid tuber rofter, and it
spread the farthest (Lambert and Currier, 1997). In a similar study (Medina et
al.,
1999), US-8 caused significantly more severe surface necrosis and deeper lesions
on tubers than US-i.
Cultivar*clonal lineage interactions have been shown in tuber inoculation
studies. Russet Burbank and Russet Norkotah had significantly more surface
necrosis and deeper lesions than Yukon Gold when inoculated with US-8 compared
to US-i. Yukon Gold, regardless of clonal lineage, had less surface and tissue
necrosis than Russet Burbank and Russet Norkotah (Medina et al., 1999). In our
study, the incidence of seed piece decay at 100 sporangialseed piece averaged 47,
31, 87% for trials 1, 2, and 3 with US-8, and 38, 28, 73% for US-il, respectively.
Our findings suggest that US-8 is more aggressive than US-i 1 in causing seed
piece decay in Russet Burbank but are equally aggressive on Russet Norkotah.
The higher concentrations of inoculum applied to the seed piece contributed
to a high incidence of seed piece decay. Although inoculum was applied as
sporangia, the possibility of post-inoculation cleavage and release of zoospores is
38
conceivable. This is most likely to have occurred in trial 3 where seed piece decay
and growth responses were more extreme (Figs. 3.2 C, 3.3 C, 3.4 C, 3.5 C) when
compared to trials 1 and 2. The water supply in trial 3 (February 9, 2001) may have
been cold enough to promote the cleavage of zoo spores, thus increasing the
inoculum concentration on the seed pieces. The average low air temperature for all
three trials was similar (14.1-14.8 C), whereas the average high air temperature for
the first two trials were slightly warmer (28.7 and 27.1 C) than the last trial (23.9
C).
Russet Burbank and Russet Norkotah differed significantly in their
susceptibility to the seedborne phase of late blight. Their plant growth and seed
piece decay responses are consistent with foliar susceptibility rankings. Russet
Burbank is moderately susceptible and Russet Norkotah is very susceptible to the
foliar phase of late blight (Inglis
et al.,
1996; Stevenson, 1993). Platt etal. (1999)
reported a higher final emergence and less seed piece decay in the more resistant
cultivars than in the more susceptible cultivars. They also noted response
differences between resistant and susceptible cultivars were less clear with US-8
because of the tendency for a greater incidence of seed piece decay with these
cultivars.
Emergence rate and aerial biomass has not been previously quantified for P.
infestans
infected potatoes. Emergence rate and aerial biomass of Russet Burbank
differed in response to US-8 or US-11,just as final emergence and seed piece
decay did. Russet Norkotah responded similarly to the two clonal lineages. It is
39
clear that the plant growth responses of emergence rate and aerial biomass are
linked to emergence and seed piece decay. Not only does seedborne inoculum of
these clonal lineages reduce emergence and increase seed piece decay, but it also
reduces the rate at which the plants emerge and how robustly they grow.
Reductions in plant vigor and rate of emergence have been shown in other plant!
pathogen systems. Duram wheat seed, for example, when infected with
Pyrenophora tritici-repentis (Died.), had reduced emergence rates, reductions in
above-ground dry matter per unit area, poor seedling emergence, and lower grain
yields (Fernandez et al., 1997).
In a study comparing seed to plant transmission of US-8 and US-I in Russet
Norkotah, US-8 produced more diseased sprouts and had a higher percentage of
seed piece decay compared to the older, less aggressive US-i lineage (Marshall and
Stevenson, 1996). In our study one transmission occurred with a US-8 inoculated
seed piece of Russet Burbank. Doster etal. (1989) suggests the greatest probability
of first late blight appearance may be in more susceptible cultivars; however, this is
not always the case, as in our study.
Russet Burbank is a late-season maturing cultivar whereas Russet Norkotah
is an early- to medium-season maturing cultivar. Late-season cultivars have a
longer period of periderm development (Johnson et al., 1997) and Lacey (1967)
and Walmsley-Woodward and Lewis (1977) suggested that tuber resistance
increases with maturity of the cultivar. Seed pieces of Russet Norkotah were
equally susceptible to US-8 and US-il. The aggressiveness characteristics of the
two genotypes may not be easily separated in the early-maturing cultivars but
readily separated in late-maturing cultivars.
The effect of seedborne inoculum of P. infestans on percent final
emergence, emergence rate, aerial biomass and seed piece decay was cultivar,
clonal lineage, and inoculum density dependent. Seed piece decay and final
emergence results support data from previous studies (Deahl, 1995; Lambert and
Currier, 1997; Platt et al., 1999), and the emergence rate and aerial biomass data
break new ground on the previously unknown effects of seedborne P. infestans on
stand establishment and plant vigor of potato.
41
CHAPTER 4
SEEDBORNE PHYTOPHTHORA INFESTANS: SEED TO PLANT
TRANSMISSION AND GROWTH RESPONSES OF
DIFFERENT POTATO CULTIVARS
Heather M. Partipilo and Mary L. Powelson
42
ABSTRACT
Seed piece to plant transmission of Phytophthora infestans occurred with
isolates of clonal lineages US-8 in Oregon and with US-li in Washington.
Transmission with US-8 was 2.3% for Russet Burbank and with US-i 1 was 0.5,
4.9, and 1.4% for Russet Burbank, Russet Norkotah and Shepody, respectively.
With US-8, final emergence and emergence rate were significantly lower in
Kennebec, Russet Burbank, Russet Norkotah, and Shepody compared to Bzura, and
with US-li, both responses were significantly lower in Kennebec, Russet Norkotah
and Shepody compared to Bzura and Russet Burbank. Plant vigor (aerial biomass)
of Bzura and Russet Burbank was significantly higher compared to Kennebec,
Russet Norkotah and Shepody; results with US-8 were inconsistent. The incidence
of seed piece decay was similar for all cultivars with US-8 whereas with US-i i
percent seed piece decay was significantly less with Russet Burbank compared to
the other four cultivars. Regardless of clonal lineage, transmission occurred more
frequently and growth responses were suppressed more often in cultivars highly
susceptible to the foliar phase of late blight.
43
INTRODUCTION
In recent years, late blight, caused by Phytophthora infestans (Mont.) de
Bary, has emerged as a significant disease of potato (Solanum tuberosum L.)
throughout North America (Fry and Goodwin, 1 997a; Johnson et aL, 1997). North
American populations of P. infestans, once predominated by US-i (metalaxyl
sensitive, Al mating type), have in the past decade, been eclipsed by newer, more
aggressive, metalaxyl insensitive, clonal lineages (Fry et al., 1993; Goodwin etal.,
1994; Hamm et al., 1994). These newer clonal lineages, whether immigrants or
newly developed lineages, are more aggressive than US-i in terms of colonization
of foliar and tuber tissues (Deahi, 1995; Fry and Goodwin, 1 997a; Goodwin et al.,
1998; Inglis etal., 1996; Miller etal., 1995, 1997; Lambert and Currier, 1997;
Marshall and Stevenson, 1996; Salas et al., 1999). In the late 1990's, the
predominant clonal lineages in the Pacific Northwest were US-8 (A2, metalaxyl
insensitive) and US-il (Al, metalaxyl insensitive) (Dorrance et al., 1999). These
clonal lineages differ in virulence complexity (Derie and Inglis, 1997) and
aggressiveness on foliage and tubers (Lambert and Currier, 1997; Miller et al.,
1995, 1997).
Prior to the appearance of these new clonal lineages, only a small
proportion of infected tubers were reported to give rise to infectious plants (Hirst
and Stedman, 1960; Van der Zaag, 1956). With the newer clonal lineages, however,
seed to plant transmission frequency is higher. In a study of transmission efficiency
in which a new and an old lineage (US-8 and US-i, respectively) were compared,
the frequency of diseased sprouts was higher with US-8 (19.4%) than with US-i
(1.9%) (Marshall and Stevenson, 1996). Despite these findings the newer clonal
lineages have not been regarded as efficient seed transmitted strains due to the high
incidence of seed piece decay (Lambert and Currier, 1997; Marshall and Stevenson,
1996; Platt
et al.,
1999).
The reaction of potato foliage and tubers to the new strains of P.
infestans
has been documented many times (Boyd, 1980; Deahi, 1995; Dorrance and Inglis,
1998; Lambert and Currier, 1997) whereas the effect of seedbome inoculum on
stand establishment and plant vigor has received less attention. Platt et
al.
(1999),
reported lower final emergence and a higher incidence of seed piece decay for seed
pieces inoculated with US-8 compared to US-i. Additionally, as both inoculum
density and incubation period increased emergence decreased and seed decay
increased (Platt et
al.,
1999).
Differences in tuber resistance to late blight and seed piece decay vary
among cultivars, and often do not correlate with foliar resistance (Davila, 1964;
Dorrance and Inglis, 1998; Doster, 1989; Inglis
Stewart
et al.,
et al.,
1996; Lapwood, 1967;
1994; Wastie, 1991; Weihing and O'Keefe, 1962). For example,
when seed pieces of several cultivars differing in tuber blight resistance were
inoculated with US-i or US-8, the less susceptible cultivars had less seed piece
decay and greater emergence than the more susceptible ones (Platt et
al.,
1999).
45
The objective of this study was to evaluate the effect of seedborne inoculum
of P. infestans on 1) seed to plant transmission of P. infestans and 2) plant growth
responses of several potato cultivars. The study was conducted in Oregon with US-
8 and in Washington with US-il in 1999 and 2000.
MATERIALS AND METHODS
Treatments and experimental design. Five inoculum densities of P. infestans
were combined factorially with 5, 6, or 7 potato cultivars for a total of 25, 30, or 35
treatments, respectively. Inoculum densities were established at 0, 2.5, 25, 250, or
2500 sporangia or zoospores per seed piece in four of six trials, and at 0, 50, 100,
400, or 800 sporangia per seed piece in two trials. Each of the inoculum
density*potato cultivar treatments was replicated four or five times and each
replication had 12 or 13 seed pieces. Field trials were conducted in 1999 and 2000
at the Oregon State University Botany and Plant Pathology Field Laboratory in
Corvallis, OR in 1999 and 2000 and at the Mount Vernon Research and Extension
Unit in Washington. Hand- or machine-planted seed pieces were spaced 23 cm
apart and 7.6 cm deep in plots 3 m long. Row alleys were 0.9 to 1.0 m wide, and
plot alleys were 0.75 to 1.5 m long. Plots in Oregon were irrigated the day after
planting. Once the non-inoculated water controls reached 90% emergence, P-days
(Sands et al., 1979) were tracked until 200 P-days had elapsed. At that time the
plots were harvested.
Inoculum, cultivars, and soils. Isolates of?.
infestans
clonal lineages US-8 in
Oregon and US-il in Washington were collected from naturally infected potato
plants in 1998 and 1999 and cultured on modified rye B agar (Caten and Jinks,
1968) at approximately 17 °C for 12-14 days. Culture plates were flooded with
sterile water (4.5 ml), and the sporangia gently dislodged with an angled stir rod.
The sporangial suspensions within each lineage were combined, filtered through
cotton cheesecloth, and adjusted to the desired inoculum density with the aide of a
hemacytometer. The suspensions were either stored at room temperature or
refrigerated for 30 mm to release zoospores. Certified seed potatoes of cvs Bzura,
Kennebec, Russet Burbank, Russet Norkotah, and Shepody in 1999, and Bannock
Russet, Bzura, Chieftain, Ranger Russet, Russet Burbank, Russet Norkotah,
Shepody, and Umatilla Russet in 2000 were stored at 6 °C until 2-5 days before
planting, at which time they were placed at room temperature to break dormancy.
Seed tubers were cut up into seed pieces weighing approximately 45-60 g either the
day of planting or the day prior. Seed pieces were atomized with spore suspensions
that were adjusted to the necessary concentrations to deliver the same volume of
water (0.23 and 0.20 mi/seed piece for US-8 and US-li, respectively) and desired
spore density per seed piece. Seed pieces were hand-planted in Oregon and
machine-planted in Washington.
In Oregon, the soil was composed of a Camas gravelly sandy loam
(taxonomic: sandy-skeletal, mixed, mesic Fluventic Haploxerolls) and received 1616-16 granular fertilizer at 560 kg/ha when rows were opened with a tractor-drawn
47
furrower. In Washington, the soil was a Skagit silt loam (taxonomic: fine-silty,
mixed, superactive, nonacid, mesic Typic Fluvaquents) and received 10-34-0 liquid
fertilizer at 608 1/ha by banding 5 cm below the furrow at the time of planting.
Response variables. Data on plant emergence and presence of stem lesions of late
blight were collected daily. Suspicious looking plants were (i) rogued out of the
plots to prevent secondary infections and (ii) incubated in the laboratory for
confirmation of late blight. At approximately 200 P-days, plants were cut off at
ground level, the foliage of each plant placed in individual bags, dried at 43 °C for
several days, and weighed. Seed pieces were dug up and evaluated for symptoms of
bacterial soft rot.
Frequency of seed piece to plant transmission of late blight for each cultivar
was calculated by dividing the number of transmission events by the number of
emerged inoculated seed pieces. Emergence and seed piece decay, expressed as
percentages, were based on the final number of emerged plants or decayed seed
pieces, respectively, divided by the number of seed pieces planted. Emergence rate,
r, expressed as % emergence/day, was based on a 6-16 day window, depending on
cultivar, starting the day of first emergence of each cultivar' s water-inoculated
control.
Data analysis: The 2500 spores/seed piece treatment was removed from the
ANOVA, regression, and mean growth and decay analyses due to overwhelming
response saturation. The water control also was not included in the analyses.
Curvilinear dose responses to increasing inoculum densities suggested
48
transformations were needed. The multiple infection transformation (Gregory,
1948) was applied for seed piece decay and calculated as
in
1
1 % seed piece decay.
For final emergence data, the multiple infection transformation was adjusted
because emerged plants, presumed as healthy, represented the
data to represent the
infected,
non infected.
For the
percent emergence was subtracted from one (1)
yielding
or more simply,
in
1
(1 - % emergence)
ln
% emergence.
After transformation data were interpreted as emergence failure. Response
variables were compared with linear regression to determine significant cultivar
differences. SAS® version 8.1 (Statistical Analysis Systems, SAS Institute, Cary,
NC) was used for all ANOVA and regression analyses. Means were separated by
Fisher's least significant difference (LSD) test.
Environmental conditions. Average air high temperatures were consistently lower
in the US-i 1 trials than for the US-8 trials, whereas average low air temperatures
were similar between locations and years. Cumulative quantities of rainfall and
irrigation were similar between locations and years. Planting day conditions were
dry for all trials except US-li in 2000 when the soil was saturated by 0.5 cm
rainfall.
RESULTS
Transmission. Transmission of US-8 occurred across a range of sporangial
inoculum densities. Transmission rates were 2.3% for Russet Burbank in 1999 and
1.7, 0.7, 4.3, 7.6, and 0.5% for Bannock Russet, Bzura, Ranger Russet, Russet
Norkotah and Umatilla Russet in 2000, respectively. Transmission occurred
between 26 and 50 days after planting (or between 1 and 35 days after emergence).
For US-li, transmission occurred with both sporangia and zoospore inocula at
rates of 0.5% (sporangia), 4.9 (sporangia) and 3.6% (zoospore), and 1.4 (sporangia)
and 3.3% (zoospore) for Russet Burbank, Russet Norkotah and Shepody,
respectively in 1999, and 1.7% in Russet Burbank in 2000. Symptoms on emerging
plants were observed between 34 and 37 days after planting (9 and 18 days after
emergence).
Final emergence (emergence failure). The interaction of potato cultivar*inoculum
density for final emergence (expressed in terms of emergence failure) was
significant (Pus8 zoospore 1999 <0.0001,
=0.1016; Pus-u
zoospore 1999
PUS8 sporangia 1999
<0.0001, Pus-u
sporangia
0.0158,
PuS.8 sporangia 2000
1999<0.000i, Pus-ui
sporangia2000
=0.0016) at both locations in both years (Table 4.1). Overall emergence of all
inoculated seed pieces, regardless of cultivar, was 32, 34, and 42% for US-8, and
51, 52, and 16% for US-il. Emergence failure in Oregon (US-8) and Washington
(US-li) was greater with Russet Norkotah, Shepody, and Kennebec than for Bzura
and Russet Burbank (Fig. 4.1). With an increase in inoculum density of US-lithe
50
Table 4.1. General linear model summaries for emergence failure, i.e. ln(1/(1-(1-%
emergence))), of seed pieces of different potato cultivars inoculated with a range of
inoculum densities of isolates of the clonal lineages US-8 and US-il of
Phytophthora infestans.
Type I
Genotype/Year
Source DF
SS
Mean
Square
F
Value
Pr>F
US-8
1999
Block
Cultivar
Zoospore inoculum density
Cultivar*Inoculum density
4
4
2
8
0.6
9.3
209.0
18.9
0.2
2.3
104.5
2.4
0.4
0.8 160
0.0008
5.6
250.6 <0.000 1
5.7 <0.0001
2.6
13.7
148.4
13.5
0.7
3.4
74.2
1.0
0.4061
5.4
0.0010
115.6 <0.0001
2.6
0.0158
3.9
238.7
4.9
18.4
1.0
1999
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
4
4
2
8
1.7
,ziI,I
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
4
6
3
18
1.6
1.0
0.2268
<0.0001
2.4
0.0710
0.1016
1.5
1.7
39.8
1.4
58.5
Us-li
1999
Block
Cultivar
Zoospore inoculum density
Cultivar*Inoculum density
0.1902
<0.0001
3
1.0
0.3
4
2
26.4
84.3
34.9
6.6
42.1
0.2
50.7
51.0
31.4
0.05
12.7
25.5
3.9
0.2
43.3
0.6
183.8
0.2
36.8
1 Li
0.7946
0.3
66.9 <0.0001
20.3 <0.0001
2.9
0.0016
8
4.4
34.2
218.4 <0.000 1
22.6 <0.000 1
1999
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
3
4
2
8
87.1
13.4
0.9061
<0.0001
<0.0001
<0.0001
AiIIII
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
3
5
3
15
33.4
23.6
1.6
51
Fig. 4.1. Relationship between inoculum density of clonal lineages US-8 and USii of Phytophthora infestans and emergence of potato seed pieces of cultivars
Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank
(RB), Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR) inoculated
with A) zoospores of US-8 in Oregon in 1999; B) sporangia of US-8 in Oregon in
1999; C) sporangia of US-8 in Oregon in 2000; D) zoospores of US-li in
Washington in 1999; E) sporangia of US-il in Washington in 1999; and F)
sporangia of US-i 1 in Washington in 2000. Seed pieces were inoculated with a
sporangial or zoospore suspension and immediately planted. Cultivars with the
greatest emergence failure have regression trend lines in the upper regions of each
graph. A) BZ: y = 0.0089x + 0.5951, R2 = 0.7937; KE: y = 0.01 14x + 1.4204, R2 =
0.7158; RB: y = 0.0186x - 0.0388, R2 = 0.9996; RN: y = 0.Oi7x + 0.3774, R2 =
0.9763; SH: y = 0.0i69x + 0.4098, R2 = 0.9809. B) BZ: y = 0.0066x + 0.2945, R2
0.9206; KE: y 0.0097x + 0.668, R2 0.8944; RB: y 0.0139x + 0.3009, R2 =
0.982; RN: y = 0.0154x + 0.3556, R2 = 0.983; SH: y = 0.0155x + 0.7924, R2 =
0.8852. C) BR: y = 0.00lx + 1.477, R2 = 0.7061; BZ: y = 9E-05x + 0.259, R2 =
0.1207; CII: y = 0.0005x + 4.0427, R2 = 0.2242; RR: y = 0.0025x + 1.0141, R2 =
0.9243; RN: y = 3E-05x + 0.4229, R2 0.008; SH: y -0.0002x + 1.9544, R2 =
0.008; UR: y -3E-05x + 0.2 182, R2 = 0.065. D) BZ: y = 0.0023x + 0.0339, R2 =
0.9984; KE: y 0.0i54x + 0.2374, R2 0.9982; RB: y = 0.0025x - 0.0061, R2 =
0.999; RN: y = 0.0l84x - 0.001, R2 = 0.9998; SH: y = 0.0144x - 0.0018, R2 =
0.9998. E) BZ: y = 0.00ix + 0.0057, R2 = 0.9997; KE: y = 0.0124x + 0.5 189, R2 =
0.9701; RB: y = 7E-05x + 0.0091, R2 = 0.9932; RN: y = 0.0146x + 1.0092, R2 =
0.9139; SH: y 0.0125x + 0.3068, R2 = 0.9925. F) BR: y 0.0021x + 3.2079, R2 =
0.4865; CH: y = 0.0032x + 2.4371, R2 = 0.6998; RB: y = 0.0017x + 0.1897, R2 =
0.9222; RN: y = 0.0008x + 4.0728, R2 = 0.3088; SH: y -0.0007x + 4.7008, R2
0.7992; UR: y = 0.0025x + 0.9705, R2 0.6284.
52
4
3
2
0
0
50
200
100
150
Zoospores/seed piece
250
0
50
0
50
200
Sporangia/seed piece
250
0
50
200
100
150
Zoospores/seed piece
250
3
J_
)
U
2
0
100
150
100
150
200
RB
250
Sporangia/seed piece
5
4
-
CH
UBR
CH
ARR
3
0
2
ii''
!RR
A
1
RN
BZ
x
UR
0
0
Fig. 4.1.
400
600
200
Sporangialseed piece
800
0
200
400
600
Sporangia/seed piece
800
53
increase in emergence failure was significant
0.0 107, Psporangia 2000
(Pzoospores 1999
<0.0084, Psporangia
1999
0.0299) for all cultivars except Russet Burbank for both kinds
of inoculum in both years, and with US-8 for all cultivars and both kinds of
inoculum in 1999 (PzoosporesO.004O, PsporangiaO.O346). At high inoculum densities
of both clonal lineages most cultivars failed to emerge except for Russet Burbank
(37% with zoospore inoculum; 67% with sporangia inoculum) and Bzura (40%
with zoospore inoculum; 52% with sporangia inoculum) with US-i 1 in 1999.
Bzura with US-8, and Russet Burbank and Bzura with US-i 1, had significantly
lower levels of emergence failure compared to the other cultivars in 1999 (Fig. 4.1).
In 2000, emergence failure of Umatilia Russet and Bzura with US-8 was
significantly less than the other cultivars. With US-i 1 in 2000, Russet Burbank and
Umatilla Russet had a significantly lower emergence failure compared to the other
cultivars (Fig. 4.1). The estimated slopes of linear regressions for Russet Burbank
and Bzura, when compared to Kennebec and Shepody differed significantly with
both zoospore and sporangial inoculum of US-li in 1999, but not with US-8 in
1999 (Fig. 4.1). Significant differences between other cultivars were not consistent
across kind of inoculum or years.
Emergence rates. The cultivar*inoculum density interaction for rate of plant
emergence was significant in five of the six field trials (Table 4.2). Emergence rates
for most cultivars significantly (PzoosporesO.0069; PsporangiaO.00O2) decreased with
increasing inoculum density of either zoospores or sporangia with US-8 in Oregon
in 1999 and US-il in Washington in 1999 (Pzoospores<O.0014; PsporangiaO.Ol2O) and
54
Table 4.2. General linear model summaries for rate of plant emergence of different
potato cultivars inoculated with a range of inoculum densities of Phytophthora
infestans. Seed pieces were inoculated with either sporangia or zoospores of US-8
in Oregon and US-i I in Washington.
Type I
Genotype/Year
Source DF
SS
Mean
Square
F
Value
Pr>F
US-8
1999
Block
Cultivar
Zoospore inoculum density
Cultivar*Inoculum density
45.8
408.2
1290.3
264.3
11.4
102.0
645.1
33.0
0.1955
1.6
14.0 <0.0001
88.5 <0.0001
4.5
0.0003
11.3
148.1
1317.4
68.6
2.8
37.0
658.7
8.6
0.4241
12.9 <0.0001
230.0 <0.0001
0.0073
3.0
47.4
1872.7
24.7
123.6
11.9
312.1
8.2
6.9
2.5
0.0500
64.6 <0.0001
1.7
0.1698
1.4 0. 1358
21.6
638.5
777.6
197.5
7.2
159.6
388.8
24.7
2.9
0.0485
63.4 <0.0001
154.4 <0.0001
9.8 <0.000 1
0.3
100.3
8
0.8
401.1
187.8
61.8
0.91 14
0.2
64.4 <0.0001
60.3 <0.0001
5.0
0.0002
3
3.1
1.0
5
222.8
29.3
27.9
44.6
4
4
2
8
1999
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
4
4
2
8
1.0
!JiI&
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
4
6
3
18
Us-li
1999
Block
Cultivar
Zoospore inoculum density
Cultivar*Inoculum density
3
4
2
8
1999
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
2000
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
3
4
2
3
15
93.9
7.7
9.8
1.9
2.0
0.1209
87.7 <0.0001
19.2 <0.0001
0.0001
3.7
55
2000 (PsporangiaO.O264). With US-8 in Oregon in 2000, there was little to no effect
of increasing inoculum density on final emergence, emergence rate, and aerial
biomass (Figs. 4.1 C, 4.2 C, and 4.3 C), but a significant effect of increasing
inoculum density on seed piece decay for many of the cultivars (Fig. 4.4 C).
Emergence rates for different cultivars within trials were significantly different at
each inoculum density (Fig. 4.2). Emergence rates in 1999 were significantly
reduced by 95.6 to 100% in all cultivars at the highest inoculum density of US-8.
Emergence rates for cultivars in US-li trials in 1999 were similarly reduced at the
highest inoculum density, with the exception of Bzura and Russet Burbank, which
were reduced 59 to 68.8% and 46.2 to 74.8%, respectively. A similar emergence
rate response occurred at the 250 spores per seed piece density, with only Bzura
and Russet Burbank in the US-li trials still able to emerge at a positive rate (Fig.
4.2). The reduction in emergence rate with increasing inoculum density was
generally greater in the US-8 trials than in the US-i 1 trials. Inoculum density of
US-8 had no effect on emergence rate of Umatilla Russet in 2000 (Fig. 4.2 C).
Russet Burbank and Bzura, in US-8 trials in 1999, did not have statistically
different slopes when compared to Kennebec, Russet Norkotah and Shepody (Fig.
4.2). Mean emergence rate for inoculated seed pieces regardless of inoculum
density was significantly (P<0.05) different among cultivars in both US-8 and US-
11 trials, with Russet Burbank and Bzura having significantly (P0.05) higher
emergence rates than the other cultivars (Table 4.3). Russet Norkotah seed pieces
inoculated with between 25 and 250 spores per seed
56
Fig. 4.2. Relationship between inoculum density of isolates of clonal lineages US-8
and US-li of Phytophthora infestans and emergence rate of potato seed pieces of
cultivars Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet
Burbank (RB), Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
inoculated with A) zoospores of US-8 in Oregon in 1999; B) sporangia of US-8 in
Oregon in 1999; C) sporangia of US-8 in Oregon in 2000; D) zoospores of US-i 1
in Washington in 1999; E) sporangia of US-li in Washington in 1999; and F)
sporangia of US-il in Washington in 2000. A) BZ: y = -0.0199x + 5.3393, R2 =
0.4542; KE: y = -0.0127x + 3.0193, R2 = 0.542; RB: y = -0.0571x + 14.024, R2
0.9048; RN: y = -0.0377x + 9.0211, R2 = 0.5864; SH: y -0.0267x + 6.4189, R2
0.6449. B) BZ: y -0.0256x + 9.6589, R2 = 0.6367; KE: y = -0.02 i3x + 5.5985, R2
= 0.6203; RB: y -0.0435x + 10.759, R2 = 0.712; RN: y = -0.03 19x + 7.8334, R2
0.7 168; SH: y = -0.0297x + 7.0896, R2 = 0.569. C) BR: y = -0.0002x + 2.0061, R2
= 0.0291; BZ: y = -0.0006x + 7.9733, R2 = 0.021; CH: y -0.000ix + 0.1531, R2 =
0.0792; RR: y = -0.0056x + 5.9589, R2 = 0.895; RN: y = -0.001 ix + 8.7401, R2 =
0.0504; SH: y = -0.0005x + 2.238, R2 = 0.0469; UR: y = -0.00 lx + 10.987, R2 =
0.353. 0) BZ: y -0.024x + 9.2911, R2 0.9246; KE: y = -0.Ol5x + 3.8952, R2 =
0.9999; RB: y = -0.0395x + 15.354, R2 = 0.9985; RN: y = -0.0529x + 12.908, R2 =
0.8195; SH: y = -0.0233x + 5.8849, R2 = 0.8031. E) BZ: y -0.0087x + 7.4975, R2
= 0.9459; KE: y = -0.0146x + 3.7101, R2 0.7371; RB: y = -0.0082x + 9.8124, R2
= 0.7615; RN: y = -0.0156x + 3.7853, R2 = 0.7193; SH: y = -0.0273x + 7.3009, R2
= 0.859. F) BR: y = -0.0003x + 0.2008, R2 = 0.3088; CH: y = -0.0017x + 1.0991,
R2 = 0.5363; RB: y = -0.0029x + 5.2062, R2 0.9058; RN: y = -0.0005x + 0.3011,
R2 = 0.3088; SH: y = 0.0002x 0.0295, R2 = 0.7992; UR: y = -0.0043x + 3.4 184,
R2 = 0.7508.
57
20
DKE
XRN
RB
RN
H2S11L
-.
10
RN
SH
BZ
SH
6BZ
KE
KE
0
50
0
I
I
100
150
I
250
200
50
0
100
200
150
250
Zoospores/seed piece
Zoospores/seed piece
20
I
I
H
E
15
I)
c)
1)
P10
E
BZ
I)
0
SF1
KE
-----RN
0
250
200
150
100
50
0
50
0
100
150
200
250
Sporangia/seed piece
Sporangia/seed piece
20
r.BR oBZ-CF1
ARR XRN oSH
Li
15
-
XRN
OSH
+UR
+____UR
10
BZ
0
5
RR
u-a--
0
r
.
RB
+
- CH
I
CH
-------------
---
SH
KIN
0
200
400
600
Sporangia/seed piece
Fig. 4.2.
800
0
200
4
UR
400
13K
600
Sporangialseed piece
800
58
Table 4.3. Mean emergence ratea (% emergence/day) of seed pieces of different
cultivars inoculated with a range of inoculum densities (2.5, 25, and 250 or 50, 100,
400, and 800) of sporangia or zoospores of Phytophthora infestans US-8 in Oregon
and US-I 1 in Washington.
Zoospore
US-8
Sporangia
2000
1999
US-i 1
Zoospore
Sporangia
1999
2000
Cultivar
1999
1999
0.lc
i.9d
Bannock Russet
6.7 b
7.0 b
7.3 a
7.8b
Bzura
3.5 cd
0.5c
0.le
Chieftain
2.4d
2.5c
i.8d
3.6c
Kennebec
4.ic
Ranger Russet
11.7a
9.la 4.2a
6.7a
RussetBurbank
8.7a
23d
0.lc
8.4b
8.Ob
4.9b
RussetNorkotah
5.5b
4.8 c
0.04c
2.ld
3.7 c
4.3 be
Shepody
3.9 bc
2.Ob
10.7a
Umatilla Russet
aMean emergence rate values within vertical columns with the same letter did not
differ significantly according to Fisher's protected least significant difference
(LSD) test (P<0.05).
-Not tested.
piece emerged 31.5, 74.2, and 96.7% slower than Russet Burbank seed pieces in
the three US-i 1 trials (Table 4.3). Russet Norkotah emerged 36.8 and 27.5%
slower than Russet Burbank in the two US-S trials in which they were compared
(Table 4.3).
Aerial biomass. The cultivar*inoculum density interaction for aerial biomass was
significant in four of the six field trials (Table 4.4). Increasing inoculum density of
US-8 and US-li had no effect on aerial biomass of Bzura in two of three field
trials, and aerial biomass of Russet Burbank was unaffected by increasing inoculum
density of US-il (Fig. 4.3). Most cultivars in the US-8 trials in 1999 had similar
Table 4.4. General linear model summaries for aerial biomass per plant (dry, g) of
potato seed pieces of different cultivars inoculated with a range of inoculum
densities of Phytophthora infestans. Seed pieces were inoculated with either
sporangia or zoospores of US-8 in Oregon and US-i 1 in Washington.
Type I
Genotype/Year
Source DF
SS
Mean
Square
F
Value
Pr>F
US-8
1999
Block
Cultivar
Zoospore inoculum density
Cultivar*Inoculum density
4
4
2
8
0.4913
0.3089
<0.0001
0.1232
688.7
979.8
15681.1
2681.7
172.2
245.0
7840.5
335.2
0.8
1.2
39.3
835.5
2807.7
16146.3
4658.5
208.9
701.9
8073.2
582.3
0.4380
0.0190
37.0 <0.0001
2.7
0.0 147
2168.5
21894.1
1227.8
14903.0
542.1
2.8
3649.0
409.3
827.9
18.8
2.11
4.3
174.6
1744.7
5478.9
511.1
58.2
436.2
2739.5
63.9
0.5 198
0.8
5.7
0.0009
36.0 <0.0001
0.8
0.5730
133.4
720.3
1226.7
635.6
44.5
1.7
1999
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
2000
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
4
4
2
8
4
6
3
18
1.0
3.2
0.0295
<0.0001
0.1027
<0.0001
Us-li
1999
Block
Cultivar
Zoospore inoculum density
Cultivar*Inoculum density
3
4
2
8
1999
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
2000
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
3
4
2
8
3
5
3
15
4.9
2235.0
206.9
474.5
180.1
613.3
79.4
0.0752
<0.0001
34.0 <0.0001
4.4
0.0006
2.5
10.0
1.6
0.1
447.0
69.0
31.6
30.0
4.6
2.1
0.9536
<0.0001
0.0052
0.0186
Fig. 4.3. Relationship between inoculum density of clonal lineages of US-8 and
US-il of Phytophthora infestans and aerial biomass per plant of potato cultivars
Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank
(RB), Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR) inoculated
with A) zoospores of US-8 in Oregon in 1999; B) sporangia of US-8 in Oregon in
1999; C) sporangia of US-8 in Oregon in 2000; D) zoospores of US-li in
Washington in 1999; E) sporangia of US-li in Washington in 1999; and F)
sporangia of US-il in Washington in 2000. A) BZ: y -0.1574x + 40.194, R2 =
0.8556; KE: y = -0.1 158x + 28.044, R2 0.7344; RB: y = -0.1 i42x + 29.3, R2 =
0.7962; RN: y -0.1017x + 25.778, R2 = 0.9371; SH: y -0.1452x + 36.928, R2 =
0.8977. B) BZ: y -0.0429x + 3 1.806, R2 = 0.9152; KE: y = -0.1559x + 39.45, R
= 0.9455; RB: y = -0.1971x + 50.728, R2 0.7537; RN: y -0.1309x + 33.711, R2
= 0.7514; SH: y -0.0927x + 22.911, R2 = 0.9515. C) BR: y = -0.019x + 43.422,
R2 = 0.4463; BZ: y = -0.0053x + 42.03, R2 = 0.3152; CH: y = 0, R = N/A; RN: y =
-0.0008x + 29.931, R2 = 0.0372; RR: y -0.0627x + 52.308, R2 0.9156; SH: y =
0.0043x + 40.625, R2 0.9985; UR: y 0.0032x + 35.06, R2 = 0.2252. D) BZ: y =
-0.0524x + 25.617, R2 = 0.9823; KE: y = -0.1 i64x + 28.967, R2 = 0.9924; RB: y =
-0.094x + 35.361, R2 = 0.9636; RN: y -0.098x + 24.728, R2 = 0.9661; Sil: y =
0.0662x + 16.528, R2 = 0.9985. E) BZ: y = -0.0055x + 15.178, R2 = 0.3243; KE: y
= -0.0677x + 16.794, R2 = 0.9794; RB: y -0.0134x + 19.006, R2 = 0.943; RN: y =
-0.0652x + 16.633, R2 = 0.8703; SH: y = -0.05x + 12.628, R2 = 0.9669. F) BR: y =
-0.005 lx + 3.2879, R2 = 0.3088; CU: y = 0, R = N/A; RB: y = -0.0049x + 15.112,
R2=0.i422;RN:y=0,R2=N/A;SH:y0,R2N/A;UR:y-0.0i33x+
8.963 6, R2 = 0.7707. N/A= not applicable.
61
D
50
DKE
0
40
30
XRN
OSH
X SH
20
RB
0 RBKE
10
0 RN
KE
RN
SH
0
I
50
0
I
I
100
200
150
250
100
150
200
Zoos pores/seed piece
50
0
Zoospores/seed piece
250
60
1
LE
50
40
RB
20
BZ
RN
I-
SH
------
0
I
I
200
Sporangia/seed piece
50
0
100
150
250
50
0
11
20
----
B°
I
-----.--- -- ------
-
-
I
N
CH ARR,
XRN 0SH
±UR
10
RB
RR
UR
CH
BR--------------------------
0
B
0
Fig. 4.3.
250
RB XRN,
OSH +UR
-(
BZ
::-+------------
--------
+ LJR
x----RN
30
150
UBR CH
SH
0
40
I
200
Sporangia/seed piece
100
AEI
50
=
200
600
400
Sporangialseed piece
800
0
RN
SH
CH
200
400
600
800
Sporangia/seed piece
62
significant (P<0.05) reductions in aerial biomass with increasing inoculum density
(Fig. 4.3 A and B). Significant differences among cultivars for aerial biomass of the
US-8 inoculated seed pieces regardless of inoculum density were inconsistent year
to year, although aerial biomass of Bzura and Russet Burbank tended to be slightly
larger than other cultivars. In the three US-il trials, plants of Russet Burbank were
significantly larger than the other cultivars at the two highest inoculum densities
(Fig. 4.3 D, E, and F). Furthermore, Russet Burbank's overall aerial biomass across
inoculum densities for US-i 1 was also significantly larger than the overall mean
biomass for the other cultivars (P<0.05). Aerial biomass of Bzura also was
significantly larger than the other cultivars in the US-i 1 trials, but not as large as
Russet Burbank. The few plants of other cultivars that did emerge at high inoculum
densities were typically stunted, weak, slow to develop, or died, and were too few
in number to calculate realistic averages. All cultivars inoculated with US-8 in
2000, except Chieftain, grew to normal size, even at the highest inoculum densities
(Fig. 4.3 C). This was not consistent with results in 1999 (Fig. 4.3 A and B). All
cultivars inoculated with US-i 1 in 2000, except Russet Burbank and Umatilla
Russet, grew poorly, even at the lowest inoculum densities (Fig 4.3 F). Aerial
biomass of Umatilla Russet, and especially Russet Burbank, was significantly
(P<0.05) larger than their counterparts at the intermediate and high inoculum
densities (Fig. 4.3 F). Estimated regression slopes for aerial biomass of the different
cultivars were not significantly different in the US-8 trials in 1999, although there
were significant differences among a few cultivars in 2000 (Fig. 4.3 A, B, and C).
63
In the US-li trials, the estimated regression slopes were significantly different in
comparisons between Bzura and Kennebec in two of three trials (Fig. 4.3 D, E, and
F). Comparisons of other cultivars were not consistent from trial to trial.
Seed Piece Decay. Cultivar*inoculum density interactions for seed piece decay
were not significant (US-8: Pzoospore 1999=0.0070; Psporangia 1999 <0.0700; Psporangia 2000
=0.1721; US-li: Pzoospore 1999 =0.7511; Psporangia 1999 <0.0001; Psporangia 2000 0.7138) in
four of six trials (Table 4.5). Seed piece decay increased significantly (PUS..8
0.0049; Pus1 iO.0096) with increasing inoculum density for most cultivars, with
the exception of Bzura with US-8 and Russet Burbank with US-il (Fig. 4.4).
Overall mean seed piece decay varied significantly by cultivar in five of six trials
(P<0.05). With US-i 1, Russet Burbank had significantly less seed piece decay than
Bzura, Kennebec, Russet Norkotah, and Shepody. Umatilla Russet, and in the 2000
US-8 and US-I 1 trials, had significantly less seed piece decay than the other
cultivars at the intermediate and high inoculum densities (Fig. 4.4 C, F). Significant
differences among estimated seed piece decay regression slopes were sporadic in
both US-8 and US-i 1 trials.
DISCUSSION
Seed to plant transmission ofF.
infestans
occurred with US-8 in Oregon
and with US-i 1 in Washington. In previous studies on seed to plant transmission,
blighted seed tubers were planted; most decayed prior to emergence resulting in
Table 4.5. General linear model summaries for seed piece decay (transformed into
ln( 1/(1 -%seed piece decay))) of potato seed pieces of different cultivars inoculated
with a range of inoculum densities of Phytophthora infestans. Seed pieces were
inoculated with either sporangia or zoospores of US-8 in Oregon and US-li in
Washington.
Type I
Genotype/Year
Source
DF
SS
Mean
Sauare
F
Value
Pr>F
US-8
1999
3.1
0.7
2.0
89.3
3.0
0.5946
0.1155
<0.0001
0.0070
2.2
0.6
0.5
1.6
1.5
96.6
8
6.3
193.2
16.4
91.9
2.0
0.7149
0.2143
<0.0001
0.0700
4
6
9.9
171.2
3
12.3
36.3
Block
Cultivar
Zoospore inoculum density
Cultivar*Inoculum density
4
4
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
4
4
2
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
2
8
2.9
8.0
184.0
24.8
0.7
2.0
92.0
1999
2.1
2000
18
2.5
28.5
4.1
2.0
1.7
19.1
0.05
0.4
112.3
0.3
2.7
1.4
0.1646
<0.0001
0.0466
0.1721
Us-li
1999
Block
Cultivar
Zoospore inoculum density
Cultivar*Inoculum density
3
4
2
8
0.1
1.5
224.6
0.9
0.1
0.8369
0.0803
2.2
654.0
0.6
<0.000 1
0.75 11
0.4
34.7
129.5
11.7
0.7549
<0.0001
<0.0001
<0.0001
0.5
6.0
2.2
0.8
0.6842
0.0001
1999
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
3
Block
Cultivar
Sporangial inoculum density
Cultivar*Inoculum density
0.4
40.6
75.9
27.4
0.1
10.2
3
1.5
5
0.5
5.8
3
29.1
6.5
15
11.1
4
2
8
38.0
3.4
,iIIII
2.2
0.7
0.09 13
0.7138
Fig. 4.4. Relationship between inoculum density of clonal lineages US-8 and US11 of Phytophthora infestans and seed piece decay of potato cultivars Bzura (BZ),
Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB),
Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR) inoculated with
A) zoospores of US-8 in Oregon in 1999; B) sporangia of US-8 in Oregon in 1999;
C) sporangia of US-8 in Oregon in 2000; D) zoospores of US-il in Washington in
1999; E) sporangia of US-li in Washington in 1999; and F) sporangia of US-li in
Washington in 2000. A) BZ: y = 0.008x + 2.1674, R2 = 0.3243; KE: y = 0.0106x +
2.0968, R2 0.502; RB: y = 0.0149x + 0.8689, R2 = 0.9995; RN: y = 0.0141x +
1.1434, R2 = 0.9237; SH: y = 0.0149x + 0.957, R2 = 0.8546. B) BZ: y = 0.006x +
1.2675, R2 = 0.4327; KE: y = 0.0148x + 0.9784, R2 = 0.8585; RB: y = 0.0146x +
1.0258, R2 = 0.8671; RN: y = 0.0161x + 0.6118, R2 = 0.9625; SH: y = 0.013x +
1.4828, R2 = 0.6393. C) BR: y 0.0023x + 1.3975, R2 = 0.9441; BZ: y 0.0022x
+ 1.0789, R2 = 0.7819; CH: y = 0.0005x + 4.2925, R2 = 0.3088; RR: y = 0.0019x +
1.3559, R2 = 0.8071; RN: y = 0.0005x + 0.9012, R2 = 0.1384; SB: y = -0.0003x +
2.3592,R2=0.021;UR:y-0.0011x+1.0941,R20.351.D)BZ:y0.016x+
0.0842,R2=1;KE:y0.0178x+0.1569,R20.9995;RB:y0.017x-0.1611,
R2
R2
R2
= 0.9944; RN: y = 0.0179x + 0.1449, R2 = 0.9975; SH: y = 0.0179x + 0.1384,
= 0.9983. E) BZ: y 0.0052x + 0.2541, R2 = 0.9037; KE: y = 0.0135x + 0.7609,
= 0.9203; RB: y 0.0006x + 0.0991, R2 = 0.8467; RN: y = 0.0147x + 0.9906,
= 0.9206; SH: y = 0.015x + 0.3647, R2 = 0.9956. F) BR: y = 4.6052, R2 = N/A;
CH:y=4.6052,R2N/A;RB:y0.0002x+3.014,R20.0104;RN:y
0.0006x + 4.2 143, R2 = 0.3088; SH: y = 4.6052,
3.2953, R2 = 0.6988. N/A=not applicable.
R2 = N/A;
UR: y = 0.002x +
5
I
A
4
KE
BZ
3
a KE
2
RB
SH
!XRN
RB
LSTh
0
50
0
200
Zoospores/seed piece
150
100
250
50
0
200
100
150
Zoospores/seed piece
250
5
C
o
RN
SH:
o
RB
KE
BZ
KE
a
BZ-<
SH
0
0
RN
-----------.
0
50
0
200
Sporangia/seed piece
100
150
250
0
o L±RR +UR:
SH
2
+
0
Fig. 4.4.
I
200
250
N
UR
BR
RR
31- UR
--400
600
200
Sporangia/seed piece
-----------RB
£
BZ 0°
0
I
150
.-
--:--
3
I
100
Sporangialseed piece
5
4
50
RB
--
.BR CH RBh
xRNoSHUR
RN
800
0
200
400
600
Sporangia/seed piece
800
67
low late blight transmission frequencies (Bonde and Shultze, 1943; De Bary, 1861;
Hirst and Stedman, 1960; Massee, 1910; Meihus, 1915; Peterson, 1947;
Pethybridge, 1911; Van der Zaag, 1956). We inoculated seed pieces and planted
them to the field within one to two hours following inoculation. Research in Maine
(Lambert et al., 1998) has shown that P. infestans is spread from blighted tubers
and seed pieces during the seed handling operation. The amount of inoculum
distributed to the seed pieces is quite variable, ranging from low to high densities
and the time from inoculation to planting can be as short as one day to as long as a
couple of weeks. As a result, the severity of seed piece infection would range from
very mild to severe. In our study, seed pieces inoculated with high densities of P.
infestans were prone to seed piece decay and high emergence failure. Seed pieces
inoculated with low to moderate densities of P. infestans emerged and exhibited
varying levels of transmission.
Based on the number of emerged plants, seed to plant transmission
averaged across cultivars, was 0.5 and 2.4% in 1999 and 2000 with US-8 versus
0.75 and 1.0% with Us-i 1. Transmission occurred in Bzura, Bannock Russet,
Ranger Russet, Russet Burbank, Russet Norkotah, and Umatilla Russet with US-8,
and only in Russet Burbank, Russet Norkotah and Shepody with US-il. Most
transmissions were observed in Russet Norkotah with both clonal lineages. In the
Pacific Northwest, late blight is usually reported first in this highly susceptible
cultivar. In a study conducted in New York (Doster et al., 1989) with US-i, seed
piece transmission usually, but not always, appeared in the susceptible cultivars
before it appeared in the moderately resistant ones.
Tubers and foliage of cultivars differ in their susceptibilities to late blight,
(Kirk et al., 2001; Inglis
al.,
etal.,
1996; Pethybridge and Murphy, 1913; Thurston et
1985). Based on foliar area under disease progress curve (AUDPC) values, the
rank order from least to most susceptible of some of the common cultivars grown
in western Washington was: Kennebec <Russet Burbank < Ranger Russet <
Shepody <Russet Norkotah (Inglis and Jolmson, 1994; Inglis etal., 1996). Platt
and McRae (1990) in eastern Canada also used AUDPC values to rank 66 cultivars
from most resistant to most susceptible. Kennebec ranked
6th,
Russet Burbank
38th
AUDPC values also were used to rank several
ranked 31st and Shepody ranked
cultivars from least to most susceptible in New York against US-8 in 1994. Russet
Norkotah and Shepody were the most susceptible, followed by Russet Burbank and
Ranger Russet; Kennebec was the least susceptible (Inglis et
al.,
1996). In our
experiments, the highly susceptible Russet Norkotah produced the highest number
of transmission events. The more foliar-resistant cultivars, Bzura and Russet
Burbank, produced fewer transmission events. Transmission frequency, therefore,
appears to be related to the susceptibility of the foliage.
Most transmission occurred between 26 and 50 days after planting with US8 and 34 and 37 days after planting with US-i 1. The time between planting and
appearance of stem lesions represents the time it took for the inoculum to infect the
seed piece, colonize its tissues and grow as mycelium up the emerging sprout.
Appel et al. (2001) have shown that potato plants grown from P. infestans infected
seed may be infected and remain symptomless. As we did not test symptomless
stems for the presence of P. infestans, we do not know if they were latently
infected. Furthermore, the experiments were terminated at approximately 200 Pdays. Had the plants been grown until regional harvest, symptoms may have
developed, providing environmental conditions were favorable for disease
expression.
Transmission efficiency may be linked to the susceptibility of the seed piece
to bacterial soft rot. Tuber susceptibility to bacterial soft rot has been shown to vary
among cultivars (Lojkowska and Kelman, 1994). The more susceptible the cultivar
is to seed piece decay, the less likely that transmission will occur because the seed
piece decays before the sprout has a chance to emerge. The cultivars that were the
least susceptible to tuber infections, Bzura and Russet Burbank, had the lowest
levels of seed piece decay resulting from seedborne inoculation by P. infestans and
these two cultivars had the lowest transmission frequencies compared to the other
cultivars. Furthermore, seedborne inoculum of both US-8 and US-il resulted in
seed piece decay, which in turn resulted in a slow rate of plant emergence and a
reduction in percent final emergence and plant vigor.
Emergence rate and aerial biomass has not been previously quantified for P.
infestans infected potatoes. Emergence rate and aerial biomass differed by cultivar
in response to US-8 and US-i 1, just as final emergence and seed piece decay did. It
is clear that the plant growth responses of emergence rate and aerial biomass are
70
linked to emergence and seed piece decay. Not only does seedborne inoculum of
these clonal lineages reduce emergence and increase seed piece decay, but it also
reduces the speed at which the plants emerge and how robustly they grow.
Reductions in plant vigor and rate of emergence have been shown in other
plant/pathogen systems. Duram wheat seed, for example, when infected with
Pyrenophora tritici-repentis (Died.), had reduced emergence rates, reductions in
above-ground dry matter per unit area, poor seedling emergence, and lower grain
yields (Fernandez et al., 1997).
The extent of seed piece decay is mediated by soil environmental
conditions. Non-inoculated seed pieces achieved 95% emergence -46-25 and -2430 days after planting in Oregon and Washington, respectively. At the two highest
inoculum densities (250 and 2500 sporangia per seed piece), average emergence
was 7.7 and 2.3% and 37.3 and 23.8% for US-S in Oregon and US-i 1 in
Washington, respectively. The percent seed piece decay for these inoculum
densities was 96.8 and 100% in Oregon and 78.1 and 99.6% in Washington. This
indicates that US-i 1 may be a less aggressive pathogen of the seed piece than US-
8, or the soil environment may have been more conducive in Washington for seed
piece decay by the soft rot bacteria.
The effect of seedborne inoculum of P. infestans on final emergence,
emergence rate, aerial biomass, and seed piece decay were cultivar and inoculum
density dependent and were significantly more pronounced in the US-li trials
compared to the US-8 trials. Seed piece decay and final emergence data support
71
previous studies which showed that planting infected seed pieces would result in
reduced stands and increased incidences of seed piece decay (Deahl, 1995;
Lambert and Currier, 1997; Plall et
al.,
1999), and the emergence rate and aerial
biomass data break new ground on the previously unknown effects of seedbome P.
infestans
on stand establishment and plant vigor of potato.
72
CHAPTER 5
SUMMARY
The changes in the Phytophthora infestans populations in the United States
over the past decade are a serious concern for the potato industry. Not only are the
newer clonal lineages insensitive to the fungicide metalaxyl, they have a shorter
latent period, produce more spores per lesion area, and are more destructive than
previous clonal lineages. As a result, late blight control strategies have become
more time consuming and costly. In order to evaluate the impact of these newer
clonal lineages of P. infestans as seedborne pathogens of potatoes, both greenhouse
and field studies were conducted.
Differences in the response of Russet Burbank and Russet Norkotah to
seedborne inoculum of the clonal lineages, US-8 and US-i 1, were significant.
Russet Burbank responded differentially to US-8 and US-li, whereas the more
susceptible cultivar, Russet Norkotah, responded similarly to both lineages. With
US-8 emergence failure was higher, emergence rates were slower, aerial biomass
was lower, and the incidence of seed piece decay was higher compared to US-Il.
To achieve the same level of response as US-8, higher amounts of seedborne
inoculum were needed.
Growth responses of Russet Burbank and Bzura were less impacted by the
effects of seedborne inoculum compared to the other cultivars. Seed to plant
73
transmission was greatest in those cultivars with the highest level of foliar
susceptibility to late blight. Regardless of degree of susceptiblity to the foliar phase
of late blight, cultivars that were less susceptible were also vulnerable to seedborne
transmission. Potato cultivar*inoculum density interactions were significant for
growth responses of final emergence, emergence rate, aerial biomass and seed
piece decay with both the US-8 and US-i i clonal lineages.
74
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Kirk, William W., Feicher, Kimberly J., Douches, David S., Niemira, Brendan A.,
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80
APPENDICES
81
APPENDIX A
SUPPLEMENTAL ANALYSES OF CHAPTER 3
Modified rye B agar:
Soak rye seed overnight in 500 ml distilled water
Macerate in blender 10-15 sec to break kernels
Microwave 3 mm on HIGH
Strain through cheesecloth and bring volume to 1 L
Add 15 g Bacto-agar
Add 2 g sucrose
Stir
Autoclave 15-18 mm at 120 °C
Cool to 55 °C
Pour
82
100
80
60
40
20
0
100
C)
1)
L20
0
r1ffl
100
80
60
40
20
Russet Burbank Russet Norkotah
Cultivar
US-li
US-8
Clonal lineage
Fig. A. 1. Percent final emergence of potato cultivars Russet Burbank (RB) and
Russet Norkotah (RN) as affected by isolates of the clonal lineages US-8 and US11 of Phytophthora infestans averaged over inoculum density applied to seed
pieces. Inoculum density ranged from 25-400 sporangialseed piece in Trial 1 (A,
D) to 50-800 sporangialseed piece in Trials 2 and 3 (B, E and C, F, respectively).
Within potato cultivar or pathogen clonal lineage, bars with the same letter did not
differ significantly according to Fisher's protected least significant difference
(LSD) test (P<0.05).
83
Fig. A.2. Effect of inoculum density of isolates of the clonal lineages US-8 or US11 of Phytophthora infestans on emergence rate (r), % emergence/day, of potato
cvs Russet Burbank (RB) and Russet Norkotah (RN) in A-D, Trial 1; E-H, Trial 2;
and I-L, Trial 3. Seed pieces were inoculated with a sporangial suspension and
immediately planted.
84
100
,-. 80
60
ARB:US-8 ro = 22.7
r0
a)
El
A50
xlOO
a)
40
r100=9.8
x-
0400;
20
X
0
I
9
8
--
r400= 1.6
r800
-
4
0- -------
x_ ---------
I
10
11
A
=0
7.4
r800 =
r400=2.1
--
-0
0
13.2
G
r400
*
A
r100='21
0
r = 24
r50 = 16
r50= 16.4
r50= 13.7 A
L.
x_
r0=21.4
r25-17.30
'025
LJ:8
RIUS8JII800
ri:
12
9
10
11
12
13
12
9
0--- --0---i
S
13
14
15
16
100
'J RB:US-11
BRB:US-11
.-.. 80
r25-24.4
r0=22.7
60
r50=21.6
a)
A
r0=24
-6
P40
a)
/7
r,00=
r50=18.2
r100=
/
20
r50=22
r0=21.4
17.4
19.6
0-
15.4
19.4
r800= 16.6
r400=
0
10
9
8
11
12
9
I
I
I
10
11
12
r800=8.6
13
12
14
13
15
16
100
9RN:US-8
RN:US-8
- 80
r0
r0= 19.8
r0= 10
r25
r0= 16.6
r50=3.6
= 21.4
= 22.5
r50 = 21.6
60
a)
r100= 19.2/
/ ci
E
20
K RN:US-8
r100= 17.4
*
4-
o
r40=2.8
r100
= 0.4
r8=2.8
0
r400 = 12.3
0
----A
0
8
9
10
11
12
9
10
12
11
13
12
-i
.-
14
15
13
16
100
DRN:US-11
-- 80
r0=21.4
60
a)
a)
r0 = 19.8
0--
40 r50= 19.8
r100= 15 A
r1oo= 19.8
r00
11.4
20
r0
r50=13.2
r25 = 18.8
--
r-
r100
9
6.8
-------1-
9
10
11
12
9
10
11
12
Days after planting
Fig. A.2.
1.2
r4000.4
r800 =
0
8
10
r504.8
13
12
13
---.--
14
15
16
a
d
_±L
20
A
b
_L
15
I)
h r
b
10
U
-
20
0
25
20
15
10
0
Russet Burbank Russet Norkotah
Cultivar
US-8
Cional
US-Il
lineage
Fig. A.3. Percent emergence/day, r, of potato cultivars Russet Burbank (RB) and
Russet Norkotah (RN) as affected by isolates of the clonal lineages US-8 and US11 of Phytophthora infestans averaged over inoculum density applied to seed
pieces. nocu1um density ranged from 25-400 sporangia/seed piece in Trial 1 (A,
D) to 50-800 sporangialseed piece in Trials 2 and 3 (B, E and C, F). Within cultivar
or clonal lineage, bars with the same letter did not differ significantly according to
Fisher's protected least significant difference (LSD) test (P<0.05).
0 5
0.4
0.3
0.2
0.1
0
0.5
'c,
U..)
[I
0.5
DUS-8
0.4
c
IUs-1l
0.3
a
0.2
h
a
a
0
Russet Burbank Russet Norkotah
Cultivar
US-8
US-li
Clonal lineage
Fig. A.4. Plant aerial biomass of potato cultivars Russet Burbank (RB) and Russet
Norkotah (RN) as affected by isolates of the clonal lineages US-8 and US-li of
Phytophthora infestans averaged over inoculum density applied to seed pieces.
Inoculum density ranged from 25-400 sporangia/seed piece in Trial I (A, D) to 50800 sporangia/seed piece in Trials 2 and 3 (B, E and C, F). Within potato cultivar
or clonal lineage, bars with the same letter did not differ significantly according to
Fisher's protected least significant difference (LSD) test (P<0.05).
87
100
80
60
40
20
[i
100
'-' 80
>
IE
0
100
C
80
a
a
60
40
20
0
Russet Norkotah
Cultivar
Russet Burbank
US-8
US-I I
Clonal lineage
Fig. A.5. Seed piece decay of potato cultivars Russet Burbank (RB) and Russet
Norkotah (RN) as affected by isolates of the clonal lineages US-8 and US-i 1 of
Phytophthora infestans averaged over inoculum density applied to seed pieces.
Inoculum density ranged from 25-400 sporangialseed piece in Trial I (A, D) to 50800 sporangia/seed piece in Trials 2 and 3 (B, E and C, F). Within cultivar or clonal
lineage, bars with the same letter did not differ significantly according to Fisher's
protected least significant difference (LSD) test (P0.05).
Table A. 1. Comparison of significant differences between estimated intercept and
slope parameters for regression of emergence, emergence rate, aerial biomass and
seed piece decay responses of potato cvs Russet Norkotah and Russet Burbank on
increasing inoculum concentrations of isolates of clonal lineages US-8 and US-Il
of Phytophthora infestans.
Regression parameter estimate
Slope
Intercept
Trial:
1
2
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
*
3
1
2
3
Emergence failure
Burbank/US-I I vs.
NorkotahfUS-Ii
BurbanklUS-8 vs.
Norkotah/US-8
Norkotah/US-l1 vs.
Norkotah!US-8
Burbank/US-ilvs.
BurbankfUS-8
Emergence rate
Burbank/US-li vs.
Norkotah!US-i 1
Burbank/US-8 vs.
Norkotah/US-8
NorkotahlUS-I I vs.
Norkotah/US-8
Burbank/US-I 1 vs.
BurbanklUS-8
*
*
0.03 15
NS
0.0652
NS
*
NS
<0.0001
NS
NS
NS
NS
NS
*
*
*
0.0003
0.0001
0.0725
*
*
*
*
0.0287
0.0009
0.0776
0.0854
0.0738
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
*
0.018
NS
*
0.0474
NS
*
*
*
0.0929
0.0389
0.0652
*
*
*
0.0007
0.0025
0.00 17
*
*
0.0277
0.0052
NS
Aerial biomass
Burbank/US-I 1 vs.
Norkotah/US-1 1
Burbank!US-8 vs.
Norkotah/US-8
Norkotah/US-i I vs.
Norkotah/US-8
Burbank/US-lI vs.
*
0.0067
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
*
*
*
0.0003
0.0812
0.0026
*
*
Burbank/US-8
Seed piece decay
Burbank/US-il vs.
0.0085
Norkotah/US-1 1
Burbank/US-8 vs.
Norkotah!US-8
0.0069
Norkotah/US-1i vs.
Norkotab/US-8
Burbank/US-il vs.
Burbank/US-8
NS
*
NS
*
*
*
*
0.0005
0.0072
0.00 13
0.0060
NS
NS
NS
NS
*
*
NS
NS
NS
NS
NS
*
*
0.0335
0.0718
0.0010
*
0.0234
0.0022
NS
0.0163
*
*
0.0008
0.0583
NS = not significant at P<O.1O; * = significant at indicated value.
NS
Table A.2. Emergence of seed pieces of potato cultivars Russet Burbank and
Russet Norkotah inoculated with sporangia of isolates of clonal lineages US-8 and
US-li of Phytophthora infestans. Seed pieces were inoculated with 25, 50, 100, or
400 sporangia per seed piece in Trial 1, and 50, 100, 400, or 800 sporangia per seed
piece in Trials 2 and 3, and immediately planted.
Emergence by treatment
Russet Norkotah
Russet Burbank
US-i 1
US-8
US-i 1
US-8
Trial
168/200
170/200
177/200
108/200
78%
84%
85%
88.5%
54%
135/200
98/200
196/200
142/200
2T
71%
67.5%
49%
98%
71%
23/200
18/200
50/200
135/200
3NT
28%
11.5%
67.5%
9%
25%
ININO transmission was found; transmission occurred; RB, Russet Burbank; RN,
Russet Norkotah.
Overall emergence
of P. infestansinoculated seed pieces
Table A.3. General linear model significance values for emergence, emergence
rate, aerial biomass, and seed piece decay interactions and main effects of cultivars
Russet Burbank (RB) and Russet Norkotah (RN) inoculated with a range of
sporangia of isolates of clonal lineages US-8 and US-il of Phytophthora infestans
in three trials.
Treatment
Interaction or main effect
I
Trial 1
Trial 2
Trial 3
<0.0001
<0.0001
0.0001
<0.0001
<0.000 1
<0.000 1
<0.000 1
<0.0001
<0.0001
<0.0001
0.003 1
<0.000 1
<0.000 1
<0.0001
0.6348
0.4794
<0.0001
<0.0001
0.0002
0.0064
0.4 190
Emergence
All
RB only
RN only
US-S only
US-i 1 only
Cultivar*Clonal lineage* Inoculum density
Inoculum density
Clonal lineage
Clonal lineage*Inoculum density
Inoculum density
Clonal lineage
Clonal lineage*Inodulum density
Inoculum density
Cultivar
Cultivar*Inoculum density
Inoculum density
Cultivar
Cultivar*Inoculum density
<0.000 1
<0.000 1
<0.0001
0.0032
0.0005
0.2204
<0.0001
0.0 145
0.00 10
0.000 1
0.0365
0.9738
<0.0001
<0.0001
0.049 1
<0.000 1
<0.0001
0.3883
Emergence Rate
All
RB only
RN only
US-8 only
US-i I only
Cultivar*Clonal lineage*lnoculum density
Inoculum density
Clonal lineage
Clonal lineage*Inoculum density
Inoculum density
Clonal lineage
Clonal lineage*lnoculum density
Inoculum density
Cultivar
Cultivar*Inoculum density
Inoculum density
Cultivar
Cultivar*Inoculum density
0.0257
0.0002
<0.0001
0.0073
<0.0001
0.2784
0.7223
<0.0001
<0.0001
0.5057
0.0724
0.0024
0.0620
0.0062
0.00 14
0.0074
0.0536
<0.0001
0.4448
0.0004
<0.0001
<0.0001
0.0 108
0.0007
0.3576
0.9308
0.06 15
<0.000 1
<0.000 1
0.0021
0.0836
0.0598
<0.0001
0.3796
<0.0001
<0.0001
0.0002
<0.0001
0.6906
0.0002
0.8975
0.0695
0.1704
0.0007
Aerial biomass
All
RB only
RN only
US-8 only
US-li only
Cultivar*Clonal lineage*Inoculum density
Inoculum density
Clonal lineage
Clonal lineage*Inoculum density
Inoculum density
Clonal lineage
Clonal lineage*Inoculum density
lnoculum density
Cultivar
Cultivar*lnoculum density
Inoculum density
Cultivar
Cultivar*Inoculum density
0.0209
0.05 12
0.2316
0.0296
0.1855
0.15 12
0.0903
0.0184
0.0219
0.0 153
0.4440
0.8608
0.32 19
<0.000 1
0.6993
0.2325
0.0012
0.0056
0.0400
0.0020
<0.0001
<0.0001
0.00 16
<0.0001
0.0046
<0.0001
0.4800
0.5898
<0.0001
<0.0001
0.0062
0.253 1
<0.0001
0.4897
I
91
Table A.3. (Continued.)
Treatment
All
RB only
RN only
US-8 only
US-1 1 only
Interaction or main effect
Seed piece decay
Cultivar*Clonal lineage*Inoculum density
Inoculum density
Clonal lineage
Clonal lineage *Inoculum density
Inoculum density
Clonal lineage
Clonal lineage *Inoculum density
Inoculum density
Cultivar
Cultivar*Inoculum density
Inoculum density
Cultivar
Cultivar*Inoculum density
Trial 1
Trial 2
Trial 3
<0.0001
0.0236
0.0117
0.0004
<0.0001
0.0569
0.0402
0.0001
0.0774
<0.0001
0.0009
0.4667
0.0023
0.1694
0.0549
0.00 1 1
<0.0001
0.1478
0.0020
<0.0001
0.9299
<0.0001
0.0021
0.0015
<0.0001
0.8433
0.0005
<0.0001
<0.000 1
<0.000 1
<0.0001
0.0533
<0.000 1
<0.000 1
0.0042
0.2087
0.0079
<0.0001
0.1835
Table A.4. Comparison of percent emergenc&' of potato cvs Russet Burbank (RB) and Russet Norkotah (RN) seed pieces
inoculated with increasing sporangial densities of Phytophthora infestans clonal lineages US-8 or US-li (left), and the
percent change in emergence compared to the control (right).
Cultivar/
Clonal lineage
Inoculum density (sporangialseed piece)
OC
25
50
100
400
800
25
50
100
400
800
Trial_1
RB
US-8
US-il
98 A
98 A
84 B
72 C
96 A
90 A
92 A
92 A
94 A
94 A
92 A
50 D
84 A
10 E
-14.3
-26.5
-49
-89.8
84 A
-2.0
-8.2
-14.3
-14.3
64 B
+2.2
-0
-2.2
-30.4
58 B
+2.2
-6.5
+4.3
-37
-12
-10
-34
-58
-
-2.0
-0
-2.0
-4.0
RN
US-8
US-I 1
86 A
90 A
96 A
Trial2
RB
US-8
IOOA
88A
90A
66B
42C
US-I 1
100 A
98 A
100 A
98 A
96 A
US-8
US-Il
100 A
82 B
80 B
18 C
16 C
-18
-20
-82
-84
100A
84AB
82B
60C
44C
-16
-18
-40
-56
-36
-74
-90
-100
-12
-24
-30
-64
RN
Trial 3
RB
US-8
100A
64B
26C
1OD
OD
US-I 1
100 A
88 AB
76 BC
70 C
36 D
US-8
US-Il
98 A
98 A
30 B
6 C
0 C
0 C
-69.4
-93.9
-100
-100
34 B
10 C
2 C
0 C
-65.3
-89.8
-98
-100
-
RN
aEmergence values within horizontal rows followed by the same letter are not significantly different (P<0.05) according to
Fisher's protected least significant difference (LSD) test. Not tested; econtrol values are repeated for both US-8 and US-i 1
for comparison against other inoculum densities.
93
Table A.5. Comparison of percent final emergenc&' for Russet Burbank (RB) and
Russet Norkotah (RN) inoculated with sporangia of Phytophthora infestans clonal
lineages US-8 or US-il.
Cultivar/
Clonal lineage
0
Inoculum density (sporangialseed piece)
400
100
25
50
Trial 1
98A
RB
US-8
US-il
84B
96A
72B
9OAB
50C
84B
94A
94A
92A
9OAB
86AB
96A
800
bC
84A
92A
RN
US-8
US-li
64B
58B
Trial2
100A
RB
US-8
88 AB
90 AB
66 B
42 B
US-il
98A
100A
98A
96A
82B
84B
Trial 3
80B
82B
18C
60B
16C
44B
64B
88A
26B
76A
lOB
OB
70A
36A
30C
34C
6C
OB
100A
RN
US-8
US-li
100A
RB
US-8
US-li
98A
RN
OB
OB
bC
2B
US-li
aEmergence values within vertical columns followed by the same letter are not
significantly different (P<0.05) according to Fisher's protected least significant
US-8
difference (LSD) test. Not tested.
Table A.6. Comparison of emergence ratesa (% emergence/day) of potato cultivars Russet Burbank (RB) and Russet
Norkotah (RN) inoculated with increasing sporangial densities of Phytophthora infestans clonal lineages US-8 or US-li
(left), and percent change in emergence rate compared to the control (right).
Cultivar/
Clonal lineage
0
25
50
Inoculum density (sporangia/seed piece)
25
400
800
100
50
100
400
800
Trial_1
RB
US-8
US-lI
24.4A
18B
14.2BC
10.2C
2.2D
-26.2
-41.8
-58.2
-91
24.4 A
25.4 A
22.4 A
20.8 A
22.6 A
+4.1
-8.2
-14.8
-7.4
US-8
US-Il
22A
22A
23.4A
19.6A
22.4A
20.6A
20A
12.8B
11.8B
+6.4
+1.8
-9.1
-41.8
20.6A
-10.9
-6.4
-6.4
-46.4
RN
Trial 2
RB
13.2BC
19.4A
7.4C
16.6A
-23.4
-1.9
-38.3
-65.4
-15
-8.4
-9.3
-22.4
17.4 A
2.8 B
2.8 B
-16.2
-12.1
-85.9
-85.9
15 AB
9.2 BC
6.8 C
-33.3
-24.2
-53.5
-65.7
16.4AB
18.2A
19.6A
19.8 A
16.6 A
19.8 A
13.2 BC
US-8
US-Il
21.4 A
US-8
US-Il
21.4A
21 A
RN
Trial_3
RB
US-8
US-il
24 A
16 B
4.8 C
1.6 D
0 D
-33.3
-80
-93.3
-100
24A
22AB
17.4BC
15.4C
8.6D
-8.3
-27.5
-35.8
-64.2
RN
0.4BC
OC
l.2C
0.4C
-100
-96
-100
-64
OC
-96
-100
-52
-88
OC
rows
followed
by
the
same
letter
are
not
significantly
different
(P<0.05)
according
aEmergence rate values within horizontal
to Fisher's protected least significant difference (LSD) test. -Not tested; ccontrol values are repeated for both US-8 and USii for comparison against other inoculum densities.
US-8
US-Il
IOA
bA
3.6B
4.8B
95
Table A.7. Comparison of emergence ratesa (% emergence/day) for Russet Burbank
(RB) and Russet Norkotah (RN) inoculated with sporangia of Phytophthora
infestans clonal lineages US-8 or US-i 1.
Cultivar/
Clonal lineage
0
Inoculum density (sporangialseed piece)
400
100
25
50
Trial 1
800
24.4 A
RB
18 B
14.2 B
10.2 B
25.4 A
22.4 A
20.8 A
2.2 C
22.6 A
US-8
23.4 AB
22.4 A
20 A
12.8 B
US-li
i9.6B
20.6A
11.8B
US-8
US-li
22.0 A
RN
20.6AB
Trial 2
21.4A
RB
US-8
16.4 A
7.4 B
18.2A
21 A
19.6AB
13.2 AB
US-li
19.4A
16.6A
16.6 A
13.2 A
17.4 AB
15 B
2.8 C
9.2 B
2.8 B
6.8 B
1.6B
15.4A
8.6A
19.8 A
RN
US-8
US-li
Trial 3
24.0 A
RB
US-8
16B
US-li
22A
4.8B
i7.4A
3.6C
0.4C
OB
10.0 B
RN
OB
OB
0B
0.4 B
1.2 C
4.8 C
US-li
aEmergence rate values within vertical columns followed by the same letter are not
significantly different (P<0.05) according to Fisher's protected least significant
difference (LSD) test. -Not tested.
US-8
Table A.8. Comparison of mean emergence rates (% emergence/day), regardless of
inoculum density (not including controls), for Russet Burbank (RB) and Russet
Norkotah (RN) inoculated with isolates of clonal lineages US-8 or US-li in 3
greenhouse trials.
Trial 3
Trial 2
Trial 1
Cultivar/
US.lic
us8*
US8*
US8*
us-.ii
USi1'
Clonal lineage
18.45
15.85'
14.5'
5.6'
22.8'
RB 11.15'
1.6
11.05
1.0
9.9
18.15
RN
19.65
*Cultivars differ significantly (P0.05); 'clonal lineages differ significantly
(P<O.05).
Table A.9. Comparison of average aerial biomass per planta (dry, g) for Russet Burbank (RB) and Russet Norkotah (RN)
inoculated with increasing sporangial densities of Phytophthora infestans clonal lineages US-8 or US-li (left), and the
percent change in aerial biomass compared to the control (right).
Cultivar/
Clonal lineage
Oc
25
50
Inoculum density (sporangia/seed piece)
25
400
800
100
50
100
400
+11.3
+3.1
+4.1
+3.1
+2.3
-1.0
-44.2
-7.0
-2.0
-7.9
-4.7
+4.3
-7.7
-22.1
-
800
Trial_1
RB
US-8
US-il
0.391 A
0.391 A
0.435 A
0.407 A
0.400 A
0.218 B
0.403A
0.403A
0.387A
0.407A
0.444 AB
0.4 13 B
0.409 B
0.463 A
0.4IOAB
0.426 AB
+4.1
-
RN
US-8
US-Il
0.444A
0.435A
0.423A
0.346B
-4.1
Trial 2
RB
US-8
US-i 1
0.346A
0.358A
0.355A
0.322A
0.318A
0.346 A
0.358 A
0.344 A
0.388 A
0.369 A
+3.5
+3.5
+2.6
-0.6
-6.9
+12.1
+6.6
US-8
0.366 A
0.366 A
0.343 A
0.358 A
0.366 A
0.331 A
0.132 B
0.241 B
0.200 B
0.156 C
-6.3
-2.2
-0
-9.6
-63.9
-34.2
-45.4
-57.4
-8.1
RN
US-Il
Trial 3
RB
O.208A
0.208 A
-
US-I 1
US-8
0.072 A
-
US-8
O.194A
0.224 A
0.180A
0.223 A
O.044B
0.216 A
OB
0.167 A
-6.7
+7.7
-13.5
+7.2
-78.8
+3.8
-100
-19.7
0.052 B
0.012 C
0C
0C
-27.8
-83.3
-100
-100
RN
-94.4
-100
-31.9 -59.7
0.004C
0.049AB
0.029BC
OC
0.072A
US-li
aAerial biomass values within horizontal rows followed by the same letter are not significantly different (P<0.05) according
to Fisher's protected least significant difference (LSD) test. -Not tested; ccontrol values are repeated for both US-8 and US11 for comparison against other inoculum densities.
98
Table A. 10. Comparison of average aerial biomass per planta (dry, g) of Russet
Burbank (RB) and Russet Norkotah (RN) inoculated with increasing sporangial
densities of Phytophthora infestans clonal lineages US-8 or US-li.
Cultivar!
Clonal lineage
0
Inoculum density (sporangialseed piece)
100
400
50
25
800
Trial 1
0.391 B
RB
0.435 A
0.403 A
0.407 A
0.403 A
0.400 B
0.2 18 B
0.3 87 B
0.407 A
US-8
0.4 13 A
US-li
0.435 A
0.409 A
0.423 A
0.463 A
0.410 AB
0.426 A
0.346 AB
US-8
US-li
0.444 A
RN
Trial 2
0.346 A
RB
US-8
0.358 A
0.355 A
0.322 AB
0.318 AB
US-il
0.358A
0.344A
0.388A
0.369A
0.343 A
0.358 A
0.366 A
0.331 A
0.132 C
0.241 BC
0.200 BC
0.156 C
0.180 A
0.223 A
0.044 B
0.216 A
OB
0.167 A
0.366 A
RN
US-8
US-li
Trial 3
0.208 A
RB
0.194 A
0.224 A
US-8
US-il
RN
0.072 B
0.0 12 B
0B
0B
0.052 B
US-8
0.029 B
0.004 B
0B
0.049 B
US-i 1
aAverage aerial biomass values (dry, g) within vertical columns followed by the
same letter are not significantly different (P0.05) according to Fisher's protected
least significant difference (LSD) test. -Not tested.
)
Table A. 11. Comparison of percent seed piece decaya of Russet Burbank (RB) and Russet Norkotah (RN) inoculated with
increasing sporangial densities of Phytophthora infestans clonal lineages US-8 or Us-i 1 (left), and percent change in seed
piece decay compared to the controls (right).
Cultivar/
Clonal lineage
Inoculum density (sporangia/seed piece)
800
25
50
100
400
Trial_1
OC
25
50
US-8
US-i 1
36D
52CD
56C
76B
94A
36 B
64 A
52 AB
66 A
US-8
2013
18B
16B
US-Il
20B
22B
26B
18B
lOB
100
400
800
RB
47 AB
+44.4
+77.8
+55.6
+44.4
+111.1
+83.3
+161.1
+30.6
52A
82A
-10
+10
-20
+30
-10
-50
+160
+310
RN
Trial2
RB
US-8
US-Il
26 C
26 AB
44 BC
42 BC
10 B
16 B
4C
4D
20B
52C
2013
58 AB
22 AB
70 A
36 A
+69.2
-61.5
+61.5
-38.5
+123.1
-15.4
+169.2
+38.5
86A
74B
84A
94A
+400
+1200
+400
+900
+2050
+1750
+2000
+2250
100 A
98 A
+6.9
-10.3
+37.9
-6.9
+69
+34.5
+72.4
+69
RN
US-8
US-Il
40C
Trial3
RB
US-8
Us-i 1
58 C
58 C
62 C
52 C
80 B
54 C
98 A
78 B
RN
+900
+840
+900
100A
+700
94A
100A
80B
+900
+820
+900
IOOA
+840
92A
IOOA
94A
US-Il
aSeed piece decay values within horizontal rows followed by the same letter are not significantly different (P<0.05)
according to Fisher's protected least significant difference (LSD) test. Not tested; ccontrol values are repeated for both US8 and US-i 1 for comparison against other inoculum densities.
US-8
IOC
lOB
101
APPENDIX B
SUPPLEMENTAL ANALYSES OF CHAPTER 4
102
Fig. B.1. Final percent emergence failure of potato cultivars Bannock Russet (BR),
Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank
(RB), Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR) inoculated
with a range of inoculum densities of Phytophthora infestans with A) zoospores of
US-8 in Oregon in 1999; B) sporangia of US-8 in OR in 1999; C) sporangia of US8 in OR in 2000; D) zoospores of US-i 1 in Washington in 1999; E) sporangia of
US-il in WA in 1999; and F) sporangia of US-i 1 in WA in 2000. Within trial,
bars with the same letter did not differ significantly according to Fisher's protected
least significant difference (LSD) test (P0.05). Values are means of seed pieces
inoculated with 2.5, 25, and 250 sporangia or zoospores per seed piece in 1999
trials, and 50, 100, 400, and 800 sporangia per seed piece in 2000 trials.
103
100
80
60
40
20
0
BZ
KE
RB
RN
SH
BZ
KE
RB
RN
SH
BZ
KE
RB
RN
SH
BZ
KE
RB
RN
SH
100
60
20
0
cc
100
80
cd
b
-
c
d
60
a
40
20
0
b
11n
BR BZ CH RR RN SH UR
Cultivar
Fig. B.1.
H
BR CH RB RN SH UR
Cultivar
104
Fig. B.2. Emergence rate (% emergence/day) of potato cultivars Bannock Russet
(BR), Bzura (BZ), Chieftain (CII), Kennebec (KE), Ranger Russet (RR), Russet
Burbank (RB), Russet Norkotah (RN), Shepody (Sn), and Umatilla Russet (UR)
inoculated with increasing zoospore or sporangial densities of Phytophthora
infestans clonal lineagesUS-8 in Oregon (A-M and AA-AD) and US-il in
Washington (N-Z and AE-AG) in 1999 and 2000. Seed pieces were inoculated and
immediately planted.
105
'UI,
80
C)
60
C)
40
20
0
I
I
23
11
I
II
13
15
17
21
19
o'--'r
13
15
17
21
19
I IJU
23
1*
13
15
17
19
21
23
25
r,,=9.5
80
00
60
C)
r25=77
40
250"
I
r2501
-$id
0 Ld
11
r250=0.48
0
r25,,,,=0
20-I
D
±
r25=2.7
DD
13
15
17
19
23
21
11
13
15
17
19
21
=0
23
Fig. B.2.
I UI,
80
60
40
20
0
11
13
15
17
19
21
23
11
13
15
17
19
21
23
I VU
80
C)
U
60
40
r250 = 0.11 0*
20
=0
r250
MRUNMR$
I
0
11
13
15
17
19
21
23
17
19
21
23
11
13
15
r,
= 7.
r100
= 6.
I
17
19
21
23
17
19
21
23
I
--
13
15
17
19
21
23
25
17
19
21
23
25
WV
80
C)
U
60
C)
E
40
20
0
11
13
15
Days after planting
11
13
15
Days after planting
13
15
Days after planting
106
100
tO
N BZ:US-1 Iz
= 9.3
t1
80
r07.8
OXXX
x
D2.5
60
r25= 10.1
r25=7.7
25
x250
40
X
o25ooa
r250-54
r257.0
o9.00
RR
._-X_
20
r25=7.7
r2500=3.2
r50 = 3.4
r255() = 2.9
0
18
20
22
24
26
30
28
22 24 26 28 30 32 34 36
Fig. B.2.
IUU
ro5.7
TKE:US-ii
KE:US-I 1z
80
(Continued.)
r0-4.7
0.000
60
r25-3.8
I5=4.8
-
40
r5=3.
A-A
..ø
20
r250=0.14
1250= 0.18
0
18
20
22
24
26
28
30
22 24 26 28 30 32 34 36
lUtJ
C)
XRB:US-11
URUS1
80
C)
r50=5.4
X400 000D
A r1004.8
= 9.2
r
60
0r0=9,8
0
*0
100J
10.3
r25
r250 = 7.7
x xO
0op
18
20
r4fl()
22
24
26
28
30
22 24 26 28 30 32 34 36
20
23
29
26
32
I Ut.)
r0-
VRN:US-11
80
*
,D
a
om,'i*.
20
22
24
ci
0
*
*
0
r25=2.0
r0=12.2
*
r50 = 0.58
r,=0
AAAA r2500
duitiiiiuiiuii*u.
26
28
30
22 24 26 28 30 32 34 36
IUU
,
U
*
* r25=5.
60
35
0
,YR.N:US11C
00
C)
18
37
r250=5.0
i:1i1
80
20
ro9.
23
26
Lzi;s.:i21
29
32
35
ro=:.6*f
-
60
r25=8.7
40
r25=5.0 /
WA
20
00 r5=O
r2500.61
*0 0
r,50=O.16
0
18
20
22 24 26 28
Days after planting
30
22 24 26 28 30 32 34 36
Days after planting
20
29
32
26
Days after planting
23
35
107
"iv
80
60
40
20
0
'
I
13
17
15
19
100,
,
0
I
23
26
29
32
35
20
23
26
29
32
35
20
23
26
29
32
35
20
I
I
I
I
25
23
21
I
80
I-
40
20
0
13
15
19
17
100
'-
21
23
25
r0
15.0
0
ACRR:U_8s
80
0
r505.7
0
-
60
r,00-
40
r,00
xx
20
r800
= 2.8
1.9
19
0
13
15
17
19
21
23
25
21
23
25
I IJU
80
60
0
40
20
0
13
15
17
19
Days after planting
Fig. B.2.
Days after planting
108
Fig. B .3. Mean emergence rate (% emergence/day) of potato cultivars Bannock
Russet (BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR),
Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and Umatilla Russet
(UR) inoculated with a range of inoculum densities of Phytophthora infestans with
A) zoospores of clonal lineage US-8 in Oregon in 1999; B) sporangia of US-8 in
OR in 1999; C) sporangia of US-8 in OR in 2000; D) zoospores of US-i 1 in
Washington in 1999; E) sporangia of US-li in WA in 1999; and F) sporangia of
US-li in WA in 2000. Within each trial, bars with the same letter did not differ
significantly according to Fisher's protected least significant difference test
(P<0.05). Values are means of seed pieces inoculated with 2.5, 25, and 250
sporangia or zoospores per seed piece in 1999 trials, and 50, 100, 400, and 800
sporangia per seed piece in 2000 trials.
109
12
10
8
6
4
2
0
BZ
KE
RB
RN
SH
BZ
KE
RB
RN
SH
12
-
10
a
-a
b
I:
b
C
bc
fln
- __________
0
BZ
KE
RB
RN
SH
BZ
RB
KE
RN
SH
12
10
8
6
Hd
C
4
2
0
Fig. B.3.
a
H
_uriH L--1
11,
b
c
[1
BR BZ Cl-I RR RN SH UR
BR CH RB RN SH UR
Cultivar
Cultivar
110
Fig. B.4. Mean aerial biomass per plant of potato cultivars Bannock Russet (BR),
Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank
(RB), Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR) inoculated
with a range of inoculum densities of Phytophthora infestans with A) zoospores of
clonal lineageUS-8 in Oregon in 1999; B) sporangia of US-8 in Oregon in 1999; C)
sporangia of US-8 in Oregon in 2000; D) zoospores of US-i 1 in Washington in
1999; E) sporangia of US-li in Washington in 1999; and F) sporangia of US-li in
Washington in 2000. Within each trial, bars with the same letter did not differ
significantly according to Fisher's protected least significant difference test
(P<0.05). Values are means of seed pieces inoculated with 2.5, 25, and 250
sporangia or zoospores per seed piece in 1999 trials, and 50, 100, 400, and 800
sporangia per seed piece in 2000 trials.
111
40
20
10
0
BZ
KE
RB
RN
SH
BZ
KE
RB
RN
SH
BZ
KE
RB
RN
SH
BZ
KE
RB
RN
SH
4o
20
E
C
10
40
30
20
a
10
b
(-1I
0
BR BZ CH RR RN SH UR
Cultivar
Fig. B.4.
1C,
C1
BR CH
RB
c
RN SH UR
Cultivar
112
Fig. B.5. Mean seed piece decay of potato cultivars Bannock Russet (BR), Bzura
(BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB),
Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR) inoculated with a
range of inoculum densities of Phytophthora infestans with A) zoospores of clonal
lineageUS-8 in Oregon in 1999; B) sporangia of US-8 in Oregon in 1999; C)
sporangia of US-8 in Oregon in 2000; D) zoospores of US-il in Washington in
1999; E) sporangia of US-il in Washington in 1999; and F) sporangia of US-li in
Washington in 2000. Within each trial, bars with the same letter did not differ
significantly according to Fisher's protected least significant difference test
(P<O.05). Values are means of seed pieces inoculated with 2.5, 25, and 250
sporangia or zoospores per seed piece in 1999 trials, and 50, 100, 400, and 800
sporangia per seed piece in 2000 trials.
113
100
80
60
40
20
0
BZ
KE
RB
RN
SH
BZ
KE
RB
RN
SH
BZ
KE
RB
RN
SH
BZ
KE
RB
RN
SH
nh:
,80
7.)
r-)
40
.
1.)
J.)
rID
0
100
aFa
a
80
,
a
b
60
C
40
20
0
Fig. B.5.
BR BZ CH RR RN SH UR
BR CH RB RN SR UR
Cultivar
Cultivar
114
Table B. 1. Reference information for the six seedborne Phytophthora infestans
field trials conducted in Oregon and Washington.
Clonal
lineage
Spore
type
Zoospore
Cv
BZ
US-8
KE
RB
RN
SH
Sporangia BZ
Corvallis,
US-8
2
KE
OR
RB
RN
SH
US-il Sporangia BZ
Mount
3
KE
Vernon,
RB
WA
RN
SH
US-li Zoospore BZ
Mount
4
KE
Vernon,
RB
WA
RN
SH
Sporangia BR
Corvallis,
US-8
5
BZ
OR
CH
RR
RN
SH
UR
Sporangia
BR
Mount
US-il
6
CH
Vernon,
RB
WA
RN
SH
UR
aID = inoculum density, spores/seed piece.
Trial
Location
Corvallis,
OR
I.D.a
0
2.5
25
Plant
day
Dry
Factorial
design
5x5x5
Dry
5x5x5
Dry
5x4x5
May
24
July 19
1999
Dry
5x4x5
May
Dry
7x5x5
Wet!
Rain
6x4x5
Dates
May
20July7
250
2500
1999
0
June 3
2.5
25
250
-July
20
1999
2500
0
2.5
25
250
2500
0
2.5
25
250
2500
May
11
July7
1999
0
50
100
July 5-
400
800
2000
176
0
50
100
May 4
-June
400
800
2000
26
115
Table B.2. Cumulative totals of seed piece to plant transmission of late blight
across a range of sporangia and zoospore inoculum densities (spores per seed piece)
in six field studies.
Clonal lineage!
Cultivar
US-8
Bannock Russet
Bzura
Chieftain
Kennebec
Ranger Russet
Russet Burbank
Russet Norkotah
Shepody
Umatilla Russet
Total
2.5
25
Inoculum density
400
50
100 250
800
2500
1
1
1
1
0
0
2
2
1
1
2
1
Total
4
2
6
13
0
1
1
0
2
2
5
0
5
6
0
20
Us-il
Bannock Russet
Bzura
Chieftain
Kennebec
Russet Burbank
Russet Norkotah
Shepody
Umatilla Russet
Total
Not tested.
0
0
0
0
1
3
5
5
4
1
4
0
12
1
0
91
1
0
1
0
0
116
Table B.3. Number of days after planting and emergence (dap and dae) that seed
piece to plant transmission occurred, and the transmission rates (%) in field trials in
Oregon (US-8) and Washington (US-i 1) in 1999 and 2000.
Lineage!
Year!Cv
IJS-8
4 of
Inoculum density (sporangia or zoospores per seed piece)
400
100
250
50
Transmission Events
25
2
23&26dae
800
1999
37 dap,
RB
2.33
2000s
50 dap,
BR
30dae
1
1.724
29 dap,
BZ
ldae
1
0.719
26dap,
RR
UR
4.255c
4.255c
l6dae
32-50 dap,
15-34dae
7.558
7.558c
35 dap,
RN
Sodap,
28dae
l0dae
2
13
& 41 dap,
18&23dae
39-47 dap,
7.558'
50 dap,
7.558c
35
24-35dae
34dae
1
0.472
Us-li
1999s
37 dap,
RB
l5dae
1
0.524
37 dap,
RN
9dae
2
4.878
37 dap,
SH
I3dae
I
1.389
1999
& 37 dap,
-16-18dae
35
RN
3
3.571
37 dap,
SH
3
l6dae
3.33
2000s
RB
2
34dap,
34dap,
-14dae
-i4dae
1.653'
1.653c
cCombined transmission frequency for multiple events within cultivar; 5sporangia;
zzoospores
Table B.4. Emergence of seed pieces of potato cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH), Kennebec
(KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and Umatilla Russet (UR)
inoculated with sporangia or zoospores of Phytophthora infestans in Oregon (US-8) and Washington (US-i 1). Seed pieces
were inoculated with 2.5, 25, 250, 2500 or 50, 100, 400, or 800 spores per seed piece and immediately planted.
Overall
Clonal
Overall translineage!
Year emerg. mission
US-8
Cultivar
BR
1999z
32%
0
-
1999s
34%
0.53
-
2000s
42%
2.4
1999z
52%
1.1
-
1999s
51%
0.75
-
2000s
16%
1.0
6/208
2.9%
58/2561
22.7%
BZ
84/240
35%
103/240
42.9%
139/180'
77.2%
CH
-
-
4/256
KE
51/240
21.3%
69/240
28.8%
-
1.6%
RR
oRB
-
102/240
42.5%
-
86/240'
35.8%
47/160'
29.4%
-
RN
SH
UR
76!239
31.8%
77/240
32.1%
172/256'
67.2%
72!239
30.1%
40/140
28.6%
51/256
19.9%
-
84/208T
901208T
40.4%
43.3%
72/208'
34.6%
-
212/256'
82.8%
Us-li
148/208
71.2%
171/208
82.2%
-
-
12/208
-
5.8%
-Not tested; Ssporangia; zzoospores; 'transmission occurred.
70/208
33.7%
59/208
28.4%
-
-
-
-
152/208
73.1%
191/209'
91.4%
121/208'
58.2%
41/208'
19.7%
2/208
0,96%
1/208
0.5%
-
57/208
27.4%
-1
118
Table B.5. Significance of effect of increasing inoculum density on emergence
failure, emergence rate, aerial biomass, and seed piece decay of different potato
cultivars inoculated with 2.5, 25, or 250 sporangia or zoospores per seed piece
(1999 trials), or with 50, 100, 400 or 800 sporangia per seed piece (2000 trials) of
Phytophthora infestans clonal lineages US-8 in Oregon or US-il in Washington.
Seed pieces were inoculated and immediately planted.
Clonal lineage
Spore Type
Cultivar/Year
Emergence Failure
Bannock Russet
Bzura
Chieftain
Kennebec
Ranger Russet
Russet Burbank
Russet Norkotah
Shepody
Umatilla Russet
EmergenceRate
Bannock Russet
Bzura
Chieftain
Kennebec
Ranger Russet
Russet Burbank
Russet Norkotah
Shepody
Umatilla Russet
Aerialbiomass
Bannock Russet
Bzura
Chieftain
Kennebec
Ranger Russet
Russet Burbank
RussetNorkotah
Shepody
Umatilla Russet
US-li
US-8
1999
1999
*0.0009
*0.0143
*0.0033
*0.0002
*0.0003
*0.0013
*<JJ1
*<ØØt
*<tHJOOl
t<QØØ1
<0.0001
*00220
NS
-
*0.0003
*0.0073
*0.0082
*0.0050
*0.0007
*0.0005
NS
*0.0378
NS
*0.0147
1999
2000
NS
NS
NS
*0.0037
-
*00105
*0.0029
-
*<ØØIJ1
<0.0001
*0.0113
1999
*00329
*<0.0001
Sporangia
2000
*<ØØØØ
*0.0001
I
*0.0006
*<00001
*<ØJ
Zoospores
Sporangia
Zoospores
-
*0.0002
*00006
-
-
-
NS
NS
NS
NS
NS
*<0O0
<0I
*<Øfl
NS
NS
NS
*0.0002
NS
NS
NS
*0.0004
-
*0.0004
*<00001
-
*0.0002
NS
NS
NS
*<00cfl
*0.0078
*0.0017
*0.0001
-
*0.0015
-
*00104
-
*00264
*0.0480
*0.0005
-
-
NS
NS
NS
NS
*0.0064
NS
NS
NS
*0.0003
NS
NS
NS
NS
NS
NS
*0.0090
*0.0006
-
-
-
NS
*0.0008
*0.0351
NS
*0.0311
*0.0049
NS
NS
NS
NS
*<000
*0.0042
NS
Seed piece decay
Bannock Russet
Bzura
Chieftain
Kennebec
Ranger Russet
Russet Burbank
Russet Norkotah
Shepody
Umatilla Russet
NS
NS
*0.0026
*<00001
*0.0012
<o.0001
*0.0001
*<QQfl
*<0J00l
*0.0013
NS
NS
-
NS
NS
NS
NS
-
NS
*0.0009
-
NS
NS
NS
NS
NS
*<QJJ
*<Ø1fl
*<J3Ø
*<0.0001
*0.0003
NSnot significant at P0.05; * = significant at indicated value; -not tested.
Table B.6. Comparison of percent final emergencea of potato cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and Umatilla Russet
(UR) at each inoculum density of zoospore or sporangial Phytophthora infestans US-8 (left), and the percent change in
emergence compared to the controls (right).
0
2.5
25
US-8
1999z
BZ
KB
RB
RN
100A
983A
25B
633A
65A
95A
1513
JOOA
IOOA
933A
Sn 933A
86.5A
Sn
UR
-
-
100A
96.7A
95A
783B
983A
983A
91.7A
100A
95.4A
100A
883B
9l.4A
-
250
Inoculum density
2.5
2500
400
800
-
-
83C
8.3C
1.7B
OC
OC
OC
-
2000s
BR
BZ
CH
RR
RN
100
70B
35B
31.7B
1999s
BZ
KB
RB
RN
SH
50
OB
5C
-5
OC
-6.7
-7.3
1.7C
-
-
-1.7
+2.7
33D
-5
26.7C
41.7B
83D
33C
1.7D
6.7C
383C
l.7D
22.9B
OC
-
OD
OC
-
-19
-6.7
-10.2
-8.6
26.IB
185B
20B
733B
86.7B
75.613
733B
893A
1.5B
1.5B
3.1B
IOOA
425B
37.5R
25BC
OB
125C
100A
100A
98.SA
73.8B
27.7B
56.9C
70.8132
63.1132
123C
23.1BC
815B
78.5B
862B
I5AC
815B
100
250
400
800
-95
-100
-98.2
-
-
-
-91.4
-96.6
-98.3
-100
-96.7
-98.2
-93.2
-100
-100
-
-
-75
-51.7
-72.4
-57.6
-61
-77.1
-74.2
-26.7
-98.3
-57.5
-26.2
-72.3
-17.3
-72.6
-13.3
-98.3
-62.5
-43.1
-87.7
-20
2500
-91.7
-100
-91.7
-97.3
-100
-100
-100
-
25C
24.6B
50
-75
-763
-30
-65
-66
-
483B
-
25
-80.6
-24.4
-96.5
-75
-29.2
-76.9
-12.5
-79
-26.7
-100
-87.5
-36.9
-84.6
-17.3
aFinal nercent emergence values within horizontal rows followed by the same letter are not sinificant1v different (P<0.05'
according to Fisher's protected least significant difference (LSD) test. -Not tested; ssporangia.zzoospores
1
-A
Table B.7. Comparison of percent final emergencea of potato cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and Umatilla Russet
(UR) at each inoculum density of zoospore or sporangial Phytophthora infestans US-il (left), and the percent change in
emergence compared to the controls (right).
0
2.5
25
50
100
-
-
250
400
Inoculum density
2.5
800 2500
25
Us-il
1999z
BZ
KE
RB
RN
SH
IOOA
98.1A
-
90.4A
55.8B
4OAC
l.9C
-1.9
-9.6
78.8A
71.2P.B
59.613
l.9C
IOOA
%2A
59.613
365C
-0
962A
100A
100A
61.5B
94.2A
IOOA
692B
OC
3.8C
OC
OC
+4
+6.2
-
1999s
BZ
KE
RB
RN
SH
-
100A
82.7A
IOOA
94.2A
98.1A
2000s
100A
76.9A
100A
98.IA
635B
32.7B
100A
15AC
82.7B
SOC
78.8B
3.8C
98.1A
OD
5.8D
-
-
-
51.9C
OC
673B
OD
OD
-
0C
173B
5.8C
673B
712B
OC
53.8R
OB
40.4C
OB
OB
7.7D
1.9B
13.5D
98.IA
82.7A
RB
RN
SH
UR
aFinal
98.IA
962A
942A
bOA
3.8B
OB
55.8B
OB
OB
32.7C
9.613
-
-
OC
OC
-0
-7
-0
-1.9
-60.5
-32.6
-15.7
-83.7
-49
-
-
250
400
800
-59.6
-97.6
-63.5
-100
-100
-
-
-
-21.2
-95.4
-1.9
-100
-0
-48.1
-100
-32.7
-100
-100
-94.1
-
-90.2
-79.1
-31.4
-96
-100
-44.2
-98.1
-93
-27.4
-100
-100
-67.3
2500
-
-44.2
-97.6
-40.4
-100
-96
-
1.9C
BR
CH
100
-9.6
-24.4
-3.8
-36.1
-26.5
-
-
50
-100
-100
-45.2
-100
-100
-92.3
-100
-100
-58.8
-100
-98
-86.5
Dercent emergence values within horizontal rows followed by the same letter are not si2nificantiv different (P<O.05'
according to Fisher's protected least significant difference (LSD) test. -Not tested; ssporangia. Zzoospores
121
Table B.8. Percent final emergencea and comparison of potato cultivars Bannock
Russet (BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR),
Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and Umatilla Russet
(UR) inoculated with a range of inoculum densities of zoospore or sporangial
Phytophthora infestans clonal lineage US-8 in Oregon in 1999 and 2000.
Inoculum density
0
2.5
25
50
100
-
-
250
400
800
-
-
2500
US-8
1999z
BZ
KE
RB
RN
SH
IOOA
63.3B
100A
IOOA
93.3A
98.3A
65B
95A
93.3A
86.5A
25BC
8.3A
15C
1.7B
OB
OB
0B
70A
35B
31.7BC
-
1999s
BZ
KE
RB
RN
SH
IOOA
96.7A
98.3A
98.3A
100A
-
8.3A
OB
5.OAB
OB
l.7B
-
-
3.3A
25A
8.3B
3.3B
48.3A
26.7BC
41.7AB
883AB 38.3ABC
22.9C
91.4A
95A
78.3B
91.7A
l.7A
6.7A
OA
OA
1.7B
OB
200
BR
BZ
CH
RR
RN
SH
95.4A
100A
89.3B
100A
IOOA
IOOA
24.6C
73.3A
1.5D
42.5B
73.8A
27.7BC
26.ICD
185BC
20C
86.7A
1.5E
37.5C
56.9B
12.3DE
78.5A
75.6A
733AB
3.IC
OD
25B
70.8A
125CD
23.1BC
63.1B
15.4C
81.5A
86.2A
8l.5A
aEmergence values within vertical columns followed by the same letter are not
significantly different (P<0.05) according to Fisher's protected least significant
difference test. -Not tested; ssporajlgia; zzoospores
UR
98.5A
122
Table B.9. Percent final emergencea and comparison of potato cultivars Bannock
Russet (BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR),
Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and Umatilla Russet
(UR) inoculated with a range of inoculum densities of zoospore or sporangial
Phytophthora infestans clonal lineage US-li in Washington in 1999 and 2000.
2.5
25
82.7B
100A
76.9B
98.IA
0
50
Inoculum density
250
100
400
800
-
-
2500
Us-il
-
1999s
BZ
KE
RB
RN
lOOA
IOOA
942AB
SH
98.1A
63.5C
82.6B
IOOA
98.1A
78.8B
100A
96.2A
94.2A
7l.2B
IOOA
OC
5.8C
-
2000s
BR
98.IA
CH
RB
RN
SH
UR
82.7B
98.1A
96.2A
94.2A
IOOA
0B
67.3A
OB
0B
98.IA
-
55.8A
100A
100A
90.4A
59.6B
96.2A
61.5B
69.2B
-
-
-
lOOA
5L9A
78.8B
3.8C
32.7C
100A
15.4D
50B
1999z
BZ
KE
RB
RN
SH
-
-
40.4A
l.9B
36.5A
OB
1.9B
59.6A
OB
3.8B
9.6BC
1.9C
17.3B
5.8C
67.3A
3.8C
OC
55.8A
7l.2A
OC
OC
32.7B
0B
-
OC
0C
53.8A
OC
OC
7.7B
OB
0B
40.4A
OB
1.9B
13.5B
aEmergence values within vertical columns followed by the same letter are not
significantly different (P0.05) according to Fisher's protected least significant
difference test. -Not tested; Ssporangia; Zzoospores
123
Table B.10. Comparison of estimated regression slope parameters for emergence
failure of potato cultivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah
(RN), Shepody (SH) and Umatilla Russet (UR) on increasing inoculum densities of
clonal lineages US-8 (Oregon) and Us-i 1 (Washington) of Phytophthora infestans.
Trial:
RB vs. BZ
RB vs. KE
RB vs. RN
RB vs. SH
BZ vs. KE
BZ vs. RN
BZ vs. SH
KE vs. RN
KEvs.SH
RN vs. SH
BRvs.BZ
BRvs.CH
BRvs.RB
BRvs.RR
BRvs.RN
BRvs.SH
BRvs.UR
BZvs.CH
BZvs.RR
BZvs.UR
CHvs.RR
CHvs.RB
CHvs.RN
CHvs.SH
CHvs.UR
RBvs.UR
RRvs.RN
RRvs.SH
RR vs. UR
RNvs.UR
SHvs.UR
Zoo spore
1999
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
-
Regression parameter slope estimates
US-li
US-8
Sporangia
Zoo spore
Sporangia
1999
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
-
-
2000
-
-
*0.0026
*0.0003
*0.0003
NS
NS
*0.0063
1999
*0.0003
*0.0298
NS
*0.0075
*0.0344
NS
*0.0087
NS
NS
NS
-
-
-
-
1999
NS
*0.0026
*0.0003
*QØØØ3
-
NS
NS
-
-
NS
NS
NS
-
-
-
-
-
-
-
-
-
-
-
NS
*0.0050
-
-
-
2000
NS
NS
NS
NS
NS
*0.0106
NS
NS
-
NS
NS
NS
-
-
-
-
-
-
-
-
-
-
NS
NS
NS
-
-
-
-
-
-
-
*00116
-
-
-
NS
-
-
-
*00078
-
-
-
-
-
-
NS
NS
NS
NS
-
-
-
NS
-
-
-
-
-
-
-
-
-
-
-
NS = not significant at P0.05; * = significant at indicated value; -not tested.
NS
NS
NS
NS
NS
-
-
NS
NS
Table B.1l. Comparison of emergence ratesa (% emergence/day) for potato cultivars Bannock Russet (BR), Bzura (BZ),
Chieftain (CII), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and
Umatilla Russet (UR) at each inoculum density of zoospore or sporangial Phytophthora infestans clonal lineage US-8 (left),
and the percent change in emergence rate compared to the controls (right).
______ ________________________
-
-
0
2.5
25
50
100
-
-
250
400
Inoculum density
2500
2.5
800
25
US-8
1999z
BZ
KE
RB
RN
SH
102A
8.1B
1.7C
3.7A
4.5A
1.OB
202A
163A
lOB
14.4A
13.OA
3.6B
2.9B
8.4A
8.9A
BZ
KE
RB
RN
SH
0.45C
OB
OC
OC
OC
OC
63B
35C
039D
2.7C
OASD
15.9A
11.6A
142A
SIB
42B
O2L1C
OD
OC
OC
122A
-
-833
-193
-505
2.7B
0.11C
OC
-
-
100
-
-
-73
-9.7
-75
+6
-65.5
-1.6
-18.9
-10.7
-48.8
-71.6
-103
OC
-14.8
-
-
-
2.5B
1 .9B
1 .9B
-822
-722
I 1.8A
7.9BC
9.IAB
5.9C
83BC
-33.1
8.9A
020B
OB
027B
OB
15.OA
SIB
6.OB
2.8B
1.9B
-97.8
-62
-22.9
-100
-60
145A
10.1B
6.5C
95B
-552
2.8B
13C
103A
2.7BC
7.5BC
1.6BC
-303
12.4A
12.9A
-77.4
-89.5
11.1A
10.OA
-132
-202
112A
800
-
-
2500
-95.6
-100
-100
-100
-100
-71.5
-94.9
-98.5
-96.8
-100
-100
-99.1
-100
-100
-
-100
I .6B
9.OA
400
-
-642
-63.8
-77.9
250
-93.6
-100
-100
-100
-100
-
12.1A
7.7B
10.4A
10.4A
-20.6
+21.6
-
-
123A
9.5A
2000s
BR
BZ
CH
RR
RN
SH
UR
-
0.65C
OB
OC
OC
-
1999s
-
50
-78.9
-50
-97
-78.9
-29.7
-100
-813
-34.5
-873
-483
-782
-87.1
-14
-22.5
aFmerence rates values within horizontal rows followed by the same letter are not sinificant1v different (P<0.05)
according to Fisher's LSD test. -Not tested; ssporangia; zzoospores
-
Table B.12. Comparison of emergence ratesa (% emergence/day) for potato cultivars Bannock Russet (BR), Bzura (BZ),
Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and
Umatilla Russet (UR) at each inoculum density of zoospore or sporangial Phytophthora infestans clonal lineage US-li
(left), and the percent change in emergence rate compared to controls (right).
0
2.5
25
50
100
-
-
Us-li
1999z
BZ
KE
RB
RN
SH
93A
l0.1A
4.7A
3.8A
15.1A
12.7B
155A
6.8A
3AC
0.14B
5.SB
16.OA
8.00
OD
73A
3.7B
2000s
BR
CH
RB
RN
SH
UR
-
7.7A
4.8A
7.OAB
93AB
92AB
5.OB
103A
2.00
8.7A
5.OB
5.4BC
0.18C
7.7B
OC
0.61C
-
-
-
2.1B
102k
038B
7.8A
9.8A
1.7B
5.4B
0.58B
OB
3.9B
9.6A
9.7A
OB
0.49C
4.8BC
OB
OB
2.9C
50
100
250
400
+8.6
-172
-19.1
-25.5
-6.6
+2.6
+26
+7.4
-
-74.8
-100
-100
-
-
32C
-13
OC
-15.8
-103
-632
-30.8
-96.8
-59
-100
5.00
-1.1
+10.8
-172
-462
-383
-753
-100
-7.4
-46.8
-
-
-935
-
-100
-100
-
OB
OC
3.1C
OB
-963
-782
-100
-93.7
-100
-100
-44.9
-51
-622
-952
0.16B
-100
-59.8
-100
-100
-100
-100
-70.1
-945
0.52D
2500
-68.8
-100
-63.4
-97
-63.6
-100
-96.9
-37
-45.6
-
800
-
-
OC
0C
OB
OC
3.7BC
OB
OB
0.53D
25
2.9C
OB
3.8B
OD
OC
-
7.8A
5.7A
122k
Inoculum density
2500 2.5
800
021C
-
8.1A
9.4A
400
-
7.7B
3.5A
14.1A
1999s
BZ
KE
RB
RN
SH
250
-100
-100
-68.4
-100
-983
-94.6
aEmergence rate values within horizontal rows followed by the same letter are not significantly different (P0.05) according
to Fisher's least significant difference (LSD) test. -Not tested; ssporangia; Zzoospores
Table B.13. Emergence rates' (% emergence/day) and comparison of potato cultivars Bannock Russet (BR), Bzura (BZ),
Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and
Umatilla Russet (UR) inoculated with increasing zoospore or sporangial inoculum densities of Phytophthora infestans
clonal lineages US-8 in OR and US-li in WA during 1999 and 2000. Seed pieces were inoculated and immediately planted.
Lineage____________________________
ID.
1999 Zoospores
RN
SH
BZ
KE
RB
US-8
BZ
0
102c
14.4b
8.4c
8.1k
3.7d
4.5c
202a
25
163a
13.Oab
8.9k
123b
12.lab
25
50
100
1.7b
l.Ob
10th
3.6b
2.9b
63a
250
400
0.65a
Ob
Ob
Ob
Ob
3.5a
Cultivars
1999 Sporangia
SH
KE RB
RN
95c 15.9a 11.6k 122b
7.7c
2.7b
0.48b
142a
10.4b
104b
5.7a
4.2ab
2.7b
024b
0.1 lb
BR
BZ
CH
9.Od
1 1.8c
8.9d
1.6d
7.9k 020d
2.5c
9.lab
&
l.9c
l.9c
5.9b
83ab
2000 Sporangia
RR
RN
SH
UR
145ab
15.th
124k
12.9ak
10.lab
6.5b
5.7c
2.8d
6.Ob
13c
112a
103a
027c
95a
2.8c
2.7c
1 1.la
Oc
7.5b
l.9c
1.6c
l0.Oa
Ob
-
800
2500
0.45a
Ob
Ob
Ob
Ob
039a
Oa
Oa
Oa
Oa
I-ll
BZ
KE
RB
RN
SM
BZ
KE
RN
SH
BR
CH
RB
RN
SH
UR
0
9.3b
12.7a
6.8k
102b
7.8c
9.8b
122a
9.6b
9.7b
16.Oa
73c
5.7b
4.8b
9Aa
15.5a
7.8ab
7.7a
8.lab
l0.lb
5.Ob
8.7a
25
7.7b
4.7c
3.8d
3.5c
15.la
2.5
14.la
8.Ob
3.7c
7.Ob
2.lc
RB
93a
92a
103a
-
2.
5.Ob
l.7c
Od
0.49c
5Aa
4.8a
0.58cd
Oc
Oc
3.9b
2.9b
Ob
021b
()c
()c
3.7a
Oc
Oc
Ob
Ob
3.la
Ob
0.16b
50
100
250
400
800
2500
3.4a
0.14b
5.5a
038cd
-
5.4b
0.18c
7.7a
Oc
0.61c
Oc
Oc
Oc
2.9a
Ob
Ob
32b
5th
Ob
3.8a
aEmergence rate (r) values within rows (horizontally, for each trial) followed by the same letter are not significantly
different according to Fisher's least significant difference (LSD) test. I.D. = inoculum density; -not tested.
0.53b
0.52b
127
Table B.14. Comparison of estimated regression slope parameters for emergence
rate of potato cuitivars Bannock Russet (BR), Bzura (BZ), Chieftain (CH),
Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah
(RN), Shepody (SH) and Umatilla Russet (UR) on increasing inoculum densities of
Phytophthora infestans clonal lineages US-8 in OR and US-i i in WA.
Zoospore
Trial:
RB vs. BZ
RB vs. KE
RB vs. RN
RB vs. SH
BZvs.KE
BZ vs. RN
BZ vs. SH
KE vs. RN
KEvs.SH
RNvs.SH
BRvs.BZ
BRvs.CH
1999
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
-
Regression parameter slope estimates
US-i 1
US-8
Sporangia
Zoospore
Sporangia
1999
2000
1999
2000
1999
NS
NS
NS
*0.0039
NS
NS
*00425
NS
NS
NS
*00095
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
-
BR vs. RB
-
-
BR vs. J?J
-
-
BRvs.RN
BRvs.SH
BRvs.UR
BZvs.CH
BZvs.RR
BZvs.UR
CH vs.
CHvs.RB
CHvs.RN
CHvs.SH
CHvs.UR
RBvs.UR
RRvs.RN
RRvs.SH
*00255
-
-
NS
NS
NS
NS
NS
NS
-
-
*00165
-
-
NS
NS
NS
-
-
-
-
-
-
-
-
-
-
-
-
-
*00250
-
-
-
-
-
-
-
NS
NS
NS
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
NS
NS
RR vs. UR
-
-
*00503
RNvs.UR
-
-
SH vs. UR
-
NS = not significant at P0.05; *
-
NS
NS
-
NS
NS
NS
NS
NS
-
-
-
-
-
-
-
-
-
-
-
significant at indicated value; -not tested.
NS
NS
Table B. 15. Comparison of average plant aerial biomassa (dry, g/plant) for potato cultivars Bannock Russet (BR), Bzura
(BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH),
and Umatilla Russet (UR) at each inoculum density of zoospore or sporangial Phytophthora infestans clonal lineage US-8
(left), and the percent change in average aerial biomass per plant compared to the controls (right).
0
2.5
25
50
100
-
-
250
400
Inoculum density
800
2500
2.5
25
50
100
-
-
250
400
800
-
-
2500
US-8
1999z
BZ
KE
RB
RN
SH
-
B
'B
14.6
47.3
-57.5
71.8
31.4A
455A
152B
B
34.7A
OC
'C
2.79
6,49
22.6A
36.8A
21.5B
22.1A
27.OA
OB
19.5
302AB
403A
OC
OB
OC
-221
245B
23.3
64.5
30.9A
35.8A
202B
-
1999s
BZ
KE
RB
RN
SH
2000s
BR
BZ
CH
RR
RN
SH
UR
-
-
-
35.6B
23.6B
25.4A
61.9A
OC
c
21.5
412A
SC
oc
12.3
17.6A
0B
OB
-8.3
-
-
-
-
-
-
293B
B
-100
-
-
30.OA
11.4
18.9
44.OA
63.2
36.6A
1.1
-6.5
69.6
9.6
263A
273B
'B
'B
OB
41.OAB
527A
3AB
C
29.4A
40.8A
35.9A
31.4A
27.8A
42.4A
38.9A
332A
.
-100
-100
13.2
5.3
325A
395A
355A
28.2
-100
93.0
35.9A
c
-100
-100
50.2
272A
432A
-
-24.3
-30.3
38.4A
423A
25.OB
-
-1.5
14.9
50.OA
37.6A
26.4A
-100
-100
12.5
39.OA
B
-
18.1
38.2
111.3
99
-36.5
342A
OA
OB
8.7
15.5
20.9A
30.OA
-100
-100
-100
-100
-
-
32.6A
40.9A
27.6A
29.6A
20.7B
27.7A
OB
-4.5
-16.7
5.1
-100
13.6
76
3.1
aAerial biomass (dry. 2/nlant values within horizontal rows followed by the same letter are not sinificantiv different
(P<O.05) according to Fisher's LSD test. -Not tested; ssporangia; Zzoos;ores; .not enough plants to sample to calculate a
true average.
Table B. 16. Comparison of average plant aerial biomassa (dry, g/plant) for potato cultivars Bannock Russet (BR), Bzura
(BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (Sn),
and Umatilla Russet (UR) at each inoculum density of zoospore or sporangial Phytophthora infestans clonal lineage US-il
(left), and the percent change in average aerial biomass per plant compared to the controls (right).
-
0
2.5
25
34.7A
21.6A
33.5AB
22.9A
21.7A
26.4A
233AB
50
100
250
Inoculum density
2500
400
800
-
2.5
25
12.1B
-23.9
-32.9
OB
38.9
11.9
13.9
50
100
-
-
Us-li
BZ
KE
RB
RN
SH
30.OA
37.5A
22.IA
16.7A
-
12.613
B
24.6A
30.4AB
24.9A
14.5A
17.SBC
OB
OB
12.1C
OB
OB
-
1999s
BZ
KE
RB
RN
SH
2000s
BR
CH
RB
RN
SH
UR
-
-
1999z
162B
13.9BC
17.7A
17.9A
13.7A
B
18.6A
13.7A
19.4A
182A
132A
113A
-
18.6A
12.7A
15.7AB
OB
OB
10.00
0B
IZOB
OB
OB
-
-
-
14.9A
13.1A
21.9A
15.8A
11.6A
I 1.4A
13.9BC
63B
B
B
800
-
-
-23
-63.9
-100
-100
-27.4
-37.7
-37.7
1.13
4.3
-22.6
-3.65
35.8
-738
4.1
-9.25
2500
-65.1
-100
-47.8
-100
-100
-63.7
8.73
-332
-3.49
400
-
223A
122A
250
B
B
13.OAB
193A
OB
OB
9.9A
OB
8.OAB
OB
OB
8.513
OB
OB
B
-55.2
-100
-35.5
-100
-100
-15.6
-100
-100
-2.15
OB
OB
13.1AB
OB
OB
-57.7
B
-132
.
-100
-100
-100
-100
-406
-11.9
-612
-402
-100
-100
-29.8
-100
-100
-100
-100
-100
aAerial biomass (dry, g/plant) values within horizontal rows followed by the same letter are not significantly different
(P<O.05) according to Fisher's LSD test. -Not tested; ssporangia; Zzoospores; .not enough plants to sample to calculate a
true average.
Table B. 17. Average plant aerial biomassa (dry, g/plant) and comparison of potato cultivars Bannock Russet (BR), Bzura
(BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (Sn),
and Umatilla Russet (UR) inoculated with a range of inoculum densities of zoospore or sporangial Phytophthora infestans
clonal lineage US-8 in Oregon in 1999 and 2000.
Inoculum density
0
2.5
25
BZ
KE
RB
RN
SH
30.9AB
35.8A
20.2B
22.6B
24.5AB
31.4AB
36.8A
21.5 IC
22.1BC
30.2ABC
45.5A
BZ
KE
RB
RN
27.6AB
29.6A
29.3A
20.7B
27.7AB
30.OAB
50
100
250
US-8
800
2500
-
-
1999z
400
A
'A
A
0A
0A
0A
0A
32.6AB
40.9AB
61.9A
41.2AB
20.9A
0A
0A
17.6B
-
0B
-
15.2B
34.7AB
27.OAB
40.3AB
A
0A
0A
I999
SH
2000s
BR
BZ
CH
RR
RN
SH
UR
34.2AB
35.6A
23.6B
25.4AB
-
B
39.OA
50.OA
37.6A
26.3B
27.3B
26.4B
42.3AB
25.OB
35.5A
C
41.OAB
29.4B
40.8AB
35.9AB
0B
A
B
0A
0A
-
38.4AB
43.2AB
27.2A
35.9A
52.7A
31.4B
30.9A
27.8A
42.4A
38.9A
C
C
33.2B
'C
32.5A
39.5A
OB
B
30.OA
44.OA
36.6A
aAerial biomass values (dry, g/plant) within vertical columns followed by the same letter are not significantly different
(P<0.05) according to Fisher's LSD analysis. -Not tested; ssporangia; zzoospores; not enough plants to sample to calculate
a true average.
Table B.1 8. Average plant aerial biomassa (dry, g/plant) and comparison of potato cultivars Bannock Russet (BR), Bzura
(BZ), Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH),
and Umatilla Russet (UR) inoculated with a range of inoculum densities of zoospore or sporangial Phytophthora infestans
clonal lineage US-li in Washington in 1999 and 2000.
Inoculum density
0
2.5
25
16.2AB
17.9AB
19.4A
13.2AB
11.3B
13.9A
13.7A
18.2A
18.6A
12.7A
50
100
-
-
250
Us-il
1999s
BZ
KE
RB
RN
SH
22.3A
17.7ABC
18.6AB
13.7BC
12.2C
2000s
BR
CH
RB
RN
SH
UR
14.9AB
13.1AB
21.9A
15.8AB
11.6B
1 1.4B
26.4AB
37.5A
22.1B
16.7B
23.3AB
24.6AB
30.4A
24.9AB
14.5B
-
-
30.OAB
-
-
0B
12.OA
OB
OB
-
-
12.IA
0B
12.6A
B
12.1A
0B
OB
-
6.3AB
.13
'C
13.OA
19.3A
B
OB
9.9A
C
oc
oc
8.OB
2500
10.OA
OB
-
34.7A
21.6A
33.5A
22.9A
21.7A
800
13.9A
B
15.7A
OB
1999z
BZ
KE
RB
RN
SH
400
17.5A
0B
OB
-
0B
OB
8.5A
OB
OB
B
0B
OB
13.1A
OB
OB
B
aAerial biomass values (dry, g/plant) within vertical columns followed by the same letter are not significantly different
(P<0.05) according to Fisher's LSD analysis. -Not tested; ssporangia; zzoospores; not enough plants to sample to calculate
a true average.
132
Table B. 19. Comparison of estimated intercept and slope parameters for regression
of aerial biomass of potato cultivars Baimock Russet (BR), Bzura (BZ), Chieftain
(CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet
Norkotah (RN), Shepody (SH) and Umatilla Russet (UR) on increasing inoculum
densities of Phytophthora infestans clonal lineages US-8 in Oregon and US-il in
Washington in 1999 and 2000.
Zoospore
Trial:
RB vs. BZ
RB vs. KE
RB vs. RN
RB vs. SH
BZ vs. KE
BZvs.RN
BZ vs. Sf1
KEvs.RN
KE vs. SH
RN vs. SH
BRvs.BZ
BRvs.Cfi
BRvs.RB
BRvs.RR
BRvs.RN
BRvs.SH
BRvs.UR
BZvs.CH
BZvs.RR
BZvs.UR
CH vs. RR
CHvs.RB
CHvs.RN
1999
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
-
-
-
-
-
CH vs. SH
-
CHvs.UR
RBvs.UR
RRvs.RN
-
RR vs. SH
RR vs. UR
RNvs.UR
SB vs. UR
Regression parameter slope estimates
Us-i 1
US-8
Sporangia
Zoospore
Sporangia
2000
1999
1999
2000
1999
NS
NS
NS
*0.0346
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
*0.0393
*0.0351
NS
N5
NS
NS
NS
NS
N5
NS
NS
N5
NS
NS
*00425
NS
NS
*00478
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
*00172
NS
*00098
NS
NS
NS
*00478
*0000 1
NS
NS
NS
*00111
*00275
*00097
NS
NS
*00543
NS
-
-
-
NS = not significant at P0.05; *
significant at indicated value; -not tested.
Table B.20. Comparison of percent seed piece decaya at harvest for potato cultivars Bannock Russet (BR), Bzura (BZ),
Chieftain (CU), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and
Umatilla Russet (UR) at each inoculum density of zoospore or sporangial Phytophthora infestans clonal lineage US-8 (left),
and the percent change in seed piece decay compared to the controls (right).
Inoculum density
0
2.5
25
50
100
-
-
250
400
800
-
-
2500
2.5
25
50
100
-
-
250
400
800
-
-
2500
US-8
1999z
BZ
24B
KE
RB
RN
36B
28C
44B
SH
12B
44B
48B
56B
40B
16B
96A
92A
68B
56B
84A
96A
100A
+833
+300
+300
+317
100A
100A
+333
+156
+178
+178
100A
100A
+100
+143
+257
+257
100A
100A
-9.1
+273
+127
+127
IOOA
100A
+333
+600
+733
-
1999s
BZ
24B
32B
KE
RB
RN
4.OB
16B
28B
4.OD
SH
6.7B
24B
20C
20B
-
2000s
-
+733
-
-
-
-
+200
+250
+317
+1975
+2400
+2400
84A
100A
100A
100A
+333
+300
IOOA
100A
IOOA
-143
+200
+257
+257
100A
+400
+1800
+2400
+2400
86.7A
100A
100A
+199
+1194
+1393
+1393
-
-
-
-
-
-
-
72A
83A
84A
76B
BR
10.7B
68.1A
70.8A
733A
85A
+536
+562
+585
+694
BZ
24B
64A
73.IA
833A
+183
+167
+205
+247
CH
RR
RN
MB
68A
96A
100A
IOOA
IOOA
+50
+563
+563
28B
72.7A
68.8A
81.4A
82.7A
+160
+563
+146
+191
+195
8.00
53.5AB
70.5A
66A
+569
781
+354
+725
SH
4.OB
783A
892A
82.7A
+1858
+2130
+1730
+1968
UR
20B
64.7A
31.9B
363B
732A
333B
27.4B
+224
+59.5
+665
+37
aSeed piece decay values within horizontal rows followed by the same letter are not significantly different (PO.O5)
according to Fisher's least significant difference (LSD) test. -Not tested; ssporangia; zzoospores
Table B.21. Comparison of percent seed piece decaya at harvest for potato cultivars Bannock Russet (BR), Bzura (BZ),
Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (Sn), and
Umatilla Russet (UR) at each inoculum density of zoospore or sporangial Phytophthora infestans clonal lineage US-i 1
(left), and the percent change in seed piece decay compared to the controls (right).
0
2.5
25
Us-il
3.8C
9.6C
212C
212C
I .9B
4.OB
3.8C
3.8C
5.8C
7.7C
1.9C
23.1C
1.9C
9.6D
5.8D
3.9C
23.7C
5.8BC
36.SC
23.TC
lOB
55B
lOB
20B
400
Inoculum density
2.5
800 2500
40.4B
6.9B
50.68
47.7B
25
-
98.1A
100A
98.1A
100A
100A
-
2000s
BR
CH
RB
RN
SH
UR
250
-
385B
1999s
BZ
KE
RB
RN
SH
100
-
1999z
BZ
KE
RB
RN
SH
50
100A
100A
+153
98.IA
+111
+52.6
+101
100A
IOOA
+0
73.1A
923A
76.9B
13.5BC
98.IA
212B
712A
100A
55.8B
98.IA
100A
100A
+105
+2.6
+205
+280
+298
-
-
IOOA
-
-
-
IOOA
+900
+900
100A
IOOA
IOOA
75A
95A
95A
85A
85A
+81.8
+850
IOOA
IOOA
IOOA
100A
100A
+81.8
+650
+375
+1900
+1600
IOOA
IOOA
85A
90A
100A
-
-
-FL100
+1900
+1700
2500
+2532
+372
+5063
+2532
+2532
+4758
+333
+3647
+942
+1624
-
-
100A
5B
800
+3747
+325
+1016
+942
+1591
+2126
+233
+611
+778
+862
-
100A
5.OB
400
-
-
100A
100A
IOOA
250
+2482
+372
+5063
+2532
+2532
-
423B
843B
100
+913
+90.6
+263
+1232
+1155
-
-
50
+900
+81.8
+750
+400
+1900
+1900
+900
+81.8
+750
+400
+1900
+1900
aSeed piece decay values within horizontal rows followed by the same letter are not significantly different (P0.05)
according to Fisher's least significant difference (LSD) test. -Not tested; ssporangia; zzoospores.
135
Table B.22. Percent seed piece decaya at harvest and comparison of potato cultivars
Bannock Russet (BR), Bzura (BZ), Chieftain (CH), Keimebec (KE), Ranger Russet
(RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and Umatilla
Russet (UR) inoculated with a range of inoculum densities of zoo spores or
sporangia of Phytophthora infestans clonal lineage US-8 in Oregon in 1999 and
2000.
0
2.5
25
Inoculum density
100
50
250
400
800
-
-
-
2500
US-8
1999z
BZ
KE
RB
RN
SH
-
24AB
36AB
28AB
44A
12B
44AB
48AB
56A
4OAB
16B
96A
92A
6SAB
56B
84AB
BZ
KE
RB
RN
SH
2000s
BR
BZ
CH
RR
RN
SH
24AB
32A
4.OB
I 6A
28A
24A
20A
20A
-
4.OB
6.7AB
10.7B
24B
-
-
-
84B
100A
MA
bOA
76A
86.7A
-
100A
100A
100A
100A
100A
100A
100A
-
-
68.1BC
68BC
96A
28B
72.7BC
53.5C
78.3AB
64.7BC
4.OB
bOA
bOA
72A
83A
MA
8.OB
IOOA
bOA
-
1999s
100A
100A
100A
100A
100A
70.8BC
64C
100A
68.8BC
70.5BC
892AB
73.3B
73.1B
100A
81.4AB
36.3C
73213
33.3C
85AB
83.3AB
100A
82.7AB
6613
82.7AB
27AC
UR
aSeed piece decay values within vertical columns followed by the same letter are
not significantly different (P0.05) according to Fisher's LSD test. Not tested;
Ssporangia; zzoospores
20B
31.9D
136
Table B.23. Percent seed piece decaya at harvest and comparison of potato cultivars
Bannock Russet (BR), Bzura (BZ), Chieftain (CH), Kennebec (KE), Ranger Russet
(RR), Russet Burbank (RB), Russet Norkotah (RN), Shepody (SH), and Umatilla
Russet (UR) inoculated with a range of inoculum densities of zoo spores or
sporangia of Phytophthora infestans clonal lineage US-il in Washington in 1999
and 2000.
ocden
0
2.5
25
50
100
-
-
250
400
800
-
-
2500
Us-li
1999s
92.3A
42.3C
73.1B
3.9B
BZ 1.9B
bOA
98.1A
KE 23.1A 23.7A 76.9AB
71213
212C
5.8B
13.5D
RB l.9B
bOA
iOOA
RN 9.6AB 36.5A 84.3A
100A
98.1A
SH 5.8B 23.iA 55.8BC
i999z
bOA
98.1A
9.6B
38.5A
BZ 3.8B
bOA
bOA
KE 2i2A 212A 40.4A
98.1A
98.1A
4.OB
6.9B
RB
l.9B
100A
100A
5.8B
50.6A
RN 3.8B
100A
iOOA
7.7B
47.7A
SH 3.8B
2000s
100A
100A
100A
bOA
lOB
BR
bOA
100A
100A
100A
CH 55A
75B
95A
85A
85B
RB
lOB
100A
100A
95A
100A
RN 2OB
100A
100A
100A
bOA
SH 5.OB
85AB
9OA
100A
100A
UR 5.OB
aSeed piece decay values within vertical columns followed by the same letter are
not significantly different (P<0.05) according to Fisher's LSD test. -Not tested;
Ssporangia; zzoospores
137
Table B.24. Comparison of estimated intercept and slope parameters for regression
of seed piece decay of potato cultivars Bannock Russet (BR), Bzura (BZ),
Chieftain (CH), Kennebec (KE), Ranger Russet (RR), Russet Burbank (RB),
Russet Norkotah (RN), Shepody (SH) and Umatilla Russet (UR) on increasing
inoculum densities of Phytophthora infestans zoospores or sporangia of clonal
lineages US-8 in Oregon and US-li in Washington in 1999 and 2000.
Trial:
RB vs. BZ
Zoospore
1999
RN
RB vs. SH
BZ vs. KE
BZ vs. RN
BZ vs. SH
KE vs. RN
KEvs.SH
RN vs. SH
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
BRvs.BZ
-
BR vs. CH
-
RB vs. KE
RB vs.
Regression parameter slope estimates
Us-I 1
US-8
Zoo spore
Sporangia
Sporangia
2000
1999
1999
2000
1999
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
*00051
NS
NS
NS
*00506
NS
NS
NS
NS
NS
NS
*ØØ39Ø
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
*0.0499
NS
NS
NS
NS
NS
NS
NS
*0.0389
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
BRvs.RB
BRvs.RR
BRvs.RN
BRvs.SH
BRvs.UR
BZvs.CH
BZvs.RR
BZvs.UR
CHvs.RR
CHvs.RB
CHvs.RN
CHvs.SH
CHvs.UR
RBvs.UR
RRvs.RN
RRvs.SH
RRvs.UR
RNvs.UR
SHvs.UR
NS = not significant at P0.05; * = significant at indicated value; -not tested.
-
-
-
-
-
138
Table B.25. Average environmental conditions for six experimental field trials in
Oregon and Washington in 1999 and 2000.
Average
air
high
temp
Trial
OR
1999z
1999s
2000s
(
C)
Average
air
low
temp
(
C)
Average
soil
temp
maximuma
(
C)
Average
soil
temp
minimum'
(
C)
21.7
23.2
24.7
9.2
9.9
10.0
25.2
26.9
22.3
16.4
18.2
17.7
18.0
19.2
18.1
9.1
-
-
9.9
9.2
-
-
Average
soil
tempa
(
C)
Total
irrigationl
rainfall
(cm)
-
11.0
12.9
15.4
15.0
16.2
14.7
12.6
12.4
15.8
-
WA
1999s
1999z
2000s
aSoji temperature taken at 4 inch depth; bpercent water content by volume, 0; cbS
at 8 inch depth; ssporangja; zzoospores