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This is to certify that the

thesis entitled

EFFECTS OF COLD TREATMENT, PHOTOPERIOD, AND FORCING
TEMPERATURE ON OENOTHERA FRUTICOSA 'YOUNGII-LAPSLEY' AND
STOKESIA LAEVIS 'KLAUS JELITTO'

presented by

Emily A. Clough

has been accepted towards fulﬁllment
of the requirements for

M. S . degree in Horticulture

 

 

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1M chlHCJD‘oOuopﬁ-p“

EFFECTS OF COLD TREATMENT, PHOTOPERIOD, AND FORCING
TEMPERATURE ON OENOTHERA FRUTICOSA ‘YOUNGll-LAPSLEY’ AND
STOKES/A LAEVIS ‘KLAUS JELITTO’

By

Emily A. Clough

A THESIS
Submitted to
Michigan State University
in partial fulﬁllment of the requirements

for the degree of

MASTER OF SCIENCE
Department of Horticulture

1 999

ABSTRACT
EFFECTS OF COLD TREATMENT, PHOTOPERIOD, AND FORCING
TEMPERATURE ON OENOTHERA FRUTICOSA ‘YOUNGll-LAPSLEY’ AND
STOKES/A LAEVIS ‘KLAUS JELITTO’
By

Emily A. Clough

A series of experiments were conducted to determine the effect of cold
treatment, photoperiod, and forcing temperature on Oenothera fruticosa L.
'Youngii-lapsley’ and Stokesia Iaevis (Hill) Greene ‘Klaus Jelitto’. ‘Youngii-lapsley’
had a nearly obligate cold requirement and, following cold treatment, behaved as
a facultative long-day plant. Only 3 weeks of cold treatment were required for
100% ﬂowering. Time to ﬂower decreased slightly as cold treatment increased
from 3 to 15 weeks. Stokesia Iaevis ‘Klaus Jelitto’ had a facultative cold
requirement and was proposed to be a facultative intermediate-day plant because
ﬂowering was most consistent and rapid under photoperiods between 12 and 13 h
both before and after cold treatment. Time to ﬂower, ﬂower number, and plant
height at ﬂower decreased as temperature increased from 14 °C to 29 °C for both
‘Youngii-Iapsley’ and ‘Klaus Jelitto’.

The ﬂowering Characteristics of five cultivars of Oenothera fruticosa were
compared under either incandescent lamps or high-pressure sodium lamps used
for daylength extension. Lamp types differed in light intensity as well as spectral
quality. Flower number was increased two to three times for ‘Youngii-lapsley', ssp.
glauca and ‘Highlight’ when high-pressure sodium lamps were used for daylength

extension compared to incandescent lamps.

To my sisters Alice C. Moore and Catherine A. Clough,

for their support, friendship, and love

ACKNOWLEDGMENTS

I would like to thank my advisor, Dr. Art Cameron, and all the members of
my committee, Dr. Royal Heins, Dr. erl Carlson, and Dr. Jim Baird, for their
support, advice, and encouragement. I greatly appreciate all the opportunities
that l have been given here to increase my knowledge and improve myself. I
thank Dr. Bridget Behe for her mentoring and inspiration.

' This research could not have been completed without the support of Dan
Tschirhart and all the undergraduate student workers and I am very grateful for
all their help. I also thank the nurseries, including Greenleaf Enterprises,
Walters Gardens, Skagit Gardens, Blooming Nursery, and Bluebird Nursery
which, very generously, provided the plant material for these experiments.

I would also like to thank my friends and colleagues for their friendship,
their insightful advice, and moral support: Sarah Bruce, Joaquin Chong, Beth
Fausey, Leslie Finical, Alison Frane, Priscilla Hockin, Kathy Kelly, Bin Liu, Mary-
Slade Morrison, Genhua Niu, Erik Runkle, and Cathy Whitman. I give special
thanks to Juan Hernandez for his love and his firm belief in me. Finally, I give

thanks to my family, for their constant love and support.

TABLE OF CONTENTS

LIST OF TABLES ................................................................................................ vii
LIST OF FIGURES ............................................................................................... ix
LITERATURE REVIEW ........................................................................................ 1
Introduction ................................................................................................ 2
Characterization of Vemalization ............................................................... 4
Effective temperatures ..................................................................... 5

Duration of cold treatment ................................................................ 6
Antivemalization and devemalization ............................................... 8

Plant age. ....................................................................................... 10

Light and vemalization ................................................................... 11

Perception of Vemalization ...................................................................... 14
Mechanism of Vemalization ...................................................................... 16
Grafting studies ............................................................................. 16

Gibberellins .................................................................................... 18

Genetics of Vemalization ......................................................................... 20
Conclusion ............................................................................................... 26
Literature Cited ........................................................................................ 27

GROWTH AND DEVELOPMENT OF OENOTHERA FRUTICOSA IS
INFLUENCED BY COLD TREATMENT, PHOTOPERIOD, FORCING

TEMPERATURE, AND PLANT GROWTH REGULATORS ................................ 32
Abstract ................................................................................................... 33
Introduction .............................................................................................. 35
Materials and Methods ............................................................................ 38
Results and Discussion ............................................................................ 44
Summary .................................................................................................. 55
Literature Cited ......................................................................................... 57

FLOWERING CHARACTERISTICS OF SEVERAL CULTIVARS OF
OENOTHERA FRUTICOSA UNDER TWO DIFFERENT LAMPS TYPES FOR

DAYLENGTH EXTENSION ................................................................................. 73
Abstract .................................................................................................... 74
Introduction ............................................................................................... 75
Materials and Methods ............................................................................. 76
Results and Discussion ............................................................................ 80
Summary .................................................................................................. 84
Literature Cited ......................................................................................... 85

EFFECTS OF COLD TREATMENT, PHOTOPERIOD, AND FORCING
TEMPERATURE ON GROWTH AND DEVELOPMENT OF STOKESIA LAEVIS

‘KLAUS JELI'ITO’ ............................................................................................... 91
Abstract .................................................................................................... 92
Introduction ............................................................................................... 94
Materials and Methods ............................................................................. 97
Results and Discussion .......................................................................... 101
Summary ................................................................................................ 113
Literature Cited ....................................................................................... 114

APPENDIX A: COMPARISON OF STOKES/A LAEVIS CULTIVARS GROWN
UNDER TWO DIFFERENT LAMP TYPES FOR DAYLENGTH EXTENSION..128

Introduction ............................................................................................ 129
Protocol .................................................................................................. 131
Summary of Results .............................................................................. 133
Literature Cited ...................................................................................... 135

APPENDIX B: EFFECTS OF COLD TREATMENT, PHOTOPERIOD, AND
FORCING TEMPERATURE IN ANEMONE HUPEHENSIS, PENSTEMON

DIGITALIS ‘HUSKER RED’, AND SAXIFRAGA ARENDSII ‘TRIUMPH’ ........... 139
Introduction ............................................................................................. 140
Protocol .................................................................................................. 142
Selected data for each species .............................................................. 145

vi

LIST OF TABLES

Table 1. Average daily air temperatures and daily light integrals from date of
transplant to average date of ﬂowering for Oenothera fruticosa ‘Youngii-lapsley’
after each duration of cold treatment .................................................................. 59

Table 2. Average daily air temperatures from date of transplant to average date
of ﬂowering for Oenothera fmticosa ‘Youngii-lapsley’ under each photoperiod..60

Table 3. Actual temperatures of houses for the time of forcing for three
developmental stages: transplant to visible bud, visible bud to ﬂower, and
transplant to ﬂower .............................................................................................. 61

Table 4. Parameters of linear regression analysis relating forcing temperature to
rate of progress from transplant to visible bud (VB), visible bud to ﬂowering (VB
to FLW) and transplant to ﬂowering (FLW) for Oenothera fruticosa ‘Youngii-
lapsley’; intercept and slope were used to calculate base temperature (T t,) and
degree-days (°days) ........................................................................................... 62

Table 5. Starting plant material; dates of arrival; cold treatment initiation; forcing;
average daily temperature, and average daily light integral for Oenothera
fruticosa ‘Fireworks’, ‘Highlight’, ‘Youngii-Iapsley’, ‘Summer Solstice’, and O.
fruticosa ssp. glauca. The labels “A” and “B” after 0. fruticosa ssp. glauca refer
to different sources for plant material. Lamp type = type of lamp used to deliver
daylength extension for 16-h photoperiods. HPS = high-pressure sodium lamps;
INC = incandescent lamps ................................................................................. 86

Table 6. Flowering characteristics of several cultivars of Oenothera fmticosa and
O. fmticosa ssp. glauca grown at 20 °C under 16-h photoperiods, delivered by
day extension with either high-pressure sodium (HPS) lamps or incandescent
(INC) lamps. All cultivars were treated with 15 weeks at 5 °C. Labels of
signiﬁcance refer to intracultivar comparisons for lamp type .............................. 87

Table 7. Average daily air temperatures and daily light integrals from date of
transplant to average date of ﬂowering of Stokesia Iaevis ‘Klaus Jelitto’ after
each duration of cold treatment ........................................................................ 116

Table 8. Average air temperatures from date of transplant to average date of
ﬂowering of Stokesia Iaevis “Klaus Jelitto’ under each photoperiod .................. 117

Table 9. Actual temperatures of houses for the time of forcing for three

developmental stages: Transplant to Visible Bud, Visible Bud to Flower, and
Transplant to Flower. ....................................................................................... 118

vii

Table 10. Parameters of linear regression analysis relating forcing temperature
to rate of progress from transplant to visible bud (VB), visible bud to ﬂowering
(VB to F LW) and transplant to ﬂowering (FLW) for Stokesia Iaevis ‘Klaus Jelitto’.
Intercept and slope were used to calculate base temperature (T,) and degree-
days (°days). .................................................................................................... 1 19

Table 11. The difference between day and night temperature (DIF) of plants of
Stokesia Iaevis ‘Klaus Jelitto’ grown under different forcing temperatures and
three developmental stages: from transplant to visible bud (VB), from VB to
ﬂowering (FLW), and from transplant to FLW .................................................. 120

Table 12. Starting plant material; number of plants per treatment; dates of
arrival, cold treatment initiation, forcing, as well as average daily temperature
and average daily light integral for Stokesia Iaevis ‘Alba’, ‘Blue Danube’, ‘Klaus
Jelitto’, ‘Mary Gregory’, ‘Purple Parasols’ and ‘Wyoming’. Lamp type = type of
lamp used to deliver daylength extension for 16 h photoperiods. HPS = high
pressure sodium lamps; INC = incandescent lamps ........................................ 136

Table 13. Flowering characteristics of several cultivars of Stokesia Iaevis grown
at 20 °C under 16 h photoperiods, delivered by day-extension with either high
pressure sodium (HPS) lamps or incandescent (INC) lamps. All cultivars were
treated with 15 weeks at 5 °C. Labels of signiﬁcance refer to intracultivar
comparisons for lamp type. Number of new leaves refers to the number of new
leaves beneath the ﬁrst ﬂower ......................................................................... 137

viii

LIST OF FIGURES

Figure 1. Responses of Oenothera fruticosa ‘Youngii-lapsley’ to various
durations of cold treatment at 5 °C for percentage ﬂowering (A), days to ﬂower
(B), days to visible bud (C), and days from visible bud to ﬂower (D) in Year 1 (I)
or Year 2 (I). Error bars represent 95% conﬁdence intervals. All symbols
represent the mean of 9 or 10 plants except for Year 1, 0 week cold treatment,
when only one plant ﬂowered. L = linear; Q = quadratic trends. ”5'
”-"Nonsigniﬂcant or signiﬁcant at P 50.01 or 0.001, respectively ....................... 63

Figure 2. Effect of cold duration at 5 °C on number of new nodes produced
during forcing in Year 2. Error bars represent 95% conﬁdence intervals. L =
linear; Q = quadratic trends. ”5' '-"'”'Nonsigniﬁcant or signiﬁcant at P s 0.05, 0.01,
or 0.001 , respectively .......................................................................................... 64

Figure 3. Effects of cold duration at 5 °C on number of ﬂowers and buds (A),
number of ﬂowering lateral shoots (B), percent ﬂowering lateral shoots (C), and
plant height (D) for Oenothera fruticosa ‘Youngii-lapsley’ in Year 1 (O) or Year 2
(I). All symbols represent the mean of 9 or 10 plants except for Year 1, 0 week
cold treatment, when only one plant ﬂowered. Error bars represent 95%
conﬁdence intervals. L = linear, Q = quadratic trends. "3' ""-'"Nonsigniﬁcant or
signiﬁcant at P s 0.05, 0.01 or 0.001, respectively .............................................. 65

Figure 4. Responses of Oenothera fruticosa ‘Youngii-Iapsley’ to various
photoperiods after 15 weeks of cold treatment at 5 °C for days to ﬂower (A),
days from visible bud to ﬂower (B), and days to visible bud (C) in Year 1 (o) and
Year 2 (I). Continual photoperiod treatments consisted of 9-h natural days
extended with light from incandescent lamps. Nl = 4-h night intenuption. Error
bars represent 95% conﬁdence intervals. L = linear“, Q = quadratic trends. ”5-
'-"-"'Nonsigniﬁcant or signiﬁcant at P s 0.05, 0.01, or 0.001 , respectively ........... 66

Figure 5. Effects of various photoperiods after 15 weeks at 5 °C on number of
ﬁnal nodes (A) and number of nodes produced during forcing (B) for Oenothera
fruticosa ‘Youngii-lapsley’ in Year 1 (I) or Year 2 (I). Continual photoperiod
treatments consisted of 9-h natural days extended with light from incandescent
lamps. NI = 4-h night interruption. Error bars represent 95% conﬁdence
intervals. L = linear; Q = quadratic trends. "3' ""'”'Nonsigniﬁcant or signiﬁcant at
P s 0.05, 0.01, or 0.001, respectively ................................................................. 67

Figure 6. Effects of various photoperiods after 15 weeks at 5 °C on number of
ﬂowers and buds (A), number of ﬂowering lateral shoots (B), number of total
lateral shoots (C), percent ﬂowering laterals (D), and plant height (E) for
Oenothera fmticosa ‘Youngii-Iapsley’ in Year 1 ( I) or Year 2 (I). Continual
photoperiod treatments consisted of 9-h natural days extended with light from

ix

incandescent lamps. NI = 4-h night interruption. Error bars represent 95%
conﬁdence intervals. L = linear; Q = quadratic trends. ”3- "”-'" Nonsigniﬁcant or
signiﬁcant at P s 0.05, 0.01, or 0.001, respectively ............................................. 68

Figure 7. Effects of temperature on time to (A, B, C) and rate of progress toward
ﬂowering (D, E, F) in Oenothera fruticosa ‘Youngii-lapsley’. The parameters of
linear regression lines are presented in Table 4. The quadratic regression lines in
graphs A, B, and C are the reciprocals of correlated linear regression lines in
graphs D, E, and F .............................................................................................. 69

Figure 8. Effects of temperature on numbers of ﬂowers and buds (A), ﬂower
diameter (B), and plant height (C) for Oenothera fruticosa ‘Youngii-Iapsley’.

Error bars represent 95% conﬁdence intervals. L = linear; Q = quadratic trends.
”5' "’"Nonsigniﬁcant or signiﬁcant at P s 0.01 or 0.001, respectively .................. 70

Figure 9. Effects of various plant growth regulators on days to ﬂower (A), plant
height (B), and ﬂower diameter (C) for Oenothera fruticosa ‘Youngii-lapsley’.
Rates of PGRs were: Ancymidol (100 mg-L“), Daminozide (5000 mg-L“),
Paclobutrazol (30 mg-L"), Chlorrnequat (1500 mg-L") and Uniconazole (15 mg-L’
1). Error bars represent 95% conﬁdence intervals .............................................. 71

Figure 10. Postharvest responses of Oenothera fruticosa ‘Youngii-lapsley’ for 12
days at 24.6 °C under a 24-h photoperiod. Error bars represent 95% conﬁdence
intervals ............................................................................................................... 72

Figure 11. Cultivars of Oenothera fruticosa and O. fmticosa ssp. glauca grown at
20°C under a 16-h photoperiod provided by a 9-h natural day plus 7-h day

extension with either high-pressure sodium lamps (labeled in the photographs as
HID for high-intensity discharge) or incandescent lamps (inc). The labels “A” and
“B” after ssp. glauca refer to different nursery sources ....................................... 89

Figure 12. Effects of various durations of cold treatment at 5 °C on percentage
ﬂowering (A), days to ﬂower (B), days to visible bud (C), and days from visible
bud to ﬂower (D) in Stokesia Iaevis ‘Klaus Jelitto’ in Year 1 (I) and Year 2 (I).
Error bars represent 95% conﬁdence intervals. L = linear; Q = quadratic trends.
NS""'"Nonsigniﬁcant or signiﬁcant at P s 0.01 or 0.001, respectively ................. 121

Figure 13. Effects of cold duration at 5 °C on number of nodes (A), number of
ﬂower buds (B), and plant height (C) in Stokesia Iaevis ‘Klaus Jelitto’ in Year 1
(I) and Year 2 (I). Error bars represent 95% conﬁdence intervals. L = linear; Q
= quadratic trends. ”5" "’"Nonsigniﬁcant or signiﬁcant at P s 0.05, 0.01, or
0.001 , respectively ............................................................................................ 122

Figure 14. Effects of various photoperiods without a cold treatment on
percentage ﬂowering (A), days to ﬂower (B), days to visible bud (C), and days

from visible bud to ﬂower (D) in Stokesia Iaevis ‘Klaus Jelitto’ in Year 1 (I) and
Year 2 (I). Error bars represent 95% conﬁdence intervals. L = linear; Q =
quadratic trends. NS-'°"-'"Nonsigniﬁcant or signiﬁcant at Ps0.05, 0.01, or 0.001,
respectively ....................................................................................................... 123

Figure 15. Effects of various photoperiods after a 15 week cold treatment at 5
°C on percentage ﬂowering (A), days to ﬂower (B), days to visible bud (C), and
days from visible bud to ﬂower (D) in Stokesia Iaevis ‘Klaus Jelitto' in Year 1 (I)
and Year 2 (I). Error bars represent 95% conﬁdence intervals. L = linear; Q =
quadratic trends. NS""'-"'Nonsigniﬁcant or signiﬁcant at P s 0.05, 0.01, or 0.001,
respectively ....................................................................................................... 124

Figure 16. Effects of various photoperiods with and without a 15—week cold
treatment at 5°C on number of ﬁnal nodes (A), number of new nodes (B),
number of ﬂower buds (C), and plant height (D) in Stokesia Iaevis ‘Klaus Jelitto’
in Year 1 (I) and Year 2 (I). Error bars represent 95% conﬁdence intervals. L =
linear; Q = quadratic trends. NS"""""Nonsigniﬁcant or signiﬁcant at P s 0.05, 0.01,
or 0.001, respectively ........................................................................................ 125

Figure 17. Effects of temperature on time to (A, B, C) and rate of progress
toward ﬂowering (D, E, F) in Stokesia Iaevis ‘Klaus Jelitto’. The parameters of
linear regression lines are presented in Table 10. The quadratic regression lines
in graphs A, B, and C are the reciprocals of correlated linear regression lines in
graphs D, E, and F ............................................................................................ 126

Figure 18. Effects of temperature on number of nodes (A), number of ﬂower
buds (B), and plant height (C) in Stokesia Iaevis ‘Klaus Jelitto’. L=linear;
Q=quadratic trends. ”5'" "’"Nonsigniﬁcant or signiﬁcant at P s 005,001, or
0.001 , respectively ............................................................................................ 127

Figure 19. Effects of cold treatment in Anemone hupehensis in Year 1 .......... 145

Figure 20. Effects of cold treatment in Anemone hupehensis in Year 2. Error
bars show 95% conﬁdence intervals ................................................................. 146

Figure 21. Effects of various photoperiods with and without a 15 week cold
treatment at 5 °C in Anemone hupehensis in Year 1 ........................................ 147

Figure 22. Effects of various photoperiods with and without a 15 week cold
treatment at 5 °C in Anemone hupehensis in Year 2. Error bars show 95%
conﬁdence intervals .......................................................................................... 148

Figure 23. Inﬂuence of forcing temperature on ﬂowering time (A,B,C) and rate of

progress toward ﬂowering (D,E,F) in Anemone hupehensis. Error bars
represent 95% conﬁdence intervals .................................................................. 149

xi

Figure 24. Inﬂuence of forcing temperature on number of nodes (A), number of
ﬂower buds (B), and plant height at ﬁrst ﬂower (C) in Anemone hupehensis. Error
bars represent 95% conﬁdence intervals .......................................................... 150

Figure 25. Effects of cold treatment in Penstemon digitalis 'Husker Red' in Year
1 ........................................................................................................................ 1 51

Figure 26. Effects of cold treatment in Penstemon digitalis 'Husker Red' in Year
2. Error bars show 95% conﬁdence intervals .................................................... 152

Figure 27. Effects of various photoperiods with and without a 15-week cold
treatment at 5 °C in Penstemon digitalis ‘Husker Red’ in Year 1 ...................... 153

Figure 28. Effects of various photoperiods with and without a 15-week cold
treatment at 5 °C in Penstemon digitalis ‘Husker Red’ in Year 2. Error bars show
95% conﬁdence intervals .................................................................................. 154

Figure 29. Inﬂuence of forcing temperature on ﬂowering time (A, B, C) and rate
of progress toward ﬂowering (D, E, F) in Penstemon digitalis ‘Husker Red’.
Error bars represent 95% conﬁdence intervals ................................................. 155

Figure 30. Inﬂuence of forcing temperature on number of nodes (A), number of
ﬂower buds (B), and plant height at ﬁrst ﬂower (C) in Penstemon digitalis
‘Husker Red’. Error bars represent 95% conﬁdence intervals .......................... 156

Figure 31. Effects of cold treatment in Saxifraga arendsii 'Triumph'
in Year 1 ............................................................................................................ 157

Figure 32. Effects of cold treatment in Saxifraga arendsii 'Triumph'
in Year 2. Error bars show 95% conﬁdence intervals ....................................... 158

Figure 33. Effects of various photoperiods with and without a cold treatment in
in Saxifraga arendsii 'Triumph’ in Year 1 ........................................................... 159

Figure 34. Effects of various photoperiods with and without a cold treatment in
in Saxifraga arendsii 'Triumph' in Year 2. Error bars show 95% conﬁdence
intervals ............................................................................................................. 1 60

Figure 35. Inﬂuence of forcing temperature on ﬂowering time (A, B, C) and rate
of progress toward ﬂowering (D, E, F) in Saxifraga arendsii ‘Triumph’. Error
bars represent 95% conﬁdence intervals .......................................................... 161

Figure 36. Inﬂuence of forcing temperature on number of nodes (A), number of

ﬂower buds (B), and plant height at ﬁrst ﬂower (C) in Saxifraga arendsii
‘Triumph’. Error bars represent 95% conﬁdence intervals ................................ 162

xii

Literature Review

Introduction

Vemalization is deﬁned as the promotion of ﬂower formation by exposure
to low temperatures (Lang, 1965). It is an inductive process, the effects of which
generally are not observed until the chilled plant is moved to higher temperatures
(Chouard, 1960; Vince-Prue, 1975). Vemalization is not required for ﬂowering of
all plant species; most that respond to vemalization originated in temperate
latitudes where it is ecologically advantageous for a plant not to ﬂower during the
winter months (Roberts and Summerﬁeld, 1987). Some species have a
quantitative, or facultative, response to a cold treatment and ﬂower without one,
but ﬂower development is hastened aﬂer a cold treatment. Plants with either a
qualitative or quantitative response to cold treatment are usually long-day plants,
although there is no deﬁnitive relationship between a vemalization requirement
and a speciﬁc photoperiod requirement (Vince-Prue, 1975). Most species native
to tropical or subtropical regions, where there is no need to avoid a period of
lethally cold temperatures, are insensitive to vemalization (Roberts and
Summerﬁeld, 1987).

The ﬁrst scientiﬁc work on vemalization was done primarily on winter
wheat and rye. Winter races are fall-planted and require the cold temperatures to
hasten ﬂowering the following spring. The spring races differ in that they do not
have a requirement for cold and will ﬂower soon after sowing. While the

phenomenon that we now call vemalization was recognized as eany as the mid-

nineteenth century (Klippart, 1857, cited by Whyte, 1948), scientiﬁc deﬁnition did
not occur until 1918 when Gassner (cited by Whyte, 1948) showed that a great
variety of plants had a cold requirement for ﬂowering.

Lysenko, working with winter rye, termed the phenomenon in his native
Russian "jarovizacija" (a combination of the word for "spring" with a sufﬁx
meaning "to make") and translated it himself into English, French, and German
as ”vemalization” (Whyte, 1948; Chouard, 1960). Lysenko was also the ﬁrst to
propose a model to explain the role of vemalization in plant development. He
called it the "theory of phasic development,” in which he suggested that plants
must pass through two irreversible phases in order to ﬂower: the temperature-
sensitive phase (therrnophase) and the light-sensitive phase (photophase)
(Chouard, 1960; Napp-Zinn, 1984). Today, we know that only a few plants
respond exactly according to this theory and it has been soundly rejected (Napp-
Zinn, 1984).

Throughout this century, a great deal of information concerning
vemalization has been compiled and the characterization of the vemalization
response is well described for many species. The genetic and physiological
aspects of vemalization, however, have yet to be described in detail. Many
genes from several different species are important in vemalization, but their

mode of action is unknown.

In this review, I will present a thorough characterization of the
vemalization response and a summary of current progress on the underlying
genetic and physiological mechanisms.

Characterization of vemalization

Gregory and Purvis deﬁned the fundamental characteristics of
vemalization in their many experiments with the rye (Secale cereale) cultivar
Petkus which consists of two races- winter and spring rye (Whyte, 1948;
Chouard, 1960; Vince-Prue, 1975). They observed that both races ﬂower faster
when kept in continuous light and that neither will ﬂower if the photoperiod is
shorter than 12 hours (in Vince-Prue, 1975). Without a cold treatment (also
called "therrnoinduction," the actual exposure of a plant to cold temperatures),
the winter race ﬂowers in continuous light after 15 weeks when 22 leaves have
been formed beneath the ﬂoral spike. The spring race ﬂowers in about 7.5
weeks and produces six to seven leaves beneath the ﬂoral spike. After a cold
treatment, the winter race behaves exactly like the spring race.

The vemalization response is seen as an aftereffect of the low-
temperature treatment (Chouard, 1960), and therefore the response is typically
measured by the time to anthesis, the leaf number beneath the ﬂower, or both
(Purvis, 1961 ). Currently, there are no genetic or physiological markers that can
be used to provide a deﬁnitive assay of the progress of vemalization during a
low- temperature treatment (Brooking, 1996); hence, the classical methods of

measuring the vemalization response (e.g., ﬁnal leaf number at ﬂower, time to

anthesis) still are used.

Effective temperatures. Effective temperatures for vemalization of many
species occur between -5 °C and 15 °C, with a broad optimum between 1 °C
and 7 °C (Chouard, 1960; Lang, 1965; Thomas and Vince-Prue, 1984). The
response generally increases with temperatures between -4 °C and 1 °C and
decreases with temperatures above 9 °C (Purvis, 1961). Although this range is
effective for most species, there are exceptions. For example, Easter lily (Lilium
Iongiﬂorum Thunb.) 'Ace' is effectively vemalized at temperatures up to 16 °C
and partially vemalized at 18 °C. No vemalization occurs at 21 °C (Weiler and
Langhans,1968)

The optimum temperature for vemalization may depend on the length of
the cold treatment (Purvis, 1961). For example, experiments with black henbane
(Hyoscyamus niger L.) and ‘Petkus’ rye showed a higher optimum temperature
when the duration was shorter. However, when the cold treatment was
extended, any temperature within the vemalization range produced the same
effect (Purvis, 1961; Vince-Pme, 1975). In contrast, experiments with the
Cineran'a L. ’Cindy Blue' showed that optimum temperature was little affected by
duration of cold treatment (Yeh et al., 1997a).

The optimum temperature also may depend on cultivar or the method by
which the vemalization response is assessed. Rawson et al. (1998) studied
several cultivars of wheat differing in their vemalization requirements at several

temperatures. The moderate winter cultivar Oxley had an optimum vemalization

temperature of 8 to 10 °C when the response was measured as days from
sowing to heading, 6 °C when measured as summed thermal time (°Cd) above a
base of 0 °C, and 3 °C when measured as minimum ﬁnal leaf number at
heading. Different optima can be obtained when the vemalization response is
measured as days from end of cold treatment to heading or days from sowing to
heading. The winter cultivar JF87%014 had an optimum temperature of 8 °C
when the response was measured as days from the end of cold treatment to
heading; 6 °C, from sowing to heading (Rawson et al., 1998).

Robertson et al. (1996) point out that there is a problem in ﬁnding an
optimum temperature for vemalization because the effectiveness of any
temperature in lowering ﬁnal leaf number is confounded with its effect on
vegetative development. They found that the saturataion rate of vemalization in
various winter-wheat cultivars (they considered vemalization saturated in
treatments in which the number of leaves initiated at the end of the treatment
equaled the ﬁnal number of leaves produced beneath the ﬂower) responded
linearly to temperatures between 5 and 14 °C. Vemalization’s effectiveness in
decreasing the number of leaves below the ﬂower decreased with temperature,
and there was no optimum temperature. They suggested that higher
temperatures were less effective because the rate of leaf primordium initiation
responds more strongly to temperature than does that of vemalization
(Robertson et al., 1996).

Duration of cold treatment. Vemalization is a quantitative process whose

intensity increases with the length of the exposure until a saturation response
(here deﬁned as no further reduction in time to ﬂower or ﬁnal leaf number) occurs
(Vince-Prue, 1975). The duration of time to saturation is species- and cultivar-
speciﬁc, but usually will occur between 10 and 100 days of low-temperature
treatment (Thomas and Vince-Prue, 1984).

Increasing durations of cold treatment inﬂuence other plant characteristics
such as height, ﬂower number, and days to ﬂower. Inﬂorescence number of
Lavandula angustifolia Mill. grown at 20 °C under a 9-hour day plus a 4-hour
night interruption (NI) increased from 2 to 11 as cold duration (at 5 °C) increased
from 0 to 15 weeks (Whitman et al., 1996). The increase in ﬂower number with
cold treatment was not as dramatic when L. angustifolia was grown under 9-hour
short days. Flowering did not occur until plants had received a minimum of 10
weeks of cold, and ﬂower number increased only slightly (from approximately 5
to 6) when cold duration was increased from 10 to 15 weeks. Inﬂorescence
number of Leucanthemum xsuperbum Bergman ex J. Ingram ‘Snowcap‘ grown
at 20 °C under NI increased from 5 to 13 as cold treatment (at 5 °C) increased
from 0 to 15 weeks (Runkle et al., 1998). Plant height of 'Snowcap‘ increased
from 14 to 22 cm as cold duration increased from 0 to 12 weeks.

Stability of the vemalization response, or the length of time that a chilled
plant maintains the inductive effects of the cold treatment, increases with
duration of cold treatment. Picard (1965) found that for Oenothera biennis L.

var. Sulfurea, the vemalized state was lost after exposure to short days (8 hours)

at 18 to 22 °C for 12 to 20 days.

Antivemalization and devemalization. High temperatures (generally above 30
°C) given either before or after the cold treatment can inﬂuence the vemalization
response. Several researchers observed that when high temperatures were
given prior to the cold treatment, there was a nulliﬁcation of, or a decrease in,
the vemalization response (Lang, 1965). This effect was termed
"antivernalization." A recent study of the effect of high temperature before cold
treatment on subsequent ﬂowering of Brassica napus L. var. annua (a plant that
has a quantitative response to cold) showed that ﬂowering of several genotypes
was delayed by the heat treatment (30 °C) (Dahanayake and Galwey, 1998).
For example, plants of genotype TB 14 exposed to a 30 °C treatment for 2 days
before an 8-week 4 °C treatment ﬂowered 8 days later than unexposed cold-
treated control plants. Extending the heat treatment from 2 to 4 days further
delayed ﬂowering of this genotype; these plants ﬂowered 13 days later than the
control plants (Dahanayake and Galwey, 1998).

Devemalization is the elimination or reduction of the vemalization
response when a heat treatment is given immediately after the cold treatment.
Temperatures from 20 to 40 °C generally cause devemalization (Napp-Zinn,
1961). Temperatures between 12 and 15 °C cause neither vemalization nor
devemalization in many winter cereals (Lang, 1965). Devemalization may occur
only when the duration of cold temperatures is relatively short. Purvis and

Gregory (1952, Cited by Purvis, 1961) found that after 8 or more weeks of cold,

winter rye could not be devemalized. They also noted that even partially
vemalized plants could not be devemalized if they were kept at a neutral
temperature for a few days before the heat treatment was applied. The
vemalization response then was deemed to be ”ﬁxed" or "stabilized" (Purvis,
1961; Lang, 1965). Recent work with the cineraria cultivars Cindy Blue and
Cindy Dark Red supports the ﬁndings of Purvis and Lang (Yeh et al., 1997b).
Temperatures of 20 °C or less promoted devemalization when the cold duration
(at 6 °C) was 1 or 2 weeks. Devemalization response increased with
temperature and length of heat treatment. Cultivars stabilized after 3 to 9 days
at 15 °C, even plants that were only partially vemalized. In contrast, Brassica
napus var. annua did not stabilize rapidly even when cooled plants were
maintained at 15 °C for one week prior to heat treatment at 30 °C (Dahanayake
and Galwey, 1998). In fact, devemalizing heat treatments were more effective
after 1 week of stabilization. It was only after 2 weeks at the neutral temperature
(15 °C) that devemalization was not as effective.

Not all species can be devemalized by a simple high temperature
treatment. A cold-requiring variety of Chrysanthemum did not devemalize
completely even when exposed to 35 °C for 30 days (Schwabe, 1955).
However, this variety was devemalized by a low-intensity light treatment of about
25 foot-candles (given by incandescent bulbs) combined with high temperature
(28 °C) for 10 to 20 days although neither treatment alone had a measurable

effect (Schwabe, 1957). Napp-Zinn (1960, cited by Lang, 1965) found that, for

Arabidopsis thaliana (L.) Heynh. , devemalization did not occur if plants were
kept in light during the high temperature treatment. Lang (1965) cautions that
the inhibitory action of high light with respect to devemalization indicated by the
results with Arabidopsis and Chrysanthemum actually may be a general
response, since many devemalization experiments were conducted in darkness
or weak light.

Plant age. The age at which plants are able to perceive cold temperatures for
effective vemalization is very species speciﬁc. Some species such as ‘Petkus’
rye and winter wheat are capable of perceiving low temperatures soon after
fertilization, while others such as Hyoscyamus niger must be at least 10 days old
(Purvis, 1961).

In many cases, younger plants require a longer duration of cold to achieve
vemalization saturation than do older plants. When Gott (1950, cited by Purvis,
1961) chilled rye plants of different ages, she found a decline in response when
plants were older than 2 weeks. Picard (1965) found that young plants of O.
biennis (with a minimum of 10 leaves) required 17 weeks of cold treatment (at 11
°C/3 °C D/N) for 100% ﬂowering, while older plants (minimum 50 leaves)
required 13 weeks for 100% ﬂowering. Recent work with two cultivars of winter
wheat (Triticum aestivum L. Pioneer 2548 and Augusta) showed that the
estimated minimum days of cold treatment required to reach saturation of the
vemalization response decreased linearly with increasing plant age at the

beginning of the cold treatment (Wang et al., 1995). These authors suggest an

10

interchangeability between days of cold treatment and plant age.

Robertson et al. (1996) proposed and tested a model to explain the
interaction between plant age and vemalization. The model predicted the ﬁnal
leaf number below the ﬂower based on the effect of temperature on the rate of
vemalization saturation and rate of leaf initiation for wheat under continuous and
intermittent low temperature. Plants grown under intermittent low temperatures
progress toward ﬂowering through a combination of rates, depending on the
temperature at any given time. When Robertson et al. (1996) ﬁtted the data of
Wang et al. (1995) to their model, they found that the model satisfactorily
predicted a range of ﬁnal leaf numbers between 8 and 21, with an r2 of 88%. For
the authors this model explained to a reasonable extent the interchangeability
between plant age and vemalization.

Plant age when the cold treatment is given can inﬂuence the stability of
vemalization. Younger plants of O. biennis had lower vemalization stability than
older plants when both were maintained under short days after cold treatment
before being moved to inductive long days (Picard, 1965).

Light and vemalization. The interactions between photoperiod, light quality,
light quantity, and vemalization are complex and inconclusive. Napp-Zinn (1984)
describes the often conﬂicting results in this area of research as discouraging
and points out that there still is too little information. He also indicates that
vemalization likely means different things in different species or even in different

genotypes of the same species.

11

Vemalization can be substituted by an appropriate photoperiod in certain
cases. Short-day vemalization, or the replacement of a cold treatment by short
days, ﬁrst was studied in the 19305 for ‘Petkus’ rye (Napp-Zinn, 1984).
Wellensiek (1960) was the ﬁrst to discover short-long day induction in a
dicotyledon, Campanula medium L., a discovery Chouard (1960) refers to as
"Wellensiek's phenomenon." Wellensiek (1960) observed that if a Campanula
rosette was grown to three months of age and then exposed to at least 4 weeks
of warm (20 °C) short days, it would ﬂower when transferred to 16-hour long
days. Flowering under short days only was never observed, even after 2 years.
Increasing the number of short days did increase the percentage of plants that
bolted, but did not regularly decrease the days to bolting. Wellensiek ( 1960)
also noted that ”the reaction to warm short days is not as regular as to cold."

An experiment using a winter race of barley (Hordeum vulgare L. 'Arabi
Abiad') showed unequivocally that short days can substitute for vemalization in
this species (Roberts et al., 1988). Photoperiods of 8 or 10 hours given after
germination were sufﬁcient to decrease the number of leaves beneath the ﬂower
by a factor of 3.3 when compared to that of plants given a 13-hour photoperiod.
The minimum number of leaves formed with short-day vemalization is 9 or 10.
Photoperiods longer than 13 hours did not increase the number of leaves
beneath the ﬂower. However, substitution by short days does not appear to be
equal to vemalization by cold treatment since ﬂowers can emerge after formation

of 6 or 7 leaves if the plant is cold-treated (Roberts et al., 1988).

12

Substitution of a cold treatment by long days has been documented for
several species. Pisum sativum L. genotype If e Sn hr kept in continuous light
did not respond to vemalization; in fact, vemalized plants grown under
continuous light ﬂower at a node slightly higher than that of unvemalized plants
(Murfet and Reid, 1974). When plants are grown under short days (8 hours),
vemalization promotes ﬂowering of genotype If e Sn hr 6 nodes lower than that
of unvemalized plants. Runkle et al. (1998) found that, for L. xsuperbum
'Snowcap', 80% of plants grown at 20 °C under NI ﬂowered without a cold
treatment, while 80% of plants grown under a 9 hour short day required a
minimum of 3 weeks at 5 °C. When Campanula Iongestyla Fomin. was grown
under 16 hour long days, plants ﬂowered without vemalization, but when the
photoperiod was reduced to 14 hour, plants required vemalization (Mathon,
1960).

Substitution of a cold treatment with light of particular radiation ratios or of
high irradiances also has been demonstrated. Bagnall (1993) showed that for
three late-ﬂowering ecotypes of Arabidopsis (’Eifel’, ‘lnnsbruck', ‘Pitztal’), time to
ﬂower and leaf number at ﬂower were halved when nonvemalized plants were
grown under ﬂuorescent and incandescent lights (R : FR = 1.0) compared to
those grown strictly under ﬂuorescent lighting (R :FR = 5.8). Bagnall terms this
phenomenon of ﬂower induction by different ratios of radiation "photoinduction."
Work by Chouard during the 1960s revealed that several species, including

Geum urbanum L. and Dactylis glomerata L., ﬂowered without cold when they

13

were kept under long days or continual light at high irradiances, usually above
14,000 Ix. Napp-Zinn (1984) suggests that this effect may be due to
photosynthesis, since it often is accompanied by a need for high mineral
nutrition.

In certain cases, the duration of light before the cold treatment can have
an effect on subsequent ﬂowering. Long days before cold treatment were
beneﬁcial for Oenothera biennis var. sulfurea because they caused a shorter
juvenile period (Picard, 1965). Under long days (16 hours) 0. biennis perceived
vemalizing cold temperatures 50 to 60 days after germination, while under short
days (8 hours), the species could not perceive cold temperatures for 5 to 6
months at 18 to 22 °C.

Experiments comparing different photoperiods during cold treatment yield
inconsistent results. Long days, short days plus a night break, or continual light
during cold treatment reduced subsequent ﬂowering of celery, while they
enhanced ﬂowering of Arabidopsis 'Stockholm' (Napp-Zinn, 1984). For
Campanula medium, there was no difference between plants exposed to long or
short days during the 5 °C cold treatment (Wellensiek, 1960). The photoperiod
during the cold treatment also had no inﬂuence on subsequent ﬂowering of O.
biennis (Picard, 1965).

Perception of Vemalization
Early experiments demonstrated that vemalization is perceived in the

shoot tip. Evidence for this conclusion came from localized cooling experiments

14

in which either the roots or shoots were cooled separately while the rest of the
plant was kept In noninductive temperatures (Lang, 1965). Gregory and Purvis
(1938, Cited by Lang, 1965) showed that even fragments of embryos, which
consisted of only the shoot tip, could respond to the low temperatures. Grafting
studies showed that only when the shoot tip itself had been exposed to low
temperatures would ﬂowering occur (Lang, 1965). Metzger (1988) found that
maintaining roots of Thlaspi arvense L. at 21 °C (while shoots were kept at 4
°C) reduced subsequent stem elongation, and he suggested that cold treatment
of tissue other than the apex may be important for integration of reproductive
development.

Since the site of perception appears to be in the shoot tip, dividing cells
may be necessary for vemalization to occur (Wellensiek, 1964; Lang, 1965). If
this supposition is true, then any dividing cell in the plant may be vemalizable.
Wellensiek (1964) provided support for this theory when he found that excised
leaves of Lunaria biennis L. given a cold treatment could regenerate plants that
immediately ﬂowered. When he cut off the lowest 0.5 cm of the petiole, where
regeneration and thus cell division takes place, the regenerated plants remained
vegetative. In contrast to Wellensiek, Metzger (1988) observed that when shoots
were regenerated from Thlaspi arvense leaf cuttings from which the lower 1 to 2
cm had been removed (which occurred in only 10 to15% of the cuttings), all
shoots immediately ﬂowered. He suggested that many cell types, not

necessarily only actively dividing cells, may become vemalized. However, since

15

the outcome of vemalization is the ability to ﬂower and ﬂowering occurs on
structures that arise from the shoot apex, it may be coincidental that the apex is

considered the site of perception (Metzger, 1988).

Mechanism of Vemalization

To date, very little is known about the mechanism of vemalization. The
role of classical plant hormones in the vemalization process is still unclear and
evidence for a ﬂower-forming hormone produced by therrnoinduced tissue is
equivocal. In 1965, Lang stated that studies into the biochemical foundations of
vemalization were inconclusive. Almost thirty years later, Hazebroek (1993)
wrote, "Essentially nothing is known about the biochemical or molecular
processes that occur during vemalization.” While attempts to elucidate the
mechanism of vemalization have been frustrating, recent genetic studies have
provided some new insight and may renew interest in the study of vemalization.
Grafting studies. In several early experiments, the subsequent ﬂowering of
nontherrnoinduced receptor plants grafted onto therrnoinduced donor plants
suggested the existence of a graft-transmissible ﬂower-forming material (Lang,
1965). Successful grafts in which the nontherrnoinduced receptor ﬂowered were
made between many different species and response types. Lang (1965)
commented that many of these experiments were performed in inductive long-
day conditions for the donor, and that ﬂowering of the receptor therefore may

have been due to the transmissible material (also called "ﬂorigen") produced in

16

response to photoperiod and not necessarily just thermoinduction. Direct
evidence for a transmissible material formed during therrnoinduction came from
grafting nontherrnoinduced Hyoscyamus niger to the short-day plant Maryland
‘Mammoth tobacco’ (Melchers, 1939, cited by Lang, 1965). The H. niger
receptor ﬂowered under both long and short days, which indicated that a
transmissible material (named 'vemalin”) was produced by the therrnoinduced
tissue. Efforts to extract substances from therrnoinduced plants that induced
ﬂowering in nontherrnoinduced plants were unsuccessful (Lang, 1965).

Grafting studies using Pisum sativum also have revealed evidence for a
transmissible substance. Reid and Murfet (1975) grafted unvemalized or
vemalized scions to unvemalized or vemalized stocks and used several different
lines (both early- and late-ﬂowering) of P. sativum. They found that chilling the
stock of late-ﬂowering lines (which contain the Sn gene) could promote ﬂowering
in unvemalized scions. In fact, vemalization of the stocks for these late-ﬂowering
lines more effectively reduced the node number below the ﬂower than
vemalization of the scions. They suggested that the Sn gene produces a
ﬂowering inhibitor and that vemalization suppresses its action. They also
suggested that vemalization is active at two sites: the shoot tip and the
cotyledons (the only node below the graft).

While ﬂowering of nontherrnoinduced receptor plants has been achieved
in grafting studies, there were many other studies in which a nonthennoinduced

receptor did not ﬂower, regardless of the state of the donor (Lang, 1965).

17

Chouard (1960) states that, aside from the success of graft transmissibility in
Hyoscyamus, ﬂowering of a noninduced receptor on a therrnoinduced donor is
not generally effective and is "only quite rarely successful."

Gibberellins. The application of gibberellins (GAs) to nonthennoinduced plants
produces a broad range of responses; for some species, GAs can induce
ﬂowering in nontherrnoinduced plants, while for others, they result in stem
elongation but no ﬂower formation (Lang, 1965). In general, treating seeds with
GAs does not effectively induce ﬂowering (Lang, 1965). Stem elongation
precedes ﬂower formation in GA-treated plants, while ﬂowering and elongation
occur simultaneously after a cold treatment (Lang, 1965).

Applying inhibitors of GA biosynthesis can inﬂuence the ﬂowering
process. For example, uniconazole, a triazol GA biosynthesis inhibitor applied 3
days before a 20-day cold treatment, delayed both stem elongation and
ﬂowering of Raphanus sativus L. (Japanese radish), a strongly facultative cold-
requiring plant (Nishijima et al., 1997). The effects of uniconazole on stem
elongation and ﬂowering reached a maximum at 2 pmollpot, at which rate
ﬂowering was delayed by 23 days and stem elongation was reduced by 48 cm.
Increasing the cold treatment from 20 to 40 days moderated the effects of
uniconazole only slightly. Days to stem elongation for plants cooled for 40 days
were reduced by approximately 13 compared to that of plants cooled for 20
days. Days to ﬂower and stem length were similar for plants given either

duration of cold treatment. Timing of the GA inhibitor application was important:

18

if the application was made during the cold treatment, it reduced stem elongation
and delaying ﬂowering, but if it was made at or 5 days after the end of the cold
treatment, ﬂowering was not delayed (Nishijima et al., 1997).

Zeevaart (1978) proposed that the response to GA may depend on using
the "appropriate GA". For Myosotis alpestris F.W. Schmidt, GA7 induced both
stem growth and ﬂowering, while GA3 induced only stern growth (Michniewicz
and Lang, 1962, cited by Zeevaart, 1978). Research of Wittwer and Bukovac
(1962) also demonstrated a differential effect on ﬂowering when different GAs
were applied to lettuce. Both GA3 and GA1 were able to induce 100% ﬂowering,
while GA, and GA5 induced 30 to 40% ﬂowering and GA; and GAB were unable
to induce it. Zeevaart (1978) suggested that plants that do not respond to GA
might not be receiving the appropriate form.

Gibberellins may inﬂuence ﬂowering of those plants with suboptimal cold
treatments. In a study on vemalization and exogenous Gas’ effect on ﬂower
induction of Brassica oleracea L. var. botrytis (cauliﬂower), Fernandez et al.
(1997) showed that GA(4+-,) accelerated ﬂowering of plants grown at 22 °C (weak
ﬂower-inducing conditions) but not 10 °C (strong ﬂower- inducing conditions).
Plants grown at 10 °C produced a ﬂower after 23 leaves had emerged,
regardless of GA application. Plants that were not treated with GA and grown at
22 °C produced a ﬂower after 38 leaves had emerged. Plants that were grown
at 22 °C and treated with GA, however, produced a ﬂower after 26 leaves had

emerged (Fernandez et al., 1997).

19

For some species, levels of GAs increase after the cold treatment (Lang,
1965; Zanewich and Rood, 1995). Hazebroek et al. (1993) found that the activity
of the enzyme kaurenoic acid hydroxylase, which converts kaurenoic acid to 7-
OH kaurenoic acid (two members of the GA biosynthetic pathway), was
increased after vemalization. In addition, the up-regulation of the enzyme was
localized in the shoot tip and no change was observed in the leaves. For
Brassica napus 'Crystal', Zanewich and Rood (1995) found that not only were
endogenous levels of GAs increased (3.1, 2.3, 7.8, 12.0, and 24.5 times higher
for GA1‘ GA3, GAB. GA19' and GAZO' respectively) after vemalization, but also the
metabolism of GAs was changed. Vemalized plants showed an increase in the
conversion of [3H]GA20 to an [3H]GA1-like metabolite and reduced conversion of
[3HjGA20 or [3H]GA1 to polar [3H] metabolites, possibly representing GA glucosyl
conjugates.

The association between GAs and the ﬂowering process also has been
indicated by GA-deﬁcient mutants. The rosette mutant of Brassica napus has
about one-tenth of the normal level of total GAs and ﬂowers very slowly
compared to the wild type (Rood et al., 1989).

Genetics of vemalization

A vemalization requirement is a heritable property. In certain species,
crosses between winter and spring races showed that the vemalization character
seemed to follow predicted Mendelian ratios (Chouard, 1960). Over the years,

genes, linkage groups, and cDNAs that either confer late ﬂowering or are

20

associated with a vemalization requirement have been identiﬁed.

Genes that inﬂuence the requirement for vemalization have been
identiﬁed in several species. For such species as Tn'ticum, Arabidopsis, and
Pisum, numbers of genes involved in vemalization have been deduced by the
study of segregation ratios. It was postulated that there are four Tn’ticum loci,
labelled Vm-1 ton-4 (Napp-Zinn, 1987). For Pisum, 20 genes initially were
identiﬁed and were alleles of four individual loci. A dominant allele at either of
two loci, Lf or Sn, confers late ﬂowering. The requirement for vemalization is
not always caused by the presence of a dominant allele. Recessive alleles
appear to cause a vemalization requirement for Tn'ticum and Arabidopsis (Napp-
Zinn, 1987). In Arabidopsis thaliana, the single FRI locus is apparently the
cause for the difference between the winter ecotypes SF-2 and Le-0 and the
spring ecotype Col. After the cold treatment, all ecotypes with the FRI locus,
either naturally occurring or introduced, ﬂower early (Lee et al., 1993). However,
the action of FRI is not necessarily based on simply presence or absence of the
locus. In the Ler background, the FRI locus causes only a delay in ﬂowering
when another locus, FLC, is present (Lee et al.,1994). Lee et al. (1994) suggest
that FRI and FLC act to suppress ﬂowering.

The FRI locus also confers a strong responsiveness to light quality. Far
red light accelerated ﬂowering of plants containing the FRI locus when they
received no cold treatment (Lee and Amasino, 1995). After a cold treatment, the

acceleration of ﬂowering time by far red light was eliminated. Since vemalization

21

did not inﬂuence the effect of far red light on petiole extension, the authors
concluded that the effects of vemalization on ﬂowering occur after far red light
perception.

In contrast to situations in which one or a few genes are responsible for
the vemalization requirement, sometimes there are cases where it appears that
many genes may be involved. Teutonico and Osborn (1995) mapped
quantitative trait loci (QTL) for ﬂowering time in Brassica rapa L. They found two
linkage groups associated with variation for ﬂowering time in unvemalized plants.
After vemalization, neither of these QTL had a signiﬁcant effect on ﬂowering
time. It is interesting to note that an RFLP locus identiﬁed with a clone from the
Arabidopsis cold-induced gene COR6.6 mapped very close to one of the B. rapa
QTL (T eutonico and Osborn, 1995). Osborn et al. (1997) compared the QTL for
ﬂowering time in B. rapa with QTLs in B. napus and A. thaliana. By aligning map
positions they found that the two QTL from B. rapa corresponded to two major
QTL for ﬂower timing already identiﬁed in B. napus. The RFLP loci were
mapped for both B. napus and A. thaliana by using Arabidopsis probes for
ﬂowering time genes and one of the Brassica QTL was collinear with the top of
chromosome 5 of Arabidopsis. This area contains the locus FLC and various
other ﬂowering loci (Lee et al., 1994). The other Brassica QTL showed fractured
collinearity with several regions of the Arabidopsis genome, one of which was
the top of chromosome 4 where FRI is located (Lee et al., 1993).

Recently, three mutants with altered vemalization responses were

22

identiﬁed at three independent loci in Arabidopsis (Chandler et al., 1996). Each
of the mutants was induced by ethyl methane sulphonate (EMS) in the ice
mutant in the Ler background, which itself shows late ﬂowering and a strong
response to vemalization. The three loci identiﬁed were named VRN1, VRN2,
and VRN3. Before vemalization, vm1-1 fca-1 ﬂowered at the same time as fca-1
but, after vemalization, ﬂowered about 9 days later (a 42% reduction of the
vemalization response); vm2-1 fca-1 differed from vm1-1 fca-1 because it
ﬂowered later than fca-1 both before and after vemalization. The upper arm of
chromosome 3 contained VRN1 (Chandler et al., 1996).

Chong et al. (1994; 1998) identiﬁed two cold-induced cDNAs (verc17 and
verc203) thought to be speciﬁc for the vemalization response in wheat. The
verc17 appeared in vemalized winter wheat tissue only; it was absent in
nonthennoinduced and devemalized plants. The verc1? CDNA had signiﬁcant
homology with such diverse genes as a L. lactis Plll-type proteinase, maturation
protein genes, and a major merozoite surface antigen gene. When wheat plants
were transformed with the antisense RNA of the vemalization-speciﬁc CDNA
ver0203 under control of the CaMV 358-promoter, it was found that ﬂowering
was greatly delayed (z160 days to ﬂower for antisense compared to 2102 days
to ﬂower for the natural orientation of the DNA). These results suggest that the
VER203 protein has a role in controlling ﬂower development in winter wheat
(Chong et al., 1998).

Although progress has been made in identifying genes involved

23

associated with vemalization, little is known about how their function in creating
the phenomenon known as vemalization. Burn et al. (1993) found that ﬂowering
in Thlaspi arvense and Arabidopsis thaliana (late ecotype) could be accelerated
signiﬁcantly if unvemalized plants were treated with 5-azacytidine, a DNA
demethylating agent. In contrast, treatment with 5-azaC did not inﬂuence
ﬂowering of vemalized plants. When the treated plants were allowed to set
seed, the resulting plants behaved as if unvemalized. After cold or treatment
with 5-azacytidine, both Nicotiana plumbaginifolia L. and Arabidopsis show
reduced levels of 5-methylcytosine in their DNA. The authors suggested that
methylation status could be a control mechanism of vemalization. Brock and
Davidson (1994) also found that 5-azacytidine as well as gamma rays (thought to
be a demethylating agent) could substitute partially for a cold treatment. The 5-
aza-C treatment induced signiﬁcantly earlier ﬂowering in both spring and winter
wheats, but the response was pronounced for the winter wheat. The gamma
rays effectively reduced ﬂowering time in the winter wheat only.

Recently, the hypothesis that the promotion of ﬂowering by vemalization is
mediated by DNA demethylation was tested by transforming Arabidopsis plants
with a methyltransferase (MET1) antisense gene (Finnegan et al., 1998). The
authors found that plants homozygous for ME T1 had 15% of normal methylation
levels and ﬂowered signiﬁcantly earlier than untransformed controls. They also
found that the promotion of ﬂowering generally was correlated with the extent of

demethylation. They tested plants of three methyltransferase antisense families

24

that differed in DNA demethylation magnitude; plants homozygous for four
copies of the antisense gene ﬂowered signiﬁcantly earlier than those
homozygous for three. Demethylation caused by the MET1 antisense transgene
did not prevent a response to vemalization. Cold treatment of antisense plants
accelerated ﬂowering compared to that of untreated antisense plants, which
indicates that demethylation caused by the MET1 antisense transgene did not
saturate the early ﬂowering response and acted additively with a cold treatment.
Studies of the inheritance of early ﬂowering used plants with the ME T1
antisense transgene and showed that demethylation caused by the transgene
did not exactly replicate early ﬂowering due to vemalization (Finnegan et al.,
1998). For wild type plants, the requirement for vemalization is reset every
generation (possibly because of remethylation during gametogenesis or
embryogenesis). Like those of wild type plants, progeny of cold-treated or
untreated antisense plants ﬂowered at the same time, which shows that the
MET1 antisense transgene does not inhibit the resetting process. However,
progeny of plants hemizygous for the transgene (and not given a cold treatment)
ﬂowered earlier than progeny of an untransformed plant. Even progeny that did
not contain the antisense transgene had reduced levels of methylation and
ﬂowered earlier than progeny of untransformed plants. Although this response
does suggest that early ﬂowering is caused by lower levels of methylation and
not the transgene itself, it also shows that early ﬂowering due to demethylation

by MET1 antisense does not replicate all aspects of vemalization. Finnegan et

25

al. (1998) suggested that there may be two processes involved if demethylation
of DNA is necessary for vemalizationu one involved in the actual demethylation,
the other involved in resetting the vemalization requirement each generation.
Alternatively, the authors suggest that there may be several methyltransferases
that methylate different sites and that the MET1 antisense transgene affects

only one of these.

Conclusion

Although a great deal of information that characterizes the phenomenon
of vemalization and the genetics involved has been generated, much is still
unknown. The complex interactions between temperature before, during, and
after the cold treatment, photoperiod, light intensity, and plant maturity make it a
difﬁcult subject to study. Regardless, a greater understanding of the genetic
mechanisms for controlling developmental processes should shed light on the
mystery of how cold temperatures are perceived and how this stimulus is

translated into the ability to ﬂower.

26

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31

Growth and Development of Oenothera fruticosa Is Inﬂuenced by Cold

Treatment, Photoperiod, Forcing Temperature, and Plant Growth Regulators

32

Abstract

The inﬂuences of cold treatment, photoperiod, forcing temperature, and plant
growth regulators on growth and development of Oenothera fruticosa L.
‘Youngii-Iapsley’ were determined. Plants were cooled at 5 °C for 0, 3, 6, 9, 12,
or 15 weeks under a 9-h photoperiod and subsequently forced in a 20 °C
greenhouse under a 16-h photoperiod. Only one plant in two years ﬂowered
without cold treatment. Time to visible bud and ﬂower decreased about 1 week
as cold duration increased from 3 to 15 weeks. Response of plants to 10-, 12-,
13-, 14-, 16-, or 24-h photoperiods or a 4-h night interruption (NI) were
determined in a 20 °C greenhouse following 0 or 15 weeks of cold treatment at 5
°C. Flowering occurred under all photoperiods only after cold treatment. Time
to ﬂower decreased about 2 weeks, ﬂower number decreased, and plant height
increased as photoperiod increased from 10 to 24 h. Days to ﬂower under NI
were similar to that of plants grown under a 16- h photoperiod. To determine the
effect of forcing temperature on ﬂowering of ‘Youngii-lapsley', plants were cooled
for 15 weeks and then forced under a 16-h photoperiod at 14, 17, 20, 23, 26, or
29 °C. Plants ﬂowered more quickly at higher temperatures but were taller and
produced fewer and much smaller ﬂowers. Days to visible bud and ﬂowering
were converted to rates, and base temperature (Tb) and thermal time to ﬂowering
(degree-days) were calculated as 4.4 °C and 606 °day. The effects of spraying
ancymidol, Chlorrnequat, paclobutrazol, daminozide, and uniconazole were

tested on plants cooled for 19 weeks and forced at 20 °C under a 16-h

33

photoperiod. Final plant height was reduced 31% and ﬂower diameter was
reduced 36% for plants sprayed with uniconazole. Plants sprayed with all other

plant growth regulators were similar to control plants.

34

Introduction

Many species of Oenothera have been cultivated since the early 18008
when they were brought from North and South America to England where they
became popular garden plants (Wiesner,1991). Oenothera fruticosa L., or
sundrops, is native to eastern North America and hardy in USDA zones 4-8.
Oenothera fmticosa is a day-ﬂowering species that typically ﬂowers in June
(Grifﬁths, 1994; Nau, 1996). In a preliminary screen, the vegetatively propagated
cultivar Youngii-Iapsley showed great ornamental ﬂowering potted-plant potential
with its long natural ﬂowering time (=4 weeks) and numerous large bright-yellow
ﬂowers (Frane, 1999). To our knowledge, no species of Oenothera is grown
currently as a pot plant; for potted plant production, detailed information on
ﬂowering requirements is needed.

Vemalization and photoperiod are two important factors regulating
ﬂowering of vegetative propagules. Vemalization can be deﬁned as the
promotion of ﬂower formation by a period of low temperatures, generally
between -5 and 15 °C, with a broad optimum between 1 and 7 °C (Lang, 1965).
A vemalization requirement often is linked to a speciﬁc photoperiod requirement,
which for many species is usually, but not always, a long-day requirement
(Vince-Prue, 1975). Flowering of many herbaceous perennials is inﬂuenced by
vemalization and photoperiod (lversen and Weiler, 1994; Whitman et al.,

1996,1997; Runkle et al., 1998).

35

Many early experiments investigating the role and mechanism of
vemalization and photoperiod in ﬂowering were performed on various species of
Oenothera and several different response types were identiﬁed. Picard (1965)
observed ﬂowering of O. biennis var. sulfurea De Vries only after a minimum
cold treatment (at 11 °C /3 °C day/night [D/N]) of 10 weeks followed by long
days 212 h. Other species of Oenothera, including 0. suaveolens, O.
Iongiﬂora, and O. stricta, had facultative requirements for vemalization followed
by an obligate requirement for long days (Chouard, 1960). Oenothera rosea
L’Herit. ex Ait. is a facultative long-day plant with no response to vemalization
(Chouard, 1960). In preliminary experiments, ‘Youngii-lapsley’ appeared to be a
facultative long-day plant with an obligate vemalization requirement (Frane,
1999)

Knowledge of the effect of temperature on plant development is important
to accurately time crop production. Without photoperiod or vemalization effects,
the rate of development increases linearly with temperature within a limited
range of growing temperatures (Roberts and Summerﬁeld, 1987). Such
responses are also evident in photoperiod- and vemalization-sensitive species
when the separate effects of photoperiod and vemalization are removed from
those of postvemalization temperatures. The relationship between temperature
and rate of development toward ﬂowering (1/DTF where DTF is days to ﬂower)
can be described as follows:

1/DTF = bo + b,*T [1]

36

where b0 and b1 are constants and T is temperature (°C) (Roberts and
Summerﬁeld, 1987).

The base temperature (T.,), or the temperature at or below which the rate
of progress toward ﬂowering is zero, and thermal time, or the number of units
(°days) of thermal time above a base temperature, required for ﬂowering can be
calculated from the constants in Equation 1 as follows:

T.,= -b,,/b, [2]

°days=1lb1 [3]

Growing temperature can affect plant appearance as well as ﬂower timing.
For Antinhinum majus L. ‘Jackpot’, there was an increase in stem length, spike
length, and number of ﬂorets as temperature decreased from 21 to 10 °C
(Maginnes and Langhans. 1961). Flower size decreases with increasing
temperature in Galinsoga parviﬂora Cavan. and Agrostemma githago L.

(Knapp, 1957); Campanula carpatica Jacq. ‘Blue Clips’ (Whitman et al., 1997);
Gail/ardia xgrandiﬂora Van Houtte ‘Goblin’, Leucanthemum xsuperbum Bergman
ex J. Ingram ‘Snowcap’, Coreopsis grandiﬂora Hogg ex Sweet ‘Sunray’ and
Rudbeckia fulgida Ait. ‘Goldsturrn’ (Yuan et al., 1998).

A potential problem in growing 0. fruticosa ’Youngii-lapsley' as a potted
plant is its relatively tall natural height (33-54 cm). Control of height by plant
growth regulator (PGR) treatment may be required to produce high-quality potted
plants. Although we have been unable to ﬁnd literature on the effect of PGRs on

O. fmticosa, Chlorrnequat (up to 3.0 pg) applications to the root zone after

37

chilling had no effect on stem elongation or ﬂowering of O. biennis (Picard,
1967). According to Picard (1967), chlormequat in doses between 50 and 650
pg applied to the apical meristem actually promoted stem elongation, while a
dose of 750 #9 decreased it. Daminozide in doses up to 550 pg applied to the
root zone after chilling decreased stem elongation and delayed ﬂowering, the
effect increasing with larger doses. A dose of 650 ,ug of daminozide completely
inhibited ﬂowering (Picard, 1967).

The objectives of our study were (1 ) to determine and quantify the effects
of cold treatment, photoperiod, and forcing temperature on ﬂowering of O.
fruticosa ‘Youngii-Iapsley’, and (2) to determine the effect of ﬁve commercially
available PGRs on ﬂowering and ﬁnal plant height of ‘Youngii-lapsley’.
Materials and Methods
General. Plants of Oenothera fmticosa ‘Youngii-Iapsley’ were received as rooted
stern cuttings in 72-cell plug trays on 29 Oct. 1997 (Year 1) and 23 Sept. 1998
(Year 2) from the same commercial producer. Upon arrival at Michigan State
University, all plants were held in plug trays and exposed to natural day lengths
(lat. 43 °N;z11-12 h) for 2 or 5 days (Year 1 or 2, respectively) until the
experiments began. Cold treatments were delivered to plants held in plug trays
in coolers set at 5 °C where plants were illuminated for 9 h-dayr1 with cool-white
ﬂuorescent lamps (F96T12/CWNHO, Philips, Somerset, NJ.) at approximately
10 umoI-mZ-st and watered as necessary (approximately 2 times per week) using

well water acidiﬁed with sulfuric acid (HZSO,) to a pH of approximately 6.0.

38

Before placement in the greenhouses (set at 20 °C day/night [D/N] unless
otherwise stated), plugs were transplanted into 13-cm square plastic pots (1 .1-L
volume) with a soilless medium containing sphagnum peat moss, composted
pine bark, vermiculite, and perlite (Strong-lite High Porosity Mix, Strong-Lite,
Pine Bluff, Ark.). Pots were spaced at approximately 22 plants/m2. Plants were
fertilized at every irrigation with a nutrient solution of well water (EC of 0.70
mS-cm‘1 and 105, 35, and 23 mg-L'1 Ca, Mg, and S, respectively) acidiﬁed with
H2SO, to a titratable alkalinity of 130 mg-L'1 CaCO3 and water soluble fertilizer
providing 125-12-125-13 N-P-K-Ca mg-L'1 (30% ammoniacal N) plus 1.0-0.5-0.5-
0.5-0.1-0.1 mg-L'1 (Fe, Mn, Zn, Cu, B, Mo) (MSU Special, Greencare, Chicago,
Ill.) The target range was 0.5-1.2 mS-cm’1 for electrical conductivity (EC) and
5.8-6.2 for pH. In the second year, it was necessary to drench all plants
transplanted after 1 Jan. 1999 twice with a 750 mg N-L'1 liquid fertilizer and K003
to raise the pH and EC into the desired ranges.

Cold duration (Expt. 1). Six durations of cold treatment were tested (0, 3, 6, 9,
12, or 15 weeks). Experiments were initiated on 31 Oct. 1997 (Year 1) and 28
Sept. 1998 (Year 2). Initial node counts on aerial shoots were not taken in Year
1 for any experiment. In Year 2, the initial number of nodes was counted at
transplant and averaged 18.1. A 16-h photoperiod was provided by four-
hundred-watt high-pressure sodium lamps (HPS) switched on at 0800 HR and off
at 2400 HR. HPS lamps provided both photoperiod and supplemental lighting

with a photosynthetic photon ﬂux (PPF) of 50 umol-mZ-s-‘ at plant height starting

39

at 0800 and continuing until the outside PPF exceeded 400 pmoI-mZ-s-L If the
outside PPF then dropped below 200 pmoI-mZ-s-' lamps were again turned on
until 2400 HR. Ten plants were removed from the cooler after each treatment,
transplanted, and placed in the greenhouse.

Photoperiod (Expt. 2). Seven photoperiods (10, 12, 13, 14, 16, and 24 h and a
4-h NI) and two cold treatments (0 or 15 weeks) were tested. Seventy plants
were transplanted on 2 Nov. 1997 (Year 1) and 28 Sept. 1998 (Year 2) and
placed in a greenhouse. Ten plants were used per treatment and treatments
were assigned randomly each year to greenhouse benches. The remaining
plants were left in the plug tray and placed in the cooler. After 15 weeks of cold
treatment, 70 plants were transplanted on 18 Feb. 1998 (Year 1) and 12 Jan.
1999 (Year 2) and placed in the same photoperiod treatments as the ﬁrst set of
70 plants. In Year 2, plants averaged 18.0 nodes.

Opaque black cloth was pulled at 1700 HR and opened at 0800 HR every
day on all benches so all plants received a similar daily light integral. Continual
photoperiods were delivered by day-extension lighting with incandescent lamps
that were turned on at 1700 HR and turned off after each photoperiod was
completed. The 4-h NI was provided by incandescent lamps that were turned on
at 2200 HR and turned off at 0200 HR. Day-extension and NI lighting with
incandescent lamps provided 1 to 3 ,umol-mZ-s' at canopy level. Supplemental

lighting was provided by HPS lamps (which delivered approximately 50

4O

pmoI-mZ-s-‘ at canopy level) between 0800 HR and 1700 HR as described for
Expt.1.

Forcing temperature (Expt. 3). On 28 Sept. 1998, plants left in the plug tray
were placed directly into the cooler for 15 weeks until 12 Jan. 1999, when they
were transplanted. At transplant, plants averaged 19.4 leaves. Ten plants were
placed into each of six greenhouses set to 14, 17, 20, 23, 26, or 29 °C. Plants
received a continual 16-h photoperiod provided by HPS lamps that were on from
0800 HR to 2400 HR and delivered approximately 90 umol-mZ-s-‘ at plant height.
Plant growth regulators (Expt. 4). Five commercially available plant growth
regulators (PGRs) were tested for their ability to control ﬁnal plant height of
‘Youngii-Iapsley’. The PGRs and rates tested included daminozide (butanedioic
acid mono-[2,2-dimethyl hydrazidel) at 5000 mg-L", paclobutrazol
([2R,3R+28,38]-1-[4-chlorophenyI-4,4-dimethyl-2-[1,2,4-triazoI-1-yl]]) at 30 mg-L'
‘, chorrnequat ([2-chloroethyl] trimethylammonium chloride) at 1500 mg-L",
uniconazole ([E]-[S]-1-[4-chlorophenyl]-4,4-dimethyl-2-[1,2,4-triazoI-1-yI]-pent-1-
ene-3-ol) at 15 mg-L'1 and ancymidol (or-cyclopropyl-or-[4-methoxyphenyl]-5-
pyrimidinemethanol) at 100 mgL‘. Plants were given a 19-week cold treatment
at 5 °C and on 6 Feb. 1999 were transplanted and placed in a greenhouse set at
20 °C. A 16-h photoperiod was provided by HPS lamps, as described for Expt.
1. The daily average temperature between transplant and average date of
ﬂowering was 20.6 °C and the average daily light integral was 14.9 mol'm2~day‘.

Plants averaged 18.2 nodes at the beginning of the experiment and were

41

allowed to establish for 10 days before the ﬁrst PGR spray. Eight plants were
sprayed with each of the chemicals until the solution dripped off the leaves
(approximately 3 mI'pIant-I). Following the ﬁrst spray, plants were sprayed every
10 days until the ﬁrst ﬂower opened. In total, there were three applications per
PGR. Eight plants were not sprayed with any chemical and served as the
control.

Preliminary postharvest evaluation. The 10 plants in the 15-week cold treatment
of Expt. 1 (Year 1) were moved to an environmentally controlled chamber on 3
Apr. 1998, approximately 1 week after the ﬁrst ﬂower opened. The average
chamber temperature (measured with a thermometer in a water bath) was 24.6
°C. Plants were given a 24-h photoperiod delivered with both cool-white
ﬂuorescent and incandescent lamps at approximately 90 ,umOI'ITIZ'S'1 (7.8
moI-mz-day‘), watered as needed (usually every day), and were monitored for 12
days for the number of open, ﬂowers, abscised, and spent ﬂowers. Number of
new open ﬂowers was calculated by subtracting the number of open ﬂowers from
the previous day from the number of ﬂowers open on the current day and adding
the current day’s number of spent and abscised ﬂowers.

Data collection and analysis. The data collected for all other experiments (Expts.
1-4) included date of ﬁrst visible ﬂower bud (without dissection) and date of ﬁrst
open ﬂower. Days to visible bud, days to ﬂower, and days from visible bud to
ﬂower were calculated for all experiments. At ﬁrst open ﬂower, total plant height

(excluding the container), number of visible ﬂowers and buds, and number of

42

ﬁnal nodes on the main stem were recorded. In Year 1, the number of ﬁnal
nodes was counted to the last visible leaf. In Year 2, the number of ﬁnal nodes
was counted to the last visible leaf and included the initial leaf count, the number
of new nodes produced during forcing was calculated by subtracting the initial
number of leaves from the ﬁnal number of leaves, and the number of new nodes
beneath the ﬁrst ﬂowering lateral was calculated by subtracting the number of
initial nodes from the number of nodes beneath the ﬁrst ﬂowering lateral. The
number of new nodes beneath the ﬁrst ﬂowering lateral was calculated only for
Expts. 2 and 3. Number of lateral shoots and number of ﬂowering lateral shoots
were recorded for Year 2 only. Flower diameter was recorded for Expts. 3 and 4.
For all experiments, plants that did not have visible buds after 15 weeks of
forcing were considered non-ﬂowering and were discarded. Plants that died
during the experiment were discarded and not included in the results or
calculations.

All experiments were completely randomized designs. Data were
analyzed using the general linear models procedure (PROC GLM)(SAS Institute,
Cary, NC.) for analysis of variance and linear regression procedure (PROC
REG) for regression models. Duncan’s mean separation test was used to
analyze the PGR experiment (Expt. 4) because of the discontinuous nature of
the treatments. All other experiments were analyzed with linear and quadratic
trend contrasts. The cold duration and photoperiod experiments (Expts. 1 and 2,

respectively) were replicated in time, and each experiment was conducted once

43

per year. The forcing temperature and PGR experiments (Expts. 3 and 4,
respectively) were each conducted only once in Year 2.

Greenhouse temperature control and daily light integral collection. Air
temperature was monitored in each greenhouse with 36-gauge (0.127-mm-
diameter) thermocouples connected to a CR 10 datalogger (Campbell Scientiﬁc,
Logan, Utah). The datalogger collected temperature data every 10 s and
recorded the hourly average. Average daily air temperatures from transplant to
average date of ﬂowering were calculated for every treatment in each experiment
and those for Expts. 1 and 2 are shown in Tables 1 and 2. Average daily
temperatures for Expt. 3 are shown in Table 3. Data for Expt. 4 are recorded
above. Temperatures in each greenhouse were controlled by a Priva
environmental computer (model CD750; Priva, De Lier, The Netherlands).

Actual average daily air temperatures were calculated and used in all analyses.
Average daily light integrals were collected at the same interval as
temperatures at canopy level by using a quantum sensor (LI-COR) connected to
the CR 10 datalogger. Daily light integrals were only collected for Expt. 1 in Year

2.

Results and Discussion

Cold duration (Expt.1). Without a cold treatment, only one out of 10 plants
ﬂowered in Year 1 and no plants ﬂowered in Year 2 (Figure 1A). This plant is the
only one that has ﬂowered without cold in any of our experiments (1 out of 180

plants tested) and its ﬂowering behavior was quite different from all other plants

44

examined. This plant ﬂowered 42 to 54 days slower (Figure 1B), produced 47 to
55 more leaves (data not shown), was 23 to 34 cm shorter (Figure 3D) and
produced about 25% the number of ﬂowers that other plants did for Year 1
(Figure 3A). Because ﬂowering without cold treatment was extremely rare, it
was considered an anomaly and was not included in the analysis. We conclude
that ‘Youngii-lapsley' can be classiﬁed as having an obligate requirement for
vemalization with the acknowledgment that the system is “leaky” and on
occasion a few plants will ﬂower without cold treatment.

In the ﬁrst year, days to visible bud decreased quadratically (P g 0.001)
and days to ﬂower decreased linearly (P 5 0.001) as cold duration increased
from 3 to 15 weeks (Figures1B and 1C). In the second year, days to visible bud
decreased linearly (P s 0.001) and days to ﬂower decreased linearly (P 5 0.001)
as cold duration increased from 3 to 15 weeks (Figures1 B and C). While
statistically signiﬁcant, the decrease in time to ﬂower was slight, 7 to 10 days.
While there were signiﬁcant year (P s 0.01), cold duration, and year X cold
duration interaction (P 5 0.001) effects on days from visible bud to ﬂower, the
differences were small (Figure 1D); the largest difference in either year was
four.

Flowering of ‘Youngii-Iapsley’ was very uniform. While there was a
signiﬁcant year effect (P 5 0.001) on days to visible bud, days to ﬂower, and
days from visible bud to ﬂower (P s 0.05), these differences were relatively small.

For example, excluding the single uncooled plant that ﬂowered in Year 1, the

45

greatest difference between the average of any of these variables in either year
was 7 days; the smallest, zero. Within each cold-duration treatment for either
year, all plants ﬂowered within 3 to 9 days.

In either year, there were no signiﬁcant trends for the number of ﬁnal
nodes measured to the last visible leaf (data not shown). In Year 2, the number
of new nodes produced during forcing decreased linearly (P 3 0.001) from 36 to
28 nodes (Figure 2). For time to ﬂower, the slight change in time to ﬂower that
occurred with increasing durations of cold treatment was only slightly correlated
(r2: 0.37) with the decrease in the number of new nodes produced during forcing
(Year 2).

In Year 1, the number of ﬂowers and buds counted at initial ﬂower
opening increased quadratically (P 5 0.001) with increased cold duration (Figure
3A). In Year 2 the trend was also quadratic (P s 0.05) but ﬂower number was
similar for plants cooled for 3 weeks or 15 weeks and highest ﬂower counts were
observed on plants cooled for 6 or 12 weeks (Figure 3A). Thrips infested plants
cooled for 6 or 9 weeks in Year 2, which could have accounted for some of the
decreased number of ﬂowers of plants cooled for nine weeks. Plants cold-
treated for 15 weeks in Year 1 were forced during February and March, while
plants cooled for 15 weeks in Year 2 were forced during January and Febnrary,
and so the higher ﬂower number seen in Year 1 could be due to naturally higher
light levels during forcing. Increasing light intensity has been shown to increase

number of ﬂowers. For Dendranthema xgrandiﬂorum Ramat. grown under a 12-

46

h day, ﬂower number increased from 7.2 to 19.0 as daily light integral increased
from 10.4 to 29.9 mol-mZ-day‘ (Warrington and Norton, 1991 ).

A count of the number of ﬂowering lateral shoots and total (vegetative
and reproductive) lateral shoots in Year 2 showed that the former increased
linearly (P s 0.01) with increased durations of cold treatment (Figure 3B) while
the latter was similar for all durations of cold treatment (data not shown). The
percentage of ﬂowering laterals increased from 69 to 78 as cold increased from 3
to 15 weeks in Year 2 (Figure 30).

Plants in Year 2 averaged 11 cm shorter over all cold duration treatments
than those grown in Year 1 (Figure 3D). In both years there was a signiﬁcant (P
5 0.001) quadratic trend for the inﬂuence of cold duration on ﬁnal plant height.
Photoperiod (Expt. 2). Without a cold treatment, no plants ﬂowered under any
photoperiod in either year. After 15 weeks at 5 °C, all plants ﬂowered under all
photoperiods. There was no signiﬁcant year effect on days to visible bud.
However, there was a signiﬁcant (P 5. 0.001) year effect on days to ﬂower as well
as a signiﬁcant (P 5 0.001) year X photoperiod interaction. The differences
between days to ﬂower over the two years were small; the greatest difference
between the average was six days under the 10-h photoperiod. Days to ﬂower
and days to visible bud decreased quadratically (P 5 0.001) by 14 (Year 1) or 19
(Year 2) as photoperiod increased from 10 to 24 h (Figure 4A and C). Under 4-h

NI, days to ﬂower were 40.4 in both years. Days to ﬂower under NI were similar

47

to that of plants grown under photoperiods of 16 h in both years and 24 h in Year
1.

There was a signiﬁcant (P g 0.001) year effect as well as a signiﬁcant (P 5
0.001) year X photoperiod interaction for days from visible bud to ﬂower. In Year
1, days from visible bud to ﬂower decreased linearly (P 5 0.001) with increasing
photoperiod (Figure 4B). However, in Year 2, the trend was quadratic (P 5
0.001). Actual differences were relatively small (< 7 days).

From these results, we conclude that ‘Youngii-Iapsley’ is a facultative
long-day plant since it ﬂowered under all tested photoperiods, but ﬂowering was
accelerated by two weeks under the longer photoperiods. The fact that no plants
ﬂowered without cold in either year supports our conclusion that ‘Youngii-lapsley’
has a nearly obligate vemalization requirement.

The ﬁnal number of nodes produced under each photoperiod did in
general reﬂect the change in ﬂower timing. In Year 1, the ﬁnal node number
decreased linearly (P 5 0.001) from 38 to 30 under photoperiods $14 to 24 h,
respectively (Figure 5A). However, in Year 2, the Change in ﬁnal node numbers
was quadratic (P s 0.05; Figure 5A). Final number of nodes in Year 2
decreased from 59 to 47 as photoperiod increased from 10 to 24 h. The number
of new nodes produced during forcing in Year 2 (Figure 5B) decreased
quadratically (P s 0.001) from 42 to 29 as photoperiod increased from 10 to 24 h.

There were no signiﬁcant trends for the number of new nodes produced beneath

48

the ﬁrst ﬂowering lateral (data not shown). Under NI, number of nodes to the
ﬁnal leaf was similar to that of plants grown under 16 or 24 h for either year.

The number of ﬂowers and buds at ﬁrst ﬂower decreased markedly
(quadratically; P g 0.001) with increasing photoperiod (Figure 6A). For example,
in Year 2, the average number of ﬂowers decreased from 129 to 36 as
photoperiod increased from 10 to 24 h. There was a signiﬁcant (P 5 0.001) year
effect but the year X photoperiod interaction was not signiﬁcant. In general,
plants grown in Year 2 produced slightly more ﬂowers. The number of ﬂowers
appears to be inﬂuenced strongly by light levels. For example, plants cooled for
15 weeks and grown under a 16-h photoperiod in Expt. 1 provided by day
extension with high-pressure sodium lamps produced 97 ﬂowers while plants in
Expt. 2 also cooled for 15 weeks and provided a 16—h photoperiod with day
extension from incandescent lamps produced 47 ﬂowers (Year 2). It was
estimated that day extension with incandescent lamps reduced the daily light
integral by 22 % compared to day extension with high-pressure sodium lamps.
This estimation was found by subtracting the amount of light available during
daylight hours (0800 to 1700 HR) (as measured by a LI-COR quantum sensor
placed on the bench at canopy height) from the amount of light available during
the full 16-h photoperiod of day extension with high-pressure sodium lamps, and
assuming that incandescent lamps (with an output of 1-3 umoI-mz-seC")

contribute essentially no light beyond the compensation point.

49

The number of ﬂowering lateral shoots and total lateral shoots decreased
quadratically (P s 0.01 for the number of ﬂowering lateral shoots; P s 0.05 for the
number of total vegetative shoots) with increasing photoperiod, while the
percentage ﬂowering lateral shoots changed little (Figure 6B and C). The
change in the number of lateral shoots under the different photoperiods had a
marked effect on plant appearance. Plants grown under photoperiods 514 h
were very leafy and ﬂoriferous while those grown under photoperiods 214 h
appeared spindly with a sparse ﬂower display. Plants grown under NI had as
many total and ﬂowering lateral shoots as plants grown under 16 h.

There was a small but signiﬁcant (P s 0.05) year and photoperiod (P 3
0.001) effect on ﬁnal plant height but the year X photoperiod interaction was not
signiﬁcant (Figure 6E). In Year 1, there were no signiﬁcant trends for the effect
of photoperiod on plant height. In Year 2, plant height increased quadratically (P
g 0.01); differences in height were small, increasing from 42 to 48 cm as
photoperiod increased from 10 to 24 h. Under NI, height was similar to that of
plants grown under 24- and 16- h photoperiods for both years and a 14- h
photoperiod for Year 1.

Forcing temperature (Expt. 3). All plants ﬂowered except for one plant in the 14
°C treatment. Actual temperatures for each greenhouse section during different
developmental stages are shown in Table 3. Days to visible bud, days from
visible bud to ﬂower, and days to ﬂower decreased as temperature increased

from =15 to :30 °C (Figure 7A-C). Increasing temperature from 15.2 to 20.6 °C

50

accelerated ﬂowering more than increasing it from 20.6 to 29.8 °C. For example,
days to ﬂower decreased 24 d from 60 to 36 as temperature increased 5.4 °C
from 15.2 to 20.6 °C, but only 11 d from 36 to 25 as temperatures increased 9.2
°C from 20.6 to 29.8 °C. Plants grown at 20.6 °C ﬂowered approximately 5 days
faster than plants cooled for 15 weeks in Expt. 1 (Year 2) which were
subsequently grown at 20.8 °C (both under a 16-h photoperiod). A possible
explanation for this difference is that the plants in Expt. 3 were provided
approximately 40 ,umoI-mz-S'1 more supplemental light than plants in Expt.1.
Such an increase in supplemental lighting using high-pressure sodium lamps
probably would increase plant temperature, potentially as much as 0.5 °C (Faust
and Heins, 1997). If true, then these plants would be expected to develop more
quickly, since temperature strongly inﬂuences plant development.

The number of ﬁnal nodes were not signiﬁcant when counted to the last
visible leaf. However, when the new nodes produced during forcing were
counted, there was a signiﬁcant (Ps0.001) linear trend (data not shown). The
number of new nodes decreased from 36 to 24 as temperature increased from
15.2 to 29.8 °C.

Flowering of ‘Youngii-Iapsley’ was very uniform in this experiment,
although variability increased as temperature decreased. All plants grown at
29.8 °C ﬂowered within 3 days of each other; at 15.2 °C, within 8 days.

There were signiﬁcant linear relationships between temperature and rate

of progress toward visible bud, from visible bud to ﬂowering, and ﬂowering

51

(Figure 7D-F). The parameters for the equations from the linear regression
analysis are given in Table 4. The reciprocal of the linear regression function
described the relationship between temperature and developmental rate well
(Figure 7A-C). Base temperatures for each developmental stage ranged from
1.5 to 7.3 °C (Table 4). The degree-days to ﬂower were 606 when days-to-
ﬂower data were used alone and 619 when data for days from transplant to
visible bud and days from visible bud to ﬂower were added. The concepts of
degree-days and base temperature (T.,) are useful in commercial greenhouse
production because they allow prediction of ﬂowering time under ﬂuctuating
temperature conditions when average temperature is known (Roberts and
Summerﬁeld, 1987). By using the average daily temperature (T ,), the days
required to complete a developmental stage can be calculated as °days/(‘l'a - T.,).
Differences between predicted and observed days for any developmental stage
and temperature were no greater than 5 (data not shown).

The number of ﬂowers decreased =84% as temperature increased from
15.2 to 29.8 °C (Figure 8A). The relationship between number of ﬂowers and
temperature was linear (P < 0.001). Flower diameter decreased from 7.0 to 4.0
cm as temperature increased, which corresponds to a threefold difference in
ﬂower area (assuming that ﬂower shape is circular) (Figure BB). There are
similar effects of temperature on ﬂower size of other herbaceous perennials such
as Coreopsis grandiﬂora (Hogg ex Sweet.) ‘Sunray’, Leucanthemum xsuperbum

(Bergman ex J. Ingram) ‘Snowcap’, Rudbeckia fulgida (Ait.) ‘Goldsturrn’ (Yuan

52

et al., 1998), Campanula carpatica ‘Blue Clips’ (Whitman et al., 1997), Coreopsis
verticillata L. ‘Moonbeam’, Campanula “Birch Hybrid’ and others (Frane, 1999).

Height decreased 35% in a quadratic fashion (P < 0.001) as temperature
increased from 15.2 to 23.8 °C (Figure 8C). As forcing temperature increased
from 23.8 to 29.8 °C, there was almost no change in plant height.

Plant growth regulators (Expt.4). There were no statistical differences among
the growth regulators or the control for days to visible bud, number of new
leaves, or number of ﬂowers (data not shown). Days to ﬂower ranged from 39 to
41 (Figure 9A). Plants sprayed with ancymidol, paclobutrazol, or chlormequat
ﬂowered approximately one day earlier than the control. Days to ﬂower were
similar for control plants and plants sprayed with daminozide or uniconazole.
Days from visible bud to ﬂower were approximately 20 for non-sprayed plants
and plants sprayed with daminozide, uniconazole, or chlormequat and 19 for
plants sprayed with ancymidol or paclobutrazol (data not shown).

Final plant height was reduced 31 % for plants sprayed with uniconazole
compared to that of the control plants (Figure 9B). No other PGR had a
signiﬁcant effect on ﬁnal plant height although higher rates of daminozide and
paclobutrazol may have reduced height signiﬁcantly. Uniconazole reduced
ﬂower diameter 36% compared to that of control plants (Fig QC). The ﬂowers on
plants sprayed with uniconazole were noticeably smaller: the 36% decrease in
diameter resulted in a 58% decrease in ﬂower area. Flower diameters were

similar for all plants treated with one of the other PGRs and for the control.

53

While daminozide and chlormequat did not reduce ﬁnal plant height, plants
sprayed with these PGRs as well as uniconazole had shorter lateral stems
compared to that of control plants (personal observation). Shorter lateral stems
changed the plants from their natural conical shape to cylindrical.

If a standard height/diameter ratio of 1.5 to 2 (height = pot plus plant;
diameter = diameter at top of plant or at greatest width) suggested for a high-
quality potted plant (Sachs et al., 1976) was used, spraying uniconazole at 15
mg-L'1 was only slightly successful for reducing height. The 30-cm height
achieved for plants sprayed with uniconazole resulted in a height/diameter ratio
of approximately 2.1 (pot height = 11 cm and diameter was approximated at 1.5
X width of pot [13 cm]). Control plants had a height/diameter ratio of 2.7. A
disadvantage of using this PGR and rate is the large reduction in ﬂower size.
Further studies using different rates of uniconazole and perhaps other PGRs
individually or in combination are needed to identify PGRs and rates that
effectively control height without such a drastic reduction in ﬂower size and
change in plant shape.

Preliminary postharvest evaluation. During 12 days of postharvest evaluation,
‘Youngii-lapsley’ maintained a good ﬂoral display. The number of open ﬂowers
reached a maximum of 53 on day 5 (Figure 10). After day 5, the number of
open ﬂowers decreased to an average of 17 on day 12. At the end of the study,
plants were in adequate condition (personal observation). In another

postharvest evaluation using plants of ‘Youngii—lapsley’ cooled for 6 weeks,

plants had a maximum of 26 open ﬂowers and maintained at least 20 open
ﬂowers for the ﬁrst ten days of the study (data not shown), only a few more
ﬂowers than plants had at the end of the 12-day study. New ﬂowers continued to
open under low light, although at a decreasing rate (Figure 10). The number of
spent ﬂowers ranged from 4 to 21 but was relatively constant during the 12 days
of the study, averaging approximately 10 per day. Over 30 ﬂowers per plant
abscised on day two; from day three onward, there were never fewer than 10
abscised ﬂowers per plant each day. The relatively high number of ﬂowers
abscised could decrease the potted plant potential of ‘Youngii-Iapsley’ since they
are unattractive and need to be removed during marketing and home display.
Summam

On the basis of these results, 0. fnrticosa ‘Youngii-Iapsley’ can be
classiﬁed as a facultative long-day plant with an obligate vemalization
requirement. This species of Oenothera is the ﬁrst that we know of with this
combination of vemalization and photoperiod requirements.

Flowering occurred consistently after a minimum cold treatment of 3
weeks followed by any photoperiod 210 h. Increasing the duration of cold
treatment up to 15 weeks resulted in slightly faster ﬂowering and more ﬂowering
lateral shoots. Although time to ﬂower is approximately 2 weeks faster under a
16-h or longer photoperiod than a 10-h photoperiod, ﬂower number decreased
and height increased as photoperiod increased from 10 to 24 h.

Plants were most attractive when grown under photoperiods s 14 h

55

because of the high numbers of vegetative and ﬂowering lateral shoots and thus
were better suited as potted plants than those grown under longer photoperiods.
Since this is a plant that responds strongly to light levels, as seen when the
ﬂower number doubled when the daily light integral doubled (Expt. 1 and 2, Year
2), supplemental lighting is necessary to produce high-quality potted plants
during winter.

Forcing temperatures between 17 and 20 °C are recommended for
forcing plants to ﬂower within 5-6 weeks from the start of transplant. However,
since there is an increase in the number of ﬂowers with a decrease in
temperature, temperatures .<.20 °C would be best for potted plant production.
Uniconazole at 15 mg-L'1 can be used to reduce ﬁnal plant height =30% but also
will decrease ﬂower diameter by 36%. In preliminary postharvest trials, ‘Youngii-
lapsley’ performed well indoors. A good ﬂoral display was maintained for the 12

days of the trial.

56

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Faust, J.E. and RD. Heins. 1997. Quantifying the inﬂuence of high-pressure
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Frane, A.J. 1999. Temperature effects on timing and bud development of
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Grifﬁths, M. 1994. Index of garden plants. Timber Press, Portland.

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Runkle, E.S., R.D. Heins, A.C.Cameron, and W.H. Carlson. 1998. Flowering of
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cold treatment. HortScience 33(6): 1003-1006.

Sachs, R.M., A.M. Kofranek, and WP. Hackett. 1976. Evaluating new pot plant
species. Florists Rev. 159(4116): 35-36,80-84.

Vince-Prue, D. 1975. Vemalization. Photoperiodism in plants. McGraw Hill,
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Whitman C.M., R.D. Heins, A.C . Cameron AC, and W.H. Carlson. 1996. Cold
treatments, photoperiod, and forcing temperature inﬂuence ﬂowering of
Lavandula angustifolia. HortScience 31(7): 1150-1153.

lbid., 1997. Cold treatment and forcing temperature inﬂuence ﬂowering of
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Wiesner, MB. 1991. Enchanted evenings: Get to know Oenothera and dusk
may be your favorite time of day. Amer. Hort. 70: 16-21.

Yuan, M., W.H. Carlson, R.D. Heins, and AC. Cameron. 1998. Effect of forcing
temperature on time to ﬂower of Coreopsis grandiﬂora, Gail/ardia
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58

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68

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71

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intervals.

72

4 /_r ‘-

Flowering Characteristics of Several Cultivars of Oenothera fruticosa under Two

Different Lamp Types for Daylength Extension

73

Abstract

Flowering characteristics of Oenothera fruticosa L. ‘Fireworks’, ‘Highlight’,
‘Summer Solstice’, ‘Youngii-lapsley,’ and ssp. glauca were determined. Two
nursery sources were used for ssp. glauca and are indicated by a label (“A” or
“3"). All plants were cooled for 15 weeks at 5 °C and subsequently grown under
a 16-h photoperiod provided by either high-pressure sodium (HPS) or
incandescent (INC) lamps to deliver daylength extension in 20 °C greenhouses.
Light quantity was increased approximately 27% when day extension was
delivered by HPS lamps rather than INC lamps. Data collected included days to
ﬂower, number of ﬂowers and buds at ﬁrst ﬂower, number of nodes on the main
stem and ﬁnal plant height. Lamp type had little to no inﬂuence on days to
ﬂower. Day extension with HPS rather than INC lamps increased ﬂower number
approximately two times for ‘Youngii—lapsley’ and ssp. glauca A, three times for
ssp. glauca B, and 3.5 times for ‘Highlight’. Day extension with INC lamps
increased plant height at ﬂower in ssp. glauca B and ‘Youngii-lapsley’.
Oenothera fruticosa ssp. glauca shows particular promise as a potted ﬂowering

plant.

74

Introduction

Oenothera fruticosa L. ‘Youngii-lapsley’ is a facultative long-day plant with
an obligate vemalization requirement and potential as a ﬂowering potted plant
(Frane, 1999; chapter 2). Several other choice selections from this species
include 0. fmticosa ‘Fireworks’, 0. fruticosa ‘Highlight’, 0. fruticosa ‘Summer
Solstice’ and O. fmticosa ssp. glauca.

Because ‘Youngii-lapsley’ manifests ﬂowering potted plant potential we
were interested in investigating that of other 0. fruticosa cultivars and O.
fruticosa ssp. glauca.

Different lamp types used for day extension profoundly affect ﬂowering
characteristics of O. fruticosa ‘Youngii-lapsley’. However, a 16-h photoperiod
provided by day extension lighting with incandescent (INC) lamps reduced the
daily light integral approximately 22% compared to day extension lighting with
high-pressure sodium (HPS) lamps. 'Youngii—lapsley’ plants grown under the
HPS lamps produced two times the number of ﬂowers produced on plants grown
under the INC lamps. Warrington and Norton (1991) found that increasing the
daily light integral increased the rate of ﬂoral development and number of ﬂower
buds in Dendranthema xgrandiﬂorum (Ramat.) Kitamura, Raphanus sativus L.,
Zea mays L., and Cucumis sativus L.

The two light types differ in photosynthetic photon ﬂux (PPF) and in
spectral quality. Incandescent lamps emit a mixture of red and far-red light that

is richer in far-red than red (ratio of red 600-700 nm to far-red 700-800 nm <1

75

[Lane et al., 1965]). High- pressure sodium lamps emit a mixture also but with
much more red than far-red light (Thimijan and Heins, 1983). For Campanula
carpatica Jacq. ‘Blue Clips’, Coreopsis grandiﬂora Hogg ex Sweet ‘Early
Sunrise’, and Coreopsis verticillata L. ‘Moonbeam’, time to ﬂower did not differ
for plants grown under a 16-h day above the irradiance saturation point, with
day-extension delivered by HPS, INC, metal halide, or cool-white fluorescent
lamps (Whitman et al.,1998). However, the different lamp types did inﬂuence
ﬁnal plant height. Campanula carpatica ‘Blue Clips’ and C. grandiﬂora ‘Early
Sunrise’ had signiﬁcantly longer stems when grown under INC lamps compared
to HPS, cool-white ﬂuorescent, or metal halide.

The objectives of this study were to determine (1) ﬂowering characteristics
(e.g., time to ﬂower, ﬂower number, ﬁnal plant height) and (2) determine the
effect of using different lamp types for day-extension lighting for O. fruticosa
‘Fireworks’, ‘Highlight’ ‘Summer Solstice’, ‘Youngii-lapsley’, and ssp. glauca.
Materials and Methods
Plant material. Plants were obtained from various commercial producers on
different dates between 28 Aug. 1998 and 28 Oct. 1998. The dates of arrival at
Michigan State University, cold treatment initiation and forcing, average daily
temperature, average daily light integral from transplant to average day of
ﬂowering, and form of starting plant material for each cultivar are shown in Table
5. We used two nursery sources for O. fruticosa ssp. glauca; one source

labeled the plants as O. fruticosa ssp. glauca, and the other labeled them as O.

76

tetragona. According to Grifﬁths (1994), O. tetragona is the same as O.
fruticosa. In the horticultural industry, many Oenothera cultivars including
‘Fireworks’, ‘Highlight’, and ‘Summer Solstice’ are labeled as O. tetragona but
are actually cultivars of O. fruticosa (Grifﬁths, 1994). The ﬂowering behavior and
growth habit of the two sets of O. fruticosa ssp. glauca plants were quite different
and for clarity, we have labeled them 0. fruticosa ssp. glauca A and O. fmticosa
ssp. glauca B, the latter referring to the plants received as O. tetragona.

Upon arrival at MSU, bare-root plants of ‘Fireworks’ and ‘Summer
Solstice’ were placed into bulb trays in which the root masses were covered with
soilless medium and put immediately in the cooler. O. fruticosa ‘Highlight’ were
received as very small ﬁeld-grown divisions and allowed to grow in 13-cm (1 .1-L)
pots under natural daylengths (lat. 43 °N) for 15 days at 20 °C before transfer to
the cooler. To control an existing Botrytis sp. infestation, O. fmticosa ssp. glauca
A were held for 15 days in the 2.5-inch pots in which they arrived before being
transferred to the cooler. ‘Youngii-Iapsley‘ and ssp. glauca B were held in plug
trays under natural daylengths for ﬁve or six days, respectively.

Cold treatments. Cold treatments were delivered to plants held in plug trays,
bulb trays in which the root masses were covered in soilless medium (Stronglite
High Porosity Mix, Stronglite, Pine Bluff, Ark.), or 13-cm pots (‘Highlight’ only) in
coolers set at 5 °C. Within the coolers, plants were illuminated for 9 h-dayr1 with
cool-white ﬂuorescent lamps (F96T12/CWNHO, Philips, Somerset, N.J.) at

approximately 10 “moi-mes“ and watered as necessary using well water acidiﬁed

77

with sulfuric acid (H2804) to a pH of approximately 6.0. All plants were given a
15-week cold treatment at 5 °C and subsequently grown in greenhouses set at
20 °C (day/night [D/N]).

Plant culture. Before placement in the greenhouses, plugs or bare-root plants
were transplanted into 13-cm square plastic pots (1 .1-L volume) with a soilless
medium containing sphagnum peat moss, composted pine bark, vermiculite, and
perlite (Strong-lite High Porosity Mix, Strong-Lite, Pine Bluff, Ark.) Since
‘Highlight’ already was transplanted into the pots, they were transferred from the
cooler to the greenhouse. Pots were spaced at approximately 22 plants/m2.
Plants were fertilized at every irrigation with a nutrient solution of well water (EC
of 0.70 mS-cm" and 105, 35, and 23 mg-L'1 Ca, Mg, and 8, respectively) acidiﬁed
with H280, to a titratable alkalinity of 130 mgoL'1 CaCO3 and water soluble
fertilizer providing 125-12425.13 N-P-K-Ca mg-L'1 (30% ammoniacal N) plus
1.0-O.5-0.5-O.5-0.1-O.1 mg-L'1 (Fe, Mn, Zn, Cu, B, Mo) (MSU Special, Greencare,
Chicago, Ill.) The target range was 0.5-1.2 mS-cm'1 for electrical conductivity
(EC) and 5.8-6.2 for pH. In the second year, it was necessary to drench all
plants transplanted after 1 Jan. 1999 twice with a 750 mg N-L'1 liquid fertilizer
and KCO3 to raise the pH and EC into the desired ranges.

Photoperiod and lamp types. All plants were provided a 16-h photoperiod
delivered by continual day-extension lighting with either HPS or INC lamps. Day-
extension lighting with INC lamps (which provided approximately 1-3 umol-mZ-s-1

at canopy level) were delivered under opaque blackcloth pulled at 1700 HR and

78

opened at 0800 HR every day. The INC lamps were turned on at 1700 HR and
turned off at 2400 HR. Day-extension lighting with HPS lamps (which provided
approximately 50 umol-mZ-s-t) turned off at 2400 HR and then turned on the
following day at 0800 HR, ﬂuctuating on and off during daylight hours using the
following regimen: at 0800, HPS lamps turned on and continued until the outside
PPF exceeded 400 umol-mZ-s-t If the outside PPF then dropped below 200
umol-mZ-s-1 lamps were again turned on until 2400 HR. Plants in the treatment in
which daylength was extended with INC lamps received supplemental lighting
from HPS lamps in the same fashion during the hours between 0800 and 1700
HR.

Data collected included date of visible bud (without dissection) and ﬁrst
open ﬂower. Days to visible bud and ﬂower and visible bud to ﬂower were
calculated for all experiments. At ﬁrst open ﬂower, total plant height (excluding
the container), number of visible ﬂowers and buds, and number of ﬁnal nodes on
the main stem were recorded.

Greenhouse temperature control and daily light integral collection. In each
greenhouse air temperature was monitored with 36-gauge (0.127-mm-diameter)
thermocouples connected to a CR10 datalogger (Campbell Scientiﬁc, Logan,
Utah). The datalogger collected temperature data every 10 s and recorded the
hourly average. Temperatures in each greenhouse were controlled by a Priva
environmental computer (model CDY50; Priva, De Lier, The Netherlands). The

average daily light integrals were recorded at canopy level using quantum

79

sensors (LI-COR) connected to the CR10 datalogger. Average daily air
temperatures from transplant to average date of ﬂowering were calculated for
every treatment in each experiment. Average daily light integral data from
transplant to average date of ﬂowering were collected only for plants under day-
extension with HPS lamps. It was estimated that day extension with INC lamps
reduced the daily light integral 22 % compared to high-pressure sodium lamps.
This estimation was found by subtracting the amount of light available during
daylight hours (0800 to 1700 HR) (as measured by a Ll-COR quantum sensor
placed on the bench at canopy height) from the amount of light available during
the full 16-h photoperiod provided by day-extension with HPS lamps, and

assuming that INC lamps (with an output of 1-3 umol-mZ-sec") contribute

essentially no light beyond the compensation point.
Data analysis. The experiment was a completely randomized design. Data were
analyzed using the general linear models procedure (PROC GLM)(SAS Institute,
Cary, NC.) for analysis of variance.
Results and Discussion

All plants ﬂowered under each lamp type used for day extension. All
cultivars ﬂowered within a relatively small range of days (41 to 51) (Table 6).
However, ﬁnal plant height ranged between 24 and 45 cm and number of ﬂowers
produced between 12 and 502. Plant appearance differed markedly between
cultivars grown under different lamp types (Figure 11). There were no

signiﬁcant effects of lamp type on ﬁnal node number for any cultivar.

80

The inﬂuence of lamp type on ﬂowering time was not great for any
cultivar. Time to visible bud was one and two days faster under INC lamps for
‘Youngii-Iapsley’ and ‘Highlight’, respectively (data not shown). Time from visible
bud to ﬂower was two or seven days faster under INC lamps for ‘Fireworks’ or
ssp. glauca A, respectively, and two days faster under HPS lamps for ‘Summer
Solstice’. Lamp-type inﬂuence on days to visible bud and days from visible bud
to ﬂower was not signiﬁcant for all other cultivars. For ‘Summer Solstice’,
‘Fireworks’, and ssp. glauca A, time to ﬂower was three, four, and six days
slower, respectively, for plants grown under HPS lamps rather than INC lamps
(Table 2). Time to ﬂower was one or two days faster for plants grown under HPS
day-extension lighting compared to that under INC lamps for ‘Highlight’ or ssp.
glauca B, respectively. Lamp type had no signiﬁcant effect on days to ﬂower for
‘Youngii-lapsley’. It is surprising that the extra light provided by day extension
with HPS lamps did not result in consistently faster ﬂowering times for all
cultivars. Increasing PPF has been shown to decrease time to ﬂower for many
species, including Raphanus sativus L., and Zea mays L. (Warrington and
Norton, 1991) and is likely due to an increase in plant temperature observed with
an increase in PPF (Faust and Heins, 1997). When Campanula carpatica ‘Blue
Clips’, Coreopsis grandiﬂora ‘Early Sunrise’, and Coreopsis verticillata
'Moonbeam’ were grown under HPS, INC, metal halide, and cool-white
ﬂuorescent lamps at similar photosynthetic photon ﬂuxes, lamp type did not

inﬂuence time to ﬂower (Whitman et al., 1998).

81

Lamp type did not inﬂuence plant height on any cultivar except that of ssp.
glauca B and ‘Youngii-lapsley’ under incandescent lamps, it increased 3 or 10
cm, respectively, compared to that when HPS lamps were used. Whitman et al.
(1998) observed that plant height was increased signiﬁcantly for Campanula
carpatica ‘Blue Clips‘ and Coreopsis grandiﬂora “Early Sunrise’ when INC lamps
rather than when HPS, metal halide, or cool-white ﬂuorescent lamps were used
for day-extension lighting.

High-pressure sodium lamps used as day-extension lighting increased
ﬂower number 2, 2. 3, and 3.5 times compared to that under INC lamps for ,
‘Youngii-lapsley’, D. fruticosa ssp. glauca A, O. fruticosa ssp. glauca B, and
‘Highlight’ respectively. Both light quantity and quality have been shown to
inﬂuence ﬂower number of various species. For example, Warrington and
Norton (1991) found that for Dendranthema xgrandiﬂorum (Ramat.) Kitamura,
grown under a 12-h day, ﬂower number increased from 7.2 to 19.0 as daily light
integral increased from 10.4 to 29.9 mol-mz-day‘. Rosa xhybn'da ‘Samantha’
plants produced 27-71% more ﬂowers when grown with supplemental light from
HPS lamps (at a PPF of 70 to 75 umol-mz-s‘1 one meter above of the pots at
night) compared to those grown under HPS lamps ﬁtted with a blue gel ﬁlter
which reduced the R : FR ratio from 120.95 to 1:2 (Roberts et al., 1993). It is
interesting to note that two cultivars (’Fireworks’ and ’Summer Solstice’) showed

no effect of lamp type on ﬂower number.

82

Although they were received labeled as the same subspecies, O. fruticosa
ssp. glauca A and B behaved very differently when grown similarly and it was not
obvious that they were the same species upon inspection. Plants labeled “B”
ﬂowered two to 10 days faster, were 8 or 9 cm shorter, and produced =1.5 to 2
times more ﬂowers than those labeled “B”. Plants labeled “8” were much more
uniform than “A”, which was expected since ssp. glauca B was vegetatively
propagated while ssp. glauca A was propagated by seed. Based on standard
deviation, variation for days to ﬂower for A was 5.9 when plants were grown
under HPS lamps and 3.6 when they were grown under INC; for B, 0.9 and 1.3,
respectively. A preexisting infestation of Botrytis sp. on O. fruticosa ssp. glauca
A could have contributed to the lower ﬂower number and slower ﬂowering time
and greater variability. Otherwise, we cannot explain their different ﬂowering
behaviors.

Because of its ﬂowering characteristics, 0. fmticosa ssp. glauca has
potential as potted plant crop and may be better suited as one than ‘Youngii-
lapsley’. Subspecies glauca B was naturally short and ﬂoriferous, particularly
when grown under a 16-h photoperiod provided by day-extension lighting with
HPS lamps. Without plant growth regulators (PGR), this subspecies has a
height/diameter ratio of 2.0, which is in the desired range of 1.5 to 2.0 for a
potted ﬂowering plant, as suggested by Sachs (1976). This ratio can be

compared to the natural height/diameter ratio of 2.7 for ‘Youngii-Iapsley’.

83

Most of the other cultivars showed some potential but had major
drawbacks. ‘Fireworks’ was naturally short but produced few ﬂowers. However,
in a preliminary study, rooted stem cuttings of ‘Fireworks’ cooled for eight weeks
and subsequently grown under a 16-h photoperiod provided by HPS for day
extension attained a height of 26 cm, produced 159 ﬂowers, and showed
excellent potted plant potential. ‘Highlight’ could have potted plant potential if
the height were controlled by PGR. ’Summer Solstice’ lacked potential because
of its natural tallness (40 cm) and relatively low ﬂower count (46 to 59).
Summary

Different lamp types used for daylength extension had only small effects
on time to ﬂower but, for some cultivars, greatly inﬂuenced ﬂower number. High-
pressure sodium lamps used for day-extension lighting drastically increased
ﬂower number of ‘Highlight’, ‘Youngii-lapsley’, and O. fruticosa ssp. glauca A and
B. Because of the large variability between 0. fruticosa ssp. glauca produced
by different sources, it is advisable to screen stock-plant material before wide-
scale production of this species is attempted. For production of ‘Youngii-lapsley’,
‘Highlight’, and ssp. glauca, using HPS lamps for day extension is
recommended for producing more attractive plants. Subspecies glauca merits

attention for its pot plant potential.

84

Literature Cited

Frane, A.J. 1999. Temperature effects on timing and bud development of
Coreopsis verticillata ‘Moonbeam’ and ﬂower induction of long-day
perennials under different night temperatures. MS Thesis, Michigan State
Univ., East Lansing.

Faust, J.E. and RD. Heins. 1997. Quantifying the inﬂuence of high-pressure
sodium lighting on shoot-tip temperature. Acta Hort. 418: 85-91.

Grifﬁths, M. 1994. Index of garden plants. Timber Press, Portland.

Lane, H., H. Cathey, and L. Evans. 1965. The dependence of ﬂowering in
several long-day plants on the spectral composition of light extending the
photoperiod. Amer. J. Bot. 52:1006-1014.

Roberts, G.L., M.J. Tsujita, and B. Dansereau. 1993. Supplemental light quality
affects budbreak, yield, and vase life of cut roses. HortScience 28(6):
621-622.

Sachs, R.M., A.M. Kofranek, and WP. Hackett. 1976. Evaluating new pot plant
species. Florists Rev. 159 (4116):35—36, 80-84.

Thimijan, R. and RD. Heins. 1983. Photometric, radiometric, and quantum light
units of measure: A review of procedures for interconversion.
HortScience 1 8:818—822.

Warrington, I.J. and RA. Norton. 1991. An evaluation of plant growth and
development under various daily quantum integrals. J. Amer. Soc. Hort.
Sci. 116(3):544-551.

Whitman, C.M., R.D. Heins, A.C. Cameron, and W.H. Carlson. 1998. Lamp
types and irradiance level for daylength extensions inﬂuence ﬂowering of
Campanula carpatica ‘Blue Clips’, Coreopsis grandiflora ‘Early Sunrise’,
and Coreopsis verticillata ‘Moonbeam’. J. Amer. Soc. Hort. Sci.
123(5):802-807.

85

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Figure 11. Cultivars of Oenothera fmticosa and O. fruticosa ssp. glauca grown at
20°C under a 16-h photoperiod provided by a 9-h natural day plus 7-h day
extension with either high-pressure sodium lamps (labeled in the
photographs as HID for high-intensity discharge) or incandescent lamps

(inc). The labels “A” and “B” after ssp. glauca refer to different nursery
sources.

89

 

 

A 'Fireworks' B 'Summer Solstice'

16hr HID 16 hr inc

C 'Highlight'

m p.
\ — “We

16 hr HID 16 hr inc 16 hr HID 16 hr inc

 

90

Effects of Cold Treatment, Photoperiod, and Forcing Temperature on Growth

and Development of Stokesia Iaevis ‘Klaus Jelitto’

91

Abstract

The inﬂuences of cold treatment, photoperiod, and forcing temperature on
growth and development of Stokesia Iaevis ‘Klaus Jelitto' were determined.
Plants were cooled at 5 °C for 0, 3, 6, 9, 12, or 15 weeks under a 9-h
photoperiod and subsequently forced in a 20 °C greenhouse under a 16—h
photoperiod. Percentage ﬂowering increased and time to visible bud and to
ﬂower decreased with increasing cold durations. Photoperiods of 10, 12, 13, 14,
16, 24 h, or a 4-h night interruption (Nl) were tested in a 20 °C greenhouse
following 0 or 15 weeks of cold treatment at 5 °C. Before cold treatment, plants
ﬂowered under photoperiods between 10 h and 14 h and one plant ﬂowered
under 24 h in Year 2. Percentage ﬂowering, time to visible bud and to ﬂower
decreased with increasing photoperiod. After cold treatment, plants ﬂowered
under all photoperiods (except 24 h in Year 1). Percentage ﬂowering, time to
visible bud and to ﬂower, and ﬂower number decreased with increasing
photoperiod. Plant height increased with increasing photoperiod. Stokesia
Iaevis ‘Klaus Jelitto’ may best be described as an intermediate—day plant since
highest ﬂowering percentage and fastest time to ﬂower were observed under
photoperiods between 12 and 13 h both before and after cold treatment. To
determine the effect of forcing temperature on ﬂowering of ‘Klaus Jelitto', plants
were cooled for 15 weeks and then forced under a 16-h photoperiod at 14, 17,

20, 23, 26, or 29 °C. Time to visible bud and to ﬂower increased and percentage

92

ﬂowering decreased at higher forcing temperatures. Plant height and ﬂower

number decreased greatly as temperature increased.

93

Introduction

Stokesia Iaevis (Hill) Greene is an herbaceous perennial native to the
southeastern coastal plain of South Carolina, Louisiana, and the panhandle of
Florida (Gunn and White, 1974). Plants produce large (approximately 10 cm
diameter) lavender blue ﬂowers usually between July and October, but in warmer
climates, such as in the southern United States, ﬂowering can occur year-round
(Fischer,1998). ‘Klaus Jelitto’ is a vegetatively propagated cultivar of Stokesia
Iaevis with large, light lavender-blue ﬂowers (Fischer,1998). Stokesia Iaevis is
used for home perennial gardens, and rarely, for commercial cut ﬂower
production (Nau, 1996). Since 1970, Stokesia Iaevis has been investigated for
its potential as an oilseed crop (Gunn and White, 1974). The achenes of
Stokesia Iaevis contain 40% oil, and of that, 70% is epoxyoleic acid (also known
as vemolic acid) which is easily converted to epoxy oil, a material used in the
manufacture of plastics (Gunn and White, 1974; Perdue et al., 1986).

Flower induction in many plant species is controlled by vemalization and
photoperiod. The promotion of ﬂowering by cold treatment is deﬁned as
vemalization while photoperiodism is the control of ﬂowering by daylength (Lang,
1965). Both vemalization and photoperiod requirements can be facultative or
obligate. Vemalization and photoperiod are inductive processes and once ﬂoral
induction has occurred, plants can be moved to noninductive conditions, and
ﬂowering will still occur (Lang, 1965). Modifying the length of the cold treatment

or photoperiods after induction has occurred can dramatically inﬂuence plant

94

 

appearance. For example, plants of Leucanthemum xsuperbum Bergmans ex J.
Ingram ‘Snowcap’ cooled for 15 weeks at 5 °C produced an average of 3
inﬂorescences under a 10-h photoperiod while they produced an average of 11
inﬂorescences under 16 h (Runkle et al., 1998). As cold treatment duration
increased from O to 15 weeks, inﬂorescence number increased by approximately
three times for plants of ‘Snowcap’ subsequently grown under a 4-h night
interruption (NI), (Runkle et al., 1998). Such manipulations of cold treatments
and photoperiod are important for producing high-quality crops. In a preliminary
experiment, ‘Klaus Jelitto’ was tested either under a 9-h short day or a 4-h Nl
before and after a 15-week cold treatment at 5 °C. ‘Klaus Jelitto’ was tentatively
proposed to be a facultative short-day plant with an obligate requirement for cold
treatment (Frane, 1999).

Knowledge of the effect of temperature on plant development is important
to accurately time crop production. In the absence of the effects such as
photoperiod or vemalization, in general, the rate of development increases
linearly with temperature within a limited range of growing temperatures (Roberts
and Summerﬂeld, 1987). Such responses are also evident in photoperiod- and
vemalization-sensitive species when the separate effects of photoperiod and
vemalization are removed from those of post-vemalization temperatures. The
relationship between temperature and rate of development toward ﬂowering
(1/DTF where DTF is days to ﬂower) can be described as follows:

1/DTF = b, + b,*T [1]

95

where b0 and b1 are constants and T is temperature (°C) (Roberts and
Summerﬁeld, 1987).

The base temperature (T.,) , or the temperature at or below which the rate
of progress toward ﬂowering is zero, and thermal time, or the number of units
(°days) of thermal time above a base temperature required for ﬂowering can be
calculated from the constants in Equation 1 as follows:

T,= -bo/b, [2]

°days=1lb1 [3]

Besides inﬂuencing rate of ﬂowering, temperature inﬂuences other
aspects of growth and development such as number of ﬂowers and plant height
at ﬂower. For Antinhinum majus L. ‘Jackpot’, there was an increase in stem
length, spike length and number of ﬂorets as temperature decreased from 21 to
10 °C (Maginnes and Langhans. 1961). Flower bud number, plant height, and
ﬂower diameter of Coreopsis grandiﬂora Hogg ex Sweet ‘Sunray’,
Leucanthemum xsuperbum ‘Snowcap’, and Rudbeckia fulgida Ait. ‘Goldsturm’
decreased as forcing temperature increased from 15 to 27 °C (Yuan et al., 1998)
We could ﬁnd no literature on forcing temperatures for ‘Klaus Jelitto' or any
cultivar of Stokesia Iaevis.

The objectives of these experiments were to describe and quantify the
effects of cold treatment, photoperiod, and forcing temperature on growth and

development of Stokesia Iaevis ‘Klaus Jelitto’.

96

 

Materials and Methods
General. Plants of Stokesia Iaevis “Klaus Jelitto' were received as crown
divisions or rooted basal cuttings in either 2.5-inch pots or in 36-cell plug trays on
15 Oct. 1997 (Year 1) and 28 Aug. 1998 or 16 Oct. 1998 (Year 2) from two
separate commercial producers. Upon arrival at Michigan State University, all
plants were held in the 2.5— inch pots or plug trays and exposed to natural
daylengths (lat. 43 °N;z11-12 h) until the experiments began. Cold treatments
were delivered to plants held in 2.5-inch pots or plug trays in coolers set at 5 °C.
Within the coolers, plants were illuminated for 9 h-day1 with cool-white
ﬂuorescent lamps (F96T12/CWNHO, Philips, Somerset, N.J.) at approximately
10 ,uﬁlO'Tﬂ’S" and watered as necessary (approximately 2 times per week) using
well water acidified with sulfuric acid (H280,) to a pH of approximately 6.0.
Before placement in the greenhouses (set at 20 °C day/night [DIN] unless
otherwise stated), plugs were transplanted into 13-cm square plastic pots (1 .1-L
volume) with a soilless medium containing sphagnum peat moss, composted
pine bark, vermiculite, and perlite (Strong-lite High Porosity Mix, Strong-Lite,
Pine Bluff, Ark.). Pots were spaced at approximately 22 plants/m2. Plants were
fertilized at every irrigation with a nutrient solution of well water (EC of 0.70
mS-cm'1 and 105, 35, and 23 mg-L'1 Ca, Mg, and S, respectively) acidiﬁed with
HZSO4 to a titratable alkalinity of 130 mg-L'1 CaCO3 and water soluble fertilizer
providing 125-12-125-13 N-P-K-Ca mg-L’1 (30% ammoniacal N) plus 1.0-0.5-0.5-

0.5-0.1-0.1 mg-L‘1 (Fe, Mn, Zn, Cu, B, Mo) (MSU Special, Greencare, Chicago,

97

Ill.). The target range was 0.5-1.2 mS-cm'1 for electrical conductivity (EC) and

5.8-6.2 for pH. In the second year, it was necessary to drench all plants

transplanted after 1 Jan. 1999 twice with a 750 mg N-L'1 liquid fertilizer and KCO3

to raise the pH and EC into the desired ranges.

Cold duration (Expt. 1). Six durations of cold treatment were tested (0, 3, 6, 9,

12, or 15 weeks). Experiments were initiated on 18 Oct. 1997 (Year 1) and 7

Oct. 1998 (Year 2). No initial node count was taken in Year 1. In Year 2, the ;
initial number of nodes was counted at transplant and averaged 9.8 nodes.

Ten plants were removed from the cooler after each treatment duration,

transplanted and placed in the greenhouse.

A 16-h photoperiod was provided by four-hundred-watt high-pressure
sodium lamps (HPS) switched on at 0800 HR and off at 2400 HR. HPS lamps
provided both the photoperiod and supplemental lighting with a photosynthetic
photon ﬂux (PPF) of 50 umol-mZ-s-' at plant height starting at 0800 and continuing
until the outside PPF exceeded 400 umol-mZ-s". If the outside PPF then dropped
below 200 umol~m2-s~' lamps were again turned on until 2400 HR.

Photoperiod (Expt.2). Seven photoperiods (10, 12, 13, 14, 16, 24 h and a 4-h
night interruption [MD and two cold treatment durations (0 or 15 weeks at 5 °C)
were tested. Seventy plants were transplanted on 18 Oct. 1997 (Year 1) and 28
Oct. 1998 (Year 2) and placed in a greenhouse. Ten plants were used per
treatment and treatments were assigned randomly each year to greenhouse

benches. The remaining plants were left in the 2.5-inch pots and placed in the

98

cooler. After 15 weeks of cold treatment, seventy plants were transplanted on
31 Jan. 1998 (Year 1) and 14 Feb. 1999 (Year 2) and placed in the same
photoperiod treatments as the ﬁrst set of seventy plants. Plants averaged 10.8
nodes in Year 1 and 10.3 nodes in Year 2.

Opaque black cloth was pulled at 1700 HR and opened at 0800 HR every
day on all benches so all plants received a similar daily light integral. Continual
photoperiods were delivered by day-extension lighting using incandescent lamps
which were turned on at 1700 HR and turned off after each photoperiod was
completed. The 4-h night interruption was provided by incandescent lamps
which were turned on at 2200 HR and turned off at 0200 HR. Day-extension and
NI lighting using incandescent lamps provided approximately 1-3 umol-st1 at
canopy level. Supplemental lighting during daylight hours was given as
described for Expt. 1, except that HPS lamps were terminated at 1700 HR.
Forcing Temperature (Expt. 3). On 7 Oct. 1998, plants left in plug trays were
placed directly into the cooler for 15 weeks until 20 Jan. 1999, when they were
transplanted. At transplant, plants averaged 10.1 leaves. Ten plants were
placed into each of 6 greenhouses set to 14, 17, 20, 23, 26, and 29 °C. Plants
received a continual 16-h photoperiod provided by HPS lamps that remained on
continuously from 0800 HR to 2400 HR and delivered approximately
90 umol-mz-s".

Data collection and analysis. The data collected for all experiments included

date of ﬁrst visible bud (without dissection) and date of ﬁrst open ﬂower. Days to

99

visible bud, days to ﬂower, and days from visible bud to ﬂower were calculated
for all experiments. At ﬁrst open ﬂower, total plant height (excluding the
container), number of visible ﬂower buds, and number of ﬁnal nodes on the main
stem were recorded. The number of ﬁnal nodes was counted to the last visible
leaf and when the initial node count was taken, included the number of initial
nodes. The number of new nodes produced during forcing was calculated by
subtracting the initial number of leaves from the ﬁnal number of leaves, and the
number of new nodes beneath the ﬁrst ﬂower (in Year 2) was calculated by
subtracting the number of initial nodes from the number of nodes beneath the
ﬁrst ﬂower. For all experiments, plants that did not have visible bud after 15
weeks of forcing were considered non-ﬂowering and were discarded. Plants that
died during the experiment were discarded and not included in the results.

All experiments were completely randomized designs. Data were
analyzed using the general linear models procedure (PROC GLM) (SAS
Institute, Cary, NC.) for analysis of variance and linear regression procedure
(PROC REG) for regression models. All experiments were analyzed with Linear
and Quadratic trend contrasts. The cold duration and photoperiod experiments
(Expts.1 and 2, respectively) were replicated in time, and conducted once per
year. The forcing temperature experiment (Expt. 3) was conducted only once, in
Year 2.

Greenhouse temperature control and daily light integral collection. Air

temperature was monitored in each greenhouse with 36-gauge (0.127—mm-

100

 

diameter) thermocouples connected to a CR 10 datalogger (Campbell Scientiﬁc,
Logan, Utah). The datalogger collected temperature data every 10 s and
recorded the hourly average. Average daily air temperatures from transplant to
average date of ﬂowering for Expts. 1 and 2 are shown in Tables 7 and 8.
Average daily temperatures for three developmental stages of plants in Expt. 3
are shown in Table 9. Temperatures in each greenhouse were controlled by a
Priva environmental computer (model CD750; Priva, De Lier, The Netherlands).
Actual average daily air temperatures were calculated and used in all analyses.
Average daily light integral data were collected only for Expt. 1 in Year 2.
The average daily light integrals were recorded at canopy level (at the same
interval as temperature data) using quantum sensors (LI-COR) connected to the
CR 10 datalogger. It was estimated that plants in Expt. 2 received approximately
78% of the daily light integral that plants received in Expt. 1. This estimation was
found by subtracting the amount of light available during daylight hours (0800 to
1700 HR) from the amount of light available during the full 16-h photoperiod of
day extension with high-pressure sodium lamps. Supplemental lighting was
similar between the houses from 0800 to 1700 HR and it was assumed that day-
extension lighting with incandescent lamps (with an output of 1-3 umol-mZ-sec")
contribute essentially no light beyond the compensation point.
Results and Discussion
Cold duration (Expt. 1). Fifty to 60 °/o of ‘Klaus Jelitto’ plants ﬂowered without a

cold treatment (Figure 12A). In Year 1, percentage ﬂowering reached 100 after

101

6 weeks of cold treatment (Figure 12A) while in Year 2, ﬂowering percentage did
not reach 100 until plants had received 15 weeks cold treatment.

Days to visible bud and days to ﬂower decreased quadratically (P s 0.01
for days to ﬂower; P g 0.001 for days to visible bud) in Year 1, although there
were no signiﬁcant trends for either variable in Year 2 (Figures 12B, C). In Year
1, time to ﬂower decreased greatly as cold duration increased from zero to 6
weeks (112 to 79 days). The decrease in days to ﬂower as cold duration
increased from 6 to 15 weeks was slight (79 to 74 days), thus it appears that
vemalization was saturated after 6 weeks of 5 °C treatment. Increasing cold
duration generally decreased variability for ﬂower timing. For example, variability
based on standard deviation decreased from 23.8 to 11.3 days as cold duration
increased from zero to 15 weeks in Year 2. Based on these results, we conclude
that ‘Klaus Jelitto’ has a facultative requirement for vemalization.

There was a large difference between the two years for plants that did not
receive any cold treatment but only small differences between the years for
plants cooled 23 weeks. Plants without a cold treatment ﬂowered slowly (112
days) in Year 1 while in Year 2, they ﬂowered relatively quickly (76 days).
Starting plant material was different between the years: 2.5-inch pots in Year 1,
and 36-cell plugs in Year 2 each received from a different nursery. Although no
initial node count was taken in Year 1, the initial node count of plants in 36-cell
plug trays averaged 9.8, which was very similar to the node counts found for

plants in 2.5-inch pots in both Year 1 and Year 2 (10.8 and 10.2, respectively),

102

which would have been similar to the node count for plants in Expt. 1, in Year 1.
We can not readily explain the different ﬂowering behavior between the
noncooled plants in the two years. The experiments were initiated within 11
days of each other between the years and, although we do not have the light
data for Year 1, we assume that plants in each year received relatively similar
amounts of light. Temperature was carefully controlled; the greatest difference
between the years was 1.2 °C, thus temperature probably did not cause the
differences in ﬂowering that we observed between the years or between the
different cold duration treatments.

There were small but signiﬁcant differences for the effect of cold treatment
on days from visible bud to ﬂower. In Year 1, days from visible bud to ﬂower
decreased quadratically (P s 0.01), while in Year 2, there was an increasing
linear (P s 0.01) trend (Figure 12D). Although signiﬁcant, the differences in time
from visible bud to ﬂower between different cold durations within a year or
between the years were relatively small: the greatest difference between
treatments within a year and treatments between years was 11 days.

While the change in ﬂower timing with increased cold treatment was only
clearly observed in Year 1, the number of nodes counted to the last visible leaf
did reﬂect earlier ﬂoral initiation with increasing cold treatment in both years
(Figure 13A). There were no signiﬁcant differences for the ﬁnal or new node
number beneath the ﬁrst ﬂower in Year 2, which reﬂects the lack of signiﬁcant

linear or quadratric trends observed in Year 2. The greatest decrease in ﬁnal

103

and new number of nodes (31 to 26 for ﬁnal nodes in Year 2) occurred as cold
duration increased from zero to six weeks, after which the change in number of
nodes was very small (26 to 25 for ﬁnal nodes in Year 2) as cold duration was
increased to 15 weeks. In addition, variability of node number (both ﬁnal and
new nodes) decreased as cold duration increased. These observations are
consistent with the hypothesis that vemalization of ‘Klaus Jelitto’ is saturated
after 6 weeks of cold treatment. The number of new nodes in Year 2 was almost
identical to the number of ﬁnal nodes in Year 1. This was most likely due to the
fact that initial leaf counts were not taken in Year 1, and the leaves present on
the plant at the beginning of the experiment had probably senesced by the time
the plant ﬂowered. The number of ﬁnal nodes in Year 1 most likely represented
the number of new nodes produced during forcing. It is interesting to note that
the faster ﬂowering observed for plants without a cold treatment in Year 2 was
not reﬂected by either the ﬁnal or new number of nodes.

There were large differences in number of ﬂower buds between the years
(Figure 13B). There were no signiﬁcant trends for the effect of cold duration on
the number of ﬂower buds in Year 1, but there was a signiﬁcant (P s 0.01) linear
increase in Year 2. The number of ﬂower buds per plant was variable but,
increased from ﬁve for noncooled plants to 13 for plants cooled for 15 weeks.

There was little effect of cold duration on plant height. In Year 1, height

decreased linearly (P 3 0.001) from 59 to 49 cm as cold duration increased from

104

zero to 15 weeks (Figure 130). There were no signiﬁcant differences for height
in Year 2.
Photoperiod (Expt. 2) Without a cold treatment, in Year 1, “Klaus Jelitto’ plants
ﬂowered only under photoperiods between 12 and 14 h; ﬂowering percentage
declined from 75 to 16 in this photoperiod range (Figure 14A). Percentage
ﬂowering was much higher for noncooled plants in the second year where all
plants ﬂowered under photoperiods between 10 and 13 h and one plant each
ﬂowered under 14 and 24 h. No plants ﬂowered under night interruption (NI)
without cold treatment in either year. While plants did not ﬂower under 16 h
without a cold treatment in this experiment, 50 and 60% ﬂowered without a cold
treatment in Expt.1 (in Year 1 and Year 2, respectively). Plants in Expt. 2 only
received about 78% of the light received by the plants in Expt. 1 which could
explain some of the difference. It has been observed for several cold-requiring
species that high light levels can induce ﬂowering without cold treatment.
Blondon and Chouard (1965) found that a cold-requiring clone of Dactylis
glomerata L. ﬂowered under a 16-h photoperiod without a cold treatment when
provided with a 16-h day at a photosynthetic photon ﬂux of 280 umol-mz-sec1
(24.2 mol-mZ-day").

In Year 2, the plants that ﬂowered under 10 h and the single plant that
ﬂowered under 14 h were very slow to ﬂower (135 or 139 days, respectively)
compared to plants under 12 or 13 h photoperiods, which ﬂowered in 81 or 86

days, respectively (Figures 14B, C, D). The plant that ﬂowered under the 24-h

105

photoperiod ﬂowered in 74 days. The two plants that ﬂowered under 14 h in
Year 1 ﬂowered 63 days faster than the one plant that ﬂowered under 14 h in
Year 2. Average daily temperature was only 1 °C higher in Year 2 compared to
Year 1, and can not explain this difference. The experiment in Year 2 started
only 10 days later than in Year 1, thus it is not likely that differing light levels
caused the difference. We have no explanation for the large difference in
percentage ﬂowering or time to ﬂower between the two years for noncooled
plants. We speculate that if we had left the plants on the bench for longer than
100 days, more plants would have eventually ﬂowered.

After the cold treatment, percentage ﬂowering was 90 or 100 under 10 h
and decreased to 0 or 10 under 24 h in Year 1or 2, respectively (Figure 15A).
Eighty and 90 percent of the plants ﬂowered under Nl in Year 1 and 2,
respectively.

Following cold treatment, days to visible bud and days to ﬂower changed
little between photoperiod treatments except for the one group of plants under
10 h in Year 1 (Figures 15B, C). In Year 1, plants grown under 10 h ﬂowered in
122 days, while plants grown under 10 h in Year 2 ﬂowered in 79 days. In Year
2, plants under 10 h were only approximately 10 days slower than plants under
other treatments. We have no explanation for the large differences for plants
under 10 h between the years. Days from visible bud to ﬂower changed little

between photoperiods. In Year 1, there was a small tendency for increasing

106

days from visible bud to ﬂower while in Year 2, there was a small tendency for
decreasing days from visible bud to ﬂower with increasing photoperiod (Figure
15D). However, differences in days from visible bud to ﬂower between each
photoperiod were small, as were the differences between years. The greatest
difference between the years for days to visible bud to ﬂower before or after cold
treatment was 11 days. Days to visible bud, day from visible bud to ﬂower, and
days to ﬂower for plants grown under NI were similar to plants grown under
photoperiods 214h in both years.

In general, cold-treated plants ﬂowered only slightly faster than ﬂowering
non-cold-treated plants, although the effect of cold treatment on ﬂower timing
differed for plants grown under different photoperiods. For example, for plants
grown under 12 h in Year 1, days to ﬂower decreased =2 weeks after cold
treatment, while days to ﬂower decreased 8 weeks after cold treatment for plants
grown under 10 h in Year 2 (Figures 14B,15B). Variability generally decreased
following cold treatment. For example, the standard deviation for days to ﬂower
of plants grown under 13h before and after cold treatment in Year 2 decreased
from 13.2 to 3.5.

The number of ﬁnal and new nodes for plants without a cold treatment
decreased linearly (P g 0.001) in Year 2, and quadratically (P g 0.001) after a
cold treatment in Year 1 (Figures 16A,B). There were no signiﬁcant trends for

either the number of ﬁnal or new nodes without a cold treatment in Year 1, or

107

following a cold treatment in Year 2. The decrease observed in both ﬁnal and
new nodes as photoperiod increased from 10 to 24 h reﬂects the decrease in
ﬂower timing seen in Year 1. In Year 2, there were no signiﬁcant trends for the
number of ﬁnal or new nodes beneath the ﬂower following cold treatment.

The lower ﬂowering percentage observed under photoperiods 214 h
together with the slower time to ﬂower under photoperiods 310 h both before and
after a cold treatment suggest that ‘Klaus Jelitto‘ does not behave similar to
either a short-day plant response or a long-day plant response. On the basis of
these results, we conclude that “Klaus Jelitto' is best described as a facultative
intermediate-day plant. Allard (1938) described intermediate-day plants as those
which ﬂower when the day is neither too long nor too short. For example,
Mikania scandens L. ﬂowered only under photoperiods of 12 to 16 h (Allard,
1938). Only a few species, including Mikania scandens L., Phaseolus
polystachios (L.) B.S.P., Eupaton'um h yssopifolium var. h yssopifolium L., a
variety of Saccharum spontaneum L. (28N. G. 292) (Allard, 1938), Salsola
komarovii ljin (Takeno et al., 1995), and Echinacea purpurea (L.) Moench
‘Magnus’ (E. Runkle, unpublished data) have been documented as intermediate-
day plants. Thomas and Vince-Prue (1997) suggested that intermediate-day
plants may be a variation of the short-day type response since short day plants
also need some light in each day to ﬂower. However, the daylength limitations

for short-day plants are fairly wide, while for intermediate-day plants, the range of

108

effective photoperiods is typically quite narrow. Alternatively, Sachs (1956)
suggested that intermediate-day plants may actually have dual daylength
requirements for ﬂowering but the long—day and short-day ranges overlap, so that
intermediate photoperiods satisfy both photoperiodic requirements. Studies are-
needed to test these hypotheses for the intermediate-day response observed for
Stokesia Iaevis ‘Klaus Jelitto’

There was no consistent effect of photoperiod on ﬂower bud number of
non-cold treated plants (Figure 160). After cold treatment, the number of ﬂower
buds decreased linearly (P g 0.001 in Year 1; P s 0.01 in Year 2) with increasing
photoperiod in both years. Flower bud number increased after a cold treatment
only for plants grown under 12-h photoperiods. Cooled plants that ﬂowered
under Nl produced as many ﬂowers as those grown under 214 h in both years.

Plant height at ﬁrst ﬂower for plants with or without a cold treatment
increased markedly as photoperiod increased from 10 and 14 h (Figure 160); for
cold-treated plants in Year 1, plant height increased from 27 to 47 cm. Plant
height for cooled plants grown under NI was similar to cooled plants grown under
13 h in Year 1 and similar to cooled plants grown under photoperiods 214h in
Year 2.

The effect of photoperiod on plant height and number of ﬂowers drastically
changed the appearance of the plants grown under different photoperiods.

Those grown under photoperiods 5.12 h were short, produced many ﬂowers, and

109

could make a very acceptable potted ﬂowering plant. However, when plants
were grown under photoperiods 213 h, the plants were too tall and produced too
few ﬂowers to be considered as a potted ﬂowering plant. Knowledge of effective
plant growth regulators would be beneﬁcial for production of ‘Klaus Jelitto’ if
plants are to be produced under long photoperiods. However, if plants of ‘Klaus
Jelitto’ are produced for cut-ﬂower production, long photoperiods may be more
appropriate for the longer stems that result under longer photoperiods.
Flowering of ‘Klaus Jelitto’ was extremely variable. There were large
differences in percent ﬂowering between years for both Expt. 1 and 2 (Figures
12A, 14A). Percentage ﬂowering in Expt. 1 was generally higher in Year 1
compared to that in Year 2, but for Expt. 2, percentage ﬂowering was much
higher in Year 2 compared to that in Year 1. For example, in Expt. 2, 100% of
plants ﬂowered under 10, 12, and 13 h in Year 2 while no plants ﬂowered under
10 h and only at 75 or 30% plants ﬂowered under 12 or 13 h, respectively, in
Year 1. This result was surprising since the plant material used for this
experiment came from the same nursery and had similar starting plant sizes in
both years (10.8 nodes in Year 1 and 10.3 nodes in Year 2). In addition to
variability for percent ﬂowering, there were wide ranges in days to ﬂower even
within a single treatment group. For example, all plants cooled for 15 weeks in
Expt. 1 (Year 2) ﬂowered over a range of 35 days, an unacceptably large period

of time for ﬂowering of a crop in the ﬂoriculture industry.

110

Forcing Temperature (Expt. 3) Percentage ﬂowering decreased from 100 at
temperatures 320 °C, to 90 at temperatures between 23 and 26 °C, and to 50 at
29 °C (data not shown). Days to visible bud, days from visible bud to ﬂower, and
days to ﬂower of ‘Klaus Jelitto’ decreased with increasing temperatures (Figures
17A, B, C). Plants forced at 15.9 °C ﬂowered in 90 days while plants forced at
29.9 °C ﬂowered in 42 days.

Rates of progress to visible bud, from visible bud to ﬂower, and to ﬂower
were linear within the studied temperature range (Figures 170, E, F). The
parameters for the linear regression analysis are shown in Table 10. The
reciprocal of the linear regression lines (shown in Figures 17A, B, C) described
the relationship between temperature and the time required to reach each
developmental stage well. Base temperatures ranged from 3.2 to 4.2. The
degrees days required to reach ﬁrst open ﬂower were 1104 when calculated from
the constants obtained from the linear regression analysis with day to ﬂower data
and 1035 when the degree days was calculated by adding the data from
transplant to visible bud and visible bud to ﬂower. Degree-days and base
temperature are important concepts in production of ﬂowering plants since they
allow for prediction of ﬂowering time in environments where the temperatures are
ﬂuctuating, and the mean temperature is known (Roberts and Summerﬁeld,
1987). Actual average days to ﬂower did not differ from predicted days to ﬂower

more than 3 days for any temperature (Figure 17C).

111

The number of ﬁnal and new nodes to the last visible leaf decreased
quadratically (P s 0.05) as temperature increased (Figure 18A), although the
actual decrease was small (29 to 23 for ﬁnal nodes). The quadratic trend of the
decrease in ﬁnal and new nodes relates to the quadratic pattern observed for the
decrease in days to visible bud, days from visible bud to ﬂower, and days to
ﬂower as temperatures increase (Figures 17A, B, C). There were no signiﬁcant
differences for the number of ﬁnal or new nodes beneath the ﬂower.

Flower number decreased 282% as temperature increased from 15.9 to
29.9 °C (Figure 18B). Others have observed that ﬂower number decreases with
increasing forcing temperature; examples include Coreopsis grandiﬂora ‘Sunray’,
Rudbeckia fulgida.’Goldsturm’, Leucanthemum xsuperbum ‘Snowcap' (Yuan et
al., 1998), and Campanula carpatica Jacq. ‘Blue Clips’ (Whitman et al., 1997).

Plant height decreased dramatically with increasing temperature (Figure
180). Tallest plants (average height of 59 cm) were those forced 18.4 °C and
the shortest plants (average of 21 cm) were forced at 29.9 °C. Plant height of
many species increases as the difference between day temperature and night
temperature increases (DIF) (Enrvin and Heins, 1995). The DIF to which plants
of ‘Klaus Jelitto’ were subjected during the developmental stages of transplant to
visible bud, visible bud to ﬂower, and transplant to ﬂower are presented in Table
11. The largest values for DIF were observed in the house set at 17 °C (actual

temperature averaged 18.4 °C during the time between transplant and average

112

day to ﬂower), which corresponds to the temperature setting where tallest plant
heights observed, thus DIF may have contributed to some of the differences in
plant height.
S_um_m_ant

Stokesia Iaevis “Klaus Jelitto‘ has a facultative requirement for
vemalization. Time to ﬂower decreased as cold treatment increased. Before
cold treatment, ﬂowering generally occurred only under photoperiods between 10
and 14 h. However, when plants were grown without a cold treatment under 16
h in high light conditions, such as provided by high-pressure sodium lamps in
Expt.1, ﬂowering occurred but at relatively low percentages (50 to 60%). After
cold treatment, plants ﬂowered under all photoperiods but ﬂowering percentage
decreased as photoperiod increased from 14- to 24-h. In Year 1, no plants
ﬂowered under 24 h. Time to ﬂower was slowest under 10 h and decreased as
photoperiod increased. Based on this study, plants of “Klaus Jelitto’ ﬂower most
rapidly, completely, and uniformly after a cold treatment under photoperiods
between 12 and 13 h and can best be described as a facultative intermediate-
day plant. Time to ﬂower and percentage ﬂowering decreased with increasing
forcing temperature. A forcing temperature of 18 °C and photoperiods between
12-13 h are recommended for maximizing percentage ﬂowering and ﬂower

number.

113

Literature Cited

Allard, HA 1938. Complete or partial inhibition of ﬂowering in certain plants
when the days are too short or too long. J. Agric. Res. 57: 775-789.

Blondon, F. and P. Chouard. 1965. Facteurs extemes capables de provoquer la
ﬂoraison du Dactylis glomerata L. Action de la temperature. CR. Acad.
Sc. 260: 6966-6969.

Erwin, J.E., and RD. Heins. 1995. Therrnomorphogenic responses in stem and
leaf development. HortScience 30: 940-949.

Fischer, T. 1998. Stoke’s Aster— Stokesia Iaevis. Horticulture 95: 34.

Frane, A.J. 1999. Temperature effects on timing and bud development of
Coreopsis verticillata ‘Moonbeam’ and ﬂower induction of long-day
perennials under different night temperatures. MS Thesis, Michigan State
Univ., East Lansing.

Gunn, CR. and GA. White. 1974. Stokesia Iaevis: Taxonomy and Economic
Value. Econ Bot 28: 130-135.

Lang, A. 1965. Physiology of ﬂower initiation, p.1380-1535. In: W. Ruhland
(ed.). Encyclopedia of plant physiology. Springer-Verlag, Berlin.

Maginnes, EA. and R.W. Langhans. 1961. The effect of photoperiod and
temperature on initiation and ﬂowering of snapdragon (Antirrhinum majus—
variety Jackpot). J. Amer. Soc. Hort. Sci. 77: 600-607.

Nau, J. 1996. Ball perennial manual: Propagation and production. Ball, Batavia,
IL.

Perdue, R.E., K.D. Carlson, and MG. Gilbert. 1986. Vemonia galamensis,
potential new crop source of epoxy acid. Econ Bot. 40: 5468.

Roberts, E.H. and R.J. Summerﬁeld. 1987. Measurement and prediction of

ﬂowering in annual crops, p. 17-50. In: J.G. Atherton (ed.). Manipulation of
ﬂowering. Buttenlvorths, London.

114

Runkle, E.S., R.D. Heins, A.C. Cameron, and W.H. Carlson. 1998. Flowering of
Leucanthemum xsuperbum ‘Snowcap’ in response to photoperiod and
cold treatment. HortScience 33(6): 1003-1006.

Sachs, RM. 1956. Floral initiation in Cestrum noctumum l. A long-short day
plant. PI. Physiol. 31: 185-192.

Takeno, K., M. Takahashi, and K. Watanabe. 1995. Flowering response of an
intermediate-day plant, Salsola komarovii ljin under different photoperiodic
conditions. J. Pl. Phys. 145: 121-125.

Thomas B., D.Vince-Prue. 1997. Photoperiodism in Plants. Academic Press,
San Diego.

Whitman, C.M., R.D. Heins, A.C. Cameron, and W.H. Carlson. 1997. Cold
treatment and forcing temperature inﬂuence ﬂowering of Campanula
carpatica ‘Blue Clips”. HortScience 32(5): 861-865.

Yuan, M., W.H. Carison, R.D. Heins, and AC. Cameron. 1998. Effect of forcing
temperature on time to ﬂower of Coreopsis grandiﬂora, Gaillardia
xgrandiﬂora, Leucanthemum xsuperbum, and Rudbeckia fulgida.
HortScience 33(4): 663-667.

115

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117

Table 9. Actual temperatures of houses for the time of forcing for three
developmental stages: Transplant to Visible Bud, Visible Bud to Flower, and
T_rsplant to Flowr

 
 
 

 
 

Develntal Stage (day)s *—

 

 

Temperature Set

 

 

POW (°C) Transplant to Visible Bud to Transplant to
Visible Bud Flower Flower
14 15.1 16.7 15.9
17 18.2 18.6 18.4
20 20.6 21.3 21.0
23 23.8 23.3 23.6
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29 29.7 30.0 29.9

 

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119

Table 11. The difference between day and night temperature (DIF) of plants of
Stokesia Iaevis ‘Klaus Jelitto’ grown under different forcing temperatures and
three developmental stages: from transplant to visible bud (VB), from VB to

 

 

Temperature Transplant to B - Trspl
setting (°C) FLW
14 0.1 1 2.03 1.08
17 1 .38 1.95 1 .69
20 0.69 1.37 1 .03
23 0.71 1 .04 0.88
26 0.46 0.97 0.76
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bud to ﬂower (D) in WaIaGA'S‘lGaus Jelitto’ in Year 1 (O) and Yea 2 (I).
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Figure 15. Effects of various photoperiods after a 15 week cold treatment at 5 °C on
percentage ﬂowering (A), days to ﬂower (B), days to visible bud (C), and days
from visible bud to ﬂower (D) in Stdres’a IaeviS‘Klaus Jelitto’ in Year 1 (I) and
Year 2 (I). Error bars represent 95% conﬁdence intervals. L = linear, Q =

quadratic trends. m""'“Nombniﬁmm or signiﬁcant at P5 0.05, 0.01, or 0.001,

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124

 

   
 

 

 

  
   
 
 
    

 

 

 

 

 

 

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Figure 16. Effects of various photoperiods with and without a 15-week cold treatment
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buds (C ), and plant height (D) in Stokesia Iaevis ‘Klaus Jelitto' in Year 1 (O) and
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125

 

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Figure 18. Effects of temperature on number of nodes (A), number of ﬂower buds (B),
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trends. “5" 1 nsigniﬁcant or signiﬁcant at Pg 0.05.0.01, or 0.001,
respectively.

127

 

 

 

Appendix A:
Comparison of Stokesia Iaevis Cultivars Grown under Two Different Lamp Types

for Daylength Extension

128

Introduction

Stokesia Iaevis (Hill) Greene is an herbaceous perennial native to the
southeastern United States from South Carolina to Louisiana, including the
panhandle of Florida (Gunn and White, 1974). With its large (=10 cm diameter),
lavender-blue ﬂowers, Stokesia Iaevis ‘Klaus Jelitto’ demonstrated good potential
as a potted ﬂowering plant in preliminary studies and forcing experiments (Frane,
1999; chapter 4). ‘Klaus Jelitto’ has a facultative requirement for vemalization
and is best described as a facultative intermediate-day plant (chapter 4).
Several cultivars of S. Iaevis exist including yellow-ﬂowered ‘Mary Gregory’,
white-ﬂowered ‘Alba’ and ‘Silver Moon’, and ‘Purple Parasols’ which has violet
ﬂowers. ‘Klaus Jelitto’, ‘Blue Danube’, ‘Wyoming’, ‘Blue Star’ and ‘Omega
Skyrocket’ all have lavender-blue ﬂowers, as does the straight species
(Armitage, 1989; Fischer, 1998). Based on the potential observed for ‘Klaus
Jelitto’, we were interested in investigating the ﬂowering characteristics of other
cultivars of Stokesia Iaevis in container production.

Different lamp types used for day-extension were found to inﬂuence
ﬂowering characteristics of S. Iaevis ‘Klaus Jelitto’. ‘Klaus Jelitto’ plants cooled
for 15 weeks and subsequently grown under a 16—h photoperiod with day
extension from HPS lamps produced approximately two times the number of
ﬂowers produced on plants grown under the INC lamps. In addition, plants of
‘Klaus Jelitto’ without a cold treatment were found to ﬂower at 50-60% under a

16-h photoperiod when HPS lamps were used for day-extension when no plants

129

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ﬂowered without cold treatment under a 16-h photoperiod when INC lamps were
used for day-extension. It was estimated that a 16-h photoperiod provided by
day-extension lighting with incandescent (INC) lamps provided a daily light
integral that was 78% of the daily light integral provided by day-extension with
high-pressure sodium lamps (see chapters 1 - 3 for explanation of estimation).
Warrington and Norton (1991) found that increasing the daily light integral
increased the rate of ﬂoral development and number of ﬂower buds in
Dendranthema xgrandiﬂorum (Ramat.) Kitamura, Raphanus sativus L., Zea
mays L., and Cucumis sativus L.

High-pressure sodium and INC lamps also differ in spectral quality as well
as intensity. Incandescent lamps emit a mixture of red and far-red light which is
richer in far-red than red (ratio of red 600-700 nm to far-red 700-800 nm < one
[Lane et al., 1965]). High pressure sodium lamps emit a mixture of red and far-
red light with far less far-red than red light compared to incandescent lamps
(T himijan and Heins, 1983).

The objectives of this study were to (1) determine ﬂowering characteristics

(eg. time to ﬂower, ﬂower number, ﬁnal plant height) and (2) determine the effect

of using different lamp types for day-extension lighting for S. Iaevis ‘Alba’, ‘Blue

Danube’, ‘Klaus Jelitto’, ‘Mary Gregory’, and ‘Purple Parasols’.

130

 

Protocol
Experimental Design: completely randomized design
Cultivars: ‘Alba’, ‘Blue Danube’, ‘Klaus Jelitto’, ‘Mary Gregory’, ‘Purple Parasols’,
and ‘Wyoming’
See Table 12 for starting plant material, dates of arrival, cold treatment, and
forcing, as well as average daily temperature and average daily light integral
during forcing. Daily light integral data were only recorded for plants under day
extension with HPS lamps.
Cold Treatment:
15 weeks at 5°C
Photoperiod and lamp types: All cultivars were treated with a 16-h photoperiod
composed of 9 h of natural light plus a 7-h daylength extension. Natural sunlight
was supplemented with light from high-pressure sodium lamps. The high-
pressure sodium lamps were turned on every morning at 0800 when natural light
(measured on outside of greenhouse roof) fell below 400 umol-mz-sec“. High-
pressure sodium lamps were terminated when ambient light level was greater
than 400 ,LLMOI'mZ'SeC'1 and were not re-initiated until ambient light level fell

below 200 pmol-mz-sec".

Daylength extension was given with either:

1) incandescent lamps (INC) (1-3 umol-mz-sec‘)

2) high pressure sodium lamps (HPS) (4O pmol-mz-seC")

131

 

RESEARCH PROTOCOL:

Upon arrival at MSU, plants were held under natural daylengths at 20 °C
until the experiment began. Bare-root plants were immediately transplanted into
bulbtrays and the root masses were covered with soilless media. Plants were
cooled at 5 °C either in bulbtrays, plug trays, or 2.5-inch pots. Following cold
treatment, plants were potted into 13-cm pots and placed in 20 °C greenhouses
under a 16-h photoperiod delivered by daylength extension from either INC or
HPS lamps.

Data collected included:

1) Initial node count

2) Date of visible bud

3) Date of ﬂowering

4) Number of ﬂower buds at ﬁrst ﬂower

5) Final node number beneath the ﬁrst ﬂower

6) Plant height at ﬁrst ﬂower

7) Number of new nodes were calculated by subtracting the number of

initial nodes from the ﬁnal nodes.

8) Days from visible bud to ﬂower were calculated by subtracting the days

to visible bud from days to ﬂower

132

 

 

Summag of Results

In general, the type of lamp used for daylength extension had little effect
on ﬂower timing for cultivars of Stokesia Iaevis. There were few statistical
differences for ﬂower timing, and where statistical signiﬁcance did occur, the

differences were small (Table 13). For example, ‘Purple Parasols' grown under

 

INC lamps ﬂowered approximately 5 days faster than plants grown under HPS IF 1
lamps. Lamp type inﬂuenced plant height of only two cultivars: ‘Klaus Jelitto’ ‘ I
was approximately 6 cm taller under HPS lamps compared to INC lamps while ,

‘Purple Parasols’ was 11 cm taller under INC lamps compared to HPS lamps. g5

Lamp type had a stronger inﬂuence on number of ﬂower buds. Bud number
increased 1.5 to 2 times for ‘Blue Danube', ‘Klaus Jelitto’ and ‘Purple Parasols’
grown under HPS lamps compared to INC lamps.

Flowering percentage varied greatly (20 to 100%) between cultivars.
‘Wyoming’ and ‘Alba’ had particularly low ﬂowering percentages 20 to 60% and
30 to 60%, respectively, for ‘Wyoming’ and ‘Alba’,. “Purple Parasols’ had a
moderate ﬂowering percentage of 70 to 80%. The lower ﬂower percentages
observed for these cultivars may have been related to small initial plant size.
Plants of ‘Alba‘ and ‘Purple Parasols’ arrived in a 72-cell tray which were
considerably smaller than the starting material of most of the other cultivars (2.5-
inch pots). Starting material for ‘Wyoming’ was single-eye bare-root divisions

with no more than 6 leaves.

133

 

Although most cultivars ﬂowered in between 61 to 85 days, had 6 to 13
ﬂower buds and were between 39 and 52 cm tall, there were several exceptions.
‘Alba’ was the slowest cultivar to ﬂower (> 100 days). ‘Mary Gregory’ and
‘Wyoming’ attained heights at ﬁrst ﬂower of approximately 27 and 29 cm (when
data for each cultivar were pooled for both lamp types due to lack of signiﬁcance)
and were much shorter than other cultivars. Starting plant material size did not
appear to inﬂuence ﬂower number since ‘Alba’ and ‘Purple Parasols’, which had
some of the smallest initial plant sizes had considerably more ﬂowers than other
cultivars. Arrnitage (1989) observed that ‘Alba’ was less ﬂoriferous than other
cultivars in garden performance, but we observed the opposite when container
produced.

Potential as a potted ﬂowering plant varied widely among cultivars. “Klaus
Jelitto’ and ‘Purple Parasols’ showed the greatest potential with numerous large
ﬂowers of either light lavender-blue for ‘Klaus Jelitto’ or deep violet for ‘Purple
Parasols’. In addition, ‘Klaus Jelitto’ had an attractive branching habit. ‘Mary
Gregory’ showed some potential with its naturally short height and small dark
green leaves but produced only a few small yellow ﬂowers. ‘Alba’, ‘Wyoming‘,
and ‘Blue Danube’ lacked potential for various reasons: ‘Alba’ and ‘Wyoming’
had very low ﬂowering percentages and for ‘Alba’ the time needed to produce a
ﬂowering plant was excessively long, while ‘Blue Danube’ was spindly, had few

ﬂowers, and tended to fall over.

134

 

Literature Cited

An'nitage, AM. 1989. Herbaceous Perennial Plants. Varsity Press, Athens, GA.
Fischer, T. 1998. Stoke’s Aster— Stokesia Iaevis. Horticulture 95:34.

Frane, A.J. 1999. Temperature effects on timing and bud development of
Coreopsis verticillata ‘Moonbeam’ and ﬂower induction of long-day
perennials under different night temperatures. MS Thesis, Michigan State

Univ., East Lansing.

Gunn, CR. and GA. White. 1974. Stokesia Iaevis: Taxonomy and Economic
Value. Econ. Bot. 28: 130-135.

Lane, H.H. Cathey, and L.Evans. 1965. The dependence of ﬂowering in several
long-day plants on the spectral composition of light extending the
photoperiod. Amer. J. Bot. 52: 1006-1014.

Thimijan, R. and RD. Heins. 1983. Photometric, radiometric, and quantum
light units of measure: A review of procedures for in interconversion.

HortScience.18: 818-822.

Warrington, I.J. and RA. Norton. 1991. An evaluation of plant growth and
development under various daily quantum integrals. J. Amer. Soc. Hort.
Sci.116(3): 544-551.

135

 

 

 

 

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Appendix B:
Effects of Cold Treatment, Phototperiod, and Forcing Temperature in Anemone

hupehensis, Penstemon digitalis ‘Husker Red’, and Saxifraga arendsii ‘Triumph’

139

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Introduction

Flowering of many temperate herbaceous perennials is inﬂuenced by four
main factors: juvenility, vemalization, photoperiod, and forcing temperature. All
of these factors inﬂuence both the quantity and quality of ﬂowering. Juvenility is
a developmental plant state during which plants are unable or only poorly able to
perceive inductive conditions such as vemalization and photoperiod.
Vemalization is the promotion of ﬂowering by cold treatment, while
photoperiodism is the control of ﬂowering by daylength. Plants can have
obligate or facultative responses to vemalization and photoperiod. Forcing
temperature inﬂuences ﬂower timing as well as plant quality features such as
plant height, ﬂower number, and ﬂower diameter. Vemalization and photoperiod
also inﬂuence plant quality features such as plant height and ﬂower number.

As herbaceous perennials have gained popularity during the past 15
years, the interest in producing them has also increased. Since consumers
prefer to buy plants that are in ﬂower, and most herbaceous perennials are not in
ﬂower in May and early June when consumers are doing most of their shopping,
producers are interested in the ﬂowering requriements of these species so that
they can produce ﬂowering plants in May and June.

The objective of these experiments was to determine the inﬂuence of
vemalization, photoperiod, and forcing temperature on three herbaceous

perennial species: Anemone hupehensis, Penstemon digitalis ‘Husker Red’, and

140

 

Saxifraga arendsii ‘Triumph’. Information from these experiments can be used to

create production schedules.

141

 

Protocol
(1) Cold Duration Experiment
Experimental Design: completely randomized design
Cold treatment: 0, 3, 6, 9, 12, and 15 weeks at 5 °C. Research protocol: 10
plants were immediately potted into 13-cm pots with soilless medium and placed
in a 20 ° C greenhouse where they were provided a 16-h photoperiod delivered
by a natural day supplemented and day extension from high-pressure sodium
lamps. Plants were cooled in the plug tray in coolers set at 5 ° C. Upon
completion of the desired cold treatment duration, 10 plants were transferred to
the greenhouse, potted into the 13-cm pots and placed in the same greenhouse
as those plants which did not receive a cold treatment.
Data collected: 1) initial node count (Year 2 only)

2) date of visible bud

3) date of ﬁrst open ﬂower

4) number of ﬂower buds at ﬂower

5) plant height at ﬂower

6) number of nodes to either last visible leaf or beneath the ﬁrst

ﬂower

(2) Photoperiod Experiment
Experimental design: completely randomized design

Cold treatments: 0 or 15 weeks at 5 °C.

142

 

 

Photoperiods: 10, 12, 13, 14, 16, 24, and a 4-h night interruption from 10:00 pm.
to 2:00 am.

Research Protocol: Half of the plants were immediately placed in coolers set at 5
°C for 15 weeks. The remaining half were potted into 13-cm pots and placed in
a 20 °C greenhouse and ten plants were placed under each photoperiod.

Plants were forced for 15 weeks after which plants not in visible bud were
discarded. Photoperiods were provided by a 9-h natural day and day extension
from incandescent lamps to the desired photoperiod. Between 8:00 am. and
5:00 pm. supplemental light light from high-pressure sodium lamps was given
when the ambient photosynthetic photon ﬂux (PPF) first fell below 400 umol-m‘
2sec“. High-pressure sodium lamps were turned off once PPF rose above 400
/.cmol-m'2-seC'1 and did not turn on again until ambient PPF fell to 200 umol-m'
2sec“. After 15 weeks of cold treatment, the other half of the plants were moved
to the greenhouse, potted into the 13-cm and placed in the photoperiod
treatments exactly as those without a cold treatment.

Data collected: same as in Cold Duration Experiment.

(3) Forcing Temperature Experiment.

Experimental design: completely randomized design

Cold Treatment: 15 weeks at 5 ° C.

Temperatures: 14, 17, 20, 23, 26, and 29 ° C (constant day and night

temperature).

143

 

Research protocol: All plants were given a 15 week cold treatment at 5 ° C.
Following cold treatment, ten plants were potted into 13-cm pots with soilless
medium and placed in each greenhouse set at one of the six temperatures.
Plants were provided with a continuous 16-h photoperiod using high-pressure
sodium lamps.

Data collected: same as for Cold Duration Experiment and Photoperiod

Experiment.

144

Anemone hupehensis

 

 

 

 

 

 

 

 

 

 

    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Anemone hupehensis

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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show 95% conﬁdence intervals.

146

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Photoperiod (h) Photoperiod (h)
Number of Flowers Plant Height at First Flower
ﬂ
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z i l E _
a 50 ‘1 l g 30
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§ 0* f o
z 81012141618202224N, 81012141618202224Nl
‘ Photoperiod (h)
+ °W°°'d Photoperiod (h) -O- 0mm“
+ lSweekoold + 15weekoold

 

 

 

 

 

 

Figure 21. Effects of various photoperiods with and without a 15 week cold treatment at
5 °C in Anemone hupehensis in Year 1.

147

Anemone hupehensis

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 
 
 

 

 

 

 

 

Flower Timing Flower Timing
Oweekatsc 15weekatsc
175 , 175 ,
,3 150 , 100.;’ a 150, A 100;D
5‘ 1251 80 3 a. 125, so 3
3 m} 60 5 3 1°01 5 so :3
a 75 C O 75 .
.§ so 4° ‘e .5 so. 5 ‘° 5
l. 251 20 3 l- 25. 2° 2
o I. . o 3 oi ... 0 g
31012141513202224m 0- 81012141618202224Nl
+ mﬁwﬂafg‘gtoperiod (h) _._ mm Wwotoperiod (h)
+ Deystoflower -I- WNW
+ Porositllowerlng + Pmﬂaverlng
Plant Node Development Plant Node Development
0 week cold 15 weeks cold
8 so 8 5°
U ‘ + Final nodes atl’lower ‘D + F“"°"°‘"“°"'
2 50‘ +Newleavesatﬂower g ‘0‘ ‘ +Mmmm
I. 30‘ ' h 20 _, Eli-N é .
E 10 . H. . . . E 10 . be . .
:1 o - - a o - - . .
z 81012141618202224Nl z 81012141618202224Nl
Photoperiod (h) Photoperiod (h)
Number of Flowers Plant Height at First Flower
g 80 l
g ‘ A 60
g 60 l g 453.
Q. , .
§ “1 in :3
0 2o 0
§ 0 1 1 1o . "e
+ Oweekcold Photo riod h Photoperiod 0')
+ 15-..... P° ‘ l 3; 3:33:33,

 

 

 

 

 

 

Figure 22. Effects of various photoperiods with and without a 15 week oold treatment at

5 °C in Anemone hupehensis in Year 2. Error bars show 95% conﬁdence
intervals.

148

 

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Number of ﬂower buds

 

 

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80

80a

Plant height (cm)
8

 

 

 

 

 

 

 

14 {e {a 2}) £2 2} 2% 23
Temperature (°C)

Figure 24. Inﬂuence of forcing temperature on number of nodes (A), number of ﬂower

buds (B), and plant height at ﬁrst ﬂower (C) in Anemone hupehensis. Error
bars represent 95% conﬁdence intervals.

150

Penstemon digitalis
'Husker Red'

 

 

 

 

 

 

 

 

 

 

 

    

 

 

 

 

 

 

 

 

 

 

 

 

 

151

 

 

 

 

 

 

 

 

 

 

 

Percent Flowering
0 80 q. .:
5
E 50 - , :
‘0' 4o ..
0
2 20 ..
0
0 l 1 4 .0 + +
o 3 6 9 12 15
Weeks at SC
. Plant Node Development
F'°‘"°' Timing Nodes to the last visible leaf
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125 l + Days to visible bud 3 30 4 I
a T + Days to ﬂower ' ' 8
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0 3 6 9 12 15 0 3 5 9 12 15
Weeks at 5c Weeks at 50
T!
3 Number of Flower Buds Plant “9'9ht at Flower
.C
C .4. -
< 300 80 ‘ MT
~ 250 ._ l
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e 150 + E 40 .L. . . =
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E 50 -- E T
g 0 I. i i : F : 0 1* l J . . . l l
g 0 3 6 9 12 15 o 3 6 9 12 15
2 W09“ at 53 Weeks at 50

 

Figure 25. Effects of cold treatment in Penstemon digitalis 'Husker Red' in Year 1.

 

 

Penstemon digitalis
'Husker Red'

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

Percent Flowering
E100 ..
h
0 80 ._
5
E 6" ‘"
E 40 T
0
2 20 ..
a
0 a i .L r : .
0 3 6 9 12 15
Weeks at SC
Plant Node Development
How" 11me Nodes beneath the ﬁrst ﬂower
15°? ' 1 «so. +~°d~wmwwwm
125 l‘ _ + Days to Visible bud . 8 -I- WW
E + Daystoﬂower l g
o 5
E ‘é’ 10 ..
3
. z
0 L : , g , § , 0 i i J. i i If:
0 3 6 9 12 15 0 3 6 9 12 15 18
ﬁg Number of Flower Buds Plant Height at HOW"
2
2 200.
'5 150 l
m < -~ "
g .5.
0 100 4» .. E
g .9
2 50 T- a
m l
g 0 % + : : : l 0 ... 1 1 + 1 1 § i
E 03691215 03691215
5 Weeks at 50 Weeks at 5c

 

 

 

 

 

Figure 26. Effects of cold treatment in Penstemon digitalis 'Husker Red' in Year 2.
Error bars show 95% conﬁdence intervals.

152

Penstemon digitalis
'Husker Red'

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Number of nodes

o—on-O——-o.

 

O

 

 

 

51012141618202224Nl

Photoperiod (h)

 

 

Flower Timing Flower Tlmlng
OweeketSC 15weekat50
200‘ , 1002 A 701 W A 1002
m 150 1 80 3 > so - 80 3
1:. t L g a 50 1 - - » I 3
1: l reoo 3 4o. hi—‘H , ‘ 60o
V 100 c a
l- . 20 g l- 10 1 20 2
0 L O n- 0 0 g
81012141618202224Nl 81012141818202224NI
Photoperiod (h) Photoperiod (h)
-.— Days to visible bud -0- Days to visible bud
+ Days to ﬂower -.- Daystoﬂower
+ Percent ﬂowering + Percent flowering
Plant Node Development
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Nodes to the last vlslble leaf
3o .
20 t

 

 

Number of Flowers

 

 

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g 250 1‘ 100
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81012141618202224Nl

 

 

 

WK!

1

 

Plant Height at First Flower

 

 

81012141618202224Nl
Photoperiod (h)

+-.— 15 week cold

 

 

Figure 27. Effects of various photoperiods with and without a 15-week cold treatment

at 5 °C in Penstemon digitalis ‘Husker Red’ in Year 1.

153

 

 

Penstemon digitalis
'Husker Red'

 

 

 

Flower Timing
0 week at 5 C

 

 

 

200
... i i100
£1501 »80°
re 3
E1001 % "508
E 50 . 40E

0... e 0 a
81012141618202224Nl

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+ Percenttlowemg

rlnL

 

 

 

 

 

 

Flower Timing
15 week at5 C
175 -
.. 150; 5 1003
1» A t
at 125. 80 it
v l
P 75‘ 40 5
.§ 5°) PM e F
l- 251 We '20 g
o“ e 1 0 o
01012141015202224111 0-
Photoperlod (h)
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+ Daystoflower
+ Percentﬂowenng

 

 

 

 

Plant Node Development
0 week cold
Nodes beneath the ﬂrst ﬂower

401 +Finalnodee. .. ..,
-Q— 3 produced during forcing

 

   

Number of nodes

 

 

 

0
81012141618202224N|

Photoperiod (h)

 

 

 

 

Number of Flowers

 

 

Number of ﬂowers

0L

8 10 12 14 16 18 2022 24 Nl

-.— 0 week cold '
+ 15 week m Photopenod (h)

 

 

 

Plant Node Development
15 weeks cold
Nodes beneath the ﬁrst ﬂower

 

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30(+,.Finalnodes. . ..
‘J+ Nodesproduceddunngiorcingl

20; l
’ t
1 I
o- f 1
01012141610202224N1

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101

 

Number of nodes

 

 

 

 

Plant Height at First Flower
100 Y i

I

75 i

 

5° ‘1

Height (cm)

25 i

r

81012141618202224Nl
h

_._ 0mm” P otoperiod (h)

+ 15week cold

0

 

 

 

 

FigLre 28. Effects of various photoperiods with and without a 15-week cold treatmert

at 5 °C in Penstemon dg‘talis ‘i-hsker Red’ in Year 2. Error bars show 95%

conﬁdence intervals.

154

 

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gl

'Husker Red'

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Penstemon digitalis
'Husker Red'

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Number of nodes

 

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Number of ﬂower buds

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Plant height (cm)

201
10.

 

 

 

0 1 1 1 4 1 1 1
1 6 1 8 20 22 24 26 28 30 32

Temperature (°C)

Figure 30. Inﬂuence of forcing temperature on number of nodes (A), number of ﬂower

buds (B), and plant height at ﬁrst ﬂower (C) in Penstemon digitalis ‘Husker
Red'. Error bars represent 95% conﬁdence intervals.

156

 

Saxifraga arendsii
'Triumph'

 

Percent Flowering

 

 

Percent Flowering

 

 

 

 

 

91215

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0 3
Weeks at SC
Plant Node Development
Flower “me nodes to last visible leaf
35 «*- 3 a 30 1'
30 i 9 3 25 ‘ .
TE 1 0 I
:1 25 - l 5 20 l ,
2:. 20 1 -~ '1 g 15 .1
E 13 1- ” ‘2' 1° 1
'- 5 i+oays to visiblebud ’ i g 5 i . .I
‘ 0 toﬂ ‘ ' ~ 1 a
TT a%ys éower 1 1 £1 0 ' 1 1 1 1 1 14
0 3 6 9 12 15 0 3 6 9 12 15
Weeks at 5C Weeks at 5C
71
'g Number of Flower Buds Plant "9'9ht at Flower
.C
3 15 ’ ‘
g 20 -;- ' - ~ 1
a A 7 1
310+ .1 ,. E1, 15,. 0A1
‘2 V E, 10 ;_
g 5 a}. . , , ., g
E 5 * .
g 0 4' 1 1 1 1 1 0 . J 1 1 . 1 1
g 0 3 6 9 12 15 0 5 5 0 12 115
2 Weeks at 5C Weeks at 5C

 

in Year 1.

157

Figure 31. Effects of cold treatment in Saxifraga arendsii 'Triumph'

 

 

 

Saxifraga arendsii
'Triumph'

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Percent Flowering
E100 1
g 80 1
.2 60 ._
IL
‘5 40 -—
0
g 20 ..
a O - 1 1 1 1
0 2 4 6 810121416
WeeksatSC
Flower Timing Plant Node Development
- _—+4=1na1nedeo
. a 120 7" +N'ewnodes
60 + ' 0 1001, . 1 . _
a 1 8
>1 40 __ C 80+ ,
ﬂ - co-
3 i 8 60 .i- .
0 20 2 e 3
.§ ; g 40 1.
.- 0 ++ Daystovisiblebud 1 g 20 T‘
DDaystoﬂower g
40:11....1 0‘ﬁ11111111
0246810121416 0246810121416
Weeks at 5C Weeks at 50
w
'2: Number of Flower Buds Plant Height at Flower
.C
"‘ 10
c ~—
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a 8 "*- A 30 '7' n . 1;
W ‘1' E 25 4- .1" , ..-;
1: + . g
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g 0246810121416 0246810121416
2 Weeks at SC Weeks at 5C

 

 

Figure 32. Effects of cold treatment in Saxifraga arendsii 'Triumph'

in Year 2. Error bars show 95% conﬁdence intervals.

158

 

 

 

Saxifraga aren dsii
'Triumph'

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Flower Timing Flower Timing
0weekat5C 15weekatSC
a, 100
.100 5 A 1 1 1000'
3 g 8°? Ni—i A .g
. 75 g 5; 60 l » 75 g
50 E g 40 i k , 50 2
ﬂ 1
. 25 5 p 20 i I I 25 E
e A_“. : a e 0 1‘5? o ' 1 . 0 3
81012141618202224NI a. 81012141618202224Nl a
Photoperiod (h) _._ daysmm‘ebghOtoPeﬁOd (h) a
—l- daystoﬂower
+ percentﬂowenng
Plant Node Development
Nodes to last visible leaf '
a
8
8 M e
h-
o 20 . g . . .
L
3 to
E .
a
2 0
81012141818202224N|
Photoperiod (h)
Number of Flowers Plant Height at First Flower
% 6 j E 25
= I 3 20
"5 4 J . E '5 x. .
b i 0 9 at
0 , ; - 10
.o 2 ._ . a
E F I 5 1
a 0 1
2 ' ' 0
81012141618202224Nl 81012141618202224Nl
Photoperiod (h) Photoperiod (h)

 

 

 

 

 

 

Figure 33. Effects of various photoperiods with and without a cold treatment in
in Saxifraga arendsii 'Triumph' in Year 1.

159

Saxifraga arendsii
'Triumph'

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Flower Timing Flower Timing
Oweekatsc 15weekatsc
a 100
C A
o >. t
75 g g » 75 s
so LT. g » 50 g
"' IL
L 25 § p 25 «E
‘M- o 3 x 0 °
81012141618202224Nl O. 81012141618202224Ni g
Photoperiod (h) ...mumw PhOtOPOTiOd ('0 °-
..— mum
+ mm
Plant Node Development
nodes to last visible leaf
a 60
O
-o
o
I: 40
.-
o
'5
.2 20
81012141618202224Nl
Photoperiod (h)
+ Final nodes
+ New nodes
Number of Flowers Plant Height at First Flower
a 12 i T 1 30
g 1° " i l g 25
g 8 ' 2. 2°
'6 6 4 1 E 15 0
3 4 l - 9 10
.o x o
E 2 4 :I:
3 , 1 .
z 0 ~ ‘ ' o .
81012141618202224N| 81012141618202224N|
Photoperiod (h) Photoperiod (h)

 

 

 

 

 

 

Figure 34. Effects of various photoperiods with and without a cold treatment in
in Saxifraga arendsii 'Triumph' in Year 2. Error bars show 95%
conﬁdence intervals.

160

Saxifraga arendsu

'Triumph'

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Saxifraga arendsii
'Triumph'

+ Number of ﬁnal nodes
... Number of new nodes

100

 

80 «- T

 

Number of nodes

 

 

 

 

 

 

 

8 4

Number of ﬂower buds

 

 

 

 

Plant height (cm)
3

 

 

 

 

 

 

 

 

L ..
.l

14 16 18 20 22 24 26 28 30 32

 

Temperature (°C)

Figue 36. Inﬂuence of forcing temperature on mmber of nodes (A), number of flower
buds (B), and plant height at ﬁrst flower (C) in Saxifraga arendsii ‘Triumph’.
Emor bars represent 95% conﬁdence intervals.

162

 

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