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This is to certify that the

thesis entitled

FLOWER INDUCTION AND CULTURAL REQUIREMENTS FOR QUICK-
CROPPING OF THE HERBACEOUS PERENNIALS VERONICA SPICATA,
PHLOX PANICULATA, LEUCANTHEMUM XSUPERBUM, ACHILLEA, GAURA
LINDHEIMERI, AND CAMPANULA

presented by

Amy Lynn Enfield

has been accepted towards fulﬁllment
of the requirements for

14.8. degree in MTG

 

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DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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_. ...——-¢———-———-— .

FLOWER INDUCTION AND CULTURAL REQUIREMENTS FOR QUICK-
CROPPING OF THE HERBACEOUS PERENNIALS VERONICA SPICATA,
PHLOX PANICULA TA, LEUCANTHEMUM XSUPERBUM, ACHILLEA, GAURA
LINDHEIMERI, AND CAMPANULA

By

Amy Lynn Enﬁeld

A THESIS
Submitted to
Michigan State University
In partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

2002

ABSTRACT
FLOWER INDUCTION AND CULTURAL REQUIREMENTS FOR QUICK-
CROPPING OF THE HERBACEOUS PERENNIALS VERONICA SPICATA,
PHLOX PANICULA TA, LEUCANTHEMUM xSUPERBUM, ACHILLEA, GAURA
LINDHEIMERI, AND CAMPANULA
By
Amy Lynn Enﬂeld
Optimized production of vegetatively propagated herbaceous perennials
requires a proper knowledge of stock plant management, propagation protocols,
appropriate vegetative bulking, and ﬂower induction and development
requirements. This project was conducted to identify these physiological and
cultural elements for six herbaceous perennial species. Stock plant
management, propagation, and vegetative bulking for Veronica spicata 'Red Fox'
and Campanula 'Birch Hybrid' required only appropriate light and temperature
because both plants were day-neutral following a ﬂowering ﬂush. Plants had an
obligate cold requirement for ﬂowering. Photoperiod control during all stages of
development was necessary for Phlox paniculata 'David', Leucanthemum
xsuperbum 'Snowcap', Achillea 'Moonshine', and Game Iindheimen' Whirling
Butterﬂies' because all were long-day plants with facultative cold requirements for
ﬂowering. Experiments were conducted to quantify the effects of propagation
environment on rooting and subsequent ﬂowering of P. paniculata ‘David’.
Rooting increased as daily light integral increased from 0.8 to 8.6 moI-m'2-d'1 but
was not affected by auxin concentration or rooting photoperiod. Days to ﬂower

decreased up to 17 days as propagation photoperiod increased from 11 to 15

hours, and cold treatment for 5 weeks decreased time to ﬂower by up to 25 days.

ACKNOWLEDGMENTS

I wish to give my sincere thanks to Dr. Royal Heins for offering me the
opportunity to complete my degree under his guidance. His patience, support,
and insight over the last few years have been invaluable.

The support and valuable insights of my other committee members, Drs.
Art Cameron, Will Carlson, and Ken Poff, have also been greatly appreciated.

A special thank-you goes to greenhouse technicians David Joeright and
Mike Olrich and their undergraduate employees for keeping the greenhouse
running, keeping my plants alive, and helping me collect data or propagate
cuttings from time to time. I would also like to mention the faculty, staff, visiting
scholars, and students. They made working at MSU very enjoyable and
memorable. I would especially like to thank my ofﬁce mates: Dr. Erik Runkle, Dr.
Hyeon-Hye Kim, Kari Robinson, Andrea Beckwith, and Jennifer Dennis for simply
putting up with me.

I would also like to thank the greenhouse growers who support MSU
ﬂoriculture research. Without their support, none of this research would have
been possible. A special mention goes to Oro Farms, Center Greenhouse, Ball
Seed Company, and Walters Gardens for donation of plant material to my
research.

Finally, I would like to thank my family and friends for all their

encouragement and support. I never would have made it here without them.

TABLE OF CONTENTS

LIST OF TABLES ................................................................................................ vii
LIST OF FIGURES ............................................................................................... x
Thesis Introduction ................................................................................................ 1
SECTION I
LITERATURE REVIEW ........................................................................................ 3
Vernalization ......................................................................................................... 4
Introduction ........................................................................................................ 4
History ................................................................................................................ 4
Effects of Low Temperatures ............................................................................. 5
Obligate versus Facultative ................................................................................ 7
Requirements of Vernalization ........................................................................... 9
Site of Vernalization ......................................................................................... 10
Effective Temperatures and Durations ............................................................. 11
Molecular and Genetic Response .................................................................... 12
DNA Demethylation ...................................................................................... 12
Vernalization Pathway .................................................................................. 13
VERNALIZA TION (VRN) Genes ................................................................... 14
FLOWERING LOCUS C (FLC) Gene ........................................................... 14
FRIGIDA (FRI) Gene .................................................................................... 16
Conclusion ....................................................................................................... 16
Herbaceous Perennials ....................................................................................... 17
Achillea ............................................................................................................ 17
Campanula ....................................................................................................... 20
Gaillardia .......................................................................................................... 22
Gaura ............................................................................................................... 25
Leucanthemum ................................................................................................ 27
Phlox ................................................................................................................ 29
Veronica ........................................................................................................... 31
Literature Cited ................................................................................................... 33
SECTION II
THE FLOWERING RESPONSE OF VERONICA SPICA TA ‘RED FOX’ TO COLD
AND BULKING TREATMENTS .......................................................................... 39

Abstract ............................................................................................................ 41

Introduction ...................................................................................................... 42
Materials and Methods ..................................................................................... 44
Results ............................................................................................................. 47
Discussion ....................................................................................................... 50
Conclusions ..................................................................................................... 53
Literature Cited ................................................................................................ 55

SECTION III
THE EFFECT OF DAILY LIGHT INTEGRAL, AUXIN CONCENTRATION, AND
PROPAGATION PHOTOPERIOD ON THE ROOTING AND FLOWERING OF

PHLOX PANICULA TA ‘DAVID’ ........................................................................... 63
Abstract ............................................................................................................ 65
Introduction ...................................................................................................... 66
Materials and Methods ..................................................................................... 68
Data Collection and Analysis ........................................................................... 72
Results ............................................................................................................. 72

, Discussion ....................................................................................................... 77
Conclusions ..................................................................................................... 82
Literature Cited ................................................................................................ 84

Thesis Conclusion ............................................................................................... 99

APPENDIX A

THE FLOWERING RESPONSE OF LEUCANTHEMUM xSUPERBUM

‘SNOWCAP’ TO COLD DURATION ................................................................. 100
Research Objective ........................................................................................ 101
Materials and Methods ................................................................................... 101
Results and Discussion .................................................................................. 103
Conclusions ................................................................................................... 105
Literature Cited .............................................................................................. 105

APPENDIX B

THE FLOWERING RESPONSE OF ACHILLEA ‘MOONSHINE’ TO COLD
DURATION, PROPAGATION PHOTOPERIOD, AND BULKING DURATION

AND PHOTOPERIOD ....................................................................................... 110
Research Objective ........................................................................................ 11 1
Materials and Methods ................................................................................... 111
Results and Discussion .................................................................................. 114
Unresolved Issues Requiring Further Research ............................................ 117

APPENDIX C
THE FLOWERING RESPONSE OF GAURA LINDHEIMERI ‘WHIRLING
BUTTERFLIES’ AND ‘SISKIYOU PINK’ TO COLD DURATION AND BULKING

DURATION AND PHOTOPERIOD ................................................................... 126
Research Objective ........................................................................................ 127
Materials and Methods ................................................................................... 127
Results and Discussion .................................................................................. 130
Unresolved Issues Requiring Further Research ............................................ 134

APPENDIX D

THE FLOWERING RESPONSE OF CAMPANULA ‘BIRCH HYBRID’ TO COLD

DURATION AND DURATION OF BULKING .................................................... 144
Research Objective ........................................................................................ 145
Materials and Methods ................................................................................... 145
Results and Discussion ........................................................ . ......................... 148
Unresolved Issues Requiring Further Research ............................................ 150

vi

LIST OF TABLES

SECTION II

Table 1. Dates of forcing following cold treatment, average air temperatures, and
average daily light integral (DLI) from date of forcing to average date of ﬂowering
for Veronica spicata ‘Red Fox’. ........................................................................... 57

Table 2. The effects of 5 °C cold treatment on ﬂowering of Veronica spicata
‘Red Fox’ ............................................................................................................. 58

Table 3. Signiﬁcance of bulking container size, pinch, and bulking duration on
ﬂowering of Veronica spicata ‘Red Fox’. ............................................................. 59

SECTION III

Table 1. Dates of forcing, average daily temperatures, and average daily light
integral from date of forcing to average date of ﬂowering for the Phlox paniculata
‘David’ propagation photoperiod (ﬂowering) experiment. .................................... 87

Table 2. Effects of daily light integral (DLI) during propagation on rooting of
Phlox paniculata ‘David’. ..................................................................................... 88

Table 3. Signiﬁcance of auxin concentration on average number of roots per
cutting, average root mass per cutting, and rooting percentage of Phlox
paniculata ‘David’ cuttings. ................................................................................. 89

Table 4. Signiﬁcance of propagation photoperiod on average number of roots
per cutting, average root mass per cutting, and rooting percentage of Phlox
paniculata ‘David’ cuttings. ................................................................................. 90

Table 5. Propagation photoperiod treatment effects on ﬂowering characteristics
of Phlox paniculata ‘David’. ................................................................................. 91

vii

APPENDIX A

Table 1. Dates of forcing, average daily temperatures, and average daily light
integrals (DLI) from date of forcing to average date of ﬂowering for

Leucanthemum xsuperbum ‘Snowcap’. ............................................................ 106
Table 2. Signiﬁcance of cold treatment on ﬂowering of Leucanthemum
xsuperbum ‘Snowcap’. ...................................................................................... 107
APPENDIX B

Table 1. Dates of forcing, average daily temperatures, and average'daily light
integral (DLI) from date of forcing to average date of ﬂowering for Achillea
‘Moonshine’ ....................................................................................................... 1 18

Table 2. The effects of cold duration on ﬂowering of Achillea ‘Moonshine’. ..... 119

Table 3. The effects of propagation photoperiod on ﬂowering of Achillea
‘Moonshine’ ....................................................................................................... 120

Table 4. The effects of bulking duration and photoperiod on ﬂowering of Achillea
‘Moonshine’ ....................................................................................................... 121

APPENDIX C

Table 1. Dates of forcing, average daily temperatures, and average daily light
integral (DLI) from date of forcing to average date of ﬂowering for Gaura
Iindheimen'. ....................................................................................................... 1 35

Table 2. The effects of cold treatment on ﬂowering of Gaura lindheimen' ‘Whirling
Butterﬂies’. ........................................................................................................ 1 36

Table 3. The effects of bulking duration and photoperiod on ﬂowering of Gaura
Iindheimen' ‘Whirling Butterﬂies’ (replicate 1). ................................................... 137

Table 4. The effects of bulking duration and photoperiod on ﬂowering of Gaura
lindheimen' ‘Whirling Butterﬂies’ (replicate 2). ................................................... 138

viii

Table 5. The effects of bulking duration and photoperiod on ﬂowering of Gaura
Iindheimeri ‘Whirling Butterflies’ (replicate 3). ................................................... 139

Table 6. The effects of bulking duration and photoperiod on ﬂowering of Gaura
Iindheimeri ‘Siskiyou Pink’ (replicate 1). ............................................................ 140

Table 7. The effects of bulking duration and photoperiod on ﬂowering of Gaura
Iindheimeri ‘Siskiyou Pink’ (replicate 2). ............................................................ 141

APPENDIX D

Table 1. Dates of forcing, average daily temperatures, and average daily light
integral (DLI) from date of forcing to average date of ﬂowering for Campanula
‘Birch Hybrid’. .................................................................................................... 151

Table 2. The effects of cold treatment on ﬂowering of Campanula ‘Birch Hybrid’.
.......................................................................................................................... 1 52

Table 3. Signiﬁcance of bulking duration and duration of cold on ﬂowering of
Campanula ‘Birch Hybrid’. ................................................................................ 153

Table 4. The effects of bulking duration and duration of cold on ﬂowering of
Campanula ‘Birch Hybrid’. ................................................................................ 154

LIST OF FIGURES

SECTION II

Figure 1. The effects of bulking duration and pinching on days to visible bud
(0,0, no pinch and pinch, respectively), days from visible bud to ﬂower (I,D, no
pinch and pinch, respectively), and days to ﬂower (V,V, no pinch and pinch,
respectively). Error bars represent the standard error of the mean. Probability of
linear and quadratic relationships indicated by L and Q, respectively,

"5 'mNonsigniﬁcant or signiﬁcant at P < 0.05, 0. 01, or 0.001, respectively. ..... 60

Figure 2. The effects of bulking duration, bulking container size (0, I, Y = 13-cm
pot, 4.4-cm plug, and 4.1-cm plug, respectively), and pinching (A and C = no
pinch, B and D = pinch) on ﬂowering percentage (A and B) and the number of
ﬂowering shoots per plant (C and D). Error bars on graphs C and D represent
the standard error of the mean ............................................................................ 61

Figure 3. The relationship between the number of ﬂowering shoots per plant and
the number of lateral inﬂorescences produced per ﬂowering shoot for Veronica
spicata ‘Red Fox’. Data points represent the means of all possible treatment
effects. Error bars represent the standard error of the mean. ............................ 62

SECTION III

Figure 1. Daily light integrals (DLI, mol-m'Z-d“) during Phlox paniculata ‘David’
propagation for each level of shading. ................................................................ 92

Figure 2. The effects of daily light integral (DLI) during propagation of Phlox
paniculata ‘David’ on average root number per cutting (A), average root mass per
cutting (B), and rooting percentage (C). Error bars represent standard error of
the mean. ............................................................................................................ 93

Figure 3. The effects of auxin concentration on root number, root mass, and
rooting percentage of Phlox paniculata ‘David’. Error bars represent standard
error of the mean. ............................................................................................... 94

Figure 4. The effects of propagation photoperiod on root number, root mass, and
rooting percentage of Phlox paniculata ‘David’. Error bars represent standard
error of the mean. ............................................................................................... 95

Figure 5. Number of days to ﬂower for Phlox paniculata ‘David’ propagation
photoperiod. Error bars represent 95% conﬁdence intervals. ............................ 96

Figure 6. Plant height and number of nodes at ﬂowering for unpinched Phlox
paniculata ‘David’ plants. Error bars represent standard error of the mean. ...... 97

Figure 7. Plant height, node number, and number of ﬂowering stems for pinched
Phlox paniculata ‘David’ plants. Error bars represent standard error of the mean.

............................................................................................................................ 98
APPENDIX A

Figure 1. The effects of cold treatment on days to visible bud (0), days from
visible bud to ﬂowering (o), and days to ﬂower (V) for Leucanthemum
xsuperbum ‘ Snow Cap’. Error bars represent 95% conﬁdence intervals. ....... 108

Figure 2. The effects of cold treatment on node number (A), plant height (B), and
ﬂower bud number (C) of Leucanthemum xsuperbum ‘Snow Cap’. Error bars
represent 95% conﬁdence intervals. ................................................................. 109

APPENDIX 8

Figure 1. Time to ﬂower for unpinched versus pinched plants of Achillea
‘Moonshine’. Error bars represent standard error of the mean. ....................... 122

Figure 2. Flowering response of Achillea ‘Moonshine’ to propagation
photoperiod. Days to visible bud (0), days from visible bud to ﬂower (0), and
days to ﬂower (V) are presented for replicates 1 (A) and 2 (B). Height (0) and
number of nodes (0) are presented for replicates 1 (C) and 2 (D). Error bars
represent standard error of the mean. .............................................................. 123

xi

Figure 3. Time to ﬂower, days to visible bud (A), days from visible bud to ﬂower
(B), and days to ﬂower (C), for Achillea ‘Moonshine’ bulked under a 10- (o), 12-
(0), or 13-h (V) photoperiod. Error bars represent standard error of the mean.
.......................................................................................................................... 124

Figure 4. Height (A) and number of nodes (B) at ﬂower for Achillea ‘Moonshine’
bulked under a 10- (o), 12- (0), or 13-h (V) photoperiod. Error bars represent
standard error of the mean. .............................................................................. 125

APPENDIX C

Figure 1. The effects of bulking duration and photoperiod on days to ﬂower (A-
C), plant height at ﬂower (D—F), and number of lateral inﬂorescences at ﬂower
(G—l) for Gaura Iindheimeri ‘Whirling Butterﬂies’. Error bars represent standard
error of the mean. ............................................................................................. 142

Figure 2. The effects of bulking duration and photoperiod on days to ﬂower (A
and B), plant height at ﬂower (C and D), and the number of lateral inﬂorescences
(E and F) for Gaura Iindheimeri ‘Siskiyou Pink’. Error bars represent standard
error of the mean. ............................................................................................. 143

APPENDIX D

Figure 1. The effects bulking duration and duration of cold on days to ﬂower (A),
ﬂowering percentage (B), number of ﬂowering stems per plant (C), and the
number of nodes present after cold treatment (D) for Campanula ‘Birch Hybrid’.
Error bars represent standard error of the mean ............................................... 155

xii

Thesis Introduction

Ten years ago the ﬂoriculture research team at Michigan State University
initiated research on the ﬂowering and cultural physiology of herbaceous
perennials. Now that the ﬂowering physiology of many herbaceous perennials is
understood, growers have the ability to begin programming ﬂowering herbaceous
perennials for speciﬁc market dates. However, before plants can be uniformly
ﬂowered on a speciﬁc date, additional research is required because there are
several problems associated with current herbaceous perennial production.

The ﬁrst problem is lack of crop uniformity, which can be caused by a
number of factors, including nonuniform propagules attributed to propagation of
cuttings from stock plants in various stages of vegetative and reproductive
development. Nonuniformity can also be caused by disease, even if propagules
are initially uniform. There is a high risk of disease with bare-root material
because plants are often stored for extensive periods in cold storage. A second
problem is that current production practices do not provide induced and
ﬂowering-size plant material for planting during the summer. Although bare—root
material is available from winter to spring, availability is generally lacking the rest
of the year, and even then plants are often diseased because they have been
stored for extended periods. Finally, vernalized plugs are not available after
early spring because the temperatures in greenhouses used by growers for
vernalization cannot be kept cool enough because of rising outside solar

radiation and temperatures. A third problem with current production practices is

that production schedules are generally lengthy. The time from planting the
starting material to ﬂower may exceed a year.

This thesis research was directed at developing a production protocol to
avoid these problems. The production protocol was termed quick-cropping. The
primary goal was to optimize the production of herbaceous perennials by
determining the proper environmental and cultural requirements for each stage of
herbaceous perennial production: stock plant management, propagation, bulking
(root establishment and vegetative growth), cold treatment, and forcing to ﬂower.
Another goal of quick-crop production was to make distinctions between
vegetative and reproductive growth by understanding the cold and photoperiod
requirements of an herbaceous perennial species so that uniform ﬂowering crops
could be produced. Six species were examined to determine the feasibility of the
quick-crop herbaceous perennial production protocol: Veronica spicata ‘Red
Fox’, Phlox paniculata ‘David’, Leucanthemum xsuperbum ‘Snowcap’, Achillea
‘Moonshine’, Gaura Iindheimeri ‘Whirling Butterﬂies’ and ‘Siskiyou Pink’, and

Campanula ‘Birch Hybrid’.

SECTION I

LITERATURE REVIEW

Vernalization
Introduction

In plants, most biological processes proceed more quickly as the
temperature rises. An exception is the promotion of ﬂowering by low
temperatures, which is known as vernalization. The importance of low
temperatures (temperatures below those optimal for growth) in ﬂower induction of

certain plants has been known since the 19th century (Bemier et al., 1981).

History

The term vemalization was derived in Russia in 1928. Lysenko initially
called the process Jaroviation. Jar means god of Spring in Russian, and spring
cereals are called Jarovoe (Chouard, 1960). The word was then translated to
vernalization. The Latin vernum means Spring.

Before the technique of vernalization had even evolved, research was
being conducted on the effects of temperature on plant development and
ﬂowering. Klebs, who may be regarded as the initiator of this branch of plant
physiology, began research before 1918 (Whyte, 1948). He proposed that it
should be possible to control and direct the growth and development processes
of a plant by exposing it under experimental conditions to the particular factors
that it was exposed to in nature (Whyte, 1948): temperature and light.

Some of the ﬁrst cold-response experiments were performed in 1918 by

Glasner (Chouard, 1960; Whyte, 1948). He wanted to determine the

physiological differences between spring and winter rye. His research showed
that spring rye does not need a cold period in order to reach the shooting stage,
whereas ﬂowering of winter rye depends on the rye’s receiving a cold period
either during or after germination. Winter rye that was germinated at 1 to 2 °C
reached the shooting stage 9, 21, or 41 d earlier than when germinated at 5 to 6
°C, 12 °C, or 14 °C, respectively (Whyte, 1948). This research showed that in
winter rye, low temperature is needed for the “release of ﬂower formation.”

A large amount of research concerning low-temperature effects on plant
development and ﬂower initiation has been conducted since Klebs and Glasner
conducted their research. Two groups studied the physiology of vernalization on
an “accurate” experimental basis. In the 19305 and 19408, Gregory and Purvis
performed experiments in London, and in the 19405 and 19505, Melchers and
Lang et al. performed experiments at Tijbingen (Chouard, 1960). Vernalization

research continues today, but it is often more genetically than physically based.

Effects of Low Temperatures

Plant development is inﬂuenced directly and inductively by numerous
environmental factors, including photoperiod, light quantity, light quality, nutrient
and water availability, and temperature. Direct effects elicit a plant response
during exposure to the environmental condition. An inductive effect occurs
sometime after the plant has been exposed to the condition but not during
exposure. Exposure to low temperatures can evoke direct and inductive

responses in plants.

Low temperatures can be used to break dormancy, during which all
primordia exist but either do not grow or grow very slowly. Generally, breaking
dormancy is thought to involve the removal of growth inhibitors so that active
growth can occur as soon as favorable conditions return. Insufﬁcient cold can
reduce the ﬂowering response. In most spring-ﬂowering woody plants, dormancy
release can be induced only by chilling the buds for a particular length of time
(Smith and Kefford, 1964). In some bulbous plants, for example, tulip and
narcissus, ﬂower initiation occurs before dormancy. Floral differentiation can
take place during the dormant period (Rees, 1985). However, in tulips, ﬂoral
stalk elongation occurs only after the bulbs have received a low-temperature
treatment (Rietveld et al., 2000). The breaking of dormancy by low temperatures
can also occur in seed. It is common in seeds of trees and shrubs and in some
temperate herbaceous perennials (Hartmann et al., 1997).

Flower initiation and development can also occur under low temperatures.
In stock, Lunaria biennis L., ln's ‘Wedgewood’, and onion, for example, ﬂoral
initials differentiate during the exposure to cold (Chouard, 1960; Thomas and
Vince-Prue, 1997). In brussels sprouts (Brassica oleracea gemmifera L.), ﬂower
initiation must take place during slow growth at low temperatures. Plants that
have not initiated an inﬂorescence at transfer to growing temperatures remain
vegetative (Friend, 1985).

When exposure to low temperatures is used for the induction and
promotion of ﬂowering, it is termed vemalization. Without a cold treatment,

vernalization-requiring plants show delayed ﬂowering or remain vegetative. ln

1960, Chouard deﬁned vernalization as “the acquisition or acceleration of the
ability to ﬂower by a chilling treatment.” As a rule, initiation of ﬂower primordia
does not occur at vernalizing temperatures. It occurs only after plants are moved
to warmer temperatures more favorable for growth (Bemier et al., 1981 ).
Numerous plant species require a vernalization treatment in order to ﬂower; for
example, Digitalis purpurea L. (foxglove), Althaea rosea (L.) Cav. (hollyhock),
Beta vulgaris L. (beet), Apium graveolens L. (celery), and Hyoscyamus niger L.

(black henbane) (Metzger, 1996).

Obligate versus Facultative

Vernalization can be deﬁned as either the acquisition of the ability to
ﬂower or the reduction in time to ﬂower. Plants that will not ﬂower without
exposure to low temperatures have an obligate vernalization response. Most
plants with an obligate vernalization response have embryos within the mature
seed that cannot be vernalized (Chouard, 1960). Plants in this category are
primarily biennials and herbaceous perennials. For example, seedlings of
Dianthus barbartus L. have an obligate requirement for vernalization (Cockshull,
1985). Neither chicory (Cichon’um intybus L.), which can be vernalized as a seed
or plant, nor Raphanus sativus L., which can be vernalized as a germinating
seed, will ﬂower unless it is exposed to a cold treatment (Demeulemeester and
De Proft, 1999; Engelen-Eigles and Enrvin, 1997).

Plants that will eventually ﬂower without a cold treatment but ﬂower faster

after cold have a facultative vernalization response, which generally results in a

reduction in leaf number and fewer days to flower. This response often becomes
more pronounced as the length of the vernalization treatment increases. Plants in
this category include annuals and herbaceous perennials. Dianthus allwoodii
and D. alpinus L. show a reduction in the number of days to ﬂower and an
increase in the total number of ﬂowers in response to cold (Wurr et al., 2000).
For certain Aquilegia L. species versus uncooled plants, 8 weeks of cooling
reduced the time to ﬂower and promoted longer peduncles (Garner and
Arrnitage, 1998). Cineran'a also shows a facultative response to vernalization.
The number of leaves formed before ﬂowering decreases as the chilling duration
increases (maximum reduction occurs after 3 to 5 weeks at 6 °C), and all
unchilled plants eventually ﬂower when grown at 18 °C (Yeh et al., 1997).

In some cases, vernalization can substitute for long days when plants
show a facultative response to vernalization. In these plants, photoperiod is the
primary ﬂower induction stimulus, but vernalization can substitute for long days
(plants will ﬂower regardless of photoperiod) or hasten ﬂowering under long days.
For example, Karlsson et al. (1993) observed 32 ecotypes of Arabidopsis
thaliana (L.) Heynh. Of the ecotypes that responded to vernalization, two
showed an obligate response, while the others showed a facultative response. In
most cases, vernalization was able to completely substitute for long days (plants
ﬂowered regardless of photoperiod). The substitution of vernalization for long
days can also be seen in Gypsophila paniculata L. Without a vernalization
treatment, plants will ﬂower only under long days; however, after vernalization

plants will ﬂower under any photoperiod (Davies et al., 1996; Shilo, 1985).

Requirements of Vernalization

A vernalization treatment is effective only on actively growing plants.
Seed of winter annuals respond to vernalization before germination if they have
imbibed water and have become metabolically active (Taiz and Zeiger, 1998).
Chandler and Dean (1994) showed that late-ﬂowering arabidopsis plants are
most sensitive to vernalization at the imbibed seed stage. When cold was
applied at that stage, plants produced fewer leaves before ﬂowering. As plant
age increased before vernalization, leaf number before ﬂowering also increased.

Most biennials, on the other hand, have to proceed through a juvenile
developmental phase in which they are insensitive to vernalizing temperatures.
They must reach a minimal size, age, or both before they become sensitive to
low temperatures. For example, under continuous light and 18 °C day/15 °C
night temperatures, chicory plants younger than 100 d do not react to
vernalization but remain rosettes after cold. Once plants reach 112 d or older,
they respond to a vernalization treatment (Demeulemeester and De Proft, 1999).
In temperate grasses, although seed vernalization is possible in some species,
the vernalization rate is higher in seedlings (Heide, 1994). The length of the
juvenile period varies widely (usually between 2 and 5 weeks), depending on the
grass species. Geum urbanum L. cannot respond to vernalization until the four-
to ﬁve-leaf stage, and then only axillary buds at a certain stage of development

are sensitive to low temperatures (4 °C) (Tran Thanh Van, 1985). The terminal

apex of the basal rosette can be vernalized only by 30 to 50 weeks of cold

treatment, whereas axillary buds are vernalized in 5 to 15 weeks (Taylor, 1997).

Site of Vernalization

Perception of vernalization occurs mainly in the meristematic zones of the
shoot apex. However, all actively dividing cells may be capable of responding to
low temperatures (Levy and Dean, 1998). Once vernalization has occurred, it is
maintained through mitosis. The vernalization requirement is reset by meiosis or
some other aspect of reproductive growth.

In biennials, the overwintering stem apex perceives the stimulus, although
there are some reports suggesting that leaves and even isolated roots are
responsive in some cases (Hopkins, 1995). A classic case of dividing cells
perceiving low temperatures is Wellensiek’s (1960) study of Lunaria annua L.
Cut leaves that were held at 5 °C produced regenerated plants that were able to
ﬂower. However, the action of the cold was limited to the base of the petiole, the
site of actively dividing cells. If the petiole was removed, the regenerated plants
failed to ﬂower. Cell division, however, is not a requirement for vernalization in
all cases; for example, winter rye and Cheiranthus allionii L. (Thomas and Vince-
Prue, 1997).

In some instances, cuttings removed from vernalized stock plants do not
require an additional cold treatment in order to ﬂower. The ﬂower induction

stimulus is transmitted in the cuttings, which has been shown in Dianthus

10

allwoodii ‘Doris’ and chicory (Demeulemeester and De Proft, 1999; Wurr et al.,

2000)

Effective Temperatures and Durations

Vernalization is a progressive process, and the effect becomes
increasingly stable as the duration of cold increases. The optimum temperature
generally ranges between 1 and 7 °C (T aiz and Zeiger, 1998). The optimum
temperature varies among plant species. For example, in cineraria, the base
temperature for vernalization is —0.3 °C, the optimum is 5.9 °C, and the maximum
is 15.8 °C (Yeh et al., 1997).

The effect of low temperatures increases with the duration of exposure
until the response is saturated. A response usually occurs after at least 4 weeks
but varies widely (<10 to >100 d) between species (Metzger, 1996; Thomas and
Vince-Prue, 1997). For example, R. sativus L. can be vernalized in as few as 40
d (Engelen-Eigles and Enlvin, 1997). A saturated vernalization response can be
found in certain ecotypes of arabidopsis after 30 to 40 d (Bagnall, 1993).

Growing G. paniculata ‘Bridal Veil’ at cool night temperatures (7 °C) results in
enhanced ﬂower yield and quality. The cool night temperature could have a
vernalizing effect large enough to cause ﬂowering in ‘Bridal Veil’, which has a low

vernalization requirement (Davies et al., 1996).

11

Molecular and Genetic Response

A great deal is known about the effects of vernalization on growth and
development of plants. On the other hand, little is known about the effects of
vernalization at the genetic and molecular levels. Vernalization is an epigenetic
phenomenon, meaning that the vernalized state is stable through mitosis but not
meiosis. Several genes have been identiﬁed in Arabidopsis thaliana (L.) Heynh
that appear to play a role in the vernalization response: FRIGIDA (FRI),
FLOWERING LOCUS C (FLC), and the VERNALIZA TION genes (VRN1 and
VRN2). It has been proposed that these genes work through several parallel
pathways, including the autonomous and vernalization pathway (Koomeef et al.,
1998). DNA demethylation may also play an important role in the activation or

deactivation of these pathways and genes.

DNA Demethylation

Burns et al. (1993) proposed that vernalization is mediated by the
demethylation of promoter genes whose expression is critical for the initiation of
ﬂowering. One hypothesis is that exposure to low temperatures decreases
methylation, perhaps by uncoupling replication and maintenance methylation
(Finnegan et al., 1998a). Work done on arabidopsis by Finnegan et al. (1998b)
showed that vernalization for 4 or 8 weeks reduced DNA methylation by 15%
compared with that of the control (unvemalized) seedlings.

5-Azacytidine (5—azaC) demethylates DNA. Treating plants with 5-azaC

can mimic the vernalization response and thus accelerate ﬂowering. With no

12

prior vernalization treatment, germinating arabidopsis seeds (vernalization-
responsive ecotypes) treated with 5-azaC showed earlier ﬂoral initiation and a
reduction in the number of rosette leaves formed at ﬂowering (Burns et al., 1993).
Furthermore, arabidopsis plants transformed with a methyltransferase (ME T1)
antisense transgene also showed a promotion of ﬂowering in the absence of a
cold treatment (Finnegan et al., 1998b).

Current research suggests that demethylation and vernalization may
activate the same pathway. However, it is now known that the methylation
patterns in plants may not reset between generations (Vongs et al., 1993), which
suggests that factors other than DNA methylation may be involved in resetting

the vernalization signal.

Vernalization Pathway

Multiple pathways control ﬂowering time in arabidopsis (Alonso-Blanca et
al., 1998; Koornneef et al., 1998): the photoperiod pathway, the autonomous
pathway, and the vernalization pathway. The vernalization pathway promotes
ﬂowering in many late-ﬂowering ecotypes of arabidopsis in response to an
extended period of cold temperatures (Simpson et al., 1999). Vernalization is
able to overcome or bypass the repressive effects of certain genes (for example,
the FLC and FR! genes). It can also compensate or substitute for the
autonomous pathway genes, which suggests that vernalization may operate
through a separate pathway parallel to the autonomous pathway (Simpson et al.,

1999). However, little else is known about its molecular nature.

13

VERNALIZA TION (VRN) Genes

In order to understand the molecular basis of vernalization, Arabidopsis
thaliana mutants impaired in the vernalization response have been identiﬁed and
analyzed. Plants with mutations in the VRN genes may be defective in either the
perception of cold temperatures or the transduction of the cold signal by the
vernalization pathway (Levy and Dean, 1998). The vm1 and vm2 mutants were
isolated according to their reduced vernalization response in the late-ﬂowering
vemalization-responsive fca-1 arabidopsis mutant (Simpson et al., 1999).
Neither vm1 nor vm2 is impaired in its ability to acclimate to low temperatures
(Chandler et al., 1996, cited in Simpson et al., 1999), which indicates that the
defect in these genes is speciﬁc to the vernalization pathway and not low-
temperature responses in general. Since the VERNALIZA TION genes have not
yet been cloned, their function is unknown. However, fca/vm1 and fca/vm2
double mutants show FLC mRNA accumulation and less reduction in ﬂowering
time, suggesting that the VRN1 and VRN2 genes may mediate the vernalization-
induced down-regulation of the FLC gene (Sheldon et al., 1999; Sheldon et al.,

2000).

FLOWERING LOCUS C (FLC) Gene
FLOWERING LOCUS C encodes a MADS-box type transcription factor
(Michaels and Amasino, 1999; Sheldon et al., 1999; Sheldon et al., 2000). It has

been identiﬁed as a “semidominant repressor of ﬂoral induction” and is believed

14

to be the central regulator of the transition to ﬂowering by vernalization (Sheldon
et al., 2000). However, the downstream target genes for FLC are unknown.

FLC is expressed most highly in the vegetative shoot apex and in roots
(Michaels and Amasino, 1999). FLC mRNA accumulates in mutants of the
autonomous pathway, which suggests that genes in the autonomous pathway
(for example, FCA, FPA, LD, and FVE) act to represses FLC activity (Simpson et
aL,1999)

According to Sheldon et al. (2000), there is a correlation between the level
of FLC transcript and the response to vernalization. Arabidopsis ecotypes with
only a slight vernalization response have low levels of FLC, even in the absence
of vernalization. Ecotypes with minimal to no vernalization response have an
undetectable level of FLC transcript, whereas ecotypes with a strong
vernalization response have a high level of FLC transcript.

Vernalization reduces the level of FLC protein present in the plant
(Michaels and Amasino, 1999; Sheldon et al., 2000). The down-regulation of
FLC and the subsequent decrease in time to ﬂower is proportional to the duration
of the cold treatment (Sheldon et al., 2000). The FLC transcript level following
vernalization is mitotically stable, just as the vernalized state is mitotically stable.
The progeny of vernalized and nonvernalized plants have the same FLC
transcript level, which means that the FLC transcript level, as well as the
vernalization requirement, is reestablished to the ground state in the progeny of a

vernalized plant (Sheldon et al., 2000).

15

FRIGIDA (FRI) Gene

FRIGIDA gene activity is also associated with late ﬂowering. The FRI
gene has been recently cloned and found to encode a protein unrelated to any
known protein (Johanson et al., 2000). FRI acts with FLC to inhibit ﬂowering.
They act through the autonomous pathway, working antagonistically to the
autonomous pathway genes. FRI apparently increases the level of FLC mRNA
(Michaels and Amasino, 1999). Michaels and Amasino (1999) suggested that
vernalization suppression of FLC expression could be mediated through the
effect of the cold treatment on FRI activity. However, Sheldon et al. (1999)
stated that the repression of FLC by the autonomous pathway is mediated by
directly targeting FLC as opposed to operating indirectly through the inactivation

of FRI.

Conclusion

Although the physical aspects of vernalization appear to be well
researched, the molecular and genetic functions of vernalization remain unclear.
Vernalization is a genetically complex physiological process. The FLOWERING
LOCUS C gene appears to play a key role in the induction of ﬂowering by
vernalization. However, it is not yet known whether FLC activity is repressed
simply by a low-temperature treatment, DNA demethylation, VRN1 and VRN2

gene activity, or a combination of these factors.

16

Herbaceous Perennials
Achillea

Achillea or yarrow has long been valued for its medicinal and even
magical purposes. Achillea millefolium L., the common variety, is known by
several names, including nosebleed, staunchweed, milfoil, and soldier’s
woundwort (Grieve, 1981). Achillea has astringent and anti-inﬂammatory
properties. It has been used against colds, cramps, fevers, kidney disorders,
toothaches, skin irritations, hemorrhages, burns, and bruises.

Achilles, a Trojan War hero, distributed yarrow among his soldiers to stop
their wounds from bleeding (Stevens et al., 1993), which is how the plant
received its genus name, Achillea. For the Navajos, it is a general cure-all, and
the British call it allheal (Stevens et al., 1993). It was also consumed by the
pioneers in an attempt to cure just about any ailment.

There are between 85 and 100 species of achillea, and they differ in
growth habit, ﬂower color, and leaf shape (Stevens et al., 1993; Turner and
Wasson, 1997). Most species are native to Europe and north and west Asia. A
handful (four or ﬁve species) can be found in North America (Turner and
Wasson, 1997). There have also been numerous cultivars produced through
breeding and selection.

Achillea is a member of Asteraceae. It varies in size from creeping alpine
varieties to tall varieties used in border gardens and as cut ﬂowers. The foliage
is fernlike, aromatic (spicy fragrance), sometimes gray, and often hairy. It prefers

full sun and high light. The gray foliage is indicative of high-light—adapted plants.

17

It is a hardy perennial that typically has large, ﬂat heads of tiny daisylike ﬂowers.
There is a wide variety of ﬂower colors, including shades of white, yellow,
orange, pink, and red. Flowering generally occurs from late spring to autumn.

Achillea is a dry-land plant and is not typically tolerant of wet conditions. It
does best in soil that is kept moderately moist. According to Stevens et al.
(1993), overhead watering of achillea is not recommended because it may
damage the ﬂowers, cause spotting on the petals, splash soil onto the foliage,
and promote the spread of disease. Constantly moist soil and excess nitrogen
can result in tall leggy plants. To reduce plant height in greenhouse production,
achillea should be grown with reduced nitrogen (approximately 100 ppm) and
water (Nausieda et al., 2000). Achillea is also tolerant of poor soil. Once it is
established, it can survive drought and other forms of neglect.

Most achillea species are facultative long-day plants, which means that
the plants will ﬂower under all photoperiods. However, they tend to ﬂower more
rapidly and consistently under long days, generally longer than 12 h (Nausieda et
al., 2000).

Achillea multiplies rapidly by rhizomes. It is easily propagated by division
in late winter. Plant clumps are usually pruned during the winter to stimulate
strong spring growth. Another form of propagation is by cuttings, which generally
occurs in early summer. The most popular species are usually clones and thus
must be propagated asexually (Nausieda et al., 2000). Rooting stem cuttings is

the common method for plug production.

18

Good cultural practices are the best insect control. A healthy, actively
growing yarrow plant is more resilient against insect attack. Although no insect
has been found to be extremely detrimental to achillea, in greenhouse
production, the most common insects encountered include aphids, leafhoppers,
spider mites, and thrips (Stevens et al., 1993).

Most disease problems arise from overwatering and when plants are
under high temperature and humidity. Foliar fungal diseases are the most
serious ones associated with achillea. Botrytis is common among cultivars
derived from ‘Taygetea’ because they have more leaves at the base of the plant
(Nausieda et al., 2000). Other foliar diseases include powdery mildew, downy
mildew, and rust. Powdery mildew is distinguished by white spots on both sides
of the leaves. Downy mildew is distinguished by yellow spots on the top of the
leaves and white mold on the bottom. A mildew problem can be reduced by
increasing space between plants, which improves air circulation around the
foliage. Rust is characterized by raised spots called pustules, which are found
on the underside of leaves and stems. Rust-infected plants should be removed
and destroyed. Another disease that affects achillea is stem rot, which is caused
by Rhizoctonia solani. It results in the decay of the stem base. This soil-borne
pathogen is controlled by allowing the soil to thoroughly dry between irrigations.

One popular achillea species is A. ‘Moonshine’, the result of a cross
between A. clypeolata and A. aegyptiaca ‘Taygetea’ (Annitage, 1989). The plant

grows to a height of approximately 18 to 24 inches. The ﬂowers are sulfur

19

yellow. The foliage is silvery-green and femlike. It was introduced in the 19505

by Alan Bloom of Bressingham Gardens in England (Armitage, 1989).

Campanula

Campanula is distributed throughout temperate zones of the Northern
Hemisphere, particularly in southern Europe and Turkey. They grow in diverse
habitats, including high alpine rock crevices, meadows, and woodlands. More
than 600 species of annuals, biennials, and perennials make up Campanulaceae
(Finical et al., 2000b).

All campanula species are long-day plants, some being facultative and
others obligate. Some species require a vernalization treatment in order to
ﬂower; others simply require a speciﬁc photoperiod. They prefer full sun, and in
some species, ﬂower number can be decreased if the plants are grown under low
light (Whitman et al., 2000).

Pollination mechanisms vary widely among campanula species. Some
species are predominantly self-pollinated, while others are cross-pollinated.
According to Nyman (1992), pollen germinability plays a large role in the
mechanism used by each species. For example, temporal overlap of high pollen
germinability and stigma receptivity is associated with self-pollinating species,
while temporal separation of high pollen germinability and stigma receptivity is
associated with cross—pollinating species.

For most campanula species, the soil pH should be maintained around 6.0

and soil fertility should be kept at moderate levels (Finical et al., 2000b; Whitman

20

et al., 2000). Campanula prefers well-drained soil. Most species are drought
tolerant, and in some cases, drought stress can delay ﬂowering.

Campanulas are easily grown from seed. Seed may be sown in late
winter or early spring. It should be sown thinly on the surface and covered with a
very ﬁne layer of sharp sand or ﬁne grit (Lewis and Lynch, 1998). Light is
beneﬁcial for germination. Established campanula plants can be divided in the
fall or spring when new growth has just started. Campanula can also be
propagated by cuttings. In the greenhouse industry, plants are propagated
primarily from stem cuttings.

Campanulas are generally trouble-free in cultivation. In the garden, the
primary pest of campanula is the slug, but it is only troublesome with some of the
more rare, succulent, smaller species. In greenhouse production, spider mite
can be a problem with certain species (Whitman et al., 2000).

Rust is probably the most troublesome disease in campanula, but again, it
is species speciﬁc. However, damping-off root rot caused by Pythium and
Rhizoctonia can sometimes be problematic. Damping-off can be prevented by
maintaining well-drained soil. Botrytis cinerea on leaves can also be problematic
in some species (Whitman et al., 2000). However, if the foliage is kept dry, the
disease should not be a problem.

One particularly interesting species is Campanula ‘Birch Hybrid’. It was
introduced by Walter lngwersen and is the result of a cross between C.
portenschlagiana and C. poscharskyana. ‘Birch Hybrid” was initially introduced

as C. xportenscharskyana. In 1945, it was given an Award of Merit along with a

21

recommendation that its name be changed. The name ‘Birch Hybrid’ came from
the nursery where it was ﬁrst propagated, Birch Farm (Lewis and Lynch, 1998).

Campanula ‘Birch Hybrid’ is a miniature campanula that grows up to 6
inches (15 cm) high and spreads up to 12 inches (30 cm) (Finical et al., 2000b).
The branching stems bear numerous open star-shaped blooms of light blue or
mauve. New ﬂowers continue to open from June through September. It is an
evergreen perennial with underground runners and small, ovate, heart-shaped,
toothed, bright green leaves. It is a rock-gardenlalpine species that requires
moist but well-drained soil in sun or partial shade (Brickell and Zuk, 1997). ‘Birch
Hybrid’ requires a vernalization treatment in order to ﬂower (Finical et al., 2000b).
Without a cold treatment, plants remain vegetative. It is a facultative long-day
plant following vernalization and is also fairly free of disease and insect

problems.

Gaillardia

According to Koning (1986),. gaillardia was ﬁrst noted in 1783. Within
Gaillardia, there are approximately 30 species ranging from annuals to biennials
and perennials, and all are members of Asteraceae. All species are native to
primarily the southwestern United States, with the exception of two South
American species. The common name blanket ﬂower arose because the colors
in the ﬂowers resembled the blankets traditionally worn by Native Americans.

Gaillardia has been used in pharmaceutical research (Koning, 1986). The

plant produces the sesquiterpene lactones: spathulins, pulchellins, and

22

gaillardins. Spathulins and pulchellins are antibiotics used for Staphylococcus
and Streptococcus. Spathulin and gaillardin, in cell cultures, inhibit human
nasopharynx carcinomas.

The plant’s ﬂowers have a long blooming season, from summer until the
ﬁrst frost. The ﬂowers are daisylike, either single or double, and can be as much
as 6 inches wide. Flower colors range from bright yellow to oranges and reds.

Gaillardia tolerates extreme heat, cold, dryness, strong winds, and poor
soil. The plants prefer full sun and well-drained, moderately fertile soil. It is
considered a quantitative long-day plant (Koning, 1986). Under short days the
plant forms a rosette.

The annual varieties are usually propagated from seed in spring or early
summer. Seed propagation is used widely for commercial production. Seeds
germinate in the light at 21 to 24 °C and under high humidity (90 to 95%) (Yuan
et al., 2000). The perennial species can also be divided in the spring or
propagated from stem cuttings. Division is used most commonly by gardeners to
control plant size and form.

Gaillardia, as a whole, is not particularly susceptible to many diseases or
insect pests. In fact, gaillardia plants can inhibit population expansion of
Protylenchus penetrans and Ditylenchus dipsaci nematodes in garden soil
(Koning, 1986). In the greenhouse, Gaillardia xgrandiﬂora Van Houtte is
susceptible to aphids (Yuan et al., 2000). Also, plants in the greenhouse are

more susceptible to aster yellows and powdery mildew.

23

Gaillardia xgrandiﬂora is a hybrid of G. an‘stata and G. pulchella and is the
most commonly grown blanket ﬂower (Turner and Wasson, 1997). The plants
form mounds up to three feet high.

Some cultivars of G. xgrandiﬂora have a distinct juvenile phase. Most of
the plant population reaches maturity when 16 nodes per plants have formed
(Yuan et al., 2000; Yuan et al., 1998a). According to research conducted by
Yuan et al. (19983), periods of cold exposure (10 to 15 weeks) enhanced the
ﬂowering percentage and greatly accelerated ﬂowering of G. xgrandiﬂora
‘Goblin’. In production, increasing the temperature from 15 to 26 °C reduced the
number of days to ﬂower by approximately 25 d for the same cultivar (Yuan et al.,
1998b). Gaillardia requires long days after cold in order to ﬂower. Evans and
Lyons (1988) showed that applications of GA4+7 could substitute for long days
and promote ﬂowering under short days in the same amount of time required by
untreated, photoperiodically induced plants.

Koning has done much work on ﬂower formation and development in G.
xgrandiﬂora. He described ﬁve distinct stages of disk ﬂower development
(Koning, 1983a, 1983b, 1984). During stage 1, ﬂowers are relatively
unpigmented and tightly closed. In stage 2, the tip of the corolla is pigmented. In
stage 3, the corolla begins to unroll and the ﬁlaments elongate. During stage 4,
the corolla unrolls completely and the style and stigma elongate. And in stage 5,
the corolla expands completely, the stigmatic surface between the branches is
exposed, and the ﬂower is pollinated. Filament elongation is controlled by auxin

(Koning, 1983a). Corolla elongation is controlled by the level of endogenous

24

gibberellin activity (Koning, 1984). Style and stigma development is controlled by
at least three hormones. Their growth is inhibited by high levels of gibberellins
during stages 1 through 3. During stages 3 and 4, high auxin triggers elongation.
Finally, at the end of stage 5, ethylene production increases and promotes

stigma unfolding (Koning, 1983b).

Gaura

The genus name Gaura translates as gorgeous (Turner and Wasson,
1997). Gaura has about 20 species of annuals, biennials, perennials, and
subshrubs. All species, which belong to Onagraceae, are native to North
America (primarily Texas and Mexico). Despite their showy ﬂowers, they are apt
to be weedy. They have simple, narrow leaves. The ﬂowers are ﬂat, star-
shaped, and pink or white and are borne on either panicles or racemes (Brickell
and Zuk, 1997).

In its native range (Texas to Louisiana) and other warm areas, gaura can
grow to four feet tall and wide. In Seattle, Washington, and Vancouver, British
Columbia, it tends to be shorter and more compact, reaching a height and width
of only about 2 feet (Farmer, 1993). Different species of gaura are broadly
interfertile, but different species in nature are isolated by a number of
mechanisms that minimize the occurrence of natural hybrids (Carr et al., 1990).

Gaura prefers full sun. It does not require excessive fertilizer or water

because many species have long ﬂeshy roots that store water. Because of this,

25

gaura is well adapted to dry areas and tolerates extended periods of drought and
heat stress.

Gaura can be propagated by using several techniques. It can be
propagated in spring or fall by division, which is used primarily to rejuvenate the
plant and control overall plant size. Gaura can also be propagated by seed,
which generally germinate in ﬁve to 11 days at 21 °C (Finical et al., 2000a).
Vegetative stem cuttings can also be propagated, and this method generally is
used in the summer. Commercially, all three means of propagation are used.

The gaura commonly sold commercially is G. Iindheimeri. It is native to
the United States/Mexico border region (Turner and Wasson, 1997). It has
loosely branched stems with tiny hairs. Flowering lasts from late spring to midfall
(Farmer, 1993). It produces long sprays of pink buds that open into white
ﬂowers, reaches a height of 4 feet, and has a spread of 3 feet (Turner and
Wasson, 1997).

In G. Iindheimeri, juvenility does not appear to affect ﬂowering.
Vegetatively propagated plants with as few as six leaves will ﬂower (F inical et al.,
2000a). It also does not require a vernalization treatment in order to successfully
ﬂower. It is considered a facultative long-day plant, ﬂowering faster under longer
daylengths. Gaura Iindheimeri also grows in a wide variety of soil types, ranging
from dry clay to sand. It appears to have no problematic diseases or insect
pests. However, from greenhouse observations, spider mites could be a

problem.

26

Research performed by Carr et al. (1990) divided gaura into eight species
according to trends in ﬂoral symmetry, fruit morphology, and plant growth habits.
It was concluded from this work that the placement of G. Iindheimeri within the
section Gaura “depends heavily on the assumptions that perennial life-cycle and

loosely clumped growth habit are secondarily derived in this distinctive species.”

Leucanthemum

Leucanthemum, part of Asteraceae, is composed of about 25 species of
annuals and perennials (Turner and Wasson, 1997). All species are native to
Europe and temperature Asia. Many botanists included these plants in
Chrysanthemum (Turner and Wasson, 1997). Leucanthemum is a clump-
forming plant with variable leaves ranging from toothed to lobed.

The most common garden leucanthemum is L. xsuperbum Bergmans ex
J. Ingram, which is better known as the shasta daisy. Leucanthemum xsuperbum
translates as superior (or superb) white ﬂower (Coombes, 1994). It has also
been classiﬁed as Chrysanthemum maximum Ramond and Chrysanthemum
xsuperbum (Turner and Wasson, 1997).

Shasta daisies were once thought to be L. maximum, a native of the
Pyrenees, but now they are believed to be the result of a cross between
maximum and L. lacustre Brot. from Portugal. Luther Burbank, a plant breeder,
ﬁrst noticed them naturalized on the slopes of Mount Shasta in Washington

(Turner and Wasson, 1997).

27

Most cultivars reach a height and spread of 2 to 3 feet. Flowers can be up
to 3 inches across and range from doubles and singles to fringed petals (Turner
and Wasson, 1997). Most plants produce flowers from summer through early
fall. Leucanthemum xsuperbum requires full sun to partial shade. They prefer
moderate to high light levels (Runkle et al., 2000a). Plants also prefer moist,
rich, well-drained soil.

Some shasta daisies are extremely sensitive to many insecticides, which
cause moderate to severe phytotoxicity, including leaf and ﬂower burn, chlorosis,
and widespread plant death (Runkle et al., 2000a). Common methods of
propagation include tip cuttings, tissue culture, and bare-root divisions.

Kessler and Keever (2000) determined that shasta daisy cultivars show a
varied response to photoperiod and vernalization time. The cultivar Becky is an
obligate longday plant regardless of vernalization. On the other hand, the
cultivars Snowcap and Snow Lady show a facultative long-day response. In all
three cultivars tested, shoot height, ﬂower shoot number, and market quality
increased, while time to ﬂower decreased with increasing vernalization up to 6
weeks under long days.

The most desirable and attractive short cultivar of L. xsuperbum is most
likely ‘Snowcap’. It was introduced by Adrian Bloom of Blooms of Bressingham,
United Kingdom (Runkle et al., 2000a).

Because of its thick ﬂeshy leaves, it requires relatively frequent irrigation,

especially under high light levels. Plants recover well from short periods of

28

drought stress, but prolonged drought stress can cause leaf margins to become
necrotic (Runkle et al., 2000a).

‘Snowcap’ has a unique ﬂowering habit in response to a cold treatment
(vernalization). Without a cold treatment, it is a qualitative long-day plant,
ﬂowering only under photoperiods longer than or equal to 16 h. With a cold
treatment, it is a quantitative long-day plant, ﬂowering faster under photoperiods
longer than or equal to 16 h (Runkle et al., 1998a). Flowering characteristics
such as increased ﬂowering percentage, improved crop uniformity, reduced time
to ﬂower, and increased ﬂower number are also enhanced by exposure to cold
temperatures.

‘Snowcap', as well as most shasta daisies, is relatively disease and insect-
pest free. In young transplants, Pythium can be a problem if plants are
overwatered (Runkle et al., 2000a). In greenhouse production, whiteﬂies, aphids,

and thrips can be problematic as well.

Phlox

When translated, the word phlox means ﬂame (Turner and Wasson,
1997). Phlox, which is a member of Polemoniaceae, contains 61 species from
North America and Siberia (Grant, 1959). Plants range from evergreen to
semievergreen annuals and perennials. Most phlox are grown for their profuse,
fragrant ﬂowers. Fossil fruits of a phlox probably close to P. sibirica L. or P.
borealis Wherry have been found in a Pleistocene deposit from Fairbanks,

Alaska (Grant, 1959).

29

Tall perennial phloxes grow easily in any temperate climate but can
require a lot of water. Annual species will grow in almost any climate, ranging
from the tropics to the coldest region. Phlox prefers sunny or partly sunny
growing areas. It thrives in moist but well-drained soil in full sun or, in drier soils,
light shade. Phlox has few disease and insect pests. The most common include
spider mites and powdery mildew.

Phlox paniculata Lyon ex Pursh, or tall garden phlox, is a commonly
grown herbaceous perennial native to the eastern United States. The terminal
ﬂower heads are produced on long stems and are composed of many small ﬁve-
lobed ﬂowers, and plants can reach a height of more than 3 feet (Turner and
Wasson, 1997). Flower color ranges from various shades of violet and red to
salmon and white. Phlox paniculata produces long-stemmed cut ﬂowers in mid
to late summer when grown under ﬁeld conditions, but demand and prices for
these stems is best during winter and spring (Garner and Armitage, 2000).

The base photoperiod for P. paniculata is approximately 13 h for uncooled
plants and less than 10 h for cooled plants (Runkle et al., 1998b). Vernalization
is not required for ﬂowering; however, cooled plants have shown increased stem
length and accelerated flowering (Garner and Armitage, 2000). Providing plants
with a cold treatment and photoperiods of less than 10 h should produce stock
plants for vigorous vegetative cuttings (Runkle et al., 1998b).

Phlox paniculata can be propagated several ways: crown division, tissue
culture, and terminal and root cuttings. Terminal cuttings from vegetative shoots

can be easily rooted in about 3 weeks (Garner and Armitage, 2000). According

3O

to Schnabelrauch and Sink (1979), clonal multiplication of P. paniculata by
conventional methods of crown division of dormant stock plants and root cuttings
has led to disease and nematode infestations during ﬁeld culture that can be

traced back to the stock material used for propagation.

Veronica

Legend tells that Saint Veronica was the woman who wiped the face of
Christ with her veil. She was rewarded with having his image imprinted on it.
Her connection to this ﬂower is that the savants of the Middle Ages thought the
markings on the ﬂowers of some species resembled the markings on the veil
(Armitage, 1989; Turner and Wasson, 1997).

Veronica’s common name is Speedwell and it is a member of
Scrophulariaceae, or the snapdragon family. Within veronica, there are between
200 and 250 species of herbaceous annuals and perennials (Runkle et al.,
2000b; Turner and Wasson, 1997). They range from creeping plants suitable for
rock gardens to 6-foot-tall giants. One species, V. ofﬂcinalis L., was substituted
for tea in Europe until the 19th century (Armitage, 1989).

Veronica ﬂowers are small. The largest ﬂower is about 1/2 inch wide
(Turner and Wasson, 1997). Blue is the predominant ﬂower color. However,
white and pink ﬂowers are also common.

Veronica are fully to moderately frost hardy. They are easy to grow in any
temperate climate. They tolerate any soil condition and will grow in full sun as

well as full shade. Veronica can be propagated many ways, including from seed

31

in the fall or spring, from cuttings in the summer, and by division in early spring or
early fall.

Veronica Iongifolia L., or long-leaf Speedwell, is native to northern and
central Europe and Asia (Turner and Wasson, 1997). It has been naturalized in
North America (Runkle et al., 2000b). It generally grows to a height of 3 feet.
The leaves are narrow and taper, are arranged in whorls, and are toothed on the
edges. The ﬂowers are ‘A inch wide and closely packed on 12-inch-long
racemes (Armitage, 1989). The inﬂorescences are generally lilac blue.

Veronica Iongifolia is a day-neutral plant following vernalization (Runkle et
al., 2000b). Plants will ﬂower regardless of photoperiod. It prefers rich soil and
warm climates. Some cultivars have thick leaves and require frequent irrigation
to prevent wilting. Powdery mildew has been known to cause trouble, and
Botrytis can be problematic on lower leaves.

The most common method of propagation is by tip cutting. Unchilled
stock plants produce cuttings with an obligate cold requirement (Runkle et al.,
2000b). Some rooted cuttings may ﬂower without a cold treatment if they were

taken from cold-treated stock plants.

32

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38

SECTION II

THE FLOWERING RESPONSE OF VERONICA SPICA TA ‘RED FOX’ TO COLD
AND BULKING TREATMENTS

39

The Flowering Response of Veronica spicata ‘Red Fox’ to Cold and Bulking
Treatments

Amy L. Enﬁeld‘, Royal D. Heins”, Arthur c. Cameronz, and William H. CarIson2

Department of Horticulture, Michigan State University, East Lansing, MI 48824

Additional index words: vernalization, pinching

Received for publication . We appreciate the greenhouse

growers providing support for Michigan State University ﬂoriculture research.
Graduate Student. Current address: Dept. of Horticulture, Clemson University,

Clemson, SC 29634.

2Professor.

3To whom reprint requests should be addressed (E-mail: heins@msu.edu).

4O

Abstract

Veronica spicata L. ‘Red Fox’ plants were treated at 5 °C for 0 through 5
weeks and subsequently forced to ﬂower under a 16-h photoperiod to determine
minimum cold requirements for ﬂowering. Plants had an obligate cold
requirement for ﬂowering. As cold duration increased through 5 weeks, ﬂowering
percentage increased from 0% to 100%. In a separate experiment, V. spicata
‘Red Fox’ plants were pinched and grown (bulked) in 13-cm pots or 4.4- or 4.1-
cm plugs for 0 through 3 weeks. Plants were then cold treated for 5 weeks at 5
°C and subsequently forced to ﬂower under a 16-h photoperiod to determine the
effects of pinching, bulking duration, and bulking container size on the number of
ﬂowering shoots per plant. Flowering percentage was greatest for unpinched
plants, irrespective of bulking container size. As bulking container size
increased, the number of ﬂowering shoots per plant increased. Unpinched plants
ﬂowered sooner than pinched plants. Time to ﬂower decreased as bulking
duration increased. Unpinched plants bulked in a 13-cm pot had more ﬂowering
shoots per plant than pinched plants bulked in a 13-cm pot. In contrast, for both

plug sizes, pinched plants had more ﬂowering shoots than unpinched plants.

41

Introduction

Understanding the ﬂowering physiology of herbaceous perennials is
important for producing a uniform ﬂowering crop. Since a ﬂowering plant is more
marketable than a vegetative plant, predictable ﬂowering of herbaceous
perennials is becoming a priority for many greenhouse growers. Minimizing
production time is also important for proﬁtability. Therefore, identifying deSIrable
herbaceous perennials for container production and understanding their ﬂowering
physiology is critical for the success of and implementation of proﬁtable
production on speciﬁc market dates. Speedwell (Veronica sp.) is one such
herbaceous perennial. Veronica is available in a variety of colors, pink, white,
and blue, and can be grown from seed or vegetatively propagated material (Nau,
1998). Veronica spicata L. ‘Red Fox’ is one particular cultivar of interest. It is
grown from vegetatively propagated material and produces spikes of rose-pink
ﬂowers. It has a compact growth habit that makes it ideal for container
production.

For V. spicata L. ‘Blue’ (Engle, 1994; Runkle 1996) and V. Iongifolia L.
‘lcicle’ (Frane, unpublished data), ﬂowering percentage increases and days to
ﬂower decreases with cold treatment. Veronica Iongifolia ‘Sunny Border Blue’
(Runkle, 1996) and V. spicata ‘Red Fox’ (Frane, unpublished data), on the other
hand, have an obligate cold requirement. Without cold, plants will not ﬂower.
However, only 0 and 15 weeks at 5 °C have been tested for V. spicata ‘Red Fox’.
Following a cold treatment, all Veronica cultivars tested have been reported as

day-neutral plants, ﬂowering regardless of photoperiod.

42

When forced to ﬂower in containers, V. spicata cultivars tend to produce a
single ﬂowering shoot, whereas V. Iongifolia cultivars tend to produce multiple
ﬂowering shoots. Many ﬂoriculture crops such as cut ﬂowers, poinsettia
(Euphorbia pulchem’ma), and other herbaceous perennials are pinched to
increase ﬂower number. In 2002 preliminary research (Enﬁeld, unpublished
data), V. spicata ‘Red Fox’ plants that were pinched immediately before cold
treatment ﬂowered, but with only one to two ﬂowering shoots per plant. Plants
that were pinched immediately after a 5-week cold treatment failed to ﬂower.
Apparently, shoot tips that were induced to ﬂower by the cold treatment were
removed when the plants were pinched following cold treatment. Thus, this data
suggest that in order to increase the number of ﬂowering shoots per plant,
pinching needs to occur before cold treatment, and a period of growth (bulking) is
needed after pinching and before cold treatment to allow lateral shoots to
develop sufﬁciently to perceive cold. A period of growth before ﬂower induction
is also needed for poinsettia so that lateral branches are the appropriate size for
the ﬁnish pot (Ecke et al., 1990).

Perception of low temperatures occurs mainly in the meristematic zones of
the shoot apex. However, Levy and Dean (1998) propose that all actively
dividing cells may be capable of responding to low temperatures. Vernalization,
or the promotion of ﬂowering by a cold treatment, has been achieved by applying
localized cooling temperatures to the stem apex of plants, and the effect seems

to be largely independent of temperatures experienced by the rest of the plant

43

(Thomas and Vince-Prue, 1997). This suggests that the apex must be present to
perceive cold.

The ﬁrst objective of this research was to identify the minimum cold
duration required for rapid and uniform ﬂowering of V. spicata ‘Red Fox’. The
second objective was to determine the effects of bulking container size, pinching,
and subsequent bulking duration following pinch on the number of ﬂowering

shoots of cold-treated V. spicata ‘Red Fox’ plants.

Materials and Methods

Cold-duration experiment. Veronica spicata ‘Red Fox’ stock plants were
received from Center Greenhouse (Denver, Colo.; Sept. 1999) and potted in 13-
cm square plastic containers (1.1 L) ﬁlled with a commercial soilless medium
composed of pine bark, ﬁbrous Canadian sphagnum peat, horticultural
vermiculite, and screened course perlite, along with a wetting agent and starter
fertilizer charge (Suremix Perlite; Michigan Grower Products, Galesburg, Mich.)
Plants were grown under a 12-h photoperiod provided by supplementing natural
daylengths with lighting from high-pressure sodium lamps from 0800 to 2000 HR.
Stock plants were pinched at three- to four-week intervals to ensure continued
branching and cutting production. Harvested cuttings were propagated in 72-cell
(0.03-L) plug trays (Landmark Plastic Corporation, Akron, Ohio).

After propagation, plants were grown (bulked) in the plug trays for an
additional 3 weeks in a greenhouse at 20 °C to establish root systems and

increase vegetative growth before cold treatment. Photoperiod was maintained

44

at 12 h as with the stock plants. Plugs then received no cold treatment or were
placed in a controlled-environment chamber for 1, 2, 3, 4, or 5 weeks at 5 °C.

Bulking experiment. Veronica spicata ‘Red Fox’ stock plants were potted
(Oct. 2001) in 13-cm square plastic containers (1.1 L) ﬁlled with a commercial
soilless medium composed of pine bark, ﬁbrous Canadian sphagnum peat,
horticultural vermiculite, and screened course perlite, along with a wetting agent
and starter fertilizer charge (Suremix Perlite; Michigan Grower Products,
Galesburg, Mich).

The experiment was replicated in time. On Nov. 28, 2002, and again on
Jan. 8, 2002, harvested cuttings were propagated in 72-cell (0.04-L) and 50-cell
(0.08-L) plug trays (Landmark Plastic Corporation, Akron, Ohio). Immediately
following propagation, half of the 50-cell and half of the 72-cell plugs were
transplanted to 13-cm square plastic containers (1.1 L). All plants were
maintained at 20 °C under a 16-h photoperiod, natural daylengths supplemented
with high-pressure sodium lamps from 0530 to 2130 HR. Plants were grown
(bulked) for 2 weeks, and then half of the 50-cell plugs, 72-cell plugs, and 13-cm
plants were pinched (two apical nodes removed). All plants were then bulked an
additional 0, 1, 2, or 3 weeks. After the appropriate bulking duration, plants were
cold treated for 5 weeks at 5 °C.

Propagation. Plug trays contained a mixture of 50% commercial medium
(Suremix Perlite; Michigan Grower Products, Galesburg, Mich.) and 50%
screened course perlite (Therm-O-Rock, East, Inc.; New Eagle, Pa.). Basal

portions of each cutting were dipped in a 1500-ppm solution of liquid auxin (DIP

45

’N GROW; Astoria-Paciﬁc, Clackamas, Ore.) before stick. Cuttings were
propagated under natural photoperiods. Propagation air temperatures were
maintained at 23 °C and bottom heat (soil temperature) was maintained at 25 °C.
A vapor pressure deﬁcit of 0.3 kPa was maintained by injecting water vapor as
needed. Cuttings were rooted and weaned from propagation 3 weeks after
sticking.

Cold treatments. Plants were maintained at 5 “C in a cooler lighted from
0800 to 1700 HR by cool-white ﬂuorescent lamps (F96T12/CWNHO, Philips,
Somerset, N.J.) The photosynthetic photon ﬂux (PPF) from the lamps was
approximately 10 pmol'm‘z's'1 at plant height. While in the cooler, plants were
watered as needed with well water acidiﬁed with sulfuric acid to 3 titratable
alkalinity of approximately 130 'mg calcium bicarbonate per liter.

General plant culture; Following all cold treatments, plugs were potted in
13-cm square plastic containers (1.1 L) containing the same commercial medium
used for the stock plants. All plants were forced to ﬂower under a 16-h
photoperiod, natural days supplemented with high-pressure sodium lamps from
0530 to 2130 HR. Plants were top-watered as necessary with well water acidiﬁed
with sulfuric acid to a titratable alkalinity of approximately 130 mg calcium
bicarbonate per liter and containing water-soluble fertilizer providing 125 N, 12 P,
125 K, 13 Ca (mg-L"; 30% ammoniacal N) plus (mg-L") 1.0 Fe, 0.5 Mn, 0.5 Zn,
0.5 Cu, 0.1 B, 0.1 Mo (MSU Special; Greencare Fertilizers, Chicago, Ill.).
Veronica spicata ‘Red Fox’ plants in the bulking duration experiment received an

additional 0.5 ppm Cu and 0.1 ppm B at every watering.

46

Greenhouse temperature control. Plants were grown in glass
greenhouses set at 20 °C. Greenhouse temperatures were controlled by a
greenhouse climate-control computer (Model CD750; Priva, De Lier, The
Netherlands). Average daily temperature and daily light integral were monitored
with a CR-10 datalogger (Campbell Scientiﬁc, Logan, Utah) by using 36-gauge
(0.013 mm in diameter) type E thermocouples and a quantum sensor (Model LI-
189; Ll-COR, lnc., Lincoln, Neb.), respectively. The datalogger collected data
every 10 seconds and recorded the hourly average. Actual average daily
temperatures and daily light integrals (cold duration experiment only) for the
beginning of forcing to the average date of ﬂowering were calculated and are
presented in Table 1.

Data collection and analysis. Dates of visible bud and ﬁrst ﬂower as well
as the number of ﬂowering shoots and lateral inﬂorescences per ﬂowering shoot
were recorded. For the cold duration experiment, plant height and number of
nodes formed below the ﬂower shoot were also recorded. A completely
randomized design with 10 observations for each treatment was used for the cold
duration experiment. A randomized complete block design was used for the
bulking duration experiment. Data were analyzed with SAS’s (SAS Institute,
Cary, NC.) analysis of variance (ANOVA), generalized linear model (GENMOD),

and general linear model (GLM) procedures.

Results
Cold-duration experiment. Veronica spicata ‘Red Fox’ had an obligate

vernalization requirement for ﬂowering. All plants remained vegetative until they

47

received at least a 3-week cold treatment (Table 2). Percentage of ﬂowering
plants increased to one-hundred percent as cold duration increased from 3 to 5
weeks at 5 °C. There was no statistical improvement in ﬂowering characteristics
(decrease in time to ﬂower, plant height, and number of ﬂowering shoots) of
ﬂowering V. spicata ‘Red Fox’ plants with increasing cold duration, although the
single plant that ﬂowered following a 3-week cold treatment took about 1 week
longer to ﬂower than plants cooled for longer periods.

Bulking experiment. Bulking container size did not signiﬁcantly affect days
to visible bud, days from visible bud to ﬂower, or days to ﬂower (data not shown).
Therefore, bulking containers were pooled for statistical analysis of time to
ﬂower.

Pinching and bulking duration signiﬁcantly affected days to visible bud and
days to ﬂower (Figure 1, Table 3), but the two-way interaction was not signiﬁcant.
Both days to visible bud and days to ﬂower decreased linearly as bulking
duration increased. The slopes of the lines for pinched versus unpinched plants
were not signiﬁcantly different, but the intercepts of the two lines were.
Unpinched plants reached visible bud and ﬂowered sooner than pinched plants.

Days from visible bud to ﬂower were signiﬁcantly affected by pinching,
bulking duration, and their interaction (Figure 1). Days from visible bud to ﬂower
had signiﬁcant linear and quadratic trends. Both the slopes and intercepts of the
lines for pinched versus unpinched plants were signiﬁcantly different. However,
although the data were statistically signiﬁcant, the difference in the number of

days from visible bud to ﬂower between pinching treatments and across bulking

48

duration averaged one day or less and horticulturally would not be considered
signiﬁcant.

The percentage of ﬂowering plants, irrespective of bulking container size
and bulking duration, was higher when plants were not pinched (Figure 2A and
B). Pinched plants, irrespective of bulking container size, did not obtain ﬂowering
percentages comparable to that of unpinched plants until they had been bulked
for 3 weeks. Flowering probability (a measure of the likelihood that a plant will
ﬂower under given treatment conditions) was strongly affected by bulking
container size, pinching, and bulking duration (Table 3). The larger the bulking
container, the higher the ﬂowering probability. The probability of plants ﬂowering
also increased as bulking duration increased. Plants that were pinched and
bulked for 3 weeks had the same likelih00d of ﬂowering as unpinched plants that
were not bulked.

The number of ﬂowering shoots per plant was signiﬁcantly affected by
bulking container size, pinching, and bulking duration, and all two-way
interactions were also signiﬁcant (Table 3, Figure 2). As bulking duration
increased, regardless of pinching, the number of ﬂowering shoots per plant
increased (Figure 2C and D) although differences among treatments were large.
For unpinched plants bulked in a 13-cm pot, the number of ﬂowering shoots
increased from about one to more than ﬁve as bulking duration increased (Figure
2C). Unpinched plants bulked in a 13-cm pot had more ﬂowering shoots than
pinched plants. In contrast, for both plug sizes, pinched plants had more

ﬂowering shoots than unpinched plants.

49

Bulking container size, pinching, bulking duration, and the two-way
interaction of bulking container size and pinching signiﬁcantly affected the
number of lateral inﬂorescences per ﬂowering shoot (Table 3). As the number of
ﬂowering shoots per plant increased, the number of lateral inﬂorescences per
ﬂowering shoot decreased (Figure 3). Plants appeared to compensate for the

lack of ﬂowering shoots by producing more lateral inﬂorescences.

Discussion

Veronica spicata ‘Red Fox’ has an obligate cold requirement for ﬂowering
(Table 2). Veronica spicata ‘Blue’, on the other hand, did not have an obligate
cold requirement; plants ﬂowered poorly without cold, but ﬂowering percentage
increased from 43 to 100 following 5 weeks at 5 °C (Engle, 1994). These results
may be misleading because plants were obtained from commercial growers and
may have accumulated some cold before initiation of the experiment (personal
communication, Royal Heins). In V. spicata ‘Red Fox’, only shoots that were
visible before cold treatment ﬂowered, which supports Metzger’s (1988) research
with Thlaspi arvense L. that found that vernalization was perceived by shoot tips
and not just the stem apex, as stated by Thomas and Vince-Prue (1997).

Removal of the shoot apex by decapitation or pinching out the growing tip
removes the source of apical dominance and induces growth of lateral buds
(Cline, 1991). Plants are pinched to increase lateral branching and ultimately
ﬂower number. The timing of pinch before ﬂower induction is important in several

potted crops, including poinsettia and Chrysanthemum. Ecke et al. (1990) state

50

that the shoot tip of poinsettia should be removed early enough to provide
sufﬁcient growing time to produce the length of stem required for the pot size.
Timing of pinch for Chrysanthemums is in accordance with their natural ﬂowering
height. Short varieties are induced to ﬂower 1 to 2 weeks after pinch; medium
varieties, the day of pinch; and tall varieties, 1 to 2 weeks before pinch (Williams
and Bearce, 1964). In this experiment, unpinched V. spicata ‘Red Fox’ plants in
13-cm pots produced more ﬂowering shoots than pinched plants in 13-cm pots.
For Kalanchoe tomentosa, pinched plants produced more lateral branches, while
unpinched plants of Columnea microphylla produced more branches than
pinched plants (Lyons and Hale, 1987).

Chrysathemum morifolium Ramat. has no ﬂower induction-Insensitive
phase following pinch. Plants can be induced to ﬂower by short-day
photoperiods immediately following pinch (Adams et al., 1998). Veronica spicata
‘Red Fox’, in contrast, has a ﬂower induction-insensitive phase. Plants require a
period of growth following pinch before they are able to respond to ﬂower
induction by vernalization.

Pinched V. spicata ‘Red Fox’ plants took a few days longer to ﬂower than
unpinched plants. Garner et al. (1997) showed that the time from planting to
harvest was longer in pinched plants of Delphinium than in unpinched plants.
Pinched Phlox paniculata Lyon ex Pursh plants require approximately 11 days
longer to ﬂower than unpinched plants (Enﬁeld, unpublished data). However, in
both examples, pinching occurred after plants were already induced to ﬂower. In

the case of V. spicata ‘Red Fox’, pinching occurred before ﬂower induction.

51

Lateral shoots of pinched plants may be large enough to perceive cold but may
not be as developed as unpinched plants before cold treatment. Therefore, a
longer growing time following cold was required for plants to ﬂower.

Differences in time to ﬂower during an experiment can be caused by
differences in temperature between treatments. As bulking duration increased
from 0 to 3 weeks, the average forcing temperature increased for replicate one
by 0.7 °C, but there was no change for replicate two. Average increase in
temperature as bulking duration increased averaged over both replicates was 0.3
°C. By applying a model developed to determine the number of days to ﬂower
for V. Iongifolia ‘Sunny Border Blue’ (Runkle, unpublished data) to V. spicata
‘Red Fox’, approximately one day can be accounted for by increased
temperatures as bulking duration increased from 0 to 3 weeks. However, there
was a'four-day difference in days to ﬂower; therefore, the decrease in time to
ﬂower as bulking duration increased was a signiﬁcant treatment effect.

The number of ﬂowering shoots increased as bulking duration increased,
regardless of bulking container size. As bulking duration increased, there was
more vegetative growth present before cold treatment. Dybing and Grady (1994)
found that the length of the vegetative growth period in ﬂax was positively
correlated with ﬂower production. As the duration of vegetative growth
increased, ﬂower production increased. Many V. spicata ‘Red Fox’ plants in the
cold-duration experiment had only one ﬂowering shoot. Plants were not pinched
and were bulked in 72-cell plug trays for 3 weeks. Three weeks in the cold-

duration experiment was equivalent to 1 week of bulking in the second

52

experiment. Unpinched plants bulked in 72-cell plug trays for 1 week in the
second experiment averaged one ﬂowering shoot per plant.

For unpinched plants, the decrease in the number of ﬂowering shoots per
plant as bulking container size decreased may be the result of a shade
avoidance response caused by a change in the red to far-red (RIFR) ratio. A low
RIFR, found In a dense plant canopy, results in reduced branching, while a high'
RIFR results in increased branching (Smith, 1994). Plants bulked in a 72-cell
plug tray are grown at a higher plant density (approximately 19 cm2 per plant)
than plants bulked in the 13-cm pot (169 cm2 per plant) and would be expected
to have fewer ﬂowering shoots because of reduced plant branching caused by a
change in the R/FR rates an total intercepted light. In 13-cm pots, as bulking
duration increased, more lateral shoots became large enough to perceive cold;
thus, the number of ﬂowering stems increased. When plants are pinched, apical
dominance is removed and lateral shoots develop. For plants bulked in plug
trays, pinching increased the number of ﬂowering shoots per plant. For plants
bulked in 13-cm pots, potential lateral shoots are actually removed with the pinch
and the overall number of ﬂowering shoots is reduced compared with that of

unpinched plants.

Conclusions
Veronica spicata ‘Red Fox’ has an obligate 5-week cold requirement for
rapid and uniform ﬂowering. Plants should not be pinched after cold because it

eliminates ﬂowering. Unpinched plants had a higher probability of ﬂowering than

53

pinched plants, at least if pinched plants are bulked 3 or fewer weeks. The larger
the bulking container, the greater the number of ﬂowering shoots. The longer the
bulking duration, at least through 3 weeks. the greater the number of ﬂowering
shoots. When V. spicata ‘Red Fox’ was bulked in a 13-cm pot, the greatest
number of shoots occurred when plants were not pinched and were bulked for 3
weeks. When V. spicata ‘Red Fox’ was bulked in a 50- or 72-cell plug tray,
pinched plants bulked for 3 weeks had the highest number of ﬂowering shoots

per plant and the highest ﬂowering percentage.

54

Literature Cited

Adams, S.R., S. Pearson, and P. Hadley. 1998. An appraisal of the use of
reciprocal transfer experiments: assessing the stages of photoperiod
sensitivity in Chrysanthemum cv. Snowdon (Chrysanthemum morifolium
Ramat.). J. Expt. Bot. 49:1405—1411.

Cline, MG. 1991. Apical dominance. Bot Rev. 57:318-358.

Dybing, CD. and K. Grady. 1994. Relationships between vegetative growth rate
and ﬂower production in ﬂax. Crop Sci. 34:483-489.

Ecke, P., Jr., O.A. Matkin, and DE. Hartley. 1990. The poinsettia manual, 3rd
ed. Paul Ecke Poinsettias, Encinitas, Calif.

Engle, BE. 1994. Use of light and temperature for hardening of herbaceous
perennial plugs prior to storage at -2.5C. MS Thesis, Michigan State
Univ, East Lansing.

Garner, J.M., SA. and Jones, A.M. Armitage. 1997. Pinch treatment and
photoperiod inﬂuence ﬂowering of Delphinium cultivars. HortScience
32:61—63.

Huang, N., K.A. Funnell, and B.R. MacKay. 1999. Vernalization and growing
degree-day requirements for ﬂowering of Thalictrum delavayi ‘Hewitt’s
Double’. HortScience 34:59—61.

Levy, Y.Y. and C. Dean. 1998. The transition to ﬂowering. Plant Cell 1021973—
1989.

Lyons, RE. and CL. Hale. 1987. Comparison of pinching methods on selected
species of Columnea, Kalanchoe, and Crassula. HortScience 22:72—74.

Metzger, JD. 1988. Localization of the site of perception of therrnoinductive
temperatures in Thlapsi arvense L. Physiol. Plant. 88:424-428.

Nau, J. 1998. Veronica (spike Speedwell). In: V. Ball (ed.) Ball RedBook, 16th
ed. Ball Publishing, Batavia, lll.

Runkle, ES. 1996. The effects of photoperiod and cold treatment on ﬂowering

of twenty-ﬁve species of herbaceous perennials. MS Thesis, Michigan
State Univ, East Lansing.

55

Smith, H. 1994. Sensing the light environment: The functions of the
phytochrome family, p. 377—416 In: R.E. Kendrick and G.H. Kronenberg
(eds). Photomorphogenesis in plants. Kluwer Academic Publishers,
Dordrecht, The Netherlands.

Thomas, B. and D. Vince-Prue. 1997. Photoperiodism in plants, 2nd ed.
Academic Press, San Diego, Calif.

Williams, C. and B. Bearce. 1964. Pinching and disbudding, p. 38—45. In:
R.W. Langhans (ed.). Chrysanthemum: A manual of the culture, disease
and insects, and economics of Chrysanthemums. The New York State
Extension Service Chrysanthemum School, Ithaca, New York.

56

Table 1. Dates of forcing following cold treatment, average air temperatures, and
average daily light integral (DLI) from date of forcing to average date of ﬂowering for
Veronica spicata ‘Red Fox’.

 

Forcing
Date of forcing Weeks of Weeks Avg. temp. Avg. DLI
following cold bulking of 5 °c (° C) (mol-m'Z-d")
Cold duration experiment
2/1/00 3 0 --‘ -
2/8/00 3 1 -- -—
2/15/00 3 2 - -
2/22/00 3 3 21.4 14.8
2/29/00 3 4 21.3 15.5
3/10/00 3 5 21.1 15.7
Bulking duration experiment
Replicate 1
2/13/02 0 5 21.7 10.2
2/20/02 1 5 21.7 10.6
2/27/02 2 5 22.1 12.1
3/6/02 3 5 22.4 12.9
Replicate 2
3l22/02 0 5 22.7 13.4
3/29/02 1 5 23.0 132
4/8/02 2 5 22.8 13.8
4/16/02 3 5 22.6 14.4

 

zDashes indicate no plants ﬂowered.

57

 

Table 2. The effects of 5 °C cold treatment on ﬂowerinqof Veronica spicata ’Red Fox’.

 

 

 

Days to Days from Days Final Final Number
Weeks Flowering visible visible bud to node plant of lateral
of 5 °C percent_aqe bud to ﬂower ﬂower numberI heiqht (cm) Inﬂor.y
0 0 -" -- - - - -
1 0 -- -- - -- - --
2 0 -- -- —- - — -—
3‘” 10 37 20 57 8 53.5 5
4 50 28 22 50 7 57.9 5
5 100 26 22 48 7 53.5 7
Signiﬁcance
Weeksat 5Cv NS NS NS NS NS NS

 

 

2Number of nodes below ﬂowers.

yNumber of lateral inﬂorescences off main ﬂowering shoot.
xDashes indicate no plants ﬂowered.

wData based on one ﬂowering plant.

"Analysis of 4- and 5-week cold treatments only.

58

Table 3. Signiﬁcance of bulking container size, pinch, and bulking duration on ﬂowering of
Veronica spicata ‘Red Fox'.

 

 

 

Days from Lateral
Days to visible inﬂorescences
Flowering visible bud to Days to Flowering per ﬂowering

Treatment probability bu ﬂower ﬂower shoots shoot
Bulking container (BC) ** -‘ - - *“ ***
Pinch (P) iii tit u *t* ** it.
Bulking duration (BD) *** *** *"* *** **” ***
PLinear __ an mu rams tat N S
F>Quadratic " NS in NS NS 1"
BC X P * -- -- -- *** **
BC X 80 NS -- -- -- *** NS
P x 80 * NS ' NS NS
BC X P X 80 -— - -- - NS NS

”$3.,“g”.

Nonsigniﬁcant or signiﬁcant at P 5 0.05, 0.01, or 0.001, respectively.
zDashes indicate data not presented/not tested.

59

 

6O

 

 

 

 

 

 

 

 

 

H N,
40 ~
‘0 L***QNS
>. d B
to 30 §<E\\~G _o
D “N O
20 : c 3: 311—, A
ﬁ
10 n
+ Visible bud no pinch + VB to FLW no plnch ~v— Flower no pinch
0 —o— Visible bud pinch —C}— V8 to FLW pinch —V- Flower pinch
0 1 2 3

Bulking duration (weeks)

Figure 1. The effects of bulking duration and pinching on days to visible bud
(0,0, no pinch and pinch, respectively), days from visible bud to ﬂower (I,Cl, no
pinch and pinch, respectively), and days to ﬂower (V ,V, no pinch and pinch,
respectively). Error bars represent the standard error of the mean. Probability of
linearﬂand quadratic relationships indicated by L and Q, respectively,

"3' ' ' Nonsigniﬁcant or signiﬁcant at P 5 0.05, 0.01, or 0.001, respectively.

60

120

 

 

 

 

 

 

 

 

 

No pinch A Pinch B
m 100 ~ . - »
8’ /v
’E 80 4 .
§
8 60 .
.‘s” /
5 4o . o/
3 + 13-cm pot I / //
“- 20 . ——I— 4.4-cm plug l r//
——v—- 4.1ocm plug j
0 N ‘ h L- '
1'3 0 who "E C Pinch D
8 5 7 _,/” 7
5
g. I. ,/ 3‘4
2 . ,/"&\
g 3 ‘ I ‘ / ‘\\\é
o
E 2 2,4 —— \ ,- -I/irI/T
3 1 T ————
z . I
0 I... Y ‘ v Y f _ .—J
0 1 2 3 0 1 2 3

Bulking duration (weeks)

Figure 2. The effects of bulking duration, bulking container size (0, I, V = 13-cm
pot, 4.4-cm plug, and 4.1-cm plug, respectively), and pinching (A and C = no
pinch, B and D = pinch) on ﬂowering percentage (A and B) and the number of
ﬂowering shoots per plant (C and D). Error bars on graphs C and D represent
the standard error of the mean.

61

 

.- I
4‘ i§f§?§f‘f‘ 5. . I: 5

Lateral inforescences per ﬂowering shoot

 

 

 

Flowering shoots

Figure 3. The relationship between the number of ﬂowering shoots per plant and
the number of lateral inﬂorescences produced per ﬂowering shoot for Veronica
spicata ‘Red Fox’. Data points represent the means of all possible treatment
effects. Error bars represent the standard error of the mean.

62

SECTION III
THE EFFECT OF DAILY LIGHT INTEGRAL, AUXIN CONCENTRATION, AND

PROPAGATION PHOTOPERIOD ON THE ROOTING AND FLOWERING OF
PHLOX PANICULA TA ‘DAVID’

63

The Effect of Daily Light Integral, Auxin Concentration, and Propagation
Photoperiod on the Rooting and Flowering of Phlox paniculata ‘David’

Amy L. Enﬁeld‘, Royal D. Heins”, Arthur C. Cameronz, and William H. Carlson2
Department of Horticulture, Michigan State University, East Lansing, MI 48824

Additional index words: vernalization

Received for publication . We appreciate the greenhouse

growers providing support for Michigan State University ﬂoriculture research.
Graduate Student. Current address: Dept. of Horticulture, Clemson University,

Clemson, SC 29634.

zProfessor.

3To whom reprint requests should be addressed (E-mail: heins@msu.edu).

64

Abstract

Experiments were performed on Phlox paniculata Lyon ex Pursh ‘David’ to
determine the effects of daily light integral (DLI) of 0.8 through 11.3 mol-m'z-d":
auxin concentrations of 0, 1500, 3000, and 6000 ppm; and photoperiods of 11
through 15 h and 9 h with a 4-h night interruption (NI) on root formation during
propagation. Cuttings were evaluated at 1-week intervals for 4 weeks. Root
number, root mass, and rooting percentage increased as DLI increased from 0.8
to 8.6 mol-m’Z-d". A DLI of 5.1 moI-m'z-d'1 produced cuttings with the most
uniform root development 21 days after propagation. An auxin concentration of
1500 ppm produced cuttings with the most uniform root development 21 days
after propagation. Propagation photoperiod did not signiﬁcantly affect rooting. A
separate experiment was performed to determine the effects of the same
propagation photoperiods and subsequent cold treatments of 0, 2, and 5 weeks
on time to ﬂower. Although plants ﬂowered regardless of propagation
photoperiod and cold treatment, days to ﬂower decreased by approximately 15 to
25 days as propagation photoperiod decreased. Time to ﬂower decreased by as
many 15 for propagation photoperiods of 13 h or less with increased cold
duration. Plant height increased with increasing cold duration, but the number of

nodes at ﬂower was not signiﬁcantly affected.

65

Introduction

Phlox paniculata Lyon ex Pursh is a member of Polemoniaceae and is
native from New York to Georgia and west to Arkansas and Illinois. Phlox
paniculata ‘David’ (a perennial garden phlox) was awarded the title Perennial
Plant of the Year 2002 by the Perennial Plant Association (Perennial Plant
Association, 2002). ‘David’ has large, fragrant, white ﬂower panicles with 2.5-cm-
diameter ﬂorets, making it an attractive candidate for ﬂowering herbaceous
perennial potted plant production. Understanding the propagation requirements
for successful rooting and the physiological requirements for uniform ﬂowering
are two important production issues.

Adventitious rooting is an essential step in the propagation of vegetative
cuttings. Daily light integral (DLI) or light quantity during propagation can
signiﬁcantly affect rooting. In most cases there is an optimum irradiance for
maximum rooting, and light intensities in excess of this value can sometimes
reduce root formation (Lovell et al., 1972). The effects of light intensity and DLI
during propagation on rooting percentage, root number, and root mass have
been examined in several species, including Acer palmatum Thunb. (Behrens,
1988), Quercus sp. (Zaczek et al., 1999), Rhododendron (Davis and Potter,
1987), and petunia microshoots (Cabaleiro and Economou, 1992). In most
cases, there was an optimal light intensity or DLI for each species, while levels
above or below the optimum range reduced or inhibited rooting.

Adventitious rooting of vegetative cuttings can also be inﬂuenced by the

presence or absence of rooting hormones. Rooting hormones, or synthetic

66

auxins, are not essential for adventitious rooting of all vegetatively propagated
plants but for crops such as poinsettia (Euphorbia pulchenima Willd. ex Klotzsch)
can speed up the rate of rooting and improve crop uniformity (Ecke et al., 1990).
Indole-3-butyric acid (IBA) and 1-napthaleneacetic acid (NAA) have been shown
to affect rooting (root number and rooting percentage) in many woody perennials
including, Clematis xjackmanii T. Moore ‘Jackmanii’ (Erwin et al., 1997), neem
(Kamaluddin and Ali, 1996), Douglas ﬁr (Copes and Mandel, 2000), and
Callinandra calothyrsus Meissn. (Tchigio and Duguma, 1998).

Phlox paniculata is a long-day plant that ﬂowers when photoperiods are
greater than or equal to 13 h (Runkle, 1996). Photoperiod during propagation
should theoretically inﬂuence time to ﬂower. One would predict earlier ﬂowering
for cuttings rooted under long days compared with those rooted under short
days. Smith and Wareing (1972) addressed the effects of storage photoperiod '
on the subsequent rooting of Populus xrobusta C. K. Schneid. The researchers
showed that cuttings have a higher rooting percentage and root number when
rooted under long days (18-h photoperiod) for 28 days than short days (9-h
photoperiod). Economou and Read (1986) found that longer and higher-quality
azalea shoot cuttings were harvested from tissue cultures under 16-h light
durations than from 24-h light durations.

Thomas and Vince-Prue (1997) deﬁne vernalization as a cold-temperature
treatment that is given to an imbibed seed or young plant and promotes ﬂowering
at subsequent higher temperatures. The botanical deﬁnition of vernalization

ignores other ﬂowering characteristics of horticultural importance. A cold-

67

temperature treatment may not be required for ﬂowering but could enhance
ﬂowering by increasing ﬂowering percentage, hastening ﬂowering, and improving
ﬂowering uniformity. There is contradicting research about cold requirements for
ﬂowering of P. paniculata. Runkle et al. (1998) showed that without cold
treatment, a P. paniculata population never reached 100% ﬂowering. On the
other hand, Garner and Armitage (2000) found that plants ﬂowered under
photoperiods longer than 10 h, and cooling of plants was not required for
ﬂowering, although it accelerated ﬂowering.

The ﬁrst objective of this research was to identify the environmental
conditions (photoperiod, daily light integral, and synthetic auxin concentrations)
during propagation that optimized rooting of P. paniculata ‘David’ cuttings. The
second objective was to determine the effects of propagation photoperiod on
subsequent time to ﬂower. The ﬁnal objective was to determine the minimum

cold duration required for rapid and uniform ﬂowering of P. paniculata ‘David’.

Materials and Methods

Plant culture. Vegetative Phlox paniculata ‘David’ cuttings were received
from Guatemala in Dec. 2001 and Feb., Mar., Apr., May, June, and July 2002.
Cuttings were propagated in 72-cell (0.04-L for propagation photoperiod and
auxin concentration experiments; 0.03-L for DLI experiment) plug trays
(Landmark Plastic Corporation, Akron, Ohio) containing a mixture of 50%
commercial medium (Suremix Perlite; Michigan Grower Products, Galesburg,
Mich.) and 50% screened course perlite (Therm-O-Rock; East, Inc., New Eagle,

Pa.).

68

Propagation environmental control. Plants were propagated in a glass
greenhouse. Propagation air temperatures were maintained at 23 °C and bottom
heat (soil temperature) was maintained at 25 °C. A vapor pressure deﬁcit of 0.3
kPa was maintained by injecting water vapor as needed. Average daily
temperature and DLI were monitored with a CR-10 datalogger (Campbell
Scientiﬁc, Logan, Utah) by using 36-gauge (0.013 mm in diameter) type E
thermocouples and line quantum sensor (Apogee Instruments, Inc., Logan,
Utah), respectively. The datalogger collected data every 10 seconds and
recorded the hourly average.

Daily light integral experiment. Beginning on June 7 and July 4, 2002,
basal portions of each cutting were dipped in a 1500-ppm solution of liquid auxin
(DIP ’N GROW; Astoria-Paciﬁc, Clackamas, Ore.) before stick. Plug trays were
propagated under one of four levels of shade: zero, one, two, or three layers of a
50% shade curtain (Ludvig Svensson, Kinna, Sweden). Light levels under each
shade treatment were monitored with a line quantum sensor (model LQSV—SUN;
Apogee Instruments, Inc., Logan, Utah). Average DLls for both replications are
presented in Figure 1.

Auxin experiment. The experiment was replicated in time beginning on
Mar. 20, Apr. 25, and May 30, 2002. Basal portions of each cutting were dipped
in one of four solutions of liquid auxin (DIP ’N GROW; Astoria-Paciﬁc,
Clackamas, Ore.) before stick: 0, 1500, 3000, or 6000 ppm. Cuttings were

propagated under natural daylengths.

69

Propagation photoperiod experiment (rooting). The experiment was
replicated in time beginning on Mar. 20, Apr. 25, and May 30, 2002. Basal
portions of each cutting were dipped in a 1500-ppm solution of liquid auxin (DIP
’N GROW; Astoria-Paciﬁc, Clackamas, Ore.) before stick. Cuttings were
propagated under one of six photoperiods: 11, 12, 13, 14, or 15 h of continuous
light or 9 h with a 4-h night interruption (NI). Natural photoperiods were extended
with incandescent lamps. For continuous photoperiodic treatments, lamps were
turned on at 1700 HR and turned off after each photoperiod was completed. The
NI was delivered from 2200 to 0200 HR.

Propagation photoperiod experiment (ﬂowering). Cuttings were
propagated on Dec. 21, 2001, and again on Feb. 8, 2002. Propagation setup
was identical to that of the rooting experiment. Cuttings were rooted and weaned
from propagation 3 weeks after sticking.

Immediately following propagation, plugs were cold treated for 0, 2, or 5
(ﬁrst replicate only) weeks at 5 °C. The chamber was lit from 0800 to 1700 HR by
cool-white ﬂuorescent lamps (F96T12/CWNHO; Philips, Somerset, N.J.) at a
photosynthetic photon ﬂux (PPF) of approximately 10 umol'm‘z‘s'1 at plant height.
While in the cooler, plants were watered as needed with well water acidiﬁed with
sulfuric acid to a titratable alkalinity of approximately 130 mg calcium bicarbonate
per liter.

Following cold treatment, plugs were potted in 13-cm square plastic
containers (1.1 L) containing a soilless commercial medium composed of pine

bark, ﬁbrous Canadian sphagnum peat, horticultural vermiculite, and screened

70

course perlite, along with a wetting agent and starter fertilizer charge (Suremix
Perlite; Michigan Grower Products, Galesburg, Mich.) All plants were forced to
ﬂower under a 16-h photoperiod, natural daylengths supplemented with lighting
from high-pressure sodium lamps from 0530 to 2130 HR. Plants were top-
watered as necessary with well water acidiﬁed with sulfuric acid to a titratable
alkalinity of approximately 130 mg calcium bicarbonate per liter and containing
water-soluble fertilizer providing 125 N, 12 P, 125 K, 13 Ca (mg-L"; 30%
ammoniacal N) plus (mg-L“) 1.0 Fe, 0.5 Mn, 0.5 Zn, 1.0 Cu, 0.2 B, 0.1 Mo (MSU
Special; Greencare Fertilizers, Chicago, Ill.). Half of the plants in each treatment
of the ﬁrst replicate were soft pinched (two apical nodes removed) 3 weeks after
potting. Half of the plants in each treatment of the second replicate were hard
pinched (six apical nodes removed) 50 days (0 weeks at 5 °C) and 35 days (2
weeks after 5 °C) after potting.

Plants were grown in glass greenhouses set at 20 °C. Greenhouse
temperatures were controlled by a greenhouse climate-control computer (Model
CD750; Priva, De Lier, The Netherlands). Average daily temperature and DLI
were monitored with a CR-10 datalogger (Campbell Scientiﬁc, Logan, Utah) by
using 36-gauge (0.013 mm in diameter) type-E thermocouples and quantum
sensors (Model Ll-189, Ll-COR, lnc., Lincoln, Neb.), respectively. The
datalogger collected data every 10 seconds and recorded the hourly average.
Actual average daily temperatures and DLIs for the beginning of forcing to the

average date of ﬂowering were calculated and are presented in Table 1.

71

Data Collection and Analysis

Rooting experiments. For the ﬁrst replication of the propagation
photoperiod and auxin concentration experiments, 10 cuttings were randomly
selected 10, 15, 20, 25, and 30 days after propagation. For all other experiments
and replications, 15 cuttings were randomly selected 1, 2, 3, and 4 weeks after
propagation. Data were collected after 1, 2, and 3 weeks in the second
replications of the photoperiod and auxin concentration experiments. Root
number and fresh root mass were recorded for each cutting. Data were analyzed
using SAS’s (SAS Institute, Cary, NC.) analysis of variance (ANOVA) and
general linear model (GLM) procedures.

Flowering experiment. Dates of visible bud and ﬁrst ﬂower as well as ﬁnal
node number, height at ﬂowering, and the number of reproductive branches
(pinched plants only) were recorded. A completely randomized design was used
Data were analyzed using SAS’s (SAS Institute, Cary, NC.) ANOVA and GLM

procedures.

Results

Daily light integral experiment. Light levels in replicate two were lower
than in replicate one (Figure 1) because whitewash was applied to the
propagation greenhouse roof between experimental replicates. Cuttings had a
minimum DLI requirement of 1.6 mol-m"°'-d'1 for rooting to occur. Rooting quality
and percentage increased as propagation DLI increased up to 8.6 mol-m’2’-d'1

and then decreased (Figure 2).

72

Daily light integral had a signiﬁcant effect on root number, root mass, and
rooting percentage after 14 days in propagation (Table 2). Plants rooted under a
DLI of 5.1 mol-m'Z-d'1 had the highest average root mass and average number of
roots, while plants propagated under 0.8 or 1.2 mol-m'Z-d‘1 of light showed no
evidence of rooting. After 21 days in propagation, cuttings rooted under 8.6
mol-m'z-d'1 had the highest average number of roots per cutting, but the number
was not signiﬁcantly different from that of cuttings propagated under 5.1 mol-m'
2«1" (Figure 2A). Cuttings rooted under 8.6 mol'm'z'd'1 had a signiﬁcantly higher
average root mass per cutting than all other treatments did (Figure 23). Rooting
percentage after 21 days in propagation was not signiﬁcantly different for light
quantities between 2.2 and 11.3 mol-m'z-d'1 (Table 2, Figure 2C). After 28 days
in propagation, there were no signiﬁcant differences in the average number of
roots per cutting, average root mass, and rooting percentage for cuttings rooted
at a DLI of 5.1 mol-m’Z-d'1 or greater.

Auxin concentration experiment. Regardless of treatment, the P.
paniculata ‘David’ cuttings rooted, although rooting trends varied with replicate.
In the ﬁrst replicate, there was no signiﬁcant difference in the average number of
roots per cutting for any evaluation time (Table 3, Figure 3A). Average root
mass, however, 25 days after propagation, was signiﬁcantly different for cuttings
dipped in a 1500-ppm auxin solution before stick versus 0 ppm and 6000 ppm
(Figure 3D), but by day 30, there were no signiﬁcant differences in root mass,
and plants from all auxin concentrations had 100% rooting (Figure 36). In the

second replicate, there was a signiﬁcant effect of auxin concentration on root

73

number beginning 12 days after propagation (Figure 38) and on root mass 22
days after propagation (Figure 3E). Twelve days after propagation, plants in the
1500-ppm treatment had signiﬁcantly more roots per cutting than those in all
other auxin concentrations and a signiﬁcantly higher rooting percentage than 0
ppm (Figure 3H). Twenty-two days after propagation, plants in the 1500- and
3000-ppm treatments were signiﬁcantly different in terms of average root mass
from 0 ppm. In the third replicate, cuttings treated with 6000 ppm had
signiﬁcantly more roots per cutting after 22 days in propagation than those
treated with 0 ppm, which also had signiﬁcantly fewer roots than plants in all
other auxin concentrations (Figure 30) after 29 days. Cuttings treated with 6000
ppm had signiﬁcantly more roots per cutting than those treated with 1500 ppm.
In terms of average root mass per cutting, 29 days after propagation, 0 ppm was
signiﬁcantly different from 6000 ppm (Figure 3F). Cuttings from all auxin
concentrations had 100% rooting after 29 days in propagation (Figure 3|).
Propagation photoperiod experiment (mating). Regardless of propagation
photoperiod, all cuttings rooted. Rooting trends varied with replicate (Table 4).
In the ﬁrst replicate, signiﬁcant differences in average root number and average
root mass per cutting were evident beginning 20 days after propagation.
Cuttings rooted under a 14-h photoperiod had the most roots (Figure 4A) and the
largest average root mass per cutting (Figure 40) after 30 days in propagation.
There was no signiﬁcant difference in rooting percentage. After 30 days, all
cuttings had rooted completely except for cuttings under the 15-h photoperiod

(Table 4, Figure 4G). The second replicate showed a signiﬁcant difference in

74

root number 21 days after propagation. Cuttings propagated under a 12-, 13—, or
14-h photoperiod had signiﬁcantly more roots per cutting than cuttings
propagated under a 15-h photoperiod (Figure 4B). There was no signiﬁcant
difference in average root mass per cutting (Figure 4E) and rooting percentage
(Figure 4H). The third replicate showed a signiﬁcant difference in root number 15
days after propagation. Cuttings propagated under a 12-h photoperiod were
signiﬁcantly different from cuttings propagated under an 11-h photoperiod (Figure
4C). Twenty-two days after propagation, there were no signiﬁcant differences in
root number, but cuttings propagated .under a 12-h, 14-h, or NI photoperiod had a
larger average root mass per cutting than cuttings propagated under a 13-h
photoperiod (Figure 4F). Fifteen days after propagation, cuttings under an 11-h
photoperiod had a signiﬁcantly lower rooting percentage than those under all
other photoperiods (Figure 4|). After 28 days, all cuttings were rooted
completely, regardless of propagation photoperiod.

Propagation photoperiod experiment (ﬂowering). Regardless of
propagation photoperiod and cold duration combination, all plants ﬂowered.
Flowering trends varied with replicate (Table 5). For replicate one, days to visible
bud and days to flower were signiﬁcantly affected by propagation photoperiod,
cold duration, pinching, and the interaction between photoperiod and cold. For
replicate two, days to visible bud and days to ﬂower were signiﬁcantly affected by
propagation photoperiod, cold duration, and pinching but not the interaction
between propagation photoperiod and cold duration. As propagation photoperiod

increased, days to ﬂower deceased by up to 28 d (replicate one) or 15 d

75

(replicate two) for unpinched plants (Figure 5A and B). For pinched plants in
replicate one, there was no obvious trend in time to ﬂower as propagation
photoperiod increased (Figure 5C). For cold-treated pinched plants in replicate
two, time to ﬂower decreased as propagation photoperiod increased (Figure 5D).
Regardless of pinching treatment, days to ﬂower decreased within a propagation
photoperiod as cold duration increased.

Final plant height was signiﬁcantly affected by propagation photoperiod,
cold duration, and pinching in the ﬁrst replicate and by propagation photoperiod
and pinching in the second replicate (Figures 6 and 7). Pinched plants were 10
to 20 cm shorter than unpinched plants. Increasing cold duration increased ﬁnal
plant height for unpinched plants in replicate one (Figure 6A), but this trend did
not occur in replicate two (Figure 6B). Cold-treated plants were approximately 5
to 7 cm taller than plants without a cold treatment for pinched plants in both
replicates. However, as propagation photoperiod increased, differences in height
between cold treatments became smaller (Figure 7A and B). Plants in replicate
two were about 10 cm shorter than replicate one plants.

The number of nodes present at ﬂowering was signiﬁcantly affected by
cold duration and pinching in replicate one and by propagation photoperiod, cold
duration, and pinching in replicate two (Figure 6C and D, Figure 7C and D).
Pinched plants had approximately two to four fewer nodes than unpinched
plants. There was no obvious trend as propagation photoperiod increased for

both ﬁnal plant height and node number.

76

The number of ﬂowering stems per plant was signiﬁcantly affected by
propagation photoperiod and cold duration in replicate one and by cold duration
in replicate two. As cold duration increased in the ﬁrst replicate, the number of
ﬂowering stems increased (Figure 7E). Cold-treated plants had fewer ﬂowering
stems per plant than plants that did not receive a cold treatment in the second
replicate (Figure 7F). Plants in replicate two had more ﬂowering stems per plant

than plants in replicate one.

Discussion

As propagation DLI increased through 8.6 mol-m‘z-d", rooting percentage,
root number, and root mass of P. paniculata cuttings also increased. Petunia
microshoots also showed an increased rooting percentage as DLI increased from
1 to 3 mol-m'z-s'1 (Cabaliero and Economou, 1992). Acer sp., Quercus sp., and
Comus kousa Hance had the highest rooting percentage when PPF was
approximately 150 to 200 pmolvm'Z-s'1 (Behrens, 1988; Zaczek et al., 1997).

For P. paniculata ‘David’, when light levels during propagation were
decreased (<2 mol'm’z-d“), it is possible that the leaves could not harvest
enough light energy for adequate photosynthesis; thus, rooting was not
promoted. Leaves of cuttings have several functions: source of assimilates
(energy), source of food, source of minerals, source of hormones and rooting co-
factors, and transpiration during propagation (Costa, 2002).

Jorgensen (1992) found that light intensities of 134 pmol-m'z-s'1 during a

24-h period (11.6 mol-m'z-d") in the winter were needed for rapid root initiation of

77

Rosa hybrids. Davis and Potter (1987) found that a 20-fold light level difference
did not affect rhododendron rooting percentage despite signiﬁcant differences in
leaf water potential, net photosynthesis, and sucrose and starch concentrations
in the cutting bases. Under low light levels (<2 mol-m'Z-d"), most P. paniculata
‘David’ cuttings did not even form callus tissue. Botrytis rot was also a problem
during propagation under the low light intensities.

DLI affects not only rooting of cuttings but also other ﬂowering
characteristics, including ﬂower number, ﬂower size, intensity of ﬂower color, and
branching. Niu et al. (2001) showed that increasing DLI from 5.7 to 17 moI-m'Z-d'
1 after visible bud increased ﬂower size and number for Campanula carpatica
Jacq. ‘Deep Blue Clips’. The researchers also showed that plants were more
compact under high than under low DLI. The P. paniculata ‘David’ plants forced
to ﬂower were shorter in the second replicate than in the ﬁrst. Average DLI in the
second replicate was higher than in the ﬁrst replicate (11 versus 17 mol-m’z-d“)
and may account for differences in plant height.

Rates of synthetic auxins effective for rooting vary with the type of cutting
propagated: microshoots for tissue culture, herbaceous, softwood,
semihardwood, or hardwood. Auxins were not required for rooting of P.
panicUlata ‘David’. However, IBAINAA applications did increase the average root
mass per cutting. Similar results have been recorded for Eucalyptus (Fett-Neto
et al., 2001) and neem (Kamaluddin and Ali, 1996). For easily rooted cuttings,
including P. paniculata ‘David’, auxin concentration (0 to 100 ppm for tissue

culture, 0 to ~6000 ppm for others) does not affect rooting percentage (Fett-Neto

78

et al., 2001; Grifﬁn et al., 1998; Kamaluddin and Ali, 1996). For hard-to-root
cuttings, including many woody species, auxin concentration does affect rooting
percentage. Difﬁcult-to-root Eucalyptus globulus Labill microcuttings had
increased rooting percentages when lBA concentrations were increased to 10
and 100 ppm (Fett-Neto et al., 2001). Semihardwood cuttings of Thuja x ‘Green
Giant’ had the most rooting when treated with lBA at 3000 or 6000 ppm (Grifﬁn et
al., 1998). Increasing lBA from 2000 to 4000 ppm favored root formation in
unwounded basal cuttings of Leucandendron discolor (Rodriguez-Perez et al.,
1997).

Auxin concentration also affects the 'number of roots formed for many
species. For P. paniculata ‘David’, the number of roots per cutting increased as
auxin concentration increased. Similar results have been seen in neem
(Kamaluddin and Ali, 1996), Mussaenda erythrophylla (St. Hilaire and Fierro-
Berwart, 2000), Helianthus debilis ‘Flora Sun’ (Norcini and Aldrich, 2000), and
Thuja x “Green Giant’ (Grifﬁn et al., 1998).

For commercial production, these data suggest auxin concentrations
should not exceed 3000 ppm for P. paniculata. The goal of most growers is to
remove plants from propagation 3 weeks after sticking, and at 3 weeks (20 to 22
days), rooting percentage, root number, and root mass were greatest when auxin
at 1500 or 3000 ppm was used.

Propagation photoperiod had no effect on root development for P.
paniculata ‘David’. Research on petunia microshoots by Cabaleiro and

Economou (1992) showed that after 10 to 15 days in propagation, cuttings under

79

a 24-h photoperiod did not differ from those under a 14-h photoperiod in root
number, length, and weight. The main site for the perception of daylength is the
leaf, but the observed responses usually take place elsewhere in the plant
(Thomas and Vince-Prue, 1997). A photoperiodic stimulus is then exported from
the leaves to the shoot meristem, which leads to the formation of ﬂoral primordia.
However, Smith and Wareing ( 1972) showed that the state of the apex in a leafy
Populus xrobusta cutting had no signiﬁcant effect on root initiation. So even if
apical meristems of the P. paniculata ‘David’ cuttings had been induced to ﬂower,
it did not affect rooting.

Subsequent time to ﬂower under a 16-h photoperiod decreased as
propagation photoperiod increased. Runkle et al. (1998) and Runkle (1996)
showed that as forcing photoperiod increased, time to ﬂower decreased. Thus,
plants had been induced to ﬂower by photoperiods during propagation, and
longer photoperiods reduced time to ﬂower. Wurr et al. (2000) showed a similar
phenomenon with Dianthus allwoodii, which has an obligate vernalization
requirement. The vernalization requirements for the cuttings were satisﬁed
before cuttings were removed from the stock plants. Visible ﬂower buds were
produced during the rooting phase of propagation, resulting in earlier ﬂowering.

Pinched plants ﬂowered later than unpinched plants. Garner et al. (1997)
found that pinched plants of Delphinium sp. took longer to ﬂower than unpinched
plants.

Vernalization and pinching appeared to independently negate the effect of

propagation photoperiod on time to ﬂower in replicate one, and time to ﬂower

8O

was synchronized by cold treatment. Runkle et al. ( 1998) found that ﬂowering
was more synchronized in cold-treated P. paniculata plants, and Suzuki and
Metzger (2001) had similar results for Osteospermum ecklonis.

Phlox paniculata ‘David’ plants that received a cold treatment ﬂowered
sooner than untreated plants, regardless of propagation photoperiod. However,
cold treatment was not required for ﬂowering. Time to ﬂower was reduced further
as cold duration increased through 5 weeks. Garner and Armitage (2000) and
Runkle et al. (1998) showed that a 15- to 16-week cold treatment accelerated
ﬂowering of P. paniculata by 50 to 65 d. Cold treatment accelerates ﬂowering in
many plants, including wheat (Gonzalez et al., 2002), Thalictrum delavayi (Huang
et al., 1999), Aquilegia L. (Garner and Armitage, 1998), and Cicer milkvetch
(Townsend and McGinnies, 1973), among others.

Plant height increased with increasing cold duration but not propagation
photoperiod. Garner and Armitage (1998) had similar results with Aquilegia:
cooling plants resulted in longer ﬂowering stems. Conversely, Suzuki and
Metzger (2001) showed that stems of Osteospermum were shorter following
vernalization. In P. paniculata ‘David’, cold treatment did not affect node number.
Therefore, increased plant height was due to longer intemodes, which is in
contrast to ﬁndings by Suzuki and Metzger (2001) in Osteospermum and
Gonzalez et al. (2002) in wheat; they found that vernalized plants had fewer
nodes and leaves at ﬂower.

Plants in the second replicate developed more branches following pinch

than plants in the ﬁrst replicate. Berghage et al. (1989) showed that growth of

81

lateral shoots of poinsettia was inﬂuenced by the pinching technique. Lateral
shoots of soft- and medium-pinched plants were shorter than those of hard-
pinched plants because of residual apical dominance. ln Chrysanthemum
production, pinching into old tissue severely limits the number of breaks (Crater,
1992). In a separate P. paniculata ’David’ experiment (data not presented),
plants were pinched 44 days after the start of long days to different depths (one,
two, three. four, or ﬁve nodes removed) to examine the effects of pinching depth
on lateral branching. The hardness of pinch did not signiﬁcantly affect the
number of branches produced. All plants developed four lateral breaks of similar
size. (Plants in the second replicate of the propagation photoperiod ﬂowering
experiment produced more lateral breaks than plants in the ﬁrst replicate
because they were actively growing at pinch. Plants had been growing 35 to 50
days before pinch. In the ﬁrst replicate, plants were pinched 21 days after
planting, and many plants had not initiated active shoot growth. Thus, many

plants produced only one or two lateral branches following pinch.

Conclusions

DLI during propagation is critical for rooting success of P. paniculata
‘David’. Cuttings should not be rooted below 2 mol-m'Z-d", with an optimal DLI
range of about 5 to 10 mol-m‘z-d". Light levels above 11 mol-m'Z-d" did not
affect rooting percentage, but root number and mass were decreased. Rooting
hormone was not required for successful rooting, but treatments of 1500 to 3000

ppm improved root number and mass. Propagation photoperiod did not affect

82

rooting of P. paniculata ‘David’ but did affect subsequent time to ﬂower. Longer
propagation photoperiods reduced subsequent time to ﬂower, and for the most
rapid ﬂowering, a 16-h or Nl photoperiod should be used. A 5-week cold

treatment reduced time to ﬂower but increased ﬁnal plant height.

83

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Norcini, J.G. and J.H. Aldrich. 2000. Cutting propagation and container
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Perennial Plant Association. 2002 perennial plant of the year Phlox ‘David’.

Available at http://wwwperennialplant.org/ppv/02ppv.html. Accessibility
veriﬁed September 4, 2002.

85

Rodriguez-Perez, J.A., A.M. de Leon Hernandez, M.C. Vera Batista, and MC.
Hoyos Rodriguez. 1997. Inﬂuence of cutting position, wounding, and lBA
on the rooting of Leucadendron discolor stem cuttings. Acta Hort.
453:29—34.

Runkle, ES. 1996. The effects of photoperiod and cold treatment on ﬂowering
of twenty-ﬁve species of herbaceous perennials. MS Thesis, Michigan
State Univ., East Lansing.

Runkle, E.S., R.D. Heins, A.C. Cameron, and W.H. Carlson. 1998. Flowering of
Phlox paniculata is inﬂuenced by photoperiod and cold treatment.
HortScience 33:1 172-1174.

Smith, MG. and PF. Wareing. 1972. The rooting of actively growing and
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St. Hilaire, R. and CA. Fierro-Berwart. 2000. Three mussaenda cultivars
propagated by stem cuttings exhibit variation in rooting response to
hormone and rooting conditions. HortTechnology 10:780—784.

Suzuki, A. and JD. Metzger. 2001. Vernalization in a greenhouse promotes and
synchronizes ﬂowering of Osteospermum ecklonis Norl. HortScience
36:658—600. '

Tchigio, I. and B. Duguma. 1998. Vegetative propagation of Calliandra
calothyrsus (Meissner). Agroforestry Systems 40:275-281.

Thomas, B. and D. Vince-Prue. 1997. Photoperiodism in plants. 2nd ed.
Academic, London.

Townsend, CE. and W.J. McGinnies. 1973. Factors inﬂuencing vegetative
growth and ﬂowering of Astragalus cicer L. Crop Sci. 13:262-264.

Wurr, D.C.E., J.R. Fellows, and L. Andrews. 2000. The effects of temperature
and daylength on ﬂower initiation and development in Dianthus allwoodii
and Dianthus alpinus. Scientia Hort. 86:57—70.

Zaczek, J.J., C.W. Heuser, Jr., and KC. Steiner. 1997. Effect of shade levels
and lBA during rooting of eight tree taxa. J. Environ. Hort. 15:56—60.

Zaczek, J.J., C.W. Heuser, Jr., and KC. Steiner. 1999. Low irradiance during

rooting improves propagation of oak and maple taxa. J. Environ. Hort.
17:130-133.

86

Table 1. Dates of forcing, average daily temperatures, and average daily light integral
from date of forcing to average date of ﬂowering for the Phlox paniculata ‘David’
propagation photoperiod (ﬂowering) experiment.

Date of forcing

 

from end of cold Average daily temperature Average daily light integral
treatment Weeks at 5 °C (°C) (molom-2-d-1)

Replicate 1

01/07/02 0 20.1 9.4

01/22/02 2 20.3 10.8

02/13/02 5 20.4 11 9
Replicate 2

03/14/02 0 22.2 16.7

03/30/02 2 23.0 17.2

 

'F'” “”“W

87

Table 2. Effects of daily light integral (DLI) during propagation on rooting of Phlox paniculata
‘David’.

DLI Average number of Average root mass

 

 

 

 

Evaluation (days) (mol-m‘z-d'1) roots per cuttings (mg) per cutting Rooting percentage
7 0.8 0a2 Ga Ga
1.2 0a 0a 0a
1.6 0a 0a 0a
2.2 0a 0a 0a
3.6 0a 0a 0a
5.1 Ga 0a 0a
8.6 Ga 0a 0a
1 1.3 0a 0a 0a
14 0.8 0b 0b Go
1.2 0b 0b Go
1.6 1b 4b 13abc
2.2 0b 1b 7bc
3.6 1b 5b 33abc
5.1 6a 32a 533
8.6 2ab 8b 47ab
11.3 2ab 5b 53a
21 0.8 0d 0d 0d
1.2 1d 1d 7cd
1.6 3cd 290d 40bc
2.2 8bcd 42bcd 73ab
3.6 14bc 134bc 100a
5.1 18ab 159b 1003
8.6 26a 320a 87a
11.3 13bc 118bcd 93a
28 0.8 Cd 0c 7c
1.2 20d 9c 40bc
1.6 20d 15c 53b
2.2 9c 102c 93a
3.6 18b 402b 93a
5.1 26a 438ab 100a
8.6 29a 639a 933
11.3 22ab 455ab 100a

 

zMean separation within each evaluation period by Tukey’s studentized range test (P = 0.05).
Numbers within a column and evaluation period with the same letter are not statistically different.

88

Table 4. Signiﬁcance of propagation photoperiod on average number of roots per cutting,
average root mass per cutting, and rooting percentage of Phlox paniculata ‘David’ cuttings.

Average number of Average root mass

Evaluation (days) roots per cuttings (mg) per cutting Rooting ﬁrcentage

 

Replicate 1
10 NS NS NS
15 NS NS NS
20 * "' NS
25 * * NS
30 * ** NS
Replicate 2
7 NS NS NS
12 NS NS NS
21 ** NS NS
Replicate 3
7 NS NS NS
15 * NS **
22 NS *** NS
28 NS NS -‘

 

NS*"“*

Nonsigniﬁcant or signiﬁcant at P _<_ 0.05, 0.01, or 0.001, respectively.
zDash indicates no variance in data.

-90

Table 5. Propagation photoperiod treatment effects on ﬂowering characteristics of Phlox

paniculata ‘Davld’.

 

Days to Days from Number of Number of
visible bud VB to Days to Final plant nodes at ﬂowering
Treatment (VB) ﬂower ﬂower heightﬁzm) ﬂower branches
Replicate 1
Photoperiod (Ph) *** NS *** * NS **
Cold duration (C) iii *ii *i* tum tit ﬁt
Pinch (Pi) tit NS tit *** *ti tit
Ph X C ** NS ** NS NS NS
Ph X Pi NS NS NS NS * *"'
C X Pi NS it NS tit *i *1
Ph X C X Pi NS NS NS NS NS NS
Phlox paniculata 'David' plants not pinched
Photoperiod (Ph) *** NS *** NS NS -‘
Cold duration (C) NS “* NS *** *** —
Ph X C NS NS NS NS NS -
Phlox paniculata 'David' plants pinched
Photoperiod (Ph) *** ** *" NS NS **
Cold duration (C) “* *** *** NS * “
Ph X C * ** NS NS NS NS
Replicate 2
Photoperiod (Ph) “* NS "* " ** NS
Cold duration (C) *** NS *** NS ‘* *"" .
PIHCh (Pi) tit NS tit tit iii iii
Ph X C NS NS NS ""’ NS NS
Ph X Pi NS NS NS NS NS NS
C x Pi it NS 9 «hit it it.
Ph X C X Pi NS NS NS NS NS NS
Phlox paniculata ’David' plants not pinched
Photoperiod (Ph) *** NS *** NS NS -
Cold duration (C) * * * * NS -
Ph X C NS NS NS ** NS -
Phlox paniculata 'David‘ plants pinched
Photoperiod (Ph) NS NS NS NS ’ NS
Cold duration (C) *** NS ’*" *** "" **
Ph X C NS NS NS NS NS NS

 

NS.*.*".“"

91

Nonsigniﬁcant or signiﬁcant at P 5 0.05, 0.01, or 0.001, respectively.
zDashes indicate branching data not collected.

 

 

 

   
  
 

 

 

 

 

 

 

 

 

 

 

Rep.1 Rep. 2
20
DLI
—o—— Olayers 11.3 8.6
....... 0....... 1 layer 51 36
15_ ——-v——— 2|ayers 2.2 1-6
—---vi—-- 3layers 1.2 0.8
‘71.:
.5
E
2 _. :‘o
7 x "y 90%00 0"wa 90000009. 0'9 60060 9°
M‘ «r r0 0 <5 " ‘5
. . PW " 0°
0 l v f r v I vvvvvv I """ I rrrrr I '
6/3 6/17 7/1 7/15 7I29
Date

I Figure 1. Daily light integrals (DLI, mol-m'z-d”) during Phlox paniculata ’David’
propagation for each level of shading.

92

 

40

 

I A
+ 7 days

—0— 14 days
30 ‘ —v— 21 days ,/
—v—- 28 days m

20*

 

 

Root number

10*

 

 

800

600 *

400*

Root mass (mg)

200 *

 

 

40* V

Rooting percentage
0)
o
‘ ‘ ‘ < 431 L _ ,
o
o
o

20* 1

'O

 

 

 

 

1i 1’ I

0 ~ (0H s 4 —e——--o
2 4 6 8 10 12

DLI (mol-m'2°d'1)

Figure 2. The effects of daily light integral (DLI) during propagation of Phlox
paniculata ‘David’ on average root number per cutting (A), average root mass per
cutting (B), and rooting percentage (C). Error bars represent standard error of
the mean.

93

 

Rep. 1

Rep. 2

 

40

 

+ Opprn

l

30 g —0— 1500 pp

 

m .
+ 3000 ppm
—9— 6000 ppm

 

20*

Root number

O

 

#0300
888.

Root mass (mg)

g

 

 

 

 

 

Rooting percentage

 

 

Figure 3. The effects of auxin concentration on root number, root mass, and
rooting percentage of Phlox paniculata ‘David’. Error bars represent standard

error of the mean.

 

 

o”

y
,/-/\7/

r

,_ .‘.___ --_+._.__.___ ,__-

 

 

5

10 15 20 25 30
Days in propagation

94

 

5

10

15

20

f

25

V

30

 

1------

35

 

 

Root number

 

 

 

  
  

 

Root mass (mg)

N15
888

 

 

 

_5
GO
GO

8

 
 

 

Rooting percentage
8

   

N
O

 

 

o
T“
i
\
'?\.
:\~
i

 

._.._.__T—-— 1 ﬁ—. '_ v--_.

15 20 25 30
Days in propagation

l
‘ I
I
I
I

.5
U!
N
O
N .
0|
0)
0
0|
—L
O

10

l

3‘

Figure 4. The effects of propagation photoperiod on root number, root mass, and
rooting percentage of Phlox paniculata ‘David’. Error bars represent standard
error of the mean.

95

Rep. 1 Rep. 2
No pinch A No pinch B

 

120

100 - a

 

CD
0

 

Pinch C Pinch D

1004 W i :jik’+ i

50 l[ -+— 0wksat§°C
—o—- 2wksat5°C
-v" kasat5°C

'_-'_'"_'_7-_'_‘ J. . ._

4o . 4 w——. . —,,s . ----s.--- . .-.-, . r I, W
11 12 13 14 15 Nl 11 12 13 14 15 Nl

Days to ﬂower
8

 

 

 

 

 

 

 

Propagation photoperiod

Figure 5. Number of days to ﬂower for Phlox paniculata ‘David’ propagation
photoperiod. Error bars represent 95% conﬁdence intervals.

96

 

100

80*

60*

Height (cm)

40*

20*

30

 

 

25*

201

151

10*

Number of nodes

-P

 

«o— -o'wks at 5 °C_‘

*. -o—- 2wksat5°CE

 

1+ 5wksat5°Cj

L_ _-____..-.s__._.__

 

 

—-—"T '__T'. r

 

 

 

Rep.1 Rep.2
A B
W9 i J
I - 2
i
F —/l s s all
C D
l .
. . ,3: . — ﬁ— —_,—_1. - -,_ -..._, ,_ -..,...-...-!
14 15 Nl 11 12 13 14 15 Nl

11 12 13

Propagation photoperiod

Figure 6. Plant height and number of nodes at ﬂowering for unpinched Phlox
paniculata ‘David’ plants. Error bars represent standard error of the mean.

97

Rep. 1 Rep. 2

 

90

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A B
80* ;L 1r l
l' ;__
,g 70 1 di/‘ 4
E 60*
.9
:‘c’
50‘r T W
+0wksat5°C
40* —o—2wksat5°C 1' H
+5wksats°c
30 1 A _J. A A ’1’: 1 ..-_-_L_ 1 1 L L ’1’! .—
C T D
254
In
*8 ‘ ’ /. \ / ¥
2 20* \ % .i f
“s . «
B
E 151
:3
2
J
wt
5 g e e . *—--*—lr’ . — s e e%-——e——-—rr—--+-—a
E
A 8 + 4
o' | I
S .
g 6‘ ‘ T I I
2 If T I
m __
8’ \ /. ..
'c 41 T I -— ‘-
0 T
3
_g
u. 2. 4
0 7 T r r Y ii . . r r r V ;/ T
11 12 13 14 15 NI 11 12 13 14 15 Nl
Propagation photoperiod

Figure 7. Plant height, node number, and number of ﬂowering stems for pinched
Phlox paniculata ‘David’ plants. Error bars represent standard error of the mean.

98

Thesis Conclusion

Research described in this thesis has successfully quantiﬁed the
information necessary for the quick-crop production method. This method
provides a successful alternative protocol for production of uniform, disease-free,
and rapid-ﬂowering herbaceous perennials. Using the quick-crop protocol,
growers will be able to produce herbaceous perennials rapidly, uniformly, and
efﬁciently year-round, thus eliminating the problems associated with current
herbaceous perennial production. Although more cultural and environmental
information is still required for these species, the production of herbaceous
perennials for a speciﬁc market date is possible with the quick-crop production

method.

99

 

APPENDIX A

THE FLOWERING RESPONSE OF LEUCANTHEMUM XSUPERBUM'
‘SNOWCAP’ TO COLD DURATION

100

Research Objective
The objective of this research project was to determine the minimum cold
duration required for rapid and uniform ﬂowering of Leucanthemum xsuperbum

‘Snowcap’.

Materials and Methods

Plant material. Leucanthemum xsuperbum ‘Snowcap’ stock plants were
potted (Sept. 1999) in 13-cm square plastic containers (1.1 L) ﬁlled with a
commercial soilless medium composed of pine bark, ﬁbrous Canadian sphagnum
peat, horticultural vermiculite, and screened course perlite, along with a wetting
agent and starter fertilizer charge (Suremix Perlite; Michigan Grower Products,
Galesburg, Mich). Plants were grown under a 12—h photoperiod provided by
supplementing natural daylength with lighting from high-pressure sodium lamps
from 0800 to 2000 HR. Stock plants were pinched at 3- to 4-week intervals to
ensure continued branching and cutting production.

Harvested cuttings were propagated in 72-cell (0.03-L) plug trays
(Landmark Plastic Corporation, Akron, Ohio) containing a mixture of 50%
commercial medium (Suremix Perlite; Michigan Grower Products, Galesburg,
Mich.) and 50% screened course perlite (Therm-O-Rock; East, Inc., New Eagle,
Pa.). Basal portions of each cutting were dipped in a 1500-ppm solution of liquid
auxin (1% indoIe-3-butryic acid and 0.5% naphthaleneacetic acid; DIP ’N GROW;
Astoria-Paciﬁc, Clackamas, Ore.). Propagation air temperatures were

maintained at 23 °C and bottom heat (soil temperature) was maintained at 25 °C.

101

"T‘T‘l.

A vapor pressure deﬁcit of 0.3 kPa was maintained by injecting water vapor as
needed. Cuttings were rooted and weaned from propagation 3 weeks after
sticking.

Plant culture. Plants were grown (bulked) in the plug trays for an
additional 3 weeks in the greenhouse at 20 °C in order to establish root systems
and increase vegetative growth before cold treatment. Photoperiod was
maintained at 12 h as on the stock plants. Following cold treatment, plugs were
. potted in 13-cm square plastic containers (1.1 L) containing the same
commercial medium used for the stock plants. Plants were forced to ﬂower
under a 16-h photoperiod (natural days supplemented with high-pressure sodium
lamps from 0530 to 2130 HR). Plants were top-watered as necessary with well
- water acidiﬁed with sulfuric acid to a titratable alkalinity of approximately 130 mg
calcium bicarbonate per liter and containing water-soluble fertilizer providing 125
N, 12 P, 125 K, 13 Ca (mg'L’1; 30% ammoniacal N) plus (mg'L‘) 1.0 Fe, 0.5 Mn,
0.5 Zn, 0.5 Cu, 0.1 B, 0.1 Mo (MSU Special; Greencare Fertilizers, Chicago, Ill).

Cold treatments. Plugs received no cold treatment or were placed in a
controlled-environment chamber for 1, 2, 3, 4, or 5 weeks at 5 °C. The chamber
was lit from 0800 to 1700 HR by cool-white ﬂuorescent lamps (F96T12/CWNHO;
Philips, Somerset, N.J.) at a photosynthetic photon ﬂux (PPF) of approximately
10 j.imol'm‘2's'1 at plant height. While in the cooler, plants were watered as
needed with well water acidiﬁed with sulfuric acid to an approximate pH of 6.0.

Greenhouse temperature control. Plants were grown in glass

greenhouses set at 20 °C. Greenhouse temperatures were controlled by a

102

 

greenhouse climate-control computer (Model CD750; Priva, De Lier, The
Netherlands). Average daily temperature and daily light integral (DLI) were
monitored with a CR-10 datalogger (Campbell Scientiﬁc, Logan, Utah) by using
36-gauge (0.013 mm in diameter) type E thermocouples and a quantum sensor
(Model Ll-189; LI-COR, lnc., Lincoln, Neb.), respectively. The datalogger
collected data every 10 seconds and recorded the hourly average. Actual
average daily temperatures and DLIs for the beginning of forcing to the average
date of ﬂowering were calculated and are presented in Table 1.

Data collection and analysis. Dates of visible bud and ﬁrst ﬂower were
recorded, as well as plant height, node number, and ﬂower bud number at ﬂower.
A completely randomized design with 10 observations for each cold treatment
was used. Data were analyzed using SAS’s (SAS Institute, Cary, NC.) analysis

of variance (ANOVA) and general linear models (GLM) procedures. Since the

' , variances for days to Visible bud, days from visible bud to ﬂower, and days to

ﬂower were not homogeneous, a log transformation was done on the data before

ANOVA and GLM were performed.

Results and Discussion

All L. xsuperbum ‘Snowcap‘ plants ﬂowered completely under long days
with or without a cold treatment (Table 2). However, as cold duration increased
from 0 to 5 weeks, time to ﬂower and variability within treatments decreased

(Figure 1, Table 2). Plants exposed to a 5—week cold treatment ﬂowered 20 days

103

sooner and the number of nodes was also reduced by four to ﬁve (Figures 1 and
2A).

The number of nodes formed at ﬂowering decreased linearly as cold
duration increased (Figure 2A, Table 2). Plant height increased and then
decreased quadratically as cold duration increased (Figure 2B). Flower number
and days from visible bud to ﬂower were not affected by increasing cold
durations (Figure 2C, Table 2).

The L. xsuperbum (formerly Chrysanthemum xsuperbum or C. maximum)
cultivars Becky, Snowcap, and Snow Lady ﬂower completely without cold,
providing they are forced to ﬂower under long photoperiods (Engle, 1994; Kessler
and Keever, 2000; Yuan, 1995). Several experiments have shown that
increased cold durations reduce time to ﬂower in L. xsuperbum (Kessler and
Keever, 2000; Runkle, 1996; Yuan, 1995). Runkle et al. (1998) showed that
complete ﬂowering of L. xsuperbum ‘Snowcap’ under a night interruption (NI)
photoperiod required no more than 3 weeks of cold (5 °C). In contrast, Shedron
and Weiler (1982) showed that ‘G. Marconi’ (C. xsuperbum Bergmans) required
between 12 and 16 weeks of cold treatment for 100% ﬂowering. According to
Runkle et al. (1998), desirable responses (e.g., increased ﬂowering percentage,
improved uniformity, reduced time to ﬂower, and increased ﬂower number) to
exposure to 5 °C for L. xsuperbum ‘Snowcap' were saturated after 6 weeks when

plants were subsequently forced under NI.

104

 

Conclusions

Although L. xsuperbum ‘Snowcap’ ﬂowers completely without a cold
treatment, time to flower is reduced and crop uniformity is increased following a
cold treatment. Therefore, at least a 5-week cold treatment followed by long

days (316 h) is recommended for ﬂowering of L. xsuperbum ’Snowcap’.

Literature Cited

Engle, BE. 1994. Useiof light and temperature for hardening of herbaceous
perennial plugs prior to storage at -—2.5C. MS Thesis, Michigan State
Univ., East Lansing.

Kessler, J.R., Jr. and G.J. Keever. 2000. Shasta daisy response to
photoperiod and vernalization. Southeastern Floriculture 10:22—24.

Runkle, ES. 1996. The effects of photoperiod and cold treatment on ﬂowering
of twenty-ﬁve species of herbaceous perennials. MS Thesis, Michigan
State Univ., East Lansing.

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 33:1003—1006.

Shedron, KC. and TC. Weiler. 1982. Regulation of growth and ﬂowering in
Chrysanthemum xsuperbum Bergmans. J. Amer. Soc. Hort. Sci.
107:874—877.

Yuan, M. 1995. The effects of juvenility, temperature, and cultural practices on

ﬂowering of Coreopsis, Gaillardia, Leucanthemum, Heuchera, and
Rudbeckia. MS Thesis, Michigan State Univ., East Lansing.

105

Table 1. Dates of forcing, average daily temperatures, and average daily light integrals (DLI)
from dlate of forcing to average date of ﬂoweringfor Leucanthemum xsuperbum ‘Snowcap’.

 

Average

Date of Weeks temperature Average DLI
forcing of 5 °C (° C) (mol-m'z-d”)

2/1/00 0 21.3 13.3

2/8/00 1 21.6 14.6
2/15/00 2 21.3 14.3
2/22/00 3 21.4 14.7
2/29/00 4 21.3 15.3
3/10/00 5 21.2 15.7

 

106

.-‘Ag*“_‘—A

 

Table 2. Signiﬁcance of cold treatment on ﬂowering of Leucanthemum xsuperbum
‘Snowcap’.

 

 

 

Days to Days from Days Final Final
Weeks Flowering visible visible bud to node plant Flower
of 5 °C oerce@e bud to ﬂower ﬂower number height (cm) number
0 100 44 23 67 16 28.3 11
1 100 44 24 68 17 30.1 12
2 100 35 24 59 15 28.7 11
3 100 30 25 55 14 29.5 12
4 100 26 25 51 13 28.1 13
5 100 22 25 47 12 26.3 12
Signiﬁcance
Weeks of cold ' *“ NS “* *"' “* NS
95% Conﬁdence intervals (weeks at 5 °C)
0 5.99 3.54 6.73 2.22 0.82 1.73
1 2.99 2.93 4.03 1.19 1.29 1.73
2 4.85 1.17 4.81 1.90 1.19 2.69
3 2.05 1.25 2.51 0.91 0.77 1 59
4 1.69 1.55 2.94 1.15 0.92 1.43
5 1.10 1.25 1.15 1.05 0.70 1.52
Contrasts
PLinear in N S iii a“ eta N S
Pmadrauc NS NS NS NS ‘“ NS

 

NS' Nonsigniﬁcant or significant at P _<_ 0.001.

107

 

 

 

80

70- J
60‘ M d

401

Days
J.
/
141

 

 

 

 

30 -t -
Pat—Q
20 - -
10 l l I l l I
o 1 2 3 4 5
Weeks of 5 °C

Figure 1. The effects of cold treatment on days to visible bud (0), days from
visible bud to ﬂowering (o), and days to ﬂower (V) for Leucanthemum
xsuperbum‘ Snow Cap’. Error bars represent 95% conﬁdence intervals.

108

 

 

20

18*

16-

 

14~

 

Number of nodes

 

12 ~ ~
10

30. _ A\ .
t/}\? \E\i

25* *

 

 

20“ -1

Height (cm)

15- «

 

10

14 4 «
T
a \
12 *1 ’/ \i ‘

Number of ﬂower buds
CD

 

 

 

0 I T r T l

o 1 2 3 4
Weeks of 5 °C

”'1

Figure 2. The effects of cold treatment on node number (A), plant height (B), and
ﬂower bud number (C) of Leucanthemum xsuperbum ’Snow Cap’. Error bars
represent 95% conﬁdence intervals.

109

 

 

APPENDIX B
THE FLOWERING RESPONSE or ACHILLEA ‘MOONSHINE’ TO COLD

DURATION, PROPAGATION PHOTOPERIOD, AND BULKING DURATION
AND PHOTOPERIOD

110

Research Objective

The ﬁrst objective of this research project was to determine the minimum
cold duration required for rapid and uniform ﬂowering of Achillea ‘Moonshine’.
The second objective was to determine whether propagation photoperiod affects
time to ﬂower of Achillea ‘Moonshine’. The ﬁnal objective was to determine
whether the duration of and photoperiod during bulking affected time to ﬂower

and overall ﬂowering quality of Achillea ‘Moonshine’.

Materials and Methods

Cold-duration experiment. Achillea ‘Moonshine’ stock plants were potted
(Sept. 1999) in 13—cm square plastic containers (1.1 L) ﬁlled with a commercial
soilless medium composed of pine bark, fibrous Canadian sphagnum peat,
horticultural vermiculite, and screened course perlite, along with a wetting agent
and starter fertilizer charge (Suremix Perlite; Michigan Grower Products,
Galesburg, Mich.) Plants were grown under a 12-h photoperiod provided by
supplementing natural daylengths with lighting from high-pressure sodium lamps
from 0800 to 2000 HR. Stock plants were pinched at 3- to 4-week intervals to
ensure continued branching and cutting production.

Harvested cuttings were propagated in 72-cell (0.03-L) plug trays
(Landmark Plastic Corporation, Akron, Ohio). Following propagation, plants were
grown (bulked) in the plug trays for an additional 3 weeks in a greenhouse at 20
°C to establish root systems and increase vegetative growth before cold

treatment. Photoperiod was maintained at 12 h as on the stock plants.

111

Plugs then received no cold treatment or were placed in a controlled-
environment chamber for 1, 2, 3, 4, or 5 weeks at 5 °C. The chamber was
lighted from 0800 to 1700 HR by cool-white ﬂuorescent lamps (F96T12/CWNHO,
Philips, Somerset, N.J.) The photosynthetic photon ﬂux (PPF) from the lamps
was approximately 10 umol'm'z's'1 at plant height. While in the cooler, plants
were watered as needed with well water acidiﬁed with sulfuric acid to an
approximate pH of 6.0. Following each cold duration, half of the plants in each
treatment were soft pinched (one node removed).

Propagation-photoperiod experiment. Achillea ‘Moonshine’ cuttings were
received from Guatemala on Feb. 15 and again on Mar. 13, 2002. Cuttings were
propagated in 72-cell (0.04-L) plug trays (Landmark Plastic Corporation, Akron,

- Ohio) under one of six photoperiods: 11, 12, 13, 14, or 15 h of continuous light,
or 9 h with a 4-h night interruption (NI). Natural photoperiods were extended with
incandescent lamps. For continuous photoperiodic treatments, lamps were
turned on at 1700 HR and turned off after each photoperiod was completed. The
NI was delivered from 2200 to 0200 HR.

Bulking duration and photoperiod experiment. Achillea ‘Moonshine’
cuttings were received from Guatemala on Dec. 31, 2001. Cuttings were
propagated under natural photoperiods in 50-cell (0.08-L) plug trays (Landmark
Plastic Corporation, Akron, Ohio).

Plants were grown (bulked) in the plug trays for 2, 4, or 6 weeks in a

greenhouse at 20 °C under one of three photoperiods: 10, 12, or 13 h. Natural

112

photoperiods were extended with incandescent lamps. Lamps were turned on at
1700 HR and turned off after each photoperiod was completed.

Propagation environmental control. Plug trays contained a mixture of 50%
commercial medium (Suremix Perlite; Michigan Grower Products, Galesburg,
Mich.) and 50% screened course perlite (Therm-O-Rock; East, Inc., New Eagle,
Pa.). Basal portions of each cutting were dipped in a 1500-ppm solution of liquid
auxin (DIP ’N GROW; Astoria-Paciﬁc, Clackamas, Ore.) before stick.
Propagation air temperatures were maintained at 23 °C and bottom heat (soil
temperature) was maintained at 25 °C. A vapor pressure deﬁcit of 0.3 kPa was
maintained by injecting water vapor as needed. Cuttings were rooted and
weaned from propagation 3 weeks after sticking.

General plant culture. Plugs were potted in 13«cm square plastic
containers (1.1 L) containing the same commercial medium used for stock plants
in the cold-duration experiment. All plants were forced to ﬂower under a 16-h
photoperiod, natural daylengths supplemented with lighting from high-pressure
sodium lamps from 0530 to 2130 HR. Plants were top-watered as necessary with
well water acidiﬁed with sulfuric acid to a titratable alkalinity of approximately 130
mg calcium bicarbonate per liter and containing water-soluble fertilizer providing
125 N, 12 P, 125 K, 13 Ca (mg-L", 30% ammoniacal N) plus (mg-L") 1.0 Fe, 0.5
Mn, 0.5 Zn, 0.5 Cu, 0.1 B, 0.1 Mo (MSU Special; Greencare Fertilizers, Chicago,
III). For the bulking photoperiod and duration and propagation photoperiod
experiments, plants received additional Cu at 0.5 mg'L'1 and B at 0.1 mg'L'1 at

every watering.

113

Greenhouse temperature control. Plants were grown in glass
greenhouses set at 20 °C. Greenhouse temperatures were controlled by a
greenhouse climate-control computer (Model CD750; Priva, De Lier, The
Netherlands). Average daily temperature and daily light integral were monitored
with a CR-10 datalogger (Campbell Scientiﬁc, Logan, Utah) by using 36-gauge
(0.013 mm in diameter) type E thermocouples and a quantum sensor (Model LI-
189; Ll-COR, lnc., Lincoln, Neb.), respectively. The datalogger collected data
every 10 seconds and recorded the hourly average. Actual average daily
temperatures and daily light integrals (cold duration experiment only) for the
beginning of forcing to the average date of ﬂowering were calculated and are
presented in Table 1.

Data collection and analysis. Dates of visible bud and ﬁrst ﬂower as well
as height at ﬂowering were recorded. For all experiments except cold duration,
the number of nodes at ﬂower was also recorded. A completely randomized
design was used. Data were analyzed using SAS’s (SAS Institute, Cary, NC.)

analysis of variance (ANOVA) and general linear models (GLM) procedures.

Results and Discussion

Cold-duration experiment. All plants ﬂowered regardless of cold
treatment. Days to visible bud and days to ﬂower were not signiﬁcantly affected
by cold treatment. Pinching did signiﬁcantly affect time to ﬂower (Table 2).
Pinched plants ﬂowered three to 10 days later than unpinched plants, depending
on duration of cold treatment (Figure 1). In general, as duration of cold

increased, the delay in ﬂowering between pinched versus unpinched plants also

114

increased. Height was not signiﬁcantly affected by cold duration or pinching.
Since plants ﬂowered completely without a cold treatment and increased cold
durations did not signiﬁcantly affect days to ﬂower, all other Achillea ‘Moonshine’
experiments were conducted without a cold treatment.

Propagation photoperiod. The photoperiod during propagation had a
small but signiﬁcant effect on days to ﬂower for replicate one but was not
signiﬁcant for replicate two (Table 3, Figure 2A and B). Height was signiﬁcantly
affected by propagation photoperiod for replicate one, with plants propagated
under a 15-h photoperiod being slightly taller (Figure 2C). However, height was
not signiﬁcantly different between treatments in replicate two (Figure ZD). In
replicate one, propagation photoperiod did not affect the number of nodes formed
at ﬂowering (Figure 2C). All treatments had 13 or 14 nodes at ﬂowering. In.
replicate two, propagation photoperiod had a signiﬁcant linear effect on the
number of nodes formed, whichstended to decrease as propagation photoperiod
increased (Figure 20). Achillea ‘Moonshine’ plants in replicate two took an
average of ﬁve days longer to ﬂower than plants in replicate one. Temperatures
between the two replicates differed only by 0.4 °C, so the difference was not
likely due to temperature.

In the ﬁrst replicate of the experiment, plants from each propagation
photoperiod were also forced under short days (9-h photoperiod) to determine
whether exposure to potentially reproductive photoperiods in propagation was
sufﬁciently long enough to induce ﬂowering. Since only three plants ﬂowered

(one plant from 15 h and two plants from NI, data not presented), we concluded

115

 

that the duration of propagation was not long enough to induce ﬂowering.
Following 15 weeks of 9-h photoperiods, the plants were moved to a 16-h
photoperiod. After 60 days in long days, the plants were still growing
vegetatively. It appears that after extended exposure to short photoperiods,
Achillea ‘Moonshine’ will not ﬂower under long days and develops an obligate
vernalization requirement. Cuttings rooted under an 11-, 12-, or 13-h
photoperiod had better root development than cuttings rooted under a 14-h, 15-h,
or NI photoperiod, but no data were collected.

Bulking duration and photoperiod. All plants ﬂowered regardless of
treatment combination. The duration of bulking, but not bulking photoperiod,
signiﬁcantly affected days to visible bud, days from visible bud to ﬂower, and
days to ﬂower from the start of long days (Table 4). As bulking duration
increased, days to visible bud increased and days from visible bud to ﬂower
decreased (Table 4, Figure 3A and B). As bulking duration increased, time to
ﬂower for plants bulked under a 10- or 12-h photoperiod increased linearly. Plant
height was signiﬁcantly affected by bulking photoperiod but not bulking duration
(Figure 4A). Bulking duration signiﬁcantly affected the number of nodes present
at ﬂowering. As bulking duration increased, the number of nodes increased
linearly, regardless of bulking photoperiod (Figure 4B). Perhaps, as experienced
by the Gaura Iindheimeri ‘Whirling Butterﬂies’ plants grown under a 9-h
photoperiod in the propagation photoperiod experiment, the bulking photoperiods

were short enough to delay ﬂowering as bulking duration increased.

116

 

Unresolved Issues Requiring Further Research

The bulking duration and photoperiod requires replication to solidify the
validity of the results.

The effects of propagation photoperiod on the rooting of Achillea
‘Moonshine’ cuttings should be examined. Although propagation photoperiod did
not affect time to ﬂower, it appeared to affect the rooting quality of cuttings.

It still remains unclear what environmental conditions before forcing to
ﬂower produce plants with multiple ﬂowering stems. All unpinched plants had a
single ﬂowering stem. For the bulking duration and photoperiod experiment, only
one bulking temperature wasused. Perhaps temperatures lower than 20 °C
during the bulking period would increase the number of ﬂowering shoots per
plant without pinching.

Achillea ‘Moonshine’ plants exposed to prolonged durations of short days
(9—h photoperiod for 15 weeks) developed an obligate cold requirement.
Regardless of photoperiod following this extended short-day exposure, plants
grew vegetatively. However, the number of short days needed before plants
require cold treatment is unknown, and the subsequent minimum cold duration

required for ﬂowering is also unknown.

117

Table 1. Dates of forcing, average daily temperatures, and average daily light integral

(DLI) from date of forcing to average date of ﬂowering for Achillea ‘Moonshine’.

 

 

Average Average
Date of Weeks of Weeks temperature DLI
forcing bulkigg of 5 °C (° C) (moI-m'Z-d")
Cold-duration experiment
2/1/00 3 0 19.8 12.1
2/8/00 3 1 19.7 12.0
2/15/00 3 2 19.4 11.8
2/22/00 3 3 19.3 13.3
2/29/00 3 4 19.1 14.4
3/10/00 3 5 19.0 16.0
Propagation photoperiod experiment
Replicate 1
3/14/02 0 (16-h force) 0 21.8 16.5
3/14/02 0 (9-h force) 0 20.3 13.5
Replicate 2
4/16/02 0 (16-h force) 0 22.2 17.8
Bulking duration and photoperiod experiment
1/29/02 2 0 199 «2
2/13/02 4 0 20.0 -
2/27/02 6 0 20.5 -

 

zDashes indicate data not presented.

118

Table 2. The effects of cold duration on ﬂowering of Achillea ‘Moonshine’.
Days to Days from

 

 

 

 

Weeks of Flowering visible VB to Days to Final plant
5 °C Pinch Percentage bud (VB) ﬂower ﬂower height (cm)
21 24 45 45
No 17 25 43 46
Yes 24 23 47 45
0 21 23 44 45
1 20 26 47 45
2 25 23 48 46
3 19 23 43 46
4 21 24 45 45
5 19 24 43 47
0 No 100 20 25 45 45
Yes 100 26 21 47 44
1 No 100 19 28 47 44
Yes 100 22 25 47 46
2 No 100 23 23 46 47
Yes 100 26 23 49 46
3 No 100 17 23 40 47
Yes 100 21 24 45 45
4 No 100 18 25 43 46
Yes 100 24 '23 47 43
5 No 100 15 25 40 48
Yes 100 25 21 46 46
Signiﬁcance
Weeks of cold NS * NS NS
Pinch ** “ ** NS
Cold X Pinch NS NS NS NS
Contrasts
Pinched plants
Cold NS NS NS NS
Pm“, NS NS NS NS
P Quadratic NS . NS NS
Unpinched plants
Cold NS NS NS NS
Pm“, NS NS NS NS
Pguadmc NS NS NS NS
Ns."."*

Nonsigniﬁcant or signiﬁcant at P 5 0.05 or 0.01, respectively.

119

Table 3. The effects of propagation photoperiod on ﬂowering of Achillea ‘Moonshine’.

Days to Days from
Propagation Flowering visible bud V8 to Days to Final plant Nodes at

 

 

 

 

 

photoperiod Percentage (VB) ﬂower ﬂower height (cm) ﬂower
Replicate 1
32 15 47 31 14
1 1-h 100 30 17 47 30 14
12-h 100 33 16 48 32 14
13-h 100 31 14 45 31 14
14-h 100 31 13 44 30 14
15-h 100 37 15 53 34 14
Nl 7O 29 15 44 30 13
Signiﬁcance
Photoperiod NS NS * “ NS
Contrasts
F)Linear . NS NS * NS
P uadratic NS * * NS NS
Replicate 2
36 17 52 33 15
11-h 100 39 16 ' 55 31 17
12-h 100 37 16 53 33 15
13-h 100 38 15 54 32 15
14-h 100 35 17 51 33 15
15—h 100 32 g 18 50 33 13
NI 100 34 17 50 34 15
Signiﬁcance
Photoperiod NS * NS NS "
Contrasts
Pm“.r * NS * NS *‘
Pguadmc NS ** NS NS NS
NS...“

 

 

Nonsigniﬁcant or Signiﬁcant at P _<_ 0.05 or 0.01, respectively.

120

Table 4. The effects of bulking duration and photoperiod on ﬂowering of Achillea ‘Moonshine’.

 

 

Weeks of Days to Days from
bulking at Bulking Flowering visible bud VB to Days to Final plant Nodes at
20 °C photoperiod Percentage (VB) flower ﬂower height (cm) ﬂower
100 31 19 50 40 18
10-h 100 30 20 50 41 18
12-h 100 31 19 50 39 18
13-h 100 31 20 51 41 17
2 100 27 21 48 40 15
4 100 31 21 52 41 17
6 100 34 17 51 40 21
2 10-h 100 25 22 47 40 15
12-h 100 28 20 48 40 16
1 3-h 100 29 21 50 40 14
4 10-h 100 32 21 53 43 17
12-h 100 30 21 51 38 16
13-h ' 100 31 21 53 41 18
6 10-h 100 34 17 51 41 21
12-h 100 36 16 52 39 22
13-h 100 33 17 50 40 20
Signiﬁcance
Bulk duration (BD) *“ “* *“ NS ”*
Bulk photoperiod (BP) NS NS NS ** NS
80 X BP * NS NS NS “
10-h photoperiod
Bulk duration *** '** *“ NS ""*
PLinear iii em. in NS a“
POuadratic NS *‘ “ NS
12-h photoperiod
Bulk duration *** “* 1... NS ***
PLinear it". it! tit N S tit
Pommm NS *** NS NS "
13-h photoperiod
Bulk duration * *** NS NS *“
PLinear *t tit NS NS m
Pguadratic NS " . NS NS

 

 

. it t“
NS! 9 I

121

Nonsigniﬁcant or signiﬁcant at P _<_ 0.05, 0.01, or 0.001, respectively

60

 

 

 

 

 

 

 

 

 

 

Unpinched
50 «
40 ~
30 -
20 ~
10 1
(I)
a O I I T I I I
D Pinched
50 A i__}/i\ 4%
40 ~
30 -
O
" ‘.‘ ‘0. ‘.<
20 _ O O
10 4 + Visible Bud (VB)
—0— VB to ﬂower
+ Flower
0 I I I I I I
o 1 2 3 4 5

Weeks at 5 °C

Figure 1. Time to ﬂower for unpinched versus pinched plants of Achillea
‘Moonshine’. Error bars represent standard error of the mean.

122

Replicate 1 Replicate 2

I + Visible bud (VB)I A B
60 ‘ —0— V3 to ﬂower ~

+ Flower I
50 4 M d W i
i

40 *
/§ I M\
30 . f/H—O/ {T

70

 

 

 

Days

I-O-‘l
IOI

20‘ J W o
W D

10*

 

 

 

 

 

 

 

 

40 — ;'I—— //~~— 20
1} C § D ~ 18
3° A‘ I i J 3X5 45:4 t ’ 16
<>———§——<>— .———{2 ~ ‘ \ l 14
75 § \5' 12
8.
E 20 1 1r 10
.9 l
a * '8
. 6
10 ~ - -
__ _j 4 {L4
F—OM Height I j
l —<>— Nodeﬂ . j 2
0 #5:?“ 4 w 1 T --//- T —- s 4 .——-~.--— ——————— /)———-—.—-—-~- 0
11 12 13 14 15 Ni 11 12 13 14 15 Nl
Propagation photoperiod

Figure 2. Flowering response of Achillea ‘Moonshine’ to propagation
photoperiod. Days to visible bud (0), days from visible bud to ﬂower (0), and
days to ﬂower (V) are presented for replicates 1 (A) and 2 (B). Height (0) and
number of nodes (0) are presented for replicates 1 (C) and 2 (D). Error bars
represent standard error of the mean.

123

Nodes (no.)

60

 

50*

40a

30*

20*

Days to visible bud (VB)

10*

60 r

 

50*

4o-

30*

Days from V8 to ﬂower

10]

60

20 - p—T—N

 

 

 

50 a M \ii

 

 

5 40 *
3
o
C
9 30 ~
(I)
>
(I)
D 20.
Photoperiod
10 . + 10-h
—o— 12-h
+ 13-h
o _m'T ‘
1 2

Figure 3. Time to ﬂower, days to visible bud (A), days from visible bud to ﬂower
(B), and days to ﬂower (C), for Achillea ‘Moonshine’ bulked under a 10- (o), 12-
(0), or 13—h (V) photoperiod. Error bars represent standard error of the mean.

I T T

3 4 5 6
Weeks of bulking at 20 °C

4‘

124

 

 

 

 

50

 

 

 

 

 

 

 

 

 

 

A
40 d AN _
M 45
’E‘ 30 ~ .
8
E
.9
i’ 20 - .
10 ~ ~
0
B
20 .1 A _,
15 a 4
(D
ID
.0
O
z
10 ~ -
5 . Photoperiod *
—o— 10-h
—o— 12-h
—v— 13-h
0 I T I T I
1 2 3 4 5 6 7

Weeks of bulking at 20 °C

Figure 4. Height (A) and number of nodes (B) at ﬂower for Achillea ‘Moonshine’
bulked under a 10- (o), 12- (0), or 13-h (V) photoperiod. Error bars represent
standard error of the mean.

125

APPENDIX C
THE FLOWERING RESPONSE OF GAURA LINDHEIMERI WHIRLING

BUTTERFLIES’ AND ‘SISKIYOU PINK' TO COLD DURATION AND BULKING
DURATION AND PHOTOPERIOD

126

Research Objective

The ﬁrst objective of this research project was to determine the minimum
cold duration required for rapid and uniform ﬂowering of Gaura Iindheimeri
‘Whirling Butterﬂies’. The second objective was to determine whether the
duration of and photoperiod during bulking affected time to ﬂower and overall

ﬂowering quality of G. Iindheimeri ‘Whirling Butterﬂies' and 'Siskiyou Pink’.

Materials and Methods

Cold-duration experiment. Gaura Iindheimeri Whirling Butterﬂies’ stock
plants were potted (Sept. 1999) in 13—cm square plastic containers (1.1 L) ﬁlled
with a commercial soilless medium composed of pine bark, ﬁbrous Canadian
sphagnum peat, horticultural vermiculite, and screened course perlite, along with
a wetting agent and starter fertilizer Charge (Suremix Perlite; Michigan Grower
Products, Galesburg, Mich). Plants were grown under a 12-h photoperiod
provided by supplementing natural daylengths with lighting from high-pressure
sodium lamps from 0800 to 2000 HR. Stock plants were pinched at 3- to 4-week
intervals to ensure continued branching and cutting production.

Harvested cuttings were propagated in 72-cell (0.03-L) plug trays
(Landmark Plastic Corporation, Akron, Ohio). Following propagation, plants were
grown (bulked) in the plug trays for an additional 3 weeks in a greenhouse at 20
°C to establish root systems and increase vegetative growth before cold
treatment. Photoperiod was maintained at 12 h as on the stock plants.

Plugs then received no cold treatment or were placed in a controlled-

environment chamber for 1, 2, 3, 4, or 5 weeks at 5 °C. Plugs were pinched

127

before cold treatment to remove any ﬂowers. The chamber was lit from 0800 to
1700 HR by cool-white ﬂuorescent lamps (F96T12/CWNHO, Philips, Somerset,
N.J.) The photosynthetic photon ﬂux (PPF) from the lamps was approximately
10 umol'm'z's'1 at plant height. While in the cooler, plants were watered as
needed with well water acidiﬁed with sulfuric acid to an approximate pH of 6.0.

Bulking duration and photoperiod experiment. Gaura Iindheimeri Whirling
Butterflies’ and ‘Siskiyou Pink’ cuttings were received from Guatemala on Dec.
31, 2001, Jan. 17,2002 (‘Whirling Butterﬂies’ only) and Feb. 15, 2002. Cuttings
were propagated in 50-cell (0.08-L) plug trays (Landmark Plastic Corporation,
Akron, Ohio).

After propagation, plants were grown (bulked) in the plug trays for 2, 4, or
6 weeks in a greenhouse at 20 °C under one of three photoperiods: 9, 10, or 12
h. Natural photoperiods were extended with incandescent lamps. Lamps were
turned on at 1700 HR and turned off after each photoperiod was completed.

Propagation environmental control. Plug trays contained a mixture of 50%
commercial medium (Suremix Perlite; Michigan Grower Products, Galesburg,
Mich.) and 50% screened course perlite (Therm-O-Rock; East, Inc., New Eagle,
Pa.). Basal portions of each cutting were dipped in a 1500-ppm solution of liquid
auxin (DIP ’N GROW; Astoria-Paciﬁc, Clackamas, Ore.) before stick.
Propagation air temperatures were maintained at 23 °C and bottom heat (soil
temperature) was maintained at 25 °C. A vapor pressure deﬁcit of 0.3 kPa was

maintained by injecting water vapor as needed. Cuttings were propagated under

128

natural photoperiods and were rooted and weaned from propagation 2 weeks
after sticking.

General plant culture. Following bulking treatment, plugs were potted in
13-cm square plastic containers (1.1 L) containing the same commercial medium
used for the stock plants in the cold—duration experiment. All plants were forced
to ﬂower under a 16-h photoperiod, natural daylengths supplemented with
lighting from high-pressure sodium lamps from 0530 to 2130 HR. Plants were
tap-watered as necessary with well water acidiﬁed with sulfuric acid to a titratable
alkalinity of approximately 130 mg calcium bicarbonate per liter and containing
water-soluble fertilizer providing 125 N, 12 P, 125 K, 13 Ca (mg'L'1; 30%
ammoniacal N) plus (mg'L'1) 1.0 Fe, 0.5 Mn, 0.5 Zn, 0.5 Cu, 0.1 B, 0.1 Mo (MSU
Special; Greencare Fertilizers. Chicago, Ill). Plants in the bulking duration and
photoperiod experiment received additional Cu at 0.5 mg'L" and B at 0.1 mg‘L'1
with every watering.

Greenhouse temperature control. Plants were grown in glass
greenhouses set at 20 °C. Greenhouse temperatures were controlled by a
greenhouse climate-control computer (Model CD750; Priva, De Lier, The
Netherlands). Average daily temperature and daily light integral were monitored
with a CR-10 datalogger (Campbell Scientiﬁc, Logan, Utah) by using 36-gauge
(0.013 mm in diameter) type E thermocouples and a quantum sensor (Model LI-
189; Ll-COR, lnc., Lincoln, Neb.), respectively. The datalogger collected data
every 10 seconds and recorded the hourly average. Actual average daily

temperatures and daily light integrals (cold duration experiment only) from the

129

beginning of forcing to the average date of ﬂowering were calculated and are
presented in Table 1.

Data collection and analysis. Dates of visible bud and ﬁrst ﬂower as well
as height at ﬂowering were recorded. For the cold-duration experiment, the
number of new leaves formed was also recorded. For the bulking duration and
photoperiod experiment, the number of ﬂowering stems for ‘Whirling Butterﬂies’
and the number of lateral inﬂorescences for ‘Siskiyou Pink’ were recorded. A
completely randomized design was used. Data were analyzed using SAS’s (SAS
Institute, Cary, NC.) analysis of variance (ANOVA) and general linear models

(GLM) procedures.

Results and Discussion

Cold-duration experiment. All G. Iindheimeri ‘Whirling Butterﬂies’ plants
ﬂowered regardless of cold treatment. The number of weeks at 5 °C had a
signiﬁcant effect on days to visible bud, days to ﬂower, and ﬁnal plant height
(Table 2). As cold duration increased, time to visible bud and ﬂower tended to
decrease linearly. However, as cold duration increased, plant height at ﬁrst open
ﬂower tended to increase linearly.

Cuttings were removed from reproductive stock plants. Flowers had to be
removed from the plugs before cold treatment. Therefore, time to ﬂower may not
be accurate for plants that were completely vegetative at the start of cold. Since

there was little difference in time to ﬂower, and since cold-treated plants were

130

taller, all other G. Iindheimeri experiments were conducted without a cold
treatment.

Bulking duration and photoperiod experiment.

Gaura Iindheimeri ‘Whirling Butterflies’. All plants, regardless of
replicate or treatment combination, eventually ﬂowered. For replicate one,
bulking duration had a signiﬁcant effect on all measured ﬂowering responses
(Table 3). Bulking photoperiod had a signiﬁcant effect on days to visible bud,
days from visible bud to ﬂower, and days to ﬂower. Plants bulked under a 12-h
photoperiod ﬂowered faster than plants bulked under the other photoperiods
(Table 3, Figure 1A). As bulking duration increased, there was little change in
time to ﬂower, but the number of ﬂowering stems decreased (Figure 1G). Plants
bulked for 4 weeks, irrespective of photoperiod, ﬂowered fastest. Plant height
decreased as bulking photoperiod increased, but plant height increased with
increasing bulking duration (Figure 10).

For replicate two, bulking duration had no signiﬁcant effect on any
measured characteristic (Table 4). Bulking photoperiod had a signiﬁcant effect
on days to visible bud, days to flower, and the number of ﬂowering stems. The
interaction between bulking duration and photoperiod had a signiﬁcant effect on
plant height. For plants bulked for 2 or 4 weeks, as bulking photoperiod
increased, ﬁnal plant height increased. For plants bulked for 6 weeks, plant
height decreased as bulking photoperiod increased (Figure 1E). Days to ﬂower
tended to decrease as bulking photoperiod increased, however, plants bulked

under a 10-h photoperiod ﬂowered fastest (Figure 1B). Bulking photoperiod

131

slightly affected the number of ﬂowering stems. In general, plants bulked under a
10-h photoperiod produced more ﬂowering stems (Figure 1H).

For replicate 3, bulking duration and photoperiod signiﬁcantly affected ﬁnal
plant height (Table 5). As bulking duration increased, plant height decreased.
Likewise, as bulking photoperiod increased, plant height decreased (Figure 1F).
Neither bulking photoperiod nor bulking duration affected time to ﬂower (Figure
1C) or the number of ﬂowering stems (Figure 1|).

Unlike the cuttings in the cold-duration experiment, the cuttings used in
this experiment were vegetative. On average, plants took 10 days longer to
ﬂower than predicted by the cold-duration experiment (Table 2). As bulking
duration increased, irrespective of bulking photoperiod, an increasing number of
plants were delayed in ﬂowering and ﬂowered poorly. The ﬂowering stems failed
to elongate and the plants remained rosettes. Although plants did eventually
ﬂower, some required 100 or more days from the start of long days to ﬂower. We
concluded that vegetative G Iindheimeri ‘Whirling Butterﬂies’ plants, like Achillea
‘Moonshine’, after prolonged exposure to short photoperiods appear to require a
cold treatment for rapid, uniform ﬂowering. The plants in the third replicate that
were bulked for 6 weeks but not planted were cold treated for 6 weeks at 5 °C.
Following the cold treatment, all plants ﬂowered rapidly and unifome (data not
presented).

Gaura Iindheimeri ‘Siskiyou Pink’. Regardless of replicate or
treatment combination, all plants ﬂowered. For replicate one, the interaction

between bulking duration and photoperiod had a signiﬁcant effect on all

132

measured ﬂowering characteristics (Table 6). Bulking duration signiﬁcantly
affected all measured Characteristics except days from visible bud to ﬂower.
Bulking photoperiod signiﬁcantly affected all measured Characteristics except the
number of lateral inﬂorescences. As bulking duration increased, regardless of
bulking photoperiod, the number of lateral inﬂorescences decreased linearly
(Figure 2E). As bulking photoperiod and duration increased, ﬁnal plant height
(Figure 2C) and the number of days to visible bud and to ﬂower (Figure 2A)
decreased.

For replicate two, bulking duration signiﬁcantly affected all ﬂower
characteristics measured (Table 7). Bulking photoperiod affected only ﬁnal plant
height. As bulking duration increased, time to ﬂower (Figure 2B), ﬁnal plant
height (Figure 20), and the number of lateral inﬂorescences (Figure 2F)
decreased.

Gaura Iindheimeri ‘Siskiyou Pink’ was more sensitive to photoperiod than
‘Whirling Butterflies’. ‘Siskiyou Pink’ did not exhibit the same dormancy problem
that Whirling Butterﬂies’ did following extended short days. For plants in the
second replicate, natural photoperiods were naturally long enough in propagation
to induce plants to ﬂower. The 6-week bulking treatment was not planted
because all plants had ﬂowered in the plug trays, irrespective of bulking

photoperiod.

133

Unresolved Issues Requiring Further Research

According to data gathered from the bulking duration and photoperiod
experiment, minimum cold requirements for Gaura Iindheimeri ‘Whirling
Butterﬂies’ should be reevaluated. The initial cold—duration experiment was
performed with reproductive plugs, so timing of ﬂowering was not accurate.

The bulking photoperiod and duration experiment should be replicated
again for G. Iindheimeri ‘Siskiyou Pink’. Photoperiod control needs to be
implemented during propagation to ensure that cuttings are completely
vegetative at the start of bulking so that accurate bulking photoperiod effects can

be determined.

134

Table 1. Dates of forcing, average daily temperatures, and average daily light integral
(DLI) from date of forcing to average date of ﬂowering for Gaura Iindheimeri.

 

Average Average
Date of Weeks of Weeks temperature DLI
forcing bulking of 5 °C 1° C) (mol-m‘Z-d")
Cold duration experiment
2/1/00 3 0 21.5 12.1
2/8/00 3 1 21.4 12.0
2/15/00 3 2 21.5 11.8
2/22/00 3 3 21.5 13.3
2/29/00 3 4 21.3 14.4
3/10/00 3 5 21.1 16.0
Bulking duration and photoperiod experiment
Replicate 1
1/29/02 2 0 20.0 --‘
2/13/02 4 0 20.3 --
2/27/02 6 0 20.5 -
Replicate 2 (‘Whirling Butterﬂies’ only)
2/28/02 2 0 20.5 --
3/17/02 4 0 20.8 --
3/29/02 6 0 -- --
Replicate 3
3/13/02 2 0 20.7 - -
3/28/02 4 0 -- --

 

zDashes indicate data not presented.

135

Table 2. The effects of cold treatment on ﬂowering of Gaura Iindheimeri ‘Whirling
Butterﬂieg’.

 

 

 

 

 

Days to Days from Days New Final
Weeks Flowering visible VB to to leaves plant
of 5 °C percentage bud (VB) ﬂovgr ﬂower formed Lno.) height (cm
0 100 22 18 40 65 40.4
1 1 00 28 1 7 44 57 42.0
2 100 22 17 38 62 44.6
3 100 20 16 35 52 45.6
4 100 19 16 34 53 44.6
5 1 00 1 8 20 38 59 44.0
Signiﬁcance
Weeks of cold ** NS ** NS *"
Contrasts
PLinear M NS *4 NS *9
F>Quadratic NS * NS NS **
NS 't.“

Nonsigniﬁcant or signiﬁcant at P 5 0.05 or 0.01, respectively.

136

Table 3. The effects of bulking duration and photoperiod on ﬂowering of Gaura Iindheimeri
Whirling Butterﬂies’ (replicate 1L

 

 

 

 

 

Bulking Days to Days
duration Bulking Flowering visible from VB Days to Final plant Flowering
(weeks) photoperiod percentage bud (VB) to ﬂower ﬂower height (cm) stems (no.)
100 37 13 49 33 7
9-h 100 39 13 52 35 7
10-h 100 39 13 52 33 7
12-h 100 33 12 44 32 6
2 100 39 13 52 28 8
4 100 32 13 45 36 8
6 100 39 11 51 37 5
2 9-h 100 41 12 53 26 9
10-h 100 41 16 57 26 8
12-h 100 35 13 47 31 8
4 9-h 100 37 14 51 40 8
10-h . 100 36 - 14 49 35 8
12-h 100 23 12 36 32 6
6 9-h 100 39 13 51 39 5
10-h 100 40 1 1 51 37 6
12-h 100 40 11 51 34 6
Signiﬁcance
Bulking duration (BD) " ** * “ *
Bulking photoperiod (BP) * * *" NS NS
BD X BP NS * NS NS NS
9-h photoperiod
Bulking duration NS NS NS ** ’
PM...” NS NS NS ** “
PQuadratic NS NS NS “ NS
10-h photoperiod
Bulking duration NS ** NS NS NS
PUnea, NS ** NS NS NS
PQuadratic NS NS NS NS NS
12-h photoperiod
Bulking duration * NS * NS NS
Pm“, NS NS NS NS NS
Pgmmm *" NS ‘ NS NS
N33.“

Nonsigniﬁcant or signiﬁcant at P 5 0.05 or 0.01, respectively.

137

Table 4. The effects of bulking duration and photoperiod on ﬂowering of Gaura Iindheimeri
Whirling Butterflies’ (replicate 2).

 

 

 

 

Bulking Days to Days
duration Bulking Flowering visible from VB Days to Final plant Flowering
(weeks) photoperiod percentage bud (VB) to ﬂower ﬂower height (cm) stems (no)
100 46 1 1 57 25 5
9-h 100 52 12 62 24 5
10-h 100 43 1 1 53 27 6
12-h 100 45 12 56 25 5
2 100 46 1 1 58 26 6
4 100 48 12 55 24 5
6 100 46 12 57 25 4
2 9-h 100 49 1 1 62 22 5
10-h 100 45 1O 55 30 6
12-h 100 45 1 1 56 27 5
4 9-h 100 57 1 1 62 21 4
10-h 100 43 12 52 24 6
12-h 100 42 12 52 28 5
6 9-h 100 51 12 61 30 4
10-h 100 41 1 1 52 26 5
12-h 100 47 12 59 19 4
Signiﬁcance
Bulking duration (BD) NS NS NS NS NS
Bulking photoperiod (BP) ** NS ** NS ‘
BD X BP NS NS NS ** NS
9-h photoperiod
Bulking duration NS NS NS NS NS
PUM, NS NS NS NS NS
PQuadram NS NS NS NS NS
10-h photoperiod
Bulking duration NS NS NS NS NS
FLW, NS NS NS NS NS
Pomrmic NS " NS NS NS
12-h photoperiod
Bulking duration NS NS NS NS NS
Pm“, NS NS NS " "
Pguadmm NS NS NS NS NS
NS.*.”

Nonsigniﬂcant or signiﬁcant at P 5 0.05 or 0.01, respectively.

138

Table 5. The effects of bulking duration and photoperiod on ﬂowering of Gaura Iindheimeri
Whirling Butterflies’ (replicate 3).

 

 

 

Bulking Days to Days
duration Bulking Flowering visible from VB Days to Final plant Flowering
(weeks) photoperiod percentage bud (VB) to ﬂower ﬂower height (cm) stems (no.)
100 39 12 50 30 6
9-h 100 39 12 50 32 5
10-h 100 39 13 51 32 6
12-h 100 39 11 49 25 5
2 100 41 12 51 33 6
4 100 39 12 49 26 5
2 9-h 100 38 11 50 35 6
2 10-h 100 45 13 54 36 7
2 12-h 100 39 11 49 28 6
4 9-h 100 40 12 51 29 5
4 10-h 100 37 1'3 48 28 6
4 12-h 100 39 11 49 23 5
Signiﬁcance
Bulking duration (BD) NS NS NS *“ NS
Bulking photoperiod (BP) NS NS NS ** NS
BD X BP NS NS NS NS NS
9-h photoperiod
Bulking duration NS NS NS * NS
10-h photoperiod
Bulking duration NS NS NS * NS
12-h photoperiod
Bulking duration NS NS NS NS NS
Ns.*.’"’."“

Nonsngniﬁcant or signiﬁcant at P _<_ 0.05, 0.01, or 0.001, respectively.

139

Table 6. The effects of bulking duration and photoperiod on ﬂowering of Gaura Iindheimeri
‘Siskiyou Pink” (replicate 1).

Bulking Days to Days Lateral
duration Bulking Flowering visible from VB Days to Final plant inﬂorescences
(weeks) photoperiod percentage bud (VB) to ﬂower ﬂower height (cm) (no.)

 

 

 

 

100 22 1 3 35 30 24
9-h 100 26 14 40 33 23
10-h 100 25 14 39 31 24
12-h 100 14 12 26 27 24
2 100 27 13 39 33 31
4 100 22 1 3 35 29 27
6 100 17 13 30 28 14
2 9-h 100 27 1 3 40 33 34
10-h 100 28 13 41 32 30
12-h 100 24 12 37 33 29
4 9-h 100 27 13 4O 31 21
10-h 100 24 14 38 30 28
12-h 100 15 12 28 27 32
6 9-h 100 24 15 39 34 14
10-h 100 23 14 37 30 14
12-h 100 3 . 1 1 14 22 13
Signiﬁcance
Bulking duration (BD) *** NS m . m
Bulking photoperiod (BP) '** *** m “ NS
80 X BP *** t “t «u ..
9-h photoperiod
Bulking duration NS *‘ NS NS *”
PLinear * " NS NS ‘**
PQuadratic NS NS NS NS NS
10-h photoperiod
Bulking duration * NS NS NS ***
PLinear " NS NS NS no
PQuadratic NS NS NS NS *
12-h photoperiod
Bulking duration *** NS m m m
PLinear *** NS *1" in .ﬂ
Pguamnc NS NS NS NS “*
Ns.‘.**.***

Nonsigniﬁcant or signiﬁcant at P _<_ 0.05. 0.01, or 0.001, respectively.

140

Table 7. The effects of bulking duration and photoperiod on ﬂowering of Gaura Iindheimeri
‘Siskiyou Pink’ (replicate 2).

 

 

Bulking Days to Days Lateral
duration Bulking Flowering visible from VB Days to Final plant inﬂorescences
(weeks) ihotoperiod percentgge bud (VB) to ﬂower ﬂower hcﬂg ht (cm) (no.)
100 4 1 1 15 12 1 1
9-h 100 6 10 15 1 1 10
10-h 100 4 1 1 16 1 1 1 1
12-h 100 3 1 1 14 15 1 1
2 100 7 1 3 2O 14 13
4 100 1 8 9 1 1 8
2 9-h 100 10 13 23 14 13
10-h 100 7 13 20 13 13
12-h 100 ~ 5 14 19 16 12
4 9-h 100 1 7 8 8 8
10-h 100 1 10 1 1 8 9
12-h 100 0 8 9 15 9
Signiﬁcance
Bulking duration (BD) *** *** *** *” ***
Bulking photoperiod (BP) NS NS NS *** NS
BD X BP NS NS NS * NS
9-h photoperiod
BUIking duration ii iii tit tit it
10-h photoperiod
Bulking duration *“ * *** ‘* "
12-h photoperiod
Bulkingduration * *” *** ‘** NS ‘

 

NS' ' ' *Nonslgniﬁcant or signiﬁcant at P _<_ 0.05, 0.01, or 0.001, respectively.

141

Replicate 1 Replicate 2 ___ Replicate 3

 

 

 

 

 

 

 

 

 

 

 

 

70 A B C
60 . . 1 ”/75 i I
a; 50 1 szy _f... , A i ' Q 1 F% 1
8 40* N/ 4 { ‘
.9
"é. 30‘ Photoperiod ‘ 1
D 20 < —O— 941 4 i
J —O— 1o.h
‘0 i + 12.11
0 L—— -- *-
D s F
40 . /§—~——-—~§ ( ‘ v
A / . ’~"‘”
/ f ,_,..—-—-"' ~ \
E 301 . V//"‘(‘ . K1). ’“"i\ [/3 . r“ \g 1
E V :at <\"' Vw/ﬁwii"? Y \\“\\;’
if 204 I » ““"““f \3 1
10 . 3
I
0 ——»—-~ —— - ——~ _ __-_(__.__ —_—- —_ _, —- -——
A G H l
5 \ z
m 8 1 -___._.>_~—/:
E \‘\\ N\\ k
g 1 _--_ _j“~~~~ Is \ \x? i
'z t ' _ . \\-‘»« - ..f.‘ 27:; f
“s ‘ 7} l
1% 2 J l
o +_-._-.- -_s_ .._.---_.,-_---.._--_i _---.-__-__..----.. __,-_.-_-~.--.. .. -4___--_.__-_.~___.. -_.-- __ .--....__J
1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 7

Weeks of bulking at 20 °C

Figure 1. The effects of bulking duration and photoperiod on days to ﬂower (A-
C), plant height at ﬂower (D—F), and number of lateral inﬂorescences at ﬂower
(G-l) for Gaura Iindheimeri ‘Whirling Butterﬂies’. Error bars represent standard
error of the mean.

142

 

50

 

 

 

 

 

 

 

 

 

 

 

Replicate 1 A Replicate 2 B
40 * Wm“
- i ‘4
g \i\
o 30 "
c
.9
g 20 4 1
0 Photoperiod!
1 ‘—O— 9-h , ‘ \‘
1o ‘ <
.0. 10-.. S
—v— 12-h
0 L ’— ‘_‘_' _.._____.. _
C D
30 « “xx j ~ 1
E J. ‘\-
.9, \i
E 20 4 4
.9
g \ ~~a
10 1 -( \ 4
l
0 4)— --—-- -—.—-——T—.-—-———-—— -—---- —————— - —-— -—---i
E j $\‘ / i l
v 30 >213”; \ 4
g l ‘1 \\ 1 |
8 ~ : i
g 20 ( \ l 1
a \x * l
E w l .
- ( g
(D
t. 10 . i \ _ J
(D
a I \i
.J
o . . . . . l . . ﬂ — . . J
1 2 3 4 5 6 1 2 3 4 5 6 7
Weeks of bulking at 20 °C

Figure 2. The effects of bulking duration and photoperiod on days to ﬂower (A
and B), plant height at ﬂower (C and D), and the number of lateral inﬂorescences
(E and F) for Gaura Iindheimeri ‘Siskiyou Pink'. Error bars represent standard
error of the mean.

143

APPENDIX D

THE FLOWERING RESPONSE OF CAMPANULA ‘BIRCH HYBRID’ TO COLD
DURATION AND DURATION OF BULKING

144

Research Objective

The ﬁrst objective of this research project was to determine the minimum
cold duration required for rapid and uniform ﬂowering of Campanula “Birch
Hybrid’. The second objective was to determine whether the duration of bulking
and cold affected time to ﬂower and overall ﬂowering quality of Campanula “Birch

Hybrid’.

Materials and Methods

Cold-duration experiment. Campanula 'Birch Hybrid’ stock plants were
potted (Sept. 1999) in 13-cm square plastic containers (1.1 L) ﬁlled with a
commercial soilless medium composed of pine bark, fibrous Canadian sphagnum
peat, horticultural vermiculite, and screened course perlite. along with a wetting
agent and starter fertilizer charge (Suremix Perlite; Michigan Grower Products.
Galesburg, Mich). Plants were grown under a 12-h photoperiod provided by
supplementing natural daylengths with lighting from high-pressure sodium lamps
from 0800 to 2000 HR. Stock plants were pinched at 3- to 4-week intervals to
ensure continued branching and cutting production.

Harvested cuttings were propagated in 72-cell (0.03—L) plug trays
(Landmark Plastic Corporation, Akron, Ohio). After propagation, plants were
grown (bulked) in the plug trays for an additional 3 weeks in a greenhouse at 20
°C to establish root systems and increase vegetative growth before cold
treatment. Photoperiod was maintained at 12 h as on the stock plants. Plugs
then received no cold treatment or were placed in a controlled-environment

chamber for 1, 2, 3, 4, or 5 weeks at 5 °C.

145

Bulking-duration experiment. On Oct. 25, 2001, Campanula ‘Birch Hybrid’
stock plants were potted in 13—cm square plastic containers (1.1 L) ﬁlled with a
commercial soilless medium composed of pine bark, ﬁbrous Canadian sphagnum
peat, horticultural vermiculite, and screened course perlite, along with a wetting
agent and starter fertilizer charge (Suremix Perlite; Michigan Grower Products,
Galesburg, Mich.). Plants were grown under a 16-h photoperiod provided by
supplementing natural daylengths with lighting from high-pressure sodium lamps
from 0530 to 2130 HR.

Harvested cuttings were propagated in 50-cell (0.08—L) plug trays
(Landmark Plastic Corporation, AkrOn, Ohio). After propagation, plants were
grown (bulked) in a greenhouse at 20 °C for 3, 4, 5. or 6 weeks. After the
appropriate bulking duration, plants were cold treated for 4, 5, 6, or 7 weeks at 5
°C.

Propagation environmental control. Plug ﬂats contained a mixture of 50%
commercial medium (Suremix Perlite; Michigan Grower Products, Galesburg,
Mich.) and 50% screened course perlite (Therm-O-Rock; East, Inc., New Eagle,
Pa.). Basal portions of each cutting were dipped in a 1500-ppm solution of liquid
auxin (DIP ’N GROW; Astoria-Paciﬁc, Clackamas, Ore.) before stick.
Propagation air temperatures were maintained at 23 °C and bottom heat (soil
temperature) was maintained at 25 °C. A vapor pressure deﬁcit of 0.3 kPa was
maintained by injecting water vapor as needed. Cuttings were propagated under
natural daylengths and rooted and weaned from propagation 3 weeks after

sticking.

146

 

Cold treatments. The chamber was lit from 0800 to 1700 HR by cool-white
ﬂuorescent lamps (F96T12/CWNHO; Philips, Somerset, N.J.) The
photosynthetic photon ﬂux (PPF) from the lamps was approximately 10 umol'm’
2's’1 at plant height. While in the cooler, plants were watered as needed with well
water acidiﬁed with sulfuric acid to an approximate pH of 6.0.

General plant culture. Following all cold treatments, plugs were potted in
13-cm square plastic containers (1.1 L) containing the same commercial medium
used for the stock plants. All plants were forced to ﬂower under a 16-h
photoperiod (natural days supplemented with high-pressure sodium lamps from
0530 to 2130 HR). Plants were top-watered as necessary with well water
acidiﬁed with sulfuric acid to a titratable alkalinity of approximately 130 mg
calcium bicarbonate per liter and containing water—soluble fertilizer providing 125
N, 12 P, 125 K, 13 Ca (mg'L‘I; 30% ammoniacal N) plus (mg'L’1) 1.0 Fe, 0.5 Mn,
0.5 Zn, 0.5 Cu, 0.1 B, 0.1 Mo (MSU Special, Greencare Fertilizers, Chicago, Ill.).
Plants in the bulking-duration experiment received additional Cu at 0.5 mg'L'1
and B at 0.1 mg°L‘1 at every watering.

Greenhouse temperature control. Plants were grown in glass
greenhouses set at 20 °C. Greenhouse temperatures were controlled by a
greenhouse climate-control computer (Model CD750; Priva, De Lier, The
Netherlands). Average daily temperature and daily light integral were monitored
with a CR-10 datalogger (Campbell Scientiﬁc, Logan, Utah) by using 36-gauge
(0.013 mm in diameter) type E thermocouples and a quantum sensor (Model LI-

189; Ll-COR, lnc., Lincoln, Neb.), respectively. The datalogger collected data

147

every 10 seconds and recorded the hourly average. Actual average daily
temperatures and average daily light integrals from the beginning of forcing to the
average date of ﬂowering were calculated and are presented in Table 1.

Data collection and analysis. Dates of visible bud and ﬁrst ﬂower and the
number of ﬂowering stems were recorded. For the bulking-duration experiment,
the number of nodes present at the end of the cold treatment was also recorded.
A completely randomized design with 10 observations for each treatment was
used. Data were analyzed using SAS’s (SAS Institute, Cary, NC.) analysis of

variance (ANOVA) and general linear models (GLM) procedures.

Results and Discussion

Cold-duration experiment Campanula ‘Birch Hybrid’ had an obligate
.vernalization requirement (Table 2). Only 10% of the plants ﬂowered after 4
weeks at 5 °C. After 5 weeks at 5 °C, all plants ﬂowered, and the average
number of ﬂowering stems per plant was six. Even though there was 100%
flowering after a 5-week cold treatment, a longer cold duration may reduce time
to ﬂower and increase the number of ﬂowering stems.

Bulking-duration experiment. Days to visible bud, days to ﬂower, and the
number of ﬂowering stems per plant were signiﬁcantly affected by bulking
duration and cold duration independently, but their interaction was not signiﬁcant
(Table 3). As cold duration increased, days to visible bud and days to ﬂower
decreased linearly (Table 4, Figure 1A). The ﬂowering uniformity of the crop also
improved with increasing cold, since the standard error for days to ﬂower I

decreased. The number of nodes present per plant after cold treatment was

148

signiﬁcantly affected by bulking duration, cold duration, and their interaction
(Table 4). When each cold treatment was evaluated independently, as bulking
duration increased, the number of nodes present per plant after cold treatment
increased linearly by 3 to 5 nodes (Table 3, Figure 1D). The number of ﬂowering
stems per plant increased with increased cold duration (Figure 1C). In general,
as bulking duration increased, days to ﬂower decreased and the number of
ﬂowering stems increased. As bulking duration increased, a shorter cold
treatment was needed for complete ﬂowering (Figure 13). Plants bulked for 3
weeks never reached 100% ﬂowering, which contradicts ﬁndings of the cold-
duration experiment. Plants bulked for 7 weeks ﬂowered completely after only 4
weeks at 5 °C.

Campanula ‘Birch Hybrid’ has characteristics of a plant with a juvenile
phase. Younger plants are less likely to ﬂower than older plants, which would
explain why plants bulked for 7 weeks had a higher ﬂowering percentage than
plants bulked for 3 weeks. However, this does not appear to be correlated with
node number, since the bulking treatments, regardless of cold duration, averaged
nine nodes per plant. Also, as bulking duration increased, the weeks of cold
required for complete ﬂowering decreased, implying that older plants perceive
low temperatures faster than younger plants.

The longer Campanula ‘Birch Hybrid’ was bulked, the more ﬂowering
stems the plants developed. As bulking duration increased, the number of nodes
per plant present after cold treatment also increased. With more nodes, there

was a higher probability of producing more ﬂowers, since ﬂower stems develop

149

from the lateral meristems. The longer the cold treatment, the more ﬂowering
stems the plant developed. On average, regardless of bulking duration, the
number of nodes did not vary between cold treatments. However, with increased
cold duration, there was an increased likelihood that the vernalization
requirement of more lateral meristems was saturated, leading to more ﬂowering

stems.

Unresolved Issues Requiring Further Research

Minimum cold requirements for Campanula ‘Birch Hybrid’ are still not
deﬁnite. In the cold-duration experiment, plants bulked for 3 weeks ﬂowered
completely after 5 weeks at 5 °C. However, in the bulking-duration experiment,
plants bulked for 3 weeks never completely ﬂowered even after 7 weeks at 5 °C.
The bulking-duration experiment should be replicated to validate the results of

the experiment.

150

 

Table 1. Dates of forcing, average daily temperatures, and average daily light integral
(DLI) from date of forcing to average date of ﬂoweringﬁor Caﬂzpanula “Birch Hybrig’.

 

Average Average
Date of Weeks of Weeks temperature DLI
forcing bulking of 5 °C (° C) (mol-m’Z-d")
Cold-duration experiment
2/1/00 3 0 «z -
2/8/00 3 1 - -
2/15/00 3 2 - -
2/22/00 3 3 - -
2/29/00 3 4 21.4 15.2
3/10/00 3 5 21.2 15.4
Bulking-duration experiment
3/8/00 3 4 22.4 15.8
3/14/00 3 5 22.4 16.1
4 4 22.4 16.1
3/22/00 3 6 22.4 16.6
4 5 22.4 16.3
5 4 22.5 17.7
3/29/00 3 7 22.5 15.5
4 6 22 5 15.5
5 5 22.6 16.6
6 4 22.6 16.7
4/8/00 4 7 22.6 17.1
5 6 22.8 18.6
6 5 22.7 18.1
4/16/00 5 7 22.7 18.2
6 6 22.8 18.7
4/26/00 6 7 23.5 18.9

 

 

zDashes indicate no plants ﬂowered.

151

Lable 2. The effects of colg treatment on ﬂowering of Campanula “Birch Hvbrid’.

 

 

 

Days to Days from Days Number of

Weeks Flowering visible VB to to ﬂowering
of 5 °C percerﬁde bud (zVB) ﬂower ﬂower stems

0 0 - - - -

1 0 -- - -- -

2 0 -- - -- -

3 0 - -- -- -

4 10 49 38 87 3

5 100 41 27 68 6

 

zDashes indicate no plants ﬂowered.

152

Table 3. Signiﬁcance of bulking duration and duration of cold on ﬂowering of Campanula ‘Birch
Hybrid’.

 

 

 

Days to Days from Number of
Flowering visible bud VB to Number of ﬂowering
percentage (VB) ﬂower Days to ﬂower nodes stems
Signiﬁcance
Bulking duration (BD) “* . ** NS «1- m m
Weeks of cold (WC) *** *** NS m u m
BD X WC " NS NS NS * NS
3 weeks of bulking
Weeks of cold NS NS NS NS NS NS
PLinear NS NS NS NS * *
PQuadratic NS NS NS NS NS NS
4 weeks of bulking
Weeks of cold NS *** NS m . m
PLinear NS *** NS in": NS mu.
PQuadratic NS NS NS NS in n
5 weeks of bulking
Weeks of c old *** ** NS n NS ..
PLinear t" * NS ** N3 in
Pommc *** NS NS NS NS NS
6 weeks of bulking
Weeks Of COld _z *** N S in: n u
F’Linear " "* " i“ u H,
POuadratic ‘ “ NS " NS '
4 weeks of cold
Bulking duration *"'* NS NS NS m m
PLinear 1“ NS NS NS “N in
Pommc NS NS NS NS NS NS
5 weeks of cold
Bulking duration * * NS .. m m
PLinear * * NS ** it" n.
Pauadrm NS NS NS NS NS NS
6 weeks of cold
Bulking duration NS " NS u m ..
F>Linear NS * NS * it n
F’t.)uadratic NS NS NS NS * NS
7 weeks of cold
Bulking duration * * NS .. . m
F)Linear * NS NS * * n.
P Quadratic NS “ NS “ NS NS
N344...“

Nonsigniﬁcant or signiﬁcant at P 5 0.05, 0.01, or 0.001, respectively.
zDashes indicate no variation within treatments.

153

Table 4. The effects of bulking duration and duration of cold on ﬂowering of Campanula ‘Birch
Hybrid’.

 

Bulking Days to Days from Number of
duration Weeks at Flowering visible VB to Days to Number of ﬂowering
Jweeks) 5 °C percentage bud (VB) ﬂower ﬂower nodes stems

84 47 14 61 9 9

4 60 57 15 71 9 4

5 92 50 14 64 9 9

6 95 45 14 60 9 1 1

7 88 39 14 53 8 1 1

3 60 53 14 67 7 4

4 95 45 14 59 10 9

5 80 47 15 62 9 8

6 100 44 14 58 10 14

3 4 3O 57 14 71 8 1

3 5 70 58 14 72 7 4

3 6 80 52 15 67 7 6

3 7 60 44 15 59 6 5

4 4 80 59 14 73 9 3

4 5 100 47 15 62 1 1 9

4 6 100 41 15 56 10 13

4 7 100 35 . 15 50 9 1 1

5 4 30 53 1.7 70 9 2

5 5 100 54 15 68 9 8

5 6 100 48 14 62 9 1O

5 7 90 38 1 5 53 8 12

6 4 100 57 15 70 1 1 8

6 5 100 43 14 57 12 16

6 6 100 40 13 55 1O 16

6 7 100 39 13 53 9 17

 

154

 

 

 

100 “““ °‘

 

 

 

 

 

 

 

 

 

 

 

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Weeks at 5 “C

Figure 1 The effects bulking duration and duration of cold on days to ﬂower (A),
ﬂowering percentage (B), number of ﬂowering stems per plant (C), and the
number of nodes present after cold treatment (D) for Campanula ‘Birch Hybrid”.
Error bars represent standard error of the mean.

155