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EFFECTS OF PHOTOPERIOD AND TEMPERATURE ON
GROWTH AND FLOWERING OF SIX ORCHID HYBRIDS

presented by

ROBERTO GERARDO LOPEZ

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EFFECTS OF PHOTOPERIOD AND TEMPERATURE ON GROWTH AND
FLOWERING OF SIX ORCHID HYBRIDS

By

Roberto Gerardo Lopez

A THESIS
Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of
MASTER OF SCIENCE
Department of Horticulture

2003

ABSTRACT
EFFECTS OF PHOTOPERIOD AND TEMPERATURE ON GROWTH AND
FLOWERING OF sux ORCHID HYBRIDS
By

Roberto Gerardo Lopez

Orchids are currently the second most valuable ﬂowering potted
ﬂoriculture crop in the United States. However, the commercial potential of the
vast majority of orchids has not been explored primarily due to insufficient
knowledge of how to regulate growth and ﬂowering. A series of experiments was
performed to determine the effects of photoperiod and temperature on growth
and ﬂowering of six orchid hybrids. Brassia Rex ‘Sakata’, Degannoara Winter
Wonderland “White Fairy’, Miltassia Charles M. Fitch ‘Dark Monarch’, and
Odontocidium Tiger Crow ‘Golden Girl’ did not ﬂower in response to a range of
photoperiods (1 O to 24 hours) or cool temperature (8 to 23 °C) treatments. In
Miltoniopsis Augres ‘Trinity’, ﬂowering percentage was greatest (290%) and was
most rapid when plants were exposed to 9-h photoperiods for 4 to 8 weeks at 20
°C and then vernalized under short days at 14 °C for 8 to 12 weeks. Similarly,
ﬂowering of Zygopetalum Redvale ‘Fire Kiss’ was promoted most when exposed
to short days at 23 °C for eight weeks followed by eight weeks of vernalization at
11 to 14 °C. Additional studies were performed to quantify the effects of
temperature on pseudobulb development, time to ﬂowering, and ﬂower longevity.

Thermal time models were developed for these processes and are presented.

DEDICATION
In memory of my grandmother, Mrs. Alicia C. Toledo (March 3, 1997) who

inspired my interest in horticulture.

ACKNOWLEDGMENTS

I wish to express my sincere appreciation to my major professor Dr. Erik
S. Runkle for his encouragement, support, guidance, and patience. I would also
like to thank him for giving me the opportunity to travel abroad to experience
horticulture outside the United States. I look fonNard to several more years of
whoppertunities. I greatly appreciate the insight, comments and advice from my
guidance committee members Royal Heins, Donald Garling and Bridget Behe. A
very special thanks to Ken Poff, Stan Howell, Royal Heins and Erik Runkle for
saving me from Biology and for introducing me to the science and industry of
horticulture, but most importantly ﬂoriculture.

To the ﬂoriculture technicians: David Joeright, Mike Olrich, Beth Fausey
and Catherine Whitman thank you for your invaluable support, assistance and
humor. I would especially like to thank my MSU friends who made my transition
to Michigan and graduate school much easier and enjoyable: Ann Bond, Matt
Blanchard, Kevin and Erin Brothers, Beth Fausey, Jennifer Dennis, Chrislyn
Drake, Janelle Glady, Grant Jones, Sonali Padhye, Lee Ann Pramuk, Kari
Robinson, Charlie Rohwer, Matthew Steinkopf, Emily Stefanski, and Alicia Wells.

Most importantly, I thank my parents and brother for their love,
encouragement and sacriﬁces they have made to help me be where I am today.
Lastly, I thank my extended family in the US. and Mexico and Joe and
Josephine Ortiz for their encouragement and support in continuing on for a

doctoral degree.

TABLE OF CONTENTS

LIST OF TABLES ................................................................................................ viii
LIST OF FIGURES ............................................................................................. xii
SECTION I
LITERATURE REVIEW ........................................................................................ 1
Vernalization ......................................................................................................... 2
Effects of Low Temperature .......................................................................... 4
Requirements for Vernalization ..................................................................... 5
Site of Perception .......................................................................................... 6
Effective Temperatures ................................................................................. 7
Obligate or Facultative Requirements ........................................................... 8
Induced State .............................................................................................. 10
Devernalization ........................................................................................... 10
Genetic and Molecular Components ........................................................... 11
VERNALIZATION (VRN) gene ................................................................... 12
FLOWERING LOCUS C (FLC) ................................................................... 13
FRIGIDA (FRI) .............................................................................. . .............. 15
DNA demethylation ..................................................................................... 16
Photoperiod ........................................................................................................ 17
Orchids ............................................................................................................... 19
Orchid Nomenclature .................................................................................. 22
Commercial Genera .................................................................................... 22
Commercial Production ............................................................................... 27
Propagation ................................................................................................ 30
Media, Nutrition and Irrigation ..................................................................... 31
lrradiance, Temperature and Photosynthesis ............................................. 33
Flower Induction ......................................................................................... 36
Effects of Vernalization and Photoperiod .................................................... 38
Flower Longevity ......................................................................................... 43
Conclusion .......................................................................................................... 44
Literature Cited ................................................................................................... 44
SECTION II

FLOWERING AND VEGETATIVE GROWTH RESPONSES OF BRASSIA,
DEGARMOARA, MILTASSIA, ODONTOCIDIUM AND ZYGOPETALUM

ORCHIDS TO PHOTOPERIOD .................................................................. 56
Introduction ...................................................................................... 58
Materials and Methods ..................................................................... 62
Results ............................................................................................. 65
Discussion ........................................................................................ 68

Literature Cited ................................................................................. 74

SECTION III

THE EFFECT OF PREVERNALIZATION PHOTOPERIOD AND
VERNALIZATION ON FLOWERING OF BRASSIA, DEGARMOARA,
MILTASSIA, MILTONIOPSIS, ODONTOCIDIUM AND ZYGOPETALUM

ORCHIDS ................................................................................................... 90
Introduction ...................................................................................... 92
Materials and Methods ..................................................................... 96
Results ............................................................................................. 99
Discussion ...................................................................................... 102
Literature Cited ............................................................................... 107
SECTION IV
PHOTOPERIOD AND VERNALIZATION INFLUENCE FLOWERING OF
MILTONIOPSIS AUGRES ‘TRINITY’ ORCHID ......................................... 124
Introduction .................................................................................... 126
Materials and Methods ................................................................... 128
Results ........................................................................................... 130
Discussion ...................................................................................... 131
Literature Cited ............................................................................... 133
SECTION V

THE EFFECT OF TEMPERATURE ON LEAF AND FLOWER DEVELOPMENT
AND FLOWER LONGEVITY OF ZYGOPETALUM REDVALE ‘FIRE KISS’

ORCHID .................................................................................................... 141

Introduction .................................................................................... 143

Materials and Methods ................................................................... 146

Results ........................................................................................... 149

Discussion ...................................................................................... 151

Literature Cited ............................................................................... 154
APPENDIX A

THE EFFECT OF TEMPERATURE ON FLOWER AND INFLORESCENCE
LONGEVITY OF MILTASSIA CHARLES M. FITCH ‘DARK MONARCH’

ORCHID .................................................................................................... 164
Research Objective ........................................................................ 165
Materials and Methods ................................................................... 165
Results and Discussion .................................................................. 167
APPENDIX B
THE EFFECT OF TEMPERATURE ON NODE DEVELOPMENT OF BRASSIA
REX ‘SAKATA’ .......................................................................................... 171
Research Objective ........................................................................ 172
Materials and Methods ................................................................... 172
Results and Discussion .................................................................. 173

vi

APPENDIX C

THE EFFECT OF LIGHT QUANTITY ON GROWTH OF FOUR ORCHIDS ..... 178
Research Objective ........................................................................ 179
Materials and Methods ................................................................... 179
Results and Discussion .................................................................. 180

vii

LIST OF TABLES

Table Page

SECTION II
Propagation dates and container sizes for orchid hybrids ............................. 77

. Average air temperature and daily light integral (DLI) from the beginning of
forcing to the end of the experiment under each photoperiod for Brassia Rex
‘Sakata’, Degannoara Winter Wonderland White Fairy’, Miltassia Charles M.
Fitch ‘Dark Monarch’, Odontocidium Tiger Crow ‘Golden Girl’ and
Zygopetalum Redvale “Fire Kiss’. ................................................................ 78

Initial leaf count and, length and number of immature and mature
pseudobulbs of Odontocidium Tiger Crow ‘Golden Girl’ and Zygopetalum
Redvale “Fire Kiss’. ...................................................................................... 79

. The effect of photoperiod on ﬁnal immature and mature pseudobulbs formed

during forcing of Brassia Rex ‘Sakata’. ........................................................ 80

. The effect of photoperiod on days to visible inﬂorescence (VI), days from
visible inﬂorescence to ﬂower (VI to FLW), and days to ﬂower from the
beginning of forcing (F LW); ﬂower bud and inﬂorescence count; and
inﬂorescence length at ﬂowering of Degannoara Winter Wonderland ‘White
Fairy’. ........................................................................................................... 81

. The effect of photoperiod on days to visible inﬂorescence (VI), days from

visible inﬂorescence to ﬂower (VI to FLW) and, days to ﬂower from the
beginning of forcing (FLW); ﬂower bud and inﬂorescence count; and
inﬂorescence length at ﬂowering of Miltassia Charles M. Fitch ‘Dark
Monarch’. ..................................................................................................... 82

. The effect of photoperiod on days from visible inﬂorescence to ﬂower (VI to

FLW) and days to ﬂower from the beginning of forcing (FLW) of
Odontocidium Tiger Crow ‘Golden Girl’. ...................................................... 83

. The effect of photoperiod on days to ﬂower from the beginning of forcing to

(FLW), ﬁnal immature and mature pseudobulb number and, ﬁnal leaf count
of Zygopetalum Redvale ‘Fire Kiss’. ............................................................ 84

SECTION III

Propagation dates and container sizes for orchid hybrids ........................... 110

viii

. Average daily light integral (moI-m'z-d") during the pre-vernalization and
vernalization treatments and for each month during subsequent forcing. ..1 11

. Actual average air temperature (°C) during the pre-vernalization and
vernalization treatments and for each month during subsequent forcing. .. 1 12

. The effect of pre-vernalization photoperiod, vernalization temperature, and

vernalization photoperiod on ﬂower bud count, inﬂorescence length and
count of Brassia Rex ‘Sakata’. Plants were forced at 23 °C under a 16-h
photoperiod. ............................................................................................... 1 13

. The effect of pre-vernalization photoperiod, vernalization temperature, and

vernalization photoperiod on ﬂower bud count, inﬂorescence length and
count of Degarrnoara Winter Wonderland White Fairy’. Plants were forced at
23 °C under a 16-h photoperiod. ............................................................... 114

. The effect of pre-vernalization photoperiod, vernalization temperature, and

vernalization photoperiod on ﬂower bud count, inﬂorescence length and
count of Miltassia Charles M. Fitch ‘Dark Monarch’. Plants were forced at 23
°C under a 16-h photoperiod. .................................................................... 115

. The effect of pre-vernalization photoperiod, vernalization temperature, and
vernalization photoperiod on ﬂower bud count, inﬂorescence length and
count of Odontocidium Tiger Crow ‘Golden Girl’. Plants were forced at 23 °C
under a 16-h photoperiod. ......................................................................... 116

. The effect of pre-vernalization photoperiod, vernalization temperature, and

vernalization photoperiod on ﬂower bud count, inﬂorescence length and
count of Zygopetalum Redvale ‘Fire Kiss’. Plants were forced at 23 °C under
a 16-h photoperiod ..................................................................................... 117

SECTION IV

. Average daily temperature and light integral during pre-vernalization,

vernalization, and forcing of Miltoniopsis Augres ‘Trinity’ (Expt. 1). ........... 136

. Average daily temperature and light integral during pre-vernalization,

vernalization, and forcing of Miltoniopsis Augres 'Trinity’ (Expt. 2). ........... 137

. The effect of ore-vernalization photoperiod and duration on days to visible

inﬂorescence (VI) and inﬂorescence count of Miltoniopsis Augres ‘Trinity’
(Expt. 1). The pre-vernalization photoperiod was delivered at 20 °C. Plants
were then vernalized for eight weeks at 14 °C under a 9-h photoperiod and
subsequently forced at 20 °C under a 16-h photoperiod. .......................... 138

. The effect of pseudobulb maturity and immature pseudobulb height on days

to visible inﬂorescence in Miltoniopsis Augres ‘Trinity’ (Expt. 1). ............... 139

. The effect of pre-vernalization photoperiod and vernalization duration on days

to visible inﬂorescence and inﬂorescence count of Miltoniopsis Augres
‘Trinity’ (Expt. 2). Pre-vernalization photoperiods were provided at 20 °C for
eight weeks. Plants were then vernalized at 14 °C under a 9-h photoperiod
and subsequently forced at 20 °C under a 16-h photoperiod. ................... 140

SECTION V

. Actual average daily air temperature of environmental chambers or

(greenhouse) for each experiment. ............................................................ 157

Parameters of linear regression analysis relating forcing temperature to rate
of progress for leaf development, from visible inﬂorescence to ﬂower, ﬂower
longevity of the ﬁrst ﬂower and inﬂorescence longevity in Zygopetalum
Redvale “Fire Kiss’. Intercept and slope were used in Eqs. [1] and [2] to
calculate base temperature (T b) and thermal time to complete a particular
developmental stage (°C-d"). ...... . ............................................................. 158

APPENDIX A

Parameters of linear regression analysis relating forcing temperature to rate
of progress to ﬂower longevity of the ﬁrst ﬂower and inﬂorescence longevity
in Miltassia Charles M. Fitch ‘Dark Monarch’. Intercept and slope were used
in Eqs. [1] and [2] to calculate base temperature (Tb) and thermal lifespan
(°C-d' ). ...................................................................................................... 169

APPENDIX B
Parameters of linear regression analysis relating forcing temperature to rate
of progress to leaf development in Brassia Rex ‘Sakata’. Intercept and slope
were used in Eqs. [1] and [2] to calculate base temperature (Tb) and thermal
degree-days (°C-d'1). ................................................................................. 175

APPENDIX C

. The effect of estimated daily light integral (DLI) on inﬂorescence and ﬂower

bud count, number of mature and immature pseudobulbs, plant height,
SPAD value, and dry shoot and root weights of Brassia Rex ‘Sakata’ grown
at 23 °C under a 16-h photoperiod. ........................................................... 182

. The effect of estimated daily light integral (DLI) on inﬂorescence and ﬂower

bud count, number of mature and immature pseudobulbs, plant height,

SPAD value, and dry shoot and root weights of Degannoara Winter
Wonderland ‘White Fairy’ grown at 23 °C under a 16-h photoperiod ......... 183

3. The effect of estimated daily light integral (DLI) on inﬂorescence and ﬂower
bud count, number of mature and immature pseudobulbs, plant height,
SPAD value, and dry shoot and root weights of Miltassia Charles M. Fitch
‘Dark Monarch’ grown at 23 °C under a 16-h photoperiod. ....................... 184

4. The effect of estimated daily light integral (DLI) on inﬂorescence and ﬂower
bud count, number of mature and immature pseudobulbs, plant height,
SPAD value, and dry shoot and root weights of Zygopetalum Redvale ‘Fire
Kiss’ grown at 23 °C under a 16-h photoperiod. ........................................ 185

xi

LIST OF FIGURES

Figure Page
SECTION I

The growth cycle of Oncidium Goldiana under greenhouse conditions ........ 20

Orchid ﬂower anatomy .................................................................................. 21
SECTION II

Growth responses of Brassia Rex 'Sakata’ to various photoperiods (NI = 4-h
night interruption). Error bars represent 95% conﬁdence intervals. (L =
linear, Q = quadratic trends; NS, **, *** nonsigniﬁcant or signiﬁcant at P s
0.01 or 0.001, respectively) ......................................................................... 85

Flowering responses of Odontocidium Tiger Crow ’Golden Girl' to various
photoperiods (NI = 4-h night interruption). Error bars represent 95%
conﬁdence intervals. (L = linear, Q = quadratic trends; NS, *, **
nonsigniﬁcant or signiﬁcant at P s 0.05 or 0.01, respectively). ................... 86

. Growth responses of Odontocidium Tiger Crow ’Golden Girl' to various

photoperiods (NI = 4-h night interruption). Error bars represent 95%
conﬁdence intervals. (L = linear, Q = quadratic trends; NS nonsigniﬁcant). 87

Flowering responses of Zygopetalum Redvale 'Fire Kiss’ to various
photoperiods (NI = 4-h night interruption). Error bars represent 95%
conﬁdence intervals. (L = linear, Q = quadratic trends; NS, *, **, ***
nonsigniﬁcant or signiﬁcant at P s 0.05, 0.01 or 0.001, respectively). Data
were pooled in E. ........................................................................................ 88

Growth responses of Zygopetalum Redvale ’Fire Kiss' to various
photoperiods (NI = 4-h night interruption). Error bars represent 95%
conﬁdence intervals. (L = linear, Q = quadratic trends; NS, **, ***
nonsigniﬁcant or signiﬁcant at P s 0.01 or 0.001, respectively). Data for Year
2 in C and D. ............................................................................................... 89

SECTION III

Responses of Brassia Rex ‘Sakata’ forced at 23 °C under a 16-h photoperiod
after 9- or 16-h prevernalization photoperiods for 8 weeks and vernalization
(11, 14, 17, 20, or 23 °C) under 9- or 16-h photoperiods for 8 weeks. Error
bars represent 95% conﬁdence intervals. Data for days to visible
inﬂorescence (VI) are for the period from the end of vernalization until VI.
.................................................................................................................. 1 18

xii

Responses of Degarrnoara Winter Wonderland White Fairy’ forced at 23 °C
under a 16-h photoperiod after 9- or 16-h prevernalization photoperiods for
8 weeks and vernalization (11, 14, 17, 20, or 23 °C) under 9- or 16-h
photoperiods for 8 weeks. Error bars represent 95% conﬁdence intervals.
Data for days to visible inﬂorescence (VI) are for the period from the end of
vernalization until VI. ................................................................................. 119

Responses of Miltassia Charles M. Fitch ‘Dark Monarch’ forced at 23 °C
under a 16-h photoperiod after 9- or 16-h prevernalization photoperiods for
8 weeks and vernalization (11, 14, 17, 20, or 23 °C) under 9- or 16-h
photoperiods for 8 weeks. Plants in the 11 and 14 °C vernalization
treatments were discarded due to severe chilling injury. Error bars represent
95% conﬁdence intervals. Data for days to visible inﬂorescence (VI) are for
the period from the end of vernalization until VI. ....................................... 120

Responses of Miltoniopsis Augres ‘Trinity’ forced at 23 °C under a 16-h
photoperiod after 9- or 16-h prevernalization photoperiods for 8 weeks and
vernalization (8, 11, 14, 17, 20, or 23 °C) under 9- or 16-h photoperiods for
8 weeks. Error bars represent 95%conﬁdence intervals. ......................... 121

Responses of Odontocidium Tiger Crow ‘Golden Girl’ forced at 23 °C under a
16-h photoperiod after 9- or 16-h prevernalization photoperiods for 8 weeks
and vernalization (8, 11, 14, 17, 20, or 23 °C) under 9- or 16-h photoperiods
for 8 weeks. Error bars represent 95% conﬁdence intervals. Data for days
to visible inﬂorescence (Vl) are for the period from the end of pre-
vernalization until VI. ................................................................................. 122

Responses of Zygopetalum Redvale “Fire Kiss’ forced at 23 °C under a 16—h
photoperiod after 9- or 16-h prevernalization photoperiods for 8 weeks and
vernalization (11, 14, 17, 20, or 23 °C) under 9- or 16-h photoperiods for 8
weeks. Error bars represent 95% conﬁdence intervals. Data for days to
visible inﬂorescence (VI) are for the period from the end of vernalization until
VI. ............................................................................................................. 123

SECTION V

Inﬂuence of forcing temperature on leaf unfolding in Zygopetalum Redvale
’Fire Kiss'. Each symbol represents individual plants. (A) shows days for the
indicated developmental stage. The solid lines represent the regression
equation using pooled data for Year 1 and 2. Data at 28.6 °C were not
included in the regression equation. Lines in (B) represent predicted values
for the rate of progress (1/days) to leaf unfolding, based on linear
regression. Statistical analysis is presented in Table 2. ............................ 159

xiii

Inﬂuence of forcing temperature on daily increase in leaf length (cm) in
Zygopetalum Redvale ‘Fire Kiss’. Each symbol represents the average of 20
plants. ....................................................................................................... 160

Inﬂuence of forcing temperature on time from visible inﬂorescence to ﬂower in
Zygopetalum Redvale ’Fire Kiss'. Each symbol represents individual plants.
(A) shows days for the indicated developmental stage. The solid lines
represent the regression equation using pooled data for Year 1 and 2.

Lines in (C) represent predicted values for the rate of progress (1/days) to
ﬂowering, based on linear regression. Statistical analysis is presented in
Table 2. ..................................................................................................... 161

Inﬂuence of forcing temperature on inﬂorescence length in Zygopetalum
Redvale ‘Fire Kiss’. The symbol represents the average of 10 plants. Error
bars represent 95% conﬁdence intervals. ................................................. 162

Inﬂuence of forcing temperature on longevity of the ﬁrst open ﬂower and
inﬂorescence of Zygopetalum Redvale 'Fire Kiss'. Each symbol represents
individual plants. (A) and (B) show days for the indicated developmental
stage. The solid lines represent the, regression equation using pooled data
for Year 1 and 2. Lines in (C) and (D) represent predicted values for the
rate of progress (1/days) to the indicated developmental stage based on
linear regression. Statistical analysis is presented in Table 2. .................. 163

APPENDIX A

Inﬂuence of forcing temperature on longevity of the ﬁrst open ﬂower and
inﬂorescence of Miltassia Charles M. Fitch 'Dark Monarch'. Each symbol
represents individual plants. (A) and (B) show days for the indicated
developmental stage. The solid lines (-) represent the regression equation.
Lines in (C) and (D) represent predicted values for the rate of progress
(1/no. days) to the indicated developmental stage, based on linear
regression. Statistical analysis is presented in Table 1. ............................ 170

APPENDIX B

Inﬂuence of forcing temperature on leaf unfolding in Brassia Rex 'Sakata’.
Each symbol represents individual plants (total of 20). (A) shows days for
the indicated developmental stage. The solid lines (—) represent the
regression equation. Lines in (B) represent predicted values for the rate of
progress (1/days) to the indicated developmental stage, based on linear
regression. Statistical analysis is presented in Table 1. ............................ 176

Inﬂuence of forcing temperature on daily increase in leaf length in Brassia
Rex ‘Sakata’. Each symbol represents the average of 20 plants. ............. 177

xiv

SECTION I

LITERATURE REVIEW

Vernalization

The physiology of ﬂowering in higher plants is an extraordinarily complex
process inﬂuenced by both autonomous and environmental regulation. In certain
plants, ﬂowering is independent of the surrounding environmental conditions,
which is known as autonomous ﬂowering. In the majority of plants, the transition
from vegetative growth (juvenility) to ﬂowering is a process determined by the
interaction of developmental regulation and environmental cues such as changes
in daylength (photoperiodism) light quantity (photon ﬂux density), light quality
(spectral composition), nutrient and water availability, and extended periods of
low temperatures (vernalization).

Some plants have an absolute requirement for speciﬁc environmental
cues for ﬂowering, which is referred to as an obligate or qualitative response. In
other plants, ﬂowering is promoted by certain environmental cues but plants will
eventually ﬂower in the absence of such a cue. These plants have a facultative,
or quantitative, response to such a cue. Horticulturally, vernalization and
photoperiod are the two most common mechanisms that control ﬂower initiation.

Vernalization is the promotion of ﬂowering of imbibed seeds or vegetative
plants by low temperatures. The word “vernalization” is the translation of
yarovizatzya, which combines the Russian root for spring with the sufﬁx meaning
“to make,” and was derived from the observation that a cold treatment made
strains of winter wheat (Triticum aestivum L.) behave like spring strains (Thomas
and Vince-Prue, 1984). Vernalization was further deﬁned by Chouard (1960) as

“the acquisition or acceleration of the ability to ﬂower by a chilling treatment".

A vernalization response is often observed in regions with low winter
temperatures, which are unfavorable for growth and reproduction. A cold
requirement prevents plants from ﬂowering until the spring when environmental
conditions are more favorable. A combined vernalization and photoperiod
requirement can ensure that ﬂowering occurs later in the spring rather than at the
end of the winter. Low temperature requirements for ﬂower induction have also
been documented in tropical orchids. They may vary from more distinct
elevation-dependant temperature ﬂuctuations required by Phalaenopsis
schillen'ana to subtle rain-induced cooling, which initiates ﬂowering in
Dendrobium crumenatum (Goh et al., 1982).

Initiation of ﬂower primordia generally does not occur at vernalizing
temperatures. After exposure to low temperatures, plants are in a vernalized
state (thermoinduced) and have the ability to ﬂower under favorable conditions
(Thomas and Vince-Prue, 1997). Depending on the species, these favorable
conditions can be long days, short days or simply higher temperatures.
However, a vernalization response is mainly observed in long-day plants, which
have extended periods of vegetative growth and ﬂower in the early summer at
high latitudes (Vince- Prue, 1975). These species may be perennials, biennials,
or winter annuals. Some well-documented examples of plants that exhibit this
behavior are winter wheat, the biennial form of henbane (Hyoscyamus niger L.)
(Chouard, 1960), Coreopsis grandiﬂora (Hogg ex Sweet) ‘Sunray’, Aquilegia

xhybrida Sims, and AchiIIea ﬁlipendulina Lam. “Cloth of Gold’ (Heins et al., 1997).

Effects of Low Temgrature

Plants respond to low temperature in ways other than ﬂowering. Often,
speciﬁc temperature regimens initiate critical steps in the life cycle: induction and
breaking of dormancy, and seed gemtination. Donnancy is often overcome
following exposure to cool temperatures for a particular duration, which removes
growth inhibitors, and allows the emergence of pre-formed buds in woody
perennials (Salisbury and Ross, 1992). The breaking of seed don'nancy by
exposure of moist seeds to low temperatures is often referred to as stratiﬁcation
or prechilling. Many seeds require a period of cold (0 to 10 °C) while in a fully
imbibed state to germinate. This ensures that seeds do not germinate in the
autumn, but rather the following spring. Generally, dry seeds do not respond to
cold treatments.

Low temperature can directly affect ﬂoral initiation and development of
brussel sprouts (Brassica oleracea gemmifera L), In's sp. ‘Wedgewood’, stock
(Matthiola incana R. Br.), honesty (Lunan'a biennis L.) and onion (AIIium cepa L.)
(Chouard, 1960; Thomas and Vince-Prue, 1997). These direct effects of low
temperatures on ﬂowering can be distinguished from vernalization, which is an
inductive phenomenon.

Plants of tropical origin may show signs of chilling injury if they are
exposed to cool, above-freezing temperatures. “Chilling injury is a physiological
response of plants and their products that results in reduced quality and loss of
product utilization following exposure to low temperatures” (Parkin et al., 1989).

Several symptoms are observed when plants are maintained at or below low

temperatures for some period of time (Lyons, 1973). For example, exposure to
temperatures of 2, 4, and 7 °C for 1, 2, 4, and 8 h resulted in spotting and pitting
of Phalaenopsis leaves (McConnell and Sheehan, 1978). The greatest amount
of injury was observed in plants subjected to 2 °C for 8 h. Symptoms ranged
from small water-soaked spots visible 0.5 h after removal from the chilling
temperatures, to pale green areas visible after 48 h. The areas then became
yellow, collapsed and were prominent after two weeks. Within three weeks, the
pitted areas began to darken and resembled virus symptoms. McConnell and
Sheehan (1978) found that hypertrophied mesophyll cells that became collapsed
between the main vascular bundles caused the pitted areas on leaves. Severity
of the response depended on the physiological age of the leaf and the duration of
the exposure to the chilling temperature. Chilling injury was conﬁned to younger

leaves between 50 to 75 % of their mature length.

Requirements for Vernalization

Plants must be mature, or beyond the juvenility phase, before they can
respond to vernalization. In most woody plants, the juvenility period may last
several years and can last up to 30 to 40 years in some forest trees (Thomas and
Vince-Prue, 1984). Herbaceous plants have juvenile periods ranging from a few
days to many weeks in duration. The terms “ripe-to—ﬂower” and “capacity to
ﬂower” are used for plants that have completed the juvenile phase of their life
cycle, but have not received the appropriate environmental conditions for

ﬂowering.

In all plant tissues studied, oxygen, water and carbohydrates must be
present for vernalization to occur (Chouard, 1960; Lang, 1965). Treating imbibed
or germinating seeds that are metabolically active satisﬁes the cold requirement
of winter annuals. Seeds can be vernalized on the parent plant, but they must
have a water content of about 40 to 50% of their dry weight. The time required
for complete vernalization of winter annuals is about 40 to 45 d.

Some biennials such as beet (Beta vulgaris L.) can be vernalized as {
seeds. The vast majority germinate in the spring, forming vegetative plants that
grow as rosettes during their ﬁrst year. With the coming of the second spring,
new leaves form and there is a rapid elongation of the ﬂowering shoot. A cold
treatment is only effective after the plant has reached a certain size.

Flowering of several perennial grasses is also promoted by cold. Some of
these grasses have a subsequent long—day requirement. Poa alpina L. and Poa
alpigena require three to four weeks of exposure to 3 to 6 °C under 8-h
photoperiods for primary induction to (initiate inﬂorescence primorida) and a
secondary induction requirement for long-days (for culm elongation,
inﬂorescence development and anthesis) (Heide, 1994). The vernalization

requirement for perennials is re-established during sexual reproduction.

Site of Perception
Perception of vernalization is believed to occur in the meristematic regions
of growing apices. In addition, all actively dividing cells may be capable of

responding to low temperatures (Levy and Dean, 1998). Experiments on celery

(Apium graveolens L.), radish (Raphanus sativus L.), sugar beet, and
Chrysanthemum indicate that low temperatures are perceived by cells in the
shoot apex (Crosthwaite and Jenkins, 1993). Chilling the roots of ﬁeld
pennycress (ThIaspi arvense L.) at 4 °C for four weeks was ineffective, whereas
chilling only the shoot tips initiated reproductive development when plants were
transferred to long days and 21 °C (Metzger, 1988). In Lunaria biennis L.,
meristematic cells in the leaf petiole could be vernalized at 5 °C under a 12-h
photoperiod, and the vernalized state was transferred to plants regenerated from
those cells (Wellensiek, 1965).

However, in winter rye (Secale cereaIe L), and Cheiranthus allionii seeds,
low temperature treatments to non-meristematic tissue promoted ﬂowering
(Thomas and Vince-Prue, 1997). In another experiment, shoots regenerated
from leaf cuttings of vernalized pennycress plants, which were fully expanded
prior to low temperatures, developed reproductively (Metzger, 1988). These
studies collectively suggest that vernalization requires cells undergoing mitosis.
However, the vernalization requirement is reestablished during meiosis and

progeny must be exposed to low temperatures to ﬂower.

Effective Temperatures

Vernalization is a quantitative process that increases in magnitude until,
with prolonged exposure, a saturation response is obtained. Horticulturally, the
effectiveness of vernalization can be evaluated as a reduction in the days to

ﬂower, increased uniformity in ﬂowering, higher ﬂowering percentage, increased

ﬂower production and vigor (Runkle et al., 1998). It is dependent on the cooling
temperature and its duration. The length and effective temperature range for
vernalization varies by species. The consistency of the cold treatment can also
impact the effectiveness of vernalization. In general, plants require several
weeks of cold to saturate the vernalization response, with 4 to 12 weeks being
typical (Michaels and Amasino, 2000). Eight days of cold causes a substantial
increase in ﬂowering of celery with maximal promotion after four weeks (Michaels
and Amasino, 2000).

The effective temperature range for vernalization is between -5 to 15 °C
with a broad optimum between 1 and 7 °C (Lang, 1965). Usually the lower limit
is set by the formation of ice crystals within the tissues. In certain plants native to
tropical regions, such as Phalaenopsis orchids, four to ﬁve weeks of
temperatures 3 20 to 22 °C are effective (Wang, 2001). Yet in some cereals, a
response to vernalization is achieved at temperatures as low as -6 °C. In some
plants that respond to vernalization, short days can substitute partially or entirely

for low temperatures (Thomas and Vince-Prue, 1997).

Obligate or Facultative Requirements

Plants that will not ﬂower unless exposed to low temperatures have a
qualitative, absolute, or obligate cold requirement. Most plants that possess this
requirement are biennials or herbaceous perennials. Annual sugar beets (Beta
vulgaris L.) are known to have a facultative response and biennials often have an

obligate requirement for vernalization (Lexander, 1985; Crosthwaite and Jenkins,

1993). In Oenothera fruticosa ‘Youngii-lapsley’, ﬂowered after receiving 2 3
weeks of cold (at 5 °C) and only one non-vernalized plant ﬂowered (Clough et al.,
2001). Whitman et al. (1996) showed that exposure to 5 °C for 10 to 15 weeks
was the primary factor promoting complete ﬂowering of Lavandula angustifolia
Mill. ‘Munstead.’

Plants in which ﬂowering is hastened after exposure to low temperatures,
but will eventually ﬂower without cold, have a quantitative, facultative, or cold-
stimulated requirement. Many winter annuals and herbaceous perennials posses
this response. For example, in Rudbeckia fulgida Ait. ‘Goldsturm’, 15 weeks of 5
°C under photoperiods 2 13 hastened ﬂowering by 25 to 30 d (Runkle et al.,
1999). Flowering of Phlox paniculata Lyon ex Pursh ‘Eva Cullum’ was hastened
from (114 to 64 d) by vernalization as photoperiod increased from 10 to 24 hours
when exposed to 15 weeks of 5 °C and ﬂowering percentages never reached
100% without cold (Runkle et al., 1998).

Facultative and obligate requirements can vary between cultivars and
species. There are three types of vernalization responses in wheat (Triticum
aestivum L.) cultivars: 1) qualitative, 2) quantitative, and 3) unresponsive
(Gardner and Barnett, 1990). Another interesting example of both facultative and
obligate vernalization requirements is that of the Oenothera species. Many
species of Oenothera, including 0. suaveolens Pers., O. Iongiﬂora L., and O.
stn'cta Lebed. ex Link, have facultative requirements for vernalization followed by

obligate requirements for long-days (Chouard, 1960). In contrast, Oenothera

fruticosa ‘Youngii-lapsley’ is a facultative long-day plant with an obligate

vernalization requirement (Clough et al., 2001).

Induced State

Flower development typically begins several days or weeks after the end
of the cold treatment. This induced state can persist several weeks or months,
varying by species. Certain cereal seeds, for example, can be moistened (to 40
percent water, which is inadequate for germination to occur), vernalized, and
then dried and maintained for months or even years without loss of the
vernalized state (Salisbury and Ross, 1992). Henbane, which requires long days
after vernalization, can be placed under short days to delay ﬂowering. No loss of
the vernalization stimulus appears in such plants after 190 short days, even after
all the original leaves exposed to the cold had died. Chrysanthemums must be
exposed to cold temperatures before they can respond to short days, and are
commonly propagated by cuttings that retain their initial vernalized condition.
Devernalization

The reversal of the vernalized state, or devernalization, can occur during
or immediately following vernalization. The most common method for
devemalization is by exposure to high temperatures of 18 to 40 °C immediately
following exposure to vernalizing temperatures (Lang, 1965) and anerobic
conditions (Chouard, 1960). If low temperature treatments have been sub-
optimal, susceptibility to devemalization increases. Devernalizing temperatures

for winter rye are 2 30 °C and must be applied for a few days and within four or

10

ﬁve days after the low temperature period (Salisbury and Ross, 1992). Exposure
to daytime temperatures of 30 °C for 2 d during or immediately after vernalization
did not devernalize Campanula ‘Birch Hybrid’ plants, while a 4 d exposure
decreased ﬂowering percentage and delayed ﬂowering by 7 to 10 d (G. Niu,
personal communication). After devernalization, many species can be
revernalized with another cold treatment.

It has also been reported that short days (SD) can lead to devemalization
in Oenothera biennis and Cheiranthus allionii (Wellensiek, 1965). However, once
the cold requirement has become saturated, the vernalized condition is extremely
stable and persists throughout the vegetative phase until the plants ﬁnally ﬂower
(Thomas and Vince-Prue, 1997). For example, in Hyoscyamus, a plant with an
absolute requirement for cold and long days, the vernalized state is retained for

over seven months when placed under short days (Lang, 1965).

Genetic and Molecular Components

While the physiology of vernalization has been studied extensively in
some species, the genetic and molecular mechanisms remain largely unknown.
Recent studies have revealed some of the molecular events that create the
requirement for vernalization. The appearance of early-ﬂowering ecotypes in the
evolution of Arabidopsis thaliana suggests that there has been strong selection in
some environments for ecotypes that do not require vernalization due to milder
winters (Johanson et al., 2000). Genetic analysis of early- and late-ﬂowering

ecotypes of Arabidopsis has identiﬁed two loci that account for most of the

11

differences in time to flowering. The products of these two loci, Flowering Locus
C (FLC), and FRIGIDA (FRI) appear to act synergistically to cause late ﬂowering
(Napp-Zinn, 1987; Lee et al., 1993; Koorneef et al., 1994). Vernalization is
believed to suppress both FRI and FLC; both alleles interact to repress ﬂowering,
with the level of FLC and FRI expression determining time to ﬂower (Koorneef et
al., 1994; Lee and Amasino, 1995; Johanson et al., 2000). The repression of

ﬂowering by FLC and FRI ensures that ﬂowering in the various ecotypes will

. 7‘3}

occur under favorable conditions in the spring.

VERNALI_ZATION (VRN) gene

Plants with a mutation in the VERNALIZA TION (VRN) gene were thought
to be impaired in their ability to perceive cold or in the transduction of the cold
signal by the vernalization pathway (Levy and Dean, 1998). To test this
hypothesis, vm1 and vm2 Arabidopsis mutants were isolated based on their
reduced vernalization response in the late-ﬂowering vemalization-response fca-1
mutant. Neither vm1 nor vm2 were impaired in their ability to acclimate to low
temperatures. However, neither mutant was able to reduce FLC mRNA in
response to low temperatures (Simpson et al., 1999). This indicates that the
defect in these genes is speciﬁc to the vernalization pathway and not to low-
temperature responses in general. Both fee I vm1 and ice I vm2 double mutants
show FLC messenger RNA (mRNA) accumulation and an increase in time to
ﬂower. This suggests that the VRN1 and VRN2 genes may mediate the

vemalization-induced down-regulation of the PLO gene (Sheldon et al., 1999;

12

Sheldon et al., 2000). The recent cloning of VRN2 indicates that the repression
of FLC by VRN2 is stably maintained and serves as a cellular memory of
vernalization (Gendall et al., 2002). It is also speculated that VRN1 and VRN2
are involved with the perception of light quality during vernalization (Levy and

Dean, 1998).

FLOWERING LOCUS C (FLC)

The FLOWERING LOCUS C (FLC) gene is thought to act as a strong
ﬂoral repressor by negatively regulating the expression of genes that promote the
transition to ﬂowering (Michaels and Amasino, 1999b). In Arabidopsis, FLC can
be found mainly in roots and vegetative shoot apices, to a lesser extent in the
leaves and stems, and is undetectable in the inﬂorescence. Exposure of
germinating seeds to low temperatures reduces levels of FLC transcript mRNA
and its protein product. Furthermore, the longer the period of exposure to cold,
the less FLC mRNA is produced and the earlier ﬂowering occurs (Michaels and
Amasino, 1999b). Levels of FLC mRNA are not affected by photoperiod or plant
age (Michaels and Amasino, 1999b).

Landsberg erecta (Ler) is an early ﬂowering ecotype of Arabidopsis. Its
late ﬂowering mutants exhibit very high levels of FLC transcript, which is reduced
after vernalization (Sheldon et al., 2000). A vernalization treatment also reduces
FLC transcript in other late ﬂowering ecotypes, which suggests FLC is a common
repressor of ﬂowering. When FLC is over-expressed, ﬂowering is delayed,

whereas in a loss-of-function mutant, ﬂowering occurs early (Koorneef et al.,

13

1994; Michaels and Amasino, 1999b). Arabidopsis lines with additional copies of
FLC never ﬂower in the absence of cold and respond as true biennials (Michaels
and Amasino, 2000). However, even when there is a complete Ioss-of-function
of FLC, plants possess the ability to respond to vernalization (Michaels and
Amasino, 2000). These ﬁndings suggest that there are two or more pathways

that lead to a vernalization response, with at least one that is FLC-independent.

I

One component of the FLC-independent pathway may be VRN1 and
VRN2 (Sheldon et al., 2000). These two genes are thought to be active in both
the FLC-dependent, and FLC-independent pathways. Mutants vm1 and vm2
have been isolated and identiﬁed as having a small vernalization response
(Chandler et al., 1996).

There are two types of FLC alleles: late ﬂowering and suppressor (Sanda
and Amasino, 1996; Sheldon et al., 2000). Late ﬂowering types are most
common and promote vegetative growth in FRI mutants. Suppressor FLC alleles
inhibit late ﬂowering in FRI mutants. Despite differences in their mode of action,
Arabidopsis ecotypes C24, Col and Ler have the same nucleotide sequence of
the coding region (Sheldon et al., 2000). Thus, it is likely that the FLC alleles in
these ecotypes differ in some aspect of their regulation, perhaps as a result of
the sequence differences in the promoter region of the FLC gene.

FLC codes for a MADS-box type transcription factor (Michaels and
Amasino, 1999b). It has been identiﬁed as a “semidominant repressor of ﬂoral

induction” and is believed to be the central regulator of the transition to ﬂowering

14

in response to vernalization in Arabidopsis. Homologue MAF1 (MADS Affecting
Flowering 1) encodes a protein very similar to FLC and has a 62% amino acid
sequence identity with FLC (Ratcliffe et al., 2001). Studies with this homologue
have shown similar results to FLC when overexpressed with the cauliﬂower
mosaic virus 35S promoter. However, late ﬂowering MAF1 were not overcome
by vernalization and were thought to act independently of FLC. Ratciffe et al.
(2001) proposed a gene family of six FLC-like genes that regulate time to ﬂower

downstream of FLC.

FRIGIDA (FRI)

FRIGIDA (FRI) gene activity is also associated with late ﬂowering in
Arabidopsis. FRI encodes a protein that promotes the accumulation of FLC
mRNA (Michaels and Amasino, 1999b; Simpson and Dean, 2002). The
predicted protein is not similar to other proteins with known functions (Johanson
et al., 2000). By promoting the accumulation of FLCmRNA, FRI can repress
ﬂoral transition to a degree where it overrides favorable conditions.

To test whether FRI acts solely through FLC, Michaels and Amasino
(2001) analyzed the ﬂowering behavior of isogenic lines containing dominant and
recessive FRI alleles in an ﬂc-3 mutant. As has been shown in previous
experiments, FRI strongly delays ﬂowering in the wild type. In the ﬂc-3 mutant,
the effect of FRI is eliminated under both long and short day conditions. Thus,
the late-ﬂowering phenotype is likely to result from an upregulation of FLC

activity.

15

_I\LA demethylation

Low temperature (vernalization) has been linked with the demethylation of
DNA (Burn et al., 1993). In this process, demethylation occurs in the promoter
region of a gene or genes whose expression is critical for the induction of
ﬂowering. Vernalization of four to eight weeks reduced DNA methylation in
Arabidopsis by 15% compared with seedlings that were not vernalized (Finnegan
etaL,1998)

Treatments with the demethylation agent 5-azacytidine (5-azaC) can
mimic the vernalization response and thus accelerate ﬂowering. With no prior
vernalization treatment, germinating Arabidopsis seeds treated with 5-azaC
showed earlier ﬂoral initiation and a reduction in the number of rosette leaves
formed before ﬂowering (Burn et al., 1993). This process is only observed in late
ﬂowering ecotypes of Arabidopsis that require vernalization; early ﬂowering
ecotypes showed no response to 5-azaC. In addition. vernalized plants ﬂowered
earlier than those treated with the demethylation agent. This suggests that
demethylation alone does not regulate the vernalization response.

In addition to causing demethylation, 5-azaC is a general inhibitor of
transcription; therefore, it is possible that the promotion of ﬂowering by 5-azaC
results from effects other than demethylation of DNA. To test this hypothesis,
Finnegan et al. (1998) used Arabidopsis plants that had reduced levels of DNA

methylation due to the presence of a methyltransferase (ME TI) antisense

transgene. They'found that the demethylation of DNA is sufﬁcient to cause early

16

 

ﬂowering and that the promotion of ﬂowering was directly proportional to the
decrease in methylation in the ME TI antisense lines.

Plants that have reduced levels of methylation show a number of
pleiotropic effects including expression of ﬂoral organ-identity genes such as
AGAMOUS, which is known to induce ﬂowering when ectopically expressed
(Michaels and Amasino, 2000). Thus, changing patterns of DNA methylation
may contribute to the epigenetic changes in gene expression that are likely
responsible for the vernalized state. However, more research is needed to

establish the molecular basis of this event.

We

Photoperiodism refers to the response of plants to the length of day. The
word is derived from the Greek roots for “light” and “duration of time.” Hillman
(1969) deﬁned photoperiodlsm as a response to the timing of light and darkness.
Plant responses inﬂuenced by daylength include bud dormancy, formation of
storage organs, asexual reproduction, leaf development, stem elongation,
germination, and ﬂower initiation and development (Thomas, and Vince-Prue,
1984).

The classiﬁcation of plants according to their photoperiodic response is
usually made on the basis of ﬂowering. With respect to ﬂower initiation, most
species’ responses to daylength can be classiﬁed into three groups. Day-neutral
plants (DNP) ﬂower regardless of the photoperiod to which they are exposed. In

short-day plants (SDP), ﬂowering occurs only in, or is accelerated by daylengths

17

shorter than a particular duration known as the “critical daylength”. Flowering in
long-day plants (LDP) occurs only in, or is accelerated by daylengths exceeding
a particular duration. Less commonly, some species have a dual daylength
requirement, Le. a period of short days followed by a period of long days, or vice
versa (SLDP and LSDP) (Thomas and Vince-Prue, 1997). Responses to
daylength can be further divided into two categories: qualitative or quantitative.
Some tropical plants of equatorial origin are believed to be more sensitive
to small differences in daylength than those from temperate regions (Sanford,
1974). An example of a tropical plant inﬂuenced by photoperiod is the epiphytic
cacti Hatiora spp, which is classiﬁed botanically as a SLDP for ﬂowering at 15-20
°C (Boyle, 1991). In its native habitat of Panara and Santa Catarina, Brazil (~26
°S lat.) the shortest civil daylength (the duration of time when the sun is 6° below
the horizon before sunrise to 6° below the horizon after sunset) is 11 h 28 min
and the critical photoperiod for photoinduction in Hatiora is 11-12 h (Boyle, 1991).
Schlumbergera tmncata and Cattleya spp are SD tropical epiphytes native
to the Organ Mountains north of Rio Janeiro, Brazil (~22 °S lat.) where the
photoperiod ranges from 11 to 13.5 h (Morrison, 2000). Commercially,
Schlumbergera is placed under 8 to 11 h short day photoperiods and night
temperatures of 13 to 15 °C for ﬂower initiation (Dole and Wilkins, 1999). In
Cattleya warscewiczii, C. gaskelliana, and C. mossiae, ﬂower induction occurs
under continuous 9-h short days at 13 °C, while ﬂowering is inhibited under 16-h

long days at 13 °C (Rotor, 1952; Rotor 1959).

18

Rohwer (2002) reported that a 10-h short day treatment followed by a
vernalization treatment at 12.5 or 15 °C increased ﬂowering percentage and
apical phylloclades ﬂowering, bud number per ﬂowering apical phylloclade of
Hatoria gaertnen'. The most uniform ﬂowering occurred when plants were
exposed to a sequence of six weeks of short days, vernalization at 8 to 15 °C for

eight weeks, followed by long-days at warmer temperatures.

Orchids

The Orchidaceae is the largest and most diverse of all plant families.
Approximately ten percent of all ﬂowering plant species are orchids, which
comprise 20,000 to 25,000 species grouped into 725 genera (Griesbach, 1985).
In addition to the natural abundance of orchids, there are > 100,000 man-made
hybrids. Orchids are indigenous to a wide array of mesic and xeric habitats,
including tropical and temperate forests, prairies, tundra and even deserts
(Morrison, 2000). In the tropics, orchids are distributed according to elevation
gradients. Diversity is highest in the montane cloud forests between 1000 to
2000 m above sea level (Morrison, 2000). The greatest abundance is found in
regions with annual rainfall of 250 cm or more.

Orchids are terrestrial, lithophytic or epiphytic as they are found growing in
soils, on rocks or on trees. Most terrestrial orchids have storage organs in the
form of corms, rhizomes, or tuberoids, while epiphytes have enlarged stems

referred to as pseudobulbs and aerial roots (Ng and Hew, 2000). The vast

19

majority of tropical orchids are epiphytic and water availability is the limiting factor

to their distribution (Fu and Hew, 1982).

 

 

¢ .- 7 to 28 days
Pseudobulb
' stage with
inﬂorescence
7 to 28 days ' 2;. / r
3
V7; / "
35 t° 49 Unsheathing sta
ge
days \\ 28 to 35 days
“t I 05/ 4
I ———’ 1&7.»
Bud stage Plantlet 35 to 49 days A
\ stage

 

Unsheathing stage with
7 to 14 days

young inﬂorescence

56 to 70 days

Pseudobulb stage with inﬂorescence

 

5cm

 

Figure 1. The growth cycle of Oncidium Goldiana under greenhouse conditions
(Hew and Yong, 1997)

In monopodial orchids such as Phalaenopsis, the stem apex grows
indeﬁnitely resulting in a single upright shoot. New leaves develop from the end

of the apical stem. As a rule, monopodials produce lateral inﬂorescences

20

Sympodial orchids such as Cattleya have repeated growth cycles producing
clumps of pseudobulbs and axillary buds. The axillary buds are present at the
base of the pseudobulb and are not normally visible because leaves cover them.

Most sympodial orchids produce terminal, lateral, or both types of inﬂorescences

(Figure 1).
anther cap
dorsal sepal
FA, - petal
column 5/ (”j/ﬂ
/" //-. j
'54“
<,
. ' VS'V’ lateral sepal
stigma I

 

Figure 2. Orchid ﬂower anatomy (Rittershausen and Rittershausen, 2001)

Orchids are considered the most evolutionarily advanced of all
monocotyledons, having specializations for pollination, water uptake and storage
in pseudobulbs, seed germination and associations with fungi. One feature
deﬁnes the orchid from all other ﬂowering plants: their stamens and pistils are
fused into a structure termed the column (gynostemium) (Figure 2). Such

monandrous orchids have a single fertile stamen with pollen massed into packets

21

termed pollinia. The ﬂowers are zygomorphic, meaning they are symmetrical

about a single plane (Morrison, 2000).

Orchidjomenclattﬂ

Following Linnaeus’s binomial system, orchids have two Latin names for
their species, e.g., Cattleya skinneri. Closely related genera are grouped into
subtribes, names ending in -inae. For example, Cattleya is in the subtribe
Laeliinae along with its relatives such as Laelia and Encyclia. Related subtribes
are then grouped into larger taxonomic units referred to as tribes; names of tribes
end in -eae. Subtribe Laeliinae is in the tribe Epidendreae. Finally, related tribes
are grouped into a subfamily, the names of which always end in -oideae. The
tribe Epidendreae is in the subfamily Epidendroideae. For hybridizations or
awards, speciﬁc plants are given clonal or cultivar names, following species
names and enclosed in single quotes such as Cattleya skinneri ‘Many’. An
award that a clone receives then follows the clonal name, e.g., Cattleya skinneri
‘Many’ CCMIAOS (certiﬁcate of cultural merit) (Morrison, 2000). There are
several national orchid societies that grant awards for ﬂower quality or cultural
excellence: the American Orchid Society (AOS), the Royal Horticultural Society

(RHS), Detsche Orchideen-Gesellschaft (DOG).

Commercial Genera
Brassia. Approximately 25 to 30 species, mainly epiphytes, make up the

genus Brassia (or the spider orchid). They are distributed from the warm forests

22

of Costa Rica and islands of the West Indies at low elevations of 200 m, to the
mountains of Brazil and Peru at elevations of 2000 to 3000 m (Rentoul, 1982).
They are characterized by compressed, oblong and cylindrical pseudobulbs
surrounded by up to three leaves at their apex and the lower portions are
sheathed by basal leaves. The inﬂorescence develops from the side of the
pseudobulb and is enclosed by the longer of the sheathing leaves or bracts.
Although closely related to the Oncidium, the ﬂowers of Brassia are distinct due
to their musky fragrance and long tail-like sepals, which range in color from pale
green to golden yellow with black markings. The genus is named in honor of the
18th century botanical artist William Brass, who collected orchids in South
America and South Africa (Stewart and Grifﬁths, 1995).

Cattleya. Cattleya is a genus composed of 60 species originating
throughout tropical regions of Central and South America. The epiphytic plant is
found growing atop trees of moist and wet forests from sea level to 1500 m in
elevation. They are characterized by the presence of cylindrical pseudobulbs of
several nodes with thick apical leaves, and at the apex is a bud primordium
capable of developing into an inﬂorescence (Morrison, 2000). There are often
other bud primordia at the basal part of the pseudobulb that give rise to
vegetative shoots (Rotor, 1952). The racemose inﬂorescence has large and
showy ﬂowers. The discovery of Cattleya (known as the corsage orchid) is
credited to William Cattley. In 1818, pseudobulbs of C. Iabiata were sent from

the Organ Mountains near Rio de Janeiro, Brazil, as packing material for other

23

ornamental plants. Cattley had the plants moved to his greenhouse where they
later ﬂowered (Morrison, 2000).

Cymbidium. Cymbidium is a genus of approximately 50 species native
from tropical Asia to Australia. They are terrestrial, epiphytic, lithophytic and
semi-epiphytic plants. A characteristic shared by most Cymbidium is the large
globose-conical or oval compressed pseudobulbs, sheathed by the base with
long and narrow leaves. The inﬂorescence is produced form the axils of the
lower leaves. The large and showy ﬂowers bear a three-lobed labellum with a
central ridged callus (Morrison, 2000).

Degannoara. Degarmoara is an epiphytic hybrid between Miltassia
cartagena x Odontoglossum gledhow that produces large pseudobulbs and
leaves that grow to 40 cm or more in height. This star shaped orchid produces
large 10 to 15 cm ﬂowers with small purple spots and yellow streaks towards the
center of the petals and sepals. The ﬂower spikes appear from large and swollen
pseudobulbs.

Dendrobium. Dendrobium (or the spray orchid) is one of the largest
genera of the orchid family, with some 900 species that are native to tropical and
subtropical Asia, Australia and various Paciﬁc Islands (Eigeldinger and Murphy,
1972). Its epiphytic origin is identiﬁed with the Latin name of the genus: dendron,
“a tree” and bios “life”. A few species are fragrant, but the scent of some can be
unpleasant. Most Dendrobium form tall cylindrical stem-like pseudobulbs with
long spikes that grow from the apex. An exception is D. nobile, where the

ﬂowers are produced in clusters of two or three from the nodes along the stem-

24

like pseudobulb. Dendrobium monilifonne, possibly the ﬁrst Dendrobium in
cultivation, is mentioned in Chinese literature as early as the Chin Dynasty (290-
307 AD). It was not until 1799 that Olaf Swartz established the genus. Early
attempts in Europe of cultivating Dendrobium failed, as most gardeners did not
understand the conditions of tropical environments.

Miltassia. Miltassia are epiphytic hybrid between Brassia verrucosa x
Miltonia spectabilis. Their growth is characterized by the presence of two apical
light green leaves on large pseudobulbs. Miltassia have deep plum purple, star
shaped ﬂowers, with pale green halos. The ﬂower spikes appear from the base of
mature and immature pseudobulbs. Flowers can last from four to six weeks.

Miltoniopsis. Miltoniopsis is an epiphytic or lithophytic genus of six
species distributed from the extremely wet cloud forest regions (610 to 2,100 m)
of Costa Rica to Peru (Baker and Baker, 1993b; Morrison, 2000). Their
sympodial growth habit is characterized by the presence of one gray-green apical
leafed pseudobulb surrounded by leaf-like sheaths. The pseudobulb is capable of
producing one or more inﬂorescences only when it is mature. The fragrant
ﬂowers are ﬂat, large and showy, ranging in color from cream to pink to magenta
to scarlet. The ﬂowers can last four to eight weeks on the plant (Baker and
Baker, 19933). John Lindley named the genus in honor of the orchid enthusiast
Lord Fitz-William Milton (1786-1857) (Berliocchi, 1996). In 1889, Godefroy-
Lebeuf separated Miltonia into two groups, Miltonia and Miltoniopsis. However,
this distinction was not ofﬁcially recognized until 1976 (Rentoul, 1982), and in

some literature the two groups are treated as one genus for registration

25

purposes. Miltoniopsis has one-leafed pseudobulbs, while Miltonia has two-
leaved pseudobulbs. Miltoniopsis are the ﬁfth most valuable potted orchid
commercially produced in the Netherlands, with 797,000 pots sold in 2001
(Barendse, 2002). Often, Miltoniopsis are referred to as the cool—growing,
Colombian miltonias or the pansy orchid.

Phalaenopsis. The genus Phalaenopsis is made up of =50 species
originating from tropical and subtropical areas of the South Paciﬁc Islands and
Asia (Baker and Baker, 1991). Their distribution in the South Paciﬁc extends
from Southern India to Australia. In Asia, they are found in China, Taiwan and
the Philippines. The greatest concentration, and the species that have had the
greatest inﬂuence on hybridizing, have originated from the Philippine Islands
(Rittershausen and Rittershausen, 2000). All Phalaenopsis are monopodial, and
the vast majority are epiphytic. The ﬁrst Phalaenopsis plants were discovered by
Rumphius in 1750, however they were not classiﬁed until 1825 when Karl Ludwig
Blume placed them into the genius Phalaenopsis. The word Phalaenopsis was
derived from two Greek words: phalaina, meaning “moth” and opsis, denoting
“resemblance”. The common name for Phalaenopsis is the “moth orchid”.
Today’s Phalaenopsis cultivars range in color from pure white, lavender, purple,
red, and yellow. Most ﬂowers are long-lasting and can stay in bloom two to four
months under favorable conditions (Wang, 1994).

Zygopetalum. Zygopetalum or the Iadybird orchid is a sympodial,
terrestrial, and epiphytic South American genus made up of z20 species. They

are native to neotropic mid-elevation mountains (1,300 to 1,700 m) of Brazil,

26

Guiana, Venezuela and Peru (Rose, 1993). Zygopetalum Redvale ‘Fire Kiss’ is
moderately compact (25- to 40-cm tall) and produces two to three, broad and
leathery leaves atop mature green pseudobulbs. Four or more leaf-like
sheathing bracts, which grow from the base, protect the immature pseudobulbs
but these bracts become dry and ﬁbrous with age (Baker and Baker, 1991). The
erect inﬂorescences emerge from the third, forth or fifth sheathing bract of
immature pseudobulbs. Lime-green and dark maroon sepals and petals,
featuring broad three-lobed Iabellums in deep magenta and white, characterize
the exotic, fragrant and waxy ﬂowers. William Jackson Hooker named the genus
in 1827, referencing the Greek word zygon (yoke) and petalon (petal or sepal),
which pertains to the thickened callus at the base of the labellum that appears to

hold together (or yoke) the petals (Monkhouse, 1994).

Commercial Production

In 1957, James Shoemaker, an economist stated, ”orchid growing has not
fully achieved the transition from a hobby to an industry” (Griesbach, 2002).
Today, orchid cultivation is still in its infancy, as it is evolving from a hobbyists’
market into a highly commercial market and international business. An example
of the developing international trade can be traced with Phalaenopsis production,
when breeding occurs in the United States (Griesbach, 2002). Selected clones
are sent to Japan for tissue culture propagation. The successful cultures are

then mass proliferated in China and sent as in vitro plantlets to the Netherlands

27

for greenhouse production. Plants are ﬁnally sent to the United States for
ﬂowering and sold to consumers.

Orchids such as Cymbidium, Dendrobium, Phalaenopsis, and Oncidium
are marketed globally as cut ﬂowers for corsages and ﬂoral arrangements, as
potted ﬂowering plants, and as bedding or aerial plants in tropical regions. In
1995, the world demand for potted orchids was 1.22 billion units of plant stock
with an estimated increase of four percent over the next ﬁve years (Hew and
Yong, 1997). According to the American Orchid Society, over 75% of all orchids
sold in the US. are Phalaenopsis (Griesbach, 2002).

In the early 1990’s, the production of potted blooming orchids began to
rise in the United States. The United States Department of Agriculture (USDA)
National Agricultural Statistical Service considered orchids to be a minor crop
and did not collect production information until 1997 (USDA, 1998). In wholesale
value, orchids have become the second most valuable ﬂowering potted crop in
the United States (USDA, 2003). In the past six years, production value has
increased 147%, with an average annual increase of 23%, and in 2002 the
estimated wholesale value was $105.6 million. The value of potted orchids
produced in Japan has experienced an increase of 1125% in 26 years.
Production in 1965 was valued at $44,000 and $49 million in 1991 (Ichihashi,
1997). The overall market value of imports and domestic production in Japan
was estimated to be $261 million in 1993 (Hew and Yong, 1997). In 1993,
Cymbidium, Phalaenopsis and nobiIe-type Dendrobium were the most widely

grown species in Japan. Phalaenopsis are currently the most valuable potted

28

crop in the Netherlands. From 1983 to 1994, the number sold through the
auction at Aalsmeer increased from 50,000 to 3,150,000 plants, and in 1994 was
valued at $62 million (Barendse, 2002; Hew and Yong, 1997). Large scale
potted production is also taking place throughout the world, including China,
Germany, and Taiwan (Griesbach, 2000).

Worldwide potted orchid production is continually increasing and is driven I“
by: 1) increasing popularity; 2) improvements in propagation; 3) grower I
acceptance of orchids as proﬁtable crops; 4) improved plant vigor, especially of
hybrids; and 5) segmentation of the supply chain (Britt, 2000). Many growers in
the United States have expanded their production beyond the traditional orchid
hobbyists and now target mass marketers such as Frank’s, Lowe’s, Home Depot,
Target, Kmart and Wal—Mart. The largest demand for potted blooming orchids at
these retail outlets is for traditional holidays such as Valentine’s Day, Easter and
Mother’s Day. However, year-round production and sales are expanding beyond
those of traditional potted plants such as Chrysanthemums and African violets
(USDA, 2003).

No ofﬁcial standards exist for the commercial production of orchids, but
the industry consensus for producing Phalaenopsis is in 15-cm pots and with six
or more ﬂower buds per plant (Wang and Lee, 1994). However, many growers
produce plants in 10- or 11.5-cm pots with fewer ﬂowers for lower prices. Until
recently, Phalaenopsis with multiple spikes and well-branched spikes are often

sold at a higher price than plants with only one spike and no lateral branches.

29

The wholesale price of a 15-cm pot is $8 to $12, with a retail price of $15 to $25
on the mass market (Wang, 2001).

Similar large-scale production is in the early stages of development for
most other orchid species, as there have been few scientiﬁc studies investigating
the relationships between environmental parameters such as temperature, light
quantity, and photoperiod on ﬂower induction. For controlled ﬂower induction to
be commercially viable, the following conditions must be satisﬁed: 1) the
methods must be simple, economical and give reproducible results for growers;
2) the quantity and quality of ﬂowers must not be adversely affected by the
treatment; 3) there should be no adverse affects on the plant in size or quality

(Hew and Yong, 1997).

Propagation

Asexual mericlonal tissue culture and sexual seed propagation are both
widely utilized as sources of orchid plantlets. Mass rapid clonal propagation
(MRCP), or the mass propagation of cuttings or stem segments, was ﬁrst
commercially utilized for propagation of Cymbidium in the early 1960s, and is
now commonly used with other orchids such as the nobiIe-type Dendrobium
(lchihashi, 1997). Seed production is somewhat more difﬁcult than tissue culture,
as seeds are extremely small, have no endospemi and have a rudimentary seed
coat (Morrison, 2000). Seeds are often grown in ﬂasks on agar medium at 21 to
24 °C for one year, and transferred to community ﬂats for 6 to 12 months.

Mortality is often high when seedlings are transferred to community trays.

30

Sexually produced plantlets are often cheaper than clones, but pose challenges
for growers due to the genetic variability.

Konow and Wang (2001), showed that an in vitro photosynthetic photon
ﬂux (PPF) of 40 or 80 umoI-m’Z-s'1 produced Phalaenopsis seedlings with 4.0 cm
roots, compared to 2.8 cm at 10 umol-m'z-s". Increased PPF also increased
fresh weight, which can lead to an earlier transfer time out of ﬂasks.

Tissue culture is one of the most rapid methods of multiplying vegetative
orchid plants from shoot tip, root tip, pseudobulb cuttings or pollen grains. The
excised tissue is sterilized, placed in ﬂasks containing liquid nutrient medium,
sealed with aluminum foil and placed on an orbital shaker. The cultured ﬂask is
then provided with illumination of about 10-to 40 umoI-m'z-s'1 for 8 to 16 h a day
at a constant temperature of 25 °C. Thousands or even millions of genetically
identical and uniform plants can be produced from the tissue in one to two years,
depending on the hybrid or species. Both sexual and asexual methods require
aseptic conditions, with speciﬁc nutrients and environmental conditions

(Anonymous, 1998).

Media. Ngtrition and Irrigation

One of the most challenging aspects of commercial orchid production is
selecting an appropriate media. The medium must not rapidly degrade, its water
holding capacity must not be excessive, it must support the plant within the
container and have a pH of 5.0 to 6.0 (Griesbach, 1985). Consequently, orchids

do not perform well in traditional peat- and perlite-based potting media often used

31

for other ﬂoricultural crops. These medias do not provide adequate drainage or
aeration and the roots can become waterlogged and rot.

Commercial orchid growers often use fresh douglas ﬁr [Pseudotsuga
menziesii (Mirb.) Franco] bark. However, fresh bark does not usually retain
adequate amounts of moisture or nitrate-nitrogen and decomposes quickly
(Wang, 2000). Wang and Gregg (1994) reported that a mix containing perlite,
Metro Mix 250 (containing peatmoss, perlite, vermiculite, ground-charred bark,
and granite sand with a balanced pH and nutrient charge), horticultural charcoal
and composted pine bark can be used to grow excellent Phalaenopsis. As a
result, growers are now using mixtures of ﬁr bark with various other materials
such as charcoal, sphagnum moss, peat, volcanic rock, rockwool, vermiculite,
and perlite. An alternative to ﬁr bark is chopped coconut coir (Coco nucifera L.)
husks of various sizes. A risk of using chopped coconut is root injury from high
salt concentrations if the coir has not been properly leached.

Studies by Wang and Gregg (1994) have illustrated the importance of
providing epiphytic orchids such as Phalaenopsis with sufﬁcient fertility
throughout greenhouse production to promote vegetative growth and ﬂowering.
Increased fertility from 0.25 to 1.0 g-liter'1 of a 20—8.6-16.6 fertilizer (50 to 200
ppm N) increased ﬂower counts from 6.7 to 8.0, the number of inﬂorescences
from 1.5 to 2.1 and leaf production from 2.2 to 3.4. Wang (1994) recommends
two hundred ppm nitrogen from a 20-20-20 fertilizer at each irrigation for most

orchids, and 10-30-20 for mature plants.

32

I

Orchid roots are sensitive to high salinity, and water high in dissolved salts
tends to injury roots (Wang, 1998b). An electrical conductivity (EC) of 1.3 to 1.5
dScm'1 or less is recommended (Wang, 1994). Root injury can occur when the
EC exceeds 3 dS-m". Cymbidium plants produced more spikes per square
meter of growing area as E.C. was increased from 0.6 to 1.4 dS-m". The ﬂower
count on those spikes was unaffected (de Kreij and van der Berg, 1990). These
results may be a function of increasing fertility since the change in EC was solely
due to increased fertilizer concentration. Roots of Phalaenopsis ‘TAM Butterﬂy’
hybrid plants in a 100% ﬁne-grade ﬁr bark were more tolerant of high salinity (1.4
dS-m") when compared to those grown in a 4:1 bark:peat medium (Wang,
1998b)

Most orchids require infrequent watering compared to other ﬂoricultural
crops. Growing medium as well as temperature, humidity and light are prime
dictators of water need. Water stress can cause decreased growth rates and
ﬂower bud or ﬂower abortion. Plants should be irrigated in the morning to allow
leaves to dry before nightfall, since moist or wet conditions on the plant can

promote incidence of diseases.

lrradiance, Temperature and Photosynthesis

Many orchidssuch as Phalaenopsis and Miltoniopsis require relatively low
light levels for growth and ﬂowering. Maximum recommended light levels are
300 to 600 pmoI-m'z-s'1 for Cattleya, 360 to 480 pmoI-m'Z-s'I for Cymbidium, 480

to 720 pmol-m'z-s'1 for Dendrobium, 200 to 400 jimol-m'z-s'1 for Miltoniopsis, 240

33

to 400 pmol-m'Z-s‘1 for Phalaenopsis, and 400 to 600 i.imol-m'2-s'1 for
Zygopetalum (Baker and Baker, 1991, 1993a; Griesbach, 1985).

Wang (1995) reported that Phalaenopsis must be exposed to light above a
certain threshold level to induce VI. Plants receiving 0 or 8 jimoI-m'Z-s'1 for 12-h
did not respond to inductive low temperatures (20 °C day/15 °C night) and
remained vegetative if kept under low light. Those plants receiving 60 or 160
meI-m'z-S'1 for 12 h perceived the low temperature treatments and ﬂowered in an
average of 28 or 34 d.

Recommended temperatures for vegetative growth of Cattleya orchids are
16 to 18 °C day and 16 °C night, due to their montane origin. However,
greenhouse studies have shown that Cattleya grown for 17 weeks in day/ night
temperatures of 32/29 °C and a light intensity of 300 pmol-m‘Z-s'1 had 4.5 times
the leaf elongation than those grown at 25/20 °C. Those under the 32/29 °C
conditions had an average of two to three lateral shoots after 24 weeks
compared to only one for those in the 25I20 °C greenhouse treatment (Krizek
and Lawson, 1974). According to Rotor (1952), 9-h short days at 18 °C
stimulated vegetative growth, as plants produced two successive growths under
this daylength than under long days or natural photoperiods.

Cymbidium require long days and day/night temperatures of 30I 25 °C for
optimal growth and pseudobulb maturity. In the hot summer months, a process
known as ‘Yama-age’ or ‘the mountain technique’ of shifting cultivation from
production areas in the lowlands to the highlands is employed in Japan. This

method ensures that cold-requiring orchids such as Cattleya, Cymbidium, and

34

Miltonia receive temperatures that accelerate vegetative growth during the
summer (lchihashi, 1997).

For most Dendrobium orchids, optimal vegetative growth is achieved at
temperatures between 24 and 30 °C. Dendrobium phalaenopsis grown at 13
and 18 °C produced one pseudobulb per year, however those at 13 °C were
short and spindly. Vegetative growth was also delayed by two months at 13 °C.

Short days at 18 °C induced earlier development of vegetative buds and the new In
growth matured at least one month earlier than those grown under natural
daylengths (Rotor, 1952). It is reported that temperatures below 10 °C may
cause leaf drop in some species.

Phalaenopsis orchids remain vegetative at temperatures above 27 to 29
°C (Sakanishi et al., 1980) and can tolerate temperatures as high as 32 to 35 °C
(Baker and Baker, 1991). Baker and Baker (1991) suggest that 17 to 18 °C is a
minimum growing temperature and that 21 to 30 °C is ideal. The base
temperature for Phalaenopsis is similar for all growth stages and ranges from
10.8 to 11.2 °C (Robinson, 2002). The thermal time to ﬂower is similar when a
model relating time from spiking to ﬂower is used (769 degree—days; Tb=10.8) or
when two models predicting 1) days to visible bud and 2) visible bud to ﬂower
(787 degree-days, Tb=11.2 and 11.0 °C) are used.

Approximately 36% of all orchid species photosynthesize via the
crassulacean acid metabolism (CAM) pathway (Hietz et al., 1999). Most thin-
leaved Cymbidium and Dendrobium nobile photosynthesize via the Calvin-

Benson cycle (C3 pathway). Due to the epiphytic nature of Phalaenopsis, the

35

efﬁcient CAM pathway can often be affected by environmental growing

conditions (Goh et al., 1983). Carbon dioxide (00;) uptake is maximized when

day/night temperatures are kept at a constant 20 °C in Phalaenopsis. However,

higher day and lower night temperatures of 25I15 °C are more favorable to C02

assimilation by CAM photosynthesis. Day and night CO; uptake increases as

light intensity increases to a saturation point of 130 jimoI-m'z’os'1 (Ota et al., 1991). ra

According to Lootens and Heursel (1998), at 20 °C day/15 °C night, CO; uptake

A A'

increases as light increases to a PPF saturation point of 180 pmol-m'z-s'1 in
Phalaenopsis cultivars ‘70’ and ‘L’. Compared with other plants, this is a
relatively low saturation point (Ota et al., 1991).

The green aerial roots of Phalaenopsis, Cattleya gigas, Epidendrum
xanthium, and Vanda suavis also photosynthesize via CAM. This can pose
challenges for commercial growers. When grown in opaque pots, the roots of
these plants grow out of their pot in search of light. Many growers avoid this
problem by growing their plants in clear or translucent pots, which allow the roots

to photosynthesize within the pot.

Flower Induction

With the exception of Vanilla, orchids are grown for the aesthetic beauty of
their ﬂowers and foliage. However, research on ﬂower initiation, induction,
development and physiology have only recently been initiated. The ﬁrst known
studies with orchid ﬂower induction were with Dendrobium crumenatum at the

Bogor Botanical Gardens in 1887 to 1898 by Treub, Massart, and Went.

36

Subsequent studies on other orchid species were performed from 1950 to 1970
in the United States by Curtis, Rotor, and Vacin; in West Africa by Sanford; in
Venezuela by Dunsterville and Dunsterville; in the Philippines by Quisumbing; in
Poland by Zotkiewicz and in Singapore by Goh (Goh et al., 1982). Research was
not conducted to determine the ﬂowering requirements of Phalaenopsis until the

19505, even though they were ﬁrst grown commercially in Europe in the early

"1

19th century during the “orchid craze.” One of the ﬁrst studies was performed by
De Vries (1950), in which he determined that if mature plants were exposed to
night temperatures below 21 °C for two to three weeks, they would eventually
ﬂower.

Similar to other ﬂowering plants, a juvenile phase exists in orchids and
they must reach a certain stage of growth before attaining the capacity to ﬂower.
Thus, sexual reproduction is delayed until plants reach a size sufﬁcient to
maintain the energetic demands of ﬂowering and seed production. This period of
juvenility varies among species and cultivars. Four to seven years are required
for many orchids to ﬂower from seed (Goh and Arditti, 1985), but many
commercially important hybrids ﬂower after 12 to 36 months of growth (Hew and
Yong, 1997). After the juvenile period has passed, environmental or other
factors can be employed to induce ﬂowering. If conditions are unfavorable,
initiated inﬂorescence buds may not all develop to maturity and bloom. However,
once buds have developed to a certain size (e.g., approximately 3 mm in Aranda

hybrids), they usually continue to develop to anthesis (Goh and Arditti, 1985).

37

Effects of VernaMion grid Photoperiod

The majority of published studies indicate that Cattleya species and
hybrids require short days and low temperatures to ﬂower. In C. warscewiczii, C.
gaskelliana, and C. mossiae, ﬂower induction occurs under continuous 9-h short
days at 13 °C, while ﬂowering is inhibited under 16-h long days at 13 °C (Rotor,

1952; Rotor, 1959). The only difference being that C. warscewiczii apparently

 

requires short days, low temperature conditions while the pseudobulb is

ICE—#9:]

developing. Flowering of C. warscewiczii under short days at 18 °C was reduced
and delayed by two to three months compared with plants under short days at 13
°C.

Goh and Arditti (1985) developed a. schedule for ﬂowering C. gaskelliana
for Christmas or New Years in the northeastern United States. They suggest
growing plants warm (2 16 °C) during the previous November, December and
January when growth normally begins. Plants should begin receiving short days
from February through September, and in the autumn, night temperatures should
be reduced to 13 °C. Flowering occurs approximately three to four months after
bud initiation. In C. Iabiata and C. schillen'ana, 16-h long days at 18 °C prevents
ﬂowering. Cattleya Iabiata and C. schiIIen‘ana will ﬂower under short days
regardless of temperature and under long days if the temperature is maintained
below 16 °C (Rotor, 1952; Rotor, 1959). Cattleya bown'ngiana grown under 8-h
photoperiods ﬂowered in 273 d, and ﬂowering did not occur under 16-h

photoperiods (Goh and Arditti, 1985).

38

Cymbidium are induced to ﬂower by warm days and cold night
temperatures (i.e., with large diurnal ﬂuctuations). No studies have found
photoperiod to have an effect on ﬂower induction (Goh et al., 1982, Goh and
Arditti, 1985). Many temperate Cymbidium orchids derived from the “Asiatic
Cymbidium Belt” are reported to require large diurnal temperature ﬂuctuations of
10 to 14 °C to initiate ﬂowers (Powell et al , 1988). According to Dole and Wilkins
(1999), temperatures of 5 to 8 °C should be maintained for optimal ﬂower
induction, then subsequently raised to 25 °C when ﬂower spikes become visible.
Cymbidium growers in California provide relatively high light intensities (600
pmol-m'z-s") and night temperatures of 10 to 13 °C for ﬂower bud initiation (Goh
and Arditti, 1985). In Japan, the temperatures commonly utilized for ﬂower
induction are between 10 to 16 °C and the cumulative temperature required is
34,000 °C hours (calculated by multiplying the hours under 10 to 16 °C by the
temperature) (lchihashi, 1997). Powell et al. (1988) reported that C. Astronaut
‘Rajah’ exposed to day/night temperatures of 26/12 °C under 14-h photoperiods
for up to six months resulted in 5.9 inﬂorescences per plant. At 20I12 °C and
26/18 °C, only 0.8 and 1.7 inﬂorescences per plant developed, respectively.
Went (1957) found that Cymbidium did not ﬂower when grown for one to two
months at 26/14 °C or 23/14 °C; inﬂorescences developed at 26I7 °C and 26I10
°C, and the best ﬂoral production occurred at 20/10 °C and 20I14 °C.

In vitro ﬂowering of Cymbidium niveo-marginatum has been achieved with
a combined treatment of cytokinin (6-benzylaminopurine), restricted nitrogen

supply with phosphorus enrichment, and root excision (pruning). In vivo, C.

39

niveo-marginatum requires four to seven years before it can ﬂower (Kostenyuk,

et al., 1999).

The optimum temperature for flower induction differs among Dendrobium
cultivars. In Dendrobium nobile, dormant buds on upper nodes of mature
pseudobulbs ﬂower in response to low temperatures. Buds on immature

pseudobulbs stay dormant and do not respond to low temperatures. Flower buds l“

‘M- .
.1...

|

I

grow up to 3 mm long with ﬁve or six scales after their induction (lchihashi,
1997). Temperatures for induction vary among cultivars. In Dendrobium nobile,
plants exposed to 13 °C produced ﬂowers regardless of photoperiod, whereas
plants held at 18 °C remained vegetative (Rotor 1952; Goh and Arditti, 1985).
Under long days ﬂowering is hastened by one to four weeks (Rotor, 1952). In
Japan, plants are moved to the mountains after the summer to provide cool
temperatures (< 15 °C) for early ﬂower induction (lchihashi, 1997). Optimal
ﬂower induction in D. Snowﬂake ‘Red Star’ is achieved by providing 25/10 °C
(day/night temperature) for 40 to 60 d. Lower day temperatures can cause leaf
yellowing, defoliation and reduced growth rates and higher temperatures can
delay ﬂower bud development (lchihashi, 1997). In D. phalaenopsis, short days
at 18 °C hastened ﬂower bud development and ﬂowering by ==6 weeks compared
to plants under long or natural daylengths at 18 °C (Rotor, 1952). At 13 °C, this
same tendency was observed, but ﬂower bud development was very slow and it
was recommended that plants be placed at 18 °C for normal opening of ﬂowers.
Long days, at either 13 or 18 °C retarded ﬂower bud initiation and development

and the delay was accentuated by lower temperatures (Rotor, 1952).

40

According to Goh and Arditti (1985), photoperiodic and low temperature
treatments can affect the levels of endogenous growth regulators. Low
temperatures and short day induction of ﬂowering in the sympodial orchids could
result from changes in the endogenous levels of growth regulators. Sakai et al.
(2000) reported on the that the injection of 100 mM 6-benzyladenine (BA) into

Dendrobium Jaquelyn Thomas ‘Uniwai Princess’ (cut ﬂower) signiﬁcantly

5'.

increased the number of ﬂowering inﬂorescences on ﬁrst year pseudobulbs
compared to untreated plants, 8.9 vs. 0.5, respectively. The injection of 100 mM
or 10 mM BA into second year pseudobulbs signiﬁcantly increased ﬂoral spray
production (6.3 and 4.0, respectively) compared with untreated plants (0.2). The
high concentrations of 100 mM BA reduced inﬂorescence length and caused the
development of abnormally formed ﬂowers. The addition of 100 mM gibberellic
acid (GA) to the100 mM BA injection solution signiﬁcantly increased -
inﬂorescence length and reduced the percentage of abnormally formed ﬂowers.
Most Phalaenopsis species and hybrids require a period of exposure to
relatively cool temperatures (< 28 °C) to trigger the elongation of the
inﬂorescence (Lee and Lin, 1984, 1987; Sakanishi et al., 1980; Yoneda et al.,
1992; Wang, 1995). This is often referred to as spiking (Wang, 1998). Flower
bud initiation occurs after the inﬂorescence has reached a size of =5 cm when
environmental conditions are favorable. Lin and Lee (1984) showed that uniform
spiking can be achieved when plants are grown at day/night temperatures of
25/20 °C or 20115 °C for four to ﬁve weeks. Although temperatures below 25 °C

can initiate VI, they do not necessarily initiate ﬂowering immediately. Once

41

spiked, plants grown at 20 °C can ﬂower almost a full month after those grown at
25 °C (Sakanishi et al., 1980). Temperatures above 25 °C can also affect
ﬂowering. When placed at 28 °C, a spike can form a vegetative air plantlet
known as a keiki instead of ﬂower buds, or buds may abort. Abortion of buds can
be avoided if the air temperature around a plant is kept below 28 °C until the
spike is approximately 5 cm in height. At this point, the spike will develop at
temperatures above the base temperature (11 °C) but not > 25 °C, because the
ﬂoral primordia have initiated and differentiated (Sakanishi et al., 1980).
Temperature has little or no effect on spike height or ﬂower size (Sakanishi et al.,
1 980).

Photoperiod does not inﬂuence ﬂower induction of Phalaenopsis (Baker
and Baker, 1991; Sakanishi et al., 1980). However, a few studies have reported
that short days enhance spiking and long days promote vegetative growth or
keikis (DeVries, 1950; Rotor, 1952; Griesbach, 1985). However, the short day
enhancement is thought to be a result of the extension of cool night temperatures
and not the day length itself (Sakanishi et al., 1980).

Robinson (2002) conducted studies to quantify the effects of temperature
(14, 17, 20, 23, 26 or 29 °C) on time from spike emergence to ﬂowering and on
plant quality. The most important factor in scheduling Phalaenopsis was proper
temperature control; daylength and light intensity had minimal effects. The
optimum temperature for ﬂoral promotion once spiking had occurred was 26 °C.
As temperature was increased from 20 to 23 °C, days to ﬂower decreased from

50 to 35 d. The rate of ﬂower, node and bud development for all the cultivars of

42

Phalaenopsis used in the investigation increased linearly as temperature
increased from 14 to 26 °C. Robinson (2002) also found that keiki formation

occurred at temperatures above 28 °C, in agreement with Sakanishi et al. (1980).

Flower Longevity
The life span of orchid ﬂowers varies considerably among genera.

Phalaenopsis ﬂowers may last for months, while other orchid ﬂowers are

l'i' T“???

ephemeral, lasting only one day or less. The full bloom period of an
inﬂorescence depends on the number of ﬂowers and the longevity of individual
ﬂowers. Factors such as air pollution, physical damage to the plant or ﬂower,
slight disturbances to the pollinia or anther caps, pollination and temperature can
considerably accelerate the senescence of ﬂowers (Goh, and Arditti, 1985).
Orchid ﬂowers are extremely sensitive to very low levels of ethylene gas
(CzH4). Ethylene at 0.05 ppm can cause ﬂowers and buds to drop within a few
days after exposure. Studies by Wang (2002) have shown that blooming
Phalaenopsis plants fumigated with 0.1 to 1.0 uLIL of the organic gas 1-
methylcyclopropene (1-MCP) for 6 h, exposed to C2H4 for 24 h and evaluated
under continuous 10 umol-m'zs'1 PPF at 23 to 25 °C were equally protected
compared to the non-MCP treated plants. Flowers on untreated ﬂowers wilted
within 2 d of exposure to C2H4 and those treated with 1-MCP lasted 27 to 34 d.
In another experiment, ﬂowers treated with 0.4 uL/L 1-MCP and then exposed to

C2H4 after 7 or 14 d wilted within 4.5 d.

43

Conclgsion

The physiology, biochemistry and genetics of ﬂowering in orchids is an
extraordinarily complex process inﬂuenced by both internal (juvenility) and
external factors (daylength and temperature). In Arabidopsis, the genetic
repression of ﬂowering via FLC and FRI genes ensures that sexual reproduction
occurs under favorable conditions. The range and complexity of ﬂowering allows
great diversity in plant responses to their given environments. These interactions
pose challenges for today’s orchid growers as consumers increasingly demand a
diversity of orchids from which to choose. As more controlled research is
performed, additional knowledge on the ﬂowering requirements will become

known, which will facilitate production of additional genera at desired sales dates.

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55

SECTION II

F LOWERING AND VEGETATIVE GROWTH RESPONSES OF BRASSIA,
DEGARMOARA, MILTASSIA, ODONTOCIDIUM AND ZYGOPETALUM
ORCHIDS TO PHOTOPERIOD

56

Flowering and Vegetative Growth Responses of Brassia, Degarmoara,

Miltassia, Odontocidium and Zygopetalum Orchids to Photoperiod

Roberto G. Lopez1 and Erik S. Runkle2

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

73'“

Additional index words: night interruption, photoperiod, potted ﬂowering plants

Received for publication . Accepted for publication . We
gratefully acknowledge funding by Michigan’s plant agriculture initiative at
Michigan State Univ. (Project GREEEN), the Michigan Agricultural Experiment
Station, and greenhouse growers providing support for Michigan State University
ﬂoriculture research.

1Graduate Student.

2Assistant Professor and Extension Specialist, to whom reprint requests should

be addressed (E-mail: runkleer@msu.edu).

57

Introduction

In the early 1990’s, the production of potted blooming orchids began to
rise signiﬁcantly in the United States. The United States Department of
Agriculture (USDA) National Agricultural Statistical Service considered orchids to
be a minor crop and therefore did not collect production information until 1997
(USDA, 1998). Since then, many growers began expanding their sales beyond
the traditional orchid hobbyists and now target mass marketers such as Frank’s,
Lowe’s, Home Depot, Target, Kmart and Wal-Mart. The largest demand for
potted blooming orchids at these retail outlets is for traditional holidays such as
Valentine’s Day, Easter and Mother’s Day. However, year-round production and
sales are expanding beyond those of traditional potted plants such as
Chrysanthemums and African violets (USDA, 2003). As a result, orchids have
become the second most valuable ﬂowering potted crop in the United States in
wholesale value. In the past six years, production value has increased 147%,
and in 2002 the estimated wholesale value was $105.6 million. According to the
American Orchid Society, over 75% of all orchids sold in the US. are
Phalaenopsis (Griesbach, 2002).

The production of orchid plants has also increased in other countries,
particularly in Japan and the Netherlands. The value of potted orchids produced
in Japan experienced an increase of 1125% in a recent 26 year span: production
in 1965 was valued at $44,000 and = $49 million in 1991 (lchihashi, 1997). The
overall market value of imports and domestic production in Japan was estimated

to be $261 million in 1993 (Hew and Yong, 1997). In 1993, Cymbidium,

58

Phalaenopsis and nobile-type Dendrobium were the most widely grown orchid
species in Japan. In the Netherlands, Phalaenopsis is currently the most
valuable potted crop. From 1983 to 1994, the number of plants sold through the
Aalsmeer ﬂower auction increased from 50,000 to 3,150,000 plants, and in 1994
was valued at $62 million (Barendse, 2002; Hew and Yong, 1997). Large-scale
potted production has also taken place in Germany and Taiwan, among others
(Griesbach, 2000). The world demand for potted orchids in 1995 was 1.22 billion
units of plant stock and was estimated to increase four percent from 1995 to
2000 (Hew and Yong, 1997).

Britt (2000) identiﬁed ﬁve reasons for the dramatic increase in worldwide
potted orchid production: 1) increasing cOnsumer popularity; 2) improvements in
propagation; 3) grower acceptance of orchids as proﬁtable crops; 4) improved
plant vigor, especially of hybrids; and 5) segmentation of the supply chain.
However, of the 20,000 to 25,000 species that comprise the Orchidaceae family,
a small number (e.g., Cattleya, Cymbidium, Dendrobium, Phalaenopsis, and
Oncidium ) are marketed globally as cut ﬂowers for corsages and ﬂoral
arrangements, as potted ﬂowering plants, and as bedding or aerial plants in
tropical regions. The commercial potential of the vast majority of other orchids
has not yet been explored partly due to insufficient knowledge of their growth and
ﬂowering responses to controlled environments.

For controlled ﬂower production to be commercially viable, the following
conditions must be satisﬁed: 1) the methods must be simple, economical and

give reproducible results for growers; 2) the quantity and quality of ﬂowers must

59

not be adversely affected by the treatment; and 3) there should be no adverse
affects on the plant in size or quality (Hew and Yong, 1997

Photoperiodism refers to the response of plants to the length of day. The
word is derived from the Greek roots for “light” and “duration of time.” Hillman
( 1969) deﬁned photoperiodism as a response to the timing of light and darkness.
Plant responses inﬂuenced by daylength include bud dormancy, formation of
storage organs, asexual reproduction, leaf development, stem elongation,
germination, and ﬂower initiation and development (Thomas and Vince-Prue,
1984). Some factors that may be inﬂuenced by daylength, such as ﬂowering
percentage and ﬂower number, are important horticulturally, yet botanically they
are often not considered photoperiodic responses.

The classiﬁcation of plants according to their photoperiodic responses is
usually made on the basis of ﬂowering. With respect to ﬂower initiation, most
plant responses to daylength can be classiﬁed into three categories. Day-neutral
plants (DNP) ﬂower regardless of the photoperiod to which they are exposed. In
short-day plants (SDP), ﬂowering occurs only under, or is accelerated by,
daylengths shorter than a particular duration known as the “critical daylength”.
Flowering in long-day plants (LDP) occurs only under, or is accelerated by,
daylengths exceeding a particular duration. Less commonly, some species have
a dual daylength requirement, i.e., a period of short days followed by a period of
long days or vice versa (Thomas and Vince-Prue, 1997).

Some tropical plants of equatorial origin are believed to be more sensitive

to small differences in daylength than those from temperate regions (Sanford,

60

1974). An example of a tropical plant inﬂuenced by photoperiod is the epiphytic
cacti Hatiora spp., which is classiﬁed botanically as a short-day long-day plant
(SLDP) for ﬂowering at 15 to 20 °C (Boyle, 1991). In its native habitat of Panara
and Santa Catarina, Brazil (~26 °S lat.) the shortest civil daylength (the duration
of time when the sun is 6° below the horizon before sunrise to 6° below the
horizon after sunset) is 11 h 28 min and the critical photoperiod for
photoinduction in Hatiora is between 11 and 12 h (Boyle, 1991). Other examples
of epiphytes that respond to photoperiod include Schlumbergera truncate and
Cattleya spp., which are SD tropical epiphytes native to the Organ Mountains
north of Rio Janeiro, Brazil (~22 °S lat.) where the photoperiod ranges from 11 to
13.5 h (Morrison, 2000). Commercially, Schlumbergera is placed under 8 to 11 h
short-day photoperiods and night temperatures of 13 to 15 °C for ﬂower initiation
(Dole and Wilkins, 1999). In Cattleya warscewiczii, C. gaskelliana, and C.

- mossiae, ﬂower induction occurred under continuous 9-h short days at 13 °C,
while ﬂowering was inhibited under 16-h long days at 13 °C (Rotor, 1952; Rotor
1959).

Since photoperiod inﬂuences ﬂowering of some tropical epiphytes, the
objective of this experiment was to determine how photoperiod inﬂuences growth
and ﬂowering of Brassia Rex ‘Sakata’, Degannoara Winter Wonderland White
Fairy’, Miltassia Charles M. Fitch ‘Dark Monarch,’ Odontocidium Tiger Crow
'Golden Girl' and Zygopetalum Redvale ‘Fire Kiss’. The orchid hybrids were
chosen based on greenhouse grower interests and suitability as potted ﬂowering

plants based on fragrance, size and ﬂoral characteristics.

61

Materials and Methods

Plant material. Plants were grown by a commercial greenhouse (Calif.) at
16 to 26 °C under natural photoperiods (37 °N lat.) with a maximum
photosynthetic photon ﬂux (PPF) of =350 umol-m'Z-s". Propagation dates and
container sizes are provided in Table 1. Five hundred Brassia Rex ‘Sakata’,
Degarmoara Winter Wonderland White Fairy’, Miltassia Charles M. Fitch ‘Dark
Monarch’, Odontocidium Tiger Crow ‘Golden Girl’, and Zygopetalum Redvale
‘Fire Kiss’ planted in a bark and perlite-based media (10-cm pots) were received
in East Lansing, Mich. on 6 May 2001 (Year 1) and 22 July 2002 (Year 2).
Zygopetalum received in Year 2 were transplanted into 13-cm pots. All plants
were maintained at =23 °C in a glass-glazed greenhouse until experiments
began. The photoperiod was a constant 16 h, consisting of natural daylengths
(42 °N lat.) with day-extension lighting from high-pressure sodium (HPS) lamps,
which delivered a supplemental PPF of =50 umol-m'z-s'1 at plant height [as
measured with a with a light quantum sensor (Apogee Instruments, Inc., Logan,
Utah)].

Photoperiod treatments. The experiment was replicated in time, beginning
on 31 May 2001 (Year 1) and 24 July 2002 (Year 2). Experimental treatments
were identical between years unless otherwise noted. Ten plants of each
species were randomly assigned to greenhouse benches each year and were
placed under each of seven photoperiods: 10, 12, 13, 14, 16 or 24 h of

continuous light or 9 h with a 4-h (2200 to 0200 HR) night interruption (NI).

62

Continuous photoperiods consisted of 9-h days completed by day extension
lighting; lamps were turned on at 1700 HR and turned off after each photoperiod
was completed. Day-extension and NI lighting (=2 umol-m’Z-s'1 at canopy level)
was provided by incandescent lamps. Opaque black cloth was pulled at 1700 HR
and opened at 0800 HR everyday on all benches so plants received a similar
daily light integral (Table 2). From 0800 to 1700 HR, HPS lamps provided a
supplemental PPF of =70 pmoI-m'zs‘1 at plant level when the ambient
greenhouse PPF was <120 umol-m'z-s“.

Greenhouse temperature and inadiance control. Plants were grown in a
glass greenhouse with a constant temperature setpoint of 20 oC. Temperatures
on each bench were measured by a theMocouple in an aspirated chamber every
10 s, and hourly averages were recorded by a CR-10 datalogger (Campbell
Scientiﬁc, Logan, Utah). To help provide uniform night temperatures of 20 °C, a
data logger controlled a 1500-W electric heater, which provided supplemental
heat under each bench as needed. Average daily air temperature from the
beginning of forcing until the end of treatments under every photoperiod each
year were calculated (Table 2). Light transmission through the greenhouses was
reduced using permanent woven shade curtains that reduced light by =55%
(OLS 50; Ludvig Svensson, Charlotte, NC.) and by applying whitewash (up to
50%) to the glass as needed so that the maximum PPF was =350 umol-m’z-s".

Plant culture. Plants in Year 1 were irrigated as necessary with well water
(containing 95, 34, and 29 mg-L‘1 Ca, Mg, and S, respectively) supplemented

with water-soluble fertilizer to provide the following (mg-L"): 125 N, 12 P, 125 K,

63

15 Ca, 1.0 Fe, 0.1 B, and Mo and 0.5 Mn, Zn, and Cu. (MSU Special, Greencare
Fertilizers, Chicago, IL). Water was acidiﬁed with H2SO4 to a titratable alkalinity
of 140 mg-L‘1 CaCOa. In Year 2 plants were irrigated as necessary with reverse
osmosis water supplemented with water-soluble fertilizer to provide the following
(mng'I): 125 N, 12 P, 100 K, 65 Ca, 1.0 Fe and Cu, 0.5 Mn and Zn, 0.3 B, and
0.1 Mo.

Data collection and analysis. Initial immature and mature pseudobulbs,
leaves per pseudobulb, and leaf length were recorded for Odontocidium and
Zygopetalum when forcing began (Table 3). The date at which the ﬁrst
inﬂorescence was visible (visible inﬂorescence, or VI) without dissection and the
date the ﬁrst ﬂower opened were recorded for each plant. At ﬂowering, the
number of VI, ﬂower buds, and nodes on immature or mature pseudobulbs below
the inﬂorescence were coUnted and inﬂorescence length was measured. Plants
that did not ﬂower after 25 or 36 weeks were considered non-ﬂowering. The
percentage of plants that initiated ﬂowers. the percentage of plants whose
ﬂowers developed normally (did not abort), days to Vl, days from VI to ﬂower,
days to ﬂower, leaf length, immature and mature pseudobulb number, and leaf-
count increase from start of forcing were calculated. The few plants that died
during the experiment were discarded and not included in the results.

A completely randomized design was used that included 10 observations
for each photoperiod. Data were analyzed using SAS (SAS Institute, Cary, NC.)
mixed model procedure (PROC MIXED). Data were pooled for all measured

characteristics, except when there was a signiﬁcant year x photoperiod

64

interaction, in which data were analyzed separately for each year. Data for
Degannoara and Miltassia was pooled for Year 1 and 2, and for ﬂower bud count
of Z ygopetalum. Experiments for Miltassia and Odontocidium were not

replicated in time.

Results

Brassia. Flowering was not inﬂuenced by any photoperiod at 20 °C and
plants remained vegetative after 36 weeks under all photoperiods (Table 4). Leaf
count increase after 36 weeks was nOt signiﬁcantly inﬂuenced by daylength (Fig.
1A). As daylength increased from 10 to 14 h, the leaf length of pseudobulbs
increased (linearly and quadratically) from 26.2 to 31.7 cm (Fig. 1B). The ﬁnal
number of immature and mature pseudobulbs produced after 36 weeks were not
inﬂuenced by any photoperiod (Table 4).

Degarmoara. Twenty ﬁve to thirty ﬁve percent of plants initiated ﬂowers
under 12- to 16-h photoperiods and under a 4-h NI during the 25 week
experiment (Table 5). Only ten and ﬁve percent of plants ﬂowered under 10 and
24 h photoperiods, respectively, so data were not included in further analysis.
Days to Vl ranged from 60 to 83 (I under 12- to 16-h photoperiods. Days from VI
to ﬂower were similar, ranging from 50 to 60 d under all photoperiods. The
average number and length of inﬂorescences per pseudobulb were not
signiﬁcantly inﬂuenced by any daylength. In addition, ﬂower number was highly
variable under all photoperiods, and was not signiﬁcantly different. Plants that

produced terminal inﬂorescences produced fewer ﬂowers and shorter

65

inﬂorescences compared to plants that developed lateral inﬂorescences
(signiﬁcantly different at P 5 0.001; data not presented).

Miltassia. Flower initiation occurred in forty to sixty percent of plants
under all photoperiods (Table 6). Many of the ﬂower buds under 24-h of light did
not develop and aborted while ﬂowers in other photoperiods opened normally.
Days to VI across all photoperiods were similar, ranging from 75 to 92 d. Days
from VI to ﬂower and days from start of forcing to ﬂower were statistically similar
under all photoperiods, ranging from 38 to 57 d and 118 to 144 d, respectively.
The average number and length of inﬂorescences per pseudobulb was not
signiﬁcantly inﬂuenced by photoperiod. Flower number was highly variable under
all photoperiods, and no signiﬁcant differences existed. Plants that produced
terminal inﬂorescences produced fewer ﬂowers and shorter inﬂorescences
compared to plants that developed lateral inﬂorescences (signiﬁcantly different at
P5 0.001; data not presented).

Odontocidium. Flower initiation was greatest under 13 and 16 h
photoperiods, 100% and 80%, respectively, but there were no apparent trends in
ﬂowering with respect to ﬂowering (Table 7). Days to Vl were not signiﬁcantly
inﬂuenced by photoperiod (Fig. 2A). Mean days from VI to ﬂower were similar
among photoperiods, ranging from 57 to 63 d. Days from the start of forcing to
ﬂower were also similar, ranging from 160 to 190 d. A statistically quadratic
relationship between photoperiod and inﬂorescence count was observed, with a
maximum at 13 to 14 h (Fig. 2B). Inﬂorescence length per pseudobulb was not

signiﬁcantly inﬂuenced by daylength (Fig. 20). Flower bud count decreased

66

linearly from 6.8 to 2.3 as photoperiod increased from 10 to 24 h (Fig. 2D).

Plants that produced terminal inﬂorescences produced fewer ﬂowers and shorter
inﬂorescences compared to plants that developed lateral inﬂorescences
(signiﬁcantly different at P 5 0.001; data not presented). Leaf count was
signiﬁcantly greater under NI than under any other photoperiod (Fig. 3A). Leaf
length during the 36 weeks was not inﬂuenced by daylength (Fig. 3B). Daylength
had no effect on the number of new immature or mature pseudobulbs formed
(Fig. 3C and D).

Zygopetalum. Year 1. Flower initiation occurred in ﬁfty to ninety percent
of plants under all photoperiods (Table 8). Sixty to eighty percent of plants
ﬂowered when grown under every photoperiod except continual (24 h) light.
Flowering occurred > 150 d after plants were placed under the various
photoperiods. Plants reached VI earlier when grown under photoperiods s 14
hours than under 2 16 h (Fig. 4A). Days from visible inﬂorescence to ﬂower
decreased linearly from 33 to 24 d as photoperiod increased from 10 to 24 h (Fig
4B). The average number of inﬂorescences produced per immature pseudobulb
was not inﬂuenced by photoperiod (Fig. 4C). Mean inﬂorescence length
decreased linearly as photoperiod increased from 10 to 24 (Fig. 4D). Mean
ﬂower bud count decreased linearly from 3.9 to 2.3 as photoperiod increased
from 10 to 24 h (Fig. 4E).

As photoperiod increased from 10 to 24 h, the ﬁnal number of leaves per
pseudobulb decreased from 12.2 to 7.0 (Table 8). Leaf count during the 36

weeks decreased linearly from 8.0 to 2.9 as photoperiod increased from 10 to 24

67

h (Fig. 5A). Leaf length was not inﬂuenced by daylength (Fig. 5B). Photoperiod
did not inﬂuence the development of immature pseudobulbs. Plants under
continual light, however, developed more mature pseudobulbs per pot compared
to those under shorter photoperiods (Table 8).

Year 2. Eighty to one hundred percent of plants ﬂowered regardless of
photoperiod; ﬂowers only aborted under continuous light (Table 8). Average
ﬂowering occurred 2 97 d after plants were placed under the various
photoperiods. Days to Vl increased linearly or quadratically from 73 to 102 d with
decreasing daylength from 24 to 10 h (Fig. 4A). Time from VI to ﬂower and
inﬂorescence count were not inﬂuenced by photoperiod. Average inﬂorescence
length deceased linearly from 33 to 24 cm as photoperiod increased from 10 to
24 h (Fig. 40).

Leaf count under all photoperiods was similar, ranging from 6.3 to 7.3,
respectively (Fig. 5A). As photoperiod increased from 12 to 24 h, leaf length
during the 36 weeks decreased linearly from 47 to 33 cm (Fig. 53). The average
number of immature pseudobulbs were similar among photoperiods (Fig 5C).
The average number of new mature pseudobulbs formed was signiﬁcantly
inﬂuenced by photoperiod, increasing linearly from 1.0 to 2.7 as photoperiod

increased from 10 to 24 h (Fig. 5D).

Discussion

Brassia. After thirty-six weeks of forcing, ﬂowering of Brassia Rex ‘Sakata

was not inﬂuenced by photoperiods ranging from 10 to 24 h of continuous light or

68

9 h with a 4-h night interruption (NI) at =20 °C. These photoperiods were chosen
since they have been successfully utilized to elucidate the ﬂowering responses of
over two hundred herbaceous perennials and potted ﬂowering plants at Michigan
State University (Heins et al., 1997, Runkle, et al., 2001). Additionally, most
orchids in their native environments are exposed to photoperiods > 10 and < 16,
depending on their latitude. Juvenility cannot be readily attributed to the lack of
ﬂowering as plants had been out of tissue culture for over three years and most
had two or more mature pseudobulbs at the beginning of forcing.

The only infomiation currently available about the native distribution of
Brassia is limited; it is an epiphyte found in the warm forests of Costa Rica and
islands of the West Indies at low elevations (200 m) and in the mountains of
Brazil and Peru (2000 to 3000 m) (Rentoul, 1982). Brassia Rex ‘Sakata’ is a
heat-tolerant hybrid between Brassia venucosa x Brassia gireoudiana. Their
large geographic distribution does not readily provide clues for what
environmental parameters may inﬂuence ﬂowering.

Initial leaf length of immature pseudobulbs was similar among
photoperiods. At the end of forcing, leaf length increase was signiﬁcantly
inﬂuenced by photoperiod. This information can be beneﬁcial to commercial
orchid growers because they can create and utilize different photoperiods to
control the size of their plants. For example, by placing Brassia under a 4-h NI,
growers can produce taller and fuller plants. Alternatively, if a grower prefers

shorter and more compact plants, a short day (eg. 10 h) would be ideal.

69

Most sympodial orchids such as Brassia that are grown for potted plant
production are from tissue culture. However, they are often not uniform and are
highly variable in their growth, and thus, uniform, complete and rapid ﬂowering
may be difﬁcult to achieve. Further investigations are needed to reveal the
ﬂowering response of Brassia Rex ‘Sakata.’ They produce seven to ﬁfteen large,
exotic, spider-like, showy and fragrant ﬂowers. The foliage however is not as
attractive as the ﬂowers; it often crinkles with age and is affected by water stress.
Behe et al. (2004) indicated that consumers rated Brassia Rex ‘Sakata’ as their
least favorite out of a sample of four orchids.

Degannoara, Miltassia and Odontocidium. Photoperiod did not have a
signiﬁcant inﬂuence on ﬂowering of Degannoara Winter Wonderland White
Fairy’, Miltassia Charles M. Fitch ‘Dark Monarch’, or Odontocidium Tiger Crow
‘Golden Girl’. Flower initiation percentage was nonuniform and incomplete
across all photoperiods in both years. For Degannoara the highest and lowest
ﬂower initiation, 35% and 5% occurred under 12- and 24-h photoperiods,
respectively. Similar results were observed for Miltassia as the highest and
lowest ﬂower initiation were 55% under 12 and 14 h and 10% under 24-h
photoperiods. Odontocidium showed the highest ﬂower initiation, 100% under a
13 h daylength. The few plants that initiated inﬂorescences under continuous
light (24 h) usually aborted in all three species.

Degannoara Winter Wonderland White Fairy’ is a hybrid between the
hybrids Miltassia Cartagena and Odontoglossum Gledhow, which makes it

difﬁcult to establish what conditions induce ﬂowering of its lineage. Further

7O

investigation using diurnal temperature ﬂuctuations and light quantity may
elucidate ﬂower induction.

Degannoara has potential as a mass-produced potted ﬂowering plant
since it has large 7 to 10 cm, white, star-shaped ﬂowers with small purple spots
and yellow streaks towards the center of the petals and sepals. In an online
survey, participants chose Degannoara over Brassia as the third most likely
orchid they would purchase (Behe et al., 2004).

Miltassia is a hybrid between the cool-growing Miltonia spectabilis and the
intermediate-growing Brassia verrucosa, resulting in a cultivar that requires warm
temperatures for optimal growth. This species may not be suitable for production
in Northern climates as the potential for Chilling injury is high (see Section III).
They exhibit symptoms of chilling injury at temperatures at or below 17 °C within
two weeks. At temperatures of 11 °C, Miltassia eventually die, lose all their
leaves and pseudobulbs within eight weeks, however a few will send up new
immature pseudobulbs.

Of the three previously mentioned orchids, Odontocidium Tiger Crow
‘Golden Girl’ has the most potential as a potted ﬂowering plant. Some of its
attributes include its large and multi branched inﬂorescences. The large and
bright yellow ﬂowers are speckled with maroon spots and can last up to a month
in a home or ofﬁce. Further investigations are needed into the ﬂowering
mechanisms of this species.

Zygopetalum. In year 1, Zygopetalum Redvale ‘Fire Kiss’ showed a

quantitative short-day photoperiodic ﬂowering response. Plants under

71

photoperiods s 13 h reached VI nearly 21 d faster than those under NI or 2 14
daylengths. Time from VI to ﬂower at =20 °C was relatively rapid (=32 (I)
compared to other orchids such as Phalaenopis, where it takes =80 d (Robinson,
2002). However, regardless of photoperiod, time to VI was long (2 117 d) and
relatively nonuniform. Inﬂorescence count was not inﬂuenced by photoperiod,
but inﬂorescence length and ﬂower bud count were. Under continuous light and
a 4-h NI, plants produced shorter inﬂorescences with fewer ﬂowers and as a
result the number of days from VI to ﬂower was =25.

Plants were uniform when they were placed under each photoperiod as
initial leaf counts and lengths were similar in both years. Compared with plants
grown under long days, those under shOrt photoperiods (14 hours or less)
developed fewer pseudobulbs per plant but each pseudobulb developed more
leaves. Similar results have been observed in Cymbidium, as it requires long
days and day/night temperatures of 30/ 25°C for optimal growth and pseudobulb
maturity (lchihashi, 1997). Cattleya and Dendrobium phalaenopsis respond
differently, according to Rotor (1952). Short days (9-h) at 18 °C stimulated
vegetative growth as plants produced 2 successive growths (pseudobulbs) under
this daylength than under long days for Cattleya. In Dendrobium phalaenopsis,
short days at 18 °C induced earlier development of vegetative buds and the new
growth matured at least one month earlier than plants grown under natural
daylengths (Rotor, 1952).

In year 2, Zygopetalum showed a quantitative long-day photoperiodic

ﬂowering response. Plants under photoperiods 2 16 h or a 4-h NI, reached VI

72

nearly =32 d faster than those under s 14-h daylengths. Days from the start of
forcing to ﬂower occurred =48 d earlier under all photoperiods in year two
compared to year one. We believe ﬂower initiation had occurred before the
plants were shipped to us. Mean days from VI to ﬂower across photoperiods
occurred in =36 d in year two, which was comparable to year one where it
occurred in =30 d. Inﬂorescence count was inﬂuenced in year two, but not in
yearone.

Initial plant material (immature pseudobulb count, leaf count and length)
was uniform, but pseudobulb count was signiﬁcantly different among
photoperiods. Plants received in year two were also nearly twice the size of
those received in year one. Interestingly, leaf length was inﬂuenced by daylength
in Year 2 as plants under continuous light or a 4-h NI had shorter leaves.

Zygopetalum is a South American genus of orchids that have fragrant
ﬂowers with lime-green and dark maroon ﬂower petals and a white and magenta
labellum. Their exotic, attractive ﬂowers and naturally compact habit (=25- to 40-
cm tall) make Zygopetalum one of the most appealing orchids that we studied.

In all the orchids we investigated, ﬂower abortion was high, and
inﬂorescent and ﬂower counts were reduced under a 24-h daylength. We
speculated that orchids that photosynthesize via CAM are adversely affected by
continuous light, as their stomata may remain closed for extended periods.

Brassia, Degannoara, Miltassia, and Odontocidium all members of the
Odontoglossum alliance, did not ﬂower in response to photoperiod. In contrast,

temperature and photoperiod inﬂuence ﬂowering of Phalaenopsis, Cattleya,

73

Cymbidium and Dendrobium. For example, ﬂower induction in Phalaenopsis
follows exposure to temperatures below 25 °C and may be promoted by short
days (Sakanishi et al., 1980; Wang and Lee, 1994). Exposure to short
photoperiods, sometimes in combination with low temperatures, induces
ﬂowering in a number of Cattleya species (Rotor, 1952). Diurnal temperature
ﬂuctuations that include cool nights induce ﬂowering in the temperate Cymbidium
Astronaut ‘Rajah’ (Powell et al., 1988) and in other hybrids of the genus
(lchihashi, 1997). Mature pseudobulbs of Dendrobium produce ﬂower buds in
response to low temperature, with effective temperatures varying between 10
and 20 °C depending on cultivar (lchihashi,1997). However to our knowledge,
few scientiﬁc studies on the effects of photoperiod on growth and ﬂowering have
been performed on orchids until now. Consequently, further investigation is

imperative for the establishment of production protocols for new species.

Literature Cited

Barendse, M. 2002. De sierteelt-toppers van 2001. Vakblad voor de Bloemisterij.
2:24-27.

Behe, B.K, R.M. Walden, R.G. Lopez, and ES. Runkle. 2004. Proﬁle of Potted
Orchid Buyers in the Midwest. Southern Nursery Association Research
Conference Proceeding. In press.

Boyle, TH. 1991. Temperature and photoperiodic regulation of ﬂowering in

‘Crimson Giant’ Easter cactus. J. Amer. Soc. Hort. Sci. 117(4):584-589.

74

Britt, J. 2000. The status of the commercial production of potted orchids around
the world. HortTechnology 10(3):435-436.

Dole, J. and H. Wilkins. 1999. Floriculture Principles and Species. Prentice-Hall,
New Jersey.

Griesbach, R.J. 2000. Potted Phalaenopsis orchid production: history, present
status, and challenges for the future. HortTechnology 10(3):429.

Griesbach, R.J. 2002. Development of Phalaenopsis orchids for the mass-
market. pp. 458-465. In: J. Janick and A. Whipkey (eds). Trends in new
crops and new uses. ASHS Press, Virginia.

Heins, R.D., A.C. Cameron, W.H. Carlson, E. Runkle, C. Whitman, M. Yuan, C.
Hamaker, B. Engle, and P. Koreman. 1997. Controlled ﬂowering of
herbaceous perennial plants, p. 15-31. In: E. Goto et al. (eds). Plant
production in closed ecosystems. Kluwer Academic Publishers, The
Netherlands.

Hew, CS. and J.W.H. Yong. 1997. The physiology of tropical orchids in relation
to the industry. World Scientiﬁc, Singapore.

Hillman, W.S. 1969. Photoperiodism and vernalization, pp. 323-328. In: M.B.
Wilkins (ed.). The physiology of plant growth and development. McGraw-
Hill, London.

lchihashi, S. 1997. Orchid production and research in Japan. In: J. Arditti and A.
M. Pridgeon (eds.). Orchid biology: reviews and perspectives, vol. Vll,
Kluwer Academic Publishers, Great Britain.

Morrison, A. 2000. The illustrated encyclopedia of orchids. Timber Press,

75

Portland.

Robinson, K.A. 2002. Effects of temperature on the ﬂower development rate and
morphology of Phalaenopsis orchid. MS. Thesis, Dept. of Horticulture,
Michigan State Univ., East Lansing.

Rotor, GB. 1952. Daylength and temperature in relation to growth and ﬂowering
of orchids. Cornell Univ. Agric. Expt. Sta. Bull. 88523-47.

Rotor, GB. 1959. The photoperiodic and temperature responses of orchids, pp.
397-416. In: C. L. Withner (ed.). The orchids. Ronald Press, New York.

Runkle, E., Heins, R.‘, and W. Carlson. 2001. Horticultural ﬂowering of perennials.
Flowering Newsletter. 34-43.

Sakanishi, Y., H. Imanishi, and G. lshida. 1980. Effect of temperature on growth
and ﬂowering of Phalaenopsis amabilis. Bulletin of the University of
Osaka, Series B. Agriculture and Biology - Osaka (Prefecture) Daigaku.
32:1-9.

Sanford, W.W. 1974. The ecology of orchids, p. 123-132. In. C.L. Withner (ed.).
The orchids: scientiﬁc studies. John Wiley and Sons, New York.

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

US. Department of Agriculture. 1998. Floriculture crops 1997 summary.
Agricultural Statistics Board, Washington DC.

US. Department of Agriculture. 2003. F loriculture crops 2002 summary.

Agricultural Statistics Board, Washington DC.

76

 

 

Table 1. Propagation dates and container sizes for orchid hybrids.

 

Out of Transplant Transplant

Species Year in vitro ﬂask to 7.5-cm pot to 10-cm Qt
Brassia Rex ‘Sakata’ 1 June 1997 June 1998 June 1999 June 2000
Degannoara Winter
Wonderland ‘White Fairy’ 1 May 1997 May 1998 May 1999 May 2000

2 3 - June 2000 June 2001
Wass’a Cha”f’s M' F'tc" 1 June 1997 June 1998 June 1999 June 2000
Dark Monarch

2 June 1997 June 1998 June 1999 June 2000
Odontocidium Tiger Crow .
, Golden Girl’ 1 - - June 2000 April 2001
ﬁg‘Pem’um Redva'e F“ 1 June 1999 June 2000 J April 2001

2 - May 2001 -- May 2002

 

2Information not available.

’PIants were directly transplanted to 10—cm pots.

77

 

 

 

Table 2. Average air temperature and daily light integral (DLI) from the beginning of forcing to the
end of the experiment under each photoperiod for Brassia Rex ‘Sakata’, Degannoara Winter
Wonderland ‘White Fairy’, Miltassia Charles M. Fitch ‘Dark Monarch’. Odontocidium Tiger Crow
‘Golden Girl' and Zygopetalum Redvale ‘Fire Kiss’.

 

 

Experimental Photoperiod ("I
duration Average DLI
Year (weeks) Species (mol-m‘Z-d") 10 12 13 14 16 24 Nl2
Average air temperature during experiment (°C)
2001-02 25 Degannoara 7.2 22.0 23.1 23.0 22.7 21.8 22.6 23.2
Miltassia
36 Brassia 7.0 21.5 22.2 22.2 22.0 21.4 22.0 22.3
Zygopetalum
2002-03 25 Degannoara 6.8 20.8 20.9 20.8 21.0 20.9 21.3 20.8
Miltassia
36 Odontocidium 6.7 20.5 20.6 20.6 20.7 20.6 21.1 20.5
Zygopetalum

 

zNl = 9-h photoperiod plus 4-h night interruption.

78

 

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79

Table 4. The effect of photoperiod on ﬁnal immature and mature pseudobulbs
formed durigng forcing of Brassia Rex ‘Sakata’.

 

 

 

 

 

Immature pseudobulb Mature pseudobulb
Photoperiod Flower number number
(h) initiation (%) Initial Final New Initial Final New
10 0 --z 5.0 - - 2.0 -
12 0 -- 6.0 -- -- 2.0 —-
13 0 -- 4.9 -- -- 3.1 --
14 0 -- 5.3 -- -- 2.8 --
16 0 -- 4.5 -- -- 2.5 --
24 0 -- 3.0 -- -- 2.5 --
Nly 0 -- 5.3 -- -- 3.0 -
Signiﬁcance
Photoperiod -- NS -- -- NS --

 

ZNot measured.
yNI = 9-h photoperiod plus 4-h night interruption.
NSNonsigniﬁcant.

80

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82

Table 7. The effect of photoperiod on days from visible inﬂorescence to ﬂower (VI
to FLW) and days to ﬂower from the beginning of forcing (F LW) of Odontocidium
Tiger Crow ‘Golden Girl’.

 

 

 

 

 

Photoperiod Flowering initiation Flower development Days
Q1) (%) 1%) VI to FLW F LW
1 0 50 50 60 1 87
12 40 4O 57 168
1 3 1 00 1 00 63 160
14 40 40 57 1 90
16 80 80 59 1 86
24 60 40 61 176
N I2 60 50 60 174
Signiﬁcance

Photoperiod NS NS
zNI = 9—h photoperiod plus 4-h night interruption.
N“"Nonsigniﬁcant.

83

Table 8. The effect of photoperiod on days to ﬂower from the beginning of
forcing (FLW), ﬁnal immature and mature pseudobulb number, and ﬁnal leaf count
of Zygopetalum Redvale ‘Fire Kiss’.

 

 

 

 

Year 1
Photoperio d . Flower Flower Final pseudobulb .
Initiation development Days to number Final leave

(h) (%) l%) FLW Immature Mature count
10 70 70 155 1.1 2.9 12.2
12 80 80 162 1.4 3.0 10.5
13 70 70 151 2.0 3.2 11.4
14 70 70 156 1.5 3.1 11.3
16 90 60 187 1.7 3.9 8.7
24 50 40 166 1.0 5.4 7.0
NF 70 70 184 0.8 4.5 9.0
Signiﬁcance

Photoperiod NS NS *** ***
Year 2
10 90 90 137 «V -- --
12 90 90 138 -- -- --
13 100 100 133 -- -- --
14 100 100 1 16 - -- ~-
16 90 90 97 -- - -
24 100 80 108 -- -- -
NV 100 100 100 - -- --
Signiﬁcance

Photoperiod ***

 

le = 9-h photoperiod plus 4-h night interruption.

yNew immature and mature pseudobulbs and leave count increase data used (Fig
5A, C & D).

“5"" Nonsigniﬂcant or signiﬁcant at P g 0.001.

84

 

Leaf count increase
#
l

 

 

38 'r 4. 4. : 4 l : l A:
364.

34-.

     

32 _.,_.. . Lit Qttt
30 ---
28 -~.

26 --

Leaf length increase (cm)

24 --

 

 

 

Photoperiod

Figure 1. Growth responses of Brassia Rex 'Sakata' to various
photoperiods (NI = 4-h night interruption). Error bars represent 95%
conﬁdence intervals. (L = linear, Q = quadratic trends; NS, **, ***
nonsigniﬂcant or signiﬁcant at P S 0.01 or 0.001, respectively).

85

 

0>+

 

 

 

Days to visible
inﬂorescence
8

 

inﬂorescence count

 

 

 

 

40 ‘ l_Ns QNS {
- \‘0

20<

 

Inﬂorescence length (cm)

 

 

12- 6 ‘T’
10‘
8.
6+ L"0NS

 

Flower bud count

 

 

0 ‘ . : ¢ .0 4. : : 10%/Lo—
10 12 14 16 18 20 22 24 Nl
Photoperiod (h)

 

Figure 2. Flowering responses of Odontocidium Tiger
Crow 'Golden Girl' to various photoperiods (Nl = 4-h
night interruption). Error bars represent 95%
conﬁdence intervals. (L = linear, Q = quadratic trends;
NS, *, **nonsigniﬂcant or signiﬁcant at P S 0.05 or 0.01,
respectively).

86

 

 

 

1: “A
N
5
5 3
15
D
8 2*
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N
3
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25‘

Leaf length
increase (cm)
8

 

 

 

2° 2/

\
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1.5 *

1.0 ‘
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0.5 1

New immature
psuedobulbs

0.0 1

 

New mature
pseudobulbs

 

 

T0 : ¢ 1 1 ¢ ‘0 : %/Loj
1012141618 20 22 24 Nl
Photoperiod (h)
Figure 3. Growth responses of Odontocidium Tiger
Crow 'Golden Girl' to various photoperiods (NI = 4-h
night interruption). Error bars represent 95%

conﬁdence intervals. (L = linear, Q = quadratic trends;
NS nonsigniﬁcant).

 

87

 

*v v v v V Y Ijhﬂ

200 ‘ A O Year1
.-

Year 2 %

Days to visible
Inﬂorescence

 

 

Days from VlSlble
inﬂorescence to ﬂower

 

 

4‘4ﬁ1 L L +//L+—«
E C
3
8 3
3 L"”o"8
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40‘
30‘
201

Inflorescence
length (cm)

 

 

 

Flower bud count
09
i——.-—1

/

//
A A A A A I
T ﬁi ﬁ

10 12 14 16 18 20 22 24 Nl
Photoperiod (h)

V
/

\\ A

 

 

Figure 4. Flowering responses of Zygopetalum
Redvale 'Fire Kiss' to various photoperiods (NI = 4—h
night interruption). Error bars represent 95%
conﬁdence intervals. (L = linear, Q = quadratic trends;
NS, *, **, ***nonsigniﬁcant or signiﬁcant at P s 0.05,
0.01 or 0.001, respectively). Data were pooled in E.

88

 

 

 

 

 

 

 

 

 

 

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10 12 14 16 18 20 22 24 Nl

Photoperiod (h)

Figure 5. Growth responses of Zygopetalum Redvale
'Fire Kiss' to various photoperiods (NI = 4-h night
interruption). Error bars represent 95% conﬁdence
intervals. (L = linear, Q = quadratic trends; NS, **, ***
nonsigniﬁcant or signiﬁcant at P s 0.01 or 0.001,
respectively). Data for Year 2 in C and D.

89

SECTION III

THE EFFECT OF PREVERNALIZATION PHOTOPERIOD AND
VERNALIZATION ON FLOWERING OF BRASSIA, DEGARMOARA,
MILTASSIA, MILTONIOPSIS, ODONTOCIDIUM AND ZYGOPETALUM

ORCHIDS

90

The Effect of Prevernalization Photoperiod and Vernalization on Flowering
of Brassia, Degarmoara. Miltassia, Miltoniopsis, Odontocidium and

Zygopetalum Orchids

Roberto G. Lopez1 and Erik S. Runkle2

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

Additional index words: potted ﬂowering orchids, short days

Received for publication . Accepted for publication . We
gratefully acknowledge funding by Michigan’s plant agriculture initiative at
Michigan State Univ. (Project GREEEN), the Michigan Agricultural Experiment
Station, and greenhouse growers providing support for Michigan State University
ﬂoriculture research.

1Graduate Student.

2Assistant Professor and Extension Specialist, to whom reprint requests should

be addressed (E-mail: runkleer@msu.edu).

91

Introduction

In the early 1990’s, the production of potted ﬂowering orchids began to
rise in the United States. Despite this, the United States Department of
Agriculture (USDA) National Agricultural Statistical Service considered orchids to
be a minor crop and did not collect production information until 1997 (USDA,
1998). In wholesale value, orchids have become the second most valuable
ﬂowering potted crop in the United States (USDA, 2003). In the past six years,
production value has increased 147% and in 2002 the estimated wholesale value
was $105.6 million. According to the American Orchid Society, over 75% of all
orchids sold in the US. are Phalaenopsis (Griesbach, 2002).

As Phalaenopsis becomes widely available from home improvement
stores to ﬂoral shops, retailers and consumers are demanding a wider
assortment of species and colors. Unfortunately, the introduction of new
ﬂoricultural crops research to eluciate production protocols. Important
considerations for the introduction of orchid species as potted ﬂowering plants
include showiness of ﬂower display, ease and length of production, crop
uniformity and size, consumer appeal, and post-production ﬂower longevity. The
ﬂowering requirements and commercial potential of other orchid species such as
the fragrant and exotic Brassia Rex ‘Sakata’, Miltoniopsis Augres ‘Trinity’, and
Zygopetalum Redvale ‘Fire Kiss’ or the showy Degannoara Winter Wonderland
'White Fairy’, Miltassia Charles M. Fitch ‘Dark Monarch’. and Odontocidium Tiger

Crow ‘Golden Girl’ have not been identiﬁed.

92

With the exception of Vanilla, orchids are grown for the aesthetic beauty of
their ﬂowers and foliage. However, research on ﬂower initiation, induction and,
development of orchids has been limited. Controlled studies to determine the
ﬂowering requirements of Phalaenopsis were not conducted until the 1950s,
even though they were ﬁrst grown commercially in Europe in the early 19th
century during the “orchid craze.” One of the ﬁrst published studies was
performed by De Vries (1950), in which he determined that if mature plants were
exposed to night temperatures below 21 °C for two to three weeks, they would
eventually ﬂower.

Some plants have an absolute requirement for speciﬁc environmental
cues for ﬂowering and in other plants, ﬂowering is promoted by certain
environmental cues but plants will eventually ﬂower in the absence of such a cue.
Horticulturally, vernalization and photoperiod are the two most common
mechanisms for control of ﬂower initiation.

Vernalization is the promotion of ﬂowering of imbibed seeds or vegetative
plants by low temperatures. Vernalization was further deﬁned by Chouard (1960)
as “the acquisition or acceleration of the ability to ﬂower by a chilling treatment”.
A vernalization response is often observed with plants native to regions with low
winter temperatures, during which conditions are unfavorable for growth and
reproduction. A cold requirement prevents plants from ﬂowering until the spring
or summer, when environmental conditions are more favorable for reproduction
and seed dispersal. A combined vernalization and photoperiod requirement can

ensure that ﬂowering occurs later in the year rather than at the end of the winter.

93

Low temperature requirements for ﬂower induction have also been
documented in tropical orchids. They may vary from distinct elevation-dependant
temperature ﬂuctuations required by Phalaenopsis schillen'ana to subtle rain-
induced cooling, which initiates ﬂowering in Dendrobium crumenatum (Goh et al.,
1 982).

Initiation of ﬂower primordia generally does not occur at vernalizing 1
temperatures. After exposure to low temperatures, plants are in a vernalized [1
state (thermoinduced) and have the ability to ﬂower under favorable conditions
for growth and reproduction (Thomas and Vince-Prue, 1997). Depending on the
species, these favorable conditions can be long days, short days or simply higher
temperatures. However, a vernalization response is primarily observed in long-
day plants, which have extended periods of vegetative growth and ﬂower in the
early summer at high latitudes (Vince- Prue, 1975). These may be perennials,
biennials, winter annuals and epiphytes.

Low temperatures, short photoperiods, or both, regulate the ﬂowering
process of Phalaenopsis, Cattleya, Cymbidium, and Dendmbium orchids (Rotor,
1952; Sakanishi et al., 1980). Cymbidium are induced to ﬂower under warmer
days than night temperatures (i.e., with large diurnal ﬂuctuations). No studies
have found photoperiod to have an effect on ﬂoral induction of Cymbidium (Goh
et al., 1982, Goh and Arditti, 1985). Many temperate Cymbidium orchids derived
from the “Asiatic Cymbidium Belt” are reported to require large diurnal
temperature ﬂuctuations of 10 to 14 °C to initiate ﬂowers (Powell et al., 1988).

Most Phalaenopsis species and hybrids require a period of (3 to 5 weeks)

94

exposure to temperatures < 28 °C to trigger the elongation of the inﬂorescence
(Lee and Lin, 1984, 1987; Sakanishi et al., 1980; Yoneda et al., 1992; Wang,
1995). Lin and Lee (1984) showed that uniform spiking can be achieved when
plants are grown at day/night temperatures of 25/20 °C or 20/15 °C for four to ﬁve
weeks.

Orchids such as Cattleya and Dendrobium nobile require speciﬁc
combinations of temperature and photoperiod for ﬂower induction. A few
published studies indicate that Cattleya species and hybrids require short days
and low temperatures to ﬂower (Rotor, 1952; Rotor, 1959). In C. warscewiczii, C.
gaskelliana, and C. mossiae, ﬂower induction occurs under continuous 9—h short
days at 13 °C, while ﬂowering is inhibited under 16-h long days at 13 °C. In
.Dendrobium nobile, plants exposed to 13 °C produced ﬂowers regardless of
photoperiod, whereas plants held at 18 °C remained vegetative (Rotor 1952; Goh
and Arditti, 1985). Long days accelerated ﬂowering by 1 to 4 weeks (Rotor,
1952). In D. phalaenopsis, short days at 18 °C hastened ﬂower bud development
and ﬂowering by =6 weeks compared to plants under long or natural daylengths
at 18 °C (Rotor, 1952).

We preformed an investigation using different combinations of photoperiod
before vernalization (prevernalization photoperiods) and vernalization
temperatures and photoperiods to determine if plants ﬂowered in response to
temperature, photoperiod, or both. Brassia Rex ‘Sakata’, Degannoara Winter
Wonderland ‘White Fairy’, Miltassia Charles M. Fitch ‘Dark Monarch’, Miltoniopsis

Augres ‘Trinity’, Odontocidium Tiger Crow ‘Golden Girl', and Zygopetalum

95

Redvale ‘Fire Kiss’, were chosen for study based on greenhouse grower interests
and suitability as potted ﬂowering plants based on fragrance, size and ﬂoral

characteristics.

Materials and Methods

Plant material. Plants were grown by a commercial greenhouse (Calif) at

- Si

16 to 26 °C under natural photoperiods (37 °N latitude) with a maximum

l‘..:.
Q.
g.

photosynthetic photon ﬂux (PPF) of =350 umoI-m'Z-s". Propagation dates and
container sizes are provided in Table 1. All species were planted in a bark and
perlite-based media (10-cm pots) and were received in East Lansing, Mich. on 6
May 2001 (Year 1) and 22 July 2002 (Year 2). Brassia, Degannoara, and
Miltassia received in Year 1 were transplanted into 15-cm pots. Zygopetalum
received in Year 2 were transplanted into 13-cm pots. All plants were maintained
at 323 °C in a glass-glazed greenhouse until experiments began. The
photoperiod was a constant 16 h, consisting of natural daylengths (42 °N latitude)
with day—extension lighting from high-pressure sodium (HPS) lamps, which
delivered a supplemental PPF of =50 umol-m'Z-s'1 at plant height [as measured
with a line quantum sensor (Apogee Instruments, Inc., Logan, Utah)].

Prevernalization photoperiods. The experiment was replicated in time and
experimental treatments were identical between years unless otherwise noted.
Two hundred plants of each species were placed at 23 °C for eight weeks under
9-h short days (SD) or 16-h long days (LD) (pre-vernalization photoperiods)

beginning on 1 September 2001 (Year 1) and 28 August 2002 (Year 2).

96

Photoperiods were created by pulling opaque blackout cloth over plants between
1700 and 0800 HR, and for the 16-h photoperiod, light from incandescent lamps
(delivering =3 umoI-m'Z-s") was provided between 1700 and 2400 HR.

Vernalization temperatures and photoperiods. On 27 October 2001 (Year
1) and 23 October 2002 (Year 2), 20 plants of each species were transferred to
greenhouses with temperature setpoints of 11, 14, 17, 20, and 23 °C (8 °C was
also utilized in Year 2). At each temperature, ten plants were placed under SD
and LD photoperiods (provided as described above with incandescent lamps),
also for eight weeks. Vapor pressure deﬁcit during the temperature treatments
was maintained at =07 kPa by the injection of water vapor as needed. Following
eight weeks at the various temperature treatments, plants were forced in a
common greenhouse at 23 °C under LD using HPS lamps.

Greenhouse temperature and irradiance control. Air temperature in each
greenhouse was measured by a thermocouple in an aspirated chamber every 10
s, and hourly averages were recorded by a CR-10 datalogger (Campbell
Scientiﬁc, Logan, Utah). Average daily light integral and air temperature from the
beginning of the pre-vernalization photoperiod treatments until the end of forcing
were calculated (Table 2 and 3). Light transmission through the greenhouses
was reduced using permanent woven shade curtains that reduced light by =55%
(OLS 50; Ludvig Svensson, Charlotte, NC.) and by applying whitewash (up to
50%) to the glass as needed so that the maximum PPF was =350 umol-m'z-s".

Plant culture. In Year 1, plants were irrigated as necessary with well water

(containing 95, 34, and 29 mg-L'1 Ca, Mg, and S, respectively) supplemented

97

with water-soluble fertilizer to provide the following (mg-L"): 125 N, 12 P, 125 K,
15 Ca, 1.0 Fe, 0.1 B and Mo, and 0.5 Mn, Zn, and Cu (MSU Special, Greencare
Fertilizers, Chicago, IL). Water was acidiﬁed with H280, to a titratable alkalinity
of 140 mg-L'1 CaCO3. In Year 2, plants were irrigated as necessary with reverse
osmosis water supplemented with water-soluble fertilizer to provide the following
(mg-L"): 125 N, 12 P, 100 K, 65 Ca, 1.0 Fe and Cu, 0.5 Mn and Zn, 0.3 B and
0.1 Mo.

Data collection and analysis. Immature and mature pseudobulbs were
counted before and after vernalization treatments. The date at which the ﬁrst
inﬂorescence was visible (visible inﬂorescence. or VI) without dissection and the
date the ﬁrst ﬂower opened were recorded for each plant. At ﬂowering, the
number of VI, ﬂower buds and pseudobulb node number at which the
inﬂorescence appeared were counted and inﬂorescence length was measured.
Plants that did not ﬂower 150 d after the end of the vernalization treatment were
considered non-ﬂowering. The percentage of plants that initiated ﬂowers, the
percentage of plants whose ﬂowers developed normally (did not abort), days to
VI, days from VI to ﬂower, and days to ﬂower were calculated. The few plants
that died during the experiments were discarded and not included in the results.

Data was analyzed using SAS (SAS Institute, Cary, NC.) mixed model
procedure (PROC MIXED). Data were pooled for all measured characteristics,
and when there was a signiﬁcant year x treatment interaction, the comparisons

were analyzed separately for each year. The experiment was replicated for

98

Brassia, Degannoara, and Zygopetalum and was performed once for Miltassia,

Miltoniopsis and Odontocidium.

Results

Brassia. The percentage of Brassia Rex ‘Sakata’ that initiated ﬂowers was
low and nonuniform regardless of pre-vernalization photoperiod or vernalization
treatment. The highest percentage of plants that initiated ﬂowers, 55%, were
those placed under a 16—h pre-vernalization photoperiod and held at 23 °C with a
LD photoperiod (Fig. 1A). Plants vernalized at 8 °C were discarded due to
severe chilling injury and not included in further analysis. Flower development
was not adversely affected by. any treatment (Fig. 1B). Vernalization temperature
alone inﬂuenced the number of days to VI after forcing (signiﬁcantly different at P
.<. 0.001) (Fig. 1C). On average, the few plants that ﬂowered at 11 °C required
=37 d to reach Vl, while those at 23 °C required =78 d. The number of days from
visible inﬂorescence to ﬂower was fairly uniform (=37 d) and was not inﬂuenced
by any treatment (Fig. 10). Flower bud count was signiﬁcantly inﬂuenced by
vernalization temperature and photoperiod; as temperature increased under LD,
ﬂower bud count generally increased (Table 4). Inﬂorescence count was not
inﬂuenced by any treatment. However, inﬂorescence length of plants vernalized
under LD was signiﬁcantly greater than those under SD, but the magnitude
varied with cooling temperature.

Degarmoara. Flower initiation was low and nonuniform in Degannoara

Winter Wonderland White Fairy’ and no trends were observed among treatments

99

in Year 1 (Fig. 2A). In Year 2, only two plants initiated ﬂowers so data was not
included in further analysis. Flower development followed a similar pattern as
ﬂower initiation and all plants that initiated ﬂowers developed to ﬂower opening
(Fig. 23). Average days to VI occurred > 100 d after vernalization across all
treatments, except in plants induced under the SD pre-vernalization photoperiod
and cooled at 11 °C with SD, which averaged =72 d (Fig. 2C). The time from VI
to open ﬂower was similar among the twenty treatments ranging from 47 to 71 d
(Fig. 2D). Flower bud count, inﬂorescence count and length were unaffected by
pre-vernalization photoperiod or by vernalization temperature and vernalization
photoperiod (Table 5).

Miltassia. Plants vernalized at 11 and 14 °C were discarded due to severe
chilling injury and not included in further analysis. Flower initiation and
development of Miltassia Charles M. Fitch “Dark Monarch’ did not reach 100
percent in any treatment. However, ﬂower initiation and development was
slightly higher in plants placed under a 9-h pre-vernalization photoperiod
compared to those placed under a 16-h pre-veralization photoperiod (Fig. 3A and
B). Days to VI and days from VI to ﬂower were similar among treatments,
ranging from 164 to 180 d, and 50 to 60 d, respectively (Fig. 3C and D). Pre-
vernalization photoperiod, vernalization temperature and photoperiod did not
inﬂuence ﬂower bud or inﬂorescence count (Table 6). As cooling temperature
increased from 17 to 23 °C, inﬂorescence length decreased from 40.4 to 28.2 cm.

Plants that produced terminal inﬂorescences produced fewer ﬂowers and shorter

100

inﬂorescences compared to plants that developed lateral inﬂorescences
(signiﬁcantly different at P 5 0.001; data not presented).

Miltoniopsis. Flower initiation of Miltoniopsis Augres ‘Trinity’ was
inﬂuenced by photoperiod before and during vernalization and by vernalization
temperatures (Fig. 4). Flower initiation was greatest (100%) when plants were
provided with a 9-h pre-vemalization photoperiod prior to being vernalized under
9-h photoperiods at 14 °C. Average days to visible inﬂorescence occurred > 160
days after plants were taken out of the temperature treatment. Inﬂorescence
count was not inﬂuenced by any inductive treatment (data not presented).

Odontocidium. Flower initiation was high (up to 100%) in Odontocidium
Tiger Crow ‘Golden Girl’, but nonuniform among treatments and no trends were
apparent (Fig. 5A). Flower development was not adversely affected by any
treatment (Fig. 5B). Plants began initiating ﬂowers during the vernalization
treatment, so days to VI were calculated from the end of the pre-vernalization
treatment (Fig. 50). Days to VI, days from VI to ﬂower, ﬂower bud count and
inﬂorescence length were not signiﬁcantly inﬂuenced by any treatment (Fig SC
and D, Table 7). Average days from VI to ﬂower among treatments was =60.
Inﬂorescence count was statistically greater when the pre-vernalization
photoperiod was 3 LD (1.6) compared to a SD (1.4). Flower number and
inﬂorescence length were signiﬁcantly inﬂuenced by the position of the
inﬂorescence (terminal and lateral) (signiﬁcantly different at P 5 0.001).

Zygopetalum. In Year 1, ﬂowering of Zygopetalum Redvale ‘Fire Kiss’

was primarily inﬂuenced by photoperiod before vernalization and by cool

101

temperature, but not by photoperiod during the vernalization treatment (Fig. 6).
In Year 2, no plants ﬂowered under any treatment after 150 d as > 85% of plants
ﬂowered one month prior to the initiation of treatments. In Year 1, the
percentage of plants that initiated and developed ﬂowers was greatest when
plants were vernalized at 11 °C. In particular, plants grown under SD before
vernalization and then transferred to 11 or 14 °C for eight weeks had the highest
ﬂower initiation and development percentages and developed VI the quickest.
None of the plants grown under a 9-h photoperiod followed by temperatures 2 17
°C ﬂowered within the duration of the experiment. When plants were exposed to
16-h photoperiods before vernalization, ﬂower initiation was generally reduced
and ﬂowering was delayed (Fig. 6A and C).

Several of the plants grown under LD then cooled at 14 °C or higher that
initiated ﬂowers did not develop to anthesis (Fig. 68). In addition, the average
time to VI when vernalized at 17 °C or higher was 2 50 d. Regardless of
treatment, time from VI to ﬂower was 30 to 39 d at =23 °C (Fig. GD). Flower bud
count was greatest (2 3.4) and inﬂorescence length was greatest (2 30.4 cm)
when plants were cooled at 11 to 14 °C (Table 8). The length of inﬂorescences

was generally shorter as vernalization temperature increased from 11 to 23 °C.

Discussion
Brassia. Pre-vernalization photoperiod, vernalization temperature, and
vernalization photoperiod did not inﬂuence ﬂowering in Brassia Rex ‘Sakata’. In

a previous study (Section II), photoperiods ranging from 10 to 24 h of continuous

102

light or 9 h with a 4-h night interruption (NI) at =20 °C did not lead to any
ﬂowering response. Brassia Rex ‘Sakata’ is a hybrid (Brassia verrucosa x
Brassia gireoudiana) bred in Hawaii for its heat tolerance with optimal vegetative
growth at or above 20 °C; it can tolerate temperatures as low as 11 °C. At
temperatures 5 8 °C, plants exhibited severe schilling injury symptoms and
eventually died after eight weeks. An investigation with day and night
temperature differentials could reveal a uniform ﬂowering response for Brassia.

Degannoara, Miltassia and Odontocidium. Photoperiod before or during
vernalization and vernalization temperature did not have a signiﬁcant inﬂuence
on ﬂowering or ﬂoral characteristics of Degannoara Winter Wonderland White
Fairy’, Miltassia Charles M. Fitch ‘Dark Monarch’. or Odontocidium Tiger Crow
‘Golden Girl.’ Flowering percentages were nonuniform and incomplete across all
treatments. In a previous experiment (Section II), ﬂowering was not inﬂuenced
by any of seven different photoperiods at =20 °C (mentioned above), in all three
species. Unfortunately, the ﬂowering response is still unknown in these hybrids
and has proven to be more difﬁcult than expected to elucidate. The complex
hybrids created between the members of the Odontoglossum orchid “alliance” to
create Degannoara, Miltassia and Odontocidium pose a challenge in determining
the environmental conditions that lead to complete, rapid and uniform ﬂowering.
However, we have gathered other important production information on these
species, which could be useful for greenhouse growers and hobbyists.

In our vernalization studies, we observed that Miltassia (Brassia

verrucosa x Miltonia spectabilis) is not a cold tolerant hybrid even though part of

103

its parentage is from the cool-growing Miltonia. At temperatures 5 17 °C, plants
exhibited symptoms of chilling injury within two weeks of exposure; by eight
weeks most plants had lost all their leaves and pseudobulbs at 11 to 14 °C,
eventually died. In a separate study, optimal ﬂower color, quality, and longevity
of Miltassia were achieved at temperatures between 20 to 23 °C (Appendix A).

Degannoara Winter Wonderland White Fairy’ (Miltassia Cartagena x
Odontoglossum Gledhow) and Odontocidium Tiger Crow ‘Golden Girl”
(Odontocidium Tiger Hambuhren x Odontocidium Crowborough) are intergeneric
hybrids that can tolerate temperatures from 8 to 28 °C. However, the overall
ﬂower quality (size and color) of Odontocidium diminished at temperatures above
23 °C.

Miltoniopsis. Flower initiation of Miltoniopsis Augres ‘Trinity’ was uniform
and complete only when plants were exposed to 9-h SD photoperiods before and
during vernalization at 11 to 14 °C. A similar response is observed in Cattleya
warscewiczii, C. gaskelliana, and C. mossiae, where ﬂower induction occurred
under continuous 9-h SD at 13 °C, while ﬂowering was inhibited under 16-h LD at
13 °C (Rotor, 1952; Rotor, 1959). Both Cattleya and Miltoniopsis are epiphytes
native to the moist and wet forests of Central and South America.

Time to visible inﬂorescence was long (> 160 d) in Miltoniopsis possibly
due to pseudobulb maturity and a warm forcing temperature. Prior to pre-
vernalization, most plants had one or two mature pseudobulbs, which we believe
could no longer be induced to ﬂower. Instead, these pseudobulbs had produced

vegetative buds (immature pseudobulbs). The immature pseudobulbs were

104

small (< 10 cm), consequently taking over ﬁve months to develop into newly
mature pseudobulbs that we believe were capable of ﬂowering. Furthermore,
after vernalization, plants were forced under 16-h LD at 23 °C, where overall
plant quality was marginal and growth was slow. As a result, the forcing
temperature was lowered to 20 °C on 7 May 2003 and a dramatic visual
improvement in leaf color and turgor was seen within a few weeks.

Miltoniopsis Augres ‘Trinity’ (Miltonia Pam-pam x Miltonia Alger) is a cool
growing hybrid with optimal growth at temperatures between 20 to 23 °C,
although it can tolerate temperatures from 8 to 26 °C. Flower size and quality is
adversely affected by high light, above 400 umoI-m’z-s1 and temperatures > 20
°C, and low humidity. Thus, Miltoniopsis is suited for potted ﬂowering plant
production in temperate climates for winter and spring holidays (Christmas,
Valentine’s Day, Easter and Mother’s Day). Sales at these times would facilitate
production schedules for greenhouse growers as they could utilize the natural
short days and cool temperatures of the fall and winter for ﬂower induction.

Other positive attributes of this genera include its compact nature (< 35
cm) and large, showy and fragrant ﬂowers that resemble pansies. The ﬂowers
can last four to eight weeks on the plant (Baker and Baker, 1993). In an online
survey of potted orchid buyers in the Midwest, participants between the ages of
20 to 62 years selected Miltoniopsis as their most preferred species among
Brassia, Degannoara and Phalaenopsis (Behe et al., 2004). Participants had the
highest average purchase intention (5.5) on a scale of 1 to 7 (1: very unlikely

and 7=very likely to purchase) for Miltoniopsis in a green plastic pot for $19.95.

105

Miltoniopsis in a bamboo pot for $29.95 (5.0) and Phalaenopsis in a black
ceramic pot for $19.95 (5.0) were the second and third most popular choices,
respectively.

For growers to predictably meet speciﬁc market dates for sales of
flowering Miltoniopsis (e.g. Valentine’s Day) several other investigations are
necessary. An easy method of identifying pseudobulbs that are capable of being
induced to ﬂower is needed to reduce the time to VI. Possible methods include
leaf or node count or pseudobulb characteristics such as width, diameter or
circumference. For the establishment of production schedules, studies on the
effects of temperature on ﬂower and pseudobulb development would also
produce valuable information. ‘

Zygopetalum. The most rapid, complete, and uniform ﬂowering occurred
when plants were grown under SDs and then vernalized at 11 to 14 °C. Time to
VI and time from VI to ﬂower occurred relatively quickly within these treatments,
19 to 22 d and 35 to 37 d, respectively. In a previous study (Section II),
Zygopetalum responded as a quantitative short-day plant (SDP) without
vernalization. Photoperiod before vernalization also inﬂuences ﬂowering in the
tropical epiphyte Hatiora spp. (Easter cactus) (Riinger, 1960; Rohwer, 2002). In
both Hatiora and Zygopetalum, ﬂowering is hastened under SD, and a period of
short days before vernalization increases ﬂowering percentage and uniformity.
Another similarity between these genera is that the maximum effective

temperature for induction is around 14 to 15 °C (Rohwer, 2002).

106

In Year 2, no plants ﬂowered after any treatment. One month prior to
experimentation, > 85% of plants ﬂowered and thus ﬂower initiation had occurred
before the plants were shipped to us. We believe that we did not provide an
adequate “rest period” before the onset of treatments, and consequently the
plants did not ﬂower.

With the preliminary production information presented here, greenhouse
growers can induce both Zygopetalum and Miltoniopsis into flower with similar
protocols. Given that a SD photoperiod prior to vernalization and temperatures
of 11 to 14 °C induced Zygopetalum, both species could be induced if also given
SD during vernalization. However, future studies are needed to further

understand and quantify the ﬂowering responses of both hybrids.

Literature Cited

Baker, ML. and CO. Baker. 1993. Miltoniopsis. Amer. Orchid Soc. Bul.
62:794—799.

Behe, B.K, R.M. Walden, R.D. Lineberger, R.G. Lopez, and ES. Runkle. 2004.
Proﬁle of Potted Orchid Buyers in the Midwest. Southern Nursery
Association Research Conference Proceeding. In press.

Chouard, P. 1960. Vernalization and its relations to dormancy. Ann. Rev. Plant
Physiol. 11:191-238.

De Vries, J. 1950. On the ﬂowering of Phalaenopsis schillen'ana RCHB. f. Annu.
Bogorienses. 1:61-76.

Goh, C.J., M.S. Strauss, and J. Arditti. 1982. Flower induction and physiology in

107

orchids, p. 213-241. In: J. Arditti (ed.). Orchid biology: reviews and
perspectives, vol. II, Cornell Univ. Press, New York.

Griesbach, R.J. 1985. An orchid in every pot. Florists’ Review 176(4548):26-30.

Griesbach, R.J. 2002. Development of Phalaenopsis orchids for the mass-
market. pp. 458-465. In: J. Janick and A. Whipkey (eds.). Trends in new
crops and new uses. ASHS Press, Virginia.

Lee, N. and GM. Lin. 1984. Effect of temperature on growth and ﬂowering of
Phalaenopsis white hybrid. J. Chinese Soc. Hort. Sci. 30(4):223-231.

Lee, N. and GM. Lin. 1987. Controlling the ﬂowering of Phalaenopsis, pp. 27-44.
In: L.-R. Chang. (ed.). Proc. Symp. Forcing Hort.Crops. Special Publ. 10.
Taichung District Agr. Improvement Sta., Changhua, Taiwan.

Powell, C.L., K.I. Caldwell, R.A. Littler, and l. Warrington. 1988. Effect of
temperature regime and nitrogen fertilizer level on vegetative and
reproductive bud development in Cymbidium orchids. J. Amer. Soc. Hort.
Sci. 113(4):552-556.

Rohwer, CL. 2002. Flowering physiology of Hatiora. MS. Thesis, Dept. of
Horticulture, Michigan State Univ., East Lansing.

Rotor, GB. 1952. Daylength and temperature in relation to growth and ﬂowering
of orchids. Cornell Univ. Agric. Expt. Sta. Bull. 885:3-47.

Rotor, GB. 1959. The photoperiodic and temperature responses of orchids, pp.
397-416. In: C. L. Withner (ed.). The orchids. Ronald Press, New York.

Ranger, W. 1960. Uber den einﬂuB der temperature und der tageslange auf die

108

bliitenbildung von Rhipsalidopsis xgraesen'. Zeitschrift FUr Botanik 48:381-
397.

Sakanishi, Y., H. Imanishi, and G. lshida. 1980. Effect of temperature on growth
and ﬂowering of Phalaenopsis amabilis. Bulletin of the University of
Osaka, Series B. Agriculture and Biology - Osaka (Prefecture) Daigaku.
32:1-9.

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

US. Department of Agriculture. 1998. Floriculture crops 1997 summary.
Agricultural Statistics Board, Washington DC.

US. Department of Agriculture. 2003. F loriculture crops 2002 summary.
Agricultural Statistics Board, Washington DC.

Vince-Prue, D. 1975. Photoperiodism in plants. McGraw—Hill. London.

Wang, Y.-T. and N. Lee. 1994. A new look for an old crop: potted blooming
orchids. Greenhouse Grower 12(1):79-80.

Wang, Y.-T. 1995. Phalaenopsis orchid light requirement during the induction of
spiking. HortScience 30(1):59-61.

Wang Y.-T. 2001. lrradiance levels affect in vitro and greenhouse growth,
ﬂowering, and photosynthetic behavior of a hybrid Phalaenopsis orchid. J.
Amer. Soc. Hort. Sci. 126:531-536.

Yoneda, K., H. Momose and S. Kubota. 1992. Comparison of ﬂowering behavior
between mature and premature plants of Phalaenopsis under different

temperature conditions. Trop. Agr. 36(3):207-210.

109

Table 1. Propagation dates and container sizes for orchid hybrids.

 

Out Transplant Transplant

Species Year in vitro of ﬂask to 7.5-cm pot to 10-cm pot
Brassia Rex ‘Sakata’ 1 June 1997 June 1998 June 1999 June 2000

2 June 1997 June 1998 June 1999 June 2000
Degannoara
Winter Wonderland 1 May 1997 May 1998 May 1999 May 2000
‘White Fairy'

2 -’ - June 2000 June 2001
was“ Char'Fs M'F'm‘ 1 June 1997 June 1998 June 1999 June 2000
Dark Monarch
M’Itqn’f’ps’s “9’95 1 — - June 2001 May 2002
Tnmty
Odontocidium Tiger Crow .
‘Golden Girl’ 1 - - June 2001 Apnl 2002
,z’.’9°p‘?’a.’“’" Redva'e 1 June 1999 June 2000 -v April 2001
Fire KISS

2 - May 2001 —- May 2002

 

zlnforrnation not available.

’Plants were directly transplanted to 10-cm pots.

110

 

 

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111

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112

Table 4. The effect of pre-vernalization photoperiod, vernalization temperature, and vernalization
photoperiod on ﬂower bud count, inﬂorescence length and count of Brassia Rex ‘Sakata’. Plants
were forced at 23 °C under a 16-h photoperiod.

 

 

 

 

 

 

Pro-vernalization Vernaizgtion Flower Inﬂorescence
photoperiod (h) Temgrature (°C) Photoperiod (h) bud count Count Length (cm)
9 9.9 1.2 42.3
16 11.5 1.2 40.3
8 3- - -
1 1 8.9 1.1 45.6
14 8.8 1.0 42.5
17 10.3 1.1 41.6
20 11.3 1.2 40.7
23 11.9 1.2 40.0
9 9.8 1.2 38.9
16 11.5 1.2 43.4
9 8 9 - - -
8 16 - - -
1 1 9 9.7 1.0 49.2
11 16 8.3 1.3 43.5
14 9 7.5 1.0 33.9
14 16 9.0 1.0 50.0
17 9 6.8 1.0 37.5
17 ' 16 12.0 1.3 48.0
20 9 10.6 1.2 41.2
20 16 11.0 1.3 42.3
23 9 9.2 1.3 33.3
23 16 13.3 1.0 49.3
16 8 9 - - -
8 16 - - -
1 1 9 -’ -- -
11 16 8.0 1.0 41.3
14 9 6.5 1.0 35.1
14 16 11.7 1.0 43.8
17 9 10.8 1.1 41.2
17 16 11.1 1.0 41.6
20 9 11.3 1.1 38.5
20 16 12.4 1.3 40.3
23 9 11.0 1.3 37.5
33 16 13.3 1.2 41 .L
Signiﬁcance
Pro-vernalization photoperiod (PVP) NS NS NS
Vernalization temperature (VT) *** NS NS
Vernalization photoperiod (VP) ** NS **
PVP x VT NS NS NS
PVP x VP NS NS *
VT x VP * NS **
PVP x VT x VP “ NS NS

 

2Plants were discarded due to severe chilling injury.
yNo plants showed visible inﬂorescence within 150 d of forcing.
"3 " "' ”Nonsigniﬁcant or signiﬁcant at P s 0.05, 0.01 or 0.001, respectively.

113

Table 5. The effect of pre-vernalization photoperiod, vernalization temperature, and vernalization
photoperiod on ﬂower bud count, inﬂorescence length and count of Degannoara Winter Wonderland
‘White Fairy’. Plants were forced at 23 °C under a 16-h photoperiod.

 

 

 

 

 

 

 

Pre-vernalization Vemaliz_ation Flower Inﬂorescence
photoperiod (h) Temgrature (°C) Photoperiod (h) bud count Count Length (cm)
9 7.1 1.5 48.4
16 7.8 1.3 49.1
8 3 - -
11 7.2 1.4 51.8
14 7.6 1.3 48.1
17 8.8 1.5 52.3
20 5.7 1.3 37.2
23 8.0 1.3 50.9
9 7.2 1.5 48.1
16 8.0 1.3 49.7
9 8 9 - - -
8 16 - - -
11 9 4.2 1.4 39.6
11 16 7.7 1.8 57.4
14 9 7.0 1.0 46.1
14 16 10.3 1.3 54.3
17 9 7.8 1.8 55.8
17 16 10.0 1.0 47.6
20 9 4.0 2.0 36.9
20 16 6.0 1.0 35.7
23 9 7.0 1.0 35.4
23 16 9.0 2.0 70.5
16 8 9 - - -
8 16 - - -
11 9 9.0 1.5 57.9
11 16 8.6 1.2 55.9
14 9 7.2 1.6 48.3
14 16 6.8 1.3 46.1
17 9 9.0 1.8 49.2
17 16 10.0 1.0 52.8
20 9 6.0 1.3 35.5
20 16 6.3 1.0 39.6
23 9 8.8 1.7 55.0
23 16 6.8 1.3 43.7
Signiﬁcance
Pre-vernalization photoperiod (PVP) NS NS NS
Vernalization temperature (VT) NS NS NS
Vernalization photoperiod (VP) NS NS NS
PVP x VT NS NS NS
PVP x VP NS NS NS
VT x VP NS NS NS
PVP x VT x VP NS NS NS
2No plants showed visible inﬂorescence within 150 d of forcing.
N$Nonsigniﬁcant.

114

Table 6. The effect of pre-vernalization photoperiod, vernalization temperature, and vernalization
photoperiod on ﬂower bud count, inﬂorescence length and count of Miltassia Charles M. Fitch ‘Dark
Monarch’. Plants were forced at 23 °C under a 16-h photoperiod.

 

 

 

 

 

 

Pre-vernalization Vernal'gtion Flower Inﬂorescence
photoperiod (In Temgrature (°CL Photoperiod (h) bud count Count Length (cm)
9 4.9 1.4 35.2
16 4.6 1.6 35.5
11 -‘ - -
14 - - -.
17 5.0 1.7 40.4
20 4.7 1.4 34.9
23 4.6 1.4 28.2
9 4.6 1.4 35.7
16 5.0 1.6 34.9
9 11 9 - - —-
11 16 -- - -
14 9 - - -
14 16 -- - -
17 9 4.4 1.7 35.4
17 16 5.0 1.6 41.6
20 9 4.4 1.3 35.9
20 16 6.2 1.4 36.8
23 9 4.8 1.0 35.6
23 16 5.2 1.4 25.8
16 11 9 - - -
11 16 - - -
14 9 - - -
14 16 - - -
17 9 5.8 1.4 45.7
17 16 4.9 2.0 40.7
20 9 5.0 1.3 36.1
20 16 2.0 1.5 15.0
23 9 3.5 1.8 23.6
.33 16 4.7 1.7 28.1
Signiﬁcance
Pre-vernalization photoperiod (PVP) NS NS NS
Vernalization temperature (VT) NS NS “***
Vernalization photoperiod (VP) NS NS NS
PVP x VT * NS NS
PVP x VP * NS NS
VT x VP NS NS NS
PVP x VT x VP * NS *

 

1Plants were discarded due to severe chilling injury.
"3- " "Nonsigniﬁcant or signiﬁcant at P s 0.05 or 0.001, respectively.

115

Table 7. The effect of pre-vernalization photoperiod, vernalization temperature, and vernalization
photoperiod on ﬂower bud count, inﬂorescence length and count of Odontocidium Tiger Crow
‘Golden Girl’. Plants were forced at 23 °C under a 16-h photoperiod.

 

 

 

 

 

 

 

Pro-vernalization Vemalz__ation Flower Inﬂorescence
photoperiod (h) Temﬂture (°C) Photgperiog (h) bud count Count Length (cm)
9 5.8 1.4 44.0
16 5.9 1.6 42.3
8 5.0 1.3 36.8
11 5.5 1.7 40.7
14 5.9 1.5 42.0
17 5.2 1.4 40.9
20 7.4 1.5 51.2
23 6.3 1.6 47.9
9 5.6 1.5 40.9
16 6.0 1.5 45.5
9 8 9 5.5 1.2 36.9
8 16 5.3 1.0 37.4
11 9 5.2 1.5 39.5
11 16 5.5 1.3 42.1
14 9 4.0 1.0 32.1
14 16 5.0 1.2 40.7
17 9 4.5 1.0 40.2
17 16 5.0 1.4 39.0
20 9 6.4 1.7 40.6
20 16 8.0 1.2 61.0
23 9 6.6 1.3 45.9
23 16 6.4 1.9 56.5
16 8 9 2.3 1.2 26.4
8 16 5.7 1.6 40.7
11 9 6.0 1.6 42.7
11 16 5.5 2.3 39.7
14 9 5.4 2.0 37.6
14 16 9.0 1.2 58.8
17 9 5.8 1.4 43.5
17 16 5.6 1.7 40.9
20 9 8.0 1.8 53.9
20 16 7.7 1.5 54.1
23 9 6.8 2.0 45.9
ﬁ23 16 5.2ﬁ 1.3 41.1
Signiﬁcance
Pre-vernalization photoperiod (PVP) NS ** NS
Vernalization temperature (VT) NS NS NS
Vernalization photoperiod (VP) NS NS NS
PVP x VT NS NS NS
PVP x VP NS us NS
VT x VP NS NS NS
PVP x VT x VP NS NS us

 

"s- ”Nonsigniﬁcant or signiﬁcant at P s 0.01.

116

Table 8. The effect of pre-vernalization photoperiod, vernalization temperature, and vernalization
photoperiod on ﬂower bud count, inﬂorescence length and count of Zygopetalum Redvale ‘Fire
Kiss’. Plants were forced at 23 °C under a 16-h photoperiod.

 

 

 

 

 

 

Pre-vernalization Vemjﬁ_zation Flower Inﬂorescence
jhotgaeriod (h) Temgraturgm) Photogriod (h) bud count Count Length (cm)
9 3.6 1.5 32.5

16 3.4 1.3 29.1
8 -’ - -
11 3.9 1.4 30.6
14 3.4 1.4 34.7
17 3.0 1.3 24.3
20 2.5 1.0 26.4
23 3.0 1.3 23.3
9 3.5 1.4 31.9
16 3.5 1.4 30.2
9 8 9 - - -
8 16 - - -
11 9 3.8 1.4 30.1
11 16 4.0 2.0 31.1
14 9 3.5 1.7 34.8
14 16 3.1 1.0 35.0
17 9 -‘ - -
17 16 - - -
20 9 - - -
20 16 - - -
23 _ 9 - - -
23 16 - - -
16 8 9 - - -
8 16 - - -
11 9 3.8 1.2 33.2
11 16 3.8 1.0 28.6
14 9 3.5 1.0 37.0
14 16 3.7 1.6 32.1
17 9 _, 1.0 ..
17 16 3.0 1.4 24.3
20 9 2.5 1.0 26.4
20 16 - - -
23 9 3.0 1.5 22.0
23 16 3.0 1 .L 24.0
Signiﬁcance
Pre-vernalization photoperiod (PVP) NS NS NS
Vernalization temperature (VT) * NS **
Vernalization photoperiod (VP) NS NS NS
PVP x VT NS NS NS
PVP x VP NS NS NS
VT x VP NS NS NS
PVP x VT x VP NS ** NS

 

zNo plants showed visible inﬂorescence within 150 d of forcing (one dash).
yFlower buds aborted (two dashes).
"3' " "Nonsigniﬁcant or signiﬁcant at P s 0.05 or 0.01, respectively.

117

 

100

 

 

 

 

 

 

A : Flower initiation (%) I B Flower development (%)
so -» . ' ; .. a g -. . .
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Photoperiod and vernalizatcion temperature

Figure 1. Responses of Brassia Rex ‘Sakata’ forced at 23 °C under a
16-h photoperiod after 9- or 16-h prevernalization photoperiods for 8
weeks and vernalization (11, 14, 17, 20, or 23 °C) under 9- or 16-h
photoperiods for 8 weeks. Error bars represent 95% conﬁdence
intervals. Data for days to visible inﬂorescence (VI) are for the period
from the end of vernalization until VI.

118

 

A 1 Flower Initiation (%) ; B Flower Development (%

 

2: mm mm}; IIII m i a}

 

 

Pre-vernalization photoperiod

16 hours

 

 

 

:3 I WW 5II IIIIIII

C Days to visible inﬂorescence D Days from visible
zoo . . ‘1’ j .. ﬁinﬂorescence to flower;

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Pre-vernalization photoperiod

 

 

 

 

 

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11'C 7'C 14‘C 17°C ZO'C 23'C

 

 

 

 

 

 

Photopericod aznd vemalizaticn temperature

Figure 2. Responses of Degannoara Winter Wonderland White Fairy’
forced at 23 °C under a 16-h photoperiod after 9— or 16-h prevernalization
photoperiods for 8 weeks and vernalization (11, 14, 17, 20. or 23 °C)
under 9- or 16-h photoperiods for 8 weeks. Error bars represent 95%
conﬁdence intervals. Data for days to visible inﬂorescence (VI) are for the
period from the end of vernalization until VI.

 

9 hours

40 ~
20 r 1
O

A . Flower initiation (%) B Flower development (° 1)

 

Pre-vernalization photoperiod

16 hours

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Days to visible inﬂorescence D Days from visible _
250 1c . " inﬂorescence to ﬂower.

 

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Photoperiod and vernalization temperature

Figure 3. Responses of Miltassia Charles M. Fitch ‘Dark Monarch’
forced at 23 °C under a 16-h photoperiod after 9-
prevernalization photoperiods for 8 weeks and vernalization (11, 14, 17,
20, or 23 °C) under 9- or 16-h photoperiods for 8 weeks. Plants in the 11
and 14 °C vernalization treatments were discarded due to severe chilling
injury. Error bars represent 95% conﬁdence intervals.

visible inﬂorescence (VI) are for the period from the e
until VI.

120

or 16—h

Data for days to
nd of vernalization

 

 

A Flower initiation.(°/o)
1004 x ’ 3
80‘ . .

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Photoperiod and vernalization temperature

250 -

9 hours

 

Pre-vernalization photoperiod

16 hours

  

 

 

 

   

 

 

 

 

 

 

 

Figure 4. Responses of Miltoniopsis Augres ‘Trinity’ forced at 23 °C
under a 16-h photoperiod after 9- or 16-h prevernalization photoperiods
for 8 weeks and vernalization (8, 11, 14, 17, 20, or 23 °C) under 9- or 16-
h photcperiods for 8 weeks. Error bars represent 95% conﬁdence
intervals.

121

 

1000A 3 Flower initiation (%) — «'3 Flower development (%). ~y

5° 4. - E . . .L

1 III. ”‘

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150 1, . _ 1 inﬂorescence to ﬂower

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Pre-vernalization photoperiod
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Pre-vernalization photoperiod

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11'C 14'C1'7C 20'C 14'C

Photoperiod and vernalization temperaturec

 

O

 

 

Figure 5. Responses of Odontocidium Tiger Crow ‘Golden Girl’ forced at
23 °C under a 16-h photoperiod after 9- or 16-h prevernalization
photoperiods for 8 weeks and vernalization (8. 11, 14, 17, 20. or 23 °C)
under 9— or 16-h photoperiods for 8 weeks. Error bars represent 95%
conﬁdence intervals. Data for days to visible inﬂorescence (VI) are for the
period from the end of pre-vernalization until VI.

122

 

A Flower initiation (%) B Flower development (%)

9 hours

 

Pre—vernalization photoperiod

16 hours

 

2? H m H 1 NH Hm mm:

C Days to visible inﬂorescence D Days from visible
100 - «- inﬂorescence to ﬂower

13 1111 , 11111111

 

9 hours

 

Pre-vernalization photoperiod
16 hours
3 8 8

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14'C 17‘ C 20' C 23'C 11' C 14' Ch 17C 23 C

Photoperiod and vernalization temperature

 

O

 

 

Figure 6. Responses of Zygopetalum Redvale ‘Fire Kiss' forced at 23 °C
under a 16—h photoperiod after 9- or 16-h prevernalization photoperiods for
8 weeks and vernalization (11, 14, 17, 20, or 23 °C) under 9- or 16-h
photoperiods for 8 weeks. Error bars represent 95% conﬁdence intervals.
Data for days to visible inﬂorescence (VI) are for the period from the end
of vernalization until VI.

123

SECTION IV

PHOTOPERIOD AND VERNALIZATION INFLUENCE FLOWERING OF

MILTONIOPSIS AUGRES ‘TRINITY’ ORCHID

124

Photoperiod and Vernalization Inﬂuence Flowering of Miltoniopsis Augres

‘Trinity’ Orchid

Roberto G. Lopez1 and Erik S. Runkle2

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

Additional index words: pansy orchid, potted ﬂowering plants, short days

Received for publication . Accepted for publication . We
gratefully acknowledge funding by Michigan’s plant agriculture initiative at
Michigan State Univ. (Project GREEEN), the Michigan Agricultural Experiment
Station, and greenhouse growers providing support for Michigan State University
ﬂoriculture research.

1Graduate Student.

2Assistant Professor and Extension Specialist, to whom reprint requests should

be addressed (E-mail: runkleer@msu.edu).

125

Introduction

Orchids have become the second most valuable ﬂowering potted crop in
the United States (USDA, 2003). According to the American Orchid Society,
over 75% of all orchids sold in the United States are Phalaenopsis or the moth
orchid (Griesbach, 2002). Currently, the wholesale price of ﬂowering
Phalaenopsis in a 15-cm pot is $8 to $12, with a retail price of $15 to $25 on the
mass market (Wang, 2003). As the market becomes saturated with
Phalaenopsis due to the widespread knowledge of its ﬂower induction
requirements, the price will likely decrease and the plant may become a
commodity. Consequently, commercial growers and retailers are already
seeking other potentially proﬁtable orchids that have consumer appeal and can
be programmed into ﬂower for speciﬁc markets dates.

Miltoniopsis, or the pansy orchid, produces inﬂorescences that are
adorned with three to six ﬂat and large (7 cm), fragrant and showy ﬂowers, which
range in color from cream to pink, magenta, scarlet, and yellow. The ﬂowers
often last on the plant for four to eight at temperatures from 14 to 20 °C
(Robinson, 2002). Due to these attributes, Miltoniopsis has become the fifth
most valuable potted orchid produced commercially in the Netherlands, with
797,000 pots sold in 2001 (Barendse, 2002).

In its native habitat, Miltoniopsis is an epiphytic and lithophytic genus of
six species distributed throughout the wet cloud forest regions (610 to 2,100 m)
from Costa Rica to Peru (Baker and Baker, 1993; Morrison, 2000). The

sympodial growth habit of this compact plant is distinguished from Miltonia by the

126

presence of a single leaf at the pseudobulb apex, which is surrounded by distinct
leaf-like sheaths.

Several outstanding hybrids have been developed in recent years, which
are mainly enjoyed by hobbyists. However, little or no information is currently
available on how to induce Miltoniopsis into ﬂower. In a previous study (Section
III), ﬂower initiation of Miltoniopsis Augres ‘Trinity’ was uniform and complete only
when plants were exposed to 9-h photoperiods before and during vernalization at
11 to 14 °C. A similar response was observed in Cattleya warscewiczii, C.
gaskelliana, and C. mossiae; ﬂower induction occurred under continuous 9-h
photoperiods at 13 °C, and ﬂowering was inhibited when the photoperiod was 16
h (Rotor, 1952; Rotor, 1959). Both Cattleya and Miltoniopsis are epiphytes
native to the humid and wet forests of Central and South America.

Further investigation is necessary to minimizing the production time of
Miltoniopsis and to understanding at what development stage a pseudobulb van
be induced to ﬂower. Casual observations indicate that Miltoniopsis is only
capable of producing an inﬂorescence when its pseudobulb(s) are swollen and
mature. However, it is not known during what deveIOpmental stage (height or
node number) an immature pseudobulb can be induced to produce an
inﬂorescence once it becomes mature.

This information will assist greenhouse growers with developing a
production schedule for complete, rapid and uniform ﬂowering of Miltoniopsis
Augres ‘Trinity’. We performed experiments to determine how varying durations

of two pre-vernalization photoperiods and how vernalization duration, inﬂuences

127

flowering of Miltoniopsis. Other objectives of this study were 1) to determine if
short days are critical prior to vernalization; and 2) to determine if pseudobulb
maturity inﬂuence ﬂower characteristics such as ﬂower initiation percentage or

time to visible inﬂorescence.

Materials and Methods

Plant material. Miltoniopsis Augres ‘Trinity’ were grown by a commercial
greenhouse (Calif) at 16 to 26 °C under natural photoperiods (37 °N lat.) with a
maximum photosynthetic photon ﬂux (PPF) of =350 pmol-m'z-s'L They were
planted in a bark and perlite-based media in June 2002 (10-cm pots) and were
received in East Lansing, Mich. on 22 July 2002. Plants were maintained at 323
°C in a glass-glazed greenhouse until experiments began. The photoperiod was
a constant 16 h, consisting of natural daylengths (42 °N lat.) with day-extension
lighting from high-pressure sodium (HPS) lamps, which delivered a supplemental
PPF of =50 pmoI-m‘z-s'1 at plant height [as measured with a line quantum sensor
(Apogee Instruments, Inc., Logan, Utah)]. Light transmission through the
greenhouses was reduced using a permanent woven shade curtain that reduced
light by =55% (OLS 50; Ludvig Svensson, Charlotte, NC.) and by applying
whitewash (up to 50%) to the glass as needed so that the maximum PPF was
=350 pmol-m'Z-s".

Pseudobulb maturity experiment (Expt. 1). Plants were grown at 20 °C
under 9—h short days (SD) or 16-h long days (LD) beginning on 26 July 2002 for

0, 4, 8, 12, or 16 weeks in a glass-glazed greenhouse. Photoperiods were

128

created by pulling opaque blackout cloth over plants between 1700 and 0800 HR,
and for the 16-h photoperiod, light from incandescent lamps (delivering =2
pmol-m'z-s'1) was provided between 1700 and 2400 HR. From 0800 to 1700 HR,
HPS lamps provided a supplemental PPF of z70 umoI-m‘z-s’1 at plant level when
the ambient greenhouse PPF was <120 umol-m'z-s”. The plants were then
cooled for eight weeks at 14 °C under SD in a controlled-environment chamber.
The photoperiod was provided by a combination of cool-white ﬂuorescent
(VHOF96T12, Philips, Bloomﬁeld, NJ ) and incandescent lamps from 0800 to
1700 HR at 150 pmol-m'z-s". After the cooling treatment, plants were grown at 20
°C under a 16-h LD in the greenhouse

Vernalization duration experiment (Expt. 2). Plants were grown at 20 °C
under SD or L0 (as described above) beginning on 26 August 2002 for eight
weeks. The plants were then cooled for 0, 3, 6, 9 or 12 weeks at 14 °C under SD
in a glass-glazed greenhouse. After the cooling treatment, plants were grown at
20 °C under L0 in the greenhouse. Light conditions were controlled as described
above.

Greenhouse temperature and inadr'ance control. Temperature on each
bench was measured by a thermocouple in an aspirated chamber every 10 s,
and hourly averages were recorded by a CR-10 datalogger (Campbell Scientiﬁc,
Logan, Utah). Average daily air temperature and light integral (DLI) were
determined for each experiment from the beginning of the pre-vernalization

photoperiod until the end of forcing (Table 1 and 2).

129

Plant culture. Plants were irrigated as necessary with reverse osmosis
water supplemented with water-soluble fertilizer to provide the following (mg-L"):
125 N, 12 P, 100 K, 65 Ca, 1.0 Fe and Cu, 0.5 Mn and Zn, 0.3 B, and 0.1 Mo
(MSU Special, Greencare Fertilizers, Chicago, IL).

Data collection and analysis. Ten plants were randomly assigned to each
treatment. Immature and mature pseudobulb count, and height and node
number of immature pseudobulbs, were recorded for Expt. 1 at the beginning of
cool treatments. Immature pseudobulbs were between one and twenty-ﬁve
centimeters in length (measured from the soil level to the apex). For Expt. 1 and
2, the date at which the ﬁrst inﬂorescence was visible (visible inﬂorescence, or
VI) without dissection and the number of inﬂorescences were recorded for each
plant. The percentage of plants that initiated ﬂowers and days to VI were
calculated. The few plants that died during the experiments were discarded and
not included in the results. A complete randomized design was used and data
were analyzed using SAS (SAS Institute, Cary, NC.) mixed model procedure
(PROC MIXED).

Results

Pseudobulb maturity experiment (Expt. 1). Flower initiation was most
complete and uniform when plants were exposed to four or eight weeks of SD
prior to vernalization (Table 3). Flower initiation never increased above 60%
when plants were placed under LD prior to vernalization for any duration. Half of

plants placed directly into the 14 °C chamber for eight weeks initiated ﬂowers.

130

Under short days before vernalization, days to VI from the end of vernalization
increased as pre-vernalization photoperiod duration increased. Inﬂorescence
count was not inﬂuenced by any treatment provided.

The maturity of a pseudobulb signiﬁcantly inﬂuenced the time to VI. For a
mature pseudobulb, time to VI occurred in 29 d compared to 122 to 158 d for an
immature pseudobulb (Table 4). Immature pseudobulbs < 7 cm did not initiate
ﬂowers within 30 weeks, when the experiment ended.

Vernalization duration experiment (Expt. 2). Increasing the duration of
cold increased ﬂower initiation percentage until 9 weeks of cooling (Table 5).
Flower initiation was greatest (2 80%) when plants were placed under 80s prior
to vernalization and vernalized for 2 9 weeks at 14 °C. Flower initiation was s
40% when plants were not exposed to a 14 °C temperature treatment. Time to
VI was not inﬂuenced by pre-vernalization photoperiod. As vernalization duration
increased from 0 to 12 weeks, time to VI decreased from 165 to 67 d if SD were
provided before cold. Inﬂorescence count was not inﬂuenced by photoperiod

prior to vernalization or vernalization duration.

Discussion

The most complete, rapid and uniform ﬂowering of Miltoniopsis Augres
‘Trinity’ occurred when plants with pseudobulbs that had just begun to swell and
mature were placed under SD for four to eight weeks of SD then cooled at 14 °C
for eight to twelve weeks under SD. These results are in agreement with results
from a previous experiment (Section III) in which plants placed under eight weeks

of SD and eight weeks of cooling had the highest ﬂower initiation percentage

131

(100%). In a separate study, 90 to 100% of Miltoniopsis Augres ‘Trinity’ placed in
environmental chambers with constant temperatures of 14, 17 or 20 °C under 9-h
SD eventually ﬂowered (Robinson, 2002). Robinson (2002) also found that time
from VI to ﬂower at 14, 17 and 20 °C under a 9-h photoperiod was 71, 70 and 61
days, respectively. Our results indicate that, production time can be reduced by
four weeks, since four weeks of SD prior to cooling is adequate for rapid,
complete and uniform ﬂowering of Miltoniopsis.

These results also illustrate the importance of providing plants with SD
before cold and SD during vernalization. Unfortunately, neither photoperiod nor
cooling can be substituted or eliminated. Sixty percent or less of plants initiated
ﬂowers when not exposed to SD before cooling (Table 3), and only 30% ﬂowered
when not provided with a cool temperature treatment (Table 5). The importance
of SD before cooling has also been observed in Hatiora, where plants exposed to
LD before cooling (7.5 to 12.5 °C for four weeks) ﬂowered poorly (SS-73%
ﬂowering). Hatiora plants exposed to SD prior to cooling had 93 to 100%
ﬂowering (Rohwer, 2002).

Similar to other ﬂowering plants, a juvenile phase exists in orchids and
plants must reach a certain stage of growth before attaining the capacity to
ﬂower. Thus, sexual reproduction is delayed until plants reach a size sufﬁcient to
maintain the energetic demands of ﬂowering and seed production. This period of
juvenility varies among species and cultivars. In Phalaenopsis, for example, the
inﬂorescence normally emerges from the third to ﬁfth node below the apical leaf

(Sakanishi et al. 1980; Yonda 1985).

132

In Miltoniopsis, pseudobulb maturity signiﬁcantly inﬂuences ﬂower
initiation and time to VI in Miltoniopsis. Time to VI increases 3100 d if the only
inducible pseudobulb on a plant is immature. If an immature pseudobulb s 6 cm
in height is placed in an inductive treatment, according to our results, it is
incapable of initiating ﬂowers. However, immature pseudobulbs 2 7 can initiate
ﬂowers. Consequently, it is important that growers have uniform plant with nearly
mature pseudobulbs to achieve the most uniform ﬂowering of Miltoniopsis.

Miltoniopsis Augres ‘Trinity’ (Miltonia Pam-pam x Miltonia Alger) is a cool
growing hybrid with optimal vegetative growth at temperatures between 20 to 23
°C, although it can tolerate temperatures from 8 to 26° C. Flower size and quality
~ were adversely affected by high light (> 400 pmol-m'Z-s‘) and high temperatures
(> 20 °C) (Robinson, 2002).

The numerous positive attributes of Miltoniopsis Augres ‘Trinity’ merit its
consideration as a potted ﬂowering plant for winter and spring holidays
(Christmas, Valentine’s Day, Easter and Mother's Day) when temperatures are
not excessive for shipping and storage to preserve ﬂower quality. Sales at these
times would also facilitate production schedules for greenhouse growers in
Northern climates as growers could utilize the natural short days and cool

temperatures of autumn and winter for ﬂower induction.

Literature Cited
Baker, ML. and 0.0. Baker. 1993. Miltoniopsis Il. Amer. Orchid Soc. Bul.

62:901—908.

133

Barendse, M. 2002. De sierteelt-toppers van 2001. Vakblad voor de Bloemisterij.
2224-27.

Griesbach, R.J. 2002. Development of Phalaenopsis orchids for the mass-
market. pp. 458-465. In: J. Janick and A. Whipkey (eds.). Trends in new
crops and new uses. ASHS Press, Virginia.

Morrison, A. 2000. The illustrated encyclopedia of orchids. Timber Press,
Portland.

Robinson, K.A. 2002. Effects of temperature on the ﬂower development rate and
morphology of Phalaenopsis orchid. MS. Thesis, Dept. of Horticulture,
Michigan State Univ., East Lansing.

Rohwer, CL. 2002. Flowering physiology of Hatiora. MS. Thesis, Dept. of
Horticulture, Michigan State Univ., East Lansing.

Rotor, GB. 1952. Daylength and temperature in relation to growth and ﬂowering
of orchids. Cornell Univ. Agric. Expt. Sta. Bull. 88513-47.

Rotor, GB. 1959. The photoperiodic and temperature responses of orchids, pp.
397-416. In: C. L. Withner (ed). The orchids. Ronald Press, New York.

Sakanishi, Y., H. Imanishi, and G. lshida. 1980. Effect of temperature on growth
and ﬂowering of Phalaenopsis amabilis. Bulletin of the University of
Osaka, Series B. Agriculture and Biology - Osaka (Prefecture) Daigaku.
3221-9.

Wang Y.-T. 2003. Potted orchids - popular and proﬁtable. Texas Agricultural
Experiement Station. 3 March 2003. <http://agresearch.tamu.edu/

orchidsdoc.htm>

134

Yonda, K. 1985. Effects of plant age and time of transfer to highland during
summer on Phalaenopsis. J. Jpn. Soc. Hort. Sci. 54:101-108.
US. Department of Agriculture. 2003. Floriculture crops 2002 summary.

Agricultural Statistics Board, Washington DC.

135

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Table 3. The effect of pre-vernalization photoperiod and duration on days to visible inﬂorescence
(VI) and inﬂorescence count of Miltoniopsis Augres ‘Trinity’ (Expt. 1). The pre-vernalization
photoperiod was delivered at 20 °C. Plants were then vernalized for eight weeks at 14 °C under a 9-
h photoperiod and subsequently forced at 20 °C under a 16-h photoperiod.

Pre-vemJali_zation

 

 

 

Duration
Photﬂeriod (h) Qrveeks) Flower initiation (%) Days to VI Inﬂorescence COLIﬂL
-’ O 50 84 1.0
9 4 90 39 1.2
8 100 65 1.3
12 60 88 1.5
16 60 89 1.5
16 4 40 61 1.3 :7
8 60 90 1.0 I‘
12 60 64 1.3 I
16 60 136 1.5 _
Signiﬁcance
Pre-vemalization photoperiod (PVP) NS NS
Pre-vemalization photoperiod duration (PVPD) * NS
PVP x PVPD NS NS

 

zPlants did not receive a photoperiod treatment prior to vernalization.
"3' 'Nonsigniﬁcant or signiﬁcant at P s 0.05.

138

Table 4. The effect of pseudobulb maturity and immature pseudobulb height on days to visible

 

 

 

inﬂorescence in Miltoniopsis Au$es ‘Trinity’ (Expt. 1).
Pseudobulb Immature pseudobulb Number of Flower Days to visible
maturity height (cm) Pla_nti initiation (%) inﬂorescence(\_/I)
Immature 6 1 5 0 3

7 - 12 30 47 158 :l: 27
13-25 25 52 122130
Mature -’ 56 57 29 :I: 11
Signiﬁcance
Pseudobulb maturity ***

Immature pseudgulb height
’No pseudobulbs at this height initiated ﬂowers.
yHeight of mature pseudobulbs not measured.
”Signiﬁcant at P .<. 0.001.

 

 

139

Table 5. The effect of pre-vemalization photoperiod and vernalization duration on days to visible
inﬂorescence and inﬂorescence count of Miltoniopsis Augres ‘Trinity’ (Expt. 2). Pre-vemalization
photoperiods were provided at 20 °C for eight weeks. Plants were then vernalized at 14 °C under a
9-h photoperiod and subsequently forced at 20 °C under a 16-h photoperiod.

 

 

 

Pre-vernalization Vernalization Flower Days to visible Inﬂorescence
Jhotgeriod (h) duraLtioniweeks) initiation (%) inﬂorescence coant
9 0 30 165 1 .7
3 30 1 84 1 .3
6 60 1 1 1 1.2
9 90 82 1.4
12 80 67 1 .6
16 0 40 182 1 .3
3 30 169 1 .3
6 60 143 1.2
9 60 1 54 1 .3
12 60 97 2.1
Signiﬁcance

Pre-vemalization photoperiod (PVP) NS NS
Vernalization duration (VD) *** NS
PVP x VD NS NS

 

”5' "Nonsigniﬁcant or signiﬁcant at P 5 0.001.

140

SECTION V

THE EFFECT OF TEMPERATURE ON LEAF AND FLOWER DEVELOPMENT
AND FLOWER LONGEVITY OF ZYGOPETALUM REDVALE ‘FIRE KISS’

ORCHID

141

The Effect of Temperature on Leaf and Flower Development and Flower

Longevity of Zygopetalum Redvale ‘Fire Kiss’ Orchid

Roberto G. Lopez‘ and Erik s. Runkle2

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

Additional index words: base temperature, degree-days, potted ﬂowering orchids

Received for publication . Accepted for publication . We
gratefully acknowledge funding by Michigan’s plant agriculture initiative at
Michigan State Univ. (Project GREEEN), the Michigan Agricultural Experiment
Station, and greenhouse growers providing support for Michigan State University
ﬂoriculture research. We also thank Cathy Whitman for assistance with data
collection.

1Graduate Student.

2Assistant Professor and Extension Specialist, to whom reprint requests should

be addressed (E-mail: runkleer@msu.edu).

142

Introduction

In the United States, potted ﬂowering plants are commonly purchased for
holidays such as Christmas, Mother’s Day, Easter, and Valentine’s Day. Thus,
greenhouse growers must be able to produce ﬂowers (either for cut ﬂowers or as
potted plants) to meet speciﬁc market dates. Plants that do not have ﬂowers, or

have ﬂowers that are too immature (e.g., only ﬂower buds) or mature (e.g.,

ﬂowers are all open), are often not sold or sold for a lower price.

l.4n h...“ I4

Potted ﬂowering orchids are produced in vast quantities throughout the
world. In 1995, the world demand for potted orchids was estimated at 1.22 billion
units of plant stock with a predicted increase of four percent over the next ﬁve
years (Hew and Yong, 1997). Orchids are the second most valuable ﬂowering
potted crop in the United States, with an estimated wholesale value of
approximately $105.6 million (USDA, 2003). However, the ﬂowering process of
the majority of orchid species is understood poorly, or not at all. Some notable
exceptions include Phalaenopsis, Cattleya, Cymbidium, and Dendrobium. In
these genera, low temperatures, short photoperiods, or both, regulate the
ﬂowering process (Rotor, 1952; Sakanishi et al., 1980; lchihashi, 1997).

The Orchidaceae is the largest and most diverse of all plant families.
Approximately ten percent of all ﬂowering plant species are orchids, which
comprise 20,000 to 25,000 species grouped into 725 genera (Griesbach, 1985).
In addition to the natural abundance of orchids, there are over 100,000 man-
made hybrids. The commercial potential of the vast majority has not yet been

explored. Important considerations for the introduction of new ﬂoricultural crops

143

include showiness of ﬂower display, ease and length of production, crop
uniformity and size, compact size, consumer appeal, and post-production ﬂower
longevity.

Zygopetalum, or the Iadybird orchid, is a sympodial terrestrial and
epiphytic South American genus comprised of 20 species. They are native to
neotropic mid-elevation mountains (1,300 to 1,700 m) of Brazil, Guiana,
Venezuela and Peru (Rose, 1993). Zygopetalum Redvale ‘Fire Kiss’ is
moderately compact (25- to 40-cm tall) and produces several broad and leathery
leaves atop mature green pseudobulbs. Four or more leaf-like sheathing bracts,
which grow from the base, protect the immature pseudobulbs but these bracts
become dry and ﬁbrous with age (Baker and Baker, 1991). The erect
inﬂorescences emerge from the third, forth or fifth sheathing bract of immature
pseudobulbs. Lime-green and dark’maroon sepals and petals, featuring broad
three-lobed Iabellums in deep magenta and white, characterize the exotic,
fragrant and waxy ﬂowers.

Scheduling a crop such as Zygopetalum to ﬂower on speciﬁc market dates
requires knowledge of the relationship between temperature and time to ﬂower.
Temperature is one of the critical factors controlling plant developmental
processes, such as ﬂowering. Consequently, modeling plant development could
help greenhouse growers with scheduling of ﬂowering crops. At temperatures
below a species-speciﬁc minimum, known as the base temperature (Tb), time to

ﬂower (days) is inﬁnite. As temperature increases rise above an optimum

144

temperature (Tom) ﬂowering is delayed. Base and optimum temperatures vary
within and between species and are related to climatic origins.

The reciprocal is often taken for developmental processes such as leaf
unfolding or time to ﬂower. The relationship between mean temperature and rate
of development towards ﬂowering (1/days, where days is the days to ﬂower) is
often linear between Tb and Tom (Roberts and Summerﬁeld, 1987) and can be
described as follows:

1/days = b0 + DJ [1]
Using constants b0 and b1, Tb and the thermal time required for ﬂowering
(degree-days, or °days) can be calculated as follows:

Tb = -bo/b1 . [2]

°days = 1/b1 [3]

Temperature not only inﬂuences time to ﬂower, but also plant
architecture and ﬂower longevity. For example, in Antirrhinum majus L. ‘Jackpot’,
time from germination to ﬂower initiation, visible bud, ﬁrst ﬂoret, and harvest
increased as temperature decreased from 21 to 5 °C (Maginnes and Langhans,
1961). Flowers of Lysimachia congestiﬂora Hemsl. lasted longer when grown at
18 °C compared to those at 26 °C (Zhang et al., 1995). Node development of
Dahlia increased linearly as temperature increased from 10 to 24.6 °C with a
maximum leaf pair unfolding rate of 0.29 leaf/day at 24.6 °C (Brondum and
Heins, 1993).

lnforrnation on the time required to reach a developmental stage is critical

to developing crop production schedules. The objectives of this study were to

145

determine the relationship between temperature and 1) leaf unfolding rate (LUR),
2) leaf expansion, 3) time to ﬂower, 4) ﬂower longevity of the ﬁrst open ﬂower and

5) inﬂorescence longevity of Zygopetalum orchids.

Materials and Methods

Plant material. Zygopetalum Redvale ‘Fire Kiss,’ plants were received and
grown by a commercial greenhouse (Calif), transplanted into 38-cell plug trays in
June 2000, and then into 10-cm pots in April 2001. In Calif., plants were grown
at 16 to 26 °C under natural photoperiods (37 °N latitude) with a maximum
photosynthetic photon ﬂux (PPF) of 3350 pmoI-m'z-s". Five hundred plants in a
bark and perlite-based media (10-cm pots) were received in East Lansing, Mich.
on 6 May 2001. They were maintained at =23 °C in a glass-glazed greenhouse
until experiments began. The photoperiod was a constant 16 h (0600 to 2200
HR), consisting of natural daylengths (42 °N latitude) with day-extension lighting
from high-pressure sodium (HPS) lamps, which delivered a supplemental PPF of
=50 pmoI-m‘z-s'1 at plant height [as measured with a line quantum sensor
(Apogee Instruments, Inc., Logan, Utah)].

Plant culture. In Year 1, Plants were irrigated as necessary with well
water (containing 95, 34, and 29 mg-L‘1 Ca, Mg, and 8, respectively)
supplemented with water-soluble fertilizer to provide the following (mg-L"): 125
N, 12 P, 125 K, 13 Ca, 1.0 Fe, 0.1 B and Mo, and 0.5 Mn, Zn, and Cu (MSU
Special, Greencare Fertilizers, Chicago, IL). Water was acidiﬁed with H2304 to a

titratable alkalinity of =140 mg-L'1 CaCOa. In Year 2, plants were irrigated as

146

necessary with reverse osmosis water supplemented with water-soluble fertilizer
to provide the following (mg-L"): 125 N, 12 P, 100 K, 65 Ca, 1.0 Fe and Cu, 0.5
Mn and Zn, 0.3 B and 0.1 Mo.

Environmental chamber temperature and photoperiod control. All
experiments were performed in walk-in controlled-environment chambers with
constant temperature set points of 14, 17, 20, 23, and 26 °C. In Year 1 of Expts.
1 and 3, an additional chamber set at 29 °C was used. In Expt. 1, Year 1, the 23
°C treatment was provided in a greenhouse. Air temperature in each chamber
was measured by an aspirated thermocouple every 10 s, and hourly averages
were recorded by a CR-10 datalogger (Campbell Scientiﬁc, Logan, Utah). The
average daily air temperatures for all experiments were calculated (Table 1). For
Expt. 1, Year 1, each chamber was divided in half with black plastic and two
photoperiods were created: 9-h of light with or without a 4-h (2200 to 0200 HR)
night interruption (NI). The 9-h base photoperiod was provided by a combination
of cool-white ﬂuorescent (VHOF96T12, Philips, Bloomﬁeld, NJ.) and
incandescent lamps from 0800 to 1700 HR at 150 pmoI-m’zs". Night interruption
lighting (=2 umol-m‘z-s'1 at canopy level) was provided by incandescent lamps.

In Expt. 1, Year 2, only a 9-h photoperiod was provided since photoperiod did not
inﬂuence leaf development in Year 1. In Expt. 2 and 3, only 9-h photoperiods
were provided.

Leaf development (Expt. 1). The experiment was replicated in time,
beginning on 12 June 2001 (Year 1) and 19 February 2002 (Year 2).

Experimental treatments were identical between years unless otherwise noted.

147

Ten plants were assigned randomly to the SD and NI sections of the walk-in
controlled-environment chamber for Expt. 1. At the beginning of the experiment,
one immature pseudobulb was identiﬁed and leaf unfolding was recorded weekly
by counting the number of leaves from the soil level to the terminal end of the
pseudobulb. The leaf length of a marked immature leaf was measured weekly
and leaf expansion rate was calculated. Plants were grown for 20 weeks, except
for those at 29 °C, in which observations were terminated after 13 weeks due to
declining growth and plant mortality.

Flower development (Expt. 2). The experiment was replicated in time,
beginning on 12 April 2002 (Year 1) and 19 March 2003 (Year 2) with ten plants
per treatment. Experimental treatments were identical between years unless
otherwise noted. Plants were grown in a glass greenhouse and on the date that
VI was ﬁrst visible (< 1 cm long), plants were transferred to one of the ﬁve
chambers until ten plants were in each chamber. The date each plant was
placed in the chamber and the date of the opening of ﬁrst and subsequent
ﬂowers were recorded for each plant. At ﬂowering, the number of ﬂower buds
and nodes on immature pseudobulbs below the inﬂorescence were counted and
inﬂorescence length was measured. Days to ﬂower and air temperature during
that period were calculated for each plant.

Flower and inﬂorescence longevity (Expt. 3). The experiment was
replicated in time, beginning on 8 August 2001 (Year 1) and 14 February 2002
(Year 2). Experimental treatments were identical between years unless

otherwise noted. Plants were grown in a glass greenhouse and on the date that

148

the ﬁrst ﬂower of an inﬂorescence opened on each plant, it was transferred to
one of the chambers. The date that each plant was placed in the chamber and
the date of ﬂower mortality (senescence) of the ﬁrst and subsequent ﬂowers were
recorded for each plant. Individual ﬂower and inﬂorescence longevity were
calculated for each plant at each temperature.

Data analysis. The experimental designs for both years were completely
randomized. Data were analyzed using SAS (SAS Institute, Cary, NC.) mixed
model procedure (PROC MIXED) for analysis of variance and linear models
procedure (PROC REG) for regression models. Data were pooled in each
experiment for all measured characteristics. Base temperature (T b) and thermal
time (°days), were calculated (Roberts and Summerﬁeld, 1987). The mean time
to ﬂower or leaf unfolding rate (LUR) and ﬂower and inﬂorescence longevity at
each temperature were converted to rates by taking the reciprocal (1ldays). The
relationship between rate of progress to ﬂowering, leaf development or
senescence (1/days) and mean temperature T in °C were determined by
Equations 1, 2, and 3. Within each developmental stage, slopes and intercepts

were computed.

Results

Leaf development (Expt. 1). Photoperiod (9—h or NI) had no signiﬁcant
inﬂuence on leaf unfolding or leaf expansion and thus data were pooled. Leaf
unfolding increased as temperature increased to 325 °C, and then began to

decrease (Fig. 1). The days required to produce one leaf averaged 46 d at 14 °C

149

and 19 d at 25 °C. The leaves of plants unfolded as a linear function until z25 °C
(Table 2). The base temperature for LUR was estimated at 6.2 °C and the °days
required to develop one leaf was 357 °C-d'1 (Table 2).

Leaf expansion was signiﬁcantly inﬂuenced by temperature (signiﬁcantly
different at P 5 0.001 ). As temperature increased from 13 to 29 °C, leaf
expansion increased (Fig 2). Leaves became mature earlier at warmer
temperatures and, thus the increase in leaf length slowed earlier at the higher
temperatures. For example, leaf expansion at 28.6 °C slowed earliest, after less
than z80 d, and at 13.4 °C, 2 120 cl elapsed following the start of the experiment
before expansion slowed.

Flower development. Time from VI to anthesis decreased with increasing
temperature (Fig. 3). Time from visible inﬂorescence to ﬂower averaged 73 d at
14 °C, and 28 d at 26 °C. Increasing the temperature by 2.1 °C from 17.4 to'19.5
°C accelerated ﬂowering more than increasing the temperature 2.5 °C from 19.5
to 22.0 °C. For example, days from visible inﬂorescence to ﬂower decreased
from an average of 67 to 43 d (24 d or 11.4 (I per degree) as temperature
increased from 17.4 to 19.5 °C, but only decreased from 43 to 33 d (10 d or 4 d
per degree) as temperature increased from 19.5 to 22.0 °C.

Rate of progress from VI to ﬂowering was linear within the range of
temperatures tested (Fig. 3). The base temperature was estimated at 6.4 °C for
time from VI to ﬂower and estimated thermal time was 556 °C-d'1 degree-days

(Table 2). Flower bud count of each inﬂorescence was not signiﬁcantly

150

inﬂuenced by temperature (data not presented). Average inﬂorescence length
varied among the temperatures, but there were no apparent trends (Fig. 4).

Flower and inﬂorescence longevity. Flower and inﬂorescence senescence
occurred more rapidly as temperature increased (Fig. 5). As temperature
increased from 14 to 29 °C, longevity of the ﬁrst open ﬂower decreased from 37 d
to 13 d. Inﬂorescence longevity followed a similar pattern, decreasing from 38 d
at 14 °C to 15 d at 29 °C. Flower longevity of the second and subsequent ﬂowers
decreased by one to three days in comparison to the longevity of the ﬁrst open
ﬂower at all temperatures studied (data not presented).

Flower and inﬂorescence longevity data were converted to rates, and a
thermal time model was developed to predict senescence at different
temperatures. Rate of progress to senescence of individual ﬂowers and
inﬂorescences was linear within the range of temperatures tested (Table 2). The
base temperatures were estimated at 3.7 and 3.6 °C and the accumulated

thermal time lifespan was 370 and 385 °C-d", respectively.

Discussion

As temperature increased from 14 to 26 °C, there was an increase in the
rate of progress to ﬂowering or senescence (and therefore a decrease in time to
ﬂowering or ﬂower longevity). Higher temperatures also caused more rapid LUR
and leaf expansion. Relative growth rate increased linearly to about =25 °C,
declining thereafter. The optimum temperature for Zygopetalum appears to be

325 °C for both LUR and time to ﬂower. However, at this temperature some

151

ﬂower buds acquired necrotic lesions and aborted soon after. Overall, plants
forced at cooler temperatures 5 20 °C were developmentally slower, had taller
inﬂorescences, and were more aesthetically attractive.

Similar results with Phalaenopsis were observed by Robinson (2002) who
found that as temperature increased from 14 to 26 °C, the rate of ﬂower, leaf, and
bud development for several cultivars increased linearly. The optimal

temperature for this orchid, which is native to tropical and subtropical areas of the

r—r-"ﬁr

South Paciﬁc Islands and Asia, appeared to be 26 °C, but plants performed best
at =23 °C (Robinson, 2002). The base temperature for a given phenophase of
Phalaenopsis was between 8 and 12 °C, which is 4 to 6 °C higher than that
reported here for Zygopetalum. This is not a surprise, since Zygopetalum are
native to neotropic mid-elevation mountains (1,300 to 1,700 m) that have cooler
climates.

Zygopetalum Redvale ‘F ire Kiss’ can be ﬂowered and scheduled for
speciﬁc market dates by manipulating greenhouse temperature. Leaf
development and ﬂower longevity were modeled as a function of temperature
and were found to accurately predict the time of these developmental processes.
To complete a developmental process, a plant must experience a speciﬁc
number of units of degree-days or thermal time above the base temperature
characteristic of that process (Roberts and Summerﬁeld, 1987). Thermal time is
often used to schedule planting and harvesting of fruit and vegetable crops. It
can also be utilized in commercial greenhouse environments, which often have

ﬂuctuating temperatures, to predict ﬂowering dates or leaf development. If the

152

average daily temperature is Ta, the days necessary to complete a
developmental process can be calculated by °days/(Ta -Tb). Using this method,
the time required to complete a developmental stage can be calculated for a
species when the average daily temperature is known. For example, time from
visible inﬂorescence to ﬂower for Zygopetalum forced at 14 °C (T b = 6.4 °C) is
estimated at (556 degree-days/7 .6 °C) = 73 d. In comparison, actual time from
visible inﬂorescence to ﬂower for plants forced at 14 °C was 75 d. Flower
longevity is also accurately predicted with a model; plants grown at 14 °C (Tb =
3.7 °C) have an estimated accumulated thermal time lifespan of (370 degree-
days/10.3 °C) = 36 d. Actual ﬂower longevity observed was 37 d.

The life span of orchid ﬂowers varies considerably among genera.
Phalaenopsis ﬂowers may last for months, while other orchid ﬂowers are
ephemeral, lasting only one day. The full bloom period of an inﬂorescence
depends partly on the number of ﬂowers and the longevity of individual ﬂowers.
Factors such as air pollution, physical damage to the plant or ﬂower, slight
disturbances to the pollinia or anther caps, pollination, temperature and ethylene
(C2H4) can considerably accelerate the senescence of ﬂowers (Goh and Arditti,
1985)

Thermal time and base temperatures can be used to predict and help
maximize the ﬂower life of potted ﬂowering plants for consumers. Achieving
optimal shipping, storage and handling temperatures between production
greenhouses and ﬂoral shops, grocery stores or nurseries could signiﬁcantly

improve ﬂower longevity (personal observation). This information could then be

153

conveyed to consumers to give them optimal satisfaction with their purchase. In
this experiment, temperatures in the range of 14 to 29 °C were tested, the Tom for
ﬂower longevity was not observed and thus is < 14 °C. Potted Zygopetalum
shows signs of chilling injury at temperatures 5 8 °C (Section III) and thus, the

Tom is likely between 8 and 14 °C. When plants were transferred from cool

- —.—

temperatures (5 17 °C) to warmer temperatures (2 23 °C), the ﬂoral labellum

often wilted within a few hours and reduced the aesthetic value and beauty of the

F“_ _.

inﬂorescence . Consequently, sudden and large changes in temperature are not
recommended for Zygopetalum as they can adversely affect ﬂower quality.

In summary, Zygopetalum perform best when grown and forced at
temperatures between 20 to 23 °C. Although plants grown at ~23 °C produced
leafs approximately two days slower than those grown at 26 °C, overall plant
appearance was visually enhanced at 23 °C as leaves did not have necrotic
lesions. Forcing temperatures above 23 °C are not recommended as ﬂower
quality is adversely affected. Flower and inﬂorescence longevity of Zygopetalum
placed in the average home or ofﬁce (=20 °C) is estimated at =23 d if prior
conditions (shipping and retail handling) were not extreme and light and water

are adequately provided.

Literature Cited

Baker, ML. and CO. Baker. 1991. Orchid Species Culture. Timber Press,

Portland.

154

Brondum, J.J. and RD. Heins. 1993. Modeling temperature and photoperiodic
effects on growth and development of Dahlia. J. Amer. Soc. Hort. Sci.
1 18:36-42.

Griesbach, R.J. 1985. An orchid in every pot. Florists’ Review 176(4548):26-30.

Hew, CS. and J.W.H. Yong. 1997. The physiology of tropical orchids in relation
to the industry. World Scientiﬁc, Singapore.

lchihashi, S. 1997. Orchid production and research in Japan. In: J. Arditti and A.

I .~

M. Pridgeon (eds.). Orchid biology: reviews and perspectives, vol. VII,
Kluwer Academic Publishers, Great Britain.

Lopez, R.G., E.S. Runkle, R.D. Heins and CM. Whitman. In Press. Temperature
and photoperiodic effects on growth and ﬂowering of Zygopetalum
Redvale ‘Fire Kiss’ orchids. Acta Horticulturae.

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

Roberts, E.H. and R.J. Summerﬁeld. 1987. Measurement and prediction of
ﬂowering in annual crops, p. 17-50. In. J.G. Atherton (ed.). Manipulation of
ﬂowering. Buttenrvorths, London.

Robinson, K.A. 2002. Effects of temperature on the ﬂower development rate and
morphology of Phalaenopsis orchid. MS. Thesis, Dept. of Horticulture,
Michigan State Univ., East Lansing.

Rose, J. 1993. Zygopetalum. Amer. Orchid Soc. Bull. 62(7):733—734.

Rotor, GB. 1952. Daylength and temperature in relation to growth and ﬂowering

155

of orchids. Cornell Univ. Agric. Expt. Sta. Bull. 885:3-47.

Sakanishi, Y., H. Imanishi, and G. lshida. 1980. Effect of temperature on growth
and ﬂowering of Phalaenopsis amabilis. Bulletin of the University of
Osaka, Series B. Agriculture and Biology - Osaka (Prefecture) Daigaku.
32:1-9.

US. Department of Agriculture. 2003. F loriculture crops 2002 summary.
Agricultural Statistics Board, Washington DC

Zhang, 0., AM. Annitage, J.M. Affolter, and MA. Dirr. 1995. Environmental
control of ﬂowering and growth of Lysimachia congestiﬂora Hemsl.

HortScience 30:62-64.

156

Table 1. Actual average air temperatures of environmental chambers or (greenhouse) for each
experiment.

 

 

 

 

Setpoint temgature (°C)
Exgriment Year 14 17 20 a3 26 39
Average air temperature during experiments (°C)
1 1 13.4 16.7 19.5 22.4 24.8 28.6
2 13.4 17.3 19.5 22.4 25.5 -’
2 1 13.5 17.4 19.5 22.0 25.5 -
3 1 13.4 17.1 19.5 25.9" 25.4 28.6
2 13.3 17.4 19.6 2_2.3 25.5 -

 

zNI = 9-h photoperiod plus-4-h night interruption.
yTemperature not utilized.
"Plants were forced in the greenhouse.

3. JV—rﬂxisw
F "I.

157

Table 2. Parameters of linear regression analysis relating forcing temperature to rate of progress
for leaf development, from visible inﬂorescence to ﬂower, ﬂower longevity of the ﬁrst ﬂower and
inﬂorescence longevity in Zygopetalum Redvale ‘Fire Kiss'. Intercept and slope were used in Eqs.

[1] and [2] to calculate base temperature (Tb) and thermal time to complete a particular

developmental stage (°C-d“).

 

Developmental Intercept (b0) Slope (b1)

stage (1ldays) (1ldays)! °C Tb (°C) °C-d'1 r2
Leaf unfolding 00174 :I: 0.00381 0.0028 1 0.0002 6.2 357 0.60“"y
V's'b'e '"ﬂmesceme -0.0116 x 0.0023 0.0018 :I: 00001 6.4 556 0.85'"
to ﬂower

“"99"” °f “'5‘ 00100 :I: 0.0047 0.0027 1 0.0002 3.7 370 0.66”
ﬂower

'"ﬂ°'e‘°.’°e”°e -0.0094 1 0.0042 0.0026 :l: 0.0002 3.6 385 0.69““
longevrty

 

2Standard error.
y”Signiﬁcant at Ps 0.001.

158

nan-w?"—
'5

r5 7..“2—1
A

 

80 . r r 1 . f

 

 

 

A .
8 Year1
' 0 Year2
60 .- ..... .. 2
">’.
(u 40* ..
D
i
20 ~~ ..g, 4
0
0.07 - °- -
A 0.06 ~ -
g 8
g 0.05 O, -
v. o
L; 0.04 -- .0 -
<0 8
0C 0.03- . . -
0.02 4 --
0.01 t l l l : ﬁ'

 

 

Temperature (°C)

Figure 1. Inﬂuence of forcing temperature on leaf unfolding
in Zygopetalum Redvale 'Fire Kiss'. Each symbol represents
individual plants. (A) shows days for the indicated
developmental stage. The solid lines represent the
regression equation using pooled data for Year 1 and 2.
Data at 28.6 °C were not included in the regression equation.
Lines in (B) represent predicted values for the rate of
progress (1ldays) to leaf unfolding, based on linear
regression. Statistical analysis is presented in Table 2.

159

12 14 16 18 2O 22 24 26 28 30

Leaf length (cm)

18 , r

 

 

Day

 

 

 

-0— 134°C
+ 16.7°C
-0- 195°C
-V— 224°C
-0— 248°C
-O— 286°C ‘

 

 

 

 

-r

80 100

Figure 2. Inﬂuence of forcing temperature on daily increase
in leaf length (cm) in Zygopetalum Redvale ‘Fire Kiss’. Each
symbol represents the average of 20 plants.

160

 

 

100 «- A»

Days

 

Rate (1ldays)

 

 

 

 

12 14 16 18 20 22 24 26 28

Temperature °C

Figure 3. Inﬂuence of forcing temperature on time from
visible inﬂorescence to ﬂower in Zygopetalum Redvale 'Fire
Kiss'. Each symbol represents individual plants. (A) shows
days for the indicated developmental stage. The solid lines
represent the regression equation using pooled data for Year
1 and 2. Lines in (B) represent predicted values for the rate
of progress (1ldays) to ﬂowering, based on linear regression.
Statistical analysis is presented in Table 2.

161

45 I I T f I I I

 

35 -- ~

 

25 Ju.

 

Final inﬂorescence height (cm)

4_. 1
l T

 

 

 

“i
T

12 14 16 18 20 22 24 26 28
Temperature (°C)

Figure 4. Inﬂuence of forcing temperature on inﬂorescence

length (cm) in Zygopetalum Redvale ‘Fire Kiss’. The symbol

represents the average of 10 plants. Error bars represent 95%
conﬁdence intervals.

162

 

 

- .
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163

APPENDIX A

THE EFFECT OF TEMPERATURE ON FLOWER AND INFLORESCENCE

LONGEVITY OF MILTASSIA CHARLES M. FITCH ‘DARK MONARCH’ ORCHID

164

p

 

Research Objective
The research objective of this investigation was to determine the ﬂower
longevity of the ﬁrst open ﬂower and total inﬂorescence longevity of Miltassia

Charles M. Fitch ‘Dark Monarch’ at temperatures from 14 to 26 °C.

Materials and Methods

Plant material. Miltassia Charles M. Fitch ‘Dark Monarch’ were grown by
a commercial greenhouse (Calif.), transplanted into plug liners in June 1998, and
into 10-cm pots in June 2000. In Calif., plants were grown at 16 to 26 °C under
natural photoperiods (37 °N latitude) with a maximum photosynthetic photon ﬂux
(PPF) of =350 umol-m'z-s'1. Plants in a bark and perlite-based media (10-cm
pots) were received in East Lansing, Mich. on 6 May 2001. They were
maintained at =23 °C in a glass-glazed greenhouse until experiments began.
The photoperiod was a constant 16 h, consisting of natural daylengths (42 °N
latitude) with day-extension lighting from high-pressure sodium (HPS) lamps,
which delivered a supplemental PPF of 50 umol-m'z-s'1 at plant height [as
measured with a line quantum sensor (Apogee Instruments, Inc., Logan, Utah)].

Plant culture. Plants were irrigated as necessary with well water
(containing 95, 34, and 29 mg-L’1 Ca, Mg, and S, respectively) supplemented
with water-soluble fertilizer to provide the following (mg-L"): 125 N, 12 P, 125 K,

13 Ca, 1.0 Fe, 0.1 B, and Mo, and 0.5 Mn, Zn, and Cu (MSU Special, Greencare

165

Fertilizers, Chicago, IL). Water was acidiﬁed with H2804 to a titratable alkalinity
of 140 mg-L'1 CBCO3.

Environmental chamber temperature and photoperiod control. The
experiment began on 9 October 2001 and was performed in walk-in controlled-
environment chambers with constant temperature set points of 14, 17, 20, 23,
and 26 °C. The average daily air temperatures during the experiment were 13.3,
17.3, 19.6, 22.5, and 25.5 °C. A 9-h photoperiod was provided by a combination
of cool-white ﬂuorescent (VHOF96T12, Philips, Bloomﬁeld, NJ.) and
incandescent lamps from 0800 to 1700 HR at 150 pmol-m'z-s“.

Flower and inﬂorescence longevity. Plants were forced in a glass
greenhouse and on the date that the ﬁrst ﬂower of an inﬂorescence opened, each
was transferred to one of the chambers. The date the plant was placed in the
chamber and the date of ﬂower mortality (senescence) of the ﬁrst and
subsequent ﬂowers were recorded for each plant. Individual ﬂower and
inﬂorescence longevity were calculated for each plant at each temperature.

Data analysis. The experimental design was completely randomized.
Data were analyzed using SAS (SAS Institute, Cary, NC.) mixed model
procedure (PROC MIXED) for analysis of variance and linear models procedure
(PROC REG) for regression models. Base temperature (T b) and thermal time, or
degree-days, were calculated (Roberts and Summerﬁeld, 1987). Flower and
inﬂorescence longevity at each temperature were converted to rates by taking
the reciprocal, and the relationship between the rate of progress to senescence

(1ldays) and the mean temperature T in °C was determined by

166

1/days = b0 + DJ [1]
where b0 and D1 are constants. Once b0 and b1 were calculated, the base
temperature, Tb, was calculated as

Tb = -bo/b1 [2]
and thermal time or degree days (°C d), was determined by
°days = 1/b1 [3]

Within each developmental stage, slopes and intercepts were computed.

Results and Discussion

Flower and inﬂorescence senescence occurred more rapidly as
temperature increased (Figure 1Aand B). As temperature increased from 17 to
26 °C, longevity of the first open ﬂower decreased from 66 to 27 d, respectively.
Inﬂorescence longevity followed a similar pattern, decreasing from 69 d at 17 °C
to 32 d at 26 °C. Flower longevity of the second and subsequent ﬂowers
decreased in comparison to the longevity of the ﬁrst open ﬂower across all
temperatures (data not presented). Plants at 14 °C were not included in the
regression analysis due to severe chilling injury that affected both the plant and
the ﬂowers.

Flower and inﬂorescence longevity data were converted to rates, and a
thermal time model was developed to predict ﬂower senescence at different
temperatures. Rate of progress to ﬂower and inﬂorescence senescence was

linear within the range of temperatures tested (Table 1). The base temperatures

167

were estimated at 12.6 (ﬂower) and 11.4 °C (inﬂorescence) and accumulated
thermal time lifespan of 385 and 455 °C-d", respectively.

Flower longevity is accurately predicted with the model; plants grown at 26
°C have an estimated accumulated thermal time lifespan of 29 d. Actual ﬂower
longevity observed was 27 d.

In this experiment, the longevity of Miltassia ﬂowers and inﬂorescences
was greatest at 17 °C. However, potted Miltassia shows signs of chilling injury
(water soaked lesions) at temperatures 5 17 °C (Section III) and thus, Top, is likely
between 18 and 20 °C. Consequently, it is important that Miltassia be shipped
and stored at 20 °C for optimal ﬂower and inﬂorescence longevity and to avoid
damage to the sensitive foliage.

Base temperature and thermal time information is important for both
greenhouse growers and hobbyists to obtain maximum ﬂower longevity, as they
often grow several species within the same environmental conditions. An
example of two orchids with completely different minimum temperature limits (Tb)
is that of Zygopetalum Redvale ‘Fire Kiss’ and Miltassia Charles M. Fitch ‘Dark
Monarch’. Zygopetalum is an epiphytic orchid from the neotropic mid-elevation
mountains of South America with a base temperature for ﬂower longevity of 3.7

°C, while the warm season orchid, Miltassia has a base temperature of 12.6 °C.

168

Table 1. Parameters of linear regression analysis relating forcing temperature to rate of progress to
ﬂower longevity of the ﬁrst ﬂower and inﬂorescence longevity in Miltassia Charles M. Fitch ‘Dark
Monarch’. Intercept and slope were used in Eqs. [1] and [2] to calculate base temperature (TD) and
thermal lifespan (°C-d“).

 

 

Developmental Intercept (b0) Slope (b1)

stage (1ldays) (1/days)/ °C Tb (°C) "C-d‘1 r2
“"99"“ °f "'5‘ 00329 a: 0.00591 0.0026 1 0.0003 12.6 385 0133'“y
ﬂower

'"ﬂmesfcence 00251 1 0.0055 0.0022 :t: 0.0003 11.4 455 0.80“”
longevrty

 

2Standard error.
y”Signiﬁcant at P 5 0.001.

tr: rm

169

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170

 

APPENDIX B

THE EFFECT OF TEMPERATURE ON NODE DEVELOPMENT OF BRASSIA

REX ‘SAKATA’

171

Research Objective
The research objective of this investigation was to quantify how
temperature inﬂuenced leaf unfolding rate and leaf expansion of Brassia Rex

‘Sakata’.

Materials and Methods

Plant material and culture. Plants were propagated and grown as
described in Appendix A, unless other wise noted.

Environmental chamber temperature and photoperiod control. The
experiment began on 11 June 2001 and was performed in controlled-
environment chambers with constant temperature set points of 14, 17, 20, 23, 26,
and 29 °C. The average daily air temperatures during the experiment were 13.4,
16.7, 19.5, 22.4, 24.8 and 28.6 °C. Each chamber was divided in half with black
plastic and two photoperiods were created: 9-h of light with or without a 4-h
(2200 to 0200 HR) night interruption (NI). The 9-h base photoperiod was
provided by a combination of cool-white ﬂuorescent (VHOF96T12, Philips,
Bloomﬁeld, NJ.) and incandescent lamps from 0800 to 1700 HR at 150 umol-m'
2s". Night interruption lighting (=2 pmol-m'z-s'1 at canopy level) was provided by
incandescent lamps.

Leaf development. Twenty plants were assigned randomly to each walk-in

controlled-environment chamber, and ten were placed under each photoperiod.

172

At the beginning of the experiment, one immature pseudobulb was identiﬁed and
leaf unfolding was recorded weekly by counting the number of leaves from the
soil level to the terminal end of the pseudobulb. The leaf length of a marked leaf
was measured weekly and leaf expansion rate was calculated

Data analysis. The experimental design was completely randomized. Data were
analyzed using SAS (SAS Institute, Cary, NC) mixed model procedure (PROC
MIXED) for analysis of variance and linear models procedure (PROC REG) for
regression models. Base temperature (Tb) and thermal time, or degree-days,

were calculated as described in Appendix A.

Results and Discussion

Photoperiod (9-h or NI) had no signiﬁcant inﬂuence on leaf unfolding or
leaf expansion and thus data was pooled. Leaf unfolding increased as
temperatures increased from 14 to 26 °C (Fig. 1). At 29 °C leaf unfolding began
to slow down. The days required to produce one leaf averaged 75 d at 14 °C,
and 12 d at 26 °C. The leaves of plants unfolded as a linear function within the
range of temperatures tested (Table 1). The base temperature for LUR was
estimated at 11.6 °C with 179 "C-d'1 degree-days (Table 1).

Leaf length was signiﬁcantly inﬂuenced by temperature (signiﬁcantly
different at P 5 0.001). As temperature increased from 13 to 29 °C, leaf
expansion increased (Fig 2). Leaf expansion was similar at temperatures from
22.4 to 28.6 °C. After 80 d, at the various temperatures, leaf length at 28.6 °C

was 3.4 times longer than of plants at 13.4 °C.

173

Higher temperatures caused more rapid LUR and leaf expansion.
Relative growth rate increased linearly to =25 °C, indicating that the maximum
temperature may be < 29 °C. These results are not surprising since Brassia Rex
‘Sakata’ was bred in Hawaii to tolerate warm temperatures. The calculated, Tb is

low (11.6 °C), but Brassia only exhibits signs of chilling injury at temperatures 5 8

°C (Section V).

ﬂ'.’ "nary-33:51

174

Table 1. Parameters of linear regression analysis relating forcing temperature to rate of progress to
leaf development in Brassia Rex ‘Sakata'. Intercept and slope were used in Eqs. [1] and [2] to
calculate base temperature (TD) and thermal degree—days (°C-d“).

 

Developmental Intercept (b0) Slope (b1)
stage (1ldays) (1/days)/ °C Tb (°C) °C-d'1 r2
leaf unfolding -0.0651 1 0.01612 0.0056 1 0.0008 11.6 179 0.37'“y

 

2Standard error.
y"'Signiﬁcant at P 5 0.001.

175

100

 

Days

 

 

Q14 .L ............................................................... co ..... -
0.12 .. ......................................................................................... -
0.10 ._ ......................................................................................... -
0.08 1
0.06 +
0.04 -
0.02 .
0.00

Rate (1ldays)

 

 

 

 

12 14 16 18 20 22 24 26 28 30
Temperature (°C)

Figure 1. Inﬂuence of forcing temperature on leaf unfolding in
Brassia Rex ’Sakata’. Each symbol represents individual plants
(total of 20). (A) shows days for the indicated developmental
stage. The solid lines represent the regression equation. Lines in
(B) represent predicted values for the rate of progress (1ldays) to
leaf unfolding based on linear regression. Statistical analysis is
presented in Table 1.

176

 

30

 

 

 

 

 

 

 

—0- 134°C
25 '1 + 167°C ,_.__
—0— 195°C . . '
—V— 22.4 °C /:/
A 20 _ ‘0‘ 248°C 0
E + 286°C '
3 3
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g3 I
g I
“—
m
0
_l
o ' . .
o
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.
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Figure 2. Inﬂuence of forcing temperature on daily increase in leaf
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average of 20 plants.

177

3:1

'00.." A

APPENDIX C

THE EFFECT OF LIGHT QUANTITY ON GROWTH OF FOUR ORCHIDS

178

Research Objective

The research objective of this investigation was to determine if daily light
integral (DLI) inﬂuences vegetative growth and ﬂowering of Brassia Rex ‘Sakata’,
Degannoara Winter Wonderland White Fairy’, Miltassia Charles M. Fitch ‘Dark

Monarch’ and Zygopetalum Redvale ‘Fire Kiss’.

Materials and Methods

Plant material. Plants were grown by a commercial greenhouse (Calif.),
Brassia, Degannoara, and Miltassia were transplanted into plug liners in May and
June 1998, and into 10-cm pots in May and June 2000. Zygopetalum were
transplanted into plug liners in June 2000 and into 10-cm pots in April 2001.
plants were grown as previously described in Appendix A. Plants were grown in
a glass greenhouse with a constant temperature setpoint of 23 °C. Air
temperature in each greenhouse was measured by a thermocouple in an
aspirated chamber every 10 s, and hourly averages were recorded by a CR-10
datalogger (Campbell Scientiﬁc, Logan, Utah). Average daily air temperature
during the experiment was 25.5 °C.

DLI Experiment. Five plants were placed under ﬁve different DLI
treatments. Light transmission through the greenhouses was reduced using
permanent woven shade curtains that reduced light by =15, 27, 50, 75 and 90%
(OLS 50; Ludvig Svensson, Charlotte, NC) to create the different DLI

treatments. Average daily light integral for each treatment from the beginning of

179

the experiment until the end of forcing was estimated by calculating the DLI in the
greenhouse without any shade multiplied by the shading percentage (Table 1).

Data collection and analysis. Inﬂorescence and ﬂower bud count, ﬁnal
immature and mature pseudobulb count, ﬁnal plant height, SPAD values
(chlorophyll content), and dry shoot and root weights were recorded. The
percentage of plants that initiated ﬂowers was calculated. The few plants that
died during the experiment were discarded and not included in the results. Data
were analyzed using SAS (SAS Institute, Cary, NC) mixed model procedure
(PROC MIXED).

Results and Discussion

Brassia. Daily light integral did not inﬂuence inﬂorescence, ﬂower bud and
mature pseudobulb count, plant height, shoot, and root dry weights of Brassia
Rex ‘Sakata’. As DLI increased from 5.5 to 0.6 mol-m’Z-d’1 immature pseudobulb
count decreased from 5.2 to 1.7. Chlorophyll content was also inﬂuenced by DLI,
as DLI decreased, SPAD values increased from 58.1 to 69.6.

Degarmoara. Inﬂorescence, ﬂower bud and immature pseudobulb count,
plant height, shoot or root dry weights of Degannoara Winter Wonderland White
Fairy’ were not inﬂuenced by DLI. Plants under the low DLI treatment had
signiﬁcantly fewer mature pseudobulbs than those at DLI > 1 mol-m'Z-d". As
daily light integral decreased from 7.2 to 0.6 mol-m'z-d", chlorophyll content

increased from 44.2 to 55.6.

180

Miltassia. Daily light integral did not inﬂuence inﬂorescence, ﬂower bud
immature and mature pseudobulb count and root dry weights of Miltassia Charles
M. Fitch ‘Dark Monarch’. Plant height decreased slightly as DLI decreased from
7.9 to 0.6 mol-m'z-d". Chlorophyll content was also inﬂuenced by DLI, as DLI
decreased, SPAD values increased from 51.0 to 63.3. Shoot dry weight
decreased from 52.6 to 32.7 g as DLI decreased from 7.2 to 0.6 moI-m'z-d".

Zygopetalum. Flower bud, immature pseudobulb count, and plant height
of Zygopetalum Redvale ‘Fire Kiss’ were not inﬂuenced by DLI. As DLI
decreased from 7.2 to 0.6 mol-m‘z-d'1 inﬂorescence and pseudobulb count both
decreased. SPAD values were greatest at 0.6 moI-m'z-d". Shoot and root dry
weights were highly inﬂuenced by DLI. As DLI decreased from 7.2 to 0.6 mol-m'
20", both shoot and root dry weight decreased almost three fold.

Interestingly, in all the orchid species investigated as daily light integral
decreased from 7.9 to 0.6 mol-m'z-d", SPAD values increased. Consequently,
plants allocated more resources into cholorophyll production than to other sinks
due to lower light levels. However, inﬂorescence and ﬂower buds, which are
resource sinks, were not signiﬁcant inﬂuenced by DLI. In all the species, as DLI
decreased, ﬂower initiation decreased and at 0.6 mol-m’z-d'1 few or no plants

initiated ﬂowers.

181

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