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This is to certify that the
thesis entitled

EFFECTS OF TEMPERATURE ON GROWTH AND FLOWERING
OF TWO PHALAENOPSIS AND TWO ODONTIODA ORCHID
HYBRIDS

presented by

MATTHEW GEORGE BLANCHARD

has been accepted towards fulfillment
of the requirements for the

MS. degree in Horticulture

 

 

MW

Major Professor’s Signature
‘24 001' Zoo 5

Date

 

MSU is an Affirmative Action/Equal Opportunity Institution

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Michig State
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To AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

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2/05 clel_RC/DateDue.indd-p.15

EFFECTS OF TEMPERATURE ON GROWTH AND FLOWERIN G .
OF TWO PHALAENOPSIS AND TWO ODONTIODA ORCHID HYBRIDS

By

Matthew George Blanchard

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Horticulture

2005

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ABSTRACT

EFFECTS OF TEMPERATURE ON GROWTH AND FLOWERING
OF TWO PHALAENOPSIS AND TWO ODONTIODA ORCHID HYBRIDS

By
Matthew George Blanchard
The production value of potted orchids in the United States has increased
tremendously in the past decade, and they are now the second-most valuable potted
flowering plant. Commercial orchid production has been impeded by the lack of
information on flowering requirements of the vast majority of orchid species and hybrids.
The objectives of this study were to determine if and how constant and fluctuating day
and night temperatures influence flowering of four orchid hybrids. Phalaenopsis Miva
Smartissimo x Canberra ‘450’, Phalaenopsis Brother Goldsmith ‘720’, Odontioda
George McMahon ‘F ortuna’, and Odontioda Lovely Penguin ‘Emperor’ were grown at
constant temperatures of 14, 17, 20, 23, 26, or 29 °C, and day/night (12 h/12 h)
temperatures of 20/14, 23/17, 26/14, 26/20, 29/17, or 29/23 °C. After 20 weeks, 280% of
plants of both Phalaenopsis hybrids had a visible inflorescence when grown at 14, 17, 20,
23, 20/14, or 23/17 °C. None of the plants were reproductive when grown at
temperatures of 29, 29/17, or 29/23 °C. In both Odontioda hybrids, 290% of plants
initiated an inflorescence that did not abort when grown at 14 or 17 °C. Time to
flowering data for Odontioda were used to develop a thermal-time model relating
temperature with inflorescence development. These results indicate that a day/night
fluctuation in temperature is not required for inflorescence initiation in these four orchid
hybrids. This research information could be used by commercial orchid growers to

improve production efficiency and schedule orchids in flower for specific market dates.

DEDICATION
In loving memory of my stepfather, David L. Goff (August 26th, 2004, aged 50) who left
this world too early. David loved the outdoors and the beautiful environment around us
and he had a special appreciation for plants and my field of study. His smile, humor, and

knowledge are sadly missed. Sweet are the memories that never fade.

iii

ACKNOWLEDGMENTS

I would like to first acknowledge my major professor, Dr. Erik Runkle for his
encouragement, guidance, and support throughout this project. His advice and insight
have been greatly appreciated during the past two years. I look forward in working with
him on future projects. I would also like to acknowledge the members of my graduate
committee, Drs. Arthur Cameron and Donald Garling for the valuable knowledge, advice,
and support they have provided during this project.

Thank you to our floriculture greenhouse technician, Mike Olrich, for his
assistance in experimental setup, expertise, and humor. I would also like to thank the rest
of the floriculture group and our undergraduate students for their patience and help in
opening and closing black-out cloth each day during these experiments. Thank you to
my fellow graduate student, Roberto Lopez for his support during my transition into
graduate school, assistance in experimental setup, and friendship. To all of my friends
and colleagues for making the Department of Horticulture at MSU an enjoyable place to
work.

Thank you to my family for all their love, support, and encouragement.
Everything you have taught me is reflected in the person that I am today. I would
especially like to thank my wonderful wife Laura, for her love, friendship, patience, and
support as I work hard to pursue my educational and career goals. You make each day
special. I look forward to many more memories as we continue the journey through life

together.

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TABLE OF CONTENTS

Page
LIST OF TABLES .......................................................................................................... viii
LIST OF FIGURES ........................................................................................................... xi
LITERATURE REVIEW ................................................................................................... 1
SECTION I
Introduction ......................................................................................................................... 2
Orchid Background ............................................................................................................. 6
History ..................................................................................................................... 6
Plant Description
Growth Habit .............................................................................................. 8
Roots ............................................. . ............................................................. 8
Leaves ......................................................................................................... 9
Flowers ........................................................................................................ 9
Phalaenopsrs .......................................... 11
History ................................. , ................................................................................. 11
Plant Description ................................................................................................... 14
Phalaenopsis Production ...................................................................................... 15
Commercial Production of Phalaenopsis ......................................................................... 19
Propagation ........................................................................................................... 1 9
Shipping Unfinished Plant Material ...................................................................... 20
Greenhouse Environment
Temperature .............................................................................................. 21
Low Temperature Requirement ............................................................... 23
Irradiance .................................................................................................. 25
Photoperiod ............................................................................................... 26
Postharvest ................................................................................................ 27
Medium and Nutrition
Growing Medium ...................................................................................... 29
Plant Nutrition ........................................................................................... 30
Physiological Changes .......................................................................................... 31
Effects of Plant Growth Regulators on Phalaenopsis
Abscisic Acid ........................................................................................................ 34
Auxin ..................................................................................................................... 35
Cytokinins ............................................................................................................. 35
Physiological Role .................................................................................... 35
Benzyladenine ........................................................................................... 36
Commercial Uses in Horticulture ................................................. 36
Effects on Growth and Flowering of C ymidium, Dendrobium, and
Aranda ........................................................................................... 38

 

 

 

 

 

 

 

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Effects on Flowering of Phalaenopsis .......................................... 4O

Ethylene ................................................................................................................ 42
Gibberellins ........................................................................................................... 43
Gibberellin Biosynthesis Inhibitors .......................................................... 44
Temperature ...................................................................................................................... 46
Average Daily Temperature .................................................................................. 46
Leaf Unfolding Rate ................................................................................. 50
Effects of Diurnal Temperature Fluctuations ....................................................... 52
Stem Elongation ........................................................................................ 53
Flowering Responses to Diurnal Temperature Fluctuations ..................... 55
Diurnal Temperature Fluctuation Requirement ........................................ 58
The Role of Day and Night Temperature ............................................................. 59
Conclusion ............................................................................................................ 62
Literature Cited ................................................................................................................. 63
SECTION II
TEMPERATURE DURING THE DAY, BUT NOT DURING THE NIGHT,
CONTROLS FLOWERING OF TWO PHALAENOPSIS ORCHID HYBRIDS ........... 74
Introduction ........................................................................................................... 76
Materials and Methods .......................................................................................... 78
Results .......................................... 81
Discussion ............................................................................................................. 84
Literature Cited ..................................................................................................... 89
SECTION III
TEMPERATURE EFFECTS ON FLOWER IN ITIATION AND DEVELPMENT OF
TWO ODONTIODA ORCHID HYBRIDS .................................................................... 100
Introduction ......................................................................................................... 1 02
Materials and Methods ........................................................................................ 104
Results ................................................................................................................. 108
Discussion ........................................................................................................... l 10
Literature Cited ................................................................................................... 114
APPENDIX A
EFFECTS OF DAILY LIGHT INTEGRAL ON GROWTH AND FLOWERIN G OF
POTTED PHALAENOPSIS ORCHIDS ........................................................................ 130
Introduction ......................................................................................................... l3 1
Materials and Methods ........................................................................................ 132
Results ................................................................................................................. 136
Discussion ........................................................................................................... 1 3 7
Literature Cited ................................................................................................... 141
APPENDIX B
EFFECTS OF TEN ORCHID MEDIAS ON PH, WATER-HOLDING CAPACITY,
AND PERFORMANCE OF THREE ORCHID GENERA ............................................ 150
Introduction ......................................................................................................... 1 5 1

vi

Materials and Methods ........................................................................................ 152
Results and Discussion ....................................................................................... 155
Literature Cited ................................................................................................... 159

vii

LIST OF TABLES

Table Page
SECTION I

1. Element, electrical conductivity (EC), and pH target values and sufficiency ranges
for Phalaenopsis growing media. Information from Anthura and Bureau IMAC
(2005) .................................................................................................................... 33

SECTION II

1. Summary of production dates, container sizes, and greenhouse environmental
conditions for Phalaenopsis Brother Goldsmith '720' and Phalaenopsis Miva
Smartissimo >< Canberra '450' preceding and during experimentation ................. 91

2. Average daily light integral (mol-m'z-d'l) at plant level per 4-week period during
experiment for Years 1 and 2 ................................................................................ 92

3. Actual average air temperature of each temperature treatment in Years 1 and 2. 93

4. Flowering percentages for Phalaenopsis Miva Smartissimo >< Canberra '450' and
Phalaenopsis Brother Goldsmith '720' after 20 weeks at constant temperature
setpoints of 14, 17, 20, 23, 26, or 29 °C, and fluctuating day/night temperature
setpoints of 20/ 14, 23/ 17, 26/14, 26/20, 29/ 17, or 29/23 °C. Data for both years
were pooled for analysis. Arcsine square root transformation was performed on
data before analysis ............................................................................................... 94

5. The effect of average daily temperature (ADT), average day temperature (DT),
average night temperature (N T), and constant temperature (CT) on visible
inflorescence (VI) percentage of Phalaenopsis Miva Smartissimo >< Canberra
'450' and Phalaenopsis Brother Goldsmith '720'. Arcsine square root
transformation was performed on data before analysis ........................................ 95

6. Comparison of visible inflorescence percentage in treatments with a similar
average daily temperature for Phalaenopsis Miva Smartissimo X Canberra '450'
and Phalaenopsis Brother Goldsmith '720'. Arcsine square root transformation
was performed on data before analysis ................................................................. 96

7. Days to visible inflorescence (VI), number of flower buds on first VI, and number
of inflorescences per plant for Phalaenopsis Miva Smartissimo >< Canberra '450'
and Phalaenopsis Brother Goldsmith '720' after 20 weeks in temperature
treatments with 210% VI ...................................................................................... 97

viii

. Days from visible inflorescence (VI) to flower, total days to flower, and total
inflorescence length at flower for Phalaenopsis Miva Smartissimo >< Canberra
'450' and Phalaenopsis Brother Goldsmith '720' in temperature treatments with
230% flowering after 20 weeks ............................................................................ 98

SECTION III

. Summary of production dates, container sizes, and greenhouse environmental
conditions for Odontioda George McMahon ‘Fortuna’ and Odontioda Lovely
Penguin ‘Emperor’ preceding and during experimentation. ............................... 116

. Average daily light integral (molm'Z-d") at plant level per 4-week period during
experiment for Years 1 and 2. ............................................................................. 117

. Actual average air temperature of each temperature treatment in Years 1 and 2118

. Visible inflorescence (VI) and inflorescence abortion percentages and days to V1
for Odontioda George McMahon ‘Fortuna’ and Odontioda Lovely Penguin
‘Emperor’ after 20 weeks during Year 1 at constant temperature setpoints of 26 or
29 °C, and fluctuating day/night temperature setpoints of 26/14, 26/20, 29/17, or
29/23 °C. All plants displayed symptoms of heat stress and were considered
unmarketable. Data are for Year I .............................. I ........................................ 119

. Days to visible inflorescence (VI), number of flower buds on first VI, and number
of inflorescences per plant for Odontioda George McMahon ‘Fortuna’ and
Odontioda Lovely Penguin ‘Emperor’ in temperature treatments with 210% VI.
Data for both years were pooled for analysis ...................................................... 120

. Parameters of linear regression analysis relating temperature to rate of progress
for time from visible inflorescence to flower in Odontioda George McMahon

‘F ortuna’ and Odontioda Lovely Penguin ‘Emperor’. The slope (b1) and intercept
(he) were used to calculate the base temperature (Tb) and degree-days (°C-d"). 121

. The effect of temperature on final pseudobulb diameter and leaf length, and
pseudobulb diameter increase and leaf length increase of Odontioda George
McMahon ‘F ortuna’ and Odontioda Lovely Penguin ‘Emperor’. Data were
collected at flower or after 31 weeks in temperature treatments. Data for Year 2
only ..................................................................................................................... 122

APPENDIX A
Summary of production dates, container sizes, and greenhouse environmental
conditions for Doritaenopsis (Dtps. White Castle >< Phal. Moon World) ‘717’,

Phalaenopsis Pink Twilight ‘ 173’, Phalaenopsis Sharon Bay ‘ 163’, and
Phalaenopsis Brother Showpiece preceding and during experimentation ......... 143

ix

. Average daily light integral (mol-m'z-d") at plant level per month during
vegetative and forcing periods ............................................................................ 144

. Visible inflorescence percentage, inflorescence abortion percentage, and
flowering percentage for Doritaenopsis (Dips. White Castle >< Phal. Moon World)
‘717’, Phalaenopsis Pink Twilight ‘ 173’, Phalaenopsis Sharon Bay ‘ 163’, and
Phalaenopsis Brother Showpiece following 20 weeks of vegetative growth at 28
°C under an average daily light integral (DLI) of 2.5, 5.5, or 9.8 mol'm'Z-d".
Plants were subsequently forced at 23 °C under an average DLI of 3.8 mol-m'Z-d".

Percentages were analyzed using a binomial distribution with logit transformation
............................................................................................................................. 145

. Days to visible inflorescence (VI), days from VI to flower, total days to flower,
number of flowers, and total inflorescence length for Doritaenopsis (Dtps. White
Castle X Phal. Moon World) ‘717’, Phalaenopsis Pink Twilight ‘ 173’,
Phalaenopsis Sharon Bay ‘ 163’, and Phalaenopsis Brother Showpiece following
20 weeks of vegetative growth at 28 °C under an average daily light integral
(DLI) of 2.5, 5.5, or 9.8 mol-m'z-d". Plants were subsequently forced at 23 °C
under an average DLI of 3.8 mol-m'z-d'l ............................................................ 146

APPENDIX B

. Summary of production dates, container sizes, and greenhouse environmental
conditions for Miltoniopsis Easter Bay ‘Claret Punch’, Paphiopedilum Claire de
Lune >< Enchanted Orient, and Phalaenopsis Brother Goldsmith '720' preceding
and during experimentation ................................................................................ 160

. Percentages and ratios of fine-grade Douglas fir bark, medium-grade chopped
coconut coir, medium-grade perlite, and long fiber Canadian Sphagnum peat used
in ten different orchid media mixes during experiment ...................................... 161

. Initial and final bulk density, porosity, and gravimetric moisture content (GMC)

of ten media mixes. The change in GMC was caluclated by subtracting the initial
GMC from the final GMC. Equations [1], [2], and [3] were used to calculate bulk
density, porosity, and GMC, respectively ........................................................... 162

LIST OF FIGURES

Figure Page
SECTION I

1. Wholesale value (million USD) of potted flowering plants produced in the United
States in 2004 (USDA, 2005a) ................................................................................ 4

2. Wholesale value [million USD (0)] and quantity sold [million (0)] of potted
orchids produced in the United States from 1996 to 2004 (USDA, 2005b) ........... 5

3. Flower structures of a diandrous orchid, Paphiopedilum, with a median petal
modified to form a pouch (A), and a monandrous orchid, Zygopetalum, with a

large and colorful labelum (B) .............................................................................. 10
4. Tumerover value (million euro) of the most important indoor plants sold at Dutch
flower auctions in 2004 (VBN, 2005a) ................................................................. 13
5. Structure of a Phalaenopsis flower ............................. p .......................................... 15

6. Wholesale value [million euro (6)] and quantity [million (0)] of potted
Phalaenopsis sold at Dutch flower auctions from 2001 to 2004 (VBN, 2003,
2005a) ................................................................................................................... 18

7. The effect of average daily temperature on rate of plant development ................ 47
SECTION II

1. Visible inflorescence percentages for Phalaenopsis Brother Goldsmith '720' (A)
and Phalaenopsis Miva Smartissimo X Canberra '450' (B) after 20 weeks at
constant temperature setpoints 14, 17, 20, 23, 26, or 29 °C, and fluctuating
day/night temperature setpoints of 20/14, 23/17, 26/14, 26/20, 29/17, or 29/23 °C.
The day and night were 12 hours each. Data were pooled for Years 1 and 2 ...... 99

SECTION III

1. Pseudobulb of an Odontioda orchid with pairs of apical and basal leaves (A) and a

visible inflorescence in the axil of a leaf sheath at the base of a mature pseudobulb
(B) ....................................................................................................................... 123

2. Visible inflorescence (VI) percentages for Odontioda George McMahon ’Fortuna'
(A) and Odontioda Lovely Penguin 'Emperor' (B) after 20 weeks at constant
temperature setpoints of 14, 17, 20, or 23 °C, and fluctuating day/night
temperature setpoints of 20/14 or 23/17 °C. The day and night were 12 hours

xi

each. VI percentages were analyzed using a binomial distribution with logit
transformation. Data for Odontioda George McMahon was pooled for Years 1
and 2. NS, *** Nonsignificant or significant at P 50.001 ................................. 124

. Effect of temperature on time from visible inflorescence to flower (A and B) and
rate of progress to flower (C and D) in Odontioda George McMahon 'Fortuna' and
Odontioda Lovely Penguin 'Emperor'. Each symbol represents an individual
plant. The solid lines represent the regression equation using pooled data for
Years 1 (D) and 2 (0). Data at 23 °C for Odontioda Lovely Penguin were not
included in regression analysis. The average daily temperature was reported for
treatments with a fluctuating day and night temperature. Parameters of linear
regression analysis are presented in Table 6. ...................................................... 125

. Influence of temperature on average flower diameter in Odontioda George
McMahon ‘F ortuna’ (0) and Odontioda Lovely Penguin ‘Emperor’ (O) at
constant temperature setpoints of 14, 17, 20, or 23 °C, and fluctuating day/night
temperature setpoints of 20/14 or 23/17 oC. The day and night were 12 hours
each. Mean separation within each hybrid by Tukey’s honest significant
difference (HSD) test at P 50.05. L = linear, Q = quadratic trends; NS, **, ***
Nonsignificant or significant at P £0.01 or 0.001, respectively.

Data for Year 2 ........................................ 126

. Influence of temperature on final pseudobulb diameter (O) and pseudobulb
diameter increase (0) in Odontioda George McMahon ‘Fortuna’ (A) and
Odontioda Lovely Penguin ‘Emperor’ (B) at constant temperature setpoints of 14,
17, 20, or 23 °C, and fluctuating day/night temperature setpoints of 20/14 or
23/17 °C. The day and night were 12 hours each. Each symbol represents the
average of 10 plants. Vertical bars indicate standard errors about the treatments
means. Data for Year 2 ...................................................................................... 127

. Influence of pseudobulb diameter on visible inflorescence percentage in
Odontioda George McMahon ‘F ortuna’ and Odontioda Lovely Penguin
‘Emperor’. Pseudobulb diameter was measured at flower or after 31 weeks in
temperature treatments. Data for Year 2 ............................................................ 128

APPENDIX A

. Daily light integral (DLI) at plant level under each light treatment during a 20-
week period of vegetative growth at 28 °C ......................................................... 147

. Average leaf span increase of Doritaenopsis (Dips. White Castle X Phal. Moon
World) ‘717’, Phalaenopsis Pink Twilight ‘ 173’, Phalaenopsis Sharon Bay ‘ 163’,
and Phalaenopsis Brother Showpiece under an average daily light integral (DLI)
of 2.5, 5.5, or 9.8 molm'z-d'I for 20 weeks at 28 °C. Mean separation within
hybrids by Tukey’s honest significant difference (HSD) test at P 50.05. L =

xii

linear, Q = quadratic trends; NS, *, **, *** Nonsignificant or significant at P
$0.05, 0.01, or 0.001, respectively ...................................................................... 148

. Chlorophyll fluorescence ratios (A) and visible inflorescence (V I) percentages (B)
for Doritaenopsis (Dtps. White Castle X Phal. Moon World) ‘717’, Phalaenopsis
Pink Twilight ‘ 173’, Phalaenopsis Sharon Bay ‘ 163’, and Phalaenopsis Brother
Showpiece following 20 weeks under an average daily light integral (DLI) of 2.5,
5.5, or 9.8 mol-m'z-d". Error bars represent 95% confidence intervals. VI
percentages were analyzed using a binomial distribution with logit transformation
and pair-wise comparisons within hybrids by chi-square (7(2) test at P $0.05 149

APPENDIX B

. Effect of ten orchid media mixes on pH during a 19-month period from 20
October 2003 to 19 May 2005. Treatment ratios represent the proportion of fine-
grade Douglas fir bark, medium-grade chopped coconut coir, medium-grade
perlite, and long fiber Canadian Sphagnum peat used in each media mix. The pH
of each media was measured using a 1:2 dilution method (1 part medium to 2
parts reverse osmosis water by volume) ............................................................. 163

xiii

SECTION 1

LITERATURE REVIEW

INTRODUCTION

Orchids are currently the second most valuable potted crop in the United States
with a total reported wholesale value of $127.6 million in 2004 (USDA, 2005a) (Fig. 1).
Since 1996, when the United States Department of Agriculture (USDA) began collecting
data for wholesale value of potted orchids, sales have increased by 172% (USDA, 2005b)
(Fig. 2). In 2004, 17.2 million potted orchids were sold at wholesale with an average unit
value of $7.41 (USDA, 2005b). In the United States, the largest state producers of potted
orchids are California ($50 million), Florida ($47 million), and Hawaii ($17 million)
(USDA 2005a). From 1996 to 2004, the number of commercial growers of potted
orchids has increased from 175 to 226 and average annual sales per grower increased
from $269,000 to $565,000 (USDA, 2005b).

The production of potted orchids for the mass market extends beyond the United
States and has global economic importance. The increased worldwide production of
orchids is attributed to a rise in consumer demand in Europe, Asia, and the United States;
advances in propagation techniques; recognition of large profit potential by growers;
improvements in breeding and selection; and a segmentation of the production chain
(Britt, 2000). In 2002, the total number of potted orchids produced in China and Japan
were 4 million and 28 million, respectively (Wang, 2004). The largest exporting
countries of potted orchids by volume include Taiwan, Thailand, the United Kingdom,
Italy, Japan, New Zealand and Brazil, while the largest importer of potted orchids is the
United States (Laws, 2002). In 2004, 1.4 million kilograms of live orchid plants were
imported into the US, with a value of $24.7 million (USDA, 2005b). The largest

EXporting countries of live orchid plants to the United States include Taiwan ($12.2

 

 

 

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million), The Netherlands ($3.8 million), and Thailand ($2.8 million). The commercial
production of potted orchids in Europe is generally for domestic consumption (Laws,
2002)

The ability for commercial greenhouse growers to produce potted flowering
plants for specific dates is economically important. The scheduling of potted flowering
plants for periods of high demand allows growers to coordinate marketing and shipping
dates, develop and implement a yearly greenhouse production plan, and potentially
increase profitability. To schedule a crop for specific market dates, an understanding of
the factors that affect plant growth and development is required. Intensive research has
been conducted on several economically important floriculture crops such as
Chrysanthemum, Easter lily, and poinsettia and production schedules have been
subsequently developed (Berghage and Heins, 1991; Erwin and Heins, 1990; Fisher et al.,
1997; Jacobson and Willits, 1998; Karlsson et al., 1989).

Scientific research on growth and development of orchids has been limited to a
few genera and detailed commercial production information is only available for hybrids
of the genus Phalaenopsis. The primary objective of this research was to quantify the
effects of constant and fluctuating temperature on inflorescence initiation and flower
development in several orchid hybrids. This information could be used to develop
production protocols that can be implemented by commercial greenhouse growers, and
improve our understanding of how environmental factors influence the flowering

physiology of orchids.

Florist

Chrysanthemums Spring Bulbs
$75.0 $53.3

    
  
  

Florist Azaleas

Orchids $41 1
$127.6
Easter Lilies
$38.5

Florist Roses

$18.0
\ African Violets

$16.3

Poinsettias
$247.8

Other
$197.5

 

Figure 1. Wholesale value (million USD) of potted flowering plants produced in the
United States in 2004 (USDA, 2005a).

140 20

 

 

 

 

 

 

+ Wholesale value [ 13
120 — -0- Quantity sold
~16
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1996 1997 1998 1999 2000 2001 2002 2003 2004

Year

Figure 2. Wholesale value [million USD (0)] and quantity sold [million (0)] of potted
orchids produced in the United States from 1996 to 2004 (USDA, 2005b).

No. of pots (million)

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ORCHID BACKGROUND

The orchid family, Orchidaceae, is among the largest of families of angiosperms,
containing over 25,000 species within 725 genera (Griesbach, 1985b). Orchids were first
classified into two major divisions by Linnaeus in 1740, but between 1830 and 1840, a
complete classification was published by botanist John Lindely, known as the father of
modern orchidology (Reinikka, 1995). Orchids are distributed in all regions of the world
except Antarctica and are found growing in many different habitats and elevation
gradients (Pridgeon, 2000). Among all of the orchid genera, the genus Vanilla has a
major economic value as a food crop. Many of the other orchid genera that are

commercially available are selected and grown for aesthetic value or botanical interest

(Griesbach, 1985b).

History

The word orchid is derived from the Greek word orchis, meaning testis, referring
to the testiculate bulbs or tubers that were found on orchid plants from the Mediterranean
region (Reinikka, 1995). The first recordings of orchids date back to 500 BC, when
Cymbidium orchids were highly desired for their fragrance and Confucius used the word
“Ian” in reference to all orchids (Rittershausen and Rittershausen, 2003). The earliest
Chinese writings on orchids were published in 290 AD, where they were depicted both
in botanical literature and paintings. In the Western hemisphere, orchids were first
recognized in 1552 by the Aztecs for the use of Vanilla as a perfume and flavoring in

foods (Reinikka, 1995).

During the end of the eighteenth century in Europe, greenhouses and
conservatories were constructed to grow many of the new plant species that were
collected from expeditions around the world (Rittershausen and Rittershausen, 2003). At
this time, large orchid collections and nurseries were established, but commerce was
limited to the wealthy (Reinikka, 1995). At the beginning of the twentieth century, the
popularity of orchids declined as a result of collecting and transportation challenges,
inadequate knowledge of propagation and cultivation methods, and expensive greenhouse
maintenance (Pridgeon, 2000). Orchid hybridization and commercial propagation
became popular after advances in symbiotic seed germination by Noel Bernard and Hans
Burgef in 1909, and the development of non-symbiotic germination procedures by Lewis
Knudson in 1922 (Griesback, 2002). The procedure to symbiotically germinate orchid
seeds involved inoculating a sterilized peat and sand medium with a symbiotic fungus
and then sowing seeds on the surface. Non-symbiotic orchid seed germination involved
sowing seeds on agar that contained salts and sugars (Griesback, 2002).

After the Second World War, commercial nurseries were established in Europe
and the United States, hybridizing and producing orchids for international markets
(Rittershausen and Rittershausen, 2003). More than 110,000 hybrids have been
registered with the Royal Horticultural Society since the first hybrid was created in 1854
(Royal Horticultural Society, 2004). Approximately 3,000 hybrids are registered each
year, most of which are propagated in a laboratory through a process called mericloning

(Pridgeon, 2000; Royal Horticultural Society, 2004).

Plant Description
Growth Habit

Orchids have been categorized into two groups according to their habit of growth:
monopodial orchids or sympodial orchids. A monopodial growth habit is characterized
by having a terminal bud that continues to grow each season, while growth in a
sympodial plant occurs through the development of axillary buds. Orchids can also be
described based on their growing habitat and substrate: terrestrial, epiphytic, or
lithophytic. Terrestrial orchids such as Cypripedium, Dactylorhiza, and Orchis, grow on
the surface of the earth and obtain water and minerals from the soil. The majority of
tropical orchids are epiphytic and grow naturally on trees, obtaining moisture and
minerals from both the air and decomposing organic matter on branches. Lithophytic
orchids such as Phragmipedium besseae Dodson and Kuhn are found growing in small
rocky crevices of harsh environments and acquire water and minerals similar to epiphytic

orchids (Rittershausen and Rittershausen, 2003).

Mtg

Terrestrial orchids have fleshy and often hairy roots for water absorption and may
utilize underground structures, such as corms, rhizomes, or tuberoids for water storage
(Elliot, 1998; Rittershausen and Rittershausen, 2003). Sympodial epiphytic orchids store
water in structures called pseudobulbs. Pseudobulbs are composed of a fibrous material
and species have different shapes and sizes, ranging from as small as a pea to the size of a
tennis ball (Rittershausen and Rittershausen, 2003). The aerial roots of epiphytic orchids

and some terrestrial orchids are enclosed in a white layer of dead cells called velamen,

which provides mechanical protection and prevents water loss from the root cortex
(Dycus and Knudsen, 1957). Lithophytic orchids have smaller, more developed roots
with greater surface area to absorb moisture. The roots of lithophytic orchids are also

strong enough to attach to rocky cliff faces or crevices (Rittershausen and Rittershausen,

2003)

Ms.

Orchids have simple leaves with varying shapes, such as long and strap-like (e. g.
C ymbidium), thick and fleshy (e.g. Phalaenopsis) or long, rounded, and terete (e. g.
Vanda) (Elliot, 1998). Epiphytic orchids usually have leaves that are persistent from year
to year, while the leaves of non-tropical terrestrial and lithophytic orchids are generally

shed seasonally (Pridgeon, 2000).

ELEM

The flowers of orchids are bilaterally symmetrical, termed zygomorphic, and the
flower structure is similar to other angiosperms, comprised of four whorls: sepals, petals,
stamens, and pistils (Zomlefer, 1994). Orchid flowers can be divided into two forms:
Diandrae and Monandrae. Genera such as Cypripedium, Paphiopedilum, and
Phragmipedium are grouped into Diandrae and have flowers that consist of two fertile
stamens on each side of the staminode, one large colorful dorsal sepal, two small lateral
sepals, two elongated lateral petals and an attractive pouch formed by a third petal (Goh
and Arditti, 1985) (Fig. 3A). The pouch functions as a trap for insect pollinators,

requiring insects to climb out and unintentionally transfer pollen from the anthers to their

abdomen (Rittershausen and Rittershausen, 2003). A majority of genera within the
orchid family are grouped into Monandrae, with flowers consisting of stigmas and
stamens fused together into a column, one dorsal sepal, two lateral sepals, and three
petals (Goh and Arditti, 1985) (Fig. 3B). The third lowermost petal, termed the labelum
or lip, is modified into a large and colorful landing platform designed for attracting
pollinating insects (Pridgeon, 2000). Orchid flowers may be either solitary on stalks,
termed scapes, or arranged in an inflorescence (Pridgeon, 2000) and can range in size
from 1 m across (Phragmipedium grande Veitch) to as small as the head of a pin (Stelis

spp.) (Rittershausen and Rittershausen, 2003).

99559.1. $99.31.-.. .7 -
Dorsal sepal “

 
  

 

 

_‘ gaminqdve
9"; L
. ateral sepal
'13! .- ‘.
gigabyte! 0';
O
,.Medi§.n Petal
A B

Figure 3. Flower structures of a diandrous orchid, Paphiopedilum, with a median petal
modified to form a pouch (A), and a monandrous orchid, Zygopetalum, with a large and
colorful labelum (B).

PHALAENOPSIS

The genus Phalaenopsis Blume derives its name from the Greek words phalaina,
meaning moth, and opsis, meaning looking like (Mayr, 1998). The common name moth
orchid describes the resemblance of the flowers to night active moth butterflies. The
inflorescence, with flowers that are arranged in ranks along a graceful arching stern, has
also been compared to the flight of moths (Nash, 2003). The genus consists of
approximately 40 species that are native to tropical and subtropical habitats of northern
Australia, China, India, Philippines, Tibet, Taiwan, and other countries in Southeast Asia
(Baker and Baker, 1991). Sweet (1980) classified the genus Phalaenopsis into 10
sections: Amboinenses, Aphyllae, Esmeralda, Fuscatae, Parishianae, Phalaenopsis,
Polychilos, Proboscidioides, Stauroglottis, and Zebrinae. Phalaenopsis hybrids have
been created with all of the known species and breeders have made selections for both the

potted plant and cut flower production markets (Griesbach, 1985b, 2002).

History

Phalaenopsis were first found and described by Rumphius in 1750, but the genus
was not classified until 1825 by Karl Ludwig Blume (Reinikka, 1995). In the early
18003, plants were first introduced in Europe and became popular during the Victorian
period from 1830 to 1900 (Christenson, 2001; Griesbach, 2002). At this time,
Phalaenopsis were primarily grown and displayed in European conservatories and
greenhouses because of the inadequate environmental conditions in homes. The first
artificial Phalaenopsis hybrid was created in 1875, but procedures for successful seed

germination were not established until 1922 when Lewis Knudson developed technology

11

for non-symbiotic seed germination (Griesbach, 2000). In the early 19005, as consumer
popularity for potted plants declined and preference for cut flowers increased, breeders
focused on selecting hybrids for floral traits. After 1960, the demand for potted
Phalaenopsis began to rise again due to new propagation techniques and improved
transportation systems, and as homes became more suitable for growing Phalaenopsis
(Griesbach, 2000). In The Netherlands, Phalaenopsis earned the highest turnover value
among indoor plants traded at Dutch flower auctions in 2004 (VBN, 2005a) (Fig. 4).
Among the almost 300 commercial orchid growers in Europe, about 90 specialize
exclusively in Phalaenopsis (Laws, 2004). Although specific sales figures are not
available for individual orchid genera sold within the US, it is estimated that
approximately 85 to 90% of all orchids sold are of the genus Phalaenopsis (Nash, 2003).
In Taiwan, Phalaenopsis account for 65% of the potted orchids produced and they are

ranked as the number one potted crop (Anthura and Bureau IMAC, 2005).

12

Chrysanthemum
625.7

  
 
 
  
 
  

Ficus
€325

Anthurium
€360

 

 

  

 

Phalaenopsis
6109.7

Figure 4. Tumerover value (million euro) of the most important indoor plants sold at
Dutch flower auctions in 2004 (VBN, 2005a).

13

 

 

 

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Plant Description

Phalaenopsis have a monopodial growth habit with short stems and are generally
epiphytic, although some species are lithophytic (Pridgeon, 2000). The leaves are broad
and succulent with an arching habit, allowing rainfall to potentially drain away from the
crown of the plant (Christenson, 2001). Although a portion of rainwater also drains
toward the crown, this leaf architecture reduces pathogen infection in nature.
Phalaenopsis have thick roots that arise from the base of the stem or lower nodes and are
usually unbranched, functioning as one of three types: aerial, prostrate epiphytic, or
substrate (Christenson, 2001). The apical meristem of aerial and epiphytic roots contain
chlorophyll and have photosynthetic functions, however the amount of carbon
assimilation is less than the amount of carbon evolved through respiration (Dycus and
Knudsen, 1957). The inflorescence, also termed spike, typically emerges from the third'
to fifth node below the top leaf and may consist of only a few flowers on a raceme to
dozens of flowers borne on panicles (Christenson, 2001; Sakanishi et al., 1980). In all
species, the sepals and petals are similar in size, shape, and color, with a labellum
comprised of three lobes (Christenson, 2001) (Fig. 5). Although the most popular flower
color is white, breeders are increasingly selecting Phalaenopsis hybrids for other colors,
shades, stripes, patterns, and combinations (Nash, 2003). A recent trend has been the
popularity of new harlequin-type Phalaenopsis created by commercial hybridizers in
Taiwan, which have flowers with dark colored blotches on top of a light-colored
background (Fitch, 2004a). New complex multi-species hybrids are also available with

wonderful fragrances (Fitch, 2004b). The longevity of flowers varies among species and

14

 

 

 

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fig;

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hybrids, ranging from 30 to 120 days in Phalaenopsis violacaea Witte and Phalaenopsis

amabilis (L.) Blume, respectively (Goh and Arditti, 1985).

Dorsal sepal ,_ ..

Petal , . '

  

Lateral sepal '

,/ I\’ ' "
Column "(labelum

Figure 5. Structure of a Phalaenopsis flower.

Phalaenopsis

Phalaenopsis production occurs around the world and it has been estimated that
125 to 175 million young plants (mericlones and seedlings) are produced annually
(Anthura and Bureau IMAC, 2005). The largest producing countries of potted
Phalaenopsis include China, Germany, Japan, The Netherlands, Taiwan, and the United
States (Griesbach, 2003). In 1993, potted Phalaenopsis orchids accounted for $103
million dollars in sales at Japanese auctions (Hew and Yong, 1997). Among all flower
auctions in The Netherlands, there was a 123% increase in potted Phalaenopsis sales
between 2001 and 2004 (VBN, 2003, 2005a) (Fig. 6). In 2004, a total of 23.8 million

potted Phalaenopsis were traded at Dutch flower auctions with a value of 6109.7 million

 

 

 

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($136 million’) (VBN, 20053). It was estimated that The Netherlands produced a total of
35 million potted Phalaenopsis in 2004 on approximately 80 hectares of production.
Phalaenopsis production in China has also increased considerably during the past ten
years and in 2003, 10 to 12 million plants were produced (Anthura and Bureau IMAC,
2005)

Taiwan currently has the largest number of breeders and growers with
approximately 89 hectares in production, producing 36 million plants in 2002 with a
wholesale value of $51 million (Fenton, 2004b; Wang, 2004). It is estimated that of the
Phalaenopsis plants that are produced in Taiwan, 80% are exported (Anthura and Bureau
IMAC, 2005). The Taiwanese government, with the goal of maintaining a central
position in worldwide potted Phalaenopsis production, is currently deveIOping a large
scale research, production, and distribution complex, named the Taiwan Orchid
Plantation (Fenton, 2004a). In 2004, the USDA amended the regulations for the
importation of plants and plant products and added Phalaenopsis orchids from Taiwan to
the list of plants that can be imported in approved growing media (USDA, 2004a).
Orchid growers in the United States are challenging this ruling because it could have a
negative economic impact on domestic commercial growers of potted Phalaenopsis
orchids.

One of the primary reasons why commercial production of Phalaenopsis orchids
has risen in the United States is that many greenhouse growers are in search of additional
potted floriculture crops to expand their product line and increase profitability. Plants are

generally finished and sold in 12 to 15-cm pots with six or more flower buds per plant

g

’ The euro-US. dollar exchange rate was calculated by averaging the daily euro-US. dollar exchange rates
for the calendar year 2004 (Federal Reserve Bank of New York, 2005). Based on this calculation, the
average euro-US. dollar exchange rate was 1.24.

16

 

 

 

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and each flower measuring 27.5 cm wide (Konow and Wang, 2001; Wang and Lee,
1994a). The wholesale price of a 15-cm pot varies considerably among markets within
the United States, ranging from $10.00 to $26.00 in 2004 (Laws, 2004). This wholesale
price is considerably higher than more traditional potted plants, such as Easter lily
($4.12), florist Chrysanthemum ($2.53), and poinsettia ($4.07) (USDA, 2005b). In The
Netherlands, the average wholesale price on the flower auction for potted Phalaenopsis
was €4.61 ($5.70) in 2004 (VBN, 2005a). However, the average wholesale price varies
considerably throughout the year and in 2003 ranged from €3.65 to €5.49 ($4.12 to
$6.20’) during summer and winter periods, respectively (Anthura and Bureau IMAC,

20051

_

’ The euro-US. dollar exchange rate was calculated by averaging the daily euro-US. dollar exchange rates
for the calendar year 2003 (Federal Reserve Bank of New York, 2005). Based on this calculation, the
average euro-US. dollar exchange rate was 1.13.

17

 

 

 

 

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120 28
+ Turnover value
100 . -0- Quantity sold — 24
. 20
80 a
9
:3 ~ 16
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2
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~ 8
2o - . 4
o I I l I 0
2001 2002 2003 2004
Year

Figure 6. Turnover value [million euro (6)] and quantity [million (0)] of potted
Phalaenopsis sold at Dutch flower auctions from 2001 to 2004 (VBN, 2003, 2005a).

18

Np. of pots (million)

 

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COMMERCIAL PRODUCTION OF PHALAENOPSIS
Commercial production of potted Phalaenopsis is divided into many segments:
breeders, propagators, finishing greenhouse growers, wholesale florist distributors, and
retailers (Laws, 2004). A segmented supply chain allows for specialization in one

fimction and results in improved plant quality and efficient production methods.

Propagation

Consumer preference in the United States has shifted from cut flowers to potted
plants, prompting breeders to develop hybrids for the mass potted plant market and to
select plant material with a compact growth habit and flowers that are fragrant, long-
lasting, or both. Phalaenopsis orchids are commercially propagated by sexual and
asexual techniques, but asexual propagation is most common due to greater plant
uniformity (Griesback, 2002). Plantlets propagated by tissue culture are grown in flasks,
which are then transferred to community pots, thumb pots, and larger pot sizes in
succession and can be sold as unfinished plants at each stage (Hew and Yong, 1997;
Konow and Wang, 2001). From clonal propagation, Phalaenopsis generally require 24 to
36 months to reach maturity, or the capacity to flower, which is relatively short when
compared with other orchid genera that can require up to 60 months (Keithly et al., 1991;
Konow and Wang, 2001). Mature plants with a 25—cm to 30-cm leaf span are often

purchased by commercial growers who finish the crop based on the scheduled market

demand (Wang and Lee, 1994a).

19

 

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Shipping Unfinished Plant Material

Commercial orchid growers in the United States commonly purchase immature
and mature plant material from growers in other countries (e. g., Taiwan and The
Netherlands). The USDA requires that orchid plants are imported into the United States
as bare-rooted plants, without orchid media. The only exception to these regulations is
the importation of Phalaenopsis in approved growing media from Taiwan. Shipping
orchids as bare-rooted plants increases the susceptibility to temperature and water stress,
which can have a negative impact on plant vigor. Su et al. (2001a) determined the effects
of temperature, relative humidity, illumination, and storage duration on the amount of
water loss and quantum efficiency of bare-rooted Phalaenopsis, and reported that
temperature was the most important factor during shipping. The weight loss in plants
stored at 25 0C, 70% relative humidity, and in darkness increased from approximately 3%
to 20% as storage duration increased from 3 to 30 days, respectively. When temperature
increased to 35 °C, weight loss decreased by approximately 28% to 62% as storage
duration increased from 3 to 30 days, respectively. There was no significant decline in
quantum efficiency of plants stored at 25 °C, whereas plants stored at 35 °C had a
significant decrease (360%) in quantum efficiency when stored for up to 30 days (Su et
aL,2001a)

A shipping temperature of 25 0C is recommended in another study. Wang (1997)
reported that chilling injury occurred in leaves of bare-root Phalaenopsis when stored at
15 and 20 °C for 4, 7, or 14 days. The time to visible inflorescence was not affected by
storage at 15, 20, or 25 °C for durations up to 14 days, whereas inflorescence emergence

was delayed by 5 to 8 days when stored for 24 days at 30 °C.

20

Greenhouse Environment
Temperature

Vegetative Phase. Phalaenopsis grown at a constant temperature of 228 °C
remain in a vegetative phase and development of the reproductive bud is inhibited (Chen
et al., 1994; Sakanishi et al., 1980; Yoneda et al., 1991). Most species will tolerate
periods at temperatures between 32 to 35 °C (Baker and Baker, 1991), however the
maximum duration at high temperature has not been determined and the specific
symptoms of heat stress have not been well described. The base temperature for
Phalaenopsis has been calculated to be between 10.8 to 11.2 °C, and is similar for all
stages of growth and development (Robinson, 2002). McConnell and Sheehan (1978)
reported that Phalaenopsis exposed to a constant temperature of 2, 4, or 7 °C for 1 hour
or more in darkness, resulted in chilling injury that was manifested as sunken, yellow,

water-soaked spots on upper leaf surfaces.

Reproductive Phase. To promote the transition from a vegetative phase to a
reproductive phase, commercial greenhouse growers reduce temperature to a day/night of
25/20 or 20/15 0C (Lee and Lin, 1984, 1987). After low temperature exposure for 3 to 5
weeks, an inflorescence (spike) will emerge through the leaf epidermis from the axil of
the third and/or fourth node below the apical leaf (Sakanishi et al., 1980). Smaller plants
(1 5-cm to 25-cm leaf span) that have not reached vegetative maturity may require cooler
temperatures (20/15 °C) or longer exposure than larger, more mature plants (25-cm to 30-

cm leaf span) (Wang and Lee, 1994b). The initiation and development of floral

21

 

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primordia does not occur until the inflorescence has reached "—35 cm in length (De Vries,
1950).

Following inflorescence emergence, there is a linear relationship between
temperature and rate of development towards visible bud and anthesis (Lee and Lin 1987;
Robinson, 2002). For example, the average time from inflorescence emergence to
anthesis at a constant average daily temperature (ADT) of 17.7, 20.0, 22.5, or 25.7 °C
was 133, 88, 64, and 53 days, respectively. The minimum time from inflorescence
emergence to anthesis occurred at 26 °C. The thermal time and the base temperature (Tb)
were both calculated for 1) days from inflorescence emergence to visible bud (454
degree-days; Tb=l 1.2 °C) and 2) days from visible bud to anthesis (333 degree-days,
Tb=11.0 °C) (Robinson, 2002). The base temperature and thermal time were calculated
using equations [3] and [5], respectively (pages 48 and 50).

In Phalaenopsis Taisuco Smile (Phal. Taisuco Bright X Phal. equestris Rchb.),
forcing temperature between 17 and 26 °C did not affect the average number of nodes,
flower count, final inflorescence height, or flower width (Robinson, 2002). In contrast,
Lee and Lin (1984) reported that plants of Phalaenopsis Dos Pueblos X Juanit had shorter
inflorescences and lower flower count when grown at a day/night temperature of 20/1 5
°C compared to plants grown at 25/20 °C. The inflorescence and flowers may abort or
the inflorescence may transition back to a vegetative phase and an air plantlet will
develop if plants are exposed to a high temperature (228 °C) before the inflorescence has
reached :5 cm in length (De Vries, 1950; Sakanishi et al., 1980). A vegetative air

plantlet is termed a keiki, the Hawaiian word for “baby” (Christenson, 2001).

22

 

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Ota et a1. (1991) measured the amount of C02 uptake in Phalaenopsis plants
grown at constant temperatures of 10, 15, 20, 25, and 30 °C and day/night temperatures
of 10/20, 25/15, 25/20, and 30/20 °C and determined that the highest amount of net CO2
uptake occurred at 25/15 and 25/20 °C. The constant temperature for greatest CO2
uptake was 20 °C. A similar study by Lootens and Heursel (1998) measured the amount
of CO2 uptake in single leaves of Phalaenopsis plants grown under a photosynthetic
photon flux (PPF) of 180 umol‘m'z-s'l and at four day/night temperature regimens of
20/15, 20/20, 25/20, or 25/25 °C, and reported that CO2 uptake was significantly greater
(14% to 21%) at 20/15 °C than at 20/20, 25/20, or 25/25 °C. A significant day/night
temperature effect also existed, in which treatments with a +5 °C day/night temperature
fluctuation had a 5% to 21% greater CO2 uptake than treatments with a 0 °C day/night
temperature fluctuation. These results collectively show that in Phalaenopsis, a positive
day and night temperature fluctuation increases CO2 absorption and presumably carbon

assimilation compared to a constant temperature.

Low Temperature Requirement

The requirement of low temperature (525 °C) for the induction of inflorescences
in Phalaenopsis has been well defined (De Vries, 1950; Lee and Lin, 1984, 1987; Rotor,
1952; Sakanishi et al., 1980; Yoneda et al., 1992). A 5 to 8 °C day/night fluctuation has
been reported to be required for inflorescence initiation and flower development (Anthura
and Bureau IMAC, 2005; Christenson, 2001). However, there has been limited research
on the interaction between day and night temperature and to our knowledge, no scientific

information exists to support this concept.

23

 

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De Vries (1950) observed that inflorescence induction occurred in Phalaenopsis
schilleriana Rchb.f. when the day temperature was occasionally above 30 °C and night
temperature was between 19 to 21 °C. Exposure to a night temperature 521 °C was
suggested as a requirement for inflorescence induction, and a high day temperature 230
°C did not have an inhibitory effect (De Vries, 1950). However, this experiment was not
conducted in a climate-controlled greenhouse and the duration of the day and night was
not reported. These results conflict with information by How and Yong (1997), in which
flowering of Phalaenopsis amabilis and Phalaenopsis schilleriana did not occur when
the day temperature was above 27 °C and the night temperature was between 12 to 17 °C.

Sakanishi et a1. (1980) investigated the effects of increasing the duration of high
temperature exposure when the average night temperature was 20 °C. As the daily hours
of temperature above 28 °C increased from 0 to 24, there was a decrease in the
percentage of inflorescence emergence and a delay in days to inflorescence emergence.
To achieve 100% inflorescence emergence in a population of plants, they had to be
exposed to at least 12 hours at a temperature of 20 °C each day (Sakanishi et al., 1980).
However, this experiment was conducted under a natural photoperiod and information
was not presented on when the high temperature exposure occurred in relation to the
photoperiod. F urtherrnore, the timing of high temperature exposure during the day to
inhibit inflorescence induction has not been determined. In other words, can high
temperature exposure inhibit flowering during the day as well as if delivered during the
night?

These experiments collectively suggest that a high day temperature can inhibit

inflorescence emergence even when the night temperature is conducive for reproductive

24

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ilUt

 

 

 

 

development. Further research is merited to clarify the effects of diurnal temperature

fluctuations on inflorescence emergence and development.

Irradiance

The effects of irradiance have been described during all stages of Phalaenopsis
production (Konow and Wang, 2001; Lee, 2000; Lootens and Heursel, 1998; Wang,
1995b, 1998a; Wang and Lee, 1994a). Phalaenopsis plantlets grown in vitro under an
instantaneous irradiance level of 40 or 80 rrmol-m'Z-s'l provided by cool-white fluorescent
lamps had increased root growth, wider leaves, and greater fresh weight than those grown
under 10 or 20 umol-m'z-s" (Konow and Wang, 2001). During vegetative grth in the
greenhouse, the recommended irradiance for mature Phalaenopsis is 240 to 400 umol-m'
2s", but the intensity should be reduced when temperature is above 30 °C (Wang and
Lee, 1994a). Lee (2000), reported that plants grown under 80 to 160 umol-m'z-s'l and
subsequently forced had significantly less root and leaf dry weight, delayed flowering,
and a lower flower count compared with plants grown under 260 to 360 umol-m’z-s".
However, the photoperiod and daily light integral (DLI) were not presented. Lootens and
Heursel (1998) determined that the saturating PPF for two Phalaenopsis hybrids grown
at 20 °C was 180 umol-m’z's". At a temperature of 25 or 30 °C, the saturating PPF was
not found at the highest irradiance measured, 300 umol-m’z-s". Photoinhibition occurs in
Phalaenopsis when grown at an irradiance above 400 umol-m'zs'l (Lee, 2000).

Information is also available on how irradiance influences the reproductive phase

of Phalaenopsis production. Wang (1995b) showed that plants grown at 20/15 °C

day/night with a 12-h photoperiod and a DLI of 2.6 or 6.9 mol-m'z-d" initiated

25

 

 

 

 

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inflorescences after 34 and 28 days, respectively. Plants grown under 0 or 0.35 mol-m'
2°d'l did not initiate inflorescences within 6 weeks. This is supported by Lee (2000), in
which all plants initiated inflorescences and flowered when the DLI during forcing was
22.2 mol-m’Z-d", independent of photoperiod. In Phalaenopsis, a reduction in light
intensity has been associated with a decrease in leaf and root development, dry matter
production, sugar concentration, and the amount of nitrogen absorbed (Kubota and
Yoneda, 1993b).

Wang (1998a) showed that inflorescence emergence could be delayed by
exposing plants to repeated weekly cycles of various days in darkness and suggested that
the inability of plants to initiate inflorescences may have resulted from low
concentrations of metabolites. Hisamatsu et al. (2001) reported that inflorescence
initiation could be delayed by holding plants in darkness at 20 °C for S60 days without
adverse effects on plant quality when returned to light and forced (i.e. the number of
flowers, length of inflorescences, and size of flowers were not affected by dark
treatment). These strategies to delay flowering could be used by Phalaenopsis growers in
tropical and subtropical climates without the use of heating systems to maintain

noninductive temperatures.

Photoperiod

Currently, there is conflicting research as to whether Phalaenopsis is
photoperiodic; some studies have suggested that short days hasten inflorescence
emergence and flowering (Goh and Arditti 1985; Rotor, 1952, 1959; Su et al., 2001b;

Went, 1957; Yoneda et al., 1991). Rotor (1952, 1959) reported that plants of

26

 

 

 

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Phalaenopsis amabilis grown at 18 °C under a 9-h photoperiod initiated inflorescences
and flowered all year, whereas plants grown under a 16-h photoperiod had one flowering
period per year. This is also supported by Went (1957), in which plants grown at 20 °C
produced more inflorescences under an 8-h photoperiod than under a 16-h photoperiod.
Data comparing the number of inflorescences between treatments was not provided.
Yoneda et al. (1991) observed that 6-year old mature Phalaenopsis grown at 22 or
23 °C and under an 8-h photoperiod initiated inflorescences and reached anthesis 7 to 9
days earlier than plants grown under a natural photoperiod. However, the effect of
daylength was not significant in this study. Sakanishi et al. (1980) suggested that the
facultative short-day response in Phalaenopsis could be a cumulative effect of low

temperature.

Postharvest

The inflorescences of Phalaenopsis are usually braced before transport using
support stakes and wire ties or clips. Stakes are often installed when the lowest bud on
the inflorescence reaches the size of a marble. When plants have at least one or two open
flowers they are ready for sale and are packaged for transport. The flowers of
Phalaenopsis are susceptible to infection by pathogens. Petal blight, caused by Botrytis
sp., can develop on open flowers as small dark spots, resulting in plants that are
unsalable. This disease manifests when inflorescences and foliage remain wet for long
periods or during conditions of high relative humidity (280%) (Anthura and Bureau

IMAC, 2005; Wang, 2003).

27

 

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dro

fro

allt

cri'

lllll

he

hill

 

 

 

ex:
fro
Fir

mi

11:

The flowers of Phalaenopsis are very sensitive to small concentrations of
ethylene: plants exposed to 0.1 mg-L'l ethylene for 24 hours had complete flower and bud
drop within three days of initial exposure (Wang, 2004). Applying 1-
methylcyclopropene (l-MCP) at 0.2 mgL'l for six hours protects Phalaenopsis flowers
from ethylene (510 mg'L"). The duration of ethylene protection by l-MCP was 4, 7,
and 10 days at 25 to 30, 20, and 15 °C, respectively (Wang, 2003).

Phalaenopsis are graded based on flower color, number of flowers per
inflorescence, inflorescence length, lateral branching of the inflorescence, and number of
inflorescences per plant. Among these characteristics, the most important grading
criterion is the number of inflorescences per plant, followed by lateral branching and the
number of flowers per inflorescence (Anthura and Bureau IMAC, 2005). In The
Netherlands, product specifications at flower auctions require potted Phalaenopsis to
have a minimum number of open flowers per inflorescence at time of trade. For
example, at least 25% of the flower must be open from 2 March to 31 October, while
from 1 November to 1 March, 25 to 50% of the flowers must be open (VBN, 2005b).
Finished plants are wrapped in individual sleeves for protection, then are transported at a
minimum temperature of 18 °C (Anthura and Bureau IMAC, 2005).

Plant damage can occur during long periods of shipping by airfreight or ground
transportation, resulting in bud drop and high percentages (up to 15%) of unsalable plant
material. In both the United States and Europe, compact and branched mini-
Phalaenopsis hybrids are now increasingly sought by store buyers because damage

during transport is reduced (Laws, 2004).

28

 

051

051

 

 

CC

SC

Sp

fir

Medium and Nutrition
GrowingMedium

A common growing medium used in early Phalaenopsis production was
osmunda, the dried fibrous root mass from a fern of the genus Osmunda. However,
osmunda is rarely used today in orchid cultivation due to its high cost, lack of quality,
and limited availability because of endangerment (Christenson, 2001). The primary
medium component now used in commercial production of Phalaenopsis is Douglas fir
[Pseudotsuga menziesii (Mirb.) Franco] bark, harvested by the logging industry on the
Pacific coast of the United States (Wang, 2000). However, Douglas fir bark has several
disadvantages: fresh bark has a low water-holding capacity; small or medium grade bark
decomposes too quickly, resulting in high water retention; it has low nutrient retention
and insufficient uniformity; and has the potential for limited availability in the future.
Thus, growers usually combine fir bark with other organic and inorganic materials,
including activated charcoal, chopped coconut husks and fiber (Coco nucifera L.), cork
(Quercus suber L.), expanded clay, osmunda fiber, peat, perlite, redwood bark [Sequoia
sempervirens (D. Don) Endl.], rock wool, Sphagnum moss, expanded polystyrene, tree
fern fiber, vermiculite, and volcanic rock (Baker and Baker, 1991; Slump, 2004).

A mixture of fine-grade fir bark and Sphagnum peat (80% and 20% by volume,
respectively) resulted in a greater leaf number, total leaf area, and shoot fresh mass
compared to plants grown in a 100% fine-grade fir bark medium (Wang, 1998b). In a
separate study, Phalaenopsis were grown in a mixture of fine-grade Douglas fir bark and
Sphagnum peat (70% and 30% by volume, respectively) or in a 100% fine-grade Douglas

fir bark medium and fertilized at each irrigation with a water soluble fertilizer (20N-8.6P-

29

 

 

 

 

 

16.6K; 200 mg N l") for one year (Wang and Konow, 2002). Plants grown in a peat and
fir bark medium had a greater leaf number, total leaf area, and leaf and root fresh weight
than plants grown in only bark. The differences in plant grth could be attributed to a
higher water-holding capacity and cation exchange capacity of peat mix compared to fir
bark alone.

One recommended media composition for growing Phalaenopsis is a mixture of
80% medium-grade fir bark, 10% long fiber sphagnurn peat moss, and 10% coarse-grade
perlite (Wang, 2003). In Japan, the primary medium for growing Phalaenopsis is
Sphagnum moss because of its high water-holding capacity, nutrient retention, slow rate
of decomposition, ease of transplanting and inserting inflorescence supports, and
widespread availability from New Zealand and China (Ichihashi, 1997).

The pH and electrical conductivity (EC) of the medium are also important factors
to monitor during Phalaenopsis production. The recommended pH and EC for growing
Phalaenopsis ranges from 5.0 to 6.0 and 1.0 to 1.5 dS-m", respectively (Griesbach,

1985a; Wang, 2003).

Plant Nutrition

Wang (1996) irrigated young Phalaenopsis seedlings with one of six water-
soluble fertilizers, having various percentages of N, P, and K, and different nitrogen
sources and potential acidity (lON-l3.1P-16.6K, 15N-4.4P-24.9K, 15N-8.7P-20.8K,
20N-2.2P-15.8K, 20N-4.4P-16.6K, and 20N-8.7P-16.6K) at 100 or 200 mg N-L". After
seven months of fertigation, leaf span, leaf size, total leaf area, and shoot and root fresh

weight were not significantly different among fertilizers within either concentration.

30

 

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Int

N I

ll 0

Gr

int

flr

21»

(l’

fir

SI.

 

ml

It

in

 

These results suggest that during production of Phalaenopsis, different balanced
fertilizers can be used with similar effects on plant growth.

Fertilizer concentration can influence the performance of Phalaenopsis.
Increasing the rate of a 20-8.6-26.6 fertilizer from 0.25 g-L'l to 1.0 g-L" (50 to 200 ppm
N), increased flower count, inflorescence diameter and length, and leaf production after
flowering, and hastened inflorescence emergence during the following season (Wang and
Gregg, 1994). Application of a fertilizer with N at 2100 mg~L”, before and after
inflorescence emergence, is reportedly important for the initiation and development of
flower primordia, as well as obtaining a high flower count and quality (Wang, 2000).
Griesbach (1985c) recommended applying 100 mg N-L'l at each irrigation from a 20N-
20P-20K soluble fertilizer for production of the Phalaenopsis hybrid ‘Toyland’
(Phalaenopsis Leucorrhoda XPhaIaenopsis Hummingbird).

One fertility strategy now recommended for commercial production of
Phalaenopsis is to use a water-soluble fertilizer at each irrigation at a rate of (mg'L'l):
200 N, 25-50 P, and a minimum of 150 K (Wang, 2003). Periodic application of calcium
from calcium nitrate at 100 mg Ca-L" and magnesium from epsom salts (magnesium
sulfate heptahydrate) at 50 mg Mg-L'l is also suggested. Table 1 provides recommended

nutrient target values and sufficiency ranges for a media analysis.

Physiological Changes
The physiological changes that occur as Phalaenopsis transitions from a
vegetative to a reproductive phase have not been completely described. During

inflorescence emergence and development, exposure to low temperature has been

31

associated with increases in: active cytokinins in leaves; active gibberellins in
inflorescences; sucrose, glucose, and fructose in inflorescences; and total nitrogen
concentration and carbohydrate levels in stems (Chen et al., 1994; Chou et al., 2000;
Kataoka et al., 2004; Kubota and Yoneda, 1993a; Su et al., 2001b), while a decrease in
the level of active abscisic acid has been measured in roots and developing inflorescences

(Wang et al., 2002).

32

Table 1. Element, electrical conductivity (EC), and pH target values and sufficiency
ranges for Phalaenopsis growing media. Information from Anthura and Bureau IMAC
(2005)

 

 

 

Element Target value (mg-L") Sufficiency range (mg-L”)
Ammonium (NH4’) <7 0 - 14
Nitrate (N03) 63 49 - 84
Phosphate (P205) 37 25 - 47
Potassium (K) 117 106 - 137
Calcium (Ca) 52 40 - 64
Magnesium (Mg) 19 10 - 29
Sulphate (S04) 19 10 - 29
Boron (B) 0.11 0.05 - 0.16
Chlorine (Cl) <53 0 - 71
Copper (Cu) 0.06 0.03 - 0.09
Iron (Fe) 0.56 ' 0.28 - 0.84
Manganese (Mn) <0.05 0 - 0.60
Molybdenum (Mo) 0.06 0.02 - 0.10
Zinc (Zn) 0.39 0.20 - 0.59
Sodium (Na) <35 0 - 35

EC 1.0 dS-m" 0.7 - 1.3 dS-m"
pH 5.8 5.0 - 6.5

 

33

EFFECTS OF PLANT GROWTH REGULATORS ON PHALAENOPSIS
Abscisic Acid

Abscisic acid (ABA) is an important hormone involved in the regulation of plant
dormancy (Taiz and Zeiger, 2002). Wang et al. (2002) measured the amount of free and
bound ABA in leaves, roots, and either dormant buds or flowering inflorescences of
Phalaenopsis during three developmental stages: 1) plants grown at 28 °C without a
visible inflorescence, e. g. dormant buds; 2) plants grown at 25/20 °C day/night with
inflorescence length of 2 to 3 cm; and 3) plants grown at 25/20 0C with an inflorescence
length of 7 to 10 cm. Plants grown at 28 °C had the highest amounts of free ABA in
roots (48.5 ng—g”) and dormant buds (31.1 ng-g”), whereas plants grown at 25/20 °C had
46% less free ABA in roots and non-detectable levels in developing inflorescences.
Levels of bound ABA, an inactive storage form, were 26 or 841% lower in roots of plants
grown at 28 °C compared to plants grown at 25/20 °C with inflorescence lengths of 2 to 3
or 7 to 10 cm, respectively.

In a separate study, injection of exogenous ABA at the beginning of low
temperature exposure (25/20 °C) inhibited the initiation of inflorescences (Wang et al.,
2002). Phalaenopsis injected with ABA at 0, 0.1, or 1.0 pg per plant had inflorescence
initiation percentages of 67, 17, or 0%, respectively. These results suggest that ABA
could regulate the reproductive transition in Phalaenopsis, in which a decrease in ABA in

dormant buds and roots is required for the initiation of flowering.

34

A1

1|
I
I
I
I
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I
r

 

Auxin

To our knowledge, only one study has examined the changes in level of
endogenous indole-acetic acid (IAA) during low temperature induction of Phalaenopsis.
Fouché et al. (1997) measured the level of IAA in leaves every day following transfer to
22/17 °C and the level of IAA level abruptly increased from 135 to 450 nmol-g'l between
day two and five, followed by a second increase from 150 to 325 nmol-g'l between day
seven and nine. The relationship between fluctuations in IAA levels and the transition

from vegetative to reproductive development is uncertain.

Cytokinins

In 1956, in search of compounds that promoted division of plant cells in culture,
Folke Skoog isolated kinetin, N6-furfuryladenine, a product formed during autoclaving of
DNA (Taiz and Zeiger, 2002). Further studies revealed that kinetin in the presence of
auxin, stimulated tobacco pith parenchyma tissue to proliferate in culture. In 1973,
Letham identified a natural compound from the immature endosperm of corn, which
promoted cell division similarly to kinetin. This compound, named zeatin (from the
Latin for corn, Zea mays L.), was a trans-6-(4-hydroxy-3-methylbut-2-enylamino) purine
(Taiz and Zeiger, 2002). Zeatin and related compounds have since been grouped under a

major class of plant hormones, the cytokinins (Crozier et al., 2000).
thsiologicfial Role

Cytokinins are biosynthesized in the apical meristem of roots and are transported

through the xylem to aerial plant organs. During the past 45 years, research has shown

35

 

lr-r-a

 

 

the involvement of cytokinins in a wide array of physiological and biochemical processes
including seed germination and dormancy, cell division, organ formation and
regeneration, reduction of apical dominance, response to pathogens, nutrient
mobilization, floral and vascular development, fruit set, fruit ripening, and senescence of
plant organs (Higuchi et al., 2004; Taiz and Zeiger, 2002). Studies have also reported a
role of cytokinins during phloem loading and unloading and an effect on assimilate

movement (Thomas and Blakesley, 1987).

Benzvl_adenine

Synthetic cytokinins include N6-substituted adenines such as kinetin (6-
furfurylaminopurine) and benzyladenine (6-benzylaminopurine, BAP). The effects of
these synthetic compounds are similar to those of endogenous cytokinins. Although
benzyladenine (BA) was the first synthetic cytokinin derived, BA has now been isolated
as a naturally occurring cytokinin in many plants and can be considered an endogenous—

like compound (Buban, 2000).

Commercial Uses in Horticulture

Cytokinins are commonly used during all stages of micropropagation: 1) initiation
into culture, 2) multiplication, 3) shoot development, and 4) root development (Thomas
and Blakesley, 1987). In commercial fruit production, BA is commonly used to regulate
canopy structure by promoting lateral shoot growth and increase cropping potential or as
a fruit thinning agent to produce higher quality fruits and increase bloom the following

season (Buban, 2000). Cytokinins are also applied exogenously to influence chlorophyll

36

production and leaf senescence in many crops. During production and in postharvest
environments, leaf yellowing can reduce the quality of potted plants and cut flowers. In
Limonium sinuatum (L.) P. Mill., BA as a dip reduced chlorophyll degradation and
senescence of cut flower stems (Serek and Reid, 2000). Han (1997) reported that spray
application of a 25 mg-L'l solution containing GA4+7 and BA prevented basal leaf
yellowing in Lilium longiflorum Thumb. ‘Nellie White’.

Benzyladenine is also used during the production of Easter cactus [Hatiora
gaertneri (Reg) Barthlott.] and Thanksgiving cactus [Schlumbergera truncata (Haw.)
Moran.] to increase the number of phylloclades and flower buds (Dole and Wilkins,
2005). In Thanksgiving cactus grown under long-days, the number of phylloclades
increased by almost 150% after BA (50 or 100 mg-L") was sprayed to runoff (Heins et
al., 1981). Application of BA at 50 mg-L'l on Easter cactus increased the total number of
flowers per plant by 85% when applied as a spray 12 days after the start of long days
(Boyle, 1995).

In miniature climbing rose (Rosa ‘Jeanne la Joie’) nine foliar spray applications of
BAP (100 mg-L") applied every two days increased the number of shoots after four
weeks by 21% and 68%, compared control and pinched plants, respectively (Richards
and Wilkinson, 1984). The application of BAP also had a significant influence on the
number of flowers eight weeks after treatment: plants treated with BAP at 10 or 100
mg-L’l had increased flower number by 112% and 175%, respectively, compared to

control plants.

37

Effects on Growth and Flowering of C ymbidium, Dendrobium, and Aranda

Benzyladenine is commonly used during the earliest stages of orchid production
as an important component in culture media for micropropgation (Tokuhara and Mii,
1993). Several studies have suggested that the application of BA on orchids may be a
useful tool to control flowering (Goh, 1977, 1979; Higuchi and Sakai, 1977; Kim et al.,
1999, 2000; Sakai et al., 2000; Yoneda and Momose, 1990).

One theory that has been proposed to explain the effectiveness of BA in
promoting flowering in some orchids suggests that inflorescence initiation in response to
inductive temperature is a result of changes in the level of endogenous cytokinins (Chou
et al, 2000; Goh, 1979). Flower initiation in many plant species is often associated with
changes in hormone levels in response to environmental factors (Zeevaart, 1976). Thus,
the application of BA during low temperature exposure may supplement the natural
increase in endogenous cytokinins and enhance inflorescence induction.

In Aranda Deborah, five repeated (daily) 2 ml injections of BAP (1 mM) or
BA+GA (1 mM and 1 mM, respectively) into stem tissues between the sixth and seventh
node increased the average number of initiated inflorescences per plant by 850 and
1500%, respectively, compared to untreated plants (Goh, 1977). lnforrnation on the
number of flowers per inflorescence or details on flower quality were not presented.

The effects of BA on the promotion of early flowering in Cymbidium sp. in vitro
have been well described (Chang and Chang, 2003; Kostenyuk et al., 1999). Kostenyuk
et al. (1999) reported that following root excision, shoots of Cymbidium niveo-
marginatum Mak grown on a Murashige and Skoog (MS) medium supplemented with

nitrogen, phosphorous, and (BA (44 uM) had a flowering percentage of 97.5% after 90

38

 

 

01

It

51

OI

 

73

 

days, while control plants were nonflowering. In a similar study, callus-derived rhizomes
(3 to 5 mm) of Cymbidium ensifolium var. misericors grown on a MS medium
supplemented with naphthalene-acetic acid (NAA) (0.28 uM) and BA (10 to 33 uM )
flowered within 100 days after culturing (Chang and Chang, 2003).

Higuchi and Sakai (1977) reported that a 1.8 mM solution of BA applied on
Dendrobium Nodoka during the beginning of the short-day and low temperature
treatment during forcing, increased the number of inflorescences per plant. The
application method and amount of increase were not presented in English. Goh (1979)
injected 1 ml of either BA (1 mM or 0.1 mM), GA (1 mM or 0.1 mM) or BA+GA (1 mM
and 0.1 mM, respectively) into mature pseudobulbs of Dendrobium Loisae ‘Dark’ and
observed that plants treated with BA or BA+GA initiated inflorescences 7 to 10 days
after the first application, whereas untreated pseudobulbs and those treated with only GA
did not initiate an inflorescence. When either BA or GA was injected into young
vegetative axillary shoots (4 to 8 cm long), inflorescence initiation did not occur. This
suggests that other hormonal factors may prevent floral initiation in actively growing
organs (e. g., auxin), or that young shoots do not have the capacity to flower.

In Dendrobium J aquelyn Thomas ‘Uniwai Princess’, a one-time treatment of five
0.1 ml injections of BA (10 or 100 mM) into 2-year old mature pseudobulbs stimulated
the production of 4.0 and 6.3 inflorescences per pseudobulb, respectively, while control
plants formed an average of 0.2 inflorescences per pseudobulb (Sakai et al., 2000). The
average length of inflorescences stimulated by injection of BA at 10 and 100 mM was
17.5 and 15.3 cm, respectively, compared with 20.3 cm of control plants. In addition,

flower area was reduced to 5.0 and 4.2 cm2, respectively, compared with 5.6 cm2 of

39

control plants and a high percentage of flowers were abnormal (i.e., petal-like growths
from the sides of the column or two anther caps present on the column) compared to
untreated plants. Incorporation of GA (10 or 100 mM) into the injection solution
increased inflorescence length and flower area, and reduced the percentage of abnormally
formed flowers (Sakai et al., 2000). The specific GA used in this study was not provided.
Campos and Kerbauy (2004) measured the concentrations of endogenous
hormones during low temperature flowering induction (25/10 °C) of Dendrobium Second
Love and reported that cytokinins (zeatin-derived forms) increased by over 360% in
lateral buds when measured 15 days after the end of low temperature exposure and levels
of ABA in lateral buds decreased by 31%. Levels of IAA fluctuated, decreasing 15 days
after low temperature exposure and increasing thereafter. These results suggest that
cytokinins may be involved during the floral transition in Dendrobium, which could

explain the effectiveness of BA in promoting inflorescence initiation.

Effects on Flowering of Phalaenopsis

Chou et al. (2000) investigated changes in the concentration of endogenous
cytokinins in the Phalaenopsis hybrid ‘Taisuco Snow’ (Phal. Mount Kaala X Phal.
Wataboushi) grown at high temperature (30/25 °C day/night) and low temperature (25/20
0C). At high temperature, active cytokinins were converted into inactive forms and
during exposure to low temperature, concentrations of active cytokinin in leaves
increased. This suggests that cytokinins may have an important role during reproductive

initiation in Phalaenopsis.

4O

The application of BA during low temperature induction of Phalaenopsis has
been reported to hasten the rate of inflorescence initiation and flowering and increase the
number of inflorescences (Ichihashi, 1997; Kim et al., 1999, 2000; Yoneda and Momose,
1990). In the Phalaenopsis hybrid J immy Hall X J immy Hall ‘J ouch Petals’, a single
foliar spray application of 200 mg-L'l BA during low temperature exposure reportedly
“promoted” inflorescence initiation and flowering (Ichihashi, 1997). Although BA
decreased the length of inflorescences in this study, application of GA3 at 100 mg-L'I
overcame the reduced inflorescence elongation.

A foliar spray application of BA (200 mg-L"), GA3 (100 mg'L") or BA+GA3
(200 mg-L" and 100 mg-L", respectively) after transfer to highland culture for flowering
(400 m above sea level) increased inflorescence emergence and decreased time to flower
in BA and BA+GA3 treatments (110 days) compared to GA; and control treatments (123
and 135 days, respectively) (Yonenda and Momose, 1990). A reproductive inflorescence
generally emerges from the leaf axil of the third, fourth, or both nodes below the apical
leaf (Sakanishi et al., 1980). However, in this study the percentage of inflorescences that
emerged from below the fourth node was different among treatments: control (1.2%),
GA3 (8.7%), BA (18.2%), and BA+GA; (31.3%) (Yonenda and Momose, 1990).

Kim et al. (2000) studied the effects of two foliar spray applications of BA (100,
200, or 400 mg-L") or BA+GA3 (100 mg'L" or 200 mg-L" of each) on the flowering of
Doritaenopsis Happy Valentine (Phal. Otohime X Dtps. Odoriko). The first treatment
application was made at the onset of cool temperature exposure (23/18 °C) and the
second application followed 10 days later. The average number of inflorescences per

plant significantly increased by 0.2 with application of BA at 200 or 400 mg-L'I

41

compared to untreated plants. As the application rate of BA increased from 100 to 400
mg-L", the length of inflorescences decreased by 2 to 7 cm. The number and length of
inflorescences did not differ significantly between treatments with BA+GA3 and
untreated plants. Application of either BA (400 mg'L") or BA+GA3 (100 mg'L'l or 200
mg-L'l of each), resulted in 5 to 13% of plants with malformed inflorescences at
emergence and 3 to 7% of plants with blasted flower buds (Kim et al, 2000).

These investigations suggest that inflorescence initiation in Phalaenopsis is
influenced by endogenous cytokinins. Application of exogenous cytokinins (e.g., BA)
during low temperature exposure may hasten inflorescence emergence, increase
inflorescence number and decrease inflorescence length. However, the application of BA
at higher rates (400 mg-L"), or in combination with GA3, may result in undesirable
effects on flower morphology and appearance. Further research is needed to determine
the optimum rate of BA and the frequency of application required to increase

inflorescence number without compromising flower quality.

Ethylene

To our knowledge, only one study has been published on the effects of ethylene
application during inflorescence induction of Doritaenopsis. Kim et al. (2000) applied
two foliar sprays of ethephon (100, 200, or 400 mg-L") on Doritaenopsis Happy
Valentine during cool temperature exposure (23/18 °C). The application of ethephon did
not influence the number of inflorescences, diameter and length of inflorescences, or
number of flowers. However, all rates of application induced basal leaf abscission and at

400 mg-L", flower buds also abscised.

42

(Iibln

fl0u'e
al.. 2C
inhibi
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I1995a.

Gibberellins

Endogenous gibberellins (GA) could increase during inflorescence induction and
flower development in Phalaenopsis (Chen et al., 1994, 1997; Kubota et al., 1997; Su et
al., 2001b). Chen et al. (1994) reported that an injection of 40 pg of GA3 overcame the
inhibition of flowering of Phalaenopsis amabilis when plants with 8-cm inflorescences
were transferred to a high temperature regimen (3 0/25 °C, day/night). Plants treated with
GA3 and grown at the high temperature or exposed to a standard induction temperature
(25/20 °C) had significantly greater concentrations of sucrose, glucose, and fructose in
inflorescences compared to untreated plants grown at 3005 °C. Gibberellin A 3 may
function by stimulating the translocation of assimilates from source leaves to the apex of
the inflorescence, where they are required for flower development (Chen et al., 1994).
These results suggest that spraying Phalaenopsis with a growth retardant that inhibits the
GA biosynthesis pathway or the translocation of GA could inhibit inflorescence
induction.

A single application of GA3 to Phalaenopsis grown in darkness does not
substitute for the requirement of light during cool temperature inflorescence induction.
When 5 ml of GA3 (1 mM) was applied as a foliar spray to Phalaenopsis grown in
darkness at 20 °C, inflorescence emergence was not observed within 36 days (Kubota et
al., 1997). Injection of GA3 (1 , 3, or 5 rig/shoot) to plants with 2-cm to 3-cm long
inflorescences grown at 30/25 °C, caused the deformation of flowers (i.e., with narrow
sepals and petals) (Chen et al., 1997). These adverse effects were prevented by injection
of BA into shoots at the same rate as GA3, four days after the GA3 treatment. Wang

(1995a) made four weekly 50 uliter injections of GA4+7 (20,000 mg-L") into a leaf axil of

43

inflo:
2) 30
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vegetative plants grown during warm summer months, and inflorescence induction did
not occur, although a severe phytotoxic response was reported.

Su et al. (2001b) examined changes in concentrations of endogenous GAs in
inflorescences 2 to 3 cm long, following transfer to day/night treatments of: 1) 30/25 °C,
2) 30/25 °C with exogenous GA3, or 3) 25/20 °C. Plants grown at 30/25 °C contained less
biosynthetically active GA] and more inactive GAg compared to plants grown at 25/20 °C
or treated with GA3. The inhibition of inflorescence development at high temperature
may be related to low levels of active GA]. These results suggest that low temperature
could reduce conversion of active GA] to inactive GAg and thus promote inflorescence

induction (Su et al., 2001b).

Gibberellin Biosmthesis Inhibitors

To our knowledge, research on the effects GA biosynthesis inhibitors on growth
and flowering of Phalaenopsis has been published once: seedlings that were dipped
completely for five seconds in paclobutrazol (50, 100, 200, or 400 mg'L") or uniconazole
(25, 50, 100, or 200 mg.'L") before planting had a 27 to 160% decrease in inflorescence
length below the first flower, compared to control plants (Wang and Hsu, 1994).
Seedlings that were dipped in daminozide (2500, 5000, or 7500 mg'L”) were delayed in
flowering by 5 to 13 days, whereas paclobutrazol and uniconazole dips had no effect on
time to flower. The delay in flowering of Phalaenopsis with daminozide may be because
this compound is an acyclohexanedione. Acyclohexanediones function by interfering
with the later steps of GA biosynthesis, thereby inhibiting the conversion of inactive GA

precursors into active GAS (e. g., GA20—>GA1 or GA.—>GA3) (Rademacher, 2000). As

44

 

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previously stated, high levels of active GA 1 may be important during stages of
reproductive development in Phalaenopsis.

A single foliar spray application of paclobutrazol (250 or 500 mgL") or
uniconazole (100 or 200 mg°L") four weeks after inflorescence emergence, reduced
inflorescence length by 3 to 6 cm (Wang and Hsu, 1994). Flower size, number of
flowers and inflorescence diameter were not influenced by any chemical treatments in
this study. To determine the effects of application timing on inflorescence length, a foliar
application of paclobutrazol (250 mg'L") was made at: pre-emergence, emergence, or
when the inflorescence was: 1.0, 2.5., 5.0, 7.5, or 10.0 cm in length. As the application of
paclobutrazol was delayed, there was less inhibition of inflorescence elongation. For
example, application of paclobutrazol at pre-emergence reduced inflorescence length by
66%, whereas application at 10.0 cm reduced inflorescence length by 20% (Wang and

Hsu, 1994).

45

pr0<
tran

irrei
life i
by Ii,

temp.

the dz

Aim

during

calcula

ADI

 

measuri
“flak.

lIle Talc

 

TEMPERATURE

Temperature influences many biochemical, metabolic, and physiological
processes that occur during crop production, including photosynthesis, respiration,
transpiration, germination, and plant development. Plant growth is defined as an
irreversible increase in weight, height, or volume of a plant cell, tissue, organ, or whole
plant, while development refers to a series of phenological stages that occur during the
life cycle of an organism (Steininger and Pasian, 2002). Plant growth is primarily driven
by light, whereas plant development is controlled by temperature. Plant responses to
temperature are influenced by the average daily temperature and the relationship between

the day temperature and night temperature.

Average Daily Temperature
The average daily temperature (ADT) is the mathematical average temperature
during a 24-hour period. When the day and night temperature is constant, ADT can be

calculated as:
ADT = [(day temperature X hours'd") + (night temperature X hours-d")] + 24 [1]
When day or night temperature is not constant, ADT can be calculated by
measuring the air temperature with thermocouples every 10 seconds and recording hourly

averages with a datalogger. Many plant responses are a function of the ADT, including

the rate of leaf unfolding and the rate of progress towards flowering. The relationship

46

 

Figure

ofa de'

related

 

“litre r

ADI.

 

 

between ADT and a rate of development is linear between the base and optimum

temperature (Fig. 7).

 

Plant Development

4—

 

 

 

 

T T

Temperature

Figure 7. The effect of average daily temperature on rate of plant development.

The rate of development is calculated as the reciprocal of time for the completion

of a developmental stage (e. g., time to germination or flowering). The function can be

related linearly to ADT as:

l/Days = be + b] X ADT [2]

where rate (l/Days) is equal to the intercept (b0) plus the product of the slope (b1) and

ADT.

47

 

pmgl

in par
—0.7-l
Iaisu

and It

[Ottarc
range 1
Progrcs

lobe:

equario

 

del'tluj

The base temperature (Tb) is the temperature at or below which the rate of

progress towards a developmental stage is zero. Tb can be estimated as:
Tb = ‘bo/br [3]

Tb can vary considerably among plant species. For example, Tb for days to flower
in pansy (Viola Xwittrockiana Gams. ‘Delta Primrose Blotch’) was calculated to be
-0.74 °C, while in tropical orchids Zygopetalum Redvale ‘Fire Kiss’ and Phalaenopsis
Taisuco Smile, Tb for flower development from visible inflorescence to flower was 3.5
and 10.8 °C, respectively (Lopez and Runkle, 2004; Niu et al., 2000; Robinson, 2002).

The optimum temperature (Top!) is the temperature at which the rate of progress
towards a developmental event is maximal. All plants have an optimum temperature
range for growth and development. For example, the optimum temperature for the rate of
progress towards flowering in pansy and vinca (Catharanthus roseus L.) was calculated
to be 21.7 °C and :35 °C, respectively (Adams et al., 1997b; Pietsch et al., 1995).

Models relating ADT and the rate of development are only valid if the following

equation is true:
Tb S ADT S Topt [4]
When temperature exceeds Top], equation [2] becomes invalid because

developmental rate begins to decrease and the response becomes nonlinear. The rate of

development when temperature is >T0pt can be described as a negative linear function of

48

 

tenipc
andSS
hour

shock
lught
leakag

(TillZI‘. l

conch
opunu
°C.h0i
expenr
'lkdtc
florteri
(1993)
Dahhct

diuneh

fUllClloi

 

  

accuni:

flit lllr'

temperature, in which developmental rate decreases as temperature increases (Roberts
and Summerfield, 1987). The decrease in plant development at high temperature results
from a decline in normal protein synthesis, which is substituted by the synthesis of heat
shock and stress proteins (Jones, 1992). In addition to biochemical changes, exposure to
high temperature causes cellular membranes to weaken and the occurrence of ion
leakage, manifested as tissue necrosis (Jones, 1992). At the maximum temperature
(Tum), development ceases and plant death may occur.

The optimum temperature for progress towards a developmental event may not
correlate with the Optimal temperature for plant quality. For example, in vinca, the
optimum temperature for the rate of progress towards flowering was calculated to be 2:35
°C, however flower size was greatest when plants were grown at 25 °C under the
experimental light conditions (Pietsch et al., 1995). Similarly, in trailing Petunia Sylvana
‘Malve’, the rate of flowering was greatest when grown at 26 °C, but branch number at
flowering was significantly greater at 318 °C (Adams et al., 1997a). Brondum and Heins
(1993) reported that Top! for days from pinch to flower in Dahlia pinnata Cav. ‘Royal
Dahlietta Yellow’ was 22.4 °C, and as ADT decreased from 22.4 to 10 °C, flower
diameter and the number of flowers increased.

As stated previously, the time to reach a development event is primarily a
function of ADT. The term “thermal time” is used to describe the amount of
accumulated temperature that is required for the completion of a developmental event.
The thermal time required to reach a developmental event 0S at a given ADT can be

calculated as:

49

 

wher
can I
be ca

units

@

a dot.
tracki
of leaf
unfold
temper
(Saint),
Potsch
(Karlss
2001),
fungi/71

ll'iIId.

 

lb and

95:1/bl [5]

where units of thermal time are degree-hour (°C-h) or degree-day (°C-d). Thermal time
can be used by plant growers to predict the occurrence of a developmental event and can
be calculated by subtracting Tb from the ADT and accumulating the amount of time, in

units of °C-h or °C-d (Roberts and Summerfield, 1987; Steininger and Pasian, 2002).

Leaf Unfolding rate

Some floricultural crops produce a set number of leaves before the occurrence of
a developmental event. The rate of progress towards an event can be quantified by
tracking the number of leaves that unfold over a period of time (day or week). The rate
of leaf unfolding per day is a function of the average 24-h plant temperature. Leaf
unfolding rate has been modeled as a function of the average daily air or plant
temperature for several commercially important potted flowering plants: African violet
(Saintpaulia ionantha Wendl.) (Faust and Heins, 1993), begonia (Begonia Xhiemalis
Fotsch.) (Karlsson, 1992), Chrysanthemum (Dendranthema grandiflora Tzvelev.)
(Karlsson et al., 1989), cyclamen (Cyclamen persicum Mill.) (Karlsson and Werner,
2001), hibiscus (Hibiscus rosa-sinensis L.) (Karlsson et al., 1991), Easter lily (Lilium
longiflorum Thumb.) (Karlsson et al., 1988), and poinsettia (Euphorbia pulcherrima
Willd. ex Klotz) (Berghage et al., 1990).

As previously stated, the response of leaf unfolding rate to ADT is linear between
Tb and Tom. As temperature increases above Tom, the rate of leaf unfolding decreases and

at temperature below Tb, leaf unfolding rate is zero. In African violet, Tb for leaf

50

 

unfoll
and l-
tempt
acceh
repon
incree
model

°C. an

plant d
crop CE
predict
rate of 1

meDLI

actual p
the rate
using p]

Iemperu

 

,. lI

unfolding was :80 °C, Top, was between 23.0 and 25.5 °C, and Tmax was 30.8 °C (Faust
and Heins, 1993). In Easter lily ‘Nellie White’, leaf unfolding rate increase linearly as
temperature increased from 14 to 30 °C, and within this range, a 1 °C increase in ADT,
accelerated unfolding by 0.094 leaves-d’l (Karlsson et al., 1988). Berghage et al. (1990)
reported that in Poinsettia ‘Annette Hegg Dark Red’, leaf unfolding rate after pinching
increased from 0.13 to 0.25 leaves-d'l as ADT increased from 15.3 to 27.8 °C. Another
model was developed to predict the leaf unfolding rate in hibiscus: between 10 and 30
°C, an increase in 1 °C hastened leaf unfolding by 0.011 leaves-d'l (Karlsson et al., 1991).

The influence of daily light integral (DLI) is often not included as a variable in
plant development models. However, during certain conditions the DLI delivered to a
crop can influence the rate of leaf unfolding. For example, a model was developed to
predict the rate of leaf unfolding in African violet based on ADT and DLI: Tom for the
rate of leaf unfolding increased from 22.6 (0.18 leaves-d”) to 25.5 °C (0.27 leaves-d") as
the DLI increased from 1 to 10 mol-m'Z-d'l (Faust and Heins, 1993).

Although the ambient air temperature is often used in plant development models,
actual plant temperature is considered to be a more accurate measurement for predicting
the rate of a developmental process. In a leaf unfolding rate model for African violet,
using plant temperature to predict leaf development was more accurate than using air
temperature. The average deviation between the predicted and observed leaf number was
63% higher when air temperature data was used compared to plant temperature data
(Faust and Heins, 1993). Faust and Heins (1998) reported that the 24-h average shoot-tip
temperature in vinca grown at 15, 20, or 25 °C was within 2 °C of the average air

temperature, while the 24-h shoot-tip temperature of plants grown at 30 or 35 °C was

51

 

dun)
shoot
radial
vapor
1992)
and n
tempt
tempt
°C hig
umol-

tempe

Effect

 

 

always 4 to 6 °C below the average air temperature. The magnitude of deviation in
shoot-tip temperature from air temperature is influenced by the amount of incoming solar
radiation and the vapor-pressure deficit (VPD). The VPD is the difference between the
vapor pressure of air when saturated with water and the actual vapor pressure (Jones,
1992). Vapor-pressure deficit affects the amount of plant transpiration during the day
and night. For example, as VPD during the night increased from 0.5 to 3.0 kPa, shoot-tip
temperature in vinca decreased by 1.3 °C (Faust and Heins, 1998). Actual plant
temperature of African violet grown at a constant air temperature of 20 °C was almost 4
°C higher on a sunny day (5300 umoltm'z-s") and l to 3 °C lower on a cloudy day (575
umol-m’z-s"). During the night, plant temperature was 2 to 5 °C cooler than air

temperature.

Effects of Diurnal Temperature Fluctuations

The relationship between the day and night temperature can influence intemode
length, leaf and shoot orientation, chlorophyll content, lateral branching, and petiole
elongation of plants (Erwin and Heins, 1995; Myster and Moe, 1995). The term DIF is
used to describe the difference between the day temperature (DT) and night temperature

(NT) and is calculated as:

DIF = DT — NT [5]

52

\YI)

 

0/'

air
at
ten

up“

temj

 

 

 

Stem Elonggtion

The effect of DIF on plant stem elongation has been studied on many common
greenhouse crops, including begonia (Myster et al., 1997), carnpanula (Campanula
isophylla Moretti) (Moe etal., 1991), Chrysanthemum (Jacobson and Willits, 1998;
Karlsson et al., 1989), fuchsia (Fuchsia thbrida hort. ex Sieb. and Voss) (Erwin and
Heins, 1995; Maas and van Hattum, 1998), Easter lily (Erwin et al., 1989), poinsettia
(Berghage, 1989; Berghage and Heins, 1991), snapdragon (Antirrhinum majus L.) and
Zinnia (Zinnia violacea Cav.) (N eily et al., 1997). The effects of DIF on stem elongation
are not the same for all plant species. For example, in bulbous crops, such as tulip
(T ulipa thbrida L.), daffodil (Narcissus pseudonarcissus L.), and hyacinth (Hyacinthus
orientalis L.), DIF does not affect stem elongation (Erwin and Heins, 1995).

The night temperature was first suggested to influence stem elongation responses
after Went (1944) observed different rates of stem elongation in tomato (Lycopersicon
esculentum Mill.) at diumally fluctuating temperatures compared to constant ones. The
term “thermoperiodicity” was proposed after concluding the presence of two different
“processes” during the day and night, where the dark process had a much lower
temperature optimum compared to the light process (Went, 1944).

Stem elongation is promoted when the day temperature is warmer than night
temperature (positive DIF). During the opposite environmental conditions, where day
temperature is lower than the night temperature (negative DIF), stem elongation is
inhibited. In Easter lily ‘Nellie White’, intemode length increased by 382% as DIF
increased from -16 to +16 °C (Erwin et al., 1989). Berghage and Heins (1991) reported

that intemode length of the second lateral shoot in Poinsettia ‘Annette Hegg Dark Red’

53

 

incr
and

resl

e10:

the
Can

1991

GA] I

comp.

elongz
14/24

COmp;

 

I997)

€nd0c

increased by approximately 2.5 cm as DIF increased from -10 to +10 °C. In snapdragon
and zinnia, stem elongation during the vegetative stage increased by 38 and 13%,
respectively, as DIF increased from -5 to +5 °C (Neily et al., 1997).

Stem elongation responses to DIF occur primarily from changes in cellular
elongation rather than cellular division, and gibberellins (GAs) are likely involved
(Grindal et al., 1998a, 1998b; Jenson et al., 1996; Myster and Moe, 1995). A reduction in
the concentration of GA; in the plant shoot has been associated with a negative DIF in
Campanula isophylla (Jenson et al., 1996) and pea (Pisum sativum L.) (Grindal et al.,
1998a). Jenson et al. (1996) reported that in Campanula isophylla ‘Hvit’, the level of
GA; was 90% lower in plants grown at negative DIF (15/21 °C, 12-h day/12-h night)
compared to plants grown at positive DIF (21/15 °C). In pea plants grown at negative
DIF (15.5/21.5 °C, 10-h day/14-h night), the amount of GA; was 60% lower than in
plants grown at constant temperature (19.0 °C) (Grindal et al., 1998a). The reduction in
GA; corresponded with a 47% decrease in stem length of plants grown at a negative DIF
compared to a constant temperature.

The application of exogenous GAs can overcome the inhibition of stem
elongation from a negative DIF. For example, intemode elongation of begonia grown at
14/24 °C (12-h day/ l2-h night) and treated with GA; increased by 78% and 45%
compared to untreated plants grown at 14/24 °C and 19/19 °C, respectively (Myster et al.,
1997). Grindal et al. (1998b) reported that in pea ‘Torsdag’ grown at a negative DIF,
endogenous bioactive GA; is converted into inactive GAg and application of exogenous

GA; or GA3 overcame the decreased stem elongation from a negative DIF.

54

 

been d

|
manor,
examd
lateral

elongri

photol

 

intemI
I

Flour

have
llhir
(Kar

I 94.

 

Commercial growers of greenhouse crops use DIF to manage plant height and as
an alternative to the use of plant growth retarding chemicals. Mathematical models have
been developed to describe the effects of DIF on stem elongation, which assist growers in
managing and predicting stem elongation based upon environmental conditions. For
example, Berghage and Heins (1991) constructed a model to predict how DIF influenced
lateral shoot elongation after pinching of poinsettia. In Chrysanthemum, intemode
elongation was modeled based on the effects of day and night temperature,
photosynthetic photon flux, end-of-day red to far-red ratio, and the position of the

intemode on the stem (Jacobson and Willits, 1998).

Flowering Responses to Diurgal Temperature Fluctuations

The effects of day and night temperature on flower induction and development
have been studied for many species including Arabidopsis thaliana (L.) Heynh.
(Thingnaes et al., 2003), Campanula isophylla (Moe et al., 1991), Chrysanthemum
(Karlsson et al., 1989), Dendrobium crumenatum Sw. (Goh and Arditti, 1985; Went,
1944), fuchsia (Maas and van Hattum, 1998), Japaenese morning glory (Pharbitis nil
Chois.) (Reese and Erwin, 1997), and poinsettia (Berghage, 1989). In some species,
flowering is inhibited when the night temperature is excessively high. For example,
flower initiation and development of poinsettia was delayed when night temperature was
>25 °C (Berghage, 1989). Plants grown at a 29 °C night temperature and a day
temperature between 14 and 26 °C initiated flower buds that did not develop to anthesis,
while plants grown at a 29 °C day temperature and a night temperature between 14 and

26 °C developed normally (Berghage, 1989).

55

 

lHFc

Moee

°C.10I
I

posith

I
gene
nanm
ngmi
Pnno
du‘l

(Rho

 

Studies on C ampanula isophylla and Fuchsia thbrida suggest that a negative
DIF could slightly promote flower initiation and development (Myster and Moe, 1995).
Moe et al. (1991) reported that in Campanula isophylla grown at a negative DIF (15/21
°C, lO-h day/14-h night), anthesis occurred 3 to 4 days earlier than plants grown at a
positive DIF (21/15 oC). The total number of flowers and buds per plant was 24%
greater in plants grown at a negative DIF compared to a positive DIF. However, these
treatment effects may have resulted from differences in ADT between temperature
regimens. Flower bud initiation and development was observed in fuchsia ‘Dollar
Princess’ grown for 8 weeks under white or orange light at a -10 DIF (15/25 °C, l2-h
day/12-h night), while plants grown at a +10 DIF (25/15 oC) did not initiate flower buds
(Maas and van Hattum, 1998).

Research on several other species has reported the promotion of flowering by a
negative DIF. For example, Reese and Erwin (1997) observed that in Japanese morning
glory ‘Violet’, exposed to 16 day/night temperature combinations between 12 and 30 °C,
flower induction percentage was greatest at 24/30 (day/night) and 30/30 °C. However,
the duration of the day and night were not equal (8-h day/ l 6-h night) and ADT was
shown to significantly affect flower initiation. Furthermore, day and night temperature
both had a significant effect on flowering percentage in this study (Reese and Erwin,
1997). The rate of flower development in three weakly photoperiodic cultivars of rice
grown at 22/22, 26/22, 30/22, 22/26, or 22/30 °C (12-h day/12-h night) was hastened by
S 19.5 days at a negative DIF compared to a positive DIF (Yin et al., 1996). In
comparison, the rate of flower development in several strongly photoperiodic cultivars,

was hastened by 513.3 days at a positive DIF compared to a negative DIF.

56

 

BY

16!

I99
l)ll

fiorr

I99

such
I990
inhib
lfios;
in fun
Oer
Rosa

appht

 

 

A negative DIF could promote flower induction in some species by increasing the
availability of assimilates and respiration rate when night temperature is higher than day
temperature (Yin et al., 1996). Alternatively, a negative DIF could decrease the amount
of endogenous GAs (e. g., GA;) that regulate flowering in some species (Grindal et al.,
1998b; Maas and van Hattum, 1998; Myster and Moe, 1995). In pea grown at a negative
DIF, it was suggested that there was a higher rate of ZB-hydroxylation of GA; (an active
form) into GAs (an inactive form), which resulted in lower levels of GA; (Grindal et al.,

1998b)

In contrast, high levels of GA; or GA3 may inhibit floral initiation in some species
such as fuchsia (Maas and van Hattum, 1998) and rose (Rosa canina L.) (Roberts et al.,
1999). Wilkins (1985) reported that flower induction in the long-day plant fuchsia was
inhibited by application of GA under long-day treatments, while application of GA
biosynthesis inhibitors promoted flower initiation in plants grown under short days. This
information is supported by King et al. (2000), in which application of either GA;, GA3,
or GA5 inhibited flowering in fuchsia ‘Lord Byron’ grown under long days. Similarly, in
Rosa canina ‘Fe'licité et Perpétue’, flower initiation was not observed after the
application of GA; or GA3 to axillary shoots (Roberts et al., 1999).

Although studies have suggested the inhibition of flowering in a few species by
specific GAs, more commonly long-day species show a positive correlation between
increases in specific endogenous GAs and flower initiation, including Arabidopsis
(Blazquez et al., 1998; Wilson et al., 1992), Lolium temulentum L. (King et al., 2003),
and Spinacia oleracea L. (Zeevart and Gage, 1993). In a few species that require long

days or vemalization for flowering, the application of GA can substitute for inductive

57

 

 

environmental conditions (Crozier et al., 2000). In the long-day grass Lolium
temulentum, GAS is transported to the shoot apex under an inductive photoperiod, where
concentrations of GA5 increase by 100% (King et al., 2003). Evidence for GA as a floral
stimulus in Lolium temulentum is further supported by the application of exogenous GA5
and GA;, which can replace the single long day required for floral initiation. Flowering
in a majority of short—day species is not affected by the application of GAs (Michaels and

Amasino, 1999).

_I_)_i_ur£al Temperature Fluctuation Requirement

Research on the requirement of a diurnal temperature fluctuation for flower
induction has been limited (Goh and Arditti, 1985; Halevy, 1990; Powell et al., 1988;
Went, 1944). During inflorescence development in Dendrobium crumenatum, flower
buds develop and then become dormant (Goh and Arditti, 1985). The release from
dormancy and subsequent flowering is inhibited at a constant or gradually increasing
fluctuation in temperature and only occurs after a rapid decrease in temperature (Went,
1944). This response is supported by Goh and Arditti (1985) in which a 5 °C rapid drop
in temperature or a gradual cooling for 24 hours resulted in simultaneous flowering nine
days later. In nature, cool rain could create a drop in temperature that promotes
flowering of Dendrobium crumenatum. Halevy (1990) reported that Scilla autumnalis L.
and Urginea maritima L. Baker remained vegetative when grown at a constant
temperature of 10, 15, or 20 °C, while those grown at a 20 °C day and 10 °C night
flowered. The term “daily therm0periodism”, was used to describe the fluctuation

between day and night temperature for these two geophytes.

58

 

SU

u e
res
cor
C17.
trea
\VI‘IC

tern;

In .47
tught
Inaxii
rhfll
hid);
consr

.Al)l

 

 

tempk-

 

Thel

 

In Cymbidium orchids, a large positive diurnal fluctuation of 10 to 14 °C was
suggested as a requirement for flower initiation (Powell et al., 1988). Cymbidium
Astronaut ‘Radjah’ grown at 20/12, 26/12, or 26/18 °C (l4-h day/lO-h night) for 27
weeks developed a total of 3.3, 11.7, or 6.2 reproductive inflorescences per plant,
respectively. The percentage of reproductive buds was highest (61.0%) at 26/12 °C
compared to 20/ 12 °C (8.6%) and 26/18 °C (20.1%). Although flower initiation in
C ymbidium Astronaut ‘Radjah’ was greatest at 26/ 12 °C, this study did not include
treatments with a constant temperature for comparison and therefore it is unknown
whether these results are because of differences in ADT or the effects of a diumal
temperature fluctuation.

A diurnal temperature fluctuation also controls seed germination in some species.
In Aristida armata Henrard, germination was promoted at a positive fluctuating day and
night temperature compared to a constant temperature (Brown, 1987). For example, the
maximum germination percentage was 80% at a constant 20 °C, and 2 92.2% when the
ADT was 20 °C, but with a 2 5 oC +DIF. Positive fluctuating temperature treatments
with the highest germination percentages had slower rates of germination compared with
constant temperature treatments. The average time to reach 80% germination when the
ADT was 17.5, 20.0, or 22.5 °C was S 1.1 days longer at positive fluctuating

temperatures than at constant temperatures.

The Role of Day and Night Temperature

The rate of plant development is a function of the ADT (assuming Tb S ADT 5

Tom) and the effects of day and night temperature are assumed to be equal (Karlsson et

59

 

11
of

res

dei
exp
tem
nigl
ohse
.AIDI

flUCU

afier
ltas c
IUDPt
(:anll

cOnci

 

leafs
least

UEaU‘

 

 

al., 1988; Roberts and Summerfield, 1987; Steininger and Pasian, 2002). However, it has
been suggested that the transition from vegetative to reproductive growth for some
species is determined specifically by the night temperature (Berghage, 1989; Camus and
Went, 1952; Roberts, 1943; Thingnaes et al., 2003; Went, 1944). Unfortunately, in many
of the studies that have reported the role of night temperature in controlling the flowering
response, the actual plant temperature was not recorded and the environmental conditions
may not have been sufficiently controlled to provide confidence in the results. A large
deviation between air temperature and plant temperature can exist during greenhouse
experiments, affecting the interpretation of data. Furthermore, during these diurnal
temperature fluctuation studies in controlled environments, the duration of the day and
night may not have been equal (e. g., 8-h day/ l6-h night). As a result, many of the
observations and conclusions from these studies could be related to differences in the
ADT between treatments and not the specific affect of a negative or positive diurnal
fluctuation.

The role of night temperature in flowering was first suggested by Roberts (1943)
after observing that flower initiation was inhibited in several plant species when the day
was cool (13 °C) and night was warm (24 °C) compared to treatments with reversed
temperature setpoints. (The duration of the day and night was not provided in this study).
Camus and Went (1952) observed similar results in tobacco (Nicotiana tabacum L.) and
concluded that temperature during the dark period controlled stem length, leaf number,
leaf shape and color, flowering time, and final fresh weight in this species. However, at
least some of their conclusions could be attributed to differences in ADT among

treatments.

60

 

ecotj
than
night
that 1

day I

plant
IIUCII
al.. I
repor
predi
nonli
the d
CUIlIl

On III

(II ffe I

In chh
nl‘ J

 

Thingnaes et al. (2003) reported that time to flower in Arabidopsis thaliana,
ecotype Landsberg erecta (Ler), was significantly affected more by night temperature
than day temperature. However, in this study there was a significant interaction of day X
night temperature and DIF X ADT on flowering time, which challenges the conclusion
that for this Arabidopsis ecotype, night temperature controls flowering time more than
day temperature.

The rate of progress towards flowering in 24 cultivars of rice was compared in
plants grown at five constant temperatures (22, 24, 26, 28, or 32 °C) and four diumally
fluctuating temperatures (26/22, 22/26, 30/22, or 22/30 °C; 12-h day/12-h night) (Yin et
al., 1996). The effects of day and night temperature on flower development in rice were
reported to be different. For example, in comparing treatments with a similar ADT, the
predicted and observed days to floWer deviated. When the data was analyzed using a
nonlinear model, which separated the effects of the day and night temperature, Top; during.
the day was 2 to 4 °C higher than Top; during the night (Yin et al., 1996). In some
cultivars used in this study, there was an interaction between day and night temperature
on flowering, which may confound interpretation of these results.

Lepage et al. (1984) suggested that day and night temperature could have
different effects on plant development as plants advance through developmental stages.
In Chrysanthemum, there was a significant correlation between the ADT and the number
of days to visible flower bud, but during flower development, developmental rate was
controlled more by the day than night temperature. There is likely an interaction of day

temperature and irradiance during flower development, which was not considered in this

61

 

511

€.\'

Cc

R0

the
byr
Iigh
tem]
Heir

nigh

 

study. Furthermore, the actual plant temperature was not recorded during this

experiment.

Conclusion

In conclusion, these studies (Camus and Went, 1952; Lepage et al., 1984;
Roberts, 1943; Thingnaes etal., 2003; Went, 1944; Yin et al., 1996) suggest that in some
plant species, responses to temperature may not only be a function of the ADT, but also
an interaction between the day and night temperature. Separating the specific effects of
the day temperature or night temperature and thermoperiod may be further complicated
by other environmental interactions (Roberts and Summerfield, 1987). For example,
light quality, irradiance, and photoperiod have been reported to interact with diurnal
temperature fluctuations to affect stem elongation in many floriculture crops (Erwin and
Heins, 1995). Similar interactions may also exist when studying the effects of day and

night temperature on flower induction and development.

62

 

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Nihon Univ. 47:71-74.

Yoneda, K., H. Momose, and S. Kubota. 1991. Effects of daylength and temperature on
flowering in juvenile and adult Phalaenopsis plants. J. Jpn. Soc. Hort. Sci. 60:651-657.

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. 36:207-210.

Zeevaart, J AD. 1976. Physiology of flower formation. Ann. Rev. Plant Physiol. 27:321-
348.

Zeevaart, J AD. and DA. Gage. 1993. ent-kaurene biosynthesis is enhanced by long
photoperiods in the long-day plants Spinacia oleracea L. and Agrostemma gihago L.
Plant Physiol. 101 :25-29.

Zomlefer, W.B. 1994. Guide to flowering plant families. Univ. N.C. Press, Chapel Hill,
NC.

73

 

 

 

SECTION II

TEMPERATURE DURING THE DAY, BUT NOT DURING THE NIGHT,

CONTROLS FLOWERING OF TWO PHALAENOPSIS ORCHID HYBRIDS

74

Temperature During the Day, But Not During the Night, Controls Flowering of Two

Phalaenopsis Orchid Hybrids

Matthew G. Blanchard’ and Erik S. Runkle2

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

Received for publication_____. Accepted for publication . We gratefully
acknowledge funding by Michigan’s plant agriculture initiative at Michigan State
University (Project GREEEN), the Michigan Agricultural Experiment Station, The Fred
C. Gloeckner Foundation, and greenhouse growers providing support for Michigan State
University floriculture research. We also thank Arthur Cameron and Donald Garling for

their contributions to this manuscript.
1
Graduate student.

2 . . . . .
Assrstant professor and extensron specralrst, to whom reprint requests should be

addressed. E-mail address: runkleer@msu.edu

75

Introduction

Orchids are currently the second most valuable potted crop in the United States
with a total reported wholesale value of $127.6 million in 2004 (US. Department of
Agriculture, 2005). Among all of the orchid genera sold within the United States, the
genus Phalaenopsis comprises a large percentage (85 to 90%) of the potted orchid sales
(Nash, 2003) because of their ease of scheduling to meet specific market dates, high
wholesale value, and long postharvest life. In The Netherlands, Phalaenopsis were the
most valuable potted plant at Dutch flower auctions in 2004, trading 23.8 million plants
valued at €109.7 million (VBN, 2005). Taiwan currently has the largest number of
Phalaenopsis breeders and young plant growers with approximately 89 hectares in
production, producing 36 million plants in 2002 with a wholesale value of $51 million
(Fenton, 2004; Wang, 2004a).

During commercial production of Phalaenopsis, plants are often grown at a
temperature of 228 °C to inhibit flowering and maintain vegetative growth (Chen et al.,
1994; Sakanishi et al., 1980). The ability to inhibit reproductive development is
important for the production of flowering plants because it allows a crop to be accurately
scheduled for specific market dates. In addition, plants that flower before they have
reached a marketable size are often of unacceptable quality (e. g.. with few flowers and
short inflorescences), and have little or no economic value.

To promote the transition from a vegetative phase to a reproductive phase in
Phalaenopsis, Lee and Lin (1984, 1987) recommended a day/night greenhouse

temperature of 25/20 or 20/15 °C. However, to our knowledge, there is no scientific

76

literature to support the suggested requirement of a day/night temperature fluctuation for
inflorescence initiation and flowering in Phalaenopsis.

A diurnal temperature fluctuation has been reported to promote flowering in other
plant species. For example, Halevy (1990) reported that Sci/la autumnalis L. and
Urginea maritima L. Baker remained vegetative when grown at a constant temperature of
10, 15, or 20 °C, while those grown at 20/10 °C day/night flowered. In C ymbidium
orchids, a large positive diurnal fluctuation of 10 to 14 °C was suggested as a requirement
for flower initiation (Powell et al., 1988). Cymbidium Astronaut ‘Radjah’ grown at
20/ 12, 26/ 12, or 26/18 °C (14-h day/lO-h night) for 27 weeks developed a total of 3.3,

l 1.7, or 6.2 reproductive inflorescences per plant, respectively (Powell et al., 198 8).

In Phalaenopsis, a positive day/night temperature fluctuation has been shown to
increase the amount daily CO2 uptake compared to constant temperatures with a similar
average daily temperature (ADT) (Lootens and Heursel, 1998; Ota et al., 1991). Lootens
and Heursel (1998) reported that daily CO2 uptake in two Phalaenopsis hybrids was 14%
to 21% greater at 20/15 °C than at 20/20, 25/20, or 2505 °C. A significant day/night
temperature effect also existed, in which treatments with a +5 °C day/night temperature
fluctuation had a 5% to 21% greater CO2 uptake than treatments with no temperature
fluctuation. These results suggest that during inflorescence induction of Phalaenopsis, a
diurnal temperature fluctuation could promote flowering by increasing photosynthesis.

The objectives of this study were: 1) to determine if a day/night temperature
fluctuation is required for flowering and 2) to quantify how day and night temperatures

influence inflorescence initiation and flowering of two Phalaenopsis hybrids.

77

Materials and Methods
Plant Material

In July 2003, mericlones of Phalaenopsis Brother Goldsmith ‘720’ and
Phalaenopsis Miva Smartissimo x Canberra ‘450’ were transplanted into 10-cm pots in
media containing 75% fine-grade Douglas fir bark,15% medium-grade perlite, and 10%
sphagnum peat (by volume) and grown in a commercial greenhouse (Nurserymen’s
Exchange, Inc., Half Moon Bay, Calif). Plants were grown at 26 °C under a natural
photoperiod (lat. 37 °N) and a maximum photosynthetic photon flux (PPF) of 280
umol-m'z-s". On 22 Sept. 2003, 240 plants were received in East Lansing, Mich., and
were subsequently grown in a glass-glazed greenhouse at a constant temperature of 29 °C
to inhibit flowering. The photoperiod was a constant 16 h (0600 to 2200 HR) consisting
of natural daylengths (lat. 42 °N) with day-extension lighting provided by high-pressure
sodium lamps (HPS) delivering a PPF of 20 to 25 pmol-m'z-s'l at plant height [as
measured with a line quantum sensor (Apogee Instruments, Inc., Logan, Utah)]. Light
transmission was reduced using woven shade curtains (OLS 50; Ludvig Svensson,
Charlotte, NC.) and whitewash applied to the greenhouse glazing so that the maximum
PPF at plant height was 150 umol'm’z-s". A summary of plant material history is
provided in Table 1. The average leaf span of the plant material at the beginning of the
experiment was 25 to 30 cm. Leaf span was measured by extending the longest opposing
leaves to a horizontal position and then measuring the length from one leaf tip to the

Opposite leaf tip.

78

Plant Culture

Plants were irrigated as necessary with reverse osmosis water supplemented with
a water-soluble fertilizer providing (mg-L"): 125 N, 12 P, 100 K, 65 Ca, 12 Mg, 1.0 Fe
and Cu, 0.5 Mn and Zn, 0.3 B, and 0.1 Mo (Greencare Fertilizers, Chicago, 111.). In Year
2, all plants were transplanted into 15-cm pots and grown in media consisting of 33%
medium-grade Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] bark (Rexius Forest
By-Products Inc., Eugene, Ore.), 45% medium-grade chopped coconut (Coco nucifera
L.) coir (Millenniumsoils Coir, St. Catharines, Ont), 11% long fiber Canadian sphagnum
peat (Mosser Lee Co., Millston, Wis.), and 11% coarse-grade perlite (OFE Intl. Inc.,

Miami, Fla.) (by volume).

Temperature Treatments

Ten plants of each Phalaenopsis hybrid were placed in each of twelve glass
greenhouse sections with constant temperature setpoints of 14, 17, 20, 23, 26, or 29 °C,
or fluctuating day/night (l2 h/12 h) temperature setpoints of 20/14, 23/17, 26/14, 26/20,
29/17, or 29/23 °C. Temperature setpoints were maintained by an environmental
computer that controlled roof vents, exhaust fans, evaporative cooling, and heating as
needed. The photoperiod was maintained at 12 h by pulling opaque black cloth from
1700 to 0800 HR and extended with light from incandescent lamps (2 to 3 umol-m'z-s'l at
plant height). The photoperiod and skotoperiod paralleled the day and night temperature
setpoints, respectively. A vapor pressure deficit (VPD) of 0.9 kPa was maintained at
each temperature treatment by the injection of water vapor. Light transmission through

the greenhouse was reduced as previously described. The average daily light integral

79

(DLI) per four week period during the experiment was between 2.4 and 4.4 mol-m'z-d”
(Table 2).

Air temperature was measured in each greenhouse section by aspirated
thermocouples (0.127-mm type E) every 10 s and hourly averages were recorded by a
CR-lO datalogger (Campbell Scientific, Logan, Utah). Temperature control during the
experiment was within $2.0 °C of the greenhouse temperature setpoints for all treatments
in both years (Table 3).

The experiment was replicated in time beginning on 1 Dec. 2003 (Year 1) and on
26 Oct. 2004 (Year 2). In each year, plants were assigned randomly to each of the
temperature treatments and grown for 20 weeks. After completion of the first replication
until the beginning of the second replication, plants were transferred to a common glass-
glazed greenhouse with a constant temperature setpoint of 29 °C to inhibit flowering.
During that period, the photoperiod was a constant 16 h (0600 to 2200 HR) consisting of
natural daylengths with day-extension lighting provided by HPS lamps delivering a PPF
of 20 to 25 pmol'm'z-s'l at plant height. The maximum PPF through the greenhouse was

maintained at 150 umoltm'z-s'l by using woven shade curtains and external whitewash.

Data Collection

The date the first inflorescence was visible without dissection (<0.5 cm) and the
date that the first flower opened was recorded for each plant. Days to visible
inflorescence (VI), days from VI to flowering, days to flowering, VI and flowering
percentages were calculated for each treatment. The total number of visible

inflorescences and the number of flower buds and flowers on the first VI were recorded

80

for each plant. On the date of flowering, inflorescence length from emergence to the first
flower and from the first flower to the inflorescence tip was measured and the total
inflorescence length was calculated. Plants without open flowers within 20 weeks of the
onset of treatments were considered non-flowering. The duration of the experiment was
20 weeks because an inflorescence usually emerges after 3 to 5 weeks following

exposure to an inductive temperature <25 °C (Sakanishi et al., 1980).

Data Analysis

A completely randomized block design was used during each year. Data were
analyzed using SAS (SAS Institute, Cary, NC.) mixed model procedure (PROC MIXED)
and pairwise comparisons between treatments were performed using Tukey’s honest
significant difference (HSD) test. Arcsine square root transformation was performed on

percentage data before analysis.

Results

Visible Inflorescence and Flowering Percentage

Temperature significantly influenced the percentage of plants that initiated a VI
and flowered (Fig. 1). After 20 weeks, 280% of plants of both Phalaenopsis hybrids had
VI when grown at l4, 17, 20, 23, 20/14 or 23/17 °C. None of the plants were
reproductive within 20 weeks when grown at temperature setpoints of 29, 29/17 or 29/23
°C. In Phalaenopsis Miva Smartissimo x Canberra, a subset of the populations were
reproductive at temperature treatments of 26, 26/14, and 26/20 °C, with VI percentages of

10, 55, and 75%, respectively. In contrast, none of the Brother Goldsmith ‘720’ plants

81

had initiated an inflorescence within 20 weeks at temperature treatments of 26, 26/14,
and 26/20 °C, respectively. All of the Phalaenopsis Miva Smartissimo x Canberra grown
at 20, 23, and 23/17 °C flowered within 20 weeks, whereas in Phalaenopsis Brother
Goldsmith, 85% and 75% had flowered when grown at 20 and 23 °C, respectively (Table
4).

Day and night temperature had different effects on promoting flowering of both
Phalaenopsis hybrids in our study: day temperature was highly significant (P $0.001),
but night temperature was not significant (Table 5). There was a significant difference in
VI and flowering percentages among some temperature treatments with a similar ADT
(Table 6). For example, in Phalaenopsis Miva Smartissimo x Canberra grown at 23,
26/20, or 29/17 °C, VI percentage was 100, 75, and 0%, respectively. Similarly, VI
percentage of Phalaenopsis Brother Goldsmith at 23, 26/20, and 29/17 °C was 90, 0, and

0%, respectively.

Time to Visible Inflorescence and Flower

Time to VI was not significantly different in plants grown at constant or
fluctuating day/night temperature treatments with a similar ADT of 17 °C. For example,
time to VI was statistically similar when grown at 17 or 20/14 °C in both Phalaenopsis
hybrids and ranged from 32 to 45 d. The time required to reach VI was greatest in
Phalaenopsis Miva Smartissimo x Canberra and Phalaenopsis Brother Goldsmith when
grown at temperature setpoints of 14 or 26/14 °C, during both years (Table 7). There
were no significant differences in time to V1 for either hybrid grown at temperature

treatments of 17, 20, and 23 °C and time to V1 ranged from 23 to 39 d.

82

Among the treatments with flowering percentages 230% after 20 weeks, time
from VI to anthesis and total time to anthesis for both hybrids generally decreased as
ADT increased (Table 8). Phalaenopsis Miva Smartissimo x Canberra and Phalaenopsis
Brother Goldsmith plants grown at 23 °C had the shortest total time to anthesis, requiring

on average 102 and 111 d, respectively.

Number of Inflorescences and Flower Buds and Inflorescence Lengt_h

The number of inflorescences per plant in both Phalaenopsis hybrids generally
increased as ADT decreased (Table 7). For example, Phalaenopsis Miva Smartissimo x
Canberra and Phalaenopsis Brother Goldsmith had the greatest number of inflorescences
per plant when grown at 14 °C (1.5 and 1.3, respectively). In addition, the number of
flower buds on the first VI was generally greater at the cooler temperatures than at the
warmer temperatures. For example, average flower bud number of Phalaenopsis Miva
Smartissimo x Canberra grown at 26/14 °C was 2.2, while plants grown at 14 °C had on
average 6.2. In Phalaenopsis Brother Goldsmith ‘720’, flower bud number was greatest
(5.7 or 5.8) in plants grown at 14, 17, and 20/14 °C. There were no significant
differences in the number of flower buds among constant and cool day/night fluctuating
treatments <26 0C with a similar ADT for both Phalaenopsis hybrids. The total
inflorescence length at anthesis was not significantly influenced by temperature in both

Phalaenopsis hybrids (Table 8).

83

Mesophyll Cell Collapse

In Year 1, after 11 weeks at the various temperature treatments, symptoms of
mesophyll cell collapse (e.g., tan irregular depressions on the adaxial leaf surface) on
Phalaenopsis Miva Smartissimo x Canberra were observed at day/night temperatures of
20/14, 26/14, 26/20, and 29/ 17 °C. Mesophyll cell collapse was not observed in
treatments with a constant temperature setpoint or in Phalaenopsis Brother Goldsmith at

any of the temperature treatments.

Discussion

Our results indicate that Phalaenopsis does not require a day/night temperature
fluctuation for inflorescence initiation, at least in these two Phalaenopsis hybrids.
Inflorescence initiation occurred in both hybrids at constant temperatures of 14, 17, 20,
and 23 °C. The inhibition of inflorescence initiation in plants grown at a constant
temperature of 29 °C supports previous results by Sakanishi et al. (1980) in which
flowering was inhibited in Phalaenopsis grown at 28 °C. In Phalaenopsis Brother
Goldsmith, none of the temperature treatments induced 100% VI during Year 1. We
postulate that this may be at least partially attributed to plant immaturity in Year 1 for this
hybrid. Wang and Lee (1994) reported that smaller plants that have not reached
vegetative maturity may require cooler temperatures or longer exposure to initiate
inflorescences than larger, more mature plants.

The difference in VI percentage among treatments with a similar ADT indicates
that inflorescence initiation in Phalaenopsis is primarily controlled by the day

temperature, and not the ADT. Wang (2004b) reported that the ‘Lava Glow’ clone of the

84

hybrid Doritaenopsis (Phalaenopsis Buddha’s Treasure X Doritis pulcherrima) grown for
29 to 36 weeks at 25/20, 20/25, 25/15, or 15/25 °C (12-h day/12-h night) had flowering
percentages of 27, 93, 0, and 100%, respectively. These results collectively suggest that
the day and night temperature have separate effects on flowering of Phalaenopsis and
that the day temperature controls flowering. When day temperature is >26 °C,
inflorescence initiation is inhibited, while at day temperatures <26 °C, inflorescence
initiation is promoted.

At temperature treatments of 26/14 and 26/20 °C, inflorescence initiation
occurred in 55% or 75% of Phalaenopsis Miva Smartissimo x Canberra plants, but did
not occur in the hybrid Brother Goldsmith. The difference in inflorescence initiation
responses between these two Phalaenopsis hybrids could possibly be attributed to a
difference in sensitivity to temperature from their varied genetic backgrounds. The
predominate species that are in the background of Phalaenopsis Miva Smartissimo x
Canberra are Phalaenopsis amabilis (L.) Blume, Phalaenopsis aphrodite Rchb.f., and
Phalaenopsis schilleriana Rchb.f., while the predominate species in the background of
Phalaenopsis Brother Goldsmith include Phalaenopsis stuartiana Rchb.f. and
Phalaenopsis lueddemanniana Rchb.f. (Wildcatt, 2004). The upper temperature limit for
inflorescence initiation in Phalaenopsis Brother Goldsmith could be lower than that of
Miva Smartissimo x Canberra. As suggested previously, the more mature Miva
Smartissimo x Canberra hybrid may have been less sensitive to temperature than Brother
Goldsmith.

The number of inflorescences per plant and flower buds on the first VI was

greatest for both hybrids when grown at the coolest temperatures (e.g., 14, 17, or 20/14

85

°C). Lee and Lin (1984) observed a similar cool temperature response in Phalaenopsis
Dos Pueblos X Juanit, in which plants grown at 20/15 or 25/20 °C had on average 2.2 and
1.2 inflorescences per plant, respectively. In another Phalaenopsis hybrid (Phal. Taisuco
Moonriver X Phal. equestris ‘Alba’), the number of flower buds on the main axis of the
first VI generally increased from 4.6 to 9.8 as the constant average daily forcing
temperature decreased from 25.5 to 14.3 °C (Robinson, 2002).

Temperature had a significant effect on total time to anthesis of Phalaenopsis in
our study. Robinson (2002) reported that following inflorescence emergence, there is a
linear relationship between temperature and rate of development towards visible bud and
anthesis. For example in Phalaenopsis Taisuco Smile, the average time from
inflorescence emergence to anthesis decreased from 190 days to 52 days as constant ADT
increased from 14.9 to 25.7 °C.

There was a significant temperature X year interaction for several observations in
our study. The difference between years is probably a result of plant maturity; the same
plant material was used in each year and there was an increase in the average leaf span
and number of leaves in Year 2. The average days to V1 and the number of flower buds
per plant were also different between years and may be related to plant maturity. In all
treatments except 14 °C, days to V1 decreased and the number of flower buds increased
between Years 1 and 2.

A major economic challenge for the production of Phalaenopsis orchids in
temperate climates is the high cost of energy for heating a greenhouse to maintain
vegetative growth. Energy is typically the second largest greenhouse production cost for

growers located in temperate climates (Bartok, 2001). In our study, inflorescence

86

initiation was inhibited in treatments with a high day temperature setpoint (e. g., 29 °C),
even when the night temperature setpoint was cool (e.g., 17 oC). Sakanishi et al. (1980)
investigated the effects of increasing the duration of high temperature exposure when the
average night temperature was 20 °C and reported that inflorescence emergence was
inhibited when plants were exposed to 212 hours at a temperature of 28 °C each day.
These results suggest that during Phalaenopsis production, a cool night temperature
setpoint could be utilized to inhibit flowering if the day temperature setpoint is
sufficiently warm (228 °C). This production strategy could have a significant economic
impact for commercial growers because approximately 80% of the energy for heating a
greenhouse is required at night (Bartok, 2001). Further research is necessary to
determine the magnitude of high temperature and minimum daily exposure to high
temperature to inhibit flowering.

The symptoms of mesophyll cell collapse on Phalaenopsis Miva Smartissimo x
Canberra at several of the fluctuating temperature treatments may be a result of very low
inlet air temperature when the day ended and the night temperature began. At the onset
of the skotoperiod, cold air (often 50 °C) was actively drawn into the greenhouse sections
until the cooler night temperature setpoint was achieved. Symptoms of mesophyll cell
collapse were not observed on Phalaenopsis Brother Goldsmith, which could be
attributed to the genetic background of this hybrid. Mesophyll cell collapse was
previously observed on Phalaenopsis after plants were exposed to a constant temperature
of 2, 4, or 7 °C for 1 hour or more in darkness (McConnell and Sheehan, 1978). The
reported symptoms were dark brown, pitted areas on upper leaf surfaces, which were

similar to our own observations with Phalaenopsis Miva Smartissimo x Canberra.

87

Orchids exposed to low water temperature (2 to 8 0C) can also result in symptoms of
mesophyll cell collapse (Jones, 2004). However, the temperature of the irrigation water
used in our study was :20 °C.

In conclusion, a day/night fluctuation in temperature is not required for
inflorescence initiation in these two Phalaenopsis hybrids. Although time to flower is
shortest at 23 °C, the number of inflorescences and flower buds per plant was greater at
cooler temperatures. In Phalaenopsis, daily CO2 uptake was reported to increase at a
. day/night temperature fluctuation compared to constant temperatures (Lootens and
Heursel, 1998). However in our study, there was no advantage of a day/night
temperature fluctuation for flowering. For example, a cool diurnal temperature
fluctuation (e. g., 20/14 or 23/17 °C) did not reduce time to flower or enhance plant
quality (e.g., number of inflorescences or flower buds). Flowering responses were
different among some treatments with a similar ADT, suggesting that the day and night
temperature have separate effects on inflorescence induction. These results also indicate
that a high day temperature can inhibit inflorescence initiation and flowering even when
the night temperature is conducive for reproductive development. This research
information could provide commercial orchid growers with new strategies to reduce

production costs and thus increase profitability.

88

Literature Cited

Bartok, J .W. Jr. 2001. Energy conservation for commercial greenhouses. Natural
Resource, Agriculture, and Engineering Service Cooperative Extension, Ithaca, NY.

Chen, W.-S., H.-Y. Liu, L. Yang, and W.-H. Chen. 1994. Gibberellin and temperature
influence carbohydrate content and flowering in Phalaenopsis. Physiol. Plant. 90:391-
395.

Fenton, L.J. 2004. The orchid heart of Asia: A report from the Asia-Pacific orchid
conference. FloraCulture Intl. l4(2):20-23.

Halevy, AH. 1990. Recent advances in control of flowering and growth habit of
geophytes. Acta Hort. 266235-42.

Jones, S. 2004. Mesophyll cell collapse. Orchids 73:738-740.

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

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

Nash, N. 2003. Phalaenopsis primer: A beginner’s guide to growing moth orchids.
Orchids 72:906-913.

Ota, K., K. Morioka, and Y. Yamamoto. 1991. Effects of leaf age, inflorescence,
temperature, light intensity and moisture conditions on CAM photosynthesis in

Phalaenopsis. J. Jpn. Soc. Hort. Sci. 60:125-132.

Robinson, K.A. 2002. Effects of temperature on the flower development rate and
morphology of Phalaenopsis orchid. MS thesis. Mich. State Univ., East Lansing.

Sakanishi, Y., H. Imanishi, and G. Ishida. 1980. Effect of temperature on growth and
flowering of Phalaenopsis amabilis. Bul. Univ. Osaka, Ser. B. Agriculture and Biology,
Osaka (Prefecture) Daigaku. 32:1-9.

US. Department of Agriculture. 2005. Floriculture crops 2004 summary. Agr. Stat.
Board, Wash., DC.

Vereniging van Bloemenveilingen in Nederland. 2005. Annual report 2004. Association
of Dutch Flower Auctions, Leiden, The Netherlands.

Wang, Y.-T. 2004a. Flourishing market for potted orchids. FlowerTech. 7(5):]4-17.

89

Wang, Y.-T. 2004b. Effects of reversed day/night temperatures on a Doritaenopsis
hybrid orchid. HortScience 39:834 (abstr.).

Wang, Y.-T. and N. Lee. 1994. Another look at an old crop: Potted blooming orchids,
part 2. Greenhouse Grower 120(2):36-38.

Wildcatt Orchids. 2004. Wildcatt orchids September 2004 database. Wildcatt Database
Co., Ames, Iowa.

90

Table 1. Summary of production dates, container sizes, and greenhouse environmental
conditions for Phalaenopsis Brother Goldsmith '720' and Phalaenopsis Miva
Smartissimo X Canberra '450' preceding and during experimentation.

 

 

Phalaenopsis hybid
Miva
Brother Smartissimo X
Description . Goldsmith '720' Canberra '450'
Received bare-root at Nurserymen's Exchange, Inc.
(Half Moon Bay, Calif.) August 2003 July 2003

Transplanted into lO-cm potsz
Temperature: 26 °C
Photoperiod: Natural daylength (lat. 37 °N)
PPF: $280 umol-m’Z-s'I

Received at Michigan State University

(East Lansing, Mich.)
Temperature: 29 °C 22 September 2003
Photoperiod: 16 h (0600 to 2200 HR)‘
PPF: s 150 umol-m‘Z-s"

7 August 2003 10 July 2003

Transferred to temperature treatments for 20 weeks 1 December 2003

Transferred from treatments to common greenhouse
Temperature: 29 °C

Photoperiod: 16 h (0600 to 2200 HR) 19 April 2004
PPF: $150 umol-m’z-s'l
Transplanted into 15-cm pots‘” July 2004
Transferred to temperature treatments for 20 weeks 26 October 2004
Termination of experiment 15 March 2005

 

 

zIl/Itedia consisting of 75% fine-grade Douglas fir bark, 15% medium-grade perlite, and
10% sphagnum peat (by volume).
’Photosynthetic photon flux.
"Natural daylengths (lat. 42 °N) with day-extension lighting provided by high-pressure
sodium lamps (HPS) delivering a PPF of 20 to 25 umol'm‘z-s‘I at plant height.
”Media consisting of 33% medium-grade fir bark, 45% medium-grade chopped coconut
coir, 1 1% long fiber Canadian sphagnum peat, and 11% coarse-grade perlite (by volume).

91

 

Table 2. Average daily light integral (mol-m’z-d") at plant level per 4-week period during
experiment for Years 1 and 2.

4-week period

 

 

Year 1 2 3 4 5
2003 to 20042 2.4 2.6 3.5 3.8 4.1
2004 to 2005y 2.7 2.5 2.4 3.1 4.4

 

ZExperimental period from 1 December 2003 to 19 April 2004.
Experimental period from 26 October 2004 to 15 March 2005.

92

Table 3. Actual average air temperatures of each temperature treatment in Years 1 and 2.

 

 

Temperature Actual temperature (°C)
setpoint (°C) Year 1 Year 2
14/142 145/143 141/135
17/ 17 17.4/ 17.4 17.2/ 16.6
20/20 202/201 21 .0/20.4
23/23 245/226 234/218
2606 258/261 262/260
29/29 291/294 288/282
20/14 20.0/13.8 19.1/13.5
23/17 21.9/16.3 22.5/16.9
26/ 14 254/143 24.9/ 13.9
26/20 25.8/ 19.4 259/202
29/ 17 27.8/ 17.1 28.6/ 17.3
29/23 28.8/22.3 29.0/23.l

 

z12-h day/12-h night temperature.

93

Table 4. Flowering percentages for Phalaenopsis Miva Smartissimo X Canberra '450' and
Phalaenopsis Brother Goldsmith '720' after 20 weeks at constant temperature setpoints of
14, 17, 20, 23, 26, or 29 °C, and fluctuating day/night temperature setpoints of 20/14,
23/17, 26/14, 26/20, 29/17, or 29/23 °C. Data for both years were pooled for analysis.
Arcsine square root transformation was performed on data before analysis.

 

 

 

 

Temperature Flowering (%)
setpoint (°C) Brother Goldsmith Miva Smartissimo
14/142 0 0
17/17 10 10
20/20 85 100
23/23 75 100
26/26 0 10
29/29 0 0
20/14 0 20
23/17 50 100
26/ 14 0 30
26/20 0 75
29/17 0 0
29/23 0 0
Significance
*** *IIUII

Temperature

z12-h day/12-h night temperature.
Significant at P g 0.001.

94

Table 5. The effect of average daily temperature (ADT), average day temperature (DT),
average night temperature (NT), and constant temperature (CT) on visible inflorescence
(VI) percentage of Phalaenopsis Miva Smartissimo X Canberra '450' and Phalaenopsis
Brother Goldsmith '720'. Arcsine square root transformation was performed on data

before analysis.

 

 

Variable ADT DT NT CT
VI percentage
Miva Smartissimo X Canberra '450' *** *** NS Hat
Brother Goldsmith '720' ** Hut NS *u

 

N5: ”: Nonsignificant or significant at P s 0.01 or 0.001, respectively.

95

Table 6. Comparison of visible inflorescence percentage in treatments with a similar
average daily temperature for Phalaenopsis Miva Smartissimo X Canberra '450' and
Phalaenopsis Brother Goldsmith '720'. Arcsine square root transformation was
performed on data before analysis.

 

 

 

 

 

 

Temperature Visible inflorescence (%)
setpoint (°C) Miva Smartissimo Brother Goldsmith
1 7/17’2 100 95
20/14 100 95
Significance NS NS
20/20 100 85
23/17 100 80
26/14 55 0
Significance ** ***
23/23 100 90
26/20 75 0
29/17 0 0
Significance *** ***
26/26 10 0
29/23 0 0
Significance NS NS
:1 LZ-h day/12-h night temperature.

’ ’ Nonsignificant or significant at P $0.01, or 0.001 , respectively.

96

Table 7. Days to visible inflorescence (VI), number of flower buds on first VI, and
number of inflorescences per plant for Phalaenopsis Miva Smartissimo X Canberra '450'
and Phalaenopsis Brother Goldsmith ’720' after 20 weeks in temperature treatments with

 

 

 

 

210% VI.
No. of flower buds No. of
Temperature Days to V1 on first VI inflorescences
setpoint (°C) Year 1 Year 2 Year 1 Year 2 per planty
Miva Smartissimo X Canberra ‘450’

14/142 52 b" 63 a 6.2 a 5.9 a 1.5 a
17/17 39 cd 32 bed 4.0 be 6.0 a 1.4 a
20/14 45 be 38 be 4.5 b 5.2 abc 1.1 b
20/20 34 d 23 d 4.2 be 5.0 abc 1.0 b
23/17 37 cd 32 bed 3.8 bc 5.4 ab 1.] b
26/14 67 a 38 be 2.2 d 4.3 be 1.0 b
23/23 34 d 29 cd 3.9 be 4.5 be 1.0 b
26/20 53 b 40 b 3.2 cd 4.0 c 1.0 b
Significance

Temperature *** *** *** *** *IIHII

Year *** *** NS

Temperature X Year *** *** NS

Brother Goldsmith ‘720’

14/14 60 ay 5.8 ay 1.3 a
l7/l7 33c 5.8a 1.1ab
20/14 40bc 5.7a 1.0b
20/20 33 c 5.2 ab 1.0 b
23/17 43 b 4.5 b 1.0 b
23/23 36 be 4.7 b 1.0 b
Significance

Temperature *** * ***

Year NS NS NS

Temperature X Year * NS NS

 

z12-h day/12-h night temperature.
yData pooled for analysis.

"Mean separation within columns by Tukey’s honest significant difference (HSD) test at

P s 0.05.
NS: " Nonsignificant or significant at P 50.05 or 0.001, respectively.

97

Table 8. Days from visible inflorescence (VI) to flower, total days to flower, and total
inflorescence length at flower for Phalaenopsis Miva Smartissimo X Canberra '450' and
Phalaenopsis Brother Goldsmith '720' in temperature treatments with 2 30% flowering
after 20 weeks.

 

 

 

 

Days from Total Total
Temperature VI to flower days to flower inflorescence
setpoint (°C) Year 1 Year 2 Year 1 ‘ Year 2 length (cm)y
Miva Smartissimo X Canberra ‘450’
20/20’ 80 b" 89a 114b 113 b 40a
23/17 86a 81 b 123a 113b 41 a
26/14 --‘” 87 ab -- 124 a 39 a
23/23 69 d 72 c 103 c 101 c 38 a
26/20 74 c 66 d 127 a 106 be 41 a
Significance
Temperature * * * * ’1‘ 1k 11! * * 31! ’1‘ 31: NS
Year NS 11:11:31! ***
Temperature X Year *** *** NS
Brother Goldsmith ‘720’
20/20 89 a 96 a 126 ay 26 a
23/17 90 a -- 127 a 30 a
23/23 73 b 87 b 111 b 29 a
Significance
Temperature *** * *** NS
Year *IIHF *** NS
Temperature X Year * NS NS
z12-h day/12-h night temperature.
yData pooled for analysis.

"Mean separation within columns by Tukey’s honest significant difference (HSD) test at
P s 0.05.

wNot included in analysis.

NS: ” "’Nonsignificant or significant at P s 0.05 or 0.001, respectively.

98

 

,0, .. . .Brother.Goldsmithzzo_. _ H .. ...,AJ

ao-w

60 _....

4o _....

20 ......

  

Miva Smartissimo’,‘Canberra'450', ._ . B

Visible inflorescence percentage

 

 

 

a. 1 o '5 o 9 b. 1 s o 1 a
" N (L f” " r’ 1°“ $4" 16‘” at)” $9" 09""
Constant

 

Day/Night
Temperature (°C)

Figure l. Visible inflorescence percentages for Phalaenopsis Brother Goldsmith '720'
(A) and Phalaenopsis Miva Smartissimo X Canberra '450' (B) after 20 weeks at constant
temperature setpoints 14, 17, 20, 23, 26, or 29 °C, and fluctuating day/night temperature
setpoints of 20/14, 23/17, 26/14, 26/20, 29/17, or 29/23 °C. The day and night were 12
hours each. Data were pooled, for Years 1 and 2.

99

SECTION III

TEMPERATURE EFFECTS ON FLOWER IN ITIATION AND DEVELPMENT OF

TWO ODONTIODA ORCHID HYBRIDS

100

Temperature Effects on Flower Initiation and Development of Two Odontioda Orchid

Hybrids

Matthew G. Blanchard’ and Erik S. Runkle2

Department of Horticulture, Michigan State University, East Lansing, M148824

Received for publication . Accepted for publication_____. We gratefully
acknowledge funding by Michigan’s plant agriculture initiative at Michigan State
University (Project GREEEN), the Michigan Agricultural Experiment Station, The Fred
C. Gloeckner Foundation, and greenhouse growers providing support for Michigan State
University floriculture research. We also thank Arthur Cameron and Donald Garling for

their contributions to this manuscript.
1
Graduate student.

2 . . . . .
Assrstant professor and extensron specralrst, to whom reprint requests should be

addressed. E-mail address: runkleer@msu.edu

101

Introduction

The production value of potted orchids in the United States has increased by
172% in the past decade, and they are now the second-most valuable potted flowering
plant with a reported wholesale value of $127.6 million in 2004 (US. Department of
Agriculture, 2005). In 2004, 17.2 million potted orchids were sold with an average
wholesale unit value of $7.41 (US. Department of Agriculture, 2005). Among all of the
orchid genera sold within the United States, the genus Phalaenopsis comprises a large
percentage (85 to 90%) of the potted orchid sales (Nash, 2003).

The ability for commercial greenhouse growers to schedule orchids into flower
during periods of high demand (e.g., holidays) requires knowledge of the environmental
parameters that regulate flower induction. However, scientific research on growth and
development of orchids has been limited to a small number of genera. Detailed
commercial production information is only available for hybrids of the genus
Phalaenopsis (Lee and Lin, 1984, 1987; Wang, 1995).

Odontioda orchids are intergeneric hybrids that are classified into the
Odontoglossum alliance (Rittershausen and Rittershausen, 2003). These intergeneric
hybrids were first created in the early 18003 by breeders in Europe that crossed two
genera, Odontoglossum H.B.K. and Cochlioda Lindl. (Carpenter, 2000). The genus
Odontoglossum is comprised of 175 species that are native to mountainous regions (1,500
to 3,500 m) of South America, while the genus Cochlioda is comprised of only five
species that are native to the Andes Mountains (2,000 to 3,500 m) of Bolivia, Ecuador,

and Peru (Pridgeon, 2000).

102

Odontioda are sympodial epiphytic orchids and produce green pseudobulbs that
have an apical pair of long narrow leaves and a shorter pair of leaves that arise from the
base of the pseudobulb (Figure 1A) (Rittershausen and Rittershausen, 2003). Similar to
other sympodial orchid genera, inflorescence primordia are initiated in the axil of a leaf
sheath at the base of a pseudobulb (Figure 1B) (Goh et al., 1982). Odontioda hybrids
have been selected by breeders for their bright and showy flowers and are available in
many color combinations and patterns (Rittershausen and Rittershausen, 2003). They are
also appealing potted plants because of their compact growth habit (30 to 45 cm), erect-
to-arching inflorescences, and long-lasting flowers (up to 30 days) (Carpenter, 2000;
Rittershausen and Rittershausen, 2003).

Odontioda hybrids are generally considered among orchid hobbyists to perform
best at night temperatures ranging from 7 to 13 °C and day temperatures between 24 to
27 °C (Miller, 1992; Rohrl, 2005). A diurnal temperature fluctuation has also been
suggested to improve vigor and plant performance (Miller, 1992; Rohrl, 2005), although
to our knowledge there is no scientific literature to support these observations. These
cool growing temperatures suggest that Odontioda orchids could be an appealing crop to
produce in temperate climates where energy for heating is a significant greenhouse
production cost (Bartok, 2001). However, no scientific information is available on the
environmental flowering requirements for Odontioda and thus, scheduling a crop to
flower for specific market dates is not possible.

The objectives of this study were: 1) to determine how constant and fluctuating
day and night temperatures influence flower initiation and 2) to quantify how temperature

controls time from visible inflorescence to flowering in two Odontioda hybrids.

103

Materials and Methods
Plant Materia_l

In June 2003, mericloned Odontioda George McMahon ‘Fortuna’ and Odontioda
Lovely Penguin ‘Emperor’ were transplanted into 10-cm pots in media containing 75%
fine-grade Douglas fir bark,15% medium-grade perlite, and 10% sphagnum peat (by
volume) and grown in a commercial greenhouse (Nurserymen’s Exchange, Inc., Half
Moon Bay, Calif). Plants were grown at 24/18 °C (day/night) under a natural
photoperiod (lat. 37 °N) and a maximum photosynthetic photon flux (PPF) of 500
umol'm'z-s". On 22 Sept. 2003, 240 plants were received in East Lansing, Mich., and
were subsequently grown in a glass-glazed greenhouse at a constant temperature of 23
-°C. The photoperiod was a constant 16 h (0600 to 2200 HR) consisting of natural
daylengths (lat. 42 °N) with lighting provided by high-pressure sodium lamps (HPS)
delivering a PPF of 25 to 50 umol-m'z-s'l at plant height [as measured with a line
quantum sensor (Apogee Instruments, Inc., Logan, Utah)]. Light transmission was
reduced using woven shade curtains (OLS 50; Ludvig Svensson, Charlotte, NC.) and
whitewash applied to the glazing so that the maximum PPF at plant height was 300

umol-m'zs". A summary of plant material history is in Table 1.

Plant Culture

Plants were irrigated as necessary with reverse osmosis water supplemented with
a water-soluble fertilizer providing (mg°L"): 125 N, 12 P, 100 K, 65 Ca, 12 Mg, 1.0 Fe
and Cu, 0.5 Mn and Zn, 0.3 B, and 0.1 Mo (Greencare Fertilizers, Chicago, 111.). In Year

2, all plants were transplanted into media consisting of 80% medium-grade Douglas fir

104

[Pseudotsuga menziesii (Mirb.) Franco] bark (Rexius Forest By-Products Inc., Eugene,
Ore.), 10% long fiber Canadian sphagnum peat (Mosser Lee Co., Millston, Wis.), and

10% medium-grade perlite (Therm-O—Rock, Inc., New Eagle, Pa.) (by volume).

Temperature Treatments

Ten plants of each Odontioda hybrid were placed in each of twelve glass
greenhouse sections with constant temperature setpoints of 14, 17, 20, 23, 26, or 29 °C,
or fluctuating day/night (12 h/12 h) temperature setpoints of 20/14, 23/17, 26/14, 26/20,
29/17, or 29/23 °C. In Year 2, constant temperature setpoints of 26 and 29 °C and
day/night temperature setpoints of 26/14, 26/20, 29/17, and 29/23 °C were not used
because of heat stress observed at these temperatures in Year 1. Temperature setpoints
were maintained by an environmental computer that controlled roof vents, exhaust fans,
evaporative cooling, and heating as needed. The photoperiod was maintained at 12 h by
pulling opaque black cloth from 1700 to 0800 HR and extended with light from
incandescent lamps (2 to 3 umol-m"’-s’l at plant height). The photoperiod and
skotoperiod paralleled the day and night temperature setpoints, respectively. A vapor
pressure deficit (VPD) of 0.9 kPa was maintained at each temperature treatment by the
injection of water vapor. Light transmission through the greenhouse was reduced as
previously described. The average daily light integral (DLI) per four week period during
the experiment was between 3.6 and 8.2 mol-m'Z-d'l (Table 2).

Air temperature was measured in each greenhouse section by aspirated
thermocouples (0.127-mm type E) every 10 s and hourly averages were recorded by a

CR-l 0 datalogger (Campbell Scientific, Logan, Utah). Temperature control during the

105

experiment was within +2.0 °C of the greenhouse temperature setpoints for all treatments
in both years (Table 3).

The experiment was replicated in time beginning on 1 Dec. 2003 (Year 1) and on
26 Oct. 2004 (Year 2). In each year, plants were assigned randomly to each of the
temperature treatments. After completion of the first replication on 19 April 2004 and
until the beginning of the second replication, plants were transferred to a common glass-
glazed greenhouse with a constant temperature setpoint of 23 °C. The photoperiod was a
constant 16 h (0600 to 2200 HR) consisting of natural daylengths with day-extension
lighting provided by HPS lamps delivering a PPF of 25 to 50 umol-m'Z-s'l at plant height.
The maximum PPF through the greenhouse was maintained at 300 umol'm'Z-s'l as

previously described. Plants that displayed symptoms of heat stress in Year 1 were not

used in Year 2.

Data Collection

The date of first visible inflorescence (VI) without dissection (<0.3 cm) and the
date that the first flower opened was recorded for each plant. Days to V1, days from VI
to flower, days to flower, VI percentage and inflorescence abortion percentage were
calculated for each treatment. The total number of visible inflorescences and the number
of flower buds and flowers on the first VI were recorded for each plant. On the date of
flowering, flower diameter (Year 2 only) and total inflorescence length from emergence
to the tip of the inflorescence were measured. In Year 2, leaf length and pseudobulb
diameter were measured at the beginning of the experiment and at flowering and the

increase in pseudobulb diameter and leaf length were calculated. Pseudobulb diameter

106

was measured at the widest point of the pseudobulb from the outer edge of a basal leaf to
the outer edge of the opposing leaf sheath using a digital caliper. Pseudobulb diameter
and leaf length measurements for plants that did not have a VI were made after 31 weeks
in each temperature. In both years, plants that did not have a VI after 20 weeks of the
onset of treatments were considered not reproductive. In Year 2, the experimental period

was 33 weeks in order to collect flowering data.

Data AnLalvsis

A completely randomized block design was used during each year. Data were analyzed
using SAS (SAS Institute, Cary, NC.) mixed model procedure (PROC MIXED) and
pairwise comparisons between treatments were performed using Tukey’s honest
significant difference (HSD) test. Visible inflorescence percentages were analyzed using
generalized model procedure (PROC GENMOD) with a binomial distribution and logit
transformation. For each Odontioda hybrid, rates of progress for time from VI to flower
were modeled as a function of average daily temperature (ADT). Data for time from VI
to flower were converted to rates by calculating the reciprocal (l/days) and linear
regression analysis was performed using linear models procedure (PROC REG). The
intercept (b0) and slope (b;) of the regression lines were used to estimate the base
temperature (Tb = —b0/b;) and the amount of thermal time (units of degree-days) that are
required from VI to flower (°C-d" = l/b;) in each hybrid (Roberts and Summerfield,

1987).

107

Results

Plant perform_ance

During Year 1, plants of both hybrids displayed symptoms of heat stress (e.g., severe
necrosis on leaf margins and apices) when grown at constant temperature setpoints of 26,
29, and fluctuating day/night temperatures of 26/14, 26/20, 29/17, or 29/23 °C. The
percentage of plants that had a VI and days to V1 were variable among these treatments
and many inflorescences aborted within each population (Table 4). Data in these

treatments were not included in further analysis.

Visible Inflorescence Percentage

Temperature had a significant influence on the percentage of plants that initiated a
VI and developed to flowering in Odontioda George McMahon ‘F ortuna’ (Years 1 and 2)
and Odontioda Lovely Penguin ‘Emperor’ (Year 2) (Fig. 2). During Year 1,
inflorescence initiation in Odontioda Lovely Penguin ‘Emperor’ was variable and 550%
of plants initiated inflorescences in all treatments. After 20 weeks at the various
temperature setpoints, 290% of plants of Odontioda George McMahon and Odontioda
Lovely Penguin (Year 2 only) had a VI when grown at 14 and 17 °C, while 550% plants

grown at 23/17 °C had a VI during the experiment.

Time to Visible Inflorescence and Flower
In both Odontioda hybrids the average time to V1 varied among treatments (52 to
86 d) and the effect of temperature was not significant (Table 5). However, time from VI

to flower in both Odontioda hybrids decreased with increasing ADT (Fig. 3). For

108

example, as temperature increased from 14 to 23 °C, time from VI to flower in
Odontioda George McMahon decreased from 94 to 55 (1. Similarly in Odontioda Lovely
Penguin, as temperature increased from 14 to 20 °C, the average time decreased from 105
to 73 d.

The rate of progress from VI to flower was linear for both Odontioda George
McMahon and Odontioda Lovely Penguin within ADT ranges of 14.2 to 23.6 °C and
14.2 to 20.1 °C, respectively. In Odontioda George McMahon, the base temperature for
development from VI to flower was calculated as 1.8 °C and thermal time for completion
of the event was estimated at 1250 °C'd’I (Table 6). The base temperature and thermal
time from VI to flower in Odontioda Lovely Penguin was calculated to be 2.6 °C and

require 111] °C-d", respectively.

Inflorescence Chgracteristics

The number of inflorescences per plant in Odontioda George McMahon was
slightly affected by temperature and ranged from 1.0 to 1.6 inflorescences per plant
(Table 5). In Odontioda Lovely Penguin, temperature had no significant affect on the
number of inflorescences per plant. The number of flower buds on the first VI were not
significantly different among treatments and averaged 8.9 and 7.4 in Odontioda George
McMahon and Odontioda Lovely Penguin, respectively. The total inflorescence length at
flower was not significantly influenced by temperature in Odontioda George McMahon
and Odontioda Lovely Penguin and averaged 26.8 and 35.0 cm, respectively (data not

presented). The diameter of the first open flower was influenced by temperature for both

109

Odontioda hybrids and showed a significant linear decreasing trend (P $0.01) as constant

temperature increased from 14 to 23 °C (Fig. 4).

Pseudobulb Diameter and Leaf Length

Temperature had a significant influence on the increase in pseudobulb diameter
and the final pseudobulb diameter of both Odontioda hybrids (P 50.001) (Table 7). As
temperature increased from 14 to 23 °C, pseudobulb diameter showed a decreasing trend
(Fig. 5). The final pseudobulb diameter was greatest in plants grown at 14 or 17 °C and
averaged 5.4 to 6.1 cm in both hybrids. The occurrence of inflorescence initiation in all
temperature treatments was quantified based on pseudobulb diameter (Fig. 6). In
Odontioda George McMahon and Odontioda Lovely Penguin, pseudobulbs with a
diameter 23.5 and 25.0 cm, respectively, had developed a VI in 260% of plants. The
increase in leaf length and final leaf length were not significantly different among
treatments (Table 7) and final leaf lengths varied from 24.6 to 30.3 cm (data not

presented).

Discussion

In our study, a high percentage of inflorescences aborted and leaf necrosis
occurred when Odontioda orchids were grown at temperatures of 26 or 29 °C for 12 or
24 h daily. These plants were determined to be of unacceptable quality for commercial
sales. A similar response to high temperature has been reported in the ladybird orchid,
Zngpetalum Redvale ‘Fire Kiss’, where flower buds on plants transferred to ADTs of

25.4 to 28.6 °C developed necrotic lesions and aborted within 20 d (Lopez and Runkle,

110

2004). Although inflorescence initiation occurred in both Odontioda hybrids when
grown at day temperatures of 26 or 29 °C, many of the inflorescences did not
subsequently develop.

In both Odontioda hybrids, the percentage of plants that initiated a reproductive
inflorescence and developed to open flowers was greatest when grown at constant
temperatures of 14 or 17 °C. Flowering in response to low temperature has been
previously reported in other orchid genera. For example, Lopez et al. (2005) reported
that plants of Miltoniopsis Augres ‘Trinity’ had the highest flowering percentage (280%)
when grown under a 9-h photoperiod at 20 °C for four to eight weeks and transferred to
14 °C for eight to twelve weeks. In Phalaenopsis, flowering was inhibited at constant
temperatures 228 °C and exposure to temperatures 525 °C for 3 to 5 weeks was required
for inflorescence initiation (Chen et al., 1994; Sakanishi et al., 1980).

There was no advantageous effect of a diurnal temperature fluctuation on
inflorescence initiation in both hybrids compared to constant temperature treatments with
a similar ADT. For example, in Odontioda George McMahon grown at 17 or 20/14 °C,
VI percentages after 20 weeks were 95 and 70%, respectively. These results suggest that
a high day temperature (20 to 23 °C) reduced the percentage of plants that initiated an
inflorescence and developed, even when the night temperature was low (14 to 17 0C). In
Odontioda Lovely Penguin, the low inflorescence initiation observed during Year 1 may
have been attributed to plant immaturity. As with other flowering plants, a juvenility
period also exists in orchids, in which a specific stage of maturity must be reached before

plants are capable of reproductive development (Goh et al., 1982).

111

In our study, a minimum pseudobulb diameter was required for uniform
inflorescence initiation: pseudobulbs with a diameter 25.5 cm, deve10ped a VI in 93% of
plants of both Odontioda hybrids. Plants grown at the coolest temperatures (14 or 17 °C)
had the greatest increase in pseudobulb diameter and thus the greatest final pseudobulb
diameter. This suggests that temperature controls the final pseudobulb size and that
pseudobulbs must be relatively large before inflorescence initiation can occur. Ichihashi
(1997) reported that in nobile-typc Dendrobium orchids, flower initiation only occurs on
mature pseudobulbs when exposed to temperatures of 7.5 to 20 °C (Ichihashi, 1997). The
specific physiological changes that occur during pseudobulb maturation in response to
cool temperatures are unknown. However, plants of Dendrobium Maloncs required a
high specific gravity (2106 mg-ml"), dry matter content (210.5%), or both for
inflorescence initiation (Ichihashi, 1997).

The rate of inflorescence development was modeled as a function of ADT for
both Odontioda hybrids and the predicted days to flower at a given temperature was very
similar to the actual time. For example, in Odontioda George McMahon grown at an
ADT of 17.0 °C, the average time from VI to flower was 82 (1, while the model predicted
74 d (1250 °C-d"/17.0 °C). The time from VI to flower in Odontioda grown at 17 °C
was considerably longer than the estimated time for Zygopetalum Redvale ‘Fire Kiss’ (39
d), but shorter than the estimated time for several Phalaenopsis hybrids (139 d) (Lopez
and Runkle, 2005; Robinson, 2002). The average time from VI to flower in Odontioda
Lovely Penguin grown at 23 °C was 22 d greater than plants grown at 20 °C. This
suggests that constant temperatures of 23 °C may be supcroptimal for inflorescence

development in this hybrid.

112

The calculated base temperatures of Odontioda George McMahon and Odontioda
Lovely Penguin during inflorescence development were similar: 1.8 and 2.6 °C. This
estimated base temperature for Odontioda is 1.3 °C lower than the estimated base
temperature of another native South American orchid genus, Zygopetalum (Lopez and
Runkle, 2004; Pridgeon, 2000). The lower base temperature in Odontioda could be
attributed to the genetic background of these intergeneric hybrids. The predominate
species in the background of Odontioda George McMahon ‘Fortuna’ and Odontioda
Lovely Penguin ‘Emperor' is Odontoglossum crispum Lindl., which is native to high
elevations (2,200 to 3,000 m).of the Andes Mountains in Columbia (Pridgeon, 2000;

. Wildcatt, 2004). In comparison, Zygopetalum is native to mid-elevations of 300 to 1,500
m (Pridgeon, 2000).

In conclusion, Odontioda orchids should be grown at temperatures 526 °C to
avoid heat stress and inflorescence abortion. Cool constant temperatures between 14 to
17 °C can be utilized to promote both inflorescence initiation and development in these
two Odontioda hybrids. At this temperature range, pseudobulbs will attain a minimum
size required for uniform flowering. Time from inflorescence initiation to flowering is
related to the ADT and can be predicted with our model. Although time from VI to
flower was shortest at warmer temperatures, flower size decreased as temperature
increased. This information could be used by commercial orchid growers when

producing Odontioda orchids in flower for specific market dates.

113

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

Wildcatt Orchids. 2004. Wildcatt orchids September 2004 database. Wildcatt Database
Co., Ames, Iowa. .

115

Table 1. Summary of production dates, container sizes, and greenhouse environmental
conditions for Odontioda George McMahon ‘Fortuna’ and Odontioda Lovely Penguin
‘Emperor’ preceding and during experimentation.

 

 

Odontioda hybrid
George Lovely
McMahon Penguin
Description ‘Fortuna’ ‘Emperor’

 

Received bare-root at Nurserymen's Exchange, Inc.
(Half Moon Bay, Calif.) 29 October 2002 13 June 2003

Transplanted into 7.5-cm potsz
Temperature: 24/18 °C (day/night)
Photoperiod: Natural daylength (lat. 37 °N) 29 October 2002
PPF”: $500 umol-m'z-s'l

Transplanted into lO-cm pots 2 June 2003 13 June 2003

Received at Michigan State University

(East Lansing, Mich.)
Temperature: 23 °C 22 September 2003
Photoperiod: 16 h (0600 to 2200 HR)"
PPF: $300 umol°m'2°s"

Transferred to temperature treatments for 20 weeks 1 December 2003

Transferred from treatments to common greenhouse

Temperature: 23 °C .
Photoperiod: 16 h (0600 to 2200 HR) 19 Apnl 2004

PPF: $300 pmol-m‘zs‘l

Transplanted into new mediaw July 2004
Transferred to temperature treatments for 33 weeks 26 October 2004
Termination of experiment 14 June 2005

 

’Media consisting of 75% fine-grade Douglas fir bark, 15% medium-grade perlite, and
10% sphagnum peat (by volume).

yPhotosynthetic photon flux.

"Natural daylengths (lat. 42 °N) with day-extension lighting provided by high-pressure
sodium lamps (HPS) delivering a PPF of 25 to 50 umol-m‘z-s" at plant height.
wlVchia consisting of 80% medium-grade fir bark, 10% long fiber Canadian sphagnum
peat, and 10% medium-grade perlite (by volume).

116

Table 2. Average daily light integral (mohm'z-d") at plant level per 4-week period during
experiment for Years 1 and 2. The maximum photosynthetic photon flux at plant height

was 300 umol-m'z-s”.

 

 

4-week period
Year 1 2 3 4 5 6 7
2003 to 20042 3.8 4.0 5.1 6.0 6.1 --“’ --
2004 to 2005y 4.1 3.6 3.8 4.8 6.9 8.2 4.5

 

zExperimental period from 1 December 2003 to 19 April 2004.
yExperimental period from 26 October 2004 to 7 June 2005.
wData not collected.

117

Table 3. Actual average air temperatures of each temperature treatment in Years 1 and 2.

Temperature setpoint (°C)

 

 

Year 14/142 17/17 20/20 23/23 20/14 23/17
1 14.5/14.3 17.4/ 17.4 202/201 245/226 20.0/ 13.8 21 .9/ 16.3
2 14.1/13.5 17.2/16.6 21 .0/20.4 23.4/21 .8 191/135 22.5/16.9

 

z12-h day/12-h night temperature.

118

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120

Table 6. Parameters of linear regression analysis relating temperature to rate of progress
for time from visible inflorescence to flower in Odontioda George McMahon ‘Fortuna’
and Odontioda Lovely Penguin ‘Emperor’. The slope (b,) and intercept (b0) were used to
calculate the base temperature (Tb) and degree-days (°C°d").

 

Odontioda Intercept (b0) Slope (b,)
hybrid (l/days) (1/days)/°C Tb (°C) °C-d" r2

 

George McMahon -0.0014 i 0.00112 0.0008 i 0.0001 1.8 1250 0.74”
‘Fortuna’

Lovely Penguin -0.0023 i 0.0024 0.0009 i 0.0001 2.6 1111 0.56'"
‘Emperor’

 

2Standard error.
"'Significant at P 50.001.

121

Table 7. The effect of temperature on final pseudobulb diameter and leaf length, and
pseudobulb diameter increase and leaf length increase of Odontioda George McMahon
‘Fortuna’ and Odontioda Lovely Penguin ‘Emperor’. Data were collected at flower or
after 31 weeks in temperature treatments. Data for Year 2 only.

 

Pseudobulb
Pseudobulb Leaf diameter Leaf length
Odontioda hybrid diameter length increase increase
George McMahon * * NS * NS
Lovely Penguin * * NS * * NS

 

“5’ ""Nonsignif1cant or significant at P $0.05 or 0.01, respectively.

122

 

 
   

Psalm—0%;
\

 
 

Bgydobulb

  

Basal leaf

  
     

Visible /
_.iflfl9'§§£§09§/

  

B

Figure 1. Pseudobulb of an Odontioda orchid with pairs of apical and basal leaves (A)
and a visible inflorescence in the axil of a leaf sheath at the base of a mature pseudobulb

(B).

123

 

    

A

- Years 1 and 2'"

 

Visible inflorescence percentage

 

 

 

17 20 23 20/14 23/17
Temperature (°C)

Figure 2. Visible inflorescence (V I) percentages for Odontioda George McMahon
'Fortuna' (A) and Odontioda Lovely Penguin 'Emperor' (B) afier 20 weeks at constant
temperature setpoints of 14, 17, 20, or 23 °C, and fluctuating day/night temperature
setpoints of 20/14 or 23/17 °C. The day and night were 12 hours each. VI percentages
were analyzed using a binomial distribution with logit transformation. Data for
Odontioda George McMahon was pooled for Years 1 and 2. NS, *** Nonsignificant or
significant at P 50.001.

124

George McMahon 'Fortuna'

Lovely Penguin 'Empero

IJ

 

140

100 —‘

Days

40*

20-

80»-

60---

I l

A

«i-

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0.020 1-

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' ul—

 

 

 

0.000

14 16

18

20 22

24

14

I T T I

16 18 20 22

Temperature °C

24

Figure 3. Effect of temperature on time from visible inflorescence to flower (A and B)
and rate of progress to flower (C and D) in Odontioda George McMahon 'Fortuna' and

Odontioda Lovely Penguin 'Emperor'. Each symbol represents an individual plant. The
solid lines represent the regression equation using pooled data for Years 1 (Cl) and 2 (0).

Data at 23 °C for Odontioda Lovely Penguin were not included in regression analysis.
The average daily temperature was reported for treatments with a fluctuating day and
night temperature. Parameters of linear regression analysis are presented in Table 6.

125

 

7.5 // //

 

   

 

 

 

a // //
O Lovely Penguin 'Emperor'
+ George McMahon 'Fortuna'
5 age
a)
g b
=5 5.5- ...... . ............... be . ...... 00.....-
a)
g ab ab a.b
E 50.. .. ...... .. ...... ”.....-
NS
4.52 , ..... —1
4.0 i l r ’ ///A ' //// r
14 17 20 23 20/14 23/17

Temperature (°C)

Figure 4. Influence of temperature on average flower diameter in Odontioda George
McMahon ‘Fortuna’ (o) and Odontioda Lovely Penguin ‘Emperor’ (O) at constant
temperature setpoints of 14, 17, 20, or 23 °C, and fluctuating day/night temperature
setpoints of 20/14 or 23/17 °C. The day and night were 12 hours each. Mean separation
within each hybrid by Tukey’s honest significant difference (HSD) test at P 50.05. L =
linear, Q = quadratic trends; NS, **, *** Nonsignificant or significant at P £0.01 or
0.001, respectively. Data for Year 2.

126

 

 

 

 

 

 

 

 

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// //
George McMahon 'Fortuna' A ‘
6- ._
i i i
A 4- a
E
A 8
E m
3 3 3
E g .
“E, .E
g a“, 2‘ E .E-
'0 3'5
.9 E .
3 m
D _ // //
o E 1 // /
g 5 Lovely Penguin 'Emperor' B‘
a a
0. 'U 6‘ . . . . . _
a 3
E g §
LL. 0. i
+ + 5~ § ...-
4'1 .4
3.1 ...}... .—
2- “mi.
1 // //
' ' ' . // i // .
14 17 20 23 20/14 23/17

Temperature (°C)

Figure 5. Influence of temperature on final pseudobulb diameter (0) and pseudobulb
diameter increase (0) in Odontioda George McMahon ‘Fortuna’ (A) and Odontioda
Lovely Penguin ‘Emperor’ (B) at constant temperature setpoints of 14, 17, 20, or 23 °C,
and fluctuating day/night temperature setpoints of 20/ 14 or 23/17 °C. The day and night
were 12 hours each. Each symbol represents the average of 10 plants. Vertical bars
indicate standard errors about the treatments means. Data for Year 2.

127

 

100 4 _

_ - George McMahon 'Fortuna'
:1 Lovely Penguin 'Emperor'

Visible inflorescence percentage

 

 

 

 

 

 

 

 

L'—
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5

Pseudobulb diameter interval (cm)
Figure 6. Influence of pseudobulb diameter on visible inflorescence percentage in
Odontioda George McMahon ‘Fortuna’ and Odontioda Lovely Penguin ‘Emperor’.

Pseudobulb diameter was measured at flower or after 31 weeks in temperature
treatments. Data for Year 2.

128

APPENDICES

129

APPENDIX A

EFFECTS OF DAILY LIGHT INTEGRAL ON GROWTH AND FLOWERIN G OF

POTTED PHALAENOPSIS ORCHIDS

130

Introduction

Orchids are currently the second most valuable potted crop in the United States
with a total reported wholesale value of $127.6 million in 2004 (US. Department of
Agriculture, 2005). Among all of the orchid genera sold within the United States, the
genus Phalaenopsis comprises a large percentage (85 to 90%) of the potted orchid sales
(Nash, 2003) because of their ease of scheduling to meet specific market dates, high
wholesale value, and long postharvest life. In The Netherlands, Phalaenopsis were the
most valuable potted plant at Dutch flower auctions in 2004, trading 23.8 million plants
valued at €109.7 million (VBN, 2005). Taiwan currently has the largest number of
Phalaenopsis breeders and growers with approximately 89 hectares in production,
producing 36 million plants in 2002 with a wholesale value of $51 million (Fenton, 2004;
Wang, 2004). I

The commercial production of Phalaenopsis consists of two basic phases: a
vegetative phase and a reproductive phase. During the vegetative phase, Phalaenopsis
plants are grown at temperatures 228 °C to inhibit flowering and maintain vegetative
growth (Chen et al., 1994; Sakanishi et al., 1980). To promote the transition from a
vegetative phase to a reproductive phase in Phalaenopsis, a day/night greenhouse
temperature of 25/20 or 20/15 0C has been recommended (Lee and Lin (1984, 1987).

The effects of irradiance on Phalaenopsis have been described for both the
vegetative and reproductive production phases (Konow and Wang, 2001; Wang, 1995,
2004). Konow and Wang (2001) reported that plants of Phalaenopsis Atien Kaala grown
under a maximum photosynthetic photon flux (PPF) of 75, 125, or 320 umol-m'2-5'l for

52 weeks had average fresh weights of 17, 36, and 61 g, respectively. Information is also

131

available on how irradiance influences the reproductive phase of Phalaenopsis
production. Wang (1995) reported that plants grown at 20/15 °C day/night with a 12-h
photoperiod and a constant daily light integral (DLI) of 2.6 or 6.9 molm'z-d'l initiated
inflorescences after 34 and 28 d, respectively. Plants grown under 0 or 0.35 mol-m'z-d‘l
did not initiate inflorescences within 6 weeks (Wang, 1995).

The recommended irradiance for vegetative grth of Phalaenopsis is relatively
low (100 to 300 umol~m'2-s") (Wang, 2004). However, to our knowledge, the effect of
light intensity during the vegetative phase on subsequent flowering has not been reported.
The objective of this study was to quantify the effects of DLI during the vegetative phase
on vegetative growth and subsequent flowering of four Doritaenopsis and Phalaenopsis

orchid hybrids.

Materials and Methods
Plant Material

On 2 Nov. 2004, clones of three bare-root immature Phalaenopsis hybrids (Pink
Twilight ‘ 173’, Sharon Bay ‘ 163’, and Brother Showpiece) and one Doritaenopsis hybrid
(Dtps. White Castle X Phal. Moon World) ‘717’ were received in East Lansing, Mich.,
from a commercial greenhouse (Floricultura Orchidaceae B.V., Heemstede, Holland).
The initial average leaf span of the plant material was 21 to 27 cm. Leaf span was
measured by extending the longest opposing leaves to a horizontal position and then
measuring the length from one leaf tip to the opposite leaf tip. Plants were planted into
1 1.5-cm pots in media consisting of 33% medium-grade Douglas fir [Pseudotsuga

menziesii (Mirb.) Franco] bark (Rexius Forest By-Products Inc., Eugene, Ore.), 45%

132

medium-grade chopped coconut (C oco nucifera L.) coir (Millenniumsoils Coir, St.
Catharines, Ont.), 11% long fiber Canadian sphagnum peat (Mosser Lee Co., Millston,
Wis.), and 11% coarse-grade perlite (OFE Intl. Inc., Miami, Fla.) (by volume). Plants
were grown in a glass-glazed greenhouse at a constant temperature of 28 °C to inhibit
flowering. The photoperiod was a constant 16 h (0600 to 2200 HR) consisting of natural
daylengths (lat. 42 °N) with day-extension lighting provided by high-pressure sodium
lamps (HPS) delivering a PPF of 20 to 25 umol-m’z-s'l at plant height [as measured with
a line quantum sensor (Apogee Instruments, Inc., Logan, Utah)]. Light transmission was
reduced using woven shade curtains (OLS 50; Ludvig Svensson, Charlotte, NC.) and
whitewash applied to the glazing so that the maximum PPF at plant height was 150

pmol-m‘z-s". A summary of plant material history is provided in Table 1.

Daily Light Integral Treatments

On 23 Nov., 2004, 15 plants of each hybrid were transferred to a glass-glazed
greenhouse with three DLI treatments created using woven shade curtains (OLS 30 and
OLS 50; Ludvig Svensson) with different light transmission values and varying
irradiances from HPS lamps (Fig. 1). The photoperiod was a constant 14 h (0600 to 2000
HR) consisting of natural daylengths with lighting provided by HPS lamps delivering a
maximum PPF of 60 umol-m‘z-s'l at plant height. Plants were grown at a constant
temperature of 28 °C and a vapor-pressure deficit (VPD) of 21 .0 kPa was maintained by
the injection of water vapor.

After 20 weeks, 12 of the largest plants of each hybrid were transferred to a

common greenhouse with a temperature setpoint of 23 °C to induce flowering. The

133

photoperiod was 16 h (0600 to 2200 HR) consisting of natural daylengths with lighting
provided by HPS lamps delivering a PPF of 20 to 25 umol-m’z-s'l at plant height. Light
transmission through the greenhouse was reduced so that the maximum PPF at plant

height was 150 pmol°m'2-s".

Air TemperaturL and Plant Culture

Air temperature was measured in each greenhouse section by aspirated
thermocouples (0.127-mm type E) every 10 s and hourly averages were recorded by a
CR-lO datalogger (Campbell Scientific, Logan, Utah).

Plants were irrigated as necessary with reverse osmosis water supplemented with
a water-soluble fertilizer providing (mg-L'l): 125 N, 12 P, 100 K, 65 Ca, 12 Mg, 1.0 Fe

and Cu, 0.5 Mn and Zn, 0.3 B, and 0.] Mo (Greencare Fertilizers, Chicago, 111.).

Data Collection

Light intensity under each treatment was measured using a quantum sensor (LI-
COR, Inc., Lincoln, Nebr.) located at plant level. The calculated average DLIs during the
20-week period were 2.5i0.9, 5.5i1.8, and 9.8-1:29 mol'm'z-d'l (Table 2). Plant leaf span
from opposing leaf tips were measured and the number of leaves were recorded at the
beginning of the experiment and after 20 weeks under each DLI treatment and the
increase in leaf span and number of leaves were calculated. The ratio of variable to
maximal chlorophyll fluorescence (F v/Fm) was measured for each plant at 20 weeks using
a portable chlorophyll fluorometer (Plant Efficiency Analyzer, Hansatech Instruments

Ltd., Norfolk, England). Measurements were made between 1400 and 1600 HR. For

134

each plant, the center of the most recently matured leaf was selected and the adaxial
surface was clipped using the manufacturer’s plastic/foam clips. Leaves were dark
adapted for 15 min before measurements were recorded.

After transfer to a common greenhouse for forcing, the date of first visible
inflorescence (VI) without dissection (<0.5 cm) and the date that the first flower opened
was recorded for each plant. Days to V1, days from VI to flowering, days to flowering,
VI percentage, inflorescence abortion percentage, and flowering percentage were
calculated for each treatment. On the date of flowering, the total number of flower buds
and flowers were recorded for each plant and the total inflorescence length from
emergence to the tip of the inflorescence was measured. Plants that did not have a VI
after 10 weeks of forcing at 23 °C were considered not reproductive. Ten weeks was
used because in other Phalaenopsis hybrids grown at 23 °C, the average time to VI was
29 to 39 d (Blanchard, 2005). Light intensity was measured as described above and the

calculated average DLI during forcing was 3.8i1.5 mol-m'z-d-l (Table 2).

Data Analysis

A completely randomized block design was used during each year. Data were
analyzed using SAS (SAS Institute, Cary, NC.) mixed model procedure (PROC MIXED)
and pair-wise comparisons between treatments were performed using Tukey’s honest
significant difference (HSD) test. Visible inflorescence, inflorescence abortion
percentage, and flowering percentage were analyzed using generalized model procedure
(PROC GENMOD) with a binomial distribution and logit transformation. Pair-wise

comparisons for percentage data were performed using chi—square (352) test.

135

Results
Vegetative Growth and Chlorophyll Fluorescence

After 20 weeks under the three DLI treatments, all hybrids except Phalaenopsis
Brother Showpiece grown under a low DLI (2.5 mol-m'z-d'l) had a significantly greater
increase in leaf span compared to plants grown under the highest DLI (9.8 mol-m'z-d'l)
(Figure 2). For example, in Phalaenopsis Pink Twilight, the average leaf span increase
of plants grown under 2.5, 5.5, or 9.8 mol'm'z'd'l was 4.8, 3.1, and 3.0 cm, respectively.
The average increase in number of leaves per plant ranged from 0.5 and 1.8 and was not
significantly different among DLI treatments (data not presented)

Chlorophyll fluorescence was influenced by DLI and plants of all hybrids grown
under a low DLI had a significantly higher F v/Fm ratio compared to plants grown under
the highest DLI (9.8 mol‘m'Z-d") (Fig. 3A). The average Fv/Fm ratio for all four hybrids

grown under 2.5, 5.5, or 9.8 mol-m'z-d'l was 0.78, 0.71, and 0.65, respectively.

Visible Inflorescence, Inflorescence Abortion. and Flowering Percentage

After 10 weeks following transfer to a common greenhouse for flower induction,
25 8% of all hybrids except Phalaenopsis Pink Twilight had a VI when previously grown
for 20 weeks at an average DLI of 2.5 molm'z-d'l (Table 3 and Fig. 3B). Inflorescence
initiation percentage of plants grown under an average DLI of 5.5 mol-m'z-d'l varied
among hybrids and ranged from 17% to 75%. All hybrids except Phalaenopsis Pink
Twilight grown for 20 weeks at 9.8 mol-m'Z-d'l had a significantly lower inflorescence

initiation percentage (550%) compared to plants grown under 2.5 mol'm'z-d'l.

136

The percentage of plants with an inflorescence that aborted was not affected by
DLI; however there was a significant difference among hybrids (Table 3). Plants of
Phalaenopsis Pink Twilight had the greatest inflorescence abortion percentages (8% to
33%) among all hybrids. All hybrids except Phalaenopsis Pink Twilight had a lower
flowering percentage when grown for 20 weeks at 9.8 mol'm'z-d'l compared to plants

grown under 2.5 mol-m'z-d'l.

Flowering Characteristics

The average time to VI, time from VI to flower, and total time to flower was not
influenced by DLI; however there was a significant difference among hybrids (Table 4).
Plants of Phalaenopsis Brother Showpiece had the shortest time to V1 (25 or 26 (1), while
plants of Phalaenopsis Sharon Bay required the longest time (42 to 45 d). Time from VI
to flower was greatest in Phalaenopsis Brother Showpiece (72 d), while in Doritaenopsis
(Dtps. White Castle X Phal. Moon World) ‘717’, time from VI to flower decreased by
313 days. The number of flowers per plant varied between 2.9 to 4.8 and was not
significantly different among any DLI treatment or hybrid. In all hybrids, total

inflorescence length was not influenced by DLI and ranged from 20.1 to 32.6 cm.

Discussion

Phalaenopsis plants grown under a low DLI (2.5 mol-m'z'd'l) during vegetative
growth had an increased leaf span and higher F v/F m ratio than plants grown under a DLI
of 9.8 mol-m'z-d". Chlorophyll fluorescence can provide information on the state of

photosystem II, which is the most susceptible component of the photosynthetic apparatus

137

to damage from excess quantities of light (Maxwell and Johnson, 2000). Thus,
chlorophyll fluorescence values can be used to estimate the photosynthetic efficiency of a
plant (Maxwell and Johnson, 2000). In our study, plants grown under 9.8 mol-m'Z-d'l had
a consistently lower F V/F m ratio than plants grown under 2.5 mol-m'z-d']. These results
suggest that plants grown under 9.8 mol-m'z-d'l were exposed to high irradiance levels
above the light saturation point, resulting in photoinhibition. Lootens and Heursel
(1998) determined that the saturating PPF for two Phalaenopsis hybrids grown at 20 °C
was 180 umol-m'z-s'l. At a temperature of 25 or 30 °C, the saturating PPF was not found
at the highest irradiance measured, 300 umol-m'zs'l. Lee (2000) reported that
photoinhibition occurs in Phalaenopsis when grown under a PPF above 400 umol-m'zs'
'. In our study, plants grown under the high DLI treatment were exposed to a maximum
PPF of 900 umol-m'zs".

The greater inflorescence initiation percentages among plants grown under an
average DLI of 2.5 mol'm'z-d'l suggest that higher DLI values may not be advantageous
for subsequent forcing. The relatively low flowering percentages among all treatments
indicate that the populations of plants were not fully mature when transferred to 23 0C for
forcing, regardless of the average DLI. Runkle et al. (2005) recommended that for
uniform inflorescence initiation and flowering of Phalaenopsis, plants should have a
minimum average leaf span of 25 cm. In our study, the average leaf spans of
Doritaenopsis (Dtps. White Castle >< Phal. Moon World) ‘717’, Phalaenopsis Pink
Twilight ‘ 173’, Phalaenopsis Sharon Bay ‘ 163’, and Phalaenopsis Brother Showpiece at

the beginning of forcing were 31.8 i 3.5, 24.5 :t 2.4, 26.3 i 2.4, and 24.6 i 3.4 cm,

138

respectively. The percentage of plants that were reproductive would have likely
increased if the duration of vegetative growth at 28 °C was extended.

We observed that Doritaenopsis and Phalaenopsis hybrids had different
inflorescence initiation percentages when compared to other hybrids grown under the
same DLI. This variation among hybrids may be attributed to differences in plant
maturity or their varied genetic backgrounds.

In this study, several flowering characteristics were not significantly affected by
DLI: time to VI, time from VI to flower, total time to flower, number of flowers, and
inflorescence length. In other greenhouse crops, light quantity has been shown to have a
significant effect on floral evocation and flower development (Moe, 1997). Pramuk and
Runkle (2005) studied the effects of DLI during the seedling stage of several bedding
plants on subsequent flowering under a common DLI. Seedlings grown under an average
DLI of 14.2 mol-m'Z-dl flowered 4 to 12 d earlier than seedlings grown under 4.1 mol-m'
2d". However, plant quality (e. g., flower bud number and plant shoot dry weight) at first
flowering generally decreased as the seedling DLI increased (Pramuk and Runkle, 2005).
In our study, differences in flowering characteristics among DLI treatments were not
observed and these results may be confounded by immaturity of the plant material.

In summary, our results indicate that during vegetative production of
Phalaenopsis, plants grown under a low DLI (2.5 mol-m'z-d'l) will have a greater
increase in leaf span and higher photosynthetic efficiency than plants grown under a
higher DLI (9.8 mol-m'z-d'l). In general, plants grown under a lower DLI during
vegetative growth will also have higher flowering percentages during subsequent forcing.

Several characteristics (e.g., time to V1) in this study were not significantly influenced by

139

DLI and may be related to the immaturity of plant material. Further experiments need to

be performed to validate our results before recommendations can be made.

140

Literature Cited

Blanchard, MG. 2005. Effects of temperature on growth and flowering of two
Phalaenopsis and two Odontioda orchid hybrids. MS thesis. Mich. State Univ., East
Lansing.

Chen, W.-S., H.-Y. Liu, L. Yang, and W.-H. Chen. 1994. Gibberellin and temperature
influence carbohydrate content and flowering in Phalaenopsis. Physiol. Plant. 90:391-
395.

Fenton, L.J. 2004. The orchid heart of Asia: A report from the Asia-Pacific orchid
conference. F loraCulture Intl. l4(2):20-23.

Konow, E. and Y.-T. Wang. 2001. Irradiance levels affect in vitro and greenhouse
growth, flowering, and photosynthetic behavior of a hybrid Phalaenopsis orchid.
HortScience 1262531 :536.

Lee, N. 2000. Phalaenopsis orchid light requirements. HortTechnology 10:43 0.

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

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

Lootens, P. and J. Heursel. 1998. Irradiance, temperature, and carbon dioxide enrichment
affect photosynthesis in Phalaenopsis hybrids. HortScience 33:1183-1185.

Maxwell, K. and N. Johnson. 2000. Chlorophyll fluorescence— a practical guide. J. Expt.
Bot. 51 2659-669.

Moe, R. 1997. Physiological aspects of supplementary lighting in horticulture. Acta Hort.
418: 17-23.

Nash, N. 2003. Phalaenopsis primer: A beginner’s guide to growing moth orchids.
Orchids 72:906-913.

Pramuk, L. and ES. Runkle. 2005. Photosynthetic daily light integral during the seedling
stage influences subsequent growth and flowering of Celosia, Impatiens, Salvia, T agetes,

and Viola. HortScience 40: 1 336-1 339.

Runkle, E., Y.-T. Wang, M. Blanchard, and R. Lopez. 2005. The orchid grower.
Greenhouse Grower 23(8):64-70.

I41

Sakanishi, Y., H. Imanishi, and G. Ishida. 1980. Effect of temperature on grth and
flowering of Phalaenopsis amabilis. Bul. Univ. Osaka, Ser. B. Agriculture and Biology,
Osaka (Prefecture) Daigaku. 32:1-9.

US. Department of Agriculture. 2005. Floriculture and nursery crops situation and
outlook yearbook. Economic Research Service, Washington DC.

Vereniging van Bloemenveilingen in Nederland. 2005. Annual report 2004. Association
of Dutch Flower Auctions, Leiden, The Netherlands.

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

Wang, Y.-T. 2004. Flourishing market for potted orchids. FlowerTech. 7(5):14-l 7.

142

Table 1. Summary of production dates, container sizes, and greenhouse environmental
conditions for Doritaenopsis (Dips. White Castle >< Phal. Moon World) ‘717’,
Phalaenopsis Pink Twilight ‘ 173’, Phalaenopsis Sharon Bay ‘ 163’, and Phalaenopsis
Brother Showpiece preceding and during experimentation.

Description Date

 

Grown at F loricultura Orchidaceae B.V. (Heemstede,
Holland) in community trays

Received bare-root at Michigan State University

(East Lansing, Mich.) 02 November 2004
Transplanted into 11.5-cm potsz
Temperature: 28 C 02 November 2004

Photoperiod: 16 h (0600 to 2200 HR)‘
PPF’: s 150 umol'm'Z-s‘I

Transferred to three daily light integral (DLI) treatments
for 20 weeks:
Calculated average DLIs: 2.5 :t 0.9, 5.5 :t 1.8, and
9.8 i 2.9 moi-mad" 23 November 2004
Temperature: 28 °C
Photoperiod: 14 h (0600 to 2000 HR)"
Vapor-pressure deficit (VPD): z 1.0 kPa

Transferred to a common greenhouse for flowering
Temperature: 23 °C
Photoperiod: 16 h (0600 to 2200 HR)x 13 April 2005
PPF: $150 umol-m'Z-s"
Calculated average DLI: 3.8 i 1.5 mol-m'z-d'l

Termination of experiment 8 August 2005

 

zMedia consisting of 33% medium-grade fir bark, 45% medium-grade chopped coconut
coir, 11% long fiber Canadian sphagnum peat, and 11% coarse-grade perlite (by volume).
yPhotosynthetic photon flux.

“Natural daylengths (lat. 42 °N) with day-extension lighting provided by high-pressure
sodium lamps (HPS) delivering a PPF of 25 to 50 umol-m‘Z-s‘l at plant height.

143

Table 2. Average daily light integral (mol-m'z-d") at plant level per month during

vegetative and forcing periods.

 

Light quantity Vegetative perioau
treatment Dec. Jan. Feb. March April Average
Low 1.9 2.5 2.7 2.9 2.8 2.5 i 0.9
Medium 4.1 4.9 5.6 6.8 7.1 5.5 i 1.8
High 6.9 9.0 10.0 12.5 11.3 9.8 :t 2.9

Forcing periody

April May June July Aug. Average
5.9 3.0 3.4 4.0 3.8 3.8 :t 1.5

 

223 November 2004 to 12 April 2005.

y13 April 2005 to 8 August 2005.

144

Table 3. Visible inflorescence percentage, inflorescence abortion percentage, and
flowering percentage for Doritaenopsis (Dtps. White Castle x Phal. Moon World) ‘717’,
Phalaenopsis Pink Twilight ‘ 173’, Phalaenopsis Sharon Bay ‘ 163’, and Phalaenopsis
Brother Showpiece following 20 weeks of vegetative growth at 28 °C under an average
daily light integral (DLI) of 2.5, 5.5, or 9.8 mol'm‘z-d". Plants were subsequently forced
at 23 °C under an average DLI of 3.8 mol-m'Z-d". Percentages were analyzed using a
binomial distribution with logit transformation.

 

 

Average DLI Visible Inflorescence
(mol-m‘2°d") inflorescence (%) abortion (%) Flowering (%)
Dtps. White Castle
2.5 58 25 33
5.5 33 0 33
9.8 17 0 17
Phal. Pink Twilight
2.5 42 8 33
5.5 58 33 25
9.8 67 17 50
Phal. Sharon Bay
2.5 83 o ' 83
5.5 17 0 17
9.8 33 0 33
Phal. Brother Showpiece
2.5 67 0 67
5.5 75 0 75
9.8 17 0 17
Significance
Hybrid NS ** NS
DLI ** NS *
Hybrid >< DLI ** NS **

 

NS' " ” Nonsignificant or significant at P s 0.05 or 0.01, respectively.

145

Table 4. Days to visible inflorescence (V 1), days from VI to flower, total days to flower,
number of flowers, and total inflorescence length for Doritaenopsis (Dtps. White Castle X
Phal. Moon World) ‘717’, Phalaenopsis Pink Twilight ‘ 173’, Phalaenopsis Sharon Bay

‘ 163’, and Phalaenopsis Brother Showpiece following 20 weeks of vegetative grth at
28 °C under an average daily light integral (DLI) of 2.5, 5.5, or 9.8 mol-m'z-d". Plants
were subsequently forced at 23 °C under an average DLI of 3.8 mol°m'2-d".

 

 

 

Total
Average DLI Days to Days from Total days Flower inflorescence
(mol-m'2°d") V1 V1 to flower to flower no. length (cm)
Dtps. White Castle
2.5 44 a2 60 d 99 abc 3.0 a 24.9 ab
5.5 39 ab 59 d 98 be 3.0 a 26.0 ab
9.8 37 abc 59 d 95 c 3.0 a 26.4 ab
Phal. Pink Twilight
2.5 31 bcd 66 be 98 be 3.0 a 20.1 b
5.5 32 be 66 bed 96 c 3.3 a 22.5 ab
9.8 28 cd 70 ab 98 bc 3.3 a 21.7 ab
Phal. Sharon Bay
2.5 44 a 63 ed 107 a 4.0 a 30.4 ab
5.5 45 a 62 ed 106 ab 3.5 a 27.1 ab
9.8 42 a 63 ed 105 abc 4.8 a 32.6 a
Phal. Brother Showpiece
2.5 25 d 72 a 97 c 2.9 a 21.3 ab
5.5 26 d 72 a 97 be 3.3 a 22.1 ab
9.8 25 cd 72 a 98 be 3.0 a 22.5 ab
Significance
Hybrid *** *** ** NS **
DLI NS NS NS NS NS
Hybrid X DLI NS NS NS NS NS
’Mean separation within columns by Tukey’s honest significant difference (HSD) test at

’ Nonsignificant or significant at P $0.01 or 0.001, respectively.

146

24

 

22- -

20 - —-- High DLI ii -
------- Medium DLI 1 ’0'
Low DLI

16: ii 'ii'li‘i -
14- Ill'llll

10 d .9. .121. ”L - '\" .~._-I|132.1 W" -.
e-i ‘" ’ ""- "iv-"i 1'11 - -. v..-

181

 

E~
.. —-.
.0
"’
I. —I—
I“.

Average DLI (mol-m'z-d")

' " I' -v 5': :1:2-' :::: 2; . ..., 5'2;
.- .. . \; . ....:..... P}. :2: :5 3:5 .: {2.3.5.51 E E: d
6 1"“! - r'-.:"--'"-.-°"- '2 as =. "25
4 d :3: .... "...... -,“,-'. 2......“ .._- ...": . 2...... , ..."... ..~ . ...... :5 1:3. .. -

21"” -

 

 

 

Dec. Jan. Feb. March April
Month

Figure 1. Daily light integral (DLI) at plant level under each light treatment during a 20-
week period of vegetative growth at 28 °C.

147

 

       
  

7
. + Dtps. White Castle
—-I:i- Phal. Pink Twilight
6 ‘ ' -9- Phal. Sharon Bay
, —O— Phal. Brother Showpiece .
8 5 LO. Q.
a.)
8
2 4 - __
o
.E
g 3 _ ._
o.
m
“a
a, 2 _. ...... .. .
_. .1
1 .1 .—l
O l I T

 

 

 

2.5 5.5 9.8

Figure 2. Average leaf span increase of Doritaenopsis (Dtps. White Castle X Phal. Moon
World) ‘717’, Phalaenopsis Pink Twilight ‘ 173’, Phalaenopsis Sharon Bay ‘ 163’, and
Phalaenopsis Brother Showpiece under an average daily light integral (DLI) of 2.5, 5.5,
or 9.8 mol-m'z-d'1 for 20 weeks at 28 °C. Mean separation within hybrids by Tukey’s
honest significant difference (HSD) test at P 50.05. L = linear, Q = quadratic trends; NS,
*, **, *** Nonsignificant or significant at P £0.05, 0.01, or 0.001, respectively.

148

0.9

 

0.8 ~

0.7 ~-

06—-

Fv/Fm

0.5...

0.4 ~

 

 

 

0.3 -
DLI Treatments
8°“ ' - 25molm 2“d

 

 

 

 

 

8, {jig/jg...» 5. 5 mol' m 2d1
E 70- i:]9.-‘2"8molmd
8
2 60-'
a)
o.
8 50-
c
8
g 407
8
E 30‘
2
.o
:a 20‘
>
10"
0..

Dtps. White Castle Phal. Pink Twilight Phal. Sharon Bay Phal. Showpiece
Doritaenopsis or Phalaenopsis hybrid

Figure 3. Chlorophyll fluorescence ratios (A) and visible inflorescence (VI) percentages
(B) for Doritaenopsis (Dtps. White Castle X Phal. Moon World) ‘717’, Phalaenopsis
Pink Twilight ‘ 173’, Phalaenopsis Sharon Bay ‘ 163’, and Phalaenopsis Brother
Showpiece2 following 20 weeks under an average daily light integral (DLI) of 2. 5, 5. 5, or
9. 8 mol m 2cl". Error bars represent 95% confidence intervals. VI percentages were
analyzed using a binomial distribution with logit transformation and pair-wise
comparisons within hybrids by chi- -square (x2) test at P <0. 05.

149

APPENDIX B

EFFECTS OF TEN ORCHID MEDIAS ON PH, WATER-HOLDING CAPACITY,

AND PERFORMANCE OF THREE ORCHID GENERA

150

Introduction

Orchids are currently the second most valuable potted crop in the United States
with a total reported wholesale value of $127.6 million in 2004 (USDA, 2005a). Since
1996, when the United States Department of Agriculture (USDA) began collecting data
for wholesale value of potted orchids, sales have increased by 172% (USDA, 2005b). In
2004, 17.2 million potted orchids were sold at wholesale with an average unit value of
$7.41 (USDA, 2005b).

During commercial orchid production, growers use many different organic and
inorganic materials to comprise the growing media, including activated charcoal,
chopped coconut husks and fiber (Coco nucifera L.), cork (Quercus suber L.), Douglas
fir [Pseudotsuga menziesii (Mirb.) Franco] bark, expanded clay, osmunda fiber, peat,
perlite, redwood bark [Sequoia sempervirens (D. Don) Endl.], rock wool, sphagnum
moss, expanded polystyrene, tree fern fiber, vermiculite, and volcanic rock (Baker and
Baker, 1991; Slump, 2004). Among all of these materials, the primary medium
component used is Douglas fir bark, harvested by the logging industry on the Pacific
coast of the United States (Wang, 2000). However, Douglas fir bark has several
disadvantages: fresh bark has a low water-holding capacity; small or medium grade bark
decomposes too quickly, resulting in high water retention; it has low nutrient retention
and poor uniformity.

In addition, Douglas fir bark has the potential for limited availability in the future.
The possible limited availability is related to the spread of a fungus, Phytophthora
ramorum S. Werres and A.W.A.M. de Cock, which causes a disease known as sudden

oak death (SOD) in the western United States (Wang and Barnes, 2004). In December

151

2004, The Animal and Plant Health Inspection Service (APHIS) issued a federal order
restricting the interstate movement of nursery stock from all commercial nurseries in
California, Oregon, and Washington (APHIS, 2004). Greenhouse grown orchids and
Douglas fir bark are both currently exempt from this federal regulation, but these
exemptions may change in the future. As a result of this and the many other problems
associated with Douglas fir bark, commercial orchid growers are looking for alternative
media combinations that have a reduced or no amount of fir bark.

The objective of this study was to determine how different percentages of fir bark,
chopped coconut coir, perlite, and sphagnum moss influence pH, water-holding capacity
and root and foliar performance of Miltoniopsis, Paphiopedilum, and Phalaenopsis.
Phalaenopsis were chosen because of their popularity among commercial orchid growers
and for their thick and smooth roots. Miltoniopsis were chosen for their fine root system,

while Paphiopedilum were selected for their thick and hairy roots.

Materials and Methods
Plant Material

On 22 Sept. 2004, 100 plants each of Miltoniopsis Eastern Bay ‘Claret Punch’,
Paphiopedilum Clair de Lune X Enchanted Orient, and Phalaenopsis Brother Goldsmith
‘720’ were received in East Lansing, Mich. from a commercial greenhouse
(N urserymen’s Exchange, Inc., Half Moon Bay, Calif). Miltoniopsis and Paphiopedilum
were received in 38-cell packs in media containing 60% medium-grade perlite and 40%
sphagnum peat (by volume). Phalaenopsis were received in 10-cm pots in media

containing 75% fine-grade Douglas fir bark,15% medium-grade perlite, and 10%

152

sphagnum peat (by volume). Plants of Miltoniopsis and Paphiopedilum were grown in a
glass-glazed greenhouse at a constant temperature of 23 °C, while Phalaenopsis were
grown at 29 °C to inhibit flowering. The photoperiod was a constant 16 h (0600 to 2200
HR) consisting of natural daylengths (lat. 42 °N) with day-extension lighting provided by
high-pressure sodium lamps (HPS) delivering a PPF of 20 to 25 umol-m'z-s'l at plant
height [as measured with a quantum sensor (Apogee Instruments, Inc., Logan, Utah)].
Light transmission was reduced using woven shade curtains (OLS 50; Ludvig Svensson,
Charlotte, NC.) and whitewash applied to the glazing so that the maximum PPF at plant

height was 150 umol-m'Z-s'l. A summary of plant material history is provided in Table 1.

Media Treatments

In Oct. 2003, ten plants of each genus were randomly selected and transplanted
into one of ten orchid media mixes. These media mixes consisted of various percentages
of medium-grade Douglas fir bark (Rexius Forest By-Products Inc., Eugene, Ore),
medium-grade chopped coconut coir (Millenniumsoils Coir, St. Catharines, Ont.),
medium-grade perlite (Therm-O-Rock, Inc., New Eagle, Pa.), and long fiber Canadian
sphagnum peat (Mosser Lee Co., Millston, Wis.) (Table 2). Plants of Miltoniopsis and
Phalaenopsis were transplanted into 11.5-cm pots, while plants of Paphiopedilum were
transplanted into 10-cm pots. Miltoniopsis, Paphiopedilum, and Phalaenopsis were
grown in a glass-glazed greenhouse at a constant temperature of 20, 23, and 29 °C,
respectively, and under a maximum PPF of 300, 140, and 150 umol'm'z-s'l, respectively.
Light transmission was reduced and the photoperiod was maintained as previously

described. Each individual plant was irrigated as necessary with reverse osmosis water

153

supplemented with a water-soluble fertilizer providing (mg-L4): 125 N, 12 P, 100 K, 65
Ca, 12 Mg, 1.0 Fe and Cu, 0.5 Mn and Zn, 0.3 B, and 0.1 Mo (Greencare Fertilizers,
Chicago, 111.). Plants were irrigated pot-by-pot and not based on a fixed watering

schedule.

Data Collection

Visual evaluations of foliage and root appearance and foliage and root
development were made after 33, 52, and 83 weeks in each of the media mixes. On the
day of evaluation, a plant of each hybrid in each media mix was randomly selected and
removed from the growing medium to evaluate the roots. On several days during the
experiment, one plant in each media mix was selected and the pH was measured with a
pH meter (Orion Soil pH Meter, Model 410; Orion Research Inc., Boston, Mass.) using a
1 :2 dilution method (1 part medium to 2 parts reverse osmosis water by volume).

At the beginning of the experiment and after 83 weeks, a sample from one plant in
each growing media was collected and immersed in reversed osmosis water for 16 h.
After 16 h, each media sample was poured into a 15-cm pot and allowed to drain for 1 h
to achieve field capacity. The volume and weight of each media were measured and each
sample was subsequently placed into a drying oven at a constant temperature of 38 °C.
After seven days, samples were removed and weighed and the bulk density, porosity, and
gravimetric moisture content were calculated for each media. Bulk density (BD) was

calculated as:

Bulk density = Ws/VS + Vp [l]

154

where BD is equal to the oven-dry weight of the sample (W5) divided by the volume of
solids (Vs) plus volume of pore space (Vp) (Brady and Weil, 1999). Porosity is expressed
as the percentage of soil volume that is occupied by water and air and can be calculated

using the equation:

Porosity (%) = (1 -— BD/PD) x 100 [2]

where particle density (PD) is assumed to be 1.0 g'cm3 (Brady and Weil, 1999). The
gravimetric moisture content (GMC) is the percentage of water per oven-dry weight of

the sample and is calculated using the equation:

Moisture (%) = [(moist soil weight — oven-dry weight)/oven-dry weight] X 100 [3]

Results and Discussion
Foliarfl Root EvaluLtio_n_s

We performed several subjective evaluations throughout a 19-month period to
determine differences in foliar and root development of the orchid genera grown in ten
media mixes. Evaluations at week 33 and 52 showed that vegetative growth and foliar
appearance were not influenced by any of the orchid media mixes for all orchid genera.
However, root development and growth were noticeably different among orchid media
mixes. For example, orchid media mixes that were composed of a high percentage

(250%) of coconut coir (e.g., treatments 2, 4, 7, 8, and 9) had reduced root growth

155

compared to the other media mixes. Treatments with a high percentage of coconut coir
also had dark discolored roots indicating possible infection by pathogens. Media mixes
that consisted of 25% coconut coir had similar vegetative growth and root grth
compared to other media mixes not containing coconut coir.

Evaluations at week 83 showed that vegetative growth and development were
distinctly different among media mixes for all orchid genera. Plants that were grown in
media mixes with a high percentage of coconut coir showed less vegetative growth than
other treatments. For example in Miltoniopsis, the number of new pseudobulbs and leaf
length were greater in plants grown in media mixes consisting of lower percentages
(325%) of coconut coir. Evaluations of root growth and development among all genera
were consistent with the results from evaluations made at 33 and 52 weeks. Several
plants of all three orchid genera in a media mix that consisted of 75% coconut coir died.

Miltoniopsis and Paphiopedilum grown in a media containing 80% bark
(treatment 10) had less root grth compared to all other treatments except treatment 2,
while Phalaenopsis performed well in 80% bark. The production of Phalaenopsis in
media containing 80% fir bark was recommended in a previous study: Wang (1998)
reported that a mixture of fine-grade fir bark and sphagnum peat (80% and 20% by
volume, respectively) resulted in a greater leaf number, total leaf area, and shoot fresh

mass compared to plants grown in a 100% fine-grade fir bark medium.
Bulk Density. Porosity. and Gravimetric Moisture Content

The initial and final bulk densities ranged from 0.07 to 0.17 g-cm3 and were

variable among all media mixes (Table 3). Media mixes that consisted of 250% coconut

156

coir generally had the greatest initial and final porosities. For example, a medium
composed of 50% coconut coir, 25% perlite, and 25% sphagnum peat (by volume) had a
final porosity of 92.7%. In all media mixes porosity increased between initial and final
measurements. These porous medias may be advantageous for commercial production
because tropical epiphytic orchids perform best in substrates that allow air around their
roots (Rittershausen and Rittershausen, 2003).

The initial GMC varied considerably different among all treatments and was
generally greatest in media mixes with the highest proportion of coconut coir. The GMC
was calculated to be _>,100% for all media mixes. These high GMC percentages are likely
influenced by the high amounts of organic material, which can increase the water-holding
capacity of the medium (Brady and Neil, 1999). In all media mixes, GMC increased
between initial and final measurements. This increase in GMC during the study suggests
that decomposition occurred in the media mixes. During decomposition of organic

material there is an increase in water-holding capacity (Brady and Neil, 1999).

15’:

The pH of each media mix was measured several times throughout the study and
all media mixes showed a decreasing trend over time (Fig. 1). For example, in
Phalaenopsis Brother Goldsmith ‘720’, the initial and final pH values for treatment 6
were 5.1 and 4.2, respectively. This decreasing trend was similar for all three orchid
genera and only data for Phalaenopsis Brother Goldsmith ‘720’ is presented. In
Phalaenopsis, the lowest pH occurred in treatment 10 (3.8) and may be related to the

high percentage (80%) of fir bark included in this media mix. The final pH of all media

157

mixes was considerably below the recommended range (5.0 to 6.5) for growing
Phalaenopsis (Anthura and Bureau IMAC, 2005). These low pH values indicate plants
should be transplanted into fresh media or the pH should be raised.

In conclusion, these results suggest that during orchid production, the percentage
of Douglas fir bark used in growing media can be reduced and supplemented with
coconut coir. In general, orchid media consisting of 25% coconut coir could be used
during the production of Miltoniopsis, Paphiopedilum, and Phalaenopsis. The increased
percentage of coconut coir in orchid media could alleviate many of the problems that are
associated with bark. In addition, we postulate that an orchid media containing 25%
coconut coir will not degrade as rapidly as a media containing a higher percentage of fir
bark. The incorporation of higher percentages (250%) of coconut coir in orchid media
resulted in decreased foliar and root development and growth, pathogen infection, and
sometimes death. Thus, to avoid these problems, orchid media should not consist of
250% coconut coir. This information could be beneficial to orchid growers seeking

alternative media mixes with reduced amounts of fir bark.

158

Literature Cited

Animal and Plant Health Inspection Service. 2004. Emergency federal order restricting
movement of nursery stock from California, Oregon, and Washington nurseries. US.
Department of Agriculture, Washington DC.

Anthura B.V. and Bureau IMAC Bleiswijk B.V. 2005. Cultivation guide Phalaenopsis:
Knowledge for professionals. Anthura B.V., Bleiswijk, The Netherlands.

Baker, ML. and CO. Baker. 1991. Orchid species culture: Pescatorea, Phaius,
Phalaenopsis, Pholidota, Phragmipedium, Pleione. Timber Press, Portland, Ore.

Brady, NC. and RR. Neil. 1999. The nature and properties of soils. 12th ed. Prentice-
Hall Inc. Upper Saddle River, NJ.

Rittershausen, B. and W. Rittershausen. 2003. Growing orchids. Hermes House, London,
England.

Slump, K. 2004. Predictions from the medium. Orchids 73:416-418.

US. Department of Agriculture. 2005a. Floriculture crops 2004 summary. Agricultural
Statistics Board, Washington DC.

US. Department of Agriculture. 2005b. F loriculture and nursery crops situation and
outlook yearbook. Economic Research Service, Washington DC.

Wang, Y.-T. 1998. Impact of salinity and media on growth and flowering of a hybrid
Phalaenopsis orchid. HortScience 33:247-250.

Wang, Y.-T. 2000. Impact of a high phosphorous fertilizer and timing of termination of
fertilization on flowering of a hybrid moth orchid. HortScience 35:60-62.

Wang, Y.-T. and L.W. Barnes. 2004. Bark and water molds. Orchids 73:378-381.

159

Table 1. Summary of production dates, container sizes, and greenhouse environmental
conditions for Miltoniopsis Easter Bay ‘Claret Punch’, Paphiopedilum Claire de Lune X
Enchanted Orient, and Phalaenopsis Brother Goldsmith '720' preceding and during

 

 

 

experimentation.
Plant material
Paph. Claire de

Milt. Eastern Bay Lune X Enchanted Phal. Brother
Description 'Claret Punch' Orient Goldsmith '720'
Rece‘ved at Nmse’yme” 3 November 2002 7 June 2002 August 2003
Exchange, Inc. (Half Moon flask communit flat bareroot
Bay, Calif.) y
Transplanted 4 November 2002 10 February 2003 7 August 2003

38-cell packz 38-cell packz 10-cm poty

Reee1vedatM1ch1gan State 22 September 22 September 22 September
Umvers‘” 2003 2003 2003
(East Lansing, Mich.)
Transplanted into one of October 2003 October 2003 October 2003
ten media mixes" 11.5-cm pot 10-cm pot 11.5-cm pot
Fm foil” and “’0‘ 3 June 2004 3 June 2004 3 June 2004
evaluation (33 weeks)
Second foliar and root 14 October
evaluation (52 weeks) 14 October 2004 14 October 2004 2004
Third foliar and root
evaluation (83 weeks) 19 May 2005 19 May 2005 19 May 2005
Termination of experiment 19 May 2005 19 May 2005 19 May 2005

 

ZMedia consisting of 60% medium-grade perlite and 40% sphagnum peat (by volume).
yMedia consisting of 75% fine-grade Douglas fir bark, 15% medium-grade perlite, and
10% sphagnum peat (by volume).
"Media mixes used in this study are provided in Table 2.

160

Table 2. Percentages and ratios of fine-grade Douglas fir bark, medium-grade chopped
coconut coir, medium-grade perlite, and long fiber Canadian sphagnum peat (by volume)
used in ten different orchid media mixes during experiment.

 

 

 

Treatment Material (%) by volume

number Fir bark Coconut coir Perlite Sphagnum peat Ratio

1 75 0 12.5 12.5 6:0:1:1
2 0 75 12.5 12.5 0:6:l:1
3 50 25 12.5 12.5 422:] :1
4 25 50 12.5 12.5 2:4:1:1
5 50 25 25 0 2:1 :1 :0
6 50 25 0 25 2:1:0:1
7 25 50 25 0 1:2:1:0
8 25 50 0 25 1:2:0:1
9 0 50 25 25 0:2:1:1
10 80 0 10 I 10 8:0:1 :1

 

161

 

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Week

Figure 1. Effect of ten orchid media mixes on media pH of Phalaenopsis Brother
Goldsmith ‘720’ during a l9-month period from 20 October 2003 to 19 May 2005.
Treatment ratios represent the proportion of fine-grade Douglas fir bark, medium-grade
chopped coconut coir, medium-grade perlite, and long fiber Canadian sphagnum peat
used in each media mix. The pH of each media was measured using a 1:2 dilution

method (1 part medium to 2 parts reverse osmosis water by volume).

163

 

   

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