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EFFECTS OF HIGH TEMPERATURE AND
PLANT GROWTH REGULATORS ON
VEGETATIVE GROWTH AND FLOWERING OF
POTTED ORCHIDS

presented by

Linsey A. Newton

has been accepted towards fulﬁllment
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EFFECTS OF HIGH TEMPERATURE AND PLANT GROWTH REGULATORS ON
VEGETATIVE GROWTH AND FLOWERING OF POTTED ORCHIDS

By

Linsey A. Newton

A THESIS

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

MASTER OF SCIENCE
Horticulture

2008

ABSTRACT

EFFECTS OF HIGH TEMPERATURE AND PLANT GROWTH REGULATORS ON
VEGETATIVE GROWTH AND FLOWERIN G OF POTTED ORCHIDS

By
Linsey A. Newton

Phalaenopsis, the most popular potted orchid, is induced to ﬂower when the day
temperature is £26 °C. Four Phalaenopsis clones were exposed to 29 °C for 0, 4, 8, 12,
or 24 h per day with the remaining hours of the day at 20 °C to determine how high day
temperature duration inﬂuenced ﬂowering. Phalaenopsis ‘Explosion’ and ‘Mosella’
required exposure to 29 °C for 8 h, while Phalaenopsis Baldan’s Kaleidoscope ‘Golden
Treasure’ and Doritaenopsis Newberry Parfait required exposure to 29 °C for 12 h, to
delay or prevent inﬂorescence initiation. A second study investigated the use of repeated

benzyladenine (BA) sprays to increase vegetative growth or ﬂowering of Paphiopedilum,
Miltoniopsis, and Odontoglossum hybrids. BA at 800 mg-L-l increased shoot number of
large Paphiopedilum in Year 1, but higher concentrations were not effective in Year 2.

In Year 2, applications of 4,000 mg-L-l BA increased the number of new vegetative
shoots formed on medium—sized Paphiopedilum and on two clones of young
Miltoniopsis. A third experiment determined the efﬁcacy of applications of 15, 30, or 45
mg~L_l paclobutrazol to inhibit inﬂorescence elongation of three Phalaenopsis clones
with tall inﬂorescences. Paclobutrazol applications inhibited inﬂorescence length of
Phalaenopsis ‘Andrew’ by 19% to 23% compared to control plants but had no statistical

effect on two other hybrids. A spray application made after ﬂower initiation caused an

undesirable clustering of the ﬂowers whereas earlier sprays did not.

ACKNOWLEDGEMENTS

I have so many people to thank! The ﬁrst thanks goes to God, who has provided
what talent I do have and has given sufﬁcient grace to see me through this journey.
Secondly, thank you to my family. You keep me grounded, remind of what life is really
about, and keep me laughing even when my car is broken down yet again. You guys
mean the world to me!

I would also like to thank my advisor Erik Runkle for this opportunity to obtain
my masters degree. I sure was not planning on going to graduate school, but you
provided a chance I did not want to pass up! I appreciate the help and advice you have
given me over the past 2% years. I also want to thank my committee members Don
Garling and Ryan Warner for their knowledge, suggestions, and time.

I owe a huge thanks to my fellow graduate students Matt Blanchard and Roberto
Lopez. Without all of your help, I would have not even made it through the ﬁrst few
months. I particularly need to thank Matt for always being willing to answer my
questions. You were such a huge help! Thanks to both of you for your friendship along
the way. It has been a truly wonderful experience working with you guys.

Mike Olrich also deserves lots of recognition. Thank you for always being
willing to make the adjustments I needed in the greenhouse, provide advice on so many
things, and teach me how things work (despite my inaptitude in anything mechanical).

Thank you to the undergraduate greenhouse workers who were always willing to

help when I needed an extra hand. You guys made the greenhouse more enjoyable!

iii

TABLE OF CONTENTS

LIST OF TABLES ............................................................................................................ vii
LIST OF FIGURES ............................................................................................................ x
SECTION I
LITERATURE REVIEW ................................................................................................... 1
Introduction ......................................................................................................................... 2
Orchid Nomenclature ...................................................................................................... 3
Orchid Morphology ........................................................................................................ 3
Carbon Fixation in Orchids ............................................................................................. 4
Effects of Temperature on Orchid Flowering ................................................................. 5
Cool Treatment or Vemalization ................................................................................ 6
Duration of Inductive Temperature ............................................................................. 7
Timing of Inductive Temperature Delivery ................................................................ 8
Daily Temperature Fluctuations ................................................................................. 9
Effects of Temperature on Flower Morphology ....................................................... 10
Effects of Temperature on Plant Hormone and Sugar Concentrations ..................... 10
Effects of Photoperiod on Orchid Flowering ................................................................ 12
Effects of Light Quantity on Orchid Flowering ............................................................ 15
Effects of Fertilization and Potting Media on Orchid Flowering ................................. 17
Cytokinins ..................................................................................................................... 19
Forms of Benzyladenine ........................................................................................... 20
Cytokinin Biosynthesis ............................................................................................. 20
Cytokinin Signaling .................................................................................................. 21
Exogenously Applied Cytokinin ............................................................................... 22
Physiological Effects of Cytokinins .......................................................................... 23
Cell Division. ........................................................................................................ 23
Leaf Expansion. .................................................................................................... 24
Organogenesis ....................................................................................................... 24
Lateral Bud Growth. ............................................................................................. 24
Flowering. ............................................................................................................. 25
Photosynthesis ....................................................................................................... 26
Translocation ......................................................................................................... 27
Senescence. ........................................................................................................... 27
Protein Synthesis ................................................................................................... 28
Uses of BA in Horticulture ........................................................................................... 28
Orchard Uses ............................................................................................................. 28
Lateral Branching ...................................................................................................... 29
Uses in Propagation .................................................................................................. 30
Uses of BA in F loriculture ............................................................................................ 30
Lateral Branching ...................................................................................................... 30
Interaction between BA and Environmental Conditions .......................................... 32
Postharvest of Potted Crops ...................................................................................... 34

iv

Postharvest of Cut Flowers ....................................................................................... 35

Propagation ............................................................................................................... 37
Flowering .................................................................................................................. 38
Effects of BA on Orchids .............................................................................................. 40
Use of BA in Tissue Culture ..................................................................................... 40
Vegetative Response of Potted Orchid Plants to BA ................................................ 41
Flowering Response of Potted Phalaenopsis to BA ................................................. 42
Flowering Response of Other Potted Orchid Genera and Intergeneric Hybrids to BA
................................................................................................................................... 44
Interaction of Cytokinins and Temperature in Orchids ............................................ 46
Interaction of Cytokinins and Other Plant Hormones in Orchids ............................. 47
Literature Cited ............................................................................................................. 49
SECTION 11
HIGH TEMPERATURE INHIBITION OF FLOWERING OF PHALAENOPSIS AND
DORITAENOPSIS ORCHIDS .......................................................................................... 63
Abstract ......................................................................................................................... 65
Introduction ................................................................................................................... 66
Materials and Methods .................................................................................................. 67
Plant Material ............................................................................................................ 67
Year 1 .................................................................................................................... 67
Year 2 .................................................................................................................... 68
Temperature Treatments ........................................................................................... 68
Year 1 .................................................................................................................... 68
Year 2 .................................................................................................................... 69
Greenhouse Environment .......................................................................................... 70
Data Collection and Analysis .................................................................................... 71
Results ........................................................................................................................... 72
Effects of High Temperature Duration and Timing on Flowering ........................... 72
Phalaenopsis ‘Mosella’ ........................................................................................ 72
Phalaenopsis Baldan’s Kaleidoscope ‘Golden Treasure’ ..................................... 73
Doritaenopsis Newberry Parfait ........................................................................... 74
Phalaenopsis ‘Explosion’. .................................................................................... 75
Effect of Plant Size on Flowering ............................................................................. 76
Effects of High Temperature Duration on Vegetative Growth ................................. 76
Discussion ..................................................................................................................... 77
Literature Cited ........................................................................................................... 100
SECTION III

EFFECTS OF BENZYLADENINE ON FLOWERING AND VEGETATIVE GROWTH
OF POTTED MIL TONIOPSIS, PAPHIOPEDIL UM, AND ODONT OGLOSS UM

ORCHIDS ....................................................................................................................... 102
Abstract ....................................................................................................................... 104
Introduction ................................................................................................................. 105
Materials and Methods ................................................................................................ 107

Plant Material .......................................................................................................... 108

BA Applications ...................................................................................................... 109

Experiment 1 ....................................................................................................... 109
Experiment 2 ....................................................................................................... 110
Greenhouse Environment ........................................................................................ 110
Odontoglossum and Miltoniopsis ........................................................................ 111
Paphiopedilum .................................................................................................... 11 1
Environmental Control ........................................................................................ 11 1
Data Collection and Analysis .................................................................................. 111
Results ......................................................................................................................... 112
Paphiopedilum ........................................................................................................ 1 12
Shoot number ...................................................................................................... 1 12
Flowering ............................................................................................................ 113
Miltom'opsis ............................................................................................................. 1 13
Shoot number ...................................................................................................... 1 l3
Flowering ............................................................................................................ 1 l4
Odontoglossum ....................................................................................................... l 14
Shoot number ...................................................................................................... 114
Flowering ............................................................................................................ 115
Discussion ................................................................................................................... 1 15
Literature Cited ........................................................................................................... 132
SECTION IV
EFFECTS OF PACLOBUTRAZOL ON INFLORESCENCE LENGTH OF POTTED
PHALAENOPSIS AND DORITAENOPSIS ORCHIDS ................................................. 136
Abstract ....................................................................................................................... 138
Introduction ................................................................................................................. l 3 9
Materials and Methods ................................................................................................ 142
Plant Material .......................................................................................................... 142
Chemical Application ............................................................................................. 142
Greenhouse Environment ........................................................................................ 143
Data Collection and Analysis .................................................................................. 143
Results ......................................................................................................................... 144
Inﬂorescence length ................................................................................................ 145
Node Length ............................................................................................................ 145
Other Characteristics ............................................................................................... 146
Discussion ................................................................................................................... 146
Literature Cited ........................................................................................................... 158

vi

LIST OF TABLES

Table 2.1. Average leaf span number of each Phalaenopsis or Doritaenopsis cultivar at
the start of the experiment for each year. Leaf span was the distance measured from the
end of one leaf to the longest opposite leaf tip. ................................................................ 83

Table 2.2. Temperature treatments used in the study. Treatments 1, 2, 5, 7, and 8 were
used in Year 1 and replicated in Year 2. Treatments 3, 4, and 6 were added in Year 2.
The temperature was maintained at 20 °C for the remaining period each day. ................ 84

Table 2.3. Actual weekly average greenhouse air temperatures in each treatment in Year
1 measured every 10 s by independent aspirated thermocouples positioned at plant level
and recorded by data loggers. For the treatments with daily changes in temperature, an
average was calculated for each of the two temperature periods within the day. ............. 85

Table 2.4. Actual weekly average greenhouse air temperatures in each treatment in Year
2 measured every 10 s by independent aspirated thermocouples positioned at plant level
and recorded by data loggers. For the treatments with daily changes in temperature, an
average was calculated for each of the two temperature periods within the day. ............. 86

Table 2.5. Effect of the duration of high temperature (29 °C) exposure on the percentage
of plants developing a visible inﬂorescence (VI), days to V1, V1 number, total ﬂower bud
number per plant, ﬂower bud number per inﬂorescence, ﬁrst open ﬂower diameter,
length of the ﬁrst inﬂorescence from the base to the ﬁrst ﬂower, and increase in leaf span
after 20 weeks of treatments of Phalaenopsis ‘Mosella’. For parameters in which the
interaction between temperature treatment and year was not signiﬁcant, data was pooled;
otherwise, mean separation was performed on each year separately ................................ 87

Table 2.6. Effect of duration and time of day of high temperature (29 °C) exposure in
Year 2 on the percentage of plants developing a visible inﬂorescence (VI), days to VI, VI
number, total ﬂower bud number per plant, ﬂower bud number per inﬂorescence, ﬁrst
open ﬂower diameter, length of the ﬁrst inﬂorescence from the base to the ﬁrst ﬂower,
increase in leaf span, and number of new leaves developed after 20 weeks for
Phalaenopsis ‘Mosella’. ................................................................................................... 88

Table 2.7. Effect of the duration of high temperature (29 °C) exposure on the percentage
of plants developing a visible inﬂorescence (VI), days to V1, V1 number, total ﬂower bud
number per plant, ﬂower bud number per inﬂorescence, ﬁrst open ﬂower diameter,
length of the ﬁrst inﬂorescence from the base to the ﬁrst ﬂower, and increase in leaf span
after 20 weeks of Phalaenopsis Baldan’s Kaleidoscope ‘Golden Treasure’. For
parameters in which the interaction between temperature treatment and year was not
signiﬁcant, data was pooled; otherwise, mean separation was performed on each year
separately. ......................................................................................................................... 89

vii

Table 2.8. Effect of duration and time of day of high temperature (29 °C) exposure in
Year 2 on the percentage of plants developing a visible inﬂorescence (V 1), days to V1, V1
number, total ﬂower bud number per plant, ﬂower bud number per inﬂorescence, ﬁrst
open ﬂower diameter, length of the ﬁrst inﬂorescence from the base to the ﬁrst ﬂower,
increase in leaf span, and number of new leaves developed after 20 weeks for
Phalaenopsis Baldan’s Kaleidoscope ‘Golden Treasure’ ................................................. 90

Table 2.9. Effect of the duration of high temperature (29 °C) exposure on the percentage
of plants deve10ping a visible inﬂorescence (VI), days to V1, V1 number, total ﬂower bud
number per plant, ﬂower bud number per inﬂorescence, ﬁrst open ﬂower diameter,
length of the ﬁrst inﬂorescence from the base to the ﬁrst ﬂower, and increase in leaf span
after 20 weeks of Doritaenopsis Newberry Parfait. For parameters in which the
interaction between temperature treatment and year was not signiﬁcant, data was pooled;
otherwise, mean separation was performed on each year separately ................................ 91

Table 2.10. Effect of duration and time of day of high temperature (29 °C) exposure in
Year 2 on the percentage of plants developing a visible inﬂorescence (VI), days to VI, VI
number, total ﬂower bud number per plant, ﬂower bud number per inﬂorescence, ﬁrst
open ﬂower diameter, length of the ﬁrst inﬂorescence from the base to the ﬁrst ﬂower,
increase in leaf span, and number of new leaves developed after 20 weeks for
Doritaenopsis Newberry Parfait. ...................................................................................... 92

Table 2.11. Effect of the duration of high temperature (29 °C) exposure on the
percentage of plants developing a visible inﬂorescence (VI), days to V1, VI number, total
ﬂower bud number per plant, ﬂower bud number per inﬂorescence, ﬁrst open ﬂower
diameter, length of the ﬁrst inﬂorescence from the base to the ﬁrst ﬂower, and increase in
leaf span after 20 weeks of Phalaenopsis ‘Explosion’ in Year 1. Phalaenopsis
‘Explosion’ was not used in Year 2 due to unavailability of this clone. .......................... 93

Table 2.12. Effect of duration of high temperature (29 °C) exposure and plant size in
Year 2 on the percentage of plants developing a visible inﬂorescence (VI), days to V1, V1
number, total ﬂower bud number per plant, ﬂower bud number per inﬂorescence, ﬁrst
open ﬂower diameter, total length and length to the ﬁrst ﬂower of the inﬂorescence,
increase in leaf span, and the number of new leaves developed after 20 weeks of
Phalaenopsis ‘Mosella’. ................................................................................................... 94

Table 3.1. Orchid hybrids used for each size in Experiment 1 and 2 ............................ 119
Table 3.2. Leaf span (cm) of Paphiopedilum and pseudobulb diameter (cm) of the
remaining orchid hybrids measured at the time of the ﬁrst BA application in each

experiment ....................................................................................................................... 1 20

Table 3.3. The actual average temperature and photosynthetic daily light integral (DLI)
for each greenhouse environment and orchid hybrid in Experiment 1 and 2. ................ 121

viii

Table 3.4. Effects of spray applications of benzyladenine (BA) on ﬂowering parameters
of small, medium, and large Miltoniopsis Echo Bay ‘Midnight Tears’ in Experiment 1. A
description of plant sizes is provided in Table 3.2; spray information is provided in the
text ................................................................................................................................... 122

Table 3.5. Effects of spray applications of benzyladenine (BA) on ﬂowering parameters
of large Miltoniopsis Echo Bay ‘Midnight Tears’ in Experiment 2. A description of plant
sizes is provided in Table 3.2; spray information is provided in the text. ...................... 123

Table 3.6. Effects of spray applications of benzyladenine (BA) on ﬂowering parameters
of large Beallara Tahoma Glacier ‘Green’ in Experiment 1. A description of plant sizes
is provided in Table 3.2; spray information is provided in the text. ............................... 124

Table 3.7. Effects of spray applications of benzyladenine (BA) on ﬂowering parameters
of large Beallara Tahoma Glacier ‘Green’ in Experiment 2. A description of plant sizes
is provided in Table 3.2; spray information is provided in the text. ............................... 125

Table 4.1. Effect of paclobutrazol concentration and application time on number of days
from visible inﬂorescence (VI) to ﬂowering, VI number, ﬂower bud number on ﬁrst
inﬂorescence to ﬂower, total ﬂower bud number per plant, and diameter of ﬁrst open
ﬂower of Doritaenopsis Andrew. Ns=Not signiﬁcant at P5005. .................................. 149

Table 4.2. Effect of paclobutrazol concentration and application time on number of days
from visible inﬂorescence (VI) to ﬂowering, VI number, ﬂower bud number on ﬁrst
inﬂorescence to ﬂower, total ﬂower bud number per plant, and diameter of ﬁrst open
ﬂower of Doritaenopsis Miss Saigon. NS,*=Not signiﬁcant or signiﬁcant at P5005,
respectively. .................................................................................................................... l 50

Table 4.3. Effect of paclobutrazol concentration and application time on number of days
from visible inﬂorescence (VI) to ﬂowering, VI number, ﬂower bud number on ﬁrst
inﬂorescence to ﬂower, total ﬂower bud number per plant, and diameter of ﬁrst open
ﬂower of Phalaenopsis ‘Smart Thing’. Ns=Not signiﬁcant at P5005 .......................... 151

Table 4.4. Effect of paclobutrazol concentration and application time on vegetative
growth (increase in leaf span and number of new leaves formed) of Doritaenopsis
Andrew, D. Miss Saigon, or Phalaenopsis ‘Smart Thing’ after 19, 18, or 16 weeks of
growth at 23 °C, respectively. Ns=Not signiﬁcant at P5005. ........................................ 152

ix

LIST OF FIGURES

Figure 2.1. Effects of high temperature (29 °C) duration on ﬂowering percentage (bars)
and mean days to ﬁrst open ﬂower (symbols) of Phalaenopsis and Doritaenopsis clones.
For clones in which the temperature treatment by year interaction was signiﬁcant for the
days to ﬁrst open ﬂower, Year 1 is represented by closed circles (-) and Year 2 is
represented by open circles (o). Flowering percentages within a clone with different
uppercase letters are signiﬁcantly different using a binomial distribution and logit
transformation. Days to ﬁrst open ﬂower within a clone and year with different
lowercase letters are signiﬁcantly different using Tukey’s honestly signiﬁcant difference
test at P5005. Vertical bars represent the standard errors of the means. ........................ 95

Figure 2.2. Effects of high temperature (29 °C) duration and time on ﬂowering
percentage (bars) and mean days to ﬁrst open ﬂower (0) of Phalaenopsis and
Doritaenopsis clones in Year 2. Flowering percentages within a clone with different
uppercase letters are signiﬁcantly different using a binomial distribution and logit
transformation. Days to ﬁrst open ﬂower within a clone with different lowercase letters
are signiﬁcantly different using Tukey’s honestly signiﬁcant difference test at P5005.
Vertical bars represent the standard errors of the means. ................................................. 96

Figure 2.3. Effects of high temperature (29 °C) duration (and average daily temperature)
on total inﬂorescence height (from base to tip) of Phalaenopsis and Doritaenopsis clones.
For clones in which the temperature treatment by year interaction was signiﬁcant, the
years were analyzed separately. Data was not analyzed for temperature treatments in
which 520% of plants ﬂowered (*). Mean separation within each clone and year was
performed using Tukey’s honestly signiﬁcant difference test at P5005. Vertical bars‘
represent the standard errors of the means. ....................................................................... 97

Figure 2.4. Effects of high temperature (29 °C) duration and time on total inﬂorescence
height (from base to tip) of Phalaenopsis and Doritaenopsis clones in Year 2. Data was
not analyzed in temperature treatments in which 520% of plants ﬂowered (*). Mean
separation within each clone and year used Tukey’s honestly signiﬁcant difference test at
P5005. Vertical bars represent the standard errors of the means. .................................. 98

Figure 2.5. Effects of high temperature (29 °C) duration (and average daily temperature)
on number of new leaves of Phalaenopsis and Doritaenopsis clones. For clones in which
the temperature treatment by year interaction was signiﬁcant, the years were analyzed
separately. Mean separation within each clone and year was performed using Tukey’s
honestly signiﬁcant difference test at P5005. Vertical bars represent the standard errors
of the means. ..................................................................................................................... 99

Figure 3.1. Effects of repeated spray applications of benzyladenine (BA) on mean
number of new vegetative shoots formed on three sizes of mixed hybrids of
Paphiopedilum in Experiment I. A description of plant size is provided in Table 3.2.
Error bars represent standard errors of the means. Means at 28 weeks within a plant size

with the same letter are not signiﬁcantly different by Tukey’s honestly signiﬁcant
difference test at P5005. ................................................................................................ 126

Figure 3.2. Effects of repeated spray applications of benzyladenine (BA) on mean
number of new vegetative shoots formed on two sizes of Paphiopedilum mixed hybrids
in Experiment 2. A description of plant size is provided in Table 3.2. Error bars
represent standard errors of the means. Means at 20 weeks within a plant size with the
same letter are not signiﬁcantly different by Tukey’s honestly signiﬁcant difference test
at P5005. ........................................................................................................................ 127

Figure 3.3. Effects of benzyladenine (BA) sprays on mean number of new vegetative
shoots formed on three sizes of Miltom'opsis Echo Bay ‘Midnight Tears’ in Experiment 1.
A description of plant size is provided in Table 3.2. Error bars represent standard errors
of the mean. Means separation is not provided because BA treatment was not signiﬁcant
at P5005 within any plant size. ...................................................................................... 128

Figure 3.4. Effects of benzyladenine (BA) sprays on mean number of new vegetative
shoots formed on three Miltoniopsis in Experiment 2. A description of plant size is
provided in Table 3.2. Error bars represent standard errors of the mean. Means at 20
weeks within a plant size with the same letter are not signiﬁcantly different by Tukey’s
honestly signiﬁcant difference test at P5005. ................................................................ 129

Figure 3.5. Effects of benzyladenine (BA) sprays on mean number of new vegetative
shoots formed on three sizes of Beallara Tahoma Glacier ‘Green’ in Experiment 1. A
description of plant size is provided in Table 3.2. Error bars represent standard errors of
the means. Means at 28 weeks within a plant size with the same letter are not
signiﬁcantly different by Tukey’s honestly signiﬁcant difference test at P5005. ......... 130

Figure 3.6. Effects of benzyladenine (BA) sprays on mean number of new vegetative
shoots formed on three sizes of Odontoglossum in Experiment 2. A description of plant
size is provided in Table 3.2. Error bars represent standard errors of the means. Means
separation is not provided because BA treatment was not signiﬁcant at P5005 within any
plant size. ........................................................................................................................ 131
Zeevaart, J AD. 1978. Phytohormones and ﬂower formation, p. 291—327. In: D.S.
Letham, P.B. Goodwin, and T.J.V. Higgins (eds). Phytohorrnones and Related
Compounds: A Comprehensive Treatise. vol. II. Elsevier/North-Holland Biomedical
Press, Amsterdam. .......................................................................................................... 135

Figure 4.1. Effects of paclobutrazol concentration and application time on inﬂorescence
length to ﬁrst ﬂower (top) and total inﬂorescence length at ﬁrst open ﬂower (bottom) for
three Phalaenopsis clones. Error bars represent standard errors. Means within clone
with the same letter are not signiﬁcantly different by Tukey’s honestly signiﬁcant
difference test at P5005. ................................................................................................ 153

xi

Figure 4.2. Effect of paclobutrazol concentration and application time on total
inﬂorescence length of Doritaenopsis Andrew during the study. Final height was
measured at ﬁrst open ﬂower. Error bars represent the standard errors of the means... 154

Figure 4.3. Effects of paclobutrazol concentration and application time on total
inﬂorescence length of Doritaenopsis Miss Saigon during the study. Final height was
measured at ﬁrst open ﬂower. Error bars represent the standard errors of the mean. 155

Figure 4.4. Effects of paclobutrazol concentration and application time on total
inﬂorescence length of Phalaenopsis ‘Smart Thing’ during the study. Final height was
measured at ﬁrst open ﬂower. Error bars represent the standard error of the means. 156

Figure 4.5. Effects of paclobutrazol concentration and application time on the length of
the intemode between the ﬁrst and second ﬂower of three Phalaenopsis clones. Error
bars represent standard errors. Means within clone with the same letter are not
signiﬁcantly different by Tukey’s honestly signiﬁcant difference test at P5005. ......... 157
Wang, Y.-T. and TY. Hsu. 1994. Flowering and growth of Phalaenopsis orchids
following growth retardant applications. HortScience 29:285-288. ............................... 159

xii

SECTION I

LITERATURE REVIEW

Introduction

Orchids have become a popular potted ﬂowering plant in the past decade. In
2005, 18 million orchid plants worth $143 million were sold in the United States (USDA,
2006). Phalaenopsis is the most common potted orchid and accounts for over 75% of the
orchids produced and sold in the US. (Griesbach, 2002). Since orchids are commonly
sold as a ﬂowering potted crop, knowing how to induce ﬂowering is a critical factor in
greenhouse production. Flowering of most orchid genera is not well understood,
although signiﬁcant progress has been made in the past decade in understanding how
environmental factors inﬂuence orchid ﬂowering physiology.

Orchidaceae is a large plant family estimated to include 859 genera and 25,158
species (Cribb and Govaerts, 2005). Although members of this family are mostly
indigenous to tropical regions, orchids can be found from within the Arctic Circle to
islands south of Australia (Cribb and Govaerts, 2005) and in grasslands, tropical forests,
and deserts (Arditti, 1992). Phalaenopsis are indigenous to India, portions of Australia,
southern New Zealand, southeast Asia, Indonesia, and the Philippine islands
(Christenson, 2001). The species native to the Philippine islands have been used the most
in breeding commercial hybrids. Other common commercially produced potted
ﬂowering orchid genera (and from where they originate) include C ymbidium (Asia to
Australia), Odontoglossum (mountainous regions of Central America and South
America), Dendrobium (India, China, Southeast Asia, and the Malaysian Peninsula),
Miltoniopsis (Central America and northern parts of South America), and Paphiopedilum

(the Far East including India, China and Southeast Asia) (Bechtel et al., 1992).

Orchid Nomenclature

Nomenclature of orchid species is similar to all other living organisms (with the
species name consisting of a genus and a speciﬁc epithet), but a unique system is used for
orchid hybrids. For orchid hybrids, a grex epithet follows the generic name. This grex
epithet represents a particular cross. Any progeny resulting from the cross of two
speciﬁc parents will have the same grex epithet. This grex epithet is not italicized and is
not enclosed by single quotation marks. Within a grex, clones are given a cultivar name,

which is enclosed in single quotation marks after the grex epithet (Arditti, 1992).

Orchid Morphology

Orchid plants can be terrestrial, epiphytic or lithophytic (Arditti, 1992).
Terrestrial orchids have roots that are anchored in the soil; lithophytes grow in more
adverse environments found on the sides of cliffs or rocks. Epiphytic orchids have aerial
roots that are exposed and attach to trees. Aerial roots have a layer of white velamen
around them except at the tip, which is green. This velamen layer protects against
mechanical damage, prevents water loss, and absorbs water (Dycus and Knudson, 195 7).
These aerial roots also contain chloroplasts and ﬁx carbon through photosynthesis (Goh,
1983)

Orchids can be further divided into two groups based on their growth
morphology: monopodial or sympodial (Hew and Yong, 2004). Monopodial orchids
have an indeterminate growth pattern, meaning the shoot can grow for an indeﬁnite
period as long as environmental conditions are favorable. In contrast, sympodial orchids

have determinate growth that usually terminates with an inﬂorescence. For the plant to

ﬂower again, the lateral buds of the ﬂowered shoot must break dormancy and develop
into new shoots. Most sympodial orchids have pseudobulbs, which are enlarged stems at
the base of the leaves of a shoot that serve as storage organs (Hew and Yong, 2004).

Orchid ﬂowers are zygomorphic, meaning they have bilateral symmetry, and have
three-colored sepals and three petals, of which the bottom one is modiﬁed into the
labellum. The male and female reproductive parts are fused in a structure known as the
column. The pollen is covered under the anther cap at the very end of the column. The
stigma is beneath both the pollinarium and rostellum on the column (Hew and Yong,
2004). The ﬂowers of Phalaenopsis are resupinate, which means the pedicel and ovary
twist so that the dorsal petal is at the top of the ﬂower (Christenson, 2001 ).

Phalaenopsis have at least two buds in the axil of every leaf: one is reproductive
and will elongate under appropriate environmental conditions to form an inﬂorescence,
and one is a vegetative bud that only grows if the main meristem of the shoot aborts or is
damaged (Rotor, 1959). The inﬂorescence also has nodes covered by bracts along the
pedicel. If the raceme is damaged or removed, the buds at these nodes can elongate and

develop ﬂowers (Christenson, 2001).

Carbon Fixation in Orchids

Thin-leaved orchids, such as Oncidium and Arundina, ﬁx carbon using the C3
cycle. In contrast, thick-leaved orchids use crassulacean acid metabolism (CAM) (Hew
and Yong, 2004), which spatially and temporarily separates ﬁxation of C02 into a C4 acid
and decarboxylation of this C4 acid (Taiz and Zeiger, 2002). In CAM plants, C02 is

ﬁxed at night and stored as malate in the vacuole. Then during the day, the malate is

decarboxylated in the chloroplast and the C02 released is reﬁxed by the C3 cycle (Taiz

and Zeiger, 2002). Phalaenopsis is one such thick-leaved CAM orchid; there is a large
increase in primary carbon ﬁxation in the evening and an increase in malic acid content

throughout the night (Endo and Ikusima, 1989). When grown under a 12-h photoperiod,

maximum C02 ﬁxation occurs 3-4 h after the start of darkness (Guo and Lee, 2006). The

optimal temperatures for C02 uptake in Phalaenopsis was a day/night temperature of
25/15 °C (Ota et al., 1991). Although mature leaves on mature Phalaenopsis plants ﬁx
carbon through CAM, younger leaves on younger plants may transition from C3 to CAM

carbon ﬁxation (Guo and Lee, 2006).

Effects of Temperature on Orchid Flowering

Temperature is particularly important in the regulation of ﬂowering of orchids.
As with many other plants, there is a certain optimum temperature for induction of
ﬂowering, which is not always the same as the temperature for optimal vegetative
growth. For example, Phalaenopsis requires exposure to temperature below 26 °C for
inﬂorescence initiation, but has the most rapid leaf development at average daily
temperatures of 27-30 °C (Krizek and Lawson, 1974; Sakanishi et al., 1980; Wang,
2007). Once Phalaenopsis have initiated inﬂorescences, which typically emerge from
the third or fourth node from the apex (Sakanishi et al., 1980), time to ﬂower is a function
of temperature. The base temperature for continued inﬂorescence development of
Phalaenopsis Taisuco Smile was estimated at 10.8 °C (Robinson, 2002). To reach
anthesis, 769 degree days (average daily temperature in °C minus base temperature in °C)

were required after the inﬂorescence ﬁrst became visible.

5

Although Phalaenopsis require temperatures below 26 °C to initiate
inﬂorescences (Lee and Lin, 1984; Sakanishi et al., 1980), inﬂorescence initiation can be
inhibited or delayed if plants are exposed to much cooler temperatures. Phalaenopsis
amabilis (L.) Blume formed more inﬂorescences and ﬂowers and had a visible
inﬂorescence four to six (I earlier at day/night temperatures of 25/20 and 20/25 °C
compared to plants at 20/15 or 15/20 °C (Wang, 2005). Plants at 25/20 or 20/25 °C
developed an average of 12 ﬂowers compared to only 8 ﬂowers on plants grown at 20/15
or 15/20 °C.

The age and size of Phalaenopsis plants can contribute some variation to
temperature-induced ﬂowering. Young Phalaenopsis plants require a longer exposure or
cooler temperature than older plants to induce ﬂowering (Ichihashi, 1997; Wang and Lee,
1994). When Phalaenopsis plants were grown at 20 °C for 25 id, inﬂorescences emerged
from only 13% of the three-year-old plants compared to 90% of the six-year—old plants
(Yoneda et al., 1992).

Cool Treatment or Vemalization

Many orchids, including Phalaenopsis, require exposure to a period of cool
temperatures, which some authors have called vemalization (Lopez and Runkle, 2006b),
to induce consistent ﬂowering. For example, Miltoniopsis Augres ‘Trinity’ ﬂowered
most consistently when plants received 8 weeks of short days (SD) followed by an 8-
week exposure to 11 or 14 °C (Lopez and Runkle, 2006b). Under these conditions, more
than 75% of the plants ﬂowered. When plants were exposed to 17 °C or higher, less than
40% of plants ﬂowered and some ﬂower buds aborted. Certain Zygopetalum cultivars

react similarly to vemalization. Eighty percent of Zygopetalum Redvale ‘Fire Kiss’

plants ﬂowered when grown under a 9-h photoperiod at 23 °C for 8 weeks before being
vemalized for 8 weeks at 11 °C (Lopez et al., 2003). Vemalization at 14 °C reduced
ﬂowering to 60% or 70%, and vemalization at 17 to 23 °C elicited no ﬂowering. Other
orchids that require low temperatures for consistent ﬂowering include some hybrids and
species of Miltom'a, Dendrobium, Cattleya and Odontioda, which all require a
temperature of about 17 0C for optimal ﬂowering (Tran Thanh Van, 1974). For example,
Miltom'a (Miltoniopsis) ‘Spring Cynthia’ X M. vexillaria (Rchb. F.) G. Nicholson and M.
‘Sein Ida Seigel’ X M. ‘Mein Ida Seigel’ hybrid seedlings ﬂowered at least 10 d earlier
when grown in the highlands of Japan, where the air temperature was about 5 °C cooler,
than in the lowlands (Matsui and Yoneda, 1997). Odontioda George McMahon ‘Fortuna’
and Odontioda Lovely Penguin ‘Emperor’ exhibited the highest ﬂowering frequency
(90%) at temperatures of 14 and 17 °C, and higher temperatures reduced ﬂowering
(Blanchard, 2005). Similarly, the Dendrobium nobile Lind. hybrid Sea Mary ‘Snow
King’ ﬂowered when vemalized at 521 °C for three weeks, but plants vemalized at 13 or
15 °C had more ﬂowers than those vemalized at 18 or 21 °C (Yen et al., 2008).
Duration of Inductive Temperature

In addition to the actual temperature, the duration of the cooling temperature also
impacts ﬂower induction. There is typically a minimum duration that the inductive
temperature must be delivered to achieve uniform ﬂowering of a population of plants.
For Phalaenopsis, visible inﬂorescences are developed after 3 to 7 weeks of growing at
day temperatures 526 °C (Lee and Lin, 1987; Tran Thanh Van, 1974; de Vries, 1950).

However, ﬂower buds do not begin initiating until the inﬂorescence is about 5 cm long.

The duration of the inductive temperature within each day is another important
factor that can impact ﬂower initiation in orchids. When plants of an unnamed
Phalaenopsis amabilis hybrid were exposed to temperatures above 28 °C for 12 h or
more, the percentage of ﬂowering plants was reduced compared to controls grown in a
greenhouse with a maximum temperature of 25 °C (Sakanishi et al., 1980). All plants
that were exposed to only 6 h of temperatures above 28 °C ﬂowered, whereas only 84%
and 46% of plants ﬂowered when they received high temperatures for 12 or 14 h,
respectively.

Timing of Inductive Temperature Delivery

In addition to the actual temperature and its duration, the time of day at which the
low temperature treatment is delivered can have a signiﬁcant impact on ﬂower induction.
In Phalaenopsis, the day temperature is more inﬂuential on inﬂorescence initiation than
night temperature or average daily temperature (Blanchard and Runkle, 2006). When
Phalaenopsis Brother Goldsmith ‘720’ and Phalaenopsis Miva Smartissimo X Canberra
‘450’ were grown at various day/night temperatures, plants grown at 29 °C during the
day and 23 or 17 °C during the night did not ﬂower (Blanchard and Runkle, 2006). In
addition, there were differences in the percentage of plants that developed visible
inﬂorescences among different temperature treatments having the same average daily
temperature, which suggests inﬂorescence initiation is not a function of average daily
temperature. Therefore, it was concluded that ﬂowering in Phalaenopsis is primarily a
function of the day temperature.

Doritaenopsis, a hybrid between the genera Doritis and Phalaenopsis, respond

similarly to temperature. Ninety-three percent of the Doritaenopsis ‘Lava Glow’ plants

at a 12-h day/ l2-h night temperature of 20/25 °C ﬂowered, while only 33% of plants at
25/20 °C ﬂowered (Wang, 2007). This also indicates that the day temperature is more
inﬂuential on ﬂowering than the night temperature. When the difference between the day
and night temperature was increased to 10 °C, all plants placed at 15/25 °C ﬂowered
whereas no plants at 25/15 °C ﬂowered.

Daily Temperature Fluctuations

Like most factors affecting orchid ﬂowering, the ﬂuctuation between day and
night temperature appears to have different effects in different orchid species and
hybrids. C ymbidium initiates ﬂower buds most reliably when placed under a warm day
temperature and a cooler night temperature (Goh et al., 1982). For example, Cymbidium
Astronaut ‘Rajah’ developed a mean of 5.9 inﬂorescences per plant when grown with a
day/night temperature ﬂuctuation of 14 °C for six months compared to only 0.8 and 1.7
inﬂorescences developed on plants with a day/night temperature ﬂuctuation of 8 °C
(Powell and Caldwell, 1988). Similarly, Dendrobium Second Love plants placed at a
day/night temperature of 25/10 °C had more ﬂower buds than plants placed at a constant
25 °C (Campos and Kerbauy, 2004). However, there was no 10 °C control, so the results
could be attributed to insufﬁcient cooling of Dendrobium.

In contrast to these examples of Dendrobium and C ymbidium, a ﬂuctuation in day
and night temperature is unnecessary to induce ﬂowering of Phalaenopsis and
Miltoniopsis. Miltoniopsis Augres ‘Trinity’ ﬂowered well at either constant temperatures
of 11 or 14 °C with a 9-h photoperiod or with a day/night temperature ﬂuctuation of
16/ 14 °C with a 12-h day (Lopez and Runkle, 2006b). Similarly, at least 80% of

Phalaenopsis Brother Goldsmith ‘720’ and Phalaenopsis Miva Smartissimo >< Canberra

‘450’ plants had initiated inﬂorescences within 20 weeks when grown at constant
temperatures of 14, 17, 20, and 23 °C and day/night temperatures of 20/ 14 and 23/17 °C.
Thus, ﬂuctuating temperatures provide no advantage to constant temperatures for
initiating ﬂowering (Blanchard, 2005).

Effects of Temperature on Flower Morphology

When manipulating temperature to control ﬂowering, the effects on ﬂower
morphology must also be taken into consideration. Similar to many other ﬂoriculture
crops, ﬂower size and number of some orchids is dependent on temperature. In
Miltoniopsis Augres ‘Trinity’, ﬂower diameter increased from 7.4 cm to 8.6 cm as the
mean daily temperature decreased from 23 to 14 °C (Lopez and Runkle, 2006a). For
most Phalaenopsis hybrids, the number of ﬂowers per plant increases as temperature
decreases within the range of 18 to 28 °C (Wang, 2004). However, in a white
Phalaenopsis hybrid, day/night temperatures of 20/1 5 °C resulted in plants with shorter
ﬂower stems, fewer ﬂorets, and more abnormal ﬂowers than in plants placed at 25/20 0C
(Lee and Lin, 1984). This discrepancy with the results of Wang (2004) could be
attributed to temperatures below 18 °C during the night, which was below the lowest
temperature used by Wang (2004).

Effects of Temperature on Plant Hormone and Sugar Concentrations '

How temperature affects the physiology of orchids to induce ﬂowering is not well
understood, but it has been proposed that changes in hormonal concentrations are
involved (Campos and Kerbauy, 2004; Chou et al., 2000; Su et al., 2001). Of particular
interest are the endogenous concentrations of cytokinins, auxins, and gibberellins. When

Dendrobium Second Love plants were placed at the inductive day/night temperatures of

10

25/ 10 °C and a 12-h photoperiod, endogenous concentrations of four forms of cytokinins
(zeatin, zeatin riboside, isopentenyladenine, and isopentenyladenosine) in lateral buds
increased by a factor of 3 to 4.5 when measured 15 d after the start of inductive
treatments (Campos and Kerbauy, 2004). These increases were accompanied by a 24%
decrease in abscisic acid (ABA) concentrations.

Increased cytokinin concentrations have also been reported in Phalaenopsis when
plants are moved to temperatures that induce ﬂowering. In particular, Chou et al. (2000)
reported higher concentrations of zeatin, zeatin riboside, and dihydrozeatin in
Phalaenopsis Taisuco Snow plants grown at inductive day/night temperatures of 25/20
°C compared with plants grown at 30/25 °C. The elevated concentrations of these free
base and riboside cytokinins (considered to be active forms) could be detected after 5 d.
In addition, plants at 30/25 °C had higher concentrations of glucoside cytokinins, which
are considered to be inactive cytokinin forms. Chou thus postulated that activation of
dormant reproductive buds is partially controlled, either directly or indirectly, by the
concentrations of free base and riboside cytokinins.

The role of auxins in orchid ﬂowering is less clear. Concentration of auxins more
than doubled 2 to 5 d after Phalaenopsis amabilis were moved to the inductive day/night
temperature of 22/17 °C (Fouche, 1997). In contrast, it took 30 d for the auxin
concentrations of Dendrobium Second Love to signiﬁcantly increase (by 57%) at a
day/night temperature of 25/10 °C known to induce ﬂowering (Campos and Kerbauy,
2004)

A third plant hormone that is thought to play a role in the control of ﬂower

initiation in orchids is gibberellic acid (GA). Shoot tips of Doritaenopsis Memoria John

11

Craig (Doritaenopsis Minho Princess >< Phalaenopsis equestris) at inductive day/night

temperatures of 25/20 °C contained twice the concentration of active GA] and half the

concentration of inactive GAg as plants grown at the ﬂower inhibiting temperature of
30/25 °C (Su et al., 2001). This suggests that plants at the warmer temperature convert

more GA, to GAg than plants at the lower inductive temperature. When plants grown at

30/25 °C were injected with 0.5 ug GA3, an active form of gibberellin, they developed as

many ﬂower primordia as plants under inductive temperature conditions, providing
further evidence that high temperature inhibits ﬂowering at least partially by preventing
an increase in the concentration of active endogenous gibberellins.

Another physiological factor that regulates ﬂowering of orchids and is affected by
temperature is sugar content. When the sucrose concentration in Phalaenopsis Secret
Dream (P. White Dream X P. Yukimai Dream) was measured in plants grown at 23 or 27
°C, plants at 27 °C had a lower concentration of sucrose per unit area within 2 weeks of
being placed at this temperature (Kataoka et al., 2004). This decreased concentration of
sucrose was correlated with a delay in inﬂorescence emergence. Plants at 27 °C had
visible inﬂorescences an average of 9 d after the control. However, it is unknown
whether the increase in sucrose concentration serves as a signal in ﬂoral induction or is a

result of the movement of photosynthate to the bud to initiate ﬂowering.

Effects of Photoperiod on Orchid Flowering
Similar to other environmental factors, the effect of photoperiod on ﬂowering of
orchids appears to be very diverse among orchid species and even cultivars. While a

number of genera, including Dendrobium and Vanda, are unresponsive to photoperiod

12

(Sheehan et al., 1965; Murashige, 1967), some economically important genera have been
reported to be photoperiodic.

Of the Cattleya species and cultivars that have been studied, the majority had
either a qualitative or quantitative ﬂowering response under SDs. Long days (LD)
inhibited ﬂowering in Cattleya warscewiczii Rchb. f., C. labiata Lindl., C. mossiae
Parker ex Hook., C. percivaliana Rchb. f., and C. trianaei Linden & Rchb. f. (Rotor,
1952). Cattleya trianaei did not require a speciﬁc photoperiod to initiate ﬂowering, but
ﬂower development only continued under short 8-h days (Holdson and Laurie, 1951;
Went, 1957). Cattleya Bengrave >< Bc. Queen Emma and C. Jean Barrow x C.
Minnehaha plants developed 9.7 or 8.0 ﬂowers per plant under natural or SDs,
respectively, while those under LDs formed a mean of only 0.6 ﬂowers per plant
(Sheehan et al., 1965).

A few researchers have claimed that Phalaenopsis is also a short-day plant (SDP).
Phalaenopsis grown under SDs ﬂowered 5 to 7 d faster than those under natural days at
22-23 °C (Yoneda et al., 1991) and had greater ﬂowering under an 8-h day than a 16-h
day (Went, 1957). Despite these results, it has been suggested that Phalaenopsis
ﬂowering is not responsive to photoperiod because the earlier ﬂowering could be
attributed to a cooler average daily temperature under SDs, which is favorable for
inﬂorescence initiation of Phalaenopsis (Ichihashi, 1997).

In some cultivars of Phalaenopsis, there is an interaction between the effects of
photoperiod and temperature on ﬂowering. Phalaenopsis Toyland, a cultivar developed
by the USDA for pot plant production, was found to be day neutral at 13 °C, but required

SDs to ﬂower when grown at temperatures >27 °C (Griesbach, 1985). A similar

13

suggestion was made by Sakanishi et al. (1980), who thought the effect of photoperiod
was secondary to the effects of temperature and only a factor when the plants were at the
critical temperature required for inﬂorescence initiation.

In a number of orchids that require cool temperatures to initiate ﬂowering,
including Cymbidium, Paphiopedilum insigne (Wall ex Lindl.) Pﬁtzer, and Dendrobium
nobile Lindl., there is no inﬂuence of photoperiod during the cool temperature on
ﬂowering (Rotor, 1959). However, in some instances the photoperiod immediately
proceeding low-temperature induction is more important than the photoperiod during
cool temperature conditions. For instance, ﬂowering of Zygopetalum Redvale ‘Fire Kiss’
was promoted most when exposure to cool temperatures was preceded by a short
photoperiod (Lopez et al., 2003). The percentage of ﬂowering plants was greatest when
plants were grown under a 9-h short-day for 4 to 8 weeks and then placed at 11 or 14 oC.
The same conditions elicited the most abundant ﬂowering of Miltoniopsis Augres
‘Trinity’, although temperature played a much larger role in stimulating ﬂowering than
did photoperiod (Lopez and Runkle, 2006b).

Similar to the effects of temperature on ﬂowering, a couple of hypotheses have
been proposed to describe the physiological effects of photoperiod on ﬂowering. Huang
et a1. (2004) suggested that an inductive photoperiod decreases total and free IAA
endogenous concentrations, which promotes ﬂowering, in Doritis pulcherrima Lindl.
When this facultative SDP was grown under 9-h days for 30 d, the total IAA
concentrations in the leaves were half that of the total IAA concentrations in plants grown

under l6-h days for the same duration. There may be some interconversion of IAA forms

14

because, although the concentrations of amide-IAA were 6.5 times less, the
concentrations of ester IAA were 3.5 times greater under SD than LDs.

In quantitative LD plants (LDP), such as Psygmorchis pusilla (L.) Dodson &
Dressler, it has been suggested that photoperiod affects ﬂowering through the
carbohydrate concentrations it allows to accumulate (Vaz et al., 2004). In such plants,
there is no critical photoperiod below which plants will not ﬂower, but as the length of
the photoperiod increases, the number of inﬂorescences increases. The increase in the
number of inﬂorescences was attributed to an increase in photosynthesis, and thus

carbohydrates, from a higher photosynthetic daily light integral.

Effects of Light Quantity on Orchid Flowering

In addition to photoperiod, instantaneous light intensity and the daily light integral
(DLI) can inﬂuence ﬂowering. Sufﬁcient light needs to be provided for photosynthesis
without causing stress on the plant. Typically, there is a minimum light intensity that
must be maintained for ﬂowering to occur. Wang (1995b) determined that Phalaenopsis
requires a minimum of 60 umol-m‘z-s'l of light to induce ﬂowering within about one
month of being placed at inductive temperatures (20 °C day/ 15 oC night). Then, if a
plant is to ﬂower a second time within a year under cool-white ﬂuorescent lighting with a
12-h photoperiod, plants must receive at least 36 timol'm'z's'l throughout the day to
provide a DLI of 1.6 mol'm'z-d'1 (Wang, 1997). However, even higher light intensities
stimulate ﬂowering of Phalaenopsis. Phalaenopsis Secret Dream (P. White Dream X P.
Yukimai Dream) seedlings had more ﬂowers per inﬂorescence and inﬂorescences per

plant when grown under a DLI of 4.3 mol-m'zd'l at 20 °C for 6 weeks than plants

15

receiving a DLI of 0.6 or 1.7 mol-m'zd'l (Kataoka et al. 2004). A number of other

orchids also require certain minimum light intensities to initiate ﬂowering or have greater
ﬂowering as light intensity increases, including C ymbidium (Rotor, 1959), Odontioda
(Kubota et al., 2005), and Vanda (Murashige et al., 1967).

In some orchids, not only is the light intensity during the ﬂower induction stage
important, but the light intensity preceding this stage can also affect ﬂowering. When

Phalaenopsis were placed at a day/night temperature of 23/1 8 °C to induce ﬂowering,

greater than 80% of plants that were previously exposed to high light (50-450 umol-m'z-s'
1) ﬂowered, while only 60% of those previously exposed to low (<60 umol-m'z-s") and

moderate light (10-100 umol-m'z-s'l) ﬂowered (Kubota and Yoneda, 1993b). This could

be attributed to greater photosynthesis occurring in plants grown under higher light,
which means more photoassimilates are available for use in ﬂower development.

Light intensity can be manipulated by orchid producers to inﬂuence the
scheduling of ﬂowering. Flowering of Phalaenopsis was delayed by 1 to 3 months,
depending on the year, without any adverse affects by exposing plants to weekly cycles
of 4 d in darkness followed by 3 d in light (Wang, 1998a). Wang (1995b) also
demonstrated that ﬂowering was delayed without any detrimental effects when plants
were placed in total darkness at 20/15 °C for 2 to 6 weeks. These techniques can be used
to delay ﬂowering until a desirable time, such as for major holidays.

Responses of ﬂowering to light intensity have been attributed to effects on sugar

and carbohydrate concentrations. After three weeks of being exposed to a DLI of only
0.6 mol'm'Z-d'l, mature leaves of Phalaenopsis Secret Dream (P. White Dream X P.

Yukimai Dream) contained lower amounts of sucrose, fructose, and total soluble sugars

l6

than plants receiving a DLI of 4.3 mol-m'Z-d'l (Kataoka et al., 2004). Inﬂorescence

emergence was also delayed by 47 (I compared to control plants and was correlated with
sucrose content. Kubota and Yoneda (1993c) reported a similar response; lack of
ﬂowering under low light was correlated with a reduction in the concentration of
reducing sugars in the plant.

However, there appears to be another factor involved in the control of ﬂowering
by light in Phalaenopsis. As expected, when Phalaenopsis Yukimai plants were placed
in complete darkness for 31 d, sucrose, glucose, fructose, and total sugar content was

reduced when compared to that before plants were placed in darkness or in plants
exposed to 250 umol-m'z-s'l for 14 h per day (Kubota et al., 1997). However, when the
plants were transferred from darkness to light, ﬂowering time was similar to plants that
were not exposed to continuous darkness. These results suggest that reduced sugar
concentrations are not completely responsible for delayed ﬂoral initiation under low light

intensities.

Effects of Fertilization and Potting Media on Orchid Flowering

Nitrogen is an inﬂuential nutrient on ﬂowering of orchids (Wang and Gregg,
1994). Phalaenopsis plants developed 24% more ﬂowers when plants received 30 mg-L'l
nitrogen at each irrigation compared with plants that received it at only every fourth
irrigation (Wang, 2000). In addition, Phalaenopsis had a dose-response to fertility;

increasing the fertilizer rate of 20N-8.6P-16.6K from 50 to 200 mg°L'l N increased

ﬂower number, stalk diameter, and inﬂorescence number (Wang and Gregg, 1994).

17

Although some orchid growers suggest that terminating fertilization or using high
concentrations of phosphorus stimulate ﬂowering of Phalaenopsis (Gordon, 1989),

neither of these techniques are effective. Phalaenopsis that received continuous
fertilization with 20N-8.7P-l6.6K at a rate of 100 mg-L'l N had a greater number of

ﬂowers than plants that stopped receiving fertilization 30 d before inﬂorescences were
visible (Wang, 2000). Phalaenopsis in which fertilization was terminated had a 34%

decrease in the number of ﬂowers and ﬂower longevity was reduced by 12 (1.
Additionally, high concentrations of phosphorus (398 mg-L'l) had no inﬂuence on the
time to inﬂorescence emergence, time to ﬂowering, or ﬂower size when compared to the
control, which received 44 mg-L'l phosphorus. In fact, the number of ﬂowers was

actually less on plants that received high phosphorus (Wang, 2000). However, some
phosphorus is required for ﬂowering, particularly during the ﬂower bud development
stage (Kubota and Yoneda, 1993a).

Potting media components and characteristics inﬂuence the availability of
nutrients, and thus ﬂowering. Phalaenopsis grown in a potting mix consisting of 70% to
80% bark and 20% to 30% peat developed more ﬂowers than plants grown in a mix
consisting of pure bark (Wang 1995a; Wang 1998b). Salinity of the media is also
inﬂuential because as the soluble salt content of irrigation water increased, the ﬂower
diameter decreased (Wang, 1998b). Plants watered with reverse osmosis water had
slightly larger ﬂowers than those watered with municipal water, which had a higher

concentration of soluble salts (Wang, 1996).

18

Cytokinins

The ﬂowering of some orchids can be manipulated using plant hormones,
speciﬁcally cytokinins. Although great advances have been made in understanding the
effects of cytokinins and how their effects are mediated, there are still many unanswered
questions, particularly with respect to cytokinin synthesis.

There are two main types of natural cytokinins: isoprenoid cytokinins and

aromatic cytokinins (Mok and Mok, 2001). They differ in the type of side chain at the N-
6 terminus, but almost all cytokinins are N6-substituted aminopurines (Taiz and Zeiger,

2002). The side chain on isoprenoid cytokinins is derived from isoprene units while that
on aromatic cytokinins is an aromatic side chain. These two types of cytokinins can
occur in four forms: the free base form; the riboside form, which has a ribose sugar
connected to the 9 N; the ribotide form, in which the ribose sugar on the 9 N contains a
phosphate group; and the glycoside form, in which a sugar molecule is connected to the
3, 7, or 9 N. The active form of cytokinins is the free base form (Taiz and Zeiger, 2002).
The most commonly occurring natural cytokinin is zeatin, but dihydrozeatin and
isopentenyladenine (iP) are also frequently present in plants (Taiz and Zeiger, 2002).
Synthetic forms of cytokinins have also been produced. The ﬁrst cytokinin
discovered was actually a synthetic cytokinin extracted from autoclaved DNA and was
named kinetin (Miller et al., 1956). Other commonly used synthetic cytokinins are
phenylureas (Mok and Mok, 2001) and benzyladenine (BA), which naturally occurs in

some plant species (Van Staden and Crouch, 1996; Nandi et al., 1989).

I9

Forms of Benzyladenine

BA occurs in multiple forms, with the free-base form being the most active (Van
Staden and Crouch, 1996). Other forms include BA ribonucleoside and BA nucleotide.
These forms are still considered to be active because they are readily converted to free
bases. The BA ribonucleoside is thought to be the form used for translocation because it
is the most abundant form of BA found in xylem sap after exogenous application of BA
(Van Staden and Crouch, 1996). The BA nucleotide is also thought to have a role in
translocation. Two less common forms of BA that are typically only found as minor
metabolites are the di- and tri-phosphates of BA ([9R-DP]BA and [9R-TP]BA). BA can
also be N-conjugated, but the conjugates are considered inactive because they are not
readily converted back to the free base (Van Staden and Crouch, 1996).
Cytokinin Biosynthesis

Cytokinin synthesis occurs in both roots and shoots of plants and in a variety of
cells (Hwang and Sakakibara, 2006). The most prevalent site of cytokinin synthesis is
thought to be the apex of the root, from where cytokinins are moved to the shoots through
the xylem. However, embryos, leaves, and immature fruit are also sites of cytokinin
synthesis (Grayling and Hanke, 1992; Taiz and Zeiger, 2002). The shoot of the plant
may play a greater role in cytokinin biosynthesis than previously thought, as shown by
grafting experiments with the rms4 mutant of Pisum sativum L., which is known to have
reduced concentrations of cytokinins in root xylem. Concentrations of cytokinins in the
root xylem were decreased when a mutatant scion was grafted to wild-type rootstock;
however, root xylem cytokinin concentrations were normal when a wild-type scion was

grafted to mutant rootstock (Beveridge et al., 1997).

20

Free cytokinins can be formed by the release of cytokinins from transfer RNA
(tRN A). Transfer RNA contains a number of nucleotides with modiﬁed bases, which are
thought to be the result of post-transcriptional processing (McGaw and Burch, 1995).
Some of the modiﬁed nucleotides are cytokinins and are released when the tRNA is
broken down. However, these cytokinins from tRNA probably do not greatly contribute
to the free cytokinin pool because their release is neither tissue speciﬁc or highly
controlled (Mok et al., 2000). A second, and probably the most prevalent way that
cytokinins are formed, is through the synthesis of iP. The enzyme responsible for the
ﬁrst committed reaction of this biosynthesis pathway in plants is adenosine phosphate-
isopentenyltransferase (IPT). It uses the substrates dimethylallyl diphosphate (DMAPP)
or hydroxymethylbutenyl diphosphate (HMDBP) and one of the adenosine 5’-
phosphates, and converts them to iP by transferring an isopentenyl group from DMAPP
to adenosine 5’-phosphate (Hwang and Sakakibara, 2006). IPT enzymes appear to
preferentially use certain 5’-phosphates because Arabidopsis thaliana (L.) Heynh. IPT
enzymes transfer the isopentenyl group to ATP or ADP more often than to AMP (Taiz
and Zeiger, 2002). The iP can be converted to multiple forms of cytokinin. However, the
structure of BA, which has a benzyl ring on the 6N-position, differs considerably from
that of isopentenyladenine and the common cytokinin zeatin, and is thought to be
synthesized in a different manner than iP cytokinins, although the details are presently
unknown (Van Staden and Crouch, 1996).
Cytokinin Signﬂg

The signaling pathway that mediates the physiological effects of cytokinins is not

yet completely understood, but some very signiﬁcant advances have been made. The

21

signaling pathway of cytokinins is believed to involve a two-component system similar to
that found in bacteria (Hwang and Sakakibara, 2006; Mok et al., 2000; Taiz and Zeiger,
2002). The two main components of this system are a sensor histidine kinase and a
response regulator (Taiz and Zeiger, 2002). The sensor histidine kinase, such as CREl of
Arabidopsis thaliana (Inoue et al., 2001), detects the presence of cytokinin and initiates
the plant response. When cytokinin binds to the receptor domain of CREl, the kinase on
its histidine kinase domain phosphorylates its receiver domain, which in turn
phosphorylates an Arabidopsis histidine phosphotransfer (AHP) protein in the cytosol.
The phosphorylated AHP protein then travels into the nucleus and phosphorylates an
Arabidopsis response regulator (ARR) protein, which stimulates transcription of type-A
ARRs. The resulting type-A ARR proteins are thought to cause the changes in cellular
function (Taiz and Zeiger, 2002; Hwang and Sakakibara, 2006).
Exogenously Applied Cytokinin

When exogenous cytokinins are applied to plants, they are converted to a number
of different compounds (Letharn and Palni, 1983). Upon uptake of the applied cytokinin,
it is usually converted to a nucleotide (McGaw and Burch, 1995). BA in particular is
partially converted to ribosylbenzyladenine (BAR) and ribosylbenzyladenine
monophosphate (BARMP), with some interconversion between the three forms, when
supplied to cut ﬂowers of Dianthus caryophyllus L. ‘Kaly’ (Van Staden et al., 1990).
However, when BA is applied to soybeans, the majority of BA taken up is cleaved to
yield an adenine and a compound similar to benzoic acid (Letharn and Palni, 1983).

Once cytokinin enters the plant, it can be moved through either acropetal or

basipetal transport. Transzeatin-type cytokinins are most common in the xylem, and iP-

22

type cytokinins are most common in the phloem (Hirose et al., 2008). Such
differentiation in location suggests that there is a selective transport system involved in
cytokinin movement. It has been proposed that components of the purine permease
family and equilibrative nucleoside transporters are responsible for the movement of
cytokinin nucleobases and cytokinin nucleosides, respectively (Hirose et al., 2008).

However it is moved, cytokinin is thought to play an important role in both short-
and long-distance signaling (Hwang and Sakikabara, 2006). Transzeatin-type cytokinins,
which comprise the majority of cytokinins found in xylem, are important in long-distance
signaling of nitrogen status. The concentration of nitrate around the roots governs the
proportion of transzeatin left in the roots or transported through the xylem (Hwang and
Sakikabara, 2006). On the other hand, cytokinin involvement in apical dominance is
more localized. Increasing cytokinin synthesis in single lateral buds of Nicotiana
tabacum L. only affected the growth of the modiﬁed bud and not any other buds nearby
(Faiss et al., 1997).
Physiological Effects of Cytokinins

Cell Division. Cytokinins were ﬁrst discovered as substances that stimulated cell
division. Concentrations of 0.001 mg-L'l of kinetin were enough to increase cell
division in a number of tissue cultures (Miller et al., 1956). Additionally, when
Nicotiana tabacum L. ‘Samsun NN’ plants were engineered to have reduced cytokinin
concentrations through increased expression of cytokinin oxidase, the number of leaf
cells produced was only 3% to 4% of that of the wild-type plant, further suggesting

cytokinins are required for the cell division necessary for leaf growth (Werner et al.,

23

2001). As more knowledge was gained on kinetin and related compounds, the number of
cytokinin-elicited physiological responses increased.

Leaf Expansion. Cytokinins are also known to promote leaf expansion. Low
concentrations (00001-0001 mg-L'l) of kinetin were effective in increasing leaf

expansion of Phaseolus vulgaris L. ‘Burpee dwarf” by 1.6 to 2.1 times within 48 h in
darkness (Scott and Liverrnan, 1956). However, there was a trade-off; while cytokinins
stimulated growth of the treated leaf, growth of nearby untreated leaves was suppressed
(Leopold and Kawase, 1964).

Organogenesis. Cytokinins interact with auxins to determine organ formation. A
high cytokininzauxin ratio in undifferentiated tissue elicits shoot production, while a low
ratio promotes root production (Skoog and Miller, 195 7).

Lateral Bud Growth. Another way by which cytokinins inﬂuence plant
morphology is through the release of lateral buds from apical dominance. Cytokinins act
antagonistically to auxins, which maintain apical dominance by inhibiting growth of
lateral buds. The presence of kinetin prevented auxins from inhibiting the growth of
excised buds of Pisum sativum L. var. Alaska (Wickson and Thimann, 195 8). A 1:1

molar ratio of auxin to cytokinin was needed for the inhibition to be prevented.
Supplying 2 mg-L'l kinetin to excised shoots with the apex left intact caused lateral buds

to grow ﬁve times as much as the untreated control. In addition, the kinetin-treated buds
of excised shoots with the apex left intact achieved 74% of the growth of buds released

from apical dominance by removal of the shoot apex (Wickson and Thimann, 195 8).
Similarly, I mg'L'l BA applied to quiescent buds on Nicotiana tabacum var. Maryland

Catterton caused them to grow for 1 week after application as the result of the stimulation

24

of DNA synthesis by the BA (Schaeffer and Sharpe, 1969). After one week, the BA was
no longer able to sustain bud growth.

Flowering. Cytokinins exert at least partial control over ﬂowering of some plants.
In a number of species, exogenously applied BA promotes ﬂowering most when plants
are exposed to conditions not quite optimal for ﬂowering (Bemier et al., 1988). For
example, cytokinin application can reduce the number of SDs needed for ﬂower
induction or induce the production of ﬂower buds under noninductive LDs in certain
SDPs, including Wolﬂia microscopica (Grifﬁth) Kurz, Lemna paucicostata Hegelm., and
Perilla (Zeevaart, 1978). In addition, ﬂower induction of explants under SDs has been
achieved by using BA or zeatin in the media of the LDP Lemna paucicostata Hegelm.
(Gupta and Maheshwari, 1970). Cytokinins have also been successfully used to at least
partially overcome the cold requirement for ﬂowering in certain cold-requiring plants
(Strivastava, 1967), including Cichorium intybus L. (Michniewicz and Karnienska, 1964).

Despite the promotive effects of exogenous cytokinins on ﬂower initiation, there
is conﬂicting evidence of the role of endogenous cytokinins. The endogenous
concentrations of the free cytokinins zeatin, hydrozeatin, and isopentenyladenine were
actually lower during the ﬂoral transition phase of Nicotiana tabacum L. var. Petit
Havana SR1 (Dewitte et al., 1999). Similarly, after one SD, which can induce ﬂowering,
Xanthium strumarium L. had only one-fourth or less of the active cytokinin
concentrations present under LDs (Henson and Wareing, 1974). On the other hand,
Nicotiana tabacum ‘Samsun NN’ transformed to have reduced concentrations of

endogenous cytokinins through increased concentrations of cytokinin oxidase had fewer

25

ﬂowers and took a longer time to ﬂower than the wild type, which suggests that
endogenous cytokinins play a role in ﬂower induction (Werner et al., 2001).

Cytokinins have been postulated to increase ﬂowering by stimulating cell division
and shortening the cell cycle (Bemier et al., 1988). When cytokinin is applied to the
meristem of a plant under conditions that are not conducive to ﬂowering, changes in the
meristem that normally occur during ﬂower induction begin to take place (Lej eune et al.,
1994). However, there are factors in addition to cytokinin involved in ﬂower initiation;
although cytokinins increased the percentage of buds that underwent mitotic activity
when applied at the beginning of just one LD in the LDP Sinapis alba L., they did not
result in ﬂower initiation under SDs (Bemier et al., 1988).

Photosynthesis. Cytokinins play important roles in the capability of plants to

photosynthesize. First, cytokinins accelerate chlorophyll synthesis when applied to plants
before exposure to light. For example, the application of l mg-L'l BA to excised

cotyledons of C ucumus sativus L. caused grana formation within 4 h, which did not occur
in non-treated seedlings (Harvey et al., 1974) and increased chlorophyll synthesis during
the ﬁrst 8 h of exposure to light (Arnold and Fletcher, 1986). Since BA application
hastens the onset of chlorophyll synthesis once the cotyledons are exposed to light, BA
most likely induces some biochemical process involved in chlorophyll synthesis while
the cotyledons are still in darkness (Arnold and Fletcher, 1986). Second, BA increased
the activity of the enzymes ribulose 1,5-diphosphate carboxylase and NADP-dependent
glyceraldehyde 3-phosphate dehydrogenase, both of which are important in the carbon

ﬁxation steps of photosynthesis (Harvey et al., 1974). Third, BA increased stomatal

26

conductance, and thus the ability to use atmospheric C02 for photosynthesis in F ragaria
>< ananassa Duch (Guo et al., 2006).

Translocation. Exogenous cytokinin application inﬂuences the translocation of

certain carbon compounds. The application of 990 mg-L'l BA increased the transport of

14C fed to a lower leaf to nearly fully-expanded leaves of Vitis vinifera L. within 24 h

after treatment (Quinlan and Weaver, 1969). Application of BA to mature leaves was
less effective. Additionally, kinetin application increased amino acid translocation and
accumulation in excised Nicotiana rustica L. leaves in both light and dark conditions.
Amino acids were translocated to the portion of the leaf to which kinetin was applied
(Mothes and Engelbrecht, 1961).

Senescence. Cytokinins can also delay senescence, which is often desirable in
horticulture. For example, 10 mg-L'l BA applied to broccoli heads caused greater

chlorophyll retention (Dedolph et al., 1962), and kinetin delayed senescence in excised
Xanthium pennsylvanicum Wallr. leaves (Richmond and Lang, 195 7). This delay in
senescence is likely the result of increased synthesis of photosynthetic enzymes and
chloroplasts and the reduction in protein- and membrane-degrading enzymes (Mok,
1994). This hypothesis is supported by a study in which BA added to media of tissue-
cultured Spirodela polyrrhiza L. caused the photosystem II reaction center to be more
stable and prolonged its efﬁciency during senescence (Liu at al., 2006). Not only does
external application of cytokinin delay senescence, but increasing endogenous cytokinin
concentrations during senescence by placing the IPT gene under the control of a
senescence-speciﬁc promoter also delayed senescence in Nicotiana tabacum ‘Wisconsin’

(Gan and Amasino, 1995).

27

Protein Synthesis. Many of the physiological effects caused by external
application of cytokinins can be attributed to increased protein synthesis. It is not known
exactly how cytokinins mediate this effect, but it has been suggested that increased
protein synthesis is caused by increased RNA synthesis or an increase in the amount of
mRNA that is transported to polysomes to be translated (McGaw and Burch, 1995).
Increased protein synthesis could occur from increased DNA synthesis, which has been
postulated to be caused by increased DNA polymerase activity through the stimulation of

an unknown factor that modiﬁes the enzyme itself (Vazquez-Ramos and Jimenez, 1990).

Uses of BA in Horticulture
BA has a wide range of applications in horticulture on a number of different
species. Some of these applications are already used commercially, while others have

more recently been discovered.
Orchard Uses

BA can be used on apple (Malus domestica Borkh.) trees as a thinning agent,
usually at a spray concentration of 50 to 100 mg-L'l and applied 14 to 21 d after full

bloom (Buban, 2000). This causes a portion of the fruit to abscise, leading to increased
fruit size and number of blooms the next year in biennial bearing species, which tend to

have heavy crop loads one year followed by lighter crop loads the next year. BA also
increased the the number of axillary shoots when 200 to 400 mg°L'l was applied several

times as a foliar spray to run-off to actively growing apple or peach [Prunus persica (L.)
Batsch] trees (Buban, 2000; Kender and Carpenter, 1972). Lateral growth was induced

only on shoots that were actively developing.

28

BA can also overcome complications with self-incompatibility in olive (Olea
europaea L.) (Voyiatzis, 1993). Dipping ﬂowers in 400 mg-L'l BA when 50% to 80% of

ﬂowers were receptive increased self-pollinated fruit set of one of the three cultivars
tested; however, the greatest fruit set in all cultivars occurred in open pollinated controls.

BA is also effective at preventing hull-splitting of nuts. A foliar spray application of 50
or 100 mg-L'I BA to pistachio (Pistacia vera L.) tree branches to run-off reduced the

percentage of hulls splitting on those branches (Rahemi and Pakkish, 2005). Since fewer
hulls split, infection by Aspergillusﬂavus, A. parasiticus, and A. niger was decreased,
and concentrations of toxic aﬂotoxins produced by these fungi were reduced.

Lateral Branching

BA is also useful in vegetable production, particularly in increasing lateral
branching. For example, a single foliar spray application of 100 to 400 mg-L'l BA in the

fall increased the number of shoots on three different asparagus (Asparagus officinalis L.)

cultivars tested within 18 d of application and the effect lasted for at least 35 d
(Mahotiere et al., 1993). However, fall applications of 25 to 100 mg-L'I BA had no

residual effect the next spring even though spear sprouting increased immediately after
the application (Uesugi et a1, 1995).
Lateral branching was also increased by the application of exogenous BA to

strawberry (Frageria >< anassa Duch.) through the increased formation of runners (Pritts
et al., 1986). A single spray application of 50 mL of 50 to 400 mg-L"l BA to each four-

plant replicate of a day-neutral strawberry was more effective than multiple applications.
However, this response may be cultivar dependent because a single application of BA did

not increase runner production in the day-neutral strawberry cultivars used by Kender et

29

a1. (1971) and Dale et a1. (1996). Although BA alone did not increase runner formation
on these two cultivars, a combination of BA and GA3 did.

Uses in Propagation

 

BA increased the number of dwarf shoots, which are used in asexual propagation,
of ponderosa pine (Pinus ponderosa Laws.) and jack pine (Pinus banksiana Lamb.)

(Cohen and Shanks, 1975; Browne et al., 2001). A spring spray application of 33 mL per
branch of 500 or 1000 mg-L'l BA on ponderosa pine increased the number of shoots that

developed buds from 0 to almost 120, but was even more effective when the terminal bud
was also removed (Cohen and Shanks, 1975). On jack pine a one-time spray application

(60 mL per plant) of 62.5 or 125 mg-L'l BA in combination with pruning increased the

number of dwarf shoots without negatively impacting subsequent rooting of the shoots

(Browne et al., 2001).

Uses of BA in Floriculture

BA is becoming increasingly useful in ﬂoriculture and is now commonly applied
to several commercially important crops. The purposes for its use are wide, including
ﬂower induction, increasing shoot number, and increasing postharvest quality and
longevity.

Lateral Branching

 

BA increases the release of dormant axillary buds in several commercial

ﬂoriculture crops, including several in the Cactaceae family. Soaking the apical end of
strawberry-pear cactus [Hylocereus trigonus (Haw) Saff.] cuttings in 50 or 100 mg'L'l

BA increased the number of cuttings that sprouted buds from 13% to 100% and the

30

number of buds per cutting from 1.0 to 1.9 or 2.4, respectively (Shimomura and F ujihara,
1980). Similarly, a spray of 200 mg-L'l BA at a volume of 1 L per 36 plants increased
the average number of shoots per plant on gold star cactus (Mammilaria elongate D.C.
‘Gold Star’) and peanut cactus (C hamaecereus silvestri Britt & Rose ‘Peanut Cactus’) by
10.7 and 11.8 shoots, respectively, compared with the control (Sanderson et al., 1986).
BA has also proved useful to increase branching of potted foliage plants. Peace

lily (Spathiphyllum >< hybrida) ‘Tasson’ treated with a drench, which was more effective
than a spray, of 10 mL per 10 cm pot of 250 to 1,000 mg-L'l BA formed 4.3 to 13 times
more basal shoots as control plants within 8 weeks of application (Henny and Fooshee,
1985). However, within 20 weeks of application, control plants had almost as many
basal shoots as those treated with BA. A BA application of 250 to 750 mg-L'l also
increased the number of basal shoots of Dieffenbachia hybrid AREC-A #7901 (Henny,
1986); three foliar sprays (about 10 mL per plant) of 750 mg-L'l BA increased the
average number of basal shoots from zero (in the control) to seven basal shoots per plant.
Branching also increased three-fold when dieffenbachia ‘Welkeri’ [Dieﬂenbachia

maculate (Lodd.) G. Don] was sprayed with 500 or 1000 ngl BA (Wilson and Nell,

1983). A single spray (about 10 mL per plant) of 250 or 500 mg'L'l BA also increased

branching of baby rubberplant [Peperomia obtusifolia (L.) A. Dietr.] by 61% or 104%,
respectively (Henny, 1985).

BA stimulates branching on certain ﬂowering crops, one of which is geranium
(Pelargonium hortorum Bailey). Two forms of BA increased the number of branches on

geranium ‘Dark Red Irene’ compared to untreated controls when applied at the time of

31

pinching (Carpenter and Carlson, 1972). The spray concentrations used were 1,000
mg-L'] of BA and 75 mg-L'l of 6-(benzylamino)-9-(2-tetrahydropyran-yl)-9H-purine,
which increased the total number of branches from a mean of 6.9 to 9 to 10. On
miniature climbing rose (Rosa ‘Jeanne la Joie’), nine spray applications of 100 mg-L'l

BA at 2-d intervals caused a 1.3 to 1.4-fold increase in the length of lateral shoots and a
2.1 to 2.8-fold increase in ﬂower number within 8 weeks (Richards and Wilkinson,
1984). Similarly, applying 0.07 to 0.1 g of a paste of 0.5% BA and 0.5% adenine directly
to lateral buds of hybrid rose (Rosa hybrida L.) ‘Forever Yours’ and ‘Regal Gold’
increased the percentage of buds that developed shoots from zero to 34 to 64 (Parups,
1971). This paste was most effective at increasing the number of lateral buds on roses
when applied to round (not ﬂattened) pea-sized buds (Ohkawa, 1979). However,
effectiveness was also dependent on the time of year that the BA was applied.

Although BA can increase the number of lateral shoots on a wide array of
ﬂoriculture CI'OpS, it may not be effective on all species. For example, concentrations of
100 to 750 mg-L'l BA applied as a foliar spray to zinnia (Zinnia elegans Jacq. ‘Envy’)
and snapdragon (Antirrhinum majus L. ‘Yellow Monarch’) did not increase the number
of shoots (Jeffcoat, 1977). However, a higher rate, more frequent applications, or both
may elicit such a response.

Interaction between BA and Environmental Conditions

The environmental conditions in which BA is applied can inﬂuence its effect on a
number of species. For example, application of 50 to 200 mg-L'I BA to Thanksgiving

cactus [Schlumbergera truncata (Haw.) Moran] and Easter cactus [Rhipsalidopsis

gaertneri (Regel) Moran] increased either ﬂower bud number or phylloclade number,

32

depending on the environmental conditions at the time of application (Ho et al, 1985;
Heins et al., 1981; Boyle et al., 1988; Boyle, 1992, 1995). Flower bud number increased
when plants were under conditions that induce ﬂowering (short days for Thanksgiving
cactus and long days for Easter cactus); the number of phylloclades increased under
conditions promoting vegetative growth.

In addition to day length, temperature can also regulate the effects of BA, such as
in brown boronia (Boronia megastigma Nees.) and white myrtle (Hypocalymma
angustifolium Endl.) (Day et al., 1994). At temperatures of 18 to 25 °C, which are

favorable for vegetative growth, three sprays (25 mL per plant) of 50 (for brown boronia)
or 200 mg'L'I (for white myrtle) BA increased lateral vegetative growth. At day/night

temperatures of 17/9 °C, which induces ﬂowering, BA decreased the time to ﬂower.
However, BA also reduced the percentage of axils ﬂowering in white myrtle, but not in
brown boronia, compared with untreated plants.

Light intensity is another environmental factor that can inﬂuence the efﬁcacy of
BA applications. BA at 100 to 500 mg-L'l increased the number of lateral shoots on

carnation (Dianthus caryophyllus L.) ‘White Sim’, fuchsia (Fuchsia L.) ‘Ridestar’,
Chrysanthemum (Dendranthema grandiﬂora Tzvelev.) ‘Bright Golden Anne’, poinsettia
(Euphorbia pulcherrima Will. ex Klotzsch) ‘Annette Hegg’, and petunia (Petunia
thbrida hort. Vilm.-Andr.) ‘Suttons Large Flowered’ by 1.5 to 2.3 times under
favorable conditions. However, under a lower light intensity, the newly initiated laterals

did not properly elongate and chlorosis occurred (Jeffcoat, 1977).

33

Postharvest of Potted Crops

 

Application of BA can increase the postharvest life of a number of potted and cut
ﬂoriculture crops. A foliar spray of BA and GA4+7 is commonly used commercially on
lower leaves of Easter lily (Lilium longiﬂorum Thunb.) to prevent lower-leaf chlorosis
and necrosis (Dole and Wilkins, 2004). A combined application of 25 mg-L'I BA and
GA4+7 inhibited leaf yellowing in plants that were placed in dark cold storage for three
weeks (Han, 1997). However, application of 500 mg-L'l BA alone only inhibited leaf
yellowing of cold-stored plants, and had no effect on plants that never received cold

storage. The reduction in respiration rate that occurs when Easter lilies are treated with

GA and BA may be the physiological basis for the delay of leaf senescence (Han, 1995).
A similar combination of BA and GA4+7 also inhibited leaf yellowing of potted
Asiﬂorum lilies (hybrids of Lilium longiﬂorum and Asiatic hybrids) and ‘Stargazer’ lilies
(Lilium spp.) (Funnell and Heins, 1998; Ranwala and Miller, 1998).

BA also inhibited leaf yellowing of some Chrysanthemum cultivars that are prone
to leaf-yellowing (Reyes-Arribas, 2000). A spray application of 50 mg-L'l BA to the
leaf-yellowing prone cultivar ‘Tara’ doubled the concentration of chlorophyll per gram
fresh weight after 12 d in darkness. However, the application of BA provided no
commercial beneﬁt to cultivars that are not prone to leaf yellowing.

Application of BA can also have a positive effect on poinsettia by reducing bract-
edge necrosis (McAvoy and Bible, 1998). A BA spray application of 100 mg-L'l to

bracts that are just beginning to show necrosis prevented further necrosis during the

34

following 34 (1. While 29% of bracts on control plants showed necrosis, only 3.5% of
bracts on the BA-treated plants developed any necrosis.
Postharvest of Cut Flowers

BA can also delay leaf yellowing, thereby increasing the postharvest life, of
several cut ﬂowers, including Peruvian lily (Alstroemeria hybrida L.) (Dai and Paull,
1991; Hicklenton, 1991), goldenrod (Solidago canadensis L.) (Philosoph-Hadas et al.,

1996), and Asiatic and Oriental lilies (Han, 2001). Spraying cut goldenrod ‘Yellow
Submarine’ stems with 2.25 mg-L'1 BA and then pulsing with 35 mg-L'l GA3 increased
postharvest leaf longevity by 75% (Philosoph-Hadas et al., 1996). Similarly, a spray

application of 25 mg-L'l BA and 25 mg~L'l GA4+7 to the leaves of Asiatic lilies ‘Geneve

and ‘Vivaldi’ and Oriental lily ‘Acapulco’ before or after 2 weeks of cold storage at 3.3

°C almost eliminated leaf yellowing and reduced bud blasting caused by cold storage

(Han, 2001). The effect of BA and GA4+7 was more complicated on ‘Stargazer’ lilies.

Although a spray of 50 mg-L'l BA and 50 mg'L'l GA4+7 delayed leaf senescence,

reduced bud blasting, and increased vase life of cold-stored potted plants, both stems and
individual ﬂowers still had a shorter vase life than those that were not cold stored. Leaf

yellowing of Peruvian lily, as measured by two color indexes, was delayed when out
stems were immediately placed in a solution of 50 mg-L’l BA for 4 h (Hicklenton, 1991).
Treatment with 100 mg-L'I BA on stems that were then packed for 2 d delayed leaf

yellowing by 4 d (57%) compared with nonsprayed stems (Dai and Paull, 1991 ).
In addition to inhibiting leaf yellowing of cut ﬂowers, BA can also increase the

longevity of ﬂowers themselves. Placing Peruvian lily stems that had been packed for 2

35

d in a 100 mg-L'l BA solution increased (by 22%) the number of days until 50% of the

petals were shed (Dai and Paull, 1991). BA treatment increased vase life of other popular
cut ﬂowers including anthurium (A nthurium andraeanum Lind. ex Andre), heliconia
(Heliconia psittacorum L. f. and H. chartacea Lane ex Barreiros) (Paull and Chantrachit,
2001), lisianthus (Eustoma grandiflorum Shinn.) (Huang and Chen, 2002), King Alfred

daffodils (Narcissus pseudonarcissus L.) (Ballantyne, 1963), and carnation (Heide and
Oydvin, 1969). Placing stems of carnation in 225 mg-L'l BAP for 2 minutes increased

the number of days inﬂorescences remained suitable for display by 3 to 5 d (a 57% to
66% increase), depending on the time of year the stems were cut (Heide and Oydvin,

1969). The vase life of lisianthus ‘Heide’ increased by 3 d (44%) when stems were
placed in a solution of 50 mg-L'l BA for 24 h (Huang and Chen, 2002). Red and pink
ginger [Alpinia purpurata (Vieill.) K. Schum] vase life increased by 1.2 to 1.9 times,
depending on the time of harvest, when cut ﬂowers were sprayed with 200 mg-L'l BA
(Paull and Chantrachit, 2001). Dipping the inﬂorescences of heliconia ‘Andromeda’ in

200 mg'L'l BA more than doubled its vase life, and spraying heliconia ‘Sexy Pink’ with
200 mg-L'l BA tripled the length of its vase life (Paull and Chantrachit, 2001). Dipping

the ﬂowers of King Alfred daffodils in 146 mg-L-l BAP increased vase life by 1 d by

delaying the loss of color from the perianth, but placing stems in water containing BA

was not effective (Ballantyne, 1963).
The effects of dipping anthurium inﬂorescences in 200 mg-L'l BA is cultivar and

season dependent. Of 15 cultivars tested, BA increased the vase life of 14 cultivars by

1.4 to 3.2 times that of the control (Paull and Chantrachit, 2001). A spray of 200 mg-L'l

36

BA to run-off on anthurium ﬂowers after shipping increased vase life in the summer, but
had no consistent effect in the winter (Fukui et al., 2005). Unfortunately, treating cut
stems with BA is not effective on all species; bird of paradise (Strelitzia reginae Aiton.),

beehive ginger (Zingiber spectabilis Griff), and uluhe fern curls [Dicranopteris linearis
(Burm.) Underwood] showed no response to 1,000 mg-L’l BA (Paull and Chantrachit,
2001), although higher rates may be effective.

BA-elicited increase in vase life has been associated with a decrease in respiration

(MacLean and Dedolph, 1962). Dipping stems of Chrysanthemum ‘Standard Yellow’ and
carnation ‘Red Sim’ in 10 mg-L'I BA decreased respiration by 13.6% and 22.2%,
respectively (MacLean and Dedolph, 1962). On the contrary, a pulse treatment of 50
mg-L'l BA for 24 h increased respiration of lisianthus (Huang and Chen, 2002).
Additional research is warranted to more clearly elucidate the physiological basis for how
BA, GA, or both inﬂuence postharvest leaf, ﬂower, and inﬂorescence senescence.

Propagation
BA is useful to the ﬂoriculture and nursery industries for propagation, including

bulb or propagule formation and seed germination. In Turk’s cap lily (Lilium martagon

L.), bulblet formation from bulb scale explants was greatest when explants were placed
on a media with 0.01 mg-L'l BA for the ﬁrst eight weeks (Rybczynski and Gomolinska,

1989). The presence of BA increased the number of bulblets formed per bulb scale
explant by over four times. BA also increased germination of dense blazing star (Liatris

spicata L.) seeds (Parks and Boyle, 2002). When seeds were soaked for three minutes in
an acetone solution of 225 or 1,127 mg-L'l BA, the ﬁnal germination percentage

increased from 61% to about 90%. In addition, time to 50% germination and time

37

between 10% and 90% germination was reduced by about 1/3 and 1/4, respectively,
compared to the untreated control.

BA can be used commercially to improve ﬁeld propagation of certain herbaceous

perennials. When daylily (Hemerocallis) ‘Happy Returns’ was sprayed with 30 mL-m'2

of 2,500 mg-L'l BA at ﬂowering, the number of divisions per plant at harvest increased
from 2.4 to 3.0 (Leclerc et al., 2006). Similarly, a single spray of 5.4 mL per plant of

2,000 to 3,000 mg-L'l BA or a drench of 20 to 40 mg BA per 0.8 L pot increased the

number of both axillary and rhizomic buds that developed shoots on hosta [Hosta
sieboldiana (Lodd.) Engl.] from none in control plants to 2.0 to 5.4 offsets per treated
plant (Keever, 1994). Plants that originally had 2 or 3 offsets had less of a response to
BA compared with plants with 0 or 1 offset, which could be attributed to stronger apical
dominance in plants that started with a greater number of offsets (Keever and Brass,

1998). Conversely, there was no increase in propagule formation when 1,250, 2,500, or
3,750 mg-L'l BA was applied at 30 mL-m'2 to Hosta ‘Gold Standard’ (Leclerc etal.,

2006). Therefore, responses to BA depend on the application rate and volume, the timing
of the application, the environmental conditions, as well as the species and cultivar.

Flowering

Application of BA can inﬂuence ﬂower morphology of ornamental plants. An
application of 2,500 mg-L'l BA in a lanolin paste around the basal plate of dormant

Tulipa bulbs caused the perianth of non-parrot tulips to be parrot-like (i.e., with frilled
petals) (Saniewski et al. 1997). It was postulated that the applied cytokinin increased the
activity of the pentose phosphate pathway, which caused the parrot-like perianth by

increasing tissue differentiation. Another species in which BA affects the ﬂower

38

morphology is protea ‘Red Sunset’ [Leucospermum cordifolium (Salisb. ex. Knight)
Fourcade X L. lineare R. Br.]. One spray application of 50 mL per shoot of 200 mg-L'l

BA at the ﬂower induction stage increased ﬂower quality by increasing stem diameter
(by 13%) of the reproductive shoot and increasing (by 16%) the number of ﬂorets per
inﬂorescence (Napier et al, 1986). Multiple applications further increased ﬂoret number
and shoot diameter as well as increased peduncle length and dry mass. On carnation
‘White Sim’ and Chrysanthemum ‘Bright Golden Anne’, a 500 mg-L'l BA spray
increased ﬂower diameter and fresh weight, with younger buds having a greater increase
in ﬂower size than more mature ﬂower buds (J effcoat, 1977). It was postulated that BA
increased the amount of assimilates ﬂowing to the developing bud or caused a change in
the water balance.

Exogenous application of BA can inﬂuence ﬂower induction in some commercial
ﬂoriculture crops, one of which is orange jessamine [Murraya paniculata (L.) Jack].
Explants of orange jessamine had the greatest ﬂowering percentage when placed on a
media containing 0.1 mg-L'I BA (Jumin and Ahmad, 1999). BA itself did not increase
ﬂowering of calla lily (Zantedeschia spp.) but it enhanced the induction of ﬂowering by

GA (N aor et al., 2004). Plantlets from tissue culture that were dipped in 200 mg-L'l GA3

and 1 mg-L’I BA prior to planting had six times more plantlets develop inﬂorescences

than those treated with only GA3.

39

Effects of BA on Orchids
Use of BA in Tissue Culture

Propagation of several orchid genera and intergeneric hybrids has been improved
by including BA in tissue culture media. Including 0.1-1.0 mg-L'l BA in the media
increases the number of protocorm-like bodies, which hastens propagation of explants of
Doritaenopsis, Phalaenopsis, and Cymbidium (Fujii et al., 1999; Tokuhara and Mii,
1993). For Phalaenopsis seedlings, including 5 to 10 mg~L'l BA in the tissue culture
media increased vegetative stem length by 37% (Duan et al., 1996). The center and
lower nodes of these elongated Phalaenopsis stems can then be used for propagation.
BA can also be used to manipulate shoot formation of orchid explants in tissue culture.

Both Cymbidiumfaberi Rolfe and C. ensifolium (L.) Swartz rhizomes required 0.1 to 4.5
mg'L"l BA in the culture media to differentiate vegetative shoots (Hasegawa et al., 1985;
Lu et al., 2001). Ascocenda Kangla seedlings responded similarly to BA. The presence
of 0.5 to 4.0 mg-L'l BA in the tissue culture media caused 2.0 to 3.2 shoots per seedling

to form in 8 weeks while the control did not form any new shoots (Kishor'and Sharma,

2008)

Including BA in tissue culture media can also induce early ﬂowering in selected
orchids. For example, when the media contained 7.4 mg-L'1 BA, C ymbidium ensifolium

var. misericors rhizomes that had been derived from callus produced more ﬂower buds

and ﬂowers (Chang and Chang, 2003). These ﬂowers were smaller than in vivo ﬂowers
but contained all ﬂoral organs. The addition of 10 mg'L'l BA to media of C ymbidium

niveo-marginatum Mak induced early ﬂowering, but ﬂowering was further increased by

40

reducing nitrogen, increasing phosphorus, and root pruning (Kostenyuk et al., 1999).
Higher concentrations of BA (1,126 or 5,631 mg-L'l) were needed during the early stages
of propagation to reduce the time to ﬂowering in Dendrobium crumenatum Swartz from

the typical 5 to 7 years to only 8 to 12 months (Meesawat and Kanchanapoom, 2006).
Although BA also promoted ﬂower bud initiation in Doriella Tiny explants, it inhibited
further ﬂower development. Including 5 mg-L'1 BA in the media for shoots of Doriella
explants derived from ﬂower stalks caused ﬂower buds to develop within 2 months, but
these ﬂower buds had to be transferred to a BA-free media to reach anthesis (Duan and
Yazawa, 1994, 1995).
Vegetative Response of Potted Orchid Plants to BA

When used as a drench or foliar spray on potted plants, BA stimulated vegetative
growth in Asconcenda, Paphiopedilum, and Miltoniopsis (Kunisaki, 1975; Matsumoto
2006; Stewart and Button, 1977). In Asconcenda, one or two applications of 750 or
1,000 mg-L'1 BA applied as a foliar spray until run-off increased the number of keikis
(small plants growing from an axil of the inﬂorescence) when it came in direct contact
with the axillary buds (Kunisaki, 1975). A single application of only 1 mg-L'l BA
applied to all leaf axils increased the number of vegetative shoots (from 0.4 to 1.4) on
ﬂowered divisions of various species of Paphiopedilum (Stewart and Button, 1977).
However, there was no effect on nonﬂowered plants, which was attributed to greater
apical dominance that was maintained. BA also promoted growth of vegetative shoots in
Miltoniopsis Bert Field ‘Eileen’ and Rouge ‘Akatsuka’ (Matsumoto, 2006). In this study,

a 50 mL drench of BA per lO-cm pot at concentrations of 5,631 and 11,263 mg-L'l

41

increased vegetative shoot number by 4 to 13 times, depending on the cultivar and the
concentration.
Flowering Regmnse of Potted Phalaenopsis to BA

Studies investigating the use of BA to increase ﬂowering of orchids are more
numerous than those reporting a vegetative response, especially in Phalaenopsis, which

is the most common potted orchid commercially produced in the United States (Wang,
2004). When 0.2 L-m" of 200 or 400 mg-L“ of 6-BA was applied to Phalaenopsis

Brother Apollo ‘070’ and Phalaenopsis Golden Treasure ‘470’as a foliar spray three
times at one-week intervals, beginning at the time of transfer to a ﬂower-inducing
temperature of 23 °C, plants produced more inﬂorescences and total number of ﬂowers
than nontreated plants (Blanchard and Runkle, 2008). The promotion of ﬂowering from
the BA applications was dependent on the cultivar: Brother Apollo ‘070’ had a mean of

1.0 additional inﬂorescences per plant while Golden Treasure ‘470’ developed 3.0
additional inﬂorescences per plant. Sprays of 200 and 400 mg-L'l increased the total

ﬂower number by 3 to 7 ﬂowers, depending on the cultivar, and decreased the number of
days until an inﬂorescence was visible by 3 to 9 d. Similarly, BA accelerated ﬂowering
when plants were transferred to the cool temperatures of the highlands of Japan
(Koshigaya, Saitama) to induce ﬂowering (Yoneda and Momose, 1990). By the time

inﬂorescences emerged on 18% of the untreated control plants, inﬂorescences had
already emerged on 44% of the plants sprayed with 200 mg-L'l BA and 60% of plants
sprayed with 200 mg'L'l BA and 100 mg-L’l GA3.

Exogenous application of BA has also increased ﬂowering in hybrids derived

from Phalaenopsis. A BA spray application of 200 mg-L'l to Doritaenopsis Happy

42

Valentine (a hybrid of Phalaenopsis Otohime and Doritaenopsis Odoriko) grown at a
day/night temperature of 23/18 °C increased the mean number of ﬂowers on each
inﬂorescence from 5.6 to 7.4 and the number of inﬂorescences per plant from 1.1 to 1.3
(Kim et al., 2000). On XDorie/la Tiny (Doritis pulcherrima >< Phalaenopsis deliciosa),

another hybrid of the Phalaenopsis Alliance that often takes 3 years to ﬂower, the
application of 1 mg-L'l of BA every other day to shoot apices of plants that were only out

of tissue culture for 1 month caused early ﬂowering (Duan and Yazawa, 1995). After 2
months of this treatment in a greenhouse with an average temperature of 25 °C, plants
that received the BA treatments developed inﬂorescences while the controls receiving no
BA did not.

The timing of BA application in relation to the start of ﬂower-inducing

temperatures can inﬂuence the effect of the application. A single application of 200
mg-L'l at 0.2 L-m'2 was generally most effective at increasing inﬂorescence number of

three Phalaenopsis or Doritaenopsis cultivars when applied one week after the plants
were moved to the 23 °C ﬂower-inducing temperature (Blanchard and Runkle, 2008).
When the BA was applied at this time, plants produced 0.4 to 1.4 more inﬂorescences
than the untreated control, depending on the cultivar. Interestingly, none of the plants
treated with BA but maintained at 29 °C developed ﬂowering inﬂorescences. Therefore,
BA can not substitute for low-temperature ﬂower induction.

In addition to potted plant production, BA can improve cut ﬂower production of
Phalaenopsis. After the inﬂorescence was cut, a 2,500 mg-L'l spray of BA increased the

number of secondary inﬂorescences, the majority of which emerged from the remaining

primary inﬂorescence (Kim et al., 1999). Higher BA concentrations (5,000 and 10,000

43

mg-L'l) increased the number of inﬂorescences, but total ﬂower number was not

increased.

Flowering Response of Other Potted Orchid Genera and Intergeneric Hybrids to BA
Application of BA increased ﬂowering of C ymbidium ensifolium ‘Tekkotsusosin’

(Lee et al., 1998); however, like in Phalaenopsis, temperature, photoperiod, and season

inﬂuenced the effects of BA. The greatest ﬂowering occurred when plants were treated
with 200 mg-L'l in the fall and subsequently grown at 30/25 °C (Lee et al., 1999; Lee et
aL,2006)

Dendrobium is another genus in which ﬂowering is promoted by application of
BA. A BA application of 400 mg-L'l to Dendrobium Nodoka during the ﬁrst half of
forcing increased the number of pseudobulbs that ﬂowered following a low temperature
treatment (Higuchi and Sakai, 1977). Injection of BA into the psuedobulb is also an
effective application method in Dendrobium. When 225 mg-L'l BA (volume not
reported) was injected by free ﬂow for 5 d into mature pseudobulbs of three Dendrobium
hybrids, the number of ﬂower buds initiated increased, and although many aborted or

failed to develop, the ﬂowering percentage of plants was 60% to 80% compared to 0% of

the controls (Goh, 1979; Goh and Yang, 1978).
Sakai et al. (2000) reported that injection of BA into pseudobulbs was useful in

breaking dormancy of lateral buds on Dendrobium grown for cut ﬂowers. Injection of a
total of 0.5 mL (through ﬁve injections) of 2,252 or 22,525 mg-L'l BA into 1- or 2-year
old pseudobulbs of Dendrobium J aquelyn Thomas ‘Uniwai Princess’ during normal early
winter ﬂowering caused the plants to ﬂower in February, which is typically the non-

ﬂowering season. All pseudobulbs injected with 0.5 mL BA at 22,525 mg'L'l developed
44

inﬂorescences, with an average of 6.3 or 8.9 inﬂorescences per pseudobulb; only 20% of
control pseudobulbs developed inﬂorescences with a mean of 0.5 inﬂorescences per

pseudobulb (Sakai et al., 2000).

Spray applications of BA on Dendrobium have not been as effective at promoting
ﬂowering as injections of BA. One spray application of 2,250 mg-L'l BA did not
inﬂuence ﬂowering of Dendrobium (Sakai et al., 2000). Although one spray application
of BA did not induce ﬂowering in a separate study, multiple sprays of 200 mg-L'l BA
increased the number of ﬂower buds that initiated and developed (Zaharah et al., 1986).
After 2 applications (104 d apart), the average number of ﬂower buds initiated per plant
was three times higher than that of the control for Dendrobium Mary Mak, Dendrobium
Madam Uraiwan, Dendrobium Elyas Omar (D. Jaquelyn Concert X D. Jester), and
Oneidium Gower Ramsey.

Similar to Dendrobium, Aranda ﬂower bud initiation and development can be
stimulated by BA. Injecting a free ﬂow of 225 mg-L'l BA (volume not reported) into
stern tissue for 5 d increased the number of ﬂower buds that initiated by 9.5 times and the
number of buds that fully developed by 12 times (Goh, 197 7). Interestingly, a similar
application of kinetin did not have any effect on ﬂower bud initiation or development.
Three treatments, at 100 to 170 d intervals, of spray application of 200 mg-L'l BA for
ﬁve consecutive days to Aranda Kooi Choo, Holtumara Loke Tuck Yip, Aranthera
Beatrice Ng, and Mokara Chark Kuan, all of which are monopodial orchids, increased the
number of ﬂoral buds initiated per plant from 3.5 to 7.5 (Zaharah et al., 1986).

Although BA can increase ﬂowering in a wide range of orchids, this is not the
case for all species. In fact, a 50 mL media drench of 5,630 or 11,260 mg-L'I BA per 10-

45

cm pot of Miltoniopsis ‘Eileen’ and Miltoniopsis ‘Akatsuka’ decreased the number of
plants that ﬂowered (Matsumoto, 2006). Of the plants treated with BA, only 33% and

58% ﬂowered, compared to 96% of the control plants. This reduction in ﬂowering was
partially mitigated by a concurrent application of 866 or 1,730 mg°L'l GA with the BA.
To our knowledge, no scientiﬁc studies have reported a stimulation of ﬂowering
of Paphiopedilum by BA. A single spray application of BA at 500 mg-L'l to
Paphiopedilum Macabre X P. glanduliferum (Blume) Stein did not stimulate ﬂowering
(Miguel et al., 2008). In addition, adding BA to an application of 866 mg-L'l GA3

actually decreased the number of plants that ﬂowered from 100% to 60%.
Interaction of Cytokinins and Temperature in Orchids

There is some evidence that endogenous cytokinin concentrations are correlated
with temperatures that promote ﬂowering in orchids. When hybrid Phalaenopsis plants
were placed at the ﬂower-promoting day/night temperature of 25/20 °C for 5 d, leaves
had higher concentrations of the active cytokinins zeatin, zeatin riboside, and
dihydrozeatin compared with plants that were placed at non-inductive temperature
regimen of 30/25 °C (Chou et al., 2000). It was postulated that the higher temperatures
of 30/25 °C converted active forms of cytokinins, which at least partially control and are
needed for ﬂowering, to inactive forms. The same phenomenon was reported in
Dendrobium Second Love, where concentrations of zeatin-derived forms of cytokinins
were increased in ﬂower buds after 15 d of being placed at the ﬂower-promoting
day/night temperature of 25/10 °C compared to plants under the non-inductive

temperature of constant 25 °C (Campos and Kerbauy, 2004).

46

Interaction of Cytokinins and Other Plant Hormones in Orchids

 

Cytokinins interact with other plant hormones to inﬂuence ﬂower induction and
development in orchids. The hormone GA is of particular interest because it has both
enhanced and inhibited the effects of BA on orchid ﬂowering. In Dendrobium and

Aranda (Goh, 1977, 1979; Goh and Yang, 1978), GA enhanced the positive effects of BA
on ﬂower initiation. For example, adding 346 mg-L'l GA to an injection of 225 mg-L’l

BA increased the number of ﬂower initials per Aranda Deborah plant from 3.8 to 6.4 and
the number of inﬂorescences that ﬂowered from 2.4 to 3.2 per plant (Goh, 1977). The

average number of days from injection to ﬂower initiation increased from 7.7 d to 12.8 d

when the GA was added to the injection solution. Similarly, adding 335 mg-L'l GA to an

injection solution of 225 mg-L'l BA increased the number of initiated ﬂower buds on

Dendrobium Lady Hochoy (Goh and Yang, 1978). On the other hand, there was no
increase in ﬂower bud initiation when GA was added to the BA injection solution of two
other Dendrobium hybrids (Goh 1979; Goh and Yang 1978).

The addition of GA to a BA application can have an antagonistic effect in
Phalaenopsis and Doritaenopsis. While a 200 mg-L'I spray of BA increased
inﬂorescence number of Doritaenopsis Happy Valentine at a day/night temperature of
23/18 °C, adding 200 mg-L'l GA3 to this application delayed ﬂowering and decreased the
number of ﬂowers per plant by 35% (Kim et al., 2000). When an equal concentration of
GA3 was added to applications of 2,500, 5,000, and 10,000 mg-L'l BA to a Phalaenopsis
hybrid after the ﬁrst inﬂorescence had been harvested, the percentage of re-ﬂowering

plants decreased (Kim et al., 1999). In a separate study, the addition of 100 mg-L'I GA3

47

to a 200 mg-L'l BA spray applied to a Phalaenopsis hybrid did not signiﬁcantly change

the effects on ﬂowering from that of BA alone except to increase inﬂorescence length by
an average of 13.4 to 15.6 cm (Yoneda and Momose, 1990).
Additional examples of an interaction between BA and GA in the induction of

ﬂowering exist on Paphiopedilum, Miltoniopsis, and Dendrobium. In Paphiopedilum

Hilo’s Batman (P. Macabre X P. glanduliferum), adding 500 mg-L'l BA to an application

of 866 mg-L'] GA3 reduced ﬂowering percentage of plants from 100 to 60 (Miguel et al.,
2008). When 5,631 or 11,263 ppm BA was applied as a drench to two Miltoniopsis
cultivars, there was a reduction in the number of plants that developed inﬂorescences
(Matsumoto, 2006). The addition of 866 or 1,732 mg-L'l GA3 to the drench prevented
some, but not all, of this decrease in the ﬂowering percentage. An antagonistic effect of
GA on BA was reported on Dendrobium J aquelyn Thomas ‘Uniwai Princess’: when an

equal concentration of BA was injected 4 d before GA3, the deformed ﬂowers and

elongation of ﬂower primordia and intemodes caused by GA3 alone was prevented (Sakai

etaL,2000)

BA also appears to have some interaction with auxins to inﬂuence ﬂowering. In
Dendrobium Lady Hochoy and D. Buddy Shepler >< Peggy Shaw, IAA prevented the

promotion of ﬂowering by BA (Goh and Yang, 1978). No ﬂower buds emerged on

lants treated with 225 mg-L'l BA and 1.75 mg-L'l IAA, while plants treated with 225
P

mg‘L'l BA alone initiated an average of 4.6 ﬂower buds per plant.

48

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SECTION II

HIGH TEMPERATURE INHIBITION OF F LOWERING OF PHALAENOPSIS

AND DORITAENOPSIS ORCHIDS

63

High Temperature Inhibition of Flowering of Phalaenopsis and Doritaenopsis

Orchids

Linsey A. Newtonl and Erik S. Runkle2

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

Additional index words: ﬂower initiation, potted plants, vegetative growth

Received for publication . Accepted for publication . We

 

 

gratefully acknowledge funding from growers providing support for Michigan State
University ﬂoriculture research and the support from the Michigan Agricultural

Experiment Station.

1 Graduate student.

2 Associate Professor of Horticulture and Extension Specialist, to whom reprint requests

should be addressed (Email: runkleer@msu.edu).

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Abstract

Phalaenopsis orchids require a day temperature 526 0C to initiate'inﬂorescences,
but the night temperature is not critical for inﬂorescence initiation. We determined the
duration of high temperature required each day to prevent inﬂorescence initiation of four
Phalaenopsis clones. In Year 1 and 2, mature potted plants were grown in separate
greenhouse sections with ﬁve daily durations at 29 °C: 0, 4, 8, 12, or 24 h. The high
temperature was centered in the 16-h photoperiod (0600 HR to 2200 HR) and the
remainder of the day was at 20 °C. In Year 2, two additional 4-h at 29 °C treatments were
added earlier (0800 HR to 1200 HR) and later (1600 HR to 2000 HR) in the day as well as
an 8-h at 29 °C treatment later in the day (1400 HR to 2200 HR). Exposure to 29 °C for 28
h inhibited inﬂorescence initiation of Phalaenopsis ‘Mosella’ and ‘Explosion’, but
Phalaenopsis Baldan’s Kaleidoscope ‘Golden Treasure’ and Doritaenopsis Newberry
Parfait required exposure to 29 °C for 212 h to inhibit inﬂorescence initiation. Flowering
was completely inhibited only when high temperature exposure time was continual for
Doritaenopsis Newberry Parfait and Phalaenopsis Baldan’s Kaleidoscope ‘Golden
Treasure’ and 12 h for Phalaenopsis ‘Mosella’. The time of the exposure to 29 °C did
not inﬂuence ﬂowering percentage, but ﬂowering of Phalaenopsis Baldan’s
Kaleidoscope ‘Golden Treasure’ was delayed when 4 h of high temperature was
delivered later in the day. In contrast, plants of Phalaenopsis Baldan’s Kaleidoscope
‘Golden Treasure’ and Doritaenopsis Newberry Parfait exposed to 29 °C for 8 h later in
the day ﬂowered earlier than those exposed to 29 °C for 8 h in the middle of the day.
Plant height generally increased as duration of exposure to 29 °C increased, but high

temperature exposure had few or no signiﬁcant effects on ﬂowering characteristics of

65

ﬂowering plants. These studies indicate that as few as 8 h of high temperature can
prevent ﬂowering of some Phalaenopsis hybrids whereas others require >12 h of high

temperature exposure.

Introduction

Orchids have become a popular and economically important potted ﬂowering
plant in the past decade. In 2007, the United States Department of Agriculture (USDA)
reported that 15.4 million potted orchids with a total wholesale value of $126 million
were sold in the United States (USDA, 2008a). An estimated 75% or more of orchids
sold are potted ﬂowering Phalaenopsis, Doritaenopsis, and their related hybrids
(subsequently referred to only as Phalaenopsis; Griesbach, 2002). Phalaenopsis has
become the most popular potted orchid partly because their ﬂowers typically last for 2 to
4 months and plants are easily maintained (Wang and Lee, 1994).

Controlled production and ﬂowering is a critical factor in ornamental plant
production. Although orchid ﬂowering is generally not a well-understood phenomenon,
signiﬁcant progress has been made in understanding the role of environmental factors,
particularly for Phalaenopsis. Temperatures below 26 °C are required for 3 to 7 weeks
for a visible inﬂorescence (VI) to develop (Krizek and Lawson, 1974; Sakanishi et al.,
1980). The day temperature, not the night temperature, primarily controls inﬂorescence
induction (Blanchard and Runkle, 2006). Once plants have initiated inﬂorescences, they
take 10 to 15 weeks to ﬂower at 20 to 23 °C (Blanchard and Runkle, 2006; Sakanishi et
al., 1980). The estimated base temperature for inﬂorescence development is 10.8 °C for

Phalaenopsis Taisuco Smile, and anthesis is reached after 769 degree days once the

66

inﬂorescence is visible (Robinson, 2002). Commercial growers can use this information
to schedule Phalaenopsis crops to bloom at peak periods of demand, such as for
Christmas, Valentine’s Day, and Mother’s Day.

The objective of this study was to determine how short or moderate periods of
high temperatures each day inﬂuence ﬂowering of mature Phalaenopsis orchids. By
providing a high day temperature, commercial growers could theoretically provide a
cooler night temperature and still inhibit ﬂowering. If effective, this practice could
reduce the amount of energy consumed for heating at night, which is when approximately

80% of the heating energy is used in temperate greenhouses (Bartok, 2001).

Materials and Methods
Plant Material

Year 1. Phalaenopsis ‘Explosion’ and ‘Mosella’ were potted on 1 Jan. 2006 and
19 Jan. 2006, respectively, in 11.4-cm (575-mL) pots using a media composed of (by
volume) 75% ﬁne-grade Douglas ﬁr (Pseudotsuga menziesii [Mirb.] Franco) bark, 15%
medium-grade perlite, and 10 % Sphagnum peat and grown at noninductive temperatures
in a commercial greenhouse in California. Plants had been vegetatively propagated
through tissue culture so that plants of each hybrid were all one clone. Plants were
received at Michigan State Univ. on 21 Nov. 2006. Upon arrival, plants were placed in a
glass-glazed greenhouse with a temperature set point of 29 °C for 32 days before the
experiment began.

Clones of Doritaenopsis Newberry Parfait and Phalaenopsis Baldan’s

Kaleidoscope ‘Golden Treasure’ were potted and grown in 11.4-cm pots as described

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above. Plants were received at Michigan State University on 22 Nov. 2005 and were
repotted in early June 2006 into 11.4-cm (725-mL) translucent pots with a media
consisting of 40% medium-grade Douglas ﬁr bark (Rexius Forest By-Products Inc.,
Eugene, OR, USA), 30% medium-grade chopped coconut (Coco nucifera L.) coir
(Millenniumsoils Coir, St. Catherines, Ontario, Canada), 15% long-ﬁbre Canadian
sphagnum peat (Mosser Lee Co., Millston, WI, USA), and 15% coarse perlite (OF E Intl.
Inc., Miami, FL, USA). These plants were then grown at 29 °C for several months before
being used in Year 1. Plant sizes at the start of the experiment are listed in Table 2.1.

Year 2. Phalaenopsis ‘Mosella’, Phalaenopsis Baldan’s Kaleidoscope ‘Golden
Treasure’, and Doritaenopsis Newberry Parfait plants were grown in 11.4-cm (810-mL)
containers using a potting mix of 80% coarse (2.5-cm) pine bark and 20% ﬁne coir at
noninductive temperatures in a commercial greenhouse in Florida. Plants were shipped
to Michigan State Univ. on 7 Sept. 2007 or 19 Oct. 2007 and were placed in a glass-
glazed greenhouse with a set point of 29 °C for 9.5 or 3.5 weeks before the second
replication of the experiment commenced. Phalaenopsis ‘Explosion’ plants were not
available in Year 2 so they were not included in experimentation.
Temperature Treatments

Year 1. Five temperature treatments were used in 2006-2007: constant 29 °C, 12
h at 29 °C, 8 h at 29 °C, 4 h at 29 °C, and constant 20 °C (Table 2.2). For the remaining
periods, a temperature of 20 °C was maintained. The hours at 29 °C were centered in the
middle of the 16-h photoperiod (0600 to 2200 HR). Nine or 10 plants of each cultivar
were moved from constant 29 °C to the temperature treatments on 22 Dec. 2006. Plants

were grown at these temperature treatments for 20 weeks, and the actual weekly average

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temperatures provided are in Table 2.3. Plants that had initiated an inﬂorescence but not
yet ﬂowered at the end of the 20-week treatment period remained at the appropriate
temperature treatment until the ﬁrst ﬂower of each plant opened and the ﬂowering data
were collected.

Year 2. Plants that had been maintained at constant 29 °C were moved to the
temperature treatments on 14 Nov. 2007 for the second replication of the experiment.
Three additional temperature treatments were added to the initial ﬁve treatments, for a
total of eight temperature treatments (Table 2.2). The additional treatments included two
treatments with 4 h at 29 °C, with the 29 °C delivered either early in the day (0800 to
1200 HR) or late in the day (1600 to 2000 HR). These treatments were provided by
moving plants between greenhouses with the desired temperatures at the appropriate
times each day, and were only provided for 10 weeks. After the ﬁrst 10 weeks, during
which time all plants in these two treatments developed VI, plants were placed in the
greenhouse that was 29 °C from 1200 to 1600 HR to provide the same average daily
temperature at which they had initiated inﬂorescences. One additional treatment of 8 h at
29 °C (1400 to 2200 HR) was also added in Year 2. For each of these treatments, the
temperature was 20 °C during the remaining periods of the day. Plants were grown at
these temperature treatments for 20 weeks, and the actual weekly averages for each
temperature treatment in Year 2 are provided in Table 2.4.

To determine if plant size inﬂuenced the response to temperature treatments, 6 to
8 large Phalaenopsis ‘Mosella’ plants were placed at temperature treatments 1, 5, and 8

in Year 2 (Table 2.2) and were compared to the moderate-sized ‘Mosella’. The large-

69

sized plants had been growing at constant 29 0C for over 2 years and so had more and
larger leaves (Table 2.1.).

Greenhouse Environment

 

Plants were maintained in glass greenhouses at the Michigan State Univ. Plant
Science Research Greenhouses in East Lansing, MI. Each temperature treatment was
assigned to one greenhouse compartment in Year 1. In Year 2, each temperature
treatment was reassigned to a greenhouse compartment, with the exception of the two
additional 4-h 29 °C treatments, which were provided by moving plants daily from one
greenhouse compartment to another at the appropriate time. Whitewash and shade cloth

were used to keep the maximum instantaneous light intensity below 400 umol'm_2-s_l.

During periods without active ventilation, the vapor-pressure deﬁcit was maintained at
1.2 kPa by the addition of steam. A 16-h photoperiod (0600 to 2200 HR) was provided by
sunlight and supplemental lighting from high-pressure sodium lamps, which provided 40
to 115 umol-m—z-s-l of light, depending on the presence or absence of shade cloth
beneath the lamps, at plant canopy. Plants were individually watered as needed with
reverse-osmosis water containing water soluble fertilizer that provided (in mg-L'l) 125 N,
12 P, 100 K, 65 Ca, 12 Mg, 1.0 Fe, 1.0 Cu, 0.5 Mn, 0.5 Zn, 0.3 B and 0.1 Mo (MSU
Special, GreenCare Fertilizers, Inc., Kankakee, IL, USA) at each watering.

Temperatures were maintained using a computerized environmental control
system (PRIVA Computers Inc., Vineland Station, Ontario, Canada), which controlled
the vents, fans, heaters, and the evaporative cooling system. Transitions between
temperatures typically occurred within 15 min due to the small size of each greenhouse

compartment. Temperature in each greenhouse compartment was measured every 10 s

70

by aspirated and enclosed thermocouples positioned at plant height and a CR10 data
logger (Campbell Scientiﬁc, Logan, UT, USA) recorded hourly averages.
Data Collection and Analysis

The dates of ﬁrst macroscopic VI and ﬁrst open ﬂower were recorded for each
plant. In addition, the number of ﬂower buds per inﬂorescence was counted, and the
diameter of the ﬁrst ﬂower, the length of the inﬂorescence to the ﬁrst ﬂower, and the
total inﬂorescence length (to the tip of the inﬂorescence) were measured at ﬁrst open
ﬂower. The effect of the temperature treatments on vegetative growth was determined by
measuring the leaf span (from tip to tip of the two longest leaves opposite of each other
when held as ﬂat as possible) at both the beginning and the end of the experiment and
counting the number of new leaves (21 cm long) produced by each plant during the 20
weeks of the experiment.

The experiment was replicated in time: from Dec. 2006 to May 2007 (Year 1) and
Nov. 2007 to Apr. 2008 (Year 2). Plants of each cultivar were randomly divided among
the temperature treatments. To analyze the percentage of plants developing VI and
ﬂowering, a binomial distribution with a logit transformation was used. Differences were
declared signiﬁcant at P5005. Mean separation was performed on all other data using
Tukey’s honestly signiﬁcant difference test at P5005 in PROC MIXED of SAS (SAS

Institute, Cary, NC, USA).

71

Results
Effects of High Temperature Duration and Timing on Flowering

Phalaenopsis ‘Mosella ’. The temperature treatments of constant 29 °C, 12 h at 29
°C, and 8 h at 29 °C prevented or reduced inﬂorescence initiation (Table 2.5) and
ﬂowering (Figure 2.1A) when compared to the constant 20 °C (control) treatment. In
contrast, 29 °C for 4 h at mid-day did not affect VI or ﬂowering percentage or time to V1
when compared to plants at constant 20 °C. However, in Year 1, but not in Year 2, 4 h at
29 °C at mid-day increased the number of days until the ﬁrst ﬂower opened (Figure
2. 1 A).

The time of the 4- and 8-h 29 °C treatments during the day did not affect the
percentage of plants initiating inﬂorescences or ﬂowering (Figure 2.2). Additionally,
there was no effect of the time of high temperature delivery on days to V1 (Table 2.6) or
days to ﬂower (Figure 2.2).

The number of inﬂorescences, total ﬂower bud number per plant, average number
of ﬂowers per inﬂorescence, and ﬂower diameter were not affected by temperature
treatment (Table 2.5). The total height of the ﬁrst inﬂorescence was increased by 19%
and 30% by the 4- or 8-h 29 °C mid-day treatments, respectively, when compared to the
height of inﬂorescences at constant 20 °C (Figure 2.3).

The timing of the 4-h 29 °C treatment inﬂuenced total ﬂower bud number per
plant and ﬂower bud number per inﬂorescence. Plants at 29 °C for 4 h during mid-day
had fewer total ﬂower buds than plants in the morning 4-h 29 °C treatment and had fewer

ﬂowers buds per inﬂorescence than plants in the evening 4-h 29 °C treatment (Table 2.6).

72

However, the time of day of the 4- and 8-h 29 °C treatments did not affect the number of
inﬂorescences, ﬂower diameter, or inﬂorescence length (Table 2.6 and Figure 2.2).

Phalaenopsis Baldan ’s Kaleidosc0pe ‘Golden Treasure’. Constant 29 °C
completely prevented inﬂorescence initiation (Table 2.7) and ﬂowering, while only 40%
of the plants at 29 °C for 12 h ﬂowered (Figure 2.1C). The percentage of plants that
developed VI was similar among plants grown at constant 20 °C and those exposed to 29
°C for 4 or 8 h at mid-day. However, exposure to 29 °C generally delayed the appearance
of VI. The 4-h 29 °C at mid-day treatment did not delay the appearance of a VI or
ﬂowering in Year 1 compared to constant 20 °C, but it did delay VI in Year 2 by two to
three weeks (Table 2.7). Exposure to 29 °C for 8 h at mid-day delayed appearance of a
VI by 4 and 8 weeks and ﬂowering by 3 and 10 weeks in Year 1 and 2, respectively. The
plants that ﬂowered in the 12 h at 29 °C treatment in Year 1 did not have a VI until
almost 5 weeks after plants at constant 20 °C.

Although the timing of day of the high temperature delivery did not affect the
percentage of plants initiating inﬂorescences and ﬂowering, it did affect the time to V1
(Table 2.8) and time to ﬂower (Figure 2.2). Plants exposed to 29 °C for 8 h late in the
day took fewer days to ﬂower than when the high temperature was delivered mid-day.
Timing of the 4-h 29 °C also inﬂuenced time to ﬁrst ﬂowering for this clone; the later the
high temperature delivery in the day, the longer it took to V1 and ﬂowering.

The effect of the duration at 29 °C on number of inﬂorescences per plant and total
ﬂower bud number per plant varied by year (Table 2.7). In Year 1, none of the
temperature treatments inﬂuenced the number of inﬂorescences, but in Year 2, plants at

29 °C for 8 h at mid-day developed fewer inﬂorescences than those at constant 20 °C.

73

Total ﬂower bud number was lower on plants exposed to 29 °C for 12 h in Year 1 and for
8 h in Year 2 compared to plants at constant 20 °C. Flower bud number per inﬂorescence
was similar among temperature treatments, but ﬁrst ﬂower diameter of plants at 8 and 12
h at 29 °C was 8% to 12% smaller than those at constant 20 °C. In Year 1, inﬂorescence
length to the ﬁrst ﬂower was greater when exposed to 29 °C for 8 h at mid-day compared
to those at constant 20 °C, but there was no effect on total inﬂorescence length (Figure
2.3). In Year 2, both 4 h and 8 h at 29 °C at mid-day increased the inﬂorescence length to
the ﬁrst ﬂower by 18% and 51% and total inﬂorescence length by 25% and 50%,
respectively, compared to plants at constant 20 °C.

Inﬂorescence length to ﬁrst ﬂower (Table 2.8) and total inﬂorescence length
(Figure 2.4) were greater whenthe 4-h 29 °C treatment was delivered late in the day
compared with in the morning. The timing of the 8-h 29 °C treatment had the opposite
effect: plants had longer inﬂorescences when the high temperature was delivered at mid-
day compared with late in the day. There was no effect of the time of day of high
temperature treatment on the number of inﬂorescences, number of ﬂower buds, or ﬂower
diameter (Table 2.8).

Doritaenopsis Newberry Parfait. The only temperature treatment that statistically
reduced inﬂorescence initiation was constant 29 °C (Table 2.9). At least 75% of the
plants developed VI in the other temperature treatments. Even though the majority of
plants exposed to 29 °C for 8 at mid-day or 12 h developed VI, the time to V1 (Table 2.9)
and ﬁrst open ﬂower (Figure 2. 1 B) was 7 to 8 weeks later than plants at constant 20 °C.
The 12 h at 29 °C treatment did not delay inﬂorescence initiation, but further

development to ﬂowering was inhibited compared to constant 20 °C; only 60% of plants

74

exposed to 29 °C for 12 h developed open ﬂowers during the experimental period (Figure
2. 1 B).

The timing of 4- and 8-h 29 °C treatments did not affect the percentage of plants
initiating inﬂorescences (Table 2.10) or ﬂowering (Figure 2.2). However, VI and
ﬂowering occurred earlier when the 8-h 29 °C was delivered late in the day compared
with when delivered mid-day.

Exposure to 29 °C did not inﬂuence the number of inﬂorescences per plant or the
ﬁrst ﬂower diameter (Table 2.9). Although the effect of temperature treatment on total
ﬂower bud number per plant and the average number of ﬂower buds per inﬂorescence
varied by year, none of the temperature treatments differed from the control in a given
year. The inﬂorescence length to the ﬁrst ﬂower was greater for plants exposed to 29 °C
for 8 or 12 h compared with that of plants at constant 20 °C in Year 1, but there was no
effect of temperature treatment in Year 2. Similarly, total inﬂorescence length of plants
in the 8-h 29 °C at mid-day treatment was greater compared with that of plants at constant
20 °C in Year 1 but not in Year 2 (Figure 2.3). The timing of 4- and 8-h treatments did
not affect the number of inﬂorescences, number of ﬂower buds, ﬂower diameter, or
inﬂorescence length (Table 2.10 and Figure 2.4)

Phalaenopsis ‘Explosion’. The only plants that initiated inﬂorescences (Table
2.11) and developed open ﬂowers (Figure 2.1D) were those grown at 29 °C for 54 h per
day. None of the plants exposed to 29 °C for 28 h developed VI. There was no
difference in days to V1 or ﬂowering, number of inﬂorescences, total ﬂower bud number
per plant, ﬂower bud number per inﬂorescence, ﬁrst ﬂower diameter, or length of

inﬂorescence to the ﬁrst ﬂower between plants at constant 20 °C or at 29 °C for 4 h.

75

However, total inﬂorescence length of plants at 29 °C for 4 h was 30% greater than
inﬂorescences at constant 20 °C (Figure 2.3).
Effect of Plant Size on Flowering

The size of Phalaenopsis ‘Mosella’ plants at the onset of the experiment did not
inﬂuence the percentage of plants that developed VI and open ﬂowers in any of the three
temperature treatments tested (Table 2.12). All plants of both sizes ﬂowered at constant
20 °C and no plants of either size ﬂowered at constant 29 °C. In the 8-h 29 0C treatment,
100% of large plants ﬂowered and 50% of the moderate-sized plants ﬂowered, but there
was no statistical difference (data not shown). Plant size also did not affect time to V1 or
ﬂowering. The moderate-sized plants ﬂowered in 109 or 115 d at constant 20 °C or in the
8-h of 29 °C treatment, respectively, while the large plants took 115 or 123 d to ﬂower
(data not shown). At both constant 20 °C and 8 h at 29 °C, the larger plants developed a
greater number of VI and total ﬂowers. Large plants developed a greater number of
ﬂowers per inﬂorescence than moderate-sized plants only at constant 20 °C. The
moderate-sized plants had larger ﬂowers at constant 20 °C, but not at 8 h at 29 °C.
Although inﬂorescence length to the ﬁrst ﬂower of large plants was greater than that of
moderate-sized plants in the 8-h 29 °C treatment, total inﬂorescence length was not
affected by plant size.
Effects of High Temperature Duration on Vegetative Growth

Overall, the average number of new leaves that developed during the 20 weeks of
the experiment increased with increasing daily duration at 29 °C, and hence, with average
daily temperature (Figure 2.3). Except for Baldan’s Kaleidoscope in Year 1, plants at 29

°C for 8, 12, or 24 h developed more leaves than plants at constant 20 °C. The effect of

76

varying durations at 29 °C on the change in leaf span was more variable among clones.
Leaf span of Doritaenopsis Newberry Parfait and Phalaenopsis ‘Explosion’ was similar
in all temperature treatments (Tables 2.8 and 2.9). In contrast, 12 h at 29 °C and constant
29 °C increased leaf span compared to plants at constant 20 °C in both Phalaenopsis
‘Mosella’ and Baldan’s Kaleidoscope ‘Golden Treasure’ (Tables 2.5 and 2.7). The 8-h
29 °C treatment also increased leaf span in Phalaenopsis Baldan’s Kaleidoscope ‘Golden

Treasure’.

Discussion

Eight and 12 h at 29 °C either prevented or delayed inﬂorescence initiation in; the
Phalaenopsis and Doritaenopsis clones studied. Twelve hours at 29 °C completely
prevented inﬂorescence initiation of all the Phalaenopsis clones except Baldan’s
Kaleidoscope ‘Golden Treasure’ in the ﬁrst year and ‘Newberry Parfait’. Plants that
ﬂowered and were exposed to an 8- or 12-h high temperature period had a delay in
appearance of VI by 25 to 50 d. Sakanishi et al. (1980) reported a high-temperature
inhibition of the emergence of a VI on Phalaenopsis amabilis; only 84% of plants
exposed to 28 °C for 12 h developed an inﬂorescence. When the high temperature was
extended by 2 h (for a total of 14 h) inﬂorescence emergence was delayed and VI
percentage was reduced to 46%. By comparison, 12 h at 29 °C was more effective at
inhibiting ﬂowering in Phalaenopsis Brother Goldsmith ‘720’ and Phalaenopsis Miva
Smartissimo X Canberra ‘450’ (Blanchard and Runkle, 2006). After 20 weeks at a
day/night temperature (12 h each) of 29/17 and 29/23 °C, none of the plants had

developed a VI. Similarly, Wang (2007) reported that none of the Doritaenopsis ‘Lava

77

Glow’ plants grown at a day/night temperature of 30/20 °C (12 h each) ﬂowered.
Apparently, the daily duration of high temperature required to prevent ﬂowering is
dependent on the Phalaenopsis or Doritaenopsis clone and the actual temperature.
Twelve hours at 29 or 30 °C is long enough to prevent inﬂorescence initiation in some,
but not all, Phalaenopsis clones.

Providing 8 h at 29 °C in the middle of the day generally delayed inﬂorescence
initiation and ﬂowering more than when at the end of the day. However, this difference
could at least partially be attributed to occasional insufficient heating to deliver 29 °C late
in the day. During periods of extreme cold weather outdoors, temperature was
sometimes lower than that desired at the very end of the 29 °C duration of the 8-h high
temperature treatment delivered in the evening. The hourly average temperature during
this 29 °C period dipped below 26 °C on 24 d during the experiment, and during 4 of the
20 weeks, the average of the last 3 hours of high temperature was below 27 °C (data not
shown).

Exposure to 29 °C for 4 h did not delay or inhibit inﬂorescence initiation in most
cases, regardless of the time of day in which it was delivered. These results support those
of Sakinishi et al. (1980) who reported that 6 h at 28 °C did not inhibit or delay
inﬂorescence initiation of Phalaenopsis amabilis compared to temperatures <25 °C. The
one exception in our study was Phalaenopsis Baldan’s Kaleidoscope ‘Golden Treasure’,
for which 4 h at 29 °C mid-day and late in the day delayed inﬂorescence initiation.

Two factors could have contributed to the differing responses of a particular clone
between years: temperature control and plant size. In Year 1, outside temperature during

weeks 7 through 9 was so cold that 29 °C could not be adequately maintained as desired

78

inside the greenhouses (Table 2.3). In Year 2, greenhouse temperature was maintained
closer to the set points during the entire experiment. This temperature difference could
explain why 45% of Phalaenopsis Baldan’s Kaleidoscope ‘Golden Treasure’ plants
initiated ﬂowers in Year 1 in the 12-h 29 °C treatment. The periods of cooler
temperatures in Year 1 could also have contributed to the fewer number of new leaves
that developed in Phalaenopsis Baldan’s Kaleidoscope ‘Golden Treasure’ and
Phalaenopsis Newberry Parfait compared to Year 2.

Differences in plant responses of the same clone between years could also be
attributed to differences in plant size at the onset of the experiments. Phalaenopsis
‘Mosella’ plants used in Year 2 had a leaf span 20 cm greater than the plants used in Year
1. Smaller plants require a cooler temperature, longer exposure to cool temperatures, or
both to initiate inﬂorescences and ﬂower (Yoneda, 1992). Thus, the larger plants used in
Year 2 could have been more sensitive to temperature with respect to ﬂowering. The
smaller Phalaenopsis ‘Mosella’ plants used in Year 1 took 13 and 52 d longer to ﬂower
at constant 20 oC and 4 h at 29 °C, respectively, compared to the larger plants used in
Year 2. However, the time to V1 did not vary by size.

There was little effect of the duration of 29 °C on inﬂorescence characteristics of
ﬂowering plants, although inﬂorescence height generally increased with increasing
duration at 29 °C. Other researchers have reported an increase in inﬂorescence length
with increasing temperature. For example, the average total inﬂorescence length of a
Phalaenopsis hybrid grown at a day/night temperature of 30/25 °C was 68% longer than

the inﬂorescences of plants at 20/15 °C (Lee and Lin, 1984).

79

The duration of 29 °C had no effect on number of inﬂorescences, number of
ﬂower buds per plant, number of ﬂower buds per inﬂorescence, or diameter of ﬁrst open
ﬂower on three of the four Phalaenopsis clones tested. However, exposure to 29 °C for 8
hours reduced both the number of inﬂorescences and number of ﬂower buds per plant of
Phalaenopsis Baldan’s Kaleidoscope ‘Golden Treasure’ in Year 2. In Year 1, the
number of ﬂower buds per plant was only decreased by exposure to 29 °C for 12 h.
Additionally, both the 4- and 8-h 29 °C treatments decreased the diameter of the ﬁrst
ﬂower of this clone.

Two temperature treatments, 12 h at 29 oC and 8 h at 29 °C late in the day, caused
small pitted spots on the leaves in Year 2, which resembled chilling injury (McConnell
and Sheehan, 1978). All three clones exhibited some damage, but Doritaenopsis
Newberry Parfait was more susceptible than the other two clones. We speculate that
these symptoms developed from the use of passive ventilation through top vents in Year
2, which allowed heat to escape rapidly as the temperature set point changed from 29 to
20 °C. In Year 1, active ventilation was used when the temperature was lowered to 20
°C, which drew air in from a heated hallway. Furthermore, we speculate that these
symptoms only occurred in these two temperature treatments because the transition from
20 to 29 °C occurred at the very end of the day, when outdoor temperatures were
generally coldest.

The physiological mechanism of high-temperature inhibition of ﬂowering in
Phalaenopsis is not well understood. It has been postulated that the synthesis or
interconversion of plant hormones, such as cytokinins and gibberellins, is involved (Chou

et al., 2000; Su et al., 2001). Cool temperatures could increase the concentrations of the

80

compounds required for inﬂorescence initiation, while high temperatures could inhibit
their accumulation. The results of this research support this hypothesis; plants exposed to
29 °C for 8 h showed an intermediate ﬂowering response in which inﬂorescence initiation
was either delayed or prevented in a portion of the Phalaenopsis plants.

The results of this study have practical applications for growers of Phalaenopsis.
To maintain uniform vegetative growth and prevent sporadic inﬂorescence initiation,
plants need to be grown at 229 °C for a minimum of 12 h each day, depending on the
clone. Extended periods at 29 °C have the added beneﬁt of a faster rate of vegetative
growth than shorter durations of high temperature.

Growers may also use these results to save energy used to heat greenhouses.
Since 12 h at 29 °C is sufﬁcient to prevent ﬂowering of some Phalaenopsis clones,
growers may not need to heat a greenhouse to 226 °C all night to prevent inﬂorescence
initiation. Reducing the temperature of the greenhouse at night, when exterior
temperatures are generally the coldest, could result in considerable energy savings. The
energy savings of heating a double-layer polyethylene greenhouse to a 12-h day/l2-h
night temperature of 29/20 °C instead of constant 29 °C in Grand Rapids, MI, is estimated
to be 14% for the month of Jan. and 74% for the month of July. In the more moderate
climate of San Francisco, CA, the estimated energy savings is 26% in Jan. and 50% in
July (USDA, 2008b).

In summary, there is a trade-off between ﬂowering and vegetative growth in
Phalaenopsis. As the duration of high temperature increases, the percentage of ﬂowering
plants decreases and vegetative growth increases. A majority of the Phalaenopsis clones

we studied required at least 12 h at 29 °C to completely prevent inﬂorescence initiation.

81

Intermediate durations of high temperature partially inhibited inﬂorescence initiation, but
4 h at 29 °C did not inhibit ﬂowering in the clones studied.

A better understanding of the duration required to prevent inﬂorescence initiation
of Phalaenopsis could be obtained through additional studies of a wider range of clones
and smaller intervals between the durations of high temperature tested. Durations longer
than 12 hours need to be tested for clones, such as Doritaenopsis Newberry Parfait, that
ﬂower even when exposed to 29 °C for 12 hours during the day. In addition, the
effectiveness of a range of temperatures between 26 and 32 °C on inhibiting inﬂorescence

initiation should be compared.

82

Table 2.1. Average leaf span number of each Phalaenopsis or Doritaenopsis cultivar at
the start of the experiment for each year. Leaf span was the distance measured from the
end of one leaf to the longest opposite leaf tip.

 

 

 

Year 1 Year 2

Cultivar Leaf span (cm) Leaf no. Leaf span (cm) Leaf no.
P. 'Mosella' 32 4.4 52 6.5

Large --Z -- 65 9.5
P. 'Explosion' 37 5.4 -- --
P. Baldan's Kaleidoscope
'Golden Treasure' 42 5.7 43 7.2
D. Newberry Parfait 46 5.5 50 5.9

 

ZPlants were not included in experimentation.

83

Table 2.2. Temperature treatments used in the study. Treatments 1, 2, 5, 7, and 8 were
used in Year 1 and replicated in Year 2. Treatments 3, 4, and 6 were added in Year 2.
The temperature was maintained at 20 °C for the remaining period each day.

 

 

Temperature Daily hours at Mean daily
treatment 29 °C Time at 29 °C temperature 4°C)
1 0 none 20.0

2 4 1200 to 1600 HR 21.5

3 4 0800 to 1200 HR 21.5

4 4 1600 to 2000 HR 21.5

5 8 1000 to 1800 HR 23.0

6 8 1400 to 2200 HR 23.0

7 12 0800 to 2000 HR 24.5

8 24 continuous 29.0

 

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Phalaenopsis 'Mosella’ A Doritaenopsis Newberry Parfait B
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Temperature Regimen

Figure 2.1. Effects of high temperature (29 °C) duration on ﬂowering percentage (bars)
and mean days to ﬁrst open ﬂower (symbols) of Phalaenopsis and Doritaenopsis clones.
For clones in which the temperature treatment by year interaction was signiﬁcant for the
days to ﬁrst open ﬂower, Year 1 is represented by closed circles (~) and Year 2 is
represented by open circles (0). Flowering percentages within a clone with different
uppercase letters are signiﬁcantly different using a binomial distribution and logit
transformation. Days to ﬁrst open ﬂower within a clone and year with different
lowercase letters are signiﬁcantly different using Tukey’s honestly signiﬁcant difference
test at P5005. Vertical bars represent the standard errors of the means.

95

 

125

 

 

 

 

 

 

Phalaenopsis 'Mosella' a
> 120
A A A A
100 - A - 115
80 . I i a - 110
60 - a i a i AB 105
a a
40 < - 100
20 - - 95
0 B B
Pha/aenopsis Baldan's Kaleidoscope
'Golden Treasure' ..
a) - 200 o
g A A A A i g
E 100 . a - 180 e:
8 b 5
'- 80 - - 160 O-
8 i 3
g 60 - AB - 140 g
'0') .9
E 40 « 3 l B - 120 a
“‘ 20 - d - 100 D
O B B
Doritaenopsis Newberry Parfait
~ 175
A A
100 - ~ 160
80 - - 145
60 A - 130
40 ‘ - 115
i i
20 « c c - 100
B
o . . ,
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o o (3° 90
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Hours at 29 °C
Figure 2.2. Effects of high temperature (29 °C) duration and time on ﬂowering
percentage (bars) and mean days to ﬁrst open ﬂower (-) of Phalaenopsis and
Doritaenopsis clones in Year 2. Flowering percentages within a clone with different
uppercase letters are signiﬁcantly different using a binomial distribution and logit
transformation. Days to ﬁrst open ﬂower within a clone with different lowercase letters
are signiﬁcantly different using Tukey’s honestly signiﬁcant difference test at P5005.
Vertical bars represent the stande errors of the means.

96

 

 

 

 

 

 

 

 

     
 
  

   

120

- Constant 20 °C

4 h at 29 °C
A 100 - - 8hat29°C
S 1:] 12 h at 29 °C
5
2
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o
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0
a)
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9’» 90‘

Phalaenopsis clone

Figure 2.3. Effects of high temperature (29 °C) duration (and average daily temperature)
on total inﬂorescence height (from base to tip) of Phalaenopsis and Doritaenopsis clones.
For clones in which the temperature treatment by year interaction was signiﬁcant, the
years were analyzed separately. Data was not analyzed for temperature treatments in
which 520% of plants ﬂowered (*). Mean separation within each clone and year was
performed using Tukey’s honestly signiﬁcant difference test at P3005. Vertical bars
represent the standard errors of the means.

97

120

 

- Constant 20 °C

:3 4 h at 29 °C (0800—1200 HR)

_ 4 h at 29 °C (1200-1600 HR)

100 ~ :1 4 h at 29 °C (1600-2000 HR)

m 8 h at 29 °C (1000-1800 HR)

_ 8 h at 29 °C (1400—2200 HR)

[E 12 h at 29 °C (0800-2000 HR) a

"be bc
40 _.. ..........

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-

 

 

&““\‘“““‘““
“\“““““\\\‘ ‘=
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Total inflorescence length (cm)
0
O
‘9 :
' —

 

Phalaenopsis clone
Figure 2.4. Effects of high temperature (29 °C) duration and time on total inﬂorescence
height (from base to tip) of Phalaenopsis and Doritaenopsis clones in Year 2. Data was
not analyzed in temperature treatments in which 520% of plants ﬂowered (*). Mean
separation within each clone and year used Tukey’s honestly signiﬁcant difference test at
P5005. Vertical bars represent the standard errors of the means.

98

 

  
     
 
   

 

 

 

- Constant 20 °C (20 °C)
4 ‘ 4 hours at 29 °C (21.5 °C)
- 8 hours at 29 °C (23 °C) C
8 [:1 12 hours at 29 °C (24.5 °C)
5 3_ — Constant29°C<29°C> c _‘ ‘ . w_ h I U c
% cl
c
”:3 2 .
a:
.o
E
3
z 1_
O _
.60”
e
090%
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Phalaenopsis clone

Figure 2.5. Effects of high temperature (29 °C) duration (and average daily temperature)
on number of new leaves of Phalaenopsis and Doritaenopsis clones. For clones in which
the temperature treatment by year interaction was signiﬁcant, the years were analyzed
separately. Mean separation within each clone and year was performed using Tukey’s
honestly signiﬁcant difference test at P3005. Vertical bars represent the standard errors
of the means.

99

Literature Cited

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

Blanchard, M.G. and ES. Runkle. 2006. Temperature during the day, but not during the
night, controls ﬂowering of Phalaenopsis orchids. J. Exp. Bot. 57:4043-4049.

Chou, C.C., W.S. Chen, K.L. Huang, H.C. Yu, and L.J. Liao. 2000. Changes in cytokinin
levels of Phalaenopsis leaves at high temperatures. Plant Physiol. Biochem.
38:309-314.

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

Krizek, D.T. and RH. Lawson. 1974. Accelerated growth of Cattleya and Phalaenopsis
under controlled-environment conditions. Amer. Orchid Soc. Bul. 43:503-510.

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

McConnell, DB. and T.J. Sheehan. 1978. Anatomical aspects of chilling injury leaves of
Phalaenopsis Bl. HortScience 13:705-706.

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

Sakanishi, Y., H. Imanishi, and G. Ishida. 1980. Effect of temperature on grth and
ﬂowering of Phalaenopsis amabilis. Bul. Univ. Osaka, Ser. B: Agr. Biol. 3221-9.

Su, W.R., W.S. Chen, M. Koshioka, L.N. Mander, L.S. Hung, W.H. Chen, Y.M. Fu, and
KL. Huang. 2001. Changes in gibberellin levels in the ﬂowering shoot of
Phalaenopsis hybrida under high temperature conditions when ﬂower
development is blocked. Plant Physiol. Biochem. 39:45-50.

US. Department of Agriculture. 2008a. Floriculture crops 2007 summary. Agr. Stat.
- Board, Wash., DC.

US. Department of Agriculture. 2008b. Virtual Grower 2.0. Agr. Res. Serv., Wash., DC.
4 Sep. 2008.
<http://www.ars.usda. gov/services/software/download.htm?softwareid=l 08>.

Wang, Y.-T. 2007. Average daily temperature and reversed day/night temperature
regulate vegetative and reproductive responses of a Doritis pulcherrima Lindley
Hybrid. HortScience 42:68-70.

100

Wang, Y.-T. and N. Lee. 1994. Another look at an old crop: Potted blooming orchids —
Part 2. Greenhouse Grower 12(2):36-38.

Yoneda, K., H. Momose, and S. Kubota. 1992. Comparison of ﬂowering behavior
between mature and premature plants of Phalaenopsis under different
temperature conditions. Jpn. J. Trop. Agr. 36:207-210.

101

SECTION III

EFFECTS OF BENZYLADENINE ON FLOWERING AND VEGETATIVE

GROWTH OF POTTED MIL T ONIOPSIS, PAPHIOPEDIL UM, AND

ODON T OGLOSS UM ORCHIDS

102

Effects of Benzyladenine on Flowering and Vegetative Growth of Potted

Miltoniopsis, Paphiopedilum, and Odontoglossum Orchids

Linsey A. Newton] and Erik S. Runkle2

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

Additional index words: cytokinin, potted plants, plant growth regulators

Received for publication . Accepted for publication . We

 

 

gratefully acknowledge funding from growers providing support for Michigan State
University ﬂoriculture research and the support from the Michigan Agricultural

Experiment Station.

I Graduate student.

2 Associate Professor of Horticulture and Extension Specialist, to whom reprint requests

should be addressed (Email: runkleer@msu.edu).

103

Abstract

Exogenous application of synthetic benzyladenine (BA) has been reported to
increase ﬂowering or vegetative growth of several orchid genera, which are an
economically important group of potted ﬂowering plants. We performed experiments to
determine if BA promoted growth of axillary vegetative shoots or ﬂowering

inﬂorescences of potted Miltoniopsis, Odontoglossum, and Paphiopedilum. A foliar
spray (vol. 0.2 L-m_2) of BA was applied ﬁve times to three sizes of plants per orchid
genera or alliance. In Experiment 1, BA was applied every 6 weeks at 0, 200, 400, or

800 mg-L_l; in Experiment 2, BA was applied every 2 weeks at 0, 1,000, 2,000 or 4,000

mg-L—l. Large Miltoniopsis and Odontoglossum plants only received one BA

application, at either the beginning of, or 4 weeks into, an 8-week ﬂower-inducing
treatment at 14 °C. All other plants, and those after the 14 °C treatment, were grown at

20 or 23 °C under a 16-h photoperiod. There were no effects of BA on ﬂowering of
Miltoniopsis or Odontoglossum, with the exception that 2,000 mg-L'l BA applied 4

weeks into the 14 °C treatment increased the inﬂorescence number of large
Odontoglossum. The ﬂowering percentages of Paphiopedilum in all BA treatments were

too small for statistical analysis of ﬂowering characteristics. In Experiment 1,
applications of 800 mg-L—1 BA increased the number of new vegetative shoots developed

on large Paphiopedilum from 0.2 to 1.1 shoots, but there was no effect of BA in
Experiment 2. The number of new shoots developed on medium-sized Paphiopedilum

and small Miltoniopsis was increased by 1.4 or 2.0 shoots, respectively, by applications

of 4,000 mg-L—l ppm. Application of BA to large Odontoglossum did not increase the

104

number of new shoots, but 800 mg‘L_1 increased the number of new vegetative shoots

developed on medium-sized plants in Experiment 1. Although BA applications had very
little effect on ﬂowering of the orchid genera and intergeneric hybrids studied, they did
signiﬁcantly increase the number of new vegetative shoots on at least one plant size of

each alliance or genus.

Introduction

Cytokinins are plant hormones that stimulate cell division in the presence of
auxins (Miller et al., 1956; Werner et al., 2001). They also affect a number of other
physiological phenomena in plants, including leaf expansion (Scott and Liverman, 1956),
organogenesis (Skoog and Miller, 1957; Klee et al., 1987; Werner et al., 2001), lateral
bud growth (Schaeffer and Sharpe, 1969; Wickson and Thimann, 195 8), ﬂowering
(Bemier et al., 1988; Gupta and Maheshwari, 1970; Strivastava, 1967; Zeevart, 1978),
translocation (Mothes and Engelbrecht, 1961; Quinlan and Weaver, 1969), senescence
(Dedolph, 1962; Mok, 1994; Richmond and Lang, 1957), and protein synthesis (McGaw
and Burch, 1995). There are numerous cytokinins, including both synthetic and natural
compounds. One synthetic cytokinin that has recently been used for application in
ﬂoriculture is benzyladenine (BA). Although BA is made synthetically, it has also been
found to naturally occur in several species (Van Staden and Crouch, 1996; Nandi et al.,
1989). As with most cytokinins, the free base form is the most active, but BA can also be
found in plants in the ribonucleoside or nucleotide form (Van Staden and Crouch, 1996).

Exogenous application of BA has proven useful for a number of purposes in

ﬂoriculture crops. It has been reported to increase branching of both woody and

105

herbaceous plants (Buban, 2000; Carpenter and Carlson, 1972), increase ﬂowering

(J umin and Ahmad, 1999), reduce leaf yellowing of both potted plants (Funnell and
Heins, 1998; Han, 1997) and cut ﬂowers (Philosoph-Hadas et al., 1996), and increase the
vase life of cut stems (Dai and Paull, 1991; Paul] and Chantrachit, 2001). One of the
most widely used applications of BA is in combination with gibberellic acid (GA) to
prevent lower leaf yellowing of Easter lily (Lilium longiﬂorum Thunb.) (Han, 1997).

BA can also be used during commercial production of potted orchids, particularly
Phalaenopsis. Three foliar spray applications of 200 or 400 mg-L-l BA at one-week

intervals, beginning at the time of transfer to an inductive temperature (525 °C),

increased the number of inﬂorescences and total number of ﬂowers on Phalaenopsis
(Blanchard and Runkle, 2008a). A spray application of 200 mg-L_l BA also increased

the number of inﬂorescences and ﬂowers per inﬂorescence of Doritaenopsis, a hybrid

between Phalaenopsis and Doritis (Kim et al., 2000). Similarly, application of 2,500
mg'L_l BA produced the greatest number of inﬂorescences and ﬂowers in plants from

which an inﬂorescence had been harvested (Kim et al., 1999). Other orchids in which
BA application has reportedly increased the number of inﬂorescences or ﬂowers include
hybrids of Cymbidium ensifolium ‘Tekkotsusosin’ (Lee et al., 1998), Dendrobium
Nodoka and Jaquelyn Thomas ‘Uniwai Princess’ (Higuchi and Sakai, 1997; Sakai et al.,
2000), Aranda Deborah and Kooi Choo (Goh, 1977; Zaharah et al., 1986), Holtumara
Loke Tuck Yip, Aranthera Beatrice Ng, and Mokara Chark Kuan (Zaharah et al., 1986).
Depending on the genus or intergeneric hybrid, either BA sprays or injection of BA into

pseudobulbs was effective.

106

In a few orchid hybrids, application of BA increased vegetative growth, which
could hasten propagation and production of young plants. For example, the application
of 750 to 1,000 mg-L—l BA on Ascocenda increased the number of keikis, which are
vegetative shoots formed on an inﬂorescence (Kunisaki, 1975). In Ascocenda Kangla,
2.0 to 3.2 shoots per seedling developed within 8 weeks when the tissue culture media
contained 0.5 to 4.0 mg-L—l BA whereas plants in a BA-deﬁcient media did not develop
any new shoots (Kishor and Sharma, 2008). Other genera in which BA has reportedly
increased vegetative growth are Paphiopedilum and Miltoniopsis. In Paphiopedilum,
application of only 1 mgL—l BA to leaf axils of ﬂowered divisions increased the average
number of shoots on the division from 0.4 to 1.0 (Stewart and Button, 1977). Similarly,
the number of Miltoniopsis vegetative shoots increased by 4 to 13 times when ‘Eileen’
and ‘Akatsuka’ plants were drenched with 50 mL of 5,631 and 11,263 tug-L" BA
(Matsumoto, 2006).

Although BA can increase ﬂower or shoot number of several orchid genera and
intergeneric hybrids, more research is needed to determine application methods and
concentrations that can be used in commercial production of this economically important
group of plants. A spray application is generally preferable for commercial use because
it involves less labor than other application methods. This study further investigated the
effects of BA sprays on the vegetative and reproductive growth, and their potential for
commercial use, on three potted ﬂowering orchid hybrids of Miltoniopsis,

Odontoglossum, and Paphiopedilum.

Materials and Methods

107

Plant Material

 

Miltoniopsis, hybrids of the Odontoglossum alliance, and Paphiopedilum were
obtained from a commercial greenhouse in California, where they had been grown in
10.8-cm (750 mL) pots (Table 3.1). Potting media was a combination of (by volume)
75% ﬁne-grade Douglas ﬁr (Pseudotsuga menziesii [Mirb.] Franco) bark, 15% medium-
grade perlite, and 10% sphagnum peat. In Experiment 1, Beallara Tahoma Glacier
‘Green’ (a hybrid of the Odontoglossum alliance), Miltoniopsis Echo Bay ‘Midnight
Tears’, and mixed hybrids of Paphiopedilum were received at Michigan State Univ.
Research Greenhouses on 11 Nov. 2006. Three sizes of each species were included in
Experiment 1: small, medium, and large (Table 3.2).

Due to the lack of a large response, the experiment was scaled back in Experiment
2 by only including two sizes of Paphiopedilum (medium and large) and Miltoniopsis
(small and large; Table 3.2). The large plants of Beallara Tahoma Glacier ‘Green’ and
Miltoniopsis Echo Bay ‘Midnight Tears’ that were used in Experiment 1 were repotted in
August, 2007 into 12.7-cm (800 mL) pots with a media containing 50% Douglas ﬁr bark
(Rexius, Eugene, OR, USA), 25% medium-size chunks of coconut coir (V grove, Inc., St.
Catharines, Ontario, Canada), 12.5% chunky peat, and 12.5% coarse (#4) perlite (Wilkin
Mining & Trucking, Caliente, NV, USA). The same media was used to repot the large
Paphiopedilum into 11.4-cm (650 mL) pots. The repotted large plants of each of these
three hybrids were used in Experiment 2. New medium-sized mixed hybrids of
Paphiopedilum, small Miltoniopsis Gerald Michael Lawless ‘Paciﬁc Star Storm’ and
Patricia Marie Linares ‘Mauna Loa’, and small Burrageara Paciﬁc Lust ‘la estrella’ (a

hybrid of the Odontoglossum alliance) were obtained from the same commercial

108

greenhouse in California in Experiment 2. These plants had been grown in 108-cm (575
mL) pots with a potting media consisting of 70% ﬁne-grade ﬁr bark, 10% medium-grade
(#3) perlite, 10% New Zealand sphagnum moss, and 5% coconut coir. Plants were
received on 9 Nov. 2007. Only 20 plants each of Miltoniopsis Gerald Michael Lawless
‘Paciﬁc Star Storm’ and Patricia Marie Linares ‘Mauna Loa’ were received, so ten of
each hybrid served as controls and 10 were treated with the highest concentration of BA.
The smallest size of Beallara Tahoma Glacier ‘Green’ used in Experiment 1 had grown
considerably and thus was used as the medium-sized Odontoglossum hybrid in
Experiment 2. The plant sizes at the start of Experiment 2 are provided in Table 3.2.
BA Applications

Foliar applications of 6-benzyladenine (BAP-10, Plant-wise Biostimulant
Company, Louisville, KY, USA) were made at three different concentrations for each

experiment. The surfactant CapSil (Aquatrols, Paulsboro, NJ, USA) was also included in

the spray at a concentration of 1.25 mL-L_l to improve contact with plant leaves. The

spray was applied at approximately 0.2 L'm—z. Ten plants for every combination of

orchid hybrid and size were treated with each concentration of BA. In addition, 10 plants
of each hybrid were not treated in each experiment and served as the control.

Experiment I . The three concentrations of BA applied to plants were 200, 400,
and 800 mg-L_l. A total of ﬁve BA applications were made at 6-week intervals, except

for large Miltoniopsis and Odontoglossum plants, which received only one application.
These ﬁve applications were made on 21 Dec. 2006, 2 Feb. 2007, 16 Mar. 2007, 27 Apr.

2007, and 7 June 2007. For the large Miltoniopsis and Odontoglossum plants, the BA

109

was applied at the start of an 8-week cooling treatment (12 Dec. 2006; see below) or 4
weeks into the cooling treatment (19 Jan. 2007).

Experiment 2. The concentrations of BA were increased to 1,000, 2,000, and
4,000 mg-L-l. A total of ﬁve applications were made at 2-week intervals: 21 Nov. 2007,

5 Dec. 2007, 19 Dec. 2007, 2 Jan. 2008, and 16 Jan. 2008. Large Odontoglossum and
Miltoniopsis received only one application, either at the beginning of (21 Nov. 2007) or
half-way through (19 Dec. 2008) an 8-week cooling treatment.
Greenhouse Environment

Plants were maintained in a glass greenhouse at the Michigan State University
Research Greenhouses in East Lansing, MI under a 16-h photoperiod. For the ﬁrst 3
weeks of Experiment 1, the 16-h photoperiod (0600 to 2200 HR) was provided by a
combination of sunlight and high-pressure sodium lamps (which delivered a PPF of 25 to

70 umol-m—zs1 at plant canopy depending on the shade cloth used). For the remainder

of Experiment 1 and the total duration of Experiment 2 the ﬁrst portion of the 16-hour
photoperiod (0800 to 2400 HR) was provided from sunlight and high-pressure sodium

lamps from 0800 to 1700 HR. Black cloth covered the plants from 1700 to 0800 HR and
incandescent bulbs that provided a PPF of 3 to 4 umol-m-Zsl at plant canopy were used

from 1700 to 2400 HR to provide the remainder of the 16-h photoperiod. Plants were

individually watered as needed with reverse-osmosis water containing water soluble
fertilizer that provided (in mg-L_l) 125 N, 12 P, 100 K, 65 Ca, 12 Mg, 1.0 Fe, 1.0 Cu, 0.5

Mn, 0.5 Zn, 0.3 B and 0.1 Mo (MSU Special, GreenCare Fertilizers, Inc., Kankakee, IL,

USA).

110

Odontoglossum and Miltoniopsis. The two smallest sizes of Odontoglossum and
Miltoniopsis were grown at a constant setpoint of 20 °C. The largest plants were grown
at 14 °C for 8 weeks to induce ﬂowering (Blanchard and Runkle, 2008b; Lopez and

Runkle, 2006). After the 8-week treatment, plants were transferred to 20 °C. The
maximum instantaneous light intensity for all plants was 600 umol'm—zsl, which was

achieved using whitewash and shade cloth. The actual average temperatures and
photosynthetic daily light integrals are provided in Table 3.3.

Paphiopedilum. The maximum instantaneous light intensity was 200
mel'm_2'S-l by the use of shade cloth and white wash. In Experiment 1, plants were

initially grown at 20 °C for 16 weeks and then were transferred to 23 °C for the last 12
weeks of the experiment to increase the rate of plant development. Plants were grown at
23 °C for the entire experiment in Experiment 2.

Environmental Control. All temperatures and supplemental lighting were
controlled using a computerized environmental control system (PRIVA Computers Inc.,
Vineland Station, Ontario, Canada) that controlled the heating system, vents, exhaust
fans, evaporative pad cooling, and supplemental lighting. Aspirated and enclosed
thermocouples positioned at plant height measured the air temperature on each
greenhouse bench. Line quantum sensors (Apogee Instruments, Logan, UT) measured
the instantaneous light intensity every 10 s. A CRlO data logger (Campbell Scientiﬁc,
Logan, UT, USA) recorded hourly averages of both‘ temperature and light intensity.
From this data, mean temperature and daily light integral were calculated.

Data Collection and Analysis

111

The leaf span and number of leaves (21 cm long) of Paphiopedilum and the
pseudobulb width of the largest pseudobulb of Odontoglossum and Miltoniopsis were
measured at the beginning of the experiments. To determine the effect of BA on
vegetative growth, the number of vegetative shoots on each plant was counted every 4
weeks beginning at the time of the ﬁrst BA application. Effects of BA on ﬂowering were
determined by recording the date of ﬁrst visible inﬂorescence (VI) and date of anthesis.
At anthesis, the number of inﬂorescences and the number of ﬂower buds per plant were
counted and the ﬁrst ﬂower diameter and total inﬂorescence length were measured. On
Odontoglossum, the inﬂorescence length to the ﬁrst ﬂower was also measured. Data was
collected for 28 and 20 weeks after the ﬁrst BA application in Experiment 1 and
Experiment 2, respectively.

Experiment 1 was performed from Dec. 2006 to July 2007 and Experiment 2 from
Nov. 2007 to Apr. 2008. Any plants that died during the experiments were excluded
from data analysis. To analyze the ﬂowering percentage of plants, a binomial
distribution with a logit transformation was used. Differences were declared signiﬁcant
at P3005. Mean separation was performed on all other data using Tukey’s honestly
signiﬁcant difference test at P3005 in PROC MIXED of SAS (SAS Institute, Cary, NC,

USA).

Results

Paphiopedilum

 

Shoot number. In Experiment 1, BA at up to 800 mg-L_l did not increase

vegetative shoot number of small or medium Paphiopedilum within the experimental

112

period of 28 weeks (Figure 3.1). However, the applications of 800 mg‘L—l increased the
number of new shoots that developed on large Paphiopedilum plants from 0.2 to 1.1
shoots. In Experiment 2, the highest concentration used (4,000 mg°L—l) increased the

number of new shoots formed on medium-sized Paphiopedilum from 1.6 to 3.0 shoots
during the 20 weeks of the experiment (Figure 3.2). The increase in shoot number was
evident within 8 weeks of the ﬁrst BA application. In contrast, BA application did not
increase the number of new shoots formed on large Paphiopedilum in Experiment 2.

Flowering. BA did not inﬂuence ﬂowering percentage of Paphiopedilum, which
was relatively low in both control plants and those that received BA applications. The
ﬂowering percentage of large plants in each treatment ranged from 20 to 50 in
Experiment 1 and 10 to 40 in Experiment 2 (data not shown). Although few of the
medium-sized plants ﬂowered in Experiment 1, 40% to 60% of them ﬂowered in
Experiment 2 (data not shown). None of the small plants ﬂowered in either experiment.
The effect of BA on the number of inﬂorescences, inﬂorescence length, and ﬂower
diameter were not analyzed because of the low ﬂowering percentages.
Miltoniopsis

Shoot number. The time of BA application did not have a signiﬁcant effect on
shoot number of large plants, and there was no signiﬁcant interaction between application

time and BA concentration. Therefore, data for the two application times were pooled for
statistical analysis. In Experiment 1, BA at up to 800 mg'L_l did not increase the number
of new shoots formed in any of the three plant sizes (Figure 3.3). The increased BA
concentrations of 1,000, 2,000, and 4,000 mg-L_l used in Experiment 2 similarly did not

increase the number of new shoots on large plants (Figure 3.4). However, application of

113

4,000 mg-L-l BA did increase the number of vegetative shoots that developed on small

plants of both Miltoniopsis Gerald Michael Lawless ‘Paciﬁc Star Storm’ and Miltoniopsis
Patricia Marie Linares ‘Mauna Loa’ (Figures 3.4). These BA-treated plants developed
1.9 or 2.1 more shoots than control plants by the end of the 20 weeks of the experiment.

Flowering. All plant sizes of Miltoniopsis Echo Bay ‘Midnight Tears’ had a high
ﬂowering percentage in Experiment 1 (Table 3.4). Flowering percentage of medium and
large control plants and those treated with BA was 90 to 100 Flowering percentage of
small plants was between 50 and 78, regardless of BA treatment. However, the only
plant size that ﬂowered in Experiment 2 was the large Miltoniopsis, of which 60% to
100% of plants ﬂowered in each treatment (data not shown; Table 3.5). In each
experiment, neither BA concentration nor application time inﬂuenced ﬂowering
percentage, days to V1 or ﬂower, inﬂorescence number, total ﬂower bud number, ﬂower
diameter of ﬁrst open ﬂower, and total inﬂorescence length of any plant size.
Odontoglossum

Shoot number. In Experiment 1, the BA applications did not have an effect on
new shoot number of small Beallara Tahoma Glacier ‘Green’ (Figure 3.5). The BA
applications to the medium-sized plants of this cultivar were more effective: 800 mg°L—l
doubled the number of new shoots formed compared to control plants. For the total
number of new shoots formed on large plants, application time and the interaction
between BA concentration and application time were not signiﬁcant in either experiment,

so the two application times were analyzed together for each experiment. In Experiment

1, large plants treated with 200 and 400 mg-L—1 BA developed fewer new shoots than

control plants whereas those treated with 800 mg-L_1 BA had a shoot number similar to

114

that of control plants. In Experiment 2, none of the BA applications increased the
number of new shoots on any of the cultivars or plant sizes tested (Figure 3.6).
Flowering. In Experiment 1, time of BA application was not signiﬁcant for any

of the ﬂowering parameters (Table 3.6). There was also no effect of 200, 400, or 800
mg°L—l BA on days to VI or ﬂowering, number of inﬂorescences, total ﬂower bud
number, ﬂower diameter of ﬁrst open ﬂower, inﬂorescence length to the ﬁrst ﬂower, and
total inﬂorescence length. In Experiment 2, only 2,000 mg-L-1 BA applied at week 4 of

the cool treatment increased the number of inﬂorescences compared to that of the control
(Table 3.7). None of the BA treatments had an effect on any of the remaining ﬂowering
parameters when compared to the control, although the interaction between BA
concentration and application time was signiﬁcant for the total number of ﬂower buds,

inﬂorescence height to the ﬁrst ﬂower, and the number of inﬂorescences.

Discussion

BA has been previously shown to increase vegetative growth or ﬂowering of a
number of orchid genera and intergeneric hybrids. This study has demonstrated that there
is potential for use of BA to stimulate vegetative growth of Paphiopedilum and small
Miltoniopsis, but not Odontoglossum at the concentrations, spray volume, and application
frequencies tested. There was no impact of the BA concentrations tested on the
ﬂowering of Paphiopedilum, Miltoniopsis, or Odontoglossum.

The condition of the plants, particularly that of Miltoniopsis used in Experiment 1,
may have confounded the results to some extent. The Miltoniopsis used in Experiment I

experienced minor to moderate chilling injury during their transport to Michigan State

115

Univ. The chilling injury caused water-soaked spots on the leaves, which turned necrotic
within a few days. These symptoms were similar to chilling injury symptoms reported on
Phalaenopsis, which appear as yellow water-soaked spots that are sometimes sunken
(McConnell and Sheehan, 1978; Wang, 2007). The chilling injury contributed to later
plant death of some plants, and although plants that died before the end of the
experiments were removed from data analysis, the remaining Miltoniopsis appeared to
have decreased vigor compared to plants that had not been exposed to cool temperatures.
The smaller plants were apparently more susceptible to chilling injury because 11 of the
40 small plants died while only 2 medium and 2 large Miltoniopsis plants died during the
28-week experimental period. Miltoniopsis plants used in Experiment 2 were much more
vigorous, which may explain why a vegetative response to BA occurred on small
Miltoniopsis plants in Experiment 2 but not in Experiment 1.

At least some of the response variability to BA within an orchid genus can be
attributed to clone variability. The small Miltoniopsis Echo Bay ‘Midnight Tears’ plants
ﬂowered, but small plants of both Miltoniopsis Gerald Michael Lawless ‘Paciﬁc Star
Storm’ and M. Patricia Marie Linares ‘Mauna Loa’ did not ﬂower. Miltoniopsis Echo
Bay ‘Midnight Tears’ is apparently more ﬂoriferous than the other two clones and

ﬂowers at a smaller size. There are reports of variations in response to BA in other
orchid genera also. Although injection of 225 mg~L_I BA (volume not reported) by free

ﬂow for 5 (1 into mature pseudobulbs induced ﬂower initiation in both Dendrobium
hybrids tested, the number of ﬂower buds initiated in D. Lady Hochoy was 4.6 times

greater than that in D. Buddy Shepler x D. Peggy Shaw (Goh and Yang, 1978).

Similarly, three spray applications of 400 mg-L—l BA increased the inﬂorescence number

116

of Phalaenopsis Golden Treasure ‘470’ by three times, but the inﬂorescence number of
Phalaenopsis Brother Apollo ‘072’ was only doubled (Blanchard and Runkle, 2008a).
Differing responses to BA in Experiment 1 and Experiment 2 were expected

given the variation in plant size, plant history, and different BA concentrations and
application frequency. For example, 800 mg-L.l BA applied at 6-week intervals
increased the shoot number of large Paphiopedilum in Experiment 1. However, in
Experiment 2, higher concentrations and more frequent applications of BA (4,000 mg-L_l

BA applied at 2-week intervals) did not increase shoot number of these large plants. This
lack of a response could at least partially be attributed to plant history; the large plants
used in Experiment 1 were repotted, randomized, and reused for experimentation in
Experiment 2. A number of the plants used in Experiment 2 had already initiated
multiple shoots from their primary shoot during Experiment 1, and these smaller lateral
shoots may not have been adequately mature to develop their own lateral shoots by
Experiment 2.

The increase in shoot number of BA-treated Paphiopedilum is consistent with

results of Stewart and Button (1977), who reported an increase in shoot number of
Paphiopedilum when 1 mg-L_1 BA was applied to the leaf axils. In addition, our results
that indicate BA can increase vegetative growth of Miltoniopsis are consistent with
Matsumoto (2006), who reported that drenches of 5,631 and 11,263 mg-L-l BA increased

vegetative shoot number on Miltoniopsis ‘Eileen’ and ‘Akatsuka’.
The BA-induced increase in vegetative growth of Paphiopedilum and
Miltoniopsis could be useful in commercial orchid production. These orchids take

considerable time to grow and adequately ﬁll a pot. BA applications could be used to

117

increase vegetative shoot number more rapidly, resulting in a full plant sooner. The
increase in shoot number from BA could also be useful in propagation to generate more
plantlets. This increase in shoot number is particularly desirable in Paphiopedilum, for
which the shoots of certain species have strong apical dominance until after ﬂowering
(Stewart and Button, 1977). However, the variability of our data indicates that more
research is needed to determine the appropriate timing, concentration, and volume of BA

to be used by commercial orchid growers.

118

 

 

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Table 3.2. Leaf span (cm) of Paphiopedilum and pseudobulb diameter (cm) of the
remaining orchid hybrids measured at the time of the ﬁrst BA application in each
experiment.

 

Relative plant size

 

 

Experiment Genus Small Medium Large
1 Odontoglossum
Beallara 1.7 2.8 4.0
Miltoniopsis
‘Midnight Tears’ 2.5 2.7 3.1
Paphiopedilum 13.6 19.1 26.0
2 Odontoglossum
Beallara -2 3.5 4.5
Burrageara 2.6 - -
Miltoniopsis
‘Paciﬁc Star Storm’ 2.7 - -
‘Mauna Loa’ 2.6 - -
‘Midnight Tears’ - - 2.7
Paphiopedilum - 1 9.4 28.3

 

ZNot included in the study.

120

Table 3.3. The actual average temperature and photosynthetic daily light integral (DLI)
for each greenhouse environment and orchid hybrid in Experiment 1 and 2.

 

 

Average
Temperature temperature Average DLI
Experiment setpoint (°C) Experimental period (°C) (mol°m_2-d-l)
1 Paphiopedilum
20 22 Dec. 2006 to 13 Apr. 2007 20.6 4.8
23 13 Apr. 2007 to 6 July 2007 24.4 4.2
Odontoglossum and Miltoniopsis
14 22 Dec. 2006 to 16 Feb. 2007 13.6 5.1
20 16 Feb. 2007 to 6 July 2007 21.6
2 Paphiopedilum
23 21 Nov. 2007 to 9 Apr. 2008 23.5 2.9
Odontoglossum and Miltoniopsis
14 21 Nov. 2007 to 16 Jan. 2008 14.1 4.7
20 16 Jan. 2008 to 9 Apr. 2008 20.9 8.4

 

121

Table 3.4. Effects of spray applications of benzyladenine (BA) on ﬂowering parameters
of small, medium, and large Miltoniopsis Echo Bay ‘Midnight Tears’ in Experiment 1. A
description of plant sizes is provided in Table 3.2; spray information is provided in the
text.

 

Flower Total VI
length

Total
ﬂower diameter

Days to

BA concentration Flowering Days ﬁrst open

 

(mg-U1) (%) to V1 ﬂower VI no. bud no. (cm) (cm)
Small plants
Control 75 73 109 2.1 3.9 7.8 15.8
200 78 84 135 2.6 5.6 6.4 14.8
400 50 81 133 2.5 5.0 6.6 14.7
800 67 80 125 2.3 3.8 6.9 17.2
Signiﬁcance NS NS NS NS NS NS NS
Medium plants
Control 100 51 96 2.4 3.8 8.5 15.8
200 100 51 101 2.0 5.1 7.7 19.1
400 90 44 98 2.3 6.1 7.6 21.0
800 100 43 97 2.2 5.0 7.5 18.4
Signiﬁcance NS NS NS NS NS NS NS
Large plants
Control 100 21 101 2.1 4.7 8.8 25.1
Application at 0 weeks
200 90 30 115 2.1 4.9 8.2 25.4
400 100 29 104 2.2 6.2 8.4 23.4
800 100 23 104 2.2 4.4 8.4 23.1
Application at 4 weeks
200 100 31 117 1.7 3.9 8.8 24.3
400 100 31 111 2.0 4.7 8.7 23.2
800 100 26 96 2.3 5.2 8.9 23.9
Signiﬁcance
BA concentration NS NS NS NS NS NS NS
Application time NS NS NS NS NS NS NS
BA concentration *
Application time NS NS NS NS NS NS NS

 

NSNot signiﬁcant at P3005 by Tukey’s honestly signiﬁcant difference test with the
exception of the ﬂowering percentage, which was analyzed using a binomial distribution
and logit transformation.

122

Table 3.5. Effects of spray applications of benzyladenine (BA) on ﬂowering parameters
of large Miltoniopsis Echo Bay ‘Midnight Tears’ in Experiment 2. A description of plant
sizes is provided in Table 3.2; spray information is provided in the text.

 

 

Days to Total Flower Total VI

BA concentration Flowering Days ﬁrst open ﬂower diameter length
(mg-L“) (%) to v1 ﬂower v1 no. bud no. (em) (cm)
Control 80 129 193 3.5 7.9 7.6 16.4
Application at 0 weeks

1,000 70 104 162 2.9 7.4 7.1 17.8

2,000 100 120 173 2.0 5.3 7.0 16.0

4,000 90 109 166 2.5 5.0 7.1 14.3
Application at 4 weeks

1,000 90 109 182 3.6 8.5 7.1 18.2

2,000 60 105 176 2.8 6.7 7.1 17.8

4,000 90 116 182 3.1 9.3 6.5 17.7
Signiﬁcance
BA concentration NS NS NS NS NS NS NS
Application time NS NS NS NS NS NS NS
BA concentration *

Application time NS NS NS NS NS NS NS

 

NSNot signiﬁcant at P3005 by Tukey’s honestly signiﬁcant difference test with the

exception of the ﬂowering percentage, which was analyzed using a binomial distribution
and logit transformation.

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O 4 8 12 16 20 24 28 32
Time after ﬁrst application (weeks)

Figure 3.1. Effects of repeated spray applications of benzyladenine (BA) on mean
number of new vegetative shoots formed on three sizes of mixed hybrids of
Paphiopedilum in Experiment 1. A description of plant size is provided in Table 3.2.
Error bars represent standard errors of the means. Means at 28 weeks within a plant size
with the same letter are not signiﬁcantly different by Tukey’s honestly signiﬁcant
difference test at P5005.

126

 

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New vegetative shoots (no.)

 

 

 

 

 

O 4 8 12 16 20 24
Time after first application (weeks)

Figure 3.2. Effects of repeated spray applications of benzyladenine (BA) on mean
number of new vegetative shoots formed on two sizes of Paphiopedilum mixed hybrids
in Experiment 2. A description of plant size is provided in Table 3.2. Error bars
represent standard errors of the means. Means at 20 weeks within a plant size with the
same letter are not signiﬁcantly different by Tukey’s honestly signiﬁcant difference test
at P<0.05.

127

 

Small

+ Omg-L'1
3 . W0 200"194:1
‘V‘ 400 mg-L'1
2 J ‘V— 800 mg'L'1

  

 

Medium

New vegetative shoots (no.)
N

 

 

Large

 

 

 

O 4 8 12

16 20 24 28 32

Time after ﬁrst application (weeks)

Figure 3.3. Effects of benzyladenine (BA) sprays on mean number of new vegetative
shoots formed on three sizes of Miltoniopsis Echo Bay ‘Midnight Tears’ in Experiment 1.
A description of plant size is provided in Table 3.2. Error bars represent standard errors
of the mean. Means separation is not provided because BA treatment was not signiﬁcant

at P5005 within any plant size.

128

 

New vegetative shoots (no.)

 

Small Miltoniopsis Gerald Michael Lawles
'Paciﬁc Star Storm' _._ Control

-V- 2,000 mg-L'1
—'- 4,000 mg-L'1

We

 

Small Miltoniopsis Patricia Marie Linares
'Mauna Loa'

 

 

mm mm

 

 

 

 

O 4 8 12 16 20 24

Time after ﬁrst application (weeks)

Figure 3.4. Effects of benzyladenine (BA) sprays on mean number of new vegetative
shoots formed on three Miltoniopsis in Experiment 2. A description of plant size is
provided in Table 3.2. Error bars represent standard errors of the mean. Means at 20
weeks within a plant size with the same letter are not signiﬁcantly different by Tukey’s
honestly signiﬁcant difference test at P3005.

129

3.0

 

Small
2.5 l ,. ,. -

" :: \
1.0 .
0.5 .

0.0 . H - - - ‘V‘ 400 mg-L'1
"‘ 800 mg-L'1

 

Medium
2.5 - , -

2.0 4

1.5 4

1.0 .

0.5 _ »~

New vegetative shoots (no.)

 

 

Large

 

 

 

 

T T T T T T

0 4 8 12 16 20 24 28 32
Time after ﬁrst application (weeks)

Figure 3.5. Effects of benzyladenine (BA) sprays on mean number of new vegetative
shoots formed on three sizes of Beallara Tahoma Glacier ‘Green’ in Experiment 1. A
description of plant size is provided in Table 3.2. Error bars represent standard errors of
the means. Means at 28 weeks within a plant size with the same letter are not
signiﬁcantly different by Tukey’s honestly signiﬁcant difference test at P5005.

130

 

Small Burrageara Paciﬁc Lust 'la estrella'
4 . + 0 mg-L'1

A ‘V‘ 2,000 mg-L'1
2 . ‘V— 4,000 mg-L’1

   

 

New vegetative shoots (no.)

 

 

 

 

 

0 4 8 12 16 20 24
Time after ﬁrst application (weeks)

Figure 3.6. Effects of benzyladenine (BA) sprays on mean number of new vegetative
shoots formed on three sizes of Odontoglossum in Experiment 2. A description of plant
size is provided in Table 3.2. Error bars represent standard errors of the means. Means
separation is not provided because BA treatment was not signiﬁcant at P5005 within any
plant size.

131

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135

SECTION IV

EFFECTS OF PACLOBUTRAZOL ON INF LORESCENCE LENGTH OF

POTTED PIL4LAENOPSIS AND DORITAENOPSIS ORCHIDS

136

Effects of Paclobutrazol on Inﬂorescence Length of Potted Phalaenopsis and

Doritaenopsis Orchids

Linsey A. Newton1 and Erik S. Runkle2

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

Additional index words: inﬂorescence elongation, plant growth regulators, potted plants

Received for publication . Accepted for publication . We

 

 

gratefully acknowledge funding from growers providing support for Michigan State
University ﬂoriculture research and the support from the Michigan Agricultural

Experiment Station.

I Graduate student.

2 Associate Professor of Horticulture and Extension Specialist, to whom reprint requests

should be addressed (Email: runkleer@msu.edu).

137

Abstract

Inﬂorescences of some Phalaenopsis and Doritaenopsis orchid hybrids can
become very tall, which can pose shipping challenges for commercial producers and be
unwieldy for consumers. We determined the efﬁcacy of paclobutrazol as a foliar spray to

inhibit inﬂorescence elongation of these genera and intergeneric hybrids. A single
application of 15, 30, or 45 mg-L_1 palcobutrazol at a volume of 0.2 L-m~2 was applied to

D. Miss Saigon, D. Andrew, and P. ‘Smart Thing’ grown at 23 °C to induce ﬂowering.
Applications were made after inﬂorescence emergence but before ﬂower initiation
(inﬂorescences were 1 to 2 cm long) or after ﬂower initiation (inﬂorescences were 10 to
18 cm long). None of the paclobutrazol applications signiﬁcantly inhibited total

inﬂorescence elongation of ‘Smart Thing’ or Miss Saigon. However, application of 15
mg-L_l palcobutrazol before ﬂower initiation and application of 45 mg-L_l palcobutrazol

either before or after ﬂower initiation inhibited total inﬂorescence elongation of Andrew
by 19% to 23%. One or more concentrations of paclobutrazol applied after ﬂower
initiation reduced the length of the intemode between the ﬁrst and second ﬂower on all
three orchid clones. Paclobutrazol delayed ﬂowering only on Miss Saigon (by 2 d) and
only when applied after ﬂower initiation. Paclobutrazol application did not affect the
number of inﬂorescences or ﬂowers, diameter of the ﬁrst ﬂower, number of new leaves
formed, or increase in leaf span. We conclude that higher concentrations or multiple
applications of paclobutrazol are likely required to effectively suppress inﬂorescence
elongation of some Phalaenopsis and Doritaenopsis hybrids with tall inﬂorescences.

Furthermore, a late spray application can cause unwanted crowding of the ﬂowers.

138

Introduction

Plant growth retardants (PGRs) are used in the production of ﬂoriculture crops to
inhibit the elongation of intemodes (Gent and McAvoy, 2000). PGRs can be used on
species that are naturally tall to reduce plant height and create a more aesthetically
pleasing shape. In addition, creating shorter plants with PGRs can reduce shipping costs
because the smaller plants require less space during shipping.

Several of the commercially available PGRs reduce intemode elongation by
inhibiting gibberellin synthesis (Gent and McAvoy, 2000). Gibberellins promote cell
elongation and cell division (Taiz and Zeiger, 2006), and thus a reduction of active
endogenous gibberellins by PGRs can reduce plant height. The triazole type of PGRs,
such as paclobutrazol and uniconazole, inhibits the cytochrome P450 dependent kaurene
oxygenase, which catalyzes the oxidation of ent-kaurene to ent-kaurenoic acid in
gibberellin biosynthesis (Grossman, 1992). The growth retardant molecule binds to the
oxygenase, which prevents oxygen from binding and inactivates the enzyme.

Paclobutrazol effectively inhibits shoot elongation of a number of ﬂoriculture
crops, including seed impatiens (Impatiens wallerana Hook.), salvia (Salvia splendens
Sello ex Nees), marigold (Tagetes erecta L.), petunia (Petunia hybrida Vilm.), Spanish
lavender (Lavandula stoechas L.), and Chrysanthemum (Dendranthema X grandiﬂorum
(Ramat.) Kitamura ‘Bright Golden Anne’) (Barrett and Neil, 1992; Gilbertz, 1992;
Papageorgiou et al., 2002). In addition, paclobutrazol can also suppress inﬂorescence
elongation. For example, a drench of paclobutrazol at 0.625 to 2.5 mg active ingredient
per plant decreased the length of the inﬂorescence of lupine (Lupinus varius L.) by 28%

to 59% (Karaguzel et al., 2004). The concentrations appropriate for effective height

139

control vary by species and cultivar, environmental conditions, and desired magnitude of

response (Gent and McAvoy, 2000). The general recommended concentration of Bonzi,

a commercial formulation of paclobutrazol, on bedding plants is 5 to 90 mg-L_l applied

at a volume of 200 to 300 mL-m_2 for a spray application, or 0.5 to 1 mg'L—l of active
ingredient for a drench application (Syngenta Crop Protection, Inc., 2002). For

herbaceous potted ﬂowering plants, the recommended trial rates are 30 mg-L-l for a

spray application and 1 mg-L—l of active ingredient for a drench.

Paclobutrazol is most effective when applied as a soil drench or sprayed on the
stem (Barrett and Bartuska, 1982). A spray application of 150 mg-L—l paclobutrazol only
to mature Chrysanthemum leaves inhibited plant height by only 22% of that achieved by
application of 150 mg-L—1 paclobutrazol to the stem (Barrett and Bartuska, 1982).

Although sprays and drenches are the most common method of application of
paclobutrazol, solid spikes placed in the media have been as effective as drenches
(Barrett etal., 1994) and bulb dips have reduced the height of some lily (Lilium spp.) and
tulip (Tulipa spp.) hybrids (Krug et al., 2005; Ranwala et al., 2002).

In addition to the method of application, the time of application of paclobutrazol
is an important factor in some species. For example, an application of 30 mg-L_l

paclobutrazol applied to Chrysanthemum ‘Bright Golden Anne’ at the time of pinch
reduced plant height by 27% compared to that of the control; the same concentration of
paclobutrazol applied 4 weeks after the pinch only had little or no effect on plant height

(Gilbertz, 1992).

140

Phalaenopsis, Doritaenopsis, and related hybrids (subsequently referred to as
only phalaenopsis), which are the most common potted ﬂowering orchids sold in the
United States (Griesbach, 2002), develop inﬂorescences from reproductive buds in the
leaf nodes of their short stems. Some clones have very tall inﬂorescences, which can
pose shipping problems for commercial producers; the taller the inﬂorescence, the greater
amount of space the plant occupies, and the greater the cost of shipping plants to their
markets.

Few studies have been published on the effectiveness of PGRs on inhibiting
extension of phalaenopsis inﬂorescences. In one study, application of 200 mg-L—l

paclobutrazol to only the young inﬂorescence caused treated plants to produce 30%
shorter inﬂorescences than control plants (Chyou, 1993). In a separate study, dipping
entire Phalaenopsis plants in 50 to 400 mg-L—l paclobutrazol or 25 to 200 mg-L—l
uniconazole inhibited inﬂorescence elongation by 9 to 31% or 22 to 42%, respectively,
compared to the controls, and the higher rates also caused the leaves and roots to become
short and thick (Wang and Hsu, 1994). Additionally, dipping plants in a PGR solution is

undesirable because pathogens could be easily spread. Foliar sprays of 250 or 500
mg-L—1 paclobutrazol reduced inﬂorescence length to ﬁrst ﬂower, but were less effective

at reducing total inﬂorescence length. As the length of the inﬂorescence at the time of
the paclobutrazol spray application increased, the inhibition of inﬂorescence elongation
decreased (Wang and Hsu, 1994).

The objective of this study was to quantify the effect of a single paclobutrazol

spray on inhibiting inﬂorescence elongation of phalaenopsis orchids.

141

Materials and Methods
Plant Material

Three different phalaenopsis clones known to have tall inﬂorescences were
obtained for experimentation: Doritaenopsis Miss Saigon (Doritaenopsis Orglade’s Puff
X Phalaenopsis Naseweis), Phalaenopsis ‘Smart Thing’, and Doritaenopsis Andrew
(Phalaenopsis Ken Ciula X Doritaenopsis Orglade’s Geos). Plants were grown in 11.4-
cm (810 mL) pots in a mix of 80% coarse (2.5 cm) pine bark and 20% ﬁne coir at a
commercial greenhouse in Florida. Mature vegetative plants were shipped to a
commercial greenhouse in Michigan and then to Michigan State University on 19 Oct.
2007. Upon arrival, all plants were placed in a glass greenhouse at 29 °C to prevent
inﬂorescence initiation until the start of the experiment. The mean leaf span of Miss
Saigon, ‘Smart Thing’, and Andrew at the beginning of the experiment was 43, 48, and

53 cm, respectively.

Chemical Application

Paclobutrazol (Piccolo, Fine Americas, Walnut Creek, CA, USA) was applied to
the phalaenopsis plants at one of two times at a concentration of 15, 30, or 45 mg-L_l.

The two application times were before ﬂower initiation (18 Jan. 2008, when
inﬂorescences were 1 to 2 cm tall) and after ﬂower initiation (4 Feb. 2008, when

inﬂorescences were 10 to 18 cm tall). The paclobutrazol was applied as a foliar spray to
leaves and developing inﬂorescences at approximately 0.2 L-m—2 and no surfactant was

added to the solution. Ten plants were randomly assigned to every combination of

paclobutrazol concentration and application time or to the untreated control.

142

Greenhouse Environment

Plants were grown under a maximum instantaneous light intensity of 400
umol-m_2°s_l, maintained by a combination of shade cloth and whitewash, and a 16-h
photoperiod provided by natural sunlight and high-pressure sodium lamps that provided
35 to 40 umol-m—z's—l at plant canopy. Plants were fertilized at each watering with a

water-soluble fertilizer dissolved in reverse-osmosis treated water that provided (in
mg-L-l) 125 N, 12 P, 100 K, 65 Ca, 12 Mg, 1.0 Fe, 1.0 Cu, 0.5 Mn, 0.5 Zn, 0.3 B and 0.1

Mo (MSU Special, GreenCare Fertilizers, Inc., Kankakee, IL, USA).

Plants were grown at 29 °C until the start of the experiment on 20 Dec. 2007, at
which time they were moved to a greenhouse at 23 °C to initiate inﬂorescences. All
temperatures were maintained using a computerized environmental system that controlled
the heating system, vents, exhaust fans, and evaporative pad cooling (PRIVA Computers
Inc., Vineland Station, Ontario, Canada). Aspirated and enclosed thermocouples
positioned at plant height measured the air temperature and line quantum sensors
(Apogee Instruments, Logan, UT) measured the instantaneous light intensity every 10 s.
A CR10 data logger (Campbell Scientiﬁc, Logan, UT, USA) recorded hourly means of
both temperature and light intensity. The actual mean temperature during the experiment

was 23.8 °C and the actual mean photosynthetic daily light integral at plant level was 4.6

Data Collection and Analysis

143

At the start of the experiment (when plants were moved to 23 0C), the leaf span
(from tip of the longest leaf to the tip of the longest opposite leaf when held ﬂat) was
measured and the number of leaves (21 cm long) was counted. At the time of the ﬁrst
paclobutrazol application, inﬂorescence length of treated and control plants was
measured. Thereafter, inﬂorescence length was measured weekly until the ﬁrst ﬂower
opened. Weekly inﬂorescence length measurements for plants treated with paclobutrazol
after ﬂower initiation began at the time of the second paclobutrazol application. Dates of
the ﬁrst visible inﬂorescence (VI) and the ﬁrst open ﬂower were recorded. When the
ﬁrst ﬂower opened, inﬂorescence length to the ﬁrst ﬂower, total inﬂorescence length
(from base to apex when held straight), length of the node between the ﬁrst two ﬂowers,
and diameter of the ﬁrst open ﬂower were measured. In addition, the number of ﬂowers
and ﬂower buds on each inﬂorescence was counted. Two weeks after the last plant of
each clone ﬂowered (19, 18, or 16 weeks after plants were transferred to 23 °C for
Andrew, Miss Saigon, and ‘Smart Thing’, respectively), the leaf span of each plant was
measured again and the number of new leaves that developed during the experiment was
determined.

Weekly inﬂorescence length measurements were analyzed as repeated measures
with an autoregressive variance/covariance structure with heterogeneous variances.
Differences were declared signiﬁcant at P3005. Mean separation with Tukey’s honestly
signiﬁcant difference test at P5005 was used to analyze all ﬂowering characteristics,

vegetative growth, and ﬁnal inﬂorescence lengths.

Results

144

Inﬂorescence length

The greatest inhibitory effect of a paclobutrazol spray on inﬂorescence length to
ﬁrst ﬂower occurred in Doritaenopsis Andrew; all three concentrations of paclobutrazol
inhibited inﬂorescence elongation to the ﬁrst ﬂower by about 20% when applied before
ﬂower initiation (Figure 4.1). The inﬂorescence length to ﬁrst ﬂower was shorter than
that of control plants on Doritaenopsis Miss Saigon treated with 30 mg-L—l paclobutrazol
before ﬂower initiation. None of the other concentrations or application times had an
effect on Andrew, Miss Saigon, or ‘Smart Thing’.

Total inﬂorescence length of all three phalaenopsis clones was not signiﬁcantly
shorter than that of the control at any point before ﬂowering (Figures 4.2, 4.3, and 4.4).
However, at ﬁrst ﬂowering, paclobutrazol inhibited total inﬂorescence elongation (by

19% to 23%) of Doritaenopsis Andrew when treated with 15 mg-L-l before ﬂower

initiation and 45 mg-L_1 applied either before or after ﬂower initiation. The other

paclobutrazol treatments did not have a statistically signiﬁcant effect on total
inﬂorescence length of Andrew. None of the paclobutrazol applications signiﬁcantly
inhibited inﬂorescence elongation of ‘Smart Thing’ or Miss Saigon at the time of the ﬁrst

open ﬂower.

Node Length

 

The effect of paclobutrazol applications on the length of the node between the
ﬁrst two ﬂowers varied by clone (Figure 4.5). Both 30 and 45 mg-L_l paclobutrazol

applied after ﬂower initiation to Doritaenopsis Andrew caused this intemode to be about

20% shorter than that of the control, which was visibly noticeable as crowding of the

145

ﬂowers. On Doritaenopsis Miss Saigon, 15 and 45 mg-L_l paclobutrazol applied after
ﬂower initiation suppressed elongation of this same node by a similar amount. In
Phalaenopsis ‘Smart Thing’, only 30 mg-L_l paclobutrazol applied after ﬂower initiation

statistically elicited a shorter intemode; this intemode was 13% shorter than that of the

control.

Other Characteristics

Paclobutrazol applied to Doritaenopsis Miss Saigon after ﬂower initiation
increased the time between VI and ﬁrst open ﬂower compared to application before
ﬂower initiation, but there was no such delay in the other two clones (Table 4.2).
Paclobutrazol did not affect the number of inﬂorescences or ﬂowers formed or the
diameter of the ﬁrst open ﬂower on any of the three Phalaenopsis clones studied (Tables
4.1, 4.2, and 4.3). There were no apparent adverse effects of paclobutrazol treatments on
vegetative growth during the experiment. In addition, treatments did not inﬂuence the
increase in leaf span or the number of new leaves formed in any clone studied (Table

4.4).

Discussion

At the concentrations tested, a single spray application of paclobutrazol inhibited
inﬂorescence length of one of the three Phalaenopsis clones. There was statistically no
effect of the time of paclobutrazol application on total inﬂorescence height, but

application time did affect the length of the intemode between the ﬁrst two ﬂowers.

146

Applications of paclobutrazol after ﬂower initiation often decreased intemode length
between the ﬁrst two ﬂowers, whereas the applications before ﬂower initiation did not.
The concentrations of paclobutrazol used were based on a preliminary trial on

Phalaenopsis ‘Promis’, which had shorter inﬂorescences than the three Phalaenopsis
clones studied in this experiment. A spray application of 30 mg-L_l when inﬂorescences

were 0.3 to 7.5 cm tall inhibited inﬂorescence length of Phalaenopsis ‘Promis’ by 24%
(data not shown). Therefore, even greater concentrations are likely required to
signiﬁcantly inhibit inﬂorescence elongation of Phalaenopsis clones with taller
inﬂorescences.

Our spray applications were more effective than those of Wang and Hsu (1994),
who reported that foliar sprays of 250 or 500 mg'L—1 paclobutrazol 4 weeks after potting

reduced the inﬂorescence length to ﬁrst ﬂower by 14 and 7%, respectively, but did not

reduce the total inﬂorescence length of the Phalaenopsis clone tested. In our study, a
spray of 45 mg-L_l was enough to inhibit total elongation of the inﬂorescence of one of

the three clones tested. Reasons for these potential differences could be the varying
responses of clones, as seen within our study.

Wang and Hsu (1994) reported a tendency for earlier applications of
paclobutrazol to inhibit inﬂorescence elongation more than later applications. For
example, inﬂorescence length to the ﬁrst ﬂower was inhibited by 55% when
paclobutrazol was applied before inﬂorescence emergence and by 22% when applied to a
5.0-cm inﬂorescence. These reports are consistent with the results of our study. The
later an application is made, the more the inﬂorescence has already elongated and the less

opportunity to inﬂuence elongation. Studies on the effects of paclobutrazol on other

147

ﬂoriculture crops have shown similar effects of application time. For example,
application of 30 mg-L_l paclobutrazol to Chrysanthemum ‘Bright Golden Anne’ 4 weeks

after pinching only inhibited plant elongation by 12% compared to application at the time
of pinch (Gilbertz, 1992).
Our results are comparable to those of Chyou (1993), who reported a 22%

decrease in inﬂorescence length when inﬂorescences were brushed with a 200 mg'L—l

paclobutrazol solution. However, the brushing application method is more labor

intensive than a foliar spray, and is therefore less likely to be used by commercial orchid
growers. In the same study, sprays of a similar concentration (250 mg-L_l) also inhibited

inﬂorescence elongation, but root and leaf length were also suppressed. With lower
concentrations of paclobutrazol, we were able to avoid these negative effects on
vegetative growth. However, data was recorded only during the experiment (16 to 19
weeks, depending on the Phalaenopsis clone), and an effect on vegetative growth may
have become apparent if plants had been monitored longer.

These results are directly applicable to growers of Phalaenopsis who would like
to produce ﬂowering plants with shorter inﬂorescences. Based on our studies and that of

other published work, we suggest that growers perform small-scale trials using
paclobutrazol solutions Z45 mg-L"l within one week of inﬂorescence emergence (when

inﬂorescences are <5 cm tall). Multiple applications of paclobutrazol may be needed to
satisfactorily control inﬂorescence length. Late applications should be avoided to prevent

crowding of the ﬂowers caused by a reduction in the distance between ﬂowers.

148

Table 4.1. Effect of paclobutrazol concentration and application time on number of days
from visible inﬂorescence (VI) to ﬂowering, VI number, ﬂower bud number on ﬁrst
inﬂorescence to ﬂower, total ﬂower bud number per plant, and diameter of ﬁrst open
ﬂower of Doritaenopsis Andrew. Ns=Not signiﬁcant at P5005.

 

 

Flower Flower Flower
Days from VI bud no. on bud no. diameter
Application time VI to ﬂower no. ﬁrst VI per plant (cm)
Control 85 1.0 10.1 10.1 10.1
Before ﬂower initiation
15 mg-L—l 83 1.0 8.5 8.5 9.7
30 mg-L’1 83 1.0 9.3 9.3 10.4
45 mg-L‘l 84 1.0 9.0 9.0 10.0
After ﬂower initiation
15 mg-L‘l 83 1.0 10.1 10.1 10.3
30 mg-L‘l 85 1.1 8.9 8.6 10.2
45 rug-L" 82 1.0 8.8 8.8 10.1
Signiﬁcance
Concentration (C) NS NS NS NS NS
Application time (AT) NS NS NS NS NS
C*AT NS NS NS NS NS

 

149

Table 4.2. Effect of paclobutrazol concentration and application time on number of days
from visible inﬂorescence (VI) to ﬂowering, VI number, ﬂower bud number on ﬁrst
inﬂorescence to ﬂower, total ﬂower bud number per plant, and diameter of ﬁrst open
ﬂower of Doritaenopsis Miss Saigon. NS,*=Not signiﬁcant or signiﬁcant at P5005,
respectively.

 

 

Flower Flower Flower
Days from bud no. on bud no. diameter
Application time VI to ﬂower VI no. ﬁrst VI per plant (cm)
Control 85 1.3 7.1 8.4 8.1
Before ﬂower initiation
15 mg-L" 84 1.2 7.1 8.2 8.2
30 mg°L—] 84 1.1 6.7 7.3 8.1
45 mg-L’1 84 1.4 7.1 9.5 8.4
After ﬂower initiation
15 mg-L‘1 84 1.2 6.7 7.8 7.7
30 mg-L_] 86 1.2 7.2 8.2 8.4
45 rug-L" 88 1.2 6.3 7.3 8.1
Signiﬁcance
Concentration (C) Ns NS NS NS NS
Application time (AT) * NS NS NS NS
C*AT NS NS Ns NS NS

 

150

Table 4.3. Effect of paclobutrazol concentration and application time on number of days
from visible inﬂorescence (VI) to ﬂowering, VI number, ﬂower bud number on ﬁrst
inﬂorescence to ﬂower, total ﬂower bud number per plant, and diameter of ﬁrst open
ﬂower of Phalaenopsis ‘Smart Thing’. Ns=Not signiﬁcant at P5005.

 

 

Flower Flower Flower
Days from VI bud no. on bud no. diameter
Application time to ﬂower VI no. ﬁrst VI per plant (cm)
Control 73 1.6 9.4 14.0 9.1
Before ﬂower initiation
15 mg-L‘l 73 1.8 9.1 15.3 8.8
30 lug-L" 74 1.6 9.6 14.3 8.5
45 mg°L_l 74 1.6 11.9 16.6 9.0
After ﬂower initiation
15 mg-L"l 74 1.8 8.9 14.5 9.0
30 mg-L—l 74 1.9 10.1 17.6 8.9
45 rug-L" 74 1.6 10.5 15.0 8.9
Signiﬁcance
Concentration (C) NS Ns NS NS NS
Application time (AT) NS NS NS NS - NS
C*AT NS NS NS NS NS

 

151

 

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Control

15 mg-L'1 before ﬂower initiation
30 mg-L‘1 before ﬂower initiation
45 mg-L'1 before ﬂower initiation
15 mg-L'1 after ﬂower initiation
30 mg-L'1 after flower initiation

45 mg-L'1 after ﬂower initiation

Inﬂorescence length to ﬁrst ﬂower (cm)

Total inﬂorescence length (cm)

 

Andrew Miss Saigon 'Smart Thing'
Phalaenopsis clone

Figure 4.1. Effects of paclobutrazol concentration and application time on inﬂorescence
length to ﬁrst ﬂower (top) and total inﬂorescence length at ﬁrst open ﬂower (bottom) for
three Phalaenopsis clones. Error bars represent standard errors. Means within clone
with the same letter are not signiﬁcantly different by Tukey’s honestly signiﬁcant
difference test at P5005.

153

 

80 /§/
+ Control

+ 15 mg-L"I before ﬂower initiation

+ -1 . . . .
30 mg-L before ﬂower initiation

"" 45 mg-L'1 before ﬂower initiation

O)
0
g

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

 
 
 
  

+ 15 mgL'1 after ﬂower initiation
"D— 30 mg-L'1 after ﬂower initiation
"‘ 45 mg-L'1 after ﬂower initiation

A
O
i

N
O
i

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Total inﬂorescence length (cm)

 

//
i I i i l // i

O 2 4 6 8 Final height
Time after ﬁrst application (weeks)

 

 

Figure 4.2. Effect of paclobutrazol concentration and application time on total
inﬂorescence length of Doritaenopsis Andrew during the study. Final height was
measured at ﬁrst open ﬂower. Error bars represent the standard errors of the means.

154

80 7f/
+ Control

+ 15 mg-L'1 before ﬂower initiation

‘A‘ 30 mg-L'1 before ﬂower initiation

"" 45 mg-L'1 before ﬂower initiation ............................................................

 

O)
O
i

+ 15 mg-L'1 after ﬂower initiation

 
 
  

‘U— 30 mg~L'1 after ﬂower initiation
"- 45 mg-L'1 after ﬂower initiation

Total inﬂorescence length (cm)

 

 

40 _ ..................................................................................................................
20 a ..................................... /. .........................................................................
O 4 ...........................................................................................................................
//
T l T l I // I
0 2 4 6 8 Final height

Time after ﬁrst application (weeks)

Figure 4.3. Effects of paclobutrazol concentration and application time on total
inﬂorescence length of Doritaenopsis Miss Saigon during the study. Final height was
measured at ﬁrst open ﬂower. Error bars represent the standard errors of the mean.

155

 

 

100 7§4
+ Control

+ 15 mg-L'1 before ﬂower initiation

‘A— 30 mg-L'1 before ﬂower initiation

-" 45 mg-L'1 before ﬂower initiation

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+ 15 mg-L'1 after ﬂower initiation
‘0‘ 30 mg-L'1 after ﬂower initiation
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Total inﬂorescence length (cm)

N
O
i

 

 

o 2 4 6 8 Final height
Time after ﬁrst application (weeks)

Figure 4.4. Effects of paclobutrazol concentration and application time on total
inﬂorescence length of Phalaenopsis ‘Smart Thing’ during the study. Final height was
measured at ﬁrst open ﬂower. Error bars represent the standard error of the means.

156

 

 

 

 

 

  

    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

E 7

8, [2 Control

(1;) [:1 15 mg'L'1 before ﬂower initiation

g 6 ‘ - 30 mg-L'1 before ﬂower initiation

'8 I: 45 mg-L‘1 before ﬂower initiation

8 5 E] 15 mg-L'1 after ﬂower initiation

3i - 3O mg-L‘1 after ﬂower initiation

'2 - 45 mg-L'1 after ﬂower initiation

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Andrew Miss Saigon ‘Smart Thing'

Phalaenopsis clone

Figure 4.5. Effects of paclobutrazol concentration and application time on the length of
the intemode between the ﬁrst and second ﬂower of three Phalaenopsis clones. Error
bars represent standard errors. Means within clone with the same letter are not
signiﬁcantly different by Tukey’s honestly signiﬁcant difference test at P5005.

157

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Barrett, J .E. and TA. Nell. 1992. Efﬁcacy of paclobutrazol and uniconazole on four
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Chyou, MS. 1993. Effect of Bonzi on the ﬂowering of Phalaenopsis. Taiwan Sugar
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Papageorgiou, 1., P. Giaglaras, and E. Maloupa. 2002. Effects of paclobutrazol and
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US. Department of Agriculture. 2008. F loriculture crops 2007 summary. Agr. Stat.
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159