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EFFECTS OF TEMPERATURE ON FLOWER DEVELOPMENT RATE AND
MORPHOLOGY OF PHALAENOPSIS

presented by
Kari Ann Robinson

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EFFECTS OF TEMPERATURE ON FLOWER DEVELOPMENT RATE AND
MORPHOLOGY OF PHALAENOPSIS.

BY

Kari Ann Robinson

A THESIS

Submitted to
Michigan State University

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
for the degree of

MASTER OF SCIENCE

Department of Horticulture

2002

ABSTRACT
EFFECTS OF TEMPERATURE ON FLOWER DEVELOPMENT RATE AND
MORPHOLOGY OF PHALAENOPSIS.
By

Kari Ann Robinson

Although Phalaenopsis orchids are now the second most valuable flowering
potted plant according to 2001 USDA statistics, little specific quantitative
information is available on the plant relating plant development to the
environment. The objective Of this investigation was to quantify the effects of
temperature on time from spike emergence to flowering. Vegetative
Phalaenopsis BL. were induced to flower then were placed into growth
compartments at different constant temperatures. An initial calibration
experiment was performed with P. Taisuco Smile, followed by validation
experiments using several cultivars. Flower, node, and bud development rate
were modeled as a linear function Of development rate. Average time to flower
increased from 10 to 26 weeks as temperature decreased from 26 to 14 °C. At
any constant temperature for any given cultivar, time to visible bud was about
60% Of the total time from spiking tO flower. Plants grown at 29 °C failed to
develop to anthesis, and most buds aborted soon after they were visible. The
thermal time from appearance Of the flower spike to anthesis was 769 degree
days with, a calculated base temperature of 10.8 °C. Node and bud development
rates also increased linearly as temperatures increased. Temperatures from 17
to 26 °C did not affect the number Of nodes and flowers, spike height, or flower

size.

DEDICATION

To the two most important people in my life, my Mother, Carol Ann Robinson and
my F iancé, Robert James Mazzaferro.

Without you, none of this would have been possible.

ACKNOWLEDGMENTS

I wish to express my sincere appreciation to Dr. Royal Heins for giving me
the opportunity to work with him and so many other amazing people and for his
support, understanding, and patience over the past two years. I’d also like to
thank the others members of my graduate committee, Dr. Aurthor Cameron and
Dr. Don Garling, for their time and advice. In addition, this work could not have
been completed without the much appreciated greenhouse technical assistance
of Dave Joeright and Mike Olrich.

To all my friends and colleagues, I thank them for their advice, support,
and most of all friendship. I could not have picked better people to have surround
myself with. You are all wonderful. l’d especially like to thank Lee Ann Pramuk
and Roberto Lopez for continuous encouragement and sanity checks. Life
would have been very boring without the both Of you.

Most importantly, I must thank my family. My mother and grandparents for
their constant and unconditional love and encouragement; my uncle, Eric Huhn
for his valuable technical support; and to my aunt, Janice Lindsay and uncle, Bob
Lindsay for allowing me to stay with them and keeping me feed so well while I
finished the last four months Of my masters.

And to Robert, thank you for just being there.

TABLE OF CONTENTS

LIST OF TABLES ............................................................................................... VI
LIST OF FIGURES ........................................................................................... Vlll
LITERATURE REVIEW ........................................................................................ 1
Introduction ..................................................................................................... 2
Orchids ............................................................................................................. 4
Background .................................................................................................... 4
Plant description ............................................................................................ 7
Phalaenopsis ................................................................................................... 8
Background .................................................................................................... 8
Plant Description ............................................................................................ 9
Commercial Production ............................................................................... 1 1
Greenhouse Environment ............................................................................ 13
Miltoniopsis ................................................................................................... 20
Background ........................................ . ......................................................... 20
Plant Description .......................................................................................... 21
Commercial Production ............................................................................... 21
Paphiopedilum charlesworthii ................................................................ 23
Background .................................................................................................. 23
Plant Description ...................... , ................................................................... 24
Commercial Production ............................................................................... 25
Modeling Plant Development ....................................................................... 27
Literature Cited .............................................................................................. 30
SECTION 1: EFFECTS OF TEMPERATURE ON PHALAENOPSIS FROM
SPIKE EMERGENCE TO FLOWERING ............................................................. 37
Introduction .............................................................................................. 39
Materials & Methods ................................................................................ 42
Results ..................................................................................................... 48
Discussion ................................................................................................ 54
Literature Cited ......................................................................................... 60
APPENDIX .......................................................................................................... 75
Introduction .............................................................................................. 76
Materials and Methods ............................................................................. 78
Results ..................................................................................................... 81
Literature Cited ......................................................................................... 83

LIST OF TABLES

LITERATURE REVIEW

Page
Developmental stages of florets in relation to flower-stalk
elongation (Sakanishi et al.,1980) ............................................... 16
Effect of high temperature above 28 °C during elongation
of flower stalks on flowering (Sakanishi et al.,1980) ....................... 17

SECTION 1

Parameters of linear regression analysis relating forcing temperature to
rate of progress to visible bud (VB) and to anthesis (FLW) and
from VB to FL in cultivars of Phalaenopsis .................................. 63

Parameters of linear regression analysis relating forcing temperature to
rate of node development in hybrids of Phalaenopsis ..................... 64

Table 3. Bud development computed from Eq. [6] [D = In(B;/ B) / f(77],
where rm = c1 + c2 "T (c1 = 0.0113 1: 0.00389 d" and 02 =

0.0189 1: 0.00177 C“ day“ ....................................................... 65

The effect of temperature on the average number of nodes, total flower
count, flowers on the main spike axis, final spike height and flower width
for Phalaenopsis “Taisuco Smile’ (repetitions 1 and 2), P. H88-145
(repetitions 1 and 2), P. H88-36, and P. H89314. . ......................... 66

APPENDIX

. The effects of temperature and photoperiod (PD) on Miltoniopsis
‘Augres’ Trinity with 9 weeks bulking greenhouse .............................. 85

2. The effects of temperature and photoperiod (PD) on Miltoniopsis

vi

‘Augres’ Trinity grown in growth chambers ........................................ 86

3. The effects of temperature and photoperiod on Paphiopedilum laserx
Charfesworthii. .......................................................................... 87

4. The effects of temperature and photoperiod on Paphiopedilum laserx
chaflesworthii grown in growth chambers .......................................... 88

vii

LIST OF FIGURES

Figure Page
LITERATURE REVIEW

1. Growth habit of Phalaenopsis (Rotor, 1952) ..................................... 10

2. Phalaenopsis flower morphology and types (Noble, 1971) ................... 11

3. A degree-day model relating rate of development as a linear

function of temperature ................................................................ 28

SECTION 1

1. Effects Of temperature on time to visible bud (VB) and flower (FLW) (A, B,

and C) and rate of progress (D, E, and F) in calibration data set
Phalaenopsis ‘Taisuco Smile’ (0). Each symbol (0) represents one spike
The parameters of linear regression lines are presented in Table 1. The
quadratic regression lines in A, B, and C are the reciprocal of the linear
regression lines in D, E, and F, respectively. ................................... 67

Deviation between predicted and observed days to from spiking to flower
for validation data sets of Phalaenopsis hybrids. ............................... 68

Effects of temperature on inflorescence node development rate of
Phalaenopsis Taisuco Smile. Data points represent the slope of Eq.

[1] calculated for node count versus time for Phalaenopsis Taisuco Smile
in the calibration data set (0). The validation data set Phalaenopsis

Taisuco Smile (o) was plotted against the regression line for comparison.
............................................................................................... 69

Estimates of k, the rate parameter in Eq. [1] for Phalaenopsis Taisuco
Smile, obtained by using nonlinear regression to fit Eq. [1] separately to
data from four temperature treatments in the calibration experiment [(0)
symbol :I: SE] and the linear function f('l7 (solid line) ........................ 70

Predicted (solid line) and observed (0, mean :I: SE) bud length for each
treatment in the calibration experiment of Phalaenopsis Taisuco Smile. .71

viii

6. Deviation between predicted and observed days for calibration data set
Phalaenopsis Taisuco Smile. ........................................................ 72

7. Percentage of plants with a primary inflorescence spike that branched and
formed either no flowering lateral branches (A), 1 to 2 (B), 3 to 4 (C), or 5
or more (D) flowering lateral inflorescences as a function of average daily
temperature for Phalaenopsis Taisuco Smile repetition 1 (o) and 2 (o)...73

8. Percentage of plants with a primary inflorescence spike that branched and
formed either no flowering lateral branches (A), 1 to 2 (B), 3 to 4 (C), or 5
or more (D) flowering lateral inflorescenoes as a function of average daily
temperature for Phalaenopsis H88-145 repetition 1 (o) and 2 (o) ......... 74

LITERATURE REVIEW

Introduction

Because of improved cultural practices, reliable and uniform hybrids, and
heightened consumer interest, Phalaenopsis BL. are quickly becoming an
important economic crop, despite lack of a specific market date. In the United
States, orchids are the second most valuable potted crop and are valued at over
$99 million wholesale (USDA, 2002). Phalaenopsis are currently the most
valuable pottted crop in Holland (Barendse, 2002). In the Netherlands,
Phalaenopsis sales have risen from 3 million pots sold in 1984 to over 9 million
pots sold in 2001 (Griesbach, 2000; Vakblad voor de Bloemisterij, 2002). The
Netherlands and Taiwan account for a large portion of potted Phalaenopsis
production, as do China, Germany, Japan, and the United States (Griesbach,
2000). In 1993, the Japanese market for potted orchids was estimated to be
$261 million, with the Netherlands accounting for $62 million and ASEAN
(Association of the South East Asian Nations) accounting for $53.7 million (Hew
and Young, 1997). It is feasible that the production of Phalaenopsis will
continue to increase and, with the development of decision support tools, have

great economic potential.

Producing flowering plants for a specific market date requires knowledge of the
relationship between temperature and flower development rate. For example,
Easter lilies, which are the fourth most valuable potted crop, are grown for a
specific date, Easter. The day after Easter, plants are worthless (Larson, 1992),

so controlling this crop’s time to flower is important. Research on Easter lily

flowering is extensive (Fisher et al., 1997a, b; Holcomb and Berghage, 2001;
Karlsson et al., 1988; Wang, 1996a; Wilkins, 1988a, b; Wilkins and Grueber,
1990), as is work on poinsettias and Chrysanthemums (Karlsson et al., 1989;

Larson, 1992), valuable potted crops with specific market dates.

Although orchids are now the second largest potted crop in the United States,
little specific quantitative information is available relating plant development rate
to temperature from the time of visible spiking to flower. The lack of complete
production information is in part Phalaenopsis having no specific market date.
Phalaenopsis can be grown and sold year-round (lchihashi, 1997), and strict
scheduling of these plants has not been needed. Also, research done on
Phalaenopsis generally has been done outside the United States, mostly in Asian
countries. The published results of these studies are not always readily available
to growers, and most of them have not been translated into English (lchihashi,
1997). Also, these studies often show conflicting results and can be difficult to
interpret. The objectives of this investigation were to quantify the effects of
temperature on time from spike emergence to flowering and develop a cohesive

growing protocol for potted orchid production.

Orchids
Background

Distribution. Orchids belong to Orchidaceae, which are distributed worldwide.
An estimated 1000 genera and 25,000 species exist (Jones and Luchsinger,

1986). Orchids are found largely in the tropics but also grow in regions of the
Arctic, semidesert areas of Australia, and throughout the United States

(Pndgeon,2000)

History. The word orchid is derived from the Greek word orchis, meaning testis
(Reinikka, 1972). In Greek culture, orchids were used as an herbal remedy for
infertility according to the teaching of the doctrine of signatures: plants could be
used to treat human ailments successfully if plant parts resembled the affected
area in color or shape. Orchids were also thought to grow from dropped animal
semen, a belief that was upheld for hundreds of years because orchid seeds are
no more than dustlike particles and virtually invisible. Orchids were largely
banished by Western Europe because of their association with Greek culture and
sexual connotations (Berliocchi, 1996). Although the early history of orchids is
normally associated with Greek culture, orchids were first recorded as early as
800 be. in paintings and literature in the Orient. The Chinese word for orchid is
Ian, a term used in ancient writing in reference to the Cymbidium orchid

(Berliocchi, 1996; Reinikka, 1972).

An increasing number of orchids were discovered during the 1600s as
exploration expanded and travel between continents became possible. Orchids
became noted more for their beauty than their healing qualities. The most
valuable orchids were Vanilla species that were used for making perfumes and
flavorings. In the early 18005, orchid collecting became a fashionable hobby
among the wealthy. During this time, the first Catt/eye and Dendmbium orchids
were introduced. Prices for orchids then began to skyrocket. Payments of $500
for a single plant and $2000 for a true “investment” were not uncommon (Logan

and Cosper, 1953).

Despite the orchid craze, the culture of orchids still remained a mystery. All
orchids were thought to need tropical conditions. They were grown in so called
stoves that were made of dense glass and had coal fires and brick flues. The
bricks were drenched with water to create steam and maintain high humidity.
These structures had no movable windows and hence were unventilated. In
1817, Joseph Hooker described the English cultivation technique as the “grave of
tropical orchids”. Using work by John Lindley (1799—1865), the father of modern
orchidology, Sir Joseph Paxton changed orchid culture when he abandoned the
stoves entirely and opened up the windows of his greenhouses, keeping them
relatively cooler (Reinikka, 1972). The plants thrived in the new environment,
and soon other growers abandoned stoves and used more practical, successful

methods to grow orchids.

During the mid-18003, the first orchid crosses were made; yet despite single
orchid pods containing between 500,000 and 1 million seeds, new hybrids were
difficult to develop because a successful way to germinate seeds still eluded
growers (Larson, 1992). The first breakthroughs for forcing germination were
made independently by Hans Bergeff in Germany and Noel Bernard in France
between 1899 and 1909. They used a symbiotic method in which seeds were
grown in association with mycorrhizae (Reinikka, 1972). Phalaenopsis seeds,
like all orchids, are incredibly tiny and have no endosperm and only a
rudimentary seed coat. The fungus assists germination by supplying the nutrients
that the endosperm would supply. Although this method of germination was
used successfully, the need for mycorrhizae as a reserve for the seeds was
questioned. In a classic article, Lewis Knudson (1922) of Cornell University
refuted symbiotic germination; he had developed an asymbiotic method by using
a sugar medium in place of the fungus. The medium was a combination of a

nutrient solution, fructose or glucose, and agar gel.

The asymbiotic method is still widely used today. It helped the commercial orchid
industry expand and made the introduction of more hybrids possible. Since the
first hybrid was developed, more than 100,000 hybrids have become available to

growers (Pridgeon, 2000).

Plarflesmption

Flowers. Orchids are thought to be the most advanced of all monocotyledons
(Pridgeon, 2000). They differ from all other flowering plants in that their stamens
and pistils are fused into a structure called the column (gynandrium). Like most
other plants in the Liliidae subclass, flowers have three sepals and three petals;
however, the sepals can be colored or green, and one of the three petals is
usually modified into a lip structure called the labellum. The flowers are

zygomorphic, meaning bilaterally symmetrical (Jones and Luchsinger, 1986).

Growth habit. Orchid root habit depends on whether these perennial herbs are
terrestrial or epiphytic. Epiphytic roots are usually covered with a silvery-gray
velamen, which helps the plant adhere to surfaces and absorb water and
nutrients. Healthy root tips are green and able to photosynthesize (Elliott, 1998).
Terrestrial orchids have hairier roots that normally have no green tip. Orchid
roots have the same basic function that all other plant roots have: to anchor the

plant on and in the medium and absorb water and nutrients.

Phalaenopsis
Background

Distribution. Most Phalaenopsis originate from tropical and subtropical areas of
the South Pacific Islands and Asia (Baker and Baker, 1991; Noble, 1971). In the
South Pacific, they range from Sri Lanka to southern India and westward to
Papua New Guinea and Australia. In Asia, Phalaenopsis is found in China,
Taiwan, and the Philippines (Christenson, 2001). Approximately 40 Phalaenopsis

species are known today (Baker and Baker, 1991).

History. Compared with other orchids such as Cymbidium and Vanilla,
Phalaenopsis is a relatively new genus in terms of its discovery. Though first
described in the mid-17503, however, Karl Ludwig was the first to classify them
as Phalaenopsis in 1825 (Noble, 1971). Phalaenopsis stems from the Greek
words phalaina, meaning moth, and Opsis, a suffix denoting resemblance

(Coombes, 1985). The common name for Phalaenopsis is the moth orchid.

Phalaenopsis was introduced in Europe during the height of the orchid craze in
the early 19th century (Christenson, 2001). However, cultural requirements of the
genus were unknown, and most plants succumbed to bacterial crown rot.
Phalaenopsis production greatly benefited from the seed germination work Of
Lewis Knudson (Christenson, 2001). In the 1940s, the first tetraploid
Phalaenopsis Doris was established (Christenson, 2001). Tetraploid flowers
have flowers greater longevity and substance, creating more demand for

Phalaenopsis as a cut flower and potted plant. Phalaenopsis are currently

propagated from seed or, more commonly, by tissue culture (Christenson, 2001).
Tissue culture has become less expensive and also results in more uniform

plants.

flant Description

Growth habit. In the wild, Phalaenopsis are epiphytic or lithophytic, with their
main axis growing somewhat horizontally away from the tree so that water drains
down the midrib of the leaves. The main axis consists of a short stem with
alternating leaves whose leaf color ranges from light green to purplish-green.
Each leaf is associated with two auxiliary buds from which an inflorescence can
form (Figure 1). Normally only the top bud elongates; the bottom bud remains
dormant unless the other bud is damaged. The inflorescence, most commonly
called a spike, grows at a right angle to the vertical host stem (Christenson,
2001). Each inflorescence has four to eight nodes below the buds, and each of
these nodes can develop into a lateral branch, that can in turn also branch,
creating a raceme. The spike normally emerges from the third to fifth node below
the top leaf (Sakanishi et al. 1980; Yonda 1985). Spike emergence from the first
or second nodes below the top leaf is uncommon. The root tips are normally
green and are able to photosynthesize. Roots are unbranched, unless they have
been damaged or are aging. The leaves Of Phalaenopsis are thick and fleshy and

usually persistent.

 

-————O. --

,..._...__. _ Leaf

  
 

Leaf -. Apical meristem
Vegetative bud
Flower bud
Flower bud
Vegetative bud
Vegetative bud

Figure 1. Growth habit of Phalaenopsis (Rotor, 1952)

Flowers. Like those of most orchids, the flowers of Phalaenopsis have three

sepals and three petals. The sepals form a triangle and are often the same color

as the petals but may be spotted or resemble the lip color. Two of the petals are

mirror images, set opposite each other, giving Phalaenopsis its moth-like

appearance. The third petal forms the lip, which has two tendrils, characteristic of

Phalaenopsis (Figure 2). The majority of Phalaenopsis are pink or white;

10

however, with hybridization, yellow and bicolored flowers have become more
common. Flowers often last from 2 to 5 months (Baker and Baker, 1991; Wang

and Lee, 1994a). Recently, purple hybrids have become available and are

popular.

   

/ Dorsal sepal
-‘ Petal

1,5; ‘ ‘ ‘ - ~ »—~--~ Column
//,'f" "3‘ L...“ . ---.....-_-- ~_. - Lip, side lobe
;' - 1“. I: ’ . I" .-__ . .-. _ .-.. _._ .. Callus

\ ‘-.‘F§_"'-'..".i' LL._.__ Lip, midlobe
r. ‘.- . -...t E- .- . ..._. Lip, tendril
~ _— -______ “ Lateral sepal

Figure 2. Phalaenopsis flower morphology and types (Noble, 1971)

Commercial Production

Standards. There is a consensus among growers of what a marketable plant
should look like; however, there are no Official standards regarding physical
specifications for commercial orchids. Most plants sold have a flower width of 7.6
cm (Wang and Lee, 1994a). Phalaenopsis with multiple and well-branched

spikes can be sold at a higher price than plants with only one spike and no lateral

branches.

Growing protocol. Phalaenopsis can be grown from seeds or as mericlones in
tissue culture; however, both methods require aseptic conditions with exact
nutrients and environmental conditions (Dole and Wilkins, 1999). However,
Phalaenopsis quickly mature and flower compared to many other orchids, with
most taking approximately 24 months from seed to flower (Wang, 1994a). Most
commercially produced Phalaenopsis in the United States are flowered from
bare-root plants with a leaf span between 20 and 30 cm and four to five mature
leaves. Plants of this size can be spiked and flowered in about four to six months.
Larger, prespiked plants can also be purchased wholesale to flower but at a

higher cost to the grower.

Plant height is not normally controlled with growth regulators, but studies by
Wang and Hsu (1994) have shown that paclobutrazol (50, 100, 200, or 400
mg'L') and uniconazole (25, 50, 100, or 200 mg'L“) used as either a 5-sec dip or
a foliar spray resulted in shorter spikes. Plants treated with a 5-sec dip showed
more uniform results but had a longer flowering delay the following year than
those treated with the foliar spray. The growth regulators did not affect flower
size or count but did delay flowering as concentration increased. Daminozide
produced no effects when applied as a dip or to foliage, at 2500, 5000, or 7500

mg'L“.

12

Greenhousi Environment

Medium and Nutrition. Although used only since the 1950s, fir bark-based
medium is the primary medium used to grow orchids, including Phalaenopsis, in
North America and the Netherlands (McLellan, 1956). Before bark-based
medium, osmunda fiber was used but was scarce and expensive. Despite the
mass use of fir bark, it has drawbacks such as quick decomposition, lack of
uniformity, inability to hold nutrients, and general lack of practicality for large-
scale potted plant production. For these reasons, other materials that provide
better water and nutrient retention, such as pure sphagnum and peat-based
medium, commonly referred to as a mud mix by orchid growers, are increasing in
popularity (Brenneise and Halgren, 2000; Ichihashi, 1997). Peat-based medium
can be mixed with various percentages of fir bark, perlite, coconut fiber, and
other materials. Peat-based media have been shown to improve Phalaenopsis
leaf growth, flower size, and number because of more lateral inflorescences
(Wang 1995b; Wang and Gregg, 1994). Medium type did not affect time to
flower (Wang, 1995b; 1996b; Wang and Gregg, 1994).

When a peat-based medium is used, a balanced water-soluble fertilizer at 1 9L1
per irrigation is recommended for Phalaenopsis (Wang, 1996b; Wang and
Gregg, 1994). Increasing fertilizer rate from 0.25 to 1 9L1 per irrigation did not
change the time to flowering during a short-term commercial forcing schedule,
but did reduced time to flower during a second force (Wang and Gregg, 1994).

A 20-20-20 water-soluble fertilizer with N at 100 mg L‘1 was recommended for

13

Phalaenopsis Toyland at each irrigation when the hybrid is grown in a bark-
based medium (Griesbach, 1985). Maintaining high N concentrations (100 mg‘L'
1) before and after spiking is important for obtaining high flower counts. In
experiments in which N was reduced or stopped during spike development,

flower counts were reduced (Wang, 2000).

lrrigating Phalaenopsis before and after flower development by using a fertilizer
that has a high P ratio reportedly results in superior flowers (Gordon, 1990).
However, in other studies, increasing P resulted in fewer flowers; it may actually
reduce flowering longevity (Wang, 2000). Also, flower development was not

affected by P concentration (Gomi et al., 1980; Wang, 2000).

lnadiance. Phalaenopsis require relatively low light levels compared with most
plants. Light levels for Phalaenopsis range from 200 to 250 umol'm'2'5'1. with a

maximum tolerance of 300 meI'm'2'8'1 (Baker and Baker, 1991). Baker and
Baker (1991) suggest that high light levels may initiate blooming in some
species; however, very high irradiance levels can severely burn the thick fleshy

leaves Of Phalaenopsis and, in severe cases, kill the plant.

Plants receiving very low light levels (8 or 0 UMOI'm‘2'8'1) do not respond to

induction temperatures and remain vegetative at any temperature if kept under

low light. Plants receiving at least 60 LIITIOI'ITI'Z'S'1 for 12 h perceived induction

treatments and flowered normally (Wang, 1995a). Additional studies have shown

14

that the suppression of spiking during low light levels is not due to low levels of

endogenous gibberellin (Satoshi et al., 1996). Growing plants at low light levels

can be an alternative to heating greenhouses to maintain vegetative plants and

reduce heating costs.

Temperature. Phalaenopsis are tropical and subtropical plants that require
warm temperatures to grow vegetatively. Plants remain vegetative above 27 to
29 °C (Sakanishi et al., 1980) and can tolerate temperatures as high as 35 °C
(Baker and Baker, 1991). Baker and Baker (1991) suggest that minimum
growing temperatures of 17 to 18 °C and 21 to 30 °C are ideal growing

conditions, but at higher temperatures Phalaenopsis will not flower.

Temperature management is important during spike development. Although
temperatures below 25 °C initiate spiking in Phalaenopsis, they do not initiate
flowering (De Vries, 1950; Sakanishi et al., 1980). Table 1 shows the floret
developmental stages (I to VII) of a given spike lenght, and Table 2 shows the

effect of high temperature at these spike lenghts.

De Vries (1950) described six stages of flower development, from spike
emergence (stage I) to stamen recognition (stage Vl). At stage V, the spike had
developed for 6 weeks and was 1.6 to 11.8 mm long. When the spike is less than
5 cm, florets 3 through 6 have not initiated the primordia of the floret (stage I),

and the spike can remain vegetative at high temperatures. A keiki, a vegetative

15

Table 1. Developmental stages of florets in relation to flower-stalk elongation
(Sakanishi et al. 1980)

 

 

Length of
Flower stalk (cm)

Order of florets
on flower stalk

Developmental stages of Florets

 

IV

V

VI

VII

 

1-5

1,2
3,4
5.6

10

1

1

 

6-10

1,2
3,4
5,6

 

11-20

1,2
3,4
5,6

Nb—bNU'I-K

 

21-30

1,2
3,4
5,6
2,3

 

31-40

1,2
3,4
5,6
7,8

GINA-l

 

41 -50

 

1,2
3,4
5,6
7,8

 

 

 

 

 

 

Nola-3‘03“...

 

 

Five Flower-stalks of each length were used for the observation.
*2 Showing the respective stage of floret development as follows,

I : Primordia of floret not appeared,
II : Primordia of floret initiated,
II I : Sepals differentiated,
lV : Petals differentiated,

V : Gynosterrnium differentiated,
VI : Anthers differentiated,

Vll : Pollen formed.

16

 

Table 2. Effect of high temperature above 28 °C during elongation of flower-stalks
on flowering (Sakanishi et al., 1980)

 

 

 

 

 

 

 

Length of Percent-age Mean days from Length of Number of
flower- stalk at of aborted flower-stalk flower stalk florets per
start of high stalks emergence to stalk
temg flowering
Control * 0.0% 103 i 8 SE. 61.8 cm 7.5
< 5 cm 15.4 59 i 5 36.0 4.1
10 cm 0.0 59 i 5 47.2 6.8
21 - 30 cm 0.0 65 i 5 48.4 5.7
41 — 50 cm 0.0 73 i- 5 59.1 6.8

 

 

 

 

 

*: Plants were grown continually in the greenhouse

air plantlet, may form instead of buds, or buds may be aborted altogether (De
Vries, 1950; Sakanishi et al., 1980). Abortion of buds can be avoided if the
temperature around the plant can be kept below 28 °C untill the spike has
reached 5 cm in height, after which the spike will develop at most temperatures
because the floret primordium is already initiated and beginning to differentiate

(Table 2).

When plants were kept at 28 °C for 6 h per day or fewer, the percentage of
spiking was unaffected, but as time at 28 °C increased to 12 h per day, spike
emergence was repressed. Plants kept at 28 °C for 24 h never spiked (Sakanishi
et al., 1980). De Vries (1950) reported that plants spiked at any temperature
between 11 and 25 °C, with the optimum temperatures for spiking being 15 to 20

°C. Although spikes grown at an average daily temperature (ADT) of 28 °C had

17

 

delayed flowering, there was little effect on size of flowers or spike height (Lee

and Lin, 1984; Sakanishi et al. 1980).

The exact reason Phalaenopsis spike below 27 °C is open to speculation (Chou
et al., 2000; De Vries, 1950; Ota et al., 1991). Many of the theories relate to 002
fixation by the plants. Phalaenopsis are crassulacean acid metabolism (CAM)
plants that fix C02 most readily at night and under relatively cool growing
conditions (Ota et al., 1991). Chou et al. (2000) demonstrated that plants grown
at a day/night temperature of 30/25 °C for 20 consecutive days showed higher
concentrations of inactive glucoside cytokinins than plants grown at 25l20 °C.
These results suggest that cytokinins may promote bud development at low
temperatures. In studies by Wang et al. (2002), Phalaenopsis hybrida Bl. spiking

was retarded when exogenous abscisic acid (ABA) was applied at 0.1 and 1.0

pg per plant.

Most Phalaenopsis can be uniformly spiked when induced at 25l20 °C day/night
(Lee and Lin, 1987). However, plant maturity can introduce varying results for
percentage and time to flower once plants have spiked (Yonda et al., 1992); in
that study, independent of temperature, six year old plants spiked two weeks
before the three year old plants. Six year old plants spiked at 100% versus 3-
year-old plants that spiked from only 13 to 80% under various temperatures for
different lengths of time (Yonda et al., 1992). Younger plants can be spiked

uniformly if given lower temperatures or longer durations at a given temperature.

18

Temperature also affects time from spiking to flowering. However, this phase of
development has not been well described. A number of studies (Lee and Lin,
1984; Sakanishi et al., 1980; 1987; Yoneda, 1985; Yoneda et at, 1991, 1992)
report the dates of spike emergence and flowering date but not ADTs that are
needed to properly determine a temperature effect on flower development.
Instead, only the minimum and maximum temperature for a given month, the
temperature settings for the greenhouse, or just the temperature the plants were

spiked at are given.

Phalaenopsis have been reported to show leaf pitting between 10 and 0 °C
(McConnell and Sheehan, 1978). This chilling injury becomes a problem when
Phalaenopsis are grown with other orchids that require cooler growing

temperatures or during shipping.

Phalaenopsis are not reported to be photoperiodic (Sakanishi et al., 1980).
However, there are a few studies that report that short days enhance spiking (De
Vries, 1950; Griesbach, 1985; Roter, 1952; Yonda et al., 1991) though this short-
day enhancement was not observed in other studies (Sakanishi et al. 1980) and
is thought to be a result of cool night temperatures resulting from the extended

night (Sakanishi et al., 1980).

19

Miltoniopsis
Background

Distribution. Miltoniopsis are native to wet forest regions of Costa Rica and Peru
(Berliocchi, 1996). Miltoniopsis species are found from 610 m to 2100 m above
sea level (Baker and Baker, 1993b). The average minimum and maximum

temperatures range from a low Of 10 °C to a high of 29 °C .

History. Miltoniopsis are named for orchid enthusiast Lord Fitz-William Milton
(1786-1857) by John Lindley (Berliocchi, 1996). In 1889, Godefroy-Lebeuf
separated Miltonia into two groups, Miltonia and Miltoniopsis. However, this
distinction was not officially recognized until the 19703 (Rentoul, 1982), and in
some literature the two groups are still treated as one genus. These genera can
be distinguished by Miltonia’s two-Ieaved pseudobulb, and Miltoniopsis’s has a
one—leafed pseudobulb. Miltoniopsis also have the classic pansy-shaped flower
that led to the common name of pansy orchid. Both of these genera have other
distinguishing features, such as rhizome type and column and lip characteristics.
Miltonia are native to Brazil, while Miltoniopsis are native to Colombia. Five or
six species of Miltoniopsis and 20 species of Miltonia have been named (Baker
and Baker,1993b; Berliocchi, 1996; Stenlvart and Griffiths, 1995). Most modern
hybrids are a complex of three species: Miltoniopsis vexillan'a (chb. F.) Godef-
Leb. , M. roezii (chb. F.) Godef-Leb. , and M. phalaenopsis (Lind. & Rchb. F.)

Garay & Dunsterv. (Baker and Baker, 1993b; Nash, 1989).

20

PlantJDescrertion

Growth habit. Miltoniopsis are epiphytes or lithophytes in the wild and have a
sympodial growth habit. Like all sympodial orchids, Miltoniopsis grow from a
pseudobulb. The pseudobulb is an enlarged stem from which flowers arise can
have one (homoblastic) or many (heteroblastic) nodes (Hew and Young, 1997).
Miltoniopsis have homoblastic pseudobulbs. The main function of the
pseudobulbs is to store food and water; they will often outlive roots and leaves

(Ng and Hew, 2000).

The pseudobulb is capable of flowering only when it is mature. If the mature
pseudobulb develops new plantlets instead of flowering spikes, it will not be able
to flower (Rittershausen and Rittershausen, 1985). The inflorescence is a
raceme with one to several flowers (Berliocchi, 1996; Stewart and Griffiths,
1995). The flowers are large, showy, and flat with a range of colors excluding

blue. Flowers can last four to eight weeks (Baker and Baker, 1993a).

The root habit is fine and similar to that of Odontoglossum, and leaves are long

and narrow, sheathing the pseudobulb (Rentoul, 1982).

Commercial Production
Miltoniopsis are the fourth most valuable potted orchid in the Netherlands, with
797,000 pots sold in 2001 (Vakblad voor de Bloemisterij, 2002); however, there

has not been any documented work to develop a growing protocol for these

21

plants. The only information available on Miltoniopsis is a handful of hobbyist-
type articles that contain similar cultivation instructions (Baker and Baker, 1993a,
b; Ortho, 1999; Rentoul, 1982; Sweet, 1978). The recommendations for growing
Miltoniopsis are to keep plants evenly moist, and light levels from 900 to 2000
foot-candles. If the leaf edges turn pink, then the plants are receiving too much
light (Baker and Baker, 1993a; Ortho 1999; 1993a). Recommended daytime
average temperatures range from 27 to 29 °C; night-time temperatures average
from 16 to 18°C (Baker and Baker, 1993a; Ortho, 1999;). Temperatures of 17 to
20 °C produce abundant flowering, but whether this is a constant ADT or an
induction treatment is not indicated (Baker and Baker, 1993a; Tran Than Van,
1974). In several articles, Miltoniopsis are not reported to be among the easier
orchids to grow (Baker and Baker, 1993a, b; Rentoul, 1982). Miltoniopsis have a
greenhouse growth habit and cycle similar to that of Oncidium (Hew and Young,

1997)

22

Paphiopedilum

Background

Distribution. Paphiopedilum are native to tropical and subtropical southeast Asia
and islands of the South Pacific (Berliocchi, 1996; Cribb, 1987; Dole and Wilkins

1999) and 60 species have been described (Cribb, 1987).

History. Paphiopedilum were previously classified into the much broader
Cypripedium until the late 19605 (Berliocchi, 1996; Rentoul, 1980). Although
given the common name lady slipper, Paphiopedilum literally means Aphrodite’s

slipper.

Paphiopedilum was discovered in India in the early 1800s (Rentoul, 1980) and
has been in cultivation since 1819, when the first plant flowered under glass in
the Liverpool Botanic Garden (Hennessy and Hedge, 1989). By 1900, 475
Paphiopedilum hybrids were registered and 40 of the 60 species were known
despite primitive germination techniques and the lack of knowledge of cultural

needs (Hennessy and Hedge, 1989).
Paphiopedilum have been used for cytology studies because of their large

chromosome size and affinity for chromosome stains. Paphiopedilum are also

thought to be one of the most ancestral of all the orchids (Cribb, 1987).

23

Plant Description
Growth habit. Paphiopedilum are considered terrestrial (Cribb, 1987), semi-
terrestrial, lithophytic, or epiphytic herbs (Hennessy and Hedge, 1989). They can

be found growing on the forest floor or low in trees.

Paphiopedilum have a sympodial growth habit and, like Phalaenopsis, have no
pseudobulb. The stems of the plant are relatively short, an inch long or shorter in
most cases, and are covered by overlapping leaves that form a fan shape.
Leaves can be mottled or entirely green. New plantlets arise from the main plant.
The Older growth is thought to act like a pseudobulb by supplying nutrients to the

developing shoots (Rittershausen and Rittershausen, 1985).

The roots of Paphiopedilum are always moist and have a less-developed root
system (Ortho, 1999). Roots have a multiseriate velamen and large brown root

hairs.

Flowers. Paphiopedilum differ from most other orchids because they have many
vegetative buds but have only one reproductive bud primordium, the most apical,
that develops into a flower (Rotor, 1952). The apical meristem will elongate while
the bud is developing. Individual flowers can last 30 to 120 days (Goh and Arditti,
1985). The bud emerges from the center of the growth. Once the plant flowers,

it will not flower again until a vegetative shoot arises.

24

Although all orchids have unique flowers, Paphiopedilum flowers are particularly
unusual. The most obvious feature is the upper dorsal sepal, which is usually
brightly colored and often used to identify a species. The two lateral sepals are
fused and called the synseplaum (Berliocchi, 1996). The flower also bears a

dominant saccate lip, which is normally the same color as the two lateral petals.

Commercial Production

Although Paphiopedilum are a popular potted plant, with over 500,000 sold in the
Netherlands during 2001, almost no published data exist describing their
commercial production. Most orchid articles and books give general
recommended cultivation for Paphiopedilum (Hennessy and Hedge, 1989;
Rentoul, 1980; Ortho, 1999; Stewart and Griffiths; 1995). Rotor (1950) reported
that Paphiopedilum insigne (Wallich ex Lindl.) Pfitz. remained vegetative above
18 °C, but when temperatures were dropped to 13 °C, flower buds initiated two to
three weeks later, and plants flowered 6 months later when maintained at 13 °C.
Paphiopedilum barbatum (Lindl.) Pfitz. remained vegetative at temperatures
above 23 °C, but flowered when temperatures were dropped to 16 to 21°C (Goh

and Arditti, 1985). These two species were not found to be photoperiodic (Rotor,

1952). Plants are use to low light tolerating 140 umol'm'z'S'1 (Dole and Wilkins,

1999), and leaves will become yellow with too much light.

25

Paphiopedilum charlesworthii have a reputation for not being easily cultivated
(Hennessy and Hedge, 1989). It is intolerant of constant high temperatures and
has a slow growth rate. Paphiopedilum chariesworthii are reported to flower
better under cool night temperatures of 10 °C, with at least a 5 °C increase for

the daytime temperature (Cribb, 1987).

26

Modeling Plant Development

Modeling plant development is a crucial part of cropping plants for a
specific market date and has been used for a wide range of agronomical crops
and horticultural crops. The most critical factor in developing a model for plant
development is temperature. Although environmental factors such as cool
temperatures, photoperiod, and plant size can induce a plant to enter a different
phenophase, it is temperature alone that determines the rate of development
throughout that phase. This is in contrast to growth, which is a nonreversible

process and includes gains in height, weight, or volume.

For any developmental process such as time to flower or number of leaves
grown in a given period, the reciprocal can be taken to give a linear function over
a given temperature range where the rate (1ldays) is equal to the slope plus the

product of the intercept temperature:

1/ Days = b0 +b1* T [1]

For plants, the rate is linear only between the base temperature (T b) and the

Optimum temperate (Topt), otherwise known as the cardinal temperatures (Figure

3). Tb can be determined by

Tb = 'b0/b1 [2]

27

Tb is the point at which the linear rate crosses the x-axis and development is
halted. Development about Ti decreases as temperatures increase. Cardinal

temperatures differ among crops or developmental stages of the same crop.

 

Topt I

Rate

 

 

 

Temperature

Figure 3 . A degree-day model relating rate of development as
a linear function of temperature

In the early 1700s, a French physicist, Rene A. F. de Reaumur, introduced the
now widely used concept of growing degree-days (Wegulo and Gleason, 2001).
Degree-days is a linear function of temperature and is computed by subtracting
Tb from the ADT. Growing degree—days are computed only for days when the

ADT is higher than base temperature:

°Days = 1/b1 [3]

28

 

 

Although this model has been widely used to predict development in plants, it
has weaknesses (Wang, 1960). The model assumes that the development rate
is a linear function; however, outside Tb and Tom, the response becomes
curvilinear. Three equations can be used to represent the relationship when the

rate of development is calculated below Tb, above Top. , and between Tb and Top,

(Steininger et al., 2002 ).

Degree-days = 0 when T,- s Tb
Degree-day = 30 + bo * T,- when Tb < Tj 5 Tom [4]
Degree-days = a1 + b1 * T,- when Tj > Topt

29

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Ore.

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Christenson, EA. 2001. Phalaenopsis: a monograph. Timber Press, Portland,
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Chou, C.C., W.S. Chen, K.L. Huang, H.C. and Yu, L.J. Liao. 2000. Changes in
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De Vries, J.T. 1950. On the flowering of Phalaenopsis schilleriana Rchb f. Ann.
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Fisher, P., R.D. Heins, and N. Ehler, N. 19973. A decision-support system for
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McLellan, RI. 1956. Fir bark - miracle? Amer. Orchid Soc. Bul. 25:81—83.

McConnell, DB. and T.J. Sheehan. 1978, Anatomical aspects of chilling injury to
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Nash, N. 1989. Miltoniopsis in the late 1980s. Amer. Orchid Soc. Bul. 58:
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Rittershausen B., and W. Rittershausen. 1985. Orchid growing illustrated.
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Rotor, G.B., Jr. 1952. Daylength and temperature in relation to growth and
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Sakanishi, Y.H., G. lmanishi, and lshida. 1980. Effect of temperature
on growth of Phalaenopsis abamibilis. Bull. Okaka Press Ser. 32: 1— 9.

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Satoshi, K., T. Hisamatsu, K. Ichimura, and M. Koshioka. 1996. Effect of light
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Steininger, J., C.C. Pasian. 2002. Extension of a thermal unit model to represent
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Sweet. 1978. The Miltoniopsis complex in horticulture. Amer. Orchid Soc. Bul.
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Wang, J.Y. 1960. A critique of the heat unit approach to plant response studies.
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Wang, Y.T. 1995a. Phalaenopsis orchid light requirements during the induction
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Wang, Y.T. 1995b. Medium and fertilization affect performance of potted
Dendobium and Phalaenopsis. Hortechnology 5: 234—237.

Wang, Y.T. 1996a. Cytokinin and light intensity regulate flowering of Easter lily.
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Wang, Y.T., 1996b. Effects of six fertilizers on vegetative growth and flowering of

Phalaenopsis orchids. Scientia Hort. 65: 191—197.

Wang, Y.T., 2000. Impact of a high phosphorus fertilizer and timing of
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Wang, Y.T and N. Lee. 1994b. Another Look at an Old Crop: Potted Blooming
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Wang, Y.T. and TS. Hsu. 1994. Flowering and growth of Phalaenopsis
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Wang, W., W. Chen, W. Chen, L. Hung, P. Chang. 2002. Influences of abscisic
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Murray In: Encyclopedia of plant pathology. John Wiley & Sons, New
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Wilkins, H.F. 1988a. Leaf unfolding rate of the Easter lily is temperature
dependent. Minnesota State Florists Bulletin. 36: 4—6.

Wilkins, H.F. 1988b. Flower bud development rate for the Easter lily is
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Wilkins, HF. and K.L.Grueber. 1990. Easter lily height control. Minnesota State
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35

Yonda, K. 1985. Effects of plant age and time of transfer to highland during
summer on Phalaenopsis. J. Jpn. Soc. Hort. Sci. 54:101—108.

Yonda, K., H. Momose, S. Kubota. 1991. Effects of daylength and temperature of
flowering in juvenile and adult Phalaenopsis plants. J. Jpn. Soc. Hort. Sci.
60(3): 651-657.

Yonda, K., H. Momose, S. Kubota. 1992. Comparison of flowering behavior
between mature and premature plants of Phalaenopsis under different
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United States Department of Agriculture (USDA). 2002. Floriculture crops 2001
summary. National Agricultural Statistics Service.

36

SECTION 1: EFFECTS OF TEMPERATURE ON PHALAENOPSIS FROM
SPIKE EMERGENCE TO FLOWERING

37

Effects of Temperature on Phalaenopsis from Spike Emergence to Flowering

Kari A. Robinson‘, Royal D. Heinsz

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

Received for publication . Accepted for publication . We
gratefully acknowledge the financial support of the Agriculture Experiment Station
of Michigan State University and greenhouse growers supportive of Michigan
State University floriculture research.

1 Graduate Assistant.
2 Professor.

38

Introduction
Because of improved cultural practices, reliable and uniform hybrids, and
heightened consumer interest, Phalaenopsis BI. is quickly becoming an important
economic crop, despite lack of a specific market date. In the United States,
orchids are the second most valuable potted crop, at over $99 million wholesale
(USDA, 2002). Phalaenopsis are currently the most valuable pottted crop in
Holland (Barendse, 2002). In the Netherlands, Phalaenopsis sales have risen
from 3 million pots sold in 1984 to over 9 million pots sold in 2001 (Griesbach,
2000; Vakblad voor de Bloemisterij, 2002). The Netherlands and Taiwan
account for a large portion of potted Phalaenopsis production, as do China,
Germany, Japan, and the United States (Griesbach, 2000). In 1993 the
Japanese market for potted orchids was estimated to be $261 million, with the
Netherlands accounting for $62 million and ASEAN (Association of the South
East Asian Nations) accounting for $53.7 million (Hew and Young, 1997). It is
probable that the production of Phalaenopsis will continue to increase, and with
the development of decision support tools, they have even greater economic

potential.

Producing flowering plants for a specific market date requires knowledge of the
relationship between temperature and flower development rate. For example,
Easter lilies, which are the fourth most valuable potted crop, are grown for a
specific date, Easter. The day after Easter, plants are worthless (Sheehan,

1992), so controlling this crop’s time to flower is important. Research on Easter

39

lily flowering is extensive (Fisher et al., 1997a, b; Holcomb and Berghage, 2001;
Karlsson et al., 1988; Wang, 1996; Wilkins, 1988a, b; Wilkins and Grueber,
1990), as is work on poinsettias and Chrysanthemums (Karlsson et al., 1989;
Sheehan, 1992), valuable potted crops with specific market dates. Although
orchids are now the second largest potted crop in the United States, little specific
quantitative information is available relating plant development rate to

temperature from the time of visible spiking to flower.

Phalaenopsis are tropical and subtropical plants, originating from areas of the
South Pacific Islands and Asia (Baker and Baker, 1991; Noble, 1971), and have
unique requirements for the induction of spiking and subsequential flower
development. Plants are known to remain vegetative above 27 to 29 °C
(Sakanishi et al., 1980) and can tolerate temperatures as high as 32 to 35 °C
(Baker and Baker, 1991). Although temperatures below 26 °C initiate spiking in
Phalaenopsis, plants do not initiate flowers until the spike is more than 5 cm long.
When spikes shorter than 5 cm are exposed to temperatures above 26 °C, the
shoot remains vegetative and forms a keiki, a vegetative plantlet, instead of

flower buds, or the flower buds abort (Sakanishi et al., 1980).

Plants will initiate flowers at any temperature between 11 and 25 °C; however,
optimum temperatures for spiking are reported to be between 15 and 20 °C
(Sakanishi et al., 1980). Phalaenopsis can be uniformly spiked when placed at

25l20 °C day/night (Lee and Lin, 1987). However, plant maturity can influence

4O

percentage of a population that flowers and time to flower after spiking (Yoneda
et al., 1992). Young plants can be spiked uniformly if given lower temperatures

or longer durations at a given temperature.

A number of studies (Lee and Lin, 1984; 1987; Sakanishi et al., 1980; Yoneda,
1985; Yoneda et at., 1991,1992 ) have reported the dates of spike emergence
and flowering but not average daily temperatures (ADT) that are needed to
properly determine a temperature effect on flower development. Instead, only
the minimum and maximum temperature for a given month or the set point

temperature of the greenhouse were given in the reports.

Phalaenopsis generally are not reported to be photoperiodic (Sakanishi et al.,
1980). However, a few studies report that short days enhance spiking (De Vries,
1950; Griesbach, 1985; Rotor, 1952; Yoneda, 1991), but this short-day
enhancement is thought to be a result not of the daylength itself but of the
extension of cool night temperatures resulting from the extended night (Sakanishi

etaL,1980)

The objective of this investigation was to quantify the effects of temperature on

time from spike emergence to flowering and determine the effects of temperature

on plant quality.

41

Materials and Methods

Plant Culture. Plants were fertilized at every irrigation with a nutrient solution of
well water acidified with H2804 to a titratable alkalinity of 130 mg CaC03 L" and
water-soluble fertilizer [125-12-125 N-P-K mg L" plus 1.0-0.5-0.5-0.5—0.1-0.1 (Fe,
Mn, Zn, Cu, B, Mo) mg L" (MSU Special, Greencare Fertilizers, Chicago, III.)].
Vapor pressure deficit was maintained around 0.7 kPa by the injection of water

vapor as needed.

Temperature Control. Greenhouse temperatures were controlled by a
greenhouse climate-control computer (Priva, Model CD750, De Lier, Holland). Air
temperatures on each bench were monitored with 36-gauge (0.127-mm-
diameter) type E thermocouples connected to CR10 dataloggers (Campbell
Scientific, Logan, Utah). The datalogger collected temperature data every 10 s
and recorded the average hourly temperature. For each experiment, actual
ADTs of air from the beginning of visible spiking until the average date of

flowering for every treatment were calculated and used in data analyses.

Model Theory. Development rate of a Phalaenopsis spike from first emergence
through a leaf blade to visible bud and flowering can be described as a linear
function of average temperature:

1/ DTF = bo+b1*T I1]

42

where days to flower (DTF) equals the intercept (b0) plus the product of the slope
(b1) and temperature (T). The base temperature (Tb) and degree—days to

maturity (°days) can be calculated from this linear relationship as

Tb = -bolb1 [2]
and

°days = 1/b1 [3]

Node development rate can also be described by the same linear relationship as

that in Eq. [1], where DTF becomes nodes per day.

Bud development was modeled by methods used by Fisher et al. (1996) for
Easter lily. They described bud development of Easter lilygrown at a constant

temperature with an exponential growth function in the form

where B is flower-bud length, Bo is initial bud length, t is time, to is time zero, and
k is a rate constant that changes with temperature. When kin Eq. [4] is
substituted by f( T) to incorporate a function of temperature, and when the
maximum bud length (Bt) and number of days (D) to first open flower are known,

Eq. [1], for any value of 8, becomes

43

B, = Be "”0 [5]
D can then be estimated by

D = In(Bf/B) ”(77 [6]

Experimental Design: Calibration. One hundred Phalaenopsis Taisuco Smile
(Phalaenopsis Taisuco Bright x P. equestris) plants were received from Taiwan
on 8 Sept. 2000. Plants were artificial hybrids, or grexes, raised from seedlings.
When bare-root plants had a leaf-span diameter of approximately 25 cm, four to
six mature leaves were potted into 30-cm pots with a medium composed of 60%
(grade 3) perlite and 40% (Sure Mix Perlite, Michigan Grower Products;
Galesburg, Mich.) peat-based medium. Plants were then held in the

Michigan State University (MSU) research greenhouses at 25 °C (day) for 12 h
and 20 °C (night) for 12 h for four weeks to initiate flower spikes (Lee and Lin,

1984). Plants were shaded to maintain an irradiance of no more than 300

pmol'm‘z'S‘l. Once spikes were visible without dissection but had not grown to
more than 2 cm, 20 plants were placed in one of five natural-photoperiod
greenhouse compartments with constant temperature set points of 14, 17, 20,
23, or 26 °C. The actual ADTs were 14.5, 17.7, 19.9, 23.3, or 25.7 °C from 8

Oct. 1999 to average time of first open flower, when data collection stopped.

Validation Experiment 1. Phalaenopsis Taisuco Smile plants arrived from Taiwan
on 8 Mar. 2001 and were potted into bark-based medium composed of 35%

medium bark, 35% small bark, 10% coarse charcoal, 10% perlite (#3), and

10% parts fine peat (Porter’s Orchids; Grand Ledge, Mich.) and spiked as in the
calibration experiment. Once flower spikes were visible, 20 plants per treatment
were placed at temperature set points of 17, 20, 23, or 26 °C. The actual ADTs

were 18.4, 21.1, 23.0, or 25.9 °C.

Validation Experiment 2. Sixty Phalaenopsis hybrids (P. Taisuco Moon river x P.
equestris ‘Alba’ (hybrid ID H88-145) plants with a 25-cm leaf span were received
from Taiwan on 19 Apr. 2001, potted into bark-based medium (Porter’s Orchids),
and then held at 28 °C until 11 May 2001, when the greenhouse temperature was
set to 25/20 °C day/night for four weeks to initiate flower spikes. Once flowering
spikes were visible, groups of 10 plants were placed into one of six long-day
growth chambers with constant temperature set points of 14, 17, 20, 23, 26, or
29°C. Actual ADTs were 14.3, 16.9, 19.5, 22.2, 25.5, and 28.6 °C. Once
plants finished flowering in each growth chamber, they were transferred to a
greenhouse set at 28 °C for additional vegetative development. The validation
experiment was repeated one year later with the same plants. Plants were
spiked in two to three weeks in the MSU greenhouses with a temperature set
point of 23 °C to initiate flower spikes. Upon spike emergence, plants were
transferred to long-day growth chambers at constant temperature set points of
20, 23, or 26 °C once spikes were visible. The ADTs were 19.5, 22.5, 19.5 °C.
Plants had produced two or more additional leaves during the previous year, and

all had a leaf span greater than 32 cm.

45

On 30 Oct. 2001, 180 additional plants of two hybrids arrived from Taiwan (P.
Asian Elegance x P. Taisuco Shen, hybrid ID H88-36, and Doritaenopsis 8090
Smith x D. Sinica Sunday, hybrid ID H89314). Twenty plants of each cultivar
were spiked in the MSU greenhouses at a temperature set point of 23 °C until
spikes emerged; plants were then moved into growth chambers similar to those

used in the calibration experiment. The ADTs were 19.5, 22.2, and 25.6 °C.

Data Collection and Analysis. Date of spiking, visible bud (VB), and flowering
(FLW) were recorded; days from spiking to VB and FLW and from VB to FLW
were calculated for each spike of all hybrids, converted to rates, and modeled as
a linear function of actual air temperature. Data were analyzed by using SAS
procedures (SAS Institute, Cary, NC, Version 8). Regression analyses were
performed by SigmaPlot (SPSS, Inc., Chicago, Ill.). There was no interaction
between different spikes on a single plant, so all spikes in a given treatment were

treated individually and pooled for analysis.

Time to appearance of each node on the inflorescence was also recorded every
three to four days to determine the rate of node development at a constant
temperature. Linear regression was performed individually for node count versus
time for each spike, and the slopes of the regression lines were plotted against
each temperature to determine the node development rate versus time.

Phalaenopsis Taisuco Smile (validation experiment 1) was used as the

46

calibration data set, since the node development data from the original calibration

set was not complete enough to model.

To model bud development, P. Taisuco Smile from validation experiment 1 were
used as a calibration data set. Five plants from each treatment were randomly
selected, and bud diameter for the first visible flower bud was recorded every two
to three days by measuring the maximum distance between the outside edges of
the true petals. The constant k was estimated for each temperature, and f(T)
was formulated according to k as in Fisher et al. (1996) by using PROC NLIN in

SAS .

Morphological response to temperature was determined by measuring number of
nodes, flowers on the main and lateral inflorescence, final inflorescence length,
flower diameter, and number of lateral branches on the main spike at first Open
flower. For each spike, the final inflorescence length was measured from the
point of spike emergence to the top of the spike, and the diameter of the first
open flower was recorded. Observations ended for each plant when the first
flower opened. The levels of significance for linear and quadratic relationships
between 0.05 and 0.001 were tested with PROC GLM in SAS. To compare data
between cultivars, a common set point temperature of 23 °C (actual temperature,
22.7 °C :I: 0.4 °C) was selected, and a means separation test was performed with

PROC GLM by using least significant differences (LSD) in SAS.

47

Results
Modeling flower development rate
Calibration: Phalaenopsis Taisuco Smile. Days to VB, days from VB to FLW, and
days to F LW decreased as the ADT increased (Fig. 1A-C). Increasing the
temperature 3.4 °C from 19.9 to 23.3 °C accelerated flowering more then
increasing temperature 2.4 °C from 23.3 to 25.7 °C. For example, days to FLW
decreased from an average of 50 to 35 d (15 d, or 4.4 d per degree) as
temperature increased from 19.9 to 23.3 °C but decreased only an additional 3 d

o ,or . per e ree as empera urerncrease rom . o . .
(35t 33 125d dg ) t t ' df 233t 257°C

The relationship between temperature and the rate of progress toward VB, from
VB to F LW, and to F LW was linear (Fig. 1D-F). Regression parameters for the
Phalaenopsis Taisuco Smile calibration data set are given in Table 1. The
reciprocal of the linear regression model closely fit the original data (Fig. 1A-C),
indicating a linear regression relating rate of progress to FLW and can be used to

predict the time to FLW.

The base temperature was similar for all growth stages of the calibration data set
and ranged from 10.8 to 11.2 °C (Table 1). The thermal time to FLW was similar
when the model relating time from spiking to FLW was used (769 degree-days;
Tb=10.8) or when the two models predicting 1) days to VB or 2) VB to FLW (787

degree-days, Tb=11.2 and 11.0 °C) were used.

48

Validation: Phalaenopsis Taisuco Smile. Plants in the validation set responded
like plants in the calibration experiment. The slope and intercept of the
regression lines were not significantly different. The deviation between predicted
and observed days to FLW of the validation set was generally within 10 d, except
for a few Observations that varied by as many as 20 d, according to the

parameters for the linear equation of the calibration data set in Table 1 (Fig. 2).

Validation: Additional cultivars. Additional cultivars of Phalaenopsis responded to
temperature as P. Taisuco Smile did, decreasing in time to FLW as temperature
increased. The regression parameters were not significantly different with the
exception of the intercept for H88-145 (1) (P S 0.05) and H89314 (P s 0.05)
(Table 1). Phalaenopsis. H88-145 (1) grown at 28.6 °C were above Tom,
developing slower than those at 25.5 °C. For this reason,plants grown 28.6 °C

were excluded from the linear regression analysis.

The parameters of Eq.[1] for all cultivars are given in Table 1, as are the
parameters for individual regression lines of each hybrid. The thermal time to
flower was similar when the model relating time from spiking to F LW was used
(892 degree-days; Tb = 11.8) or when the two models predicting first days to VB
and then VB to FLW were used (827 degree—days; Tb = 9.9 and 10.1 °C). The
deviation between predicted and observed days to FLW was generally within :I:

10 d according to the parameters for the linear equation of the calibration data

49

set in Table 1 (Fig. 2). The exception was H88-145(1), which deviated as much

as 64 days from the predictive model in days to F LW at 14 °C.

Modeling node development rate

Calibration: Phalaenopsis Taisuco Smile. Appearance of nodes on the
inflorescence spike increased linearly in the 14.5 to 25.7 °C temperature range
(Fig. 3), and the base temperature was 9.9 °C (Table 2). Each 1 °C increase in
temperature from 14.5 to 25.7 °C increased the node development rate by an
average of 0.016 nodes/d. Regression parameters for the Phalaenopsis Taisuco

Smile calibration data set are given in Table 2.

Validation: Phalaenopsis. Additional hybrids of Phalaenopsis responded similarly
to temperature as P. Taisuco Smile did, increasing node development as
temperature increased, and the slope and intercept of the regression parameters
were not significantly different from the calibration experiment slope and intercept
(Table 2). The parameters of the regression equation plotted for Taisuco Smile
and H88-145 are given in Table 2, as are the parameters for individual

regression lines of each hybrid. Node development data for H8836 and H89314

were incomplete and were not used as a validation for the calibration experiment.

50

Modeling bud development rate

Calibration: Phalaenopsis Taisuco Smile. Bud elongation and development rates
and the estimated constant k increased linearly for buds up to 15 mm long as
temperature increased from 18.4 to 25.7 °C (Fig. 4). A linear function (k = c1 +
csz), statistically significant at P s 0.05, was fit to the estimated k so that Eq. [4]

became

B ___ 30 (at + c2 'T)(t—to) [7]

where 01 (d ") and 02 (C'1 d") are constants. When Eq. [7] was fit to the entire
data set simultaneously, c1 and C; were estimated to be 0.0113 :t 0.00389 d ’1
and 0.0189 :I: 0.00177 C" d", respectively. The model closely fit the bud width
data (Fig. 5). The model generally predicted the bud diameter for any given day
within 2 to 3 d. (Fig. 6). Table 3 represents the bud development model when in

the form of Eq [6].

Morphological data

Phalaenopsis Taisuco Smile. Temperature also affected the number of lateral
branches on the primary flowering axis (Fig. 7 AD). Over half of the plants
grown at an ADT of 25.7 or 14.5 °C had no lateral branching (Fig. 7 A). When
the plants were grown at 23.3 or 194°C, they were almost twice as likely to form
one to two lateral flowering branches than those grown at 25.7 or 14.5 °C (Fig. 7
B). Plants grown at 17.7 °C also had a high percentage (40%) of plants

producing one or two lateral branches (Fig. 7B). Although few plants developed

51

three or four flowering lateral branches, the percentage decreased from 36% to
6% when plants were grown at an ADT increased from 17.7 to 23.3 °C. No

plants in the calibration data set produced more than four lateral branches.

Lateral branching for both replications of Phalaenopsis Taisuco Smile was similar
(Figure 7 AD). Phalaenopsis. Taisuco Smile replication one had less lateral
branch overall compared with replication two, regardless of temperature. Many
of the plants in repetition two (49%) produced three to four lateral branches and,
in some cases, five to seven lateral flowering inflorescences. In comparison,
only 17% of the plants produced three or more spikes, regardless of temperature
in replication two (Figure 7 C). Plants producing one or two lateral branches

seemed to do so irrespective of temperature.

Temperature had little or no impact on Phalaenopsis Taisuco Smile’s number of
nodes and flowers, height, or flower size (Table 4). The number of nodes on the
inflorescence spike was consistently seven from 17.7 to 25.7 °C for Phalaenopsis
Taisuco Smile. Plants at 14.5 °C averaged about one less node. Main axis
flower count per plant increased from 14.5 to 19.9 °C and decreased from 19.9 to
25.7 °C, which resulted in a quadratic trend at P < 0.05 for replication 1, but no
trend was detected in replication 2. Total flowers per plant varied greatly,
depending on the magnitude of lateral branching. Total spike height was shorter

for plants grown at 14.5 °C compared with warmer temperatures; however, there

52

was no significant trend. Temperature had an inconsistent effect on flower width

from 16 to 26 °C.

Additional hybrids. Later branching in the additional cultivars occurred
infrequently. For 17 to 26 °C, 70% or more Of P. H88-145 did not produce any
lateral branches (Fig. 8A). Of the plants that produced one or two lateral
branches, as temperature decreased from 26 to 23 °C the percentage of
branching increased for both repetitions of P. H88-145. Sixty-five percent of
plants grown at 14 °C produced at least one flowering lateral branch (Fig. 8A-C).
Phalaenopsis 88366 and P. 89314 did not produce any lateral branches at any of

the temperature treatments.

Temperature did not affect the average number of nodes, flowers, final height, or
final flower width for the other cultivars (Table 4). Only the flower width of P.
Taisuco Smile was linear at P s 0.05. Morphological traits also differed greatly
between repetitions of the same hybrids when temperature set points were
compared at 23 °C. Neither repetition of Taisuco Smile differed significantly at P
_<_ 0.05, except for the total number of flowers. Repetition 2 of P. Taisuco Smile
had an average of 28.7 flowers compared with repetition 1, which had 18.4
flowers. Similarly, P. H88-145 repetitions responded similarly, except for flower
count and final spike height. Morphological traits differed at P s 0.05 and

between hybrids when temperature set points at 23 °C were compared (Table 4).

53

Discussion

Phalaenopsis can be flowered and scheduled for a specific market date by
controlling greenhouse temperature. Flower, node, and bud development were
modeled as a function of temperature and were found to accurately predict the

developmental times of these factors.

The optimum temperature for Phalaenopsis appears to be 26 °C; the base
temperature for a given phenophase, between 8 and 12 °C (Table 1). The rate of
flower, node, and bud development for all cultivars of Phalaenopsis used in this
study increased linearly to increasing temperatures from 14 to 26 °C. Validation
experiments using Phalaenopsis H88-1454 had an additional treatment of 28 °C,
which appears to be above the optimum temperature for that hybrid from spiking
to VB being the rate of development was slower at 28 °C than at 26 °C.
However, from VB to FLW, the rate of development continued to increase from
26 to 28 °C. When these plants were placed into the growth chambers at 28 °C,
all had spikes measuring from 0.5 to 1.0 cm long; however, only three developed
buds, and of those, only one flowered, producing one flower on the main axis.
The remaining plants grown at 28 °C returned to a vegetative state by either
aborting the spike, or in a few cases, forming vegetative keikis on the spikes
instead of buds. These findings are consistent with these Of Sakanishi et al.

(1991), who reported that plants grown above 27 to 29 °C remained vegetative.

For this study, plants above the optimum temperature and outside the linear

response range were not included in the regression.

Comparing Phalaenopsis flowering rates to other reports in literature is difficult
because the actual growing temperatures, or the length of the time at the
described day/night temperatures, are not given. For example, Lee and Lin
(1987) reported that plants being grown at day/night temperatures of 20l15 °C,
25l20 °C, and 30I25 °C required 205, 104, and 67 d, respectively, from spike to
FLW. From the model developed from our study, assuming day and night
temperature were in 12-h increments, plants should have flowered in 114, 65,
and 46 d from spiking if grown at an ADT of 17.5, 22.5, and 27.5 d, respectively.
If the days from spike to LFW for the Lee and Lin (1987) were to correspond with
our study, the ADTs would have to have been 14.5, 18.2, and 22.3 °C,
respectively. Discrepancies in the two data sets may be the result of differing
definitions of what visible spiking was, inaccurate temperature monitoring in the
Lee and Lin (1987) experiment, or differing plants sizes and hybrids. Sakanishi
et al. (1980) also report the time to F LW decreased as temperature increased,
but only the minimum and maximum growing temperatures are reported. For
experiments performed in this study, Phalaenopsis hybrids grown at ADTs of
17.7, 20.0, 22.5, and 27.5 °C required an average of 66, 49, 36, and 30 d,
respectively, to reach VB from spiking and 133, 88, 64, and 53 d to FLW from
spiking. At any constant temperature for any given cultivar, time to VB was about

60% of the total time from spiking to flower.

55

Yoneda et al. (1992) reported that plant maturity affected time to spike and
subsequent FLW. In validation experiments for our study, two replications using
Phalaenopsis H88-145 were performed. The second replication included plants
that had grown for an additional year after flowering in replication one.
Phalaenopsis H88—145 replication two did not develop faster from spike to FLW
than when these plants were spiked and flowered the previous year. The more
mature, larger plants spiked in 14 i 5 d from the start of cooling compared to
plants in the first replicate, which spiked in 28 :I: 3 d from the start of cooling,

which is consistent with other studies (Yoneda, 1985; Yoneda et al., 1992).

The effects of temperature on node development rate have not been reported in
other studies. The regression line fit the calibration set well (Fig. 3) (12 = 0.98)
and estimated a Tb of 9.9 °C (T able 2), which is close to the estimated Tb for

' flower development (Table 1). Individual data for node development and flower
development agreed. For example, when an average node count of seven is
used to estimate the time to produce a spike to VB from the node development
model at 26 °C, the spike is predicted to take 28 d and 30 d from spiking to VB

according to the flower development model.
The model used for relating bud development to temperature performed well in

the calibration data set, predicting the bud width within 4 d for a given day and

temperature (Fig. 5 and 6). This model is accurate only for buds that are shorter

56

to 15 mm, or about 3 to 5 d before the bud opens. Bud development beyond 15
mm does not develop according to the same linear function. A validation
experiment was not performed, but should be conducted with P. Taisuco Smile
before being implemented. The parameters of this model are not assumed to be
accurate for large flowering hybrids, but it may be possible to use this model on a
relative scale for any size flower if the maximum bud size before opening and the

days from spiking to VB are known.

Lateral branching was also influenced by temperature (Fig. 7 and 8); however,
the potential for Phalaenopsis to develop lateral branches was also cultivar
dependent. Of the 4 cultivars in this experiment, only P. Taisuco Smile and P.
H88-145 formed lateral branches. Both of these cultivars share a parent, P.
equestris, which is used for breeding because of its branching habit (D. Garling,
personal communication). The reason some cultivars branch and others do not
is not understood, but the reason plants branch better from 17 to 23 °C may have
a simple answer. Ota et al, (1991) reported that Phalaenopsis, which are CAM
(Crassulacean Acid Metabolism) plants, have the greatest nocturnal uptake of

C02 at 20 °C.

Temperatures in the range used for commercial production of Phalaenopsis, 17
to 26 °C, did not affect the number of nodes and flowers, spike height, or flower
width, but these factors did vary between cultivars. Other studies have reported

the effect of temperature on the number of flowers and spike height, but results

57

are contradictory. Yoneda et al. (1992) reported that P. Jimmy Hall x P. (Dos
Pueblos x Anne) grown at 20 °C had more flowers and shorter spikes than when
grown at 25 °C. Lee and Lin (1984) also report that spikes on plants grown at a
day/night temperature of 20/15 °C were shorter than those on plants grown at
25l20 °C for P. Dos Pueblos x P. Juanit, but plants grown at 20/15 °C had fewer

flowers than those grown at 25/20 °C.

Temperatures beyond the range of 17 to 26 °C, those approaching Tb and Tom,
had negative effects on morphological characteristics. Temperature treatments of
14 °C produced plants that had fewer flowers and nodes than others of the same
hybrid. Phalaenopsis Taisuco Smile averaged 20 cm shorter than P. Taisuco
Smile grown at higher temperatures. Conversely, P. H88-145 flowered at 14 °C
and were 3 to 25 cm taller than those grown at higher temperatures.
Phalaenopsis H88-145 grown at 28 °C produced a number of nodes similar to
those grown at other temperatures; however, of 10 plants, only one progressed
to FLW, and that plant had only one flower. Phalaenopsis H88-145 grown at 28
°C were also the shortest of all plants in the treatments, at an average of 25.5 cm
long. These data reconfirm that 28 °C is above the Top. for growing

Phalaenopsis.

In summary, Phalaenopsis perform best when grown at an ADT of =23 °C.
Although plants grown at =23 °C progressed to VB and FLW approximately
seven to 10 d later than those grown at 26 °C, some hybrids grown at an ADT Of

23 °C had the additional benefit of forming lateral branches. Also, although our

58

study included four cultivars Of various parentages, other cultivars might be more
sensitive to being grown at 26 °C, which may be above their optimum growing
temperature. Growing plants at cooler temperatures (from 17 to 20 °C) will not
harm them and may enhance lateral branching, although time to FL increases

greatly, from 64 to 133 d respectively.

59

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

62

Table 1: Parameters of linear regression analysis relating forcing temperature to
rate of progress to visible bud (VB) and anthesis (FLW) and from VB to FLW in
cultivars of Phalaenopsis. The intercept and slope were used to calculate the
base temperature (T b) and degree-days. All I2 significant at P < 0.0001. All
regression lines were compared to the calibration data set Taisuco Smile for
significant differences between the slope and intercept.

 

 

Hybrids Intercept (b0) Slope (b1) Tb Degree-
(1Id) [(1/d)/°C] (°C) dgs
Spiking to V8
Taisuco Smile (1)2 -0.0248 1 1.86E-3" -0.0022 1 8.70E-5 11.2 454 0.84
Taisuco Smile (2) -0.0264 1 4.48E-3NS 00023 1 1.93E-4NS 11.5 436 0.60
H88-145 (1) -0.0129 1 1.89E-3*“ -0.0017 1 8.52E-5NS 7.5 578 0.77
H88-145 (2) 00370 1 4.18E-3NS -0.0029 1 1.85E-4NS 12.8 347 0.80
H8836 -0.0277 1 7.26E-3NS 00023 1 3.20E-4NS 11.9 431 0.78
H89314 -00171 1 1.15E-2NS -0.0021 1 5.10E-4NS 8.3 484 0.48
All hybrids 00219 1 1.52E-3N3 00021 1 6.93E-3Ns 9.9 468 0.73
mmnw
Taisuco Smile (1) .00330 1 2.80E-3 .00030 1 1.30E-4 11.0 333 0.81
Taisuco Smile (2) -0.0202 1 5.69E-3NS -0.0024 1 2.29E-4NS 8.3 409 0.53
H88-145 (1) 00249 1 4.07E--3NS 00027 1 1.81 E-4NS 11.0 442 0.64
H88-145 (2) -0.0487 1 5.74E-3NS -0.0036 1 2.55E-4NS 13.7 280 0.76
H8836 -0.0406 1 1205-2“ 00033 1 5.28E-4NS 12.4 306 0.72
H89314 00452 1 1.2262 -0.0036 1 5505-4NS 12.5 276 0.73
All hybrids 00329 1 2.04E-3 ”3 -0.0030 1 9.32E-5NS 10.6 353 0.74
Spiking to FLW
Taisuco Smile (1) -0.0141 1 8.05E-4 00013 1 3.7454 10.8 769 0.90
Taisuco Smile (2) 00152 1 1.62E-3NS -0.0013 1 7205-5“ 11.4 751 0.77
H88-145 (1) 00094 1 9.54E-4NS -0.0011 1 42415-5NS 8.7 933 0.84
H88-145 (2) 00205 1 1.59E-3NS —0.0016 1 7.06E-5NS 12.8 627 0.89
H8836 -0.0157 1 2.59E-3NS 00013 1 1.14E-4NS 11.9 762 0.90
H89314 -00115 1 3.54E-3NS 00012 1 1.60E-4NS 9.5 824 0.78
All hybrids -0.0132 1 6195-4NS -0.0012 1 2.81 E-SNS 11.8 892 0.84

 

The intercept and slope were used to calculate the base temperature (Tb) and degree-days. All I2

were significant at P < 0.0001. All regression lines were compared to the calibration data set
Taisuco Smile for significant differences between the slope and intercept.
"5' *, *‘, *** Nonsignificant or significant at PS 0.05, 0.01, or 0.001, respectively.

1 S.E.

’ Replication ( 1) and (2)

63

Table 2: Parameters of linear regression analysis relating forcing temperature to
rate of node development in hybrids of Phalaenopsis. The intercept and slope
were used to calculate the base temperature (Tb). All r2 significant at P < 0.0001.

All regression lines were compared to the calibration data set Taisuco Smile for
significant differences.

 

 

Hybrids Intercept (bo) Slope (b1) Tb
(1/d) [(1/d)/°C] (°C) r2
Taisuco Smile (1)2 -0.1568 1 1.53E-2 -0.0158 1 1.60E-3 9.9 0.97
Taisuco Smile (2) -0.1585 1 9295-2 ”3 -0.0114 1 4.12E-3 "5 7.5 0.79
H88-145 (1) -0.1277 1 1.36E-2 "5 -0.0136 1 9.21E-4 "3 9.4 0.96
H88-145 (2) -0.1873 1 1.64E-3 "5 -0.0179 1 7.24E-3 "3 10.5 0.86

 

The intercept and slope were used to calculate the base temperature (Tb). All F were

significant at P < 0.0001. All regression lines were compared to the calibration data set
Taisuco Smile for significant differences.

"3' *, “, *** Nonsignificant or significant atPs 0.05, 0.01, or 0.001, respectively.
2
SE.

V Replication (1) and (2)

Table 3. Bud development computed from Eq. [6] [D = ln(Br/ B) / f(T)], where

rm 1= c1 1 02 "T(01 = 0.0113 1 0.00389 d '1 and 02 = 0.0189 1 0.00177 c"
day'

 

 

Bud width Temperature °C
(mm) 18 20 22 24 26
1 59.8 55.2 51.2 47.8 44.8 ‘
2 44.5 41.0 38.1 35.7 33.3
3 35.5 32.8 30.4 28.4 26.6
4 29.2 26.9 25.0 23.3 21.9
5 24.2 22.4 20.8 19.4 18.2
6 20.2 18.7 17.3 16.2 15.1
7 16.8 15.5 14.4 13.5 12.6
8 13.9 12.8 11.9 11.1 10.4
9 11.3 10.4 9.7 9.0 8.5
10 8.9 8.3 7.7 7.2 6.7
11 6.8 6.3 5.9 5.5 5.1
12 4.9 4.5 4.2 3.9 3.7
13 3.2 2.9 2.7 2.5 2.4
14 1.5 1.4 1.3 1.2 1.1
15 0.0 0.0 0.0 0.0 0.0

 

65

Table 4. The effect of temperature on the average number of nodes, total flower
count, flowers on the main spike axis, final spike height and flower width for
Phalaenopsis Taisuco Smile (repetitions 1 and 2), P. H88-145 (repetitions 1 and
2), P. H88-36, and P. H89314.

 

 

Number of
Treatment Actual Number of Number of Flowers on Final spike Flower
Hybrid temperature temperature nodes flowers main axis height (cm) width (mm)
Taisuco Smile
Rep 1 14 14.9 5.8 8.9 4.8 27.7
17 17.7 7.6 22.4 10.8 51.9
20 19.9 7.1 22.8 13.5 55.1
23 23.3 7.2 a2 18.4 b 12.5 a 53.1 ba 60.0 b
26 25.7 7.7 16.8 11.5 59.7 64.2
L‘ 0*
Rep 2 17 20.2 7.2 37.4 13.7 69.6 68.9
20 21.0 7.3 35.3 14.5 67.5 73.1
23 22.9 7.5 a 28.7 a 13.3 a 57.7 a 63.7 b
26 25.6 7.5 18.7 13.3 54.5 63.5
L.
H88-145
Rep 1 14 13.5 6.1 25.6 9.8 55.8 M
17 16.9 6.2 5.3 5.2 47.6 54.3
20 19.5 6.9 9.4 7.8 52.4 58.0
23 22.2 6.1 a 7.7 ab 73 ch 40.6 c 63.4 b
26 25.5 6.6 4.6 4.6 37.4 62.3
29 28.5 6.0 0.2 0.2 25.5 M
Rep 2 20 19.5 6.8 10.8 9.1 48.7 59.0
23 22.5 7.3 a 9.3 c 7.1 b 49.4 b 65.5 b
26 25.5 6.2 10.0 9.8 43.1 61.5
H88-36 20 19.5 7.7 7.3 7.3 69.8 92.7
23 22.5 5.6 bc 7.0 c 7.0 cb 47.8 bc 83.6 a
26 25.6 5.7 3.8 3.8 49.2 92.0
H89314 20 19.5 4.6 4.5 4.5 39.9 75.5
23 22.5 4.4 c 3.8 c 3.8 c 35.6 d 82.0 a
26 25.6 4.3 2.0 2.0 28.0 85.9

 

* Significant at P s 0.05. The absence of letters under a cultivar in a column indicates no

significance. L and Q indicate a linear or quadratic trend, respectively

Plants grown at a temperature set point of 23 °C were used for hybrid comparisons.

Temperatures were started at spike emergence and continue to the first open flower. All

parameters were measured when the first flower opened.

2 Mean separation only within plants grown at 23°C by Least Significant Difference at P = 0.05.

66

Spike to VB VB to F LW Soike to FLW

 

 

Er

200‘ - , A ,B,‘ A .c.
150
1201

 

Days
on
O

 

 

 

 

1d
.°
0
.5

 

 

 

 

 

0.00:1 .---.1W,,,__. 1 e. 1 1 .- . . . L. E. 1 1
_12 15 18 21 24 27 12 15 18 21 24 27 12 15 18 21 24 27

Temperature (°C)

Figure 1. Effects of temperature on time to visible bud (VB) and flower (FLW) (A,
B, and C) and rate of progress(D, E, and F) in calibration data set Phalaenopsis
Taisuco Smile (0). Each symbol (0) represents one spike. The parameters of
linear regression lines are presented in Table 1. The quadratic regression lines in
A, B, and C are the reciprocal of the linear regression lines in D, E, and F,
respectively.

67

 

601

501

30/
201
104

-10 .
-20 .
-30 .

\\

Taisuco Smile

 

601

501

30 ,
10 <
-10 4

-20 4
-30 4

H88-145 (1 )

\

 

60*

H88-145 (2)

\\

 

Predicted minus Observed days to flower

-20 1
-30 4

1
\ \

H8836

.............................................................

 

60‘

50‘

302
10‘

-10 4
-20 4

‘WK

H89314

 

 

-30 4

 

Figure 2. Deviation between

1 7 20 23 26

Temperature (°C)

14

predicted and observed days to from spiking to

flower for validation data sets of Phalaenopsis hybrids.

68

 

030

Y = -0.1568 + 0.0158 x ADT
0.25 - 72 = 0.97

020-1

015'-

Nodes/d

010-

 

0.05 T

 

 

 

000 r r r r r
14 17 20 23 26

Temperature (°C)

Figure 3. Effects of temperature on inflorescence node development rate of
Phalaenopsis Taisuco Smile. Data points represent the slope of Eq. [1]
calculated for node count versus time for Phalaenopsis Taisuco Smile in the
calibration data set (a). The validation data set Phalaenopsis Taisuco Smile (0)
was plotted against the regression line for comparison.

69

0.070

 

 

 

 

Y = 0.0113 + 0.00189 x T
0.065 - r2 = 0.99
'73 0.060 1
X
"5
.5 0.055 -
78'
.§
3 0.050 -
0.045 -
0.040 4 ,

T T

17 20 23 26
Temperature (°C)

Figure 4. Estimates of k, the rate parameter in Eq. [1] for Phalaenopsis Taisuco
Smile, obtained by using nonlinear regression to fit Eq. [1] separately to data
from four temperature treatments in the calibration experiment [(6) symbol :I:
SE] and the linear function f(‘l) (solid line).

70

 

15‘

 

13‘ 25.7
11-
94
7- o
5- o
31!
1.
15- .
23
13-
o
11-
o
94
74
54
3‘!

.5
L

 

Bud width (mm)

 

 

 

 

 

 

0 5 10 15 20 25 30 35
Days from visible bud

Figure 5. Predicted (solid line) and Observed (o, mean :t SE) bud length for each
treatment in the calibration experiment of Phalaenopsis Taisuco Smile.

71

 

 

 

 

 

6—l
">’~ 4
3 e
'U
a)
E 2‘
o
(D
.D
O
m 0 i |
3
E
E O
1 1 1
§ 8
E 4- o o
o.

6~ o

14 17 20 23 26

Temperature (°C)

Figure 6. Deviation between predicted and observed days for calibration data set
Phalaenopsis Taisuco Smile.

72

 

70 1N0 lateral branching A
60 ~
50 .
40 ~
30 -
20 4
10 «

0
70 « 1-2 lateral branches B

60*
501
40‘
301
201
101

0
70 1 3-4 lateral branches C

601
50‘
401
301
201
10*

0
70 l5 or more lateral branches D

60‘
501
401
301
201

10‘ O\O/O\O—_
0 4 . 1 .

14 17 20 23 26
Temperature (°C)

(

 

 

Percent

 

 

 

 

Figure 7. Percentage of plants with a primary inflorescence spike that branched and formed
either no flowering lateral branches (A), 1 to 2 (B), 3 to 4 (C), or 5 or more (D) flowering lateral
inflorescences as a function of average daily temperature for Phalaenopsis Taisuco Smile
repetition 1 (e) and 2 (o).

 

100 - NO lateral branching
90 4
80 4
70 -
60 1
50 J
40 4
30 4
20 l
10 4

0 4

100 4 1-2 lateral branches B
90 1
80 4
70 4
60 4
50 4
40 4
30 4
20 1
10 4

0 4

100 4 3-4 lateral branches C
90 1
80 4
70 1
60 4
50 4
40 4
30 ~

20-
10: O/Q\O
0~ O C

14 17 20 23 26
Temperature (°C)

    

 

Percent

 

 

 

 

 

 

Figure 8. Percentage of plants with a primary inflorescence spike that branched and formed
either no flowering lateral branches (A), 1 to 2 (B), 3 to 4 (C), or 5 or more (D) flowering lateral
inflorescences as a function of average daily temperature for Phalaenopsis H88—145 repetition 1
(o) and 2 (o).

74

APPENDIX

75

Introduction

Miltoniopsis, commonly called the pansy orchid, is native to wet forest
regions of Costa Rica and Peru (Berliocchi, 1996) and is found from 610 m to
2100 m above sea level (Baker and Baker, 1993a). The average minimum and
maximum temperature for their climate is 10 °C to 29 °C, respectively, in more
heat-tolerant species.

Miltoniopsis is currently the fourth most valuable potted orchid in the
Netherlands, with 797,000 pots sold in 2001 (Vakblad voor de Bloemisterij,
2002). However there has not been any published work to develop a growing
protocol for these plants. The only information available on Miltoniopsis is a
handful of articles that contain similar cultivation instructions (Baker and Baker,
1993a, b; Nash 1989; Ortho, 1999; Rentoul, 1982). The recommendations for
growing Miltoniopsis are to keep plants evenly moist, and grow them under low
light levels. Pink leaf edges are an indication that the plants are receiving too
much light (Baker and Baker, 1993a; Ortho, 1999; Nash, 1989). The
recommended daytime average temperature ranges from 27 to 29 °C and the

night temperature averages from 16 to 18 °C (Baker and Baker, 1993a; Nash,

1989; Ortho, 1999). Temperatures of 17°C to 20 °C, reportedly produce
abundant flowering, but there is no indication if this is a constant ADT or an

induction treatment (Baker and Baker, 1993a; Tran Than Van, 1974).

76

Paphiopedilum are native to tropical and subtropical southeast Asia and islands
of the South Pacific (Berliocchi, 1996; Cribb, 1987; Dole and Wilkins, 1999), and

60 species are known (Cribb, 1987).

Although Paphiopedilum are a popular potted plant, with over 500,000 sold in the
Netherlands during 2001, almost no data exist describing their commercial
production. Most orchid articles and books give general cultivation for
Paphiopedilum (Hennessy and Hedge, 1989; Ortho, 1999; Rentoul, 1982;
Stewart and Griffiths; 1995). Only one refereed journal article has been
published dealing with the cultivation of Paphiopedilum. Rotor (1952) reported
that P. insigne remained vegetative above 18 °C, but when temperatures were
dropped to 13 °C, flower buds initiated two to three weeks later and plants
flowered six months later when maintained at 13 °C. Paphiopedilum. barbatum
remained vegetative above 23 °C but flowered when temperatures were dropped
to 16 to 21 °C (Goh and Arditti, 1985). Plants were not photoperiodic (Rotor;

1952)

77

Materials and Methods

Plant culture. Plants were fertilized at every irrigation with a nutrient
solution of well water acidified with H2804 to a titratable alkalinity of 130 mg
CaCOa L‘1 and water-soluble fertilizer [125-12-125 N-P-K (mg L") plus 1.0-0.5-
0.5-o.5-o.1-o.1 Fe, Mn, Zn, Cu, B, Mo (mg L") (MSU Special, Greencare

Fertilizers, Chicago, III.)].

Temperature control. Greenhouse and growth chamber
temperatures were controlled by a greenhouse climate-control computer (Priva,
Model CD750, De Lier, Holland). Air temperatures on each bench were
monitored with 36-gauge (0.127-mm-diameter) type E thermocouples connected
to CR10 dataloggers (Campbell Scientific, Logan, Utah). The datalogger
collected temperature data every 10 s and recorded hourly. Vapor pressure
deficit was maintained around 0.7 kPa by the injection of water vapor as needed.
For each experiment, actual daily ADTs from the beginning of visible spiking until
the average date of flowering for every treatment were calculated and used in

data analyses.

Experimental design: flower induction without bulking. On 5 May 2001,
500 M. Augres ‘Trinity’ and P. laserx chariesworthii prepotted in a bark-based
medium arrived from Nurserymen’s Exchange in Half Moon Bay, Calif. Plants
were held at 23 °C under natural photoperiods until 8 June 2001, when 120

nonflowering Miltoniopsis plants with at least one mature and two immature

78

pseudobulbs were transferred to environmental growth chambers. Also, 120
nonflowering Paphiopedilum plants were transferred to growth chambers. Ten
plants of each genera were placed in either long days (LD) of 9 h (from 2200 to
0200 HR) with a night interruption from incandescent lamps or short days (SD) of
9 h in one of six chambers with temperature set points of 14, 17, 20, 23, 26, or 29

°C. The ADTs were 13.5, 16.9, 19.6, 22.4, 25.5, and 28.6 °C. Cool-white

florescent lights were placed so that irradiance averaged 150 umol'm'z's‘1- At 31
weeks, observations for Miltoniopsis were terminated for plants held at 23, 26,
and 29 °C because of lack of response or plant mortality. Observations of
Paphiopedilum held at 29 °C were also terminated at 31 weeks after the start of
treatments because of response or plant fatality.

Experimental design: flower induction following bulking. Plants were held
at 23 °C under natural days for nine weeks after arrival. On 1 July 2001, 200

plants were covered with black cloth from 1700 to 0800 HR, incandescent lamps

at 3 pmol'm'z'S'1 were switched on from 1700 to 2400 HR to create a 16-h LD.
Plants were divided into two groups on 1 Sept. 2001; the first group was
maintained with a 16-h; the second, a 9-h SD. Both groups were maintained at
23 °C. Eight weeks later on 26 Oct. 2001, each of the two groups was divided
again and placed under LDs or $05 into one of five greenhouse compartments
with constant temperature set points of 11, 14, 17, 20, or 23 °C, so that each of
the 20 treatments had 10 plants. All plants were returned to 23 °C natural days

on 21 Dec. 2001.

79

Data collection and analysis. For all plants in the temperature experiment
without bulking, days to visible spiking, spiking to flowering, and days to flower
were recorded. Also flower longevity, final flower size, number of flowers, and
spike height were noted at the end of the experiment.

For all plants, the length of the flowering spike was measured from the
base of the pseudobulb to the tip of the spike once plants began to spike once a
week. Date of flowering was recorded when the first flower opened. Flower
diameter was measured at the maximum diameter of the true petals.

For Miltoniopsis experiments conducted in the greenhouse, days to visible
spike, number of visible spikes from 21 Dec. 2001, and number of new shoots
and mature bulbs that had formed from 26 Oct. 2001 to 27 June 2002 were
recorded. Paphiopedilum data included days to visible spiking, days from
spiking to flowering, and days to flower. Also flower longevity, number of flowers,

and flower size were noted at the end of the experiment.

80

Results

Flower induction experiments with M. Augers ‘Trinity’ and P. laserx

chariesworthii did not provide any conclusive results (Tables 1-4).

Miltoniopsis in the flower induction experiments with nine weeks of bulking
provided no significant differences in the number of new mature bulbs or
reproductive spikes formed (Table 1). At the conclusion of the experiment, plants
at the 11 and 14 °C inductive temperature treatments did not spike, but if the
experiment had been allowed to continue, these plants probably would have
spiked according to results from our experiments without nine weeks of bulking.
Plants in the warmer inductive treatments (20 and 17 °C) had spiked, but buds
aborted soon after they were visible. Although the reason for bud abortion is
unknown it possibly was high light or temperature or a combination of the two.
Of plants that did spike, time to visible spiking from the end of inductive
temperature and photoperiod treatments was approximately a week shorter for

plants in the SD bulking treatments (Table 1).

Miltoniopsis in the flower induction experiment without bulking responded to
temperatures and photoperiod (Table 2). Plants at a constant ADT from 23 to 29
°C never spiked under either photoperiod. Plants grown at an ADT of 20 °C
spiked and flowered under SD; however, no plants in the 20 °C LD treatment

spiked. All plants at 14 and 17 °C spiked, but only treatment at 17°C resulted in

81

100% spiking and flowering. Time from the start of treatments to visible spike

was inconsistent across photoperiods.

Paphiopedilum laser x chartesworthii showed no photoperiodic responses and

flowered randomly at all temperatures in both experiments (Tables 3—4).

82

Literature Cited

Berliocchi, L. 1996. The orchid in legend and lore. Timber Press, Portland,
Ore.

Baker, ML. and C. Baker. 1993a. Miltoniopsis. Amer. Orchid Soc. Bul. 62:
794-799.

Baker, ML. and C. Baker. 1993b. Miltoniopsis ll. Amer. Orchid Soc. Bul. 62:
901-908.

Cribb, P. 1987. The genus Paphiopedilum. Timber Press, Portland, Ore.

Dole J.M. and H. F. Wilkins. 1999. Ochidaceae: floriculture principles and
species. Prentice Hall, Englewood Cliffs, N.J.

Goh, OJ. and J. Arditti. 1985. Orchidaceae: handbook of flowering. CRC
Press. Boca Raton, Fla.

Hennessy, E.F. and TA Hedge. 1989. The slipper orchids. Acorn Books,
Randsburg, Kansas City, Mo.

Nash, N. 1989. Miltoniopsis in the late 19803. Amer. Orchid Soc. Bul. 58:
1 040—1094.

Ortho. 1999. All about orchids. Merideth Publishing Group, Des Moines, Iowa.

Rentoul, J.N. 1982. Growing orchids. Timber Press, Portland, Ore.

Rotor, G.B., Jr. 1952. Daylength and temperature in relation to growth and
flowering of orchids. Cornell Univ. Agr. Expt. Sta. Bul. 88521-46.

Stewart, J. and M. Griffiths. 1995. Manual of orchids. Timber Press, Portland,

83

Ore.

Tran Than Van, M. 1974. Methods of acceleration of growth and flowering in a
few species of orchids. Amer. Orchid Soc. Bul. 43:699—707.

Vakblad voor de Bloemisterij, 2002. June 7 (23a): 88—89.

84

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