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GROWTH AND DEVELOPMENTAL RESPONSES
OF HYBRID GERANIUMS TO

LIGHT AND TEMPERATURE

by

Charles Lee Bethke

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

DOCTOR OF PHILOSOPHY

Department 0+ Horticulture

1986

ABSTRACT
GROWTH AND DEVELOPMENTAL RESPONSES OF HYBRID GERANIUMS
TO LIGHT AND TEMPERATURE
by
Charles L. Bethke

Vegetative and reproductive development of Eelacgggium
hggtgfium - Bailey in response to: time, irradiance, day and
night temperature, and supplemental lighting was studied.
Flower development in response to supplemental light was
found to be in+luenced by irradiance level, temperature and
duration of irradiance, and age of the plants. Days to
anthesis was more closely correlated with mean daily
irradiance (r = 0.921) than with total cumulative irradiance
(r = -O.863). A threshold irradiance was necessary for
simultaneous reductions in days to flower and number of
.nodes in ’Ringo Scarlet’. A hypothesis for the' high

irradiance phenomenon is presented.

ii

Prediction equations were developed for days to
initiation. visible bud. and anthesis. Irradiance and day
temperature were shown to have the greatest influence on
flower initiation and development to visible bud. while
temperature alone was most contributory from visible bud to
anthesis. Three-dimensional response surface plots were
developed to graphically represent the functions.
Prediction equations were also developed for total plant
height, leaf area, and shoot fresh and dry weight as
functions of time, irradiance, and day and night

temperatures.

iii

Guidance Committee:

The paper format is adopted for this dissertation in
accordance with departmental and university regulations.
All sections are to be submitted to the Journal of the

abscissa Sesistx is: bettisultucal §sieose for publication-

iv

ACKNOWLEDGEMENTS

To give thanks to all those who have challenged,
encouraged, supported, and assisted me during the course of
my study is simply insufficient. The appreciation and
expression of gratitude will only be expressed in the works
and deeds performed as a result of the growth.

Special gratitude is extended to my major professor,
Dr. william H. Carlson, for his help, encouragement,
support, patience and example.

Deep appreciation is extended to the members of my
guidance committee: Drs. R. Heins, M. Bukovac, C. Cress,
and A. Lang for their input, assistance. direction and
patience.

Special thanks is given to my classmates and colleagues
for their input, suggestions, comments and encouragement.

A dedication of this work is extended to my children:
Heather Marie, Ryan Lee and Trevor David for their unending
understanding, encouragement, support and sacrifices.

It is with deepest affection that I express my
gratitude to my wife, Michalyn, for her many sacrifices
during the course of this endeavor, also for her assistance
in the preparation of this manuscript.

Financial support was provided by the Michigan State
University Agricultural Experiment Station for which I am

forever grateful.

TABLE OF CONTENTS

Page
LIST OF TABLESIDOIII.IIDIICIIOCODIODIIICOIIOOIUIOIOIO Viii

LIST OF FIGURESOOIIIIOIIII-IIIIIIIIIIIOIIIIIIIO...... :<i

LITERATURE REVIEW....................................
History of Production Techniques.................
Environmental Influences.........................
Plant Growth Modeling............................ lo

Literature CitEdIIIIIIIIICCOIIOICOO-IIIIIIIIIODOI 2(o’

ll 45 [:1 IL-‘J

SECTION I The effects of supplemental irradiance
period and irradiance levels on days to flower
and node number in hybrid geraniums.............. 30
Abstract......................................... 31
Introduction..................................... 32
Materials and Methods............................ 34
Results and Discussion........................... 38
Summary and Conclusions.......................... 45
Literature Cited................................. 61

SECTION II Effects of high irradiance and temperature
on early flowering in hybrid geraniums........... 64
Abstract......................................... 65
Introduction..................................... 66
Materials and Methods............................ 68
Results and Discussion........................... 71
Summary and Conclusions.......................... 78
Literature Cited................................. 90

SECTION III Modeling reproductive development in
hybrid geraniums................................. 94
Abstract......................................... 95
Introduction..................................... 97
Materials and Methods............................ 99
Results and Discussion........................... 102
Summary and Conclusions.......................... 111
Literature Cited................................. 138

SECTION IV Modeling vegetative development in
hybrid geraniums................................. 143
Abstract......................................... 144
Introduction..................................... 145
Materials and Methods............................ 147
Results and Discussion........................... 150

Vi

TABLE OF CONTENTS - Qggtigueg

Page

Summary and Conclusion........................... 175
LiteratL‘r—e CitEdIICIIIIIOOIIIIIIIIIIIIIIIClio-OI. 17B
181

SUMMARY AND CONCLUDING STATEMENTS....................

vii

LIST OF TABLES

Table Page
SECTION I

1. Effects of age and duration of supplemental
irradiation (65 ums-im-E) on days to anthesis,
lateral branching, and total bud count in
Eelscgeflism DQCSQCHQ - Bailey ’Sprinter

scar-lat,IIIIIIIIOIOIIIIIOIIIIIIOIOIIIIIIOIOOOOOI 47
2. Effects of PPF and irradiance period on the

number of nodes and days to flower in

Eelacqgoigm bectecsm - Bailev ”Sprinter

scarlet,.IIIIllIII...IIII-III.III-.IIIIIIOOIIIOI 48

3. Prediction equations for days and nodes to

flower in EELSEQQDLQO DQCEQEQE ' Bailey

’Sprinter Scarlet as functions of mean daily

and total cumulative photosynthetic photon

flux as predictive variables.................... 50

4. Analvsis of variance for the influence of
supplemental irradiance on days and nodes to

flower in Eelacgeoium bettecsm - Bailey
,SDr-inter scar-let:IIIOIIOIOIOII...III-IOOOIIIOII 51
SECTION II

1. Effects of temperature and duration of
continuous irradiation (240 ums-lm-Z) on
the days and nodes to anthesis in
Eglargggigm ngctgggm - Bailey ’Jackpot’......... 82

H

Analvsis of variance for the effects of age,

irradiance. and duration of treatment on

days and nodes to flower in Eelaggggigm

hggtgggm - Bailey “Sprinter Scarlet’............ 83

SECTION III

1. Influence of PPF. day and night temperature
on the reproductive development of Eglaggggigm
ggfitgcum - Bailey ’Ringo Scarlet’............... 113

g. Average effects of PAR. day and night temperature
on the reproductive development of EQLQCQQOLQO
hortorum — Bailey ’Ringo Scarlet”............... 114

viii

LIST OF TABLES - Continued

Table

3.

10.

Significance of the polynomial contrasts of

PPF, and day and night temperature on repro-
ductive responses in Eelacgeoism persecum -
Bailey ’Ringo Scarlet’..........................

Predictions for days from sowing to floral
initiation in Eelacggoism bgctscsm - Bailey
,Ringo scarlet.‘.III-I.CCIICICIIIICCIOIIIIOOOCIII

Prediction equations for days from sowing
to visible bud in Eelacgsoium bectecem -
Bailey ’Ringo scarlet,I.I‘ll-IIIIICOIIIIOIIOIIII

Prediction equations for days from sowing
to anthesis in Eelacgeoism bettecsm -
Bailey ’Ringo Scarlet’..........................

Prediction equations for days from initiation
to visible bud in Eelacggpibm hectares -
Bailey ’Ringo Scarlet’..........................

Prediction equations for days from visible bud
to anthesis in Eelacgepism DQEEQCHE - Bailey
’Ringo scar-lat,-IDill-IIIIQIIIIOCOIIIIIOIIII-III

Prediction equations for days from initiation
to anthesis in EELSCQQDlHO DQEEQEHO ‘ Bailey
,Ringo scarlet,.lIIIIIIIIIIOIIIOIIIIII-IIIIIIOCI

The difference in observed (Y) and predicted
(Y) reproductive responses of Eglaggggigm
hggtgggm - Bailey ’Ringo Scarlet”...............

SECTION IV

Mean influences of PPF, day and night temperature
on the vegetative development of Eglargggigm
Qggtgcgm - Bailey ’Ringo Scarlet’...............

Average effects of PPF, day and night temperature,
and time on the vegetative development of
EELSCQQDLHO DQCEQCHQ ‘ Bailey ”R1090 Scarlet’
averaged over all treatment combinations........

Significance of the polynomial contrasts

of PPF. day and night temperature and time

on vegetative development in EELSCQQOLHQ
Qggtgfigm - Bailey ”Ringo Scarlet’...............

ix

Page

118

119

122

16C)

161

162

LIST OF TABLES - Continued

Table Page
4. Prediction equations for plant height of

Eelacqeoiud bectecsm - Bailey ”Ringo Scarlet’

as a function of PPF, day and night tem-

peratLIr-95 and time-IIIICIOOIIICIOI...IIIOOIIIII. 163

5. Prediction equations for leaf area of

Eelacgeoibm bectbcsm - Bailey ’Ringe Scarlet”
as a function of PPF, day and night tem-
perature, and time.............................. 164

6. Prediction equation for fresh weight of
Eslacgguism bectecum - Bailey ’Ringe
Scarlet’ as a function of PPF, day and
night temperature, and time..................... 165

7. Prediction equations for dry weight of
Eelacgeoism bectecsm - Bailey ’Ringo
Scarlet’ as a function of PPF, day and
night temperature, and time..................... 166

LIST OF FIGURES

Figure Page
SECTION I

1- Days to anthesis in Eelacqsoism bettecsm -
Bailey ’Sprinter Scarlet” when supple-
mentally irradiated with high pressure
sodium lights at a PPF of 65 + 8 ums-lm-2
continuously for different durations............ 52

2. The relationship of total and mean daily

cumulative PPF photosynthetic photon flux

on the days to flower and node number in

Eelacgeniem bettecsm - Bailey ”Sprinter
Scarlet’........................................ 54

3. Effects of continuous supplemental high
pressure sodium irradiation on the node
number (A), and days to anthesis (B) in
Eelacggoism bsctscsm - Bailey ”Sprinter
Scarlet” when applied for 18 or more hours

aday.IIIIII.IUD-OI...III-IIOICCIOIUIUOOI...-IOI 5J9
SECTION II

1. Effects of duration of continuous irradiance
(240 ums-lm—2) on days and node number from
treatment to anthesis at 300C in Eglgggggigm
hgctgcgm - Bailey ’Ringo Dolly”................. B4

2. Mean effects of irradiance, plant age, and

duration of treatment at 300C on days from

treatment to anthesis and percent early

induction in Eelacgeoism bactecsd - Bailey

”Sprinter Scarlet”.............................. S6

3. Mean effects of irradiance. plant age, and

duration of treatment at 300C on nodes from

treatment to anthesis and percent early

induction in Eelacgeoium bsctecsm - Bailey

”Sprinter Scarlet’.............................. 88

SECTION III
1. Predicted days to initiation for Eglaggggigm
gggtgcgm - Bailey ”Ringo Scarlet” as

effected by PPF, day and night temperature ..... . 123

xi

Figure Page

2. Predicted days to visible bud for Pelaggggigm

Qgcggcgm - Bailey ’Ringo Scarlet’ as effected

by PPF, day and night temperature............... 125
3. Predicted days to anthesis for Eglaggggigm

Qggtgggm - Bailey ’Ringo Scarlet’ as effected

by PPF, day and night temperature............... 127

4. Predicted reproductive responses at night
temperature 16°C for Eelacgeoism 59:39:99 -
Bailey as effected by irradiance and day
temperatures during different stages of
development..................................... 129

u. The relative influence of light, day and

night temperature on reproductive development

at different stages in Eelacgeoism bsctecsm -

Bailey ”Ringo Scarlet”.......................... 13

SECTION IV

1- F’lant height of Eelacgeoism bectscsm -
Bailey ’Ringo Scarlet’ as a function of

time, PPF, day and night temperature............ 167
2- Leaf area of Eelacgeoism bectscsm - Bailey

’Ringo Scarlet’ as a function of time, PPF,

day and night temperature....................... 169

a- Fresh weight of Eelacgeoism bectecsd -
Bailey ’Ringo Scarlet’ as a function of
time. PPF, day and night temperature............ 171

4- Dry weight of Eelacgeuism bettecsm -

Bailey ”Ringo Scarlet” as a function
of time, PPF, day and night temperature......... 173

xii

INTRODUCTION
Hybrid geraniums (Belargggigm hgrtgfigm - Bailey) and
zonal geraniums (Pelaggggium hgrtgggm — Zonale) are among

the most popular floriculture products in the world today.
According to the USDA floriculture survey (71), nearly 65

million dollars worth of geraniums were produced in the

United States in 1984, and a value of nearly 10 million
dollars was produced in Michigan alone. Only Ohio and
Pennsylvania exceed Michigan in the quantity of geraniums
produced annually.

Since the first development of seed propagated
geraniums (Nittany Lion Red) in the 1960’s (30), continuous
improvements in the cultivars and their earliness of
flowering has occurred. The market for seed-propagated
geraniums has been expanding steadily because of decreased
costs of seed compared to the cost of cuttings, decreased
loss as a result of diseases in stock plants and rooting
beds, decreased plant size which yields increased production
density, and increased garden performance. Separate markets
are developing for seed and cutting—propagated geraniums.
The zonals (cutting—propagated) are being used more as
specimen and container plants while the hybrids (seed—
propagated) are being used largely in ground beds and for
large plantings.

Currently, many advances are being realized in the
production of hybrid geraniums. The advent of the plug
production system (small individual containers or cells

attached together in one sheet), mechanical seeders,

2
improved seed germination, supplemental lighting, and the
application of the computer to control greenhouse
conditions, all have resulted in many important advances in
the way we produce hybrid geraniums. The usefulness of the
computers is dependent on the amount of information
available which defines the reproductive and vegetative
responses to the greenhouse environment. It was the focus
of this study to investigate the physiological responses of
hybrid geraniums to light and temperature and to begin to

develop functional models of these responses.

LITERATURE REVIEN:

This review of literature focuses on the influences of
environmental factors, primarily light and temperature, on
the vegetative and reproductive development of hybrid
geraniums. Emphasis is given to information useful in
developing a clearer understanding of the vegetative and
reproductive responses to environmental factors at different
stages of development. Information useful to the
development of functional plant growth models is included
with an eye toward application in computer-controlled
greenhouses.

BI§IQBX QE EBQQQQIIQN IEQBMQQESA

The introduction of the first popular seed geranium
’Nittany Lion Red”, by Craig (30) started a revolution in
the geranium industry. Many shifts in cultural practices

and cultivars have occurred since this event. While the

first cultivars took from 120 to 140 days to flower from

sowing, improved cultivars and selections reduced the
flowering time to 100 to 120 days (5). It was found that
with the application of the growth regulator (2-

chloroethyl) trimethylammonium chloride (cycocel), the plant
size could be controlled and flowering enhanced by 5 to 7
days (24). The use of this growth regulator also allowed
for increased plant densities in the greenhouse. In the
early 1980’s plug production, the use of supplemental
lighting, and further improvements in cultivars made it
possible to produce finished marketable plants in 80 to 100

days. The application of silver thiosulfate prior to the

4

anthesis (59), has further increased the market quality of
the hybrid geranium. Improved cultivars, including seed-
propagated tetraploids (zonal types), increased use of
supplemental lighting, and the use of computers (operating
on models based on physiological responses) to control
greenhouses will likely reduce the time to produce a quality
product by an additional 20 to 30 days. This will mean
significant increases in profit for producers, better
performance to the consumers, and improved energy savings in
this day of environmental concerns.
ENYIBQBE‘EBIBE IBELQENQEELA

The two most important factors that are both highly

influential and yet manageable at least to a certain extent,

in the production of hybrid geraniums, are temperature and

light. Temperature responses can be divided into day and
night temperatures. Light responses fall into two
physiological catagories, photosynthetic and

photomorphogenic.
Eflggggyggbgtig responses deal largely with influences

of irradiance levels on the growth and energy supply to the

plant. The responses are usually associated with higher
irradiance levels. In photosynthetic studies, Armitage
(’7

z. 6) has shown that the light compensation point in hybrid

geraniums is temperature dependent. At a temperature of

20°C, the light compensation point is near 46 pmols_lm-L,

.and at 320C, the light compensation point is at about 75

‘pmols_1m—L. The light saturation point is about 1100
—1 -2 o -1 -2

ymols m at 32 C but about 700 pmols m at temperatures

5
o .
below 15 C. Thus, at low temperatures, less respiration and
less photosynthesis are occurring.

Ehgtgmggghggggig responses are generally considered to
be growth responses to the light environment and are nearly
always independent of photosynthesis but are not easily
seperated. However, they are somewhat dependent on
photosynthetic products for the energies needed to perform
the photomorphogenic responses. Photomorphogenic responses
have been defined by Nareing and Phillips (74) as "the
developmental strategies plants adopt when growing in the
light." These responses have been associated but not always
strictly related to the phytochrome system and are usually
considered to occur at relatively low irradiance levels.
However, a number of responses have been associated with
high irradiance (43, 55). From studies using low
irradiance, the geranium is considered a day—neutral plant
(64). However, responses to extended periods of high levels
of irradiance have resulted in earlier flowering with
decreased numbers of nodes to the first flower (7, 25, 27,
28, 63).
lccagiaose and Ismeecatsce Eiissts so Eleueciog

Early flowering responses of hybrid geraniums have been

associated with the application of high levels of
irradiation both supplementally in the greenhouse (2. 7, 8,
9, 25, 27, 35, 63, 70) and artificially in the growth

chamber (2, 13, 77, 78). Photosynthetic photon flux (PPF)
and cumulative photosynthetic photon flux (CPPF) in the 400-

-700 nm range have been related to the time from seeding to

6
anthesis (7, 31, 35, 70). Craig and Walker (31) showed that
flowering occurred naturally at a nearly constant total
CPPF. They suggest the endogenous production of a
hypothetical substance which influences floral initiation.
The substance is independent of the photoperiod and the
number of days from germination but dependent on cumulative
solar energy and temperature. Using low levels of
cumulative supplemental irradiation, Carpenter and Rodrequez
(27) found no reduction in the time to flower from the first
four weeks of lighting, but by extending the lighting an
additional two weeks, a 20 to 30 day reduction in the time
to flower was obtained. In addition, the number of nodes to
the first flower was reduced by two to six. Likewise,
Norton (63) produced flowering plants 3 weeks earlier by
applying 67 days of supplemental irradiation to young
plants. Armitage and Tsujita (7) indicated that high
pressure sodium (HPS) light was more effective in reducing
time to flower than low pressure sodium (LPS) light. They
also found in their spring crop that CPPF was significantly
correlated to days to flower. Their results indicated that
an intensity by duration interaction may exist which is
cultivar specific. In a study reported by Erickson et al.
(35) 41 to 65 percent of the variability in days to flower
was related to the CPPF. However, CPPF when measured from
sowing to flowering may not be as important as the
irradiation received prior to the visible bud stage. In the
work of Armitage (2), the time to visible bud was negatively

correlated to irradiance at a given temperature whereas

7
after the visible bud stage irradiance was no longer
significant but temperature was. Heins (45) has also
demonstrated a greater influence of temperature than
irradiance on the time from visible bud to flowering.

An early flowering potential has been observed when
high irradiance was coupled with high temperatures.
Mastalerz (56) produced flowers on the cultivar (Carefree
white in 60 days using a growth chamber with flourescent

light) at intensities of about 2000 foot-candles

-1 —2

(approximately 350 pmols m ) for 18 hours a day. Armitage
(2) observed visible buds as early as 33 days after sowing,
and flowering in nearly half the normal production time, 65

days, by applying continuous irradiation at a PPF of 375

a

-1 ‘4'. O
‘pmols m and at a temperature of 30 C. Randolph and Law

(77), in 1967, noticed macroscopic buds in 21 days on plants
exposed to continuous high irradiance levels. White (78)
has observed macroscopic buds 36 days after treatment on the

cultivar Red Elite when irradiated at approximately 390

H

“'1 “'2. D
‘pmols m and temperatures between 18 and 22.5 .

Flowering occurred in the cultivar Cherry Diamond 29 days
from sowing when supplemental irradiation was applied during
the night hours and when daily high temperatures ranged from
o o o

30 C to 37 C and night lows were above 23 C (13, 15).

To date no clear definitions or systematic studies of
the factors which are involved in producing the early
flowering responses in geraniums have been advanced. In

many species high irradiance levels have been known to

influence the induction of flowers. African violets

(Saigtggglia) (32, 53), Rudbeckia (62), snapdragon

(Antirrhinum) (69), and roses (Rgsa gyggiga L

) (10, 28, 48,
61), all show increased flowering responses to treatments of
high irradiance. Floral initiation has been observed under
prolonged periods of high irradiance levels in QOSQSLLLS
arvensis L; (65), Rhododendron sg; (Azalea) (18), and

Alstromeria (44, 54).

~—-—-~—--——_

In photomorphogenic studies of Brassica gamggstgig

<36). Ebacbitis oil; <37. 68). and Sioaesis ales; (19).
increased flowering responses were found to occur under
treatments of high irradiance. Bodson et al. (19), studying
the effects of high irradiance on S; alga, suggest that
light sensing reactions in addition to photosynthesis are
likely to contribute to the induction of flowers.

The phytochrome system and phytochrome intermediates
have been implicated in high irradiance response (34, 72).
In the early studies of photoinduction, Hamner (41) found
that high irradiance levels, over long time periods, were
necessary for expression of the flowering response in
soybean (Glygigg max). Conversely, in the long day plant,
radish (Raghaggg gatiygg 5,), low light, crowding, and a
high far-red to red ratio yielded increased flowering and
decreased root development (75). Shading and decreases in
irradiance have decreased flowering in geraniums and
snapdragons (39, 69) as well as in Leucospermum (49).

In geraniums, some incidental observations suggest that
flower induction may possibly be a high irradiance response

(HIIR) (15). Reportedly (11), a grower in New York removed

9
some of the upper foliage from vegetative young plants to
allow the light to get down into the shoot tip of the plant.
He claimed earlier and more uniform flowering from this
practice. Riese (66) suggested that decreased plant size
and spreading of the leaves, as a result of application of
cycocel, allows increased light into apical meristem of the
plant. He suggested that increased light to the center of
the plant is the explanation for the increased earliness
resulting from cycocel sprays. In a study of planting time
and flowering response (3) little additional earliness was
achieved from earlier sowings. Sowing as much as 7 weeks
earlier resulted in only 2 weeks earlier flowering. Ambient
radiation and daily irradiance periods increased toward
spring so photosynthetic increases could be responsible for
the accelerated development. Note that each cultivar aged
as spring approached. Also, day temperatures became higher
in the greenhouse as spring approached thus influencing

growth rates.

Iggagiaggg leyglg have been known to influence
induction of flowers since the studies of Hamner (41). In
E; gamgestgis flowering was related to an interaction of the
irradiance level and irradiance period (36). Maximum

responses occurred when the irradiance levels were the
highest and the irradiance period the longest. Schneider et
a1. (67) demonstrated that a minimum intensity of light
.during the long day was necessary to produce flowers
Hygsgyamgs giggg. With increased intensity, there was an

increased flowering response. In geraniums. the effects of

10

varying levels of irradiation on growth and flowering have
been studied by a number of researchers (2, 7, 8, 15, 25,
27, 63, 70). The effects on geraniums appear to be similar
to effects observed for other species. In nearly all cases,
the greatest responses were observed when the irradiance was
the highest and the length of irradiance was the greatest.
Iemgegatgce is known to influence the response of many
plants to inductive stimuli (12, 72). It is well
established that photoperiodic responses can be temperature
dependent. I B

gamggstgig Cv. ceres, the most flowering

n :.
0
occurred at 25 C (36). The percentage of flowering increase
with increases in both the intensity and the duration of the
irradiance at that temperature. Murneek (62) studying the
long-day plant nggggkia gigglgc, concluded that high
temperatures may substitute for long days in induction. In
geraniums Tsujita (70), Armitage (6) and White (79) have all
shown that higher temperatures can decrease time to

flowering. Additional earlier flowering was obtained when

the plants were irradiated continuously at high temperatures

Qggatigg of inductive conditions is of importance, too.
Hamner (41) has shown that the duration of irradiance
treatment is critical to changing the reproductive status of
soybeans. In many photoperiod studies, it is documented
that a sufficient duration or number of cycles (23, 67) of
inductive conditions are necessary for floral initiation.
In some plants, e.g. a cultivar of B. camgestcgs, only one

.day of high irradiance is necessary for flowering (36, 72).

11
Other cultivars and species require several days (12) to
induce flowering. Armitage (2) found in a limited study,
that a treatment as short as nine days at high irradiance
levels and high temperatures can result in more rapid
flowering in geraniums. Previously, it was thought that
four to six weeks of continuous lighting was necessary to
influence the time to flower and in some cases the node
number (8, 13, 25, 26, 48, 62).

ggyggility, which insures that a plant reaches a given
stage before it is capable of responding to reproductive
stimuli, exists in many herbaceous species. This condition,
often called "ripeness-to—flower", is discussed in detail in
the texts of Vince-Prue (72) and Bernier et al. (12). A
reduction in the extent of the conditions necessary to
induce flowering has frequently been observed due to aging
(12, 19, 41).

The phenomenon of juvenility as it relates to flowering
responses to high irradiance has also been studied in
several other species. In EDQCBQIS nil (37) the older the
plants the more responsive they became. In Sigaggig alga
(19) the number of long-day cycles required for induction is
6 to 7 cycles at an age of 15 days, 2 cycles at 30 days, and
1 cycle at 60 days. At 8 days, only a minimal response was
observed. In a study of geraniums, by Armitage, (1) it was
found that at least 6 leaves were necessary to induce
flowering in the cultivar Sooner Red. In the short—day
plant Chrysanthemum mggifigligm, different cultivars have

-h-h-~---—-——

been shown to vary in the time required to overcome the

12
Juvenile period (12). Also, in a specialized study of E1599
sativum (Garden Pea) the level of a genetically controlled

inhibition of flowering was found to decrease as the plants
aged (12).

Ripeness-to-flower may also be a factor in the
responses of geraniums. It is thus apparent that any
possible effects of age and responsiveness to treatment must
be considered when examining flowering responses in
geraniums.

Iotlseoses at tight and Iemoecatece so Begstatixe Qezeleemeots

In addition to the reproductive responses to light and
temperature, vegetative responses are known to influence
height, leaf area, and fresh and dry weight.

Igtal glagt ggiggt has been shown to be increased by
limited PPF (39, 79), and to be decreased by applications of
supplemental irradiation (25, 27, 70). Moderate night
temperatures have been shown to increase plant height (1,
26, 35. 52, 57). Tsujita (70) obtained taller plants in the
cultivar ’Encounter Red’ at a NT of 17°C than at 13°C, and
Konjoian and Tayama (52) obtained the tallest plants at
night temperatures of 160C. While shorter plants develop
under higher and lower temperatures, earlier flowering
occurrs at the higher temperatures. Carpenter and Carlson
(26) produced the tallest plants with day temperatures of
22-24OC and low night temperatures.

White and Warrington (79), examining the effects of

split-night-temperatures, found no differences in flowering,

but in view of the other factors the range of temperatures

13

studied in their work were not sufficient to show night

temperature responses. In a comparison of 14 cultivars
grown in Michigan (DT = 21 + 30C) and in Georgia (DT = 26 +
30C) (4), plants grown under the warmer days in Georgia
averaged 4.3 cm taller. Merritt and Kohl (57) have shown

that, in the cultivar ”Mustang’, both soil temperature and
irradiance period, as well as their interaction, had a
significant influence on plant height during vegetative
development. The tallest plants were produced under long
irradiance periods (13 hr) with little or no influence of
temperature. However, under short irradiance periods (9
hr), taller plants were produced in the cooler (180C)
temperatures. It appears that, under short days, mean daily
irradiance became low, and, as a result, elongation was
increased and flowering delayed.

Leaf age; is influenced by a number of factors. White
and Warrington (79) showed that in the absence of growth
regulators, high light significantly decreased leaf area as
did high OT and low NT. The lowest leaf area was obtained
at UT = 20°C and NT = 20°C. CCC treated plants tended to
show the same temperature responses, but the differences
were not significant. Total leaf area increased over time
in what appears to be a quadratic form in a study of Merritt
and Kohl (57). In some instances, short irradiance periods
(9 hr) also decreased leaf area. Armitage (2) demonstrated
that increasing DT resulted in decreased leaf thickness and

number of palisade layers. Specific leaf weight increased

with increased PPF and decreased with increased temperature.

14

Thus, we see that the geranium leaves are very responsive to
the environment in which they are developing. The
partitioning of photosynthates during the organogenesis is
apparently complex.

Leaf area has also been shown to be important to flower
development. Armitage (1) suggests that a critical leaf
area is necessary to produce flowers. This is similar to
the hypothesis of this author (14). Accordingly high
irradiance must be received by a plant of sufficient
maturity before initiation of flowers can occur.

If one wishes to limit leaf area in geraniums, growth
regulators have been shown to be very effective (60).

Egggh agg ggy weight appear to be greatly influenced by
temperature. However, low irradiance levels have been
reported to yield higher fresh weight (27, 39) than high
irradiances. Supplemental irradiance has been shown in some
cases to increase fresh weight where ambient light was
limited (78). Specific leaf weight is reported to increase
with increased irradiance (6).

White and Warrington (78) have shown a build-up of

carbohydrates at low night tempertures in the form of sugars

and starch throughout the plant. This build-up may account
for some of the weight gain. Armitage et al. (2) found
that, as temperatures increased, the specific leaf weight

decreased as did leaf thickness. It is thought that the
accumulation of carbohydrates increased at low DT, resulting
in increased dry weight as described by White and Warrington

(78). Short irradiance periods coupled with high

15

temperatures have also resulted in decreases in shoot dry
weight (77).

The observations of reproductive and vegetative
responses to irradiance and temperature are thus spread over
a wide range of experimental conditions and stages of
development. It is apparent that irradiance and day and
night temperatures are among the most influential factors
involved in the responses. It has, then, been the focus of
this study to examine systematically the influences of
temperatures and light and to define the physiological
responses to these factors (acting independently and
interactively), and to produce functional models of these
responses.

ELBUI QBQEIB EQQEEIL‘IEA

Plant growth modeling can be said to have begun with
Blackman (16) and the application of the compound interest
law to plant growth. This was applicable to single factor
studies under controlled conditions. However, in studies
involving two or more factors, more sophisticated approaches
of collecting data and defining responses are necessary.
Gardiner et a1. (38) demonstrated that the factorial
approach of collecting data to define demonstrated responses
is very efficient. The more elaborate the desired equation
used to describe the response, the more levels of each
variable are required (20). Over extensive regions. a
high degree equation can be used to represent the full
response surface. The fitting could require a very large

-number of experimental units using the factorial method. To

16

cover the experimental region with a minimal number of
treatments, Box and Hunter (21) and Gardner et al. (38) have
developed a central composite design. In this design the

k
number of treatments required is 2 + 2k + 1 for k factors.

-v

Thus, for 3 factors, 15 treatment combinations are required.
Careful attention is needed in selecting the central
location and the distance of the points from the origin.
According to Box (20), some important considerations to be
met when examining a composite design are: 1. The design
should permit the errors of estimate of points on the fitted
surface to be small. 2. The biases in the estimated
coefficients, which may occur if the assumed equation were
representationally inadequate, should be small. 3.
Provisions should be made to estimate certain coefficients,
or contributions of them. and those of higher order than in
the assumed form of the equation fitted.

Box and Hunter (21) have further proposed designs which
provide constant variance of the estimated coefficients at
points equidistant from the center of the xperimental
region. In this design, the reliability of the estimated
response at any point X .....X depends on the distance of
the points from the center andknot on the direction. They
are thus termed rotatable designs. They are not affected by
rotation with respect to the origin. They are geometrically
very similar to the composite design except that the points
k/4

along the axes are required to be at + 2 units out. This

is 1.68 with 3 variables, and 1.414 with 2 variables.

17
In both the central composite design and the rotatable
design, the coding is the same and the central unit can be
replicated to find the standard error. Thus the error will
have N1 — 1 degrees of freedom where N is the number of

replications at the central unit.

Davies (33) has presented an application of the central

composite design in industrial experiments. He indicated
that the central composite design is among the most
efficient in determining the independent and interactive
effects of the dependent variables. Hill and Hunter (46)
presented a useful review of the use of response surface

methods with special emphasis on their application and

methodology. In their review, the versatility and
application to a number of interacting experimental
conditions was clear. Box and Youle (22) have further

extended the application and the exploration of the response
surface techniques. These researchers showed that studying
the form of the developed empirical surfaces can shed light
on the process and can make possible development of a theory
of the process.

Hinchen (47) depicted graphically the application of
multiple regression equations as they apply in production
chemistry. Much emphasis was placed on the expected yields
under a given set of conditions. Kissell and Marshall (51)
studied the multi-factor resonses of cake quality in
response to the ratios of the basic ingredients and
effectively modeled results using the response surface

techniques.

18

In biological response surface techniques, using the
central composite design, calf nutrition was studied by
Chandler et al. (29). They developed complex response
surface models to a number of interacting nutritional
factors. In plant sciences, the nutritional influence of
copper, iron, and molybedenum on the growth of lettuce has
been effectively studied using the response surface
technique (40). Metcalf et al. (58) used the multiple
regression and response surface techniques to define and
predict the survival and root growth of wheat and barley
from freezing and drought stress.

In floriculture, Hammer and Langhans (42) used response
surface techniques to study the effects of irradiance, root
temperature, day length, and air day and night temperature

in controlled environmental growth chambers on Helianthus

aggggs and giggia elegags. Fresh and dry weight of shoots
and roots, and total dry weight for H, aggggg were
successfully modeled using response surfaces. No

significant model could be fitted to the ;, glegagg data.
Armitage et al. (6) fitted response surfaces to time—to-
flower, dry weight, leaf areas, vegetative height, and
chlorophyll and anthocyanin contents in Tagets patula, using
variables of irradiance and day and night temperatures.
Harlsson (50) modeling the growth of QDCXSSOEOEOUO
mggifiQLng, effectively used the central composite design
and response surface techniques to develop a functional

relationship between irradiance and day and night

temperatures on the time to flower, shoot length, flower

19
size, and dry weight. In this work, a discussion of the
classical and functional approaches to plant growth modeling
is presented. Strong emphasis is made on the partitioning
of the photosynthetic products to different plant parts as
expressed in the dry weight models.

It is thus clear that the use of the central composite
design, multiple regression techniques, and response
surfaces, are well-suited to the study of growth responses
of hybrid geraniums to irradiance and day and night

temperatures.

20

LITERATURE CITED

1. Armitage, A.M. 1982. Relationship of light intensity,
node number and leaf area to flowering time in hybrid
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Congress, Vol. II Abstract No. 1792.

2. Armitage, A.H. 1980. Effect of light and temperature on
physiological and morphological responses in Hybrid
Geraniums and Marigold. Ph.D. Thesis. Michigan State
University. pp. 65-70.

3. Armitage, A.M., and B.M. Hamilton. 1983. Scheduling
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4. Armitage, A.M., C.L. Bethke, and W.H. Carlson. 1981.

I Greenhouse trials of hybrid geranium production.
Bedding Plants Inc. News. Oct, pp. 1-2.

5. Armitage, A.M. and W.H. Carlson. 1979. Hybrid geranium
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6. Armitage, A.M.,_ W.H. Carlson, and J.A. Flore. 1980.
The effect of temperature of quantum flux density on
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7. Armitage, A.M. and M.J. Tsujita. 1980. The effect of
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21
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22

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Expt. Stat. Res. Rpt. 302.

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23
Carpenter. W.J. 1974. High intensity lighting in the
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flowering of geranium cv. Carefree Scarlet by high
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Carpenter, W.J. and R.C. Rodrequez. 1971.
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Craig, R. and D.E. Walker. 1963. The flowering of
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24
495.
Drumm, H., R. Wildermann, and H. Mohr. 1975. The
"High-Irradiance Response" in anthocyanin formation as
related to the phytochrome level. Photochem. and
Photobiol. 21:269-273.
Erickson, V.L., A. Armitage, W.H. Carlson, and R.M.
Miranda. 1980. The effect of cumulative
photosynthetically active radiation on the growth
and flowering of the seedling geranium, Eglacgggigg
x ggctgggm Bailey. Hort. Sci. 15(6):815-817.
Friend,D.J.C. 1968. Photoperiodic response of Egaggiga
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Friend, D.J.C. 1975. Light requirements for
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Hartmann, R.M. 1966. A general hypothesis to interpret

’High Energy Phenomena’ of photomorphogenes1s on the
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366.

Healy, W.E., H.F. Wikins, and M. Celusta. 1982. Role
of light quality, photoperiod, and high-intensity
supplemental lighting on flowering of Algtgggmggia
”Regina’. J. Amer. Soc. Hort. Sci. 107(6):1046-1049.
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Jacobs, 6. 1983. Flower initiation and development in
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Harlsson, M.G. 1984. Influence of temperatures and

irradiance on growth and development of ngysggtgegum

U!
U!

26

gggifgligm ’Bright Golden Anne’. MS Thesis Michigan
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Lin, W.C. The effect of soil cooling and high intensity
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27
University.
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UI

J. Amer. Soc. Hort. Sci. 10
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28
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29
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——_~-~-—-—-

30

SECTION I

THE EFFECTS OF DAILY SUPPLEMENTAL IRRADIANCE PERIOD

AND IRRADIANCE LEVELS ON DAYS TO FLOWER AND

NODE NUMBER IN HYBRID GERANIUMS

31

ABSTRACT:
Supplemental lighting of greenhouse-grown hybrid
geraniums (Eglggggigm Qgfitgggm — Bailey ”Ringo Scarlet”)

using high pressure sodium lamps reduced time to anthesis.

Irradiances (Photosynthetic Photon Flux PPF in the 400—700

-1 —2

nm range) of 45‘pmols m or higher decreased time to
anthesis when supplied for 18 or more hours a day or as a 4
or 12 hr night break. Supplemental irradiance treatments of
.. -'3
65 ‘pmols 1m T for 14, 28, and 42 days given to 10-day-old
plants reduced time to anthesis by 9.6, 43.2, and 50.4 days,
respectively. When supplied to 40~day~old plants the time
to anthesis was reduced by 22.8, 25.4, and 26.5 days
respectively. When the application of supplemental light
was delayed, equal delays in the flowering response were
observed. Mean daily cumulative photosynthetic photon flux
(CPPF) provided a better correlation to days to flower than
did total CPPF. Ninety-three percent of the variation in
days to anthesis and 87% of the variation in node numbers
could be described as functions of mean daily CPPF. A
threshold irradiance response which was observed at a PPF of
45 ‘pmols-lm-L (3.9 moles d-l) reduced days to anthesis and
node numbers simultaneously. Ninety-five percent of the

variation in node numbers was correlated in a linear

function with days to flower.

32

INTRODUCTION:

Under natural winter—spring conditions, hybrid
geraniums (Eelacqegium bectecum - Bailey) flower in 100 to
140 days (2, 3) and require large quantities of heat and
greenhouse space. Early flowering in response to

supplemental irradiation has been reported (1, 9, 14, 17).
However, many growers supplying supplemental light have
experienced only limited success in reducing the time to
flower.

Reports in the literature provide little explanation of
these failures. According to Post (15), photoperiod is not
a significant factor in geranium flowering. Craig and
Walker (11) suggested that cumulative solar energy was a
major environmental factor controlling flowering in this
crop. They (11) suggested that a nearly constant quantity of
accumulated solar energy was necessary for flowering.
Erickson et al. (12) recently reported that 41% to 65% of
the variability in days to anthesis was related to
cumulative irradiance. According to Armitage (4), the time
to visible bud was negatively correlated with irradiance at
a given temperature. After the visible bud stage, irradiance
was less effective than temperature in influencing time to
flower. Carpenter and Rodrequez (9), found that the time to
anthesis was not affected by the first four weeks of
supplemental light. A six—week period of supplemental light
reduced time to anthesis by 20 to 30 days and reduced the
number of nodes produced before the first flower. Similarly

in the northwestern United States, Norton (14) produced

33

flowering plants three weeks earlier by applying 67 days of
supplemental irradiation.

Since supplemental irradiation has been shown to cause
earlier flowering in hybrid geraniums and only limited

systematic studies of the response have been reported, it

was decided to study and to quantify the conditions
necessary for flowering. It is the expectation that this
information will lead to more efficient production

techniques.

34
MATERIALS AND METHODS

CULTURAL PRACTICES:

Similar cultural practices were used in three
experiments on the cultivar Sprinter Scarlet. A peat—lite
medium composed (by volume) of 50% fibrous peat, 25%
vermiculite, and 25% perlite was used both as germination
and growing medium. Seeds were planted in the medium and

o 0
covered to a depth of 0.5 cm, then germinated at 22 + 2 C.

Plants were watered as needed using a water soluble
fertilizer 20N - 8.7P - 16.7K) to provide 200 mgl-1
nitrogen at each watering. Greenhouse temperatures were
maintained at 17 + 2 C nights (1800 to 0800 hours) and 21 +

2 C days (0800 to 1800 hours). From May through September
ambient light was reduced to about 65% of incident radiation
by means of white washing the greenhouse.

SUPPLEMENTAL LIGHTING:

All supplemental lighting was provided using 400 and
1000 watt high pressure sodium lamps. Treatment
Photosynthetic Photon Flux in the 400 to 700 nm range
(irradiance, PPF) were measured using a Li-Cor (Lincoln,
Nebraska) Lambda Li-190s quantum sensor. Ambient daily
cumulative irradiance (CPPF) was recorded using a Kysor
intigrator recorder. Treatment irradiances were checked and
adjusted every 14 days by changing the height and location
of the lamps over the plants. The supplemental irradiance

periods varied with the treatments in each experiment.

35

EXPERIMENT 1:

The effect of supplemental light duration on flowering
in young seedlings was studied. On November 17. ten—day~old
seedlings were transplanted into 6 cm square plastic
containers and immediately placed in the greenhouse under

continuous (24 hours/day) supplemental irradiation of 65 + 8

—1 -2
‘pmols m for periods of 14, 28, and 42 days. Control
plants recieved no supplemental light. At the end of each
treatment period. 32 plants were randomly selected and

placed on an unlighted adjacent bench. After all treatments
were completed, the plants were potted into 10-cm clay pots,
randomized, and grown to flowering under ambient greenhouse
conditions. The days to anthesis, defined as the opening of
the first floret, were recorded.

EXPERIMENT 2:

In experiment 2. the effect of supplemental light
duration on flowering of older plants was studied. Fifteen-
day—old seedlings from an October 7 sowing were transplanted
to clay pots. 10-cm in diameter, and grown under ambient
greenhouse conditions. When the plants were 40 days old,

treatments of 14, 28, and 42 days of continuous (24

-—1 -z

hours/day) supplemental irradiance (PPF = 65 + 84pmols m )
were started. Other treatments were started when the plants
were 54 and 68 days old and were continued until anthesis.
Control plants were lighted: 1) from 3 days after
transplanting to anthesis, 2) from 40 days old to anthesis,
or 3) not at all. All groups consisted of single plants

replicated 8 times. Days to anthesis, the number of lateral

36

branches 1 cm long or longer, and the number of visible buds
per plant were recorded at the time when all plants had
reached anthesis.

EXPERIMENT 3:

A third experiment, designed to study the effects of
quantity. intensity and duration of the daily supplemental
irradiance, was started on August 16. Seventeen-day-old
seedlings which had been planted directly into 4-cm square
plastic containers were placed in the greenhouse under 42
combinations of supplemental light differing in irradiance
levels and daily irradiance periods (Table 3). The
treatments were arranged factorially in a split-plot design.
The main plot consisted of 6 supplemental irradiance period
treatments: 1) 4 hours of lighting from 0000 to 0400 hours,
2) 12 hours during the night from 1900 to 0700 hours, 3) day
extension to 15 hours of light from 0700 to 2200 hours, 4)
18 hours from 0700 to 0100 hours, 5) 21 hours from 0700 to
0400 hours, and 6) continuous supplemental lighting, 24
hours/day. In the split of the main plot, plants were
arranged within each treatment at different locations under
the lamps to provide PPF of 15, 30, 45, 60, 75 and 90

— _o
1pmols 1m b. The greenhouse ambient light lasted from

approximately 0700 to 2100 hours. The unlighted control

—1 —2

plants received less than 3‘pmols m of the supplemental
irradiation as scattered light 24 hours/day. After 33 days
of treatment, the plants were removed from the supplemental
light and potted into 10-cm square plastic pots, and grown

under ambient greenhouse light. The daily CPPF, date of

37

anthesis and the number of nodes on each plant from seed
emergence to first anthesis were recorded. The total crop
CPPF was determined by summing the daily ambient CPPFs and

the daily supplemental CPPFs from seed to anthesis.

38

RESULTS AND DISCUSSION:

Continuous supplemental irradiation applied to 10-day-
old seedlings (Experiment 1) for a period of 14 days reduced
the average time to anthesis by 9.6 days (Figure 1), while
the 28 and 42 day treatments reduced the time to anthesis by
43.2 and 50.4 days respectively. While large reduction in
time to anthesis occurred from lighting during the 14 to 28
day treatment period, only small decreases in time to
anthesis occurred from the last 14 days of supplemental
irradiation. These results, which are similar to those
obtained by others (4, 5, 6, 8, 9), raise a number of
questions: Is an accumulation of radiant energy necessary
for flower induction as suggested by Craig and Walker (11)?
Is a certain minimum average daily CPPF necessary as was
suggested by Ericksan et al. (12)? Were the young plants at
first in a juvenile state, i.e. unable to respond to the
irradiation, until they matured sufficiently during the
treatments? Is there a high irradiance response in which a
certain duration of irradiance is required before initiation
occurs?

In addition to the questions, above results provide
other information. The 'smaller reductions in time to
anthesis that occurred from the first two weeks of
irradiation. as well as those differences that occurred
between 28 and 42 days of treatment, may reflect the
additional growth mainly due to increased photosynthetic
activity. The differences between 14 and 28 days of

'supplemental lighting may be due to both increased

39

photosynthetic activity and to a high irradiance induction-
like response in plants that are sufficiently mature to
respond to the irradiance stimuli.

In Experiment 2, time to anthesis was reduced by all
supplemental light treatments given to forty-day-old plants
when compared with the unlighted control plants. However,
time to anthesis was longer than for the continuously
lighted control plants (Table 1). None of the responses to
the duration of supplemental light were significantly
different, i.e., in 40-day-old plants 14 days of
supplemental irradiation was as effective as 42 days. The
small differences between 14, 28, and 42 day treatments may
have been due to increased photosynthetic activity during
the longer light treatments.

On plants that were irradiated at the age of 54 and 68
days, delays in anthesis were approximately equal to the
number of days before the supplemental irradiation began.
It is noteworthy that the plants lighted from 18 days old to
anthesis (lighted control) flowered an average of 46.4 days
earlier than the unlighted control, and 20.3 days earlier
than all plants irradiated 22 days later. Significant
differences in days to anthesis existed between plants given
supplemental irradiation at 40. 54, and 68 days of age, but
no significant differences were found between plants
irradiated at 68 days and the unlighted control. It 'is
likely that, with sufficient ambient light, at 68 days,
flower initiation had already occurred when the supplemental

light treatment was started. Floral initiation of the

4O

meristem was found to occur in spring crops at about this
age in the work of Miranda (13).

Few small differences occurred in the time span from
the beginning of supplemental lighting to anthesis. Only
plants lighted while very young (18 days old) or for a short
period of time (14 days) took significantly longer to reach

anthesis. The data indicate that flower initiation may be

occurring during the period immediately following
application of supplemental irradiation. This flowering
response may require a sufficient duration of high

irradiance on plants that have completed a juvenile phase.

It is possible that the induction may result from the

increased photosynthesis or from a high irradiance
photomorphogenic induction, altered by the supplemental
irradiation treatments. On plants irradiated for 28 or

more days (Table 1), an increase in lateral branches was
observed. The number of buds per plant were not
significantly increased unless the irradiance treatments
began early, before forty days, and continued to first
anthesis. Shorter term irradiation (14 to 42 days)
decreased the time to anthesis and did not significantly
increase lateral branching.

Comparing the results of the light treatments applied
to old (40 days old, Exp. 2) and young (10 days old, Exp. 1)
plants, it appears that the older plants are more responsive
to the supplemental irradiation treatments. This is not
surprising since the sensitivity of other herbaceous species

to inductive stimuli can increase with increasing age. In

41
the snort-day plant chysaptbsosm genitaliso. different
cultivars have been shown to vary in the time required to
grow out of the juvenile phase. In one study with Pisum

gaggygg (garden pea) the level of genetically controlled
flowering inhibiton was found to decrease as the plants aged
(7). This ripeness-to-flower may also be a factor in the
responses of geraniums to high irradiance levels.

In the study of the effects of responses to
supplemental irradiance levels and daily irradiance period
(Exp. 3), plants treated with daily irradiance periods
greater than 15 hours flowered in less time and with fewer
nodes when supplemental irradiance levels exceeded 45
‘pmols-1m_L (Table 2). Plants in the control group flowered
in an average of 138 days with an average of 19.4 leaves
preceeding the first inflorescence. Plants receiving high
levels of irradiation flowered an average of 78 days earlier
and the number of nodes to first inflorescence was reduced
by an average of 10.9. No reduction in days to flower or
node number was observed at any irradiance level when the
dailv supplemental irradiance period was only 15 hours.
Significant decreases in days to anthesis and node number
were observed when the supplemental irradiance levels were
greater than 45 pmolsfllmflg and the irradiance period was 18
hours or longer, or when there was a night interruption.
Four and 12 hours of supplemental irradiation as a night

interruption. were as effective as the 18 hours, 21 hours,

or continuous (24 hours/day) irradiance periods.

42

Many treatments providing the same quantity of
supplemental irradiation at different irradiance levels and

daily' periods yielded different results. Plants in

—’

5

treatment No. 1 received 42.8 mol M of supplemental
irradiation over the duration of the treatment and flowered

in an average of 131.0 days having 10.0 nodes to anthesis.

r5

-’

Treatment 36 also received 42.8 molM T of supplemental
irradiation and flowered in 82.3 days with an average of
only 8.5 nodes. Treatments 2 and 28, 3 and 30, 17 and 24
and 22 and 24, also received the same quantities of
supplemental CPPF over the same period but showed wide
differences in both days to flower and node number. These
results indicate that the quantity of accumulated CPPF is
not as important as the incident irradiance level and daily
irradiance period. Irradiance periods longer than 15 hours
were not effective in reducing time to anthesis.

Plots of the data demonstrating relationships between
total CPPF, mean daily CPPF and days to flower or node
number are presented in Figure 2. Since the plots appear
non-linear the logarithmic, squared, and cubed
transformation .of the CPPF terms were submitted to a step-
wise addition multiple' linear regression analysis.
Equations which most significantly define the relationships
are presented in Table 3. A positive linear relationship of
days to anthesis with total CPPF accounted for 74% of the
variability in days to anthesis and 59% of the variability
in the number of nodes to anthesis: these correlations

'indicate that the slower flowering treatments were exposed

43

to a greater quantity of CPPF, while plants that were
induced to flower earlier flowered with less total CPPF.
Correlations to the mean daily CPPF yielded coefficients of
determination as high as 93.4% and 84.8% for regression
equations which included logarithmic and linear terms.
These relationships yielded negative correlations indicating
that with increased mean daily CPPF there is a decrease in
the days to flower. It thus appears from the results that
mean daily CPPF may be a better predictor of flowering
response than the total CPPF.

In correlating the days from sowing to anthesis (Y)
with the number of nodes to flower (X), a correlation
coefficient of 0.974 was obtained for the linear
relationship Y = 3.6 + 7.62 X. The high positive
correlation indicates that early flowering may be associated
with morphogenic resonses producing early floral initiation
and less nodes to first anthesis. The greater number of
nodes is associated with later flowering and apparently
later floral initiation despite the greater amount of
accumulated radiant energy.

The intensity of supplemental irradiation significantly
influences the days and nodes to anthesis (Table 4). Linear
and quartic terms are significant in relation to days to

anthesis. Linear, quadratic and cubic and quartic terms are

significant in relation to node number. Plots of the means
related to the level of supplemental irradiance are
presented in Figure 3. The plots demonstrate the

simultaneous decrease in days to flower and node number with

44

increased supplemental irradiation. Note that the greatest

reduction in both days to flower and node number occur

-1 -2

around a critical level, or threshold, of 45‘pmols m , in
the fall crop. Again, the close relationship of days to
anthesis and node number is observed in the Simultaneous
shift of both responses to the increased supplemental

irradiance.

45

SUMMARY AND CONCLUSIONS:

The number of lateral branches increased when
supplemental irradiation was provided for 28 or more days.
The number of buds per plants was increased when lighting
began at a young age and continued until anthesis.
Supplemental irradiances above 20‘pmols-1m-L in combination
with photoperiods longer than 15 hours were effective in
reducing the time to anthesis in these experiments.

The quantity of light received by the crop was not as
important as the daily irradiance. Mean daily CPPF provided
a better estimator of days to anthesis than the crop total

CPPF. The number of days to anthesis was highly correlated

(r = 0.937) to the number of nodes. A critical supplemental

-—1 -z

irradiance of 45 pmols m was observed when supplied for
15 or more hours daily. The decreased node numbers and
accelerated flowering response to supplemental irradiance,
extended high irradiance periods, and night interruption
treatments, raise the question that a photomorphogenic
response, by definition of Wareing and Phillips (16), may be
occurring. This may be a high irradiance induction response
which occurs in plants when they are sufficiently ripe-to-
flower, or a response to added photosynthates produced by
the added light. Based on field observation and other
unreported experimental data, the length of the juvenile
phase, the critical irradiance, and the duration of high
irradiance, may vary in each cultivar thus giving
differences in days to anthesis of cultivars selected for

commercial production. It is possible that wide differences

46

may exist in cultivars not selected for spring production or
rejected by breeders as not being desirable under current
production practices.

It is apparent that when supplemental irradiation is
applied to geraniums which are suffic1ently mature to flower
and high enough irradiance levels are present for long daily
irradiance periods, consistent reductions in the time to

anthesis and node number can be expected.

Table 1.

Effects of a e and duration of supplemental irradiation
(65pmols'1m‘ ) on days to anthesis, lateral branching,
and total bud count in Pelargonium hortorum - Bailey
'Sprinter Scarlet”.

 

 

 

Age Duration Days from Days from Lateral Buds
at of sowing lighting branches per
lighting lighting to anthesis to anthesis per plant plant
- 0 days 135.2 - 7.3 2.8
18 to anthesis 88.8 70.9 10.8 9.1
40 14 days 112.4 72.4 7.5 3.9
40 28 days 109.9 69.9 11.4 4.6
40 42 days 108.8 68.8 11.4 4.9
54 to anthesis 122.5 68.5 11.3 4.6
68 to anthesis 134.5 66.6 13.0 4.0
H. S. D.2 - 8.1 5.2 4.0 2.5

 

z Tukey‘s w test (honestly signifigant difference), ak=0.05.

48

Table 2. Effects of PPF and irradiance period on the number of

nodes and days to flower in Pelarggnium hortorum - Bailey

 

'Sprinter Scarlet'.

 

 

 

 

 

54phmenufl.tnemmeus BoAnflxsis
Inmdtnme#_ MD T T DD

xx pmmfiiwr‘ mes emf we” we” we

1 24 15 1.30 42.8(a)Y 1431.1 10.99 131.0

2 24 30 2.59 35.5(b) 1501.0 13.18 130.6

3 24 45 3.89 128.2(0) 1298.4 16.12 81.2
4 24 60 5.18 170.9 1353.2 16.70 84.2

5 24 75 6.48 213.8 1292.3 19.48 67.0

6 24 90 7.78 256.7 1313.1 21.01 62.6

7 21 15 1.14 37.6 1476.7 10.01 150.0

8 21 30 2.27 74.9 1545.0 10.91 145.6

9 21 45 3.40 112.3 1358.7 14.74 94.2
10 21 60 4.53 149.6 1419.7 15.11 95.8
11 21 75 5.67 187.1 1431.1 16.21 90.0
12 21 90 6.81 224.6 1416.5 17.70 85.2
13 18 15 0.98 32.2 1424.4 10.77 134.8
14 18 30 1.94 64.1 1450.9 11.38 128.0
15 18 45 2.92 96.3 1313.4 14.46 95.4
16 18 60 3.89 128.2 1338.0 15.33 91.8
17 18 75 4.86 160.4(d) 1387.2 16.00 88.2
18 18 90 5.84 192.6 1226.7 19.64 63.4
19 15 15 0.81 26.8 1483.9 10.22 147.8
20 15 30 1.62 53.4 1458.8 10.84 134.8
21 15 45 2.43 80.2 1529.3 10.52 146.0
22 15 60 3.24 106.9(e) 1552.6 11.01 142.2
23 15 75 4.05 133.7 1591.6 12.00 137.6
24 15 90 4.86 160.4(d) ' 1635.1 12.29 145.4
25 12w 15 0.65 21.4 1376.9 11.13 125.0
26 12 30 1.30 42.4 1409.1 11.24 126.2
27 12 45 1.95 64.2 1295.8 14.00 93.8
28 12 60 2.59 85.5(b) 1320.4 14.25 94.8
29 12 75 3.24 106.9(e) 1246.7 15.91 82.8
30 12 90 3.89 128.2(0) 1211.6 17.23 70.8
31 4X 15 0.22 7.2 1446.2 9.75 150.4
32 4 30 0.43 14.3 1420.0 10.21 140.2
33 4 45 0.65 21.4 1278.3 12.63 104.8
34 4 60 0.86 28.5 1163.3 14.40 82.8
35 4 75 1.08 35.6 1173.1 14.57 81.2
36 4 90 1.30 42.8(a) 987.6 12.00 82.3
Ambient control 1394.3 10.22 138.0

H.s.0.Z 300.2 4.48 42.8

49

Table 2. (continued)

‘<><Z<C‘.

Period of irradiance expressed in hours.

Intensity of irradiance expressed in Photosynthetic Photon Flux
(PPF) in the 400-700 nm range, umols’lm'z.

Mean daily cumulative photosynthetic photon flux in mm"2 over
the crop life.

Total cumulative photosynthetically active radiation in mm-
over the life of the crop.

Summation of ambient and supplemental irradiation.

Daily average of the ambient and supplemental irradiation.
Treatment during the ambient night period.

Treatment as night break (0000-0400 hrs).

Letters in paranthesis. indicate pairs of treatments of the same
quantity of supplemental irradiation but at different times and
intensities.

Honestly significant difference determined using Tukey's
procedure 04: 0.05

2

50

Table 3. Prediction equations for days and nodes to flower in
Pelargonium hortorum - Bailey 'Sprinter Scarlet' comparing
mean daily and total cumulative photosynthetic photon flux
as predictive variables.

 

 

 

 

Dependent Independent Prediction Regression statistics

variable variable equationZ F-ratio sign.x R17
days MD CPPFX 243.4-9.8(x) 1030.2 *** .848
days MD CPPF 843.6+l6.6(X)-855.6(logX) 1282.2 *** .934
days T CPPFW -148.4+0.1866(X) 536.9 *** .744
days T CPPF -20.7+6.7E-5(X2) 556.8 *** .753
nodes MD CPPF 32.1-1.27(X) 473.2 *** .721
nodes MD CPPF -62.8-47.7(1ogX) 679.1 *** .788
nodes T CPPF -17.3+0.0233(X) 262.0 *** .589
nodes T CPPF 1.4+8.39E-6(x2) 269.0 *** .595

 

Z Equations were developed through step-wise addition regression
analysis, including lenear, quadratic, cubic and loglo trensformed
terms.

Y Significance of the regression equation; ***,aL= 0.001.

X MD CPPF = mean daily cumulative photosynthetic photon flux.

W T CPPF = total cumulative photosynthetic photon flux during
the life of the crop.

Table 4.

Analyms of variance for the influence of supplemental

irradiance on days and nodes to flower in Pelargonium hortorum

- Bailey 'Sprinter Scarlet'.

 

 

 

. De rees of .
Variable Source fgeedom F-ratio Significancez
Days
Between Levels 6 34.3 444
Linear 1 186.4 444
Quadratic 1 1.0 n.3,
CUbiC 1 3.8 11.5.
Quartic 1 5.4 4
Within levels 147
Nodes
Between Levels 6 31.2 444
Linear 1 90.0 ***
Quadratic 1 5.8 44
Cubic 1 3.9 *
Quartic 1 7,4 **
Within levels 147

 

Z significance of the variable and it's trends; n.s. = not significant,

4 UK: 0.05, **

CC? 0.01,

*** OK= 0.001.

52

Figure 1. Days to anthesis in Pelargonium hortorum - Bailey
'Sprinter Scarlet' when supplementally irradiated
with high pressure sodium lights at a PPF of 65:8

,pmol s’lm“2 continuously for different durations.

DAYS 10 ANTHESIS

150

 

53

 

 

0 14

DAYS OF CONTINUOUS

I H30 «05)

28 42

IRRADIATION

Figure 2.

54

The relationship of mean daily and total cumulative
PPF to the days to anthesis and node number in

Pelargonium hortorum - Bailey 'Sprinter Scarlet'.

 

(A) The effect of mean daily PPF on days to
anthesis in each plant.

(B) The effect of total cumulative PPF on days
to anthesis in each plant.

(C) The effect of mean daily PPF on nodes to
anthesis in each plant.

(D) The effect of total cumulative PPF on nodes
to anthesis in each plant.

55

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56

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on

 

 

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57

 

 

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Figure 3.

59

Effects of continuous supplemental high pressure
sodium irradiation on the node number (A), and

days to anthesis (B) in Pelargonium hortorum -

 

Bailey 'Sprinter Scarlet' when applied for 18

or more hours a day.

Oil

60

 

 

 

 

 

 

(o—o) S M! 0
am
i‘ r
5
9! 0|

(H) 8300“

PPF (umol Hm")

61

LITERATURE CITED:

1‘.

Armitage, A.M. 1980. Effect of light and temperature
on physiological and morphological responses in Hybrid
Geraniums and Marigold. Thesis. Michigan State
University. pp. 65-70.

Armitage, A.M., C.L. Bethke, and W.H. Carlson. 1981.
Greenhouse trials of hybrid geranium production.
Bedding Plants Inc. News. Oct, pp. 1—2.

Armitage, A.M. and W.H. Carlson. 1979. Hybrid geranium
greenhouse pack trials - 1979. Bedding Plants Inc.
News. July.

Armitage, A.M., W.H. Carlson, and J.A. Flore. 1980. The
effect of temperature of quantum flux density on the
morphology, physiology, and flowering of hybrid
geraniums. J. Amer. Soc. Hort. Sci. 106:643-647.
Armitage, A.M. and M.J. Tsuijita. 1980. The effect of
supplemental light source, illumination and quantum flux
density on the flowering of seed-propagated geraniums.
J. Hort. Sci. 54:195-198.

Armitage, A.M., M.J. Tsujita, and F.H. Harney. 1978.
Effects of cycocel and high intensity lighting on
flowering of seed propagated geraniums. J. Hort. Sci.
53:147-149.

Bernier, 6., J.M. Hinet, R.M. Sachs. 1981. The
Physiology of Flowering — Vol. I The Initiation of
Flowers. CRC Press, Inc. Boca Raton, Florida. pp. 108-

109.

10.

11.

13.

14.

62

Carpenter, W.J. 1974. High intensity lighting in the
greenhouse. Res. Rpt. 255. Michigan State University
Agricultural Expt. Stat. East Lansing.

Carpenter, W.J. and R.C. Rodrequez. 1971. Earlier
flowering of geranium cv. Carefree Scarlet by high
intensity light treatment. Hort. Sci. :206-207.
Carpenter, W.J. and R.C. Rodrequez. 1971. Supplemental
lighting effects on newly planted and cut-back
greenhouse roses. Hort. Sci. :207-208.

Craig, R. and D.E. Walker. 1963. The flowering of
Pelargonium hortorum - Bailey seedlings as affected by
cumulative solar energy. Proc. Amer. Soc. Hort. Sci.
83:772-775.

Erickson, V.L., A. Armitage, W.H. Carlson, and R.M.
Miranda. 1980. The effect of cumulative
photosynthetically active radiation on the growth and
flowering of the seedling geranium, Pelargonium hortorum
Bailey. Hort. Sci. 15(6):815-817.

Miranda, R.M. and w.H. Carlson. 1980. Effect of timing
and number of applications of chlormequat and ancymidol
on the growth and flowering of seed geraniums. J. Amer.
Soc. Hort. Sci. 105(2)§273-277.

Norton. H.A. 1973. Stimulating earlier blooming of seed
geraniums with high intensity lighting. Flor. Rev.
153:25,b7-68.

Post, H. 1942. Effects of day length and temperature on
growth and flowering of some florists crops. Cornell

Univ. Agr. Exp. Sta. Bul. 787:1~70.

63

16. Wareing, P.F. and I.D.J. Phillips. 1981. Growth and
Differentiation in Plants. Pergamon Press Elmsford,New
York.

17. white, J.W. and P.E. Randolph. 1971. Geraniums from

seeds - Flowering plants. ”Geraniums” A Penn State
Manual Editor J.W. Mastalerz. Pub. by Penn. Flower

Growers Univ. Park, Pa. pp. 196-211.

64

SECTION II

EFFECTS OF HIGH IRRADIANCE AND TEMPERATURE 0N

EARLY FLOWERING IN HYBRID GERANIUMS

65
ABSTRACT:

Treatments of hybrid geraniums (Pelaggggigm hggtgggm -
Bailey) in growth chamber with short periods of continuous
irradiation and temperature decreased the days and number of
nodes produced from sowing to anthesis. A non-inductive
juvenile phase from germination to between the 4th and 5th
leaf was identified in the cv. Ringo Scarlet. Continuous
(24 hours/day) irradiances (Photosynthetic Photon Flux, PPF)
providing at least 10.4 mol d“1 (120 ‘pmols-lm-L) was
effective in reducing the days and nodes from sowing to
anthesis when applied for 12 or more days at 30°C. When PPF
was higher, shorter durations of treatment were required for
early induction. Temperature increased from 20°C to 30°C
decreased the time of continuous irradiance treatment
necessary for early induction. Under high irradiances (240
‘pmols_1m-;) and high temperatures (300C) early induction
responses occurred in 83% of the population from 9 days of
treatment. An earlier induction response was indicated due
to the simultaneous decrease in node numbers and days to

anthesis. An hypothesis to describe a possible high

irradiance induction response is presented.

66

INTRODUCTION:

Finding methods to decrease the normal time to flower
(100 - 140 days) in hybrid geraniums (Eglécgggigg hggggggm ~
Bailey) has been a goal of many floriculturalists for some
time.

Early flowering of geraniums has been observed with the
application of high levels of supplemental irradiation under
greenhouse (1, 3, b, 9, 11, 14, 18, 23) and growth chamber
(6, 26, 27) conditions. High irradiance coupled with

moderate to high temperatures have been shown to accelerate

flowering (2, 27). Armitage (2) observed visible buds in 33

days after sowing on plants exposed to continuous
-1 -2 o

irradiation at 375 pmols m and 30 C, they flowered in 65

days, nearly half the normal production time. Randolf and

Law (27), obtained macroscopic buds in 21 days on plants
_.1 ..',)

‘-

exposed to high (about 375‘pmols m ) levels of continuous
irradiance. white (26) observed macroscopic buds on the cv.

Red Elite 36 days after beginning irradiation with

"1 “.5.

approximately 390 ‘umols m at 18 to 22.5 C. Anthesis

occurred in 29 days from sowing in the cv. Cherry Diamond
0 0
when plants were grown at 30 to 37 C days with supplemental

—1 -—2

irradiation applied at BO‘pmols n during the night hours
(5).

High irradiance levels have been known to influence the
induction of flowers in many species, for example; African
Violets (Séigtgaglig) (10), Rudbeckia (17), Snapdragon
(Agtigghiggm) (22), and Roses (Egg; Dyggigg), (4, 5, 14).

Increased floral induction has been observed under prolonged

67

periods of high irradiance in Agagallig arvensis L.

(Pimpenal) (19), Rhododendron s9. (Azalea) (7), and

In geraniums, no clear definition of the factors
involved in early flowering has been advanced. Many varying
observations of the potential for early flowering have been
reported. For reliable application to production it was
necessary that the factors which yield the early flowering
be defined. Understanding the response would be useful. not
only in accelerating geranium production but also in studies
of the physiology of flowering. It was the purpose of this
study to examine those factors which were thought to

influence initiation of flowering in hybrid geraniums.

68

MATERIALS AND METHODS

CULTURAL PRACTICES:

Three experiments were conducted, and similar cultural
practices were used in all of them. A peat-lite medium
composed (by volume) of 50% fibrous peat, 252 vermiculite,
and 25% perlite was used both as a germination and a

transplant medium. Seeds were sown, covered to a depth of
o o

I") I",

0.5 cm and germinated at 22 + 2 C. Plants were watered as

needed in a constant liquid feed program using a water

soluble fertilizer (2ON - 8.7P - 16.7K) to provide 2C)Q}.tgl-1

nitrogen at each watering. Greenhouse temperatures were
0 o o o

maintained at 17 + 2 C night and 21 + 2 C days.

GROWTH CHAMBER CONDITIONS:

All light and temperature treatments were performed in
growth chambers. Lighting was from cool-white fluorescent
lamps only. The irradiance at the upper surface of the
plant was measured at the beginning of each treatment and
checked weekly. It varied by not more than + 12% of the
indicated irradiance levels. Temperature was maintained at
the specified treatment conditions and checked daily varying
not more than + 20C.

EXPERIMENT 1:

The duration of continuous light treatment was studied

using mature winter-grown vegetative plants of the cultivar

Ringo Dolly. On December 14, four treatments of eight

plants each began. The plants were grown in b-cm square

plastic containers and averaged 4.3 leaves at treatment. An
-1 -1

irradiance of 240‘pmols m was maintained continuously (24

69

hours/day) for 3, 6, and 12 days. An untreated control
remained in the greenhouse. After treatment, the plants
were grown under greenhouse conditions. Time to anthesis

and the number of nodes to the first inflorescence were
recorded and the data was subjected to an analysis of
variance.
EXPERIMENT 2:
The effect of temperature and duration of irradiation
were investigated using the cultivar JackPot. Continuous
-1 -2

irradiance of 240 pmols m was applied to mature winter
0 0

grown plants in combination with temperatures of 20 , 25 ,
and 30°C (+ 10C) for 3, 6, and 12 days. Seventy-seven-day-
old plants having 10 nodes each were selected at random for
treatments which started on December 14. Five replications
were grown and treated in 5-cm square plastic containers.
Days to anthesis and node number to first anthesis were
recorded and an analysis of variance performed.

EXPERIMENT 3:

The interactive effects of plant age, irradiance, and
the duration of light treatment were investigated in a 3 x 3
x 5 factorial arrangement of treatments. Plants were
selected for treatment from a September 30th sowing of the
cultivar Sprinter Scarlet into 5 x 7 x 9 cm plastic

containers, treatments of six plants each at the age of 18,

24. and 30 days were subjected to irradiance levels of 60,

-1 —2

120, and 240‘pmols m for periods of Q, 3, 6, 9, and 12
days. At the beginning of the treatment the 18-day-old

plants averaged 2.0 expanded leaves while the 24 and 30-day-

70

old plants averaged 3.3 and 4.6 leaves respectively. The
number of nodes that emerged during treatment and the number
to anthesis were recorded along with the date of the

beginning of anthesis. An analysis of variance was performed.

71
RESULTS AND DISCUSSION:

The age of the plants at treatment and the interaction
of irradiance and temperature, and the duration of
continuous xposure to the treatments all appear to
influence the inductive response.

Duration of Light and Temperature:

Continuous irradiation of the plants with 240
‘umols—lm—g for 12 days at 300C decreased the time to anthe~
sis by an average of 51.6 days, and the number of nodes
before the first inflorescence by an average of 14.1 (Exp.
1, Fig. 1). Three or 6 days of treatment had no significant
effect on flowering, compared to the control. In experiment
2 (Tab. 1), similar results were observed from 12 days of
treatment, at 250 or 30°C. Seventeen percent of the
population did flower earlier from only 6 days of irradiance
(240 ‘pmols-lm-L) and temperature (30°C) treatments. In
Experiment 3 (Fig. 2 and 3) 50% of the 30-day-old plants
responded to only 6 days of irradiance and temperature
treatment at 240‘pmols-1m-L.

The results reported here are in agreement with
previous observations where flowering time and numbers of
nodes to first inflorescence were decreased in plants
exposed to high irradiance levels over extended periods (2,
9, 11, 18, 23). Armitage (2) reported that 9 days of

_ -0
continuous high irradiance (375 pmols 1m b) was effective in
decreasing the time to flower. This data is in agreement

with his: they show that the higher levels of irradiation

supplied to mature plants at higher temperatures required

72

shorter irradiance periods for early induction. Carpenter
and Rodrequez (9), Tsujita (23), and Norton (18) found 28 to
42 days of continuous light was necessary to yield a
significant reduction in the time to anthesis. Age of the
plants at treatment as well as the temperature and
irradiance levels appear to have influenced the results
previously reported.

In traditional photomorphogenic studies, it is well
documented that a given duration or number of cycles (13,
24) of inductive conditions are necessary for floral
initiation. In one cultivar of Eggggigg ggmggggggg (turnip
rape), only one day of high irradiance is necessary to
induce flowering (12).

Age:

The data indicate that sufficient plant development is
necessary in geranium seedlings before inductive responses
to high irradiance and temperature can occur. Results from
Experiment 3 are presented in Figure 2 and 3. Eighteen—day—

old plants, having an average of 2.0 leaves expanded to at

least 0.75 cm in. diameter, did not respond to any
combination of treatments. In 24-day-old plants, averaging
3.3 expanded leaves at treatment, 17, 50 and 83 percent of

the population flowered earlier from 6, 9, and 12 days of
-1 ..."_3

h

treatment with 240 ‘pmols m . The 30—day-old plants,
averaging 4.6 expanded leaves at treatment, showed early
flowering of 50. 83 and 100 percent of the population from
6, 9 and 12 days of treatment at irradiance of the 240

-1 —2

'pmols m . As treatment continued, the 24—day-old plants

73

developed sufficiently and responded like the older plants.
In all cases, node numbers to first anthesis followed a
pattern similar to days to anthesis (Figure 3).

The average rates of new leaf emergence in experiment 3
were 0.28, 0.35, and 0.39 leaves per day at the low, medium
and high irradiance levels. The 30-day-old plants,
averaging 4.6 leaves each at the beginning of the irradiance
treatments, were the most responsive to treatments. Nine

-1 -2

days of treatment at 240‘pmols m were sufficient to yield

early flowering in a 50% of the population of the 24-day-old

-1 -:.>

plants. When treated for 12 days at 240‘pmols m , 100% of
the population showed decreased days to flower and node
numbers. Experiment 1 and 2 were performed on older plants
and in each case 9 or more days were needed to yield a
response. Thus, growth past an average of 4.6 leaves was of
minimal additional benefit in increasing the responsiveness
in the cultivars studied.

The phenomenon of Juvenility in flowering responses to

high irradiance has been reported in other species. In
Ehggagitig Q11 (21), the older the plants, the more
responsive they became to light. In Siggggig algg the

number of long-day cycles required for induction was 6 to 7
at 15-days-old, 2 at 30—days-old, and 1 at 60—days-old. It
is note worthy that in the B-days-old plants only a minimal
response was observed (8). In a study of hybrid geraniums
by Armitage (1) it was found that the first 6 to 8 leaves
may be necessary to influence flowers in the cultivar Sooner

Red.

74

Ripeness-to-flower is important in the cultivars
reported here. It appears that an average of 4.6 leaves or
more are necessary in ’Sprinter Scarlet’. However in some

cultivars currently being studied, flowers differentiated
after the third plastchron (6). Thus, the extent of
juvenility is likely cultivar-dependent and probably
contributes to the relative earliness of each cultivar.
TEMPERATURE:

Results from the study of the effects of temperature
and duration of irradiance treatments on winter grown 77-
day-old plants (Experiment 2, Table 1) indicate that
interactions were significant for both days to anthesis and
number of nodes from sowing to the first inflorescence.
Early flowering and reduction of node number occurred in 50%
of the population with as few as 6 days of treatment at
300C, and with 12 days of treatment all the plants flowered
earlier. At 25°C all plants of the population treated for
12 days flowered earlier and node numbers were again
significantly decreased. At 20°C, only 20% of the
population flowered earlier and with less nodes from the 12
day treatment. It is suggested that if the 200C treatment
were maintained for a longer period of time, a response to
the high irradiance may have occurred in a greater

percentage of the population. The rate of induction was

slower at cooler temperatures.

Many photomorphogenic responses are influenced by
temperature. In Egaggigg ggmgggtgig ’Ceres’, the greatest
o

flowering response occurred at 25 C (12). The percentage of

75

flowering increased with increases in both irradiance and
duration of irradiance. Murneek (17), studying the long day
plant, Egggggkig 9199195, concluded that high temperatures
may be substituted for long days in induction. In
geraniums, Armitage (2) has obtained results similar to
those reported here. Observations of White (26) also
indicate a very significant effect of temperature.
Flowering in the cv. Cherry Diamond was obtained in 29 days,
but only when high temperatures (23—37OC) were present
throughout the vegetative and reproductive phases (6).

It is apparent that at irradiance levels of 240
‘pmols-lm-L temperature and duration interact under con-
tinuous irradiation to influence floral induction. With
higher temperatures and longer durations of continuous
irradiance, increased flowering responses were observed in
the cv. JackPot. Additional field observations indicate
that cultivars may vary considerably in their responsiveness
to temperatures and durations of irradiance. This
interaction of temperature and duration of irradiance may

also be of importance under natural conditions. In geranium

production an earlier sowing provides only a small change in

the time of flowering compared to a later sowing (2). It
can be speculated for hybrid geraniums that flower
initiation may not occur until a developed plant is

exposed to enough long periods of high irradiance for a
sufficient number of nearly consecutive days. The number of

days may be reduced when the temperatures are higher.

Additional study of this hypothesis would be helpful in

 

 

 

76

growing spring geranium crops.
IRRADIANCE LEVELS:

The effects of different irradiance levels on the
inductive responses to continuous irradiation at 30°C were
studied in combination with the duration of treatment and
age of plants (Exp. 3). The results are presented in
Figures 2 and 3 and Table 2. Irradiance levels had a strong
influence on both time to anthesis and number of nodes to
the first inflorescence (Table 2). Significant interaction
of irradiance with the age of the plants and duration of
treatment is evident in the data.

The age of the plants at the beginning of treatment had
a great effect on the responses to the irradiance levels.

Eighteen-day-old plants showed no significant response to

the irradiance treatments. In 24-day-old plants,
._1 _’7

at.

irradiances of 240 ‘pmols m reduced time and nodes to
first inflorescence in 17, 50 and 100 percent of the
treatment populations from 6, 9, and 12 days of treatment.

In 30—day-old plants 3, 6, 9, and 12 days of irradiance of
-1 -0

‘-

240 pmols m reduced days and nodes to anthesis in 17, 50,
83, and 100 percent of the population. Increased age at the
beginning of treatment reduced the duration of treatment

required for induction. In 30-day-old plants an irradiance

-1 —2

of 120‘pmols m for 6, 9, and 12 days induced earlier

.' .'

flowering in 33, 50, and 50 percent of the population, but

in 24—day-old plants flowering time and nodes were decreased

-1 -2

only by the 12 day exposure to the 120 “umols m . No

responses were observed in treatments at 60 ‘pmols m ,

 

77

regardless of the age of the plants or the duration of
treatment. Generally, at lower irradiances and with younger
plants, longer periods of treatments were required.

The mean daily cumulative PPF has been highly
correlated to the days to flower in the previous section (I)
of this dissertation. The dependency of geraniums on
irradiance levels for induction and/or development of flower
primordia is apparent. Converting the treatment levels into
mean daily cumulative Photosynthetic Photon Flux (CPPF), 120

.. ....'T) ..
‘pmols 1m T of continuous irradiation provides 10.4 mol d 1

- -7 _
and 240 ‘pmols 1m b provides 20.4 mol d 1. In literature
”critical irradiance“ levels for flower induction have been
reported. Erickson et al. (11) proposed that a mean dialy
CPPF of above 9.0 was necessary for accelerated anthesis
when supplemental light was applied. The data of Tsujita
(23) indicated that a mean daily CPPF of near 10 was
required to induce flowers when supplemental light was
supplied. It is interesting here to note that with
continuous irradiance treatments for as short as 9 days at
10.4 mol d"1 applied to 30-day-old plants, decreased node
numbers and time to anthesis occurred in 50% of the

population. A response to a threshold or ”critical

irradiance” level is apparent.

78

SUMMARY AND CONCLUSIONS:

The work presented here, coupled with field observation
and information in the literature, has led to a number of
conclusions about flowering in hybrid geraniums.

1. Reproductive responses to high irradiance was
dependent on the age or maturity of the plants. Plants were
not responsive until they passed through a Juvenile phase
which in the cv. Ringo Scarlet lasted through about the
fourth leaf.

2. Irradiance levels influenced induction. Continuous

_ -8
irradiances of 2404pmols 1m ‘ decreased days and number of
nodes from sowing to anthesis when applied for 9 days at
30°C. Lower irradiances, 120‘pmols-1m—2, were effective
when the plants were treated for a duration of 12 or more
days.

3. Temperature also influenced induction. Days and
number of nodes from sowing to anthesis were decreased from

0
continuous treatment with temperatures of 30 C and

-1 —2

irradiances of 120 pmols m . Lower temperatures were
effective at higher irradiances or when given for longer
durations.

4. Treatment duratiOn was dependent on the irradiance
level and temperature as well as the maturity of the plants.
On 30-day-old plants durations as short as 6 days resulted
in some decrease in the number of days and nodes to
anthesis. Consistent early induction was obtained from 12

— -’?
days on continuous irradiation with 240 ‘pmols 1m 7.

'Decreased temperatures or irradiance levels increased the

79

duration of treatment necessary for early induction.

5. Cultivars differed in response. Although this
aspect was not studied here, field observations indicate
cultivar differences in the length of the juvenile phase,
the minimum irradiance needed for induction, and the
duration of the irradiance.

Large reduction in node numbers were associated with
small changes in the rates of leaf emergence, thus,
flowering responses to irradiance levels are the likely
result of inductive responses in addition to accelerated
growth rates.

HYPOTHESIS:

Since high irradiance levels were required to obtain
early flowering in a large percentage of the population,
since the response was not simply a growth response, and
since the number of nodes decreased along with earlier
flowering, it appears that the response may be called
photomorphogenic as defined by Wareing and Phillips (25) and
is high irradiance and temperature dependent.

Photosynthesis may also play a significant role in the

response. This response might best be termed a HIGH
IRRADIANCE INDUCTION RESPONSE (HIIR). Further
investigation, may show that the high irradiance is

necessary over a given daily period and for a given number
of consecutive days. If this were the case, a more
descriptive term might be ”photon—flux-periodism" or simply
"flux-periodism" in which a given irradiance could be

necessary for a given daily interval and for a certain

80

series of days to provide for induction and/or
differentiation of flowers. This phenomenon if more
thoroughly explored may assist in defining why a number of
plants demonstrate a given irradiance requirement for
flowering (5, 17, 19). Further identifying and understanding
this phenomenon may also help explain why shaded portions of
many plants, having relatively independent meristematic
regions, produce less flowers than those in full sun, and
why many long day plants require sufficient daily duration
of high irradiance to flower. The long day requirement may
be pa protraction of a high irradiance requirement in these
species.

The present and future observations made require an
orderly explanation of the phenomena surrounding flowering
in hybrid geraniums. A reasonable hypothesis for the early
flowering response in hybrid geraniums, based on present
literature, field observations. and the data presented here
might take the following form.

A high irradiance induction response exists in hybrid
geraniums. A cultivar dependent Juvenile phase must be
passed before floral induction in the meristem is possible.
A cultivar dependent series of nearly consecutive days of

sufficiently high irradiance and temperature over a long

enough daily period (flux period) are necessary to
provide both the photomorphogenic stimuli and the
photosynthates necessary for floral initiation and/or

development. Shaded and winter grown plants seldom receive

sufficient flux—periods to induce flowers, especially to

f
a

P..—

.lli' '

.Hlu

81

meristematic regions or leaves subtending those regions.
Upon removal of the reproductive stimuli a gradual
depletion of the flowering growth will occur until only

vegetative growth remains.

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83

Table 2. Analysis of variance for the effects of age, irradiance,
and duration of treatment on days and nodes to flower in
Pelargonium hortorum - Bailey 'Sprinter scarlet'.

 

 

 

 

Factor Degrees of Nodes Days.
Freedom F Sig. FZT F Sig. F

Age 2 19.01 *** 11.26 ***
Irradiance 2 31.86 *** 26.29 ***
Duration 4 15.19 *** 8.49 ***
Age x Irr. 4 5.76 *** 4,77 444
Age x Dur. 8 6.14 *** 4,71 444
Irr. x Dur. 8 7.80 *** 5,17 444
Age x Irr. x Dur. 16 2.08 ** 1.67 n.s.

 

2 Significance of the factor or the interaction of factors;

n.s. = not significant, **d-= 0.01 , ***°&= 0.001

84

Figure 1. Effects of duration of continuous irradiance
(240 umol s‘lm'z) on days and node number from
treatment to anthesis at 30°C in Pelargonium

hortorum - Bailey 'Ringo Dolly".

 

DAYS

85

3
CONTINUOUS

 

12
IRRADIANCE

 

Figure 2.

86

Mean effects of irradiance, plant age, and duration of

treatment at 30°C on days from treatment to anthesis

Z

and percent early induction in Pelargonium hortorum -

 

Bailey 'Sprinter Scarlet'.

(A) 3 days of continuous irradiance.
(B) 6 days of continuous irradiance.
(C) 9 days of continuous irradiance.
(D) 12 days of continuous irradiance.

2 number adjacent to plotted means indicate the percentage
of the treatment population to reach anthesis in 55 days
or less from the beginning of treatment.

DAY S 10 ANTH ESIS

200

150

100

150

100

 

87

374:2: .‘Fiko

 

 

 

 

 

 

 

17
-0— ll days old 50
—o-— 24 .. '-
—o—n -- .
3 6
F
0
I7
50
B
83
' :33
9 1 2 '
O. 120 240 ID 120 24'

IRRADIANCE (umol 5"m'2)

Figure 3.

88

Mean effects of irradiance, plant age, and duration of
treatment at 30°C on nodes from treatment to anthesis

and percent early induction2 in Pelargonium hortorum -

 

Bailey 'Sprinter Scarlet'.

(A) 3 days of continuous irradiance.
(B) 6 days of continuous irradiance.
(C) 9 days of continuous irradiance.
(D) 12 days of continuous irradiance.

2 number adjacent to plotted means indicate the percentage
of the treatment population to reach anthesis with the
emergence of 12 or less nodes from the beginning of
treatment.

NO DES TO ANTHESIS

IO

 

89

.-O- 1: days old
-o— 30

3

 

 

I 1 L
0 0
0
0 17
50
50
83

l L L

60 120 240

 

 

50

O)

 

50
67
100
1 2 100
60 120 240

IRRADIANCE (umol s"m")

j-l

90

LITERATURE CITED:

1. Armitage, A.M. 1982. Relationship of light intensity,
node number and leaf area to flowering time in hybrid
geranium. Abstracts, XXIst International Horticultural
Congress, Vol. II Abstract No. 1792.

2. Armitage, A.H. 1980. Effect of light and temperature on
physiological and morphological responses in Hybrid
Geraniums and Marigold. Ph.D. Thesis. Michigan State
University. pp. 65—70.

3. Armitage, A.M., and B.M. Hamilton. 1983. Scheduling
bedding plants for the Southeast using the "classical”
method of production. Bedding Plants, Inc. News XIV:
No. 12. pp. 4-6.

4. Armitage, A.M. and M.J. Tsuijita. 1979. The effect of
supplemental light source, illunination and quantum
flux density on the flowering of seed-propagated
geraniums. J. Hort. Sci. 54:195-198.

5. Asaoka, M., and R.D. Heins. 1982. Influence of
supplemental light and perforcing storage treatment on
the forcing or ’Red Garnette’ Rose as a pot plant.
J. Amer. Soc. Hort. Sci. 107(4):548-552.

6. Bethke, C.L. 1983, Geraniums in fifty days. Proceedings
of the XIV Bedding Plants Inc.. Conference-Grand Rapids,
MI.

7. Bodson, M. 1983. Effect of photoperiod and irradiance on
floral development of young plants of a semi-early and a
late cultivar of azalea. J. Amer. Soc. Hort. Sci.

108(3):382-386.

.Hu

1C).

11.

13.

14.

1.6-

91

Bodson, M., R.W. Hing, L.T. Evans, and G. Bernier. 1977.

The role of photosynthesis in flowering of the long—day
plant .Sigggig alga. Aust. J. Plant Physiol.
4:467-78.
Carpenter, W.J. and R.C. Rodrequez. 1971. Earlier
flowering of geranium cv. Carefree Scarlet by high
intensity light treatment. Hort. Sci. 6:206~207.
Conover, C.A., and R.T. Poole. Light acclimitization of
African violet. Hort. Sci. 16(11):92- 3.
Erickson, V.L., A. Armitage, W.H. Carlson, and R.M.
Miranda. 1980. The effect of cumulative
photosynthetically active radiation on the growth
and flowering of the seedling geranium, Eglgggggigm
Qgctgcgm Bailey. Hort. Sci. 15(6):815-817.
Friend,D.J.C. 1968. Photoperiodic response of Bgaggigg
ggmggstfiis cv. Ceres. Physiol. Plant. 21:990-1002.
Hartmann, R.M. 1966. A general hypothesis to interpret
“High Energy Phenomena’ of photomorphogenesis on the
basis of phytochrome. Photochem. and Photobiol. 5:349-
366.
Heins, R.D. 1979. Influence of temperatures on flower
development of geranium ’Sprinter Scarlet’from visible
bud to flower. BPI News. Dec. p.5.
Jacobs. G. 1983. Flower initiation and development
in nggggpggmgm gy. Red Sunset. J. Amer. Soc. Hort.
Sci. 108(1):32-35.
Mancinelli, A.L. and R.J. Downs. 1967. Inhibition of

flowering of Xanthium Egggylyagiggm Wallr. by

.IIL

17.

18.

19.

20.

’3’")
43.35.

Pr?
5.0--

24.

92

prolonged irradiation with Far Red. Plant Physiol. 42:
95—98.

Murneek, A. E. 1940. Length of day and temperature
effects in Egggggkig. Bot. Gaz. 102:269—279.

Norton, R.A. 1973. Stimulating earlier blooming of
seed geraniums with high intensity lighting. Flor.Rev.
153:25, 67-68.

Ouedado, R.M. and D.J. Friend. 1978. Participation
of photosynthesis in floral induction of the long day
plant Aggggllig ggygggig L. Plant Physiol. 2:802-806.
Schneider, M.J., H.A. Borthwick, and S. B. Hendricks.
1967. Effects of radiation on flowering of Hygggygmgg
Niggg. Amer. J. Bot. 54(10):1241-1249.

Shinozaki, M. 1974. Floral initiation and growth
of Eggcgigig all, a short-day plant, under continuous
light. Mechanisms of Regulation of Plant Growth, R.L.
Bieleski, A.R. Ferguson, M.M. Cresswell, eds.
Bulletin 12, The Royal Soc. of New Zealand, Wellington.
pp. 299-303.

Stefanis, S.P. and R.W. Langhans. 1982. Snapdragon
production with supplemental irradiation from high-
pressure sodium lamps. Hort. Sci. 17(4):601-603.
Tsujita, M.J. 1982. Supplemental high pressure sodium
lighting and night temperature effects on seed
geraniums. Can. J. Plant Sci. 62:149—153.

Vince-Prue, D. 1975. Photoperiodism in plants. McGraw-

Hill Berkshire, England.

93

Wareing, P.F. and l.D.J. Phillips. 1981. Growth and
differentiation in plants. Pergamon Press Elmsford,
New York.

White, J.W. 1983. Personal communication. Penn. State
Univ.

White, J.W. and P.E. Randolph. 1971. Geraniums from
seeds - flowering plants. "Geraniums" A Penn State
Manual, Editor J.W. Mastalerz. Pub. by Penn. Flower

Growers, Univ. Park, Pa., pp.196—211.

94

SECTION III

MODELING REPRODUCTIVE DEVELOPMENT

IN HYBRID GERANIUMS

95
ABSTRACT:

Functional relationships relating reproductive
responses to irradiance and day and night temperatures in
hybrid geraniums (Eglgggggigm bggtgggm - Bailey cv. ”Ringo
Scarlet’) were developed. Predictors for time from sowing
to the primary stages of initiation, visible bud and
anthesis, were formulated using multiple linear regression
analysis. Predictors of the interval between the primary
stages were fit to the differences of the means. Eighty-one
percent of the variation in days to initiation and visible
bud and up to 55% of the variation of days to anthesis were
accounted for by functions including the variables:
irradiance, day temperature, and night temperature. The
relative influence of these variables changed with advances
in stage of development. Irradiance was most significant at
the time of floral initiation and remained influential
through differentiation to visible bud. In the early stages
of growth increased day temperature accelerated the rate of
initiation and bud development. However, day temperature
was most influential in the development from visible bud to
anthesis. Night temperature effects were comparatively
small at all stages. No single function could effectively
predict the reproductive developmental responses without
consideration of plant age or stage of development. A
schematic representation of the relative influence of
irradiance and day and night temperatures at stages of
development is presented. A "Critical Irradiance” level was

necessary to accelerate flower initiation and bud

96

ce

[[1

development. Cuboid presentations of response surf
models graphically represented the four-dimensional dynamics

of the models.

97

INTRODUCTION:

In the production of hybrid geraniums, new
technological developments give rise to a need for
development of functional whole-plant models. The

developments include: the recognition of a high degree of
flowering responsiveness to light and temperature, the
availability of interactive computing facilities used in
greenhouse environmental control, and the widespread use of
supplemental lighting in crop production. Functionally
defined relationships can be useful in crop production to
predict responses and find optimum production conditions.

The functions can also provide clearer definitions of both

separate and interacting influences on physiological
responses.
In floriculture crops, predictive models which

simulate both separate and simultaneous changes in light and
temperature inputs are limited (1, 22). In hybrid seed
propagated geraniums, differences have been observed in the
reproductive responses to: irradiance (photosynthetic photon
flux) reported as PPF, measured in the 400-700 nm range) (5,
6, 10, 12, 16, 17, 18, 27, 33), day temperature (DT) (10,

11, 20, 33), and night temperature (NT) (15, 23, 31, 33).

Although many useful findings and temperature
recommendations for production have been reported (13,
18, 27. 30) little information is available on the

simultaneous influences of light and of day and night
temperatures. In addition stage of development has often

confounded the interpretation of the data (15, 16, 17, 18,

98

27, 30). Recent work (3, 11, 12, 20, 34) indicates that
plant maturity and the stage of reproductive development
must be considered in studying the responses of geraniums to
environmental factors.

It was the purpose of this study to develop
representative functional models of reproductive responses
to irradiance and day and night temperature during the

different stages of development in hybrid geraniums.

99
MATERIALS AND METHODS:

Similar culture practices were used in all phases of
the experiment. A peat-lite medium composed (by volume) of
50% fibrous peat, 25% vermiculite, and 25% perlite was used
both as a germination and growing medium. Seeds of the

cultivar ’Ringo Scarlet’ were sown into 5 cm square plastic

0

pots covered to a depth of 0.5 cm, and germinated at 22 +
o

2 C. Plants were watered as needed with a constant liquid

feed program using a water soluble fertilizer (20N - 8.7P -

16.7K) to provide 200 mg/l nitrogen at each watering. A day—
night cycle of 14 and 10 hours was used. Greenhouse

o o o o
temperatures were set at 17 + 2 C night and 21 + 2 C
days. Ten days after emergence the plants were transferred
to the growth chamber treatments. Lighting was provided
using cool white fluorescent lamps. The irradiances at the
upper surface of the leaf canopy were measured weekly using
a Li-Cor (Lincoln Nebraska) Li-185B meter and Li-19OSB
quantum sensor (measuring in the 400-700 nm range). The
distance from the lamps was adjusted weekly to maintain the
desired levels of irradiance. Temperature was checked daily
and varied by not more than +2OC. When plants were 37 days
old, a spray application of 1500 mg/l of (2-chloroethyl)
trimethylammonium chloride, chlormequat (CCC), was made to
simulate current production practices. At the age of 49

days, the plants were repotted into 9-cm square plastic pots

and grown pot-to-pot to simulate production spacing.

100

A 3-factor, 5-level central composite design was used
(Table 1). The ranges for the 3 factors were 50 - 450
-1 -2 o
‘pmols m for PPF and 10-30 C for day temperature (DT), (14
0

hours) and 10-30 C for night temperatures (NT) (10 hours).
Data were collected on 9 plants at seven day intervals
beginning with day 36 and extending to day 78 with

additional samplings when all 9 plants reached visible bud

and anthesis. On treatments 1 and 2, two week sampling
intervals were used because of the slow growth rate. Dates
of visible bud and anthesis were recorded. Visible bud was

defined as the day when buds reached a diameter of 0.5 cm or
larger. Anthesis was the day when a single petal began to
reflex to a horizontal position. Leaf area, fresh weight,
dry weight and plant height to the surface of the uppermost
leaf were recorded and are presented in another section.
Apical meristems were preserved in FAA (50% ethyl alcohol,
10% formaldehyde, 5% glacial acetic acid and 35% distilled
water), dehydrated with tertiary butyl alcohol and
infiltrated with paraffin (21). At a later date the
meristems were dissected and examined under a microscope for
evidence of reproductive differentiation. Reproductive
differentiation, i.e. flower, initiation, was considered to

--r

have occurred if development reached stage 3 as described by
Wetzstein and Armitage (31).

An analysis of variance, polynomial analysis, and
multiple regression analysis were performed using the

’Oneway’ and ’Regression’ subroutines of SPSS (26), (Tables

1 through 9). Linear, and linear—interaction terms along

101

with squared and cubic terms of irradiance and day and night
temperature were regressed on days to initiation, visible
bud and anthesis. Comparison of the simplest and the most
complex equations for each response was made. Step—wise
addition of all factors with a significant (0.05) impact on
the descriptiveness of the equation, in the presence of the
previously added factors, provided the simplest function. A
second equation was developed that included linear terms
forced into the function, followed by step-wise addition of
the remaining significant (0.05) terms. In a third
equation, all terms were forced into the equation.

Three dimensional surface and contour plots (Figure 1
through 3) were developed using the ’Surface 11’ plotting
system (28). Equations with linear terms forced-in were
used to develop the contoured surfaces. To unitize the
surface plots, the height of each surface was adjusted to a
percentage of the surface with the greatest range. A
schematic representation of the relative influence of the
treatment at each stage was developed considering the simple

correlations of each variable at each stage (Figure 4).

102
RESULTS AND DISCUSSION:

PPF levels were most influential on reproductive
development at all stages. Linear, quadratic, and cubic
terms (Table 3) most effectively describe variations in
response to PPF levels.

Day temperature variations produced significant linear
and quadratic initiation responses. In extending the
treatments to visible bud, only linear functions were
significant. To anthesis, linear, quadratic as well as
cubic DT terms were again significant. These changes in
responsiveness to DT during stages of growth are in support
of the findings of Heins (20) and Armitage (1).

Responses to night temperature were minimal compared
with OT and PPF. When treatments are extended to anthesis,
the highest significance of NT was observed.

In the regression analysis, PPF factors were
significantly negatively correlated with days to initiation
and visible bud and less highly correlated to anthesis
(Table 4 through 6). NT as a linear function is not
significantly correlated with days to initiation, visible
bud, or anthesis. NT interactions with PPF or DT yielded
significant correlations. Many significant responses to
changes in NT are reported in the literature (13, 23, 30).
In view of these reports it was decided that, despite the
low significance of linear NT 1n the treatments used, the
Ivariable would be submitted as one of the predictive
factors. The apparent description of some responses to NT

is presented in Figures 1 through 4. Future work may more

103

closely define these NT responses.

Regression coefficients and their significance in the
presence of other terms indicate the relative importance of
each variable at their respective stages of development
(Table 4 through 9). Although equations with all terms
forced in provided the highest correlation with the data,
equations with only linear terms forced in appear to provide
nearly as complete a definition of the response without an
overfit model. Equations with only significant terms added
into the model had fewer terms but were less traditional in
that higher order terms were included in the absence of the
lower order terms.

Primary prediction equations for the time from sowing
to initiation, visible bud and anthesis were determined from
raw data. Secondary equations, describing responses between
the primary stages were fitted to the interval between the
primary predictors using differences in treatment means.
They thus describe the physiological responses for the
intervals between the primary stages. The responses are
presented in Figure 4. As a result, the predictors can be
fitted together to form a unit which covers sequentially all
developmental stages.

Up to 81% of the variation in days to initiation and to
visible bud, and 50% to anthesis are accounted for in the
primary predictors. Up to 97% of the variation of the mean
difference from initiation to visible bud and up to 78% from
visible bud to anthesis are accounted for in the secondary

' predictors containing all factors. In predicting the time

104

from initiation, through visible bud, to anthesis. Up to
93% of the variance of the mean difference is accounted for.
This decrease in accountability is likely the result of
physiologically different responses at different stages.

The precision of these predictors appears to be within
the ranges presented by other authors. Erickson et al.
(18), under greenhouse conditions, achieved 41 to 64%
correlation of days to anthesis with cumulative PPF.
Armitage (1) found up to 99% description of photosynthetic
rates in geraniums as a quadratic polynomial of PPF when
held at a constant temperature. Ninety—three percent of the
variation in days from sowing to flower was described as a
function of mean daily PPF (10). And up to 97% of the
variation in days from visible bud to anthesis was described
using a second-order function of temperature under a given
light condition (1).

Predicted values deviate by less than 10% from the
observed means (Table 10). Limited and uniform distribution
of the residuals for the initiation and anthesis predictors
indicate adequacy of the equations. For anthesis, the
equation underestimates at PPF 50 and 250 when temperatures
are low and overestimates for PPF levels around 150 and
above 350 when temperatures are high. However, over the
full range of treatments, the anthesis predictor estimates
close to the observed responses. The models, thus, can be
considered to be a reliable representation of the responses
to light and temperature for the cultivar ’Ringo Scarlet’

when grown under constant environmental conditions.

105

In comparing the predicted values for anthesis to the
data in the literature, the model predicts values within 0
to 9 days of the reported results for similar cultivars.
Tsujita (30) flowered plants of the cultivar ’Encounter Red’

0 o
in 103 days at DT = 22 , NT = 17 , and ambient light

-—1 —2

(averaged about 175‘pmols m on a 14 hour basis). The

model predicts 101 days. With ambient plus supplemental

-1 -2

light (245 pmols m ), flowering occurred in 89 days. The

model predicts 93 days. Miranda (25), had a Feb. 23 sowing
o o

of ’Ringo Scarlet’ grown at DT = 22 and NT = 17 with an

estimated mean PPF, on a 14 hour basis, of near 175

-1 r2

pmols m which flowered in 95 days (predicted 96). With
NT variations, Konjoian and Tayama (23) observed a 17-day
increase in the time to flower from an 110C drop in NT. The
model predicts only a 9 day increase. White and Warrington
(33) have demonstrated no effect of NT at higher PPF levels;
this is in approximate agreement with the model.
Differences in OT can explain the differences observed in a
recent comparison of cultivars grown in Michigan and Georgia
(4). Many comparisons of the data indicate a close
correlation of the predicted values and observed trends.
Thus these models closely represent what happens in many
similar cultivars in response to a wide range of
environmental combinations.

Day temperature was significantly negatively correlated
to reproductive development at all stages. In the interval
between visible bud and anthesis, the highest simple

correlation to any of the variables was realized (r = _

106

0.6180). Also very important is the effect of high DT on
initiation. It appears that increasing temperature at or
near the time of initiation has the greatest influence on
reproductive development, especially when light levels are
low. The influence of DT on initiation is also reflected in
the visible bud and anthesis data. It appears that the
developmental influence of DT, relative to NT and
irradiance, increases to initiation and then decreases until
visible bud. After visible bud, DT becomes very important.
With increased irradiance levels, the influence of DT
decreases for all stages except visible bud to anthesis.
Interactions of DT with PPF and NT are discussed later.

Variations in irradiance were negatively correlated to
the rate of reproductive development (Table 4 through 9).
The highest simple correlation was in the interval from
initiation to visible bud (r = -0.5864). Time from sowing
to initiation was nearly as highly correlated (r = -0.5192).
These findings correspond to those previously observed (5,
20). The importance of high irradiance during early stages
of development have been reported (12).

The influence of irradiance can most accurately be
described in functions which include both lower and higher
order terms. The equations presented in Tables 6 through
11 emphasize the impact of PPF on the responses, while
Figures 1 through 4 clearly depict the degree of response to
each of the primary stages. In development to visible bud

an irradiance threshold is apparent in the rapid drop in
—1 —2

days around the irradiance of 200‘pmols m (Figure 4, B

107

and D). However, limited data from sowing to initiation did
not yield a function which reflects the presence of a
distinct threshold for that stage. The author suspects that
more detailed studies of initiation may demonstrate an
irradiance threshold response in the interval from sowing to

initiation and after the juvenile phase has been passed.

The "critical irradiance" appears to fall in the PPF range
-2 -1

from 150 to 250‘pmols m and it is suspected that the

critical irradiance level is cultivar dependent. The data

of Tsujita (30) indicates that a critical cumulative PPF,

equivalent to a 14-hour daily irradiance of near 200
-1 -2 o
Hmols m . is necessary to achieve flowering at DT 22
o
and NT = 17 . Erickson et al. (18) suggest that a mean daily
-1 -1 -2

PPF of greater than 9.0 mol d (175 pmols m for 14 hours)

is necessary for earlier induction. In previous work,
irradiance treatments have been confounded by daily
variations in PPF for periods before and after the critical
induction period. The present work provides data from
controlled, simulated conditions, separated by developmental
stages, and yields a clearer definition of the responses
during each stage.

Comparing the apparent threshold PPF levels for
reproductive development with a photosynthetic curve for

geraniums (5), we see that irradiance levels for initiation

are much lower than light saturation levels. According to

Armitage (5) the light saturation point is near a PPF of
-1 -2

1&mm1‘pmols m and the compensation point is near 70
-1 -2 o

lumols m at 25 C.

108

Irradiance alone does not fully explain the variance in
reproductive responses. Temperature influences the degree of
response. NT increases result in decreases in time to
visible bud and anthesis at low DT but has little effect
when DT is high. One can speculate that in this C-3 plant,
photosynthetic products are likely fully metabolized at
higher DTleaving little reserves for night growth. When DT
is low, photosynthates may accumulate during the day, and
during the night growth may continue. Thus, the effect of
the following NT may be important. The models demonstrate a
greater response to NT after cool days. White and
Warrington (34) found no significant impact on soluble
sugars and carbohydrates or on the rate of reproductive

development from varying NT when irradiance and DT were

high. In the work of Carpenter and Carlson (15), NT showed
0
a strong influence under moderate day temperatures (22-24 C)
—1 -2

and high irradiance (PPF of approximately 475‘pmols m ).
Day temperatures have a large influence on the
reproductive response to the initiation and to the visible
bud stages (Figures 1 and 2). Increased DT greatly
increases the rate of initiation at all irradiance levels,
but at lower irradiances the increase per degree is much
greater. The responses that occur prior to visible bud are
reflected and accumulate in the visible bud and anthesis
responses. However, in the interval from visible bud to
anthesis, no apparent interaction of light and temperature
exist. while DT had the greatest influence on the rate of

'development.

109

Night temperature was less significant than day
temperature or PPF in influencing reproductive responses.
In separating out NT effects, little influence was observed
over the broad range and combination of treatments studied
here. The interactions discussed previously indicate that
if DT is near optimum, NT may be reduced to low levels
without greatly affecting the rate of reproductive
development to the visible bud stage. After visible bud,
the relative influence of the NT becomes greater. If DT is
suboptimal for the irradiance, increases in NT have a
greater effect. Thus, the cooler the DT under high light,
the greater the effect of NT. These suggestions are in line
with the observations of White and Warrington (33).

Figure 5 provides a schematic overview of the relative
reproductive developmental influences of each of the three
factors studied. Note that both day and night temperature
are equally influential during germination (stage A).
During the vegatative juvenile phase (B) the influence of
PPF rises. At that stage, the growth rate becomes important
in developing sufficient leaves (3) to respond to the high
irradiance. Photosynthates produced are subject to
metabolism and thus the influence of temperature remains
high. Once juvenility is passed and the mature phases
begin, shifts in responsiveness occur, apparently
irrespective of photosynthetic needs. During the inductive
phase (C) irradiance levels become very critical. The need
for high irradiance persists to visible bud. This author

has observed, in a number of marginally inductive light

110

conditions, that very young buds fail to fully develop in
low irradiance. The aborted buds often remain on the stem,
while vegetative growth continues. In the flowering stage
(D) , the impact of light greatly declines while OT and NT
appear to be much more influential. When light is limited
during the flowering stage, flowering occurs but quality is
reduced. In the stages subsequent to first anthesis (E),
the author suspects a continued need of high irradiance for
Continued reproductive development in any given active
Meristem. After continued periods of growth in the shade,
geraniums continue to develop leaves but cease to flower
Llntil high irradiance is present (19). It is apparent that
E3 survival strategy exists. In the continued development of
the meristem, a balance of vegetative and reproductive
growth must exist. This balance is controlled in response
to the day and night temperatures and the light received by

the plant.

."f

I)

(“i

111

SUMMARY AND CONCLUS I ON:

The functional relationships found in these experiments
r-enoresent responses of a single cultivar to controlled
eerrvironmental conditions. These responses closely agree
vvi'th reported data from greenhouse studies with similar
chiltivars. The models are thus considered to be reasonably
r‘eepresentative of responses in the field and for similar
c:L41tivars. The functions are useful in distinguishing
FDFTysiological changes and the influence of each of the
Gerivironmental parameters over the developmental stages.
Ilr'radiance appears to be required at or above a critical
l-eevel before floral initiation occurs.

Day temperatures interact with irradiance to accelerate
i riitiation and development to visible bud. From visible bud
tic: anthesis temperature alone was of greatest significance.
ER "critical irradiance“ appears to be necessary for
i riduction and may be necessary through to visible bud. All
tlffie developmental stages are accelerated by increasing
tLGemperatures up to about 28°C. Night temperature appears to
EDGE important only when irradiance is high and DT is low.

From the data presented here it can be concluded that:

1. A single functional relationship describing
'"EECJroductive development cannot be employed. Consideration
"HJESt be given to the stage of development.

2. Separate functions which represent stages of

c"EE‘V'Ealopment can predict the observed responses.

112

3. Graphic representation of the functions can readily
be used to examine the physiological responses and observe
the effects of single and interacting factors.

4. The relative influences of irradiance and day and
night temperature vary with the stages of development
(Figure 5). A more thorough examination of the juvenile and
i nitiation stages should be made to more clearly describe
the responses.

5. Irradiance and DT, alone, and interacting, are very
i nfluential in reproductive development. NT appears to have
1 ess effect under most conditions. More extensive studies

C31: NT relative to DT are necessary to define the impact of

'\11" on reproductive development.

113

Table 1. Influence of PPF, day and night temperature on the reproductive

development of Pelargonium hortorum - Bailey 'Ringo Scarlet'.

 

 

 

 

 

Treatment Treatment Environment Average No. of Days to
number PPFu DTv NTw initiationx visible budy anthesisZ
1 50 20 20 93.0 154.9 190.4
2 150 15 15 80.5 112.2 155.0
3 150 25 15 56.0 71.4 91.4
4 150 15 25 72.8 117.2 141.9
5 150 25 25 53.8 72.8 88.6
6 250 20 20 61.5 75.6 114.8
7 250 10 20 74.5 93.6 130.1
8 250 30 20 43.2 59.7 78.2
9 250 20 10 61.1 80.0 121.7
10 250 20 30 - 72.7 118.8
11 350 15 15 58.3 87.4 134.6
12 350 25 15 44.3 64.2 82.2
13 350 15 25 69.0 78.8 120.4
14 350 25 25 47.8 69.2 80.3
15 450 20 20 50.2 65.3 113.4

 

photosynthetic photon flux in the 400-700 nm range.
day temperatures °C

night temperatures 0C

as observable under 10X disecting sc0pe

first observed with a diameter of near 0.5 cm
first emergence of a single petal of one floret

N~<><z<c

114

Table 2. Average effects of PPF, day and night temperature on the
reproductive development of Pelargonium hortorum -
Bailey 'Ringo Scarlet' over all treatments and interactions.

 

 

 

 

Treatment Average number of days to
EHV1r°nment Initiation Visible Bud Anthesis
PPFZ
50 93.0 154.9 190.4
150 63.8 88.7 110.0
250 62.1 73.7 109.7
350 55.4 73.9 97.7
450 50.2 65.3 113.4
DTY
10 74.5 93.6 130.1
15 70.0 96.6 137.2
20 62.2 79.4 114.1
25 51.0 69.5 85.4
30 43.2 59.7 78.2
NTX ’
10 62.2 79.6 121.7
15 59.5 81.7 106.3
20 64.5 86.0 114.4
25 64.5 79.6 100.2
30 60.0 63.7 118.8
Z photosynthetic photon flux . in the 400-700 nm range.

Y day temperature in 0C,3
X night temperature in C.

115

Table 3. Significance of the ploynomial contrasts of PPF, and day and
night temperature on reproductive responses in Pelargonium
hortorum - Bailey 'Ringo Scarlet'.

 

 

Response Significancez

 

 

Environmental
Factor initiation visible bud anthesis
PPF
B e twe en Leve 1 S 9:9,“): 7?** *3???
Linear 3'01“}: :‘n’n‘: :‘n‘n‘:
Qudratic 44 444 444
Cllb i C :1“): :1“. 5': 5’0“:
Deviations * * ***
Day Temperature
Between Levels *** *** ***
L ine ar :31“): 7'0‘0‘.’ faint
Quadratic * n.s. *
Cubic n.s. n.s. ***
Deviations n.s. n.s. ‘ n.s.
Night Temperature
Between Levels n.s. n.s. n.s.
Linear n.s. n.s. n.s.
Quadratic n.s. n.s. n.s.
Cubic n.s n.s. n.s.
Deviations n.s. n.s. ‘ n.s.

 

2 significance of the factor in describing the developmental response;
*A=0.0S, *f‘d= 0.01, *** “‘= 0.001, n.s. = not significant
Y Photosynthetic photon flux in the 400-700 nm range.

116

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Table 10. The difference in observed (Y) and predicted ($3 reproductive
responses of Pelargonium hortorum - Bailey 'Ringo Scarlet'.

 

 

 

 

 

 

Treatment Environment (Y - Y W
Y TX . . . . . . .
PPF DT N initiation ViSible bud antheSis
150 15 15 -o.3 4.5 6.8
150 25 15 3.7 -O.9 3.0
150 15 25 2.0 -3.9 10.4
150 25 25 1.5 0.9 5.7
250 20 20 -0.8 0.1 -2.5
250 10 20 0.2 -0.3 -7.0
250 30 20 -4.3 -0.1 -3.1
350 15 15 3.0 -0.9 5.3
350 25 15 1.7 3.1 3.1
350 15 25 -1.3 1.3 9.4
350 25 25 4.5 -l.8 4.8
2 Photosynthetic. phgton flux in the 1400-700 nm range.

Y day temperature in C.

X night temperature in C.

W differences from the observed (Y) and predicted (Y) values using
the function with the linear terms forced in.

123

Figure 1. Predicted days to initiation for Pelargonium hortorum -

 

Bailey 'Ringo Scarlet' as effected by PPF, day and night

temperature.
* DT = 15°C NT = 15°C
0 DT = 20°C NT = 20°C
A DT = 25°C NT = 25°C

124

 

 

 

  

 

 

30 0
S'1 m‘2 l

PPF [umol

200

125

Figure 2. Predicted days to visible bud for Pelargonium hortorum -

 

Bailey 'Ringo Scarlet' as effected by PPF, day and night

temperature.
* DT = 15°C NT = 15°C
0 DT = 20°C NT = 20°C
A DY = 25°C NT = 25°C

126

 

 

  
 

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can , com

 

127

I’igure 3. Predicted days to anthesis for Pelargonium hortorum -

 

Bailey 'Ringo Scarlet‘ as effected by PPF, day and night

temperature.
* DT = 15°C NT = 15°C
0 DT = 20°C NT = 20°C
= 25°C NT = 25°C

ADT

128

 

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129

Predicted reproductive responses at night temperature

16°CZ for Pelargonium hortorum - Bailey as effected by

 

irradiance, and day temperature at different stages of

development.

(A) Days
(B) Days
(C) Days
(D) Days
(E) Days
(F) Days

Z The shaded

from
from
from
from
from
from

sowing to floral initiation.
initiation to visible bud.
visible bud to anthesis.
sowing to visible bud.
initiation to anthesis.
sowing to anthesis.

areas represent predictions outside the
range of the experiment at night temperature 16°C
in the central composite design.

130

A . Days from sowing to floral initiation.

5050 H 150 . 250 350 45!

 

131

B . Days from initiation to visible bud.

5t? ~ .250 350 ’ ., 453°

 

132

C . Days from visible bud to anthesis.

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133

D . Days from sowing to visible bud.

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45° , - ~m~9°

 

PPF

E . Days from initiation to anthesis.

34° °°° 3°°° 35°...

 

135

F. Days from sowing to anthesis.

 

136

Figure 5. The relative influence of light, day and night temperatures
on reproductive development at different stages of

development in Pelargonium hortorum - Bailey 'Ringo Scarlet'.

 

(A) Germination.

(B) Vegetative (juvenile) phase.

(C) Initiation to visible bud phase.

(D) Visible bud to first anthesis phase.
(B) Equilibrium phase.

137

 

 

 

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138

LITERATURE CITED:

1.

Armitage, A.H. 1980. Effect of light and temperature
on physiological and morphological responses in Hybrid
Geraniums and Marigold. Ph.D. Thesis. Michigan State
University. pp. 65-70.

Armitage, A.M. 1982. Relationship of light intensity,
node number and leaf area to flowering time in hybrid
geranium. Abstracts, XXIst International Horticultural
Congress, Vol. II Abstract No. 1792.

Armitage, A.M. 1984. Effect of leaf number, leaf
position. and node number on flowering time in hybrid
geranium. J. Amer. Soc. Hort. Sci. 109 (2):233-23 .
Armitage, A.M., C.L. Bethke, and W.H. Carlson. 1981.
Greenhouse trials of Hybrid Geranium Production.
Bedding Plants Inc. News. October, pp. 1-2.

Armitage, A.M., W.H. Carlson, and J.A. Flore. 1980.
The effect of temperature and quantum flux density on
the morphology, physiology, and flowering of hybrid
geraniums. J. Amer. Soc. Hort. Sci. 106:643-647.
Armitage, A.M., and B.M. Hamilton. 1983. Scheduling
bedding plants for the Southeast using the "classical"
method of production. Bedding Plants Inc. News XIV:
No. 12. pp. 4-6.

Armitage, A.M. and M.J. Tsuijita. 19779. The effect
of supplemental light source, illumination and quantum
flux density on the flowering of seed-propogated

geraniums. J. Hort. Sci. 54:195-198.

139
Armitage, A.M., M.J. Tsujita, and R.M. Harney. 1978.
Effects of cycocel and high intensity lighting on
flowering of seed propogated geraniums. J. Hort. Sci.
53:147-149.
Armitage, A.M. and H.Y. Wetzstein. 1984. Influence of
light intensity on flower initiation and
differentiation in hybrid geranium. Hort. Sci. 19
(1):114-116.
Bethke, C.L. 1984. The effect of high irradiance and
temperature on flowering in Eglacgggigm x hgctgcgm -
Bailey. Hort. Sci. 19 (S):633. (Abstr.)
Bethke, C.L. 1983. Geranium flowering in 50 days with
temperature and light. Proceedings of the Sixteenth
International Bedding Plant Conference, Grand Rapids,
Michigan. October, 1983. pp.128—135.
Bethke, C.L. 1984. Super fast Geraniums. Greenhouse
Manager, Vol. 3 No. 4 pp.72-85.
Carlson, w.H. 1976. How growth retardants affect seed
geranium varieties. Michigan State University Agr.
Expt. Stat. Res. Rpt. 302.
Carpenter, W.J. 1974. High intensity lighting in the
Greenhouse. Res. Rpt. 255. Michigan State University
Agr. Expt. Stat. East Lansing.
Carpenter. W.J., and N.H. Carlson. 1970. The
influence of growth regulators and temperatures on
flowering of seed-propogated geraniums. Hort. Sci.

5:183—184.

140

Carpenter. W.J. and R.C. Rodrequez. 1971. Earlier
flowering of geranium cv. Carefree Scarlet by high
intensity light treatment. Hort. Sci. 6:206-207.
Craig, R. and D.E. Walker. 1963. The flowering of
;el§[gggigm hggtgfigm - Bailey seedlings as affected by
cumulative solar energy. Proc. Amer. Soc. Hort. Sci.
83:772-776.

Erickson, V.L., A. Armitage, N.H. Carlson, and R.M.
Miranda. 1980. The effect of cumulative
photosynthetically active radiation on the growth and
flowering of the seedling geranium, Eglgcgggigm x
Qgctgcum - Bailey. Hort. Sci. 15 (6):815-817.

Gourley, J.H., and G.T. Nightingale. 1922. The
effects of shading some horticultural plants. N.H.
Agr. Sta. Tech. Bul. 203:4-5.

Heins, R.D. 1979. Influence of temperatures on flower
development of geranium ’Sprinter Scarlet’ from visible
bud to flower. BPI News. December p.5.

Johansen, D.A. 1940. Plant microtechnigue. McGraw-
Hill. New York.

Harlsson. M.G. 1984. Influence of temperatures and
irradiance on growth and development of Qggysagthemgm
mggifgligg ’Bright Golden Anne”. MS Thesis Michigan
State University, East Lansing, Michigan.

Konjoian. P.S. and H.K Tayama. 1978. Production

schedules for seed geraniums. Ohio Flor. Assoc. Bul.

26.

27.

28.

'1'. C) .

31.

141

Lin, W.C. The effect of soil cooling and high intensity

supplementary lighting on flowering of Alstcgemeci

3.11

iRegina’. 1984. Hort. Sci. 19 (4):SlS—Slb.

Miranda. R.M. and N.H. Carlson. 1980. Effect of
timing and number of applications of chlormequat and
ancymidol on the growth and flowering of seed
geraniums. J. Amer. Soc. Hort. Sci. 105 (2):273-277.
Nie, N.H., C.H. Hull, J.G. Jenkins, K. Steinbrenner,
and D.H. Bent. 1875. Statistical Package for the
social sciences (SPSS). 2nd edition. McGraw-Hill Inc.,
New York.

Norton, R.A. 1973. Stimulating earlier blooming of
seed geraniums with high intensity lighting. Flor.
Rev. 1u3:25, 67-68.

Sampson. R.J. 1975. Surface 11 Graphics System
(revision one). No. 1 Series on Spacial Analysis,
Kansas Geological Survey, 1930 Ave. A, Campus West
Lawrence. Kansas.

Stefanis, S.P. and R.W. Langhans. 1982. Snapdragon
production with supplemental irradiation from high-
pressure sodium lamsp. Hort. Sci. 17 (4):bOl-603.
Tsujita, M.J. Supplemental high pressure sodium
lighting and night temperature effects on seed
geraniums. Can. J. Plant Sci. 62:149—153.

Wetzstein, H.Y. and A. Armitage. 1983. Inflorescence
and floral development in Eglaggggigg x hgctgfigm. J.

Amer. Soc. Hort. Sci. 108 (4):S93-SOO.

"V. "\
. .
&'& I

142

white, J.W. and P.E. Randolph. 1971. Geraniums from
seeds — Flowering plants. ”Geraniums” A Penn State
Manual Editor J.M. Mastalerz. Pub. by Penn. Flower
Growers University Park, PA pp.196—211.

White, J.W. and I.J. Warrington. 1984. Growth and
development responses of geranium to temperature, light
integral, C02, and Chlormequat. J. Amer. Soc. Hort.
Sci. 109 (S):728-73=.

white, J.W. and I.J. Warrington. 1984. Effects of
split-night temperature, light, and chlormequat on
growth and carbohydrate status of Eglaggggigm x

hortorum. J. Amer. Soc. Hort. Sci. 109 (4):458-463.

143

SECTION IV

MODELING VEGETATIVE DEVELOPMENT

IN HYBRID GERANIUMS

144

ABSTRACT:

Mathematical equations describing vegetative growth of
hybrid geraniums (Eglgggggigm ggctgcgg - Bailey) in
response to irradiance and day and night temperatures over
time were developed using response surface techniques. A
central composite design employing irradiances
(photosynthetic photon flux. PPF) from 50 to 450‘umols-1m—L
and day and night temperatures ranging from 100 to 300C,
with samplings of plants from 36 days old to anthesis.
provided data to develop predictons for total plant height,
leaf area, shoot fresh and dry weight.

Up to 57% of the variance in plant height and leaf
area, 55% in shoot fresh weight. and 47% in dry weight
could be explained using a function of time, irradiance,
with day and night temperatures. Only 10.6% of the
variance in percent dry weight could be described using

these variables.

Height was greatest at 20 C day and night temperatures.

Leaf area was greatest with high day and low night
temperatures. Fresh weight was most strongly influenced by
night temperature. However, the greatest fresh weight

occurred from the interaction of high night temperatures and
low day temperatures. Low day temperatures over time
yielded the greatest dry weight.

Height, leaf area. and fresh and dry weight increased

h

with increasing irradiance up to 150 ‘pmols m . Cuboid
presentations of the response surface models graphically

represent the five dimensions of the model.

145
INTRODUCTION:

In computerized greenhouse crop production, precise
definition of developmental responses to separate and
interacting environmental conditions has become increasingly
important. The need to optimize greenhouse crop
environments while minimizing inputs of total energy and
other resources require functional definitions of
responses to environmental factors. Modern computing
facilities allow the constant monitoring and control of the
greenhouse environment. By using predictive models and
these facilities we can continuously and simultaneously
monitor and alter the environment to assist in producing the
desired product in a given time. However, there are few
useful predictive models for floriculture crops which
simulate both separate and simultaneous changes in responses
to input variables (1, 13, 14).

In hybrid geraniums (Eglgggggigm Qgctgggm - Bailey)
many differences have been observed in vegetative responses
to irradiance (S, 7, 9, 11, 12. 13), day temperature (4, 13,
22) and night temperature (8, 15, 20, 21, 22). With the
ability to induce early flowering using high irradiance
treatments (6), the need to predict the time and conditions
required to produce a plant of a given marketable size is
apparent. Vegetative growth models are useful to predict
the size of a plant at a given age and to determine
container size and plant production density necessary to

obtain the desired product in the time allowed.

146
The purpose of this study was to develop representative
functional relationships for hybrid geraniums by describing
vegetative developmental responses to environmental factors
over time. These models may be useful in predicting

responses to the production environment.

147

MATERIALS AND METHODS

Similar culture practices were used in all phases of
the experiment. A peat—lite medium composed (by volume) of
50% fibrous peat, 25% vermiculite, and 25% perlite was used
both as a germination and growing medium. Seeds of the
cultivar ’Ringo Scarlet’ were sown into S-cm square plastic
pots covered to a depth of 0.5 cm, and germinated at 220 +
20C. Plants were watered as needed with a constant liquid
feed program using a water soluble fertilizer (20N - 8.7p -
16.7K) to provide 200 mg/l nitrogen at each watering. A
day-night cycle of 14 and 10 hours was used. Greenhouse

o o o

temperatures were maintained at 17 + 2 C night and 21 +
20C days. Ten days after emergence the plants were
transferred to the growth chamber treatments. Lighting was
provided using cool white fluorescent lamps. The
irradiances at the upper surface of the leaf canopy were
measured weekly using a Li-Cor (Lincoln Nebraska) Li-lSSB
meter and Li-190SB quantum sensor (measuring in the 400-700
nm range). The distance from the lamps was adjusted weekly
to maintain the desired levels of irradiance. Temperature
was checked daily and varied by not more than +20C. When
plants were 37 days old, a spray application of 1500 mg/l of
(2-chloroethyl) trimethylammonium chloride, chlormequat
(CCC), was made to simulate current production practices.
At the age of 49 days, the plants were repotted into 9-cm

square plastic pots and grown pot—to-pot to simulate

production spacing.

148

A E-factor. S—level central composite design was used
(Table 1). The ranges for the 3 factors were 50 - 450
‘umols-lm—L for PPF and 10—300C for day (DT) and night
temperatures (NT).

Data were collected on 9 plants in each treatment at
seven-day intervals beginning with day 36 and extending to
day 78. with additional samplings when the plants reached
visible bud and anthesis. On treatments 1 and 2 two week
sampling intervals were used because of the slow growth
rate. Dates of visible bud and anthesis were recorded.
Visible bud was defined as the day when buds reached a
diameter of 0.5 cm or larger. Anthesis was defined as the
day when a single petal began to reflex to a horizontal
position. Leaf area, shoot fresh weight, dry weight and

plant height to the surface of the uppermost leaf were

recorded and are presented in another section.

An analysis of variance, polynomial analysis, and
multiple regression analysis were performed using the
’Oneway’ and ’Regression’ subroutines of SPSS (18). The
results are reported in Table 1 through 9. Linear, and

linear interaction terms along with squared and cubic terms
of irradiance and day and night temperature were regressed
on days to initiation, visible bud, and anthesis.
Comparison of the simplest and the most complex equations
for each response was made. Step-wise addition of all
factors with a significant (0.05) impact on the
descriptiveness of the equation, in the presence of the

prev1ously added factors, provided the simplest function. A

149

second equation was developed that included linear terms
forced into the function, followed by step-wise addition of
the remaining significant (0.05) terms. In a third
equation, all terms were forced into the equation.
Three-dimensional surface and contour plots (Figure 1
through 3) were developed using the ”Surface 11’ plotting
system (19). Equations with linear terms forced in were
used to develop the contoured surfaces. To unitize the
surface plots, the relative height of each surface was
adjusted to a percentage of the surface with the greatest

range.

150
RESULTS AND DlSCUSSlON

PLANT HEIGHT:

Plant height is the product of two forms of
environmental responses: reproductive responses determining
the node number at which flowers are initiated (5), and
vegetative responses determining the size of the cells and
organs. This study is focused primarily on defining the
vegetative development, however some influence of the
environment on the reproductive development enters into
these results.

Looking at simple linear correlations, aside from time,
PPF showed the greatest simple correlation to plant height
while NT had the lowest (Table 4). Averages over all

sampling times (Table 2) indicate that the tallest plants

0

are produced at 20 C day and night and a PPF of 150
-1 —2

,pmols m . Both high and low day and night temperatures

and high irradiance produced the shortest plants.

Significant linear, quadratic and cubic responses to PPF are
present (Table 3). Responses to DT are best described using
quadratic and cubic terms and to NT using quadratic terms.
Over time, height changes are best described as a linear
function of time. However, at the median ages, some slowing
of growth occurred and thus higher order terms are
necessary. A leveling-off of the rate of increase in plant
height occurred at the time when the majority of the plants
.were in the early stages of reproductive development. At
this time, meristems subtending the reproductive apex became

dominant and resumed vegetative elongation. This has also

151

been suggested in the work of Merritt and kphl (lo).

Prediction equations which account for up to 57% of the
variation in plant height (Table 4) produce a dome shaped
(Figure 1) response surface because of the prevalence of
positive linear, negative quadratic, and cubic terms. The
interaction of irradiance and DT was negatively correlated
to height and had a significant influence on the accuracy of
the equation in describing the response.

In observing the description of the response as
presented in the prediction equations (Table 4 and Figure

_ ...."3

1), height increased to a PPF of about 225‘pmols 1m L and
then decreased as irradiance increased. The steepness of
the dome-shaped response to both DT and NT became greater as

the irradiance increased. This interaction of PPF with

temperature indicates that as irradiance increased above 225

....1 _.",'.‘

‘-

,umols m both low and high temperatures produce shorter
plants, while little effect is observed in the intermediate
temperature regions. Also at higher DT, flower initiation
occurs at a lower node number.

Night temperatures have been shown by many to influence
plant height (3, 8, 10, 15, 16, 20). Tsujita (20) obtained
taller plants in the cv. Encounter Red at a NT of 170C than
at 130C. Konjoian and Tayama (15) produced the tallest
plants at night temperatures of 16°C. At higher and lower
temperatures, the plants were shorter. Earlier flowering
occurred only at the higher temperatures. Carpenter and
Carlson (8) produced the tallest plants with day

0 o
'temperatures near 22-24 C and 10 C night temperatures. No

152

differences because of night temperatures were observed by
White and Warrington (22 in studying the effects of split
night temperatures. The range of temperatures studied in
that work was however not sufficient in the presence of the
other factors to show a NT response. Low PPF has been
shown to cause increases in total plant height in a number
of studies (11, 12, 20). Also, application of supplemental
irradiation has been shown to decrease plant height (7, 9,
20). In general, these observations correspond to those
used in the model presented here (Table 4).

While no data was taken, total plant height appears to
be influenced by petiole elongation until the canopy becomes
dense, and after that by shoot elongation and an increase in
internode length.

Overall, limiting plant height can be achieved by
reducing either day or night temperatures below 18°C.
Raising day temperatures above 240C will reduce plant height
as a result of decreasing node numbers and causing earlier
onset of reproductive development. When rapid reproductive
development is desired, higher temperatures may best be
employed to decrease plant height while decreasing the nodes
to the first flower and producing smaller plants. Where
time is not a factor and short plants are desired, one can
choose to reduce temperatures and reduce height.

Growth regulators and limited water supplies remain an

important tool in height control of geranium. It is

apparent that with the often excessive height development in

153

intermediate temperature regions, and the need to keep crop
timing on schedule, growth regulators may remain the single
most effective means of height control. Repeated
applications of chlormequat (CCC) can effectively be used to
manage plant height (17). It is suggested that if the model
predicts excessive height for a given growth regime, then
height may be more easily controlled by growth regulator
than by water, temperature, or irradiance manipulation.
Thus the application of the height predictor may be
effectively used to predict when growth regulators are
needed.

LEAF AREA:

Prediction equations describing up to 57% of the
variance in leaf area were developed (Table 5). In
comparing the linear influences, time provided the greatest

simple effects, while both PPF and NT exceeded DT. OT and NT

interactions also were influential. The greatest leaf area
—1 —2
is produced at irradiances of 150 pmols m with a DT of
o o o
25 C and a NT of 15 or 20 C (Table 1). Averaging the main

effects (Table 2) of temperature appear to present an

inaccurate representation of the simple effects because of

the strong interactions over the range of treatments
studied.
Over time, linear and higher~order terms are

significant in describing the development of the leaf
canopy. A general slowing in the development of the leaf
area corresponded to the time of reproductive development in

each treatment. This response is similar to that observed

154
for height. For a time, the plant is initiating and

developing floral primordia instead of leaf primorida.

A PPF of around 150‘umols-1m-L produces the greatest
leaf area. At PPFs below 150 pmols-lm-£, leaf areas
decrease.. but, as irradiance increases above 150
‘pmols‘lm—L leaf areas also decrease.

The effects of temperature on leaf area are more
complex. Linear and cubic terms are most effective in
describing DT responses. While linear terms are most
effective in describing simple NT responses (Table 3), the
interrelationship of DT with NT is more important in
influencing the leaf area. At high DT, NT responses have a
negative slope, while at low DT, NT responses yield a
positive slope. Thus, NT responses rotate while moving up
on the DT axis. Similarly, DT responses yield a negative
slope at low NT and a positive slope at high NT. In the
cuboid representations (Figure 2) it can be seen that
rotation for DT is greater than for NT. The rotations are
less at low irradiances. It may be that, if DT is
sufficient for the plants to metabolize photosynthetic
assimilates, the leaf area is not increased by increased
night temperature and in fact it is decreased. If DT is not
high enough for the plants to metabolize the photosynthetic
assimilates, then increases in NT produce an increase in
leaf area. Thus, DT increases produced increased leaf area
at low NT, while DT increases resulted in decreased leaf

area at high NT.

155
White and Warrington (22) showed that in the absence of
growth regulators high light significantly decreased leaf
area as did high OT and low NT. These data agree with the
trends of the model. In a study of Merritt and Kohl (16),
total leaf area increased in what appears to be a quadratic

form, over time. They also found that short irradiance

periods (9 hrs) decreased leaf area in some instances.

Leaf area has been shown to be important to flower
development. Armitage (2) suggests that a critical leaf
area is necessary to produce flowers. This is similar to

the hypothesis, described in Section III of this
dissertation, where it is shown that high irradiance must be
received by the plant after a juvenile phase is passed so
that initiation of flowers can occur.

FRESH WEIGHT:

Up to 55 percent of the variance in fresh weight can be
explained using factors of time, irradiance, and day and
night temperatures. Time had the highest simple correlation
to fresh weight (Table 6). NT had a simple negative
correlation. DT alone did not appear to influence fresh
weight. However, DT interacting with NT served to explain
some of the variance in the regression analysis.

Over time, fresh weight increased in a quadratic
manner. No leveling-off in the initiation to visible bud
stage was apparent as with height and leaf area. From these
data it can be implied that fresh weight continues to
increase because of the development of reproductive organs

during that phase.

156
-1 -2
Irradiances below 150‘umols m produced the lowest

average fresh weights (Table 2). Linear, quadratic and

cubic. terms are necessary to describe the response to PPF.

-1 -2
At PPFs above 150,pmols m little additional increase in
fresh weight occurred. The greatest fresh weight was
-1 —2
observed at an irradiance of 150 ‘pmols m . This

agrees with observations for leaf area and plant height.
When irradiances are low, it appears that the plant produces
more light harvesting facilities and therefore greater fresh
weight increases. In the literature, lower irradiance
levels have been reported to yield higher fresh weight (9,
10). Supplemental irradiance has been shown in some cases
to increase fresh weight where ambient light was limited
(11). Specific leaf weight is reported to increase with
increased irradiance (4).

Night temperatures have a significant impact on fresh
weight. Decreased night temperatures yield decreased fresh
weight, but over time, the accumulation of fresh weight at
low temperatures appears to result in final plant weights
near those achieved at a higher NT. White and Warrington
(22) have shown a build-up of carbohydrates in the form of
sugars and starch throughout the plant at low night
temperatures. This build—up may account for the weight
gain. Armitage (1) found that, as temperatures increased,
the specific leaf weight decreased as did the leaf
thickness.

Day temperature interacted with NT. As NT increased,

'fresh weight increased at a greater rate at low DT than at

157

high DT. High NT and low DT yielded the highest fresh
weight in young plants; however, in older plants the
interaction is less, presumably because of the build—up of
unused photosynthates and of lower respiration rates.

DRY WEIGHT:

Only 45 percent of the variance in dry weight can be

explained using factors of time, irradiance, and day and

night temperature. Time had the highest simple correlation
with dry weight (Table 8). PPF was negatively correlated
with dry weight. DT showed some influence over time and NT

appeared to have little impact.

Over time, dry weight increases could be explained
using linear and quadratic terms (Table 3). No leveling-off
of dry weight during the induction to visible bud stage was
observed. The interaction of DT over time shows that, as
time progressed, the build-up of dry weight was greater at
low DT than at high DT.

Irradiance responses appear to require terms up to and

_1 ,_-::'

including the cubic term. Irradiances below 150 pmols m
yielded reduced dry weights. The model predicts losses in
-1 —2
dry weight for irradiances below 100 ,pmols m and day
0 o

temperatures below 22 C with NT of 16 C or higher.
Armitage (1) indicated that the light compensation point at
DT of 25°C is 68‘umols—1mug. Thus, a loss of stored
carbohydrates would be expected at lower irradiances.
Apparently, as temperature increases respiration

increases, at the expense of accumulation of photosynthetic

products, resulting in a decrease in the rate of dry weight

158
gain at high DT. The hinged rising-plane response (Figure
4) indicates that build up of dry weight is greater at low
DT than at high DT regardless of NT.

The accumulation of carbohydrates, as described by
White and Warrington (22), is increased at low DT. Short
irradiance periods coupled with high temperatures have
resulted in lower shoot dry weight (16). It is suggested
that under long irradiance periods increases in dry weight
can be expected.

NT in this study had little effect on dry weight. In a
more detailed study focusing on the effects of NT over a
smaller range of treatment combinations, some effects may be
observed. NT was found to have a great influence on the
shoot fresh weight while it had little effect on shoot dry
weight. It is suggested that the total dry matter remains
relatively stable but the partitioning within the shoots, of
the photosynthetic assimilates, may change as a result of
changes in NT. While the total dry weight is about the same
over all night temperatures used, the fresh weight is higher
at high NT, and plants are taller at moderate NT and have
greater leaf areas at low NT.

DRY WEIGHT TO FRESH WEIGHT RATIO:

Low irradiances and high DT yielded the lowest percent
dry weight (Table 1). Linear and quadratic responses to PPF
and time were found (Table 2), while linear responses to DT
were also present. No significant responses to NT could be
identified. Some changes could be correlated to irradiance

(r = 0.1845) and DT (r = —0.14ss). Only a limited portion

III

159

”t-
3..

of the variance (r = 0.1064) could be defined in the
multiple linear regression analysis using the environmental
factors studied in this experiment. It is thus determined
that the predictor for the percent dry weight does not yield
sufficiently reliable values and that a more detailed study
may be necessary to develop a reliable predictor for the
percent dry weight. Also useful is the fact that with
increased irradiance there was an increase in the percentage
of dry matter. Over all the treatments, from 7.0 to 18.4

percent of the fresh weight was dry matter.

160

Table 1. Mean influence of PPF, day and night temperature on the
vegetative development of Pelargonium hortorum - Bailey
'Ringo Scarlet'.

 

 

 

 

 

Treatment Treagment Engironmgnt Plant Leaf Fresh Dry Percentage
number PPF" DT‘ NTn height area weight weight dry weight
1 50 20 20 8.8 98.6 5.0 0.43 7.0
2 150 15 15 9.5 139.1 14.0 3.37 12.6
3 150 25 15 10.8 163.7 15.3 2.77 10.1
4 150 15 25 9.1 150.7 14.0 2.92 12.8
5 150 25 25 9.3 176.3 13.3 2.53 11.2
6 250 20 20 10.4 139.6 13.0 3.02 16.9
7 250 10 20 8.2 134.0 15.0 2.99 15.6
8 250 30 20 7.9 101.8 9.8 1.48 12.0
9 250 20 10 7.8 101.8 11.8 2.08 17.2
10 250 20 30 - - - - -
11 350 15 15 8.1 111.5 13.3 3.45 14.5
12 350 25 15 9.4 165.1 15.0 2.62 11.6
13 350 15 25 7.9 105.1 12.9 2.95 21.6
14 350 25 25 8.2 170.0 12.5 1.98 10.9
15 450 20 20 8.6 139.9 12.4 2.71 15.5
2 photosynthetic photxni flux: in the 400-700 nm range.
Y day temperature in 0C.
X night temperature 0C.
W plant height to the top of the leaf canopy measured in cm.
V plant leaf area measured in cm .
U plant shoot fresh weight measured in grams.
T plant shoot dry weight measured in grams.
8 percentage of the shoot fresh weight that is dry weight.

161

 

 

 

 

Table 2. Average effects of PPF day and night temperature, and time
on the vegetative development of Pelargonium hortorum -
Bailey 'Ringo Scarlet' averaged over all treatment carbinations.
Treatment Plant Leaf Fresh Dry Percentage
environment height area weight weight dry weight
PPFU
50 8.8 84.0 5.0 0.50 7.0
150 9.7 156.3 14.2 2.90 11.7
250 9.6 129.4 12.8 2.75 16.1
350 8.4 134.3 13.4 2.76 14.8
450 8.6 139.9 12.4 2.71 15.5
DTT
10 8.2 134.0 15.2 2.99 15.6
15 8.7 126.3 13.6 3.15 15.4
20 9.7 129.9 11.9 2.63 15.7
25 9.4 167.9 14.0 2.48 10.9
30 7.9 101.8 9.7 1.48 12.0
NTS
10 7.8 100.4 11.8 2.10 17.2
15 9.5 146.1 14.4 3.00 12.1
20 9.6 131.4 12.1 2.60 15.1
25 8.6 144.8 13.2 2.60 14.3
30 - - - - -
Days R
35 3.8 32.6 1.9 0.22 11.5
49 5.7 69.7 3.9 0.71 11.5
56 6.5 98.2 5.5 0.60 11.3
63 '8.0 - 7.4 0.77 10.9
70 7.7 95.7 8.8 1.16 12.4
77 ‘ 9.7 126.5 11.3 1.35 12.0
84 10.6 170.2 13.6 1.62 15.8
91 11.1 199.6 16.9 2.11 12.6
anthesisQ 14-0 - 33.5 5.52 18.4
2 plant height to the top of the leaf canopy measured in cm.
Y leaf area measured in cm .
X plant shoot fresh weight measured in grams.
W plant shoot dry weight measured in grams.
V percentage of the shoot fresh weight that is dry weight.
U photosynthetiC’ fihq§1fl1 flux: in the 400-700 nm range.
T day temperature in C6
S night temperature in C.
R the sampling at 35 days is from treatment number 6 only.
0 samples were taken at anthesis and were not included in the analysis.

Table 3.

162

Significance of the polynomial contrasts of PPF, day and
night temperature and time on vegetative development in
Pelargaonium hortorum - Bailey 'Ringo Scarlet'.

 

 

. Plant Leaf Fresh Dr Percenta e
EnVironmental Factor . Y . Y W . g
height area weight weight dry weight
U
PPF
C v T I O I o
B e twe en Leve 1 8 far..- :::':" :.-7'::': :1“..- 93h":
Linear *S'fi’.‘ n . s . 7': n . S . *7?
Quadrat ic *7? n . S . 7':‘.'.'. 7': 71‘7’.‘
Cub 1C 71': :':~.'.':': 729:9.- :': n . S .
Deviations n.s. *** *** n.s. n.s.
Day Temperature
Be twe en Leve 1 S 71“}??? *7??? *7? *7“ 7':
Linear n.s. * n.s. *** **
Quadratic *** n.s. n.s. n.s. n.s.
Cubic * **° * n.s. n.s.
Deviations n.s. *** ** n.s. n.s.
Night Temperature
Between Levels 44* *** « n.s. n.s.
Linear n.s * n.s n.s. n.s.
Quadratic *** n.s. n.s. n.s. n.s.
Deviations n.s. ***‘ ** * *
Time
Between Levels *** *** *** *** n.s.
7: n .‘ as. C n 1“ 0:71:76.
Linear '*9 *‘9 *’* 4" n.s.
Quadratic n.s *** *** n.s. n.s.
Cubic n.s. n.s. n.s. n.s. n.s.
Quartic ** *** n.s. n.s. n.s.
Deviations *** n.s. n.s. n.s. n.s.

 

Z plant height to the top of the leaf canopy measured in cm.
Y leaf area measured in cmz.
X plant shoot weight measured in grams.

W plant shoot dry weight measured in grams.

V percentage of shoot fresh weitht that is dry weight.

in the 400-700 nm range.

T significance of the factor in describing the developmental
response; * ot= 0.05, *‘k aL= 0.01, *4"? d= 0.001, n.s.= not

UphoUmynthetic photon flux

significant.

163

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Figure 1. Plant height of Pelargonium hortorum - Bailey 'Ringo

 

Scarlet‘ as a function of time, PPF, day and night

temperature.

(a) 90 days old.
(b) 70 days old.
(c) 50 days old.

Or

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168

 

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169

 

Figure 2. Leaf area of Pelargonium hortorum - bailey 'Ringo
Scarlet' as a function of time, PPF, day and night

temperature.

(a) 90 days old.
(b) 70 days old.
(c) 50 days old.

170

(two) can Ion

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

171

Figure 3. Fresh weight of Pelargaonium hortorum - Bailey 'Ringo

 

Scarlet' as a function of time, PPF, day and night

temperature 0

(a) 90 days old.
(b) 70 days old.
(c) 50 days old.

172

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173

Figure 4. Dry weight of Pelargonium hortorum - Bailey 'Ringo

 

Scarlet' as a function of time, PPF, day and night

temperature.

(a) 90 days old.
(b) 70 days old.
(c) 50 days old.

174

[- 3.0
- 2.0
-1.0
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N
(B) IIIBI-M Ma

 

300

225

PPF

175
SUMMARY AND CONCLUSION

The application of response surface methods and the
central composite design to the study of whole plant
physiological responses in hybrid geraniums has resulted in
expansion of our knowledge on how geraniums respond to the
environment. Three dimensional response surface
presentations of complex functional relationships
graphically represent the responses.

The functional relationships employing environmental
inputs of irradiance, and day and night temperatures over
time can describe a large portion of the variance observed
in vegetative development. Over a wide range of
environmental conditions, up to 57% of the variance in plant
height and leaf area, 34% of the variance in shoot fresh
weight, and 45% of the variance in shoot dry weight, and
only 10.6% of the variance in the fresh weight to dry weight
ratio could be described.

Total plant height is greatly influenced by irradiance
and day and night temperatures. Day and night temperatures

- -9

of 18-240C and irradiance of 150‘pmols 1m h yielded the
tallest plants. The shortest plants were produced at high
irradiance and low or high day and night temperatures. The
model may be most effective in predicting when the
application of growth regulators is necessary to achieve the
desired height.

' Leaf area responses are very complex. Increases in

I:

leaf area occur with increased irradiance to about 150

«A'—

‘pmols m after which a steady decrease occurs. Day and

176
night temperatures interact in a reciprocal manner. High
day temperatures yield low leaf areas when NT is high but
when “NT is low the leaf area is high. At low day
temperatures and high NT leaf area is high, and low at low
NT. Over time, leaf area increases slow down at the time of
flower bud development. The lowest leaf area is produced at
high day and night temperatures. The highest leaf areas

occur when either day or night temperature is high and the

—1 —2

irradiance is in the lower regions (below 150 ‘pmols m ).
The complexity of the leaf area responses indicates that
partitioning of photosynthate is highly regulated to
optimize the light harvesting efficiency of the plant.

Fresh weight was most influenced by NT and irradiance
in addition to time. Differences in DT showed interactions

with differences in NT over time. Irradiances below 150

-1 --2

umols m yielded smaller plants. The highest fresh

-1 -—2

weights were observed at irradiances of 150 ‘pmols m . A

general leveling off of fresh weight occurred above 150

-1 -2

,pmols m . High NT increased fresh weight rapidly in the
early stages of development. However, in the later stages
of development, plants grown at low NT showed a continued
gain in fresh weight to levels at or above those grown at a
high NT.

Dry weight is most highly influenced by PPF and DT
aside from time. DT is negatively correlated to dry weight
and NT has little effect on dry weight. Over time, the
accumulation of dry weight is greater at low DT and high

- PPF .

177

The fresh weight to dry weight ratio was not consistent

enough for the development of a reliable predictor.
However, the data did indicate that, as irradiances
increased, the percent dry weight increased and, as the DT

increased, the percent of dry weight decreased.

In summary, irradiance and day and night temperatures
can serve as effective predictive variables for plant
height, leaf area and fresh and dry weight during
vegetative development of hybrid geraniums. Functional
relationships have been developed which provide useful
definitions of vegetative responses. These predictors can
be used to anticipate responses to any growth regime and
thus assist in the decisions necessary to grow the desired

product.

178

LITERATURE CITED:

1.

Armitage, A.H. 1980. Effect of light and temperature
on physiological and morphological responses in Hybrid
Geraniums and Marigold. Ph.D. Thesis. Michigan
State University, pp. 65-70.

Armitage, A.M. 1982. Relationship of light
intensity, node number and leaf area to flowering time
in hybrid geranium. Abstracts, XXIst International
Horticultural Congress, Vol II Abstract No. 1792.
Armitage, A.M. 1984. Effect of leaf number, leaf
position, and node number on flowering time in hybrid
geranium. J. Amer. Soc. Hort. Sci. 109 (2): 233-236.
Armitage, A.M., C.L. Bethke, and W.H. Carlson. 1981.
Greenhouse trials of Hybrid Geranium Production.
Bedding Plants Inc. News. October, pp. 1-2.

Bethke, C.L. 1984. The effect of high irradiance
and temperature on flowering in Eglacgggigm ggfitgcgm -
Bailey. Hort. Sci. 19 (5):633. (Abstr.)

Bethke, C.L. 1983. Geranium flowering in 50 days with
temperature and light. Proceedings of the Sixteenth
International Bedding Plant Conference, Grand Rapids.
Michigan. October, 1983. pp. 128-135.

Carpenter, W.J. 1974. High intensity lighting in the
Greenhouse. Res. Rpt. 255. Michigan State University
Agr. Expt. Stat. East Lansing.

Carpenter, W.J., and W.H. Carlson. 1970. The influence
of growth regulators and temperature on flowering of

seed—propagated geraniums. Hort. Science 5:183-184.

1C).

11.

H
1. 2‘

14.

16.

179

Carpenter, W.J. and R.C. Rodrequez. 1971. Earlier
flowering of geranium cv. Carefree Scarlet by high
intensity light treatment. Hort. Science 6:206-207.
Craig, R. and D.E. Walker. 1963. The flowering of
Eglgggggigm Dgrtgrgm - Bailey seedlings as affected by
cumulative solar energy. Proc. Amer. Soc. Hort. Sci.
3:772-776.

Erickson, V.A., A. Armitage, W.H. Carlson, and R.M.
Miranda. 1980. The effect of cumulative photosyn-
thetically active radiation on the growth and
flowering of the seedling geranium, Eglgcgggggm x
ugctgcgg Bailey. Hort. Sci. 15 (6):815-817.
Gourley, J.H., and G.T. Nightengale. 1922. The effects
of shading some horticultural plants. N.H. Agr. Sta.
Tech. Bul. 203:4-5.

Hopper, D.A. 1985. Investigation of modeling the growth
of the hybrid seed geranium. MS Thesis, Michigan State
University, East Lansing, Michigan.
Karlsson, M. G. 1964. Influence of temperature and
irradiance on growth and development of Qggygggtngggm
ggfiifgligm ’Bright Golden Anne’. MS Thesis Michigan
State University, East Lansing, Michigan.
Konjoian, P.S. and H.K. Tayama. 1978. Production
schedules for seed geraniums. Ohio Flor. Assoc. Bul.
579:1-2.
Merritt, R.H. and H.C. Hohl, Jr. 1985. Photoperiod and

soil temperature effects on crop productivity efficiency

and growth of seedling geraniums in the greenhouse. J.

180
Amer. Soc. Hort. Sci. 110(2):204-207.

17. Miranda, R.M. and W.H. Carlson. 1980. Effect of timing
and number of applications of chlormequat and ancymidol
on the growth and flowering of seed geraniums. J. Amer.
Soc. Hort. Sci. 105 (2):273-277.

18. Nie, N.H., C.H. Hull, J.G. Jenkins, K. Steinbrenner,
and D.H. Bent. 1975. Statistical Package for the
social sciences (SPSS), 2nd edition. McGraw—Hill Inc.,
New York.

19. Sampson, R.J. 1975. Surface 11 Graphics System (rev.
1). No. 1 Series on Spacial Analysis, Kansas Geological
Survey, 1930 Ave. A. Campus West Lawrence, Kansas.

20. Tsujita, M.J. Supplemental high pressure sodium light-
ing and night temperature effects on seed geraniums.
Can. J. Plant Sci. 62:149-153.

21. White, J.W. and I.J. Warrington 1984. Growth and
development responses of geranium to temperature, light
integral, Co , and Chlormequat. J. Amer. Soc. Hort. Sci.

o
109 (5):728-735.

22. White, J.W. and I.J. Warrington. 1984. Effects of split-
night temperature, light, and chlormequat on growth and
carbohydrate status of Eelgrgggigg x hortorum. J. Amer.

Soc. Hort. Sci. 109 (4):458-463.

181
SUMMARY AND CONCLUDING STATEMENTS

Much greater definition of the responses of hybrid
geraniums to light and temperature are available as a result
of this work. Vegetative and reproductive development in
response to: time, irradiance, day and night temperature,
and supplemental light was studied. Flower development in
response to supplemental light was found to be influenced by
irradiance level, temperature and duration of irradiance,
and age of the plants. Days to anthesis was more closely
correlated with mean daily irradiance than with total
cumulative irradiance. A threshold irradiance level of
at least 10 mol clay--1 was necessary for simultaneous
reductions in days to flower and number of nodes in ’Ringo
Scarlet’. A hypothesis attempting to explain the flower
induction response was presented.

Prediction equations were developed for days to
initiation, visible bud, and anthesis. Irradiance and day
temperature were shown to have the greatest influence on
flower initiation and development to visible bud, while
temperature alone was most contributory from visible bud to
anthesis. Three-dimensional response surface plots were
developed to represent the functions graphically.
Prediction equations were also developed for total plant
height, leaf area, and fresh and dry weights as functions of
time, irradiance, and day and night temperatures.

Much of the existing contradictory data and
unexplainable responses are explainable in the light of this

‘work. However, more questions can now be raised and the

182

need for more extensive work with hybrid seed—propogated

geraniums is evident.

 

 

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