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This is to certify that the
thesis entitled
Developing a Best Management Practice

For Catharanthus roseus (L.)

 

presented by

Grace M. Pietsch

has been accepted towards fulfillment
of the requirements for

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Major professor

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MSU In An Affirmative AotiorVEquol Opportunity lnotltwon
WM!

DEVELOPING A BEST MANAGEMENT PRACTICE
FOR CAIHARAMHUS ROSEUS (L.)

By

Grace M. Pietsch

A THESIS
Submitted to
Michigan State University

in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

1993

ABSTRACT
DEVELOPING A BEST MANAGEMENT PRACTICE
FOR CATHARANTHUS ROSEUS (1,.)

By

Grace M. Pietsch

Iron chlorosis and low temperatures are major problems when growing
Catharanthus roseus (L.). The cultural parameters that cause chlorosis were studied with
‘Grape Cooler’ vinca plants. Overwatcring and low temperatures created conditions
conducive to chlorosis. The effects of five day settings (15 to 35C), five night settings
(15 to 35C), and three light levels (50% shade and ambient and supplemental light) were
determined for vinca. Average daily temperature (ADT) was calculated for the 25
DTINT combinations. Curves for flower deve10pment rate and leaf unfolding rate were
derived from regression analysis of the data and compared to develop a prediction model.
The effect of DIF on intemode elongation was studied. Plants responded to the DIF
treatments. Flower size was measured and determined to be greatest at a day settings

of 25C and under supplemental light.

ACKNOWLEDGMENTS

I would like to thank the millions of people who have helped me through this thesis,
but there would not be enough room ifI did. Therefore, thanks. Special recognition
needs to go out to a few of the people who made this work possible and bearable.
My Major Professor, Dr. Carlson, who kept at me to finish everything. My other
boss, Dave Freville, who gave me all the time I needed to finish his work. My mom,
who convinced me that playing with flowers was a good career choice. Dr. Heins, to
whom I should have talked much sooner than two months before this was due. Sandy
Allen, who made life interesting and kept things in perspective. Tom Wallace, who
was a great sounding board for my ideas. Cara Wallace, my substitute mother, oops,
I mean my editor! Mark Yelanich, the computer genius of the lab and office mate.
Jim Brown-Faust, who knows everything except how to put things back where they
belong. Bill Argo, who gives good advice on how to write a thesis. And last, but
not least, my two best friends, Larry Neuhardt III and Elaine Davis, who kept me
sane throughout my two plus years of life in

Michigan.

iii

TABLE OF CONTENTS

List of Tables .................................................................................... vi
List of Figures ................................................................................... vii
Introduction ...................................................................................... 1
Literature Review ............................................................................... 2
Temperature ............................................................................ 6
Irradiance ................................................................................ l 1
Plant Modelling ........................................................................ 13
Objectives ............................................................................... 16
Literature Cited ................................................................................. 18
A Study of Iron Chlorosis in Catharanthus roseus L.
‘Grape Cooler’
Introduction ............................................................................. 23
Materials and Methods ................................................................ 24
Results ................................................................................... 26
Discussion ............................................................................... 27
Conclusion .............................................................................. 30
Tables .................................................................................... 31
Figures ................................................................................... 33
Literature Cited ........................................................................ 35

iv

The Effect of Day and Night Temperature and Light Level
on Catharanthus roseus L. ‘Grape Cooler’

Introduction ............................................................................. 36
Materials and Methods ................................................................ 38
Experiment 1 .................................................................. 38
Experiment 2 .................................................................. 38

Data analysis ............................. l ..................................... 39
Results ..................................... 40
Discussion .............................................................................. 42
Conclusion .............................................................................. 45
Tables .................................................................................... 47
Figures ................................................................................... 49
Literature Cited ........................................................................ 67
Appendix A .................................................................................... 69

10.

11.

LIST OF TABLES

Weekly chlorotic ratings - average number of

chlorotic leaves out of eight to ten per plant. Weeks 3, 4, and 5

are averaged over 144 plants. Weeks 6 and 7 are averaged

over 108 plants. Week 8 is averaged over 72 plants ........................... 31

Analysis of variencc for degree of chlorosis after
five weeks ............................................................................... 31

Tissue analysis of plant material from 36 plants after five
weeks of treatments ................................................................... 32

Condition of the vinca roots after five weeks
of treatments. Numbers are means of 36 plants. ................................. 32

Regression analysis for flower development rate
between years. Y = b0 + bl (ADT) ................................................ 46

Regression analysis for flower development rate
between 50% shade and ambient light levels.
Y=bo+b,(ADT)....... .............................................................. 46

Calculate values for degree day/leaf-pair and base
temperature using LUR regression lines ............................................. 47

Calculated days to unfold one leaf-pair based on LUR
regression lines ............................................................................ 47

Average fresh and dry weights for root and shoot at
time to flower under 50% shade ..................................................... 69

Average fresh and dry weights for root and shoot at
time to flower under ambient light .................................................. 70

Average fresh and dry weights for root and shoot at
time to flower under supplemental light ............................................ 71

vi

10.

LIST OF FIGURES

Average number of chlorotic leaves out of eight
to ten total after five weeks of treatments ......................................... 33

Curves of flower development rate and predicted days
to flower for 50% shade .............................................................. 48

Curves of flower development rate and predicted days
to flower for ambient light ........................................................... 51

Curves of flower development rate and predicted days
to flower for supplemental light ..................................................... 53

Curves of flower development rate and predicted days
to flower for combined shade and ambient treatments .......................... 55

Curves of leaf-pair unfolding rate for 50% shade and
ambient and supplemental light ...................................................... 57

Comparison of curves for predicted days to unfold
one leaf-pair and days to flower .................................................... 59

Curves of predicted days to flower using predicted days
to unfold one leaf-pair curve. The numbers above each
line represents the number of leaf-pairs already on the plant ................... 61

Comparison of intemode elongation under
(a)average day temperature, (b)averagc night
temperature, (c)constant temperature, and (d)DIF ............................... 63

Comparison of flower diameter under (a)average day

temperature, (b)averagc night temperature, and
(c)constant temperature ............................................................... 65

vii

INTRODUCTION

The bedding-plant industry in America was valued at $3.12 billion in 1992
(Agricultural Statistics Board, 1993). The most popular crops at that time included
petunias, geraniums, marigolds, impatiens, and pansies; however, many other crops are
becoming more popular as newer varieties and more cultural information are developed.
One of these crops, vinca, is increasing in popularity because of its heat and drought
resistance and new cultivars, which are more resistant to cooler temperatures (the Cooler
series), have larger flowers (the Tropicana series), and are winning awards in America
and Europe (the Pretty in series and Parasol). Because of the increased interest in this
plant, there is a need for cultural information to help growers avoid some of vinca’s
major problems: chlorosis, root rots, and slow growth. Some of these problems are
easier to solve than others, and many of them are linked.

Different environmental factors - light, temperature, and moisture - affect how
a plant will grow and mature. There is an optimum range under which normal growth
will occur. A maximum and minimum value exist for each factor and can be determined
by experimentation. Thus, crops can be grown to determine the optimal ranges for each
factor. Once the optimum range is determined, many of the cultural problems can be

eliminated and higher-quality plants can be produced.

LITERATURE REVIEW

Catharanthus roseus L. , or Madagascar vinca, is a perennial in its native habitat,
but is cultivated as an annual in cooler climates. Vinca is a member of the Apocynaceae,
or dogbane, family, which is characterized by milky sap. Until recently, Catharanthus
roseus was classified as Vmca rosea. It has often been confused with Vinca major (grave
myrtle) and Vinca minor (periwinkle), which are members of the same family. Both of
these vines are used extensively in landscaping.

Although vinca is thought to have originated in tropical America, it was first
discovered on the island of Madagascar. The southwestern part of Madagascar where
vinca grows wild receives 20 to 59 inches of precipitation yearly (Preston-Mafiam,
1991). The area has an annual average of 25 to 26C, although temperatures sometimes
reach as high as 40C during the summer months. Vinca thrives under these conditions,
which makes it an excellent plant for use in hot, dry climates.

Madagascar vinca can be recognized by its upright habit and simple, opposite
leaves, which are l to 2 inches long, entire, oblong, and glossy. The flowers are
quinquemerous salverform, 1 to 1 1/2 inches across, and found singly or in pairs in the
leaf axil. Flower color ranges from light purple to pink to white, with or without a red

”eye” (Bailey, 1976; Smith, 1977).

3
Bedding plants compose 35% of floriculture crops grown in the USA.

(Agricultural Statistics Board, 1993), and vinca accounts for up to 4% of the flatted
bedding-plant market, a number that is quickly increasing. It is ranked number three in
the southern states, popular there because of its heat and drought tolerance (Colgrave,
1992). It is also very pollution tolerant, making it a good crop for larger, warmer cities.

With increased production of vinca, production problems are perceived as being
more prevalent. Growers are having difficulty with the plants from germination onward.
Germination is divided into four stages, as defined by Koranski (1988). Stage one is the
most critieal of the four and lasts from sowing until radicle emergence, a period of one
to seven days; however, the same stage for vinca lasts three to five days. Germination
can be slowed or stopped when temperatures are kept too low. Carpenter and Boucher
(1991) found that optimum germination settings for three vinca cultivars were 25 to 30
or 35C. Carlson (1992) and Koranski and Laffe (1988) suggested germinating vinca at
32 to 35C for three days and then dropping the setting to 25 to 30C. Both temperature
recommendations are much higher than those for bedding plants such as geraniums (20
to 25C), marigolds (24 to 27C), impatiens (21 to 27C), petunias (21 to 27C), or begonias
(23 to 28C) (Karlovich and Sanford, 1992; Koranski and Laffe, 1988).

Many growers are having trouble once vinca reaches stage three - growth and
development of true leaves (Koranski and Laffe, 1988) - because plants grow very slowly
and often become diseased. Slow growth is frequently caused by low temperatures in
the greenhouse (Thomas and Gilbertz, 1992). When it is caused by a combination of low

temperatures and high moisture levels, conditions are optimum for many diseases such

4
as Rhizoctonia root rots, to which vinca is very susceptible (Bethke, unpublished 1990;

Harris'and Davies, 1978; Powell, 1989; Thomas and Gilbertz, 1992; Carlson, 1992).
The fungus is spread by splashing water; therefore, it thrives when plants are kept too
wet (Gildersleeve and Ocumpaugh, 1989). Since vinca’s native climate is dry, high
moisture levels in the soil may be detrimental.

In other plants, high moisture also affects the overall growth (de Graaf-van der
Zande, 1990). Petunias grown at three constant pF, or , values of 1.7 (wet), 2.5
(humid), and 4.0 (dry) showed increased height, fresh and dry weight, total leaf area,
number of buds and open flowers, and side shoots with buds as moisture levels
increased. Verbena grown at a constant pF value of 4.0 were shorter and took longer
to reach saleable stage than those grown under a variable watering strategy of saturation
and then dryness before resaturating. In both cases, plants grown at lower moisture
levels were not as tall or well branched as those grown at higher moisture levels.

This type of watering strategy can be used as a growth regulator to keep plants
shorter. The same watering strategy can be used for vinca. If plants are still too tall,
chemical growth regulators can be used. A-rest, B-nine, and Bonzi are registered for use
on vinca plugs, although leaf injury may occur with Bonzi. These three growth
regulators may also be used on vinca bedding-plant flats, as can Sumagic (Bailey, 1991).
Sumagic applied at low concentrations (0.5 to 3.0 ppm) before bud initiation may
decrease time to flower (Bridgen and Smith, 1988).

Another problem associated with vinca is chlorosis caused by iron deficiency.

Because iron is immobile in the plant, deficiency symptoms appear in new growth, while

5

older growth remains green. The first signs are interveinal chlorosis of younger leaves.
If the deficiency is not corrected, new leaves will be completely white, containing little
or no chlorophyll. As much as 80% of the total iron found in plants is in the chloroplast
and is utilized in heme pigments such as chlorophyll and Fe-S clusters or ferredoxins
(Mengel and Kirkby, 1987). Metabolic processes are severely limited when iron is
deficient. Without ferredoxins, which are an important component of the electron
transport chain as well as many other biological processes, and heme pigments, which
are the building blocks of chlorophyll, photosynthesis would not occur. Iron is classified
as a micronutrient because it is required by the plant in small quantities. Often iron
deficiency is correlated to high manganese content in the plant. These two elements
compete for uptake, and if Mn2+ is more available in the medium than Fe“, more Mn
will be incorporated. When pH is above 7, iron becomes insoluble and thus unavailable
to the plant. Acidic soils contain higher levels of soluble iron than do calcareous soils
(Mengel and Kirkby, 1987). Many field soils and potting media are mixed with lime to
raise the pH, which can induce chlorosis in susceptible plants.

Gildersleeve and Ocumpaugh (1989) used field soils with high CaCO3 content to
quantify iron chlorosis in subterranean clover. Clover was transplanted into modified
field soils and put under saturated conditions for two weeks. It was then rated for
chlorosis using a scale of 0 (no chlorosis) to 4 (dead). The field soils were analyzed to
determine their chemical composition; soils with clay content and high Ca and P
appeared to influence the expression of chlorosis, a conclusion corroborated by work

done on soybeans. Morris, Loeppert, and Moore (1990) showed a positive correlation

6

between soil clay content and chlorophyll concentration. In both cases, chlorophyll
concentration is highly correlated to iron chlorosis. While the experimental work on iron
was conducted on other crops, it is assumed that the same dynamics of iron activity occur

in vinca.

Temperature

Temperature influences the growth and maturation rates of plants. A general
growth-response curve shows that there are several important temperature set points that
determine how the plant will grow. The low temperature extreme at which plants do not
grow is called the base temperature. Plant growth increases until it reaches an optimum
temperature, beyond which it decreases rapidly until the plant dies at a maximum
temperature. Plant growth rate is linear as temperature increases from the base
temperature to the optimum temperature (Heins, 1990). The point at which each of these
temperatures occurs is different for each plant. The base temperature is defined as the
lowest temperature at which plants are not killed or damaged, but at which no growth
can be recorded. This temperature is being used more frequently to store plug trays until
nwded. Recent work at Michigan State University has shown that crops such as
geraniums, petunias, pansies (Iange, Heins, and Carlson, 1991), and alyssum (Heins and
Wallace, 1992) can be stored for up to four weeks at temperatures as low as DC with or
without light. Other crops such as impatiens (Lange, Heins, and Carlson, 1991),
marigolds (Heins and Lange, 1991), New Guinea impatiens, and vinca (Heins and

Wallace, 1992) need temperatures above 7.5C to be stored without injury. The latter

7

.plants were susceptible to chilling injury at cooler temperatures, whereas the former
could withstand much colder temperatures.

Heat delay occurs when plants are grown at temperatures above the optimum, but
below the maximum. Optima for Chrysanthemums and Easter lilies are 18C (Karlsson
et al. , 1989) and 24C (Heins, 1990), respectively. Above these temperatures, flowering
is delayed and plants do not mature as quickly. Bedding plants often have a higher
optimum temperature, although it varies as much as base temperature. The maximum
setting for geraniums is about 32C (Armitage, Carlson, Flore, 1981), while impatiens
do well at 30 and 35C (Lee, Barrett, and Nell, 1990).

Temperature affects plants in different ways. Average daily temperature (ADT)
influences leaf-unfolding rate, flower development rate, and plant growth or development
rate (Heins and Erwin, 1990; Hendricks, 1990; Moe and Heins, 1990). DIF, or the
difference between day (DT) and night temperature (NT), influences intemode length,
or plant height (Heins and Erwin, 1990; Moe and Heins, 1990). The response to DIF
is quantitative, varying from plant to plant, and is most effective during rapid growth
stages (Moe and Heins, 1990). DIF is quantified by DT - NT. When DT is higher than
NT, DIF is positive; when NT is higher than DT, DIF is negative. Intemode length
increases as DIF moves from negative to positive, which causes plant height to increase.
Most DIF work has been done on poinsettias, Chrysanthemums, and Easter lilies. A
predictive curve for poinsettia intemode elongation rate has been determined and allows
growers to adjust crop growth based on the rate of intemode elongation. By adjusting

DIF, the final length of each intemode can be predicted (Berghage and Heins, 1991).

8

Growers are able to monitor the rate of plant growth by using a technique called
graphical tracking (Heins and Carlson, 1990). The plants’ height is tracked from a
specified point in time, such as pinch date or transplant date, until they reach a
marketable stage. Minimum and maximum curves are graphed to show target minimum
and maximum heights over time. Graphical tracking is currently being used extensively
for poinsettias, mums, and lilies.

Plants grown at the same DIF will have similar heights at flower because of
similar intemode elongation (Erwin, Heins, and Karlsson, 1989; Heins and Erwin, 1990;
Hendricks, 1990), although they will mature at different rates because of different ADT.
Plants grow faster as ADT increases until the optimum temperature is achieved.

ADT affects time to flower; a higher ADT decreases the time, as demonstrated
in such diverse crops as Oxypetalum caeruleum, a cut flower ( Armitage et al. , 1990),
Impatiens wallerana, a bedding plant (Lee, Barrett, and Nell, 1990), and Lilium
longiflorum, a pot plant (Erwin, Heins, and Karlsson, 1989). Armitage, Carlson, and
Flore (1981) found that as temperature increased from 15 to 32C, days to flower for
geranium decreased almost linearly. For Chrysanthemums, a DTINT combination of
18/17C was the optimum for flower development (Karlsson et al., 1989). As
temperatures increased or decreased, time to flower increased. At low light levels,
combinations of 30C and 10 or 30C inhibited flowering even under short days. Optimum
temperature can be used to force a crop to flower in the shortest time.

The optimum temperature for days to flower may be different than that for flower

size. The optimum DTINT combination for flower size in Chrysanthemums was 20/ 15

9

to 16C (Karlsson et al. , 1989). The average temperature was the same as that for
flowering, but the day and night combination was different. Impatiens grown at a
DTINT regime of 24/ 18C had larger flowers than those grown at 30/24C or 35/30C
(Lee, Barrett, and Nell, 1990). Days to flower were not reported; therefore, a
comparison between days to flower and flower size cannot be made. . Geraniums,
however, had the largest flowers at 15C, whereas time to flower was optimum between
24 and 28C (Armitage, Carlson, and Flore, 1981; White and Warrington, 1988).

If the number of nodes needed for flowering is known, it can be used to
determine the time to flower, a concept that has been extensively studied. When plants
are placed under favorable flowering conditions, there is still vegetative growth before
they became reproductive (Holdsworth, 1956). Holdsworth tried to reduce leaf number
on Xanrhium and Eupatorium adenophorum using nutrition levels and daylength.
Starvation of the seedlings reduced leaf number significantly. Holdsworth concluded,
however, that the concept of minimum leaf number may not be viable. Collins and
Wilson (1974) examined the relationship between leaf stage and total number of nodes
present. Using the period from flower initiation to flower, they developed an equation
to define it: time = (number of leaves to be expanded)(rate of leaf expansion).
Armitage (1984) found that the critical leaf number for flowering in geraniums was six
to eight; the minimum node number for flowering was fifteen. The arrangement of the
six to eight leaves was critical. Leaving six leaves within the first eight nodes caused

no delay in flowering.

10
Leaf-unfolding rate (LUR) is a function of ADT and is defined as the time it takes

for one leaf to reach a predefined size at a given temperature. Karlsson, Heins, and
Erwin (1988) determined LUR for ‘Nellie White’ Easter lily to be linear as temperature
increased from 14 to 30C. A prediction curve could be developed to determine
temperature set points and to time crops. Hibiscus rosa-sinensis had a linear LUR
between 10 and 30C, which was accurate until the appearance of flower buds (Karlsson
et a1. , 1991). Poinsettias experienced a delay during which LUR was slower after plants
were pinched. After three leaves had unfolded, LUR could be predicted based upon a
prediction equation (Berghage, Heins, and Erwin, 1990). LUR decreased in all cases as
temperature increased in the defined ranges.

The effect of temperature on vinca has been studied recently because of the slow
growth observed at lower temperatures. Vinca grows best when temperature set-points
are higher than those for other plants. Carpenter and Boucher (1991) demonstrate this
with higher temperature set points for germination. Higher temperature set points for
growing vinca are gaining more publicity as more is learned about the plant. Set-point
recommendations for stage four of germination in 1991 were reported as 18 to 20C
(Scullin, 1991), whereas by the end of 1992, the recommendation for stage four was to
keep settings above 20C (Thomas and Gilbertz), although lower temperatures are still
reported (Dill, 1993). The literature has focused on temperatures nwded for growing
the crop. These studies have not looked at the effects of ADT on flowering, LUR, or

flower diameter, or the effects of DIF on plant height.

l 1
Irradiance

Light is the most important factor in plant growth. Many plant functions, such
as photosynthesis, phototropism, and photoperiodism, are controlled by the quantity and
quality of light the plant receives. These functions are grouped and described by the
term photomorphogenesis (Vince, 1960). Plant growth can be optimized in a greenhouse
situation if the effects of photomorphogenesis on greenhouse crops are known.

Supplemental lighting is one way of increasing the amount of light a plant
receives. As photosynthetic photon flux (PPF) increased, time to flower for
Chrysanthemums decreased and flower diameter increased (Karlsson et al., 1989).
Gagnon and Dansereau (1990) reported 4.3 times as many flowers on gerbera plants
grown under 16 hours of 90 pmol - m’2 - 3‘1 than on those grown under ambient light in
the fall. The light level also significantly increased height, width, and top dry weight
of gerberas grown in the fall.

Supplemental high-pressure sodium (l-IPS) lighting reduced time to flower and
increased fresh weight and stem length for snapdragons grown during the winter (Stefanis
and Langhans, 1982). Another cut-flower crop, Oxyperalum caeruleum, showed a
decrease in stem length as PPF increased, although stem diameter and number increased
(Armitage et al. , 1990). These differences in stem elongation under supplemental lights
may be due to species variations or lighting application.

Bedding plants show different responses to supplemental lights. Impatiens,
marigolds, petunias, and zinnias were affected differently when grown under one to four

weeks of supplemental lighting (Carpenter and Beck, 1973). Impatiens showed no

12
significant differences in fresh weight between lighted and unlighted plants regardless of

the treatment length. Marigolds, petunias, and zinnias, however, showed significant
differences in fresh weight when exposed to three or four weeks of continuous
supplemental lighting. Days to flower greatly decreased when all four bedding plants
were exposed to continuous supplemental lighting. Petunias flowered much faster when
exposed to 16 hours of supplemental lighting. In another study, petunias benefitted from
up to 10 days of continuous lighting at 83 umol . rn’2 . s" when it was applied to seedlings
at least five days after emergence (Graper, Healy, and Lang, 1990). Days to flower
were significantly decreased after transplant. When the irradiance level was increased
to 120 umol - m"- s’1 , petunia seedlings showed the greatest response.

Begonias responded like petunias when given supplemental light. Using a
procedure similar to that used for petunias, Graper and Healy (1990) found that 10 days
of continuous supplemental lighting applied up to 25 days after emergence significantly
decreased days to transplant in begonia seedlings. Higher light intensities also decreased
time to transplant. Kessler, Armitage, and Koranski (1990, 1991) achieved similar
results. They found that applications of 16 hours of light at 125 umol - m‘2 - s" for two
weeks had the greatest effect on time to flower. Exposing plants to longer periods of
supplemental lighting or higher or lower light levels was not as effective. Treatments
in this experiment were begun two weeks after seedling emergence, and seedlings were
lighted for 0, 2, 4, 6, or 8 weeks.

Geraniums have been studied for a different reason. Flower initiation is directly

related to light; therefore, much work has been done to determine the quantity and type

13
of light needed. Erickson et al. (1980) suggested that the relationship between days to

flower and photosynthetically active radiation (PAR) may be linear at low light levels
until a threshold level between 6.89 and 9.01 pE- m‘2 ~day‘ is reached. White and
Warrington ( 1988) determined that 975 mol - m'2 of light is nwded from emergence to
macrobud for earliest initiation and development of ‘Red Elite’ geraniums. Light did not
greatly affect geranium plants after the macrobud stage, a conclusion that is supported
by work done by Armitage, Carlson, and Flore (1981). They showed that bud
development was not significantly affected by light level. Development from seedling
to visible bud, however, was highly correlated to light level. Light levels below 30
uE - rn'2 - s" were not great enough to initiate visible bud.

The light source can be important in determining what kind of PAR the crops will
receive. Armitage and Tsujita (1979) studied the differences between high-pressure and
low-pressure sodium (HPS and LPS, respectively) lights and their effects on flower
initiation in geraniums. They found that LPS lamps did not promote flowering at any
intensity or duration, whereas HPS produced many of the results mentioned above. They

concluded that LPS lamps are not useful in producing geranium seedlings.

Plant Modelling

In this review, each factor has been considered as an individual occurrence, but
this is not the case. Light and temperature interact to create optimum environments for
plant growth. Many of the experiments noted have used both temperature and light to

determine the effects on plant growth. In the case of geraniums, light is important for

l4

flower initiation, while temperature influences the spwd of subsequent flower initiation
(Heins, 1979; White and Warrington, 1988). Flowering is delayed by extreme
temperatures, low light levels, or both. In chrysanthemums, high day or night
temperatures in combination with low light levels (less than 1. 8 mol - day" - m") prevented
flower initiation under short-day conditions (Karlsson et al. , 1989). By raising the light
level, flower initiation did occur, but plants took much longer to flower than at lower
temperatures. By looking at how temperature and light interact to affect plant growth
and flowering, models can be developed to predict a plant’s growth. These models can
then be used by growers to determine environmental parameters to best fit their
production practices. Because of the growth of computer technology and accessibility,
computers can be used to monitor and adjust the environmental conditions set by the
grower (Karlsson, Heins, and Carlson, 1983).

Graphical tracking is the simplest approach to plant modelling. It is already
being used to monitor plant growth and determine cultural practices such as applying
growth retardants or changing temperatures on crops like poinsettia, mums, and lilies
(Heins and Carlson, 1990). This type of modelling gives growers a window in which
to keep crops on schedule, assuming the timing of the crop is known. Graphical tracking
does not show the effects of different temperatures or light levels on the plants. It
merely tells a grower if the plants are on schedule or not.

A model for determining the window for a specific crop needs to be developed
before graphical tracking can be used for it. Different ways of approaching these models

can be found. Larson (1990) investigated a mechanistic approach to modelling. He

15

examined the use of integrated temperature, light, and daylength models in which each
component could be modeled separately or combined into one equation, which became
more complex as each component was included. This complex equation should be better
able to predict growth of a plant over time; however, as the model becomes more
complex, it is more likely to contain errors. Therefore, Larson suggested keeping the
model simple.

Karlsson, Heins, and Carlson (1983) looked at two different approaches to plant
modelling: photosynthetic maximization and whole-plant modelling. The photosynthetic
maximization model contrasts standard conditions with optimum ones for plant growth.
To determine optimum photosynthetic conditions, plants were grown at various
temperatures and CD; set points, and photosynthesis was measured. A regression
equation was calculated from the data and used to determine optimum temperature and
C02 concentration. This type of modelling takes advantage of the amount of light a plant
receives and optimizes temperatures and C02 concentrations to maximize photosynthesis
in the plant. Temperature and CO2 concentration are adjusted to compensate for light
levels. Whole-plant modelling looks at how plants grow under various day and night
temperature combinations and light regimes.

Determining which type of modelling to use depends on what will be done with
the information. Mechanistic models are good as computer models. The information for
mechanistic models can be developed or tested using either of the other two models.
Photosynthetic maximization models can be used if optimum photosynthetic conditions

can be maintained. This modelling technique is useful if only one crop is being grown.

l6
Whole-plant modelling gives information on crop growth under optimal and suboptimal

conditions. When many crops are grown together, it can be used to determine the best
conditions to satisfy most of the plant requirements. Scheduling can be timed by the
parameters that best fit all crops that will be grown together. This same technology

could be used on the production of vinca.

Objectives

Much has been accomplished in determining the best ways to produce crops like
petunias and geraniums; but new crops are appearing all the time and also need defined
production optimums. Studies must be conducted to determine the best way to grow
these crops. At the same time, many problems can be avoided or overcome by finding
the causes and correcting them before the damage is irreversible. The research in the

following papers was designed and executed with the following objectives:

1. to determine the environmental factors that induce iron chlorosis in

vinca,

2. to determine the effects of ADT on vinca flowering, LUR, and
flower diameter and use the data to develop a predictive model for

vinca flowering,

17

3. to determine the effects of DIF on intemode elongation and plant

height of vinca, and

4. to determine the effects of different light regimes on flowering and

plant growth of vinca.

Literature Cited

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. and M.J. Tsujita. 1979. The effect of supplemental light source,
illumination, and quantum flux density on the flowering of seed propagated
geraniums. J. Hort. Sci. 54(3):196-198.

Armitage, A.M., W.H. Carlson, and LA. Flore. 1981. The effect of temperature and
quantum flux density on the morphology, physiology, and flowering of hybrid
geraniums. J. Amer. Soc. Hort. Sci. 106(5):643-647.

Armitage, A.M., N.G. Seager, I.J. Warrington, D.H. Greer, and J.' Reyngoud. 1990.
Response of Oxypetalum caeruleum to irradiance, temperature, and photoperiod.
J. Amer. Soc. Hort. Sci. 115(6):910-914.

Bailey, DA. 1991. Chemical growth retardants for bedding plants. North Carolina
Flower Growers’ Bulletin 36(2): 1-6.

Bailey, L.H. 1976. Hortus third: a dictionary of plants cultivated in the United States
and Canada. MacMillan. New York, New York.

Berghage, R.D., R.D. Heins, and J.E. Erwin. 1990. Quantifying leaf unfolding in the
poinsettia. Acta Hort. 272:243-247.

Berghage, RD. and RD. Heins. 1991. Quantification of temperature effects on stem
elongation in poinsettias. J. Amer. Soc. Hort. Sci. 116(1):l4-18.

Bridgedon, M. and M. Smith. 1988. A sneak peek at Sumagic. Greenhouse Grower
6(11):70-7l.

Carlson, W. H. 1992. One to grow on: how to grow vinca. Greenhouse Grower
lO(2):16-l7.

Carpenter, W.J. and GR. Beck. 1973. High intensity supplementary lighting of
bedding plants after transplanting. HortScience 8(6):483-484.

18

l9

Carpenter, W.J. and J .F. Boucher. 1991. Germination and storage of vinca seed is
influenced by light, temperature, and relative humidity. Florida Agr. Expt. Sta.
J. Ser. (in press).

Colgave, C. 1992. Vinca beats bad press and grows in popularity. Greenhouse Product
News. 2(9):32.

Collins, W.J. and LB. Wilson. 1974. Node of flowering as an index of plant
development. Ann. Bot. 38:175-180.

de Graaf-van der Zande, M.Th. 1990. Watering strategies in bedding plant culture:
effect on plant growth and keeping quality. Acta Hort. 272:191-196.

Dill, RA. 1993. Powerhouses of the plug industry. Greenhouse Grower. 11(11):10-
15.

Erickson, V.L., A. Armitage, W.H. Carlson, and RM. Miranda. 1980. The effect of
cumulative photosynthetically active radiation on the growth and flowering of the
mdling geranium, Pelargonium x horrorum Bailey. HortScience 15 (6):815-817.

Erwin, J .E., R.D. Heins, and M.G. Karlsson. 1989. Thermomorphogenesis in Lilium
longiflorum. Amer. J. Bot. 6(1):47-52.

Gagnon, S. and B. Dansereau. 1990. Influence of light and photoperiod on growth and
development of gerbera. Acta Hort. 272: 145-151.

Gildersleeve, RR. and W.R. Ocumpaugh. 1989. Greenhouse evaluation of

subterranean clover species for susceptibility to iron-deficiency chlorosis. Crop
Sci. 29:949-951.

Gildersleeve, RR. and W.R. Ocumpaugh. 1989. A greenhouse technique for screening
Thfoliwn seedlings for iron-deficiency chlorosis. J. Plant Nutr. 12(10):ll41-
1152.

Graper, DP. and W. Healy. 1990. Synergistic acceleration of Begonia semperflorens
development using supplemental irradiance and soil heating. Acta Hort.
272:255-259.

Graper, D.F., W. Healy, and D. Lang. 1990. Supplemental irradiance control of
petunia seedling growth at specific stages of development. Acta Hort. 272:153-
157.

Harris, DC. and D.L. Davis. 1987. A disease of Vinca rosea caused by Rhizopus
stolomfer. Plant Path. 36:608-609.

20

Heins, RD. 1979. Influence of temperature on flower development of geranium
‘Sprinter Scarlet’ from visible bud to flower. BPI News (Dec):5.

Heins, RD. and J. Erwin. 1990. Understanding and applying DIF. Greenhouse
Grower 8(2):73-78.

Heins, RD. 1990. Choosing the best temperature for growth and flowering.
Greenhouse Grower 8(2):57-63.

Heins, RD. and W.H. Carlson. 1990. Understanding and applying graphical tracking.
Greenhouse Grower 8(5):73-80.

Heins, RD. and N. Lange. 1992. One temp can fit all. Greenhouse Grower.
10(4):30—36.

Heins, RD. and T.F. Wallace, Jr. 1992. Systems for storage of bedding-plant plugs.
Research report to Bedding Plants Foundation, Inc. (Dec).

Hendriks, L. 1990. Current status of environmental research on potted and bedding
plants in Europe with special emphasis on temperature. Acta Hort. 272:71-78.

Holdsworth, M. 1956. The concept of minimum leaf number. J. Expt. Bot. 7(21):395-
409.

Karlovich, P. and M. Sanford. 1992. Tips for successful germination. Greenhouse
Manager. 11(8):36-39.

Karlsson, M., R.D. Heins, and W.H. Carlson. 1983. Development of environmental
strategies based on plant growth models. Acta Hort. 147:153-160.

Karlsson, M.G., R.D. Heins, J.E. Erwin, R.D. Berghage, W.H. Carlson, and LA.
Biembaum. 1989. Irradiance and temperature effects on time of development
and flower size in chrysanthemum. Scientia Hort. 39:257-267.

Karlsson, M.G., R.D. Heins, J.O. Gerberick, and M.E. Hackmann. 1991. Temperature
driven leaf unfolding rate in Hibiscus rosa-senensis. Scientia Hort. 45:323-331.

Karlsson, M.G., R.D. Heins, and J.E. Erwin. 1988. Quantifying temperature-
controlled leaf unfolding rates in ‘Nellie White’ Easter lily. J. Amer. Soc. Hort.
Sci. 113(1):70-74.

Kessler, R., A.M. Armitage, and D. Koranski. 1990. Effect of supplemental light and
duration of exposure on growth and flowering of Begonia semperflorens. Acta
Hort. 272:137-144.

21

Kessler, R., A.M. Armitage, and BS Koranski. 1991. Acceleration of Begonia x
semperflorens-cultorum growth using supplemental irradiance. HortScience
26(3):258-260.

Koranski, D. and S. Laffe. 1988. How to grow 32 plug crops. GrowerTalks 52(8):59-
61.

Lange, N., R.D. Heins, and W. Carlson. 1991. Store plugs at low temperatures.
Greenhouse Grower 9(1):22-28.

Lange, N., R. Heins, and W. Carlson. 1991. Another look at storing plugs.
Greenhouse Grower 9(2): 18—24.

Larson, R.V. 1990. Plant growth modelling by light and temperature. Acta Hort.
272:235-242.

Lee, W., J .E. Barrett, and TA. Nell. 1990. High temperature effects on the growth
and flowering of Impatiens wallerana cultivars. Acta Hort. 272:121-127.

Mengel, K. and LA. Kirkby. 1987. Principles of plant nutrition. 4th ed. International
Potash Institute, Bern, Switzerland.

Moe, Roar, and RD. Heins. 1990. Control of plant morphogenesis and flowering by
light quality and temperature. Acta Hort. 272:81-89.

Morris, D.R., R.H. Loeppert, and TJ. Moore. 1990. Indigenous soil factors
influencing iron chlorosis of soybeans in calcareous soils. Soil Sci. Soc. Amer.
54:1329-1336.

Powell, C. 1989. Understanding and controlling black root rot disease. GrowerTalks
52(Mar):34-38.

Preston-Maflran, K. 1991. Madagascar: a natural history. Facts on File, New York,
New York.

Scullin, L. 1991. Production of annual vinca. Proc. Alabama Nurseryman’s Summer
Seminar, Alabama Nurseryman’s Association. Birmingham, Al.

Smith, J .P. 1977. Vascular plant families. Mad River Press, Inc., Eureka, California.

Stefanis, J .P. and R.W. Langhans. 1982. Snapdragon production with supplemental
irradiation from high pressure sodium lamps. HortScience 17(4):601-603.

22

Thomas, P.A. and DA. Gilbertz. 1992. Why can’t you grow quality vinca?
Greenhouse Manager 11(8):48-55.

Agriculture Statistics Board. 1993. Floriculture crops: 1992 Summary. USDA, Natl.
Agr. Stat. Serv., Agr. Stat. Board, Washington, DC.

Vince, D. 1960. Photomorphogenesis in plant stems. Biol. Rev. 39:506-536.
White, J.W. and LI. Warrington. 1988. Temperature and light integral effects on

growth and flowering of hybrid geraniums. J. Amer. Soc. Hort. Sci.
1 13(3):354-359.

A Study of Iron Chlorosis in Catharanthus roseus (L.) ‘Grape Cooler’

A study of Iron Chlorosis in

catharanthus roseus tn.) ‘Grapo Coolor'

Introduction

Catharanthus roseus L. , or Madagascar vinca, has grown in popularity as a
bedding plant because of its heat and drought tolerance. With increased production,
vinca susceptibility to iron chlorosis caused by cultural parameters such as medium pH,
water content, and temperature is a common grower concern (Scullin, 1991; Thomas and
Gilbertz, 1992).

Iron is taken up by the plant in the reduced, or Fe“, form. As pH increases
from 4 to 7, iron is oxidized to the Fe3+ state. Above a pH of 7.4, iron reacts with
hydroxyl groups and forms insoluble precipitates (Mengel and Kirkby, 1987). A peat-
based medium pH of 5.5 to 6.5 is usually recommended to ensure that all elements,
including iron, are available to the plant.

The amount of water in the medium influences air space, which influences the
oxygen concentration. As oxygen concentration decreases, favoring anaerobic
conditions, iron will be in a reduced state (Fe“) and more available to the plant (Mengel
and Kirkby, 1987). Moisture content also affects vinca growth. Vinca is more
susceptible to chlorosis and root rot disease when overwatered (Thomas and Gilbertz,

1992).

23

24

The rate of nutrient uptake is regulated by metabolic processes and, therefore,
decreases as plant growth decreases. Thus, the degree of chlorosis exhibited is more
severe if the temperature is below the optimum range. Vinca growth is slowed and
stunted below 20C. The objective of this research was to determine how each of these
factors (medium pH, moisture content, and temperature) influences the degree of

chlorosis expressed.

Materials and Methods

‘Grape Cooler’ vinca seeds were sown in 288 plug trays filled with Metro Mix
360 (Grace Sierra Co.,Allentown, Pa.) and covered with vermiculite 11 Jan. 1993.
Trays were covered with clear plastic and placed at 25C in a greenhouse and allowed to
germinate.

A 7:3 peat:perlite (Fisons Canadian Sphagnum Moss Peat) medium was mixed
and divided into thirds. To provide three different pH ranges, one-third received 3.0
kg/m3 dolomitic lime and 1.8 kg/m3 gypsum, one-third received 5.2 kg/m3 dolomitic lime
and 1.2 kg/m3 gypsum, and one-third received 5.2 kg/m3 dolomitic lime, 1.2 kg/m3
hydrated lime, and 0.6 kg/m3 gypsum. All other nutrients were added to each medium
at rates of 0.6 kg/m3 Ca(NO3)2, 0.6 kg/m3 KNO3, 0.3 kg/m3 MgSO4, and 1.2 kg/m3
superphosphate with trace elements provided by Micromax (Grace Sierra Co. , Allentown,
Pa.) at 0.7 kg/m’. These lime levels were chosen to bring the media pH into ranges of
4.0 to 5.0, 5.5 to 6.5, and 7.0 to 8.0, respectively. The initial pH of the three media

were 4.2, 4.35, and 4.9, respectively. To monitor changes in media pH and EC, media

25
samples for pH and electrical conductivity (EC) readings were collected from plants

under the same water treatments, but not from plants used for determining the degree of
chlorosis or other determinations. Each medium was within 0.4 pH units of the target
ranges by the second week of the experiment.

Water treatments were based on the percentage of available water. Several cell
packs with rooted seedlings were watered to container capacity, weighed, allowed to dry
to the wilting point, and reweighed. The difference between these weights was the
amount of water available to the plants; it was multiplied by 50% , 75%, and 100% and
then added to the weight at the wilting point to determine the final weights for each
treatment. Water (28 to 80 ml) was added to the cell packs every 24 hours to keep them
at the specified weights.

Growth chambers were set at 15, 20, and 25C, and lighting was provided by cool-
white florescent lamps for 12 hours per day at 100 umol-s" - rn‘2 (4.3 mol -day" ~m’2).
Each chamber held up to four 1.2- x 0.8-meter movable benches.

Seedlings were sorted and transplanted into 32-cell flats filled with one of the
three premixed media on 25 Feb. 1993. Treatments were randomly assigned to each
group of four cell packs, and plants were moved to the appropriate growth chamber.
Treatments were replicated three times with a block represented by the plants placed on
one bench. The experimental design used was a split-split plot with the main plot split
for temperature; the second, for water treatment. Plants were watered every 24 hours

with either tap or distilled water to maintain the pH of the media based on the pH tests

26

of the extra plants. Each cell in all treatments was fertilized after four weeks with 7 ml
of KNO, and NI-LNO3 at 300 ppm N and K. ‘

Plants were evaluated weekly, and the number of chlorotic leaves was counted.
A leaf was considered chlorotic if 50% or more of the leaf was chlorotic. One cell pack
per treatment was removed after five weeks. Medium pH and EC were tested for each
cell, and the condition of individual plant roots and shoots was evaluated to correlate
with the degree of chlorosis. Analysis of variance was performed on the data for degree
of chlorosis in the shoot. Tissue samples were collected and dried, and two samples
were sent to a lab for spectrum analysis. These samples were chosen to correspond with

the plants that exhibited either the most or the least chlorosis.

Results

Plants began to show signs of chlorosis within the first two weeks and became
more chlorotic as growth continued through the sixth week (Table 1). There were no
differences between the pH treatments (Table 2). Plants at the low pH range showed the
same number of chlorotic leaves as those kept at the medium and high pH levels. Media
pH had no effect regardless of water or temperature treatment. Therefore, pH was
combined across water and temperature treatments.

The degree of chlorosis was affected primarily by the amount of water applied,
which was most apparent at 25 C (Fig. 1). There was more chlorosis when plants were
kept at 100% available water than at 50%. As temperatures decreased, the differences

in degree of chlorosis between water treatments were not as great, but the treatment with

27
100% available water still showed the most chlorosis; plants became very chlorotic and

died, presumably because of root—rot pathogens. Fungus gnats and algae were present
mainly on the high moisture content media. Plants at 50% available water had the least
degree of chlorosis. Chlorosis on plants at 75 % available water varied, affecting 0% to
100% of the leaves. Cell moisture fluctuated significantly because of air currents in the
growth chambers, causing some cells to dry more than others.

Plants held at 15C grew slower, and the bottom leaves turned yellow. Chlorosis
was most severe at this temperature. As the air setting increased from 15 to 25C,
chlorosis decreased. At 25C, chlorosis became a function of water treatment. Leaf size
and number were greater at 25C than at 20 or 15C, with the largest plants at 50%
available water.

Since pH treatments were not significantly different, tissue samples were
combined across media pH for water and temperature treatments. Tissue samples from
plants with either the least or most chlorosis were anayzed for elemental concentration.
The chlorotic tissue had much lower concentrations of all elements tested (Table 3); zinc,
manganese, iron, and aluminum concentrations were more than 50% lower in the

chlorotic tissue.

Discussion
Medium pH is important in determining nutrient availability. The recommended
pH range is 5.5 to 6.5 for peat-based media. The media pH treatments in this study

were designed to be above, at, or below this range. High pH in the medium has been

28

cited as a cause of chlorosis in vinca (Scullin, 1991; Thomas and Gilbertz, 1992). The
source of iron in the media affects iron availability to the plant. Mattis and Hershey
(1992) demonstrated that vinca develops abnormal roots when grown in nutrient solutions
containing iron-EDTA or iron-DTPA fertilizers. In this experiment, micronutrients were
provided in a nonchelated form. The lack of pH effect could be due to the initial pH
being below the desired levels. Media pH levels did not reach desired levels until after
the second week of the experiment, but when samples were collected after the fifth week,
pH levels were already at desired levels, and still there were no differences in leaf
chlorosis.

The amount of water in the container was the prime factor that determined the
degree of chlorosis, which was exacerbated by cool temperatures. Vinca was most
chlorotic in media kept at container capacity and low temperatures. Under situations in
which the medium approaches anaerobic conditions, such as when the plants are at
container capacity, iron is in the reduced state and should be more readily available
(Mengel and Kirkby, 1987).

If iron is available to the plant but is not being taken up, something other than
availability must induce chlorosis. If chlorosis cannot be explained by availability
factors, something may be inhibiting root uptake. Factors that influence ion uptake
include nutrient availability, competitive inhibition, efficiency of roots in taking up
nutrients, and physiology of roots (Moore, 1977).

Ions that compete with iron for uptake include Mn, Cu, Zn, and other divalent

heavy metals. If any of these competes with iron for uptake, it’s concentration increase

29

should be revealed by tissue analysis. Zn and Mn show significant decreases in tissue
concentrations, and Cu shows some decrease (Table 3). Therefore, iron uptake is not
competitively inhibited by uptake of the elements listed.

Using iron and other nutrients, efficiency of uptake has been studied (Hershey,
1991). Plants are considered efficient if they are able to lower the pH of the surrounding
medium to take up the nutrient in question. In this experiment, the cultural methods that
influence chlorosis were studied, not the mechanisms by which nutrients are taken up;
therefore, there are no data showing whether the plants are efficient in iron uptake. The
lower amounts of other nutrients in chlorotic tissue could mean that uptake of more than
just iron is limited and may indicate that the problem is not caused by inefficiency of the
roots.

Deformed roots that cannot take up nutrients could possibly cause chlorosis.
Plants grown at high water concentrations had little or no root growth after five weeks;
whereas those grown at low water concentrations showed normal root growth (Table 4).
The patterns of root growth seem to follow closely the degree of chlorosis, which could
be an indication that the physiological state of the roots may be the main factor that
causes inhibition of nutrient uptake. The lower concentrations of all elements in the
chlorotic plants support this conclusion. Root physiology and it’s effect on ion uptake

in vinca needs to be studied further.

30

Conclusion

Chlorosis in vinea has been attributed to iron deficiency. In this experiment, the
concentration of all elements in chlorotic plants was lower than that in green plants. The
chlorosis may not be just an iron deficiency, but could be due to the physiological state
of the roots under adverse conditions, which include low temperatures and high moisture
levels in the medium. Avoiding these conditions by raising greenhouse temperatures and

allowth the plants to dry between waterings will help prevent vinca chlorosis.

31

Table 1. Weekly chlorotic ratings - average number of chlorotic leaves out of eight
to ten per plant. Weeks 3, 4, and 5 are averaged over 144 plants. Weeks 6 and 7
are averaged over 108 plants. Week 8 is averaged over 72 plants.

 

 

 

 

Temp Percent Weeks of treatments

water 3 4 5 6 7 8

25 100 3.0 4.6 3.9 3.2 1.9 2.1
75 1.2 1.5 1.1 0.8 0.6 0.9

50 0.1 0.1 0.1 0.8 0.0 0.0

20 100 2.8 4.4 4.4 4.6 3.8 3.6
75 2.2 2.6 2.5 2.2 1.6 1.3

50 1.0 0.4 0.2 0.1 0.0 0.0

15 100 2.6 4.0 4.2 4.3 3.9 3.8
75 3.0 3.7 3.2 3.3 2.7 2.9

50 2.2 2.3 1.6 1.2 0.7 0.7

Table 2. Analysis of varience for degree of chlorosis after five weeks.

 

 

 

 

 

iource MS F

Water 406.86 150.598 ***‘
Water x temp 15.23 5.363 **
Error A 2.70

Media pH 2.14 0.070 ns
pH x water 3.92 0.127 ns
pH x temp 5.10 0.166 ns
pH x water x temp 3.88 0.126 ns
Error B 30.74

IIIS, illlli’ I'll“: Nonsrgnrircant OI' srgnrircant at F=U.UI an: 6.“, I'CSPOCUVCI)’.

32

Table 3. Tissue analysis of plant material from 36 plants after five weeks of

 

 

 

 

 

 

 

 

 

treatments.

Nutrient ( %) Chlorotic Green tissue Percent

tissue decrease _

Phosphorus 0.47 0.57 17.5%
Potassium 2.25 3.41 34.0%
Magnesium 0.44 0.69 36.2 %
Calcium 0.73 1.25 41.6%

Nutrient (ppm) I
Zinc 47 95 50.5%
Manganese 105 471 77.7%
Copper 8 11 27.3%
Iron 49 119 58.8%
Boron 94 104 9.6%
Aluminum 48 101 52.5 %

 

Table 4. Condition of the roots after five weeks of treatments. Numbers
are means of 36 plants.

 

Percent available water

 

 

Temperature 100 75 50
15C 2.1 :1; 0.8 2.9 i 1.5 4.8 :1; 0.6
20C 2.4 j; 1.2 3.5 :1; 1.3 4.9 i 0.4
25C 3.2 :t 1.5 4.6 :I: 1.0 4.9 :1: 0.7

 

l = no roots present, 5 = roots in excellent condition

33

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34

 

 

Chlorosis of Vinca

 

 

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35

, ’ Literature Cited

Hershey, D.R. 1991. Iron deficiency stress response of Tolmiea menziesii. J. Plant
Nutr. 14(11):1145-1150.

Mattis, P.R. and D.R. Hershey. 1992. Vinca roots need proper iron source.
Greenhouse Manager. 11(5):82-84.

Mengel, K. and LA. Kirkby. 1987. Principles of plant nutrition. 4th ed.
International Potash Institute, Bern, Switzerland.

Moore, DP. 1977. Mechanisms of micronutrient uptake by plants, p.171-198. In:
R.C. Dinauer (ed.). Micronutrients in Agriculture. Soil Sci. Soc. Amer.
Madison, WI.

Scullin, L. 1991. Production of annual vinca. Proc. Alabama Nurseryman’s
Summer Seminar, Alabama Nurseryman’s Association. Birmingham, Al.

Thomas, RA. and DA. Gilbertz. 1992. Why can’t you grow quality vinca?
Greenhouse Manager 11(8):48-55.

The Effect of Day and Night Temperature and Light Level
on Catharanthus roseus (L.) ‘Grape Cooler’

The Effect of Day and Night Temperature and Light Level

on Catharanthus roseus (L.) ‘Grape Cooler’

Introduction

The bedding-plant industry produces over 1.5 billion plugs each year to supply
consumers with a variety of annuals (Dill, 1993). Geraniums, petunias, impatiens, and
begonias have dominated the market for many years, but with 4% of the total sales for
1991, Catharanthus roseus L. , or Madagascar vinca, is becoming an important crop
(Agriculture Statistics Board, 1993). Therefore, environmental information such as
growing temperatures and light levels nwds to be studied to determine optimum
conditions for growing vinca.

Air temperature affects plant growth two ways; average daily temperature (ADT)
influences the growth or developmental rate, while the difference between day and night
temperature (DIF) affects the height or intemode length of the plant (Heins and Erwin,
1990). These effects were demonstrated on species like poinsettia (Berghage, Heins, and
Erwin, 1990; Berghage and Heins, 1991), Easter lily (Erwin, Heins, and Karlsson,
1989), chrysanthemum (Karlsson etal., 1989), and hibiscus (Karlsson et al., 1991), and
on such bedding plants as geranium (Heins, 1979; Armitage, Carlson, and Flore, 1981;

White and Warrington, 1988) and impatiens (Lee, Barrett, and Nell, 1990).

36

37

Crops can be produced for a specific market date under commercial conditions.
Many species of bedding plants are grown together, and if the cultural requirements for
each crop are known, species with similar growing conditions can be placed together.
In commercial production, vinca is often placed with crops grown at cooler temperatures,
which may slow or stunt growth. (Thomas and Gilbertz, 1992).

The amount of light the plant receives influences flowering time and size.
Karlsson et al. (1989) showed that as photosynthetic photon flux (PPF) increased, time
to flower decreased and flower diameter increased in chrysanthemums. Carpenter and
Beck (1973) studied the effects of light on four bedding-plant species: impatiens,
marigolds, petunias, and zinnias. They found that four weeks of supplemental lighting
caused shorter, more compact plants that flowered earlier. Graper, Healy, and Lang
(1990) determined that the application of 5 to 10 days of supplemental HPS on ten-day-
old petunia seedlings decreased time to flower. The effects of supplemental light on
vinca have not been studied, but it would be useful to know how light affects time to
flower and flower size.

This experiment had three main objectives: (1) to develop a prediction model for
days to flower in vinca, (2) to determine the effect of various DIF regimes on vinca
intemode length, and (3) to determine the effects of temperature and light on flower

diameter.

38
Materials and Methods

Experiment 1. Five 4.0- x 4.7-meter greenhouse sections were maintained at constant
15, 20, 25, 30, and 35C. Each 0.9- x 2.7-meter bench was given a different PPF level.
One bench was covered with 50% mesh shadecloth, one was equipped with 2 HPS lamps
that provided 12 hours of supplemental light at 250 to 300 pmol-m‘z-s“ (10.8 to 13.0
mol-m'2-day"), and the third bench provided ambient light levels. Extraneous light was
minimized by aluminum foil hung from the HPS lamps.

Plug trays of eight-week-old Catharanthus roseus L. ‘Grape Cooler’ were
received and transplanted into 32-cell (eight 4-pack) flats filled with Baccto potting
medium (Michigan Peat Co. , Houston TX) on 5 March 1992. There were three
replications, each consisting of one flat. Each flat was assigned a day and night
temperature, a light level, and a replication number. Two different sowing dates were
recorded for the plugs, so replications were first sorted by sowing date and then by plant
height. Flats were moved every 12 hours to provide 25 DTINT environments.
Movement of plants took an average of 30 minutes. Plants were kept under the same
light treatments.

Flowering dates for first flower, 50% flower per flat, and 100% flower per flat
were recorded daily. Height, node number, fresh weight of roots and shoots, and dry

weight of roots and shoots were recorded weekly.

Experiment 2. Plugs were received and transplanted 15 March 1993, and were used as

a verification of the 1992 experiment. Plants were treated like those used the previous

39

year, with a few modifications. Plants under constant temperature were rearranged each
time the other plants were moved to simulate stress effects on plants moved between
chambers. Soluble salts and pH were checked weekly and subirrigation water was
adjusted to keep salt levels stable. Supplemental light intensities were 200 pmol-m'z-s"
(8.6 mol-m'z-day").

As each flat came into full flower, it was marked and removed after data from
the week were collected. Dry weights were not recorded, but all other measurements,
including flower size, number of leaf nodes at first flower, and intemode length, was
recorded weekly. The uppermost leaf pair on transplants that received constant
temperature treatments were marked and leaf-pair numbers were counted every other

day.

Data analysis. Flowering data for both years were converted to rates, and regression
lines were plotted through the data. Lines were compared statistically using the
procedure by Snedecor and Cochran (1967). Similarities between ambient and 50%
shade regression lines were observed and compared statistically using the same
procedure. The inverse of each regression line was calculated and plotted.

Linear regression analysis was performed on leaf-pair numbers collected until half
the flat was in flower to determine leaf-pair unfolding rates (LUR) at specific
temperatures. These data were then combined for treatments that had flowered, and

linear regression analysis was performed to create a curve over temperature. The slope

40

and y-intercept of each line were used to calculate base temperature and degree-day per
leaf pair. The inverse of each LUR curve was calculated and plotted.

The leaf node of first flower was determined by averaging the data collected. The
number of leaf pairs on the plant at flower was determined by averaging the total number
of leaf nodes when the plants first flowered. The number of leaf pairs at transplant was

counted and averaged to determine the initial leaf pairs.

Results

As ADT increased, days to flower decreased at all light levels (Figures 2b, 3b,
and 4b). Plants with an ADT of 15 or 17.5C had not flowered under ambient or 50%
shade conditions when the experiment was terminated eight weeks after transplant.
Plants under supplemental light flowered earlier than those at the other two light levels,
but did not flower under an ADT of 15C.

No statistical differences were found between regression lines for flower
development rate for plants grown under 50% shade, but there was a difference in the
y-intercept for those grown under ambient light (Table 5). This difference was not large
enough to be horticulturally significant, so the data for shade and ambient light were
combined for both years. However, data for supplemental light could not be combined
because of the differences between the two years.

Curves and their inverses for flower development rate were plotted for each of
the light treatments (Figs. 2, 3, and 4). These curves showed that as air temperature

increased from 15 to 35C, flower development rate increased and days to flower

41
decreased. Comparisons of regression lines for 50% shade and ambient light showed that

there were some differences (Table 6), but when the data were examined at set points
most often seen horticulturally (17.5 to 22.5C), these differences were not large enough
to be important. Therefore, data were combined for these treatments, and regression
lines for flower development rate and days to flower were plotted (Fig. 5).

LUR regression lines for ambient and supplemental light treatments were
parallel (Fig. 6). The slope for 50% shade was different than that of the other two
treatments; therefore, the data for ambient and 50% shade could not be combined. The
degree days required to unfold one leaf pair were calculated using the slopes of the
regression lines. They showed that as light level increased, the degree days per leaf pair
decreased (Table 7). Base temperature was calculated and determined to be between 10
and 12C.

Plotting the inverse of the LUR regression lines gives the time required to unfold
one leaf pair (Table 8.). By determining the number of leaf pairs on the plant at time
to flower and subtracting the number at transplant, the number of leaves to unfold before
the plant flowers can be determined. There was an average of 9.3 leaves on the plant
when flowering occurred, and the average number of leaves unfolded at the time the
plugs were transplanted was 4.9; therefore, approximately 4.4 more leaves had to unfold
after transplant before the plants would flower. Plotting the curve for 4.4 leaves to
unfold with the prediction curve for days to flower showed that the curves were similar
(Fig. 7). Therefore, the curve for days to unfold one leaf pair could be used to predict

days to flower. Figure 8 shows the curves for plants with three (top line) to eight

42

(bottom line) leaves under each light treatment. By determining the number of leaves
on a plant, the days to flower can be predicted using these curves.

DIF affects intemode elongation of a plant. Figure 9 shows the effect of day,
night, and constant temperature and DIF on the elongation of vinca stems. Day and
night effects were obtained by averaging day settings across all night temperatures or
night temperatures across all day settings. As day temperature increased from 15 to
35C, intemode length increased, which corresponded to a greater increase in intemode
length with a positive DIF.

Observations of flower size during the first experiment led to measuring of flower
diameter in the second. Flower diameter was greatly influenced by both day temperature
and light level (Fig. 10). Flowers were largest at a day setting of 25C under

supplemental light.

Discussion

The rate of growth from transplant to flower in vinca was influenced by
temperature and was slowed considerably when the air setting was below 20C at all light
levels, which was expected because vinca is tolerant to high temperatures (Thomas and
Gilbertz, 1992; Scullin, 1991). The 50% shade treatment and ambient light yielded
similar growth rates, while the rate under supplemental light was slightly faster.
Comparison of the 1993 supplemental-light rate curve with the other two treatments
showed that the slopes were similar, but the y-intercept was different, which suggested

that the supplemental lights generated heat and raised the temperature of plants that were

43
under them. For petunia seedlings, Graper and Healy (1991) showed that plant

temperature under HPS lights was four to five degrees above that of plants under ambient
light. Vinca shoot-tip temperatures under HPS lights were generally two to three
degrees above shadecloth and ambient light at 35C. Further studies by Faust
(unpublished data) indicated that as air setting decreased from 35 to 15C, vinca shoot-tip
temperature under supplemental light remained one to two degrees above that of plants
under ambient light. The greatest differences in flowering rates were seen at the lower
temperatures, and the rise in temperature under supplemental lights may have caused the
earlier flowering times.

The flower development-rate lines for supplemental light between the two years
could not be combined. The intensity of the HPS lamps was different between the two
years because different lamps were used. The amount of ambient light changed the
effectiveness of the supplemental light. Plants were lighted during the day, which means
that ambient light levels were supplemented. On a cloudy day, when ambient light levels
were below 10 to 15 mol-m’z-day“, HPS lights increased the total amount of light the
plants received. On a sunny day, when the ambient light levels were greater than 15 to
20 mol-m‘z-day", HPS lights did not have as great an effect. During the two years in
which these experiments were conducted, plants received different amounts of radiation;
therefore, the capacity for supplemental lighting to affect the plants differed. This type
of experimental error had to be considered when the data were analyzed. Other factors
that could have contributed to the differences between the rates included temperature

controls, time to move plants, and judgmental error in determining days to flower, etc.

44
Leaf-pair unfolding-rate (LUR) data were collected to determine plant growth

rate. Plants grown under supplemental light (Fig. 6) had a faster LUR, which could
have been caused by the elevation of temperatures under the lights. However, the slope
of the curve for the plants under 50% shade is different from that of the other two
treatments. The slower growth rate at the higher air temperatures may be due to the
lower light levels. The lines for 50% shade and ambient light intersect at 20C,
suggesting that the low air temperature is slowing growth enough to delay flowering
regardless of light levels. The predicted number of days to unfold one leaf pair shows
a large difference between 20 and 25C at all light levels (Table 8), which suggests that
air settings of 20C or below are too low for vinca. By increasing the air temperature 5
degrees, the number of days to unfold one leaf pair will decrease by three to four days,
meaning that flowering will be decreased 15 to 20 days if five leaf pairs must be
unfolded.

The difference between day and night temperature (DIF) influences intemode
elongation. According to Heins and Erwin (1990), intemode length is affected more
when DIF is positive than when it is negative (Fig. 9d). Figures 9a and b show the
effect of increasing the day and night temperatures. Day temperature had a greater effect
on the elongation of intemodes, which explained the greater response of plants to a
positive DIF. Figure 9c shows the effect of constant temperature on intemode length.
As temperature increased, intemode elongation increased, which accounts for some of
the variation in intemode length under DIF. In most cases, intemodes were measured

when the entire flat had come into flower, but at the lower temperatures, not all plants

45

flowered. Thus, plants were not as mature, and intemodes may not have been fully
expanded.

The amount of light and the day temperature affected flower diameter. Flowers
were largest when they received supplemental light at 25 C (day). Flowers were over 0.5
cm larger under supplemental light than under 50% shade. A day setting in the range
of 25 to 30C was optimum for flower size. The difference between ambient and
supplemental light levels was not as great. At higher light levels, plants were able to
accumulate more photosynthates, which they could incorporate into the flowers. An
increase in fresh and dry weight has been reported under higher light levels in bedding
plants such as impatiens, petunias, marigolds, and zinnias (Carpenter and Beck, 1973)

and is due to the increased accumulation of photosynthates.

Conclusion

Time to flower for vinca is influenced by temperature; it decreases as temperature
increases. The prediction curves developed can be used by growers to determine
temperatures for growing vinca and predict the time it will take the plants to flower. Air
settings below 20C slowed growth and delayed flowering. Vinca grew best and flowered
faster when given an average setting between 25 and 30C.

Supplemental light decreased time to flower, but the decrease may actually have
been a result of the heat generated by the lamps. Supplemental light also increased
flower size and had the greatest effect on cloudy days. There may have been some

benefit to lighting the plants on cloudy days or extending the photoperiod.

46
Vinca plants responded as expected to DIF , and the temperature treatments could

be used for height control. By keeping plants around 25C rather than at a lower setting,

flower size was maximized, plants grew normally, and flowering was earlier.

47

Table 5. Regression analysis for flower development rate between years.
Y = be + bl (ADT)

 

 

 

 

 

 

 

 

Year Variable 50% shade Ambient Supplemental
1992 b0 -0.0155 -0.0206 -0.0094
b, 0.0017 0.0020 0.0017
1993 b0 -0.0152 -0.0191 -0.0178
b, -0.0017 0.0019 0.0020
Comparison of slopes F = 0.0245 F = 5.1235 F = 8.5223
n.s. * **
Comparison of intercepts F = 2.4157 F = 3.0977 F = 3.1543
n.s. n.s. "‘
ns, *, ** Nonsignificant or sIgnifrcant at P=0.0§ an: 0.01, respectively.

Table 6. Regression analysis for flower development rate between 50% shade and
ambient light levels. Y = bo + bl (ADT)

 

 

 

 

50% shade Ambient Comparisons
b0 -0.0151 -0.0196 20.2347 **
b, 0.0017 0.0019 4.7449 *

 

{5: Significant to E=.05 an: .0T, respectively

48

Table 7. Calculated values for degree days/leaf-pair and base temperature
using LUR regression lines.

 

 

50% shade
Ambient

Supplemental

 

Light level

 

 

 

126.6 10 0
94.3 11 9
82.0 11 l

 

Table 8. Calculated days to unfold one leaf-pair based on LUR regression lines.

 

 

 

Light level
Temperature 50% shade embient Supplemental
15 22 27 19
20 12 1 l 9
25 8 7 6
30 6 5
35 5 4 4

 

49

Figure 2. Curves of flower development rate and predicted days to flower for 50%
shade.

0.06

0.05

0.04

0.03

0.02

Flower Development Rate

0.01

0.00

80
70
60
50
40
30

Days to Flower

20

10-

Figure 2

50

 

 

 

 

 

 

 

 

 

 

Average Daily Temperature (C)

a. Y = —o.0151 + 0.0017 (ADT)

)— -n
5 1O 15 20 25 3O 35 4C
Average Daily Temperature (C)

II- b. -
Y = 1 / (-0.0151 + 0.0017 (ADT)) _
5 10 15 20 25 30 35 4C

51

Figure 3. Curves of flower development rate and predicted days to flower for
ambient light.

52

0.06 l l I I T l

 

a. Y = -o.orea + 0.0019 (ADT)
0.05 -

0.04 -
0.03 -

0.02

I

Flower Development Rate

0.01 -

 

 

0.00 I I I I J

 

 

5 10 15 20 25 3O 35
Average Daily Temperature (C)
80 u u

40

 

70-

50-
40-

Days to Flower

 

20-

10 _Y = 1 / (-0.0196 + 0.0019 (ADT))

 

 

 

o I I I I I I
5 1 O 1 5 20 25 30 35

Average Daily Temperature (C)

figureB

53

Figure 4. Curves of flower development rate and predicted days to flower for
supplemental light.

0.06

0.05

0.04

0.03

0.02

Flower Development Rate

0.01

0.00

80
70
60
50
40
30

Days to Flower

20
10

Figure4

54

 

 

 

 

 

 

 

 

 

Average Daily Temperature (C)

o
o
l— . u
o a
can - . . on
Io ‘— :‘/ :
. . ,' 3 R: -
o" _. .
_ 0 /.° ° .
' 9 o 1992
= -o.ooe4 + 0.0017 (ADT)
o 1993 -
= -0.0178 + 0.002 (ADT)
5 10 15 20 25 30 35 40
Average Daily Temperature (C)
L- .1
5 10 15 20 25 30 35 40

55

Figure 5. Curves of flower development rate and predicted days to flower for
combined shade and ambient treatments.

56

0.06 I I I I I I

 

a. Y = -0.0173 + 0.0018 (ADT)
0.05 -

0.04 -
0.03 -

0.02 -

Flower Development Rate

0.01 -

 

 

 

 

0.00 I I I I I
5 10 15 20 25 30 35

Average Daily Temperature (C)
80 r r

40

 

70-

50-
40-

Days to Flower

 

20-

10 y = 1 / (-0.0173 + 0.0018 (ADT)

 

 

 

O I I I I I I
5 1 0 1 5 20 25 30 35

Average Daily Temperature (C)

Figure 5

57

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59

Figure 7. Comparison of curves for predicted days to unfold one leaf-pair and days
to flower.

80
70
60
50
40
3O
20
1 0

Days to Flower

7O
60
50
40
3O
20
1 0

Days to Flower

70
60
50
40
30
20
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Days to Flower

Figure7

60

 

   

Days to flower ..

Days to unfold 4.4 leaf pairs -

 

Days to flower

Days to unfold 4.4 leaf pairs

1 l I I I

 

 

 

Days to unfold 4.4 leaf pairs

 

l I I J l

 

15 20 25 30 35 40
Average Daily Temperature (C)

61

Figure 8. Curves of predicted days to flower using predicted days to unfold one leaf-
pair. The numbers above each line represents the number of leaf-pairs already on the
plant.

1 80
1 60
1 40
1 20
1 00
80
60
40
20

1 60
1 40
1 20
1 00
80
60
40
20

1 60
1 40
1 20
1 00
80
60
40
20

Predicted Days to Flower Predicted Days to Flower Predicted Days to Flower

1

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Figure 10. Comparison of flower diameter under (a)average day temperature,
(b)averagc night temperature, and (c)constant temperature.

66

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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25
Average Daily Temperature (C)

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Literature Cited

Armitage, A.M., W.H. Carlson, and LA. Flore. 1981. The effect of temperature
and quantum flux density on the morphology, physiology, and flowering of
hybrid geraniums. J. Amer. Soc. Hort. Sci. 106(5):643-647.

Berghage, R.D., R.D. Heins, and J.E. Erwin. 1990. Quantifying leaf unfolding in
the poinsettia. Acta Hort. 272:243-247.

Berghage, RD. and RD. Heins. 1991. Quantification of temperature effects on
stem elongation in poinsettias. J. Amer. Soc. Hort. Sci. 116(1):]4-18.

Carpenter, W.J. and GR. Beck. 1973. High intensity supplementary lighting of
bedding plants after transplanting. HortScience 8(6):483-484.

Dill, R.A. 1993. Powerhouses of the plug industry. Greenhouse Grower.
11(11):]0-15.

Erwin, J.E., R.D. Heins, and M.G. Karlsson. 1989. Thermomorphogenesis in
Lilium longzflorum. Amer. J. Bot. 6(1):47-52.

Graper, D.F., W. Healy, and D. Lang. 1990. Supplemental irradiance control of

petunia seedling growth at specific stages of development. Acta Hort.
272:153-157.

Graper, D.F., and W. Healy. 1991. High pressure sodium irradiation and infrared
radiation accelerate Petunia seedling growth. J . Amer. Soc. Hort. Sci.
116(3):435-438.

Heins, RD. 1979. Influence of temperature on flower development of geranium
‘Sprinter Scarlet’ from visible bud to flower. BPI News (Dec):5.

Heins, RD. and J. Erwin. 1990. Understanding and applying DIF. Greenhouse
Grower 8(2):73-78.

67

68

Karlsson, M.G., R.D. Heins, J.E. Erwin, R.D. Berghage, W.H. Carlson, and LA.
Biembaum. 1989. Irradiance and temperature effects on time of development
and flower size in chrysanthemum. Scientia Hort. 39:257-267.

Karlsson, M.G., R.D. Heins, 1.0. Gerberick, and M.E. Hackmann. 1991.
Temperature driven leaf unfolding rate in Hibiscus rosa-senensis. Scientia
Hort. 45:323-331.

Lee, W., J.E. Barrett, and T.A. Nell. 1990. High temperature effects on the growth
and flowering of Impatiens wallerana cultivars. Acta Hort. 272: 121-127.

Scullin, L. 1991. Production of annual vinca. Proc. Alabama Nurseryman’s
Summer Seminar, Alabama Nurseryman’s Association. Birmingham AL.

Snedecor, G.W. and W.G. Cochran. 1967. Statistical methods, 6th ed. The Iowa
State Univ. Press, Ames.

Thomas, RA. and D.A. Gilbertz. 1992. Why can’t you grow quality vinca?
Greenhouse Manager 11(8):48-55.

Agriculture Statistics Board. 1993. Floriculture crops: 1992 Summary. USDA,
Natl. Agr. Stat. Serv., Agr. Stat. Board, Washington, DC.

White, J.W. and LJ. Warrington. 1988. Temperature and light integral effects on

growth and flowering of hybrid geraniums. J. Amer. Soc. Hort. Sci.
113(3):354-359.

Apendix A

69

Table 9. Average fresh and dry weights for root and shoot at time to flower under
50% shade.

 

 

I i

 

 

1992 1993

Temperature fresh weight dry weight fresh weight
day night root shoot root shoot root shoot
35 35 1.44 7.00 0.33 0.76 0.93 3.29
35 30 1.30 5.18 0.32 0.60 1.10 3.17
35 25 1.89 6.63 0.36 0.74 1.15 3.61
35 20 1.56 7.97 0.35 0.92 1.65 4.22
35 15 1.44 6.69 0.33 0.78 1.20 3.45
30 35 1.23 6.73 0.29 0.69 0.88 3.62
30 30 1.91 5.44 0.24 0.59 1.21 4.10
30 25 1.83 7.67 0.33 0.82 1.29 4.54
30 20 1.34 6.89 0.29 0.80 1.15 4.07
30 15 1.85 9.10 0.28 1.09 1.12 3.52
25 35 1.21 5.06 0.31 0.57 1.00 3.52
25 30 1.41 5.43 0.35 0.62 1.05 3.74
25 25 1.60 7.03 0.32 0.81 1.05 3.69
25 20 1.56 5.57 0.35 1.03 1.05 3.50
25 15 1.88 7.42 0.39 1.01 1.07 3.75
20 35 0.98 4.45 0.25 0.54 0.95 3.15
20 30 1.07 5.09 0.27 0.64 1.12 3.27
20 25 1.80 6.24 0.33 0.77 1.25 3.13
20 20 2.17 7.30 0.31 0.90 0.56 2.08
20 15 A1 A A A A A

15 35 1.07 4.03 0.21 0.49 0.84 3.01
15 30 1.17 4.29 0.25 0.50 1.16 3.69
15 25 1.91 7.43 0.32 0.92 0.58 2.00
15 20 A A A A 0.47 1.54

_ . -_ -_ -_ __ A , _ _ A

   
 

_15

 

 

 

Table 10. Average fresh and dry weights of root and shoot at time to flower under

 

'70

 

 

ambient light.
1992 1993
Temperature fresh weight dry weight fresh weight
day night root shoot root shoot root shoot
35 35 1.56 8.78 0.37 1.04 1.55 6.47
35 30 1.58 7.83 0.40 0.94 1.67 6.27
35 25 2.50 9.84 0.46 1.13 1.64 6.03
35 20 2.26 10.28 0.49 1.24 1.44 6.46
35 15 1.52 8.47 0.35 1.13 2.61 6.00
30 35 1.30 7.57 0.36 0.86 1.87 6.77
30 30 1.62 8.87 0.39 1.00 2.42 6.81
30 25 2.06 10.63 0.41 1.20 1.96 6.45
30 20 1.98 9.51 0.42 1.19 1.37 5.45
30 15 2.43 11.59 0.50 1.44 1.21 6.38
25 35 1.61 8.47 0.32 0.95 1.29 5.33
25 30 1.93 9.94 0.41 1.10 0.90 4.30
25 25 1.38 7.71 0.28 1.01 0.76 3.79
25 20 2.51 11.25 0.45 1.39 0.99 3.03
25 15 1.32 10.18 0.40 1.31 0.84 3.88
20 35 1.52 7.52 0.46 0.86 1.85 4.77
20 30 1.45 6.67 0.36 0.84 1.31 4.88
20 25 2.17 9.58 0.41 1.28 1.55 5.04
20 20 3.26 11.45 0.51 1.51 2.36 5.53
20 15 A1 A A A 0.32 1.04
15 35 1.08 5.52 0.24 0.65 0.86 2.60
15 30 1.55 6.46 0.31 0.80 1.10 3.52
15 25 2.35 9.89 0.42 1.36 1.71 4.74
15 20 1.02 8.36 0.52 1.28 0.64 1.73
_ __ A A _ A A A

7 15

 

 

 

A

 

71

Table 11. Average fresh and dry weight for root and shoot growth at time to flower
under supplemental light.

 

 

 

1992 1993

Temperature fresh weight dry weight fresh weight
day night root shoot root shoot root shoot
35 35 1.44 7.33 0.41 0.87 2.87 6.87
35 30 1.77 8.39 0.48 1.03 1.63 7.98
35 25 1.50 9.84 0.36 1.14 1.63 8.64
35 20 2.27 11.91 0.46 1.36 1.66 8.58
35 15 2.40 11.63 0.60 ' 1.51 3.09 10.11
30 35 1.08 7.43 0.31 0.90 2.02 8.25
30 30 1.12 8.32 0.32 0.97 2.14 8.08
30 25 2.28 12.63 0.47 1.44 2.12 9.24
30 20 2.22 9.40 0.43 1.09 2.30 8.32
30 15 2.02 11.31 0.54 1.52 2.07 7.00
25 35 2.03 7.97 0.71 1.05 1.79 8.74
25 30 2.13 9.67 0.64 1.23 2.69 8.74
25 25 2.45 13.66 0.52 1.60 2.81 7.51
25 20 2.44 12.26 0.60 1.67 1.62 7.32
25 15 2.90 12.96 0.73 1.84 2.29 6.84
20 35 2.88 12.80 0.57 1.44 1.40 5.49
20 30 4.54 13.25 0.88 1.46 1.97 6.93
20 25 2.45 12.53 0.51 1.63 1.52 5.91
20 20 2.74 11.17 0.51 1.50 1.93 5.67
20 15 2.82 12.43 0.50 1.66 0.55 2.26
15 35 1.85 9.14 0.48 1.26 1.23 6.21
15 30 2.02 8.03 0.53 1.11 1.83 7.45
15 25 2.88 9.60 0.55 1.28 1.13 4.50
15 20 2.22 11.58 0.52 1.90 1.32 1.05
15 10.29 0.71 1.78 A A1

 

 

 

   

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