Influence of production light levels, fertilizer regimes, moisture stress conditioning, uniconazole and retail water reg...

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Title:
Influence of production light levels, fertilizer regimes, moisture stress conditioning, uniconazole and retail water regimes on the landscape performance of Catharanthus Roseus, "Cooler Peppermint"
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vi, 160 leaves : ill. ; 29 cm.
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Chapman, Brent Maynard, 1962-
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Catharanthus roseus -- Ecology   ( lcsh )
Catharanthus roseus -- Fertilization   ( lcsh )
Catharanthus roseus -- Growth   ( lcsh )
Environmental Horticulture thesis, Ph.D   ( lcsh )
Dissertations, Academic -- Environmental Horticulture -- UF   ( lcsh )
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non-fiction   ( marcgt )

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Thesis:
Thesis (Ph.D.)--University of Florida, 1997.
Bibliography:
Includes bibliographical references (leaves 140-159).
Statement of Responsibility:
by Brent Maynard Chapman.
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Typescript.
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Vita.

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University of Florida
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INFLUENCE OF PRODUCTION LIGHT LEVELS, FERTILIZER REGIMES.
MOISTURE STRESS CONDITIONING. UNICONAZOLE AND RETAIL WATER
REGIMES ON THE LANDSCAPE PERFORMANCE OF CATHARANTHUS ROSES
'COOLER PEPPERMINT'













By

BRENT MAYNARD CHAPMAN


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


1997















ACKNOWLEDGMENTS


The author would like to thank the members of his committee, Drs. Jim Barrett, Terril

Nell, Edward Gilman, Kimberlyn Williams and Jerry Bennett, for giving someone that

could only pursue his graduate work on a part-time basis a chance to do so and for

believing that I could accomplish my goal. As someone who counts learning as one of the

great pleasures in life, I thank all of my professors for sharing their knowledge, skills and

philosophies and for serving as role models for my own teaching career.

A very large feeling of gratitude is extended to everyone who works behind the scenes

in the Environmental Horticulture Department to make learning and earning a degree

possible, including Mary Ann Andrews, Carolyn Bartuska, Jackie Host, Candy Kellinger,

Ria Leonard, Marie Nelson, Bart Schutzman, Robert Smith, Bob Weidman, Diane Weigle

and Judy Wilson. I would also like to acknowledge Dr. Dennis McConnell and Bodie

Vladimirova for assisting me with my anatomical work and for allowing me to use their

laboratory space.

I count my experiences with the many graduate students with whom I met and worked

with as one of the true rewards of pursuing a graduate degree and thank them for their

assistance and fellowship.

Finally, none of this work would have been remotely possible without the supportive

foundation provided by my wife, Cathy, my family and University Lutheran Church.















TABLE OF CONTENTS





ACKNOWLEDGMENTS ............................................... ii

ABSTRACT ...................................................... v

CHAPTERS

1 INTRODUCTION ...................... ............ ............ 1

2 LITERATURE REVIEW ......................................... 3
Selection of a Research Model Plant ................................ 3
Water Relations of Bedding Plants During Their Life Cycle ............... 4
Postproduction Performance as Related to Production Practices:
Nonbedding Plant Floriculture Crops ................................ 5
Postproduction Performance as Related to Production Practices:
Bedding Plants ............................................... 6
Plant Mechanisms for Maintaining Adequate Internal Water Relations ...... 10
Morphology and Anatomy and Plant Water Relations .................. 12
Growth Retardants and Plant Water Relations ........................ 19
Moisture Stress Conditioning and Plant Water Relations ................ 21
Nitrogen Supply and Plant Water Relations ......................... 28
Summary .................... .............. ..... .......... 30
3 DIURNAL FLUCTUATIONS OF STOMATAL CONDUCTANCE,
TRANSPIRATION, XYLEM WATER POTENTIAL AND
PHOTOSYNTHESIS IN CATHARANTHUS ROSES .............. 32
Introduction ................................................. 32
M materials and M ethods ......................................... 32
Results and Discussion ............................. ...... ...... 34










4 ANATOMICAL AND PHYSIOLOGICAL EFFECTS OF PRODUCTION
LIGHT AND WATER REGIMES ON THE GREENHOUSE GROWTH
AND LANDSCAPE PERFORMANCE OF CATHARANTHUS ROSES
'COOLER PEPPERMINT' ...................................... 39
Introduction .................................... ........ 39
M materials and M ethods ....................... ................ 43
Results and Discussion ......................................... 49
5 EFFECTS OF PRODUCTION FERTILIZER, WATER REGIME AND
UNICONAZOLE ON THE GREENHOUSE GROWTH AND
LANDSCAPE PERFORMANCE OF CATHARANTHUS ROSES
'COOLER PEPPERMINT' ...................................... 82
Introduction ................................................. 82
Materials and Methods ............................. ......... .. 85
Results and Discussion ......................................... 89
6 EFFECTS OF PRODUCTION WATER REGIME AND UNICONAZOLE
AND RETAIL WATER REGIME ON THE LANDSCAPE
PERFORMANCE OF CATHARANTHUS ROSES
'COOLER PEPPERMINT' .................................... 121
Introduction ................................ ....... ... 121
M materials and M ethods ........................................ 123
Results and Discussion ....................................... 125
7 CONCLUSIONS .......................................... 135


LITERATURE CITED ............................................... 140

BIOGRAPHICAL SKETCH ................................. .......... 160















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy


INFLUENCE OF PRODUCTION LIGHT LEVELS, FERTILIZER REGIMES,
MOISTURE STRESS CONDITIONING, UNICONAZOLE AND RETAIL WATER
REGIMES ON THE LANDSCAPE PERFORMANCE OF CATHARANTHUS ROSEUS
'COOLER PEPPERMINT'

By

Brent Maynard Chapman

December, 1997


Chairperson: Dr. James E. Barrett
Major Department: Environmental Horticulture

A series of experiments were conducted to evaluate and quantify the effects of

production light levels, fertility rates, moisture stress conditioning, uniconazole

concentration and spray time and retail watering regimes n the landscape growth of

Catharanthus roseus 'Cooler Peppermint' under different landscape fertility levels.

Single seedling plugs were planted into 10-cm containers. Two production light levels

of "high" (1,550 /umol m2 s-1) and "low" (1,025 tmol mn2 s-'), two production fertility

concentrations of"low" (50 ppm N) and "high" (150 ppm), five moisture stress

conditioning levels during production of "WW" (well watered), "LW+l"(well watered

until the last 2 weeks of production then allowed to wilt for 1 day between waterings),









"W+l" (allowed to wilt for 1 day between waterings), "W+3" (allowed to wilt for 3 days

between waterings) and "WW+Uniconazole" (well watered, treated with uniconazole),

two uniconazole treatment times during production of"week 3" (3 weeks after plug

transplanting) and "week 5" (5 weeks after plug transplanting), five uniconazole

concentrations of 0, 1, 2, 4 and 8 mg liter', two retail watering regimes of"WW" and

"W+l" and two landscape fertility levels of "low" (0.38 lb. N/1000 ft2) and "high" (1.5 lb.

N/1000 ft2) were researched.

Light microscopy procedures were undertaken to evaluate treatment effects on

stomatal densities, total stomata per leaf and leaf cell dimensions and arrangements.

Physiological parameters investigated included stomatal conductance, transpiration per

unit leaf area, osmotic adjustment and turgor loss points. Changes in plant height, width

and size were determined at the end of greenhouse production and every 2 weeks in the

landscape. Days to flower, flower diameters, leaf areas and root:shoot ratios were

measured at the end of production. Shoot dry weights were determined at the end of

production and after 6 weeks in the field.

The research showed that Catharanthus will grow best in a landscape when fertilized

during production with 50 ppm N, given a "W+1" production water regime, maintained

well watered in the retail setting and planted in a landscape bed in full sun that is

maintained well watered and receives 1.0 lb. N/1000 ft2/month. Ifa chemical growth

retardant is to be used in lieu of the "W+I" regime, uniconazole between 2 and 4

mg liter' should be applied to foliage 3 weeks after plug transplanting.















CHAPTER 1
INTRODUCTION


Gardening has become America's number one past-time. Eighty percent of US

households undertake some form of gardening (Ball, 1996). This activity creates an

enormous demand for plant material and related supplies. In 1995 floriculture crops

generated $3.27 billion of wholesale sales in the US, up 1% from 1994 (Osborne, 1996).

The wholesale value of bedding plants in 1995 was $1.32 billion, up 3% from 1994.

Florida, the number two floriculture producer, generated $613 million in sales, up 2%

from 1994. Bedding plants represent the fastest growing sector of the floriculture industry.

In spite of these impressive numbers, it has been reported that as much as 20% of

floriculture products become unsalable, damaged or reduced in price after grower

production (Armitage, 1993). One could only wonder what the floriculture sales figures

would be if the plants were more attractive at the retail outlets and performed better in

landscape situations. As far back as the 1970s improved marketing and customer

satisfaction were stated as requirements for continued growth and expansion of the

bedding plant industry (Voigt, 1979). Apparently not much has changed in nearly 20

years since Armitage stated that "This potential loss of confidence in our product (due to

poor retail and landscape performance) is the single most important factor that can

undermine the floricultural industry" (p. 3). Producing plants that can retain their quality











under potentially adverse retail sale and landscape conditions is more necessary than ever

to sustain and increase the market for bedding plants. In particular, producing bedding

plants in a manner that improves their performance under drought or drought-like

conditions can aid in further increasing the demand for these plants.

Much research has been done in the areas of crop breeding and environmental

production conditions to assist bedding plant growers in efficiently producing an attractive

and profitable crop. However, very little data exist to demonstrate how production

techniques affect the postproduction performance of bedding plants once they leave the

greenhouse.

The objective of this study was to investigate how production conditions affect the

postproduction performance of bedding plants. Specifically, the roles of production light

levels, watering regimes, fertilizer concentrations, growth regulator applications and retail

water regimes were studied to determine their effect on the performance ofCatharanthus

roses 'Cooler Peppermint' in landscape bed settings. Anatomical and physiological

procedures were implemented to characterize the effects of production conditions on leaf

size and structure, stomatal density, stomatal conductance, leaf water potential,

transpiration, osmotic adjustment and turgor loss points. These research parameters were

selected because of their interactive role in affecting plant water relations and

photosynthetic capacities. Plant growth and flowering were also monitored during

production and postproduction phases. Developing protocols for the efficient,

environmentally sensitive and profitable production of bedding plants that will perform

more satisfactorily in retail and landscape settings was the ultimate focus of this research.















CHAPTER 2
LITERATURE REVIEW


Selection of a Research Model Plant


Catharanthus roseus (L.) Madagascar periwinkle, Apocynaceae, was selected as the

model plant to study in this research project. The plant is commonly referred to as

periwinkle or vinca in the landscape and gardening trades. As the first common name

implies, it is native to Madagascar which is in USDA hardiness zone 10 (Griffiths, 1994).

Catharanthus grows as a shrubby perennial reaching heights of 60 cm. The leaves are

elliptic, entire, grow between 2.5 and 5.0 cm long and possess a glabrous and glossy

surface. The flowers are actinomorphic with five nonoverlapping to slightly overlapping

petals that are arranged in a whorl fashion to form a perfect circle. Flower colors range

from pure white to all shades of violet, rose and red. Some are white with rose centers or

"eyes."

As a bedding plant, periwinkle is used for seasonal color during the warm months of

the year. It is killed by a frost but can reseed itself in semitropical and tropical climates,

where it can become invasive. The plant thrives in moist, well drained soils, tolerates salt

and prefers full sun. It can be susceptible to root rots in soils with poor drainage or if

overwateredDue to recent breeding efforts that have produced more compact plants and

new flower color ranges, periwinkle's popularity and thus importance as a bedding plant is











quickly rising (Beytes, 1996). It is now one of the top ten bedding plants produced and

sold in the US.

As a research plant, periwinkle's heat tolerance readily lends itself to both greenhouse

and outdoor conditions common to Florida's spring and summer seasons. Its growth habit

and leaf structure make anatomical and physiological measurements simpler and reliable as

compared to other species of bedding plants. Due to the importance of Catharanthus's

natural alkaloids for cancer treatment, some basic research on its water relations has

already been completed (Virk and Singh, 1990). A limited amount of research has also

been conducted on greenhouse production parameters for periwinkle as well (Pietsch et

al., 1995).


Water Relations of Bedding Plants during their Life Cycle


Most species of plants used as bedding plants in the landscape and gardening industries

are mesophytes. These plants rely on constant access to intermediate levels of moisture in

order to complete their life cycle in an efficient and productive manner. Lack of water to

bedding plants, leading to plant stress, can be caused by small volumes of media in the

root zone, low water holding capacity of the media, lack of moisture supplied to the

media, poor root development, damaged roots or high evapotranspiration rates due to

rapid air movement, high light, high temperatures and/or low relative humidity (Armitage,

1993). In order to maximize growth rates and thus profits, producers of bedding plants

usually avoid stressing the plants by supplying optimum water during production. It has

been standard practice, however, to reduce the watering frequency at the end of









5

production to "harden" the plants for shipping and market. Due to improper manipulation

of light and temperatures as well as less than optimum watering, bedding plants more

often than not experience slight to severe water stresses at the retail setting. These

stresses often result in a poor quality plant. Likewise, many bedding plants experience

water stress once installed in the landscape or garden, resulting in less than desired

landscape performance. The relevant issue, then, is whether production practices are

helping or hindering the plant's ability to conserve water in retail and landscape settings

where adequate water is often lacking.


Postproduction Performance as Related to Production Practices:
Nonbedding Plant Floriculture Crops


Much research has been conducted that shows cultural production practices can have

dramatic effects on how well plants perform in postproduction situations. The appearance

of container grown Ficu beamin and Brassaa actinophlla that had been in an interior

environment for 10 weeks was superior for plants that had been previously acclimatized

under 40% or 80% shade for five or more weeks as compared to plants grown in full sun

(Conover and Poole, 1975). 'Amy' and 'Annette Hegg Dark Red' poinsettias, Euphorbia

pulchenrima. lost fewer leaves under interior conditions when the plants were shifted to

low light intensity (300 umol m'2 s') one or three weeks prior to being moved to interior

conditions versus staying under high light intensity (500 gmol m'2 s') until being moved to

interior conditions (Nell and Barrett, 1986). Christmas begonias, Begonia spp., grown

under low relative humidity (50%) and high light intensities (10,000 Ix) were found to











produce plants that had the highest sale time quality as well as keeping quality (Fjeld.

1986). Chrysanthemum plants fertilized with 100% nitrate form fertilizer lasted 10 days

longer than plants receiving 100% ammonia form nitrogen fertilizer (Roude. 1988).

Propagators of plants via tissue culture must acclimate the plantlets to more harsh

environments than what the plants experience in vitr. Much research has been conducted

that shows this successful acclimation (Bennett and Davies, 1986; Donnelly and Daubeny,

1986; Gmitter and Moore, 1986; Preece and Sutter, 1991; Simmons, 1984; Zhang and

Davies, 1986). Diaz-Perez et Wa. (1995) concluded from their studies that the water

relation characteristics and acclimatization issues of tissue cultured plants are not

fundamentally different from that of plants grown out of culture. Experiments cited above

indicate that plants can be successfully acclimated during production, thus enabling them

to perform more satisfactorily in postproduction situations.


Postproduction Performance as Related to Production Practices: Bedding Plants


The research that has been conducted specifically on bedding plants has been limited

and has mainly focused on studying cause and effect relationships at the applied level.

Little research has been conducted on the physiological mechanisms or anatomical

changes that may be responsible for these results. A general overview of what applied

research has been done will be presented before a more in depth review of the

physiological and anatomical literature is given.

Nelson et al. (1980) found that the keeping quality of both Tagetes and Imatiens was

improved when plants were grown under a greater temperature variation between day and











night. It was suggested that the night temperature be lowered prior to shipping.

A low frequency of irrigation during production was found to increase the

postproduction life of etunia compared to a high frequency (Armitage. 1986). Crops of

petunia and verbena produced under a constant low moisture level were found to have a

low ornamental value at marketing stage (de Graaf-van der Zande, 1990). However, the

same plants showed an excellent level ofregrowth and longevity after being planted

outdoors.

The fertilizer regime under which the bedding plants are produced can affect plant

development in the greenhouse and postproduction performance. Petunia that received

constant 100 ppm N fertilizer until anthesis exhibited increased postproduction life

compared to plants that received no fertilizer once visible bud stage occurred (Armitage.

1986). Nell et al. (1994) found a similar result with geraniums. Pelargonium that received

continuous greenhouse fertilization (150 ppm N) produced more flowers when

transplanted into landscape beds as compared to those plants that received no fertilizer for

1 to 3 weeks prior to flowering in the greenhouse. In the same study, the growth of

Catharanthus, Savia and Impatiens was reduced when greenhouse fertilization was

terminated for more than 1 or 2 weeks prior to flowering. After 6 weeks in the landscape

beds, Catharanthus overcame the effects of reduced fertilization during production.

However, for Salvia and Impatiens, their landscape growth was less when greenhouse

fertilization was terminated 3 or 4 weeks prior to flowering compared to the controls.

In addition to fertilizer termination timing, fertilizer application concentrations and

sources used during production play an important role in the ability of plants to handle











postproduction stress. Armitage (1993) reported that increasing fertilizer levels during

production decreased the survival of marigolds in simulated retail environments. Jacques

se al (1992) found similar results with Tagetes and Impatiens. They showed that fertilizing

marigolds and Impatiens in soil and soulless media with nitrogen levels greater than 100

mg N/L did not improve overall growth but did reduce shelf-life. This nitrogen rate also

yielded the greatest number of flowers on Tagetes. In terms of landscape establishment,

Dufault (1986) found that Cucumis melo transplants conditioned with increasing nitrogen

rates in the greenhouse had more severe transplant shock than those conditioned with low

nitrogen. Dufault did, however, go on to report that the negative consequences of higher

nitrogen levels could be lessened by increasing the phosphorous and potassium levels.

Conversely, the root growth of Lycopersicum transplanted into the field was found to

increase with each increasing level of N (up to 350 mg liter') supplied in the greenhouse

(Liptay and Nicholls, 1993). High nitrogen levels are known to promote shoot growth

over root growth in many crops (Masson gt ad., 1990, 1991; Tremblay and Senecal, 1988).

Masson's study showed that Lycopersicum was an exception to this trend, which quite

likely accounts for Liptay and Nicholl's findings. It has been shown that transplants with

well developed root systems recover more quickly from transplant shock (Weston and

Zandstra, 1986). This finding suggests that a high root:shoot ratio is more desirable

outcome for transplant production. Thomas and Latimer (1995) reported that root

development was the critical factor in the production of high-quality Catharanthus.

Thomas and Gilbertz (1992), with Latimer (1995), also showed that a high N03 to NH4

N ratio, a micronutrient source in the sulfate form, a soil pH near 5.5 and the use of a high









9

porosity peat-based rather than bark-based mix enhanced Catharanthus root growth during

production. Therefore, the level and source of nitrogen supplied to bedding plants during

the greenhouse production phase must be considered as an important factor in the future

landscape performance of those plants.

Plant growth retardants are routinely used in the production of bedding plants to

control plant size. This control of size not only can improve the appearance of the plants,

but can also aid in their shipping and marketing (Armitage, 1993). Research has been

conducted that shows both positive as well as negative effects of growth retardants

applied during production on postproduction performance. For example, Verbena sprayed

with paclobutrazol and uniconazole showed reduced stem growth in the greenhouse as

well as improved performance in the landscape due to reduced lodging (Davis and

Andersen, 1989). Daminozide has been reported to extend the shelf life of bedding plants

(Seely, 1985). The effect of growth retardants on flowering time has been found to be

quite variable. Early flowering ofPerlargonium was found to be enhanced by plant

growth regulators (Latimer and Killingsworth, 1988). Znnia flowering time was not

affected by paclobutrazol (Cox and Keever, 1988) or by ancymidol (Armitage t al.,

1981), but was found to be delayed by daminozide (Armitage gt il., 1981).

Growth retardants applied in the greenhouse have also been demonstrated to yield

negative effects on the growth rate of Zinnia, Impatiens and Tagetes in the landscape

(Latimer, 1991). Zinia sprayed with paclobutrazol or ancymidol in the greenhouse

showed reductions in height 7 weeks after being transplanted into the landscape. Zinnia

sprayed with daminozide or subjected to wilt cycles in the greenhouse showed no carry











over effect in the landscape. Impatiens sprayed with paclobutrazol in the greenhouse

showed reductions in height and quality 7 weeks after being transplanted into the

landscape. Imatiens sprayed with daminozide or subjected to wilt cycles in the

greenhouse showed reduced width and quality after 5 and 7 weeks in the landscape.

Ancymidol was found to have no effect on the landscape performance of Imatiens.

Shoot dry weight gain ofTagetes was found to be reduced during the first week of

landscape establishment by daminozide, ancymidol or water stress. Tagete sprayed with

40 ppm paclobutrazol, 5000 ppm daminozide or 200 ppm ancymidol showed decreased

final quality. However, there were no differences found in the final heights or widths of

the Tagete from any of the greenhouse treatments. This finding indicated that the growth

retardant effects had disappeared by the end of 7 weeks in the field.

Studies have been conducted that show an increase in container volume can delay the

onset of wilting and thus potentially improve the performance of bedding plants in the

retail setting (Gehring and Lewis, 1979a). The addition of hydophilic polymers

(hydrogels) to the growing medium has resulted in bedding plants grown in standard 72

per cell flats that show a 27% delay in wilting (Gehring and Lewis, 1979b). Not all

production practices, however, have been effective in increasing the postproduction

performance of bedding plants. The use ofantitranspirants did not result in prolonged

shelf life for any of the bedding plants studied by Gehring and Lewis (1979c).


Plant Mechanisms for Maintaining Adequate Internal Water Relations


Many people have classified plants according to their mechanisms for dealing with lack











of water. Perhaps the most useful classification for floriculturists is that proposed by

Kramer (1983). Kramer has classified plants into drought escapers, syn. avoiders. and

drought tolerators. Drought escapers complete their life cycle before serious plant water

deficit develops. Kramer divides drought tolerators into two groups plants that postpone

dehydration and those that increase their tolerance to dehydration. Plants that postpone

dehydration do so by maintaining a high water potential in spite of an external water

stress, primarily by reducing transpiration rates. Plants can accomplish this by dropping

leaves, reducing leaf area, developing thicker cuticles, rolling leaves, closing stomata

and/or growing a greater (usually deeper) root system (Levitt, 1980). Some plants can

also partially acclimate to drought situations by adjusting their internal water relations

osmotically so as to maintain turgor. Osmotic adjustment could be advantageous in

situations of highly variable rainfall by enabling root expansion into new water sources to

continue between rainfalls. Stomatal response may be more successful where crop growth

depends on stored water from seasonal rainfall followed by longer periods of drought.

Most agricultural researchers working with water stress will classify plants as one of the

above described drought tolerators. Thus, they approach their water relations research

primarily from either a stomatal or an osmotic adjustment venue.

Bedding plants, specifically Catharanthus. may benefit from both mechanisms of

tolerating drought. One mechanism may actually be more beneficial than the other

depending on whether the plants are in a retail or a landscape setting. In retail settings, it

would be more beneficial for bedding plants to postpone dehydration because of no new

media available to explore for additional water resources. In landscape settings it would











be better for the plants to acclimate to dehydration, thus allowing stomata to be at least

partially open for carbon gain that would be useful for establishment.


Morphology and Anatomy and Plant Water Relations


Morphological and anatomical characteristics of plants have a great influence on their

drought resistance/tolerance. The structural characteristics that are associated with the

ability of a plant to survive under dry conditions are referred to as xeromorphic

characteristics. These characteristics include reduced transpirational area, thickened

leaves and epidermis, decreased cell size and intercellular spaces, increased vascular tissue

area and enhanced root:shoot ratio (Oppenheimer, 1960).

On the whole plant level, it has been well documented that the root:shoot ratio of

perennial plants increases as water becomes limiting (Baser et al., 1981; Chung and Trlica,

1980; Davidson, 1969b; Evenari et al., 1977; Finn and Brun, 1980; Nash and Graves,

1993; Schwintzer and Lancene, 1983; Troughton, 1960). The increase in root growth is

caused by a shift in the partitioning of dry matter more towards roots rather than shoots

(Lambers, 1983). Abscisic acid synthesis induced by water stress has been correlated with

this shift in growth pattern (Creelman it al., 1990). Roots have been found to maintain

turgor pressure more effectively under water stress than shoots (Schildwacht, 1988).

Westgate and Boyer (1985) previously stated that the maintenance of water potential

gradients in roots due to differential solute accumulation enabled water to continue to be

supplied to enlarging cells. This maintenance of increased turgor pressure and water

potential gradients in roots could explain the shift in dry matter accumulation from shoots









13
to roots. Even though dry matter accumulation usually shifts from shoots to roots during

water stress, both shoot and root biomass are usually less than for plants that have not

experienced water stress. However, VanDerZanden (1994) reported that for Fragari

chiloensis water stress significantly reduced above ground dry matter production but root

dry matter production was not affected. Total dry matter production was reduced

between 26% and 35%, depending on the clone, for drought stressed Fragaria plants

compared to controls. A higher root:shoot ratio could aid in the establishment of bedding

plants into the landscape.

One undesirable effect of water stress at the whole plant level that should be noted is

the potential for a delay in flowering time. Panicle emergence in Orza was found to be

delayed by 10 days when plants were grown under water stress conditions (Turner et il.,

1986a).

At the leaf level, irradiance levels during growth stages can cause significant changes in

a plant's morphology and anatomy, influencing the future drought resistance/ tolerance. It

has been documented that plants grown under higher irradiances develop leaves that are

very different morphologically than the same plants grown under lower irradiances

(Givnish, 1988). Many plant species grown in full sun have been found to produce smaller

and thicker leaves than when grown under reduced light levels (Boardman, 1977; Conover

and Poole, 1975; Conover et al., 1982; Fails et al., 1982a, 1982b; Johnson et al., 1982a;

McClendon and McMillen, 1982; Milks t al., 1979; Mott and Michaelson, 1991; Vidal et

il., 1990). Sims and Pearcy (1992) found that the leaves of Alocasia grown in full sun

were 41% thicker with a 52% greater mesophyll thickness than plants grown under 20%









14

shade. This increase in leaf thickness was due to an increase in both cell size and number.

Even though the individual leaves of plant species grown under lower light levels are

larger (Knecht and OLeary, 1972). Vidal et al. (1990) reported that the leaf area per plant

was less for shade-grown Fatia than for sun-grown plants. Niklas and Owens (1989)

found a similar result with Plantago. Plants growing in shaded environments typically

have smaller root systems, longer shoot intemodes, an increase in the ratio of petiole

length to lamina width and an increase in leaf area per unit dry weight (Doley, 1978;

Nobel, 1986; Wilson and Cooper, 1969). Lower leaf masses/area, larger stomata, lesser

stomata densities, lower palisade/spongy mesophyll ratios and lower mesophyll cell

surface/leaf area ratios have also been reported for plants growing under lower light

conditions (Conover and McConnell, 1981; Cormack and Gorham. 1953; Fails t al.,

1982a; Givnish, 1988; Johnson et ig., 1982b; Lee e al., 1988; Sims and Pearcy, 1992;

Vidal et a., 1990).

Moisture availability during stages of active growth can also cause significant changes

in a plant's morphology and anatomy, influencing the future drought resistance/tolerance

of that plant. Plants growing under conditions of water deficits usually have reduced leaf

areas (Bebb and Turner, 1976; Boyer, 1970; Connor and Palta, 1981; Hsiao, 1973;

Pearson, 1980). In addition to reduced leaf areas, Yigna grown under increasing levels of

drought were found to have lower shoot dry weight, number of leaflets and reduced leaflet

area (Turk and Hall, 1980). In a similar study of Phaseolus, water- stressed plants were

found to have a higher specific leaf weight (Bonanno and Mack, 1983). The authors

attributed this increase in leaf weight to more cell wall material per unit area and/or an











increase in solute and/or starch accumulation in the cells. The number of cells in the

leaves of plants subjected to water stress, however, is usually the same as nonstressed

controls (Brouwer, 1963). Water stress has also been shown to produce thicker cuticles

on plant leaves (Treshow, 1970). In a study of four species of Brassica there was an

increase of epicuticular wax deposits as drought intensity during production increased

(Ashrafand Mehmood, 1990). Greater amounts ofepicuticular wax have been shown to

be associated with adaptation to dry habitats ofMedicago (Galeano t al, 1986) and in

Trifolium regens and T. incarnatum (Moseley, 1983). The wax content of the cuticle can

be more important than the thickness of the cuticle in reducing water loss from leaves

(Kramer, 1983).

The light and moisture levels under which a plant is grown can also affect stomatal

characteristics. For example, Mott and Michaelson (1991) showed that Ambrosia leaves

produced at high light intensities were amphistomatous stomataa occur on abaxial and

adaxial surfaces), while those produced at low light intensities were hypostomatous

stomataa occur on abaxial surface only). Stomatal density has been shown to decrease for

plants grown under low vs. high light levels due to an increase in leaf area (Gay and Hurd,

1975; Wang and Clark, 1992b; Wild and Wolf, 1980). However, Kubinova (1991) found

no significant difference in foliar stomatal frequency of Hordeum exposed to differing light

conditions. Mott and Michaelson (1991) showed that stomatal density increased on the

upper surface of Ambrosia leaves but decreased on the lower surface with increasing light

intensity. Stomatal density was found to increase with increasing water stress on both leaf

surfaces of Glyvine due to a decrease in leaf area (Ciha and Brun, 1975). Wang and Clark











(1992a) reported similar results with Triticum. A greater stomatal density because of

water stress was found to be accompanied by a reduction in stomata pore size in leaves of

Cassava (Connor and Palta, 1981). Even though stomatal density changes with leaf area,

the total number of stomata per leaf has been found to remain fairly constant (Ciha and

Brun, 1975; Knecht and O'Leary, 1972). In addition, absolute stomatal density and

distribution have been reported to vary among species and cultivars (Willmer, 1983).

Stomatal density has been proposed as an indicator of transpiration in plants. However,

no significant correlation was found in Antirhinu between daily transpiration and

stomatal density (Rutland et g~ 1987). In the same study, daily transpiration was found to

be significantly correlated with leaf area as well as total number of stomata per plant, as

determined from stomatal frequencies and leaf areas. A similar correlation between water

loss and total stomata per leaf was found in Coleus, Epipremnm. Peperomia

Chrysanthemum and Ficus (Rajapakse et al., 1988). Water-use efficiency, however, has

been positively correlated with stomatal density (Shearman and Beard, 1973). Another

factor to consider when looking at transpiration is diffusive resistance or its inverse,

stomatal conductance. Stomatal conductance is a function of the number (frequency), size

and degree of opening of stomata (Lugg and Sinclair, 1979; Pospisilova and Solarova,

1980). When soil water is adequate, stomatal aperture is the main determinant of stomatal

conductance because it is extremely variable under the influence of atmospheric factors

(Burrows and Milthorpe, 1976). When water stress develops and stomata close,

differences in stomatal frequency and size may become more important in transpiration

(Wang and Clark, 1993a). Stomatal conductance has been reported to be higher for











leaves produced under sun versus shade (Boardman, 1977; Bjorkman. 1981: Mott and

Michaelson, 1991).

At the cellular level, water stress is known to have many effects. Water availability can

cause anatomical variation ofmesophyll cells to occur during leaf development (Kramer.

1983). This variation can be found in the number ofmesophyll cells and/or in the cell

dimensions themselves. Cells of drought hardened leaves ofBrassica were found to be

more angular compared to the rounder cells of nonstressed leaves (McBurney, 1992).

Water stress has also been reported to produce smaller mesophyll cells, less extensive

intercellular spaces, thicker cuticles and increased lignification (Treshow, 1970).

McConnell and Host (1980) exhibited both cross and peridermal sections of water-

stressed Pereskia. lemon vine, that showed a reduction in mesophyll intercellular spaces

and an increase in the number of palisade layers. Leaves of plants watered every 14 days

had more strongly differentiated palisade layers with more cells than the leaves of plants

watered every 7 days (McConnell and Host, 1983). Such anatomical changes have been

shown to increase water-use efficiency in other plants (Nobel, 1980). Changes in

mesophyll cell anatomy result in varying amounts of internal leaf area available for carbon

dioxide absorption per unit leaf surface area, which can affect both photosynthesis and

water use efficiency. An increase in mesophyll surface area per unit leaf area (A"/A)

should yield higher photosynthetic rates and higher water use efficiencies. Triticum with

smaller mesophyll cells and a greater A"/A had a greater photosynthetic capacity than

winter wheat with larger mesophyll cells (LeCain et al., 1989). In a study of SliX,

maximum net photosynthesis rates were found to be correlated with greater A'"/A











(Patton and Jones, 1989). A"/A was found to increase 50% at the same leaf thickness

for water stressed Enceia farinosa compared to well-watered plants (Cutler et al., 1977).

The water stressed plants were also found to have smaller mesophyll cells. Smaller cells

should maintain turgor to lower water potential values due to a greater percentage of

bound water. In a similar study, Am/A increased approximately 40% in leaves of

Plectranthus parviflorus when soil water potential was decreased from 0 to -10 bars

(Nobel, 1977). Similar results have been shown to occur with high versus low light

conditions. Kubinova (1991) found that leaves of Hordeum were thicker and had a higher

A"/A when grown under higher irradiances. Other plant species have been found to

respond similarly (Chabot and Chabot, 1977; Longstreth et al, 1985; Nobel et al.. 1975).

It should be noted that changes in mesophyll anatomy do not always result in a change in

photosynthetic capacity and/or efficiency as reported by Foote (1994) with Fragaria.

Plant cell walls are flexible structures that can change in response to a changing

environment (Fincher and Stone, 1981). The flexibility of plant cell walls is expressed as

the modulus of elasticity (E). Cells with rigid walls have a higher E than cells with more

flexible walls. It has been reported that the cell walls of most plants become more elastic

with decreasing turgor potential (Colombo, 1987; Roberts et aL, 1981; Tyree and Jarvis,

1982). Cell wall elasticity is an important factor in turgor maintenance. Knapp (1984)

argued that plants with more elastic walls (lower E) will have a lower water potential at

zero turgor. In other words, the plants will maintain turgor longer as water potential

declines. On the other hand, cells with rigid walls undergo a smaller decrease in volume

and water content for a given decrease in water potential than do cells with elastic cell











walls (Kramer, 1983). Bowman and Roberts (1985) suggested that more rigid cell walls

(higher E) would have a lower water potential for a given change in water volume which

would maintain a steeper water potential gradient that would facilitate the continued

uptake of water from drying soils. Either a decrease or an increase in cell wall elasticity

could benefit plants during water stress, depending on various factors including stress

intensity and duration and the plant's physiological status and survival strategy. For

example, cells with rigid walls lose turgor rapidly with water loss which is a mechanism

that may be important for stomatal closure or leaf rolling and folding in some grasses.

Melkonian et al. (1982) found in Triticum that three cycles of water deficits decreased cell

wall elasticity. Conversely, Barker et a. (1993) reported that for the C3 grasses studied

more flexible cell walls were the result of exposure to water stress. Similarly,

preconditioning ofPicea mariana with osmotic stress was shown to help the seedlings

maintain turgor during subsequent exposure to water stress (Zwiazek and Blake, 1989).

This turgor maintenance was later shown to be due to an accumulation of soluble sugars

and an increased cell wall elasticity (Blake et 1a., 1991).


Growth Retardants and Plant Water Relations


Plants treated with growth retardants have shown increased resistance to

environmental stresses, including drought (Barrett and Nell, 1982; Cathey, 1964; Morandi

et al., 1984). Treated Pins elliottii (Asher, 1963), Lycopersicum (Mishra and Pradhan,

1968; Pill get ., 1979) and Phaseolus (Plaut et al., 1964) lost less water due to reductions

in transpiration. Growth retardants affect transpiration by either increasing stomatal











resistance to diffusion and/or by effecting changes in leaf morphology (Atkinson and

Chauhan. 1987; Barrett and Nell, 1981; Barrett and Nell 1982). The primary change in

leaf morphology is a reduction in leaf area due to a gibberellin inhibition. It was found

that Lycopersicu treated with chlormequat had reduced transpiration because of reduced

stomatal aperture (Mishra and Pradhan. 1968). Stomata of treated plants were closed by

80% one day after treatment, 30-40% after six days and 20% after 14 days. In a later

study, the wilting of Lycoersicu plants treated with cycocel or daminozide was delayed

4 days as compared to control plants when water was withheld 59 days after the final

applications of growth retardants (Mishra and Pradhan, 1972). Three weeks after

treatment, Euphorbia pulcherrima drenched with chlormequat or ancymidol had reduced

whole plant transpiration by 12 and 24%, respectively (Barrett and Nell, 1981). In another

poinsettia study, total evapotranspiration was reduced by 20% in ancymidol treated plants

compared to controls (Barrett and Nell, 1982). The retardants did not alter the plants'

transpiration rate as measured by water loss per unit leaf area or unit shoot dry weight.

Rather, the reduced water loss was due to reductions in leaf area. Similar results have

been reported for Chrysanthemum (Bryan, 1989) and Helianthus (Wample and Culver,

1983). However, Asamoah and Atkinson (1985) found that Prunus rootstocks treated

with paclobutrazol exhibited reduced water loss on both a total plant as well as on a unit

leaf area basis. Total water use and transpiration were also reduced on Malus and Prunus

rootstocks treated with paclobutrazol (Atkinson and Chauhan, 1987). The reduced

transpiration was found to be due to increased stomatal resistance as well as from a

reduction in leaf area. Hibiscus drenched with uniconazole showed a 33% reduction in









21

water used compared to controls (Steinberg t al., 1991). Chemically treated plants had a

smaller leaf area and individual leaves had a lower stomatal density, conductance and

transpiration rate than control plants.

The application of chemical growth retardants can produce other effects besides

changes in stomatal behavior and reductions in leaf area. Growth retardants can produce

positive changes such as decreased plant height by shortening internodes (Andrasek, 1989;

Barrett and Nell, 1989; Barrett and Nell, 1992; Bryan, 1989; Davis et al., 1987). increased

number of flowers per plant (Andrasek, 1989), hastened flowering (Andrasek, 1989),

darkened foliage color by concentrating chlorophyll (Andrasek. 1989; Bryan, 1989) and a

greater root:shoot ratio (McConnell and Struckmeyer, 1970). On the other hand, growth

retardants can produce negative changes such as reduced flower size (Andrasek, 1989),

slow landscape establishment (Latimer, 1991) and potential plant distortions. These

studies show that growth retardants not only can aid in the production of a more compact

and salable bedding plant, but can also be used to produce plants that are better able to

tolerate periods ofsuboptimum water supplies that may be experienced after leaving the

greenhouse environment.


Moisture Stress Conditioning and Plant Water Relations


Moisture stress conditioning refers to the intentional exposing of plants to one or more

wilt cycles during their production period in an attempt to acclimate them to future water

deficits. Much research has been undertaken that shows many plants undergo osmotic

adjustment during periods of water deficits (Ackerson and Hebert, 1981; Edwards and











Dixon, 1995; Gupta and Berkowitz, 1987; Matthews and Boyer. 1984: Osonubi and

Davies, 1978; Premachandra et al., 1992; Seiler, 1985; Seiler and Johnson, 1988). In

higher plants, osmotic adjustment refers to the lowering of osmotic potential due to the

net (active) accumulation of solutes (Jones and Turner, 1980). The solutes that

accumulate during osmotic adjustment include sugars, amino acids, organic acids.

alkaloids, proline and glycine betaine (Hanson and Hitz, 1982). Osmotic adjustment in

response to water deficits can either fully or partially maintain plant turgor. Turgor

maintenance for a plant under water stress can allow for continued photosynthesis and

plant growth by helping to keep stomata at least partially open, allowing for carbon

dioxide to reach the chloroplasts. A higher degree of osmotic adjustment does not always

result in increased stomatal opening. Premachandra et al. (1992) found that the Zea

cultivars with a higher degree of osmotic adjustment did not maintain higher stomatal

conductance than the cultivars with a lower degree of osmotic adjustment. However,

Hordeum genotypes with higher levels of induced osmotic adjustment by drought stress

showed decreased reductions in growth compared to genotypes that underwent less

osmotic adjustment (Blum, 1989). In a study of the response of four Brassica species to

drought stress, B. napu had both the greatest osmotic adjustment and shoot fresh weight

(Ashrafand Mehmood, 1990). Osmotic adjustment in Condor wheat allowed for the

maintenance of a greater chloroplast volume at low water potentials, which resulted in

greater photosynthetic rates (Gupta and Berkowitz, 1987). Sorghu plants exposed to

water stress over a period of 15 days osmotically adjusted and had a higher net daily

carbon gain per unit of gross carbon input when compared to plants that were irrigated











daily (McCree, 1986). In fact. the water-stressed Sorghum plants continued to gain

carbon throughout the stress cycle. Rodriguez-Maribona t al. (1992) showed that a

positive linear relationship existed between yield and osmotic adjustment in Pisum grown

under drought stress. In a later study with Vigna and Beta it was concluded that both

osmotic adjustment and stomatal control of water loss were necessary to be able to

lengthen the irrigation cycle so as to maximize water savings (McCree and Richardson,

1987).

Melkonian and Wolf (1995) discovered that it required a minimum of two water stress

cycles before Cucumi exhibited osmotic adjustment. However, Edwards and Dixon

(1995) showed that just one drought episode was able to initiate osmotic adjustment in

huja occidentalis. Turner g al. (1986b) discovered for Q~za cultivars that the degree of

osmotic adjustment was correlated with the cumulative stress days above a threshold

cumulative leaf water potential of-16 to -17 MPa days. In addition to moisture-stress-

conditioning lowering a plant's osmotic potential at full turgor and water potential at zero

turgor, this conditioning may also result in a higher bound water content and dry

weight/turgid weight ratio, which also would assist the plant in maintaining growth under

future water stress periods (Clayton-Greene, 1983). Finally, in Helianthus, moisture stress

conditioning resulted in the acclimation of photosynthesis to lower water potentials by

both stomatal and chloroplast acclimation (Matthews and Boyer, 1984). It should be

noted that genotypic differences often exist within a plant species that affect the

occurrence and degree of osmotic adjustment (Ackerson, 1980, Johnson et al., 1987;

Mojayad and Planchon, 1994; Seropian and Planchon, 1984; Sobrado and Turner, 1983;









24

Tan et a., 1992; Virk and Singh 1990). Bennett e al. (1981). however, did not find any

significant differences in the leaf water potential at which zero turgor potential occurred

among the genotypes of peanut studied.

In addition to moisture stress conditioning affecting osmotic adjustment, it can

influence stomatal behavior, in particular stomatal resistance/conductance. Stomata

operate to meet two often conflicting requirements: (a) maximizing carbon dioxide

assimilation and (b) preventing the reduction of plant water status to substantially

damaging levels (Bradford and Hsiao, 1982). Stomatal conductance is affected by relative

humidity, carbon dioxide concentrations, light and soil moisture. Many studies have

shown that stomatal closure can be induced by soil drying before there is any measurable

change in the total water potential or turgor potential of the shoots (Bates and Hall, 1981,

1982; Blackman and Davies, 1985; Davies t al., 1980; Gollan t al., 1986; Gowing C al.,

1990; Kuppers e al., 1988; Passioura, 1980; Saab and Sharp, 1989; Zhang and Davies,

1989, 1990a; Zhang and Davies, 1987). It has been proposed that roots sense soil drying

and produce chemical signals which can move through the transpirational stream to affect

processes in the shoots that lead to stomatal closure. Specifically, increased ABA

concentration in the apoplast surrounding the guard cells makes more ABA available to

ABA receptors present on the outer surface of the plasmalemma of the guard cells

(Hartung and Davies, 1991). In Za and Helianthus, soil drying was found to increase the

synthesis ofabscisic acid (ABA) by the roots which then moved into the shoots via the

transpirational stream and inhibited stomatal opening and leaf growth (Zhang and Davies,

1987; Zhang and Davies, 1989, 1990a). A study with Phaseolus. which has higher











concentrations of ABA than Zea and Helianthus even under well watered conditions,

suggested that the control of stomata occurs by the redistribution of existing ABA (Trejo

and Davies, 1991). Evidence that moisture stress conditioning can affect either osmotic

adjustment or stomatal resistance or both, depending on the species, has been reported

from recent work done with Ihuja occidentalis (Edwards and Dixon, 1995). An earlier

study of Pereskia showed that the transpiration rates of previously water-stressed plants

were found to be lower than in unstressed plants, showing an effect on stomatal resistance

(Kaufmnann and Levy, 1976). Another factor that can affect stomatal conductance is leaf

age. Jordan t al. (1975) found that the younger leaves of Gosspium kept their stomata

open to lower water potentials than older leaves. The recovery of stomatal aperture lags

behind the rehydration of a plant following a stress period. This lag of stomatal recovery

has been attributed to a persistent effect ofabscisic acid produced during the stress period

(Bengtsson et al., 1977; Fischer et al., 1970). Rapid recovery of stomatal aperture when

water is once again available would be advantageous in increasing carbon assimilation

rates, although a more rapid depletion of the new water reserves in the soil would also

occur. Once again, genetics can play a substantial role in how stomata respond to

drought. For example, Nicotiana tabacum usually grown under adequate water supplies,

responded to drought by reducing leaf area but not leaf conductance (Pearson, 1980). N.

rustic. normally grown with a limited water supply, responded to drought by reducing

both leaf area and leaf conductance, which resulted in a much greater decrease in canopy

conductance.









26
Other research has been conducted to evaluate the influence of the rate of water stress

development on net photosynthesis, leaf conductance and leaf turgor potential. Sorghum

that experienced slower rates of water deficits had more osmotic adjustment than plants

that experienced rapid water deficits (Jones and Rawson, 1979). Plants that experienced

the more rapid developing water deficits also had lower net photosynthesis and reduced

water-use efficiencies. In the same study, the authors also found that prior water stresses

most helped the plants during subsequent water stresses when the time between recovery

from stress and the onset of the next drying cycle was less than one week, and when leaf

water potentials dropped rapidly during the subsequent stress period. Jones et al. (1985)

also reported that with fruit trees a rapid development of water stress may impede osmotic

adjustment. Thomas gt al. (1976) conducted an experiment to determine if field-grown

Gossypium exhibited similar stomatal behavior to Gossypium and other plants grown in

containers under greenhouse conditions. It stands to reason that field-grown plants would

require a longer period of time to develop comparable stress to plants grown in the limited

rooting volume of a container. Thomas showed that the stomata of field-grown cotton

subjected to water stress remained open to lower leaf water potentials than the control

plants. This change in stomatal response in the field occurred without the plants showing

visible signs of wilting. These results were similar to those found previously on chamber-

grown plants that had experienced more frequent but shorter water stress periods (Brown

t al, 1976). Sobrado and Turner (1983) found that the osmotic adjustment of field-

grown Helianthus was considerably smaller than the maximum degree of osmotic











adjustment observed at more severe levels of stress imposed in the greenhouse by other

researchers (Jones and Turner, 1980; Takami g al., 1981, 1982).

Moisture stress conditioning research has also been conducted with bedding plants.

Photosynthesis in hybrid Pelargonium was found to decline at a slower rate as soil

moisture levels dropped if the plants were previously exposed to a single moisture stress

cycle (Armitage et al., 1983). Salvia plants that had been exposed to four nonlethal dry-

down cycles prior to measurements being taken showed a 30% reduction in

evapotranspiration per unit leaf area and a 32% reduction on a per plant basis when

compared with control plants (Eakes et al., 1991a). The leafturgor potential was also

higher at any given leaf water potential for moisture-stress-conditioned plants. The water-

stressed plants were able to maintain higher turgor potentials due to osmotic adjustment.

In another study, moisture-stress-conditioned Savia maintained greater photosynthetic

rates during day 2 of a wilt due to reductions in water loss during day 1 and due to the

plants' ability to maintain photosynthesis at a lower leaf water potential (Eakes et al.,

1991b). The authors also reported that the moisture stress conditioned plants had higher

water-use efficiencies than control plants. Catharanthus has also been shown to

osmotically adjust in response to the slow and gradual development of moisture stress

(Virk and Singh, 1990). It was found that the polar water soluble alkaloids were the main

contributors of osmotic adjustment in periwinkle. The cultivar of periwinkle studied that

had the greatest drought tolerance also was found to have a higher level of bound water

and cell wall extensibility compared to the other less drought-tolerant cultivars.











Research has also been conducted to determine the effects of water stress on

subsequent plant growth. Ficus beDnamina exhibited reduced growth during three short-

term water rationing treatments (Fitzpatrick, 1983). However, the plants then showed

accelerated growth after the water rationing ceased. This recovery phenomenon was not

found in the other two plant species studied, Philodendron sellout and Brassaia

actinophylla. Both of these species showed reduced growth for more than two months

after termination of short-term water rationing. Hall (1993) reported that Medicago

plants subjected to drought stress produced a greater leaf area than the controls upon

release from the drought stress. The same study found that stem length and dry matter

yield was reduced in stressed plants during periods after water stress was removed.


Nitrogen Supply and Plant Water Relations


Fertilization has a tremendous impact on plant growth. Nitrogen, in particular, has been

reported by several investigators to interact with water to affect plant yields

(Barker et al., 1983; Crowther, 1934; Hearn, 1975). The effects of nitrogen and water

supply on stomatal behavior has been shown to be variable between plant species and

between greenhouse and field studies. It has been reported that suboptimal nitrogen

increases stomatal closure of Gossypium in response to water stress (Radin and Ackerson,

1981; Radin gt al., 1982). This stomatal closure has been attributed to a greater

accumulation of abscisic acid in stressed leaves as well as a greater stomatal response to

abscisic acid. Similar effects of nitrogen on stomatal behavior has been seen in Camellia

(Nagarajah, 1981), Zea (Bennett et al., 1986) and Panicum (Ludlow and Ng, 1976) grown











under controlled environments but not in Triticum (Morgan, 1986). Coffea (Tesha and

Kumar, 1978), Avena (Zwicker, 1965), Phaseolus (Shimshi, 1970a), Panicum grown

outdoors (Ludlow, 1976) and Gossvpium grown outdoors (Radin et al.. 1991). Radin e

al. (1985) found that the stomata of irrigated Gossypium fertilized with high nitrogen

remained open to water potentials that were below the wilting point during the early part

of the growing season. However, the stomata of low nitrogen plants closed at water

potentials closely associated with the wilting point throughout the season. Ultimately, the

effects of low nitrogen on plant water relations and water use were such that 10-cm

irrigations produced as much yield and a higher water-use efficiency than 15 cm

irrigations. The greater drought tolerance of low nitrogen Triticum plants in Morgan's

study (1986) was related to changes in internal water relation traits, particularly an

increase in cell wall rigidity that resulted in a greater retention of water at lowered water

potentials, rather than increased stomatal sensitivity. Shimshi (1970b) found that nitrogen-

deficient Phaseolus failed to open their stomata as widely and to close them as tightly as

nitrogen-supplied plants. When soil moisture was high, the transpiration rates of nitrogen-

supplied plants were higher than those of nitrogen-deficient plants. As soil moisture

decreased to levels that caused plant wilt, the transpiration rates of nitrogen-supplied

plants dropped below those of nitrogen-deficient plants. He concluded that nitrogen

deficiency impairs the ability of the plants to adjust their water status to changes in soil

moisture stress by regulation of stomatal transpiration and of sap-solute concentration.

Bennett et al. (1986) found that field-grown Zea given high nitrogen was less affected by

water stress than low-nitrogen plants. They observed that high-nitrogen plants were able











to maintain leaf turgor, open stomata and higher rates of individual leaf transpiration

despite similar reductions in leaf water potentials between high and low-nitrogen plants

during periods of low soil water availability. Bennett also proposed that the lower

osmotic potential of high-nitrogen plants could have contributed to the extraction of more

water from the soil profile. Similar reductions in osmotic potential at lower leaf water

potentials for high-nitrogen plants were found in Helianthus leaves (Radin and Boyer,

1982) and Raphanus ivus leaves (Hegde, 1987) but not in Gossypium leaves (Radin and

Parker, 1979). Johnston and Fowler (1992) discovered that nitrogen fertilization affected

the leaf conductance of wheat differently depending upon the plants' physiological stage of

development. Increased nitrogen levels resulted in increased pre-anthesis leaf

conductances and decreased post-anthesis conductances. The differences found in how

nitrogen and water stress interact to affect the water relations in the crops reported here

may be due to their respective mechanisms for tolerating drought, ie. osmotic adjustment

versus water conservation strategies such as stomatal closure.


Summary


The manner in which a floriculture crop is produced has measurable effects on its

postproduction performance. These effects can be attributed to both anatomical and

physiological changes that develop during production of the crop. Any production

practice that would enable bedding plants to conserve moisture at a retail setting and aid

establishment in the landscape, without increasing production costs, would be extremely

desirable. Many bedding plants are routinely produced with some type of growth-









31

regulator application. In addition to reducing plant size. these chemicals can also reduce

transpiration rates by reducing leaf area and/or increasing stomatal resistance. The use of

chemical growth regulators can thus improve the performance of bedding plants in a retail

setting, but evidence exists that such growth regulators can also slow landscape

establishment (Latimer, 1991). Moisture stress conditioning, commonly used to reduce

plant growth before the widespread availability of chemical growth regulators, is being

investigated recently as an alternative to chemicals. Moisture stress conditioning during

production has been found to promote osmotic adjusment in bedding plants (Eakes, et ai.,

1991b; Virk and Singh, 1990). Osmotic adjustment could allow for turgor to be

maintained at lower water potentials, keeping stomata at least partially open for carbon

assimilation which would be advantageous for landscape establishment under conditions of

less than ideal moisture. The effect of moisture stress conditioning on stomatal resistance

is still unclear. Thus, moisture stress conditioning may or may not improve the

performance of bedding plants in a retail setting, where increased stomatal resistance

would be an advantage. An extremely limited amount of research has been done on

bedding plants that compares the use of chemical growth regulators and moisture stress

conditioning during production on postproduction performance. How nitrogen

fertilization and moisture stress conditioning during production affect postproduction

performance of bedding plants is also an area that has received very little research

attention. Finally, the relationships that have been reported between production factors

and postproduction performance of bedding plants have not been explained at an

anatomical or physiological level.















CHAPTER 3
DIURNAL FLUCTUATIONS OF STOMATAL CONDUCTANCE.
TRANSPIRATION. XYLEM WATER POTENTIAL AND
PHOTOSYNTHESIS IN CATHARANTHUS ROSES


Introduction


A preliminary investigation was undertaken to determine the diurnal fluctuations of

stomatal conductance, transpiration, xylem water potential and photosynthesis in

Catharanthus roses 'Cooler Peppermint'. The goal of this investigation was to determine

the most appropriate time during the day for taking physiological measurements for

evaluating water stress in subsequent studies. Diurnal xylem pressure potential curves

exist for a variety of woody angiosperms and various crop species (Richie and Hinckley,

1975). However, the exact diurnal behavior of Catharanthus roses was not known

before the initiation of these studies.


Materials and Methods


Seedlings ofCatharanthus roses 'Cooler Peppermint' grown in 390 plug trays were

shipped from Natural Beauty in Apopka, Florida, to Gainesville, Florida on 10 Mar. 1994.

The 18 x 18 mm plugs were transplanted into 10 cm diameter by 8 cm deep plastic

containers using Vegro Clay Mix (Verlite Co, Tampa, Florida) medium on 11 Mar. All

plants were thoroughly watered and spaced on wire mesh benches in a Lexan-covered











greenhouse. Since some plugs contained multiple plants, all but one plant per container

were basally cut with a pair of scissors. Plants were maintained well watered as necessary

throughout the experiment and the plants never experienced wilting conditions. Liquid

fertilizer derived from 20% N, 4.3% P, 16.6% K was applied at a concentration of 150

ppm N during each watering. All plants were thoroughly watered at 2100 hours on the

day before diurnal measurements were taken.

Beginning at 0600 hours and continuing until 2000 hours on 30 April 1994.

measurements were taken every 2 hours on five plants. Average greenhouse irradiance

and vapor pressure for each 2-hour time interval were recorded (Figure 3-1).

Photosynthesis was determined with a portable photosynthesis system (Li-Cor, Inc. Model

LI-6200) with a flow rate of 945 mol m3 and a leaf area of 24 mm x 36 mm.

Measurements were taken from the youngest, fully expanded leaf. Leaf abaxial water

vapor conductance, transpiration, light, relative humidity, leaf temperature and air

temperature were determined with a steady state porometer (Li-Cor, Inc. Model Li-1600),

using a 2-cm2 aperature and an average atmospheric pressure of 104 KPa. Measurements

were taken from the same leaf as the photosynthesis readings.

Xylem water potential was determined with a Scholander (1965) pressure chamber

(PMS Instrument Co., Model 600). Six- to eight-cm stem tip cuttings were removed

from each plant and the two lower leaves were removed at the petiole base with a sharp

razor blade and then the cutting was immediately placed in a small plastic bag containing a

moist paper towel to inhibit desiccation during measurements (Barrett and Nell, 1983).

Pressure was increased at a rate of 0.6 MPa per minute until a drop of moisture was seen










34

exuding from the cut portion of the stem. at which time the xylem water potential reading

was taken.

Stomatal conductance values were calculated as the inverse of the diffusive

resistance readings taken from the porometer. Stomatal conductance, transpiration. xylem

water potential and photosynthesis values were averaged for each measurement time and

standard deviations were calculated.


Results and Discussion


Stomatal conductance was zero at 0600 hours, a predawn reading, and rose rapidly,

reaching its peak value of 743 mmol m2 s' at 1400 hours (Figure 3-2). Leaf conductance

then dropped slightly to 649 mmol m2 s' at 1600 hours and proceeded to drop rapidly

until reaching zero again at 2000 hours. Transpiration followed a similar trend to leaf

conductance (Figure 3-2). Transpiration was zero at 0600 hours, rose slightly to 0.812

mmol m-2 s-' at 0800 hours and rose rapidly, reaching its peak value of 16.40 mmol m-2 s'

at 1400 hours. Transpiration then dropped rapidly until reaching zero again at 2000

hours.

Predawn xylem water potential was -0.24 MPa at 0600 hours, fell slightly to -0.27

MPa at 0800 hours and then fell rapidly to -0.94 MPa at 1400 hours (Figure 3-2). Xylem

water potential proceeded to fall very slightly to its lowest value of -0.97 MPa at 1600

hours, at which time it increased to -0.33 MPa by 2000 hours. This diurnal xylem water

potential curve is similar to a generalized diurnal xylem pressure potential curve presented











by Richie and Hinkley (1975) and to the curve reported by Pivorunas (1982) for well

watered 'Gloria' azalea.

Predawn net carbon gain was -1.55 /mol m2 s'' at 0600 hours (Figure 3-2). Net

photosynthesis at 0800 hours was 3.21 umol m2 s', rose rapidly to its peak value of 26.99

smol m2' s-' at 1200 hours, dropped slightly to 24.41 umol m2 s' at 1600 hours and

declined rapidly to -0.56 Mmol m'2 s' at 2000 hours. Even though stomatal conductance

continued to increase until 1400 hours, photosynthesis reached its peak at 1200 hours,

indicating that photosynthesis had reached its saturation point.

Stomatal conductance and transpiration followed very similar diurnal curves (Figure

3-2), indicating that stomatal opening is a good indicator of transpirational water loss in

Catharanthus rose under the environmental conditions present in the greenhouse during

this study. This pattern was not observed with well watered 'Gloria' azalea where

stomata underwent partial closure after maximum opening at 1000 hours without a

corresponding decline in transpiration (Pivorunas, 1982). The author attributed the

continued high rate of transpiration even after partial stomatal closure to a high vapor

pressure deficit.

Stomatal conductance and transpiration both started to decline in Catharanthus from

their peak rates at 1400 hours. However, xylem water potential remained constant

between 1400 and 1600 hours, at which time it reached its lowest level. In other words,

the water lost from the plants was not being regained until two hours after the stomata

began to close, which represents a two hour lag. Thus, the best time to measure xylem

water potential in well watered Catharanthus roses 'Cooler Peppermint' was found to









36
occur between 1400 and 1600 hours, when xylem water potential was fairly constant and

at its lowest level. This low level represents the period during the day when the plants

were experiencing the greatest amount of leaf water deficit.













37



1600
1400 -
S1200 -
S1000 -

E 600-
E 600 -
400-
200 -
0
0600 0800 1000 :00 1400 1600 1800 2000



0.4


S 3.3-
'-5


o 015- C
.0.16

0.05 -
0
0600 0800 1000 '200 1400 1600 1800 2000





Figure 3-i Average greenhouse irradiance and vapor pressure for each two hour time
interval on 30 Apr. 1994.
























-' -
E
u) o
o E


a


0600 0800 1000 1200 1400 1600 1800 2000


0600 0800 '000 :200 1400 1600 1800 2000


900-
M,-
800 -

800 -
500-
400-
3 :0-
:00 -
'00 -
3 -


0600 0800 :000 1200 1400 1600 1 00 2000


-0.25 -

-05-

-0.75 -

-1 -


-1.25


0600 0800 1000 1200 1400

TIME (EDT)


1600 1800 2000


Figure 3-2 Diurnal cycles of photosynthesis, transpiration. stomatal conductance and

xylem water potential in well-watered Catharanthus roseus 'Cooler Peppermint' on

30 Apr. 1994.















CHAPTER 4
ANATOMICAL AND PHYSIOLOGICAL EFFECTS OF PRODUCTION LIGHT
AND WATER REGIMES ON THE GREENHOUSE GROWTH AND LANDSCAPE
PERFORMANCE OF CATHARANTHUS ROSES 'COOLER PEPPERMINT'


Introduction


Much research has been done in the areas of crop breeding and environmental

conditions during plant production to assist bedding plant growers in efficiently producing

an attractive and profitable crop. Bedding plant growers have recently become more

aware of the need for improved postproduction performance, both in retail and landscape

settings (Armitage, 1986; Hammer, 1988). Armitage (1993) has compiled the latest

recommendations for how to modify light, temperature, irrigation and growth regulator

applications during plant production for several major species of ornamental bedding

plants with the goal of improving postproduction performance. However, very few

studies have been performed where anatomical and physiological changes have been

investigated to evaluate and explain the effects of the production environment on the

postproduction performance of ornamental bedding plants in actual retail and/or landscape

settings.

Morphological and anatomical characteristics of plants have a great influence on

their drought resistance and/or tolerance. Structural characteristics such as reduced leaf

transpirational area, a thickened leaf and epidermis, decreased cell size and intercellular











spaces, increased vascular tissue area and enhanced root:shoot ratio are associated with

the ability of a plant to survive under dry conditions (Oppenheimer, 1960). Plants grown

under conditions of water deficits were shown to have reduced leaf areas (Bebb and

Turner, 1976; Boyer, 1970; Connor and Palta, 1981; Hsiao. 1973; Pearson, 1980).

Stomatal density was found to increase with increasing water stress due to a decrease in

leaf area (Ciha and Brun, 1975; Wang and Clark, 1992b). Even though stomatal density

changes with leaf area, the total number of stomata per leaf has been found to remain fairly

constant (Ciha and Brun, 1975; Knecht and O'Leary, 1972). Higher light (Kubinova,

1991) or water stress during growth (Kramer, 1983 can cause mesophyll cells to decrease

in both number and/or size. An increase in mesophyll surface area per unit leaf area

(A'/A) can result in higher photosynthetic rates and higher water use efficiencies (LeCain

et al., 1989; Patton and Jones, 1989). Changes in mesophyll anatomy have not always

resulted in changes in photosynthetic capacity and/or efficiency (Foote, 1994). No

literature was discovered that reported using anatomical studies to explain the effects of

production light and water regimes on the postproduction performance of a bedding plant.

Given what is known for other plants, it was expected that producing Catharanthus under

higher light and water stress would result in smaller mesophyll cells that would improve

the plants' water relations and photosynthetic capacity in the field, allowing for faster

establishment and growth.

Eicus benamina (Conover and Poole, 1975) and Euphorbia pulche (Nell and

Barrett, 1986) performed better under interior conditions when grown under lower light

levels during the last stages of production. The improvements in interior performance











were attributed to a decrease in light compensation points. Lower leaf dry weight/area,

larger stomata, lower stomata densities, lower palisade/spongy mesophyll ratios and lower

mesophyll cell surface/leaf area ratios have been reported for other plants growing under

lower light conditions (Conover and McConnell, 1981; Cormack and Gorham, 1953; Fails

et al., 1982a; Givnish, 1988; Johnson et da., 1982a; Lee ?t al., 1988; Sims and Pearcy.

1992; Vidal et a, 1990). However, little work has been done to test the effect of reduced

production light levels on the postproduction performance of bedding plants in a landscape

setting. Because light was not a limiting growth factor for Catharanthus in the field, it was

expected that producing plants under lower light levels in the greenhouse would not yield

any great advantage in terms of field growth. However, a potential interaction between

lower greenhouse light levels and water stress during production on mesophyll cell size

was investigated.

Moisture stress conditioning during production was reported to improve the growth

and/or yield of several agronomic crops when exposed to future moisture stress periods

(Ackerson and Hebert, 1981; Brown et a ., 1976; Gupta and Berkowitz, 1987, Matthews

and Boyer, 1984). Plants conditioned to moisture stress maintained greater stomatal

conductance and levels of photosynthesis during subsequent moist stress conditions when

compared to the well-watered controls. Increased photosynthesis in conditioned plants

was attributed to positive osmotic adjustment and/or by stomatal and chloroplast

acclimation to lower water potentials. Catharanthus roses was shown to osmotically

adjust in response to the slow and gradual development of moisture stress (Virk and

Singh, 1990).











Photosynthesis in Pelargonium was found to decline at a slower rate as soil moisture

levels dropped if the plants were previously exposed to a single moisture stress cycle

(Armitage et al 1983). Salvia exposed to four nonlethal dry-down cycles showed a 30%

reduction in evapotranspiration per unit leaf area and higher leafturgor potentials at any

given leaf water potential over well-watered controls (Eakes et al., 1991 a). Conditioned

Savia maintained greater photosynthetic rates in the greenhouse during day 2 of a wilt

due to reductions in water loss during day 1. The conditioned plants were also able to

maintain photosynthesis at a lower leaf water potential (Eakes et al., 1991b). None of the

plants in the above two studies were evaluated in a real-world retail and/or landscape

setting to see if the physiological gains from moisture stress conditioning during

production actually resulted in any postproduction benefit.

Some evaluations of the postproduction performance of vegetable transplants has been

done in field settings. No improvements in the field establishment ofBrassica were gained

when the plants were subjected to drought stress during production (Latimer, 1990). This

water stress, however, was very mild as the plants were only allowed to wilt for 2 to 4

hours before being thoroughly rewatered. Armitage and Kowalski (1983) found that

growing Petuni x hyrbida with less frequent irrigation regimes improved postproduction

plant quality. No physiological processes were measured that may have assisted in

explaining these results. Also, these plants were evaluated in postproduction chambers

and did not receive any moisture stress following production.

The objective of this study was to use leaf anatomy and physiological characteristics to

evaluate and explain the effects of two production light levels and four production water











regimes on the postproduction performance of Catharanthus in landscape beds.


Materials and Methods


Experiment 1. This experiment was conducted to investigate the effects of production

light levels and water stress on the transpiration per unit leaf area, osmotic adjustment and

turgor loss point of Catharanthus ros 'Cooler Peppermint'.

Seedlings were grown in 390 plug trays were shipped from Natural Beauty

Greenhouses in Apopka, Florida, to Gainesville, Florida on 6 June 1996. The 18 x 18 mm

plugs were transplanted into 10-cm diameter by 8-cm deep plastic azalea containers using

Vegro Clay Mix (Verlite Co., Tampa, Florida) medium on 7 June. All plants were

thoroughly watered and spaced on wire mesh benches in a Lexan-covered greenhouse.

Since some plugs contained multiple plants, all but one plant per container were basally

cut with a pair of scissors. Plants were maintained well-watered as necessary and never

experienced wilting conditions during the subsequent 2-week period.

On 21 June, all plants were placed into a randomized, complete block design with five

plants per experimental unit and three replications. The experiment was 2 x 4 factorial

with 2 light levels and 4 water stress regimes. The two light regimes were "high" (full

greenhouse irradiance levels which averaged 1,550 mol m2 s-' at midday) and "low"

(67% of full greenhouse irradiance levels which averaged 1,025 .imol mf2 s"' at midday).

The four watering regimes were "WW" (plants were maintained well watered throughout

the entire experiment), "LW+1" (plants were maintained well watered until the last two

weeks of the experiment during which time they were allowed to wilt for one day between











waterings), "W+l" (plants were allowed to wilt for one day between waterings

throughout the production period for a total of seven dry down cycles), "W+3" (plants

were allowed to wilt for three days before between waterings throughout the production

period for a total of six dry down cycles). Liquid fertilizer derived from 20% N, 4.3% P.

16.6% K was applied at a concentration of 150 ppm N during each watering throughout

the experiment.

To determine transpiration per unit leaf area all plants were thoroughly watered at

0700 hours on 29 July and excess water was allowed to drain. At 0900 hours, each

container was enclosed in a plastic bag and weighed at 0900, 1300, 1700 and 2100 hours.

The following day, total leaf area was determined for each plant using a portable leaf area

machine (Li-Cor, Inc. Model Li-3000A). Transpiration per unit leaf area (mmol m2 s')

was calculated for each time interval and data were subjected to analysis of variance and

Tukey mean separation.

To construct pressure-volume (PV) curves, 10 plants were randomly selected from

each of the high light x water treatments during the week of 1 Aug. Due to the time

required to obtain reliable data, the only low light x water treatment selected for study was

the W+1 treatment. This water treatment was selected to compare the effects of high

versus low production light because of preliminary research that showed the landscape

benefits of the W+1 water treatment. Plants were placed in a dark room and well watered

the evening before pressure-volume measurements were to occur to ensure full turgor.

Xylem water potential was measured with a Scholander pressure chamber (PMS

Instrument Co., Model 600). One six- to eight-cm stem tip cutting was removed from











each plant. The two lower leaves were removed at the petiole base with a sharp razor

blade, and the cutting was immediately placed in a small plastic bag containing a moist

paper towel to inhibit desiccation during measurements (Barrett and Nell 1983). Pressure

was increased at a rate of 0.6 MPa per minute until a drop of moisture was seen exuding

from the cut portion of the stem, at which time the xylem water potential reading was

taken. After being removed from the pressure chamber, the cutting was then weighed.

This procedure was then continually repeated on the same cuttings for a total of 12 to 16

cycles. After all measurements were taken, the cuttings were dried in a 70 C drying oven

for 1 week and dry weights were determined. A pressure-volume curve was then

manually constructed for each plant by plotting the inverse of the water potential versus

the corresponding relative water content (RWC). RWC = [(fresh weight of cutting after

each cycle dry weight)/(fresh weight at full hydration dry weight)] x 100. From each

pressure-volume curve, the osmotic potential at full turgor (inverse of y-intercept) and

turgor loss point (point at which the linear and curvilinear portions of the PV curve joined)

were determined for each plant (Cheung et al., 1976). Data were subjected to analysis of

variance and Tukey mean separation.


Exeriment 2. This experiment was conducted to investigate the effects of production

light levels and water stress on the cellular leaf anatomy, stomatal conductance and

growth ofCatharanthus roseus 'Cooler Peppermint' at the end of 6 weeks of production.

Subsequent landscape performance as affected by production conditions was then studied.









46

Seedlings were obtained as previously described on 16 Mar. 1995 and transplanted into

10-cm diameter by 8-cm deep plastic azalea containers using Vegro Clay Mix (Vegro Co.,

Tampa, FL) medium on 17 Mar. Plants were thoroughly watered and spaced on wire

mesh benches in a Lexan-covered greenhouse and pruned to one plant per container.

Plants were maintained well watered as necessary and never experienced wilting

conditions during the subsequent 2-week period. Liquid fertilizer derived from 20% N,

4.3% P, 16.6% K was applied at a concentration of 150 ppm N during each watering

throughout the greenhouse portion of the experiment.

On 31 Mar., all plants were placed into a randomized, complete block design with five

plants per experimental unit and three replications. The experiment was a 2 x 4 x 2

factorial with 2 production light levels, 4 production water stress regimes and 2 landscape

fertilizer levels. Light regimes were "high" (full greenhouse irradiance levels which

averaged 1,467 pmol m' s-' at midday) and "low" (67% of full greenhouse irradiance

levels which averaged 1,033 umol m2s s' at midday). Watering regimes were "WW",

"LW+1","W+l" and "W+3".

The date of first flowering for each plant was recorded. The greenhouse production

phase of the experiment was terminated on 17 May, and plant height, two plant widths,

flower diameter and shoot dry weights were determined for five plants from each light x

water treatment. Plant height was measured from the level of the medium to the top of

the plant. Two plant width measurements were taken perpendicular to each other and

averaged to determine average plant width. Plant width and plant height were added and

divided by two to calculate average plant size. Flower diameter was measured on a











terminal flower that was completely open. Shoot dry weight was determined by

harvesting all plant tissue above the medium, drying in a 700 C drying oven for 7 days and

weighing.

At 0700 hours on 19 May, 10 plants from each light x water treatment were well

watered. Between 1300 and 1500 hours on 19 and 20 May, diffusive resistance on the

abaxial leaf surface and leaf abaxial water vapor conductance were measured on five

plants from each light x water treatment. Conductance was determined with a steady state

porometer (Li-Cor, Inc. Model Li-1600), using a 2-cm2 aperture and set for an

atmospheric pressure of 104 pPa. Measurements were taken from the youngest, fully-

expanded leaf. Stomatal conductance was calculated by taking the inverse of diffusive

resistance.

On 4 April., the underside of the most recently expanded leaves of five plants from

each greenhouse light x water treatment were marked. On 19 May, a leaf six nodes up

from the marked leaf was harvested and its leaf area was determined with a portable leaf

area machine (Li-Cor, Inc. Model Li-3000A). Stomatal densities were calculated from

microscopic examinations of impressions of the abaxial and adaxial leaf surfaces on clear

fingernail polish (Stoddard, 1965). The total stomata per leaf for each side and the grand

total of stomata per leaf for both sides were calculated. For anatomical examination, the

leaf opposite the one used for stomatal investigations was harvested, killed in FAA,

dehydrated in tertiary butyl alcohol, embedded in paraffin, sectioned at 10 um and stained

with toluidine blue (Sakai, 1973).











Soil in landscape beds had a sand texture, a pH of 6.5. a very high level of available

phosphorous (120+ ppm P) and a medium level of available potassium (48 ppm K). Five

plants per replication from each greenhouse light x water treatment were planted in each

landscape fertilizer treatment area on 20 May. The two fertilizer regimes were "low"

(0.38 lbs of N/1000 ft2 with 0.25 lbs of N supplied per month or "high" (1.5 lbs N / 1000

ft2 with 1.0 lbs N supplied per month). The fertilizer used was Nutricote 14-14-14 type 70

(14%N, 3.0% P, 11.6% K) and was incorporated to a depth of approximately 6 inches

with a rototiller. Spacing was 12-inches apart. The plants were watered as needed with

a drip irrigation system for the duration of the landscape portion of the study. The plants

were never allowed to wilt in the field.

Height and two widths were measured on each plant on 20 May, 4 June, 16 June and 2

July. Plant height was measured from the soil level to the top of each plant. The two

widths were taken perpendicular to each other and then averaged to determine average

plant width. Average plant size was calculated by adding plant height to the average plant

width and dividing by two. The landscape portion of the study was terminated on 3 July

at which time all tissue above the soil line was harvested, placed in a drying oven at 700 C

for 1 week and weighed to determine shoot dry weight. Change in plant height, width and

average size was calculated for each 2-week time interval and for the entire time (6 weeks)

in the landscape bed. All data were subjected to analysis of variance and Tukey mean

separation.











Results and Discussion


Effects of Production Environment on Anatomy (Experiment 2)

No interaction between the greenhouse light and water stress levels was found in

regards to leaf size at the end of production. The leaf size of plants grown under higher

light was significantly smaller than plants grown under low light (Table 4-1). Increasing

levels of water stress resulted in significantly smaller leaf sizes (Table 4-1). These effects

of production light and water stress levels match results reported on other species (Bebb

and Turner, 1976; Boardman, 1977; Boyer, 1970; Connor, 1981; Conover and Poole,

1977; Conover et al., 1982; Fails t al., 1982a, 1982b; Hsiao, 1973; Johnson Ct al., 1982a;

McClendon and McMillen, 1982; Milks et al., 1979; Mott and Michaelson, 1991; Pearson,

1980; Vidal t al., 1990) and show that the light and water stress levels used in this study

were different enough from each other to produce differences in plant growth.

Table 4-1 Effects of two greenhouse light levels and four water regimes on leaf size of
Catharanthus roses 'Cooler Peppermint' after 6 weeks of production.

Leaf Size (cm2)* Leaf Size (cm2)*
Water regime^ Light level
WW 20.2 a High 14.3 a
LW+I 18.6 b Low 17.2 b
W+1 13.7 c
W+3 10.5 d

Tukey Studentized Range (HSD) Test: means within column followed by the same letter
are not different at P=0.01. Means calculated on 5 replicates.
^ Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last 2
weeks of production (LW+1); wilt maintained for 1 day prior to watering (W+1); wilt
maintained for 3 days prior to watering (W+3).












Neither light nor water stress treatments had an effect on adaxial stomatal density

(Table 4-2). There was a significant interaction (P=0.0001) between greenhouse light and

water stress levels on abaxial stomatal density. Leaves grown under high light had higher

abaxial stomatal densities than leaves grown under low light for all water stress treatments

except the most severe, W+3 (Table 4-2). Similar results on other crops was reported by

Conover and McConnell (1981), Cormack and Gorham (1953), Fails et al, (1982a),

Givnish, (1988), Johnson etal. (1982a), Lee metal. (1988), Sims and Pearcy (1992) and

Vidal et al. (1990). Water stress had no effect on abaxial stomatal density in leaves grown

under low light and only produced a difference in leaves grown under high light at the

W+3 level, where the density was less (Table 4-2). Ciha and Brun (1975), Manning et al.

(1977) and Wang and Clark (1992) reported Phaseolus, Pium and Triticum. respectively,

showed increasing stomatal densities with increasing water stress on both leaf surfaces.

They contributed this increase in stomatal density to a decrease in leaf area.

There was a significant interaction (P=0.0092) between greenhouse light and water

stress levels on total stomata per leaf. There was not a significant difference in total

stomata per leaf between plants grown under high versus low greenhouse light levels

(Table 4-3). There was not a significant difference between the WW and LW+1 plants,

but increasing water stress from WW to W+l and W+3 resulted in reduced total number

of stomata per leaf (Table 4-3). Because the LW+1 plants were maintained well watered

until the last two weeks of the study, the sample leaves had not been exposed to the water

stress, accounting for the lack of differences between the WW and LW+1 plants.











Table 4-2 Effects of two greenhouse light levels and four water regimes on stomatal
density ofCatharanthu roseus 'Cooler Peppermint' after 6 weeks of production.

Adaxial stomatal density (stomata/mm-)*
Water regime^ High light level Low light level

WW 24.0 39.2

LW+I 22.4 35.2
W+1 22.4 31.2

W+3 21.6 28.8



Abaxial stomatal density (stomata/mm2)*
Water regime High light level Low light level
WW 228 ab 181 c

LW+1 229 ab 193 c

W+1 215 b 184 c

W+3 196 c 194 c

Tukey Studentized Range (HSD) Test: means within each table followed by the same
letter (in or between columns) are not different at P=0.05. Means calculated on 15
replicates.
^ Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last 2
weeks of production (LW+1); wilt maintained for 1 day prior to watering (W+1); wilt
maintained for 3 days prior to watering (W+3).









52

Table 4-3 Effects of two greenhouse light levels and four water regimes on total stomata
per leaf of Catharanthus roseus 'Cooler Peppermint' after 6 weeks of production.

Total stomata per leaf*
Water regime^ High Low
WW 47,500 ab 49.700 a

LW+1 42,800 b 46,800 ab
W+l 29,600 c 33,600 c

W+3 20,800 d 21,700 d

Tukey Studentized Range (HSD) Test: means followed by the same letter (in or
between columns) are not different at P=0.05. Means calculated on 5 replicates.
^ Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last 2
weeks of production (LW+1); wilt maintained for 1 day prior to watering (W+1); wilt
maintained for 3 days prior to watering (W+3).


This study demonstrated that greenhouse light and water stress levels affect the final

leaf area and abaxial stomatal density of Catharanthus. The plants that were grown under

the high light level had smaller leaf sizes and greater abaxial stomatal densities at the end

of 6 weeks of production, although they had the same total number of stomata per leaf as

the plants grown under the low light.

In regards to water stress, Ciha and Brun (1975) and Knecht and O'Leary (1972)

reported that stomatal densities increased with increasing water stress due to decreases in

leaf area, the total number of stomata per leaf remained fairly constant. In the present

study, stomatal densities were not affected by increasing water stress even though leaf

areas decreased. As a result, the total number of stomata per leaf decreased with

increasing water stress.









53

Greenhouse light and water stress levels also had effects at the cellular level. Smaller

ground parenchyma cells, particularly at the base of the petiole, and smaller intercellular

spaces were evident with increasing water stress during production (Figures 4-1 and 4-2).

An increase in xylem cell wall thickening due to sclerification and a decrease in xylem cell

diameter were also the results of increasing water stress (Figures 4-3 and 4-4). Manning

t al (1977) found similar results in Pisum grown under various degrees of moisture stress.

The development of a double palisade mesophyll layer became more evident as water

stress increased in plants grown under the high light (Figure 4-5). McConnell and Host

(1983) reported this doubling of the palisade mesophyll layer in water-stressed Pereskia.

For plants grown under the low light level, the palisade mesophyll layer became more

disrupted with increased water stress but did not appear to become double as seen for the

high light plants (Figure 4-6). Also for the low light plants, the spongy mesophyll cells

became smaller and more compacted with increased water stress when compared with the

control plants (Figure 4-6). These findings are consistent with those of Treeshow (1970),

Cutler et al. (1977), Manning et a. (1977) and Nobel (1977). Smaller mesophyll cells

result in a greater A"/A mesophylll surface area per unit leaf area). A greater A'/A was

shown to increase photosynthetic rates and increase water use efficiency in some species

(LeCain et al., 1989; Patton and Jones, 1989). In terms of the upper epidermal cells of the

leaf blade, increasing water stress produced smaller and less isodiametric cells. (Figure

4-7). McBurney (1992) reported similar findings in drought-stressed Brassica. No visual

differences in leaf blade thicknesses were observed between either the light or water stress

treatments. Other researchers (Boardman, 1977; Conover and Poole, 1977;









54

Conover et al., 1982; Fails st al., 1982a. 1982b; Johnson et al.. 1982a; McClendon and

McMillen, 1982; Milks t al., 1979; Mott and Michaelson, 1991; Vidal gt al.. 1990)

reported thicker leaves for plants grown in full sun. As noted above, most of the

anatomical differences observed were due to the water stress treatments rather than the

light level treatments.


















CAMB


Figure 4-1 Cross-section through leaf petiole that expanded during production in high light. A WW, B LW+1, C W+1,
D W+3. LB leaf blade. CAMB cambium. X xylem. GRPAR ground parenchyma. Dimension bar = 22 mm.








































Figure 4-2 Cross-section through leaf petiole that expanded during production in low light. A WW, B LW+ 1, C W+1, D W+3.
LB leaf blade. CAMB cambium. X xylem. GRPAR ground parenchyma. Dimension bar = 22 nun.








































Figure 4-3 Cross-section through leaf petiole that expanded during production in high light. A WW, B LW+1, C W+1, D W+3.
LB Leaf blade. CAMB cambium. X xylem. XCW xylem cell wall. P phloem. Dimension bar = 18mm.







































I ^--l 4 \. E A "L^Vl trS L- I. A N
Figure 4-4 Cross-section through leaf petiole that expanded during production in low light. A WW, B LW+1, C W+I, D W+3.
LB Leaf blade. CAMB cambium. X xylem. XCW xylem cell wall. P phloem. Dimension bar = 18 mm.







































Figure 4-5 Cross-section through leaf blade that expanded during production in high light. A WW, B LW+1, C W+1, D W+3.
LB leaf blade. PM palisade mesophyll. SM spongy mesophyll. Dimension bar = 18 mm.








































Figure 4-6 Cross-section through leaf blade that expanded during production in low light. A WW, B LW+1, C W+1, D W+3.
LB leaf blade. PM palisade mesophyll. SM spongy mesophyll. Dimension bar = 18 mm.








































Figure 4-7 Cross-section through leaf blade that expanded during production. A high light, WW. B high light, LW+ 1. C -high light, W+ 1.
D high light, W+3. E low light, WW. F low light, LW+1. G low light, W+ 1. H low light, W+3. Dimension bar = 22 nnm.











Effects of Production Environment on Physiology (Experiments 1 and 2)

Osmotic Adjustment

Pressure-volume curves were constructed to calculate osmotic potential at full turgor.

osmotic adjustment and water potentials for turgor loss points. All water stress levels

produced lower osmotic potentials than the WW controls (Table 4-4). No significant

differences in osmotic potential were found between the three water stress levels under

high light. Due to constraints imposed by the research procedure, the only comparison

made between plants grown at high versus low light levels was for the W+l treatment.

For the W+1 treatment, plants grown under the high light levels exhibited a lower osmotic

potential.

The osmotic potentials of the other treatments were subtracted from the osmotic

potential of the WW controls to determine the amount of osmotic adjustment that

occurred during production (Table 4-4). Plants from all water stress levels underwent

osmotic adjustment compared to the WW controls. That moisture stress conditioning can

result in osmotic adjustment in Catharanthus agrees with the findings reported by Virk and

Singh (1990). For the W+l treatment, plants grown under high light showed a greater

amount of osmotic adjustment than plants grown under lower light (Table 4-4). No

significant differences in osmotic adjustment were found between the three water stress

levels under high light. These results indicate that increasing the severity and/or earliness

of water stress during production ofCatharanthus does not significantly increase the

amount of osmotic adjustment that occurs.











When compared with the WW controls, plants from all treatments lost turgor at a

lower water potential (Table 4-4). Eakes et al. (1991b) reported similar findings with

moisture stress conditioned Salvia. No significant differences were found between the

three water stress levels under either light level, once again indicating no physiological

benefit from more severe and/or earlier water stress with growing Catharanthus.




Table 4-4 Effects of two greenhouse light levels and four water regimes on the osmotic
potential at full turgor, osmotic adjustment and turgor loss points of Catharanthus roses
'Cooler Peppermint' after 6 weeks of production.



Water x Light Osmotic potential Osmotic Turgor loss point
treatment" at full turgor adjustments (MPa)* (MPa)*
(MPa)*
WW*High -1.18 c -0.00 a -1.43 b
LW+l*High -1.47 ab -0.29 bc -1.67 a
W+l*High -1.51 a -0.33 b -1.75 a

W+1*Low -1.41 b -0.23 c -1.66 a
W+3*High -1.53 a -0.35 b -1.72 a

* Tukey Studentized Range (HSD) Test: means followed by the same letter (in columns)
are not different at P=0.05. Means calculated on 10 replicates.
^ Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last
2 weeks of production (LW+1); wilt maintained for 1 day prior to watering (W+l); wilt
maintained for 3 days prior to watering (W+3).
z Osmotic adjustment = osmotic potential of WW control osmotic potential of treatment












Stomatal Conductance

There was a significant interaction (P=0.0001) between greenhouse light and water

stress levels for stomatal conductance of plants measured at the end of 6 weeks of

production on 19 May. For the WW control and the LW+1 treatment, plants grown

under high light had higher stomatal conductances than plants grown under low light

(Table 4-5). Stomatal conductance was reported to be higher for leaves produced under

sun versus shade for other species (Boardman, 1977; Bjorkman, 1981; Mott and

Michaelson, 1991). This effect is most likely due to leaves produced under higher light

having higher stomatal densities, as reported earlier in this study on Catharanthus. There

were no differences due to light for the W+1 and W+3 treatments (Table 4-5). For plants

produced under high light, increasing water stress resulted in lower stomatal

conductances, with W+1 and W+3 not being significantly different from each other. Other

researchers have also shown that moisture stress conditioning can reduce leaf conductance

and/or transpiration (Eakes etal., 1991 a; Edwards and Dixon, 1995; Kaufinann and

Levy, 1976; Pearson, 1980). The reductions in stomatal conductance in the above studies

were attributed to a reduction in stomatal aperture. The reductions in stomatal

conductance in this study on Catharanthus can be explained, at least in part, by the

reduced abaxial stomatal densities due to water stress that were earlier reported. Even

though stomatal aperture was not measured in this study, it most likely had a role as well

in the stomatal conductance results reported here. Moisture stress conditioning can

increase ABA concentrations in the stomata guard cells, causing them to partially or











completely close (Zang et l., 1987). There is a lag time after the plants again receive

water before the stomata return to their pre-stressed aperture. The effect of increasing

water stress on stomatal conductance was not as dramatic for plants produced under low

light. Perhaps the stomata guard cell ABA concentrations did not increase as much due to

increasing water stress or the guard cells were less sensitive to ABA under lower light

conditions. All water stress levels under lower light resulted in stomatal conductances

statistically equal to each other, but were all lower than the WW control (Table 4-5).

Table 4-5 Effects of two greenhouse light levels and four water regimes on the stomatal
conductance of Catharanthus roseus 'Cooler Peppermint' on 19 May 1995 at 1300 hours.

Stomatal conductance (mmol m"2 sec')*
Water regime^ High Low
WW 751 a 590 b

LW+1 574 b 428 cd

W+1 392 cd 446 c

W+3 336 d 437 cd

Tukey Studentized Range (HSD) Test: means followed by the same letter (in or
between columns) are not different at P=0.05. Means calculated on 15 replicates.
^ Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last
2 weeks of production (LW+1); wilt maintained for 1 day prior to watering (W+1); wilt
maintained for 3 days prior to watering (W+3).


The same plants measured above were allowed to dry down for 24 hours. Diffusive

resistances were measured again at 1300 hours and stomatal conductances were calculated

(Table 4-6). There was a significant interaction (P=0.0029) between greenhouse light and

water stress levels. The only situation where light levels produced a significant effect was

for the WW controls, where stomatal conductance was higher for the plants grown under











the high light. For plants produced under both light levels, increasing production water

stress regimes generally resulted in higher stomatal conductances. The differences

between the three production water stress treatments under the high light were not

statistically different from each other. The low light only resulted in differences between

the LW+I and W+l plants. The results from the second day are not surprising when one

takes into account the fact that the plants' total leaf areas were not equal (Table 4-7).

With each increasing level of production water stress, the finished plants had smaller total

leaf areas. Other researchers reported similar effects of moisture stress on leaf area (Nash

and Graves, 1993; Manning et al., 1977; Martens, 1988). Reductions in leaf areas due to

moisture stress are attributed to lower water potentials available for cell expansion (Boyer,

1970). Because the WW controls had the largest total leaf area, they had depleted the

available water supply in the container medium by the time the second measurements were

taken. This water stress caused these plants to close their stomata which resulted in their

very low stomatal conductances on the second day. The stomatal conductances of the

LW+1, W+ 1 and W+3 plants were still high the second day because they had less total

leaf area to deplete the container medium water supply and thus were not experiencing as

much water stress. The LW+1, W+l and W+3 plants also underwent osmotic adjustment

as previously reported, which may have also contributed to these plants being able to

maintain higher stomatal conductances after this 24 hours of dry down.











Table 4-6 Effects of two greenhouse light levels and four water regimes on the stomatal
conductance ofCatharanthus roses 'Cooler Peppermint' on 20 May 1995 at 1300 hours.

Stomatal conductance (mmol m sec ')*
Water regime^ High Low
WW 53 d 13 e
LW+1 199 bc 132 c
W+1 235 ab 285 a

W+3 265 ab 265 ab

Tukey Studentized Range (HSD) Test: means followed by the same letter (in or
between columns) are not different at P=0.05. Means calculated on 15 replicates.
A Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last
2 weeks of production (LW+I); wilt maintained for 1 day prior to watering (W+1); wilt
maintained for 3 days prior to watering (W+3).


Table 4-7 Effects of two greenhouse light levels and four water regimes on total leaf area
ofCatharanthus roses 'Cooler Peppermint' after 6 weeks of production.

Total leaf area (cm 2 )*
Water regime^ High Low
WW 1780 a 1600 b
LW+1 1620 ab 1410 c
W+l 851 d 824 d

W+3 639 e 599 e

* Tukey Studentized Range (HSD) Test: means followed by the same letter (in or
between columns) are not different at P=0.05. Means calculated on 15 replicates.
A Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last
2 weeks of production (LW+1); wilt maintained for 1 day prior to watering (W+1); wilt
maintained for 3 days prior to watering (W+3).











Whole-plant Transpiration

Transpiration per unit leaf area (mmol m'2 s') was calculated between 0900 and 1300

hours after 6 weeks of production (Table 4-8). There was a significant interaction

between greenhouse light and water stress treatments (P=0.0002). No differences due to

production light levels were found in any of the water treatments. Also, no differences

were discovered among any of the three water stress treatments. However, for plants

grown under the high light level all water stress levels resulted in plants that transpired

less than the WW controls. The lag affect of ABA concentrations on stomatal opening

could explain this finding. For plants grown under the lower light level the only plants to

transpire less than the WW controls were the plants given the LW+1 water stress

treatment. When Catharanthus is grown under high light conditions, water loss due to

transpiration could be reduced in retail and/or landscape settings by producing the plants

under a water stress regime.

The current industry practice of growing the plants well watered until the last two

weeks of production appears to be the best approach for reducing future water loss due to

transpiration for both high and low light produced Catharanthus. Growing the plants

under more severe and earlier water stress conditions did not reduce transpiration rates

after 6 weeks of production How long the affect of these production treatments would

carry over into a retail and/or landscape setting was not evaluated in this study. Armitage

(1986) reported that a less frequent irrigation regime during production did increase the

postproduction life of petunias compared to a more frequent regime. The effect of











irrigation frequency on transpiration rates either at the end of production or later in the

plant's life was not measured in the above study.

Table 4-8 Effects of two greenhouse light levels and four water regimes on transpiration
ofCatharanthus roses 'Cooler Peppermint' between 0900 and 1300 hours after 6 weeks
of production.

Transpiration/unit leaf area (mmol m' s-')*
Water regime^ High Low
WW 28.4 a 26.6 ab

LW+1 23.2 cd 21.8 d

W+I 22.7 cd 25.1 abcd
W+3 24.9 bcd 24.8 bed

Tukey Studentized Range (HSD) Test: means followed by the same letter (in or
between columns) are not different at P=0.05. Means calculated on 15 replicates.
^ Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last
2 weeks of production (LW+1); wilt maintained for 1 day prior to watering (W+1); wilt
maintained for 3 days prior to watering (W+3).


Greenhouse Growth

The effects of two greenhouse light levels and four water regimes on flowering date,

flower size, plant height, plant width, plant size and shoot dry weight were determined

after six weeks of treatments. There was no interaction between light and water stress

levels on date to first flower. Plants produced under high light flowered 2.5 days later

than plants grown under low light (Table 4-9). Increasing water stress delayed flowering

(Table 4-9). There was a significant interaction (P=0.0373) between light and water

stress levels for flower diameter. The only difference due to light level was found for the

W+3 plants, where plants grown under high light had larger flower diameters than plants











grown under low light (Table 4-10). Increasing water stress tended to reduce flower size

(Table 4-10). All flower diameter differences due to water stress treatments were

significantly different from each other except LW+1 was equal to W+1 for both light

levels (Table 4-10).



Table 4-9 Effects of two greenhouse light levels and four water regimes on days to first
flower ofCatharanthus roseus 'Cooler Peppermint' during greenhouse production.

Days to first Days to first
flower* flower*
Water regime^ Light level
WW 23.1 b High 25.7 a

LW+1 22.3 a Low 23.2 b
W+l 25.0 c

W+3 27.3 d

Tukey Studentized Range (HSD) Test: means within column followed by the same 1
letter are not different at P=0.05. Means calculated on 15 replicates.
^ Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last
2 weeks of production (LW+1); wilt maintained for 1 day prior to watering (W+1); wilt
maintained for 3 days prior to watering (W+3).











Table 4-10 Effects of two greenhouse light levels and four water regimes on flower
diameter ofCatharanthus roses 'Cooler Peppermint' after 6 weeks of production.

Flower diameter (cm)*
Water regime^ High Low
WW 5.08 a 4.99 a

LW+1 4.57 b 4.52 b

W+l 4.63 b 4.41 b
W+3 4.05 c 3.56 d

Tukey Studentized Range (HSD) Test: means followed by the same letter (in or between
columns) are not different at P=0.05. Means calculated on 15 replicates.
^ Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last
2 weeks of production (LW+1); wilt maintained for 1 day prior to watering (W+1); wilt
maintained for 3 days prior to watering (W+3).


No interaction was found between light and water stress levels for plant height,

average width or plant size at the end of 6 weeks of greenhouse production. The two

light levels did not result in plant height, width or size differences. Water stress levels had

an effect on plant height, width and size (P=0.0001). Increasing water stress produced

shorter plants, narrower plants and smaller plants (Table 4-11). Manning et a (1977),

Martens (1988) and White and Holcomb (1974) have also shown the effects of moisture

stress in reducing plant height. Moisture stress limits plant growth by reducing turgor

levels necessary for cell division and elongation and by reducing essential metabolic

processes required for plant growth and development (Hsiao, 1973). The results of this

study show that water stress is an effective means of controlling plant size in

Catharanthus.











Table 4-11 Effects of four greenhouse water regimes on height, width and size of
Catharanthus roseus 'Cooler Peppermint' after 6 weeks of production.

Water regime^ Height (cm)* Width (cm)* Size (cm)*
WW 24.1 a 27.1 a 25.6 a
LW+I 21.0 b 23.4 b 22.2 b
W+1 15.6 c 17.2 c 16.4 c

W+3 12.9 d 14.6 d 13.7 d

Tukey Studentized Range (HSD) Test: means within column followed by the same
letter are not different at P=0.05. Means calculated on 15 replicates.
^ Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last
2 weeks of production (LW+1); wilt maintained for 1 day prior to watering (W+1); wilt
maintained for 3 days prior to watering (W+3).


A significant interaction between light and water stress levels was found for shoot dry

weight at the end of 6 weeks of greenhouse production (P=0.0042). Difference dues to

light were found only at the WW and LW+I water stress levels where plants grown under

low light had a higher shoot dry weight (7.19 versus 6.1 g for WW plants and 5.75 versus

4.89 g for LW+1 plants). Greater water stress resulted in less shoot dry weight under

both light levels, except there was no differences between W+1 and W+3 for plants grown

under high light. Other researchers (Eakes et al, 1991a; Latimer, 1990; VanDerZanden,

1994) have reported similar reductions in shoot dry weights from water stress.

Landscape Growth

No significant interactions among greenhouse light x greenhouse water x field

fertilizer, greenhouse light x field fertilizer or between greenhouse water x field fertilizer

were found for any measures of plant performance measured between 0 and 6 weeks in









73
the field. Fertilizer rate had a significant effect on change in width and size between 0 and

2 weeks and change in height, width, size and shoot dry weight between 0 and 6 weeks in

the field (Table 4-12). The higher fertilizer rate resulted in plants that were taller, wider,

larger and with greater shoot dry weights. There was no difference between fertilizer

rates for change in height between 0 and 2 weeks. The results of this field study show the

importance of nutrient availability for more rapid establishment and growth of

Catharanthus in a landscape setting.

Table 4-12 Effect of two slow-release fertilizer rates on the growth of Catharanthus
roses 'Cooler Peppermint' in a field landscape setting between 20 May and 2 Jul. 1995.
Data averaged for all greenhouse treatments.

Growth Mass
(cm)* (g)*
Ferti- Change Change Change Change Change Change Shoot
lizer. in Ht. in Ht. in Width in Width in Size in Size Dry Wt.
after 2 after 6 after 2 after 6 after 2 after 6 after 6
weeks weeks weeks weeks weeks weeks weeks
High 1.74 a 11.40 a 4.14 a 20.20 a 2.94 a 15.80 a 35.60 a
Low 1.72 a 8.17 b 2.21 b 13.00 b 1.97 b 10.60 b 26.50 b

*Tukey Studentized Range (HSD) Test: means followed by the same letter (in columns)
are not different at P=0.05. Means calculated on 15 replicates.

There was a significant interaction between greenhouse light and water stress levels for

the change in height (P=0.0332) and change in size (P=0.0247) between 0 and 2 weeks in

the field. Only greenhouse water stress levels had a significant affect (P=0.001) on change

in plant width. Greenhouse light levels had no effect on change in plant height (Table 4-

13). Height growth differences were only found between the LW+1 and W+3 plants that

were grown under the high light (Table 4-13). The W+3 plants grew more in height.











Increasing greenhouse water stress levels resulted in greater increases in plant widths

between 0 and 2 weeks in the field (WW, 0.97; LW+1. 2.77; W+1, 4.20; W+3, 4.79 cm).

The LW+I and W+l treatments were statistically similar, as were W+l and W+3.

Greenhouse light levels had no effect on change in plant size between 0 and 2 weeks in the

field (Table 4-13). Increasing levels of greenhouse water stress resulted in greater

changes in plant size (Table 4-13). This study shows that growing Catharanthus in a

greenhouse under moderate to severe water stress cycles can cause a greater change in

plant size during the first 2 weeks of establishment in a landscape field setting.

Table 4-13 Effects of two greenhouse light levels and four water regimes on the change in
plant height and size of Catharanthus roseus 'Cooler Peppermint' between 0 and 2 weeks
in the field.
Change in plant height (cm)*
Water regime^ High Low
WW 3.00 ab 1.38 b
LW+I 1.70 b 1.96 b

W+l 2.93 ab 1.73 b
W+3 4.12 a 2.24 ab

Change in plant size (cm)*
Water regime" High Low
WW 1.39 cd 1.00 d
LW+I 0.91 d 2.10 bcd
W+l 3.56 ab 2.86 be
W+3 4.67 a 3.21 abc
* Tukey Studentized Range (HSD) Test: means within the same table followed by the
same letter (in or between columns) are not different at P=0.05.
^ Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last
2 weeks of production (LW+1); wilt maintained for 1 day prior to watering (W+l); wilt
maintained for 3 days prior to watering (W+3).









75

A significant interaction between greenhouse light and water stress levels did not occur

for changes in plant height, width, size and shoot dry weights between 0 and 6 weeks in

the field. It was also found that greenhouse light levels by themselves produced no

significant differences for any of the above parameters. Increasing levels of greenhouse

water stress did result in greater changes in plant height. width and size between 0 and 6

weeks in the field (Table 4-14). Even though plants grown in the greenhouse under

increasing water stress grew more in size after 6 weeks in the field, their shoot dry weight

gains were less (Table 4-14). This finding could be due to differences in leaf and stem

thicknesses, leaf and stem numbers and/or distribution of photosynthates to shoot versus

root tissues. This study shows that growing Catharanthus in a greenhouse under moderate

to severe water stress cycles can cause greater changes in plant size 6 weeks after being

established in a landscape field setting.

Table 4-14 Effects of four greenhouse water regimes on the change in plant height,
width, size and shoot dry weight of Catharanthus roses 'Cooler Peppermint' between
0 and 6 weeks in the field.
Growth (cm)* Mass (g)*
Water regime^ Change in Ht. Change in Change in Size Change in
after 6 wks. Width after 6 after 6 wks. shoot dry wt.
wks. after 6 wks.
WW 8.81 be 13.68 c 11.24 b 30.26 a

LW+1 7.85 c 15.26 be 11.55 b 29.12 a
W+l 10.30 ab 18.15 a 14.22 a 25.21 b
W+3 12.21 a 19.52 a 15.86 a 22.90 b
Tukey Studentized Range (HSD) Test: means followed by the same letter (in columns)
are not different at P=0.05. Means calculated on 15 replicates.
^ Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last
2 weeks of production (LW+1); wilt maintained for 1 day prior to watering (W+1); wilt
maintained for 3 days prior to watering (W+3).











There was not a significant two or three-way interaction among the greenhouse light

and water stress levels and the field fertilizer rates for overall plant size between 0 and 6

weeks in the landscape. Increasing levels of greenhouse water stress resulted in smaller

plants (P=0.0001)(Table 4-15). The high fertilizer rate produced the largest plants

(P=0.0001)(Table 4-15). Since the plants from the various treatments were not all the

same size when they were planted in the field, looking at the final size after 6 weeks would

not give as accurate picture of what growth actually occurred in the field as looking at

changes in plant size. For example the WW plants finished in the field with the largest

size, but they also started in the field with the largest size (Table 4-11). In reality, the

WW plants exhibited the smallest change in size during the 6 weeks in the field (Table 4-

14). The WW plants were installed into the field in this study at a larger size than they

would normally be in a commercial situation. Since the goal of bedding plant

establishment in the field is to have the plants fill in and touch as quickly as possible,

moisture stress conditioning during production at the W+1 level would best achieve this

goal without significantly delaying production time or flower size.









77

Table 4-15. Effects of four greenhouse water regimes and two field fertilizer rates on the
overall plant size ofCatharanthus rse 'Cooler Peppermint' between 0 and 6 weeks in
the field.

Water regime^ Overall size (cm)* Field Fertilizer Overall size (cm)*
WW 37.6 a High 37.0 a
LW+1 35.8 b Low 32.0 b

W+I 32.8 c

W+3 31.8 d
Tukey Studentized Range (HSD) Test: means followed by the same letter (in columns)
are not different at P=0.05. Means calculated on 15 replicates.
^ Water regime: well watered (WW); wilt maintained for 1 day prior to watering for last
2 weeks of production (LW+I); wilt maintained for 1 day prior to watering (W+l); wilt
maintained for 3 days prior to watering (W+3).


The greenhouse light and water stress levels evaluated in this study produced

anatomical and physiological differences in Catharanthus. The changes due to water stress

allowed for improved landscape establishment and growth. Even though the two

greenhouse light levels resulted in plants with different leaf areas, stomatal densities,

stomatal conductances and degrees of osmotic adjustment, no effects due to light were

detected on the field growth ofCatharanthus either after 2 or 6 weeks. Perhaps this is due

to the fact that the two light levels did not produce plants with differences in total stomata

per leaf, transpiration per unit leaf area or in turgor loss points, all factors that have a great

influence over plant water status and photosynthetic capacity. It should be noted again

that plants in this study did not experience noticeable water stress (i.e. wilting) in the field,

although some stress may have occurred that would affect stomatal closure (Bates and

Hall, 1981, 1982; Blackman and Davies, 1985; Davies t al., 1980; Gollan et ., 1986,









78

Gowing et al., 1990; Kuppers et al.. 1988: Passioura, 1988; Saab and Sharp. 1989; Zhang

and Davies, 1989, 1990a; Zhang t al., 1987). That these two production light levels did

not help nor hinder the establishment of Catharanthus in the field under well watered

conditions gives growers some leeway on what light levels they may consider for growing

this particular crop ifpostproduction performance is a concern.

Moisture stress conditioning of Catharanthus during greenhouse production benefitted

landscape establishment and growth. The goal of establishing ornamental bedding plants

in a landscape setting is to have them fill in the bed and flower as quickly as possible.

Unlike establishing vegetable transplants in the field, where the goal is to maximize yield,

increase in plant size is given a higher emphasis for ornamental bedding plants over

increase in shoot dry weight. Increasing water stress levels in the greenhouse resulted in

increased plant height, width and size to a small extent after 2 weeks in the field. After 6

weeks in the field, however, a much greater increase in plant height, width and size was

realized by growing the plants under increasingly severe water stress cycles in the

greenhouse. Since there was not a significant difference between the W+1 and W+3

treatments, it is suggested that the W+1 treatment be used so as not to delay greenhouse

flowering and/or reduce flower size without realizing any added benefit in postproduction

performance. Latimer (1990, 1991) did not find any improvement in field establishment

ofBrassica oleracea Zinia or Tagetes when plants were moisture stress conditioned in

the greenhouse. However, the plants were only allowed to wilt for 2-4 hours before being

rewatered. Drought conditioning in the greenhouse decreased lateral growth and quality

ofImpatiens in the field (Laitmer, 1991).











Moisture stress conditioning during greenhouse production resulted in anatomical

and physiological changes that could account for the improved growth in the field.

Energy for plant establishment in the field must come from stored carbohydrates, readily

available sugars and/or from the production of new sugars. If the production level of

new sugars can at least be maintained once the plants are placed into the field, then

establishment and growth should exceed that of plants whose sugar production decreases

due to water conserving measures such as closing stomata. forcing the plant to deplete

stored food reserves. The anatomical and physiological changes reported in this study

resulted in plants that were potentially able to better tolerate moisture stresses in the field

without reducing photosynthetic capacity. For example, increasing greenhouse water

stress resulted in plants with smaller spongy mesophyll cells which results in a greater

A'"/A that can lead to increased photosynthetic rates and water-use efficiency (LeCain el

al, 1989; Patton and Jones, 1989). Increasing greenhouse water stress produced plants

that had fewer total stomata per leaf. The reduction in stomata density explained why

transpiration per unit leaf area was lower for plants grown under increasing water stress

levels (Rajapakse et al, 1988; Rutland et al, 1987). Stomatal conductances were also

found to be lower for moisture-stress-conditioned plants. Therefore, even under

conditions where field soil moisture was adequate, plants that were grown under water

stress conditions lost less water due to reductions in stomatal apertures (Burrows and

Milthorpe, 1976). Plants that lose less water, either due to fewer stomata and/or smaller

apertures, were better able to maintain mesophyll water potentials necessary to keep

photosynthesis from declining. In spite of fewer stomata and lower stomatal









80

conductances which would reduce the amount of carbon dioxide entering the mesophyll,

moisture stress conditioned plants were apparently able to maintain photosynthesis at a

level which resulted in more growth in the field compared to the well watered controls.

The ability of moisture stress conditioned plants to maintain turgor at lower water

potentials due to fewer stomata and/or lower stomatal conductances and greater osmotic

adjustment outweighed the reduced amounts of carbon dioxide entering the leaf.

Plants from all greenhouse water stress levels were shown to have osmotically

adjusted compared to the WW controls. This osmotic adjustment allowed the plants to

reach lower water potentials before losing turgor. Maintaining cell turgor and

chloroplast volume allowed photosynthesis to continue at these lower water potentials

(Eakes et al., 1991b; Gupta and Berkowitz, 1987; Matthews and Boyer, 1984; McCree,

1986). How long this benefit from osmotic adjustment continued without the plants

being subjected to more water stress cycles was not certain. However, it has been shown

to last long enough to keep plants from experiencing as much water stress during the

critical first week of field establishment (Jones and Rawson, 1979).

From the treatments evaluated in this study, it is recommended that Catharanthus

roeus 'Cooler Peppermint' be produced under either light level with a water regime

consisting of allowing the plants to wilt for one day between thorough waterings,

beginning 2 weeks after plugs are transplanted. This treatment will result in compact,

well-proportioned plants acceptable for shipping and marketing that will establish

quickly in a landscape bed setting. A water regime that is any more stressful will not

yield any significant gain in landscape growth relative to the increased production time









81
and reduction in flower size.















CHAPTER 5
EFFECTS OF PRODUCTION FERTILIZER. WATER REGIME AND
UNICONAZOLE ON THE GREENHOUSE GROWTH AND LANDSCAPE
PERFORMANCE OF
CATHARANTHUS ROSEUS 'COOLER PEPPERMINT'


Introduction


Because of economic factors, a goal of most commercial greenhouse producers of

ornamental bedding plants is to produce as many crops as possible during the season. For

many crops, the use of high levels of water and fertilizer are necessary to achieve this fast

growth rate. Chemical growth retardants are used to produce a compact plant so it will be

of acceptable size for shipping and marketing. Many of these greenhouse practices are

being shown to have negative effects on the postproduction performance of these bedding

plants (Armitage, 1993). Plant conditioning, or hardening, during production by adjusting

nutrient and/or water regimes is receiving increased attention as a way to produce sturdy

plants with a high level of photosynthetic reserves that are capable of quick establishment

and growth in the landscape (Dufault, 1994; Latimer, 1990).

Pre-transplant conditioning has been defined as the process of nutritionally

conditioning seedlings during the greenhouse production phase to predispose the seedlings

to tolerate transplant stresses better, recover quickly from transplant shock and enhance

earlier yields (Dufault, 1986). Cucumis grown with increasing rates of nitrogen in the









83

greenhouse had a greater occurrence of transplant shock than those conditioned with low

nitrogen (Dufault, 1986). Lower nitrogen levels were shown to promote root growth

over shoot growth in many crops, thus increasing their root:shoot ratio (Masson t al..

1990, 1991; Tremblay and Senecal, 1988). Transplants with well developed root systems

recovered more quickly from transplant shock (Weston and Zandstra, 1986).

Conditioning seedlings with low pre-transplant nutritional conditioning before field

planting has been shown to be more beneficial than hardening with total nutrient

withdrawal (Armitage, 1986; Garton and Widders, 1990; Nell et al., 1994).

Eakes et al. (1991a) defined moisture stress conditioning as the controlled exposure of

plants to moisture deficits during production. Moisture stress conditioning during

production was reported to improve the growth and/or yield of several agronomic crops

when exposed to future moisture stress (Ackerson and Hebert, 1981; Brown gt aW., 1976;

Gupta and Berkowitz, 1987; Matthews and Boyer, 1984). Petunia grown under a low-

frequency irrigation regime exhibited improved postproduction quality (Armitage and

Kowalski (1983b). Moisture stress conditioning of both Salvia (Eakes et al. 1991a) and

Catharanthus (Virk and Singh, 1990) were found to improve their physiological tolerance

to lower water potentials due to osmotic adjustment, but neither of these studies evaluated

the plants' postproduction performance in landscape beds.

Chemical growth retardants are commonly used in the commercial production of

bedding plants to produce plants that are compact, making them easier to ship and more

attractive to the consumer. However, the carry over effect of these growth retardants into

a landscape setting has only recently started to be a concern. Latimer (1991) showed that











Zini, Impatiens and Tagetes all experienced reduced landscape establishment and

growth to various degrees from the three growth retardants studied, paclobutrazol.

daminozide and ancymidol. Tagetes growth continued to be reduced by drench treatments

in the greenhouse of paclobutrazol for up to 138 days after treatment (Keever and Cox.

1989). Plants where paclobutrazol was foliar applied did not experience reductions in

growth for as long. Residual effects may be more important with the use of the new

triazole compounds, such as paclobutrazol and uniconazole, which appear to be active in

plants for longer than the older growth retardants (Davis t al., 1988). Chemical growth

retardants have also been shown to improve the stress tolerance of treated bedding plants

in the landscape by modifying plant anatomy and/or physiology (Armitage et al., 1981;

Cathey, 1964; Davis and Andersen, 1989; Seeley, 1985).

The purpose of this research was to evaluate the effect ofpretransplant- nutritional-

conditioning, moisture-stress-conditioning and a chemical growth retardant (uniconazole)

on the subsequent establishment and growth of Catharanthus in a landscape field setting

with two slow-release fertilizer rates. Uniconazole translocates exclusively in the plant

xylem (Dalziel and Lawrence, 1984). It reduces plant growth by inhibiting the first three

steps ofent-kaurene oxidation, blocking the oxidation ofkaurene to kaurenoic acid and

thus inhibiting gibberellin biosynthesis (Rademacher et al., 1984). The goal of the first

experiment was to determine the proper time to apply and concentration of uniconazole so

that plants leave the greenhouse with an acceptable size and appearance and yet will not

suffer any reductions in growth once they are planted in a landscape setting. Another goal

of this experiment was to determine if fertilizer in the landscape can be used to help









85

overcome any potential residual effects from a greenhouse-applied growth retardant. The

goal of the second experiment was to determine if producing Catharanthus under lower

than commercially standard nitrogen levels would have any negative effects on greenhouse

growth and/or landscape performance under two different slow-release fertilizer rates.

Also, the second experiment was designed to compare the effectiveness of moisture stress

conditioning versus a commercially used plant growth retardant in producing a compact

plant that would also perform well in the landscape.


Materials and Methods


Experiment This experiment was designed to investigate the effects ofuniconazole

greenhouse application time and concentration on the subsequent landscape growth of

Catharathhus roses 'Cooler Peppermint'. Seedlings were grown in 390 plug trays were

shipped from Natural Beauty Greenhouses in Apopka, Florida, to Gainesville, Florida on 2

April 1993. The 18 mm x 18 mm plugs were transplanted into 10-cm diameter by 8-cm

deep plastic azalea containers using Vegro Clay Mix (Verlite Co., Tampa, FL) medium on

3 April. All plants were thoroughly watered and spaced on wire mesh benches in a Lexan-

covered greenhouse. Since some plugs contained multiple plants, all but one plant per

container were basally cut with a pair of scissors. Plants were maintained well-watered as

necessary throughout the experiment and never experienced wilting conditions. Liquid

fertilizer derived from 20% N, 4.3% P, 16.6% K was applied at a concentration of 150

ppm N during each watering throughout the greenhouse portion of the experiment.









86

On 26 April, all plants were placed into a randomized, complete block design with five

plants per experimental unit and three replications. The experiment was a 2 x 5 x 2

factorial with 2 uniconazole application times, 5 uniconazole concentrations and 2

landscape fertilizer rates. The two times that uniconazole was applied were "week 3"

(applied 3 weeks after plugs were transplanted) or "week 5" (applied 5 weeks after plugs

were transplanted). The five concentrations of uniconazole were "control" (0 mg-liter').

"low" (1 mg-liter'), "medium" (2 mg-liter'), "high" (4 mg-liter') or "very high" (8

mg-liter'). The two landscape fertilizer rates were "low" (0.38 lbs of N/1,000 ft2 with

0.25 lbs of N supplied per month) or "high" (1.5 lb of N/1.000 ft2 with 1.0 lb of N

supplied per month). The fertilizer was Nutricote 14-14-14 type 70 (14% N. 3.0% P,

11.6% K) and was incorporated into the top 6 inches of soil with a rototiller.

Uniconazole was applied at the volume of 2 quarts solution per 100 ft2. The

greenhouse production phase of the experiment was terminated on 12 May. At this time

plant height, plant width and shoot dry weight were determined. Plant height was

measured from the level of the medium to the top of the plant. Two plant width

measurements were taken perpendicular to each other and averaged to determine average

plant width. The average plant width was added to the plant height and divided by two to

calculate average plant size. Shoot dry weight was determined by harvesting all plant

tissue above the medium level, drying in a 70 C drying oven for 7 days and weighing.

Soil in landscape beds had a sand texture, a pH of 6.5, a very high level of available

phosphorous (120 ppm+ P) and a medium level of available potassium (48 ppm K). The

plants were planted 12-inches apart on 14 May. Plants were watered as needed to avoid









87

visible wilting with a drip irrigation system for the duration of the landscape portion of the

study. Watering occurred on a daily or every-other-day basis.

Height and two widths were measured on each plant on 15 May. 31 May. 12 June and

23 June. Average plant width and plant size were determined for each date. The

landscape portion of the study was terminated on 29 June at which time all tissue above

the soil line was harvested, placed in a drying oven at 700 C for one week and weighed to

determine shoot dry weight. Change in plant height, width and size was calculated for

each two-week time interval and for the entire time (6 weeks) in the landscape. All data

were subjected to analysis of variance and regression analysis.

Experiment 2. This experiment was designed to investigate the effects of production

fertility, production moisture-stress-conditioning and greenhouse applied uniconazole on

the subsequent landscape performance ofCatharanthus. Seedlings were obtained as

described previously on 6 June 1996 and transplanted into 10-cm diameter by 8-cm deep

plastic azalea containers using Vegro Clay Mix (Verlite Co., Tampa, FL) medium on 7

June. Plants were thoroughly watered and spaced on wire mesh benches in a Lexan-

covered greenhouse and pruned to one plant per container. Plants were maintained well-

watered and never experienced wilting conditions during the subsequent 2-week period.

On 21 June, all plants were placed into a randomized, complete block design with five

plants per experimental unit and three replications. The experiment was a 2 x 3 x 2

factorial with 2 greenhouse fertilizer concentrations, 3 water regimes and 2 landscape

fertilizer rates. The two greenhouse fertilizer concentrations were "low" (50 ppm N) and

"high" (150 ppm N). Liquid fertilizer derived from 20% N, 4.3% P, 16.6% K was used











for both fertilizer concentrations during the greenhouse portion of the experiment. The

three water regimes in the production phase were "WW" (plants were maintained well

watered throughout the entire experiment), "W+1" (plants were allowed to wilt for one

day before being watered again) and "WW+Uniconazole" (plants were maintained well

watered and sprayed with 2 mg-liter' uniconazole on 28 June). The two landscape

fertilizer rates were "low" (0.38 lbs of N/1000 ft2 with 0.25 lbs. of N supplied per month)

or "high" (1.5 lbs of N/1000 ft2 with 1.0 lb of N supplied per month). The fertilizer was

Osmocote 14-14-14 (90 day release time) and was incorporated into the top 6 inches of

soil with a rototiller.

The greenhouse production phase of the experiment was terminated on 26 July. At

this time plant height, width and size were determined. Plant size and mass were

measured as described in Experiment 1.

The plants were installed on 28 July in the same landscape bed using the same

procedures as described for Experiment 1. Height and two widths were measured on each

plant on 28 July, 12 Aug., 26 Aug. and 9 Sept. Average plant width and plant size were

determined for each date. The landscape portion of the study was terminated on 10 Sept.

at which time all tissue above the soil line was harvested, placed in a drying oven at 700 C

for 1 week and weighed to determine shoot dry weight. Change in plant height, width and

size was calculated for each two-week time interval and for the entire time (6 weeks) in

the landscape. All data were subjected to analysis of variance and Tukey mean separation.












Results and Discussion


Experiment 1- Greenhouse Growth

There was a significant interaction between uniconazole application time and

uniconazole concentration in their effects on plant height, width and size at the end of the

greenhouse production phase (P=0.0001). For application at week 3, increasing

concentrations of uniconazole were found to decrease final greenhouse height (Figure

5-1), width (Figure 5-2), size (Figure 5-3), total leaf area (Figure 5-4) and shoot dry

weight (Figure 5-5). Regression analysis gave the best fit for all of the above growth

parameters with a linear model (P=0.0001). I think that plants treated with uniconazole

between 2 and 4 mg-liter' possessed the most desirable size and proportion for marketing.

For application at week 5, increasing concentrations of uniconazole produced no

significant differences in plant height (Figure 5-1), width (Figure 5-2) or size (Figure 5-3)

at the end of greenhouse production. That no difference in plant growth occurred for this

application time was not surprising for the growth retardant was only applied 2 days

before measurements were taken.


















I
Week 3

Week 5


0 1 2 4 8
Uniconazole (mg/liter)


Figure 5-1 Effect of uniconazole application time and concentration on final plant height
in the greenhouse. Week 3: y=14.04 -0.71x, r=.74; Week 5: n.s.


Week 3
v
Week 5


0 1 2 4 8
Uniconazole (mg/liter)


Figure 5-2 Effect of uniconazole application time and concentration on final plant
width in the greenhouse. Week 3: y=16.71 -0.53x, r=.76; Week 5: n.s.


V V V V


r


























0 1 2 4 8
Uniconazole (mg/liter)


Week 3
Week 5
Week 5


Figure 5-3 Effect ofuniconazole application time and concentration on final plant size
in the greenhouse. Week 3: y=15.38 -0.62x, r=.78; Week 5: n.s.


600

500

400

300

200

100


Week 3


0 1 2 4 8
Uniconazole (mg/liter)
Figure 5-4 Effect of uniconazole concentration at week 3 on final total leaf area in
the greenhouse. Week 3: y=557 -17x, r.81.














2.5

2

1.5
Week 3
o 1
o
0
ei 0.5

0
0 1 2 4 8
Uniconazole (mg/liter)
Figure 5-5 Effect ofuniconazole concentration at time 3 on final shoot dry weight
in the greenhouse. Week 3: y=2.16 -0.07x, r=.36.


Experiment 1 Landscape Growth

A three-way interaction between effects of uniconazole time, concentration and

landscape fertilizer rate did not exist for change in plant height, width or size during the

first 2 weeks in the field (Table 5-1). There was a significant interaction between effects

of time of uniconazole application and concentration on changes in plant height, width and

size (Table 5-1). Regression analysis gave the best fit for all of the above growth

parameters with a linear model. When uniconazole was applied at 3 weeks in the

greenhouse, increasing concentration resulted in greater height growth (Figure 5-6).

When uniconazole was applied at 5 weeks in the greenhouse, increasing concentration

resulted in less height growth. Uniconazole concentration did not affect change in plant

width for week 3, although increasing concentrations resulted in smaller changes in plant

width for week 5 (Figure 5-7). Change in size increased as uniconazole concentration











increased for week 3 and decreased as concentration increased for week 5 (Figure 5-8).

Plants grown at the high field fertilizer rate had greater increases in plant widths (8.39

versus 6.93 cm) and size (5.81 versus 5.08 cm), but had no effect on height growth (3.23

versus 3.24 cm) between 0 and 2 weeks in the field.


Table 5-1 Significance of uniconazole application time, concentration and landscape
fertilizer rate on change in plant height, width and size of Catharanthus rose 'Cooler
Peppermint' between 0 and 2 weeks in the field. Experiment 1.


Effect

Fertilizer

Time

Fertilizer*Time

Concentration

Time*
Concentration

Fertilizer*
Concentration

Fertilizer*Time*
Concentration


Change in:

Height (cm)

Significant at P =

0.9460

0.0001

0.8344

0.0502

0.0021


0.6136


0.9356


Width (cm)


0.0072

0.0001

0.4696

0.0269

0.0045


0.3644


0.4710


Size (cm)


0.0471

0.0001

0.5304

0.0654

0.0001


0.4609


0.7447
























Week 3
Week
Week 5


0 1 2 4 8
Uniconazole (mg/liter)


Figure 5-6 Effect of uniconazole application time and concentration on change in plant
height after 2 weeks in the field. Week 3: y=3.49 +0.13x; Week 5: y=3.09 -0.16x, r=.47.


'i








0 1 2 4 8
Uniconazole (mg/liter)


W
Week 3

Week 5


Figure 5-7 Effect of uniconazole application time and concentration on change in plant
width after 2 weeks in the field. Week 3: n.s.; Week 5: y=7.38 -0.25x, r=.63.




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