THE EFFECT OF LIGHT INTENSITY ON THE INITIATION AND DEVELOPMENT OF FLOWERBUDS IN THE SAINTPAULIA

44 Pages·2.347 MB·English

by  STINSON, RICHARD FLOYD

THE EFFECT OF LIGHT INTENSITY ON THE INITIATION AND
DEVELOPMENT OF FLOVJER BUDS IN THE SAINTPAULIA
Dissertation
Presented in Partial Fulfillment of the Requirements
for the Degree Doctor of Philosophy in the
Graduate School of The Ohio State
University
By
RICHARD FLOYD STINSON, B.S., M.S.
The Ohio State University
1952
Approved by:
X . X"
/} '
Adviser
ACKNOWLEDGMENT
The author wishes to extend his appreciation to Prof. A. Laurie
and Dr. L. C. Chadwick for their helpful suggestions and guidance
during the course of this study.
He also expresses his thanks to Dr. R. A. Popham of the Botany
Department for his interest and guidance in the anatomical aspects
of the problem.
An expression of gratitude is also due the African Violet
Society of America for granting a fellowship under which this work
was done.
The author also thanks Dr. K. S. Nelson and Mr. F. C. Galle
for their suggestions and assistance in the preparation of the
photomicrographs.
Appreciation is also expressed to those undergraduate students
who assisted in growing the plants.
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TABLE OF CONTENTS
Introduction .............................................. 1
Review of Literature........................................2
Early Indications of Floral Initiation ............... 2
Differences Between Vegetative and Floral Apices . . . . 3
Factors Influencing Floral Initiation ................. h
Factors Effecting Floral Development ................. 6
Order of Floral Organ Initiation ..................... 8
Procedure..................................................10
Results ....................... 13
Photomicrographs of Stages in Initiation and
Development................................... 16
Table 1. The Earliest Appearance of Each Stage . . . . 31
Discussion.................................................32
Conclusions........................... 3ha
Literature Cited ......................................... 35
Autobiography ........................................... 10
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INTRODUCTION
In recent years, Saint pauHa ionantha has bee cane an important
commercial potted plant crop in the United States. In wholesale
dollar returns, it ranks as the ninth most important potted plant
crop in the United States according to figures released by the
U. S. Department of Commerce in the 1950 Census (53). Its whole­
sale value for 1949 was about one million dollars.
Many commercial and amateur growers experience occasional
difficulty in attempting to bring about flowering in this plant.
It is thought that the primary cause of this difficulty may be
insufficient light. Laurie and Kiplinger (30) and Post (43)
suggest that the optimum light intensity for growth and flowering
of this plant is between 800 and 1000 foot-candles. The plants
may be damaged by death of leaf tissues at higher light intensities,
and low light intensities have been observed to reduce vegetative
growth and flowering.
It was not known whether failure of the plants to flower at
low intensities was due to their failure to initiate flowers, or to
failure of the flowers to develop after having been initiated, as
has been found to occur in Rosa (29) and Chrysanthemum (41). The
purpose of this study was to determine the effect of various light
intensity conditions upon floral initiation and development in
Saintpaulia ionantha.
REVIEW OF LITERATURE
Early Indications of Floral Initiation
The first evidence of a change from a vegetative to a reproduc­
tive type of growth has been found to occur in a number of different
ways.
A broadening and flattening of the stem apex has been observed
as the first evidence of floral initiation in Better Times rose
(29), pineapple (27) (57), tomato (10), citrus (17), Concord grape
(52), and garden pepper (9)* The first evidence of floral initiation
in Dipsacus (39), Rubus (12), and Hydrangea macrophylla (50) (54)
has been reported as a broadening and rounding of the stem apex.
It appears from the literature that there is essentially no
change in the shape of the stem apex at the time of floral initiation
in tulip (4&), Vinca rosea (4), and Frasera carolinensis (36).
Only one worker reports finding the floral apex smaller than
the vegetative apex. Brooks (7) reporting on Amygdalus communis
states, "At the time the flower bud is initiated, the surface of the
apex covers an exceedingly small area in comparison with that of the
leaf bud in a similar stage of development, for the width of the
flower bud apex between the bud-scale primordia is only 50 microns,
whereas, the leaf-bud type is 150 microns--
Internal Changes
A number of investigators have found internal anatomical changes
that seem to be the first evidence of the change of a vegetative
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apex into a flowering shoot. These internal changes frequently
precede changes in the shape and organization of the stem tip,
which indicate that floral initials are about to be formed,
Xn Garrya elliptica (46), it was found that floral initiation
was indicated by the formation of a narrower medulation zone in the
stem apex.
It has been reported that the first indication of floral
initiation in azalea Coral Bell (28) is a change in the shape of the
pith cells from their flattened form and regular chain arrangement
to an isodiametric shape with less prominent chains of cells.
The absence of a cambial zone and an elongation of the cells in
that area indicates the initiation of the capitulum in Chrysanthemum
morifolium (41)* The initiation of floret primordium in this
composite is first recognized by periclinal divisions in Layer II
of the “tunica.11
In Phlox drummondi (37), the first indication of a change from
a vegetative to a floral apex is the loss of decussate phyllotaxis.
Differences Between Vegetative and Floral Apices
Among the first individuals to study vegetative and floral shoot
apices were Gregoire (18) and Mujuxadar (35) • They concluded that
there is a fundamental difference between these types of shoot apices.
More recent workers agree that physiologically there is a
fundamental difference, but ontogenetic ally there is none. Popham
and Chan (41), in their study of Chrysanthemum morifolium concluded
that the receptacle represents a continued, hut specialized de­
velopment of the vegetative shoot apex while the flower head and
vegetative shoot apex are unlike enough to be thought of as
fundamentally different.
Kasapligil (26) working with Umbellularla found that the
organization of the vegetative inflorescence, and floral apices
are so similar that they may be represented by a single diagram.
He also points out that similar conclusions have been reached by
others working with Bubus and Vinca. McCoy (36) reported similar­
ly ^or Frasera carolinensis, and Esau (13) has cited numerous
papers in support of this concept. Arber (2), suggests that the
inflorescence appears in many respects to represent the inter­
mediate between a vegetative shoot and a flower.
Factors Influencing Floral Initiation
The causes of flowering in plants have been studied by a
number of workers. Thompson (56) points out that the results of
numerous experiments by many workers have shown that the initiation
of flowering in plants may be influenced by many factors including
temperature, light, length of exposure, and age or size of plants.
To these could be added food supply and phytohormones.
Temperatures before floral initiation may affect the time of
flowering according to a study undertaken by Grainger (17). Low
temperatures during the period of floral initiation have been found
to inhibit floral initiation in azalea Coral Bell (28) and. Camellia
5.
(5). It has been reported for Chrysanthemum morifolium (41) that
the capitulum is formed under this condition, but that further
development is inhibited. Floral initiation in Hydrangea
macrophylla (51) is reported to be unaffected by low temperatures.
Reporting on their work on the effect of length of day and
night upon the growth of plants, Garner and Allard, (15) found that
although the duration of light may control the attainment of the
reproductive stage in many plants, the intensity from one-fourth to
full normal sunlight is not an important factor in the attainment
of that stage. However, they state: "In all species thus far studied,
the rate of growth is directly proportional to the length of dally
exposure to light."
Bonner (5) found that the number of flower buds produced by
Camellias under favorable conditions of temperature and photoperiod
is markedly influenced by light intensity, high light intensities
increasing the number of flower buds set.
In their study of floral initiation in the greenhouse
chrysanthanum, Popham and Chan (41) report: "Brief exposures to short
photoperiod followed by continued long photoperiod initiate the
capitulum, but further differentiation does not take place." When
short photoperiods were not discontinued, floral initiation took
place, indicating that the initiation of flowering in this plant is
strongly influenced by day length.
A number of experimenters have found evidence that photosynthetic
activity at the time of floral initiation may be an important factor.
.
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Defoliation of Hydrangea macrophylla just prior to the usual floral
initiation period has been reported (44) (54) to completely inhibit
floral initiation. Other workers (50) using the same plant, but
reducing the photosynthetic rate by lowering the light intensity,
concluded that low carbohydrate accumulations had no influence on
floral initiation in this plant.
Working with apple, several workers (16) (20) (21) (22) concluded
that the number of floral initials formed appears to bear a
quantitative relationship to the foliage area.
Others using mango (45), castor bean (49), soybeans (38), and
citrus (1) have concluded that the reduced photosynthetic activity
adversely influences flowering in the plants they studied.
Furuta (14) has found that variations in the nitrogen levels of
the soil in which chrysanthemums are growing influence neither the
time of floral initiation nor the number of flower buds initiated.
Experimental evidence has strongly suggested to a number of
workers (17) (31) (32) (55) that floral initiation and development
is influenced by phytohormones. Other workers using apple (20),
chrysanthemum (8) (41), pineapple (57), and Xanthium (6) (19) have
reached similar conclusions.
Factors Effecting Floral Development
A number of investigators have studied the effects of various
environmental factors upon differentiation and development of floral
primordia. Among the factors studied have been photoperiod, tempera­
ture, food supply, and nutrition.
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Austin (3) studied the influence of the length of photoperiod
on the vegetative and reproductive development of several plants.
He found that the development of flower buds after their initiation
was quantitatively hastened in Rudbeckia bicolor superba and
retarded in Delphinium a.iacis by increased length of photoperiod.
In Cosmos sulphureus and Impatiens bakami ana the length of the
photoperiod had no observable influence on the development of the
flower bud after it had been initiated.
In a study of greenhouse chrysanthemum, Furuta (14) found that
although flower bud initiation of chrysanthemums seems to be
independent of day length alone, the development of flower buds
depends upon continuous short photoperiods.
MacDougal (34) found lesser degree of differentiation in
etiolated plants of several species when compared to plants exposed
to light.
Howlett (23) found that the development of tomato flowers is
influenced by light and nitrogen supply.
Delay in flower bud development of chrysanthemum, resulted when
very little nitrogen was available in the soil in which they were
growing (14).
Temperature has been found to influence floral development in
onion (47) and camellia (5). Temperature variations were found to
have no influence on flower bud differentiation in hydrangea (24).
A hereditary factor has been suggested as influencing the
different rates of floral development in early and late varieties