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CHEMICAL INDUCTION OF STAMINATE FLOWERS ON GYNOECIOUS

CUCUMBER (Cucumis sativus)

 

By

LaMoine Devon Anhder

AN ABSTRACT

Submitted to the College of Agriculture, Michigan State University of
Agriculture and Applied Science in partial fulfillment of
the requirements for the degree of

MASTER OF SCIENCE

Department of Horticulture

1959

: . . . . (.1

Approved w/ : . . .. ' A...

 

LA MOINE DEVON ANHDER ABSTRACT

Suppression of staminate flowers on lines segregating gynoecious
plants was not achieved with Maleic Hydrazide, Alpha-naphthaleneacetic
acid or 2—3-5 rri-iodobenzoic acid.

Application of N-para-chlorophenylphthalamic acid to gynoecious
plants did not alter their sex expression. Staminate flowers were induced
on gynoecious plants with foliar applications of gibberellic acid (A-3).
Concentrations varying from 100 ppm to 5, 000 ppm were effective. In-
duced staminate flowers produced viable pollen and self and sib pollina-

tions using this pollen resulted in gynoecious progenies.

CHEMICAL INDUCTION OF STAMINATE FLOWERS ON GYNOECIOUS

CUCUMBER (Cucumis sativus)

 

By

LaMoine Devon Anhder

A THESIS

Submitted to the College of Agriculture, Michigan State University of
Agriculture and Applied Science in partial fulfillment of
the requirements for the degree of

MASTER OF SCIENCE

Department of Horticulture

1959

ACKNOWLEDGEMENTS

The author wishes to express his sincere appreciation and thanks
to Dr. C. E. Peterson for his advice and supervision in planning the in-
vestigation and in the preparation of this thesis.

The writer is grateful to Drs. S. H. Wittwer and J. C. Rallard
for their advice and suggestions on the experiments.

Acknowledgement is expressed to Drs. S. Honma, F. C. Elliot,
and D. J. DeZeeuw for their helpful review of the manuscript.

The writer is indebted to his wife for her encouragement and

sacrifices made throughout these investigations.

TABLE OF CONTENTS

Page
INTRODUCTION ...................... 1
REVIEW OF LITERATURE . . . ........... . . . 2
MATERIALS AND METHODS ................ 6
A. Breeding Lines ................... 6
B. Chemical Treatments . . . . ............ 7
C. Data Recorded . ................. . 12
RESULTS ......................... 13
A. Staminate Flower Suppression ........... 13
B. Staminate Flower Induction ............ . 13
DISCUSSION AND CONCLUSIONS ............... 23
A. Staminate Flower Suppression ........... 23
B. Staminate Flower Induction ............. 23
SUMMARY ..... , ................... 2?

LITERATURE CITED .................... 28

INTRODUCTION

Standard pickling cucumber varieties are monoecious and the ratio
of staminate to pistillate flowers is approximately 25 to 1. A recent
cucumber introduction from Korea, PI 220860, produced a number of
completely pistillate (gynoecious) plants as well as monoecious types.
The incorporation of this gynoecious flowering habit into pickling cucum-
bers resulted in the development of lines with varying degrees of
"femaleness", ranging from gynoecious to normal monoecious. The
plant breeder faced two problems in using this new introduction in
developing methods for the economical production of hybrid cucumber
seed; 1) Staminate flower removal would still be necessary if lines with
low staminate-pistillate flower ratio were used as female parents.
2) Gynoecious lines would eliminate the necessity for staminate flower
removal, but these lines could not be maintained.

The principal objectives of this work were first, to determine if
the relatively few staminate ﬂowers produced on certain lines not homozygous
for the gynoecious character could be completely suppressed by the use of
growth regulating chemicals, and second, to determine if staminate flowers
could be induced on gynoecious lines by the use of growth regulating chem-

icals.

REVIEW OF LITERATURE

The available literature on the flowering habit of plants in response
to environment and growth regulating chemicals is so extensive that gener-

ally only material pertaining to Cucurbitaceae and more specifically Cucumis

 

_s_a_tiv_t_1_s has been considered in this review.

Studies of the nodal sequence of ﬂower types in the normal monoecious
cucumber by Currence (1) and Nitsch _e_t_aLl_. (21) indicate that the type of
ﬂower which develops in a given leaf axil varies with the ﬂower's position
on the plant. A gradual shifting from staminate to pistillate ﬂowers oc-
curring as the plant ages.

Tiedjens (24), Edmond (2), Nitsch eta}: (21), Ito and Saito (9, 10)
found that the length of photoperiod exerts a modifying inﬂuence on ﬂower
type. Long days increased the number of staminate ﬂowers, while a
reduction of light increased pistillate ﬂower formation and decreased the
number of 'staminate ﬂowers. Ito and Saito (9, 10) also observed that
warm nights apparently intensified the effect of long days. The effect of
long days and warm nights was proportional to the duration of the treat-
ment. In the same series of experiments Ito SE _a_1_. (5) state that by pinch-
ing the main stem, staminate ﬂowers of the Japanese cucumber were trans-

formed into bisexual ﬂowers, pistillate flowers and into somewhat mal-

formed lateral branches. They concluded that since all cucumber ﬂowers
in the primordial stages bear both sets of sex organs, the sex expression
shifts according to the physiological condition of the node at which the
ﬂowers are borne, responding variably to environmental conditions and
the age of the plant.

Other factors inﬂuencing sex expression have also been reported.
Tiedjens (24) found that maturing fruit exert an inhibitory effect on the
production of pistillate flowers as well as on the development of the plant.
Varietal differences in sex expression have been described by Edmond (2)
and Kumazawa _e_t_ 31'. ( 13). High nitrogen and low water favor staminate
ﬂower induction under long days and high night temperatures and low
nitrogen resulted in earlier pistillate ﬂower production according to Ito
and Saito (12). They found the effects of nitrogen and water, however,
were masked when the plants were maintained under short days and at low
night temperatures.

Numerous growth regulating chemicals have been employed in the
study of cucumber sex expression. Laibach and Kribben (14, 15, 16, 17, 18)
applied alpha-naphthaleneacetic acid (NAA) in a lanolin paste to the petiole
stub of the second leaf of cucumbers and obtained an increase in the num-
ber of pistillate ﬂowers. Spraying of terminal growth, although less ef-

fective, also increased the number of pistillate ﬂowers. NAA has been

reported by Ito and Kato (4) to produce pistillate ﬂowers even under long
day light conditions.

The effect of NAA on the sexuality of a dioecious plant, Cannibus
£3913 (hemp) was determined by Heslop-Harrison (3). In genetically
"male" plants, applications of O. 5% NAA in a lanolin paste to leaves arising
at the third node, induced pistillate flowers at sites which would normally
be occupied by staminate ﬂowers.

The use of indole—3-acetic acid by Laibach and Kribben (16, 17)
induced pistillate ﬂowering in cucumbers at concentrations higher than
required for NAA. Applications of 2-3-5 tri-iodobenzoic acid (TIBA)
alone or in combination with other growth regulators did not inﬂuence
sex expression. Rehm (23) used TIBA on watermelon and observed that
more pistillate ﬂowers were produced, but staminate flowers were never
fully suppressed. Ito and Saito (6) report that TIBA applied to Japanese
cucumber slightly retarded pistillate flower formation and that 2-4-
dichlorophenoxyacetic acid accelerates pistillate ﬂower formation.
Wittwer and Hillyer (26) reported the suppression of staminate ﬂower
buds in acorn squash for three to four weeks in the greenhouse following
treatment with maleic hydrazide. The most effective treatment was 250
ppm applied when the first true leaf was fully expanded and again when

the fourth or fifth leaf had expanded.

Yabuta and Hayashi (27) noted that gibberellin increased the number
of staminate ﬂowers preceding the first pistillate ﬂower in monoecious
plants. Wittwer and Bukovac (25) found the effects of gibberellin on cucum-
bers paralleled thoSe of long days and low nitrogen levels in delaying the
formation of pistillate ﬂowers. The effects of various concentrations of
gibberellin upon root elongation of germinating seedlings of several plants,
including the cucumber, have been reported by Wittwer and Bukovac (25).

Tiedjens (24) indicated that the control of sex expression is by
some chromosome mechanism. A predominately pistillate cucumber
developed by Kumazawa g El; (13) is not affected by day length and tem-
perature and is additional evidence of genetic control of sex expression.
Peterson and Ballard (22) recently developed completely gynoecious lines
that are not inﬂuenced by day length and temperature. The inheritance of

sex expression has not been fully determined.

MATERIALS AND METHODS

A. Breeding Lines

 

Seed of the various lines used in this experiment was obtained from
the cucumber breeding project at Michigan State University. The following
breeding lines with known ﬂowering habits were used:

1) M. S. U. 131-2, an inbred line known to frequently
produce gynoecious plants.

2) M. S. U. 129, a gynoecious inbred line which produces
an occasional staminate ﬂower.

3) M. S. U. 1123, a completely gynoecious Fl line resulting
from a cross between M. S. U. 129 and a predominantly pistillate
Japanese pollen parent.

4) M. S. U. 713-1, 713-2, 713-2, and 713-21, homozygous
gynoecious sister lines in which chemical induction of staminate
ﬂowers on otherwise completely gynoecious plants had been accom-
plished.

5) SMR-12 and SMR-l8, standard monoecious varieties.

All cucumbers used with the exception of the Japanese cucumber were

black spined pickling types.

 

B. Chemical Treatments

 

l) Staminate ﬂower suppression in 1958.

Suppression of staminate ﬂower productions on MSU line 131-2 by
foliar applications of growth regulating chemicals in aqueous solutions
was investigated.

MSU 131-2 was planted on the Horticultural Farm June 24, 1958
in plots consisting of three replications of ten plants each. Maleic hydra-
zide was used at concentrations of 250, 500 and 750 ppm. Alpha-naph-
thaleneacetic acid was used at concentrations of 100, 200 and 400 ppm
with 0. 1 percent wetting agent (Tween 20) added. 2-3-5-tri-iodobenzoic
acid was dissolved in acetone and used at concentrations of 25, 50 and 200
ppm. Each concentration of the above chemicals was sprayed on the
entire plant at various stages of growth. Thirty non-treated plants were
rogued for staminate ﬂowers at the ten node stage. Forty additional
plants were used as controls.

2) Staminate ﬂower induction 1958.

To induce staminate ﬂowers on MSU 129, a gynoecious inbred line,
the potassium salt of gibberellic acidl in powdered form was used in aqueous

solution at concentrations of 100 and 250 ppm with O. 1 percent wetting

1/
" Supplied by Merck and Company, Rahway, New Jersey as the potassium

salt of gibberellin A3 (gibberellic acid) commercially available under the
trade name, Gibrel.

agent (Tween 20) added. N-para-chlorophenylphtha1amic acid was dissolved
in acetone and used in aqueous solution at concentrations of 10, 20 and 100
ppm. Each concentration was applied to plants at various stages of develop-
ment in plots of five plants each replicated three times. Twenty-five plants
were maintained as controls.

3) Staminate ﬂower induction, greenhouse 1958.

Observations in the field in 1958 indicated the need for further inves-
tigations with gibberellic acid. A commercial emulsion of gibberellic acid
was used. Plantings were made August 20, in 8-inch pots in the greenhouse.
Potted plants of MSU line 1123 were randomized into six plots of three plants
each, and replicated three times. In one treatment 250 ppm of gibberellic
acid was applied at the unfolding of the first true leaf and again at the tenth
true leaf. Additional treatments were four applications at each of four con-
centrations - 250, 500, 1000 and 1500 ppm made at weekly intervals begin-
ning at the unfolding of the first true leaf. Three plants were left untreated
until approximately 25 nodes could be identified for sex expression. After
it had been determined that no staminate ﬂowers had formed, these plants
were sprayed three times at weekly intervals with 1500 ppm of gibberellin.
Six plants of pickling cucumber variety SMR-18 and six plants of MSU 129
were sprayed four times with 250 ppm at weekly intervals beginning with

the unfolding of the first true leaf.

4) Staminate ﬂower induction 1959.

Gynoecious plants in breeding lines grown in the greenhouse during
the winter of 1958-59 were chemically treated to induce staminate ﬂowers.
Self pollination of these plants resulted in the availability of homozygous
gynoecious lines for field work in 1959. Four of these gynoecious lines
and the monoecious varieties SMR-12 and SMR-18 were used in a series of
field experiments conducted in 1959. The plants for these experiments
were started in the greenhouse and transplanted to the field while in the
cotyledon leaf stage. The aerial parts of plants to be treated were sprayed
with aqueous solutions of either the emulsified or powdered form of the
potassium salt of gibberellic acid (A-3). No wetting agents were used.
Concentration of l, 000, 1, 500, 2, 000 and 5, 000 ppm were used. The 5, 000
ppm concentration was applied in one treatment after complete unfolding of
the first true leaf. Each of the remaining concentrations was applied in
two treatments. One treatment when the first true leaf unfolded and again
seven days later, the other when the first true leaf unfolded and again
fourteen days later.

The commercial emulsion was used in the treatment of MSU line 713-1
and variety SMR-IZ to determine if gynoecious and monoecious cucumbers '
vary in their response to gibberellic acid. Solutions of 100 ppm were applied

at weekly intervals for a total of three applications beginning with the unfolding

10.

of the first true leaf. Solutions of 250, 500, 1000 ppm were applied at the
first true leaf stage and again seven days later. A control plot was main-
tained for each of the .two lines. Each plot contained five plants, and treat-
ments were replicated three times.

A method for increasing a gynoecious line was investigated by grow-
ing MSU 713-5 in a 12 by 80 foot screen isolation cage provided with a small
hive of bees. The plants were grown in two rows four feet apart with 12
inches between plants in each row. One row was maintained as a control
and the other was divided into four duplicated plots of six plants each. A
standard concentration of gibberellic acid at 1, 500 ppm was used. The
plants were sprayed at weekly intervals beginning just before the unfolding
of the second true leaf. The plants in one plot received a single application,
in another, two applications, in another three applications, and the final
plot received a total of four applications. The bees were placed with the
cage after the final spray application.

The possibility of producing staminate ﬂowers on gynoecious line
MSU 713-2 by germinating seeds in an aqueous solution containing the potas-
sium salt of gibberellic acid was investigated. Thirty-five seeds were
placed in each of five Petri dishes June 22, 1959 on four thicknesses of paper

toweling. The toweling in four Petri dishes was soaked with 7 milliliters of

ll.

gibberellic acid at one of the following concentrations: 10 ppm, 100 ppm,
1, 000 ppm or 10, 000 ppm. The fifth Petri dish contained distilled water.
The dishes were placed in a seed germinator at a temperature of 82’F.
Twenty-four hours later 15 germinating seedlings from each dish were
transplanted into peat pots filled with soil. After 48 hours in the germinator
another 15 seedlings from each dish were transplanted into peat pots.
Fifteen seeds of SMR-18 were placed in each of two Petri dishes, one a
control, the other treated with 7 milliliters of gibberellic acid at 10,000
ppm. The seedlings were removed after 48 hours and transplanted into peat
pots. On June 29, all transplanted seedlings were placed in the field in
plots of five plants each, replicated three times.

Soil applications of gibberellic acid in an inert clay carrier were used
on remnant plants of the gynoecious lines. Treatments were 44. O and 88. 0
micrograms of gibberellic acid per plant. To insure uniform availability,
35 pounds of soil were removed from an area approximately 12 inches square
and 6 inches deep. The soil was thoroughly mixed with the gibberellin-clay
formulation and replaced. A single transplant was then planted in the soil.
Five plants were used for each concentration. Plants used as control were
transplanted in undisturbed soil.

The final experiment consisted of single foliar applications of gibberellic

acid on gynoecious plants at the ten node stage at concentrations of 2, 500,

12.

5, 000, 10, 000 and 20, 000 ppm in an effort to establish the concentration of

the commercial emulsion of gibberellic acid necessary to cause injury.

C. Data Recorded

 

The nodal sequence of staminate and pistillate ﬂower development on
the main stem of each individual plant was mapped in each experiment.
Nodes were classified as having no visible ﬂowers present, staminate ﬂowers
present, pistillate ﬂowers present, or in some cases as having both stam-
inate and pistillate flowers, regardless of whether or not all of the ﬂowers
reached maturity. A record was kept of the number of staminate ﬂowers
opening each day in the isolation cage. This record began July 20 when the

first staminate ﬂower opened and continued through August 6.

13.

RESULTS

A. Staminate Flower Suppression

 

MSU line 131-2 exhibited considerable heterozygosity as evidenced by
the amount of segregation in the control plots. There was no observable
difference in the sex expression of treated and untreated plants. TIBA at
50 and 100 ppm and more than one application of 25 ppm resulted in death
of all terminal growth. The occurrence of several completely gynoecious
lines in breeding plots, and the discovery that staminate ﬂowers could be
produced on genetically gynoecious plants, eliminated the need for artifi-
cally suppressing staminate ﬂowers. This newly available genetic control
of staminate ﬂower production turned attention to improving methods of

stimulating staminate ﬂower production on gynoecious plants.

B. Staminate Flower Induction

 

1) Summer 1958

Plants of MSU 129 treated with N-para-chlorophenylphthalamic acid
at the 100 ppm concentration gave evidence of mild burning of the leaves
within two days after each application. No other differences in appearance
or sex expression between any of the N-para-chlorophenylphthalamic acid
treated plants and non-treated plants were observed.

Plants of MSU 129 treated with gibberellic acid responded for short

l4.

intervals after each application with rapid and erect terminal growth. A
slight yellowing of the young leaves was observed. A more noticeable
effect was an increase in the number of staminate ﬂowers formed. Plants
given three applications at 250 ppm produced almost ten times as many
staminate ﬂowers as the untreated plants. The observed results and a
schedule of treatments for gibberellic acid are found in Table I.

2) Greenhouse 1958

The effects of gibberellic acid at 250, 500, l, 000 and 1, 500 ppm on
MSU line 1123 grown in the greenhouse during the fall of 1958 are shown in
Table II. The number of nodes at which staminate flowers appeared in-
creased with each increase in concentration of gibberellic acid. No stam-
inate flowers were found on the control plants. Successful hand pollinations
were made on plants in each of these treatments. Three plants treated at
1, 500 ppm after identification of approximately 25 pistillate nodes, produced
several staminate ﬂowers at approximately the 45th node. Four applica-
tions at 25 ppm at weekly intervals on six plants of MSU line 129 produced
staminate ﬂowers on five plants. The same treatment on six plants of
variety SMR 18 resulted in theearliest pistillate ﬂower appearing at node 24.

No control plants of SMR 18 or MSU 129 were maintained.

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3) Summer 1959

The results of the potassium salt of gibberellic acid at concentra-
tions of l, 000, l, 500, 2, 000 and 5, 000 ppm on MSU line 713-21 in 1959
are recorded in Table HI. One application at S, 000 ppm resulted in 9. 5
staminate ﬂowers per 100 nodes. Two applications of each of the other
concentrations at a 14 day interval resulted in a higher number of staminate
flowers per 100 nodes than two applications at a 7 day interval. Each in-
crease in concentration resulted in a higher number of staminate flowers
than lower concentrations applied at the same frequency. The effect
ranged from 2. 9 to 10. O staminate ﬂowers per 100 nodes. Plants showing
malformed terminal growth of the main stem were observed in all treat-
ments. Clusters of pistillate flowers and tendrils, large forked tendrils,
or several long petioled leaves at the stem terminal resulted in a deter-
minate type growth. These distortions were found only on the main stem
and usually seven or eight nodes beyond the last staminate ﬂower. Control
plants showed very little distortion of this type.

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at a concentration of 100 ppm resulted in 5. 5 more staminate ﬂowers per
100 nodes than were observed on untreated plants (Table IV). The same
treatment applied to MSU line 713-1 resulted in 0. 7 more staminate

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trations of 250, 500 and l, 000 ppm each applied twice resulted in a greater
number of induced staminate flowers on the monoecious plants than on the
gynoecious plants. A schedule of treatments and results are in Table IV.

Applications of emulsified gibberellic acid at 1, 500 ppm to gynoecious
line MSU 713-5 in an isolation cage resulted in production of sufficient pollen
for seed increase. The total number of staminate flowers induced increased
with each successive spray application. The sequence of nodes at which
staminate ﬂowers appeared followed a definite pattern. A single application
resulted in staminate ﬂowers at two or three consecutive nodes beginning
at approximately node seven. Two single applications at a seven day inter-
val produced two or three consecutive staminate nodes beginning at approx-
imately node seven, and two or three more beginning at approximately node
13. Three and four single applications at a seven day interval produced a
short series of staminate nodes beginning at approximately node seven,
another beginning at approximately node 13 and one or two staminate nodes
beginning at approximately node 22. Normal pistillate ﬂowers occurred be-
fore and after each series.

In the isolation cage some of the fruit in the row of gynoecious control
plants contained less than a full set of seed. This was not observed in the row
of treated plants. It is estimated that 3 to 4 pounds of viable seed will be har-
vested from the cucumbers in this 12 by 80 foot cage. A schedule of treat-

ments and results are shown in Table V.

21.

.50.0 0.05 0... 000 0.0.0.0. :0 o .050... .3005. ON 0005 50.. 00:0..0 >0... 00 00.0000 0.03 0.030.".

 

 

 

N
0.0.00 0. m:.:0..w0.. 003 .00. 00.. 000000 0.... :0..00......0 .0... .0 0.00 :O
.
w. 3:.
2 .3.
. . 5....
o o. . m. N. 0 30.. com.
S 05..
2 .3.
N .8 . .2 o w .3. E... 80.
FN 000..
v 3:. .00.. com.
12 .2: , 2 R 0.5.
o .. m .N a. .N 25. E... 80.
o .o o .o .1. - .0..:0U
N .00...
50.0 0.05 .0 0000: oo. .00 .00 0.030.. 0.00.580 0.00... .00..00......0 505.00....
0.030.. .0 .0050: 0M0.0>< .0 .0050: 0&0.0>< .80.... .0 00.09

 

 

o... 0.000 .8028.
.8 a. 5.50 0-2. 00.2 050 00.55 08685.0 .8 .000 0.00.0.0... .0 200805.. .3000 .o .800 2...

> ”.130...

22.

Sex expression of gynoecious line MSU 713-2 was not altered in plants
grown from seeds germinated in gibberellic acid at concentrations up to 10, 000
ppm. All plants in.each treatment remained gynoecious in the field up to
August 6. No observable effect on sex expression of the normal monoecious
variety of SMR-18 resulted from the germination of seed in gibberellic acid
at 10, 000 ppm. Lateral root and root hair development was suppressed and
the hypocotyl was noticeably elongated in seedlings of both varieties at all
concentrations. Mild distortion of early leaves on plants grown from seeds
germinated for 48 hours in concentrations of 10, 000 ppm were observed in
the field. This distortion persisted in the affected leaves but subsequent
growth was normal throughout the season.

Gynoecious plants transplanted into soil containing gibberellic acid
produced no staminate flowers. Growth habit of these plants was not notice-
ably different from the controls.

A single foliar application of gibberellic acid emulsion to gynoecious
plants at 5, 000, 10, 000 and 20, 000 ppm resulted in burning of leaves and
death of terminal growth. Death of the plant did not occur and new lateral
growth appeared a short time later. No apparent injury resulted from the .

2, 500 ppm application.

23.

DISCUSSION AND CONCLUSIONS

A. Staminate Flower Suppression

 

Suppression of staminate flowers on segregating line MSU 131-2 was
not achieved by applications of maleic hydrazide. alpha-naphthaleneacetic
acid or tri-iodobenaoic acid. Death of terminal growth resulted after two
applications of TIBA at 25 ppm and a single application at 50 or 200 ppm.
Growth habit and sex expression of plants treated with NAA and M. H. were
not visibly different from non-treated plants.

Further investigations of the chemical suppression of staminate
ﬂowers were not conducted because of the discovery of completely gynoecious
cucumber lines and the successful induction of staminate ﬂowers on geneti-

cally gynoecious plants.

B. Staminate Flower Induction

 

Plants of MSU 129, a line known to produce an occasiOnal staminate
ﬂower, were treated with N-para-chlorophenylphthalamic acid. The sex
expression of treated plants was not observed to be different from the con—
trols. Slight burning of the leaves resulted at a concentration of 100 ppm
but the plants soon recovered.

Staminate ﬂowers were induced on gynoecious cucumber plants by

foliar applications of gibberellic acid at concentrations varying from 100 ppm

24.

to 5, 000 ppm. Pollen smears indicated that pollen from induced staminate
ﬂowers was fertile. Fruit resulting from sib and self pollinations matured
normally, produced viable seed, and plants grown from this seed were
gynoecious.

A wide range of environmental conditions has not altered the sex
expression of gynoecious plants. This indicated that complete genetic con-
trol of gynoecious sex expression is possible and can be utilized in cucumber
breeding and hybrid seed production.

Gynoecious plants crossed with normal monoecious types produce
gynoecious Fl progenies. The induction of staminate flowers on these
gynoecious F 1 plants by the use of gibberellic acid enables production of
F2 populations and provides the means for a more complete study of inher-
itance of sex expression.

Hybrid cucumber seed using monoecious lines has not been feasible
due to the amount pf hand labor required to remove staminate ﬂowers or
to make hand pollinations. The use of gibberellic acid to induce staminate
flowers and produce female parent inbred lines will have wide application
in the future development of F 1 hybrids. This technique can also be ex-
pected to find use in commercial hybrid seed production.

Gibberellic acid applied at the unfolding of the first true leaf in

1959 induced the first staminate ﬂower at approximately the fifth node.

Germination of seeds in gibberellic acid for 48 hours at concentrations as high
as 10, 000 ppm produced no staminate flowers. It appears that the ﬂower
primordia are not sufficiently developed 48 hours after seed germination to
be affected by gibberellic acid, or that root applications are less effective
than foliar applications in altering sex expression of gynoecious plants.

The appearance of pistillate ﬂowers at nodes between series of
staminate nodes on plants sprayed at seven day intervals indicates the
possibility of increasing the number of staminate ﬂowers produced in a
given length of time by spraying at shorter intervals. A more uniform con-
tinuous staminate ﬂower production would produce a more abundant supply
of pollen for the increase of gynoecious breeding lines.

The results obtained by spraying gibberellic acid on monoecious
SMR-12 and gynoecious MSU 713-1 at the same concentrations, suggests
that the amount of gibberellic acid required to produce a staminate ﬂower
at a node normally producing only pistillate ﬂowers may be greater for
gynoecious than for monoecious plants.

Staminate ﬂower induction became increasingly difficult on gynoecious
plants as they matured. Apparently once the plant has developed a number
of pistillate ﬂowers, clearly establishing the gynoecious habit, it is diffi-
cult to interrupt this pattern and induce staminate ﬂowers. The observed

results support the conclusions of Laibach and Kribben (18) who stated that

26.

the formation of pistillate flowers requires a higher concentration of growth
substances than is required for staminate ﬂower formation. They indicated
that growth substances must reach a certain minimum concentration for a
pistillate ﬂower to be formed. Formation of a pistillate ﬂower depletes

the accumulated supply of the "pistillate producing" growth substances and
the plant reverts to staminate flower production. The cycle is repeated
throughout the life of the plant. This would account for the normal monoeci-
ous ﬂowering habit of cucumber plants. It would also support the theory
that gibberellic acid has an inhibiting effect on the synthesis of a growth
regulating substance produced in gynoecious plants, changing the natural
balance in the plant rather than directly inﬂuencing ﬂower differentiation.
The delayed effect of gibberellic acid, its non-persistence and its apparent

lesser inﬂuence on older plants substantiate this theory.

27.

SUMMARY

The objectives of this work were to determine if staminate ﬂowers
produced on certain lines not completely gynoecious could be suppressed by
growth regulating chemicals and to determine if staminate ﬂowers could be
induced on gynoecious plants by the use of growth regulating chemicals.

Complete suppression of staminate ﬂowers by foliar applications
of Maleic Hydrazide at 250, 500 and 750 ppm, Alpha-naphthaleneacetic acid
at 100, 200 and 400 ppm, or 2-3-5- tri-iodobenzoic acid at 25, 50 and 200
ppm was not achieved.

The sex expression of gynoecious plants was not observed to be
affected by N-para-chlorophenylphthalamic acid at concentrations of 10, 20
or 200 ppm.

Staminate ﬂowers were induced on completely gynoecious plants by
foliar applications of gibberellic acid at concentrations. varying from 100 ppm
to 5, 000 ppm. Fruit resulting from the use of pollen from induced staminate
ﬂowers produced normal viable seed. Plants grown from this seed were com—
pletely gynoecious.

Through the use of gibbe rellic acid on gynoecious plants in an isolation
cage provided with bees, seed increase was accomplished.

The incorporation of gynoecious ﬂowering habit into pickling cucumber
lines and the use of gibberellic acid to induce staminate ﬂowers on gynoecious

plants will have important application in the production of hybrid cucumber seed.

28.

LITERATURE CITED

1. Currence, T. M. 1932. Nodal sequence of flower type in cucumber.

Proc. Amer. Soc. Hort. Sci. 29: 477-479.

Edmond, J. B. 1930. Seasonal variation in sex expression of certain

cucumber varieties. Proc. Amer. Soc. Hort. Sci. 27: 329-332.

3. Heslop-Harrison, J. 1956. Auxin and sexuality in Cannibus sativa.

4.

6.

IO.

 

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Ito, H. , and T. Kato. 1953. Factors responsible for the sex expres-

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, K. Hashimoto and T. Saito. 1954. Factors

 

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1957. Factors responsible for the sex expression

 

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1957. Factors responsible for the sex expression of

 

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11.

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29.

Ito, H., and T. Saito. 1957. Factors responsible for the sex expression

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. 1958. Factors responsible for the sex expression

 

of Japanese cucumber. IX. Effects of nitrogen application and watering
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. 1950 a. Der Einﬂuss von Wuchsstoff

 

auf die Blutenbildung der Gurke. Naturwissenschaften 37: 114-115.

. 1950 b. Uber die Bedeutung der B-

 

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. 1951 c. Der Einﬂoss von Wuchsstoff

 

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. 1951 d. Die Bedeutung des Wuchsstoff

 

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20. Lang, Anton, James A. Sandoval, and Ahmed Bedri. 1957. Induction

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960-964.

 

30.

21. Nitsch, J. P., E. B. Kurtz Jr., J. L. Liverman and F. W. Went. 1952.
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22. Peterson, C. E.. and J. C. Ballard. 1958. Development of gynomonoecious
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