MODIFICATION OF FLOWERING, SEX EXPRESSION
AND FRUITING OF SELECTED CUCURBITS BY
A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
To myr parents, wife, daughter, and
friends this dissertation is humbly
dedicated wiith affec tion.
ACKN~;OTLLED:E SY 'l S
The author wishes to express his sincere appreciation to
Dr. B. D. Thomnpson, profes or of Y .LL'tie Crc s, for his guidance
and assistance during the pr -r of thii study and for his helpful.
criticism in pr i"::1 thiis nscipt.
T'he helpful advice and asitae of thie ot ir members- of
the supervisory co ~itter, Dr. A, P-. Lorz Dr. V. F. Nettles,
Dr. A. A. Cook, and Dr. R. C. Smit h, is a teful ly acknn~~ icaged
DeeF p i7" ni atn is alo' et 't to all bes of the
Vegetable Crops D Lcn for t ir in eres ata coraion d r-
ing the years, to thie D tnn or V' Latle Cr for provides
the research facilities a sar of thec fin racial supq r, and? to
Dr. S. H. t-, L for provide. 1aoa 'pc- and eiP. lt n Id
for so:i or this ::sr'~.
TAB;LE OF CONTEN~TS
Acknowledgments -------------------------------------- iii
List of Tables --------------------------------------- vi
List of Figures -------------------------------------- viii
Abstract ------------------------------------------- ix
Chapter 1 Introduction ---------------------------- 1
Chapter II Review of Li~trature -------------------- 3
Genetic S~ctors ---------------------
Environmental Tactors -------------- 5
Chemical iactors -------------------- 6
Chapter III M~aterials ani Me~thods ------------------- 103
GrowJth R~egulating Chemicals --------- 10
Field ------------------------------- 11
Greenhouses -------------------------- 14
Mleasurements and Evaluations -------- 16
Chapter IV Results --------------------------------- 18
Field ------------------------------- 18
Effect of Application Time ------ 18
Cucumber -------------------- 18
Squash ---------------------- 18
Un~termelon ------------------ 19
Effect of Concentration --------- 20
Cucumber -------------------- 20
Squash ---------------------- 21
10 ~-----------~----- 22
Gr~nlaus e ---- --- ------ ----~~-- 23
:::i'nt C:l:' ij r,^t~3t --- ----- 2/5
J -~- --~--- --- ---- 25
Ti--- -- --~--- 2.6
-- - --- ~ 51
-----c ---- -- ---- ----- C .L
Ci btr\ )is611 ; i ------- ----------------- ------- 4
LIST OF TABLES
1. Flower Sex Expression and Marketable Yield of
Cucumb~ePr Grow~n in Spring 19657 in Response to
Chemical Regulators and Their Application Time 33
2. Flower Sex Expression and Na~rketable Yield of
Squash Grown in Spring 1967 in Response to
Chemical Regulators and Their Application Time 34
3. Flower Sex Expression and Marketable Yield
of Watermelon GrowJn in Spring 1967 in Response
to Chemical Regulators and Their Application Time 35
4. Effects of Chemical Regulators and Different
Concentrations on Vegetative Growth, Flower Sex
Expression and Miarketable Yield of Cucumber
Grown in Spring 1968 36
5. T'he Irnfluence of Chemical Regulators and Concen-
trations on Flower Sex Expression and M~arketable
Yield of Cucumber Grownl in Fall 1968 37
6. Th~e Influence of Chemical regulators and Concen-
trations on Flower Sex Expression and Mlarketable
Yield of Squash GrowJn in Fall 1968 38
7. Effects of Chemical Regulators and Different
Chemical Concentrations on Vegetative Growth,
Flower Sex Expression, and Markectable Yield
of Watermelon Grown in Spring 1968 39
8. Effects of Chemical Regulators and Different
Concentrations on Vegetative Growth, Flower
Sex Expression, and Mlarketable Yield of
Cantaloupe Grownm in Spring 1968 40
9. T'he I-nfluence of Chemical Regulators on
Vegetative Grow~th, Flower Sex Expression, and
Marketable Yield of Cantaloupe Grown in Fall 1968 41
10. The Influence of the Different Regulators and
Their Interaction on Vegetative Growath and Sex
Expression~ of Yellow Straightneck Squash 4?
11. Vegetative Growcth and Sex Expression of Yellowc
Straightneck Squash in Response to Treatmfnts
with Chemical R. lators 43
12. Effects of the D~ifferent CI-. ;cal Re- .' tors and
Their Interaction on Vcg D tiv@ Crowth~ and Se
Expression of Zucchini Squ '. 44
13. Effects of the Different Ch rraical = latrors and
Their Intieractions on V native Growth anid
Expression of Zucchint Sqjuash 45
14. Fresh and Dry FWe' 'ts of Zucchini Squerbi Plants
in R~esp~ons to til Difkcr nL Ciieical lators 46
15. The Iif leie of the Dif.rt IC 4 1ca intors
on Niucleic A~cid Conat u of S iirr C4 i, Plants
and Flowc~cr Buds 47
LIST OF FIGURES
1. Schematic Review of the Overall Plant Growth
and DP~eveloment of the Cucurbitaccous Plants
in General. 68
2. Stem Elongation of Field Grown Cucumber (Fall,
1968) in Response to Treatments with Different
Chemical Regulators. 69
3. Effects of the Different Chemical Regulators on
Stem Elongation of Field Grown Zucchini Squash
(Spring, 1969). 70
4. Effects of the Different Chemical Regulators
and Their Interactions on Stem Elongation of
Field Grownm Zucchini Squash (Spring, 1969). 71
5. Influence of Regulators on Vegetative Grow~th,
Sex Expression, and Marketable Yield of Cucumber
(Fall, 1968). 72
6. Effects of Regulators on Vegetative Growth,
Sex Expression, and Marketable Yield of
Squash (Fall, 1968). 73
7. Regulators' Effects on Vegetative Growth, Sex
Expression, and Marketable Yield of Cantaloupe
(Spring, 1968). 74
8. The Influence of Regulators on Vegetative Growth,
Sex Expression, and Marketable Yield of Canta-
loupe (Fall, 1968). 75
9. Effects of Regulators on Sex Expression and
Marketable Yield of Watermelon (Spring, 1967). 76
10. Regulators' Effects on Sex Expression and
MIarketable Yield of Watermelon (Spring, 1968). 77
Abstract of Dissertation~ Presented to the Graduate Coun~cil
of the University of Florida in Partial Fclfill ntt of the Requircm nts
for the degree of Doctor of Philosoph~y
Niohar d Abdrl- ~hran
Chairman : Dr. B. D. T'` Ion
Major Depair t>-nt : l' etb Cr
An exp si j
growth re I1ath
were, first: to
to induce conecu
Crol : u .
Cllco-lh i -
were m~ale. e h ~-l
indole tic sc ?
aetal p .a wrar design
c' 1 'als for nadif ent
fruit of cuut 't co
incers calins, ,c i h
itration of foG 1 ; ?P
to dict raili th~ :ac l
d in1 tlls stdcs '1 rf:
.ue-CL:uni _" 1 'Flg
'Yel ow St. ,turck' an
'.-1 t rlstern Gra
aidc trii' e1i '. ai
d, ani ;li: iic a id.
ed to stud ' use of
ion of flo ris.. ,s :
ercs tot 1 yield, and/or
SIwhichz th; se !alato
:cu~er- -C~currri s at~i us ,
it' 1I,' sniio sq~u 'l--
'Z iccini,' and waJt r-
y.' 'CalS selected
t', napiiiacc f ic acid,
Applicain we by
r :e see in c' '. 1l solutions.
art li~i inhibited v t stive
d <'aic c pji t'll *i flo, r for-
ri' vclttiv jio;i, 0 h n
spraying the fol' oi by so '
Tr-eatnentse with~ : IllL ~
growth, suprese st-tia '7
mation. Trarxt r ill CA in
staminate and suppressed pistillate flo;:er formation.
Early and total yields were increased by spraying the plant
with 100 ppm of MIH, NAA~, or TIAA at the four-leaf stage, in all of
the four crops. However, con~centrationl of yield in a shorter har-
vesting period resulted from treatments w~ith TIBA at 50 or 100 ppm
and NA at 150 or 200 ppm.
Experimental results, observations, and a review of pertin-
ent literature appear to support the following hypothesis: Floral
primordium in m~onoecious crops passes through a bisexual- stage
after which it expresses itself into one sex form or another
according to the physiological and environmental conditions. The
ratio of endogenous levels of auxins to gibberellin playi an impor-
tant role in sex expression. The higher the ratio the more the
tendency to female sex expression and the lower the ratio the more
maleness the tendency. This role might be as a direct result from
the effect of these hormones on gene expression and repression, or
ain: indirect result of their effect on plant growth and metabolism.
On the same basis, NAAI might modify sex expression by in-
creasing auxin levels in the tissues or by diluting the effect of
GA. HowJever, MH and TIBA may be exerting their effect through
a direct interaction with IAA and GA to modify their ratio, inhibi-
tion of polar transport of auxin through the stem, thus increasing
the level of IAA~ around floral primordia, or inhibition of plant
growth which might result inl an accumulation of auxin and increase
their level in the stem and around the floral primordia.
IN~TRO.I c 10-"
Sex expression in flo- ring plants F--
many research workers during th last cen u- <
early work reflected genetic interest, L': m
search workers have b en can erued ~i th t'
' rost of the
r. Lu re-
Some of the trost impra~ asp
itacee r re the int cal el 'ri o
pressions, floweir form tion, I uit se.
opment are necessary stp 1ed to
factors \< ich- control th fl iei p
corllbi I ion to prodorre delahi rI l
is tics to achieve this en. ,1 e c
only sexual dilfferent tation but. Li L
tion of pistillate or h 'Ithroic
ti on d pils
Factors interact; to eo 11 l
genetic, environ sntal, and chE IiCal.
duct '- on Lue use of .thn-r 101
of s e e- csio IF evr, litti o
th~e practical ,, ligation of r :crh
s ci thc tlo B t'e Cvcu b-
e ci: Bu. proc :s. Se 9 x
an fruit. vat~l- r r' c 1i~~-
'crop pro cetic .
ccs us b in tleitIpe
5n 'nc [.~tn tlrcc-
ace il ics 1ol iirnav no?
c of a ce an propor-
oi-ers onGich fruit prodne-
ex exrsitn ir: p.7 are.
M~uch r sach has 1c con-
ch i h:il for Triodi fica tion
fort ha 1 -n dir et to1"1
findi g .
In planning thie program for this study, two questions were posed.
First, are any of the reported growth- regulating chemicals of practi-
cal use in the production of cucurbits in Florida? Second, what is
the mechanism by which these chemicals produce their effects?
A series of field experiments was conducted to evaluate the
effects of three chemicals--maleic hydrazide, naphthaleneacetic
acid, and triiodobenzoic acid--in order to achieve one or more of the
following objectives: 1) to increase the earliness of the crop,
2) to produce higher total yield, 3) to concentrate flowering into
a shorter period to enhance the possibility of a single mechanical
harves t. Gibberellic acid and indole acetic. acid were also used in
order to compare their effects as endogenous growth regulators with
the preceding chemlicals.
A series of greenhouse experiments was conducted to compare
the effects of these three chemicals wJith indole acetic acid and
gibberellic acid and their interactions on the physiology of growth
and flowering of squash plants (Cucurbita pepo). These experiments
were designed to establish, if possible, a hypothesis which could
explain the role of these growth regulators in the physiology of
sex expression in cururbits.
REVIEW OF LITERATUTI'T
The experim ntal modification of sex expression essentially
concerns individual on'o -ies; otherwise it means the changes in
flowering b bits of individuals t'*.-selvc Sex expression of a
flowering plant ref rs to the ability of suchi pl .t to produce one
or more sex form of flo ~r, their no 'l :r, and p sitions on1 the
Sex expresos in cucurbits is a clr racteristic nr 'ified by
genetic, envircnie: 'l, an' c 't 1a factors. Tiedj in 1928.
(101) was one of t
the study of se~x Ci -esiem in cucurbits. He co idere e rlier
invesj:ti tor of sex e3Xpre~sb ion in1 plants in~ tht<-c groups: a
group of inves ti. tors of sex inl-ritance w~ho roc .-'_.ed only
gone tics as the d t < ,inii m o' nism, an > L .~ who clair 9c
that envi amet is the b sis of se det rition, and a third
whio took an int- r .Jiate 1 i it an con i ? Lte problem from
several points of viewJ.
Genetic Fac 1,
In hlis theory at 1ut sex evolution in pl .ts, CorT n inl
19, in 3r*ii),assurcd that the evolution of sexual type was from
herniaphlroditt to the int 'Liate forr s, androrrnonoccious, tri-
mencilR a i LL ttcnc to t'e extre~ for<
androecious, monoecious, and gynoecious. Every type of sex ex-
pression is represented in Cucurbitaceae. But, according to
Yampolsky (113), the monoecious expression is the most common, the
dioecious next, and the hermaphroditic Is very rare.
As a result of crossing monoecious with andromonecious vari-
eties of cucumber, cantaloupe, and watermelon, Rosa (93) concluded
that the moncoccious expression is dependent upon a single dominant
genetic factor in all three species. Tiedjens (101) reported on a
peculiar cucumber plant which was stunted in its growth and almost
completely pistillate. This character seemed to be controlled by
one recessive factor.
Whitakcer's (107) survey of sex expression in 49 distributed
varieties among eight species and four genera of cultivated
Cucurbitacccae reported the following:
1. Each species is characterized by a specific
qualitative type of sex expression.
2. Quantitative differences in sex expression
may exist between varieties within a given
3. Staminate flowers are greatly inl the major-
ity at all times in all forms.
4. Somne evidence exists for environmental con-
trol of sex expression.
Environmental Fac tors
Four variables of plant: environ ont--nu tri tion, mois ture ,
light regime, and Leopllerature--may dir-ectly inflaicnce sex; explres-
sion in plants.
Nutrition--The evide ze bearing upon the influence of min-
eval nutrition on sex expr ssioni is miore subst-;ntial for mionoecious
species than for dio vious. As early as 1 I' er (44C), workiiz
~i th s ra tio in monocc ious ec ers a pu ; ins, found that the
proportion of staminate to pistillate floiwers could be changed
miaterially by groa'r thec plants inr diff ren~t soils. Tiedjens (101)
reported that additional nitt nraci Le p 'o ution of flowers
of both sexes in cucu rs, with Io inc -s in the pistillate
flowJers than in the st rinate. M:inina (71) found tiia p 'iodic
nitrco cn fertilization favor f }<~~rs while pe i ic applica let
of pota wiuml :- < -' ma .1
effect of nitr-, ,I on incer in, the r tio of pistillate to stam-
inate flow cr in g?. rk~ins. Similar results were port 2 by
Cunnin. 'l (25) in w e meln 2, ,, ranel (13) in < 0 11.-,e anid
water : lon~s, and Hopp (47) in butt -nut squa h.
M~ois;ture.--MIiinin and l : te eiitch (77) report that mis-
ture conditica-s affected the onset of flowe~rirg in cucum Low
humidity acscllrated the appearance of stamninate flowers, while
hi bI humidity hastened the 0: st of p~istillate floe s. They also
ob erved that plants o:n- in rnist or dry soils pr-oduced st m ntax
and pistillarr flos< -~ sillult ly,~sS, but the aperac o c
pistillate flowers was hastened under high soil moisture condi-
Flight P.-rir--. --Tiedjens (101) demonstrated that exposing
cucumber plants to a longer photoperiod increased the number of
staminate flowers, wJhile thei number of pistillate flowers increased
and the number of staminatq decreased under reduced light condi-
tions. Edmond (29) and Mliller (70) reported that long days of high
light intensity favored staminate flower production in cucumbers,
whereas short days with low~ light intensity favored pistillate
flow~ers. Similar effects were obtained by Nitsch (76) in squash
and gherkins, by Ito and Saito (50 and 51) on Japanese cucumbers,
by Brantley (13) on cantaloupes and watermelons, and by Galun (37)
Temperature.--The work done by Nitsch (76), Wittwer and H-illyer
(110), Ito and Saito (50 and 51), Fujieda (30) and others. indicated
that high temperatures generally increased staminate flower produc-
tion while low temperatures increased pistillate flower production.
However, it should be noticed that temperature had a more profound
effect during the dark period than during the light period. This
explains thle interaction between temperature and photoperiod in the
results reported by many research workers (13, 29, 22, and 101).
Carbon Monoxide.--The earliest reports on chemical control of
sex expression of cucumbers appear to have been obtained prior to
1938 by Russian workers (L4). In 1938 MIinina (71) found that treat-
ing cucumber plants during the seedling stage with wood-stove
gases modified their vregeative growth, increcased thec number of
female flowers, and increased both fruit set and yield. In 1947,
both MIinina and Tylkina discover d that the effect is mainly due
to thle car-bon monoxide in those gases (iim44). Si (1ar results wecre
reported by Czao (27).
Ethylene.--Kitsch (76) was not able to mlodify sex expression
of acorn squash by exp osre to .u thln in cone Ientrations of 100
ppm for a period of 24 ho1s
Acotylen.--Moha-~niik (69) repiortcd that treating c uceumber1
plants w~ith acetylene gas resulted in an incretl~S inl thC) 1inur' of
female flo ~rs, inc ::s in h yie ld of fruits, and an advant .nta n
of ma tuir ty .
Mlethylen Blue.--' ojnS, (75) chairn d bt.la cucumber p].ar~
fi-rom seed reaited wiJth 0. R ICIentl solutionl of a thyicue blue for
24 hours at 22 to 2.50 C prode'u 5 2 pesn ir pistillate flowers
and 45 percent m > fruits. Thes wer als :. .L r LL an controls,
and resulted in [ p rc :t increa in tin ) isld by wei 't.t
MIaleic Hlydr it' .-- (91) de ntrated that sprayin, w\ater-
melon st <'li- with maleic h, 'n 'ide ( ) induced miale sterility
and in~ltiarer i t' '< eness of the plants. Uiittes. and Htillyer (110)
treated squs. pl 3 by di, ping or spr ing with MIl1 solutions.
Treatments resulted in plants that prodiuced the usual number (ceight
to ten) of pistillate flo c-rs in normal spotial arra < aeit w~ith
no sta L ii~t flo 3Jrr. Si ilar r sults <,T 1lso report 'd by P ;Sd
and Ty., i (; ) o. litLr iurd, by C~ohelry (22) onl 1. L n lons
and bottle gourds, and by Kali and Dhillon (55) on bottle gourds.
Triiodobenzoic Acid.--Wittwer and Hillyer (110), working with
cucumbers, squash, and watermelons, showed that spraying the plants
with triiodobenzoic acid (TIBA) reduced the male/female ratio by
suppressing the development of staminatP flowers. Trying and
Zawawil (52) found that spraying cucumber and cantaloupe plants with
25 ppm of TIBA increased the number of female (100 to 200 percent)
and male flowers but lowered male/female ratio. They also reported
that application of TIBA to cucumbers at the onset of bloom increased
the number of fruits but did not affect total yield. However, the
same treatment increased both the number of fruit and total yield
Naphthaleneacetic Acid.--In a series of studies in 1950 and
1951, Laibach and Kribben (in 44) reported that application of
naphthaleneacetic acid (NAAE) or indol~eacetic acid (IAA0 in 1 percent
lanolin paste to cucumber plants 16 to 18 days old promoted the female
and suppressed the male sex expression and decreased the total number
of flowers formed on the plants. Nitsch (76) obtained similar re-
sults on acorn squash. He was able to lowJer the location of the
first pistillate flower from the 20th to the 9th node by spraying the
plants at the two-leaf stage with 100 ppm of NAA. Similar results
on the e-ffect of NAA~ on sex expression were reported by Wittwer and
Hillyer (110) on cucumbers and squash, by Ito and Saito (48) on
cucumbers, and by Brantley and W~arren (13) on watermnelons and
Gibberellic Acid.--W~ottwa~re and Bukovac (111), in 1958, w~ere
the first to report. on the effect of gibberellic acid (GA0 on modi-
fying flower-sex; expression of cucun! vs. They found that GA
treatments consistently increased the number of staminate flowers
preceding the first pistillate flowe~r. Simiilar effects wJere also
reported by Galun (36) in 1959. In 1960, I person and Anhder (83)
were able to induce th~e formation of functim 1l staminate flowers
on completely fel lee plants of L'u gy
713-21. They also obsarve~d an increa e in s 'mnat flowecr pro-
duction as the con entr~ation n numb r of applicatLon of GA
Bukovaic ar' Wittli :r (17) dci 't~nc that foliar application
of 100 ppm GA to young secedl of pickli -L ~ cuct rs during
two weeks of short-d.. cxposure minrk dly redye the effect of
short photoporit on h (s pistillnte flooe t~ion. Th ey
also reported thaL di, : 1h ..ve o. gpocio e c unirs in
100 ppm GA solution induced the formation of s' iin te flowers.
Long photopcriod enhianced the pror:0tive effect of GA,not by in-
creasing the n er of nc ~inis pro' d st nate flo.. c., but:
by increasi- tir nu rbc of stmin ite flo c:s at ea no e'.
Miitchtell an N~itt:e (73) cy arte that GA t nicts of
gyncedious cucum 3r indu d on uninterrupted sequec of staminate
flowers from L1e se through the ninth nodes. Few plants produced
mixed node "of pistillai a : sta 11nate flos als at th~e sam nod 3"
irme diately pree 'i tli r .e '0io to Lh pistillate phase Similar
effects of GAZ wire reported t r'- ase and Tanaka (43), Clark and
K~enney (23), and Pike a0 1 etcrson (85 and 86) on Synoecious cucumbecr
MATERIALS ANVD NETLHODS
Several chemicals which can change the sex of flowers have
been reported. Three of these chemicals were selected according
to their promise as efficacious modifiers. They are cheap, safe
to handle, and represent three different families of chemical
compounds. These three regulators were:
1. Mlaleic Hydrazide (HH~).
2. Naphthaleneacetic Acid (NAA4).
3. 2,3,5-Triiodobenzoic Acid (TIBA).
Two additional regulators, gibberellic acid and indoleacetic
acid (GA and IA~A, respectively), were used to compare their effects
as endogenous plant hormones with other regulators and to study
their interactions with other regulators.
Fresh chemical solutions were prepared by dispersing the
growth regulating substance in surfactant, Triton X-100 (0.1 per-
cent of the final concentration), and adding water. Chemicals
were applied to foliage with a hand sprayer until the run-off
The research work of these studies consisted of two parts--
a field phase and a greenhouse phase. Th~e field phase was de-
signed to evaluate the effect of the different treatments on
c ...nios pis : ci
icnn c 5 i- Lfi -
;-al in~r- ti 1 on
our tlc ss ( p~pli-
: dt in
I-lll cn oe lant
cr s"h, 5x::3
aid 1:~ t
rtri lo s.
~tcliz ~ .ae
l o trol 1le' i'
ih tcr .1l Fierio
"i?- i. d k;~~~a
the following manner:
Time of application
The first set of experiments was started in March, 1967.
Its purpose was to determine the best time of application- of ME3,
NAA, and TIBA. A concentration of 100 ppm was selected from
recommendations by other workers (4t6, 73, and 110). The treat-
ments were 100 ppm each of MH, NAA, or TIBA. Each chemical was
applied as a single spray at the two-leaf stage, a single spray
at the four-leaf stage, or twJo spr-ays at the two- and at the
four-leaf stage. These nine treatments plus a water control,
each with Triton,w~ere applied to cucumbers, squash, and w~ater-
The second set of experimlents was begun inl M~arch, 1968ji, to
suythe effect of different concentrations of eachchmal
Concentrations used were 100, 150, and 200 ppm of MIH and NAA, 25
and 50 ppm of TIBA, and the control treatments. Treatments were
applied at the two-leaf stage to plants of cantaloupes, cucumbers,
The third set of experiments was conducted during the 1968
fall season on cantaloupes, cucumbers, and squash. Treatments
were 100 and 200 ppm MHI, 100 and 200 ppm of NAA, 25 ppm of TIBA,
100 ppm of GA, 100 ppm of IAA, a mixture of GA and IAA at 50 ppm
each, and the control. The objectives of these experiments were
to compare the effects of MHT-, NAFA, and TIBA with GA and IAA on
the plant growth and development and to evaluate the effects of
these treatments on either earliness or concentration of the
yield into a shorter harvestin; period.
An additional field experiment was conducted during the
spring of 1969 to compare the effect of different regulators on
plant growth and der lopm at of 'Zucehini' plants growJn under
greenhouse w~ith those growncf under field cond~itions. Plants :r
started in the greenhioujse in peat pots. Chemicals wecre applied
as a single spray at the four-leaf stage. Treatme ts were indi-
vidual regulators or co nationss of twro. 1-con
each was 100 ppm.. Plants were transplanted to the fi ldl one day
after treatments, an~d measurer l-nts cjr taken on both tative
and repr-oducetive growth .rl the oiwi. S es on .
All treat~nit nts : ev ated < the b sis of the following
1. V,~ tative
on the pla
'.as plant length, no hber of
,n trbr of lateral branch a deveclopcd
.nts, and the r latile size of the
ai percent of the control.
2. Flowering and sex x pr sio by det ~..0 L
a. The node position of the first st rinate
and pistillate flo :tcs.
b. The nort r of days from pl tinl to anth< iss
of the first sta iinate and pistillate flowers.
c. The number of staminate and pistillate flowers
developed 1du-ing the firsl two0 wcks of flot .r-
d. Tl f< ica to mnale floi ratio.
3. Yield from five plants by number and weight of
marketable fruits as graded as Fancy by the
U. S. Standards. Cantaloupes and watermelons
were harvested three times during a three-weeks'
harvesting season. Cucumber and squash were
harvested three times each waeek in the first
experiment and once a week in the rest of the
experiments for a harvest period of four weeks.
Fruits harvested in the first w~eeke were considered
as early yield for all crops.
All greenhouse experiments were conducted on the University
of Florida campus at Gainesville, Florida. Plants were grown in
benches containing soil described as fine, loose sand, low in
organic matter, with a pH around 6.5.
Squash was selected as an experimental standard plant for
the following reasons:
1. Its development is fast.
2. It has a single dominant stem and no lateral
3. It is monoecious with a limited number of large
flowers which can be identified and counted easily.
'Early Prolific Straightneck' summer squash was used in
early experiments and Zucchini type in later ones. 'Zu~cchini'
hybrid plants were more uniform and produced single flower buds
at each node.
Growth regulating chemicals w~ere applied to the plants as
seed soaking treat ats or foliar spray w~ith concentrations of
100 ppm. Seeds were soak 'd for 12 hours in Petri dishe on fil-
ter paper m~oisten d with and fl
regulators. A small hand spr -
o L< on the solution of cow~th
.r uas used to a Tly foliar sprays.
ie four-leaf st
tly in 1 i 's soil or in p at
Ic nh. Fer Li -wr was
rl~ Lc tilz c (6-8-8) at a
acre, Soi c1 1 ture ras k lt
betee 60 and ..\ i, and relative
du ; th cxcrir'natl period.
<< .1 L ble.'- aa
ot within th block h din n-
ncd: wo plants. One plant was
fres 1 dry < !i~ 't detrl Ena-
45 da to obt Ln flo ~rin da 3.
re nd gr -'ose spase, diffseriut
ec. Experit uts 1, 2, and 3
Seedling plants aere s at th
Seeds were sown eithe dir~c
pots for lat r transplanthi to :'
supplied in twc~o application nE e.
rate equivalent to 900 pourd p.r
near option ,n i air temperatures as
humidity ave about 65 pi en
A rand C Je block c' I
used for all es Li ints. Eachi pl
sions of- 1.5 x 1.5 feet and conitai
removed at the .1 of 21 da for
tions, and tle other wcas 1 ft for
Because of the liiiits in tin
experiments w~ere conducted in seq
ted on 'Yellowj Strai 't i
ic" to de terniin
of diffetn tr I1 tors and their ce 'bir
the see 3 '/or spr ii. LLe p1 ts twith
ppra, on 1 La grow~th` and s e pcsion.
ducted on 'Zucchint' usi GAi and ~IAL tre
Howe e, rii. t 5 .~a d ' 5d to st i
tions, applied by a..
.solution of 100
Expgri .nt 4 wa con-
etments aipplied as before.
'r the efT t of sprn -ir.v
the plants at the four-leaf stage with different regulators and
their combinations on plant growth and sex expression.
Measurements and Evaluations
Treatment evaluations were based on the following determi-
1. Length of the plant at 45 days after planting,
as measured from the cotyledons to the apex.
2. Number of internodes at 45 days after planting
counting beyond the cotyledons.
3. Number of male and female flower buds developed
4. Node position of all female flower buds.
5. Fresh and dry weight of plants at the age of 21
days after planting.
a. The above-ground portion of the plant was
harvested, cleaned from any attached dirt
with a small brush, and weighed to determine
the fresh weight per plant. Each plant was
placed in a paper bag, dried in a forced-air
oven at 680C. for 72 hours, and dry weight
6. Total DNA and RNA contents of seedling plants, un-
differentiated buds, male and female flower buds.
a. For the measurement of DNA and RNA, plant
tissues were homrogenized in an ice-cold
Omni-Mixer for five minutes with 5 percent
sucrose in 10-z.38.gC12 and K;C1 solution,
centrifugedc and filtered through a glass
wool pad to re: >:0 cell walls and other debris.
Aliquots of the supernatant were used for
analysis. Totzl DNA and RA
by the cie we and Roc .. t'ts. (94). Nucleic
acid In .ipitare Ip adding perchloric
acid (0.5 ) to aliqrrot~s. The precipitate vas
washed 1 sus. ion and resdimentation in
cold per lre e it I Lipids and chl~orophyl~l
were r mvtd by L <~i; tw~ic i~n an oth -,
eth 1,i andJ chlouroformn IixurL (2:2:1 V:V:V) .
The RNA was separated from DNA by adding
0.6 M KOH to the pellet and hydrolyzing for
18 hours at room tfm .Laur then DNA? was
precipitate 1 ..1': perchloric acid. The
absorbanee of both I and Ri4.i <::tracts was
determined at 265 mu in a Beckman Du Spectro-
photo< Wtr, andl rl ` -: wecre referred to
standard curves for obt;.ilt._ quantitative
Effect of application tire
Cucumnber.--All treatments modified sex expression during the
first tw~o weeks of flowering either by~ increasing the number of
pistillate flowers, decreasing the number of staminate flowers, or
by both. Results of the spring 1967 experiment on cucumber are
shown1 in Table 1. M~aleic hydrazide increased the number of early
pistillate flowJers and early yield in terms of number and weight
of fruits harvested. This indicates a direct correlation between
the number of early fruit harvested as a result of maleic hydrazide
treatment. However, such a r-elationshipp was niot tr'ue inl thie case
of NAA and TIBA. None of NAA treatments had any significant effect
on yield. Treatments with TIBA at the two-leaf stage or at both
two- and four-leaf stages suppressed both pistillate and staminate
flower formation, decreased the total yield significantly, and
there was no early yield. Treatments wJith TIBA at the four-leaf
stage had no significant effect on pistillate flowers, decreased
early yield, and had no significant effect on total yield.
Squash.--The results of the spring 1967 experiment show that
MIH at the two-leaf stage and TIBA at the four-leaf stage were the
only two treatments which reduced the number of days to anthesis
and hastened thie development of female flowers. All of the
treatments increased the fernale/male flower ratio by reducing
the number of male or increasing the number of female flowers
developed on the plants during the first tw~o wJeeks of flow~ering
Spraying the plants with 100 ppm of either lMH or NAA at the
two-leaf st::;.. 'ncr-e-sed the early yield without any significant
effects on total yield. Treatments of NAAi at thie four.-leaf stage
or at both the two- and four-leaf stage reduced the early yield.
All1 TIRA trentm nts, Iialeic hydrazide at the four-leaf stay;
and NAAt at four-leaf st-- tr (L ant dect based total yield in
both number and weight of m -irkctahle fruits harvested.
'a termelon .- -` sprb, 1 7 results indicate that all treat-
mients of FM decreased the nun wr of days to anthesis, hastened the
female flowecr develop mnt, and incre .:ed the total number of
flowe~irs. Tr at .nts of hNti d TIBA delayed the flo~~ri rk by
either incer in- the numb c of days to anthesis or decreasing
the number of flowers developed in the first two weeks of flowier-
ing. However, early NAA~u a late TIBA sprays hastened female
flowecr app Ince (Table 3).
All. tre lm nts of M11~ and early treatm nt: of NAA increased
the early yield. How~\ever, total yield was increased by treat-
ments with 1'1I at four-leaf stage, and NAA st two-leaf stage, in
terms of nurl hr and weight of fruits harvested. Treatment w~ith
NAA at four-leaf stage incer .ud the weight of early fruits
without aiffcti t iir nu 'cr
Treatment with TIBA at four-leaf stage increased the total
number but not the weight of fruits harvested, due to smaller
fruit size. The rest of TIBA treatments decreased both early
and total yield.
Effects of concentrations
Cucumber.--The results of the spring 1968 experiment indi-
cated that all of the treatments had inhibitory effects on vegeta-
tive growth as they decreased the length of main stem, internodes,
and lateral branches (Table 4). Higher concentrations were more
inhibiting than lower ones. Treatments of TIBA were more inhibit-
ing than both maleic hydrazides and NAA. All concentrations of
FM increased the number of laterals developed on the plants. On
the contrary, 50 ppm of TIBA was sufficient to reduce laterals,
dwarf the plants, and keep them at the rosette form for a period
of more than three weeks after treatments.
All treatments lowered the node position of the first pistil-
late flower. All except 50 ppm TIBA hastened the appearance of
early pistillate flowers, and the female/male flower ratio was
increased by all treatments. Such increases in the ratio were
caused by an increase in the number of pistillate flowers (100,
150, and 200 ppm PnI, 100 ppm NAA, and 25 ppm TIBA) or a decrease
of the number of staminate flowers (all treatments except 100 ppm
maleic hydrazide) or by both (50 ppm TIBA).
Treatment with }n~- at 100 ppm was the only treatment to
increase the number of early fruits and both fruit number and
weight of the total yield. The rest: of the treatments reduced
early yield, and that NAAZ 100 ppm, decreased the total yield.
Fall 1968 experimental results showed that treatment with
GA did not affect: the number of days before flowering. However,
it did increase the number of r ile flowers developed during the
first: two weeks of flowerial Treaitment with IAA induced early
femaleness by decreasing the n er of days before thle first
pistillate flower and incretasin the num : of pistillate flowers.
A mixture of GA and IAA~I had an efft-t s~i Llar to that: of IAA for
total but not early pistillate 20werls (Tab~le 5).
Treatments with NIH and TfIEA had an lffcct on flowie'ring
similar to that of IAAu. HowJever, FAA~ treatments inhibited stami-
nate flower develop at,, and cnum itra ion of 200 pp, decreased
both number of stam Date and pistillate floe rs.
Early yield was increa cd in num1 c of fruits harvested by
100 andt 200 ppm of P;II and by GA +- IAA~ mixture. Hloweiver, it in-
creased in weight by 100 ppm waleic hyd 7tide and GA +- IAA mixture.
Treatments w~ith 100 ppm NAZA, 25 ppm TIBA, and 100 ppm GA gave no
early yield and decreased total yield.
Sprayin. the plants wJith 100 ppm malcic hydrazide, 100 ppoi
IAA, or a mixture of GA + IAAZ at 50 ppm of each, increased total
yield in ter of both~ number and weight of marketable fruit
Squash.--T~he fall 1968 ezp i e ntal results will showi that:
IAA delayed male and hastened l~e flowers development, GA had
an oppiiite effect, chile a mi>'.l- of GA +t IAA~ treatment- delayed
both n~l 1 f mle flower formiation (Table 6).
Concentration of 100 ppm 1M hastened the female flowJer
development without affecting male flowers. However, 200 ppm of
MR increased the number of days before the first male flower
appearance. Both 100 and 200 ppm NAA treatments delayed male and
female flower development and reduced the number of flowers con-
With regard to yield, MH~ 100 ppm was the only treatment to
increase both early and total yield during the four weeks harvest-
ing period. All other treatments except MH 200 ppm and IAA 100
ppm reduced or gave no early yield during the first week of har-
vest. MIoreover, NAA at 200 ppm and GA 100 ppm reduced the total
yield by more than 50 percent.
Watermelon.--All of the treatments reduced the length of
main stem and the length of internodes, with more inhibitory-
effects from the higher concentrations. All concentrations of
MIH and TIBA and NAA at 100 ppm increased the number of lateral
branches. However, the average length of laterals was less than
the control in all treatments (spring 1968 results, Table 7).
All treatments changed sex expression during the first two
weeks of flowering toward femaleness. They lowered the node
position of the first female flower, hastened thle appearance, and
increased the number of female flowers developed on the plants.
Treatment with MH at 100 ppm increased both the early and
the total yield. Concentrations of 150 ppm MH and 100 ppm NAA
increased early yield slightly. While 25 ppm of TIBA had a non-
significant increase in total yield, treatment with 50 ppm
decreased thle early yield.
Cantaloupe.--The results of the spring experiment on the
effect of the different cor. imtrations of PIEI NuAA4, and TIBA on
vegetative growth, se e xp region, and yield are shown in Table 8.
N~aleic hydrazide treatus ps reduced the size of plants by
decreasing the len th of thle nrain stua, and the numb~ler and length
of internodes. How evei, thcy had increased the number of laterals
developed on the plants. .' thal < (Leti acid treatments had
similar effects on the size and 1 thof plants but they did not
affect the nu 1 r of laterrlF. I ;ic 1 .. Toi acid treau ents had
more severe inhibitory offccts on v tati~ve i Itowt. And they
also reduced or cli iineted the d vlon 1 a of laterals.
All of the LI~hnns 2 tr ei: ex aesion by reducing
by increasin_, the~ fc< 116/1 ab flo:e L 1 i Such increa in the
rztic wze eit-her th: rcsalt of iccrcasing Lle n- of female
florw rs, reducing Lt. nu 1 of male flo es, or a co bination
Treatn ilts of 1! ? and 150 ppnr oT lf in a t the: only ones to
increase both early and total yield. Concentrations of 200 ppm
of NAA and 50 ppm of TIBA ; no early yield, and instead delayeJ
the fruit development to the later harvests. The rest: of the
treat aets had no s; ltricant of, ;t on tl. yield.
The results of the f 11 1968 exp rim it help in co prrin
the effects of NHI, MAAi, and 's no on cantaloupe plants w~ith those
of GAZ, IAAI, and th~e control (: :1e 9).
Although both GA and IAA treatments had increased the size
of the plants, GA increased the length of the plants while IhA
decreased both number and length of internodes. Maleic hydrazide
slightly inihibited the vegetative growth by reducing size of the
plants and length of internodes but it increased the number of
laterals. Both NAA and TIBA treatments severely inhibited the
vegetative growth by reducing length of main stem, number of
internodes, and number of laterias1.
The treatments with MHI, TIBA, and IAA had similar effects
on sex expression. They hastened female flower development and
increased the female/male flower ration.
Both NA4A and TIBA reduced the number of male flowers. Gibbe-
rellic acid delayed the appearance of female flowers and increased
the number of males.
Yield results indicate that while }RI, TIBA, and IAA treat-
ments had increased the total yield significantly, M~H wJas the only
treatment to increase earliness. Both NAA and TIBA decreased the
early yield and tended to delay the harvest.
The control treatments
'`Yellow~-Straightneck.'--Plants grown from seeds soaked in
water produced a stem of about 15-16 cm. in length, an average
of 10 internodes, 9 pistillate and 22 staminate flower buds per
plant, at 45 days after planting (Tables 10 and 11).
'Zucchini.'--Plants grownm fromn seed soaked in water had an
average of about 13 internodes and 1.5 female flower bud per
plant with the first female carried at the tenth node position.
A spray with~ GA at the four-leaf stage increm~edd plant elongation
and shifted sex expression slightly toward maloness. A spray
with IAA had no significant effect on vegetative growth and
shifted sex expression slightly to:- rd femoaloness (Table 12).
thle seed in GA incer 'd plant len th, nurnb r of internodes, and
shifted sex express 1 toward malen s. A subsequent spray with
GA at the four-leaf sta~ increased plant 1 th, number of inter-
nodes, malone-ss, and total number of flower buds over seed treat-
ment alone. Ho\i ver, a subequ t: spray w~ith IAA decreased the
effect of GA soaking on plant 1 ni th, incer 3d its effect on~
number of inter< >' 3, and shifted the se: c arsion slightly
toward femakene s (r .10s 10 and 11).
'Zucchini.'--So. 1it s ed in GAl inceas 1 vl ,tative gro~trh
by increasing both plant: lent b and number of internod s. It
shifted sex expression toward L .1eness. A subsequent spray with
GA had a more stimulating eff e on vcegetativir growth and pro-
duced completely male plants. A subsequent spray with Z~IAA tended
to reduce the st;. i I;._ effect: of G4. This spray with IAA~
reduced the effect of GA seed soaking on sex expression (Table 12).
Sprayi n thie plant with GA increased plant 1 I th and both
fresh and dr-y weight. However, percent dry 1. i. 'lt was the same
as the control. It slightly increased the male tendency of the
plants and pr-oduced thle first fe 110 flowcer buds at the 11th node
position (T '0~ 13 and 14I).
'Y' 11 -'P i ' r11.'--Soaking the seed in LAA4 decrease ed
plant length, shifted se expression strongly tc red f 11aen-ess,
and incrascdd the total nuber of flor at buds developed on the
plants. A subsequent spray with lIL\ at the four-le~af st ag increased
the inhibitory effect of seed treatment on vege ative .th and
had a similar effect on : ex pression. H-owever, a sbeunt spray
of GA ovcecrne .completely and reversed the inhibitioni s -d soaking
on vegetative growth and incr-eased the r mer of male :oie buds
'Zucchi~-.--ni.'--ceIdoaetc acid applied bey sorikino the seed
in IAA had very little effect on ve stative LIo th. It shifted
sex expression towaard femaleness. A su' equent spray with GA
stimulated the ve atative growth and rev esed the effect of IAA
seed treatment on sex expression. However, a subsequent spray with
IAA~ caused more inhibtion to plant length than ~LAA seed treatment
alone. 'Iiis spray caused miore feale tendency than either seed
treatment or plant spray alone (Table 12).
Spraying the plants at the four-leaf stage with IALA decreased
plant length, fresh and dry weight, and increased percent dry
weight. This spray increased the number of female and decreased
the number of male flower buds, causing a strong female tendency
in sex expression.
Spraying with a mixture of GA plus IAA~ promoted vegetative
growth b3y incr-easing both plant length, numl~ber of interniodes, fr-esh
and dry wecight; however, it decreased prcount dry weight. The
tendency toward femaleniess in sex: expression was less than IAAi
applied alone (Tables 13 and 14).
'Yellow-Straightneckx.'--Soaking: the seed in N'd inhiibited
vegettiv growt by dcresi bohpan egh n henm
of in~ter-nodes. It also incrFeased the number of feamic buds and
decreased the number of male flo< ~r buds. A subsequent spray with
GA completely 01 *,-ic the eff t of se 3 trc l nt with MHi on
plant length andi sex e ,r asionl, but had less effect thian spraying
with GAc alone. A2 subsequent spray with IAA d :reased the inhibi-
tion of MH- seed treatment without affecting sex, expression. How-
ever, sp~rayin wc~ith IA4 alone b a les inhibitory effect on
vegetative grei th and a nore sti 1szt; ef t on flowering than
F31 seed so;.i~i tr
femaleness (Table 10).
'Zucchini.'- -S pr .~ 1 t plants at LLe four-leaf stage
with MHi~ alone inhibited :. :tive growth, decreased both fresh
and dry wJeight, and inceae re Et dry we~i 0. It also
decreased the r 1 rr of ma1 and incre d the nu r of female
flower buds. Spray~ir with a mixture of MIH and GAi increased t'e
number of interne .s, d exsi~ dr '11i 'st, but did not af' t
sex expr Lson. ver, s:. Eng with a mixture of NHT- and JAA
had mor-e inhibitory effect on <-tative growth than ..1 alone.
It also decreased fresh weight, dry weight, and percent dry weright,
and ince 0s f le ten 't. (.2bles 13 and 14).
'Yellow-Straightn_.,'--eck'-Se soaking in NAA decreased plant
length, number of internedes and number of flower buds developed
on the plants, with more inhibition of the male than female flower
buds. A subsequent spray wiith GA decreased the inhibitory effect
of NAA seed treatment on vegetative growth, but it had no effect
on sex expression. A subsequent spray with IAA had an effect
similar to that of GA (Table 11).
'Zucchini.'--Spraying the plants at the four-leaf stage
with NAA or with a mixture of NAA plus GA or NAA plus IAA decreased
the number of internodes. Spraying with NAA inhibited vegetative
growth, decreased both fresh and dry weight, and increased the
female tendency. A mixture of NAA plus GA increased plant length,
decreased dry weight, and decreased the female tendency. A mixture
of NAA plus 1AA had an effect similar to that of NAA alone (Tables
13 and 14).
'Yellow-Straight~neck.'--Seed soaking in TIBA had a severe
inhibitory effect on vegetative growth and reduced flowering by
decreasing the number of male flower buds by more than 50 percent.
This shifted sex expression toward femaleness. A subsequent spray
with GA reduced the TIBA effect on plant length and increased the
number of male flower buds over TIBA seed treatment alone. How-
ever, a subsequent spray wjith IAA reduced the inhibitory effect of
TIBA on both plant length and number of internodes. This spray
increased both number of male and female flower buds over TIBA seed
treatment alone (Table 11).
'Zucchini.'--All treat -nts of plant spryn i11 ith IILA
and its mixture with either GA or IAA had a sev : inh~ibitor
effect on the vegetative growJth and decreasir. both freshi and dry~
weigh ts Spraying the plants w~ith a mixture of I1 plus GA
caused less inhibition than spraying with either TIl~ aloe or
TIBA plus IAA. Treatment w~ith TIBA incre t .i f 1al te no .
However, the presence of GA in the spr decrear:0d sui c ff et~,
but the presence of LAZA increased thre femalii tscnd .. ." thi~~ plants
(Tables 13 and 14).
Results reported~ in Table 15 shori nucleic acid conte a
of the whole plants, undifferentiaited buds, fema)<. end male flover
buds, and thle eff es of diff it se d sil I ( an :ln sp ,t
ing treate nts with growth r glating c cic 'll onr theao! n
These results can be sum n-i;*3 as follous
1. Untre'ted fermale flo er buds ba o' l '. ; c< 0 ts
of DNA and RNA than both undi ffere 'iae a 1
male flo :~e buds. On the ot'e hi 1, :~l 1 f!c
buds had less D::A and more I' cont .'s tl .i tLe
2. Soaking the se is in GA in J v 1. c ont elr L
of one 1 ': old Seedl.- ,, but h 3 no effect on
nucleic acid contents of older plants. Subsequent
spray wJith GA after seed soaking in water in-
creased both DNA and RNA contents of the plants.
Subsequent spray with CA after GA-seed soaking
decreased DNA and increased RNA contents of the
plants more than those soaked in GA alone. Sub-
sequent spray with GA after IAA-seed soaking had
3. Soaking the seeds in GA decreased DNA contents
and increased RNA contents of undifferentiated
buds. Subsequent plant spray with GA after seed
soaking in water or GA decreased DNA and increased
RNA contents of undifferentiated buds more than
seed soaking alone. However, subsequent plant
spray with GA after IAA-seed soaking increased
4. Soaking the seeds in IAA increased DNJA contents
of young seedling, but had no effect on older
plants. Spraying the plants produced from water-
soaked seed with IAA increased their contents of
bothi DNA and RNA. Plants which were. produced
from either GA-soaked seed or IAA-soaked seed
had higher RNA contents when sprayed with IAA
than those unsprayed.
5. Soaking the seeds in IAA increased RNA contents
of undifferentiated flower buds more than soaking
in water. Subsequent plant spray with IAA after
seed soaking in either water or IAA~ increased
RNA content of undifferentiated buds. On the
other hand, subsequent plant spray with LAAi after
seed soaking in GA increased both DNA and RNA
contents of the undifferentiated buds.
6. Seed soaking in NH incr 1se DNIA contents of
young se dling but had no effect on the old r
7. Soakir the s bd in NAALF decrccsed RNA content
of yourr rs cdilt andl both RNA and DNYA con-
tents of olde plan a.
8. Seed so.-':in;, in TIBA decr 3se DN`A and RNiA
contents of both young see 110r and older plants.
9. Seed son lin in NHl or TIBA incre 3e RE:A contents
of undifferentiated flowe~r buds, but: had no signi-
ficant effects on DNIA contents. Se 1 sro Ain in
NA~A had no significant effect on nucleic acid
contents of the undifferentiated flower buds.
10. The female flowe~r buds did not show any si lifi-
cant: differences in their DNA. contents as a
result of thec different treafrents. How~ever,
they had lower RNA contents as a result of seed
soaking treatments in GA, MH, or NAA1.
11. All GA-seed soaking treatments increased RNA
contents of the male flower buds. Seed soaking
in NHC or N'AA decreased RNA contents of female
buds. Soaking the seeds in TIBA decreased both
DNA and RNA contents of the female flower buds.
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TREATMENTS VEGETATIVE GROWTH SEX EXPRESSION
Seed Plants Plant Number of Average Number of
Soaked S pray ed Leng th Inte rnod es Flower Buds
in with in cm per Plant Developed per Plant
9 CJ Total
H20 15.0 9.5 9.5 22.0 31.5
GA ---- 31.1 10.8 4.0 28.0 32.0
GA GA 42.1 13.3 3.0 32.5 35.5
GA IAA 28.7 12.5 11.0 21.0 33.0
IAA ---- 10.9 9.8 17.5 19.0 36.5
IAA IAA 10.4 8.3 15.5 18.0 33.5
IAA GA 23.4 10.5 13.5 24.0 37.5
H20 ---- 14.5 10.0 8.3 21.5 29.8
H20 GA 20.3 9.0 4.8 24.5 29.3
1-120 IAA 13.3 10.8 16.3 20.3 36.6
MH ---- 9.5 8.5 10.5 16.3 26.8
MH GA 1 4.3 8.5 7.0 22.3 29 .3
MH IAA 10.8 12.5 10.5 16.3 28.8
L.S.D. 5% Level 1.6 0.8 1.2 2.5 1.8
THE INFLUENhCE OF THIE DIFFERENT REGULATORS AND~ TiHEIR,
INTERACTION7 ONd VEGETATIVE GROWTHI AN\D SEX EXPRESSION
OF YELLOW; STRAIGHTN7ECK; SQUASH:
VEGETA1 TV G H SEX EXPRESS ION
OF YELZLOW S1 '11. TECK S IN.E TO TREAaTM~ENTS
WI:TH C .
TREAT: f'IS VLGE i SEX EXE :LSSION
Seed Plants Plant Number of Average Number of
Soaked Sprayed L th Internedes Flower- Bud s
in wi th in cra per Plant Developed pe~r Plant
0 6 Total
H20 16.0 9.0 8.0 21.0 29.0
GA 30.0 9.8 5.0 24.0 29.0
GA IA25.0 10.3 7.0 23.0 30.0
IAA 16.0 11.0 17.0 20.0 37.0
IAA GA 20.0 11.5 16.0 23.0 39.0
NAA 11.0 6.5 7.0 11.0 18.0
NAA GA 16.0 7.5 7.0 12.0 19.0
NAA IAA 14.0 8.5 7.0 11.0 18.0
TIBA 7.0 6.3 8.0 10.0 18.0
TIBA GA 14.0 6.5 7.0 13.0 20.0 -
TIBA IAA 12.0 8.0 11.0 12.0 22.0
L.S.D. 5% Level 1.2 .6 1.4 2.0 2.1
TREATENiTS VIEGETATIVE G-ROn!TH SEX EXIPRESSION~
Seed Plants Plant Number of Average Number of
Soaked Sprayed Leng th Internodes Flower Buds
in with in cm per Plant Developed per Plant
Experiment 4. i Toa
H20 20 12.8 1.5 11.3 12.8
H20 GA 24 13.3 0.3 13.0 13.3
H20 IAA 21 13.3 2.5 11.0 13.3
GA 40 14.5 0.5 14.0 14.5
GA GA 59 15.0 0.0 17.5 17.5
GA IAA 31 12.5 1.0 11.5 12.5
IAA 18 11.8 2.8 9.0 11.8
IAA GA 30 13.8 1.5 12.3 13.8
IAA IAA 15 11.8 3.3 8.5 11.8
L.S.D. 5% Level 1.3 .7 .6 1.2 1.2
EFFECTS OF THE DIFFERENT CHEMICAL REGULATORS
AND THEIR INTERACTION ON
VEGETATIVE GROIJTHI AND SEX EXPRESSION
OF ZUCCHINI SQUASH
0.9 0.5 0.7 1.4
Tiul. ub -
EFFECTS OF TH1E DIFFERENT CHEI-:CAL REGULATORS
AND DEI'i>. Ih'TY:RACTi Ii ;; ON\
VEGETAT I! C :I AND1 Sr" EXPRESSIONS
1 L i. < X: 1' s 3IOij
at the four-laf
Ex perim nt 5 -
GA + IhAA
~,i: < iuner of
Flo Jr Buds
Plant Ku I r of
Inltern 'd e
MHl +I GA
MIH t IhAA
NAA +1 GA
NAA + IAA
TIBA + C .
TIBA + IAA
L.S.D. 5% Level
HJATER (Control) 253 16.7 6.58
GA 303 17.2 5.66
IAA 220 15.4 7.00
GAcIAA 300 17.1 5.70
MH 203 16.2 7.96
MH + GA 230 16.7 7.24
MH +IAiA 193 15.5 8.01
NAiA 190 12.9 6.76
NAA+-GA 238 13.6 5.69
NAA+IAA 218 13.2 6.06
TIBA 170 12.2 7.15
TIBA+- GA 225 13.6 6.02
TIBA+i IAA 203 13.0 6.40
L.S.D. 5% Level 24 0.4 0.32
FRESH AND DRY WEIGHTS OF ZUCCHINI SQUASHI PLANTS
IN RESPONSE TO TRE DIFFERENT
Plants Sprayed at
the Four-leaf Stage
FRESH AND DRY' WEIGHT OF PLANTS
Two Weeks After Treatment
Fresh Weigh t Dry Weight Percent
gm./Plant gm./Plant Dry Weig~ht
4 4) 4
0\ \o 0
-r N N\
O O O
NN1 C\ << O
5: W 000
The results of these studies indicated that each of the growth
regulators used had a profound effect not only on flower sex expres-
sion, but also on plant growth and fruit growth and development.
In order to discuss these results, a description of vegetative growth,
flowering, and fruiting habits of the crops used must be mentioned.
A great number of research papers report on either flowering or
fruiting habits of cucurbits, but there is little descriptive infor-
mation on the overall plant growth and development of these crops or
other economic crops.
Three of the crops used in these studies, namely cantaloupe,
cucumber, and watermelon, are alike in their vegetative growth habits.
They have a main stem from which arise lateral branches, "primary
branches," at the basal nodes. Several secondary shoots arise from the
lateral branches. Squashes used in these studies wJere of the bush
type which differ from the previous crops by their much shortened
internodes and lack of lateral branching.
Flowers in these crops are borne singly or in clusters in the
axils of the leaves. The sequence of floral production has been
studied by many researchers (19, 25, 26, 42, 76, 101, and 107). They
showJed that as the vine progresses in its development, sex expression
undergoes a gradual change fromn strongly staminate to strongly pistil-
late phases. Such change can be measured qualitatively as sex of the
flowJer produced and quantitatively in terms of the ratio between
stamninate and pistillate flow~ers.
Fruit setter.* in cucurbits has been the subject of several
investigators suchi as Bushnell (19), Cunni~n-h. (25), McGlasson (67),
Porter (88), Rosa (93), and Tiedj as (101). They have reported cyclic
setting of fruits which followed the production of' pistillate flowers
in a cyclic time and pattern. The cycle of fruit setting consisted
of alternative setting and nonsettin ; periods with the la th and
frequency of these periods :-. ' waith cjes, envj~ieromt, and
physiol ,,i< conditions.
In thre light of the previous studies, as wJell as the results
of thle present invest! nation, a sc' -ntic figure is pr < ated here
to illustrate th relation hips b 1~ee the different stel s of plant
growth and developm t of the cucurbitae.
111ustrations in Fi 1 cr 1 repr set the chronol. ;cal relation-
ships of the different develop mntal. st which resulted front superim-
posin~ the different curves of 1<
setting: and fruit ~ravth. Inlc curves are general and can be
applied to any of the crops used in this study; however, the size
of the curves and their units ni 't be chlanged with a particular
Durir its developm at from seed to maturity the cucurbit plant
exhibits a double sigmioid growth curve. Within a normal growing sea-
son there are three different and distinctive phases:
First: A period of strictly vegetative growth which
lasts for about six wJeeks after planting. This period is
characterized by a fast, uniform rate of growth, development
of lateral branches, and ends with flower initiation.
Second: A period of standstill in new vegetative
growth which lasts for two weeks and is characterized by
the beginning of the flowering phase and th:e occurrence of
early flowering and fruiting cycles. HIall (42) stated, "the
period between the origin of flower primordia and syngamy was
characterized in all series by diminished differentiation of
newa vegetative organs. During this period, however, there
occurred the maximum gains in leaf area and internode elonga-
tion. On the whole, it was also a period of low water and salt
intake." The first fruit setting cycle takes place at the end
of this period; however, both resurgence of vegetative growth
and formation of early fruit take place at the same time (42).
Third: A period of acceleration in both vegetative and
reproductive growth. In this period there is a large comnpe-
tition for food materials between vegetative parts, developing
fruits, flower formation, and newly fertilized ovaries. Such
competition plays an important role in crop production, not
only on the number of fruit produced but also on their quality
and harvest date.
Porter (88) reported that weakly growing runners resulted in
poor fruit set in watermelon, Wolf and Hartman (77) were able to
increase the percentage of fruit set by restricting the vegetative
growth of muskmnelons with various types of pruning. On the other
hand, Cunningham (25) and Nylund (79) found th~at leaf pruning caused
a quantitative decrease in fruit set.
Various reports have indicated that the growth of individual
cucurbit fruit followt a sigmoid curve (7, 59, 67, 77, 82, 90, and
108), Final fruit size in cucurbits depends on both rate of growthl
and duration during the ex-ponential phase. W~hen th~e exponential
rate is highi~final size is a~tt-i d earlier. This illustrates the
importance of the balance between vie; t tive and fruit: growth during
The re Ilts o' thes stude 'f : in accordance wJith the pro-
vious rr~. .Ls (2, 7, 12, 13, 32, 39, 41, 46, 115, and 116) on thle
effects of LLe rr allators us 1 on the v-
The observatios 'e~ during the first e ri nt~ns indicated that
each of the r. Et rl Ilators u 'd--n
inhibitory e fects on plant eth. Those effects w~ere different
with di~ffernt treaty ats and different crops.
In go .al, plants tr<'tId with ~MH ere less inhibited in
their growth ani recotto 3 faster thlan those treated wcith NAA and
TIBA. Double sprays of these r *ulators were more inhibitive th~an
single spray treatments.
In all of the crops u 0d in theSC studi s--cantaloupe, cucum-
ber, sqruash, and w;atermeloi-n-- r i~lcts three weeks after treatment.
indicated thai th~e can cetration used of :'1, ;1 1, TIIC.', and IAA~
inhibited .t tstive -row~th th~r- : decreas~ir both the 1.n thi and
thec no 7 er of i atrnod I of the r lin st .n. Gibberellic acid incron ed
both the number and the length. of internodes of the main stem
(Tables 4, 5, 6, 7, 8, and 9).
Maleic hydrazide was the most effective regulator inl breaking
apical dominance. It increased the number of lateral branches in
cucumber, cantaloupe, and watermelon; however, it slightly decreased
their length. These are typical effects of FR~I on the growJth of mnany
plants (115 and 116).
Although the results show that TIBA inhibited lateral develop-
ment, it must be mentioned that plants treated with TIBA had more
laterals than those of the control, but they appeared later in the
growing season. It would appear that TIBA was a strong growth inhib-
itor to both terminal and lateral bud primordia soon after treatments;
however, after its effect was diluted by time, it induced breaking of
the apical dominance by inhibiting the polar transport of auxin (2, 7,
45, 59, 77, and 104).
Figures 2, 3, and 4 are presented to illustrate the effects of
the different regulators on the early stages of growth of cucumber
plants grownm in the fall of 1968 and 'Zucchini' squash plants grown
in the spring of 1969. It appears that these effects are directly
related to both flowering and fruit development.
In cucumber, concentrations of 100 ppm of EDI or NAA slightly
reduced the length of the main stem, but their effects on total plant
growth were different. Plants treated with TMH had more laterals and
consequently more leaves formed on the plants than those treated
with NAA. Plants treated with TIBA were. much more dwarfed than those
treated with ~M or NAA, and their growth was retarded for a longer
period. Such effects were similar to those found in cantaloupe
In squash, since there are no laterals developed on the plant,
one can use plant length as well as number of internodes as good
indicators for plant growth. Treatment with GA stimulated plant
growth, while the rest of the r- ulators had inthibitory effects
in the followJing order: IAAI, ME~, NAAZ, and TT:
The results of the greenhouse experiments on both 'Yellow
Straightneck' and 'Zucchini squash are similar, and t' lead to
concrete conclusions about the interaction b et 1e natural and syn-
thetic plant rr i.l tors used in tims :1 lie -. 0 ri tions were:
1. Summer squash plants were not goo in'icators of
sex expression because of theo cluster of floral buds in the
axil of each leaf inst< of a i 'e bud, as in 'Zucchini '
2. There wa a sii ilority in thec grow~th response to
the addition of GA and I '~ between squashi plants and dwrarf
varieties of corn, peas, and bean plants (15, 24, 59, and 84).
3. Treatments which affected sc? express "ca also
tended to cause ch al in plant c!lon tion. For example,
GA caused an incre se in shoot 1 tth and the plant pr-oduced
more male flowers, and IAAs inhibited plant (1II tion and
a good indicator for t'o interaction betwreen natural (GA and
IAAZ) and synthetic (MH~, h'Al. and TIBA) r I.1ators.
4t. At the conce~ntr- 110 of 100 ppa used in these
experiments, GA increased plant length by increasing both
number and length of the internodes, IAA reduced both
number and length of internodes, and treatment with a com-
bination of both GA and IAAt resulted in an intermediate effect.
Gibberellic acid exerts its effect on both cell expansion and
cell division (15, 16, 36, 45, 95, and 111.). Similar results were
also reported by Brian and Hemming (24) on pea, Sachs (95) on
Hyoscymus, and Phinney (84) on corn. In contrast to GA, IAA in
higher concentrations inhibited both cell division and expansion which
wras demonstrated on different: plants as early as 1937 by Went and
Thimann (105). Observed interactions between GA and IAA, were similar
to those reported by other research workers (15, 16, 24, 36, 38,
45, 56, 77, 95, and 111).
Since the effects of GA plus IAA treatments were less than
those of GA alone but higher than those of IAA alone, one may say
that GA reversed the inhibition caused by IAA, or that IAA reduced the
elongation caused by GA alone. Such effect might be a result of a
balance in the ratio between GA and IAA within the plant.
Under the field condition (Fig. 4), a simultaneous spray with
GA and IAA stimulated plant growth more than GA spray alone. This
effect indicated a positive synergism, and was also reported before
(24, 36, 45, 56, and 110).
Maleic hydrazide reduced both length and number of internodes
in all experiments under both field and greenhouse conditions. Sim-
ilar results have been reported on many plants (115 and 116). Rehm
(91) reported that MHI affects only the terminal growing par-ts of the
plant. HowJever, in Avwena coleoptile 2MH inhibits both cell elongation
and cell division (115).
The findings of these studies indicate that GA interacted with
MH to overcome its inhibitory effect (Tables 10, 13, 14, and 16);
IAA could partially overcome the effect of B1UI if applied after MBl
treatment (Table 10); if both MH and IAA wJere applied together they
caused more growth inhibition than either alone (Tables 13 and 16).
These findings are in agreement wlith other investigators (Kato 
and Riddell ), wiho found that GA could reverse the inhibitory
effects of 11R. In peas, Brian and Hemning (16) susggsted that the
inhibition of shoot growth caused by lin- is due primarily to the
activity of "GA-like"' hormone. Results obtained by Olsen, Kulescha,
and Pilet (24), however, indicated tha7t ;ini does modify the endogenous
auxin contents of plant tissues, a 1 did not support the idea that
PDI is anti-auxin. Moreover there is some indication that: HHF may
increase slightly the level of free aux~in in pea roots (Audus ).
Naphthaleneacetic acid had more inhibitory effects on plant
growth than IAA (Tables 11 and 13). Both the number and the length
of internodes were reduced by NAAt. Treatments with lIAA did not
overcome the inthibition caused by- NAA; hor-evrey GA completely reversed
the inhibition caused by FLi on both num er and length of internodes.
This is in completed accord zce with the findings reported by Laibach
and K~ribben (44S), Kacto (56), and Galun (35) on cucurbitaceous crops,
and w~ith many other research wolrkers on ornamental and fruit crops.
Triiodobenzoic acid severely inhibited plant grouth and
reduced bath an bar and length of internodes. Treatmenits with? IAA
were more effective in overcoming TIBA inhibition on the number of
internodes than plant length (Tables 11 and 13). These findings
indicate that TIBA might exert its inhibition by blocking the action
of both endogenous IAA and GA on plant gp~roth~.
Galston 1947, reported that TIBA caused morphological changes
in soybeans such as shortening of the internodes, loss of apical
dominance and opinasty of young leaves. His observation,that TIBA
inhibited thee action of aLuxin in the Avena Test, suggested that TIBA
might act as anti-aux;in. However, there was no evidence to supply
convincing proof of this idea. Audus and Shipton (7) suggested that
it was possible that the inhibition of auxin action in this test was
due to a general growth inhibition not specifically connected with
auxin. It is well accepted that TIBA has a high specific capacity
for modifying the polar transport of auxin in plant tissues (45; 59,
77, and 104).
The idea of floral bud bisexuality is not new. Schaffner and
Yampolsky (44) repeatedly pointed out that there cannot be a total
loss of genetical capacity for the expression of the sex not normally
manifest in an individual, for it is usually possible through environ--
mental agencies to evoke functionally perfect male organs in female
plants, and vice versa.
This idea, along with the findings of Ito and Saito (48, 49
and 50), and Atsmon and Galun (5) supports the conclusion that floral
buds in the cucurbitaceous plants are bisexual in nature. This means
that during development from primordia to anthesis the cucurbitaceous
floral bud passes through various stages. All floral buds pass
during their ontogeny through a bise-ual stage. Unisexuality is
attained by suppression of the pistillate structure in the male, and
the staminate structure in the female. A hor-maphrodite flower is
produced by the development of both sex organ~s.
Based on his studies on hemap as well as on a reviewJ of lit-
erature, Heslop-Harrison (1,4) 5, .-c.-sted that sex expression is regu-
lated by the level of a growth substance (florj .e ), and that there
were twJo different thresholds. TLe lowerr threshold represented the
transition from the vc~~ t tive state to the staminate phase, and the
higher threshold rep~rescnted the shift'. front thle staminate to the
pistillate sex express ... But "florigen" itself wa ,and still is,
in the realmi of hI-I t 's.
Arguing fron- their fi,,J.i. wcith cucumber, Laibach and Kribben
(44) have suggested that the sexuality of a flooiir is depen~dant upon
the concentration of native auxin levels available to the leaf axil.
during the period of flower fo:.. tion. This vic<: eint is supported by
the findings of many others (5, 6, 35, 37, 44, 45, 49, 50, 59, and
In his review~ article (92), Resende, in 1967, described the
degree of flower develop ant (floral gradient front vegetative to floral
flowJer) as it may' be ce tol 1ed by the ratio of growth promoters to
growth inhibitors. Thie hi :,, this ratio, the more vegetative the
flower will be, and thle very hi 's values will lead to a total 1(e~;.
sion to thc is~ ~i tive state. He also Fla- < -tda hypjothlesi s which
may be so ~iai:-d 3 o follows: Sex: expression in angii.; is
controlled by a group of structural genes, subgroups of whr~ich are
responsible for the calyx, the gynoecium, the corolla, and the
androecium. The activation of these genes is governed by the estab-
lish~ment of a specific ratio of growth promoters to growth inhibitors.
The balance of this ratio of growth regulators (morphoregulators) is
postulated to be controlled by a system of additive genes, wJhich reg-
clate expression and repression of the structural genes.
If, therefore, the former system (structural genes) is a Fixed
one, all the variation covering genotypically determined monoecia,
dioecia, gynodioecia, gynomonoecia, and andromonoecia (IHestergaard,
) might be explained taking into account simply the variation
within the additive genes regulating the balance of growth promoters
to growth inhibitors. HZowever, this system? does not cast any light
on the nature of these growth promoters and inhibitors.
It might be helpful here to quote from the review~ article on
the physiology of flowJer and fruit development by Nitsch (77), "As a
whole, there seems to be a correlation between the development of
certain flowecr parts. Thus, factors which favor the development of
ovary also favor that of sepals, those favoring stamen development
favor also the development of corolla."
The results of the current studies on sex expression are in a
complete agreement with the findings of other investigators (5, 6, 17,
36, 38, 45, 56, 59, 77, 85, 86, 103, 111, and 112) in that GA promoted
maleness and supressed femaleness of the plants. In the field exper-
iments (Tables 3, 5, and 7), GA treatments enhanced the appearance
and increased the number of stamiinate flowers. Gibberellic acid also
delayed the appearance of either pistillate (in cucumber and squash)
orhermaphrodite (in cantaloupe) flowers. Inodoleacetic acid treat-
ments had completely opposite effects to those of GA. Inodoleacetic
acid enhanced pist-illate florwer production and reduced the staminate
phase. Houicver, in both cucumber and squash~ (Tables 3 and 5) treat--
ments w~ith a mixture of IAA~ and GA delayed flowerine in general by
decreasing the total number of florwers developed during the firsti
week of flowJering, but in the follow. weeki sex expression wras
shifted touarrd fecalene 3.
Experimental results in thre gre .house wecre similar to thone
of the field, but they p~ut more e En'is on thie interaction betwoc~
the different regulat ,s affect'.: plant gr~owth and sex expression.
The availability of a 'Zucchini' hybrid minimized the possibility of
any genetic variability beturcon plants which might affect plant
growth and sex expression.
From the results of the first experience (Table 10), it is
safe to conclude? that GA treatnrents alone stimulated vegetative
extension and shifted sex expression~ toward maleness. Naphthalenea-
cotic acid on the other hand inhibited e10 to n Howiever, one
should notice two other effects: first, wrhen seeds uocre soaked in
CA, a consequent spray wcith IAAr did not: reduce the effect of GA on
elongation, but it did reverse the e:Ff-c on sex expression; second,
when seeds were soaked in IAA, a subsequent spray with CA produced
its stinrulatin- g effect on el. -Ition but did not affect sex expression.
This latter effect mi;--'lt be explained on the basis that seed soot~i
in GA di~d not: exert: its effect on sex expression im cliately, and a
subsequent IAA spray might have modified the ratio IkAAGA before
the sex expression of most floral primordia is established. On the
other hand, seed soaking in IAA might have an immediate and prolonged
effect on the sex expression of floral primordia, or GA sprays did
not modify the ratio of endogenous IAA/GA enough to supress female
In the 'Zucchiini' squash experiments (Tables 12, 13, and 14),
GA seed soaking or plant spray treatments shifted sex expression
towJard maleness by changing the sex of the floral buds on the upper
nodes (the nodes from 10 to 13 carried female flowers in the control
plants), and seed soaking plus plant spray with GA produced completely
male plants. Indoleacetic acid treatments increased female tendency
by modifying the sex of the floral buds located on the nodes from 6
to 11 of the treated plants. However, in cases where both GA and IPAA
were applied on the same plants, sex expression was almost like that
of the control plants.
The above results lead to the conclusion that sex expression
in the cucurbitaceous plants might be controlled through the levels
of endogenous auxin and gibberellin in the plant. Whether or not
these levels have a direct or indirect effect on sex expression, it
is clear that high levels of GA favored vegetative extension, form-
ation of staminate flowers, and prolonged the staminate phase. High
levels of auxin, on the other hand, inhibited vegetative extension,
shortened the staminate phase, and increased and accelerated mor-
phologically and chronologically the formation of pistillate flowers.
At present there seems to be considerable evidence which supports
that conclusion. The fact that synthetic auxins increase the ratio
'of pistillate to staminate flowers in cucurbits has been reported
by many researchers (12, 13, 22, 35, 46, 49, 59, 77, 110, and 112).
This may be caused by either an increase in the relative number of
female. flowers, a decrease in male ones, or both. Actually synthetic
auxins reduce thle number of 8ale7 flowers to such an extent that thiey
have been suggested as a means of inducing miale sterility in plants
(44, 45, 46, 91, and 110).
Galun (35) was not able to detect any significant differences
in thec auxin contents of norI- 1, monoecious and purely gynoccious
plants of cucumber. However, he wJas able to show in a later in vitro
experiment that very young flower primordia of cucumber excised from
nodes wihich1 would have former' maile flowJers could be caused to develop
into female flower buds if 0.1 mg/1 of IAA was added to the nutrient
It is clear also from thle w~ork done waith GA (17, 37, 38, 43, 83,
and 86) that this hormone does not only alter sex ratio in monoccious
cucurbits, but it: also causes the production of staminate flowers on
completely gynoocious lines of cucumber.
According to the foregoing results and evidence, the following
bypothiesis appears to be wJarranted:
1. The sex of flower primordia in monoecious cucurbits
passes thrull :) a bisexual stage and is expressed as male or
female due to the physiological and environmental factors.
2. Sex expression in cucurbits is controlled by the
ratio of auxins to gib' rel11ins in the plant especially in
the tissues in the suibapical region of differentiation and
within floral primordia before the bisexual stage. The higher
this ratio the greater tendency for female sex expression, and
the lower the ratio the more male the tendency.
3. Endogenous levels of auxin and gibberellins could
control sex expression directly or indirectly--directly through
the effect of GA and IA~A per se on gene repression and dere-
pression, and indirectly through the effect of these two hor-
mones and their interaction with other plant regulators on
plant growth, development, and metabolism. In any case, higher
levels of GA favor vegetative extension and male sex expression;
however, high levels of IAA tend to inhibit vegetative growth
and induce female sex expression.
Such a hypothesis is in agreement writh the assumption of
Resende (92) on the effect: of growth promoters and growth inhibitors
on genes and sex expression. It is also supported by the ideas and
the findings of other investigators (5, 6, 12, 17, 37, 41, 43, 45, 56,
59, 76, 77, 83, 85, 110, 111, and 112).
It does not contradict the assumption of the flowering hor-
If indeed florigen
mone (florigen) as suggested by Chailakhyan (21).
is in existence and it is either composed of twao hormones, gibberellin
and anthesin, then we can say that IAA might play its role by modify--
ing the proportion of these two hormones and their action on both
flowering and sex expression. Or it may be more reasonable to assume
thiat such a hormonal complex (florigen) is merely a polymer of differ-
ent plant hormones and thie proportional ratio of these hormones is
the determining factor in regulating plant growth and development.
Following t;he same line of reasoning, one could conclude the
follow ng: First: the effect of NAAM on sex expression might be
a direct effect as a synthetic auxin wh~ich~ favors female sex expros-
sion, or an indirect effect through the modification of endogenous
levels of IAA and GA~. Second: both TIBAS and 181 hand similar effects
on vegetative growth and sex expression, and their action might be
attributed to one or more of the follow:~ echanisms:
1. They inhibit and retard is; t'tive growth and
extension: changes I: "ch1 might result in a build up in IAAi
levels in th~e plant tissues, especially in the stel..
2. They hnve a direct off ct on theL inhibition of thle
polar transyoit of IAAii in thie sten~ c---iny a build up of IAA
levels in thec apex a- in the area of priniordial differentia-
3. They have ant moistic fects and reactions toward
CA which block or dilute its action on both vegetative growth
and sex expression.
Fruit Crlo'-t' i D.
The phyisioL~ ;I 1 'n chronological determination~sof market-
able yields of cucunter and summer squash are different from those
of cantaloupe and waterwelon. Cucuin'er and squash fruits are harves-
tod at: about 6 to 12 days from thF- til of fruit set while they are
phlysiologically ir iture. However, cantaloupe and water. 10n fruits
are harvested in th~e physiolo ii 11y mature stage after about 35 to
50 da a from thie tirac of fruit. set. Both cucumber and squash plants
develop and se nu: aros fruits which are mrulti-l arvested during a
4 to 8 week harvesting period. In other words, fruits which are set
and developed early in the season, if harvested at the proper time,
do not compete writh those wJhich~ are set and developed later in the
season. Regardless of th-e number of pistillate flowers developed
and fruit set on cantaloupe and watermelon plants, each plant is able
to support and develop only 1 to 3 marketable fruits within the nor-
mal growing season.
In both squash and cucumber the number of marketable fruit is
dependent on the number of pistillate flowers developed and set per
plant, and earliness of the crop is a function of both fruit setting
time and the rate, of fruit growth and development. On the other hand,
earliness and total yield of cantaloupe and waatermelon do not depend
on the. number of pistillate flowers as much as they are dependent on
the time of fruit setting and the rate of fruit growth and develop-
ment. The earlier the fruit sets and the faster it develops, the
earlier it can be harvested and the higher will be the early yield.
Results of the three seasons experiments with cucumber (Tables
1, 4, and 5) indicate that all treatments of MH in spring 1967,
treatment with 100 ppm FM in spring 1968, and both 100 ppm and 200
ppm treatments of MH in fall 1968 increased the number of fruits
harvested early. However, treatments with 150 and 200 ppm PM in
spring 1968 decreased early yiel~d. These different effects of concen-
trations might be due to different plant responses in the spring than
that in the fall. All of MH treatments in all experiments increased
the number of pistillate flowers developed early in the first two
weeks, but there were different effects on the inhibition of vegetative
growth. Double spray treatments in 1967 and higher concentrations in
1968 had more inhibitory and lasting effects than those of single
sprays and lo::er concentration (Tables 1 and 4 and Figures 2 an~d 5).
These results also indicate that early yields were in proportion to
vegetative grourth and number of pistillate flow~ers. On the basis
of these results, wJe can say that all treatments with FEDI enhanced
early formation of pistillate flowers and inhibited vegetative
growth. Those treatments which slightly inhibited growth reduced
the competition between vegetative and fruit growth, and, as a result,
increased early yield. Other treatments caused more inhiibition to
vegetative development which reduced the ability to support the
developing fruits and reduced early yield.
In the same way, we can explain the results of both NAA and
TIBA treatmen-ts. N~aphthaleneacetic acid treatments had more and
TIBA the most inhibitive and lasting effect on vegetative and repro-
ductive grow~th and development. However, effects of GA, IAA and a
mixture of GA and IAAZ treatments on yield were directly related to
their effects on both vegetative growth and sex expression.
ResuLlts with squash shout that treat .Tts with MHii and NAA~
at the two-leaf stage in spring 1967 and ~M 100 ppm were the only
treatments wh~ich1 increased early yield, wJhile the rest of the treat-
ments had no effect, decreased yields, or resulted in no early yield
at all (Tables 2 and 6). These results are different from those of
cucumber beca se the number of flower buds and the number of leaves
in squash are merely dependent on the number of developed internodes
on thle ni n stcn. The -. treat .1t~s which slightly decreased vegetative
growth also accelerated the development of early fruits and increased
early yield; however, the rest of the treatments inhibited growth
by decreasing both length and number of internodes and number and
size of leaves which decreased plant metabolites and delayed fruit
growth and development.
This conclusion is also supported by results of treatments with
higher concentrations of NAA and TIBA which resulted in dwarf plants
that produced smaller fruits with either abnormal shape or size..
Early and total yield of watermelon and cantaloupe is directly
related to the state of vegetative growth. Treatments which enhance
early development of pistillate flowers might also increase early
yield, if the competition between vegetative and fruit growth in
the earlier stages of fruit development was decreased. Such was the
case wiTth the treatments of 100 and 150 ppm iM in the spring 1968
and hM and IAA in the fall 1968 in cantaloupe (Tables 8 and 9), and
all treatments with MRI and NAA at the two-leaf stage in 1967 and
100 and 150 ppnn MR andl 100 ppm NAA in 1968 in watermelon (Tables 3
and 7). Treatments which decreased the vegetative growth severely
delayed both fruit setting and fruit growth and development, decreased
the number of fruit in early harvest, or delayed yield to the later
harvests. Such are clearly illustrated in the results of treatments
with TIBA and highi concentration of NAA (Figures 7, 8, 9, and 10).
Total yield is a direct result of the number and size of
fruits which ar;e marketable at harvest time. It depends on the
number of fruit set early in the season and their rate of development
during the growing season. These two characteristics are directly
related to thle number of pistillate flowers, percent fruit setting,
and the comnpetition between vegetantive and reproductive growth. Total
yield wJas increased in cantaloupe by treatment with lower concentra-
tion of MH, TIBA and IAA~, and by NH1 and NAA1 in watermelon. These
results might be attributed to the effect of these treatments on
increasing thle number of early pistillate flowers, the ratio of
fruit settinZ, and the acceleration of fruit growthi.
I---r---------~ --- a-- -------~--~car~
1 2 3
4 5 6 7 8 9 b 10 11 2 13 14
Weeks from Planting
.re 1. Schematic R~eview of the Overall Plant
Growth and Development of the Cucurbitaceous
Plants in General.
/ .. MH-100 ppm
/ ~..* NAA-100 ppm
I. TIBA-25 ppm
10 20 30 I0 50 6`0 10I 20
Days after Plantir
30 40 50 60]
Figure 2. St mE1-:a -tion of Field Grown Cucumber
(Fall, 1968) in Response to Treatments
with Different Ch. Tical Regulators.
10 20 30 40 50 60 70
Days after Planting
Effects of Different Chemical
Regulators on Stem Elongation
of Field Gror-m Zucchini Squash
(Spring, 1969) .
10 20 30 40 50
Effects of the Different Chemical Regulators
and Their Interac Lions on Stem Elongation of
Field Grow~n Zucchini Squash (Spring, 1969).
GA + IAA
(/j/.* 1H + IAA
AA +- GA
,'i'IBA + GA;
/ .TIBA + 1tAA
A2 + IAA, .i
/ / .''T IB A
/ / .*'.
60 70 10 20 30 40 50 60 70
Days after Planting
I I I I
GA + IAA
Figure 5. Influence of Regulators on Vegetative
Growth, Sex Ex;pression, and Mlarketable
Yield of Cucumber (Fall, 1968).
0 100 200 100 200 25 100 100 50 ppm
Check ---MIH--- ---NAAZ-- TIBA GA IAA GA + IAAt
Figure 6. Effects of Regulators on Vegetative Growth,
Sex Expression, and Mlarketable Yield of
Squash (Fall, 1968).
18 2n Hr s
-- --1-- -- -N A -- --- IE~ ~t H r e T I A -
Catlop (Srn, 98
- - -uL-~p~x~- -rrjaL--~a
--pC-W _~_LL I\\I
3rd Harves L
1s t Harvest
Figure 8. The Influence of R. ailators on Vegetative
Growth, Sexc Expression, and MIarketable
Yield of Cantaloupe (Fall, 1968).
- ---C~ub --I~-~L~*~ILZL-`~-
Check 2 4 2+4 2 4 2+4 2 4 2+4
----MIH----- -----NAA----- -----TIBA-----
Effects of Regulators on Sex Expression and
Marketablee Yield of Watermelon (Spring, 1967).
n ~ Early
_ __ I
0 100 150 200 100 150 200
25 50 ppm
Figure 10. Regulators' Effects on Sex Expression
and Marlke table Yield of W~a c ono
SUIRLORY AND CONCLUSION
Studies were conducted using some growJth regulating chemicals
to modify the flow~ering and sex expression of cucurbits and to achievr
one or more of the followJing objectives: to increase earliness of
the crop, to increase total yield, or to concentrate flowJering and
fruit set into a shorter period. Crops used in these studies were
cucumber, summer squash, cantaloupe, and watermelon. Growth regula-
tors selected were MH, NAA, TIBA, CA, and IAA.
The experimental program was divided into a field phase to
study the effect of spraying the plants wFith regulators on the pro-
duction of these crops, and a greenhouse phase to determine the
mechanism by which these regulators produced their effects.
All th~e treatments modifiedl plant girowrth, sex expressionl, and
fruiting under both greenhouse and field conditions. Treatments with
MIH, NAA, TIBA, and IAA reduced vegetative growth, suppressed stamin-
ates, and enhanced pistillate flower development. MIultiple applica-
tions and higher concentrations of these chemicals inhibited plant
growth more than a single application or lower concentrations.
Treatments with GA increased vegetative growth, enhanced staminate,
and suppressed pistillate flower production.
Early and total yields were increased by applications of 100
ppm of MH, NALA, or IAA in a single spray at the four-leaf stage in
all crops. Treatments with TIBA at 25, 50, or 100 ppm~, 1M at 200
ppm, and NAA~ at 200 ppm shiowed promising results for harvest
Ex-perimental results, observations, and a review of pertinent
literature appear to support the follo; L. hypothesis:
1. The sex: of flo::er pr~i. rdia in monoecious cucur-
bits passes thiroughi a bisexual. st: c and is expr-essed as
male or female due to phy~siolt :.. I. and environmentally f-ctors.
2. Sex expression in cucurbits is controlled by the
ratio~ of auxin to gibbtsrllins within flower priia
tissue~s before thle bise 1a st .. The I-' he this ratio the
greater the tenldency for feri Ies an' LIi lo\_er the ratio
thle core male the to Lnc
3. El1d11- avl .s og "au or giL 11elins could
control sex exiprsio : Lc3. L's t iir efects on aren
expr asion and r peso, or i ii-c.el1, thrage their effects
on other plant hor nne, plant: mc .bolism, or plant development.
It is reasonable to conclude the follow' : First: thle effect
of NAAi on s -: expression r `t be a direct effect: as a synthetic
auxin wh:ic' favors female s :i expression, or an indirect effect
through the modification of endo~eeous levels of IA\A and GA. Second:
TIBA and >0 had similar effects on vegetative growth and sex expres-
sion, and t'oir action r;. Lt be attribute 1 to one or more of th~e
follor- i- r .-. ios:
1. They inhibit : ret. :d I. _ Itive growth and
ext niont; changes wJhich raigh-t result: in an increase of IAA~
lovcl in thie plant; LE :u especially in the stem.
2. They have a direct effect: on the inhibition of the
polar transport of IAAZ in the stem, causing a build up of
IAA levels in the apex and in the area of primordial differ-
3. They have antagonistic effects and reactions
toward GA whiich1 block or dilute its action on both vegeta-
tive grow~th and sex.
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