Citation
Modification of flowering, sex expression and fruiting of selected cucurbits by growth-regulating chemicals

Material Information

Title:
Modification of flowering, sex expression and fruiting of selected cucurbits by growth-regulating chemicals
Creator:
Abdel-Rahman, Mohamed, 1941-
Publication Date:
Copyright Date:
1970
Language:
English
Physical Description:
91 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Chemicals ( jstor )
Cucumbers ( jstor )
Flowering ( jstor )
Flowers ( jstor )
Fruiting ( jstor )
Fruits ( jstor )
Plant growth ( jstor )
Plant nutrition ( jstor )
Plants ( jstor )
Vegetative growth ( jstor )
Dissertations, Academic -- Vegetable Crops -- UF
Plant growth inhibiting substances ( lcsh )
Plants, Effect of chemicals on ( lcsh )
Vegetable Crops thesis Ph. D
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1970.
Bibliography:
Includes bibliographical references (leaves 81-89).
Additional Physical Form:
Also available on World Wide Web
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Mohamed Abdel-Rahman.

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University of Florida
Holding Location:
University of Florida
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Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Resource Identifier:
030472714 ( AlephBibNum )
37680415 ( OCLC )
ACN4021 ( NOTIS )

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Full Text







MODIFICATION OF FLOWERING, SEX EXPRESSION
AND FRUITING OF SELECTED CUCURBITS BY

GROWTH-REGULATING CHEMICALS














MOHAMED ABDEL-RAHMAN














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


1970






















DEDICATION



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


Page


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




iv





















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


Table Page

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?










Table


Page-


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


Figure Page

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


viii








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








By

Niohar d Abdrl- ~hran


August, 1970



Chairman : Dr. B. D. T'` Ion
Major Depair t>-nt : l' etb Cr


An exp si j

growth re I1ath

expression, and

were, first: to

to induce conecu


period; second:




Crol : u .

'Ashley,' cnnta3

Cllco-lh i -

melon--Ct ;

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 :


crp objcctile

ercs tot 1 yield, and/or

fruit-
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.















CHAPTER I

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'


process.


drawn the

.Althe


ijorit-y of

'.ioL


nttention of

' rost of the

r. Lu re-

of thris


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


ct




',


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-


i,

f'


f


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.















CHAPTER II

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

plant.

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

species.


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.






-5-


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-

tions.


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)

on cucumbers.


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).


Chemical Factors

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

in cantaloupe.


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

cantaloupes.









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

increased.

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














CHAcPTER III

MATERIALS ANVD NETLHODS


Gr~OwthI-Reg;uililgtn Chemicalsal

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

point.

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


- 10-





-11-


c ...nios pis : ci







Fie ld


ne ft


icnn c 5 i- Lfi -

;-al in~r- ti 1 on

' of


1.-y '



'ly


our tlc ss ( p~pli-

: dt in


I-lll cn oe lant


cr s"h, 5x::3






aid 1:~ t


eii L













di ~~


t'~ F


rc 5


rtri lo s.


~tcliz ~ .ae

l o trol 1le' i'

ih tcr .1l Fierio

"i?- i. d k;~~~a


-cribcd in





-LI-


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-

melons.

Concentration

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,

and watermelons.

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





-13-


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

criteria:


1. V,~ tative

internode

on the pla

plants as


'.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-

Ing.

d. Tl f< ica to mnale floi ratio.






-14-


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.


Greenhouse

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

shoots.


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


w~ere con


ted on 'Yellowj Strai 't i


ic" to de terniin


the effects


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






-16-


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-

nations:


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

on plants.


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

determined.


6. Total DNA and RNA contents of seedling plants, un-

differentiated buds, male and female flower buds.






-17-


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

amounts.















.CHAPTER IVT

RES ULTS


Field

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


-18-




-19-


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

(Table 2).

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






-20-


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





-21-


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

harvested.

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).





-22-


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-

siderably.

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.






-23-


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

the nu
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

of both.

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).





-24-


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.


Greenhouse

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





-25-


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).


Gibberellic Acid

'Yellow-Straihl go
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).




r),
-1.0-


Indoleacetic Acid

'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

(Table 10).

'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





-27-


tendency toward femaleniess in sex: expression was less than IAAi

applied alone (Tables 13 and 14).


Mraleic Hydrazide

'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).





-28-


Naphthaleneacetic Acid

'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).


Triiodobenzoic Acid

'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






-29-


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).


Nucleic Acids

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

undifferentiated ones.


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






-30J-


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

similar effects.


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

RNA contents.




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.





-31-


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

plants.


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,






-32-



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.






-33-


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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

EXPERTIMENT 1:

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


EXPERIMENT 2:


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


-42_-


TABLE 10

THE INFLUENhCE OF THIE DIFFERENT REGULATORS AND~ TiHEIR,
INTERACTION7 ONd VEGETATIVE GROWTHI AN\D SEX EXPRESSION
OF YELLOW; STRAIGHTN7ECK; SQUASH:















TABLE 11

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
Experiment 3:

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


-43-





















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


-44-


TABLE 12

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


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-45-


TABLE 13

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


Plant Sprayed
at the four-laf


Ex perim nt 5 -

WATER (Control)

GA

IAA

GA + IhAA


~,i: < iuner of
Flo Jr Buds


Node Pos.
First




10

11


Plant Ku I r of


I th




14.7

23.3

12.3

17.5


Inltern 'd e




9.3

9.7

9.0

10.7


8.3

11.7

7.7


2.0

1.5

4.5

2.8


9.0

9.5

5.3

7.3


11.0

11.0

9.8

10 0


9.5

15.3

9.0


12.8

15.5

13.0


3.0

2.5

4.0


7.5

9.5

5.0


10.5

12.0

9.0


MH

MHl +I GA

MIH t IhAA


NAA

NAA +1 GA

NAA + IAA


TI;A

TIBA + C .

TIBA + IAA


8.3

8.7

7.7


3.3

2.8

4.0


10.0

10.5

8.3


8.0

13.1

9.3


10.5

10.0

9.5


L.S.D. 5% Level






















~I_


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


-46-


TABLE 14

FRESH AND DRY WEIGHTS OF ZUCCHINI SQUASHI PLANTS
IN RESPONSE TO TRE DIFFERENT
CH-EMICAL, REGULATORS


TREATMENTS
Plants Sprayed at
the Four-leaf Stage
with


FRESH AND DRY' WEIGHT OF PLANTS
Two Weeks After Treatment
Fresh Weigh t Dry Weight Percent
gm./Plant gm./Plant Dry Weig~ht





-47-

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CRAhPTER\ V

DISCUSSION


General

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


-48-










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

crop.

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:





-50-


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





-51-


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

this period.





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





-52-


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





-53-


period. Such effects were similar to those found in cantaloupe

and watermelon.

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 '

squa'sh .

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

increa
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






-54-


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





-55-


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 [56]

and Riddell [24]), 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 [7]).

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





-56-


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).


Sex Expressi~on

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





-57-


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

77).

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





-58-


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,

[106]) 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





-59-


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






-60-


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

sex expression.

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





-61-


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

medium.

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





-62-


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.





-63-


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-

tion.

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





-64-


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





-65-


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





-66-


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





-67-




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.








































































Figu


I---r---------~ --- a-- -------~--~car~


-68-


mx8
a 7
Ok

ora


LC 1
0C


H

cm


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.


15





-69-


110


H20
/ .. MH-100 ppm
/ ~..* NAA-100 ppm




I. TIBA-25 ppm


MH-200
**ppm

/ NAA-'\200
ppm
/ /


//


!!/
Iff


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.





-70-


GA

/, H20
, IAA

MH NA



TIBA


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) .


Figure 3.

























































10 20 30 40 50


Figure 4.


Effects of the Different Chemical Regulators
and Their Interac Lions on Stem Elongation of
Field Grow~n Zucchini Squash (Spring, 1969).


-71-


GA + IAA


40




30




20




10




t0


S40




30




20




1 0


GA
1120 H20
NH+ GA

(/j/.* 1H + IAA


















HO0
AA +- GA

,'i'IBA + GA;
/ .TIBA + 1tAA

A2 + IAA, .i
/ / .''T IB A

./


/


1


/ **
/ '


/ -'


N



/ NAA

/A


/ / .*'.


60 70 10 20 30 40 50 60 70
Days after Planting




























































I I I I


~72-


100


STotal

~aEarly


V)
U
d
W P~
H




8
~lcl
o


50




30

20

10


O
Check


100 200
---MHI----


100 200
---NAA---
TREATME~NTS


100
IAA


50 ppm
GA + IAA


25 100
TIBA GA


Figure 5. Influence of Regulators on Vegetative
Growth, Sex Ex;pression, and Mlarketable
Yield of Cucumber (Fall, 1968).


0 d


n





-73-


m ~100




4O 0
a3 u


60



20









Tota



a 2


10



00






5



0 100 200 100 200 25 100 100 50 ppm
Check ---MIH--- ---NAAZ-- TIBA GA IAA GA + IAAt
TREATMENTS

Figure 6. Effects of Regulators on Vegetative Growth,
Sex Expression, and Mlarketable Yield of
Squash (Fall, 1968).





-74-


100

80


So
20 k

C3C



60

wMO





oo


3r Hrvs
18 2n Hr s







So





33


-- --1-- -- -N A -- --- IE~ ~t H r e T I A -



Catlop (Srn, 98





























- - -uL-~p~x~- -rrjaL--~a


--pC-W _~_LL I\\I


-75-


100


80


60



20


20






0.





20





12


8





0


x O

o C
0 o
Ho










O

o



C0 \-
11


3rd Harves L
2nd Harvest
1s t Harvest


100 ppni


C -


100 25
TREIATIENT"S


Figure 8. The Influence of R. ailators on Vegetative
Growth, Sexc Expression, and MIarketable
Yield of Cantaloupe (Fall, 1968).


I id'




































- ---C~ub --I~-~L~*~ILZL-`~-


-76-


III O


Total

Early


250

200

150

100

50


Check 2 4 2+4 2 4 2+4 2 4 2+4
----MIH----- -----NAA----- -----TIBA-----
TREATMENTS


Figure 9.


Effects of Regulators on Sex Expression and
Marketablee Yield of Watermelon (Spring, 1967).




















LTotal



n ~ Early


_ __ I


-77-


1 -

0

200 -

160 -

120

80-


o0


0 100 150 200 100 150 200


Check -----MH------


------NAA------


16
~S1P


I Total
6 Early


25 50 ppm
---TIBA---


Figure 10. Regulators' Effects on Sex Expression
and Marlke table Yield of W~a c ono
(Spring, 1968).














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


-78-





-7'3-


ppm, and NAA~ at 200 ppm shiowed promising results for harvest

concentrations.

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.





-80-




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-

entiation.

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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PAGE 1

MODIFICATION OF FLOWERING, SEX EXPRESSION AND FRUITING OF SELECTED CUCURBITS BY GROWTH-REGULATING CHEMICALS By MOHAMED ABDEL-RAHMAN A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THB DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1970

PAGE 2

AQR'CULTURAL LIBRARV UNIVERSITY OF FLORIDA I I I III I I 3 1262 08552 4436

PAGE 3

DEDICATION To my parents, wife, daughter, and friends this dissertation is humbly dedicated with affection.

PAGE 4

ACKNOWLEDGMENTS The author wishes to express his sincere appreciation to Dr. B. [) . Thompson, professor of Vegetable Crops, for his guidance and assistance during the program of this study and for his helpful criticism in preparing this manuscript. The helpful advice and assistance of the other members of the supervisory committee, Dr. A. P. Lor?. , Dr. V. F. Nettles, Dr. A. A. Cook, and Dr. R. C. Smith, is gratefully acknowledged. Deep appreciation is also extended to all members of the Vegetable Crops Department for their interest and cooperation during the years, to the Department of Vegetable Crops for providing the research facilities and some of the financial support, and to Dr. 5. H. West for providing laboratory space and equipment needed for some of this work. 111

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TABLE OF CONTENTS Page 111 Acknowledgments List of Tables vi List of Figures viii Abstract ix Chapter 1 Introduction 1 Chapter II Review of Literature 3 Genetic Factors 3 Environmental Factors 5 Chemical Factors 6 Chapter III Materials and Methods 10 Growth Regulating Chemicals 10 Field 11 Greenhouse 14 Measurements and Evaluations 16 Chapter IV Results 18 Field 18 Effect of Application Time 18 Cucumber 18 Squash 18 L'at erne Ion 19 Effect of Concentration 20 Cucumber 20 Squash 21 IV

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TABLE OF CC S (continued) Page Watermelon 22 Cantaloupe 23 Greenhouse 24 The control treatments 24 Gibberellic Acid 25 Indoleacetic Acid 26 Lc Hydrazide 27 Naphthaleneacetic Acid 2d Triiodobenzoic Acid oleic Acids 29 Chapter V Discussion 48 Genenl 48 Vegetative Growth 51 Sex Expression 56 Fruit Growth and Development 63 ion 78 Bibliogra: 81 Biographical E 90

PAGE 7

LIST OF TABLES Table Page 1. Flower Sex Expression and Marketable Yield of Cucuisber Grovjn in S n rln°' 1967 in P.es^onse to Chemical Regulators and Their Application Time 33 2. Flower Sex Expression and Marketable 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 Grown 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 Marketable Yield of Cucumber Grown in Spring 1968 36 5. The Influence of Chemical Regulators and Concentrations on Flower Sex Expression and Marketable Yield of Cucumber Grown in Fall 1968 37 6. The Influence of Chemical Regulators and Concentrations on Flower Sex Expression and Marketable Yield of Squash Grown in Fall 1968 38 7. Effects of Chemical Regulators and Different Chemical Concentrations on Vegetative Growth, Flower Sex Expression, and Marketable Yield of Watermelon Grown in Spring 1968 39 8. Effects of Chemical Regulators and Different Concentrations on Vegetative Growth, Flower Sex Expression, and Marketable Yield of Cantaloupe Grown in Spring 1968 40 9. The Influence of Chemical Regulators on Vegetative Growth, 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 Growth and Sex Expression of Yellow Straightneck Squash 4? VI

PAGE 8

Table Page 11. Vegetative Growth and Sex Expression of Yellow Straightneck Squash in Response to Treatments with Chemical Regulators A3 12. Effects of the Different Chemical Regulators and Their Interaction on Vegetative Growth and S Expression of Zucchini Squash 44 13. Effects of the Different Chemical Regulators and Their Interactions on Vegetative Growth and Sex Expression of Zucchini Squash 45 14. Fresh and Dry Weights of Zucchini Squash Plants in Response to the Different Chemical Regulators 46 15. The Influence of the Different Chemical Regulators on Nucleic Acid Contents of Summer Squash Plants and Flower Buds 47 VII

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LIST OF FIGURES Figure Page 1. Schematic Review of the Overall Plant Growth and Development of the Cucurbitaccouc 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 A. Effects of the Different Chemical Regulators and Their Interactions on Stem Elongation of Field Grown Zucchini Squash (Spring, 1969). 71 5. Influence of Regulators on Vegetative Growth, 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 Cantaloupe (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 Marketable Yield of Watermelon (Spring, 1968). 77 Vlll

PAGE 10

Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy By Mohamed Abdel -Rahrran August, 1970 Chairman: Dr. B. D. Thompson Major Department: Vegetable Crops An experimental program was designed to study the use of growth regulating chemicals for modification of flowering, sex expression, and fruiting of cucurbitaceous crops. The objectives were, first: to increase earliness, to increase total yield, and/or to induce concentration of flowering md fruit-set into a shorter period; second: to determine the mec! by which these regulators pi od net theii ii Tec t . Crops used in these studies were cucumberCucumis sativus , 'Ashley, 1 cantaloupe-Cucumis roelo , 'Florida #1,' summer squash-C ucurbita pepo , 'Yellow Straightneck' and 'Zucchini,' and watermelon -C_2_tjj£llj£S_j£uJLg_£ ri s_ , 'Charlston Gray.' Chemicals selected were maleic hydrazide, triiodobenzoic acid, naphthaleneacetic acid, indoleacetic acid, and gibberellic acid. Applications were by spraying the foliage or by soaking the seeds in chemical solutions. Treatments with \, and IAA inhibited vegetative growth, suppressed staminate and enhanced pistillate flower formation. Treatments with GA induced vegetative g , enhav IX

PAGE 11

staminate and suppressed pistillate flower formation. Early and total yields were increased by spraying the plant with 100 ppm of MH, NAA, or IAA at the four-leaf stage, in all of the four crops. However, concentration of yield in a shorter harvesting period resulted from treatments with TIBA at 50 or 100 ppm and NA at 150 or 200 ppm. Experimental results, observations, and a review of pertinent literature appear to support the following hypothesis: Floral primordium in monoecious 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 plays an important 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 an indirect result of their effect on plant growth and metabolism. On the same basis, NAA might modify sex expression by increasing auxin levels in the tissues or by diluting the effect of GA. However, MH and TIBA may be exerting their effect through a direct interaction with IAA and GA to modify their ratio, inhibition of polar transport of auxin through the stem, thus increasing the level of IAA around floral primorcia, or inhibition of plant growth which might result in an accumulation of auxin and increase their level in the stem and around the floral primordia. x

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CHAPTER I INTRODUCTION Sex expression in flowering plants has drawn the attention of many research workers during the last century. Although most of the early work reflected genetic interest, the majority of recent research workers have been concerned with the physiology of this process . Some of the most important aspects of the biology of the Cucurbitaceae are the integral elements of the flowering process. Si pressions, flower formation, fruit set, and fruit growth and development are necessary steps leading to good crop production. Many factors which control the flowering process must be in the proper combination to produce desirable fli ind fruiting characteristics to achieve this end. These characteristics would involve not only sexual differentiation but the time of appearance and proportion of pistillate or hermaphroditic flowers on which fruit production depends. Factors interacting to control sex expression in plants are tic, environmental, and chemical. Much research has been conducted on the use of growth-regulating chemicals for modification of sex expression. However, little effort has been directed toward the practical application of research findings. -1-

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In planning the program for this study, two questions were posed, First, are any of the reported growthregulating chemicals of practical 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 harvest. Gibberellic acid and indole acetic acid were also used in order to compare their effects as endogenous growth regulators with the preceding chemicals. A series of greenhouse experiments was conducted to compare the effects of these three chemicals with 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.

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CHAPTER II REVIEW OF LITERATURE The experimental modification of sex expression essentially concerns individual ontogenies; otherwise it means the changes in flowering habits of individuals themselves. Sex expression of a flowering plant refers to the ability of such plant to produce one or more sex forms of flowers, their numbers, and positions on the plant . Sex expression in cucurbits is a characteristic modified by genetic, environmental, and chemical factors. Tiedjens, in 1928. (101) was one of the earliest workers who directed his efforts to the study of sex expression in cucurbits. He considered earlier investigators of s< sion La plantb in three groups: a group of investigators of sex inheritance who recognized only genetics as the determining mechanism, another group who claimed that environment is the basis of sex determination, and a third who took an intermediate position and considered the problem from several points of vi Genetic Factors In his theory about sex evolution in plants, Correns, in 1928 (in 106) , assumed that the evolution of sexual types was from hermaphrodites to the. intermediate forms, andromonoecious , trimonoecious, and gynomonoccious ; thence to the extreme forms, -3-

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-4androecious, monoecious, and gynoecious . Every type of sex expression is represented in Cucurbitac&ae. 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 v?ith andromonecious varieties of cucumber, cantaloupe, and watermelon, Rosa (93) concluded that the monoecious 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. Whi taker'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 species . 3. Staminate flowers are greatly in the majority at all times in all forms. 4. Some evidence exists for environmental control of sex expression.

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Environmental Factors Four variables of plant environment—nutrition , moisture, light regime, and temperature --may directly influence sex expression in plants. Nutrition . --The evidence bearing upon the influence of mineral nutrition on sex expression is more substantial for monoecious species than for dioecious. As early as 1844 , Heyer (44), working with sex ratio in monoecious cucumbers and pumpkins, found that the proportion of staminate to pistillate flowers could be changed materially by growing the plants in different soils. Tiedjens (101) reported that additional nitrogen increased the production of flowers of both sexes in cucumbers, with more increase in the pistillate flowers than in the staminate. Minina (71) found that periodic nitrogen fertilization favored : less while periodic application of potassium favored maleness in cucumbers. Hall (42) confirmed the effect of nitrogen on increasing the ratio of pistillate to staminate flowers in gherkins. Similar results were reported by Cunningham (25) in watermelons, Brantley (13) in cantaloupes and watermelons, and Hopp (47) in butternut squash. Moisture . --Mining and Matzekevitch (77) reported that moisture conditions affected the onset of flowering in cucumbers. Low humidity accelerated the appearance of staminate flowers, while high humidity hastened the onset of pistillate flowers. They also observed that plants grown in moist or dry soils produced staminate and pistillate flowers simultaneously, but the appearance of

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-6pistillate flowers was hastened under high soil moisture conditions . Light Regime . --Tied j ens (101) demonstrated that exposing cucumber plants to a longer photoperiod increased the number of staminate flowers, while the number of pistillate flowers increased and the number of staminate decreased under reduced light conditions. Edmond (?9 ) and Miller (70) reported that long days of high light intensity favored staminate flower production in cucumbers, whereas short days with low light intensity favored pistillate flowers. 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) on cucumbers . Temperature . --The work done by Nitsch (76), Wittwer and Hillyer (110), Ito and Saito (50 and 51), Fujieda (30) and others, indicated that high temperatures generally increased staminate flower production 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 the interaction between temperature and photoperiod in the results reported by many research workers (13, 29, 22, and 101). Chemical Factors Carbon Monoxide . --The earliest reports on chemical control of sex expression of cucumbers appear to have been obtained prior to 1938 by Russian workers (44). In 1938 Minina (71) found that treating cucumber plants during the seedling stage with wood-stove

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-7gases modified their vegetative growth, increased the number of female f lowers , and increased both fruit set and yield. In 1947, both Minina and Tylkina discovered that the effect is mainly due to the carbon monoxide in those gases (in 44 ). Similar results were reported by Czao (27). Ethylene . --Nitsch (76) was not able to modify sex expression of acorn squash by exposure to ethylene in concentrations of 100 ppra for a period of 24 hours. Acetylene . --Mehanik (69) reported that treating young cucurober plants with acetylene gas resulted in an increase in the number of female flowers, increase in the yield of fruits, and an advancement of maturi ty . Methylene Blue . --Naugol jnyh (75) claimed that cucumber plants from seed inaLed with 0.03 percent solution of methylene blue for 24 hours at 22 to 25° C produced 62 percent more pistillate flowers and 45 percent more fruits. These were also heavier than controls, and resulted in 85 percent increase in the yield by weight. Maleic Uydrazide . --Rehm (91) demonstrated that spraying watermelon seedlings with maleic hydrazide (MH) induced male sterility ed femaleness of the plants. Wittwer and Hillyer (110) treated squash plants by dipping or spraying with MH solutions. Treatments resulted in plants that produced the usual number (eight to ten) of pistillate flowers in normal spatial arrangi ra nt with no staminate flowers. Similar results were also reported by Prasad and Tyagi (89) on bitter gourd, by Chondhury (22) on watermelons

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8and bottle gourds, and by Kali and Dhillon (55) on bottle gourds. Triiodoben zo ic Acid . --Wittwer and Killyer (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 staminatf flowprs . Irving and Zawawi (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 in cantaloupe. Naphthaleneacetic Acid . --In a series of studies in 1950 and 1951, Laibach and Kribben ( in 44) rep0 rted that application of naphthaleneacetic acid (NAA) or indoleacetic 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 results on acorn squash. He was able to lower 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 effect of NAA on sex expression were reported by Wittwer and Hi 1 Iyer (110) on cucumbers and squash, by I to and Saito (48) on cucumbers, and by Brantley and Warren (13) on watermelons and cantaloupes .

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-9Gibberellic Aci d . --Wottwere and Bukovac (111), in 1958, were the first to report on the effect of gibberellic acid (GAO on modifying flower-sex expression of cucumbers. They found that GA treatments consistently increased the number of staminate flowers preceding the first pistillate flower. Similar effects were also reported by Galun (36) in 1959. In 1960, Peterson and Anhder (83) were able to induce the formation of functional staminate flowers on completely female plants of the gynoecious cucumber line MSU 713-21. They also observed an increase in staminate flower production as the concentration and number of applications of GA increased. Bukovac and Wittwer (17) demonstrated that foliar application of 100 ppm GA to young seedling of picklingtype cucumbers during two weeks of short-day exposure markedly reduced the effect of short photoperiod on hastening pistillate flower formation. They also reported that dipping the leaves of gynoecious cucumbers in 100 ppm GA solution induced the formation of staminate flowers. Long photoperiod enhanced the promotive effect of GA,not by increasing the number of nodes which produced staminate flowers, but by increasing the number of staminate flowers at each node. Mitchell and Wittwer (73) reported that GA treatments of gynoecious cucumbers induced an uninterrupted sequence of staminate flowers from the second through the ninth nodes. Few plants produced mixed nodes "of pistillate and staminate flowers at the same node" immediately preceding the reversion to the pistillate phase. Similar effects of GA were reported by Hayase and Tanaka (43), Clark and Kenney (23), and Pike and Peterson (85 and 86) on gynoecious cucumber

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CHAPTER III MATERIALS AND METHODS Several chemicals \i7hich 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. Maleic Hydrazide (MH) . 2. Naphthaleneacetic Acid (NAA) . 3. 2,3,5-Triiodobenzoic Acid (TIBA) . Two additional regulators, gibberellic acid and indoleacetic acid (GA and IAA, 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 percent of the final concentration), and adding water. Chemicals were applied to foliage with a hand sprayer until the run-off point. The research work of these studies consisted of two parts-a field phase and a greenhouse phase. The field phase was designed to evaluate the effect of the different treatments on 10-

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11plant growth and development and determine the economic significance. The greenhouse phase was designed to reveal information on the role of these growth-regulating chemicals in the physiology of flovjering and :pression. Field All fi conducted at Gainesville, Florida. The soil was classified as Kanapaha fine sand, and it was described as loose fine sand, acid, and low in organic matter. The crops used were: 1. Cantaloupe-Cucumis melo 'Florida #1.' 2. Cucumber-Cucuinis sativus 'Ashley.' 3. Summer squash— Cucurbita pepo 'Early Prolific Straightneck. ' 4. rmelon-Ci trullus vulgaris 'Charleston Gray . ' A randomized complete-block design with four blocks (replicates) was used for all experiments. Treatments were arranged in single-row plots with each plot containing five hills of one plant •ing distances used were 5x2 feet for squash, 5x3 feet for cucumbers, 6x4 feet for cantaloupes, and 9 x 5 feet for watermelons. Fertil! :ites, method of cultivation, and insect and disease control w< • in accordance with . oral practices for the North Central Florida area. The field work was conducted during different seasons during the years of 1967 and 1968. These experiments can be described in

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-12the following manner; Ti me of application The first set of experiments was started in March, 196 7. Its purpose ii/as to determine the best time of application of MH, NAA, and TIBA. A concentration of 100 ppm was selected from reconmiendations by other workers (46, 73, and 110). The treatments 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 two sprays at the twoand at the four-leaf stage. These nine treatments plus a water control, each with Triton, were applied to cucumbers, squash, and watermelons . Concentration The second set of experiments was begun in March, 1968, to study the effect of different concentrations of each chemical. Concentrations used were 100, 150, and 200 ppm of MH 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, and watermelons . The third set of experiments was conducted during the 1968 fall season on cantaloupes, cucumbers, and squash. Treatments were 100 and 200 ppm MH, 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 MH, NAA, 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

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13yield into a shorter harvesting period. An additional field experiment was conducted during the spring of 1969 to compare the effect of different regulators on plant growth and development of 'Zucchini' plants grown under greenhouse with those grown under field conditions. Plants were started in the greenhouse in peat pots. Chemicals were applied as a single spray at the four-leaf stage. Treatments were individual regulators or combinations of two. The concentration of each was 100 ppm. Plants were transplanted to the field one day after treatments, and measurements were taken on both vegetative and reproductive growth during the growing season. All treatments were evaluated on the basis of the following criteria: 1. Vegetative growth as plant length, number of internodes, number of lateral branches developed on the plants, and the relative size of the plants as a percent of the control. 2. Flowering and sex expression by determining: a. The node position of the first stamina I and pistillate flowers. b. The number of days from planting to anthesis of the first staminate and pistillate flowers. c. The number of staminate and pistillate flowers developed during the first two weeks of flowering. d. The female to male flower ratio.

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-143. 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 week 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 week were considered as early yield for all crops. Greenhous e Ail 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 shoots . 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. 'Zucchini'

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15hybrid plants were more uniform and produced single flower buds at each node. Growth regulating chemicals were applied to the plants as seed soaking treatments or foliar spray with concentrations of 100 ppm. Seeds were soaked for 12 hours in Petri dishes on filter paper moistened with and floated on the solution of growth regulators. A small hand sprayer was used to apply foliar sprays. Seedling plants were sprayed at the four-leaf stage. Seeds were sown either directly in bench soil or in peat pots for later transplanting to the benches. Fertilizer was supplied in two applications of complete fertilizer (6-8-8) at a rate equivalent to 900 pounds per acre. Soil moisture was kept near optimum, air temperature was between 60 and 80°F, and relative humidity averaged about 65 percent during the experimental period. A randomized block design with four complete blocks was used for all experiments. Each plot within the block had dimensions of 1.5 x 1.5 feet and contained two plants. One plant was removed at the age of 21 days for fresh and dry weight determinations, and the other was left for 45 days to obtain flowering data. Because of the limits in time and greenhouse space, different experiments were conducted in sequence. Experiments 1, 2, and 3 were conducted on 'Yellow S traigh tneck' to determine the effects of different regulators and their combinations, applied by soaking the seed and /or spraying the plants with aguous solution of 100 ppm, on plant growth and sex expression. Experiment 4 was conducted on 'Zucchini' using GA and IAA treatments applied as before. However, riment 5 was designed to study the effect of spraying

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-16the 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 determinations : 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 on plants. 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 68°C for 72 hours, and dry weight determined. 6. Total DNA and RNA contents of seedling plants, undifferentiated buds, male and female flower burls.

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-17For the measurement of DNA and RNA, plant tissues were homogenized in an ice-cold Omni -Mixer for five minutes with 5 percent -3 sucrose in 10 M.MgCl 2 and KC1 solution, centrifuged and filtered through a glass wool pad to remove cell walls and other debris, Aliquots of the supernatant were used for analysis. Total DNA and RNA were determined by the Ogur and Rosen method (94). Nucleic acid was precipitated by adding perchloric acid (0.5N) to aliquots. The precipitate was washed by suspension and resedimentation in cold perchloric acid. Lipids and chlorophyll were removed by washing twice in an ether, ethanol, anu chloroform mixture (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 temperature, then DNA was precipitated by adding perchloric acid. The absorbance of both DNA and RNA extracts was determined at 265 mu in a Beckman Du Spectrophotometer, and readings were referred to standard curves for obtaining quantitative amoun t s .

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. CHAPTER IV RESULTS Field Effect of a p plication time Cucumber . --All treatments modified sex expression during the first two 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 shown in Table 1. Maleic hydrazide increased the number of early pistillate flowers 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 relationship was not true in the 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 twoand four-leaf stages suppressed both pistillate and staminate flower formation, decreased the total yield significantly, and there was no early yield. Treatments with 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 MH 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 -18-

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•19and hastened the development of female flowers. All of the treatments increased the female/male flower ratio by reducing the number of male or increasing the number of female flowers developed on the plants during the first two weeks of flowering (Table 2). Spraying the plants with 100 ppm of either MH or NAA at the twoleaf stage increased the early yield without any significant effects on total yield. Treatments of NAA at the four-leaf stage or at both the twoand four-leaf stage reduced the early yield. All TIBA treatments, maleic hydrazide at the four-leaf stage and NAA at four-leaf stage treatments, decreased total yield in both number and weight of marketable fruits harvested. Watermelon . --The spring 1967 results indicate that all treatments of MH decreased the number of days to anthesis, hastened the female flower development, and increased the total number of flowers. Treatments of NAA and TIBA delayed the flowering by either increasing the number of days to anthesis or decreasing the number of flowers developed in the first two weeks of flowering. However, early NAA and late TIBA sprays hastened female flower appearance (Table 3). AH treatments of MH and early treatment of NAA increased the early yield. However, total yield was increased by treatments with MH at four-leaf stage, and NAA at two-leaf stage, in terms of number and weight of fruits harvested. Treatment with NAA at fourleaf stage increased the weight of early fruits without affecting their number.

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-20Treatment 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 indicated that all of the treatments had inhibitory effects on vegetative 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 inhibiting than both maleic hydrazides and NAA. All concentrations of MH 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 pistillate 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 Mil, 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 MH at 100 ppm was the only treatment to increase the number of early fruits and both fruit number and

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•21weight of the total yield. The rest of the treatments reduced early yield, and that NAA 100 ppm, decreased the total yield. Fall 1968 experimental results shoved that treatment with GA did not affect the number of days before flowering. However, it did increase the number of male flowers developed during the first two weeks of flowering. Treatment with IAA induced early femaleness by decreasing the number of days before the first pistillate flower and increasing the number of pistillate flowers. A mixture of GA and IAA had an effect similar to that of IAA for total but not early pistillate flowers (Table 5). Treatments with MH and TIBA had an effect on flowering similar to that of IAA. However, NAA treatments inhibited staminate flower development, and concentration of 200 ppm decreased both number of staminate and pistillate flowers. Early yield was increased in number of fruits harvested by 100 and 200 ppm of MH and by GA + IAA mixture. However, it increased in weight by 100 ppm maleic hydrazide and GA + IAA mixture. Treatments with 100 ppm NAA, 25 ppm TIBA, and 100 ppm GA gave no early yield and decreased total yield. Spraying the plants with 100 ppm maleic hydrazide, 100 ppm IAA, or a mixture of GA + IAA at 50 ppm of each, increased total yield in terms of both number and weight of marketable fruit harves ted . Squash . --The fall 196S experimental results will show that IAA delayer' male and hastened female flov;ers development, GA had an opposite effect, while a mixture of GA + IAA treatment delayed both male and female flower formation (Table 6).

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-22Concentration of 100 ppm MH hastened the female flower development without affecting male flowers. However, 200 ppm of MH 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 considerably . With regard to yield, MH 100 ppm was the only treatment to increase both early and total yield during the four weeks harvesting period. All other treatments except MH 200 ppm and IAA 100 ppm reduced or gave no early yield during the first week of harvest. Moreover, 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 MH 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 the 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 nonsignificant increase in total yield, treatment with 50 ppm decreased the early yield.

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23Cant^loup e . --The results of the spring experiment on the effect of the different concentrations of MH , NAA, and TIBA on vegetative growth, sex expression, and yield are shown in Table 8. Maleic hydrazide treatments reduced the size of plants by decreasing the length of the main stem, and the number and length of internodes. However, they had increased the number of laterals developed on the plants. Naphthaleneacetic acid treatments had similar effects on the size and length of plants but they did not affect the number of laterals. Triiodobenzoic acid treatments had more severe inhibitory effects on vegetative growth. And they also reduced or eliminated the development of laterals. All of the treatments affected sex expression by reducing the number of days before the first female flower appearance and by increasing the female/male flower ratio. Such increase in the ratio \:cc either the result of increasing the number of female flowers, reducing the number of male flowers, or a combination of both. Treatments of 100 and 150 ppm of MH were the only ones to increase both early and total yield. Concentrations of 200 ppm of NAA and 50 ppm of TIBA gave no early yield, and instead delayed the fruit development to the later harvests. The rest of the treatments had no significant effect on the yield. The results of the fall 1968 experiment help in comparing the effects of MH, MAA, and TIBA on cantaloupe plants with those of GA, IAA, and the control (Table 9).

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24Although both GA and IAA treatments had increased the size of the plants, GA increased the length of the plants while IAA decreased both number and length of internodes. Maleic hydrazide slightly inhibited 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 lateriasl. The treatments with Mil, TIBA, and IAA had similar effects on sex expression. They hastened female flower development and increased the female/male flower ration. Both NAA and TIBA reduced the number of male flowers. Gibberellic acid delayed the appearance of female flowers and increased the number of males . Yield results indicate that while MH, TIBA, and IAA treatments had increased the total yield significantly, MH was the only treatment to increase earliness . Both NAA and TIBA decreased the early yield and tended to delay the harvest. Greenhouse The control treatments ' Yellow-Straigh tneck . ' --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 grown from seed soaked in water had an average of about 13 internodes and 1.5 female flower bud per

PAGE 36

-25plant with the first female carried at the tenth node position. A spray with GA at the four-leaf stage increased plant elongation and shifted sex expression slightly toward maleness. A spray with IAA had no significant effect on vegetative growth and shifted sex expression slightly toward femaleness (Table 12). Gibberellic Acid ' Yel lowStraightnec k. ' --Gibberellic acid applied by soaking the seed in GA increased plant length, number of internodes, and shifted sex expression toward maleness. A subsequent spray with GA at the four-leaf stage increased plant length, number of internodes, maleness, and total number of flower buds over seed treatment alone. However, a subsequent spray with IAA decreased the effect of GA soaking on plant length, increased its effect on number of internodes, and shifted the sex expression slightly toward femaleness (Tables 10 and 11). ' Zucchini . ' -Soaking seed in GA increased vegetative growth by increasing both plant length and number of internodes. It shifted sex expression toward maleness. A subsequent spray with GA had a more stimulating effect on vegetative growth and produced completely male plants. A subsequent spray with IAA tended to reduce the stimulating effect of GA. This spray with IAA reduced the effect of GA seed soaking on sex expression (Table 12). Spraying the plant with GA increased plant length and both fresh and dry weight. However, percent dry weight was the same as the control. It slightly increased the male tendency of the plants and produced the first female flower buds at the 11th node position (Tables 13 and 14).

PAGE 37

-26Indoleacetic Acid ' Yellow-Straightneck . ' --Soaking the seed in IAA decreased plant length, shifted sex expression strongly toward f emaleness , and increased the total number of flower buds developed on the plants. A subsequent spray with IAA at the four-leaf stage increased the inhibitory effect of seed treatment on vegetative growth and had a similar effect on sex expression. However, a subsequent spray of GA overcame completely and reversed the inhibition of seed soaking on vegetative growth and increased the number of male flower buds (Table 10). ' Zucchini . ' --Indoleacetic acid applied by soaking the seed in IAA had very little effect on vegetative growth. It shifted sex expression toward femaleness. A subsequent spray with GA stimulated the vegetative growth and reversed the effect of IAA seed treatment on sex expression. However, a subsequent spray with IAA caused more inhibtion to plant length than IAA seed treatment alone. This spray caused more female tendency than either seed treatment or plant spray alone (Table 12). Spraying the plants at the four-leaf stage with IAA 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 by increasing both plant length, number of internodes, fresh and dry weight; however, it decreased preccnt dry weight. The

PAGE 38

-27tendency toward femaleness in sex expression was less than IAA applied alone (Tables 13 and 14). Maleic Kydrazide 'Yellow-Straightneck. '--Soaking the seed in MH inhibited vegetative growth by decreasing both plant length and the number of internodes. It also increased the number of female buds and decreased the number of male f lover buds. A subsequent spray with GA completely overcame the effect of seed treatment with MH on plant length and sex expression, but had less effect than spraying with GA alone. A subsequent spray with IAA decreased the inhibition of Mil seed treatment without affecting sex expression. However, spraying with IAA alone had a less inhibitory effect on vegetative growth and a more stimulating effect on flowering than Mil seed soaking treatment and shifted sex expression toward femaleness (Table 10) . ' Zucchini . ' --Spraying the plants at the four-leaf stage with MH alone inhibited vegetative growth, decreased both fresh and dry weight, and increased percent dry weight. It also decreased the number of male and increased the number of female flower buds. Spraying with a mixture of MH and GA increased the number of internodes, decreased dry weight, but did not affect sex expression. However, spraying with a mixture of MH and IAA had more inhibitory effect on vegetative growth than MH alone. It also decreased fresh weight, dry weight, and percent dry weight, and increased female tendency (Tables 13 and 14).

PAGE 39

Naphtha leneace tic Acid ' Yellow-Straightneck . '--Seed soaking in NAA decreased plant length, number of internodes and number of flower buds developed on the plants, with more inhibition of the male than female flower buds. A subsequent spray with CA 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 i^ith 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 IAA had an effect similar to that of NAA alone (Tables 13 and 14). Triiodobenzoic Acid ' Yellow-Straigb-tneck . ' --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. However, a subsequent spray with IAA reduced the inhibitory effect of TIBA on both plant length and number of internodes. This spray

PAGE 40

29increased both number of male and female flower buds over TIBA seed treatment alone (Table 11). ' Zucchini . ' --All treatments of plant spraying with TIBA and its mixture with either GA or IAA had a severe inhibitory effect on the vegetative growth and decreasing both fresh and dry weights. Spraying the plants with a mixture of TIBA plus GA caused less inhibition than spraying with cither TIBA alone or TIBA plus IAA. Treatment with TIBA increased the female tendency. However, the presence of GA in the spray decreased such effect, but the presence of IAA increased the female tendency of the plants (Tables 13 and 14). Nucleic Acids Results reported in Table 15 show nucleic acid contents of the whole plants, undifferentiated buds, female and male flc buds, and the effects of different seed soaking and plant spraying treatments with growth regulating chemicals on the amounts. These results can be summarized as follows: 1. Untreated female flower buds had higher contents of DNA and RKA than both undifferentiated and male flower buds. On the other hand, male flower buds had less DNA and more RNA contents than the undifferentiated ones. 2. Soaking the seeds in GA increased RNA contents of one week old seedlings, but had no effect on nucleic acid contents of older plants. Subsequent

PAGE 41

30spray with GA after seed soaking in water increased both DNA and RNA contents of the plants. Subsequent spray with GA after GA-seed soaking decreased DNA and increased RNA contents of the plants more than those soaked in GA alone. Subsequent spray with GA after IAA-seed soaking had similar effects. 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 RNA contents . Soaking the seeds in IAA increased DNA contents of young seedling, but had no effect on older plants. Spraying the plants produced from watersoaked seed with IAA increased their contents of both 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 uns prayed.

PAGE 42

-315. 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 IAA after seed soaking in GA increased both DNA and RNA contents of the undifferentiated buds. 6. Seed soaking in MH increased DNA contents of young seedlings, but had no effect on the older plants . 7. Soaking the seeds in NAA decreased RNA content of younger seedlings, and both RNA and DNA contents of older plants. 8. Seed soaking in TIBA decreased DNA and RNA contents of both young seedlings and older plants. 9. Seed soaking in MH or TIBA increased RNA contents of undifferentiated flower buds, but had no significant effects on DNA contents. Seed soaking in NAA had no significant effect on nucleic acid contents of the undifferentiated flower buds. 10. The female flower buds did not show any significant differences in their DNA contents as a result of the different treatments. However,

PAGE 43

-32they had lower RNA contents as a result of seed soaking treatments in GA, MH, or NAA. 11. All GA-seed soaking treatments increased RNA contents of the male f lower buds. Seed soaking in MH or NAA decreased RNA contents of female buds. Soaking the seeds in TIBA decreased both DNA and RNA contents of the female flower buds.

PAGE 44

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PAGE 45

-34,-j 3 O h H g M W H CO o o p4 M o M M Pm Pm r< as erf CO o M CO CO Ph X w x w CO erf M « CO h erf o p H o >-^ erf :=> o o w W erf O CO M r S O K c_> Q co s~s e p DO o 3 o o 00 co o X

PAGE 46

-35a H £ W roo EO M fn >* CO ?2 H o » --. u H ,J er.. --: erf o w fa K H C h 0: CO rrf r. as p.. x ^ cc o 00 |J c-: O W H Pm O f i CO erf o H < .J < O M I oo m -J J 6 : C O o g 5 p o U HI CJ

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36-

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PAGE 49

-38w 5 9 w H Q H 25 W 5 | CO 25 Pn M W H X

PAGE 50

-39w J 5 to O Q M -! H td < M 3 U PQ Z < O H O Id H [ J < u 1-1 S o H Z id td f>4 M o g Cfl O cj 2 co vO p on z 1-1 < o z a m O Pi M Ph CO CO 1/3 _ id Z Pi M Ph o X Pi Id O CO r : O W rd Q ) H S«1 J < C_> M s tl-. o ££ c_> f*4 o Cfl CJ W I i w H H -••: H W C w > o co f-r • in d 2 E c : O o a u CJ CO NO r-4 CN ^

PAGE 51

-4000 w 9 Q J W m 25 o n as H 25 W o 2; o u H 25 a ca fn Pn M O a oo o> (71 05 o O 2 25 O H H 05 CO on CO CO w o5 a Cm M X W 25 X O W OS co O 05" W W Cm o M S CJ Pn o 00 H O w Pn PH w 3 o a > M En < H W O w > 25 O o 4 < H -25 1 < CO • m en o 00 o CO cm o o oo m o ro 00 oo o
PAGE 52

-41w w •J CO Pi

PAGE 53

-42TABLE 10 THE INFLUENCE OF THE DIFFERENT REGULATORS AND THEIR INTERACTION ON VEGETATIVE GROWTH AND SEX EXPRESSION OF YELLOW STRAIGHTNECK SQUASH TREATMENTS Seed Soaked in Plants Sprayed with VEGETATIVE GROWTH Plant Number of Length Internodes in cm per Plant SEX EXPRESSI ON Average Number of Flower Buds Developed per Plant EXPERIMENT 1 Total H 2

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-43TABLE 11 VEGETATIVE GROWTH AND SEX EXPRESSION OF YELLOW STRAIGHTNECK SQUASH IN RESPONSE TO TREATM . WITH CHEMICAL REGULATORS TREATMENTS

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TABLE 12 EFFECTS OF THE DIFFERENT CHEMICAL REGULATORS AND THEIR INTERACTION ON VEGETATIVE GROWTH AND SEX EXPRESSION OF ZUCCHINI SQUASH -44TREATMENTS

PAGE 56

TABLE 13 EFFECTS OF THE DIFFERENT CHEMICAL REGULATORS AND THEIR INTERACTIONS ON VEGETATIVE GROWTH AND SIX EXPRESSION OF ZUCCHINI SQUASH -45TREATMENTS

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-46TABLE 14 FRESH AND DRY WEIGHTS OF ZUCCHINI SQUASH PLANTS IN RESPONSE TO THE DIFFERENT CHEMICAL REGULATORS TREATMENTS Plants Sprayed at the Four-leaf Stage with FRESH AND DRY WEIGHT OF PLANTS Two Weeks After Treatment Fresh Weight Dry Weight Percent gnu /Plant gro, /Plant Dry Weight WATER (Control) GA IAA GA-t-IAA 253 303 220 300 16.7 17.2 15 .4 17.1 6.58 5.66 7.00 5.70 MH MH+GA MH +IAA NAA NAA-!GA NAA + IAA 203 230 193 190 238 218 16.2 16.7 15.5 12.9 13.6 13.2 7.96 7.24 8.01 6.76 5.69 6.06 TIBA TIBA+ GA TIBA + IAA 170 225 203 12.2 13.6 13.0 7.15 6.02 6.40 L.S.D. 5% Level 24 0.4 0.32

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-47-

PAGE 59

CHAPTER V DISCUSSION General The results of these studies indicated that each of the growth regulators used had a profound effect not only on flower sex expression, 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 information 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 were 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 showed that as the vine progresses in its development, sex expression -48-

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-49undergoes a gradual change from strongly staminate to strongly pistillate phases. Such change can be measured qualitatively as sex of the flower produced and quantitatively in terms of the ratio between staminate and pistillate flowers. Fruit setting in cucurbits has been the subject of several investigators such as Bushnell (19), Cunningham (25), McGlasson (67), Porter (88), Rosa (93), and Tiedjens (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 nonsetting periods with the length and frequency of these periods varying with species, environment, and physiological conditions. In the light of the previous studies, as well as the results of the present investigation, a schematic figure is presented here to illustrate the relationships between the different stages of plant growth and development of the cucurbitaceae. Illustrations in Figure 1 represent the chronological relationships of the different developmental stages which resulted from superimposing the different curves of vegetative growth, flowering, fruit setting, and fruit growth. These 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 might be changed with a particular crop. During its development from seed to maturity the cucurbit plant exhibits a double sigmoid growth curve. Within a normal growing season there are three different and distinctive phases:

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-50First: A period of strictly vegetative growth which lasts for about six weeks after planting. This period is characterized by a fast, uniform rate of groi%'th, 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 the occurrence of early flowering and fruiting cycles. Hall (42) stated, "the period between the origin of flower primordia and syngamy was characterized in all series by diminished differentiation of new vegetative organs. During this period, however, there occurred the maximum gains in leaf area and internode elongation. 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 competition 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 niuskmelons with various types of pruning. On the other

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51hand, Cunninghan (25) and Nylund (79) found that leaf pruning caused a quantitative decrease in fruit set. Various reports have indicated that the growth of individual cucurbit fruit follow a sigmoid curve (7, 59, 67, 77, 82, 90, and 108), Final fruit size in cucurbits depends on both rate of growth and duration during the exponential phase. When the exponential rate is high } final size is attained earlier. This illustrates the importance of the balance between vegetative and fruit growth during this period. Vegetative Gro wth The results of these studies are in accordance with the previous reports (?, 7, 12, 13, 32, 39, 41, 46, 115, and 116) on the effects of the regulators used on the vegetative growth of plants. The observations made during the first experiments indicated that each ot the main regulators used — namely MH, NAA, and TIBA — had inhibitory effects on plant growth. Those effects were different with different treatments and different crops. In general, plants treated with MH were less inhibited in their growth and recovered faster than those treated with NAA and TIBA. Double sprays of these regulators were more inhibitive than single spray treatments. In all of the crops used in these studies — cantaloupe, cucumber, squash, and watermelon — measurements three weeks after treatment indicated that the concentrations used of MH, NAA, TIBA, and IAA inhibited vegetative growth through decrea.siir-, both the length and the number of internodes of the main stem. Gibberellic acid increased

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-52both 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 in 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 MH on the growth of many plants (115 and 116) . Although the results show that TIBA inhibited lateral development, 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 inhibitor 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 grown 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 Mil or NAA slightly reduced the length of the main stem, but their effects on total plant growth were different. Plants treated with MH 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 MH or NAA, and their growth was retarded for a longer

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-53period. Such effects were similar to those found in cantaloupe and watermelon. 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 regulators had inhibitory effects in the following order: IAA, Mil , NAA, and TIBA. The results of the greenhouse experiments on both 'Yellow Straightneck ' and 'Zucchini' squash are similar, and they lead to concrete conclusions about the interaction between natural and synthetic plant regulators used in these studies. Observations were: 1. Summer squash plants were not good indicators of sex expression because of the cluster of floral buds in the axil of each leaf instead of a single bud, as in 'Zucchini' squash. 2. There was a similarity in the growth response to the addition of GA and IAA between squash plants and dwarf varieties of corn, peas, and bean plants (15, 24, 59, and 84). 3. Treatments which affected sex expression also tended to cause changes in plant elongation. For example, GA caused an increase in shoot length, and the plant produced more male flowers, and IAA inhibited plant elongation and increased femaleness. Therefore, one can use plant length as a good indicator for the interaction between natural (GA and IAA) and synthetic (Mil, NAA. and TIBA) regulators. 4. At the concentration of 100 ppm used in these

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-54 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 combination of both GA and IAA 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 Phinncy (84) on corn. In contrast to GA, IAA in higher concentrations inhibited both cell division and expansion which was 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. Similar results have been reported on many plants (115 and 116) . Rehm (91) reported that Mil affects only the terminal growing parts of the

PAGE 66

-55plant. However, in /.vena eoleoptile MH 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 MH if applied after MH treatment (Table 10) ; if both MH and IAA were applied together they caused more growth inhibition than either alone (Tables 13 and 16) . These findings are in agreement with other investigators (Kato [56] and Riddell [24]), who found that GA could reverse the inhibitory effects of MH. In peas, Brian and Hemming (16) suggested that the inhibition of shoot growth caused by MH is due primarily to the activity of "GA-like" hormone. Results obtained by Olsen, Kulescha, and Pilet (24), however, indicated that MH does modify the endogenous auxin contents of plant tissues, and did not support the idea that MH is anti-auxin. Moreover there is some indication that MH may increase slightly the level of free auxin in pea roots (Audus [7]). 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 NAA. Treatments with IAA did not overcome the inhibition caused by NAA; however, GA completely reversed the inhibition caused by NAA on both number and length of internodes. This is in complete accordance with the findings reported by Laibach and Kribben (44), Kato (56), and Galun (35) on cucurbitaceous crops, and with many other research workers on ornamental and fruit crops. Triiodobenzoic acid severely inhibited plant growth and reduced both number and length of internodes. Treatments with IAA

PAGE 67

56were 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 growth. Galston 1947, reported that TIBA caused morphological changes in soybeans such as shortening of the internodes, loss of apical dominance and epinasty of young leaves. His observation that TIBA inhibited the action of auxin in the Avena Test, suggested that TIBA might act as anti-auxin. 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). Sex Expressio n 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 environmental 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 prinordia to anthesis the cucurbitaceous

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57floral bud passes through various stages. All floral buds pass during their ontogeny through a bisexual stage. Unisexuality is attained by supression of the pistillate structure in the male, and the staminate structure in the female. A hermaphrodite flower is produced by the development of both sex organs. Based on his studies on hemp as well as on a review of literature, Heslop-Harrison (44) suggested that sex expression is regulated by the level of a growth substance (f lorigen) , and that there were two different thresholds. The lower threshold represented the transition from the vegetative state to the staminate phase, and the higher threshold represented the shifting from the staminate to the pistillate sex expression. But "f lorigen" itself was, and still is, in the realm of hypothesis. Arguing from their findings with cucumber, Laibach and Kribben (.44) have suggested that the sexuality of a flower is dependant upon the concentration of native auxin levels available to the leaf axil during the period of flower formation. This viewpoint is supported by the findings of many others (5, 6, 35, 37, 44, 45, 49, 50, 59, and 77). In his review article (92), Resende, in 1967, described the degree of flower development (floral gradient from vegetative to floral flower) as it may be controlled by the ratio of growth promoters to growth inhibitors. The higher this ratio, the more vegetative the flower will be, and the very high values will lead to a total regression to the vegetative state. He also suggested a hypothesis which may be summarized as follows: Sex expression in angiosperms is

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-58controlled by a group of structural genes, subgroups of which are responsible for the calyx, the gynoecium, tbe corolla, and the androecium. The activation of these genes is governed by the establishment 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, which regulate 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 (Westergaard , [106]) might be explained taking into account simply the variation within the additive genes regulating the balance of growth promoters to growth inhibitors. However, 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 flower and fruit development by Nitsch (77) , "As a whole, there seems to be a correlation between the development of certain flower 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 experiments (Tables 3, 5, and 7), GA treatments enhanced the appearance and increased the number of staminate flowers. Gibberellic acid also

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59delayed the appearance of either pistillate (in cucumber and squash) or hermaphrodite (in cantaloupe) flowers. Inodoleacetic acid treatments had completely opposite effects to those of GA. Inodoleacetic acid enhanced pistillate flov:er production and reduced the staminate phase. However, in both cucumber and squash (Tables 3 and 5) trea ments with a mixture of IAA and GA delayed flowering, in general by decreasing the total number of f lorers developed during the f i: . week of flowering, but in the following week sex expression was shifted toward f emaleness . Experimental results in the greenhouse were similar to those of the field, but they put more emphasis on the interaction between the different regulators affecting plant growth and sex expression. The availability of a 'Zucchini hybrid minimized the possibility of any genetic variability between plants which might affect plant growth and sex expression. From the results of the first experiment (Table 10) , it is safe to conclude that GA treatments alone stimulated vegetative extension and shifted sex expression toward maleness. Naphthaleneacetic acid on the other hand inhibited elongation. However, one should notice two other effects: first, when seeds were soaked in GA, a consequent spray with IAA did not reduce the effect of GA on elongation, but it did reverse the effect on sex expression; second, when seeds were soaked in IAA, a subsequent spray with GA produced its stimulating effect on elongation but did not affect sex expression, This latter effect might be explained on the basis that seed soaking in GA did not exert its effect on sex expression immediately, and a

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-60subsequent IAA spray might have modified the ratio IAA/GA 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 f.loral primordia, or GA sprays did not modify the ratio of endogenous IAA/GA enough to supress female sex expression. In the 'Zucchini' squash experiments (Tables 12, 13, and 14), GA seed soaking or plant spray treatments shifted sex expression toward 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 IAA 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, formation 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 morphologically and chronologically the formation of pistillate flowers. At present there seems to be considerable evidence which supports

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-61that 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 the number of male flowers to such an extent that they have been suggested as a means of inducing male sterility in plants (44, 45, 46, 91, and 110). Galun (35) was not able to detect any significant differences in the auxin contents of normal, monoecious and purely gynoecious plants of cucumber. However, he was able to show in a later in vitro experiment that very young flower primordia of cucumber excised from nodes which would have formed male flowers could be caused to develop into female flower buds if 0.1 mg/1 of IAA was added to the nutrient medium. It is clear also from the work done with GA (17, 37, 38, 43, 83, and 86) that this hormone does not only alter sex ratio in monoecious cucurbits, but it also causes the production of staminate flowers on completely gynoecious lines of cucumber. According to the foregoing results and evidence, the following hypothesis appears to be warranted: 1. The sex of flower primordia in monoecious cucurbits passes through 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 gibberellins in the plant especially in

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-62the tissues in the subapical region of differentiation and within floral primordia before the bisexual stage. The higher tbis ratio the greater tendency for female sex expression, and the lower the ratio the more male the tendency. 3. Endogenous levels of auxin and gibber ellins could control sex expression directly or indirectly — directly through the effect of GA anH IAA per se on gene repression and derepression, and indirectly through the effect of these two hormones 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 with 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 hormone (f lorigen) as suggested by Chailakhyan (21) . If indeed f lorigen is in existence and it is either composed of two hormones, gibberellin and anthesin, then we can say that IAA might play its role by modifying the proportion of these two hormones and their action on both flowering and sex expression. Or it may be more reasonable to assume that such a hormonal complex (florigen) is merely a polymer of different plant hormones and the proportional ratio of these hormones is the determining factor in regulating plant growth and development.

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-63Following Lhe sane line of reasoning, one could conclude the following: First: the effect of NAA on sex expression might be a direct effect as a synthetic auxin which favors female sex expression, or an indirect effect through the modification of endogenous levels of IAA and GA. Second: both TIBA and MH had similar effects on vegetative growth and sex expression, and their action might be attributed to one or more of the following mechanisms: 1. They inhibit and retard vegetative growth and extension: changes which might result in a build up in IAA levels in the plant tissues, especially in the stem. 2. They have a direct effect on the inhibition of the polar transport of IAA in the stem causing a build up of IAA levels in the apex and in the area of primordial differentiation. 3. They have antagonistic effects and reactions toward CA which block or dilute its action on both vegetative growth and sex expression. Fruit Growth and Development The physiological and chronological determinations of marketable yields of cucumber and summer squash are different from those of cantaloupe and watermelon. Cucumber and squash fruits are harvested at about 6 to 12 days from the time of fruit set while they are physiologically immature. However, cantaloupe and watermelon fruits are harvested in the physiologically mature stage after about 35 to 50 days from the time of fruit set. Both cucumber and squash plants develop and set numerous fruits which are multi-harvested during a

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-6t 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 with those which are set and developed later in the season. Regardless of the 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 normal 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 earlu'ness 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 watermelon 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 development. 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 MH 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 MH in spring 1968 decreased early yield. These different effects of concentrations might be due to different plant responses in the spring than that iii 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

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65growth. Double spray treatments in 1967 and higher concentrations in 1968 had more inhibitory and lasting effects than those of single sprays and Lover concentration (Tables 1 and 4 and Figures 2 and 5) . These results also indicate that early yields were in proportion to vegetative growth and number of pistillate flowers. On the basis of these results, we can say that all treatments with MH 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 inhibition 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 treatments. Naphthaleneacetic acid treatments had more and TIBA the most inhibitive and lasting effect on vegetative and reproductive growth and development. However, effects of GA, IAA and a mixture of GA and IAA treatments on yield were directly related to their effects on both vegetative growth and sex expression. Results with squash show that treatments with MH and NAA at the two-leaf stage in spring 1967 and MH 100 ppm were the only treatments which increased early yield, while the rest of the treatments 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 because the number of flower buds and the number of leaves in squash are merely dependent on the number of developed internodes on the main stem. Those treatments which slightly decreased vegetative

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•66growth 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 with the treatments of 100 and 150 ppm MH in the spring 1968 and MH and IAA in the fall 1968 in cantaloupe (Tables 8 and 9), and all treatments with MH and NAA at the two-leaf stage in 1967 and 100 and 150 ppm MH and 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 high concentration of NAA (Figures 7, 8, 9, and 10). Total yield is a direct result of the number and size of fruits which are 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

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-67related to the number of pistillate flowed, percent fruit setting, and the competition between vegetative and reproductive growth. Total yield was increased in cantaloupe by treatment with lower concentration of MH, TIBA and IAA, and by MH and NAA in watermelon. These results might be attributed to the effect of these treatments on increasing the number of early pistillate flowers, the ratio of fruit setting, and the acceleration of fruit growth.

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68100

PAGE 80

-69B o s: c *1 110 •{ 100 90 80 70 60 50 40 30 20 10 H o / ... MH-100 ppm / .-••'' „ NAA-100 ppm ' / / ' / / TIBA-25 ppm / MH-200 ppm / / NAj / / / / / / / / / ppm 10 20 30 40 50 60 10 20 30 40 50 60 Days after Planting Figure 2. Stem Elongation of Field Grown Cucumber (Fall, 1968) in Response to Treatments with Different Chemical Regulators.

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-70B u 60 a P-. 40 30 20 10 10 20 30 40 50 60 70 Days after Planting Figure 3. Effects of Different Chemical Regulators on Stem Elongation of Field Grown Zucchini Squash (Spring, 1969).

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•71GA + IAA 40 30 20 • 10 6 o 60 c 40 . 30 20 10 H 2 /^m + ga ,'/ m ///MI + IAA NAA + GA H 2 ,TIBA + GA ' .TIRA + IAA 10 20 30 40 60 70 10 20 30 40 Days after Planting 50 60 70 Figure 4. Effects of the Different Chemical Regulators and Their Interactions on Stem Elongation of Field Grown Zucchini Squash (Spring, 1969).

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-72K

PAGE 84

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PAGE 85

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PAGE 86

-75H o ei o w > M H W w w H 9 S o u 4-1 c o o 14-1 o a z

PAGE 87

7625

PAGE 88

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PAGE 89

SUMMARY AND CONCLUSION Studies were conducted using some growth regulating chemicals to modify the flowering and sex expression of cucurbits snd tn achieve one or more of the following objectives: to increase earliness of the crop, to increase total yield, or to concentrate flowering and fruit set into a shorter period. Crops used in these studies were cucumber, summer squash, cantaloupe, and watermelon. Growth regulators selected were MH, NAA, TIBA, GA, and IAA. The experimental program was divided into a field phase to study the effect of spraying the plants with regulators on the production of these crops, and a greenhouse phase to determine the mechanism by which these regulators produced their effects. All the treatments modified plant growth, sex expression, and fruiting under both greenhouse and field conditions. Treatments with MH, NAA, TIBA, and IAA reduced vegetative growth, suppressed staminates , and enhanced pistillate flower development. Multiple applications 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, NAA, or IAA in a single spray at the four-leaf stage in all crops. Treatments with TIBA at 25, 50, or 100 ppm, MI at 200 -78-

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-79ppm, and MM. at 200 ppm showed promising results for harvest concentrations. Experimental results, observations, and a review of pertinent literature appear to support the following hypothesis: 1. The sex of flower primordia in monoecious cucurbits passes through a bisexual stage and is expressed as male or female due to physiological and environmental factors. 2. Sex expression in cucurbits is controlled by the ratio of auxin to gibberellins within flower primordial tissues before the bisexual stage. The higher this ratio the greater the tendency for femaleness and the lower the ratio the laore male the tender. 3. Endogenous levels of auxin or gibberellins could control sex expression directly through their effects on gene expression and repression, or indirectly through their effects on other plant hormones, plant metabolism, or plant development, It is reasonable to conclude the following: First: the effect of NAA on sex expression might be a direct effect as a synthetic auxin v "avors female sex expression, or an indirect effect through the z»odif ication of endogenous levels of IAA and GA. Second: TIBA and MH had similar effects on vegetative growth and sex expression, and action might be attributed to one or more of the following mechanisms: 1. They inhibit and retard vegetative growth and extension; changes which might result in an increase of IAA levels in the plant tissues especially in the stem.

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-802. They have a direct effect on the inhibition of the polar transport of IAA in the stem, causing a build up of IAA levels in the apex and in the area of primordial differentiation. 3. They have antagonistic effects and reactions toward GA which block or dilute its action on both vegetative growth and sex.

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8663. Lewis, D. 1942. The evolution of sex in flowering plants. Biol. Review. Cambridge Phil. Soc. 17:46-67. 64. Loehwing, W. F. 1938. Physiological aspects of sex in angios perms. Bot. Rev. 4:581-625. 65. Mazaeva, M. M. 1957. Effect of magnesium fertilization and its role in plants. Botan. Zhur. 42:571-582. (C . A. Vol. 51, No. 1842g). 66. McCollum, J. P. 1934. Vegetative and reproductive responses associated with fruit development in the cucumber. Cornell Agr. Exp. Sta. Mem. 163:1-2 7. 67. McGlasson, W. G. and Pratt, H. K. 1963. Fruitset patterns and fruit growth in cantaloupe ( Cucumis melo L. var. Reticulata Naud.). Proc. Amer. Soc. Hort. Sci. 83:495-505. 68. McKenzie, J. I. and Tiessen, H. 1968. The effect of the near ultra violet light on the physiological development of cucumbers Cucumis sativus , Cultivar Spartan Dawn. Hort. Sci. 3:101. 69. Mehanik, F. J. 1959. Acetylene treatment as a method of increasing the formation of fruitful female flower in cucumber. Dok. Veses. Akad . Seljsk. 21:20-3) Hort. Abstr. 29:1426. 70. Miller, C. H. and Hughes, G. R. 1968. Harvest indices for once-over harvested pickling cucumbers. Hort. Science. 3:128. 71. Minina, E. G. , 1938. On the phenotypical modification of sex characters in higher plants and other external factors. C. R. Acad. Sci. USSR 21:298-301. (C . A. Vol. 33, No. 4292), 72. Mitchell, J. W. and Linder, P. J. 1957. Absorption and trans location of plant regulating compounds. Atomic Energy and Agriculture. Amer. Assoc. Adv. Sci. 165-182. 73. Mitchell, W. D. and Wittwer, S. H. 1962. Chemical regulation of : f sex expression and vegetative growth in Cucumis sativus L. Science 1.36:880-881. 74. Muller, H. J. 1932. Soma genetic aspects of sex. Amer. Naturalist. 66:118-138. 75. Naugoljnyh, V. N, 1959. Changing of the sex characters in cucumbers to increase their productivity. (Russian) (Bot. Zornal 40:715-719) Hort. Abstr. 26:2778.

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BIOGRAPHICAL SKETCH The author, Mohamed Abd el -Rahman , was born on July 3, 1941, in , — OJ c . _.. — . , _.^o, .»~ ..^.^ -. „._„«*. v_~ j.^^„. ^a^. n« ui .u.. "-^to 1 ' School in Cairo. He attended the College of Agriculture, University of Ain-Shams, in Cairo, from September, 1958 to June, 1962. During that period he obtained the highest grade point average in his class of 600 students, and he received the state's awards and scholarships for the most outstanding student. In June, 1962, he graduated with grade A and honor degree and received the national award for the best graduate in Agriculture in 1962 from President Carnal Abdel-Nasser . From September, 1962 to October, 1965, he served as instructor in the Department of Botany, College of Agriculture, University of Ain-Shams, Cairo, and while teaching he completed the requirements for the Master of Science degree in Plant Pathology in 1965 at the same department. He entered the University of Florida in January, 1966, and completed his work toward the degree of Doctor of Philosophy in August, 1970, from the Department of Vegetable Crops. He is a member of the American Society for Horticultural Science, Florida State Horticultural Society, and the American Society of Plant Physiologists. He is married to the former Miss Janine M. Neerdaels and they have a daughter, Magda. -90-

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This dissert ation was p^ ' under the. direcl Lon of Lhe of the candidate's supervisory committee and has tu approved by all members of that committee. It was sul ; to the Dean of the College o r .' ' Lturi ' to the Graduate Council, 1 was approved as pa. I fulfillment of the requin cits for t di of Doctor of Philosophy. , 1970. y Iknn, College of Agrii i, Ci. School Supervisory, Comi lan V