Plant growth regulators can be natural or synthetic compounds that modify physiological processes in plants. The main classes of plant growth promoters discussed are auxins, gibberellins, and cytokinins. Auxins promote cell elongation, root formation, and fruit development. Gibberellins promote stem elongation, seed germination, and flowering. Cytokinins promote cell division. Ethylene and abscisic acid are major growth inhibitors and promote processes like fruit ripening and senescence. The document provides examples of how these growth regulators are used commercially in vegetable crops to stimulate seed germination, break dormancy, induce flowering and parthenocarpy, control sex expression, improve fruit set and yield, and enhance quality.

1. PLANT GROWTH REGULATORS IN
VEGETABLE CROPS
1
Basavaraj Panjagal
Ph.D Research Scholar
Basavaraj Panjagal

2. CONTENTS
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3. INTRODUCTION
A Growth regulator is
- An organic compound,
- Can be natural or synthetic
- It modifies or controls one or more specific
physiological processes within a plant but the sites
of the action and production are different.
• If the compound is produced within the plant, it is
called plant harmone.
• Both internal plant harmones and lab created harmones
are called plant growth harmones
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4. Definition of growth regulators by different scientists
• Phillip (1971) defined growth harmone as substances which are
synthesized in particular cells and are transformed to other cells where in
extremely small quantities influence the developmental process.
• Phill Olaiya (2013) stated that bio-regulators are endogenous or
synthetically produced substances that can control one or more specific
biochemical and physiological functions of many species probably by their
influence on gene and enzymic interactions.
• Prajapathi et.al.(2015) stated that although, photosynthesis supplies the
carbon and respiration supplies the energy for plant growth, a groupof
chemicals produced by plants known as plant growth regulators control the
growth and development of plant.
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5. • Auxin was the first hormone to be discovered in plant and at
one time discovered to be only naturally occurring plant
growth hormone (Prajapati et.al., 2015)
• Three types of plant hormones Auxins, Gibberelines and
Cytokinins and these were discovered in the early decades of
the twentieth century, in 1930’s and in 1960’s , respectively
(Thomas, 1956)
History of Growth Regulators
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6. CLASSIFICATION OF GROWTH REGULATORS (GR’S)
ON THE BASIS OF ORIGIN
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NATURAL GR’S SYNTHETIC GR’S POSTULATED GR’S
•Produced by some
tissues in plant.
• also called
Endogenous
hormones.
•Eg: Auxins,
Gibberlins,
Cytokinins, Ethelene,
Ascorbic acid
•Produced artificially
and similar to
natural hormone in
physiological activity.
•Also called
Exogenous
hormones.
•Eg: 2,4-D, NAA, IBA,
2,4,5T, Morphactin,
Cycocel ,Maleic
hydrazide etc
•Also produced
spontaneously in the
plant body, but their
structure and
function is not
discovered clearly.
•Eg: Florigen,
Vernalin.
(Meena.2015)
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7. Classification of growth regulators
Sl.No Growth regulator Example
1. Auxins IAA, IBA, NAA, 2,4-D
2. GIbberellins Gibberellic acid (GA, GA3, GA7)
3. Cytokinins Kinetin, Zeatin
4. Ethylene Ethylene, Ethephon, Ethrel
5. Dormins Abscisic acid
6. Flowering hormones Florigen, Anthesin, Vernalin
7. Synthetic growth retardants CCC, Phosphon D, Morphactins,
Maleichydrazide etc
8. Miscellaneous synthetic
substances
Synthetic auxins, synthetic cytokinins etc
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8. Major group of plant growth regulators
• Plant growth promoters
- Auxins
- Gibberellins
- Cytokinins
• Plant growth inhibitors
- Ethylene
- Abscisic acid
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9. Plant Growth Promoters
Auxin
• The word Auxins has been derived
from a Greek word auxen- “ to grow
/ increase”.
• First isolated from human urine.
• These are generally produced by the
growing of stem and roots of the
plants.
• This was the first group of plant
hormones discovered.
• Types of Auxin
i. Natural Auxin : IAA
ii. Synthetic Auxin : IBA, NAA, 2,4-D
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10. FUNCTIONS OF AUXINS
• It causes cell elongaton by loosining of the cell wall.
• Promotes secondary growth of stem through
cambium activity.
• Promotes callus and root formation in cutting.
• Restores apical dominance.
• Induction of flowering.
• Increases fruit setting & size.
• Delays leaf abcission
• Prevention of premature drop of fruits
• Develops parthenocarpic fruits
• Acts as herbicide at higher concentration
• Inhibition of prolonged dormancy
• Inhibiting aging processes in tissues
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11. GIBBERELLINS
• Second most important growth hormone
• Gibberellins are named after the fungus Gibberella fujikuroi, which
causes rice plants to grow abnormally tall.
(Kurosawa et.al.,1930)
Gibberellin produced in the shoot apex mainly in the leaf primordial
(leaf bud) and root system, hence they translocates in the plant in
both directions.
Now 135 different Gibberellins are available.
The most commonly occuring gibberellins is GA3.
(Meena, 2015)
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12. FUNCTIONS OF GIBBERELLINS
• It induces maleness
• Promotes growth of dwarf plants
• Possesses pollenicide effect
• Replaces chilling and light requirements of plants
• Promotes seed germination
• Used for breaking of dormancy
• Delays senescence of fruits
• Enhances seedless fruits
• For stem elongation
• Accelerates flowering in long day plants
• Intensifies transpiration, photosynthesis and
respiration.
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13. CYTOKININ
• They were first isolated from
coconut milk.
• They are synthesized in root
apex, endosperm of seeds,
young fruits where cell
division takes place
continuously.
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14. FUNCTIONS OF CYTOKININ
• Cell division
• Cell enlargement
• Induce flowering in shoot day plants
• Dormancy of certain light sensitive seeds
such as lettuce can also be broken by
kinetin treatment.
• Delays leaf senescence
• Inhibit apical dominance and help in growth
of lateral buds. Therefore, it is also known
as anti-auxins.
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15. GROWTH INHIBITORS
• Ethylene
• Ethylene is a colourless gaseous hormone.
• Found in ripened fruits, flowers and leaves
and nodes of stem.
• Synthesis of ethylene is inhibited by
carbon dioxide and requires oxygen.
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16. FUNCTIONS OF ETHYLENE
• Induces ripening of fruits.
• Promotes abscission and
senescence of leaf, flowers
etc.
• Induction of Femaleness :
Cucumber, squash, melon.
• It stimulates the formation
of adventitious roots.
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17. ABSCISIC ACID
• It is also known as dormins, which acts
as anti-Gibberelins.
• It is synthesized in leaves of wide
variety of plants.
• Responsible for dosing stomata during
drought conditions, hence acts as plant
stress hormone
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18. FUNCTIONS OF ABSCISIC ACID
• Promote tuberization
• Induces senescence of leaves, abscission of leaves,
flowers and fruits.
• It induces dormancy of buds and seeds as opposed
to Gibberellins, which breaks dormancy.
• It inhibits seed germination and development.
• ABA also plays important role in controlling stomata
opening and closing.
(Prajapati,2015)
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19. Other Plant Growth Regulators
• BRASSINOSTEROIDS
• Brassinosteroids have been recognized as sixth
class of plant hormone.
• Brassinolide was the first identified
brassinosteroid and was isolated from extracts of
rapeseed (Brassica napus) pollen in 1979.
• It stimulates cell elongation and division, resistance
to stresses.
• They inhibit root growth and leaf abscission.
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20. MORPHACTINS
• Morphactins are the group of
substances which act on morphogenesis
and modulate the expression of plants.
• Role of morphactins
• Seed germination – inhibition
• Growth of seedlings – inhibit
• Stem elongation – dwarfing effect
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21. COMMERCIAL USE OF PLANT
GROWTH REGULATORS IN
VEGETABLE CROPS
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22. SEED GERMINATION
• In tomato, pre sowing seed
treatment with 100 ppm IAA, IBA
and NAA enhanced the seed
germination.
(Olaiya et.al.,
2009)
• In muskmelon, soaking of seeds
in ethephon at 480 mg/litre of
water for 24 hours improves
germination in muskmelon at
low temperature. 22
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23. SEED GERMINATION
• Pre sowing treatment of seed
with GA3 and KNO3 @50
ppm enhanced germination
of endive and chicory,
respectively.
(Tzortzakis, 2009)
IAA, NAA @ 20 ppm
enhances seed germination
in okra.
(Khan
et.al.,2013)
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24. SEED DORMANCY
• Seed dormancy is main problem
in Potato and Lettuce.
• Chemicals which have been reported to break
the rest period are GA3, Ethylene chlorhydrin
and Thiourea.
• Lettuce is another vegetable in which
treatment with GA3 or cytokinin has been
reported to break seed dormancy induced by
high temperature
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25. SEED DORMANCY
• Breaking the dormancy in potato comprise
the vapour treatment with Ethylene
chlorhydrin ( 1 litre per 20q) followed by
dipping in thiourea (1% sol.) for 1 hour and
finally in GA (1 mg/l) for 2 seconds.
• Soak the tubers in 1% aqueous solution of
Thiourea for 1 hour or solution containing
5-10 ppm GA3 for 10-20 minutes can be
used to break the dormancy of potato.
(Byran, 1989)
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26. FLOWERING
• NAA 50 ppm has been reported to induce early flowering in
paprika.
(Kannan et al., 2009)
• Plants sprayed with 300 ppm GA3 were earliest to flower and
recorded highest number of fruits and yield per plant in tomato.
• Application of GA @ 50 mg/l to young leaves of non-flowering
varieties of potato, when floral buds had just formed, resulted
in flower induction in all varieties.
• Gibberellic acid has been reported to ibduce early flowering in
lettuce.
(Sharma et.al., 1992)
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27. SEX EXPRESSION
• The treatment with growth regulators has been
found to change sex expression in cucurbits, okra
and pepper.
• GA3 (10-25 ppm), IAA (100 ppm) and NAA (100
ppm) when sprayed at 2-4 leaf stage in cucurbits,
then they have been found to increase the number
of female flowers.
(Hume et.al.,1983)
• Whereas, GA3 (1500-2000 ppm), silver nitrate
(300-400 ppm) and silver thiosulphate (300-400
ppm) sprayed at 2-4 leaf stage induces male flower
production in cucurbits.
(Hatwal et al., 2015)
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28. PARTHENOCARPY
• Plant growth regulators helps to stimulate the fruit development
without fertilization (Parthenocarpy).
• 2,4-D at 50 ppm when applied at anthesis showed better
performance over other in parthenocarpic fruit development in
kakrol. (Choudhary et.al., 2007)
• Seed treatment with 2,4-D @ 2-5 ppm gives early fruit set and
leads to parthenocarpy in tomato. (Meena, 2015)
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29. • Staminate flowers were induced in
parthenocarpic line of cucumber through
use of plant growth regulator GA3 1500
ppm and silver nitrate @ 200-300 ppm by
four sprays at 4 days interval.
• In brinjal, application of 2,4-D at 2-5 ppm
in lanolin paste to cut end of styles or as
foliar sprays to freshly opened flower
cluster has been reported to induced
parthenocarpy.
(Singh and Ram, 2004)
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30. Stimulation of fruit set
• Poor fruit set is a major problem in tomato,
brinjal and chillies which is frequently caused
by adverse weather conditions during flowering.
• Plant growth regulators such as PCPA (20-25
ppm) and 2,4-D (1-5 ppm), Kinetin (5 ppm), NAA
(10 ppm) and GA3 (10 ppm) reported to enhance
fruit set under both normal and adverse
weather conditions, when applied at flowering
stage in tomato, brinjal and chillies.
(Prajapati et.al., 2015)
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31. Hybrid seed production
• Bioregulators have also been used for
maintenance of gynoecious lines in
cucurbits.
• Growth regulators loke GA3 (1500-2000
ppm) and chemical like silver nitrate (200-
300 ppm) induces the male flowers on
gynoecious cucumber.
• Exogenous application of silver
thiosulphate (300-400 ppm) induces the
male flower in gynoecious muskmelon.
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32. Gametocides
• Some PGR’s possesses gametocidal action to
produce male sterility which can be used for F1
hybrid seed production.
• MH at 100 to 500 ppm appeared most effective in
inducing a high level of male sterility in eggplant,
okra, peppers and tomato, without detrimental
influence on female fertility.
(Saimbhi et al., 1978)
• A high concentration of gibberellic acid (2%) was
found to act as a gametocide for the common onion
(Allium cepa L.), when sprayed in the beginning of
the bolting process.
(Meena et.al.,1973)
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33. FRUIT RIPENING
• Application of ethephon at 1000 mg/l at
turning stage of earliest fruits induced
early ripening of fruits thus increasing
the early fruit yield by 30-35%.
(Prajapati, 2015).
• Post harvest dip treatment with
ethephon at 500-2000 mg/l has also
been reported to induce ripening in
mature green tomatoes.
(Gould, 1992)
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34. FRUIT YIELD
1. TOMATO
- Spraying with 60 ppm GA3 10 days before transplanting increased
the yield per ha of variety Roma.
(Naeem et.al.,2001)
- Spray with 6 ppm 2,4-D gave highest yield of tomato.
(Patel et.al.,2014)
2. BRINJAL
- Foliar sprays of 2,4-D @ 4 ppm gave the highest yield of brinjal.
(Patel et.al., 2012)
- Seed treatment with 10 ppm GA3 or IAA gave the highest yield in
brinjal
(Sharma et.al.,1992).
3. CHILLI
- Foliar sprays of 2 ppm 2,4-D, 40 ppm NAA and 10 ppm GA3 gave
28.75%, 13.61% and 2.30% higher fruit yield over control,
respectively. (Choudhary et.al., 2006)
- Spraying plants with 10 ppm NAA gave significantly highest fruit
yield (277.8 g/plant). (Sultana et.al.,2006)
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35. EFFECT OF GROWTH REGULATORS ON QUALITY
OF VEGETABLE
Growth
Regulators
Concentr
ations
(ppm)
Methods of
Application
Crops Effect on
quality
GA3 15 Foliar spray Muskmelon Improve rind
thickness
GA3 5-15 Foliar spray Cauliflower,
cabbage
Increase head
or curd size
GA3 50 Foliar spray Lettuce &
chinese
cabbage
Increases dry
matter,protein
& ascorbic acid
content
PCPA 50 Foliar spray Tomato Increases
sugar and
vitamin C, but
reduces acidity
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36. EFFECT OF GROWTH REGULATORS ON QUALITY OF
VEGETABLE
Growth
Regulato
rs
Concentrati
ons (ppm)
Methods of
Application
Crops Effect on quality
CCC 250 Foliar spray Potato Increases TSS and
vitamin C content in
tuber
Cytozyme 1% Foliar spray Garden
pea
Increase vitamin C,
reducing sugars and
total sugars
Ethephon 250 Foliar spray Tomato Increase TSS
NAA 50-70 Seed
treatment
Chilli Increases amino acid
and vitamin C content in
fruits.
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(Bahadur and Singh,2014)
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37. List of plant growth regulators and their important uses in vegetable crops
GROWTH
REGULATORS
CONC.
(mg/L)
METHODS OF
APPLICATION
CROPS ATTRIBUTES
AFFECTED
Cycocel (CCC) 250-500 Foliar spray Cucurbits,
tomato, okra
Flowering, sex
expression, fruit yield
P-
Chlorophenoxy
Acetic Acid
(PCPA)
50 Foliar spray Tomato Fruit set and Yield
Ethephon
(CEPA)
100-500 Foliar spray Cucurbits,
orka and
tomato
Flowering, fruiting, sex
expression and yield
2000 Post-harvest Tomato,
chillies
Fruit ripening
Gibberellic acid
(GA)
10 Foliar spray Watermelon,
tomato
Sex expression,
fruiting, yield
Indoleacetic
acid (IAA)
10-15 Foliar spray Okra,
tomato,
brinjal
Seed germination fruit
set and yield
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38. GROWTH
REGULATORS
CONC(
mg/L)
METHODS OF
APPLICATION
CROPS ATTRIBUTES AFFECTED
Naphthalene
acetic acid
(NAA)
20 Seedling
roots
Tomato,
brinjal, onion
Growth and yield
10-20 Foliar sprays Chillies and
tomato
Flower drop, fruit set and
yield
25-30 Seed/foliar Okra, tomato,
brinjal, onion,
cucurbits
Seed germination, growth
and yield
Naphthoxyacet
ic acid (NOA)
25-100 Seed / foliar Tomato, okra Germination, growth and
yield
Silver nitrate 500 Foliar spray Cucumber Induction of male flower in
gynoecious lines
Silver
thiosulphate
400 Foliar spray Muskmelon Induction of male flower in
gynoecious lines
2,3,5-tri-
iodobenzoic
acid (TIBA)
25-50 Foliar sprays Cucurbits Flowering, sex expression
and yield
Source: Chadda and
Kalloo,1993) 38
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39. Precaution in Growth Regulator Application
• Growth substances should be sprayed
preferably in the evening hours.
• Avoid to spray in windy hours.
• Spray should be uniform and wet both the
surface of leaves.
• Use growth substances at an appropriate stage
of plant growth is of great importance.
• Chemical should be completely dissolved before
application.
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40. • Use always fresh solution of chemicals.
• Use PGR’s strictly at recommended concentration.
• Solution should always be prepared in distilled
water only.
• Fine spray can be ensured by hand automizer. It is
most economical and effective method od spray.
• Wash the machine / pump after each spray.
• Repeat the spray within eight hours, if chemical is
wash out due to rain.
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41. Constraints in the use of growth regulators
• The difference in sensitivity of each plant
species or even cultivars to a given
chemical treatment prevent easy
prediction of the biological effects.
• The cost of developing new plants growth
regulator is very high, due to which they
are very much costly.
• Screening for plant growth regulatory
activities entails high costs and is very
much difficult.
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42. • Some synthetic plant growth regulators cause
human health hazzards.
eg: Dominozide.
• Lack of basic knowledge of toxicity and mechanism
of action.
• Inadequate market potential.
• Lack of support from agricultural researchers in
public and private sectors.
• Difficulty in identification of proper stage of crop
at which the growth regulators should be applied.
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43. FUTURE THRUST
• Most of the biological processes associated are
polygenic, so gene transfer may be difficult and hence
the use of PGR’s may be beneficial for short
imperatives.
• PGR’s provide an immediate impact on crop
improvement programmes and are less time consuming.
• Applications PGR’s must lead to quantifiable
advantages for the user.
• Industries involved in development of PGR’s should be
well informed about the latest scientific development in
production of PGR’s.
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44. • Plant growth regulators should be recognized as
more than academic curiosities.
• They are not only interesting but profitable to use
to grower, distributor and manufacturer.
• More research is needed to develop simple,
economical and technical viable production systems
of PGR’s.
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45. CONCLUSION
• Plant growth regulators has an immense potential in vegetable
production to increase the yield, quality; synchronization in
flowering, earliness, cold and high temperature, fruit setting,
sex modification, increase post-harvest life and resistance to
biotic and abiotic stresses of vegetables to better meet the
requirements of food supply in general.
• But more research is needed to develop simple, economical
and technical viable production system of bio-regulator.
• Bio-regulator must be toxicologically and environmentally
safe.
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