Transcript Role of plant growth regulators in Vegetable Crops

Plant Growth Regulator ?

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 action and production are
different.
Classification of PGR’s
Sr. No. Growth regulator
Example
1
Auxins
IAA, IBA, NAA, 2,4-D
2
Gibberellins
Gibberellic acid
3
Cytokinins
Kinetin, Zeatin
4
Ethylene
Ethylene
5
Dormins
Abscissic Acid
6
Flowering hormones
Florigen, Anthesin, Vernalin
7
Miscellaneous natural sunstances
Cyclitols, Vitamins, Phytochrome,
Traumatic substances etc.
8
Phenolic substances
Coumarin
9
Synthetic growth retardants
CCC, Phosphon D, Morphactins, Maleic
hydarzode (MH) etc.
10
Miscellaneous synthetic substances
Synthetic
etc.
auxins, synthetic cytokinins
Major classes of PGR’s
1.
Auxins
2.
Gibberellins
3.
Cytokinins
4.
Ethylene
5.
Abscisic acid
Plant Growth
Promoters
Plant Growth
inhibitors
Plant Growth Promoters
Auxins
 The
word Auxins has been derived
from a Greek word auxein- “to
grow/increase”.
 It was first isolated from human urine.
 These are generally produced by the
growing apex of stem and roots of the
plants.
Types of Auxins
 Natural
 Synthetic
Indole-3-Acetic acid
(IAA)
IBA, 2,4-D, NAA
Functions of Auxins
1. Apical dominance


Terminal buds prevent
the development of
lateral buds on plant
stem.
Pinching of terminal
bud stops flow of
Auxins down the stem
and allows side shoots
to develop.
Pinching promotes the
lateral bud initiation
2. Root initiation and development
 Applied
on cuttings to
stimulate root growth
and development.
3. Phototropism

Auxins are responsible
for
plants
bending
towards light.

They
move
down
towards shaded side of
the stem and cause
cells to elongate.
4. Parthenocarpy
 Auxins
induces parthenocarpy i.e., formation of
seedless fruits without fertilization
5. Inhibition of abscission layer
 Formation
of an abscission
layer at the base of petiole or
pedicel results in shedding of
leaves, flowers or fruits.
 Auxins
inhibit abscission, as
they prevent the formation of
abscission layer.
6. Used as weedicide
 Many
synthetic auxins are
used as selective weed
killers and herbicides.
 2,
4-D is used to destroy
broad leaved weeds.
 It
does not affect mature
monocotyledonous plants.
7. Flowering
Foliar
spray
of
NAA and 2, 4 - D
induces
in
flowering
many
plants.
crop
8. Storage

Auxins such as NAA
is used to prevent the
sprouting of potato
tubers.

Hence, increases the
storage life of the
produce.
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).

Are produced in the shoot apex mainly in the leaf primordial
(leaf bud) and root system, hence they translocates easily in the
plant in both directions.

More than 60 types of Gibberellins are known today.
Functions of Gibberellins
1. Stem elongation


Gibberellins
cause
internodes to stretch in
relation
to
light
intensity. Less is the
light intensity more
will
be
internode
length and vice versa.
Stimulate stem growth
through cell elongation
and cell division.
3. Seed germination and Seedling growth

Used commercially
in stimulating seed
germination
seedling growth.
and
4. Seed dormancy

GA3 is used to break the
seed
dormancy
of
freshly harvested seeds
in many vegetable crops
such
lettuce.
as
potato
and
Sprouting in Potato
Cytokinins

They were first isolated from coconut milk.

Miller, Skoog and their coworkers isolated the growth
factor responsible for cellular division from a DNA
preparation calling it as Cytokinins (1950).

They are synthesized in root apex, endosperm of
seeds, young fruits, where cell division takes place
continuously.
Functions of Cytokinins

Promotes cell division, cell enlargement and
cell differentiation (used in tissue culture).

They prevent aging of plants.

They inhibit apical dominance and help in
growth of lateral buds.

Therefore it is also known as anti-Auxins.
Plant Growth Inhibitors
Ethylene

Ethylene is a colourless gaseous hormone

Found in ripening fruits, flowers and leaves
and nodes of stem.

Synthesis of ethylene is inhibited by carbon
dioxide and requires oxygen.
Functions of Ethylene
 It
induces ripening of fruits.
 Promotes
abscission and senescence of
leaf, flowers etc.
 In
cells it only increases the width not the
length.
Abscisic Acid

It is also known as dormins, which acts as antiGibberellins.

It is synthesized in leaves of wide variety of
plants.

Responsible for closing stomata during drought
conditions, hence acts as plant stress hormone.
Functions of Abscisic Acid
 It
induces dormancy of buds and seeds as opposed
to Gibberellins, which breaks dormancy.
 Involved
 It
with leaf and fruit abscission (fall).
inhibits seed germination and development.
 ABA
also plays important role in controlling
stomata opening and closing.
Relative concentration of some plant hormones
Plant part
Auxins
Gibberellins
Cytokinins
Abscisic acid
Shoot tip
+++
+++
+++
+
Young leaves
+++
+++
+++
+
Elongating stem
++
++
+++
+
Lateral buds
+
++
+
++
Flower and fruits
+
+
++
+
Developing seeds
+
+++
++
++
Mature leaves
+
+
+
+++
Lateral shoot
+++
++
++
+
Mature stem
+
+
+
+
Root
+
+
+
+
Root tip
+
++
+++
+
+++ High concentrations ++ Medium concentration + Low concentration
Commercial Use
of PGR’s in
Vegetable crops
Seed Germination
Pre- showing treatment of seed with growth regulators
has been reported to enhance seed emergence.
In tomato, higher germination with GA3 at 0.5 mg/l,
and 2,4-D at 0.5 mg/l has been reported.
Soaking of seeds in ethephon at 480 mg/l for 24 h
improved germination in muskmelon, bottle gourd,
squash melon and watermelon at low temperature.
Seed Dormancy
 Seed Dormancy is the main problem in potato where freshly
harvested tubers fail to sprout before the termination of rest period.
 Chemicals which have been reported to break the rest period are
GA, ethylene chlorhydrin and thiourea.
 The treatment which has been used for breaking of dormancy in
potato comprise the vapour treatment with ethylene chlorhydrin (1
liter per 20 q) followed by dipping in thiourea (1% sol.) for 1h
finally in GA (1 mg/l) for 2 seconds.
Flowering
 Induction of flowering in plants which otherwise fail to
flower has also been reported with the use of various
plant growth regulators.
 Application of GA at 50 mg/l to young leaves of nonflowering varieties of
potato , when floral buds had
just formed, resulted in flower induction in all varieties.
 GA has been reported to induce early flowering in lettuce.
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.
 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.
Hybrid seed production
 Some plants growth regulators possess gametocidal actions to
produce male sterility which can be used for F1 hybrid seed
production.
 The chemicals which has been reported to show good performance
are GA3 in onion, 2,3- dichloroisobutyrate ( 0.2 to 0.8 %) in egg
plants, muskmelon, okra, onion, root crops, spinach and tomato and
TIBA in cucumber, egg plants, onion, and tomato.
 GA3 at 100 mg/l can also be used for inducing male sterility in
pepper.
Hybrid seed production….conti
 Use of ethephon (100 ppm) has been used for producing temporary female
lines in some cucurbits .
 Successful F1 hybrid in Butter-nut squash has been made by using female
line produced with ten weekly sprays of ethephon.
 Plant growth regulators have also been used for maintenance of gynoecious
lines.
 In cucumber, silver nitrate at 500 mg/l has been reported to be effective in
inducing male flowers on gynoecious lines of cucumber.
 However, in muskmelon foliar sprays of Silver thiosulphate at 400 mg/l
was found best for induction of male flower on gynoecious lines.
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)
have been reported to enhance fruit set under both normal and
adverse weather conditions, when applied at flowering stage in
tomato, brinjal and chillies.
Parthenocarpy
 Plant growth regulators helps to stimulate the fruit
development without fertilization (parthenocarpy).
 In brinjal, application of 2,4-D at 0.00025 % in lanolin paste
to cut end of styles or as foliar sprays to freshly opened
flower cluster has been reported to induced parthenocarpy.
 GA3 (100 ppm) also used to develop parthenocarpic fruits in
cucumber.
Fruit Ripening
 Ethephon, an ethylene releasing compound, has been reported
to induce ripening in tomato and pepper.
 Field application of ethephon (1000 ppm) at turning stage of
earliest fruits induced early ripening of fruits thus increasing
the early fruit yield by 30-35%.
 Post-harvest dip treatment with ethephon at 500-2000 ppm has
also been reported to induce ripening in mature green
tomatoes.
Fruit Yield
 Tomato: Soaking of seed in GA3 (5-20 ppm) and CIPA (10-20 ppm),
2,4-D (0.5 ppm) have been reported to improve fruit yield in tomato.
 Brinjal: Soaking of seedlings roots in NAA (0.2 ppm) and ascorbic
acid at (250 ppm) have been reported to produce higher fruit yield.
 Chillies and Peppers: Foliar sprays
of
GA3 (50 mg/l) at fruit
setting or planofix (NAA 10 ppm) double sprays (at flowering and 5
week later) decreased flower shedding and gave better fruit yield in
chillies.
List of plant growth regulators and their important uses in vegetable crops
Growth regulators
Conc.
(mg/l)
Method 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, okra
and tomato
Flowering, fruiting, sex
expression and yield
2000
Post- harvest
Tomato, chillies
Fruit ripening
Gibberellic acid
(GA)
10
Foliar spray
Water melon,
tomato
Sex expression, fruiting ,
yield
Indoleacetic acid
(IAA)
10-15
Foliar spray
Okra, tomato,
brinjal,
Seed germination, fruit set
and yield
Contd…
Naphthalene
acetic acid
(NAA)
0.2
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
Naphthoxyaceti 25Seed/ foliar
c acid (NOA)
10
0
Tomato, okra
Germination, growth and yield
Silver nitrate
500
Foliar spray
Cucumber
Induction of male flower in
gyn, lines
Silver
thiosulphate
400
-
Musk melon
Induction of male flower in
gyn, lines
2,3-5, triiodobenzoic
acid (TIBA)
25-50
Foliar
sprays
cucurbits
Flowering, sex expression and
yield
Tricontanol
2
Foliar
sprays
Chillies and peas
Fruit set and yield
Source :Chadha and Kalloo,1993
Precaution in Growth Regulator Application

Growth substances should be sprayed preferably in the
afternoon.


Avoid to spray in windy hours.
Spray should be uniform and wet both the surface of
leaves.

Add surfactant or adhesive material like Teepol, Tween20 are Gum with growth substances @ 0.5 – 1.0 ml/l
solution.

Use growth substances at an appropriate stage of plant
growth is of great importance.
Contd…

Chemical should be completely dissolved before use over
plant.

Use always fresh solution of chemicals.

Solution should always be prepared in distilled water
only.

Fine spray can be ensured by hand automizer. It is most
economical and effective method of spray.

Wash the machine/pump after each spraying.

Repeat the spray with in eight hours if chemical is wash
out due to rain.
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 predication 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.

Some synthetic plant growth regulators cause human
health hazards e.g. dominozide.
Contd…

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.
Conclusion and 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 of PGR’s must lead to quantifiable
advantages for the user.

PGR’s
must
be
specific
in
their
toxicologically and environmentally safe.
action
and
Contd…

Industries involved in development of PGR’s should be
well informed about the latest scientific development in
production of PGR’s.

Plant growth regulators should be recognized as more
than academic curiosities. They are not only interesting
but profitable to use to grower, distributor and
manufacture.

There is need for some plant growth regulators which can
inhibit photo- respiration in plants.

More research is needed to develop simple, economical
and technical viable production systems of PGR’s.