PLANT GROWTH REGULATORS

2. DR. RAJENDRA PRASAD CENTRAL AGRICULTURAL UNIVERSITY
PUSA (SAMASTIPUR) BIHAR - 848125
DEPARTMENT OF HORTICULTURE
CREDIT SEMINAR
On
Response of PGRs (Plant Growth Regulators) in Vegetable Crop’s Physiology.
Speaker:
DINESH
M.Sc.(Ag.) Vegetable Science 2nd year
Registration no.- M/HORT.(VS)/485/2020-21
(Deptt. of Horticulture, Dr. RPCAU, PUSA)
Seminar incharge :
Dr. Udit Kumar
Associate Professor
(Deptt. of Horticulture, Dr. RPCAU, PUSA)

3.  Introduction
 Definition and History
 Classification and Functions
 Commercial use
 Case studies
 Precautions
 Constraints in the use
 Conclusion

4. INTRODUCTION
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.
If the compound is produced within the plant, it is called as plant
hormone.
Both internal plant hormones and synthesized hormones are called
plant growth regulators.
Plant growth regulators (PGRs) defined as natural or synthetic compounds that affect
developmental or metabolic processes in plants, at low dosages.

5. Definition of PGR by different Scientists
Thimann (1948) stated that a plant hormone is an organic compound synthesized in
one part of a plant and translocate to another part where in very low concentration, it
causes a physiological response.
Phillip (1971) defined growth hormone as substances which are synthesized in
particular cells and are transferred to other cells where in extremely small quantities
influence the developmental process.
Moore (1974) stated that it is an organic chemical substance other than nutrients
which are active in low concentration in promoting, inhibiting or otherwise modifying
growth and development may be called growth regulators.

6. Characteristics of plant growth regulators
These are essential organic compounds other than nutrients for plants.
Required concentration – very low, comparing with the requirement of mineral and
vitamin for plant.
The biosynthesis of plant hormones within plant is more diffuse and not always localized.
Plant hormones are not nutrient, but chemicals that in small amounts promote and
influence the growth, development, and differentiation of cells and tissues.
A single PGR can control or regulate different aspect of growth.

7. 1. Growth promoting hormones
o Increase the growth of plants.
o e.g. Auxins, Gibberellins, Cytokinins etc.
2. Growth inhibiting hormones
o Inhibit the growth of plants.
a. Naturally occurring inhibitors – ABA, Ethylene
b. Synthetic inhibitors – Morphactins, Chlorocholine chloride (CCC), AMO-1618, Maleic Hydrazide
(MH)
Auxins
Gibberellins
Cytokinins
Abscisic Acid
Ethylene
Plant growth promoter
Plant growth inhibitor

8. The word Auxins has been derived from a Greek word ‘auxein’- “to grow/increase”.
It was first isolated from human urine.
Active sites of auxin synthesis are meristem of apical buds, embryo of seed, young expanding
leaves in the presence of light than in dark.
Movement in plant - basipetal in stem and acropetal in roots.
Types of Auxins
Natural - Indole-3-Acetic acid (IAA)
Synthetic - IBA, 2,4-D, NAA
Tryptophan is the precursor of IAA and zinc is required for its synthesis.
Auxins

9. The cell enlargement is induced by auxin.
Enhances the size of carpel and hence earlier fruit formation.
Apical dominance or bud inhibition (suppression of growth of lateral buds).
Promotes formation of female flowers (feminization).
The development of fruit without pollination and fertilization is called parthenocarpy
(by spraying with dilute solution of IAA & IBA).
Used as effective weedicides or herbicides (2,4D is a selective weed killer as it is
toxic to broad leaved plants and in low concentration it is useful in preventing preharvest fruit
drop).
 As root inducer (mostly – IBA). Other auxins used as rooting agent are NAA, IAA etc
Functions of Auxin

10. Gibberellins are named after the fungus Gibberella fujikuroi ,
which produces foolish seedling disease of rice or bakanae disease.
Yabuta, Hayashi and Kahnbe first isolated active principle toxin secreted by the fungus-
gibberellin.
Sites of synthesis - young leaves (major site), root tips and immature seeds.
Chemical gibberellins are related to terpenoids and its precursor is kaurene.
Movement - in all directions and in all tissues including phloem and xylem..
Gibberellins

11. Stem elongation
Seed germination and Seedling growth
Breaking of seed dormancy
Promotes bolting & flowering – long day/cold requirement (Gibberellins
induces cell division and cell elongation when bolting take place).
Flowering and sex expression (male flowers production).
Exogenous application of gibberellins also induces the production of parthenocarpic fruits.
Functions of Gibberellins

12. Miller, Skoog and their coworkers isolated the growth factor responsible for cellular division
from a DNA preparation calling it as Cytokinins (1950).
First isolated from coconut milk.
Precursors of cytokinin is either adenine or adenosine.
Translocation - through xylem.
Mobility - polar and basipetal.
Cytokinins are found in abundance in young roots, leaves and young fruits and are synthesized
in the meristematic regions of the plants.
Cytokinins
Types
Naturally occurring - zeatin, isopentenyladenine (IPA) etc.
Synthetic - kinetin, N-N diphenylurea, 6-benzylaminoprine(BAP) etc.

13. Promotes cell division, cell enlargement and cell differentiation (used in tissue
culture).
Delay the senescence of leaves and other organs (prevent aging of plants).
promote femaleness in male flowers
They inhibit apical dominance and help in growth of lateral buds. Therefore it
is also known as anti-Auxins.
Cytokinins are quite effective in breaking the dormancy of seeds and some
other plant organs. For e.g., seeds of Lectuca sativa.
Functions of Cytokinins

14. Ethylene is a colourless gaseous hormone.
In higher plants, most of the plant parts produce ethylene. Meristematic region and
nodal regions are main site for ethylene biosynthesis
Found in ripening fruits, flowers and leaves and nodes of stem.
Precursor - methionine.
Synthesis of ethylene is inhibited by carbon dioxide and requires oxygen.
Available form - gaseous (ethophon) and liquid (etheral).
Ethylene

15. It induces ripening of fruits.
Promotes abscission and senescence of leaf, flowers etc.
In cells it only increases the width not the length.
induces femaleness in monoecious flowers as in cucurbits like cucumber.
Functions of Ethylene

16. It is also known as dormins, which acts as anti-Gibberellins.
ABA is a naturally occurring growth inhibitor in plants.
Precursor - mevalonic acid or xanthophylls (violaxanthin).
ABA is a naturally occurring growth inhibitor in plants.
It is synthesized in leaves of wide variety of plants.
Responsible for closing stomata during drought conditions, hence acts as plant stress
hormone.
Abscisic Acid

17. It induces dormancy of buds and seeds as opposed to Gibberellins, which breaks
dormancy.
Involved with leaf and fruit abscission (fall).
It inhibits seed germination and development.
ABA also plays important role in controlling stomata opening and closing.
Functions of Abscisic Acid

18. Brassinosteroids are a class of polyhydroxysteroids that have been recognized
as a 6th class of plant hormones.
Brassinosteroids were first explored by mitchell et al nearly 45 years ago.
Brassinolide was the first isolated brassinosteroid in 1979, when pollen from
Brassica napus.
Shown to promote stem elongation, cell division and the biologically active
molecule was isolated.
The potential role of BRs in pathogen defense has also examined.
Brassinosteroids

19. Jasmonates activate the synthesis of stress protein, commercially, jasmonic acid
and its volatile methylester (MeJa) can be purchased.
Jasmonates promote leaf senescence, fruit ripening, tuber and bulb formation,
dormancy development and breaking.
It has been observed that jasmonates promote regeneration of shoots and roots.
 Enhancement of meristem formation.
Jasmonates/ Jasmonic acid

21.  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. (Meena, 2015)
Seed Germination

22.  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.
Seed Dormancy

23. Breaking the dormancy in potato comprise the vapour heat treatment with
ethylene chlorhydrin (1 litre per 20 q) followed by dipping in thiourea (1% sol.) for
1h & 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).

24. NAA 50ppm has been reported to induce early
flowering in paprika. ( Kannan et al., 2009)
Plants sprayed with 300ppm GA3 were earliest
to flower and recorded highest number of fruits
and yield per plant in tomato. ( Sharma et al.,1992)
Gibberellic acid has been reported to induce
early flowering in lettuce.
Flowering

25. 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.
Sex Expression

26. Application of silver thiosulphate followed by silver nitrate @ 400 ppm was found better
for induction of staminate flowers, in gynoecious lines of cucumber. (Hatwal et al., 2015 )
Application of ethephon at two true leaf stage to both Cucurbita maxima and Cucurbita
pepo caused suppression of male flowers and increase in numbers of female flowers. Thus
gave rise to an increase in the ratio of female to male flowers per plant. ( Hume et al., 1983 )

27. 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. (Choudhury et al., 2007)
Seed treatment with 2,4-D @ 2-5ppm gives early fruit
set and leads to parthenocarpy in tomato. (Meena,
2015).
Parthenocarpy

28. Staminate flowers were induced in parthenocarpic line of cucumber through use of
plant growth regulator GA3@ 1500 ppm and silver nitrate @ 200-300ppm by four sprays
at 4 days interval. (Singh and Ram, 2004).
In brinjal, application of 2,4-D at 2.5ppm in lanolin paste to cut end of styles or as foliar
sprays to freshly opened flower cluster has been reported to induced parthenocarpy.

29. In tomato, 75 ppm conc. of 4- CPA resulted
not only the highest increase in fruit set
(32.19%) but also increased the yield by
64.99%. (Baliyan et al., 2013)
Fruit set in bottle gourd can be increased by
spraying the plant twice at 2 and 4 true-leaf
stage with MH @ 400ppm and TIBA @ 50ppm.
(Meena, 2015)
Stimulation of fruit Set

30. PGRs have also been used for maintenance of
gynoecious lines in cucurbits.
Growth regulator like GA3 (1,500- 2000ppm) and
chemical like silver nitrate (200-300ppm) induces the
male flowers on gynoecious cucumber .
Exogenous application of silver thiosulphate (300-
400ppm) induces the male flower in gynoecious
muskmelon .
Hybrid Seed Production

31. 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)
Fruit Ripening

32. 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 6ppm 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 10ppm 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. (Choudhaury
et al., 2006)
• Spraying plants with 10 ppm NAA gave significantly highest fruit yield (277.8
g/plant). ( Sultana et al., 2006)

34. Objective:-
To study the effect of naphthalene acetic acid (NAA) and
Gibberellic acid (GA3 ) on growth and yield of tomato cv kashi vishesh.

35. Materials and Method
Tomato cv. Kashi Vishesh
PGRs – GA3 & NAA
Stock solution – GA3 and NAA (1000 ppm each)
Working solution 4 levels -
Spraying – 15 Days interval
GA3 – 20, 40, 60 and 80 ppm
NAA – 25, 50, 75 and 100 ppm

36. Treatment
% Fruit
set
No. Of
fruits/plan
t
Fruit
weight
(g)
Fruit
length
(cm)
Fruit
width
(cm)
Rind
thickness
(cm)
Fruit
yield
(q/ha)
Control 30.6 13.2 80.5 4.3 4.4 0.40 380.7
GA 20PPM 35.4 18.7 85.1 4.8 4.92 0.45 396.2
GA 40PPM 40.2 22.7 120.2 5.06 5.21 0.48 418.6
GA 60PPM 47.3 26.2 125.7 5.92 6.20 0.52 446.5
GA 80PPM 51.6 30.2 130.8 6.46 6.86 0.56 483.6
NAA 25PPM 32.1 18.5 84.1 4.6 4.72 0.44 390.5
NAA 50PPM 37.7 21.7 118.2 4.82 4.90 0.45 402.7
NAA 75PPM 44.5 23.4 121.8 5.78 6.11 0.50 433.6
NAA
100PPM
49.1 24.7 128.6 6.08 6.38 0.55 474.2
CD (0.05) 3.42 9.50 6.48 1.23 1.01 NS 12.6
Treatments of GA3 and NAA and their impact

39. The fruit yield per hectare significantly increased with the application of NAA and GA3
as compared to control.
The maximum fruit yield (483.6q/ha) was obtained with application GA3 @80 ppm
closely followed by NAA@ 1000 ppm (474.2q/ha).
The possible reason for increasing in fruit yield per hectare is due to increase in number
of fruits per plant, average fruit weight and fruit yield per plant.
These results are in conformity with the finding of Akhtar et al., (1996) and Soha et al.,
(2009).
From these results, it may be inferred that the application of GA3 @80 ppm or NAA 100
ppm may be adopted to enhance the productivity of tomato.
Result

40. Objective:-
To study the effect of GA3 and Cycocel on growth, yield and protein content of
pea in two varieties namely cv. Aparna and cv. Azad-P-1.

41. Materials and Method
Pea cv. Aparna and cv. Azad-P-1
PGRs – GA3 & Cycocel (10, 100, 250, 500, 1000 micro gram / L)
Surface sterilization of seeds – 0.01 % HgCl2
Washing with Distilled Water & Air drying seeds
Soaking seeds – 12 Hours
Air drying and sowing in bed

42. Treatments
(Gibberellic acid)
No. of flowers/plant No. of pods/plant Seed yield
(q/ha)
0 ppm 17.25 17.20 11.77
10 ppm 17.38 17.33 12.32
100 ppm 19.41 19.37 13.29
250 ppm 21.83 21.73 13.79
500 ppm 17.96 17.92 11.97
1000 ppm 16.70 16.65 11.78
Treatments of Gibberellic acid and its impact

43. Treatments
(Cycocel)
No. of flowers/plant No. of pods/plant Seed yield
(q/ha)
0 ppm 17.25 17.20 11.77
10 ppm 17.33 17.27 12.31
100 ppm 19.32 19.26 13.19
250 ppm 22.07 22.02 14.15
500 ppm 20.94 20.88 12.56
1000 ppm 17.23 17.11 11.47
Treatments of Cycocel and its impact

44. Both GA3 and Cycocel brought about an improvement in morphological
and yield attributes of pea. Highest yield and protein content under the
influence of growth regulators might be due to activation of various internal
mechanisms related with plant growth and metabolism.
Result

45. Growth substances should be sprayed preferably in the evening hours.
Avoid to spray in high velocity of wind.
Spray should be uniform and wet both the surface of leaves.
Add surfactant or adhesive material like Teepol, Tween- 20 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.
Chemical should be completely dissolved before application.
Precaution in growth regulator application

46. 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 of spray.
Wash the machine/pump after each spray.

47. 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.
Constraints in the use of growth regulators

48. Some synthetic plant growth regulators cause human health hazards
e.g. 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.

49. 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. Plant Growth Regulators environmentally safe.
Conclusion

50. References
Prasad, R. N., Singh, S. K., Yadava, R. B., & Chaurasia, S. N. S. (2013). Effect of GA3 and NAA on growth
and yield of tomato. Vegetable Science, 40(2), 195-197.
Bora, R. K., & Sarma, C. M. (2006). Effect of gibberellic acid and cycocel on growth, yield and protein
content of pea. Asian Journal of Plant Sciences.
Olaiya, C. O., & Adigun, A. A. (2010). Chemical manipulation of tomato growth and associated biochemical
implications on flavonoid, lycopene and mineral contents. African journal of plant science, 4(6), 167-171.
Mishra, S., Sharma, A. K., Sharma, D., Sharma, R. S., & Meena, R. P. 2015. Assessment of Molecular
Diversity Analysis in Muskmelon (Cucumis melo L.) Genotypes in Relation To Drought Tolerance.Green
Farming, 6(2), 259-262.
Tzortzakis, G. N. (2009). Effect of pre-sowing treatment on seed germination and seedling vigour in endive
and chicory. Horticultural Science, 36(3), 117-125.
Nagar, S., Mauyra, I. B., & Hatwal, P. K. (2015). Maintenance of gynoecious line of cucumber, Cucumis
sativas L through induction of staminate flower using silver nitrate and silver thiosulphate. International
Journal of Farm Sciences, 5(3), 67-73.
Hume, B., & Lovell, P. (1983). Role of aminocyclopropane‐l‐carboxylic acid in ethylene release by distal
tissues following localized application of ethephon in Cucurbita pepo. Physiologia plantarum, 58(1), 101-106.
Chowdhury, R. N., Rasul, M. G., Islam, A. A., Mian, M. A. K., & Ahmed, J. U. (2007). Effect of plant growth
regulators for induction of parthenocarpic fruit in kakrol (Momordica dioica Roxb.). Bangladesh Journal of
Plant Breeding and Genetics, 20(2), 17-22.

51. Thank you!