Role of Plant Growth Regulators in Flower Crops

Abstract

The plant growth regulators are enormously important agent in the
integration of developmental activities. Environmental factors often exert
inductive effects by evoking changes in hormones in metabolism and
distribution within the plant. Apart from it, they also regulate expression of
intrinsic genetic potential of plants. Manage the genetic expression has been
demonstrated for the phytohormones at both transcriptional and translational
levels. Their exogenous application helps to improve the different
economically important and market desirable characteristics of flower crops.
The use of plant growth regulators is being practiced by the commercial
growers of ornamental plants and flower crops as a part of cultural practice.
There are different factors contributing to the efficacy of plant growth
regulators and the method of application plays key role in determining the
effectiveness of plant growth regulators, as PGRs can be effective if properly
absorbed by plants.

Full text

ADVANCES
IN
HORTICULTURE
Volume - 10
Chief Editor
Dr. Sarvesh Kumar Lodhi
Assistant Director Ext (Horticulture), Directorate of Extension,
S.V.P. University of Agri. & Tech., Meerut, Uttar Pradesh, India
Co-Editor
Dr. Vijay Kumar
Ph.D., Plant Pathology, Dr. Y S Parmar University of Horticulture and
Forestry, Nauni, Solan, Himachal Pradesh, India
AkiNik Publications
New Delhi

Contents
S. No.
Chapters
Page No.
1.
Role of Plant Growth Regulators in Flower Crops
01-15
(E Sathyanarayana and Divya K)
2.
Vegetables for Nutritional Security and Play Important Role
in Human Diet
17-37
(Deepak Maurya, Shirin Akhtar, Vishal Tripathi and Ankit Kumar Pandey)
3.
Importance of Osmotic Dehydration in Fruits and Vegetables
Preservation
39-52
(Sunil, Neelash Chauhan, Vipul Chaudhary, Vaishali, Vikrant Kumar and
Ratnesh Kumar)
4.
Production Technology, Post-Harvest Management and
Value Addition of Sarpagandha
53-70
(Siba Prasad Mishra, Aditya Kiran Padhiary and Alok Nandi)
5.
Varieties and Production Technology of Okra
71-84
(Shardulya Shukla and Ankita Sharma)
6.
Tomato Cultivation Practices
85-118
(Banothu Rambabu and J. Karunakar)
7.
Water Requirement and Water Management in Vegetable
Crops
119-137
(Usha Kumari, Sudeepa Kumari Jha and Madhuri Pradhan)
8.
Waste to Wealth with Special Reference to Coconut,
Arecanut and Oil Palm
139-161
(Praveen R, Bandyopadhyay A, Surendra Babu M and Anjaneyulu A)

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Chapter - 1
Role of Plant Growth Regulators in Flower Crops
Authors
E Sathyanarayana
Department of Floriculture, Indira Gandhi Krishi
Vishwavidyalaya, Raipur, Chhattisgarh, India
Divya K
Landscape Architecture, SKLTS Horticultural University,
Rajendranagar, Hyderabad, Telangana, India

Page | 2

Page | 3
Chapter - 1
Role of Plant Growth Regulators in Flower Crops
E Sathyanarayana and Divya K
Abstract
The plant growth regulators are enormously important agent in the
integration of developmental activities. Environmental factors often exert
inductive effects by evoking changes in hormones in metabolism and
distribution within the plant. Apart from it, they also regulate expression of
intrinsic genetic potential of plants. Manage the genetic expression has been
demonstrated for the phytohormones at both transcriptional and translational
levels. Their exogenous application helps to improve the different
economically important and market desirable characteristics of flower crops.
The use of plant growth regulators is being practiced by the commercial
growers of ornamental plants and flower crops as a part of cultural practice.
There are different factors contributing to the efficacy of plant growth
regulators and the method of application plays key role in determining the
effectiveness of plant growth regulators, as PGRs can be effective if properly
absorbed by plants. Furthermore, development to focus the variables that can
affect the response of plant to plant growth regulators will help to increase
the efficiency of PGRs and avoid phytotoxicity which can maximize their
productivity.
Keywords: plant growth regulators, flowers, growth regulation, metabolism
Introduction
Flowers are associated with mankind since the dawn of the civilization.
They are symbol of love, beauty and tranquillity. In India, we have been
growing and using flowers for time immemorial. Flowers have become
integral part of our day to day life. Its use particularly for religious and social
offering has been on the increase due to changing life style. This has led to
the appreciation of the economic importance of flowers in addition to its
aesthetic value.
Globally, more than 140 countries are involved in cultivation of
floricultural crops. In India about 309 thousand hectares area was under

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cultivation in floriculture during 2017-18. In India, production of flowers
was 1,806 million tonnes of loose flowers and 704 million stems cut flowers
in 2017-18. The country has exported 25105.21 million tonnes of floriculture
products to the world for the worth of Rs. 479.42 crores in during 2015-16.
The major export destinations are United States, Netherlands, Germany,
United Kingdom, United Arab Emirates, Japan and Canada (APEDA 2017).
Plant growth regulators or phytohormones are organic substances
produced naturally in higher plants, controlling growth or other
physiological functions at a site remote from its place of production and
active in minute amounts. Thomann proposed the term Phyto hormone as
these hormones are synthesized in plants. Plant growth regulators include
auxins, gibberellins, cytokinins, ethylene, growth retardants and growth
inhibitors. Auxins are the hormones first discovered in plants and later
gibberellins and cytokinins were also discovered.
Factors Affecting Efficiency of PGRs: The effects of PGRs in plants
depend on various factors which play important role to achieve expected
results. These factors include the application method, time of application,
concentration of PGRs, plant species and also the environmental conditions
in which plants are grown (Grzesik, 1989). The intensity of applications is
also considered an important factor affecting the efficacy of PGRs, as some
plants respond well to a single application, but in most of cases, multiple
applications are beneficial to attain good results (Carey et al., 2007). The
other supplementary factors may include the chemical properties of PGRs
solution, particularly the pH, which plays a key role in the absorption of
PGRs by the plants. We discuss the application methods and their possible
advantages over one another.
Application Methods: There are various methods of application of
PGRs in plants reported in literature, mostly including foliar application
(Sajjad et al., 2014), drenching (Matsumoto, 2006), pre-plant sowing
(Currey and Lopez, 2010), seed priming (Pill and Gunter, 2001), pasting
(Saniewski et al., 2010), capillary string (Carswell et al., 1996) and injection
(de Vries and Dubois, 1988). The most commercially adopted methods for
ornamental plants are foliar spray, drenching and pre-plant. The research in
methods of application of PGRs reported that their early application such as
dipping before planting and substrate drenching at planting time are helpful
in obtaining desired results and also supportive in the efficient use of these
chemicals (Ranwala et al., 2005). The possible effects of PGRs depend on
their method of application due to the difference in their mode of absorption
by the plant, as some chemicals are absorbed only through root, leaves or

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stem, and some are absorbed through all mentioned organs having an
advantage to apply in either way, as ancymidol is absorbed by the roots,
stem and also leaves while B-Nine is only absorbed through foliar sprays but
Bonzi and sumagic are absorbed through the stem and root zone (Latimer,
2009). Foliar application and soil drenching are the most common methods
being used by commercial growers (Lee and Rho, 2000) and relatively
higher concentrations of PGRs are used in case of foliar sprays. The high
concentration of some PGRs can cause toxicity to the plant, sometimes
resulted in stunted growth (Cox and Keever, 1988) and also increases the
input cost. Foliar application can be more effective if applied at the right
stage of growth for controlling specific characters and it requires information
about the phenology of the target plant. The plant response to foliar
application also depends on the absorption rate and absorption is driven by
the environmental conditions, temperature and humidity are the most
important. Slightly high temperature, high humidity and longer drying time
are reported to increase the absorption of PGRs in plants.
Soil drenching is efficient method and PGRs are used in relatively lower
doses but residual effects of PGRs are retained in pots which sometimes
harm the plant. Drenching has advantage over foliar sprays because it
ensures the uniformity of treatment as each plant receives the measured
amount of PGRs and absorption occurs through root zone. This method is
suitable for PGRs having efficient absorption through root medium
(Sanderson et al., 1988). Substrate drenching requires more labor compared
to other methods; hence, it may not be cost effective if the labour is heavily
paid in that area.
Pre plant soaking of plant material in PGRs is reported an efficient
method but their use is relatively less common on commercial scale (Sajjad
et al., 2015). This method has advantages of time and labor saving, accurate
dosage over other methods, but disposal of residual solutions can be
problematic (Larson et al., 1987) as some PGRs including paclobutrazol,
uniconazole, ancymidol etc. cause toxicity to the surrounding environment
when disposed in an open environment. This problem can be solved by
applying the used solutions as a substrate drench for another time (Krug,
2004). There are certain factors which affect the effectiveness of this
method, and the most important are the concentration of PGRs and duration
of dipping of plant material in the solution (Ranwala et al., 2002).
Application of PGRs in lower dose favors their use economically on large
scale and use of low doses are effective if the duration of dipping is
increased, as increase in duration may increase the absorption of chemical
which can accelerate effectiveness.

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Auxins: Auxins promote stem elongation, inhibit growth of lateral buds
(maintains apical dominance). They are produced in the stem, buds, and root
tips. Example: Indole Acetic Acid (IAA). Auxin is a plant hormone
produced in the stem tip that promotes cell elongation. Auxin moves to the
darker side of the plant, causing the cells there to grow larger than
corresponding cells on the lighter side of the plant. This produces a curving
of the plant stem tip toward the light, a plant movement known
as phototropism.
Auxins are well known to initiate and stimulate the rooting of stem
cuttings (Hartmann et al., 2002), using a basal quick-dip in a concentrated
solution. Auxins are widely used in commercial plant propagation to
increase rooting percentage, hasten root initiation, increase the number and
quality of roots, and encourage uniformity of rooting. The most widely used
auxin for commercial rooting is IBA (Karimi et al., 2012). The two synthetic
materials, indole-3-butyric acid (IBA) and naphthalene acetic acid (NAA),
were even more effective than the naturally occurring or synthetic IAA for
rooting and widely used in rooting of tissue culture produced micro cuttings.
Both IBA and NAA (alone and combination) has been proved effective in
initiating roots in cuttings. These two hormones are reported to show
synergistic effect when used in combination of different concentrations.
Plant Propagation
There are three methods of propagation employed in flower crops viz.,
asexual or vegetative methods; sexual (through seed) and micro-propagation
(through tissue culture). Majority of ornamental plants are propagated by
vegetative methods such as stem and leaf cuttings, by bulbs, corms and
tubers.
A) Vegetative Propagation
Rose, chrysanthemum, carnation, gerbera. Auxins (IBA, NA. A and
IAA) are extensively used for rooting of the cuttings. The most commonly
and widely used auxin in promoting rooting is IBA (Indole Butyric acid)
followed by NAA and IAA. The mixtures of two or more auxins are more
effective (synergistic effect).
There are 3 Methods of Auxins Application for Inducing Rooting
1. Prolonged soak treatment for 24 hours at low concentrations (25-
100 ppm)
2. Quick dip method-dipping the basal portion of the cuttings in higher
concentrations of 1000-10000 ppm for 5 seconds to 2 minutes

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depending upon the nature of the cuttings, whether they are soft or
hard wood
3. Dipping the wet basal portion of the cuttings in tale mixed with
auxin (500-12000 ppm)
The success of rooting depends on some external and internal factors
like rainy season is the best, Photoperiod, Light, Temperature, Aeration,
Humidity, nutrient status of the cutting and endogenous auxins level in the
cutting for e.g. For bougainvillea, hard wood cuttings are used for their
propagation, 1000-3000 ppm, IBA in quick dip method is the best. NAA at
1000 ppm increase the percentage of rooting and reduce the time taken for
rotting.
B) Seed Propagation: All seasonal flowers, marigold, antirrhinum,
pansy, coreopsis, gaillardia, larkspur, petunia, phlox, Verbena,
sweet alyssum, candytuft, sweet sultan, lupine, etc
Seed treatment with lower doses of gibberellic acid improves
germination percentage, seedling vigour, final population stand, etc in many
seed propagated seasonal flowers.
C) Micro-Propagation: Orchids, Carnation, and Gerbera, Anthurium.
Cytokinins and auxins are widely used as supplements for induction
of shoots and roots, respectively in the tissue cultured plantlets
Susaj et al. (2003) reported that maximal rooting percentage was
recorded by using IBA 500 ppm for both cultivars (91% and 89%,
respectively), the maximal number of roots (50 and 47 roots) and the longest
roots at the end of vegetation (31 and 28 cm) were recorded by using IBA
1000 ppm, but the strongest roots and healthier seedlings were developed by
using IBA 500 ppm. Krishnamurthy et al. (2017) observed that significant
effect on all sprouting and growth parameters. Maximum bud sprouting
(78.8%), days to sprout (6), number of leaves / plant (10), chlorophyll index
(39.3 mg/g) in rose cuttings were recorded at 1500 ppm of IBA. The
optimum level of IBA was found in the range of 1000 and 1500 ppm, while
no such effect was evident of NAA. of these, IBA was superior to NAA for
its strong synergistic effect on all growth parameters.
Gibberellins: The most characteristic effects of GA3 on shoot growth
are increase in inter-node extension, leaf-growth, diameter of plant, number
of flowers, induce flowering and enhanced apical dominance. In its effects
on leaf expansion and on some forms of dormancy, GA3 simulates light. In
most photoperiodically sensitive plants, particularly in the form of long-day
photoperiod, induces increased shoot growth. GA3 has a similar effect. There

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is thus a fundamental unity in the effects of GA3 on plant development, in
which GA3 closely simulates effects usually induced in nature either by
exposure to light or by vernalization (Brian et al., 2008). It also has stimulant
effect on germination (Shohani et al., 2014). Gibberellins function as plant
growth regulators influencing a range of developmental processes in plants
life like stem elongation, germination, breaking dormancy, flowering, sex
expression, enzyme induction and leaf and fruit senescence. Spraying of GA3
recorded maximum plant height, plant spread and a greater number of leaves
and branches in chrysanthemum and other flowering plants (Lal & Mishra,
1986; Sujatha et al., 2002; Kumar et al., 2003; Rana et al., 2005).
Gibberellins initiates early flowering in many ornamental plants and
increases the number of flowers. Spraying of GA3 induced early flowering,
increased size of the flowers, fresh weight and dry weight of flowers in
Chrysanthemum (Nagarjuna et al., 1988); (Koriesh et al., 1989). Gibberellic
acid has been found beneficial in enhancement of plant growth and flower
production in marigold (Girwani et al., 1990). It has been reported that GA3
regulates the plant growth through both cell division and cell enlargement.
Spraying of GA3 gave maximum number of flowers per plant, flower weight
and flower yield (Kumar et al., 2003), while stalk length and spathe length
increase with foliar application of GA3 in anthurium (Dhaduk et al., 2007).
Whereas, (Devadanam et al. 2007) observed minimum number of days
required for spike emergence maximum spike length with foliar spray of
GA3. Lower concentrations of GA3 decreases number of days to 50%
flowering, increases number of leaves, spike girth, spike length, rachis
length, floret length and floret diameter in marigold and tuberose (Panwar et
al., 2006; Devadanam et al., 2007).
Seed Set and Yield
GA3 at lower concentration (5-10 ppm) improves fruit set and seed yield
in many of the seasonal flowers viz., pansy, petunia, phlox, and cineraria.
Seed treatment (by soaking) with IBA S ppm or GA3 5-10 ppm for 12-24
hours increased seed yield significantly than the control plants in balsam.
This is also improving the germination percentage. Kinetics (BA 100 ppm)
and GA3 (100 or 200 ppm) once or twice as foliar sprays improves the corms
and bulb yield in gladiolus, tuberose etc.
Plant Height Control
Growth retardants like Maleic hydrazide, SADH, CCC, B-nine are used
for height control of ornamental plants especially those grown in pots
terraces. Most of the retardants are specific in their action. A particular
retardant may dwarf only a particular plant species while it may not be

Page | 9
effective for others. An ideal growth retardant should be one which will be
universally effective, non-phy1otoxic and will prolong the postharvest. Life
without leaving any harmful residual effect. Many growth retardants are
available commercially for greenhouse flower production.
Among many plant growth regulators, chlormequat chloride (CCC)
(known commercially as Cycocel) is recommended for height control in
poinsettias, azaleas, geraniums and hibiscus. The chemical can be sprayed
onto the plant or applied directly to the substrate (1,000 to 3,000 mg/litre),
however a number of applications are necessary for efficacy. Furthermore,
possible side effects are chlorotic spots produced on the expanding leaves,
and high concentrations can cause necrotic spots on the plant. Paclobutrazol
(marketed as Cultar) is another plant growth regulator for height control that
can be effective when applied to the substrate at concentrations of 2 to 90
mg/litre.
Wanderley et al. (2014) studied that chlormequat chloride (CCC) had no
effect on the growth of A. graminifolia at the concentrations used whereas
paclobutrazol was effective in reducing the height of Arundina graminifolia
plants at a concentration of 5 mg/litre. However, concentrations of 10 and 20
mg/litre paclobutrazol were toxic to the plants, killing the new shoots. Sable
et al., (2015) reported that lowest plant height was observed in treatment
CCC 750 ppm spray. Minimum number of leaves/ plant (10.8) and leaf area
(64.8 cm2) were recorded in CCC 250 ppm/plant as foliar spray. Wasker et
al., (2015) studied that lowest plant height was observed in treatment CCC
750 ppm spray. Minimum number of leaves per plant and leaf area in
gladiolus was recorded in CCC 250 ppm per plant as foliar spray.
Dormancy Breaking
The chemicals like ethylene chlorohydrins or Ethereal, Ethephon,
Thiourea, Hydrogen cyanamide (Dor-break or Dormex) are used for
breaking the dormancy of gladiolus corms and cormels. Soaking in 1000
ppm ethereal for 24 hours breaks the dormancy in gladiolus.
Prevention of sprouting is also essential in certain cases like transporting
the bulbous material or storage of the material in order to reduce the
mortality following the sprouting. PGR's like Propyl gallate, MH, SADH, etc
can be used for extending the dormancy period.
Baskaran et al. (2014) studied that earliness in corm sprouting, spike
emergence, maximum duration and value of propagation coefficient was
recorded in GA3 500 ppm. Nomita et al., (2013) revealed that Application of
GA3 at 200 ppm induces early emergence of shoot (16.77 days), produced
maximum number of leaves (9.06) per plant, maximum spike length (92.66

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cm) and rachis length (72.25 cm). The ethylene releasing compound
(CEPA2-chloro ethyl phosphonic acid) promotes the germination of dormant
gladiolus corms (Ginzburg, 1974). And according to Denny and Miller
(1934) and Denny et al., (1938) reported that use of 3-5 ml of 40 per cent
ethylene chlorohydrin per litre of air space within a closed container for 3-5
days hastened sprouting of five gladiolus cultivars. But room temperature
was found effectively for early sprouting with application of ethephon 1000
ppm (Bhalla and Singh, 2000). Another statement reported by Umrao et al.,
(2006) where 500 ppm ethrel produced significantly the higher number of
sprouts per corm than its lower and higher doses and control.
According to Padmalatha et al., (2013) found that 2% solution to be
highly effective in breaking the dormancy of corms with high percentage of
sprouting, more number of buds sprouted per corm and number of big
cormels per plant was increased significantly and again Padmalatha et al.,
(2014) reported that 2% solution more effective in increasing the vegetative
growth but Chahal et al., (2013) reported that 500 ppm solution significantly
increased the plant height excluding spike up to maximum (50.71 cm).
Cytokinins: Cytokinins first endogenous cytokinin was isolated from
maize kernels named as zeatin. Synthetic cytokinins are kinetin,
benzyladenine and ethoxy methyladenine. There are some major roles of
cytokinin in the plants like Cell divisions, elongation and enlargement,
induction of flowering, apical dominance-overcoming, delay senescence,
tissue culture morphogenesis, breaking dormancy and improves the nitrogen
metabolism.
Extension of Cut Flower Life
The vase life of cut flowers can be prolonged significantly by adding
Kinetics, Ethylene inhibitors (MCPI), HQ compounds in the vase water.
Gibberellin helps in delaying senescence. It promotes the opening of
immature buds in gladiolus. Outer bracts of Gladiolus regulate production of
alpha-amylase Saeed et al., (2013) reported that the application of GA3 at
25–50 mg/litre renders the highest results for improving the vase life and
quality of gladiolus cut flowers.
Cytokinins play important role in delaying senescence. Level of
cytokinins decreases with ageing. BAP in holding solution delay senescence
of tuberose, Dip treatment of BA increases vase life of Anthurium. Mature
coconut water is considered as a rich source of sugar, electrolytes and
growth regulators such as auxin, gibberellins and cytokinin (Mamaril et al.,
1986) Agampodi and Jayawardena, 2007 observed that Anthurium cut
flower variety wild pink when treated with 50% Coconut water with 0.23%
NaOCl shows longest vase life (21 days). Coconut water has been
successfully used to increase the post-harvest life of Gerbera (Nair et al.,
2000)

Page | 11
Ethylene: A hydrocarbon gas, and commonly known as a ripening
hormone induces senescence in many flowers. Some important effects of
ethylene are: Sleepiness of petals in carnation, Epinasty in Poinsettia,
Abscission of petals or whole flowers, Inhibition or promotion of bud
opening in roses. Celikel et al., 2002 studied the effect of 1-MCP and
promalin on oriental lily and observed that 1- MCP play an important role in
preventing post-harvest deterioration of buds and flowers caused by
ethylene.
Apical Dominance/Enhancing Lateral Branching
To overcome the apical dominance, the routine is pinch or stop the main
shoot which enables production of lateral shoots, e.g. Carnation,
chrysanthemum. Use of PGR's like MH (600 or 1000 ppm), ethephon,
benzyl adenine etc. promotes branching (lateral shoots) equal to that
obtained through pinching. TIBA 25 ppm produces more branches than
pinching in marigold.
Regulation of Flowering
Growth regulators can be used for advancing or delaying the flowering
and also to induce uniform flowering in several flower crops. Seed set can
also be improved\'th foliar sprays of growth regulators. Thus, PGR's can be
used to enhance, hasten or delay the flowering time in several flower crops.
GA3 - 5-25 ppm causes early flowering in antirrhinum. GA3 - 10 ppm
applied 140 days after planting increases the number and size of flowers.
GA3 - I00 or 200 ppm in dahlia induced early flowering.
In general, auxins (NAA or IAA) at higher doses (>100 ppm) delay
flowering. GA3-100 & 150 ppm or 2, 4-D (1 ppm) and or IAA (150 ppm) at
early bud stage increases the flower size and weight.
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