Plant regeneration in eggplant (Solanum melongena L.): A review

Abstract

Eggplant is highly responsive to various tissue culture techniques. Somatic embryogenesis and direct organogenesis are widely studied protocols in this crop, but potential of regeneration varies with genotype, explant and culture media supplemented with different combination and concentration of growth hormones. The genotype is the most important factor affecting somatic embryogenesis and organogenesis. Embryogenic competence occurs even within explant segments. Among growth regulators, auxins and cytokinins are of more significance as their ratio determines callogenesis, rhizogenesis, embryogenesis and regeneration in eggplant. Organogenesis and somatic embryogenesis related gene expression has been studied and transcripts have been analyzed through molecular studies. Efficient plant regeneration protocols would make a platform for exploitation of useful somaclonal variations, mutation breeding, induction of di-haploids, and genetic transformation with economically important genes for the improvement of eggplant.

Full text

Vol. 13(6), pp. 714-722, 5 February, 2014
DOI: 10.5897/AJBX2013.13521
ISSN 1684-5315 ©2014 Academic Journals
http://www.academicjournals.org/AJB
African Journal of Biotechnology
Review
Plant regeneration in eggplant (Solanum melongena L.):
A review
M. K. Sidhu1*, A. S. Dhatt1 and G. S. Sidhu2
1Department of Vegetable Science, Punjab Agricultural University, Ludhiana, 141004 India.
2School of Agricultural Biotechnology, Punjab Agricultural University, Ludhiana, 141004 India.
Accepted 5 January, 2014
Eggplant is highly responsive to various tissue culture techniques. Somatic embryogenesis and direct
organogenesis are widely studied protocols in this crop, but potential of regeneration varies with
genotype, explant and culture media supplemented with different combination and concentration of
growth hormones. The genotype is the most important factor affecting somatic embryogenesis and
organogenesis. Embryogenic competence occurs even within explant segments. Among growth
regulators, auxins and cytokinins are of more significance as their ratio determines callogenesis,
rhizogenesis, embryogenesis and regeneration in eggplant. Organogenesis and somatic embryogenesis
related gene expression has been studied and transcripts have been analyzed through molecular
studies. Efficient plant regeneration protocols would make a platform for exploitation of useful
somaclonal variations, mutation breeding, induction of di-haploids, and genetic transformation with
economically important genes for the improvement of eggplant.
Key words: Callus, somatic embryogenesis, organogenesis, hypocotyl, cotyledon, leaf.
INTRODUCTION
Eggplant (Solanum melongena L., 2n = 2x = 24) is a widely
adaptive and highly productive vegetable crop of tropical
and subtropical regions world, which suffers from various
abiotic and biotic stresses particularly insect-pests (Singh
et al., 2000; Kaur et al., 2004). To control the pests, various
biological and biochemical control measures have been
recommended, but cryptic nature of the pest is a big
hindrance in efficient management. Consequently, growers
use excessive and un-recommended pesticides, which is
a matter of concern for food safety, environmental degra-
dation, pest resistance and economics of the crop. The
non-availability of resistance in cultivated, cross-incom-
patibility with wild relatives (Solanum mammosum,
Solanum incanum and Solanum grandiflorum) and
inadvertent linkage drag of undesirable genes (Baksh and
Iqbal, 1979) are problems in developing intrinsic plant
resistance through conventional breeding approach.
Thus, use of biotechnological techniques can be an
alternative approach to tackle such issues.
In eggplant, somatic embryogenesis was first reported
from immature seed embryos of two different cultivars by
culturing on MS (Murashige and Skoog, 1962) medium
with supplementation of indole-3-acetic acid (IAA) (Yamada
et al., 1967). Although, this crop is most amenable to in
vitro culture, still its genetic make-up, explant and culture
media affect its regeneration potential (Kantharajah and
Golegaonkar, 2004). Genotype and explant are the most
important factor affecting somatic embryogenesis and its
*Corresponding author. E-mail: mksidhu@pau.edu. Tel: 919463664452.
Abbreviations: MS, Murashige and Skoog; BAP, 6-benzylamino purine; NAA, naphthalene acetic acid; IAA, indole,3,acetic acid;
IBA, indole,3,butyric acid; ZT, zeatin; KN, kinetin; NOA, naphthoxy acetic acid; TDZ, thidiazuron. 2,4-D, 2, 4-dichlorophenoxyacetic
acid; BA, 6, benzyladenine; GA3, gibberellic acid; TIBA, 2,3,5-triiodobenzoic acid; PCR, polymerase chain reaction; ADC, arginine
decarboxylase.

further regeneration (Afele et al., 1996; Sharma and
Rajam, 1995(a or b?); Dobariya and Kachhadiya, 2004;
Franklin et al., 2004; Huda et al., 2007; Mir et al., 2008).
The response of growth hormones in the culture media is
also variable within genotype and explant for somatic
embryogenesis and organogenesis (Slater et al., 2003).
The plant tissue culture methods also provide base for
the improvement of crop. To induce somaclonal variations,
in vitro mutations, herbicide tolerance, di-haploid induction,
genetic transformation of economically important genes
and development of somatic hybrids, efficient plant
regeneration protocol is required. Such advance tech-
niques in combination with conventional breeding give a
momentum to the improvement of a crop. Thus, realizing
the prospects for future research, relevant literature to
“Plant regeneration in eggplant (Solanum melongena L.)”
has been reviewed.
PLANT REGENERATION
Eggplant is highly amenable to cell, tissue and organ
culture (Kantharajah and Golegaonkar, 2004). Plant
regeneration from tissues of eggplant can be achieved
via embryogenesis (Ammirato, 1983) and organogenesis
(Flick et al., 1983). It can be done directly from cultured
explants or from calli of cell suspension (Fassuliotis et al.,
1981), anther (Khatun et al., 2006), microspore (Miyoshi,
1996; Lian et al., 2004) and protoplasts (Saxena et al.,
1981, 1987; Kim and Shin, 2005; Oda et al., 2006; Borgato
et al., 2007).
Somatic embryogenesis
Somatic embryogenesis is the process of a single cell or
a group of cells initiating the developmental pathway. It
was first reported in eggplant from immature seed
embryos cultured on MS medium supplemented with IAA
(Yamada et al., 1967). In general, it is independent or
inversely related to organogenesis (Matsuoka and Hinata,
1979). The different factors such as genotype, explant,
combination of growth hormones and some other factors
affect somatic embryogenesis in eggplant (Kantharajah
and Golegaonkar, 2004).
The genotype is the most important factor affecting
somatic embryogenesis and significant quantitative
differences in their capacity to form embroids among
different species like S. melongena, S. melongena var.
insanum, Solanum gilo, Solanum integrifolium and their
F1 hybrids, cultivars, and inbred lines (Alicchio et al.,
1982; Gleddie et al., 1983; Ali et al., 1991; Rao, 1992;
Anisuzzaman et al., 1993; Huda et al., 2007; Mir et al.,
2008, Zayova et al., 2008; Chakravarthi et al., 2010; Kaur
et al., 2011a and 2013). The differential responses for
regeneration of adventitious shoots and somatic embryos,
number of days to shoot initiation and mean number of
Sidhu et al. 715
shoots per callus (Sharma and Rajam, 1995a; Afele et
al., 1996; Dobariya and Kachhadiya, 2004) are also there
among cultivars. The molecular investigation using poly-
merase chain reaction (PCR) of different cultivars for the
induction of somatic embryos indicated that embryogenic
response is due to differences in mRNA expression and
consequently gene expression patterns (Afele et al., 1996).
The type of explant is also an important factor for
induc-tion of somatic embryos in eggplant (Kantharajah
and Golegaonkar, 2004). The use of immature seed
embryo (Yamada et al., 1967; Swamynathan et al.,
2010), hypo-cotyl (Alicchio et al., 1982; Sharma and Rajam,
1995a; Zayova et al., 2008; Swamynathan et al., 2010,
Ray et al., 2010, Kaur et al., 2011a and 2013), cotyledon
(Alicchio et al., 1982; Fari et al., 1995b; Zayova et al.,
2008; Tarre et al., 2004; Huda et al., 2007; Swamynathan
et al., 2010; Kaur et al., 2011a and 2013), leaf (Alicchio et
al., 1982; Macchia et al., 1983; Gleddie et al., 1986; Rao
and Singh 1991; Ray et al., 2010; Kaur et al., 2011a and
2013), root (Jahan and Syed, 1998; Franklin et al., 2004;
Mir et al., 2008; Swamynathan et al., 2010; Ray et al.,
2010), anther (Khatun et al., 2006), microspore (Miyoshi,
1996 and Lian et al., 2004) and protoplasts (Saxena et
al., 1981 and 1987, Kim and Shin, 2005, Oda et al., 2006;
Borgato et al., 2007) have showed different potential for
somatic embryogenesis. The differences in regenerative
potential of callus, number of shoots and time required for
rege-neration in sub-cultures are observed also
(Dobariya and Kachhadiya, 2004). The embryogenic
competence varies even within hypocotyl and leaf
segments (Sharma and Rajam, 1995b; Magioli et al.,
2001), which can be due to gradient phytohormones
(Ulvskov et al., 1992), develop-mentally regulated genes
(Momiyama et al., 1995), distri-bution of polyamine
content, arginine decarboxylase (ADC) activity and
metabolism correlated with the position in eggplant
(Fobert and Webb, 1988; Sharma and Rajam, 1995a,
1995b; Yadav and Rajam, 1997; Yadav and Rajam, 1998).
Size and age of explant did not affect callus-initia-tion
response, but showed marked influence on shoot rege-
neration response (Prakash et al., 2012).
Growth hormones like auxins, cytokinins, gibberellins
and abscisic acid play role in plant regeneration. However,
auxins and cytokinins are of more significance as their
ratio determines callogenesis, rhizogenesis, embryo-
genesis and regeneration. Among auxins, naphthalene
acetic acid (NAA), 2, 4-dichlorophenoxyacetic acid (2, 4-
D), and IAA generally favour callogenesis and naphthoxy
acetic acid (NOA), indole butyric acid (IBA) promotes
rhizogenesis (Kamat and Rao, 1978; Fobert and Webb,
1988) in eggplant. However, different concentrations of
NAA required for callusing (0.8 mgL-1), rooting (0.016
mgL-1), embryoid formation (8.0 mgL-1 NAA) and shooting
(no NAA) (Matsuoka and Hinata, 1979; Swamynathan et
al., 2010). Growing medium supplemented with IBA
resulted in white, friable, and slow growing callus with
roots; NAA gave green and fast growing callus; 2, 4-D

716 Afr. J. Biotechnol.
induced early callus (Macchia et al., 1983; Anwar et al.,
2002). Prolonged and continued callus sub-culture on
medium containing 2,4-D progressively lose its ability to
regenerate (Reynolds, 1986). Callus induction and somatic
embryogenesis on different medium supplemented with
different auxins (Alicchio et al., 1982; Gleddie et al., 1986;
Saito and Nishimura, 1994; Sharma and Rajam, 1995a; Fari
et al., 1995b; Magioli et al., 2001; Picoli et al., 2000; Mir et
al., 2008) is listed in Table 1. Among several cytokinins,
kinetin (Kin) is effective for shoot bud regeneration (Kamat
and Rao, 1978; Alicchio et al., 1982). Other cytokinins 6-
bemzylamino purine (BAP) or thidiazuron (TDZ) (Kaparakis
and Alderson, 2002), BAP (Picoli et al., 2000), 6-BA (Li et
al., 2003) also produced highest percentage of somatic
embryos in different explants of eggplant as listed in
Table 1. The cytokinins not only inhibit the NAA-induced
embryogenic response, but also act synergistically to pro-
mote callus growth (Gleddie et al., 1983).
Cytokinin-auxin interactions either promoted or
inhibited the development of shoots and roots depending
upon their ratio in the medium (Kamat and Rao, 1978). The
rege-neration also depends upon the type and
concentration of cytokinin. The high concentrations of
benzyladenine and all concentrations of kinetin promoted
organogenesis, while low concentrations of
benzyladenine induced somatic embryogenes as well as
organogenesis (Reynolds, 1986). Generally, higher level of
auxins and lower of cyto-kinine favours somatic
embryogenesis. MS / LS medium supplemented with
combination of 10 mgL-1 2, 4-dichloro-phenoxyacetic acid
and 1 mgL-1 kinetin (Reynolds, 1986), 2ip (γγ-
isopentyladenine) and IAA (Fassuliotis, 1975), 8 mgL-1
NAA and 0.1 mgL-1 Kin (Rao and Singh, 1991,
Swamynathan et al., 2010), Zeatin @ 2 mgL-1 and NAA
@ 0.01 mgL-1 (Fari et al., 1995), 1 mgL-1 NAA and 2 mgL-
1 BAP (Salih and Al-Mallah, 2000), NAA or IBA at 0.5
mgL-1 (Anwar et al., 2002), 6-BA+ ZT (Zeatin) and 6-
BA+IAA or ZT+ IAA (Yu et al., 2003; Li et al., 2003), 2.0
mgL-1 NAA + 0.05 mgL-1 BAP, 2.0 mgL-1 NAA and 0.5
mgL-1 BAP, 2 mgL-1 2,4-D + 0.05 mgL-1 BAP and 2 mgL-1
NAA+2.5 mgL-1 BAP (Rahman et al., 2006; Huda et al.,
2007; Hossain et al., 2007; Zayova et al., 2008;
Chakravarthi et al., 2010) induced the callus in eggplant
(Table 1).
Gene expression during initial stage of somatic
embryogenesis in eggplant revealed that 2,4-D induces
specific alteration in gene expression due to differential
display of RNA (Momiyama et al., 1995). In spite of this,
an antioncogen homolog and the activation of retro-
transposon were described during early stages of
somatic embryogenesis (Momiyama et al., 1996).
Differential display and restriction fragment length poly-
morphism (RFLP) analysis resulted in the identification of
one organogenesis and two somatic embryogenesis
related transcripts (Bucherna et al., 2001).
The frequency of embryogenesis depended on optimal
ratio of NO3- : NH4+ (2:1) in the medium. The optimal su-
crose concentration of the medium was 0.06 M, whereas,
elevated or reduced level inhibited the embryo-genesis in
eggplant (Gleddie et al., 1983). Sucrose concentrations of
0.2 - 0.5% induced somatic embryo-genesis, 1% led to
embryogenesis and shoot regene-ration and 2%
provoked maximum shoot regeneration, whereas,
increased sucrose levels from 3 to 5% decreased the
regenerating ability. The lowered sucrose concen-tration
from 2 to 0.2% also caused complete bleaching, which
can be used for selection of herbicide-resistant mutants
(Farooqui et al., 1997). The pesticides like Endlosulfan,
Rogor and Kitazin in relation to their concentrations also
affected callus induction and multiple shoot formation in
eggplant. The callus growth decreased with increasing
level of pesticides in medium. Some concentrations (50 -
500 ppm) of pesticides in the medium also formed
abnormal callus growth and shoot induction. Among
pesticides, Rogor (25 ppm) induced maximum callus
(76.0%) and shoots (11.0), whereas, Kitazin 45% EC
showed more inhibitory effect than the Endosulfan and
Rogor (Sammaiah et al., 2011a, 2011b).
Plant regeneration from tissue culture of S. melongena
L. can be achieved via embryogenesis (Ammirato, 1983)
and organogenesis (Flick et al., 1983). Light could help
the development of adventitious rooted shoots from callus
(Macchia et al., 1983; Salih and Al-Mallah, 2000). High
concentration of 2ip and low concentration of IAA led to
differentiation of leaflets with morphogenetic variation in
leaves and cytological studies of plants indicated them
genetically aberrant (Fassuliotis, 1975). LS medium without
hormones also regenerated plant from callus (Alicchio et
al., 1982). Also, MS medium supplemented with different
concentrations and combinations of cytokinins and auxins
(Table 1) produced more shoot primordial and rooted
shoots in calli derived from cotyledon, hypocotyls, leaf and
root explants (Macchia et al., 1983; Anwar et al., 2002;
Yu et al., 2003; Franklin et al., 2004; Rahman et al.,
2006; Chakravarthi et al., 2010). Plants regenerated
through somatic embryogenesis had somaclonal varia-
tions. Frequencies of somaclonal variations in leaf shape,
plant height, fruit shape and pollen fertility was higher
with NAA than that of 2, 4-D (Hitomi et al., 1998). There-
fore, the future research would determine the importance
of new somaclonal lines for genetic variability of eggplant
(Zayova et al., 2010, 2012).
Organogenesis
Organogenesis is the morphogenesis of plantlets directly
from explants without the intervention of callus in the
culture. This omits the callus and embryoid phases, reduces
use of auxin from the in vitro culture and leads to direct
formation of new shoots from the explants. Anatomically
and histolosically, longitudinal sections of leaf explants
formed numerous meristematic zones within the tissue,
that subsequently converted into shoot buds (Mukherjee
et al., 1991). The formation of shoot buds was characterized

Sidhu et al. 717
Table 1. Somatic embryogenesis in eggplant.
Explant
Somatic embryogenesis
Shoot induction
References
Immature embryo
cultures
MS + IAA
Yamada et al.
(1967)
Hypocotyl
MS + 0.016 mgL-1 - 0.8 mgL-1 NAA (callus), MS
+ 8.0 mgL-1 NAA(embryogenesis)
Hormone free MS
Matsuoka and
Hinata (1979)
Hypocotyl, otyledon,
leaf
LS+ 0.4 mgL-1 2,4-D
Hormone free LS
Alicchio et al.
(1982)
Leaf
MS+10 mgL-1 NAA
Basal MS
Gleddie et al.
(1986)
Leaf
Kao/ NT (liquid)+ 10 mgL-1 NAA or Kao/
NT(liquid)+ 2 mgL-1 2,4-D, Kao/ NT(liquid)+ 1
mgL-1 2,4-D
Kao/ NT (solid)+ 10 mgL-1 NAA
or Kao/ NT(solid)+ 2 mgL-1 2,4-
D, Kao/ NT(solid)+ 1 mgL-1 2,4-D
Gleddie et al.
(1986)
Stem segments
MS+ 10mgL-1 2, 4-D +1 mgL-1 kin
MS+ +1 mgL-1 kin
Reynolds (1986)
Cotyledon
MS+1.0-5.0 mgL-1NAA
Hormone free MS
Fobert and Web
(1988)
Hypocotyl
MS+ 0.5-2.0 mgL-1 2,4-D
Hormone free MS
Ali et al. (1991)
Leaf
MS+ 8 mgL-1NAA + 0.1 mgL-1 Kin
Basal MS
Rao and Singh
(1991)
Leaf
MS +0.5-2.0 mgL-1 NAA
Basal MS
Rao (1992)
Cotyledon
50 αM 2,4-D
half-strength MS solid medium
without hormones
Saito and
Nishimura( 1994)
Hypocotyl, cotyledon
and leaf
MS+ 32.2 µM (hypocotyls) and, MS + 10.7 µM
(cotyledon and leaf)
-
Sharma and
Rajam (1995a)
cotyledon
TMG+ 2 mgL-1 Zeatin + 0.01 mgL-1
NAA(callus), TMG+4 mgL-1 NAA(SE)
TMG+ 2 mgL-1 Zeatin + 0.01
mgL-1 NAA(callus), TMG+4 mgL-
1 NAA(SE)
Fari et al. (1995)
Leaf
10.73 mM NAA+0.5m M putriscine
-
Yadav and
Rajam (1997)
Stem and leaf
MS+ 1 mgL-1 NAA + 2 mgL-1 BAP
MS+ 1 mgL-1 NAA + 2 mgL-1 BAP
Salih and Al-
Mallah (2000)
Hypocotyl,
cotyledon, leaf,
epicotyl
MS + 54 αM
½ MS+1% phytagel
Magioli et al.
(2001)
Hypocotyl and
cotyledon
MS +2.5-10.0 mgL-1 NAA
-
Picoli et al.(
2000)
Leaf
MS +2 mgL-1 6-BA+0.5 mgL-1 IBA,
MS +2 mgL-1 6-BA+0.5 mgL-1 NAA
MS +2 mgL-1 6-BA+0.5 mgL-1
IBA, MS +2 mgL-1 6-BA+0.5 mgL-
1 NAA
Anwar et al.
(2002)

718 Afr. J. Biotechnol.
Table 1. Contd.
Cotyledon, hypocotyl
MS +1.0-2.5 mgL-1 6-BA
MS +1.0-2.5 mgL-1 6-BA
Yu et al. (2003)
cotyledon
54 mM NAA
MS basal
Tarre et al.
(2004)
Root
MS + 0.45 mM TDZ (Thidiazuron) and 13.3 mM
BA (6-benzyladenine)
MS + 0.45 mM TDZ (Thidiazuron)
and 13.3 mM BA (6-
benzyladenine)
Franklin et al.
(2004)
Cotyledon and young
leaf explant
MS+1 mgL-1 BA
MS+2 mgL-1 KIN
MS+1 mgL-1 BA+1mgL-1 KIN
MS+2 mgL-1 BA+1mgL-1 KIN
MS+2 mgL-1 KIN+1 mgL-1 BA
MS+2 mgL-1 BA+2 mgL-1 KIN
MS+1 mgL-1 BA
MS+2 mgL-1 KIN
MS+1 mgL-1 BA+1mgL-1 KIN
MS+2 mgL-1 BA+1mgL-1 KIN
MS+2 mgL-1 KIN+1 mgL-1 BA
MS+2 mgL-1 BA+2 mgL-1 KIN
Dobariya and
Kachhadiya
(2004)
Cotyledon and midrib
MS+ 2.0 mgL-1 NAA and 0.05 mgL-1 BAP
MS+ 2.0 mgL-1 Zeatin and 1.0
mgL-1 BAP
Rahman et al.
(2006)
Cotyledon
MS+ 2.0 mgL-1 NAA and 0.05 mgL-1 BAP, MS+
1.0 mgL-1 BAP+ 0.5 mgL-1 GA3
MS+ 2.0 mgL-1 NAA and 0.05
mgL-1 BAP, MS+ 1.0 mgL-1 BAP+
0.5 mgL-1 GA3
Huda et al.
(2007)
Cotyledon
MS+ 2.0 mgL-1 NAA + 0.05 mgL-1 BAP, MS+ 2.0
mgL-1 2,4-D+ 0.05 mgL-1 BAP,
MS+ 0.75 mgL-1 NAA+ 1.5 mgL-1
BAP,
MS+ 2.0 mgL-1 NAA+ 0.5 mgL-1
IBA
Hossain et al.
(2007)
Hypocotyl, cotyledon
and root
MS+ 1.0mgL-1 NAA (hypocotyls), 1.5 mgL-1 NAA
(cotyledon) and 2.0 mgL-1 NAA (root)
MS+ 2.5 mgL-1 IAA + 0.5 mgL-1
BAP
Mir et al. (2008)
Cotyledon hypocotyl
MS + 2.0 mgL-1 NAA + 0.5 mgL-1 BAP
Hormone free MS
Zayova et al.
(2008, 2012)
immature seed
embryo, cotyledon,
shoot
MS+ 10.5 mgL-1 NAA(cotyledon), MS+ 8.0
mgL-1 NAA+ 0.1 mgL-1 KN ( seed embryos)
Hormone free MS medium
Swamynathan et
al. (2010)
Hypocotyl, root, leaf
MS + 2.0 mgL-1 BAP + 0.5 mgL-1 NAA
MS + 2.0 mgL-1 BAP + 0.5 mgL-
1 NAA
Ray et al., 2010
Cotyledon
MS+ 2 mg/ mgL-1 l NAA+2.5 mgL-1 BAP
MS+2.5 mgL-1 each BAP and KN
Chakravarthi et
al. (2010)
Cotyledon
MS + 2 mgL-1 NAA
MS+0.5 mgL-1 IAA +3.0 mgL-1
BAP
Sammaiah et al.
(2011a& 2011b)
Hypocotyl,
cotyledon and root
MS+2.5 mgL-1 /l IAA + 0.5 mgL-1 BAP
MS+2.5 mgL-1 IAA + 0.5 mgL-1
BAP
Mir et al. (2011)
Hypocotyl, cotyledon
and leaf
MS + 1.5 mgL-1 IBA + 1.0 mgL-1 BAP
MS + 2.5 mgL-1 BAP + 1.0 mgL-
1 kin + 0.2% activated charcoal
Kaur et al. (2013)
shoot
tip, hypocotyls,
leaves, stem
MS+0.6 mgL-1 2, 4-D
MS+0.2 mgL-1 BAP, MS+0.6
mgL-1 NAA, MS + 0.4 mgL-1 IAA
Robinson and
Saranya (2013)

Sidhu et al. 719
Table 2. Organogenesis in eggplant.
Explant
Direct organogenesis
References
Hypocotyl
MS + 2.8-11.4 µM IAA, MS + 4.7 µM KIN, MS + 2.3-4.6 µM ZT
Kamat and Rao 1978
Leaf
MS + 2.0 mgL-1 Kin+ 88mM sucrose, MS + 2.0 mgL-1 Kin+ 5.5
and 11mM glucose
Mukherjee et al., (1991)
Leaf
MS + 1.0 mgL-1 BAP +0.5 mgL-1 ZT
Perrone et al., 1992
Hypocotyl, cotyledon and leaf
MS + 11.1 µM BA and 2.9 µM IAA
Sharma and Rajam, 1995a
Cotyledon
TMG + 2 mgL-1 Kin
Fari et al., 1995
Leaf
MS + 0.1 μM TDZ and MS + 10 or 20 μM2ip
Billings et al., 1997
Leaf
MS + 0.001-1 μgml-1TDZ and MS + 5-20 μgml-1 2ip
Jelenkovic and Billings 1998
Leaves and cotyledons
MS + 0.2 wm TDZ
Magioli et al., 1998
Cotyledon and hypocotyl
MS + 0.1 mgL-1 IAA
Picoli et al., 2000
Leaf and stem
MS + 0.5 mgL-1 NAA
Taha and Tizan, 2002
Cotyledon and leaf
MS + 0.1 or 0.2 µM TDZ
Gisbert et al., 2006
Cotyledon, hypocotyl, shoot tip ,
root
MS + 1.0 mgL-1 BAP + 1.0 mgL-1 Kin
Sarker et al., 2006
Meristem
MS(liquid)+ 2.0 mgL-1 BAP, MS(semisolid)+ 2.0 mgL-1 BAP+1
mgL-1 NAA, MS(semisolid)+ 1.0 mgL-1 BAP
Sharmin et al., 2008
Cotyledonary nodes
MS + 2.0 mgL-1 BAP + 1.0 mgL-1 2iP
Kanna and Jayabalan, 2010
Hypocotyls, cotyledon and leaf
MS + 2.5 mgL-1 BAP + 1.0 mgL-1 KN
Kaur et al., 2011
Cotyledon
MS+ 1.0 mgL-1 Zeatin
Prasad et al., 2011
Leaf
MS+ 1.0 mgL-1 TDZ+ 4.02 g/l nitrogen, +2.36% sucrose
Naveenchandra et al., 2011
Cotyledon, hypocotyl and leaf
MS + 2.0 mgL-1 BAP + 0.5 mgL-1 Kn
Shivraj and srinath, 2011
Cotyledon nodal segments and
shoot tip
MS + 2.0 mgL-1 BAP + 1.0 mgL-1 Kn
Bhat et al., 2013
Hypocotyl (inverted)
MS + 0.5 mgL-1 TDZ
Mallaya and Ravishankar,
2013
by the appearance of shoot apex with the developing leaf
primordial (Sarker et al., 2006). Genotype played important
role in organogenesis of the shoots directly from the
explants. Different varieties and species such as Solanum
aethiopicum, Solanum macrocarpon showed different
potential in direct plant regeneration, where, 70 - 100%
explants with a mean of two to seven shoots per explant
were obtained (Gisbert et al., 2006; Sarker et al., 2006;
Shivraj and Srinath, 2011).
The direct regeneration potential also varied with the
tissue system used on a well defined medium. Different
explants had differential response to regeneration (Sharma
and Rajam, 1995a; Magioli et al., 1998; Zhang, 1999;
Taha and Tizan, 2002; Sarker et al., 2006; Gisbert et al.,
2006; Kanna and Jayabalan, 2010; Shivraj and Srinath,
2011; Kaur et al., 2011) on different media combinations
containing cytokinins and auxins. Hypocotyl and cotyledon
explants had different morphogenetic potential for numbers
of adventitious shoots (Sharma and Rajam, 1995a; Zhang,
1999). Explant age also affected regeneration as younger
leaves showed better organogenesis than mature ones
(Zhang, 1999).
Different growth regulators such as auxins and
cytokinins have been used for direct organogenesis (Table
2). Among these, auxins had influenced the regeneration of
shoot buds and roots in eggplant (Kamat and Rao, 1978).
Presence of any cytokinin in the media led to shoot
organogenesis from leaf explants (Gleddie et al., 1983;
Polisetty et al., 1994). However, combinations and con-
centrations of auxins and cytokinin should be optimum for

720 Afr. J. Biotechnol.
having maximum number of regenerated shoots in egg-
plant (Mukherjee et al., 1991; Fari et al., 1995; Magioli et
al., 1998; Zhang, 1999; Picoli et al., 2000; Sarker et al.,
2006). Combinations of two cytokinins had shown
proficient shoot differentiation (2 to 7 shoots per explant)
in eggplant (Iannamico et al., 1993; Billings et al., 1997;
Jelenkovic and Billings, 1998; Gisbert et al., 2006; Shivraj
and Srinath, 2011; Kanna and Jayabalan, 2010).
Low sugar concentrations enhanced shoot
regeneration, where, higher concentration of glucose and
lower of sucrose showed better effects (Mukherjee et al.,
1991; Polisetty et al., 1994). Shoot regeneration process
had also been affected by the gelling agents and agar
was found superior to gerlite (Perrone et al., 1992).
Peptone had no effect on reducing hyperhydric shoots of
S. melongena and S. integrifolium. Culture vessels with
gas-permeability by membrane filter reduce the
percentage of hyperhydric shoots and increased survival
rate than sealed vessels (Takamura et al., 2006).
Elongation and rooting of plantlets
Small shoots require elongation in vitro. Hormone free
MS or 1/2MS has been most frequently used for the
elongation plantlets in eggplant (Gleddie et al., 1983;
Magioli et al., 1998; Franklin and Sita, 2003; Franklin et
al., 2004; Gisbert et al., 2006; Sarker et al., 2006;
Borgato et al., 2007; Mir et al., 2011). Sometimes, MS
fortified with gibberellic acid (GA3) (0.1 to 1.5mgL-1)
(Shivraj and Srinath, 2011), 0.5 mg/l 2,3,5-triiodobenzoic
acid (TIBA) and 0.1 mg/l GA3 (Naveenchandra et al.,
2011) Zeatin and Augmentin (Billings et al., 1997)
elongated eggplant shoots also.
Eggplant developed roots upon transfer to medium
containing IAA (Fassuliotis, 1975), hormone-free MS
medium (Saxena et al., 1981; Gleddie et al., 1983; Taha
and Tizan, 2002; Gisbert et al., 2006; Sarker et al., 2006)
and MS medium containing 0.1 -1.5 mgL-1 3-indol butyric
acid (Jahan and Syed, 1998; Borgato et al., 2007;
Sharmin et al., 2008; Chakravarthi et al., 2010; Shivraj
and Srinath, 2011; Zayova et al., 2012; Robinson and
Saranya, 2013, Bhat et al., 2013). Half strength MS
medium containing 0.08 mgL-1 NAA also developed roots
of 90% shoots (Kanna and Jayabalan, 2010). Half-
strength MS medium supplemented with 0.6 wm IAA
(Magioli et al., 1998) and 5.0 mg sucrose and 2.5 gl-1
gellan gum (Kim and Shin, 2005; Oda et al., 2006)
induced rooting of plantlets. Quarter strength hormone
free MS medium induce roots also (Dobariya and
Kachhadiya, 2004), however, MS+ 3.0 mgL-1 BAP was
used for better root induction with respect to average
number (14 - 15) and mean length (12 cm) (Rahman et
al., 2006).
Hardening and field establishment
Most of the species grown in vitro require acclimatization
process in order to ensure that sufficient number of plants
survive and grow vigorously on transferring to the soil. It
took 3-4 months from initiation to establishment in pots ex
vitro for 99% survival rate (Polisetty et al., 1994), however,
rooted plants can be acclimatized in 14 days with 80%
success (Salih and Al-Mallah, 2000; Taha and Tizan,
2002; Chakravarthi et al., 2010; Kanna and Jayabalan,
2010; Shivraj and Srinath, 2011; Kaur 2011a, b). Rooted
shoots were transferred for establishment in polythene
bags filled with a potting mixture of sand, soil and FYM in
1:2:1 ratio (Dobariya and Kachhadiya, 2004). The
plantlets were successfully established in polycarbonated
polyhouse with 100% survival rate (Bhat et al., 2013).
When root system was developed well, plants were
hardened in the glass house and transferred to the field
for flowering, fruiting and seeding (Kamat and Rao, 1978;
Gleddie et al., 1983; Jahan and Syed, 1998; Magioli et
al., 1998; Franklin et al., 2004; Sarker et al., 2006).
CONCLUSIONS
Research work has mainly been focused on the develop-
ment of regeneration protocol, somaclonal variations and
their physiological as well as morphological aspects in
eggplant. An efficient plant regeneration protocol is a pre-
requisite for the exploitation of various biotechnological
techniques. However, practical utility of the basic protocol
is still far away. It can serve as a platform for the transfer
of economically important traits through genetic engi-
neering, inducing somaclonal variations, in vitro muta-
tions, double-haploids induction, development and utilize-
tion of somatic hybrids, determining herbicide or pesticide
tolerance limits in eggplant. Therefore, a remark-able pro-
gress can be made in eggplant improvement through the
combination of conventional and biotechnological
approaches.
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