Molecular Plant Breeding 2016, Vol.7, No.13, 1-11
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For callus induction and somatic embryogenesis of cereals, the best ex-plant sources are immature embryos (Wu
et al., 2002; Pellegrineschi et al., 2004). Callogenesis and organogenesis can be easily obtained from immature
embryos culture in wheat (Eapen and Rao, 1985; Redway et al., 1990). Best explant for regeneration is immature
embryos which can be obtained from callus culture. In case of embryogenesis, the developmental stage of
immature embryos is very important (Sears and Deckards, 1982).
6 Effect of Media on Callus Induction and Regeneration in Wheat
Concentration of growth regulators and type of medium can play a vital role in efficient regeneration system in
wheat for embryo culture. Raja et al. (2008) proposed that callus induction is better in N6 than MS media.
Likewise for regeneration, BAP is far better than kinetin. Exogenous applications of growth regulators can affect
the endogenous concentration, control of growth regulators and their biochemical aspects as well. Optimum
concentration of 2,4-D can be used for maximum callus induction (Munazir et al., 2010). Regeneration and callus
induction can be affected by both auxin and different sugar types. Sugar responses rely on type of auxin to be used
(Mendoza and Kaeppler, 2000). In mature and immature culturing of embryos, higher concentration of 4mg/l of
2,4-D is proved to be the best for Callogenesis but this concentration is harmful for regeneration of plants
(Khurana et al., 2002). From mature embryos, embryogenic callus formation is best at 1.5 mg/l 2,4-D medium
while in case of non-embryogenic callus, quantity of 2,4-D concentration may be increased up to 6 mg/l (Yasmin
et al., 2001).
A medium that contains 2,4-D 4 mg/l can produce large callus while maximum number of callus formed at 6 mg/l.
Maximum number of developed plants can be achieved at 1 mg/l kinetin concentration. Under lab conditions
development of plantlets on M10 medium was excellent and this medium proved best for rooting and propagation
of plantlets. Picloram and Dicamba showed healthiest callus production as compared to 2, 4-D. Concentration of
these growth regulators is as important as 2, 4-D concentration. Picloram helped in increasing the numbers of
shoot growth while when higher concentration of 2, 4-D used, necrotic callus and jair like growth can be observed.
Higher concentration of Dicamba does not have significant effect on shoot growth but it may have effect on
regeneration. (Parmar et al., 2012) observed different media and cultivars effect on Organogenesis and
Callogenesis on wheat. MS media proved best as compared to N6 medium but different cultivars showed different
responses to growth regulators at different levels. Genotypes like Inqlab-91 and Lasani-8 respond to a maximum
induction of callus (90%) and (78.8%) at 3 mg/l of 2, 4-D concentration. Tatara genotype showed 4.43% callus
formation at 2 mg/l, Chakwal-97 77.08% at 2.5 mg/l while Khyber and GA-02 expressed 74.30% and 65.97%
induction of callus respectively at 3.5 mg/l 2, 4-D. Without 2, 4-D in medium, there is no formation of callus
(Rashid et al., 2012). Proliferation and callus induction between different hormones, mostly Auxins are most
effective regulators. Callus induction and proliferation in cereals showed maximum response when 2,4-D was
used in mediums (Wen et al., 1991). Carbon presence in media acts as an osmotic agent which completes their
requirements for energy due to the photosynthetic activity
’
s reduction under in-vitro conditions. Sugar affected
the physiology of cell, its growth and differentiation massively (Gibson, 2000). Carbon source of organogenesis
and Callogenesis have to be improved so a reliable source of Carbon should be used for callus induction and
regeneration in plants (Mendoza and Kaeppler, 2002). Regeneration of shoot can also be affected by carbon
source (Kim et al., 2003).
7 Effect of Gelling Agent on Callus Induction and Regeneration
Different gelling agents can be used for solidification of media which helps embryos on top of culture mediums.
In plant tissue culture mostly agar is used as gelling agent (Clapham, 1973; Chu, 1978; Wang and Chen, 1980;
Liang et al., 1987). In wheat anther culture, agarose medium has been shown to enhance the embryo induction
(Henry et al., 1984; Lucketet al., 1991). Agarose is very costly but in different studies like wheat (Henry et al.,
1984), Barley (Powell et al., 1988 and Mourtizen and Holm, 1992), Maize (Nitsch et al., 1982, Dieu and Beckert,
1986), Rice (Chaleff and Stolarz, 1981) and Rye (Flehinghaiset al., 1991), it is proposed that by using agarose
medium, induction rate can be increased. Recently different studies showed that agar medium has inhibitory
