1. INTRODUCTION
Jatropha (Jatropha curcas L.) is a succulent shrub or small tree,
which belongs to the large Euphorbiaceae family. It is a multi-purpose
plant which has been exploited for various purposes such as soil erosion
control, firewood, hedges, green manure and traditional medicines
(Carels, 2013). On the other hand, the seed oil of Jatropha is also used
as soap manufacturing ingredient, paints and as a biodiesel to
substitute kerosene (Kumar and Sharma, 2008). Among many other
attributes and importance of Jatropha, in recent years it has gotten
special attention for being a priority feed stock in production of
biodiesel.
Biodiesel is an alternative diesel fuel made from different types of
renewable sources such as plant oils and animal fats. It is
environmentally friendly fuel with low emission profiles and also
non-toxic and biodegradable (Abdulla et al., 2011). Among the
plant species producing raw materials for biofuels, Jatropha is one of
the plant species that stimulates the highest interest in tropical and
subtropical regions. It has been identified as most suitable oil seed
bearing plant due to its various favorable attributes like high oil
content, hardy nature, adaptability in a wide range agro-climatic
conditions, need for less irrigation and less agricultural inputs, pest
resistance, short gestation periods and suitable traits for easy
harvesting (Heller, 1996; Edrisi et al. , 2015).
Because of the increased interest in the potential of Jatropha as an
energy plant, more attention is given to methods that allow the mass
production of elite material. However, several challenges remain before
that plant biomass can be commercially exploited. Its supply on a large
scale requires massive production of phenotypically uniform plant
material of a very high quality within a short time-frame that is
adapted to the growth conditions of the plantation areas (Medza
Mve1et al. , 2013).
Traditionally Jatropha is propagated through seed and vegetative
cutting. The most common method to obtain Jatropha plantlets is by seed
germination, which can be severely limited by poor seed viability, low
germination percentage, inadequate rooting in growth plants in small
pots and the delayed rooting of seedlings (Openshaw, 2000). Vegetative
propagation of Jatropha through stem cuttings has been achieved however
the established plants are not deep rooted and hence, they easily get
uprooted when cultivated in lands with poor top soil (Openshaw, 2000).
Therefore, to improve cultivation of this crop, the traditional
inefficient mode of propagation should be changed and proper techniques
need to be studied and put in place for mass production of the Jatropha
plants.
The in vitro multiplication would be a useful alternative method
for mass production of plant. It offers an opportunity for large scale
production of uniform disease free planting material in a relatively
short period of time and independent of the season (George, 2008).
Callus induction, culture and regeneration optimization in vitroare important steps in the process of plant propagation and genetic
transformation (Oliveira et al. , 2017). Therefore, efficient
callus induction and in vitro regeneration system is highly
required to enhance the use of modern techniques in genetic improvement
(Pan et al ., 2010; Jose et al., 2012). Callus also can be
used for long term conservation of plant tissues by maintaining them
under slow growth conditions, and as target tissue for genetic
transformation (Ali et al ., 2007).
Among factors influencing the process of in vitro callus
induction, the plant growth regulators (PGRs) can be considered as one
of the most important ones. Two relevant classes of PGRs that are used
to control organ and tissue development are the auxins and cytokinins
(Ismail et al ., 2013). Both callus induction and plant
regeneration from explants require the presence of appropriate
concentrations and combinations of plant growth regulators in the
culture media (Kalimuthu et al. , 2007). A sub-optimal culture
medium may cause physiological disorders or death of tissue. Studies of
auxins and cytokinins separately or their combinations to initiatein vitro callus induction and regeneration in Jatropha were
reported (Sujatha et al., 2005; Deore and Johnson, 2008; Oliveiraet al. , 2017). In addition, genotypic differences in shoot
organogenesis have been observed in a wide range of plant species
including Jatropha. It has been reported that regeneration in Jatropha
is highly genotype dependent (Kumar and Reddy, 2010; Kumar et
al ., 2010; Mweu et al ., 2016). Keeping in view of the importance
of the crop and its propagation methods, the present study was designed
to optimize the concentrations and combinations of different growth
regulators on callus induction and proliferation of shoots from three
Jatropha accessions using leaf explants.