The depletion of world petroleum reserves, oil price hikes and the increased environmental concerns have stimulated the search for alternative sources to petroleum based fuel, including diesel fuel. Biodiesel extracted from vegetable oil is one such renewable alternative under consideration. The production of biodiesel would be cheap as it could be extracted from non-edible oil sources (Openshaw, 2000; Francis et al., 2005; Chhetri et al., 2008; Dermibas, 2009).
Jatropha curcas L. (physic nut), a non-edible oil bearing and drought hardy shrub with ecological and other advantages belonging to the family Euphorbiacea, was found to be a potential renewable source of biodiesel (Raju and Ezradanam, 2002; Chhetri et al., 2008; Idu et al., 2009). In recent years, the plant has received extensive attention due to its medicinal importance and for its seed oil as a potential commercial source of biodiesel. The oil can be used as a mixed fuel for diesel/gasoline engines after transesterification (Achten et al., 2007; Abdullah et al., 2011; Ram et al., 2012). The seed or oil is not edible due to the presence of a toxic substance known as curcin (Joubert et al., 1984 and Makkar et al., 1998). The oil is conventionally used in making soaps, dyes, candles, paints, lubricants and medicinally as a purgative (Kumar and Sharma, 2000; Misra and Misra, 2010).
Conventionally, the seeds and cuttings are used for its propagation but the constraints to seed germination caused by dormancy induced by hard seed coat, poorly developed endosperm and abortion of hybrid embryos in seeds and the seasonal limitation of cuttings are the major constraints. It has also been reported that vegetative cuttings are not deep rooted and are easily uprooted as they do not form a tap root system (Sujatha and Mukta, 1996; Openshaw, 2000; Idu et al., 2009). To overcome the above mentioned difficulties in conventional methods, in vitro cultivation of the plant is the better option as it offers rapid and continuous supply of better planting materials (Sardana et al., 1998; Sathya, 2007; Ram et al., 2012). The evaluation of micropropagated J. curcas has revealed that they were at par with seed propagated plants in terms of yield and yield related traits (Sujatha and Mukta, 1996; Ahmed et al., 2012).
Plant tissue culture and micropropagation techniques play a great role in genetic conservation programs and management of botanical collection of plants in a very efficient manner (Smith, 2000; Kyesmu et al., 2004; Sathya, 2007). Embryo culture techniques can eliminate the constraints to seed germination caused by seed coat and endosperm and provide a long term storage of germplasm in a disease and insect free form (Okezie et al., 1994).
In vitro grown plants are devoid or insufficient of photosynthesis, due to growth taking place in condition unsuitable for photosynthesis. So, they need a readily available source of carbon which is usually provided in the culture medium at 3 % (Garcia et al., 2002; Sadhu, 2007; Okafor et al., 2012; Ram et al., 2012; Rafique et al., 2013). Murashige and Skoog medium (MS) is the most commonly and widely used culture medium in most plant tissue culture laboratories (Jesus et al., 2003; Kyesmu et al., 2004; Ram et al., 2012). Among the sugars, sucrose is used as a principal carbon source for in vitro plant culture probably because it is the most common carbohydrate in the phloem sap of many plants. The carbon source serves as energy and osmotic agent to satisfy the energy need and support the growth of plant tissue in vitro (Paiva and Otoni, 2003; Misra and Misra, 2010; Ram et al., 2012).
However, optimum level of sucrose varies for different crops or species (Paiva and Otoni, 2003; Hartmann et al., 2007; George, 2008). The optimization of medium composition in general and sucrose in particular is an important approach to hasten the micropropagation process and improve the quality of regenerated plantlets through culture of cells, tissue and organs (Lin et al., 2002; Jesus et al., 2003; Paiva and Otoni, 2003; Danso et al., 2011).
This study aimed at in vitro plantlet regeneration and further optimization for suitable sucrose concentration requirement. The experiment was conducted to evaluate the efficacy of sucrose as a carbon source and different sucrose concentrations on in vitro plantlet regeneration of J. curcas from mature zygotic embryo explants.
In view of these, the objectives of this study were:
- To establish the optimum level of sucrose as carbon source for high frequency in vitro plantlet regeneration of Jatropha curcas
- To study the extent to which the various growth parameters of plantlets produced are influenced by the carbon source employed in this study.