India is one of the highest petroleum consuming nations in the world. India's economy has often been unsettled by its need to import petroleum. This coupled with deleterious effects of increased use of fossil fuels on the environment makes it imperative for us to find an environment friendly replacement. Bio-fuels, has been considered as a viable option to replace fully or partially India's dependence on fossil fuels. Jatropha curcas is a plant with tremendous untapped potential as a source of biodiesel. It is a monoecious shrub with staminate (male) and pistillate (female) flowers being present on same inflorescence. The inflorescence has more male flowers as compared to female flowers; the average male to female flower ratio being 29:1 [1]. This ratio leads to a very poor seed yield. A change in flower sex ratio towards a greater number of female flowers could increase seed yield and hence oil yield making the plant a commercially viable option. Phytohormones are important factors regulating floral sex expression in plants [2, 3, 4, and 5]. Among phytophormones the role of Auxin, Ethylene and Gibberellin (GA) has been widely studied and is documented in recent studies [6, 7, and 8]. The effect of exogenous phytohormones on flower sex ratio depends on species of plant. GA has been shown to promote female flowers in maize and castor bean, but on contrary it increases masculine features in hemp, spinach and cucumber [9, 10]. In several plant species such as Arabidopsis and Tomato, GA deficiency leads to male sterility because of abnormal anther development [11, 12]. Though most studies have reported an increase in fruit yield in response to GA, Almeida et al. [13], have reported decreased fruit yield in response to GA in oranges.

They have attributed this to increase immature fruit fall as a result of increased length of peduncle. Here, we report the role of GA and 2, 4-D in altering the number of flowers, female: male flower ratio, fruit yield and oil yield. The results reported here would have a significant commercial implication for biodiesel production.

Fifteen months old plants were used for this study. The foliar buds of the plants were sprayed thrice at an interval of 5 days with GA and 2, 4-D at two different concentrations (50 and 100 ppm) alone. Observations were made till the fruit development was complete. GA and 2, 4-D treatment resulted in an increase in total number of flowers in a concentration dependent fashion. GA at 50 and 100 ppm resulted in an increase in total number of flowers by 15% and 42% respectively (Table 1). There was a negligible increase in flower number with 2, 4-D at 50 ppm while plants treated with 2, 4-D 100 ppm showed best result with an increase of 52%. The role of GA in regulation of flowering has been well studied and molecular events involved have been deciphered. It has been shown that GA regulates the development of flowers by activation of LFY and AP1 genes. GA activates the floral meristem LFY signal which up regulates AP1 promoter which results in flowering [16]. Thus from this study, it can be concluded that GA and 2, 4-D can be used as a potent phytohormone to increase yields from Jatropha plants.

The other obvious morphological change brought about by GA application was a pronounced increase in length of peduncle (Figure 1). This effect was more in peduncle of female flowers which showed an increase of 4 and 6 folds in plants treated with 50 and 100 ppm GA as compared to control (Figure 2). The peduncle of male flower also increased in length but increase was only 1 to 2 folds respectively at 50 and 100 ppm treatments of GA as compared to control. The flip side of an increase in length of peduncle was greater withering of fruits. It was observed that there was higher fruit fall in plants treated with 100 ppm of GA as compared to 50 ppm. Increased length of peduncle leads to weaker peduncle and it causes withering of fruits before it matures. Fruit fall is a process of senescence which is regulated by ethylene. However, there is a good crosstalk between GA and Ethylene which mediates the senescence in plant [17].

A consequence of increase peduncle length was fruit fall. When fruit yield was calculated the highest yield was from plants treated with 100 ppm 2, 4-D as compared to 50 and 100 ppm GA (Figure 3). 2, 4-D 100 ppm shows significant good results as compared to 2, 4-D 50 ppm. Also, there was no significant change in seed weight with GA and 2 4-D 100ppm treatments when compared with control. Seed weight was significantly higher in GA 50 ppm (Figure 4). The oil content in seeds showed appreciable decrease with GA treatment indicating that the fatty acid synthesis pathway is also not up regulated. The oil content in the seeds increases with 2, 4-D 100 ppm (Figure 5), which means that 2, 4-D 100 ppm increases the flux of fatty acid pathway. In conjunction with oil content, the fatty acid profile did not change by phytohormones application (Table 2).

GA and 2, 4-D treatment on Jatropha curcas foliar bud increases the number of female flowers and fruit yield. GA at higher treatment increases female flowers however it did not result in correspondingly high fruit yield due to increased withering of immature fruits. Withering of immature fruits could be due to greater peduncle length. Using inhibitors to decrease peduncle length may help in capitalizing on the increase number of female flowers. 2, 4-D at higher concentration increases the number of flowers and fruit yield. Applying the results of such studies to the field could help to increase the potential of Jatropha curcas as a bio-fuel crop.

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