Effects of gamma irradiation on the performance of Jatropha (Jatropha curcas L.) accessions

This study aimed to assess the effects of mutation by using gamma ray on the performance of jatropha plants. The study was conducted at PAIR BATAN. Jatropha seeds obtained from the collection farm of SBRC LPPM IPB and PT Indocement Tunggal Prakarsa Tbk in Gunung Putri, Bogor, were irradiated. The irradiated seeds were grown in Jonggol Trial Farm of IPB. Gamma irradiation was conducted by using a GCM 4000A device. Treatments consisted of irradiation doses, irradiation methods, and accessions. Irradiation doses given were 175, 200, 225 Gy, and no irradiation (control). Irradiation methods consisted of acute, intermittent, and split-dose. Accessions used in this study were Dompu, Medan, Bima, Lombok, ITP II, IP2P, and Thailand. Results of the study were analysed until 5 months after planting showed that gamma ray mutation gave stimulating and inhibiting effects on similar traits. Irradiation dose of 225 Gy was good to be given in acute, intermittent, and split-dose methods. Irradiation effects were found to be significant in jatropha accessions. Effects of irradiation on production will be published soon.


Introduction
Jatropha produce fruits whose seeds contain oil that can be used as fuel for cooking, lighting, and biodiesel feedstock (1). Depending on their places of origins, jatropha seeds contain oil of up to 40.96% with an average figure of 36.43% (2). Jatropha fruits are found in inflorescents formed from pollinated female flowers. Most fruits contain three seeds but some may have up to four seeds containing oil. The amount of oil that can be produced was found to be positively correlated with the number of inflorescents, number of harvested fruits per plant, and number of total fruits per plant, dry seed weight, and seed diameter (3). Dry seed weight is the idiotype commonly used as an indicator of superior variety of jatropha plant as it is correlated with oil production. Dry seed production was significantly correlated with plant height, branch diameter, number of secondary branches per plant, number of productive branches per plant, number of inflorescents per plant, number of fruits per plant, number of seeds per plant, and dry weight of 100 seeds (4). Another research also shown that jatropha production was affected by number of inflorescents per plant and number of seeds per plant (5). Therefore, these characters can be used as important characters for the selection of jatropha plant. However, not all characters which were correlated with high production of jatropha had high variability and heritability (3). Therefore, not all of those characters can be used as the selection Other research showed that only number of inflorescents per plant and number of fruits per plant could be used selection criteria for high productivity of jatropha as they had wide genetic variability, high heritability, and high genetic advance (3,4,5,6). Narrow genetic variability from the observed characters indicated that the accessions of jatropha from various places in Indonesia were relatively uniformed although they came from geographically different origins. By using molecular markers to detect genetic variability of jatropha in India, it was found high level of uniformity among different genotypes. This meant that the accessions of jatropha currently available had narrow variability. In other words, current population was relatively uniformed, introduction from other countries, crossbreeding, or mutation was needed (7,8).
Mutation is an effective method to improve genetic variability. It has been proven to improve the genetic variability of jatropha (9,10,11). Gamma irradiation is very important in mutation breeding. Mutagenesis can be used to improve genetic variation (12). Therefore, this study was aimed at analyzing the performance of jatropha produced by gamma irradiation.

Materials and Methods
The study was conducted at the Center for Isotopes and Radiation Application (PAIR), National Nuclear Energy Agency (BATAN). Jatropha seeds obtained from the collection farm of SBRC LPPM IPB and PT Indocement Tunggal Prakarsa Tbk in Gunung Putri, Bogor. The irradiated seeds were grown in Jonggol Trial Farm of IPB. As the jatropha seed availability was limited, the irradiation of it was done in two stages in March and April 2014. Gamma irradiation was conducted by using a GCM 4000A device. Treatments consisted of irradiation doses, irradiation methods, and accessions. Irradiation doses given were 175, 200, 225 Gy, and no irradiation (control). Irradiation methods consisted of acute, intermittent, and split-dose. Accessions used in this study were Dompu, Medan, Bima, Lombok, ITP II, IP2P, and Thailand. In acute irradiation method, irradiation was done only once in the proposed doses. In intermittent method, irradiation was done twice in full doses. The irradiation was repeated within 1 week interval.
In split-dose method, irradiation was done twice. The dose in the second irradiation was half of it in the first irradiation. Irradiated seeds were grown on a nursery bed for 2 months before they were moved into the field. Planting was done in a planting distance of 2 m x 2 m. Planting holes were prepared in 3 weeks prior to planting time. Five kilograms of manure (organic fertilizer) was put into each planting hole. One seed was planted in each planting hole. Morphological observation was done to assess the effects of irradiation on jatropha plants resulted from irradiated seeds (M1). The observation was done on seed germination, plant height, number of leaves, number of branches, number of inflorescents, and number of fruits per inflorescent. Means of plant growth rate in nursery bed were measured to assess the effects of irradiation and accessions used. Meanwhile, observation data from the field were obtained from individual plant. Data were subjected to an analysis of variance by using SAS 9 application.

Effects of irradiation on mutant seed germinability (M1)
The germination rate (%) of M1 irradiated seeds is shown in Table 1. Theoretically, irradiated seeds undergo genetic or physiological changes. Yet, when irradiated seeds can still germinate and grow into intact plants, then this is an indication that the irradiation done creates changes which are naturally acceptable (13). From the germination rate indicated that the irradiation dose and method applied were naturally acceptable for jatropha seeds. Among all irradiated jatropha accessions, ITP II accession had the highest germinability (80.8%) although it was not different from those of Lombok (80.7%), Bima (60.6%), Medan (59.3%), and Dompu (79.25%) accessions. It was shown that some irradiated seeds had higher germination rates than control and lower doses groups. These included seeds of Lombok accession treated with intermittent dose of 175 Gy, Dompu accession treated with intermittent dose of 200 Gy, and Lombok, Bima, and Medan accessions treated with split dose of 225 Gy. Another research also found that gamma irradiation at the doses of up to 200 Gy did not cause a seed damage although it lowered seed germination rate especially in jatropha of IP-3A variety (14). The germination rates found in this study also showed a stimulation effect of irradiation on seed germination. Higher doses of irradiation can effect on higher germination rate of jatropha seeds (14,15). Responses to gamma irradiation were also found to be different in each accession.  Effects of gamma irradiation in the field Based on field observation within 5 months after planting, it was found that the treatments given to the seeds resulted in various plant growths. Gamma irradiation gave significant effects on the growth of jatropha plants of different accessions. The growth of treated jatropha plants is shown in Table 4. Like on seed germination, gamma irradiation gave stimulating and inhibiting effects on jatropha plant growth. These were indicated by plant height in 5 MAP, number of inflorescents and number of fruits per inflorescent in 4 MAP. The average plant height in 5 MAP was 84.5 cm with average number of branches of 5.3. In 4 MAP, the average number of inflorescents per plant was 2.7. As shown in Table 4, irradiation doses and methods were found to be effective in improving plant growth. In plant breeding, induced mutation is an effective way to improve the variability of the existing germplasms and it can be used to improve plant varieties (16). Other report shown that mutation gave positive or negative effects on plant height (15,17). This phenomenon was also found in gladiolus plant, where gamma irradiation, at certain dose, was found to not only stimulate but also inhibit plant height growth (18). This might be caused by the fact that irradiation not only stimulates but also inhibits the    This study shown that for different accession, the effects of irradiation were different. Radio sensitivity of the irradiation given varied among plant species (20). The difference in radio sensitivity among cultivars or breeding lines is directly related to their genetic. This might occur as each accession has different base sequence. The frequency of mutant occurrence is affected by different base sequences in various plant genetic (21).

Conclusions
It was concluded that gamma irradiation gave both stimulating and inhibiting effects on the morphological and agronomical characters observed. Acute, intermittent, and split dose 225 Gy irradiation tended to give stimulating effects in jatropha. Irradiation effects were different among accessions.

Acknowledgement
Funding support from Ministry of Research and Technology through the 2014 Sinas Incentive Program was acknowledged.