Evaluasi genetik daya hasil dan sifat penting lainnya pada jarak pagar (Jatropha curcas L.) untuk mendukung perakitan varietas baru berdaya hasil tinggi

Abstract

To develop high yielding varieties of physic nut (Jatropha curcas L.), an important oil producing crop needed to support development of renewable energy resources program in Indonesia requires genetic evaluation of the germplasm. The collected genetic data are important for designing the appropriate Jatropha breeding program. The objectives of this research were to evaluate: 1) morphological and yield potential performances of selected J. curcas genotypes, 2) genetic variance and heritabilities of important characters and their correlation with yield, 3) combining ability of selected genotypes and their heterotic values, 4) existence of inbreeding and outbreeding depression, and 5) inheritance of hermaphrodite flower characters of monoecious and tri-monoecious parent types. Results of the experiment indicated that 60 J. curcas genotypes evaluated exhibited a wide variation in number of branches, days to flowering, number of inflorescences, bunches, fruits and nuts per plant. Number of branches, inflorescences and bunches were positively correlated with number of fruits and nuts per plant while days to flowering was negatively correlated with all generative characters. The ten selected genotypes exhibited high phenotypic variation in number of branches, days to flowering, number of inflorescences, bunches and fruits. The coefficient of variation (CV) for all of these characters were generally > 20 %. Days to flowering, number of inflorescences, bunches and fruits exhibited wide genotypic variation with genetic variability coefficients (GVC) as high as 21,89; 29,77; 32,08; and 33,75, respectively. They also showed a wide genetic variability (2g > 2 2g) and high broad sense heritability (h2bs  50). Therefore, days to flowering, number of inflorescences, bunches and fruits could be used as selection parameters. Moreover, number of total branches was especially usefull since it showed positive correlation to a number of yield component character. The ten selected parents exhibited different values of combining ability and they all had DGU/DGK > 1. Such value indicated a greater additive gene effects than the non-additive ones. High yielding genotypes, such as 3012-1 and PT 15-1, generally exhibited high GCA for a number of characters (days to flowering, width of canopy, number of total branches, inflorescences, and fruits) while medium yielding genotypes, such as PT 33-2, exhibited high GCA only for number of inflorescences, total branches, and fruits characters. Those three promising genotypes could be selected and used as a base population to develop high yielding synthetic J. curcas variety with the characteristics of early flowering. Results of the experiment also demonstrated that crossing among high and medium yielding parents were able to potentially produce very high yielding progenies. Depending on the observed characters, either selfing or outcrossing may results in depression in several F1 populations. Outbreeding depression reduced up to 31 – 76 % of fruit numbers yielded per plant. In the last experiment, hermaphrodite flower occured mostly at 6 months after sowing and the frequencies it occurrences ranged from 7-83 % of the total flowers. Hermaphrodite flowers of tri-monoecious plant exhibited better fruit set than that of monoecious. Hermaphrodite flowers exhibited higher fruit set (average: 80 %) than those of female flowers (average: 50 %), respectively. Hermaphrodite flowers were not maternally inherited and it might be controlled by single dominant gene.