Genetic Variation And Diversity Of Jatropha Curcas L.

Jatropha curcas L. belonging to the family Euphorbiaceae is a deciduous, multipurpose shrub or small tree up to 6 m tall. Its natural distribution range is centre in Mexico and Central America. It has been extensively cultivated outside its natural range, and become naturalized throughout the tropical and subtropical regions due to the ease of propagation either by seed or cuttings. The species is a highly effective, renewable bio-energy tree species because the seed can be extracted for bio-diesel oil.The main objective of this study was to determine the genetic diversity of J. curcas using genetic material deriverd from sources within China and many other countries. Field growth indices:seed morphology, branching habit, fruit yield, seed oil content and molecular diversity were determined. The results showed the relationship between J. curcas populations and suggested the probable sources of original introductions into China. The results also provided a basis for genetic improvement by selection of superior genotypes in terms of growth, high seed yield and high oil content. Main results obtained from this study are described as follows.1. J. curcas seeds from 8 countries 40 sources were included in the study. The 1000-seed weightand 1000-seed kernel weight were quite different between populations. The 1000-seed weight,1000-kernel weight, seed length, seed width, seed oil content, kernel oil content and seed germination and seedling growth were determined. The results showed that seeds from Mali were the heaviest and those from India were generally the lightest; Seed weight of the Chinese sources was around the overall mean. In term of seed size, Indian and Chinese seeds were smaller than other countries. The range of seed oil content among the 40 sources was 14.85-40.17%, while the kernel oil content was 34.02-61.39%. Seed germination varied form 1.7% to 90.80%. Mean diameter and height of three-month-old seedlings were 25.73 cm and 1.09 cm respectively. The highest oil content was recorded for seed from Mali. Overall, there were marked variations in seed length, seed width, seed weight and oil content. At last 10 populations with high oil content could be used for further research.2. The field growth indices at 2 years age of 195 families of China and at 1 year old of 37 clones were assessed. Analysis results revealed that survival differed significantly at family level but not at province level, while height, diameter at ground level, number of fruiting branches and fruit yield varied at province and county levels but not at family level. The family trial results showed that overall mean survival, height, diameter at ground level, number of fruiting branches and fruit yield were 93.65%,1.97 m,6.85 cm,1.38 per tree and 20 per tree respectively. Clone trial results showed that mean survival, height, first order branch (FOB), second order branch (SOB) and fruit yield were 84%,101.48 cm, 2.77,1.67 and 16.5 respectively. Analysis of variance indicated that there were no differences in height at county and clone levels. Survival and SOB differed at county and clone levels. FOB and fruit yield varied at clone level but did not differ at county level.The results described above show that families and clones of J. curcas from different counties and provinces performed differently in many growth characteristics. Thus, genetic variations in J. curcas exist and it is possible to make selection for superior genotypes.3. Amplified fragment length polymorphism (AFLP) was used to determine the genetic diversity among 37 Chinese populations and 1 Indonesia of J. curcas grown in a seed source trial in Hainan. Nine AFLP primer combinations were used to generate a total of 246 fragments, of which 72 (26.99%) were polymorphic. Three marker attributes: polymorphism information content (PIC), marker index (MI) and Resolving power (RP), were all found to be reliable to determine the discriminatory power of the nine primer combinations.The Jaccard's similarity coefficient showed a high similarity range from 0.866 to 0.977, suggesting a low genetic diversity among the 38 populations. The UPGMA-based dendrogram and biplot of a principal component analysis did not reveal a clear pattern of groupings by geographic locations of the seed sources; populations from across different provinces were mixing in the same groups. The low genetic diversity and a lack of variation pattern among the populations in China suggest that it is necessary to import new germplasm preferably from the species'natural distribution range to broaden the genetic base for improvement program.4. Four selected AFLP fluorescence primer combinations were employed to test the genetic diversity of 310 individuals from 64 populations from ten countries. Eighty nine AFLP markers were observed. The genetic diversity parameters at species level was PP= 18.31%, Na= 1.183, Ne= 1.117, H= 0.070, I= 0.103. The genetic differentiation coefficient was 0.5057 which indicated that 50.57% variability occurred between populations. The gene flow was 0.473.All the genetic diversity parameters Pp, Na, Ne, H and I had similar tendency in these ten countries. Mexico had the highest genetic diversity followed by Vietnam, India, Thailand, Papua New Guinea, China, Philippines, Mali and Indonesia.The genetic distance of these 64 populations varied form 0.002 to 0.308. The UPGMA dendrogram was built according to Nei's genetic distance. The 64 populations were clustered into 4 main groups, i.e. mixed Asian group, India group, China group and Mexico group. The populations clustered in the same group are likely to be introduced from the same original population. The cluster result had some relationship with geographic distribution, but within each group there was no relationship with geographic distribution.5. Thirty seven SSR-ESTs were obtained from 13,201 EST sequences. Among these 37 SSR-ESTs, dinucleotide repeat was more dominant motif than trinucleotide repeat. For dinucleotide repeat, GA and GT were the most abundant motif. As for trinucleotide, AAG was dominant. The length of SSR repeat was between 18 bp and 45 bp, the mean length was 27.69 bp. At last 37 EST-SSR primers were gained, of which 28 worked for J. curcas, and 7 primers were polymorphic. The amplified loci ranged from 2 to 14.This study showed variations in many growth characteristics of J. curcas from a wide range of seed sources through seed and field growth assessment. These results indicate that it is feasible to select genotypes which possess fast growth and high seed oil contents. Molecular analysis confirmed low genetic diversity among Chinese populations, suggesting the need to introduce more genetic material to broaden the genetic base in China.