Establishment of new strategies to quantify and increase the variability in the Brazilian Jatropha genotypes

The genetic diversity of Brazilian Jatropha (Jatropha curcas) germplasm collection (BJGC), which consists of 192 accessions, has been previously reported based on the evaluation of a limited number of RAPD and SSR markers. In addition, accessions from other countries (Guatemala and Mexico) were introduced to this collection without prior information on their relation with the existing collection. Thus the objective of this study were to develop and validate a panel for high-density genome-wide molecular markers for Jatropha; to compare the diversity of the germplasm collected in Brazil and the materials introduced and/or generated by crossing selected genotypes; and to determine whether the germplasm introduction strategies and the controlled crossings were efficient in generating/increasing the genetic variability available to the breeding program. This study reported an evaluation on the existence and on the structure of the genetic diversity of a core collection of 92 accessions by using DArT and SNP markers. The genotyping-by-sequencing approach allowed genotyping 747 polymorphic SNP and 4007 DArTs. The pairwise genetic dissimilarity was estimated according to the Jaccard's coefficient, and clustered by the UPGMA and Tocher's clustering methods The genetic diversity distribution was assessed by the analysis of molecular variance (AMOVA). The mean dissimilarity between accessions was low (0.165), and it confirmed that the diversity of the BJGC is very limited. Cluster analysis demonstrated that the introduced genotypes were divergent, and they formed a separate group, indicating that new introductions such as these will be important to promote future efforts on genetic breeding. Accordingly, data from SNP also confirmed the development of a significant amount of genetic variability within families (65%), which probably resulted from the use of the Mexican accession that was found to be considerably divergent when compared with the Brazilian accessions. These results indicate that breeders should focus on two main strategies to generate variability in the BJGC: introduction of new accessions from other countries and crossings between potential genotypes.