Identification of Stylosanthes guianensis varieties using molecular genetic analysis.

Background And Aims: The botanical classification of Stylosanthes guianensis is controversial, and few studies have used molecular markers to analyse this species. We used microsatellite markers to study the genetic diversity and population structure of S. guianensis and compare our results with the current infraspecific botanical classification.

Methodology: A representative sample from the S. guianensis Brazilian germplasm collection (150 accessions) was analysed using 20 microsatellite loci. A model-based Bayesian approach implemented in the software STRUCTURE was used to assign accessions into clusters. A dendrogram was constructed based on Roger's genetic distances.

Principal Results: The number of alleles per locus varied from 2 to 11, with an average of 4.7. The observed (H(O)) and expected (H(E)) heterozygosity values varied from 0 to 0.58 (mean of 0.18) and from 0.04 to 0.83 (mean of 0.55), respectively. Nine groups were assembled in STRUCTURE, and these groups were consistent with clusters inferred from the genetic distances and taxonomic varieties described for S. guianensis. The G(ST) among the nine groups was 0.46.

Conclusions: The low H(O) and the G(ST) values observed are in agreement with the outcrossing rate (26 %) estimated for this species. The data indicate a high genetic diversity among and within the botanical varieties and suggest that microsatellite-based information can be combined with classical taxonomy to elucidate infraspecific levels.