Stylosanthes sp. aff. S. scabra: A putative diploid progenitor of Stylosanthes scabra (Fabaceae)

Stylosanthes sp. aff. S. scabra is an undescribed taxon showing affinities with the allotetraploid species S. scabra, but distinct in a number of attibutes. Several collections show potential as forage for clay soils in northern Australia. Twelve accessions have been analysed using STS (sequence-tagged-sites) as genetic markers, and they all displayed STS phenotypes of typical diploid species. Taking into account their morphological similarities, the STS analysis provides strong evidence that Stylosanthes sp. aff. S. scabra might be a diploid progenitor of the allotetraploid S. scabra. This speculation was supported by cytological examinations. Somatic chromosome numbers of two of these accessions were counted and both were found to be diploid (2n=20). The level of polymorphism among the 12 Stylosanthes sp. aff. S. scabra accessions, estimated using randomly amplified polymorphic DNA (RAPD) as markers, was 7.8%, and the dissimilarity value between Stylosanthes sp. aff. S. scabra and S. viscosa (the other putative progenitor of S. scabra) was 89%