PHYLOGENETIC ANALYSIS OF SACCHARUM S.L. (POACEAE; ANDROPOGONEAE), WITH EMPHASIS ON THE CIRCUMSCRIPTION OF THE SOUTH AMERICAN SPECIES

Premise of the study: Polyploidy and reticulate evolution are often a complication for discovering phylogenetic relationships between genera and species. Despite the huge economic importance of sugarcane (Saccharum officinarum-Poaceae, Andropogoneae), the limits of the genus Saccharum and its species are complex and largely unresolved, involving both polyploidy and reticulate evolution. This study aimed to assess the phylogenetic relationships of Saccharum s.l., including Erianthus and Tripidium, as well as investigate the taxonomic circumscription of the South American species of the genus. Methods: Molecular cloning and sequencing of five regions of four low-copy nuclear loci were performed, including Aberrant panicle organization 1 (apo 1), Dwarf8 (d8), two exons of Erect panicle2 (ep2-ex7 and ep2-ex8), and Retarded palea 1 (rep 1). Concatenated trees were reconstructed using Maximum Parsimony, Maximum Likelihood, and Bayesian Inference analyses. Key results: The allopolyploid origin of Saccharum was demonstrated using evidence from nuclear genes. The samples of Saccharum s.l. grouped in two distinct clades, with S. arundinaceum and S. ravennae (= Tripidium, or Erianthus sect. Ripidium) apart from all other species analyzed of the genus. Saccharum angustifolium, S. asperum, and S. villosum correspond to distinct clades (different species). The plants with intermediate morphology between Saccharum angustifolium and S. villosum presented a pattern of paralogues consistent with a hybrid origin. Conclusions: Saccharum s.l. is polyphyletic and Tripidium should be recognized as a distinct genus. However, no strong evidence was found to support the segregation of Erianthus. The taxonomic circumscription of the South American species of the genus was resolved and the occurrence of natural hybrids was documented. Better understanding of the phylogenetic relationships of Saccharum and relatives may be useful for sugarcane breeders to identify potential taxa for interspecific and intergeneric crosses in the genetic improvement of sugarcane.