Phylogenetic analysis of Saccharum (Poaceae; Andropogoneae) with emphasis of the circumscription of the South American species

Abstract

Premise of the study: Polyploidy and reticulate evolution are often a complication for discovering phylogenetic relationshipsbetween genera and species. Despite the huge economic importance of sugarcane ( Saccharum offi cinarum-Poaceae, Andropogoneae),the limits of the genus Saccharum and its species are complex and largely unresolved, involving both polyploidyand reticulate evolution. This study aimed to assess the phylogenetic relationships of Saccharum s.l. , including Erianthus andTripidium , as well as investigate the taxonomic circumscription of the South American species of the genus. Methods: Molecular cloning and sequencing of fi ve regions of four low-copy nuclear loci were performed, including Aberrantpanicle organization 1 ( apo 1), Dwarf 8 ( d 8), two exons of Erect panicle 2 ( ep 2 -ex 7 and ep 2 -ex 8), 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 Saccharums.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 distinctclades (different species). The plants with intermediate morphology between S. angustifolium and S. villosum presented a patternof paralogues consistent with a hybrid origin. Conclusions: Saccharum s.l. is polyphyletic and Tripidium should be recognized as a distinct genus. However, no strong evidencewas found to support the segregation of Erianthus. The taxonomic circumscription of the South American species of thegenus was resolved and the occurrence of natural hybrids was documented. Better understanding of the phylogenetic relationshipsof Saccharum and relatives may be useful for sugarcane breeders to identify potential taxa for interspecifi c and intergenericcrosses in the genetic improvement of sugarcane.