A New Allopolyploid Species of Saccharum (Poaceae ‐ Andropogoneae) from South America, with Notes on its Cytogenetics

Abstract

Allopolyploidy is a major mode of speciation in flowering plants and particularly in the grass tribe Andropogoneae, which includessugarcane (Saccharum officinarum) and relatives. A new species of Saccharum from South America (S. intermedium) is described here, supported bymorphological, molecular and cytogenetic evidence. Previous molecular analyses indicated an allopolyploid origin of the new species throughinterspecific hybridization between S. angustifolium and S. villosum. The new taxon has intermediate morphology between the two parental species.Cytogenetic analyses of the three species were performed, including chromosome counts, meiotic regularity, and pollen viability and morphology.The new taxon is hexaploid (2n = 60), while the parental species are triploids (2n = 30), confirming the ploidy level suggested by the number ofparalogues in phylogenetic trees based on low-copy nuclear genes. This represents the first chromosome count for S. intermedium and a new cytotypefor S. villosum. Although both parental species are triploids, they surprisingly exhibited regular meiosis and high pollen viability, indicating they aremale-fertile, as is the hexaploid new species. Data on geographic distribution and phenology is also presented, aswell as a key for the South Americanspecies of Saccharum.