A phylogenetic study of the South African representatives of the tribe Andropogoneae (Poaceae)

[摘要] English: The tribe Andropogoneae makes up half of the grass subfamily Panicoideae, withapproximately 85 genera and 960 species (Hartley 1958, Clayton and Renvoize 1986).The genera of the tribe are typically tropical with only a few species extending beyondthe tropics into warm temperate regions. From information available it is clear that theAfrican representatives form an integral part of the tribe. In this study we onlyconcentrated on the South African representatives of the tribe.The tribe Andropogoneae has been studied extensively over the last millennium,but there is still an uncertainty about the true basic chromosome number. Previousmolecular studies include sequencing of the ndhF, GBSSI and phytochrome B.The morphological variation in the tribe provides an interesting context toexamine. This study focused on the sequencing of plastid chloroplast gene trnL-F andnuclear ribosomal DNA the Internal Transcribed Spacer (ITS) to determine thephylogenetic relationships within the tribe.In this study the chromosome numbers of 58 specimens were determined. Thegenetic chromosome numbers varied with n = 5, 9, 10, 10, 11, 20, 30. For the first timethe basic diploid number of n = 5 was observed in the genus Andropogon. Urelythrumaggropyroides was studied for the first time with a somatic chromosome number of 2n =20.The absence of multivalent and prevalence of bivalents in this study indicate thatthe genomes of the specimens studied are homologous. This lead us to the conclusionthat the tribe consists of allopolyploid species, derived from interspecific hybridizationand chromosome doubling.Both the trnL intron and trnL-F intergenic spacer was sequenced. Analysis of thetrnL-F gene included 56 accessions and 61 accessions for the ITS gene. Combinedanalysis of both ITS and trnL-F included 59 accessions. Sequencing data indicatedCymbopogon to be a diploid progenitor of Hyparrhenia and Andropogon of Bothriochloabladhii. Reticulate evolution was demonstrated in nrITS alleles. ITS and trnL-F datasupports the inclusion of Arundinella in Andropogoneae and rejects the subtribal classification of Clayton and Renvoize (1986). This data also does not support thedivision of the tribe into awned and awnless genera and does not support the 'coreAndropogoneae lineage as previously been observed. Most genera in the tribe arepolyphyletic, suggesting a much more complex nature for the South Africanrepresentatives.Molecular data could not prove the basic chromosome number but supported thematurity of the polyploid complex for the South African specimens.

[发布机构] University of the Free State