Phylogenetic relationships of the genus Lachenalia with other related liliaceous taxa

[摘要] English: Lachenalia is a small bulbous geophyte of the family Hyacinthaceae, endemic to South Africa and first described in 1787 by Jacquin. There is a large degree of variation in the genus and some species overlap morphologically with other genera such as Polyxena and Massonia , and it is very difficult to delimit the species. There are currently approximately 120 species described, but new species are frequently described. Several authors attempted to subdivide the genus (Baker, 1897; Crosby, 1986; Duncan, 1988 & 2002). Lachenalia has a tremendous cultivation potential, and 25 new cultivars have been introduced since 1966. A cytogenetic, as well as a molecular study, was conducted to try and solve problems with the classification in the genus, and to provide answers to the breeders regarding infertility problems between interspecific crosses. The chromosome numbers of a few species were determined by examining meiotic and mitotic chromosomes in order to guide the breeders in their hybridisation studies. The numbers obtained during this study were combined with results of previously studies to try and determine the original basic chromosome number(s) in the genus. Several basic chromosome numbers have been reported in the genus, i.e. x = 5/10, 7, 8, 9, 11 and 13. The majority species have a basic chromosome number of x = 7, followed by x = 8 and then x = 11. Polyploidy is common, occurring in 40% of the species in the genus. The number x = 7 has mainly diploids, 28.6% tetraploids and a few hexa - and octaploids and, therefore, represents a young mature polyploid complex. The numbers x = 8 and x = 11 both forms young polyploid complexes. According to this information, it can be concluded that x = 7 were the original basic number, from which x = 8 and x = 11 evolved. The hypothesis on the evolution of the chromosome numbers were tested by sequencing the trnL-F region of the chloroplast genome. This region was also sequenced to try and provide answers for the taxonomists on the difficult task of classifying and delimiting the genus. The phylogenetic position of the genus in relation to other liliaceous plants also needed to be determined. The basic chromosome numbers were superimposed on the cladogram, and a definite correlation between chromosome numbers and monophyletic groups were obtained. Several monophyletic clades formed, dividing the cladogram into four distictive groups: the 'L. juncifolia, 'Lachenalia 1, 'Lachenalia 2 and 'L. zebrina groups, and several subgroups. The position of these groups and subgroups confirms the hypothesis that x = 8 evolved from x = 7. It also indicated that several hybrids prevail within the genus, explaining the delimitation problems and the variation in basic chromosome numbers. The genus Polyxena are included within the Lachanalia clade, indicating that this genus should either be included in the genus, or Lachenalia should be split into several genera. Polyxena could also have introduced new chromosome numbers and variation in the genus by hybridisation. The cladogram confirms that Polyxena is the closest relative of Lachenalia , followed by Massonia and Whiteheadia . This study indicated that the cytogenetic and molecular data support one another. The trnL-F region is useful to study phylogenetic relationships on genus or higher taxonomic levels, but the addition of other genes will probably provide more answers for the classification and evolution of the genus.

[发布机构] University of the Free State