A molecular systematic study of the genus Encephalartos

[摘要] English: The extant cycads (Cycadophyta) are divided into three families, with 11 genera (Johnson 1959, Stevenson 1990), and at least 210 species (Stevenson et al. 1995). In this study a molecular systematic study was done on the genus Stangeria T. Moore from the family Stangeriaceae, and the genus Encephalartos Lehm. from the family Zamiaceae. Fifty eight specimens representing 35 species of the genus Encephalartos, and one specimen from the genus Stangeria, Stangeria eriopus (Kunze) Nash were used. The effect and behaviour of hybrids in cladistic analysis were also investigated, such that they might be detectable during cladistic analysis. A pilot study of two molecular techniques, RAPD and DAF was done to determine the applicability, time effectiveness and most suitable primers for a molecular systematic study using these techniques. All the RAPD primers tested gave a high coefficient of similarity and adequate number of characters per specimen. The speed and simplicity of the RAPD technique, combined with the findings of the pilot study, made this an ideal method to generate a large amount of fingerprinting data for a phylogenetic assessment of the genus Encephalartos. Three variations of the DAF technique were tested in the pilot study i.e. simple DAFs, tecMAAP and multiplex DAFs. The coefficient of similarity was high in all the primers, with an increasing number of characters per specimen being generated. The multiplex DAF technique was the most successful, and most cost effective DAF variation. tecMAAP is also a very useful method in this study, but prior cleavage with restriction endonuclease, makes this a time consuming method. Multiplex DAFs combined with simple DAFs were, therefore, applied to more specimens in this study. Phylogenetic relationships were determined using the computer software PAUP, and the genetic distances between species were also determined, The RAPD and DAF cladograms show some correspondence, but also some discrepancies as expected because of the low resolution in the cladograms. Combining the data sets increased the resolution of the cladogram. The molecular results concur with morphological and biochemical studies that have been done on the species in this study, as observed in the close relationship between Encephalartos cupidus and E. eugene-maraisii, and E. umbeluziensis and E. villosus. The RAPD and DAF techniques were also successfully applied in hybrid analysis. An increase in hybrids to the cladistic analysis, do influence the tree topology, but not the cladogram resolution, with an increased tree length. Hybrids, therefore, are no more problematic cladistically than the increased inclusion of specimens. In this study the molecular techniques RAPD and DAF have proven to be a fast and cost effective method in successfully generating fingerprints for phylogenetic analysis.

[发布机构] University of the Free State