Phylogeny meliaceae using Molecular, Phytochemical and Pollen Morphology

Research project P 14150 Phylogeny of Meliaceae using Molecular, Phytochemical and Pollen Morphology Mary Rosabelle SAMUEL 08.05.2000 Family Meliaceae consists of about 600 species and its distributed throughout the tropics. It is economically important chiefly because of its high quality timber including the true mahoganies (Swietenia mahogani) and toon (Toona ciliata). The family is chemically marked by the presence of tetranortriterpinoids (limonoids, meliacins) which are of considerable commercial interest especially as insecticides. The neem tree (Azadirachta indica) has a host of uses, such as pest control and inexpensive medicines for birth control. Even in spite of its high economic importance, taxonomic treatment of this family is not very clear. Therefore different modern methods have to be adopted to check the classical grouping of genera and tribes. In a recent taxonomic treatment of the genus Aglaia, a wide species concept was adopted in which in many species even the most indicative morphological characters like floral morphology, indumenturn etc., show much variation. Molecular methods are now generally accepted as the most reliable approach to reconstruct the phylogeny in plants. Conserved genes such as plastid rbcL, matK and nuclear rDNA 26S genes could be used at higher taxonomic level in Meliaceae. Highly evolving rDNA ITS (Internal Transcribed Spacers) and plastid intergenic spacers (atpB/rbcL) and trnL spacer sequences could be used at species level in Aglaia. The DNA based phylogenetic tree will be compared with the distribution of bio-active compounds between taxa, and pollen morphology.

Meliaceae are a woody family widely distributed throughout the tropics and subtropics. They occur in a variety of habitats from rain forests and mangrove swamps to semi-deserts. The timbers of certain Meliaceae are some of the most sought after in the world, such that natural stands have been much depleted. Meliaceae are also sources of biologically active compounds which have aroused considerable commercial interest. They also have numerous medicinal effects in humans and animals (anti-cancer and AIDS research). Despite the economic importance of Meliaceae, systematic boundaries in the family have remained unclear until now. The intricate taxonomic history of Meliaceae and the fact that the problem of taxa delimitation (subfamilies, tribes, genera, species) based on morphology alone has not been solved satisfactorily up to date, make clear that there is need for additional research. Molecular techniques can be used to investigate genetic diversity and structure of and relations among taxa. These data provide helpful tools for taxa delimitation especially in plant groups where the number of diagnostic morphological characters is limited and parallel evolutionary trends obscure phylogenetic relations. We therefore carried out phylogenetic analyses of Meliaceae, including representatives of all four currently recognized subfamilies, using different DNA markers from the nuclear and the plastid genome. Results exemplified for subfamilies and genus Aglaia (Meliaceae) Results of our analyses support the recognition of only two subfamilies (Melioideae and Swietenioideae). The members of the two small monogeneric subfamilies, Quivisianthe and Capuronianthus, fall within Melioideae and Swietenioideae, respectively, supporting their taxonomic inclusion in these groups. Aglaia is the largest genus of Meliaceae and occurs in the tropics of S.E. Asia, the Pacific islands and N. Australia. It comprises more than 100 species and presents more taxonomic problems in species delimitation than any other genus of the family. This resulted in the adoption of a wide species concept, by which taxa contain considerable morphological variation. We compared DNA data to recently collected data on chemical profiles of the respective taxa of Aglaia. Our data indicate paraphyly of Aglaia (inclusion of genera Lansium and Reinwardtiodendron) and the existence of at least three instead of two entities with respect to Aglaia: a) the core group of section Amoora (dehiscent fruits) with close relations to Lansium and Reinwardtiodendron, b) a group comprising morphological intermediates between the two sections (A. teysmanniana, A. lawii), and c) the members of section Aglaia (indehiscent fruits). Moreover, our data indicate that complex species in the genus are more heterogeneous, i.e., probably containing more than one taxon each, than taxonomically isolated species.