Phylogenetics & Biogeography of Nicotiana sect.Suaveolentes

The genus Nicotiana belongs to the plant family Solanaceae that has a great economic importance. This family includes several major crop species (e.g. potato Solanum tuberosum, tomato S.lycopersicum, eggplant - S. melongena, chilli peppers Capsicum spp., Tobacco - Nicotiana spp), as well as ornamentals (e.g. Petunia spp.). In this proposal we are investigating the section Suaveolentes of genus Nicotiana, which is largely endemic to Australia. Section Suaveolentes appears to be the result of natural ancient allopolyploidisation, i.e. hybridisation between individuals belonging to two, not closely related species accompanied by whole genome doubling. As new species of Nicotiana sect. Suaveolentes evolved and chromosome numbers decreased, they occupied dry interior of central and southern Australia, where they are now most diverse. However presently, two radically different explanations exist for the current distribution of N. sect. Suaveolentes in Australia. Previously, the researchers in Australia believed that the ancestor of Nicotiana sect. Suaveolentes is approximately 20 million years old and, like nearly all other Australian plant groups, formerly widespread across the continent, long before aridification commenced seven million years ago. Thus, it was accepted that the current distributions of the modern set of species are due to vicariance over 20 million years.In contrast to this, recent work done using molecular clock methods and a small number of species in section Suaveolentes and found that the age of the section is only six million years. Dispersal into the Eremaean Zone only commenced as recently as two million years. To test these two different opinions on the distribution of this section in Eraemean zone, we propose to get a well resolved phylogenetic tree for the 45 species of Suaveolentes having Nicotiana africana as outgroup using high throughput DNA sequencing technique. This technique will deliver tens of thousands of variable sites that are expected to provide great power for phylogenetic inference and species delimitation. A population level analysis based on the same technique will investigate population-level evolutionary processes in order to understand in detail the evolution of this group. This information will be used to investigate the historical demography of this group, including timing, which will give a clue about distribution of sect. Suaveolentes as well as population size variation and geneflow. Well resolved phylogenetic relationships will also clarify the biogeographical pattern and changes in chromosome numbers and genome sizes across the section Suaveolentes.

This project had a good impact on the public, having Nicotiana experts and field guide in Australia helped collection of material needed in time. Seed material from the collected species were established in the glass house (at the quarantine glass house) of the Kew, Royal Botanical Gardens. Established seedlings were closely observed and studied carefully. New species identified in this study was described by both painting and drawing. Thus many people contributed for the project. The lab work was done by trained technicians in the laboratory of the Division of Systematics and Evolutionary Botany, Postdoc involved in the project played a big role in publishing the work. This outcome is useful for Scientists and others working on Nicotiana (Solanaceae) as well as other plant groups.