4Institute of Biophysics, Academy of Sciences of the Czech Republic, CZ-61265 Brno, Czech Republic
The genus Nicotiana (Solanaceae) has 76 species in 13 sections and makes an excellent model system to study plant chromosome evolution and speciation. The base chromosome number is n =12, but the numbers can vary at both the diploid and tetraploid levels. The genus’ centre of diversity is S. America, most species occur in South/North America, and one large section, Suaveolentes, is found in Australia (and one species in Africa). The Australian distribution of Suaveolentes arose as a consequence of recent long-range dispersal. We have embarked on a systematic analysis of karyotype evolution in the genus by combining molecular phylogenies derived from multiple gene sequences and karyotype/chromosome analysis using FISH and molecular biology. We report patterns of chromosome divergence between diploid and polyploid sections and in sections of different ages. We show relationships between rates of speciation and of karyotype divergence.