The potential of molecular analysis and interspecific hybridization for azalea phylogenetic research

Plants belonging to the Rhododendron subgenera Pentanthera (deciduous) and Tsutsusi and Azaleastrum (evergreen) are called azaleas. Concerning their mutual phylogenetic positions, the Pentanthera subgenus is closer to evergreen rhododendrons (subgenera Rhododendron and Hymenanthes) than to the Tsutsusi subgenus. Both azalea types are important ornamentals with a long breeding tradition. Different hybrid groups are often named after the supposed principal ancestor species. Apart from the scientific sound purposes as taxonomy and reconstruction of phylogenetic and cross-hybridization processes taking place in natural populations, most of the presented genetic research has been initiated with practical breeding applications in mind. First, we report on interspecific hybridization in Rhododendron breeding as a tool to delineate species. The capability to cross species and the occurrence of fertilization barriers can give insight into speciation. Molecular techniques for phylogenetic and kinship research have been evaluated to a great extent. First, some studies using comparative gene sequencing are presented; this approach was then widened to the use of molecular markers to reveal more detailed genetic relationships. Finally, the use of candidate genes as functional markers for the assessment of genetic diversity is presented. This opens new research lines to the genetic mapping of plant traits and azalea genomics.