Breeding strategies to increase genetic variability in Hibiscus syriacus

In an attempt to introgress an increased growth vigour and improved flowering into H. syriacus two different breeding strategies were followed. A first approach focused on creating hexaploid H. syriacus plants. This was done by crossing tetraploid H. syriacus cultivars with colchicine doubled (octoploid) H. syriacus ‘Oiseau Bleu’ seedlings. The generated hexaploid progeny had an increased growth vigour compared to tetraploid cultivars. The F1 seedlings were also sterile. Out of the hexaploid F1 population an improved blue flowered plant was selected and multiplied. The second strategy emphasized on the interspecific hybridization between H. syriacus and H. paramutabilis. When used as a seed parent, H. paramutabilis failed to set fruits. However, in reciprocal crosses flowers reacted by fruit setting. Also in these crosses a high number of fruits aborted in an early stage of development. Germination of the surviving seeds occurred within 2-3 weeks. The generated seedlings grew vigorously. Leaves of all seedlings had an intermediate morphology compared to those of H. paramutabilis and H. syriacus, indicating that the obtained progenies were true interspecific hybrids.