Use of genetic resources to develop new commercial Rhododendron simsii hybrids

Abstract

Rhododendron simsii Planch. hybrid or pot azalea is the most important ornamental plant in Belgium. At least four different species (R. simsii, Rhododendron indicum, Rhododendron scabrum and Rhododendron mucronatum) have contributed to modern hybrids. These species are found in parts of China and Japan. R. simsii introduced the early flowering trait and the ability to produce flower sports. The other species contributed to the diversification of flower color (purple, carmine red), large flowers and specific plant habitus. The Instituut voor Landbouw-, Visserij- en Voedingsonderzoek (ILVO) holds a large gene bank of pot azalea accessions and their wild relatives. To safeguard this gene bank, the core collection is also partly kept in cryopreservation. Gene bank accessions are used for both genetic studies and breeding. In recent years, we have specifically focused on introgression of traits such as new flower and growth forms, fragrance, and disease resistance. The introduction of such specific traits from a wild species into elite breeding material is time consuming, as several backcrosses are necessary. For some characteristics, i.e., disease resistance, adapted screening methods have been developed that enable us to select more adequately.