Alternative in vitro breeding techniques to induce compactness in woody ornamentals

As gardens get smaller, the demand for potted and compact cultivars of woody ornamentals increases. Therefore, the goal of this project is to develop protocols for alternative in vitro breeding methods to induce compactness within Elaeagnus, Escallonia, Osmanthus and Sarcococca.
A collection of species and cultivars has been compiled and contains 28 Elaeagnus, 25 Escallonia, 18 Osmanthus and 16 Sarcococca species. We will characterize our collection based on genome size, chromosome number, and phenotypical traits such as growth habit, winter hardiness and leaf and flower parameters. Within Escallonia yet determined genome sizes vary between 1.05 pg/2C and 1.33 pg/2C. We started in vitro initiation of all 4 genera which already resulted in an in vitro stock of 5 Escallonia species and 1 Sarcococca species on Murashige and Skoog based medium. New trials on McCown Woody Plant Medium are pending.
These in vitro initiated plants are used to develop protocols for inducing genetic mutation by gamma-irradiation, polyploidisation and insertion of rol-genes. A preliminary polyploidisation experiment on 2 Escallonia species has shown that the mitotic inhibitors oryzalin or trifluralin are the most efficient polyploidy inducers in Escallonia. We obtained up to 24% E. rubra tetraploidization using 150 µM trifluralin, compared to only 2.8% tetraploids using 1000 µM colchicine, in a 2 days experiment.
Escallonia, Elaeagnus, Sarcococca and Osmanthus plants resulting from mutagenesis, polyploidisation or Rhizobium transformation experiments will be evaluated for their added value compared to the existing assortment.