Induction of Tetraploids in Escallonia spp.

Hanne Denaeghel1, Katrijn Van Laere1, Leen Leus1, Tom Eeckhaut1, Stefaan Werbrouck2, Johan Van Huylenbroeck1, Marie-Christine Van Labeke3
1 ILVO, Institute for Agriculture and Fisheries Research, Plant Sciences Unit - Applied genetics and breeding
Melle, Belgium.
2UGent, Faculty of Bioscience Engineering, Department of Applied Biosciences
9000 Gent, Belgium.
3 UGent, Faculty of Bioscience Engineering, Department of Plant Production
9000 Gent, Belgium.
[email protected]
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 created and contains 28 Elaeagnus, 25 Escallonia, 18 Osmanthus and 16 Sarcococca species. This collection is characterised based on genome size, chromosome number, and leaf and flower parameters. Also growth habit and winter hardiness will be evaluated. We started in vitro initiation of all 4 genera which already resulted in an in vitro stock of 3 Escallonia species on MS based medium. New trials on McCown WPM are promising in Escallonia and pending for Elaeagnus, Osmanthus and Sarcococca. These in vitro initiated plants are used to develop protocols for inducing genetic mutation by gamma-irradiation, polyploidisation and insertion of rol-genes. A polyploidisation experiment on 2 Escallonia species has shown that the mitotic inhibitors oryzalin or trifluralin are the most efficient polyploidy inducers. We obtained up to 24% E. rubra tetraploidization using 150 µM trifluralin, compared to only 2.8% tetraploids using 1000 µM colchicine. A chronical treatment on E. rubra reveals up to 54% tetraploids after 6 weeks on 5µM trifluralin and 12% octaploids. Further experiments for polyploidisation on different Escallonia species are in execution. The effect of polyploidisation on introducing compactness will be evaluated. Four species of Escallonia were cocultured with Rhizobium rhizogenes bacteria, each species with 4 different strains of Rhizobium. Three species show root growth after 4 weeks on two of the bacteria strains. From these roots, whole plants will be regenerated on which compactness will be evaluated. Experiments with R. rhizogenes will be conducted also for Elaeagnus, Osmanthus and Sarcococca.