S05 - Session O4 - Ri technology as a breeding tool to create compact ornamentals

Authors: Siel Desmet, Ellen De Keyser, Johan Van Huylenbroeck, Danny Geelen, Emmy Dhooghe *

In ornamental horticulture, a compact growth habit is often achieved by application of plant growth regulators. To minimize the harmful exposure to these plant growth regulators for growers and to establish a more sustainable and environmental-friendly plant production, we used the Ri technology as a breeding tool to generate new cultivars that are less dependent on chemical growth inhibition and are genetically more compact. In this study, we examined the effect of co-cultivation of tissue cultured explants with natural wild-type bacterial strains of Rhizobium rhizogenes on compactness. R. rhizogenes modifies the host plant nuclear genome by inserting oncogenes ( rol genes). Expression of these rol genes results in excessive formation of adventitious roots which are referred to as hairy roots. Plants regenerated from hairy roots typically display extensive lateral branching and reduced apical dominance. These traits are reminiscent to the compactness obtained upon treatment with chemical plant growth inhibitors. We were able to introduce the rol genes into different types of ornamentals, a.o. Osteospermum fruticosum , Sinningia speciosa and Viola spp. We will report on the methodology used, the bottlenecks to overcome and the morphology of the regenerated plants in the different plant genera. Moreover, we will describe the variation in copy-numbers of the transferred genes and the number of inserts in the plant genome.