Breeding for compact growth using rhizogenic agrobacteria: evaluation of a technique for woody ornamentals

A general trend of consumer interests, living more and more in an urban environment, drives growers to search for more compact plants that are suitable for smaller gardens or balconies. Compactness is often achieved by application of chemical growth regulators. Since sustainability is becoming an important issue for consumers, growers are searching for alternative and environment-friendly methods to control plant growth. In this study, we focus on the introduction of rol genes from Rhizobium rhizogenes to induce compactness in woody ornamentals: Escallonia, Rhododendron and Rosa. For all three genera, induction of hairy roots was successful, depending on the explant and the strain. Hairy root induction for Escallonia was the most efficient when using leaf explants, however Escallonia illinita showed better results with nodal segments. Nodal segments were also the most efficient explant for inducing hairy roots in Rosa. Induction of hairy roots in Rhododendron was achieved by the application of sonication and vacuum infiltration.