Use of alternative breeding techniques for woody ornamentals (ALTERBOOM)

The Alterboom project focused on the use of alternative in vitro breeding techniques (polyploidization and introduction of rol-genes). The aim was to examine to which extent these can result in variation in the phenotype of ornamental tree nursery crops. The specific aim was to achieve varieties of Escallonia and Sarcococca with compact growth. Private gardens are becoming increasingly smaller, which indicates a strong interest in ornamental trees in specific (compact) growth forms that can also be used as patio plants. Until now, new cultivars in the ornamental tree crops are often the result of a "lucky strike", are found in seedling populations, or are spontaneously generated mutations. Targeted or alternative breeding techniques are hardly exploited in woody ornamentals.

During this project we succeeded in developing an in vitro regeneration for Escallonia and Sarcococca. A large in vitro stock of these plants has been used, which has leaded to the optimalization and application of specific protocols for chromosome doubling and rhizogenesis transformation. We have used cell division inhibitors for chromosome duplication. Rol-genes can be introduced through a co-cultivation with Rhizobium rhizogenes. The efficiency of the different techniques has been evaluated. The researchers characterized the obtained plant material genotypically and phenotypically using molecular techniques. The plant material was simultaneously evaluated for the morphological characteristics that are important for commercial applications.

There is a great demand for new and high-quality cultivars in export-oriented floriculture. To facilitate this product innovation, a method has been developed from applied scientific research to induce the rol genes of rhizogenes bacteria in hairy roots. Regenerating these hairy roots into new plants is still a bottleneck that requires further research. Within this project, a protocol was also set up for efficient chromosome doubling in Escallonia. The phenotypic effects of this appear to be highly variable and genotype-dependent. The intended characteristic of compactness has been successfully induced in certain genotypes. Other characteristics, such as cold tolerance, can also find a commercial application. Within a follow-up process, the obtained chromosome doubled plants are evaluated under field conditions. Valorization takes place in collaboration with Best-Select: any new ILVO cultivars are marketed by them in accordance with the ILVO-BestSelect partnership contract.