Hybrid rose breeding: improving seed production efficiency

The creation of a new rose variety is a process that takes at least five years. A general prerequisite for a successful breeding programme is to obtain wide offspring on which selection of seedlings with the desired traits can be performed. However, rose cultivars are characterised by low seed set and poor seed germination which hinder the achievement of a high number of seedlings. The main objective of this study was to explore the potential of improving seed production efficiency during the first phase of the breeding process. Experiments were initially conducted to gain insight into the fertility of pollen donors and their effect on a successful hybridization. To this end, we studied the crossing results of a 14 years old private company breeding database. High correlations were found between the number of seeds produced per hybridization and either the pollen diameter or the percentage of normal pollen, thus allowing the development and validation of a prediction model for seed set based on pollen quality. Subsequently, to deepen the knowledge about embryo development in hybrid roses, we studied the embryo morphogenesis of two floribunda roses at seven time points, from 3 to 60 days after pollination (DAP). Embryos were fully developed at 15 DAP while seeds at 30 DAP. In parallel, the abscisic acid (ABA) content in the developing embryos decreased to basal level from 30 DAP on. Finally, since rose breeders need reliable and efficient germination protocols to exploit all vital embryos, a third experi¬mental work was set to evaluate practice oriented treatments to enhance seed germ¬ination. Both chemical and microbial seed scarifications were carried out. It is clear that a complex combination of multiple treatments needs to be applied to overcome the physical restrictions of the seed coat and the physiological dormancy. As a result of this multi-objective approach, which addressed the main aspects of the first year of the rose breeding programme, a number of practical-oriented solutions are proposed.