New strategies for improving varietal creation in Rosa

The creation of new rose varieties is a process that takes at least five years. A general prerequisite for a successful breeding program is to obtain wide offspring on which selection of seedlings with the desired traits can be performed. However, modern rose cultivars are characterized by low seed set
and poor seed germination which hinders the achievement of a high number of seedlings. Premature death of developing embryos due to incompatibility and delayed germination, caused by seed dormancy, are the most important causes.
The main objective of this study was to improve hybrid tea seed production efficiency. 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 the Nirp International 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 (Pipino et all., 2011).
Subsequently, to deepen the knowledge about seed development, we studied the embryo morphogenesis of two floribunda roses at seven time points, from 3 to 60 days after pollination (DAP). Embryos resulted fully developed at 15 DAP while seeds at 30 DAP. In parallel, the abscissic acid (ABA) concentration determined in the developing embryos showed basal levels from 30 DAP on.
Based on these results, we focused on in vitro techniques which may be used to rescue abortive or dormant embryos, thus increasing the numbers of plants obtained from crosses resulting in very few viable seeds, or to shorten the time needed to obtain seedlings. Our results suggest that the optimal time point for performing embryo rescue in hybrid tetraploid roses is between 15 and 30 DAP.