Breeding program of sweet potato and yacon in Belgium: Flowering induction, optimisation of tissue culture techniques, and development of molecular markers

This research project is part of "Yacobat", an open source breeding program for the development of new varieties of sweet potato (Ipomoea batatas) and yacon (Smallanthus sonchifolius) adapted to Belgium, with VIVES college, as coordinating centre. In one hand, the VIVES collection of sweet potato has 21 varieties. Most of those varieties flower too late or do not flower in the local climate, so few varieties were grafted on closely related Ipomoea spp. to induce flowering. In the first experiment of the 8 rootstock tested, “Gradpa Otto” was the one that had the best balance between grafting efficiency and flower induction efficiency (44.4 per cent and 70 per cent). In the second experiment, “Star of Yalta” had the best grafting efficiency (78.5 per cent) from the 4 rootstock tested. From the flowers obtained in the first grafting experiment, the pollen viability was analysed. Five germination media with different concentrations of sucrose were tested. But, only pollen from “Evangeline” germinated and only in the media with 30 per cent of sucrose. The ploidy level of the collection was hexaploid (2n equal to 6x) analysed by flow cytometry, with “Evangeline” as external reference. Due the high incidence of virus in sweet potato, meristem culture optimization was necessary to regenerate and to preserve a virus free collection in vitro. Of the two formulations tested, M2 (MS plus 2mg per l BAP plus 0,01 mg per l NAA plus 1 mg per l GA3) provided higher number of fully functional new plants. For the molecular assessment of the collection two molecular markers were tested. ISSRs provided poor results with a great lack of reproducibility. While, 5 microsatellites allowed to evaluate the genetic variability and to characterize the varieties within the collection. In the other hand, the VIVES collection of yacon has 11 varieties. Most of those varieties flowers too late in the local climate, so two different approaches were tested to induce flowering in yacon. Short-days treatment failed, so, grafting on the close related sunflower (Helianthus annuus) was tested. Of the three varieties tested “Pacino Gold” was the rootstock that had the best grafting efficiency (37.7 per cent) but the flower induction efficiency was still unknown at the moment of collecting the results. Afterwards, the pollen viability analysis was tested in a single evaluation with FDA staining obtaining a low viability (8 per cent). The ploidy level of the collection was octoploid (2n equal to 8x) analysed by flow cytometry with 103 as external reference, except for 107 and 110 which were doubtful (possibly tetraploid and hexaploid). To reduce the maintenance work of the yacon tissue culture collection was necessary to reduce its growing rate in vitro. 9 formulations were tested and finally, WPM supplemented with 0.5 and 2 mg per l BAP provided the best results. For the molecular assessment of the collection ISSRs markers were tested. 4 ISSRs primers allowed evaluating the genetic variability of the VIVES collection. However, further experiments are required to confirm their reproducibility