OVERCOMING CROSSING BARRIERS IN TULIPA L.
Recently we studied in vitro pollination, ovary-slice and ovule culture for Tulipa in compatible (T. gesneriana 'Christmas Marvel' and 'Leen van de Mark') and incongruent (T. gesneriana 'Christmas Marvel' and 'Leen van de Mark' with T. praestans 'Zwanenburg') combinations. In vitro pollination of a compatible combination appeared to be successful, but the seeds are smaller and the number of seeds is less than after pollination on the plant. Ovary-slice and/or ovule culture was set up at various time intervals and resulted for all treatments in germinated embryos for the compatible combinations. Ovary-slice culture can be performed in an earlier stage as ovule culture. The later the treatment started the more ovules germinated. The incongruent combination of T. gesneriana x T. praestans showed entering of some pollen tubes in ovules, resulting in a few germinating ovules when ovary-slice culture followed by ovule culture was applied. This means that in vitro techniques are probably successful for overcoming post-fertilization barriers for incongruent combinations.