Approaches for selection of sexual St. John's wort strains (Hypericum perforatum L.} for combination breeding

St. John's wart (Hypericum perforatum L.) reproduces pseudogameous facultatively apomictical/y and it is, in general, tetrapJoid. The high level of apomixis makes the combination of aspired characteristics of different donors in common progenies, difficult by controlled crossing. Only 2.6% of the 139 plant populations investigated were obligatory sexual. These investigations were aimed at testing methods for the development of tetrap/oid sexual forms which can be used as maternal partners in crossing programmes. Progenies of diploid sexual individual plants originating from selected populations revealed proportions of diploid sexual plants of between 49.6 and 96.3%. The progenies of two tetrap/oid sexual plants had 34.9 and 71% sexual reproduction. The rates of tetraploid sexual plants in progenies of sexual trip/aid plants, generated by crossing diploid and tetraploid parents, were 7.1-53.8%. The rate of tetrap/oid sexual plants after co/chicine treatment of seeds of diploid sexual plants was very low. These investigations show that the selection of tetra plaid sexual plants for combination breeding is possible in principle. The reproductive types of the plants were assigned by flow cytometry determination of the DNA-content of the embryos and the endosperms of a mixture of about 50 seeds/plant. For the assignment of reproductive types, more repetitions with a bulked seed screen and also single seed analysis should be used in future investigations because the accuracy of the reproductive type differentiation and therefore the selection response can be improved.