Interspecific crosses were made between 76 Tulipa gesneriana cultivars and 28 botanical Tulipa species. Tulipa gesneriana proved fully congruent (all cross-combinations giving hybrid progeny) with members of the subsection Gesnerianae, was moderately affiliated (50% of all cross-combinations giving hybrid progeny) with representatives of the subsection Eichleres, and was found to be incongruent with most other Tulipa species (except T. stapfii of the subsection Oculussolis).Relationships between T. gesneriana and some representatives of the subsection Eichleres were addressed in more detail. Seeds were harvested in all cross-combinations, but the number of seeds depended on the T. gesneriana cultivar used as the female partner. Apparently, the maternal genotype did affect pre-or post-fertilization processes.T. gesneriana was not crossable with T. kaufmanniana of the subsection Spiranthera. In this specific case, however, a bridge cross was used to overcome incongruity. For this, T. kaufmanniana was first combined with T. greigii, and the hybrid was subsequently crossed with T. gesneriana.These results demonstrate possibilities for interspecific cross-combinations in tulips and have offered opportunities for the introduction of desired new traits in the cultivated tulip.

Embryo-rescue was studied as a means to overcome post-fertilization barriers in interspecific crosses in the genus Tulipa . With compatible T gesneriana L. cultivar crosses, ovule culture was found to be superior to isolated embryo culture. Complete plantlet formation was possible from an embryo size of about 0 .5 mm onwards .In the interspecific cross T gesneriana x T kaufmanniana, which is hampered by embryo breakdown, successful rescue of abortive embryos was demonstrated . Optimal embryo-rescue was achieved in cultures started seven to nine weeks after pollination . With cultures initiated at a later time, the rate of success decreased . A low number of germinative seeds were obtained after normal ripening of the seed pods, but by using ovule culture the efficiency of seedling formation could be increased dramatically .The ovule culture procedure will allow novel crosses and will offer new possibilities for the introduction of desirable genes into tulip cultivars .

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In order to investigate the inheritance of flower colour in tulips, seven cultivars were crossed and selfed in a diallel . Of these parents and their F,'s the relative amounts of carotenoids, delphinidin, cyanidin, pelargonidin, quercetin and kaempferol were determined .For delphinidin, quercetin and kaempferol only additive gene action was determined, and for carotenoids, cyanidin and pelargonidin also non-additive gene action and plasmic differences .Biosynthesis of delphinidin and pelargonidin was only found when cyanidin was present, while synthesis of delphinidin and pelargonidin was antagonistic .