Hibiscus rosa-sinensis is an ornamental shrub in tropical and subtropical
regions. Limitation of its use as an outdoor ornamental plant in a temperate climate is due to chilling sensitivity. Cold hardiness is a highly complex trait, involving multiple genes. Improvement of H. rosa-sinensis for increased chilling tolerance by conventional breeding is unlikely because there is a lack of genetic information in relation to this trait within this species. In the Hibiscus genus, cold hardiness is available, but only in a few species. Attempts to create cold tolerant Hibiscus plants resembling H. rosa-sinensis suitable for Nordic climate have not been successful so far. In ornamental breeding wide hybridization is a major source of genetic variation, and can also be a promising approach to introgress cold hardiness in H. rosa-sinensis. The objective of the present study is to evaluate the possibilities of interspecific hybridization between H. rosa-sinensis and cold tolerant Hibiscus species. The main focus was to identify prefertilization hybridization barriers using microscopic methods. Pollen viability was determined by staining with acetocarmine. An attempt to resolve the ability of pollen grains to germinate was made in vitro using artificial medium. In situ
pollen germination and pollen tube growth were monitored using staining with aniline blue. Crosses between H. rosa-sinensis and H. syriacus or H. moscheutos, did not result in seed formation, due to hybridization barriers.