Interspecific crosses within the Streptocarpus subgenus Streptocarpella and intergeneric crosses between Streptocarpella and Saintpaulia ionantha genotypes

Within the family Gesneriaceae, the two related genera Saintpaulia and Streptocarpus contain species that are used as ornamental potted plants. Crosses within the genus Streptocarpus subgenus Streptocarpella and between Streptocarpus and Saintpaulia ionantha were carried out to produce new ornamental plants. Crossing barriers were localised, and methods to overcome these barriers were tested.The in vitro germination ability of pollen was determined; germination varied from 3 to 85% among genotypes. A high correlation coefficient of 0.99 was found between the assessment of pollen viability using staining with 2,5-diphenyl tetrazolium bromide (MTT) and in vitro germination. From crosses of nine Streptocarpus species from the subgenus Streptocarpella, 11 hybrids were established. Hybridity was confirmed in five of these crosses by morphological and RAPD (random amplified polymorphic DNA) marker analysis.An embryo rescue technique was used in an attempt to overcome existing post-zygotic barriers in intergeneric crosses between S. ionantha and Streptocarpus species. Despite swelling of the ovules, which is usually considered as an indicator for successful fertilisation, no germination of plants from embryos was observed with this method.

► Pollen viability can reliably be determined by in vitro germination or MTT staining.
► Streptocarpus and Saintpaulia pollen can be stored for 6 months at −20 °C.
► Interspecific hybridisation in Streptocarpus is a promising breeding tool.
► For intergeneric hybridisation Streptocarpus should be used as female parent.
► Intergeneric hybrids were not obtained due to post-fertilisation barriers.