Protoplast isolation and culture from Streptocarpus, followed by fusion with Saintpaulia ionantha protoplasts.

摘要

To produce new ornamental plants by combining Saintpaulia ionantha and Streptocarpus, two closely related genera of the family Gesneriaceae, protoplast fusions were accomplished. Various tissues were evaluated as potential starting materials for protoplast isolation from Streptocarpus saxorum x S. stomandrus and S. caulescens. Sufficient protoplast yields between 2 and 3.6x105 g-1 fresh mass with high viabilities from 68-96% were obtained from the leaves of in vitro shoot cultures, which were grown in liquid medium in the dark. After 14 days of culture, cell divisions reached frequencies between 2.1 and 5.5%, depending on the species, and vigorously growing calluses were obtained. However, only root formation was induced on these calluses; no shoot induction was achieved. For the protoplast fusion, polyethylene glycol was applied and an appropriate fusion protocol was developed. The fusion rate, which was determined by cell nucleus staining with ethidium bromide, reached up to 35% binuclear protoplasts. Cell divisions were observed in four fusion experiments between two Streptocarpus species and two Saintpaulia ionantha varieties, and in two of these experiments, callus formation was also observed. To identify possible hybrid calluses, calluses were preselected by flow cytometry and analysed with RAPD markers. In 27 out of 30 tetraploid calluses the DNA bands from the Streptocarpus parent were dominant or were the only ones detected, in one the bands from the Saintpaulia parent, and only two calluses with bands of both parents were observed. This evidence supports the notion that successful fusions between Saintpaulia and Streptocarpus are possible, but no plants could be regenerated from the hybrid calluses.