Somatic hybridisation as a potential tool for Pelargonium improvement

Every year, millions of garden geraniums are being produced for decoration throughout the world. They have been derived from the wild species of Pelargonium indigenous to South Africa. Interspecific crossings may allow the use of the broad genetic pool of the genus Pelargonium. Since such crossings remain difficult, somatic hybridisation could be an alternative to overcome crossing barriers. Here, we present the production of asymmetric somatic hybrids between P. × hortorum ‘Antik Pink’ and Pelargonium wild species 662. Hypocotyl protoplasts of ‘Antik Pink’ and mesophyll protoplasts of 662 were isolated. Before fusion, mesophyll protoplasts of 662 were irradiated with UV light at 254 nm and 0.07 J cm^-2. Thus, the cell division of wild species 662 was completely inactivated as it was shown for the irradiated protoplast control. The irradiated protoplasts did not develop further in protoplast culture medium. Protoplast fusion was performed using polyethylene glycol 6000. Already after one week, the cell wall was re-established and the cells proliferated well in protoplast culture medium. On solid media, protoplast calli developed shoots. Thirty-five plants were planted in soil. RAPD profiles of 12 hybrid plants displayed characteristic DNA fragments of both protoplast donors. By RFLP, the cytoplasmic genome of the regenerated plants was analysed. In six fusion plants, DNA recombination of mitochondrial and plastid genome occurred. By flow cytometry, the DNA amount of the plants was investigated. Protoplast donor ‘Antik Pink’ and 35 fusion plants had nearly the same peak position indicating that only a small part of 662 DNA was included in the asymmetric somatic hybrids. Plants flowered and 32 plants including nine somatic hybrids formed seeds.