Protoplast fusion for the generation of unique Pelargonium plants

Pelargonium occupies a prominent place among bedding and especially balcony plants. The genetic diversity of the current range of Pelargonium cultivars is very limited due to strict incompatibility barriers between different species. For the future it is important to broaden the genetic variability. New colours and shapes are desirable but the primary goal today is the resistance against bacterial diseases. In wild geraniums resistances against Xanthomonas hortorum pv. pelargonii and Ralstonia solanacearum have been found. Somatic hybridization among Pelargonium species represents a real alternative to sexual crossings. Target-orientated fusions were realized with two resistant wild Pelargonium genotypes. Different experimental conditions for the protoplast fusion were tested, including the biology of the plant material (various genotypes and tissues), physical and chemical factors. Both established methods, chemical fusion by PEG and electrofusion, have been performed. By modifying the culture conditions, it was possible to induce cell divisions, formation of microcolonies up to calli. The induction of further development of calli was always extremely difficult. Mostly, the calli have shown a severe browning and endophytes. In at least 11 experiments plants succeeded to regenerate. The plants have been extensively characterized (phenotypically, molecularly, and flow-cytometrically). Selected plants with modified appearance or ploidy were transferred to soil and adapted to the greenhouse conditions. Additionally, some plants with the fusion partner P. graveolens and a changed DNA content were investigated for the profile of volatile components by GC analysis. Compared with the parent’s plants the GC analysis revealed new or absent volatiles in fusion plants. The successful completion of fusion experiments underlines the feasibility of somatic hybridization for Pelargonium with the aim of increasing the genetic variability.