Hybridization between Pelargonium acetosum L’Hér. and Pelargonium ×peltatum

Pelargonium acetosum L’Hér. is a wild species from South Africa with decorative bluish foliage. Only few reports describe crossings between P. acetosum and P. peltatum L’Hér. (or P. ×peltatum). Therefore, information about hybridization barriers is limited. In this study, two different genotypes of Pelargonium acetosum (AC1 and AC2) were crossed with the diploid P. ×peltatum ‘Tornado Fuchsia’ (PTF). Embryos and F1 hybrids from the combination AC1 × PTF were hampered by chlorophyll deficiencies. Embryos and seeds of the combination AC2 × PTF were underdeveloped. The reciprocal combination PTF × AC1 did not show any fruit set. The combination PTF × AC2 resulted in low numbers of seeds, which were normally developed. Hybrids from seeds were only obtained from the combinations AC1 × PTF and PTF × AC2. Embryo rescue of the combinations AC1 × PTF and AC2 × PTF resulted in few but viable hybrids. Flowers of all hybrids had shrivelled anthers and proved to be sterile. The occurrence of most hybridization barriers varied strongly between the different combinations and depended on both the genotype and the direction of cross-breeding. The bluish leaf colour did not appear among the F1. To overcome hybrid sterility a polyploidization is suggested.