POLYPLOID BREEDING OF WILD SOUTH AFRICAN PLECTRANTHUS (SPURFLOWERS) AS NEW FLOWERING POT PLANTS

Plectranthus has been bred to utilize indigenous South African floricultural resources. Diploid species were relatively incompatible in crosses. In order to overcome diploid F₁ hybrid sterility allotetraploids were created on growing shoots of infertile diploid (2n=28) hybrid selections, using colchicine. Tetraploids had enlarged leaves and flowers and showed loss of vigour but seed fertility was restored. In order to obtain sterility and restore vigour in tetraploids, triploid crosses (4n×2n) were made. Triploid status (3n=42) of some plants was verified using flow cytometry. Triploids were, typically, sterile with large flowers and in which hybrid vigour was restored. The use of a new generation of non-invasive triploids, now under testing, is promising compared with diploids. New Plectranthus cultivars have recently been introduced to south China for testing, research and development by the SCNU in Guangdong province. Preliminary results at SCNU in south China are positive for some cultivars.