Bertling, Isa.Hannweg, Karin Fiona.2016-10-142016-10-1420152015http://hdl.handle.net/10413/13497Doctor of Philosophy in Agriculture (Horticultural Science)Polyploidy is a naturally-occurring phenomenon in plants and has been reported as an important pathway for evolution and speciation; it is estimated that a large percentage of flowering plants are polyploid in origin. Although the first plant polyploid was discovered over a century ago, the genetic and evolutionary implications of polyploidy have not been fully elucidated. On a more practical level, there are many opportunities for utilizing induced polyploidy as a valuable tool in traditional plant breeding programmes. South Africa has the highest recorded plant species density in the world, however, many of these species have only marginal potential due to size and other constraints. Induced polyploids may be expected to exhibit one, or more, of the following characteristics resulting in the improvement or the development of new economically important plants: larger tuber, rhizome or root size; increased flower or fruit size; enhanced flower colour intensity, improved drought tolerance, increased bio-mass; improved photosynthetic capacity; larger and/or thicker leaves; dwarfism; increased secondary metabolite production, e.g. medicinal compounds. Several plant species (Crocosmia aurea, Tetradenia riparia, Siphonochilus aethiopicus and Plectranthus esculentus) were selected for the induction of polyploidy and various horticultural characteristics evaluated. Methods for the successful induction of polyploidy were developed for all selected species. By evaluating various horticultural characteristics of the induced polyploids it was determined that flower size, plant vigour and nematode resistance, as well as essential oil content and bioactivity could be significantly improved in all tested species. Induced polyploidy could, therefore, have a significant impact on the development of economically-viable novel crops indigenous to southern Africa.en-ZAPolyploidy.Indigenous crops -- South Africa.Transgenic plants -- South Africa.Theses -- Horticultural science.Thesis