................................................................................................................................................. iii Opsomming ............................................................................................................................................ iv Acknowledgements ................................................................................................................................. v Publications arising from this thesis ...................................................................................................... vi List of Figures ......................................................................................................................................... x List of Tables ......................................................................................................................................... xi List of Abbreviations ............................................................................................................................ xii Chapter 1: General Introduction ....................................................................................................... 15 Aims, Objectives and Layout of Thesis ............................................................................................ 19 Literature cited: ................................................................................................................................. 20 Chapter 2: Evolutionary and Physiological Overview of Plant Parasitism .................................. 24 2.