......................................................................................................................................xii CHAPTER 1: GENERAL INTRODUCTION.....................................................................................1 CHAPTER 2: LITERATURE REVIEW .............................................................................................5 2.1. Seed vigour ...........................................................................................................................5 2.2. Deterioration factors that influence seed vigour...................................................................5 2.3. Seed vigour tests ...................................................................................................................7 2.3.1. Non-standard temperature as vigour test............................................................8 2.3.2. Accelerated ageing test.......................................................................................8 2.3.3. Saturated accelerated ageing test........................................................................9 2.4. Predicting emergence of vegetable seed using vigour tests..................................................9 2.5. Improving vigour of onion seeds though priming ..............................................................11 2.5.1. Germination and priming .................................................................................12 2.5.2. Factors affecting priming .................................................................................13 a) Temperature ...............................................................................................14 b) Oxygen availability....................................................................................14 c) Osmotic potential .......................................................................................15 d) Duration of treatment.................................................................................16 e) Seed quality................................................................................................16 f) Drying.........................................................................................................17 University of Pretoria etd – Fessehazion, M K (2005)