(White Clover) and Trifolium Uniflorum
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Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author. Analysis of seed production traits in interspecific hybrids between Trifolium repens (white clover) and Trifolium uniflorum A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Breeding and Genetics at Massey University, Palmerston North, New Zealand Muhammad Naeem 2013 I dedicate this effort to my homeland PAKISTAN i ii Analysis of seed production traits in interspecific hybrids between Trifolium repens (white clover) and Trifolium uniflorum Trifolium repens L. (white clover) is an important component of New Zealand’s pastoral and herbage seed industries. It has delicate shallow roots vulnerable to drought and pest attack. T. uniflorum is a wild species, adapted to dry environments, with deep woody roots but poor vegetative growth and only 1-3 florets per head. Hybridization was done to incorporate the drought tolerance and root characteristics of T. uniflorum into white clover. The primary hybrids (F1 and BC1F1) showed poor seed production. The project aimed to analyse this problem and improve seed production by further hybridization and selection. The hybrids expressed high variation for almost all seed production traits. Heads per plant, florets per head and seeds per floret were important determinants with moderate to high heritabilities. The derived traits seeds per head, florets per plant and seeds per plant expressed low-moderate to moderate heritabilities. Flowering pattern showed high heritability. No negative correlations between seed production and root traits were found. Whereas nodes per stolon favoured head production, stolon production had a negative effect on nodes per stolon. No negative associations between head production, persistence and foliage production of the hybrids were observed. No cytoplasmic influences were evident. The hybrids showed, higher self fertility and a wider gap between potential and actual seed yield than white clover. The BC1F1 generation produced low numbers of heads per plant and seeds per floret. Intercrossing coupled with recurrent selection improved variation, fertility and realization of potential seed yield. The second backcrossed and intercrossed generations had high seeds per floret and plant. Backcrossing of selected hybrids effectively recovered the white clover phenotype and created new variation. The BC2F1 and BC3F1 generations expressed the better head production ability of T. uniflorum combined with the bigger head size of white clover. Seed production capability of the hybrids was successfully restored. More genetic variation was created in the hybrids for future breeding and selection endeavours. iii iv Acknowledgements I acknowledge Massey University for providing me with a learning atmosphere, AgResearch for making available an excellent working environment, and the Higher Education Commission of Pakistan for awarding me a scholarship to pursue this endeavour. I am grateful to Professor Warren Williams for his patience and guidance which played a pivotal role in successful completion of this research. He offered me the topic of my interest to work on, and provided me a friendly working atmosphere to plan, work and learn independently as well as in a team. He remained available and supportive throughout this study. I am thankful to Professor Peter Kemp and Dr. James Millner for their valuable contributions in planning the research and finalizing the thesis. Professor Peter Kemp was very supportive in all stages of my research, right from finding a co-supervisor in an area of my interest until completion of this thesis. I am very thankful to Isabelle Williams for being always ready to guide and provide any practical help needed. She developed primary hybrid plants from which selected material formed the basis of this research project. I am also very grateful to Keith Widdup at Lincoln who selected the plants from the primary hybrids to be used in this project. His highly efficient selection provided a strong base to the project. This research work was not possible without the help of Brian Mackenzie who provided all infrastructure support, Michelle Williamson who provided administrative assistance and Paco Alvarez who helped me in getting the root data. I also acknowledge Dr. Wajid Hussain and Professor R. G. Thomas for their help with the literature review. I appreciate the refreshing company of my friend Ihsan Ullah. This project was a typical breeding work, involving a lot of time and labour. Its accomplishment was not possible without the remarkable support of my wife Sumera Abdul Rehman. She was always there whenever I needed any practical or emotional support. My friend Ibrar Ahmed remained helpful to me, from planting the first cuttings of the starting material until the submission of the thesis. v I am grateful to the Creator, who created wonderful things to get explored. I always felt and enjoyed the blessings of my parents and support of all my extended family. My father has always been a source of inspiration for me. The support of all above mentioned sources made this study a pleasant experience. I am very thankful to all of them. vi TABLE OF CONTENTS Abstract iii Acknowledgements v List of Figures xi List of Tables xiv List of Plates xvii List of Abbreviations xviii Chapter 1 INTRODUCTION 1 1.1 Background 1 1.1.1 General background 1 1.1.2 Specific background 3 1.2 Importance of the study 3 1.3 Hypothesis and objectives 4 1.4 Methodology 5 1.5 Phases of the study 7 Chapter 2 LITERATURE REVIEW 10 2.1 The New Zealand seed industry 10 2.1.1 White clover seed 12 2.2 White clover seed production 15 2.2.1 Pollination 17 2.2.2 Ovule abortion 19 2.2.3 Inflorescences 21 2.2.4 Peduncle 22 2.2.5 Environment 23 2.2.6 Seed crop management 24 2.2.7 Growth regulators 29 2.2.8 Relationship between vegetative and reproductive growth 30 2.2.9 Molecular analysis 32 2.3 Wide hybridization 33 2.3.1 Biology of wide hybridization 34 2.3.2 Prefertilization barriers 36 2.3.3 Post fertilization barriers 37 2.3.4 Chromosomal contribution 38 vii 2.3.5 Genic contribution 40 2.3.6 Endospermic contribution 41 2.3.7 Genomic imprinting 43 2.3.8 Rapid recovery of the recurrent parent 44 2.3.9 Contribution of mating designs 46 2.4 Wide hybridization in agriculture 47 2.4.1 Early history 48 2.4.2 Artificial wide hybridization 49 2.5 Wide hybridization among Trifolium species 50 2.5.1 The genus Trifolium 50 2.5.2 Wide hybridization 52 2.6 Interspecific hybridization of white clover 56 2.6.1 White clover 56 2.6.2 Hybridization with T. ambiguum 57 2.6.3 Hybridization with T. occidentale 60 2.6.4 Hybridization with T. nigrescens 62 2.6.5 Hybridization with T. uniflorum 65 2.7 Summary 70 Chapter 3 EXPLORING VARIABILITY 72 3.1 Introduction 72 3.2 Materials and methods 72 3.2.1 Measurements 74 3.2.2 Selection criteria 77 3.3 Analyses and results 79 3.3.1 Exploring the existing variation 79 3.3.2 Differences in parental effects 89 3.3.3 Association among the traits 90 3.3.4 Developing selection criteria 93 3.3.5 Improving variation for future use 100 3.4 Summary 100 Chapter 4 MANAGING VARIABILITY 102 4.1 Introduction 102 4.2 Research questions 102 viii 4.3 Materials and methods 103 4.3.1 Plant material 103 4.3.2 Experimental plans 106 4.3.3 Measurements 110 4.4 Analyses and results 112 4.4.1 General features of the data 112 4.4.2 Potential and actual seed setting 115 4.4.3 Associations among the traits 117 4.4.4 Differences in parental effects 123 4.4.5 Difference in family effect 135 4.4.6 Inheritance of the traits 142 4.4.7 Difference in generation effect 147 4.5 Summary 150 Chapter 5 TRAIT ASSOCIATION AND COMPARING MATING 151 DESIGNS 5.1 Introduction 151 5.2 Research questions 151 5.3 Material and methods 151 5.3.1 Plant material 151 5.3.2 Experimental plans 154 5.3.3 Measurements 160 5.4 Analyses and results 164 5.4.1 General features 165 5.4.2 Seed development in T. uniflorum 168 5.4.3 Potential and actual seed setting 171 5.4.4 Associations among the traits 174 5.4.5 Differences in parental effects 181 5.4.6 Relationships among families 186 5.4.7 Inbreeding effects 191 5.4.8 Inheritance of the traits 196 5.4.9 Effects of different mating designs 210 5.5 Summary 224 ix Chapter 6 DISCUSSION 227 6.1 Seed production of the hybrids 229 6.1.1 Fertility of the hybrids 229 6.1.2 Differences between potential and actual seed yields 231 6.2 Associations among the traits 232 6.2.1 Reproductive traits 233 6.2.2 Vegetative traits 235 6.2.3 Root traits 237 6.3 Genetic variation 238 6.3.1 Sources of variation 238 6.3.2 Levels of variation 243 6.4 Inheritance of the traits 246 6.4.1 Progeny comparisons 246 6.4.2 Narrow sense heritability 251 6.5 Inbreeding depression 252 6.6 Effects of different breeding strategies 253 6.6.1 Parental species 254 6.6.2 Hybrid generations 256 6.6.3 Important generations 262 Chapter 7 CONCLUSION 264 7.1 Conclusion 264 7.2 Future work 268 REFERENCES 269 APPENDICES 283 1 Sequence of main steps for all experiments 283 2 Details of families involved in study of inheritance of flowering pattern 284 3 Mean daily temperature and sunshine data for 2007-2011.