About the companion website xiii

1 Introduction 1

1.1 Requirements of plant breeders 1

1.2 Evolution of crop species 4

1.2.1 Why did hunter-gatherers become farmers? 4

1.2.2 What crops were involved? And when did they arise? 5

1.3 Natural and human selection 8

1.4 Contribution of modern plant breeders 8

Think questions 11

2 Modes of Reproduction and Types of Cultivar 13

2.1 Introduction 13

2.2 Modes of reproduction 15

2.2.1 Sexual reproduction 15

2.2.2 Asexual reproduction 16

2.3 Types of cultivar 17

2.3.1 Pure-line cultivars 17

2.3.2 Open-pollinated cultivars 17

2.3.3 Hybrid cultivars 18

2.3.4 Clonal cultivars 18

2.3.5 Synthetic cultivars 18

2.3.6 Multiline cultivars 18

2.3.7 Composite-cross cultivars 19

2.4 Annuals and perennials 19

2.5 Reproductive sterility 19

Think questions 19

3 Breeding Objectives 21

3.1 Introduction 21

3.2 People, politics and economic criteria 22

3.3 Grower profitability 25

3.3.1 Increasing harvestable yield 26

3.3.2 Selection for yield increase 27

3.4 Increasing end-use quality 28

3.4.1 Testing for end-use quality 30

3.5 Increasing pest and disease resistance 31

3.6 Types of plant resistance 34

3.7 Mechanisms for disease resistance 35

3.8 Testing plant resistance 36

3.9 Conclusions 38

Think questions 38

4 Breeding Schemes 40

4.1 Introduction 40

4.2 Development of pure-line cultivars 40

4.2.1 Homozygosity 41

4.2.2 Breeding schemes for pure-line cultivars 43

4.2.3 Number of segregating families and selections 46

4.2.4 Seed increases for cultivar release 46

4.3 Developing multiline cultivars 47

4.3.1 Backcrossing 48

4.4 Development of open-pollinated population cultivars 49

4.4.1 Breeding schemes for open-pollinating population cultivars 49

4.4.2 Backcrossing in open-pollinated population cultivar development 51

4.5 Developing synthetic cultivars 51

4.5.1 Seed production of a synthetic cultivar 53

4.6 Developing hybrid cultivars 53

4.6.1 Heterosis 55

4.6.2 Types of hybrid 58

4.6.3 Breeding system for F1 hybrid cultivars 58

4.6.4 Backcrossing in hybrid cultivar development 59

4.6.5 Hybrid seed production and cultivar release 60

4.7 Development of clonal cultivars 61

4.7.1 Outline of a potato breeding scheme 61

4.7.2 Time to develop clonal cultivars 62

4.7.3 Sexual reproduction in clonal crops 63

4.7.4 Maintaining disease-free parental lines and breeding selections 64

4.7.5 Seed increase of clonal cultivars 64

4.8 Developing apomictic cultivars 64

4.9 Summary 65

Think questions 65

5 Genetics and Plant Breeding 68

5.1 Introduction 68

5.2 Qualitative genetics 68

5.2.1 Genotype/phenotype relationships 70

5.2.2 Segregation of qualitative genes in diploid species 70

5.2.3 Qualitative loci linkage 72

5.2.4 Pleiotropy 76

5.2.5 Epistasis 76

5.2.6 Qualitative inheritance in tetraploid species 77

5.2.7 The chi-square test 79

5.2.8 Family size necessary in qualitative genetic studies 81

5.3 Quantitative genetics 82

5.3.1 The basis of continuous variation 82

5.3.2 Describing continuous variation 83

5.3.3 Relating quantitative genetics and the normal distribution 86

5.3.4 Quantitative genetics models 87

5.3.5 Testing the models 90

5.3.6 Quantitative trait loci 97

Think questions 101

6 Predictions 104

6.1 Introduction 104

6.1.1 Genotype × environment interactions 104

6.1.2 Genetically based predictions 105

6.2 Heritability 106

6.2.1 Broad-sense heritability 107

6.2.2 Narrow-sense heritability 108

6.2.3 Heritability from offspring – parent regression 109

6.3 Diallel crossing designs 110

6.3.1 Griffing’s analysis 111

6.3.2 Hayman and Jinks’ analysis 116

6.4 Cross prediction 119

Think questions 120

7 Selection 125

7.1 Introduction 125

7.2 What to select and when to select 125

7.2.1 Qualitative trait selection 126

7.2.2 Quantitative trait selection 126

7.2.3 Positive and negative selection 126

7.3 Response to selection 127

7.3.1 Association between traits or years 129

7.3.2 Heritability and its limitations 130

7.3.3 Methods of selection 131

7.3.4 Errors in selection 133

7.4 Applied selection 136

7.4.1 Number of genotypes in initial populations 136

7.4.2 Early generation selection 139

7.4.3 Intermediate generation selection 141

7.4.4 Advanced generation selection 143

7.4.5 Analysis of location trials 146

7.5 Cross prediction 151

7.5.1 Univariate cross prediction 152

7.5.2 Multivariate cross prediction 157

7.6 Parental selection 159

7.6.1 Phenotypic evaluation 160

7.6.2 Genotypic evaluation 160

7.6.3 Parental combinations 161

7.6.4 Germplasm collections 162

Think questions 163

8 Broadening the Genetic Basis 168

8.1 Induced mutations 168

8.1.1 Methods of increasing the frequency of mutation 169

8.1.2 Types of mutation 169

8.1.3 Plant parts to be treated 170

8.1.4 Dose rates 170

8.1.5 Dangers of using mutagens 171

8.1.6 Impact of mutation breeding 171

8.1.7 Practical applications 172

8.2 Interspecific and intergeneric hybridization 174

8.2.1 Characters introduced to crops from wild related species 174

8.2.2 Factors involved in interspecific or intergeneric hybridization 175

8.2.3 Post-fertilization 176

8.2.4 Hybrid sterility 176

8.2.5 Backcrossing 176

8.2.6 Increasing genetic diversity 177

8.2.7 Creating new species 177

8.3 Plant genetic transformation 177

8.3.1 A glimpse at the genetic transformation of plants 179

8.3.2 Some applications of genetic engineering to plant breeding 181

8.3.3 Cautions and related issues 183

Think questions 183

9 Contemporary Approaches in Plant Breeding 185

9.1 Introduction 185

9.2 Tissue culture 185

9.2.1 Doubled haploids 185

9.2.2 Some potential issues 186

9.2.3 In vitro multiplication 188

9.3 Molecular markers in plant breeding 188

9.3.1 Theory of using markers 188

9.3.2 Types of marker systems 190

9.3.3 Molecular markers 191

9.3.4 Uses of molecular markers in breeding programmes 192

9.3.5 Issues with markers 195

9.3.6 The increasing availability of genome sequences 195

Think questions 197

10 Practical Considerations 198

10.1 Introduction 198

10.2 Experimental design 198

10.2.1 Unreplicated designs 199

10.2.2 Randomized designs 201

10.2.3 The increasing role of linear mixed model approaches to analyse breeding data 203

10.3 Greenhouse management 204

10.3.1 Artificial hybridization 204

10.3.2 Seed and generation increases 206

10.3.3 Evaluation of breeding lines 206

10.3.4 Environmental control 207

10.3.5 Disease control 207

10.3.6 Economics 208

10.3.7 Experimental design in the glasshouse 209

10.4 Field plot techniques 209

10.4.1 Choice of land 209

10.4.2 Plot size and replication 211

10.4.3 Guard rows and discard rows 212

10.4.4 Machinery 212

10.5 Use of computers in plant breeding 214

10.5.1 Data storage and retrieval 215

10.5.2 Field plan design 217

10.5.3 Clerical operations 217

10.5.4 Data collection 217

10.5.5 Data analysis 218

10.5.6 Selection 219

10.5.7 Data transfer 220

10.5.8 Statistical consultation 220

10.5.9 Ease of use 220

10.6 Release of new cultivars 220

10.6.1 Information needed prior to cultivar release 221

10.6.2 Value in release 221

10.6.3 Cultivar names 222

Think questions 222

11 Current Developments in Plant Breeding 223

11.1 Intellectual property and ownership issues 223

11.1.1 Patents 223

11.2 The impact of biotechnology 225

11.3 The regulation of genetically modified plants 227

11.4 Plant breeding as a career 228

Further Reading 229

Suggested Answers to Think Questions 230

Index 271

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