Plant Diseases (eBook)

Front Cover 
1 
Plant Diseases: Epidemics and Control 4
Copyright Page 
5 
Table of Contents 
8 
PREFACE 6
CHAPTER 1. The Control of Plant Disease Studied as Part of Epidemiology 18
1.1. The Population of Pathogens 18
1.2. Epidemics and Biological Warfare 19
1.3. The Language of Epidemiology. Some Expressions 20
1.4. A Suggested Order of Reading the Chapters 21
1.5. The Spread of Disease and Its Bearing on the Technique of Field Experiments 22
CHAPTER 2. About Interest on Money. Logarithmic Increase 24
Summary 8
2.1. Interest is Proportional to Initial Capital 24
2.2. Interest per Cent and Interest per Unit 25
2.3. Simple Interest 25
2.4. Discontinuous Compound Interest 25
2.5. Continuous Compound Interest 26
2.6. Continuous Compound Interest Seen in Another Way 28
2.7. Equivalent Rates of Continuous and Discontinuous Compound Interest 29
2.8. Variable Rates of Continuous Compound Interest 30
2.9. Consistent Units of Time 30
2.10. Natural Logarithms 31
2.11. Logarithmic Increase 31
Exercises 32
CHAPTER 3. The Logarithmic and the Apparent Infection Rates 34
Summary 34
3.1. Statement of the General Problem of This Book 34
3.2. The Intermittent Increase of Disease 35
3.3. The Percentage and the Proportion of Disease 37
3.4. Logarithmic Increase of Disease and Increase That Is Not Logarithmic 37
3.5. The Meaning of Infection Rates 38
3.6. The Words, "per Unit," Again 39
Exercises 39
CHAPTER 4. How to Plot the Progress of an Epidemic 45
Summary 9
4.1. The Increase of Disease with Time 45
4.2. Two Ways in Which Disease Can Increase with Time. "Compound Interest Disease'' and "Simple Interest Disease" 47
4.3. Increase of Disease by Multiplication. "Compound Interest Disease" 48
4.4. The Increase of Disease without Multiplication. "Simple Interest Disease" 50
4.5. The Correction Factor (1 — x) 51
4.6. The Reason for Using Log [1/(1 — x)] When There Is No Multiplication 53
Exercises 54
Epilog 56
CHAPTER 5. The Basic Infection Rate 57
Summary 57
5.1. The Basic Infection Rate and the Latent Period 57
5.2. The Incubation Period 58
5.3. Some Biological Meanings 60
5.4. The Early Stages of Artificially Induced Epidemics of Stem Rust of Wheat 61
5.5. The Relation between r and R 64
5.6. How R Changes as an Epidemic Progresses 65
5.7. The Relation between r and R 67
5.8. The Products prl, pr, and pR 68
5.9. The Limit to the Explosiveness of an Epidemic 69
5.10. A Discontinuous Infection Model 70
5.11. Period of Infection is Reduced to a Point Each Year and p is 1 Year 71
Exercises 72
CHAPTER 6. The Latent Period 76
Summary 76
6.1. Logarithmic Increase of Infection with p and R Constant 77
6.2. The Variation of rl with Time, with p and R Constant 79
6.3. The Variation of rl as an Average Value over an Interval of Time 81
6.4. The Effect of a Prolonged Period of Inoculation on the Variation of rl 82
6.5. The Effect of Variation of the Latent Period p on the Variation of rl 83
6.6. A Wider Interpretation of rl 
84 
6.7. The Error from Using a Constant Mean Value p in Eq. (5.7) Instead of a Constant Value p 85
6.8. Increase of Infection beyond the Logarithmic Phase with p and R Constant 86
6.9. The Estimation of rl after the Logarithmic Stage of an Epidemic 87
6.10. Three Arbitrary Stages in an Epidemic 89
Exercise 91
CHAPTER 7. Average Values of Infection Rates. Increase of Populations of Lesions and of Foci. Independent Action of Propagules 92
Summary 92
7.1. The Relative Infection Rate as an Average 92
7.2. The Logarithmic Infection Rate 93
7.3. The Growth of an Individual Lesion in Relation to the Growth of a Population of Lesions 94
7.4. The Growth of Foci 94
7.5. The Spread of Pathogens in Relation to the Focal Pattern 97
7.6. The Growth of an Individual Focus in Relation to the Growth of a Population of Foci 99
7.7. The Mass Increase of Foci 102
7.8. Massed Foci of Potato Blight. The Epidemic S 105
7.9. The Independent Action of Propagules. The General Problem 106
7.10. The Independent Action of Propagules. Puccinia graminis, Phytophthora infestans, and Some Other Pathogens 109
CHAPTER 8. Corrected Infection Rates 111
Summary 111
8.1. Correction of rl and r for the Growth of the Host Plants 111
8.2. Correction for Removals 114
8.3. Relation between the Corrected Basic Infection Rate Rc and r 116
8.4. Balance in Epidemics 118
8.5. Relation between Rc and r 118
8.6. A Threshold Theorem 119
8.7. The Threshold Theorem and Control of Disease by Fungicides 120
8.8. The Threshold in Epidemics of Two Systemic Diseases 123
8.9. Looking Back 124
Exercises and Examples 125
CHAPTER 9. Stochastic Methods in Epidemiology 128
Summary 128
9.1. Transforming Proportions of Disease 128
9.2. Sampling Errors of Estimates of Infection Rates 130
9.3. Deterministic and Probability Methods in Epidemiology 130
9.4. Multiple Infections with Systemic Disease 130
9.5. The Overlapping of Local Lesions 132
9.6. The Influence of Numbers 133
9.7. Comparisons with Medical Epidemiology 133
CHAPTER 10. A Guide to the Chapters on Control of Disease 135
10.1. The General Proposition 135
10.2. Control Measures That Reduce x0: Sanitation, Vertical Resistance, and Chemical Eradication, 136
10.3. Control Measures That Reduce r: Horizontal Resistance and Protectant Fungicides 137
CHAPTER 11. Sanitation with Special Reference to Potato Blight 139
Summary 139
11.1. A Definition of Sanitation 139
11.2. How the Infection Rate Affects the Benefit from Sanita-tion 141
11.3. The Effect of the Sanitation Ratio 143
11.4. The Effect of Sanitation on Disease after the Logarithmic Phase 144
115. The Use of Eqs. (11.1) and (11.2) when Disease Is in Foci 145
11.6. Phytophthora infestans from Potato Cull Piles 145
11.7. Focal Outbreaks and General Epidemics of Potato Blight 147
11.8. The Change from Focal Outbreaks to General Epidemics 149
11.9. The Delay of the General Epidemic as a Result of Destroying Cull Piles 150
11.10. Cull Piles and Blight Forecasts 151
11.11. The Increase in Yield as a Result of Sanitation 152
CHAPTER 12. Sanitation with Special Reference to Wheat Stem Rust 154
Summary 154
12.1. Potato Blight and Wheat Stem Rust Contrasted and Compared 154
12.2. Stem Rust and Barberry Eradication 156
12.3. Focal Outbreaks and General Epidemics of Wheat Stem Rust 160
12.4. Barberry Eradication and Wheat Stem Rust in Northwestern Europe 161
12.5. The Relation between Sanitation and the Percentage of Stem Rust in Ripe Fields 162
12.6. The Reduction by Sanitation of Loss in Yield 164
12.7. The Relation between Loss of Yield and the Area under Stem Rust Progress Curve 167
12.8. The Infection Rate in Relation to Benefits Gained from Sanitation 172
12.9. Potato Blight and Wheat Stem Rust Compared Again 173
CHAPTER 13. Sanitation and Two Systemic Diseases. Sanitation when Other Things Are Not Equal 174
Summary 174
13.1. Common Bunt of Wheat and Fusarium Wilt of Tomatoes 174
13.2. The Relation between the Number of Spores and Infection of Wheat by Bunt 175
13.3. The Relation between the Number of Spores and Infection of Tomatoes with Fvsarium Wilt 177
13.4. The Effect of Sanitation on Disease of the "Simple Interest" Type 178
13.5. The Benefit of Reducing Systemic Disease by Sanitation 179
13.6. Dependability of Sanitation as a Method of Disease Control in Relation to rt 180
13.7. Sanitation in Relation to the Absolute Amount of Initial Inoculum 182
13.8. A Comparison between "Simple Interest" and "Compound Interest" Disease in Relation to Sanitation 183
Exercise 186
CHAPTER 14. Vertical and Horizontal Resistance against Potato Blight 188
Summary 188
14.1. The Relation between Races of Phytophthora in festans and Resistance Genes in the Potato 188
14.2. The Mutability of Races of Phytophthora infestans 190
14.3. Vertical and Horizontal Resistance 191
14.4. The Unimportance of Vertical Resistance in Varieties without R Genes 194
14.5. The Distribution of Races 197
14.6. The Effect of Popularity on the Behavior of R-Types toward Blight 197
14.7. The Place of Vertical and Horizontal Resistance in Epidemiology 201
14.8. Analysis of Kirste's Findings: the Effect of Vertical Resistance 202
14.9. Analysis of Kirste's Findings: the Effect of Horizontal Resistance 206
14.10. Other Evidence for a Difference in Horizontal Resistance 207
14.11. Some Published Assessments of Blight Resistance 208
14.12. The Vertifolia Effect 211
14.13. Blight on Solanum demissum 212
14.14. Blight on Mixtures of Clones 213
14.15. What Vertical Resistance Implies 214
14.16. The Manifestations of Horizontal Resistance 215
14.17. The Quantitative Determination of Horizontal Resistance when There Is Also Vertical Resistance 216
14.18. The Deficiency of Horizontal Resistance in Commercial Varieties 218
14.19. Breeding Potato Varieties for Resistance to Blight 220
CHAPTER 15. A Note on the History of Stem Rust Epidemics in Spring Wheat in North America 223
Summary 223
15.1. The Problem in the Spring Wheat Area of North America 223
15.2. Some Early History 224
15.3. Waldron's Evidence 225
15.4. The Evidence of Stakman and Fletcher 226
15.5. The First Class Epidemics 227
15.6. Some Conclusions 228
CHAPTER 16. Plant Disease in Biological Warfare 229
Summary 229
16.1 Epidemics as Explosives 229
16.2. Vertically Resistant Crops as a Target 229
16.3. Wheat Stem Rust as an Example 230
16.4. Stem Rust Races that Can Overcome Vertical Resist-ance 230
16.5. Weather Adverse to Epidemics 231
16.6. Horizontal Resistance for Defense 232
16.7. Horizontal Resistance to Stem Rust 234
16.8. Quantitative Interpretation of the Evidence 235
16.9. The Transition 237
Exercise 239
CHAPTER 17. The Bases of Vertical Resistance 240
Summary 240
17.1. Introduction 240
17.2. The Different Response of Horizontal and Vertical Resistance to Diversity of Varieties 240
17.3. The Dependence of Vertical Resistance on Varietal Diversity 241
17.4. A Reason Why Vertical Resistance Is Commonly Chosen to Protect Varieties 241
17.5. Diversity and Novelty 242
17.6. The Fitness of Simple Races on Simple Varieties 243
17.7. Evidence for Stabilizing Selection of Simple Races of Puccinia graminie tritici 245
17.8. Vertical Resistance without Novelty 248
17.9. Natural Stability in Vertical Resistance 249
CHAPTER 18. General Resistance against Disease 251
Summary 251
18.1. General Resistance 251
18.2. Results of Troutman and Fulton and of Holmes 252
18.3. The Commonness of Resistance 254
18.4. The Need to Stress Affinities 255
18.5. The Search for General Resistance 255
CHAPTER 19. The Choice of Type of Resistance 257
Summary 257
19.1. The Aims of Plant Breeding 257
19.2. The Difficulty about Generalizing 258
19.3. The Usual Preference for Vertical Resistance 258
19.4. The Case for Vertical Resistance 259
19.5. The Possibility of Improving Vertical Resistance 259
19.6. The Choice of Horizontal Resistance when There Has Been a Record of Varietal Change 260
19.7. The Choice of Horizontal Resistance when rt Is High 262
19.8. The Choice of Horizontal Resistance when There Is Danger of a Vertifolia Effect 262
19.9. The Choice of Horizontal Resistance when There Is Danger of Biological Warfare 264
19.10. The Choice of Horizontal Resistance when Fungicides Are Used 264
CHAPTER 20. The Quantitative Effect of Horizontal Resistance 266
Summary 266
20.1. The Components of Horizontal Resistance 266
20.2. Changing the Basic Infection Rate 267
20.3. A Return to Tables 16.3 and 16.4 268
20.4. Relative Insensitivity of the Apparent Infection Rate to Change when the Basic Rate Is High 270
20.5. The Effect of a Change of the Latent Period on the Apparent Infection Rate 271
20.6. The Effect of Removals on the Apparent Infection Rato 273
20.7. The Effect of Resistance 275
20.8. The General Simplification 276
CHAPTER 21. Control of Disease by Fungicides 277
Summary 277
21.1. The Fungicide Square 277
21.2. Laboratory and Glasshouse Experiments with Phytophthora infestans 279
21.3. The Performance of Fungicides against Potato Blight in the Field 280
21.4. Citrus Black Spot and Apple Scab 284
21.5. The Calculated Effect of Horizontal Resistance or Adverse Climate on the Degree of Fungicidal Activity Needed 285
21.6. Other Calculated Effects 286
21.7. Variable Results with Fungicides and the Need for Recording r 288
21.8. The Timing of Application of Protectant Fungicides 288
21.9. Eradicant Fungicides in Relation to the Infection Rate 289
21.10. The Fungicide Frontier 290
21.11. The Forgotten Factor 291
CHAPTER, 22. How Disease Spreads as It Increases 292
Summary 292
22.1. Increase and Spread of Disease 292
22.2. The Spread of Wheat Stem Rust 293
22.3. The Spread of Potato Blight 294
22.4. Wheat Stem Rust and Potato Blight Contrasted Again 297
22.5. The Flattening of Gradients 298
22.6. Increasing Disease and Increasing Scale of Distance of Spread 299
22.7. The Behavior of Populations of Pathogens and of Individual Propagules the Disease Triangle
CHAPTER 23. The Cryptic Error in Field Experiments 302
Summary 302
23.1. Errors of Representation in Results from Plots in a Field Experiment 302
23.2. An Experiment with Tomato Fruit Diseases 305
23.3. An Experiment with Leaf Rust of Wheat 306
23.4. An Experiment with Stem Rust of Wheat and Rye 307
23.5. The Deposition of Spores 309
23.6. Some Calculations for Potato Blight 309
23.7. Large's Observations on Potato Blight 310
23.8. The Inadequacy of Guard Rows in Conventional Designs 312
23.9. The Gradient Fallacy 312
23.10. The Gradient Fallacy Illustrated 313
23.11. The Cryptic Error 314
23.12. Where the Onus of Proof Lies 314
23.13. The Error when Unsprayed Plots Represent Unsprayed Fields 315
23.14. The Loss of Air-borne Spores from Plots and Fields 315
23.16. The Effect of the Size of Plot 316
23.17. The Effect of Shape of Plot 316
23.18. Interference between Plots 317
23.19. Different Types of Experiment 317
23.20. The Screening and Ranking of Fungicides in the Field 318
23.21. Quantitative Comparison of Fungicide Treatments 319
23.22. Experiments with Plots That Differ Greatly in Disease 321
23.23. Variety Trials 323
23.24. The Conservative Error Theory 324
23.25. The Field Side of the Story 325
APPENDIX 326
REFERENCES 343
AUTHOR INDEX 354
SUBJECT INDEX 357