Epidemiology and Management of Root Diseases

1 Inoculum.- 1.1 Role of Inoculum in Root Disease Epidemics.- 1.1.1 Concepts of Inoculum.- 1.1.2 Soil Fungistasis.- 1.1.3 Inoculum Potential.- 1.1.4 Inoculum Efficiency.- 1.1.5 Inoculum Density.- 1.1.6 Spheres of Influence on Inoculum.- 1.2 Forms of Inoculum.- 1.2.1 Primary Inoculum.- 1.2.2 Secondary Inoculum.- 1.3 Survival of Inoculum.- 1.3.1 Idealized Survival Curve.- 1.3.2 Transformation of Survival Curves.- 1.4 Quantifying Inoculum in Soil.- 1.4.1 Direct Counts.- 1.4.2 Bioassays.- 1.4.3 Soil Assays.- 1.4.4 Chemical Assays.- 1.4.5 Serological Assays.- 1.5 Inoculum Density-Disease Relationships.- 1.5.1 Inoculum Density-Infection Court Relations.- 1.5.2 Transformation of Inoculum Density-Disease Curves.- 1.5.3 Usefulness of Transformed Inoculum Density-Disease Curves.- 1.5.4 Probability Models for Inoculum Density-Disease Relations.- 1.6 Concluding Remarks.- References.- 2 Host Roots.- 2.1 Introduction.- 2.2 Root Growth and Energy Availability.- 2.2.1 Specific Tissue Contributions.- 2.2.2 Characterization of Relevant Root Tissues.- 2.3 Root System Plasticity.- 2.3.1 Conceptual Frameworks for Root System Structure.- 2.4 Evaluation of Root Systems.- 2.5 Host Susceptibility.- 2.5.1 Host Influences on Susceptibility Alterations.- 2.5.2 Environmental and Cultural Factors in Susceptibility Alterations.- 2.6 Measuring Susceptibility Alterations.- 2.7 The Future.- References.- 3 Mycorrhizae.- 3.1 Distribution and Ecological Impact of the Mycorrhizal Symbiosis.- 3.2 Productivity of Cultivated Mycorrhizal Plants.- 3.3 Mycorrhizae — Root Disease Relationships.- 3.3.1 Mechanisms Decreasing the Impact of Soilborne Pathogens in Mycorrhizal Root Systems.- 3.3.1.1 Direct Interactions of Mycorrhizae and Soilborne Pathogens.- 3.3.1.2 Indirect Interaction of Mycorrhizae and Soilborne Pathogens.- 3.3.2 Role of Mycorrhizal Fungi as Biocontrol Organisms — Significance of the Known Biological Effects in Practical Plant Production.- 3.3.3 Mycorrhizae in Integrated Plant Production.- 3.4 Future Research.- References.- 4 The Soil Environment.- 4.1 Introduction.- 4.2 Components of the Physical Soil Environment.- 4.2.1 The Soil Matrix.- 4.2.2 The Soil Solution.- 4.2.3 The Soil Atmosphere.- 4.2.4 Soil Temperature.- 4.3 Influence of Edaphic Factors on Roots and Pathogens.- 4.3.1 Root Growth and Spatial Arrangement.- 4.3.1.1 Soil Matrix Effects.- 4.3.1.2 Soil Solution and Atmosphere Effects.- 4.3.1.3 Epidemiological Significance of Altered Root Growth.- 4.3.2 Pathogen Activity.- 4.3.2.1 Soil Matrix Effects.- 4.3.2.2 Soil Solution and Atmosphere Effects.- 4.3.2.3 Soil Temperature Effects.- 4.3.3 Host Disposition.- 4.3.3.1 Soil Solution and Atmosphere.- 4.3.3.2 Soil Temperature Effects.- 4.3.3.3 Mechanism of Predisposition.- 4.4 Conclusions.- References.- 5 Estimating Disease Severity and Incidence.- 5.1 Role of Disease Assessment in Root Disease Epidemiology.- 5.1.1 The Need for Disease Assessment.- 5.1.2 Goals of Disease Assessment.- 5.2 Signs and Symptoms.- 5.3 Root and Shoot Symptoms.- 5.3.1 Physiological Relationships.- 5.3.2 Environmental Effects.- 5.3.3 Temporal Aspects.- 5.4 Disease Assessment.- 5.4.1 Illusions and Hazards of Disease Assessment.- 5.4.2 Methodology.- 5.4.2.1 Visual Estimates.- 5.4.2.2 Electronic Techniques.- 5.5 Sampling Considerations.- 5.5.1 Sampling Pattern.- 5.5.2 Sample Numbers and Costs.- 5.6 Recommendations.- References.- 6 Temporal Aspects of the Development of Root Disease Epidemics.- 6.1 The Shapes of Disease Progress Curves.- 6.2 The Dynamics of Infection and Disease.- 6.2.1 Primary Infection.- 6.2.1.1 Infection of Plants from a Large Reservoir of Inoculum in Soil.- 6.2.1.2 Root Growth and Decay of Inoculum.- 6.2.2 Secondary Infection.- 6.2.2.1 Root-to-Root Spread.- 6.2.3 Linking Primary and Secondary Infection with Allowance for Root and Inoculum Dynamics.- 6.2.3.1 Growth Equations.- 6.2.3.2 Computer Simulation: An Alternative Approach.- 6.2.4 The Death of Roots, Latent and Infectious Periods.- 6.2.5 Antagonistic Interactions.- 6.2.5.1 Curves That Rise and Fall.- 6.2.5.2 Mechanistic Analyses of Antagonism.- 6.3 Epidemiological Comparison of Treatments for the Control of Disease.- 6.3.1 Comparison of Disease Progress Curves.- 6.3.1.1 Statistical Strategy.- 6.3.1.2 The Contribution of Individual Observations.- 6.3.2 Estimating Trends When There Are Few Data Points.- 6.3.2.1 Analysing Trends Within and Between Seasons.- 6.3.2.2 Allowance for Variable Sampling Intervals, Sampling Frequency and Period of Observation.- 6.3.2.3 Analysis of Trends to Interpret Suppression of Disease.- 6.3.3 Selecting the Disease Variable.- References.- 7 Spatial Aspects of the Development of Root Disease Epidemics.- 7.1 Importance of the Spatial Dimension for Analyzing Root Disease Epidemics.- 7.2 Aspects of Spatial Processes.- 7.2.1 Biological, Chemical, and Physical Attributes.- 7.2.1.1 Inoculum Sources, Dispersal, and Infection.- 7.2.1.2 Process and Pattern.- 7.2.2 Temporal Stability of Pattern as an Epidemic Attribute.- 7.2.3 Spatial Scale and Dimension.- 7.3 Dispersal of Pathogen Propagules.- 7.3.1 Dispersal of Foliar vs. Soilborne Pathogens.- 7.3.1.1 Wind Dispersal of Soilborne Pathogens-Crop Debris.- 7.3.1.2 Wind Dispersal of Soilborne Pathogens-Perfect States.- 7.3.1.3 Wind Dispersal of Soilborne Pathogens — Aerosols.- 7.3.2 Dispersal in Water.- 7.3.3 Dispersal in Soil.- 7.4 Spatial Pattern of Propagules and Diseases.- 7.4.1 Spatial Pattern of Soilborne vs. Foliar Pathogens and Associated Diseases.- 7.4.2 Data, Sampling Units, and Approaches.- 7.4.3 Descriptive and Analytical Methods.- 7.4.3.1 Fitting Probability Distributions.- 7.4.3.2 Indices of Aggregation.- 7.4.3.3 Blocked Quadrat Variance.- 7.4.3.4 Spatial Autocorrelation Analysis.- 7.4.3.5 Transect Analysis.- 7.4.3.6 Two-Dimensional Lattice or Distance Class Analysis.- 7.5 Applications of Spatial Analysis in Root Disease Epidemiology and Management.- 7.5.1 Determination and Interpretation of Temporal and Spatial Scales.- 7.5.2 Design and Sampling of Experiments.- 7.5.3 Establishing Crop Loss Estimates.- References.- 8 Host Resistance.- 8.1 Introduction.- 8.2 Terminology.- 8.3 Components of Partial Resistance to Root Pathogens.- 8.4 Measurement of Resistance Components.- 8.5 Disease Avoidance and Disease Escape.- 8.6 Tolerance.- 8.7 Examples of Host-Pathogen Systems.- 8.7.1 Black Shank of Tobacco.- 8.7.1.1 Components of Resistance.- 8.7.1.2 Avoidance and Tolerance.- 8.7.2 Black Root Rot of Tobacco.- 8.7.2.1 Components of Resistance.- 8.7.2.2 Avoidance and Tolerance.- 8.7.3 Cylindrocladium Black Rot of Peanut.- 8.7.3.1 Components of Resistance.- 8.7.3.2 Avoidance and Tolerance.- 8.7.4 Verticillium Wilt of Tomato.- 8.7.4.1 Components of Resistance.- 8.7.4.2 Avoidance and Tolerance. 266.- 8.8 Summary.- References.- 9 Chemical Management.- 9.1 Strategies for Use of Chemical Pesticides.- 9.1.1 Soil Fumigation.- 9.1.2 At-Plant Applications of Fungicides.- 9.1.3 Seed Dressings.- 9.1.4 Postplant Treatments.- 9.2 Types of Chemical Pesticides.- 9.2.1 Nematicides.- 9.2.2 Soil Fungicides.- 9.2.2.1 Soil-Applied Fungicides Under Development.- 9.2.3 Seed Treatments.- 9.2.3.1 New Cereal Seed Treatments Under Development.- 9.2.4 Fungicides for Actively Growing Plants.- 9.3 Chemical Management Approaches.- 9.3.1 Protective vs. Curative Applications.- 9.3.2 In-Furrow and Band vs. Broadcast Applications.- 9.3.3 Use of Chemical Pesticides in Conjunction with Biologics.- 9.3.4 Slow-Release Formulations.- 9.3.5 Residual Effects of Fungicides on Pathogens.- 9.3.6 Risk vs. Benefit.- 9.4 Summary.- References.- 10 Biological Management.- 10.1 Ecological Opportunities for Biocontrol.- 10.1.1 Identification of Low Ecological Diversity.- 10.1.2 Creation of Ecological Simplicity.- 10.2 Strategies for Biocontrol.- 10.2.1 Protection of the Rhizosphere or Spermosphere.- 10.2.1.1 Antibiosis.- 10.2.1.2 Competition.- 10.2.1.3 Exclusion.- 10.2.1.4 Combined Mechanisms.- 10.2.2 Plant-Mediated Biocontrol.- 10.2.3 Impeding Movement of the Pathogen.- 10.2.4 Destruction of the Pathogen.- 10.3 Successful Implementation of Biocontrol.- 10.3.1 Constraints to Biocontrol.- 10.3.2 Forecast for Biocontrol.- References.- 11 Cultural Management.- 11.1 Approaches to Cultural Management.- 11.1.1 Quarantine.- 11.1.2 Soil Disinfestation.- 11.1.3 Tillage.- 11.1.4 Crop Rotations.- 11.1.5 Planting Date and Plant Spacing.- 11.2 Strategies for Use of Cultural Management.- 11.2.1 Tillage.- 11.2.2 Soil Fertility.- 11.2.3 Soil Water.- 11.2.4 Soil Temperature.- 11.2.5 Integrated Pest Management.- 11.3 Limitations.- 11.3.1 Climate.- 11.3.2 Physical Properties of Soils.- 11.3.3 Production Systems.- 11.3.4 Residue Management.- 11.3.5 Survival of Inoculum.- 11.4 Novel Approaches.- 11.4.1 Equipment.- 11.4.2 Organic Amendments.- 11.4.3 Soil Solarization.- 11.5 Conclusions.- References.