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**“I think this is a landmark achievement in aerobiology because it rigorously and beautifully describes the theory of spore dispersal in the atmosphere and gives practical aspects about how to study spore movement and use the results for developing disease management strategies.”**

—Larry Madden, Distinguished Professor in Plant Protection at Ohio State University (Wooster) and Former President and APS Fellow

- Explains the many processes and factors behind a particle's release, transport, and deposition on distant plants
- Synthesizes current and foundational research scattered across multiple scientific disciplines
- Illuminates the physical characteristics of pollen and spores that determine outcrossing potential in GM crops and the long distance spread of plant diseases

**PRINT EDITION**Item No. 45423

### By Donald E. Aylor

Author Donald E. Aylor, Ph.D., has more than 40 years of experience modeling and conducting experiments in aerobiology using a variety of crops and propagules, techniques, and mathematical tools. His high-quality research in this area is nationally and internationally recognized.*Aerial Dispersal of Pollen and Spores*is a unique, valuable, and comprehensive 432-page reference covering the many complex factors and effects encompassing the movement of spores through the air. It synthesizes material scattered across the literature of multiple disciplines in one single place—and adds many insights through new research in this important area of study.

It uniquely emphasizes the critical, interacting biophysical processes that control the dispersal of particles in the atmosphere. By shining a greater light on these biophysical processes, scientists will get many new and valuable perspectives that can be applied to their research and to understanding models behind the spread of pathogens and genetic material in the atmosphere.

*Aerial Dispersal of Pollen and Spores*serves as a valuable reference for researchers, graduate students, and advanced undergraduates in the fields of plant pathology, plant biology, meteorology, agronomy, and agricultural engineering. It is also well positioned as an important teaching resource across several disciplines, including plant pathology, botany, and aerobiology.

In addition to being a valuable reference and teaching resource,

*Aerial Dispersal of Pollen and Spores*has a variety of important uses. It helps…

- Researchers and practitioners to evaluate the relative importance of nearby and faraway sources of inoculum.

- Breeders to assess outcrossing potential and pollen mediated gene flow (PMGF) in the environment.

- Botanists to evaluate physical characteristics of pollen and spores.

- Plant biologists to access information typically assessable to physicists, leading to the undertaking of more quality interdisciplinary studies.

*Aerial Dispersal of Pollen and Spores*covers dozens of topics within the study of pollen and spore dispersal, such as the physical properties, forces, and processes affecting pollen and spores—in motion and at rest; pollen and spore survival; infection and fertilization efficiency; wind and wind transport models; cross fertilization; pollen mediated gene flow; precision agriculture practices applied to aerially dispersed pathogens; infectious periods and opportunity for disease spread; aerial sampling, and more (

*for a more comprehensive list of topics, view the ‘Contents’ tab*).

## Aerial Dispersal of Pollen and Spores

## CHAPTER 1: Introduction

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**Significance of Aerobiology**

Disease Spread

Fungicide Resistance

Pollen-Mediated Gene Flow

**Brief Historical Perspective on Aerobiology**

Central Problem in Aerobiology

Disease Spread

Cross Fertilization

Focus on the Air–Substrate Interface

**Framework for the Study of Aerial Dispersal**

Working Definition of a Model

Main Elements in the Model Framework

**Plan for the Book**

Central Problem in Aerobiology

## CHAPTER 2: Patterns of Disease Spread

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**Patterns of Disease Spread**

Categories of Disease Wave Front Trajectories

**Phenomenological Descriptions of Spore Dispersal and Disease Spread**

Classical Empirical Dispersal Formulae

Combined Effects of Deposition and Dilution

Normalization of Dispersal Formulae

Autoinfection and Alloinfection

** Spatial–Temporal Patterns of Disease Spread **

Stochastic Nature of Disease Spread

Summary

APPENDIX: Power Law Exponent b for a Finite-Length Line Source

Stochastic Nature of Disease Spread

Summary

APPENDIX: Power Law Exponent b for a Finite-Length Line Source

## PART ONE: Biology and Biophysics

## CHAPTER 3: Physical Properties, Forces, and Processes Affecting Pollen and Spores, in Motion and at Rest

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**Particle Size, Shape, and Specific Gravity **

Forces and Particle Motion

Aerodynamic Drag

Settling Speed

Stokes Flow Regime

Correction for Small Particles

Correction for Large Particles

Nonspherical Particles

Particle Density

Measurement Techniques

Clusters

Effect of Altitude in the Atmosphere

** Stop Distance **

Stokesian Particles

Non-Stokesian Particles

** Electrostatic Force **

Effect of an Electric Field on Deposition

Effect of an Electric Field on Detaching Conidia

** Adhesion **

Inertial Forces During Leaf Shaking and Vibration

Summary

Forces and Particle Motion

Aerodynamic Drag

Settling Speed

Inertial Forces During Leaf Shaking and Vibration

Summary

## CHAPTER 4: Release Mechanisms (Liberation)

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** Two Kinds of Spore Release Mechanisms **

Passive Spore Release

Force for Removal

Wind Speeds Necessary for Removal

Entrainment of Very Small Particles by Wind During Dry Weather Conditions

Passive Liberation with Variable Removal Thresholds

Launch of Spores by Rain Splash

**Active Spore Release **

Spore Size and Discharge Distance

Relative Discharge Distance of Ascospores in Air and in Water

**Spore Release in Response to Changing Humidity **

A Conjecture

Spore Production on the Undersides of Leaves

**Diurnal Patterns of Spore and Pollen Release **

Summary

APPENDIX: Approximate Description of Splash Droplet Trajectories

Passive Spore Release

Summary

APPENDIX: Approximate Description of Splash Droplet Trajectories

## CHAPTER 5: Deposition Processes

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**Relationship Between Aerial Concentration and Deposition **

Sedimentation

Inertial Impaction

Theoretical Values of E*i*

Empirical Values of E*i*

Interception

Reduction of Collection Efficiency Due to Particle Rebound and Re-Entrainment from Surfaces

Impaction in Unsteady Airflow

** Turbulent Deposition **

Combined Effects of Sedimentation, Impaction, and Turbulent Deposition

Deposition Velocity

Wet Deposition by Washout

Average Versus Nonaverage Rainfall

Relative Importance of Dry and Wet Deposition

**Particle Residence Times in the Atmosphere **

Summary

Sedimentation

Inertial Impaction

Combined Effects of Sedimentation, Impaction, and Turbulent Deposition

Deposition Velocity

Wet Deposition by Washout

Summary

## CHAPTER 6: Inactivation of Pollen and Spores

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**Two Measures of Survival**

Loss of Viability During Exposure to Ultraviolet Radiation

Sensitivity of Attached and Detached Spores to Filtered and Unfiltered Sunlight

Apparent Insensitivity of Maize Pollen to UVB

Shelf Regions of Survival Curves

Tail of the Distribution and the Need for Large Sample Sizes

**Loss of Viability Due to Dehydration **

Model for Determining Pollen Mortality Due to Dehydration

Loss of Water Versus Time: Equilibrium Moisture Values

Relationship Between Germination and Water Potential

Initial Increase in Germination and the Shelf Region for Survival of Pollen and Spores

Evaporation Rate of Splash Droplets

** Survival of Pollen and Spores During Ascent and Descent in the Convective Boundary Layer**

Infection and Fertilization Efficiency

Quantitative Inoculation and Pollination

Efficiency Expressed on a Land Area or a Plant Area Basis

One Spore, One Infection

Multiple Infection Transformation

Mass Action

** Summary **

Loss of Viability During Exposure to Ultraviolet Radiation

Infection and Fertilization Efficiency

## PART TWO: Meteorology and Micrometeorology

## CHAPTER 7: Wind Flow and Particle Movement

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** Particle Motion Determined by the Wind **

Unresolved Motion and the Necessity to Adopt a Statistical Approach

Brief Introduction to Micrometeorological Statistics

Notation Used for Mean and Fluctuating Quantities

Covariances

Probability Density Function

** Convective Fluxes of Mass, Heat, and Momentum **

Length and Time Scales of Turbulence

Power Spectra

Kolmogorov Similarity Theory

**Summary **

Unresolved Motion and the Necessity to Adopt a Statistical Approach

Brief Introduction to Micrometeorological Statistics

Length and Time Scales of Turbulence

## CHAPTER 8: Brief Overview of Boundary Layer Processes: Basis for Wind Description

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**Surface Energy Balance and Growth of the Daytime Boundary Layer **

Depth of the Mixed Layer

**Atmospheric Vertical Structure and Layering **

Atmospheric Stability and Vertical Mixing in the Atmosphere

Static Stability

Dynamic Stability

**Idealization of the Vertical Mixing Process and Scale of Eddies Near the Ground **

Summary

Atmospheric Stability and Vertical Mixing in the Atmosphere

Summary

## CHAPTER 9: Wind Description

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**Conceptual Layers in the Atmosphere**

Wind in the Horizontally Uniform Surface Layer

Mean Horizontal Wind Speed

Monin–Obukhov Similarity Theory

Velocity Fluctuations

Lagrangian Time Scale

** Wind Profiles in Plant Canopies**

Mean Wind Speed

Canopy Height: A Scale Length for Wind Statistics in Canopies

Wind Parameterization Inside a Plant Canopy

Wind in the RSL Above the Canopy

Graphic Summary of Wind Profiles

Difference Between *u* and *s*

Parameterization of Eddy Diffusivity

Gusts in Plant Canopies

Lulls in the Wind Inside Plant Canopies

Time and Length Scales of Airflow in Plant Canopies

** Wind in the CBL **

Key Characteristics of Air Motions in the CBL

Conjugate Power Laws

Vertical-Velocity PDF

Parameterization of the Vertical-Velocity PDF

Turbulence Vertical Profiles

Merged SL and CBL Parameterization

**Disturbed Wind Flows **

Wind Flow Disturbed by Crops and Porous Barriers

**Mesoscale Flows **

Ash Rust

Tree Pollen and Ragweed Pollen

White Pine Blister Rust

Annosus Root Rot

**Turbulence in the ABL During Rain **

Summary

Wind in the Horizontally Uniform Surface Layer

Summary

## PART THREE: Modeling Wind Transport of Pollen and Spores

## CHAPTER 10: Concentration, Flux Density, and Conservation of Particles

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**Particle Concentration **

Volume-Averaged Concentration

Time-Averaged Concentration

Eulerian and Lagrangian Approaches

** Conservation of Mass **

Particle Flux Density and the Advection– Diffusion Equation (K-Theory)

Limitations of K-Theory

Integrated Horizontal Flux

Some Selected Solutions of the Advection– Diffusion Equation

** Gaussian Puff and Gaussian Plume Models **

Gaussian Puff

Gaussian Plume

Dry Deposition, Wet Deposition, and Survival for a Gaussian Plume

Basic Assumptions Underlying Gaussian Puff and Plume Models

** Summary **

## CHAPTER 11: Lagrangian Stochastic Simulation of Wind Transport

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** Particle Flux Density and Concentration in LS Models **

Particle Trajectories in One-Dimensional Turbulence

Conservation of Particles Revisited

** LS Model for the Atmospheric Surface Layer **

Langevin Equation for Homogeneous Turbulence

Langevin Equation for Inhomogeneous Turbulence

** Modeled Particle Deposition in a Plant Canopy **

Layered Canopy

** Modeled Particle Deposition on the Ground **

Comparison of the LS Model to Field Data

Comparison of the LS, K-Theory, and Gaussian Plume Models for the Special Case of Approximately Homogeneous Turbulence

LS Model for the Convective Boundary Layer

One-Dimensional LS Model for Weightless Particles

Modification of One-Dimensional LS Models for Heavy Particles

Crosswind-Integrated Concentration

** Outer Scales of Turbulence and Lagrangian Coherent Structures **

Summary

Comparison of the LS Model to Field Data

Comparison of the LS, K-Theory, and Gaussian Plume Models for the Special Case of Approximately Homogeneous Turbulence

LS Model for the Convective Boundary Layer

Summary

## CHAPTER 12: Escape of Spores from a Canopy

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**Escape Fraction Defined **

Escape Fraction Under Near-Neutral Atmospheric Conditions

Time Scales for Deposition and Escape

Deposition Dominated by Sedimentation

Deposition by a Combination of Sedimentation and Impaction

Vertical Distribution of Spores in a Canopy

Use of More Complex Models

** Escape Fraction Under Highly Convective Conditions **

Source Emission Rates Determined from Vertical Concentration Gradients

Summary

Escape Fraction Under Near-Neutral Atmospheric Conditions

Source Emission Rates Determined from Vertical Concentration Gradients

Summary

## CHAPTER 13: Framework for Aerial Dispersal Modeling

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** Introduction **

General Form of the Spatial Transport Equation

Single Source–Single Receptor (SS–SR) Particle Dispersal Model

Multiple Sources and Receptors

Lower Boundary Condition

Increasing the Vertical Scale in the Downwind Direction

**Particle Release Rate (Source Strength) **

Temporal Production of Pollen and Spores

Quasi-Steady-State Assumption

**Spatial Production of Inoculum **

Vertical Distribution of Spores in a Canopy

Horizontal Distribution of Spores in a Canopy

**Transport Function **

Flexibility of a Lagrangian Transport Model

Air Parcel Trajectories

Trajectory Analysis on a Landscape Scale

**Summary **

General Form of the Spatial Transport Equation

## PART FOUR: Applications of Aerobiological Models

## CHAPTER 14: Long-Distance Dispersal

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** Introduction **

Disease Spread Horizons

**Conditions for Occurrence of an Epidemic or Pandemic **

Constraints Imposed by the Green Wave and the Golden Wave

**Model Framework **

Transport and Diffusion Model

Advance of a Disease Front in a Discontinuous Spatial Distribution of Hosts

**Examples of Calculating LDD **

Daily Production of Spores

Time Course of Spore Release and the Escape Fraction

Transport and Dilution

Losses Due to Dry Deposition

Survival of Spores During Flight

Deposition of Spores at the Target

Integrated Deposition for a Transport Event

** Rate of Spread of Disease Fronts over Long Distances **

Northward Spread of TBM and WSR in the United States

Critical Gap Width

Why Does WSR Spread Faster Than TBM?

LDD of the Potato Late Blight Pathogen

** Summary **

## CHAPTER 15: Cross Fertilization in Maize

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** The Model **

General Form of the Spatial Transport Equation

Quasi-Steady-State Assumption

Lagrangian Transport Function

Pollen Deposition on Silks

Properties of the Transport Function

Vertical Flux of Pollen at Silk Height

Hybrid Seed Production

Fertilization Algorithm Used in the Model

** Comparison of Dispersal Models with Outcrossing Data **

Large Pollen Source and Small Receptor Plots

Large Source Within a Larger Receptor Field

Effect of Doubling the Source Field Size

Effect of Reducing the Amount of Protective Pollen in the Receptor Field

Semiempirical Model for Outcrossing

** Summary **

APPENDIX: Mass Action Assumption for Fertilization Rule

APPENDIX: Mass Action Assumption for Fertilization Rule

## CHAPTER 16: Crop Mixtures and Interplantings

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**Interplantings and Crop Mixtures**

Dispersal Functions with a Defined Length Scale

Interplantings

Mixtures

**Dispersal Functions with an Increasing Length Scale **

Normalization of Dispersal Functions Revisited

**Autoinfection: Spore Dispersal on the Leaf and the Plant Scales **

Dispersal on the Leaf Scale

Vertical Dispersal on the Plant Scale

**Summary **

Dispersal Functions with a Defined Length Scale

## CHAPTER 17: Small Plot Experiments

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** Inoculum Pressure in Adjacent Plots**

Phenomenological Model

Lagrangian Stochastic Model

**Effect of Plot Size and Shape on Inoculum Loss and Gain**

Square Plots in Close Proximity

**Summary**

## CHAPTER 18: Using Precision Agriculture to Manage Aerially Dispersed Pathogens

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** Introduction **

Zones of Disease Development Around a Focus

Model of Disease Progress

Comparison of PA Applied to Bean Rust Versus Potato Late Blight

Summary

Zones of Disease Development Around a Focus

Model of Disease Progress

Comparison of PA Applied to Bean Rust Versus Potato Late Blight

Summary

## CHAPTER 19: Integrated Pest Management and Decision Support Systems

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** Aerial Dispersal of Apple Scab Inoculum **

Overview of Disease Spread

Model Framework for Dispersal of Ascospores

In-Orchard Contribution to the Aerial Concentration of Ascospores

Wind Profiles in Orchards 324

Ascospore Release Rate

Long-Distance Transport Between Orchards

Relative Risks from In-Orchard and External Sources of Inoculum

Effect of Unsteady Rainfall on Deposition

Effect of Groundcover on Ascospore Escape

Summary of Section

** Aerial Dispersal of Potato Late Blight Inoculum**

Overview of Disease Spread

Rate of Sporangia Release from a Canopy

Transport and Survival of Inoculum

Model Validation Using Unmanned Aerial Vehicles

Infectious Period and Opportunity for Disease Spread

Summary of Section

** Aerial Dispersal of Soybean Rust Inoculum **

Summary

Summary

## CHAPTER 20: Aerial Sampling

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** Introduction **

Types of Samplers

Gravitational Samplers

Suction Samplers

Impaction Samplers

** Detection Limits **

Sampling Rate and Detection Limit

Sentinel Plots: Detecting the First Spore in a Field or a Region

**Placement of Ground-Based Samplers in a Field **

Effect of Sampler Height

**Deployment of Mobile Airborne Sampling Platforms **

Horizontal Positioning and Flight Patterns

Vertical Positioning

Temporal Changes of Concentrations Aloft

**Summary **

Types of Samplers

## CHAPTER 21: Limitations of Models and Challenges for Future Research

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**APPENDIX: Lists of Symbols, Acronyms, and Abbreviations**

REFERENCES

INDEX

REFERENCES

INDEX

**“I think this is a landmark achievement in aerobiology because it rigorously and beautifully describes the theory of spore dispersal in the atmosphere and gives practical aspects about how to study spore movement and use the results for developing disease management strategies.”**

—Larry Madden, Distinguished Professor in Plant Protection at Ohio State University (Wooster) and Former President and APS Fellow

*“Exceptionally well written, organized, and presented... unreservedly recommended.”*

—Reviewers Bookwatch

Format: 8.5” × 11” hardcover

ISBN: 978-0-89054-542-3

Pages: 418

Images: 69 color images and 135 black and white images

Publication Weight: 4 lbs