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Aerial Dispersal of Pollen and Spores
Aerial Dispersal of Pollen and Spores
  • 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

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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.
The dispersal of pollen and spores by wind is central to some of the biggest challenges in science today, such as the spread of food-supply-threatening plant diseases; the rapid and widespread adoption of genetically modified (GM) plants in agriculture and their potential for pollen-mediated gene flow in the environment; and the presence and role of bioaerosols in cloud processes.

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

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

CHAPTER 2: Patterns of Disease Spread

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
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

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
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
Inertial Forces During Leaf Shaking and Vibration

CHAPTER 4: Release Mechanisms (Liberation)

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
APPENDIX: Approximate Description of Splash Droplet Trajectories

CHAPTER 5: Deposition Processes

Relationship Between Aerial Concentration and Deposition
Inertial Impaction

Theoretical Values of Ei
Empirical Values of Ei
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

CHAPTER 6: Inactivation of Pollen and Spores

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

PART TWO: Meteorology and Micrometeorology

CHAPTER 7: Wind Flow and Particle Movement

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
Probability Density Function
Convective Fluxes of Mass, Heat, and Momentum
Length and Time Scales of Turbulence

Power Spectra
Kolmogorov Similarity Theory

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

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

CHAPTER 9: Wind Description

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

PART THREE: Modeling Wind Transport of Pollen and Spores

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

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

CHAPTER 11: Lagrangian Stochastic Simulation of Wind Transport

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

CHAPTER 12: Escape of Spores from a Canopy

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

CHAPTER 13: Framework for Aerial Dispersal Modeling

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

PART FOUR: Applications of Aerobiological Models

CHAPTER 14: Long-Distance Dispersal

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

CHAPTER 15: Cross Fertilization in Maize

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
APPENDIX: Mass Action Assumption for Fertilization Rule

CHAPTER 16: Crop Mixtures and Interplantings

Interplantings and Crop Mixtures
Dispersal Functions with a Defined Length Scale

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

CHAPTER 17: Small Plot Experiments

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

CHAPTER 18: Using Precision Agriculture to Manage Aerially Dispersed Pathogens

Zones of Disease Development Around a Focus
Model of Disease Progress
Comparison of PA Applied to Bean Rust Versus Potato Late Blight

CHAPTER 19: Integrated Pest Management and Decision Support Systems

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

CHAPTER 20: Aerial Sampling

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

CHAPTER 21: Limitations of Models and Challenges for Future Research

APPENDIX: Lists of Symbols, Acronyms, and Abbreviations

Publish Date: 2017
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

By Donald E. Aylor

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