Plant Disease Epidemiology- A lecture for MS students (BAU)
Upcoming SlideShare
Loading in...5
×
 

Plant Disease Epidemiology- A lecture for MS students (BAU)

on

  • 2,487 views

 

Statistics

Views

Total Views
2,487
Views on SlideShare
2,487
Embed Views
0

Actions

Likes
0
Downloads
85
Comments
3

0 Embeds 0

No embeds

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel

13 of 3 Post a comment

  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment
  • This template can be used as a starter file for presenting training materials in a group setting. Sections Right-click on a slide to add sections. Sections can help to organize your slides or facilitate collaboration between multiple authors. Notes Use the Notes section for delivery notes or to provide additional details for the audience. View these notes in Presentation View during your presentation. Keep in mind the font size (important for accessibility, visibility, videotaping, and online production) Coordinated colors Pay particular attention to the graphs, charts, and text boxes. Consider that attendees will print in black and white or grayscale. Run a test print to make sure your colors work when printed in pure black and white and grayscale. Graphics, tables, and graphs Keep it simple: If possible, use consistent, non-distracting styles and colors. Label all graphs and tables.
  • This template can be used as a starter file for presenting training materials in a group setting. Sections Right-click on a slide to add sections. Sections can help to organize your slides or facilitate collaboration between multiple authors. Notes Use the Notes section for delivery notes or to provide additional details for the audience. View these notes in Presentation View during your presentation. Keep in mind the font size (important for accessibility, visibility, videotaping, and online production) Coordinated colors Pay particular attention to the graphs, charts, and text boxes. Consider that attendees will print in black and white or grayscale. Run a test print to make sure your colors work when printed in pure black and white and grayscale. Graphics, tables, and graphs Keep it simple: If possible, use consistent, non-distracting styles and colors. Label all graphs and tables.
  • Give a brief overview of the presentation. Describe the major focus of the presentation and why it is important. Introduce each of the major topics. To provide a road map for the audience, you can repeat this Overview slide throughout the presentation, highlighting the particular topic you will discuss next.
  • This is another option for an Overview slide.
  • What will the audience be able to do after this training is complete? Briefly describe each objective how the audience will benefit from this presentation.
  • Microsoft Engineering Excellence Microsoft Confidential Is your presentation as crisp as possible? Consider moving extra content to the appendix. Use appendix slides to store content that you might want to refer to during the Question slide or that may be useful for attendees to investigate deeper in the future.

Plant Disease Epidemiology- A lecture for MS students (BAU) Plant Disease Epidemiology- A lecture for MS students (BAU) Presentation Transcript

  • WELCOME PPATH 503: Epidemiology and Forecasting of plant disease K. M. GOLAM DASTOGEER LECTURER DEPARTMENT OF PLANT PATHOLOGY BANGLADESH AGRICULTURAL UNIVERSITY
  • Epidemic Gr. Epi=upon, among and Demons=people Epidemic What is among people "Change in disease intensity in a host population over time and space." Change: often increase -- a dynamic process Disease: dealing with diseases, not just the pathogen (or plant/crop) Host: Organism infected (or potentially infected) by another organism Population: a population phenomenon Time and space: two physical dimensions of interest.
  • 3 Epiphytotic Unger (1833), Whetzel (1920's) However, equally valid meaning from Greek: "what is in (or among) a population" ("demio") "Epidemic" used for plants for a long time….. •1728: Duhamel 1691,1842: book titles •1858: Kuhn 1901: Ward Thus, no valid reason to use "epiphytotic“ Therefore the issue has been resolved!!! NOTE: If one used epiphytotic (instead of epidemic), then one should use epiphytotiology instead of epidemiology! -(Epiphytology is the study of epiphytes).
  • Epidemiology • Study of epidemics. • Science of disease in populations. Vanderplank (1963) • Ecology of disease. • Study of the spread of diseases, in space and time, with the objective to trace factors that are responsible for, or contribute to, epidemic occurrence. • The science of populations of pathogens in populations of host plants, and the diseases resulting therefrom under the influence of the environment and human interferences. 4
  • History (ancient to modern times) Disease 5 Hippocrates (~400 BC): First use of "epidemic", widespread disease (human diseases Theophrastus (~340 BC): Plant diseases in fields, Environmental influences Pliny (~50 AD): Plant diseases; soil; climate Duhamel de Monceau (1728 AD): Disease progress curves, Comparison of plant and animal epidemics Late 19th Century and forward… Kuhn (1858) - 1st textbook of plant pathology Ward (1901): book "Diseases in Plants" emphasized ecology (populations) of disease Jones (1913) - role of the environment Gaumann (1946): "Principles of Plant Infection” -Disease spread, -Conditions leadin to an epidemic, -'Infection Chain' (= disease cycle), -compare with medicine (diseases of humans)
  • 6 Large (1952, and others) -Disease progress curves -Crop losses -Disease assessment (measurement) Horsfall & Dimond (1960)- "Plant Pathology, Volume 3" -Populations -Inoculum density:disease relations -Spore dispersal -Analysis (mathematics) -Forecasting, prediction -Traditional definition ---> Modern definition Gregory (1963, 1973) "The Microbiology of the Atmosphere" -spore dispersal, disease spread Aerobiology Vanderplank (1963) (used to be van der Plank) "Plant Diseases: Epidemics and Control" -Populations -Rates (dynamic processes) -Analysis, mathematics -Models, theory -Link epidemiology and control -Established the science of plant disease epidemiology Other pioneers: Zadoks (1960-1995), The Netherlands Kranz (1968-1995), Germany Waggoner (1960-mid --1980s), USA S. Nagaranjan 1983-India Note: many developments in other fields… Ecology, medical epidemiology, Biomathematics, etc.
  • Elements of an Epidemic 1.Host 2. Pathogen 3. Environment Interactions of the 3 main components are described by the disease triangle. The Disease Triangle Disease development is also affected by 4. Time 5. Humans Disease Tetrahedron Interactions of the 5 components are described by the disease pyramid.
  • Elements of an Epidemic (cont’) i. Genetic resistance or susceptibility of Host –Vertical Resistance –Horizontal Resistance ii. Degree of genetic uniformity of host in a particular field –Monoculture, especially Clones –Natural, Intermingled Populations iii. Type of crops - Annual crops & foliar or fruit diseases develop much more rapidly (in weeks) - Perennial woody diseases take longer time to develop (in years) iv. Age of host plants - Some plants are susceptible only during growth period & become resistant during mature period 8 How the Plant Affects Development of Epidemics
  • How Pathogens Affect Development of Epidemics i. Levels of virulence –Faster Production of Larger # Inoculum ii. Quantity of inoculum near hosts iii. Type of reproduction of the pathogen –Monocyclic –Polycyclic •Responsible for most Sudden, Catastrophic Epidemics –Polyetic iv. Ecology of the pathogen –Reproduce on Surface of Aerial Parts of Plant –Reproduce inside Plant –Reproduce on Infected Plant Parts in Soil v. Mode of spread of the pathogen –Breezes or Strong Winds •Most Sudden & Widespread Epidemics –Inoculum Carried by Airborne Vectors –Wind-Blown Rain –Carried on Seed, Tubers, Bulbs –Beetles –Pathogens Spreading through Soil •Usually Local, Slow-Spreading Diseases of Considerable Severity Elements of an Epidemic (cont’)
  • Elements of an Epidemic (cont’) 3. Environmental factors i. Moisture - Rain, dew, high humidity - Dominant factor in diseases caused by oomycetes, fungi, bacteria & nematodes ii. Temperature - Affects disease cycles of pathogens Disease development is also affected by 4. Time Time factors  Season of the year  Duration & frequency of favorable temp. & rains  Appearance of vectors, etc. 5. Humans  Site Selection & Preparation  Selection of Propagative Material  Introduction of Exotic Pathogens  Cultural Practices  Disease control measures I ntroduction of new pathogens or disease How Humans Affect Development of Epidemics
  • Monocyclic pathogen A monocyclic pathogen completes just one disease cycle per season. In monocyclic pathogens the primary inoculum is the only inoculum available for the entire season, and there is no secondary inoculum and no secondary infection. Can you think of some examples of monocyclic  Soilborne pathogens are usually monocyclic due to physical constraints-- inoculum is not dispersed within the growing season. 11
  • Monocyclic Disease 12 • Examples: smuts, rusts, which require two alternate hosts, many soil-borne diseases, root rots and vascular wilts • In general, there are three types of plant diseases that tend to produce only one infection cycle per host cycle (1) postharvest diseases, (2) diseases caused by soil-borne plant pathogens, and (3) rusts without a urediniospore stage.
  • 13 Some rust and smut fungi are monocyclic because their life cycles take a full season to complete. Oat smut Cedar-apple rust
  • Polycyclic pathogens/Disease 14 Pathogens that produce more than one (2 to 30) infection cycle per crop cycle Disseminate primarily by air or airborne vectors (insects) Responsible for epidemics on most crops downy mildews, late blight of potato, powdery mildews, leaf spots and blights, grain rusts, and insectborne viruses. In polycyclic fungal pathogens, the primary inoculum often consists of the sexual spore or sclerotia. once primary infection takes place, large numbers of asexual spores (secondary inoculum) are produced at each infection site and these spores can themselves cause new (secondary) infections that produce more asexual spores for more infections.
  • 15
  • Polyetic(multiyear) pathogens  polyetic(multiyear) pathogens: In some diseases of trees,fungal vascular wilts,phytoplasmal declines, and viral infections, pathogen may not complete a disease cycle, it may not produce inoculum that can be disseminated and initiate new infections, until at least the following year and some may take longer.  Such diseases are basically monocyclic, but if they take more than a year to complete the cycle, they are called polyetic • Several rusts of trees and the mistletoes,they attak several years to go through all the stage sof their life cycle and to initiate new infections. Dutch elm disease, cedar apple rust, white pine blister rust, and citrus tristeza 16
  • 17 Disease progress curve for a typical monocyclic pathogen
  • Disease progress curve for polyclicic epidemic 18
  • Why use disease progress curves? 19 ‐ Compare control measures ‐ Compare effect of environment on disease development ‐ Predict future disease development ‐ Disease forecasting for improved control
  • 20 •All Measurable Components Considered –Virulence of Initial Inoculum –Effects of Environment –Crop’s Disease Resistance –Crop’s Growth Stage –Length of Time Plant & Pathogen Interact –Effectiveness of various Disease Management Strategies –Weather Stations or Sensors over Crop Canopies •Mathematical Equations Developed to Describe the Epidemic •Models often Limited to specific Climates & Regions •Some Models Better than Others •Refined over Time when Additional Data can Be Included Modeling Epidemics
  • Why modeling? 21 Summarize the behavior of a disease in a population Provide quantitative estimates of the relationships of interest Identify the critical factors driving epidemics A model to simplify reality that describes and predicts disease behavior used to predict the effect of disease control strategies or their timing
  • 22 To reduce disease incidence, x, at any point in the epidemic: 1. Reduce initial inoculum, x0 2. Reduce rate of infection, r 3. Reduce duration of epidemic, t
  • 23 Diseases caused by monocyclic pathogens are analogous to investment with simple interest; diseases caused by polycyclic pathogens are analogous to investment with compound interest. Disease increase in plant populations is sometimes compared to the increase of invested capital over time.
  • • With simple interest, capital grows at a constant rate (the interest bearing capital remains unchanged). • With compound interest, invested capital grows at an increasing rate over time as the earned interest is reinvested. 24
  • • To reduce disease incidence, x, at any point in the epidemic: • 1. Reduce initial inoculum, Xo • 2. Reduce rate of infection, R • 3. Reduce duration of epidemic, t 25
  • 26
  • 27
  • 28 Measuring Disease in a Population Disease incidence Actual number or proportion of plants diseased Number diseased out of total number of plants observed Disease severity •Area of plant tissue affected by disease •For many diseases, severity is the area of plant surface covered by lesions •Measured using assessment scales or by determining the area under a disease progress curve (AUDPC) 3. Yield loss •The proportion of yield that the grower will not be able to harvest due to disease •Results in economic loss
  • 29 1. Molecular tools  Polymerase Chain Reaction (PCR), Enzyme Linked Immunosorbant Assay (ELISA), DNA Fingerprinting, etc.  For rapid & accurate detection & identification of pathogens 2. Data management  Geographic Information System (GIS), Global Positioning System (GPS), Remote Sensing, etc.  To assist in disease control strategies 3. Disease modeling & forecasting  To predict the probability of outbreaks New Tools in Epidemiology
  • Disease-gradient or dispersal curve • The amount of disease is greater near the source of inoculum 30 •The amount of disease decreases with increasing distance from the source
  • Managing Epidemics • Monocyclic Model X = XoRt • Polycyclic Model: X = Xoert • Two ways to reduce X (disease): • Reduce the initial inoculum X0 – delay onset and reduce the duration of the epidemic • Reduce the rate of disease development (R or r) 31
  • Effect of X0 on Epidemic Development X0 depends upon: • inoculum from previous crops within a field • inoculum from crops in adjacent fields 32 X0 is affected by: • destroying infested plant debris • removing diseased plants • chemical seed treatments • protective fungicides • race specific disease resistance‐ • biological control agents targeted at initial inoculum
  • 33
  • Effect of r on Epidemic Development r depends upon: • reproductive potential of the pathogen • virulence of the pathogen • susceptibility of the host • conduciveness of environment r is affected by: • non-specific disease resistance • systemic fungicides • cultural practices that alter environment • removal of diseased plants 34
  • 35
  • Disease Control Effect of Reducing Primary Inoculum 36
  • Mathematical modeling in plant disease epidemiology • Monomolecular: – appropriate for modeling monocyclic epidemics – also called negative exponential model • Exponential – also known as the logarithmic, geometric or Malthusian model. • Logistic – more appropriate for most polycyclic diseases – most widely used for describing epidemic • Gompertz – appropriate for polycyclic diseases as an alternative to logistic models. Gompertz model has – an absolute rate curve that reaches a maximum more quickly and declines more gradually than the logistic – models 37 1. Disease progress curves
  • 38
  • 2. Linked differential equations (LDE) 3. Area under disease progress curve (AUDPC) • generally used to make comparison between treatments • to evaluate the resistance of plant species • Computer simulation – EPIDEM – MYCOS – EPIMAY – EPIVEN – EPIMUL – EPIDEMIC – PLASMO 39
  • 40
  • Applications of Geographic Information Systems and Geostatistics in Plant Disease Epidemiology and Management • These satellites broadcast signals containing time and position information. GPS receivers on the ground collect the satellite signals and determine position in a spherical coordinate system such as latitude and longitude or a planar coordinate system 41 Global positioning systems (GPS) • GPS receivers determine location and are among the most important tools for spatially referencing agriculture data. • GPS depends on a system of navigation satellites operated by the U.S. Department of Defense (the NAVSTAR system).
  • GIS • GIS relates the data collected by GPS to other sources of geo- referenced information. • GIS has the ability to integrate layers of spatial information and to uncover possible relationships • The process of transforming one layer of spatial information to match a second layer is called registration . 42 • A GIS is a computer system capable of assembling, storing, manipulating, and displaying data referenced by geographic coordinates. • GIS can now be installed on any recent model desktop computer
  • There are two main forms of GIS data: vector and raster. • In vector data sets, map features such as points, lines, and polygons are organized and manipulated in a database. • In raster data sets, the data are organized as a matrix of numerical values and referenced spatially by row and column position 43
  • Geostatistics • a statistical model appropriate for estimates across continuous areas • Create surface maps based on point samples or observations. • A surface map is a map with an area shaded in a color or gray scale keyed to a variable. 44
  • 45
  • Benefits • provides a tool for the refined analysis of traditional and contemporary biological/ecological information on plant diseases. • It will aid practitioners in the design of disease management in IPM programs, particularly on a regional scale. • It will also provide a way of analyzing and communicating results of regional programs on a continuing basis. 46
  • 47 Books Recommended
  • Two more books • Plant disease Epidemiology–S. Nagaranjan- India • A text book of plant pathology- H. Ashrafuzzaman-Bangladesh 48
  • 49