plant disease development chapter 4. objectives clarify the factors for successful disease...
TRANSCRIPT
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Plant Disease
Development
Chapter 4
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Objectives
Clarify the factors for successful disease development Identify stages in disease development Be familiar with disease triangle
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Disease Triangle
Factors For Successful Disease Development
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Three important components of plant disease :
Susceptible host Virulent pathogen Favourable environment
For disease to occur all three of these must be present.
Disease Triangle
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Level of virulence Adaptability Dispersal efficiency Survival efficiency Reproductive fitness
1. Properties of Pathogen
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Susceptibility Growth stage & form Population density & structure General health
2. Properties of Host
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Temperature Rainfall / Dew Leaf wetness period Soil properties Wind
3. Properties of Environment
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Inoculation Penetration Infection Growth and Reproduction Dissemination of Pathogen
Stages in Disease Development
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Inoculation : The arrival of pathogen on the host
Inoculum : The pathogen (s) that land on the host or
: Any part of the pathogen that can initiate infection
1. INOCULATION
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Primary inoculum : An inoculum that survives the dormant period & caused the first infections
Primary infections : Infection caused by primary inoculum
Secondary inoculum : An inoculum produced from
primary infections Secondary infections: Infection caused by secondary inoculum
Types of Inoculum
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Landing or arrival of inoculumGermination of spores and seeds (fungus)Hatching of nematode eggsAttachment of Pathogen to Host (virus and bacteria)Recognition Between Host and Pathogen (Pathogen recognize the host)
Inoculation Process
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The initial invasion of a host by a pathogen
1. Direct Penetration
Direct with haustoriaDirect, subcuticular onlyDirect intercellular mycelliumDirect, intercellular mycellium with haustoria Direct with appressorium (A), penetration peg (PP) and intracellular mycelium (IM)
2. PENETRATION
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Direct With Haustoria
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Direct, subcuticular only
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Direct, Intercellular Mycelium
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Direct, Intercellular Mycelium with
Haustoria
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Direct with appressorium (A), penetration peg (PP) &
intracellular mycelium (IM)
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2. Penetration Through Natural Openings
Stomata Lenticels (opening on fruits, stems and tubers –filled with loosely connected cells – allow the passage of air) Hydathodes (permanently open pores at the margins and tips of leaves)
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3. Penetration Through Wounds
Through various types of wounds Natural cracks between main and lateral roots Openings made by fungus
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Establishment of pathogen with vulnerable cells or tissues of the host and obtain the nutrients from them
Successful infection will produce symptoms
3. INFECTION
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Incubation period : The time interval between inoculation and the appearance of disease symptoms
Latent infection : The state in which a host is infected with a pathogen but does not show any symptoms
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The pathogen will grow and multiply within the infected host.
Fungi – sporesViruses – replicated by the cellNematodes – reproduce by means of eggs
4. GROWTH & REPRODUCTION
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Pathogens are disseminated by several ways:
By airWhile airborne – spores touch wet surfaces – get trapped – air movement stops / rains – washed out
From the air – brought down by rain drops
Winds also helps spreading by blowing away rain splash droplets containing pathogens
5. DISSEMINATION
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By water
Pathogens in the soil – dissemination by rain / irrigation water that moves on the surface / through soil
By Insects, Nematodes & other Vectors
Transmitted by insects during feeding, movement from plant to plant
Nematodes can also transmit virus internally
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By Seed and Transplanting process
Transported to other fields
Are sold and transported to other areas
By human
Through handling of diseased and healthy plants
Tools (pruning shears)
Transporting contaminated soil on their feet / equipment
Contaminated container
Using infected seed / nursery stock