Plant Disease Triangle, Disease Tetrahedron and Disease Pyramid, Disease epidemiology

Disease and disease triangle
The disease triangle is one of the first fundamental principle of the factors involved in disease causation. The existence of a disease caused by a biotic agent absolutely requires the interaction of a susceptible host, a virulent pathogen and an environment favorable for disease development. Conversely, plant disease is prevented upon elimination of any one of these three causal components.
Elements of Disease Development
1. THE HOST:
In our production system, regardless of planted crop the cultivars may be
Resistant: Possessing qualities that hinder the development of a given pathogen; the host is infected little or not at all.
Susceptible: Lacking the inherent ability to resist disease or attack by a given pathogen; non-immune.
Tolerant: The ability of a plant to sustain the effects of a disease without dying or suffering serious injury or crop loss; also the amount of toxic residue allowable in or on edible plant parts.
2. THE PATHOGEN:
virulent (capable to develop the disease) or
avirulent (non-capable to develop the disease) in a particular crop plant.
3. THE ENVIRONMENT:
The environment is probably the single most delimiting factor for the development of a plant disease situation. Without a conducive environment, a plant disease will not occur. In most cases, a conducive environment involves high humidity, or free moisture on the leaf surface in the form of dew as well as moderate temperatures.
In case of four-dimensional disease pyramid (Tetrahedron) with “time” added.
At the last human also added as disease causing elements in this pyramid.
4. Time
 Time is the key component , disease does not occur instantaneously, even in situations where a conducive environment remains present for an extended period of time. Time is required for the pathogen to infect the plant and produce characteristic lesions as well as produce sporulation or increase population.
5. Human: Human activities plays important role,
 Site Selection & Preparation
 Selection of Propagative Material
 Introduction of Exotic Pathogens
 Cultural Practices (sowing time, method, out of season crops)
 Disease control measures (chemical type/dose selection,)
 Introduction of new pathogens or disease (quarantine measures)
Disease
Pathogen
Host
Environment
Disease triangle
Epidemiology
Transmission
Control measures
Outbreak
Prevention
Infectious disease
Non-communicable disease
Vector-borne disease
Zoonotic disease
Public health
Pandemic
Contagious
Immune system
Viral infection
Bacterial infection
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#Prevention
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#NonCommunicableDisease
#VectorBorneDisease
#ZoonoticDisease
#PublicHealth
#Pandemic
#Contagious
#ImmuneSystem
#ViralInfection
#BacterialInfection
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