Introduction to plant pathology

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Amjad khan Afridi
Introduction to Plant Pathology
Disease = disturbance from plant pathogen or environmental factor that interferes with
plant physiology
Causes changes in plant appearance or yield loss
Disease results from:
• Direct damage to cells
• Toxins, growth regulators, or other byproducts that affect metabolism
• Use of nutrients and water or interference with their uptake
Plants Diseases Triangle
Pathogen Host
Virulent pathogen: Susceptible
Fungi, Bacteria, -- Crop
Viruses, Nematodes, -- Cultivar
Nycoplasmas and
Spiroplasmas
Favorable Environment
Air temperature Soil fertility Rainfall
Soil Temperature Soil type Relative humidity
Soil pH Soil Moisture
Mazz’s Disease Pyramid
 The interaction of components of plant disease can be expanded to include time and
humans.
 Time is often considered as the fourth component of plant disease development.
DISEASE

2. 2
Amjad khan Afridi
 The four components together can quantify the amount of disease.
 The human equation can affect the three components of the disease triangle and should be
considered as a fifth component in disease development.
Host Factors
 All plants can be considered hosts
 Degree of genetic uniformity – crop plants – inbred lines
 Age – affects disease development depending on plant-pathogen interaction
 There are different levels of susceptibility, which include:
– Immune - cannot be infected.
– Susceptible - can be infected.
– Resistant - may or may not be infected, and is the plant able to prevent the
pathogen from killing it. ie. defense compounds
Pathogen Factors
 Amount of inoculum
 Pathogen genetics
 Virulence of the pathogen
Type of reproduction:
– Monocyclic
– polycyclic

3. 3
Amjad khan Afridi
Ecology and mode ofspread
 Air
 Soil
 Seed
 Vector dependency
Environmental Factors
 Moisture
 Temperature
 Effect of human culture practice
– Monoculture
– Amount of inoculum: seed quality, disease residues, rotation, alternate host
– Introduction of new pathogens
Disease Development
Every infectious disease requires a series of sequential events in order for disease to develop.
Specific characteristics are unique for each disease.
General events are:
1. dispersal of the pathogen to the host
2. penetration and infection of the host
3. invasion and colonization of the host
4. reproduction of the pathogen
5. pathogen dispersal
6. pathogen survival between growing seasons and/or in the absence of a host
Jab Ho Jati Hy Der Ghar Ko Aane Men
Dekhti Hy Raah Mere Aane Ki Maan Meri
Jo Dekhleti Hy Zara C Takleef Meri
To Ho Jaati Hy Be-Qarar Maan Meri
Agar Kho Jao’on Men Soch Men Apni
To Ho Jaati Hy Pareshan Maan Meri