Plant pathology is the study of diseases that affect plants. It examines the microorganisms and environmental factors that cause plant diseases, as well as methods for preventing and controlling diseases. Plant pathogens include viruses, bacteria, fungi, nematodes, and other microbes that infect plants and cause damage. A key goal of plant pathology is minimizing crop losses from diseases, which globally account for 36.5% of annual losses. Understanding plant diseases and their causes is crucial for improving global food security.

1. Introduction, History and Importance of
Plant Pathology
Introductory Plant Pathology
3(2-1)
Dr. Shahbaz Talib Sahi
Dr. Safdar Ali
Department of Plant Pathology
University ofAgriculture Faisalabad

2. Plant Pathology:
It is the study of microorganisms and of environmental factors that cause
disease in plants; the mechanism by which these induce disease in plants and
methods of preventing or controlling the disease.
Pathogen:
Any organism or micro-organism which lives, feeds and multiplies on host
and also cause disease is called pathogen.
Parasite:
Any organism which lives feeds and multiplies on host but could not cause
disease.
Disease: It is a physiological disorder or structural abnormality that affects the
quality and quantity of the produce
A Plant Pathologist attempts to improve the
chances
for survival of plants

4. Plant Pathology is a demanding subject
with many aligned sciences
Worldwide annual Crop losses 36.5%
10.2 % is due to insects
14.1 % is due to diseases
12.2 % is due to weeds

5. Concept of disease in plants
 Disease in plants can be defined as:
 The series of invisible and visible responses of plant cells and tissues to a
pathogenic microorganism or environmental factor that result in adverse
changes in the form, function, or integrity of the plant and may lead to
partial impairment or death of plant parts or of the entire plant.
 In some disease, hyperplasia or hypertrophy occur to produce abnormal
amorphous overgrowths (tumors) or abnormal organs.
 Types of plant diseases
 leaf spot, blight, canker, damping-off, dieback, mosaic, rot, scab, shot
hole, vascular wilt, downy mildew, powdery mildew, rust, smut, gray
mold, anthracnose, chlorosis, stunting, blast, gall

6. The DiseaseTriangle
Amount of Disease
Total of conditions favoring susceptibility
Host

8. 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.
 The human equation can affect the three
components of the disease triangle and
should be considered as a fifth
component in disease development.

9. 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

10. Current
Phytopathological
threats in Pakistan
Bacterial
Leaf Blight
of Rice
Decline
of Fruit &
Forest
Plants
Rusts of
Wheat
Gram
Blight,
CLCuV

11. Further Disciplines in Plant Pathology
Plant
Pathology
Plant
Virology
Diagnostic
Plant
Pathology
Molecular
Plant
PathologyPlant
Mycology
Plant
Bacteriology
Plant
Nematology

12. Plant Diseases in historical perspective
1845
late blight of potato caused starvation in Ireland
1942
Brown leaf spot of rice caused Bengal Famine
1992
Cotton leaf curl virus caused 80% reduction in
Pakistan

13. o The history of Plant Pathology is as old as human
civilization
o Homer (1000 B.C.) mentioned therapeutic
properties of sulphur on plant diseases
o Democritus (470 B.C.) controlled the blights by
sprinkling plants with olive oil
o Theophrastus (300 B.C.), a pupil of Aristotle, father
of Botany. He believed that God controlled the
weather that “brought about” the diseases. He
considered plant diseases as the wrath of God, so
these can be avoided if people do things that
please the God.
HISTORY OF PLANT PATHOLOGY

14. o Spores of wheat rust fungus observed under
compound microscope for the first time
(Leeuwenhoek, 1667)
o Tillet (1755) in France reduced number of smut
wheat plants by treating seed with copper
sulphate before planting
o De-Bary (1861) proved that a fungus
(Phytophthora infestans) is the cause of late
blight of potato

15. o Needham (1743) observed nematodes in wheat
galls for the first time and root-knot nematode in
cucumber root galls
o Pasteur and Koch (1876) first time showed that
anthrax is caused by a bacterium and first plant
bacterium was discovered in 1885
o In 1886, Mayer reproduced the „Tobacco Mosaic‟
disease by injecting juice from infected tobacco
plants into healthy tobacco plants

16. Disease Management
o In 1600s farmers used brine (sodium chloride solution) to
control the bunt of wheat
o In mid 1700s, sodium chloride was replaced with copper
sulphate
o In early 1800s, lime-sulphur and aqueous suspensions of
sulphur were recommended for the control of mildew of fruit
trees
o In 1885, Millardet discovered the magical Bordeaux Mixture for
the of downy mildew of grapes in France
o In 1913, organic mercurial compounds
o In 1965, the first systemic fungicide „carboxin‟

17. o Antibiotics, primarily streptomycin, were first used
to control plant diseases in 1950
o Flemming (1928) used Penicillium notatum as
biocontrol
o late 1980s, genetic engineering was introduced
Tissue culture, GMOs
o In the early 1990s, non-toxic chemicals called
plant defense activators were synthesized which
activate the plant defense system

18. The major objectives of plant pathology
o To study the causes (biotic & abiotic) of plant
diseases
o To study the mechanism of plant disease
development
o To study the interaction between plant and
pathogen in relation to environment and time
o To develop effective system of management of
plant diseases to minimize the losses

19. VIRUSES
Harmful aspects
o Cotton leaf curl disease is caused by CLCuV
o Tobacco mosaic disease is caused byTMV
o Tomato Mosaic Disease is caused byToMV
o Sugarcane mosaic disease is caused by ScMV
Beneficial aspects
o Used to kill insects as bio control agents
o Used in genetic engineering
o Colour breaking agent in ornamental plants
IMPORTANCE OF MICRO-ORGANISMS

20. BACTERIA
Harmful aspects:
o Xanthomonas axonopodis causes canker disease in citrus
o Erwinia amylovora causes fire blight of pear and apples
o Soft rot of vegetables caused by Erwinia carotovora
Beneficial aspects:
o Used as a vector in genetic engineering
o Used for fermentation process (milk to yogurt )
o Important for symbiosis process e.g. Rhizobium
o Used for antibiotic preparation e.g. Streptomyces
o Used in transgenic cotton (Bt. Cotton)

21. Harmful aspects:
 Economic losses due to diseases
 Causes citrus decline in citrus
 Wheat ear cockle and root-knot disease is caused
by nematodes
Beneficial aspects:
 Used to control insects by biological method
 Improve soil fertility
NEMATODES

22. Harmful aspects:
 Destroy Leather, paper, timber and textile industry
 Food industry specially pickles and pasteurized foods
 Cause field crop diseases
 Poisonous mushrooms which called as death caps e.g. Amanita
spp.
Beneficial aspects:
 Used in fermentation e.g. yeast
 Edible as mushrooms
 Easy to handle for research purposes
 Antibiotic penicillin is formed from fungus penicillium
 Some beneficial fungi are helpful to fertile the soil
 Coelomyces used as biological control to kill mosquitoes
FUNGI