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 of Agriculture Faisalabad

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

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

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

The Disease Triangle

Amount of Disease

Total of conditions favoring susceptibility Host

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.

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

Current Phytopathological threats in Pakistan

Bacterial Leaf Blight

of Rice

Decline of Fruit &

Forest Plants

Rusts of Wheat

Gram Blight, CLCuV

Further Disciplines in Plant Pathology

Plant Pathology

Plant Virology

Diagnostic Plant

Pathology

Molecular Plant

Pathology Plant Mycology

Plant Bacteriology

Plant Nematology

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

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

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

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

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‟

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

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

VIRUSES

Harmful aspects

o Cotton leaf curl disease is caused by CLCuV

o Tobacco mosaic disease is caused by TMV

o Tomato Mosaic Disease is caused by ToMV

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

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)

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

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