This document provides an introduction to the fundamentals of plant pathology. It discusses key concepts such as the definition of a plant disease, disease cycle, and the interaction between the host, pathogen, and environment (known as the disease triangle). It also outlines the importance of plant pathology in reducing crop losses and ensuring food security, and provides a brief history of the development of plant pathology in India with contributions from notable scientists. The overall objectives of plant pathology are to study the causes and mechanisms of plant diseases and develop management strategies to control diseases and minimize losses.

1. Pat 201 - Fundamentals of plant pathology (2+1)
Presented by,
K. Vignesh., M. Sc., (Ag.), Ph. D., DCA., DABM., PG – DOLG.,
INTRODUCTION

2.  Plant Pathology is a branch of agricultural science that deals with the
study of fungi, bacteria, viruses, nematodes, and other microbes that
cause diseases of plants.
 Plants diseases and disorders make plant to suffer, either kill or reduce
their ability to survive/ reproduce.
 Any abnormal condition that alters the appearance or function of a
plant is called plant disease.
Definition

3.  Anon (1950) defined the disease as "harmful deviation from normal
functioning of physiological processes".
 According to Stakmann and Harrar (1957) plant disease is "a
physiological disorder (or) structural abnormality that is deleterious to the
plant / to any of its parts / products / that reduces their economic value".
In general disease is an interaction among the host, parasite and the
environment.

4. The term 'Pathology' is derived from two greek words 'pathos' and 'logos'.
'Pathos' means suffering and 'logos' means the study / to speak / discourse.
Therefore if etymologically means "study of suffering".
Thus the plant pathology is the "study of suffering plants".
When the plant is suffering i.e. not developing and functioning in the manner it is
expected, then it is called as diseased.
Due to this abnormality, the productivity of the plant is reduced or lost.

5. Importance of Plant Diseases
 The study of plant diseases is important as they cause loss to the plant as well as plant
produce. The various types of losses occur in the field, in storage or any time between
sowing and consumption of produce.
 The diseases are responsible for direct monitory loss and material loss. Plant diseases still
inflect suffering on untold millions of people worldwide causing an estimated annual
yield loss of 14% globally with an estimated economic loss of 220 billion U. S. dollars.
 Fossil evidence indicates that plants were affected by different diseases 250 million year
ago. The Plant disease has been associated with many important events in the history of
mankind of the earth.

6. The crop loss due to diseases is estimated to be approximately 30-50%.
Cultivated plants are often more susceptible to diseases than are their wild relatives.
Important environmental factors that may affect development of plant diseases are
temperature, relative humidity, soil moisture, soil pH, soil type, and soil fertility.
Each pathogen has an optimum temperature for growth. High soil-moisture levels favors
development of destructive water mold fungi, such as species of Aphanomyces, Pythium
and Phytophthora.
High humidity favors development of the great majority of leaf and fruit diseases caused
by fungi and bacteria.
Soil pH, a measure of acidity or alkalinity, markedly influences a few diseases, such as
common scab of potato and club root (Plasmodiophora brassicae) of crucifers.

7. Raising or lowering the levels of certain nutrients also influences the development of some
infectious diseases. Most control measures are directed against inoculums of the pathogen
and involve the principles of exclusion and avoidance, eradication, protection, host resistance
and selection, and therapy.
 The earliest known writings make references in the ravages of plant diseases.
 There are references in the religious literature about the occurrence of plant diseases.
 Rigveda, Atharveda (1500-500 BC), the Artha Shastra of Kautilya (321 -186 BC), Vishnu
Puran (500 AD), Agnipuran (500-700 AD) etc are some ancient books in which they have
mentioned the plant diseases and other enemies of plants along with the methods to control
them.

8.  The man in the Vedic period were aware of the fact that these diseases are caused by
microorganisms.
 Symptoms of plant diseases are also mentioned in Holy Bible, Shakespear's poems and
drama's. The early man considered the disease to be the curse of God on man for his
wicked deeds.
 The early man celebrated "Robigalia", a special holiday during which they offered
scarifies of red dogs, fox and cows in an attempt to please the rust god "Robigus“, goddess
“Rubigo” and keep him from sending the rust disease to their crop.
 Robigalia is celebrated even today on every spring around April 25 by the graduates of
department of plant pathology and microbiology at Texas A&M university.

9.  Late blight of potato (Phytophtora infestans) caused severe potato
losses in much of Northern Europe in the 1840's but it absolutely
destroyed the potato crop in Ireland in 1845 and 1846 and caused
the great "Irish famine". The destruction of potatoes caused
widespread famine that resulted in the death of hundreds of
thousands of people and the emigration of more than one and half
million people from Ireland to the United States. Wheat rust has
been another disease that has appeared in epiphytotic form from
time to time in many countries.

10.  In the fag end of the second world war (1943),
Bengal had to face a serious famine (Bengal
famine). One of the reasons to which this
famine has been attributed is the loss in the yield
of rice due to attack of Helminthosporium
oryzae leaf spot disease which had been
affecting the crop for last several years.

11. Scope and responsibilities of plant pathology is unlimited. Its ultimate goal is to prevent
and control plant diseases of economic importance. Responsibilities of the science of
plant pathology may be summarized as under.
Study of etiology, symptoms, predisposing factors and recurrence of such diseases.
Plant pathology deals with different aspects of plant diseases and has wide scope than
human pathology which only deals with only one aspect i.e. plant health.
The branch focuses on understanding how hosts, pathogens, and environments interact to
cause plant diseases and on understanding how to control plant diseases.
Scope and Objectives of Plant Pathology

12.  In recent years plant pathologists have begun to specialize in particular aspect. The
fields in which notable advances have been made are:
 Interaction between host and pathogen at chemical, molecular and genetic level.
 Plant virology, Mycology, chemistry of fungi toxicity.
 Disease forecasting and Plant Quarantine.

13. On practical aspects much advances have been made in plant protection
chemicals; breeding for disease resistance. Increased population emphasizes the
application of all possible means to meet the food requirements
 Expansion of crop area
 Improved methods of cultivation
 Increased use of fertilizers
 Improved varieties
 Increased irrigation
 Crop protection

14. Plant Pathology (or) Phytopathology is one among the branches of agricultural science that
deals with cause, etiology, resulting losses and management of plant diseases with four major
objectives.
1. Study the disease(s) / disorders caused by biotic and abiotic agent(s)
2. Study the mechanism(s) of disease development
3. Study the interaction between plant and the pathogen in relation to the overall environment
4. Develop suitable management strategy to surmount the diseases and to reduce the loss.
Objectives

15. Historyof Plant Pathologywithspecial reference to Indian work
The development of science of Plant Pathology in the modern era in India as in other countries
followed the development of mycology. The study of fungi in India was initiated by Europeans in
the 19th century. They used to collect fungi and send the specimens for identification to the
laboratories in Europe.
 During 1850-1875, D.D. Cunningham and A. Barclay started identification of fungi in India
itself. Cunningham made a special study of rusts and smuts. DD Cunningham identified the
causal organism of red rust of tea in Assam caused by Cephaleurous virescens.
 K.R. Kirtikar Pusa (1885) was the first Indian scientist who collected and identified the fungi
in the country.
 TS Ramakrishan Studies and contributed to genera Pythium, Phytophthora, Colletotrichum,
and the rusts. Wrote monograph on 'Diseases of Millets‘ published by ICAR

16.  E.J. Bulter who is also known as the ‘Father of Plant Pathology’ in India, initiated an exhaustive
study of fungi and diseases caused by them in 1901 at Imperial Agricultural Research Institute at Pusa
(Bihar). During his stay of 20 years in this country, he made a scientific study of mostly fungal plant
diseases known in India at that time. The diseases studied by him for the first time included wilt of
cotton and pigeon pea, different diseases of rice, toddy palm, sugarcane, potato and rusts of cereals.
He wrote a monograph on ‘Pythiaceous and Allied Fungi’; and a classic text book, ‘Fungi and
Diseases in Plants’ in 1918.

17.  J.F. Dastur (1886-1971), a colleague of Butler, was the first Indian Plant Pathologist who is credited with
detailed studies of fungi and diseases in plants. He studied the genus Phytophthora and diseases caused by it in
castor and potato. He is internationally known for the establishment of Phytophthora parasitica from castor.
 T.S. Sadasivan developed the concept of vivotoxins and worked out the mechanism of wilting in cotton due to
Fusarium oxysporum f.sp. vasinfectum.
 Mitra in 1937 AD recorded Tilletia indica, a new bunt (Karnal bunt) on wheat. The disease was thought,
erroneously, to be soil borne. Later studies showed that it was air borne, and the infection was not systemic
(Mundkar 1943 AD)
 G.S. Kulkarni published exhaustive information on downy mildew and smuts of sugarcane and pearl millet.
 B.B. Mundkur started work on control of cotton wilt through varietal resistance. He was also responsible for
the identification and classification of large number of Indian smut fungi. His most significant contribution to
plant pathology will be remembered through the ‘Indian Phytopathological Society’ which he started almost
single handedly in 1948 with its journal ‘Indian Phytopathology’. He also authored a text book entitled, ‘Fungi
and Plant Diseases’.

18.  M.K. Patel (Father of Indian plant bacteriology) established a school of plant bacteriology at the College
of Agriculture, Poona (Pune). He reported the first new species, Xanthomonas uppalii on Ipomoea
muricata in 1948. Advocated the family Phytobacteriaceae to include all plant pathogenic bacteria.
 M.K. Patel, V.P. Bhide and G. Rangaswami pioneered the work on bacterial plant pathogens in India.
 Yeshwant Laxman Nene reported “Khaira” disease of rice at Pantnagar due to zinc deficiency (1965
AD) and authored the book "Fungicides in Plant Disease Control"
 Dr. K.C. Mehta (Father of Indian Rust) of Agra College, Agra investigated the life cycle of cereal rusts
in India during the first half of 20th century. Wrote monograph on "Further studies on cereal rust in
India''.
 Dr. R. Prasada trained by Dr K.C. Mehta continued the work on rusts and added to the knowledge of
linseed rust.
 Luthra and Sattar (1953) developed the solar heat treatment of wheat seed for the control of loose smut.

19.  S N Das Gupta carried out exhaustive studies on black tip of mango.
 G. Rangaswami authored 'Diseases of Crop Plants in India' and 'Bacterial Plant Diseases in India.
 Jeevan Prakash Verma started the pioneering work on Xanthomonas campestris pv. malvacearum
causing bacterial blight of cotton. He laid a solid foundation of Indian Plant Bacteriology with his
students.
 A. Mahadevan studied biochemical changes in diseased plants and enzymes. He wrote the book
''Microorganism in Diseased Plants"
 S. Nagarajan and H. singh (1975) Formulated 'Indian Stem Rust Rules' for Puccinia graminis tritici
 S. Nagarajan (1978) Using climatic and weather based informations to identify Puccinia path in India.
 CD Mayee contributed to the understanding of the ground nut rust, sunflower downy mildew. Wrote
'Phytopathometery'.
 RS Singh Wrote ''Plant diseases", a book known as 'Bible of Plant Pathology.

20. K.R. Kirtikar E.J. Bulter J.F. Dastur B.B. Mundkur
Y. L. Nene
Dr. K.C. Mehta G. Rangaswami S. Nagarajan

21. Disease and disorder
These two terms carry the same meaning i.e., malfunctioning of physiological
processes in the plant. However, if the malfunctioning of the plants is due to biotic cause
(living organism) which is infectious, it is termed as disease, whike the malfunctioning due to
abiotic (non-living) cause which is non-infectious, it is termed disorder
Causal organism/causal agent
It is an organism which is a part of causal complex to cause a disease.
Ex: Plasmopara viticola - causal organism of downy mildew of grapes.
Pathogen
It is an entity, usually a micro-organism that can incite a disease.
Concepts and terms in Plant Pathology

22. Parasite
It is an organism living on or in another living organism (host) and obtaining food from the latter.
Pathogenicity
The ability of a pathogen to cause a disease.
Pathogenesis
The sequence of events in disease development from initial contact between pathogen and host to
completion of syndrome.
Disease Cycle - The sequence of events in recurrence of a disease in successive seasons.
Symptom - The external and internal reactions or alterations expressed by a plant externally as a result of a
disease.
Ex: Sigatoka disease of banana – Mycosphaerella musicola.

23. Sign - The visible structure of a pathogen or its parts or products seen on diseased host tissue.
Ex: Powdery mass of powdery mildew fungi – Erysiphales order.
Pycnidia in leaf spots caused by Septoria lycopersici on tomato.
Syndrome - The totality of effects produced in a plant by a disease. This includes both symptoms and signs.
Biotroph - An organism which, regardless of ease with which they can be cultured in nature, obtains its food
from the living tissues on which it completes life cycle (or) an organism that can live and multiply only on
another living organism.
Ex: Plasmopara viticola – Downy mildew of Grapevine.

24. Hemibiotroph - An organism which attacks living tissues in the same way as biotrophs, but will
continue to grow and reproduce even after tissue is dead.
Ex: Alternaria solani – Early blight of potato and tomato.
Perthotroph - An organism which kills host tissue in advance of penetration and then lives
saprophytically
Ex: Fusarium oxysporum f. sp. cubense – Panama Wilt of Banana.
Necrotroph - An organism which has no relation with living cells and obtains its food from dead
organic tissues.
Ex. Rhizopus.

25. Inoculum
The pathogen or its parts that can cause infection on the host.
Inoculum Potential - It is defined as the number of independent infections that are likely to occur
in a given situation in a population of susceptible healthy tissues. This is considered to be the
resultant action of the environment, the virulence of the pathogen to establish an infection, the
susceptibility of the host and the amount of inoculum used.
Infection - The establishment of a parasite within a host plant.

26. Incubation Period - The period of time between penetration of a host by a pathogen and the
first appearance of symptoms on the host.
Predisposition - It is the condition of the host which operates before infection by a pathogen
and its affect on the susceptibility of the host rather than directly affecting the pathogen.
Hypersensitivity - Increased sensitivity by the host at the site of infection as shown by rapid
cell death which prevents further growth of the pathogen and spread of infection.

27. There are three factors for the development of a disease viz.,
virulent pathogen, susceptible host and favorable environment for
the pathogen. The interaction of host, pathogen and environment have
often visualised as a triangle, generally referred to as disease triangle.
Each side of the triangle represents one of the three components. The
size of each side is proportional to the sum total of the characteristics of
each component that favour the disease. If the three components of the
disease could be quantified, the area of triangle would represent the
amount of disease in a plant.
Disease Triangle

28. Disease Pyramid/Tetrahedron
The disease triangle, used to describe interaction of three
components of plant disease, can be expanded by including time as the
fourth component. The amount of each of the three components of the
triangle as well as their effect on each other in the development of disease is
affected by time (e.g. the duration of favourable weather conditions at which
the host and the pathogen may co-exist). The interaction of these four
components can be visualised as a tetrahedron or a pyramid, in which each
plane represents one of the components. The figure is referred to as disease
pyramid or tetrahedron. If the four components of the disease pyramid could
be quantified, the volume of tetrahedron would be proportional to the
amount of disease on a plant or in a plant population.