plant pathology

1. Fundamentals of Plant Pathology
PPP-211
Theory: Introduction to the science of plant pathology, its
objectives, scope and historical background. Classification of
plant diseases, symptoms, signs, and related terminology.
Parasitic causes of plant diseases (fungi, bacteria, viruses,
phytoplasma, protozoa, algae and flowering parasitic plants),
their characteristics and classification. Non-parasitic causes of
plant diseases. Infection process. Survival and dispersal of
plant pathogens. Plant disease epidemiology, forecasting and
disease assessment. Principles and methods of plant disease
management. Integrated plant disease management.
Practical: Familiarity with general plant pathological
laboratory and field equipments. Study of disease symptoms
and signs and host parasite relationship. Identification and
isolation of plant pathogens. Koch's postulates. Preparation of
fungicidal solutions, slurries, pastes and their applications.

2. Suggested Readings
• Plant Pathology (5th ed) by G N Agrios
• Introduction to Principles of Plant Pathology
by R S Singh
• Plant Pathology by R S Mehrotra
• Modern Plant Pathology by H C Dube
• Fundamentals of Plant Pathology by V N
Pathak, N K Khatri & M Pathak

3. Introduction to the Science of Plant Pathology
Phytopathology = Phytos = Plant + Pathos = Suffering /
disease/ailments + Logus = Study
Branch of Science dealing with the study of causes, etiology,
resulting losses and management of plant diseases
Disease = Dis + Ease
Plant Disease: It is a malfunctioning process in plant body
caused by continuous irritation by some agent which results in
some suffering or symptom production.
or
Disease is a sum total of the altered and induced biochemical
reactions in plant system or part brought about by any biotic,
mesobiotic or abiotic factor leading to malfunctioning of
physiological processes and ultimately manifesting at cellular
and / or morphological level.

4. Pathogen = Pathos + Generating
Plant Pathogen: Any agent or entity which can induce disease
in plants. eg. Fungi, bacteria, viruses, viroids, mollicutes
(phytoplasmas, spiroplasmas, RLO’s) etc.
Pathogens bring about the irritation processes resulting in
development of disease by following ways:
• By utilizing the host cell contents
• By causing death of cells or by interfering with their
metabolic activities through enzymes, toxins and growth
regulators
• By weakening of tissues due to continuous loss of nutrients
• By interfering with translocation of food, minerals and water

5. Importance of Plant Diseases
• Direct losses
• Yield losses
• Post harvest losses
• Human health hazards : ergotism and mycotoxicoses
• Indirect losses
• Cost of pesticides and other inputs for disease
management

6. • Diseases of International / National Importance
• Cereal rusts - Worldwide
• Cereal smuts - Worldwide
• Ergot of rye and wheat - Worldwide
• Late blight of potato – Irish Famine (1945), worldwide
• Brown spot of rice - Asia, Bengal famine (1943)
• Southern corn leaf blight - U S , epidemic in 1970s
• Powdery mildew of grapes - Worldwide
• Downy mildew of grapes - US, Europe
• Chestnut blight - US, Epidemic (1904 – 1940)
• Dutch elm disease - US, Europe
• Coffee rust - Asia, epidemic ( 1870 – 1880s), South America (1970 onwards
• Sugarcane mosaic - Worldwide
• Citrus tristeza - Africa, Americas
• Peach yellows Eastern US, Russia, Asia
• Cadung cadund of coconut - Phillipines
• Banana bunchy top - Asia, Australia, Egypt, Pacific Islands
• Apple scab - Asia (India)
• Premature leaf fall of apple – Asia (India)

7. Objectives of Plant Pathology:
To study the living, non living and environmental
causes that induce the disease
To study the mechanisms of disease development by
pathogens
To study the interactions between the plants and
the pathogen
To develop strategies for managing the diseases and
reduce crop losses caused by them.

8. History of Plant Pathology
Rigveda (3700 BC) • Oldest mention of plant diseases like blight, powdery mildew, rust
and tumours on trees and worship of Sun God and Agni God to avoid
those.
• Two facts came out from verses in the Vedas:
Visible and invisible creatures entered the body and caused the
disease
Sun, heat and fire killed these poisonous creatures
• Mentioned the therapeautic properties of sulfur on plant diseases
Homer (1000BC)
Democritus (470
BC)
Susruta (400 BC)
• Recommended control of plant blights by sprinkling plants with olive
grounds left after extraction of olive oil
• Made a mention about the plant diseases and suggested that “just as
the proper season, good soil, water and vigorous seed produce a
healthy plant”
• Made a mention of powdery mildew and rust in his book “Krishi
Prasar” and invoked the Wind God to move them away from his field
Parashar (400BC)
The Ancient Era

9. Theophrastus
(384-322 BC)
• Wrote two books “Historia Plantarum” and “De Causis Plantarum”
and mentioned about plant diseases like rusts, mildews and blights
etc) and expressed the opinion that these diseases were caused
due to bad nutrition and bad air which occurred due to wrath of
God.
• Romans at that time used to celebrate a festivals called “Robigalia”
in which they used to sacrifice red dogs, foxes, and cows in attempt
to please and pacify the so called God of Rusts “Robigus” so that it
did not send rusts to destroy their crops.
• In his book “Vrikshayurveda” divided plant diseases in two
categories: Internal and External
• Internal diseases were caused by inroads of foreign organisms into
the plant body
• External diseases were attributed to non-parasitic injuries by heat,
frost, wind, soil acidity, water stress and poor quality seed.
• For cure of both types of diseases Surapal prescribed the
treatment of pits for planting trees and treatment of seeds etc.
• A higher plant mistletoe was proposed as a parasite of plants which
takes its food from the host plant and makes it sick.
Surapal (1000AD)
1200 AD

10. Fungal Pathology
Mid 1600s
(France)
Thoullier (1670)
(France)
• A group of French farmers noted that wheat rust was always more
severe on wheat near barberry bushes than away from those. They
asked French Govt. to pass a legislation that would force towns to
cur barberry bushes to protect wheat crop.
• Observed that ergotism or Holy Fire , a dreadly disease of human
beings was associated with the consumption of contaminated
grains
Robert Hook (1669)
England
Antonius van
Leeuwenhoek(1675)
(Dutchman)
• Invented double lensed compound microscope and discovered the
“cell”
• Developed the first microscope
Antonius van
Leeuwenhoek(1683)
(Dutchman)
• Described the bacteria seen with his microscope
Pier Antonio Micheli
(1729) Italian
• Described many genera of fungi and illustrated their reproductive
structures.
• He proposed that fungi arise from their own spores rather than
spontaneously, but nobody believed him
• He is Considered the Father of Mycology
The Modern Era

11. Tillet (1755)
French
• Showed that the number of wheat plants infected with covered
smut could be increased by dusting wheat kernels with smut dust
i.e. spores before planting
• He believed that it was a toxin produced by black powder and not
the fungus which produced the disease
• He could also reduce the number of smutted wheat plants by
treating the smut treated kernels with copper sulphate
• Classification and nomenclature of fungi
• Believed that microorganisms were the result and not the cause of
diseases
• Persoon wrote “Synopsis Methodica Fungorum”
• Fries wrote “Systema Mycologicum”
• Poineered the germ theory of plant disease and proved that the
diseases are caused by microorganisms
• He studied the germination of wheat bunt spores and by mixing the
spores with clean seed, he could reproduce the disease
• He discovered the life cycle of bunt fungus
• He also suggested chemical treatment with copper sulphate for the
control of wheat bunt
• He also mentioned the fungicidal and fungistatic properties of
chemicals
Persoon (1801) &
Fries (1821)
Prevost (1807)
French

12. • Observed pleomorphism in rust fungi and produced illustrated description
of rust and smut fungi
• They also confirmed the findings of Prevost
• Irish famine due to potato late blight in Europe
• Potato late blight is caused by a fungus but they could not prove it
experimentally
• Foundation of modern Plant Pathology
• Father of Modern Plant Pathology
Tulasnebrothers
(RL Tulasne & C
Tulasne)
French
1845 (1830-1845)
Van Martius
(1842),
Morren (1845) &
Berkeley (1846)
Anton de Bary
(1831-1888)
German
1853 • He confirmed the findings of Prevost
1861 • He experimentally proved that the fungus Phytophthora infestans was the
cause of potato late blight
• He owns the credit of detailed study of late blight fungus , its
nomenclature and experimental proof of organisms being plant
pathogens
• He studied other diseases like rusts, smuts, downy mildews and rots
• Discovered the heteroecious nature of rust fungi
1886 • He reported the role of enzymes and toxins in tissue degradation caused
by Sclerotinia sclerotiorum

13. Kuhn (1870s) • Contributed significantly to the studies of infection and development of
smut in wheat plants
• Promoted the development and application of control measures
particularly seed treatments for cereals
• He also written the first book on Plant Pathology “Diseases of Cultivated
Crops, Their Causes and Their Control” in which he recognized that plant
diseases are caused by unfavorable environment but can also be caused
by parasitic organisms like insects, fungi and parasitic plants
• Developed the methods of artificial culture of microorganinsms
Brefeld (1875 –
1912)
Erikson (1894)
Swedish
Biffen (1905)
• Discovered the phenomenon of variability in fungi and reported the
existence of physiological races in the rust fungi
• Described inheritance of resistance to yellow rust in two varieties of
wheat and their progenies on the basis of Mendelian laws of inheritance
• While working with diseases of cotton, watermelon and cowpea
developed varieties resistant to disease
• Distinguished disease resistance from disease escape and disease
tolerance
• Discovered physiological specialization in fungi causing rust and powdery
mildews of cereals
• Observed that colonization of resistant Bromus sp. by Puccinia dispersa
was accompanied by necrosis of host cells adjacent to fungus
Orton (1909)
Ward (1903) &
Salmon (1903-04)
Ward (1902)

14. E C Stakman
(1915)
• Reported that due to continuous evolution of races and biotypes on
botanical species of rust fungi, their pathogenic capability goes on
changing in their favour and as a result the resistance capability of host
also shows changes
• While working on resistance of wheat to Puccinia graminis observed the
rapid cell death around the sites of penetration in resistant hosts and
thus he coined the term “Hypersensitivity” to this response
• It was reported that pectic enzymes produced by fungi played a
significant role in their ability to cause disease
• Experimental proof of role of toxins in black spot of pear caused by
Alternaria sp.
• Role of cellulases was implicated in plant disease development
1915
Tanaka (1933)
Japan
1940s
K O Muller and H
Borger (1940)
• While working on resistance of potato late blight, they first defined
phytoalexins as the antimicrobial compounds synthesized and
accumulating at the sites of infection or stress
• Elaborated the phenomenon of hypersensitivity
Gaumann (1946)
H H Flor (1946) • Worked with linseed (Flax) rust and gave the “Gene for Gene” concept
od disease resistance and susceptibility. According to Gene for gene
concept: for every gene for resistance or susceptibility in the host, there
must be matching genes for avirulence or virulence in the pathogen

15. Cruickshank
(1963)
• Confirmed the accumulation of antimicrobial plant metabolites called
phytoalexins during pathological processes and their role in resistance.
Van der Plank
(1963)
1970s
• Suggested two kinds of resistance known as Vertical and Horizontal
resistance
• It was demonstrated that plant cells and protoplasts could be selected in
culture for resistance to a pathogen toxin and that plants with an altered
response to infection by the pathogen could be regenerated from these
cultured cells
Bacteriology
Luis Pasteur
(1861-63)
• While working on different bacteria he proposed the “Germ Theory”
and proved it experimentally
Robert Koch
(1876)
Robert Koch
(1887)
• Gave the conclusive demonstration and irrefutable proof that anthrax
disease of cattle was caused by a bacterium Bacillus anthracis .
• Gave four postulates known as “Koch’s postulates” which must be
satisfied before a particular microorganism isolated from a diseased
plant can be accepted as a cause of disease.
• Reported for the first time that a plant known as fir blight of apple and
pear was caused by a bacterium named Erwinia amylovora
• Main contributor to the discovery of most of bacterial plant diseases.
• Founder of phytobacteriology due to his discoveries and the
methodologies he introduced for study of bacterial plant diseases
• First to notice and study the crown gall disease (1893-94) and compared
the galls to cancerous tumors of human and animals.
T J Burril (1882)
E F Smith (1895 –
1920)

16. Fisher - Smith
controversy
(1895 – 1903)
• Alferd Fisher of Germany did not agree with the findings of Smith that
bacteria could cause diseases in plants as he was of the view that
bacteria can not enter the plant cells then how could they cause
diseases in plants. He emphasized that the bacteria seen by other
scientists in plant cells were accidental invaders and were not able to
cause diseases. This controversy continued for seven years but in the
end Smith won the battle
• Reported the role of cytolytic enzymes in soft rots caused by bacteria
• Wild fire toxin and its action
• Biocontrol of crown gall with Agrobacterium radiobacter strain 84
L R Jones (1905)
A C Braun (1955)
New and Kerr
(1972)
Chilton et al.
(1977)
• Crown gall bacterium Agrobacterium tumefaciens transforms normal
plant cells into tumor cells by introducing its plasmid into them , part of
which gets inserted into host DNA.
Virology
Adolf Mayer.
(1882 -86)
German
• Reported that tobacco mosaic was caused by neither a microorganism
nor due to nutritional imbalance.
• Demonstrated the contagious nature of the causal agent
• Proved tthat boiling of infected plant sap destroyed the infectivity of
causal agent
• Confirmed the findings of Mayer
• Reported that the causal agent could pass through bacterial proof filter
and this filtered sap retained the infectivity for months
D Ivanoswski
(1892)
Russian

17. M W Beijerinck
(1898)
Dutch
• Concluded that the causal agent of tobacco mosaic was other than a
microbe. The agent could diffuse through porcellin filters and could not
pass through agar gel
• He named the agent “Contagium vivum fluidum” meaning a contagious
living fluid or virus
• Founder of Virology
• Crystallized the virus protein of TMV and this crystalline substance
remained infective
• Concluded that virus was a autocatalytic protein that could multiply
within living cells
• Showed that TMV was a nucleoprotein and contained phosphorus
W M Stanley
(1935)
F C Bawden & N
W Pirie (1936)
Kausche et al
(1939)
Gierer and
Schramm (1956)
1975
• Saw the virus particles for the first time with the help of electron
microscope
• Showed that TMV nucleic acid free from its protein coat could alone
cause infection provided it was protected from inactivation
• Production of monoclonal antibodies
• Development of Enzyme Linked Immunosorbent Assay (ELISA)
technique.
• Reported that potato spindle tuber disease was caused by a small,
naked, single stranded circular molecule of infectious RNA which he
called as “viroid”.
1977
Diener (1971)

18. Other causes of plant diseases
Needham (1743)
English
Kuhn (1857)
N A Cobb (1913 –
1932)
• Observed nematodes inside the abnormally rounded wheat kernels
but he failed to show that they were the cause of disease
• Reported the stem nematode (Ditylenchus dipsaci)
• Studied the structure of many nematodes and classified them
• He coined the term “Nematology” and developed many techniques
for the study of nematodes
• Father of Nematology
• Was first to show that club root disease of cabbage was caused by a
Woronin (1878)
fungus that has now been shown to be a protozoan
plasmodiophoromycete “Plasmodiphora brassicae”
• Flagellate protozoa had been found in latex bearing cells of plants in
family Euphorbiaceae but were thought to be residing in latex
without causing disease
• Found flagellates infecting the phloem of coffee trees and causing
abnormal phloem formation and wilting of trees
• Presented convincing evidence of pathogenicity of flagellates to
coffee trees
• Flagellates were reported to be associated with several diseases of
coconut and oil palm trees in South America and Africa
Lafont (1909)
Stahel (1931)
Vermeulen
(1963)
1976

19. Doi et al (1967)
Japan
Ishiie et al (1967)
• Observed mollecutes i.e. wall less mycoplasma like bodies in the
phloem of plants exhibiting witches’ broom and yellowing type
symptoms
• Showed that these mycolplasma like bodies and symptoms
disappeared temporarily when the infected plants were treated
with tetracycline antibiotics
• These could not be cultured on artificial media
• Observed a motile helical, wall less microorganism associated with
corn stunt disease which they called as Spiroplasma and this
organism could be cultured and characterized
• MLOs were named as Phytoplasmas
• Another group of fastidious prokaryotes was discovered causing
citrus greening disease
• These organisms were also phloem inhabiting but had definite cell
Devis et al (1972)
1990s
1973
wall and were susceptible to both penicillin and tetracycline
antibiotics indicating them to be true bacteria but difficult to
culture (fastidious).
• Discovery of Gram negative bacteria Xyllella fastidiosa, a xylem
inhabiting fastidious bacteria causing Pierce’s disease of grapewine
• The organism for citrus greening was identified as Liberobacter spp.
1987
1990s
These type of fastidious bacteria were earlier known as Rickettsia like organisms (RLOs) just
because of their resemblance to Rickettsia but they are not true Rickettsia)

20. Control of plant diseases
Prevost (1807) • Recommended the use of copper sulphate as seed treatment for the
control of wheat bunt
• Discovery of Bordeaux mixture (copper sulphate + lime + water ,
4:4:50) for the management of downy mildew of grapes.
• Discovery of Burgundy mixture (sodium carbonate in place of lime)
• Organic mercurial compounds were introduced in the market
• Discovery of penicillin (It was not effective against plant diseases but a
experimentation started in this new field )
• First dithiocarbamate fungicide (thiram) was discovered
• Antibiotics primarily streptomycin was used to control bacterial plant
diseases and after some time cycloheximide was also used
• Few strains of bacteria resistant to antibiotics were noticed
P M A Millardet
(1882) France
1887
1913
Alexander
Fleming (1928)
1934
1950
1954
1962 • Rachel Carson’s book of “Silent Spring” published which
vividly described the dangers of polluting the environment with
poisonous chemicals and documented several cases of bird and fish
deaths due to accumulation of pesticides in the food chain
• Strains of fungal pathogens were found to be resistant to certain
protective fungicides
1963

21. Mid 1960s • All mercurial fungicides were banned by U S Govt and soon after that
DDT and chlorinated hydrocarbons were also banned
• Tetracycline antibiotics were shown to control plant diseases caused by
mollecutes and which later proved to be effective against fastidious
bacteria
1967
Von Schmeling • Introduction of systemic fungicides Oxathiins (carboxin and
and Kulka (1966) oxycarboxin)
1968 - 69 • Confirmation off systemic activity of pyrimidines (1968) and
benzimidazoles (1968,69)
Ciba Geigy Co.
(1973)
• Developed metalaxyl effective against Oomycetous fungi which was
launched in market in 1977
Plant Pathology in India
D D Cunningham • Started identification of fungi in India.
& A Berclay (1850 • Cunningham made a special study on rusts and smuts
– 1875)
K R Kirtikar • First Indian scientist who collected and identified the fungi in this
country
• The first Indian Universities established at Kolkata, Bombay and Madras
and these emphasized the studies on fungal taxonomy
• The University of Madras was the first to take up Plant Pathology as a
subject
1857

22. • Later Universities of Allahbad and Lucknow also took up the plant
disease aspects of Mycology
• Imperial Agricultural Research Institute (IARI) established at Pusa,
Bihar
• First Government College of Agriculture was established at Kanpur
• Joined as an Imperial Mycologist at IARI, Pusa in 1905 and served in
that capacity for 20 years
• He initiated an exhaustive study of fungi and diseases caused by them
in India
• He trained a team of plant pathologists who took over the work after
him
• He gave detailed account of diseases like wilt of cotton and pigeonpea,
different diseases of rice, toddy palm, sugarcane, potato and rusts in
cereals
• He studied the Pythiaceous and allied fungi and wrote a monograph
on them
• In 1918 he published a textbook entitled “Fungi and Disease in
Plants” from Kolkata
• He left India in 1920 to take over as the first Director of Imperial
Mycological Institute (IMI) which was later renamed as
Commonwealth Mycological Institute (CMI) in England
• Father of Indian Plant Pathology
1905
1906
E J Butler (1905 –
1920) a medical
doctor

23. J F Dastur • He was a collegue of Butler and was the first Indian Plant Pathologist
to conduct detailed studies on fungi and plant diseases
• His special field of studies was genus Phytophthora and diseases
caused by it in castor and potato
• He is internationally known for establishing the Phytophthora
parasitica from castor
• Published exhaustive information on downy mildew and smuts of
sugarcane and pearl millet
• Studied wilt of cotton, smut of sugarcane and ergot of sorghum
• Started work on control of cotton wilt through varietal resistance
which lead to reduction in losses due to diseases in Maharashtra
• He also identified and classified a large number of Indian smut fungi
• He established single handedly the Indian Phytopathological Society
in 1947 and the first volume of its journal Indian Phytopathology was
published in 1948
• He also authored a textbook “ Fungi and Plant Diseases”
• Outstanding contribution to the knowledge of disease cycle of cereal
rusts in India
• He also added knowledge of linseed rust
• Wrote two monographs on rust fungi
• Published the first edition of the book “Fungi of India” which has been
frequently updated from time to time
G S Kulkarni
S L Ajrekar
B B Mundkar
K C Mehta
(Agra College)
Butler and Bisby
(1931)

24. S N Dasgupta &
T S Sadasivan
S N Dasgupta
T S Sadasivan
• Strong schools of fundamental plant pathology especially biochemistry
of host pathogen interaction were started under their leadership at
Lucknow and Madras Universities
• Conducted extensive studies on controversial black tip disease of
mango
• Developed the concept of vivotoxins and worked out the mechanisms
of wilting in cotton due to Fusarium oxysporum f sp vasinfectum
• He also demonstrated the production of fusaric acid by the fungus
Fusarium oxysporum f sp vasinfectum
• Worked on bacterial plant pathogens in India
• Father of Indian Phytobacteriology
M K Patel
V P Bhide & G
Rangaswami
M J
Thirumalachar
• Also pioneered the work on bacterial plant pathogens
• Conducted extensive studies on smuts and rusts
• Associated with Hindustan Antibiotics Limited at Pimpri (Pune) and due
to this association, several antifungal antibiotics were discovered
• Developed solar heat treatment procedure for the control of loose smut
of wheat
• Developed new information on the spread of black, brown and yellow
rusts in India
J C Luthra
L M Joshi

25. S Nagrajan • Epidemiological investigations made by him using climatic and weather
based information lead to the identification of Puccinia path in India
• Imperial Agricultural Research Institute was shifted from Pusa to Delhi
and renamed as Indian Agricultural Research Institute
• Organized teaching in Mycology and Plant Pathology as a part of
Agricultural Science was started here.
• Later the institute started giving the PG degree in the subject
• First of all the PG degree programme was started in Plant Pathology at
Govt College of Agriculture, Kanpur
• First Agricultural University was established at Pantnagar, Uttranchal
(then UP)
• Indian Society of Mycology and Plant Pathology established at Udaipur
with its publication named “Indian Journal Of Mycology and Plant
Pathology” which was later renamed as “Journal Of Mycology and
Plant Pathology”
• Indian Society of Nematology was established which started its journal
“Indian Journal of Nematology” as its publication
• Dr Y S University of Horticulture and Forestry, Nauni, Solan (HP) was
established which was first of its kind in Asia.
1934
1945
1960
1971
1971
1985

26. Thank you all
A.Swaroopa rani