the uploaded subject "introduction to plant pathogens/ pathology" is deals with plant diseases which is caused by plant pathogens like fungi, bacteria, virus, phytoplasma, spiroplasma and viroids etc. and also provides basic information regarding all plant pathogens and their characters and life cycles

1. Prepared by
N. HIMA SHANKAR REDDY
M.Sc., Plant Pathology
Annamalai University
INTRODUCTION TO PLANT PATHOGENS
HISTORY OF PLANT PATHOLOGY
1676 -Antonvon leeuwenhoek (Dutch 1632-1729)-
 Developed the 1st
microscope (some books mentioned the years 1675,1676,1679)
 1st
publications on Bacteria (1683)
1729 -Pier Antonio Micheli (Italy)-
 “Founder and Father of mycology”
 He wrote a book “ Nova Plantarum genera” in 1729
 Proved that disease is caused by spores
1755 - Matheiu Du Tillet (france)-
 Considered as “Great grandfather of Phytopathology”
 Proved bunt of wheat is contagious (external transmission)
1761-1836 - C. H. Persoon (France)-
 “Founding father of systemic mycology”,
 Published “Synopsis methodica fungorum” (1801)
1807 - Benedict Prevost (France)-
 Experimentally proved role of micro-organism in causation of the diseases (Life cycle
of bunt fungus)
 Demonstrated the control of what smut spores germination by steeping seeds in a
copper sulphate solution
E.M. Fries (Sweden) -
 Linneaus of mycology, Father of systemic mycology
 Wrote a book called “Systema mycologicum” in 1821 (starting point in nomenclature
of fungi)
1803-1889 - M. J. Berkeley (England)-
 Coined the term “ Mycology”
 Founder of British mycology
1858- J. G. Kuhn (Germany)-
 Published 1st
text book in plant pathology “ The diseases of cultivated crops, their
causes and their control” in 1858
1831-1888 - Heinrich Anton De Bary (Germany):-
 Largely Considered as “ Father of Plant pathology”, “Father of Modern Plant
Pathology” and “Father and founder of modern Experimental Plant Pathology”
 He wrote a book
“Comparative Morphology and the Biology of Fungi, Myceteoza and bacteria” (1866)
 Introduced the terms ”Haustoria / Sinkers”, ”Symbiosis”, ”Teletospores”,
“Myceteoza”, Autoecious and Heteroecious rust, and “Chlamydospores”
 His students are M. S. Woronin (Russia), O. Brefels (Germany), A. Millardet (France),
H. M. Ward (England), W. G. Farlow (USA) and Fisher (Switzerland)
 Discoverd the life cycle of Phytophthora infestans (late blight of potato) that causes
Iirish famine.

2. 1839-1901- Robert Hartig-
 Father of “Forest plant pathology”
 Published book “Important diseases of forest trees” in 1874
“Diseases of trees” in 1882
1880 H. M. Ward (England) -
 “Father of tropical plant pathology”
 Emphasises the Role of environment on epidemiology of coffee rust gave the
briding host theory in 1903
 Recognised necrotic active defence in Bromus, later known as hypersentive
response
1882-1885 PMA Millardet (France)-
 Discovered “Bordeaux mixture” for the control of downy mildew of grapes
 This discovery is considered as serendicity discovery (accidental discovery)
 Bordeaux mixture Composition 1:1:100 (1gm of copper sulphate, 1gm of hydrated
lime, 100lit water)
 The original formula developed by Millardet contains 5 lbs of CuSO4 + 5 lbs of lime
50 gallons of water.
 The chemistry of Bordeaux mixture is complex and the suggested reaction is:
CuSO4 + Ca (OH) 2 = Cu(OH) 2 + CaSO4
 “Bordeaux” (founded in June 7,1441 ) is the university name in France.
1845-1920 – Pier Andrea Saccardo (Italy) –
 His famous book is “ Syllome fungorum ” (26 volumes)
1886- 1971- J. F .Dastur –
 First Indian plant pathologist, internationally known for the establishment of genus
Phytophthora and diseases caused by castor (Phytophthora parasitica) and potato
 1st
president of the “Indian Phytopathological Society” (IPS) in 1948.
 Reported the 1st
plant viral diseases in India (Sugarcane mosaic virus)
1874- 1943 – Edwin John Butler (Ireland)-
 1st
Imperical Mycologist in India
 Considered as ‘ Father of modern plant pathology in India”, “ Father of Indian
mycology”
 His book was “ Fungi and disease in plants” in 1918
1928 – Alexander Fleming (United Kingdom) –
 Isolated Penicillin from Pencillium notatum
 Shared noble prize in Physiology and medicine along with Ernst B. Chain & Howard
Walter Florey in 1945
When I woke up just after dawn on September 28, 1928, I certainly didn't plan to
revolutionise all medicine by discovering the world's first antibiotic, or bacteria
killer. But I suppose that was exactly what I did.
— Alexander Fleming
1940 – K. O. Muller and H. Borger –
 Coined the term “Phytoalexins”( antimicrobial compounds in plants)

3.  The 1st
phytoalexin is “Pisatin ”(produced from Pea plant), The molecular formula is
C17H14O6
1946 - H H Flor –
 Gave gene for gene hypothesis of plant-pathogen genetic interaction whilst working
on rust (Melampsora lini) of flax (Linum usitatissimum)
 He proposed the term "Avirulence gene"(Avr)
 ( Gene for gene hypothesis :- One is a plant gene called the resistance (R) gene. The
other is a parasite gene called the avirulence (Avr) gene. Plants producing a specific R
gene are resistant towards a pathogen that produces the corresponding Avr gene
product.
1947 – B. B. Mundukur –
 Started Indian Phytopathological Soeiety (IPS)
 Worked on cotton wilt in Bombay state, published Ustilaginales in india
 First issue of the journal “ Indian phytopathology” in 1948
 Published a text book “ Fungi and plant diseases “ in 1949, which was a second book
of plant pathology after Butller
1952 – G. Pontecorvo and JA Roper -
 Discovered parasexuality in Aspergillus nidulans
(parasexuality : - plasmogamy, karyogamy and meiosis not occurs in a regular stage )
 J A Roper reported the hormonal control of sexuality in fungi
1952. Kittleson – introduced the Capton( kittleson killer) as a fungicide
1963 – J. E. Vander Plank –
 Considered as “Father of Epidemiology”
 Published “Plant Disease Epidemics and Control ” in 1963
1964 – Norman E. Borlaug (USA) –
 Developed semi-dwarf, high-yield stem rust resistant wheat varieties
 He was often called “ The father of the Green Revolution”
 he was awarded the Noble Peace Prize in 1970 in recognition of his contributions to
world peace through increasing food supply
 He worked in the fields of Agronomy, Plant pathology and Genetics ( Ph.D. in plant
pathology and genetics)
1966 – Von Schmeling and Marshal Kulka – Discovered the 1st
systemic fungicide (Carboxin)

4. HISTORY OF PLANT PATHOLOGY IN INDIA
1885 - K R Kirtikar – First Indian scientist who collected and identified fungi
1886-1971 – JF Dastur -
 First Indian plant pathologist, internationally known for the establishment of genus
Phytophthora and diseases caused by castor (Phytophthora parasitica) and potato
 1st
president of the “ Indian Phytopathological Society” (IPS) in 1948
1914 - 1999 – M. J. Thirumalachur –
 He was known for the development of antifungal antibiotics such as Aureofungin,
 Written a Book “ Antibiotics in Plant disease control ”
M K Patel –
 Considered as “ Father of Indian Plant bacteriology”
 Started the school of Plant Bacteriology at college of Agriculture (Pune)
 Found out “Patel agar”( medium for isolating and culturing of Crown gall bacterium)
also worked on crown gall bacterium
 Advocated the family Phytobacteriacae with seven genera viz., xathomonas,
Phytobacterium, Aplanobacter, Corynebacterium, Agrobacterium, Erwinia and
plectobacterium to include all pathogenic bacteria.
Y.L. Nene-
 Reported khira disease of rice is due to ‘Zinc’ deficiency
 Authored the book “ Fungicides in plant disease control” (Y. L. Nene & P. N.
Thapliyal) and “The pigeon pea”
1892-1950 - K. C. Mehta –
 Considered as “Father of Indian Rust”
 Studied epidemiology of cereal rust in india
 Wrote monograph on “Further studies on cereal rust in India”
1896 -1952 – B. B. Mundukar
 Established Indian Phytopathological society with the Journal “ Indian
phytopathology”
 Wrote “ Fungi and Plant Diseases” in 1949
 ‘Monograph on Ustilaginales of india’ and the ‘Supplements to fungi of india’ and
Gerena of rusts in collaboration with M. J. Thirumalachur.
1975 – S. Nagarajan and H. Singh – Formulated “Indian Stem Rust Rules” for Puccinia
graminis tritici
1978 – S. Nagarajan and Joshi – Identified Puccinia pathway

5. BACTERIA
Ehrenberg (1829) – Coined the term “Bacteria”
1675 – Leeuwenhoek –
 Developed 1st
microscope, Considered as ‘Father of Bacteriology’
 Developed hundereds of microscopes and obtain a magnification of 50-300
diameters.
 Also discovered the Spermatozoa and the red blood cells
 1st
publication in bacteria was in 1683
(Dear god what marvels they are so small a creature – Leeuwenhoek)
1858 – Louis Pasteur (France) –
 Father of “modern bacteriology” and “Founder of Microbiology”
 Formulated germ theory of diseases and demolished the spontaneous generation
theory
 Developed the principles of vaccination, microbial fermentation and pasteurization.
 Created the first vaccines for Rabies and Anthrax
 Book “memoir on the organized bodies which exist on the planet”
 (Pasteurization:- Heat-treatment process that destroys pathogenic microorganisms
in certain foods and beverages.
Pasteurization of milk of about 62.8° C (145.04° F) for 30 minutes
1876 -Louis Pasteur and Robert Koch -They proved that anthrax disease of cattle was
caused by specific bacterium.
1876 -Robert Koch (Germany)
 Described the theory called "Koch's postulates."(out of 4 , 3 was given by Robert
Koch 4th
was given by E. F. Smith)
 He established the principles of pure culture technique.
 “Father of Modern Bacteriological Techniques”, “Father of Microbial Techniques”
“Founder of Modern Bacteriology”.
 Identified the specific causative agents of tuberculosis, cholera, and anthrax
1878 - T. J. Burill (America) –
 First time proved that fire blight of apple and pear was caused by a bacterium (now
known as Erwinia amylovora) in 1878.
 Initially the was called Mycrococcus amylovorus (today known as Erwinia amylovora)
 He is the “Founder of Phytobacteriology”.
1884 – Christian Gram-
 Developed bacterial staining technique
 Based on staining bacteria can be divided into gram positive(+ve) and gram negative
(-ve)
1901-1920 - E. F. Smith (U.S.A)
 He is also called as "Father of Phytobacteriology".

6.  Wrote the 1st
text book on bacterial diseases “Introduction to Bacterial Diseases of
plants” in 1920.
F. W. Twort (1915), F. D’ Herelle (1917) – Discovered Bacteriophage individually.
1928 – Alexander Fleming (United Kingdom) –
 Isolated Penicillin from Pencillium notatum
 Shared noble prize for the chemotherapeutic use of penicillin in Physiology and
medicine along with Ernst B. Chain & Howard Walter Florey in 1945
 Fleming published his findings in the British Journal of Experimental Pathology in
June 1929
1931- Knoll and Ruska- Invented the electron microscope
Selman A. Waksman –
 Considered as “Father of soil microbiology” and “Father of antibiotics”
 Discovered the antibiotic ‘Streptomycin’ (Streptomyces griseus)
 Awarded Noble Prize in Physiology of Medicine in 1952 ( for the discovery of
streptomycin)
1948 – M. K. Patel –
 Considered as “ Father of Indian Plant bacteriology”
 Started the school of Plant Bacteriology at college of Agriculture (Pune)
 Found out “Patel agar”( medium for isolating and culturing of Crown gall bacterium)
also worked on crown gall bacterium
 Identified a new species of plant pathogenic bacterium from India in 1948, namely
Xanthomonas campestris pv. uppalii
1967 - Y. Doi et al –
 Discovery of Mycoplasma like organisms (in mulberry dwarf disease
 The organisms were renamed as Phytoplasma in 1994, at the 10th Congress of
the International Organization for Mycoplasmology.
1972 – Davis et al – First observed Spiroplasma (in corn stunt diseases)

7. VIROLOGY
 Virus :-
 Plant viruses are sub-microscopic, infectious, obligate intracellular
parasites, which do not replicate without a living host.
 Virus is derived from Latin word which means - Poison/ Venom/Slimy liquid
 Study of Plant viruses and virus like pathogens is called – Plant Virology
HISTORY:-
 1886 – Adolf Mayer (Germany)-
 Coined the term ‘Mosaic’
 He thought that the causal agent was the bacteria.
 He called sap transmission of tobacco disease is ‘Mosaikkrankheit’
 Later he performed experiments with Chamber land filter paper, even though
the virus retains infectivity.
 1892 – D. Ivanovsky (Russia) –
 Proved that the causal agent of tobacco mosaic disease could pass through
bacteria proof filters.
 Concluded that the causal agent of tobacco mosaic (virus) is smaller than
bacteria.
 1898 – Beijerinck –
 Founder and Father of Virology / Father of Environmental Ecology
 Performed agar diffusion experiments and coined the term ‘Virus’
 He called the liquid material of virus is “Contagium vivum fluidum” which
cause the repeated infection in Tobacco mosaic virus
 1915 – Twort, 1917 -F. D. Herelle – Individually discovered bacteriophages
 1929 – Mckinney –
 Developed cross protection/ pre-immunization technique for control of citrus
tristeza virus (CTV)
 Cross protection was 1st
used against TMV
 1935 – W. M. Stanley –
 American biochemist, virologist
 Done Purification/ Crystallisation of virus (by using ammonium sulphate)
 He received Nobel Prize in 1946 (for crystallisation of virus)
 He believed that virus was an autocatalytic protein that could multiply with in
the living cell
‘A virus is a virus’. It is neither a living organism nor a non-living chemical, but
something between and betwixt Andrew Lwoff

8.  Molecular plant pathology work can be initiated with W. M. Stanley
 1936 – F. E. Bawden and N. W. Pirie –
 Demonstrated that virus is a nucleoprotein which consists both nucleic acid
and protein
 1939 – Kausche et al – Saw virus particles (TMV) for the first time with the help of
electron microscope
 1956 – Gierrer and Schramm –
 Showed that nucleic acid is the infectious agent
 Also investigated about double standard RNA viruses (ds RNA)
 1967 – Doi et al – First observed Phytoplasma (In mulberry dwarf disease)
 1971 – Dienner and Raymer – reported 1st
viroid disease potato spindle tuber viroid.
 1972 – Davis et al – First observed the Spiroplasma (in Corn stunt disease)
 1976 – Voller et al, 1977 – Clark and Adams – Developed ELISA technique and used
ELISA in Plant virus detection.
The Four Koch postulates (Robert koch)
1. The organism must always be present, in every case of the diseases.
2. The organism must be isolated from a host containing the diseases and
grown in Pure Culture .
3. Samples of the organism taken from pure culture cause the same diseases
when inoculated into a healthy, susceptible animal in the laboratory
4. The pathogen must be re-isolated and on comparison with original culture it
must be found to be identical)
Note - 4th
Koch postulate was given by E. F. Smith

9. General characters of fungi
 The branch of biology that deals with fungi is called ‘Mycology’
 Fungus is a Latin word which means ‘Mushroom’
 Fungi (definition)- Fungi is eukaryotic, achlorophylls, spore bearing organisms that
can reproduce by both sexual and asexual manner and can obtain nutrients through
haustoria
 Eg – Yeast, mould, rusts, smuts and mushrooms
Morphological characters of fungi
 Thallus – Entire body of fungus is called thallus (mass of hyphae constitute to form
thallus). Vegetative/ somatic thallus gives rise to reproductive structures, from which
spores are produced either sexuall or sexually
 Holocarpic – whole thallus is converted into one are more reproductive
structures
Eg – Synchytrium and Olphidium
 Eucarpic – only a portion of thallus become reproductive
Eg – Oomycota, Ascomycota and Basidiomycota
 Mycelium – filamentous vegetative body of the fungus is called mycelium/ Single
thread of hyphae
(or)
The hyphal mass or network of hyphae constituting the body (thallus) of the fungus is
called as mycelium
 Hypha - Individual branch of mycelium which are generally uniform in thickness,
usually about 2-10 μm in diameter. The hyphae may be septate or aseptate
 Coenocytic hyphae - The aseptate or non-septate hyphae having the nuclei
scattered in the cytoplasm (obscene of septa/ cross walls).
 Septate hyphae- The hyphae have septa having perforations through which
cytoplasmic strands, containing nuclei can migrate from one cell to the
other. (presence of septa)
 Doipore septa
 It is a complex type septa with barrel shaped central pore and hemi spherical
cap is called parenthosome/ pore cap
 Dolipore septum is formed in Agaricomycotina certain basidiomycetes.
 Plasmodium – Naked,motile multinucleated mass of protoplasm is called plasmodium
 Rhizomorphs: Thicker root like aggregates. Also called mycelial cords
 Sclerotium: It is a hard and compact vegetative resting structure resistant to
unfavourable conditions. It is mostly made up of pseudoparenchymatous cells
Eg – Sclerotium, Rhizoctonia, Sclerotinia, Claviceps
Septa – The cross walls which divide the hypha into cells are called septa

10.  Stroma: some fungi also develop mat like structures which contain the fruiting
bodies.
 Fungal cell structure
 Fungal cell wall is made up of Chitin + glucan, whereas
 Oomycota cell wall is made up of cellulose
 Zycomycota cell wall is made up of Chitosan chitin
 Special somatic structures
 Appresorium – It is the anchoring organ/ attachment organ of fungi
 Haustorium – It is absorbing organ, which absorb nutrients from host.
 Rhizoid – short root like filamentous outgrowth devoid of nuclei
Eg - Rhizopus
 Hyphal modifications
Mycelium of higher fungi is organised into loosely or compactly woven tissues,
called fungal tissues/ plectenchyma. They are of two types
 Prosenchyma – loosely woven fungal tissues in which the individual hypha
lie parallel to one another
 Pseudoparenchyma: compactly woven fungal tissue with more or less
isometric resembling parenchyma of higher plants
 Stromata – Compact matters like structure made up of parenchyma and
pseudoparenchyma usually form fruiting bodies off fungi of various shapes and
sizes
Eg – Acervuli (Colletotrichum), Sporodochia (Fusarium)
 Reproduction in fungi
 Spore – minute, simple and basic reproductive unit of fungus, which are
capable of growing into a new thallus. The process of formation of spores
are called Sporogenesis/ Sporulation
 Sporangia – It is a sac like structure in which spores are formed
 Sporangiphore – sporangia are produced at the end of the of the
undifferentiated or on specialized spore bearing structure are called
Sporangiphone
1. Asexual reproduction – It does not involve the union of nuclei or gametes
and hence called as somatic or vegetative reproduction
 Spores are produced by asexual are production are celled
mitospores/ asexualspores
A. Fission – parent cell divides into two daughter cells by constriction. The
nucleus is divided into two halves b formation of transverse septum
Eg – Yeast
B. Budding – Small outgrowth or bud produced from the parent cell
enlarges gradually and nuclei migrates into the growing bud an then bud
eventually breaks off to form the new thallus
C. Fragmentation – Small fragment of hyphae detached from the parent
mycelium to grow into new thallus. These small fragments/spores are
called arthrospores/Oidia
Eg– Powdery mildew

11. Flagellum – Hair like structure that serves a motile cell (locomotory organ)
 Anterior (episthocont) –
 Posterior (opisthocont) -
Axoneme – feather like a central rachis, the hair of flagella is called flimmers
hairs/ mastogoneme
Conidia- a spore produced asexually by various fungi at the tip of a specialized
hypha.
Conidiophore – The conidiophore may be free or aggregation of aggregated to
form compound conidiophore/ fruiting bodies on which conidia
are produced
Zoospores – Motile asexual spores of Oomycota produced with in zoosporngium.
They are always naked (without cell wall)
Planospores = motile spores = Swarm spores
Aplanospores = non motile spores
Chlamydopsores - Thick walled resting spore formed either single or in chains from
terminal or intercalary cells o the hyphae eg – Fusarium, Saprolegnia
 It is thick walled and contains reserve food materials to withstand
unfoavorble conditions
Gemmae – Chlamydospores dispersed inn water currents is called gemmae

12. 2. Sexual reproduction –
Three typical phases occurs in sequence during sexual reproduction
A. Plasmogamy - Union of protoplasts bringing their nuclei togeather
within the same cell
B. Karyogamy – Fusion of two nuclei result in the formation of zygote/
diploid nuclei. The organ in which karyogamy takes place is celled
Zeugites
C. Meiosis – Fused diploid nucleus undergoes meiosis, which reduced
the number of chromosomes to haploid. The organ in which meiosis
takes place is celled Gonotoconts
Types of plasmogamy
i. Planogametic copulation/ Gametogamy
a) Isogamy/ isogamous fertilization – fusion of isogametes of
same size and shape
Eg – Olphidium and Synchytrium
b) Anisogamy/ anisogamous fertilization - fusion of
anisogametes in which gametes are morphologically similar
but differ in size
Eg – Allomyces
Asexual fruiting bodies –
A. Pycnidium – It is a hallow , flask shaped or globose fruiting bodies with
narrow circular mouth called ostiole. It has a wall made up of multilayer
pseudoparenchymatous sterile tissue, called peridium. The inner wall of
the fruiting body is lined with numerous short conidia called
pycnidiospores
Eg – Macrophomina phaseolina, Diplodia natalensis, Botrydiplodia
theobromae
B. Spordachium – It is a hemispherical, barrel shaped compound conidiophore
produced by Fusarium, Tubercularia and Epicoccum. It consists of cushion
shaped aggregation of hyphae in the lower part and expresses the conidia
on the upper part.
C. Acervuli – It is a saucer shaped depressed pseudoparenchymatous
aggregation of hyphae which develops beneath the surface of the host with
a bed of closely packed parallel simple conidiophores
Eg – Colletotrichum, Pestalotia
D. Synemma – loose aggregation of branched or unbranched erect
conidiophore to form dene fascicle, similar to mycelial strands
Eg – Ceratocystis, Graphium
E. Sori – Spore bearing hyphae eg – Smut sori, Rust sori

13. c) Heterogamy/ ooplanogametic copultion – fusion of motile
male gametes with non-motile female gametes
Eg - Monoblephariales
ii. Gametangial contact/ Gametangiogamy –
Fusion of two morphologically distinguishable gametangia with
undifferentiated protoplasm and nuclei. The gametes pass either
through pore dissolved at the point of contact called Fertilization
tube/ trichogyne
iii. Gametangial copulation/ Aplanogametic copulation/ Gametangy
a) Hologamy – entire content of one gametangium passes into
another through pore developed in the gametangial wall at
the point of contact
Eg – Yeast
b) Direct fusion/ isogamous copulation – two morphologically
similar gametangia fuse and to become a single cell
Eg - Mucor and Rhizopus
c) Anisogametangial copulation - fusion between unequal
gametangia
Eg - Zygorhyncus
iv. Spermatization – some fungi produce numerous, non-motile minute,
spherical uninucleate spores are called spermatia, which are
produced from the flask like sexual apparatus called spermagonium
v. Somatogamy – no sex organs are produced, but the undifferentiated
somatic cells functions as gamtes
 Homothallic - Fungi in which every thallus is sexually self-fertile.
The male gametes fertilize the female gametes of the same
mycelium
Eg - common in Ascomycota and rare in Basidiomycota
 Heterothallic – The fungal thallus is sexually self-sterile and
requires another compatible thallus of different mating types for
sexual reproduction. The male gametes fertilize the female
gametes of another sexually compatible mycelium.
The phenomenon of heterothallism was reported by
A. F. Blakeslee (1904) in Mucor
Eg – Oomycota, Zygomycota and Basidiomycota
Types of sexual spores –
 Oospore – globose, yellow to dark brown with two layer wall and a
central oil globule in the form of lipids as food material
 Zygospore - thick walled resting diploid sexual spore
 Ascospore - haploid sexual resting spore
 Basidiospore - exogenous sexual spore

14. Parasexual reproduction – Plasmogamy, karyogmy and meiosis takes place in
sequence but not at specified points in life cycle. The phenomenon of parasexuality
was first discovered by Pontecarvo and Roper in 1952 in Aspergillus nidulans

16. 1. Life cycle of club root of cabbage – Plasmodiophora brassicae
Systemic classification :-
Domain – Eukarya
Kingdom – Protozoa
Phylum – Plasmodiophoromycota
Class - Plasmodiophoromycetes
Order – Plasmodiophorales
Family – Plasmodiophoraceae
Genus – Plasmodiophora
Species – brassicae
Symptoms – roots decay, followed by yellowing, permanent wilting or retarded
growth, hypertrophy and hyperplasia occurs
LIFE CYCLE
Infected host roots gets decayed, spores are released into soil, the spores
germinated immediately with the help of root exudates. During germination a naked
spherical pears shaped uninucleate zoospore with biflagellate of unequal length
A phase
 Zoospores get attached to the surface of the roots
 Eventually, inactivation of flagella, retraction of axonemes and encystment of
zoospores takes place
 By punching the host cell the zoospores entered into the host cells, these
zoospores are called multinucleate primary plasmodium or ‘Myxoamoeba’
 The protoplast increases in size and undergoes cruciform divisions resulting in
formation of plasmodium
 Later these multinucleate segments are delimited, each one develop into a
zoosporangium
 The plasmodium consists of several sporangia. The sporangia become attached
to the to the host cell
 Each sporangium form 4-8 uninucleate biflagellate zoospores are released
through a pore, lateron zoospores function as a gametes
B phase
 Zoospore settled on the root hairs, shreds flagella and entered into the cortex of
the root cells
 Each of binucleate plasmodium enlarges and undergoes repeated mitotic
divisions to form multinucleate body referred as multinucleate secondary
plasmodium
Hypertrophy – abnormal enlargement of cells (increase in number of cells)
Hyperplasia – increase in number of cells (increase cell divisions)

17.  These multinucleate secondary plasmodium get hypertrophied and takes place
club
 The karyogamy takes diploid nuclei are formed, then after meiosis
 Akarote stage – Diploid nuclei of the plasmodium at the time of spore formation
forms a special phase, during this phase the nuclei seem to be disappear and
reappears during prophase of meiosis.
 Several haploid resting spores are formed and they liberate and infect host.
(Note - while studying keep the diagram with you, then it will be very easy to
understand)
2. Life cycle of damping off of vegetables – Pythium aphanidermatum
Systemic classification :-
Domain – Eukarya
Kingdom – Chromista
Phylum – Oomycota
Class – Oomycetes
Order – Pythiales
Family – Pythiaceae
Genus – Pythium
Species – aphanidermatum
Symptoms
 Pre emergence damping off – seeds and radicles rots before the seedling emergence
out of the soil
 Post emergence damping off – newly emerging seedlings are killed at ground level
after emerge from the soil
Asexual reproduction –
 Mycelium consists of coenocytic hyphae, hyphae is both intercellular and
intracellular. No haustoria are produced
 Pythium produces simple branched and globose zoosporangia (produces at terminal
or intercalary)
 Germination is either zoospores on germtube, sporangiospore consists of sporangia
with bubble like vesicle, the sporangial protoplast moves rapidly through tube into
vesicle and appears remains delimitation of zoospores takes place
 Zoospore are released in a rocking motion and bounces on the vesicle
 The reniform zoospores are biflagellate with anterior tinsel and posterior whiplash
type, spores come in rest and encyst and germinate by producing germ tube
Sexual reproduction
 Sexual reproduction is oogmous and takes place by gametangial contact
 The male sex organ is antheridium and female is oogonium
 Upon the gametangial contact, a fertilization tube develops and penetrates the
oogonial wall and enter the periplasm
 In the meantime meiosis takes place only functional nuclei remains, other
disintegrate.

18.  Now male nuclei passes to female nuclei (oosphere) through fertilization tube, which
forms zygote
 The oospore develop a thick wall around it self and germinate by using germination
tube (if favourable conditions occurs it germinates, otherwise it undergoes resting
period)
3. Life cycle of late blight of potato – Phytophthora infestans
Domain – Eukarya
Kingdom – Chromista
Phylum – Oomycota
Class – Oomycetes
Order – Pernosporales
Family – Pernosporaceae
Genus – Phytophthora
Species – infestans
Symptoms – ‘Phytophthotra’ means plant destroyer, water soaked light brown lesions
develop on the leaves and later enlarges and cover the entire leaf, petiole and stem. Rotten
portion emits characteristic odour.
Asexual life cycle –
 Sporangia are borne aerial sympodially branched sporangiophore arise directly from
internal mycelium
 Hyphae is inter and intracellular profusely branched and produced finger like
haustoria
 The sporangiophores are with characteristic swellings at the nodes of indeterminate
growth
 On falling suitable host the sporangia germinate (< 15o
C) favours the zoospore
production, high temperature favours the germ tube formation (> 20 o
C)
Sexual life cycle
 Sexual reproduction takes place means of antheridia and oogonia of opposite mating
types
 Oogonia penetrates and go through the antheridia and form a globose structure
above the antheridia is called amphigynous antheridia
 Migration of antheridium nucleus into oogonial wall by fertilization tube
 The fertilized egg secretes a heavy wall around it self and become oospore
 Oospore germinates by means of germ tube and produces zoospore and produced
new thalli.

19. 4. Life cycle of wheat stem rust – Puccinia graminis tritici
Domain – Eukarya
Kingdom – Fungi
Phylum – Pucciniomycota
Sub phylum - Pucciniomycotinia
Class – Puccniomycetes
Order – Pucciniales
Family – Pucciniaceae
Genus – Puccinia
Species – graminis
Stage spores Colour Appearance
O Pycniospores Hyaline Upper
I Aeciospores Yellow Lower
II Uredospores Golden brown Primary host
III Teliospores Black Primary host
IV Basidiospores Hyaline Soil debris
Symptoms – Red colour rust pustules appears in stem and leaves. Alternate host is Barberry
Life cycle – When wheat crop attains maturity the uredinia appears on rut pustules and
developed as urediniospores, these are single celled, which contains enormous amount of
food reserves for long distance dissemination, at the end of the wheat season it starts to
produce less urediniospores and more teiospores.
Telia are black, elongated, bi-celled, dark brown in colour, it is a resting spore which
represents sexual apparatus of the fungus in which karyogamy ad meiosis takes place, when
favourable conditions occurs its germinate and produce basidispores of opposite mating
types
Basidiospores infect barberry but not wheat, several basidiospores produce flask
shaped pycnium. Several pycnia of opposite mating types are generally formed in the same
leaf. On the corresponding to the lower surface it produce aecia
Aeciospores it contains reserve food material, the aeciopsores can’t germinate on
berberry and germinate on wheat leaf.
Types of teliospores –
Types of teliospore Example
Single celled teliospore Uromyces
Double celled teliospore Puccinia
Multicelled teliopsore Phragmidium
Durnip shaped uredospore Hemileia
Kidney shaped teliospore
Crust like telispore Melampsora
Parachute like teliospore Ravenelia

20. Types of rust –
 Autoecious rust – Completes its entire life cycle in a single host
 Heteroecious rust - Requires genetically two hosts to complete their life cycle
 Autoecious macrocyclic rust – Eg – B – Bean rust
F – Flax rust
S - Sunflower rust
S - Safflower rust
 Autoecious demicyclic rust – Eg – Rubus orange rust – Gymnoconia peckiana
 Heteroecious macrocyclic – Eg – Wheat stem rust – Puccinia graminis tritici
White pine blister blight – Cronartium rubicola
 Heteroecious demicyclic – Eg – Cedar apple rust – Gymnosporangium juniperi
viriginianae

21. Taxonomy of fungi and fungi like organisms
Taxonomy is a part of biological science which deals with the study of naming and
classification of organisms
Grouping of fungi and fungi like organisms by taxonomists
Taxonomist Groupings / classification Name of the grouping
Linnaeus (1753) 2 kingdoms Vegetabilia
Animalia
Ernst Haeckel (1866) 3 kingdoms Protista
Plantae
Animalia
Herbert Copeland
(1956)
4 kingdoms Monera
Protista
Plantae
Animalia
Whittaker (1969) 5 kingdoms Monera
Protista
Fungi
Plantae
Animalia
Carl Woese (1977) 6 kingdoms Eubacteria
Archaebacteria
Protista
Fungi
Plantae
Animalia
Chatton (1937) 2 empires Eukaryota, Prokaryota
Carl Woese (1990) 3 domains Bacteria
Archaea
Eukarya
Systematics of fungi and fungi like eukaryotes
The nomenclature is the branch of systematics that determines the correct scientific
name for taxon. The naming of fungi was previously governed by International Code of
Botanical Nomenclature (ICBN)
Each fungus has unique scientific name that indicates its taxonomic placement
among other organisms. The scientific names are Latin names assignee to particular fungus
based on binomial system of nomenclature of to identify organisms throughout the world.
The first part is binomial name is the genus and the second is the Specific species the genus

22. and species have no fixed endings. The genus name maybe common to several species, but
the combination applies to only one species in the entire system of classification.
The rules of writing scientific names
1. Binomial system – Use two names, generic name and species name. the genus and
species have no fixed endings
2. Trinomial nomenclature – Add a third name to the binomial to provide further
information of the organism (eg – forma specialis, race, pathovar)
3. Author’s name – Place the name of the taxonomists who were the first person who
gave the names to given organism and the end of the binomial, and abbreviate
Guidelines for writing scientific names
 Capitalize first letter of generic name, while the rest, including whole of species, in a
small cases. Leave a single space between genus name and species name. in case
where the author’s name is to be included use standard abbreviation for the author
name.
 Use Italics for genus name and species name, but not the author name, in hand
written manuscript, or when use a type writer with no Italics, underline that are to
be italicized.
Name lower the species level are to be treated in the same way as the binomial, i.e.
italicized note that the whole subspecies, forma specials, race, variety, etc. which are
abbreviated are not italicized
Eg – Fusarium oxysporum f.sp. vasinfectum (G.F.Atk) W.C. Synder & H. N.Hansen
According to the International Code of Nomenclature for algae. fungi and plants (ICN), the
following ‘suffixes’ are used for phyla and other categories of a fungal taxon
Phylum ends with – mycota
Sub-phylum ends with – mycotina
Class ends with – mycetes
Subclass ends with - mycetidae
Order ends with – ales
Family ends with – aceae

23. Difference between Eukaryotes and prokaryotes
S.no Eukaryotes prokaryotes
1 Possess advanced cellular organism Show primitive cellular organisms
2 Cell wall is made up of cellulose
(plants), chitin (fungi)
Cell wall is made up of peptidoglycan
(mucopeptides)
3 Membrane bound organelles such as
ER, golgi complex, mitochondria,
chloroplast and vacuoles are present
Membrane bound organelles such as ER,
golgi complex, mitochondria, chloroplast
and vacuoles are absent
4 Ribosomes are larger made up of 80S
units
Ribosomes are smaller made up of 80S
units
5 Genetic material is found in well
organised chromosomes
Genetic material is not found in well
organised chromosomes
6 DNA is long and liner, histone bound DNA is shorter and circular, not histone
bound
7 Cell divides by mitosis and meiosis Cell divides by fission
8 9+2 arrangement of flagella Flagellum is single fibrillar type

24. Bacteria
 The term bacteria was coined by – Ehrenberg
 Size of bacteria ranges from – 0.5 to 1.0 µm breadth and 2.0 to 5.0 µm in length
 Bacteria belongs to prokaryota (contains a primitive type of nucleus and lacking of
well-defined membrane like fungi {except blue green algae}).The bacteria are smaller
than fungi and measures about 0.5-1.0*2.0-5.0µm
 Anton van leeuwenhoek (1676 ) discovered the microbial world with his simple
microscope .
‘’Dear god what marvels they are in so small a creature’’
Leeuwenhoek
 Morphological features of bacteria
Morphologically the bacteria are rod shaped (bacilli), spherical (cocci), spiral (spirilli),
coma shaped (vibrios) or thread like (filamentous)
 Rod shaped bacterium is called - Bacillus
Bacilli (singular : Bacillus)
 Monobacillus – A single rod shaped bacterium
 Diplobacillus – Rod shaped bacterium arranged in pairs
 Streptobacillus – A chain of rod shaped bacterium
 Spherical shaped bacterium called - Coccus
Cocci (Singlular : Coccus)
 Monococcus - A single spherical bacterium
 Diplococcus - A pair of spherical bacteria
 Tetracoccus – A group of four spherical bacteria
 Streptococcus – A chain of spherical bacteria arranged in a single row
 Staphylococcus – A group of cocci bacteria forming irregular shapes
 Sarcina – Cocci arranged in cubes if eight
(link - Side share < classification of bacteria< Hima shankar)
 Bacterial nucleus is called - Genophore (by Ris, 1961) composed of ds DNA
Bacteria was coined by Ehrenberg
Father of bacteriology – Anton van leewenhoek
Father of plant bacteriology – E. F. Smith
Father of Indian plant bacteriology – M. K. Patel

25.  Structure of bacterial cell
Cell wall - The cell walls of bacteria and cyanobacteria differ from plants in being made of
peptidoglycan/ mucopepetide and not cellulose.
Mucopeptide is a polymer of NAG (N-acetyl glucasamine) and NAM(N-acetyl muric
acid) joined by b 1-4 linkage
The cell wall of gram+ve
and gram-ve
bacteria are differ in their chemical composition. The
wall of Gram+ve
bacteria is homogenious containing 85% more of mucopeptides and simple
polysaccharide ,like teichoic acid which are polymers of ribitol and glycerol
phosphates,teichoic acid serves as antigen and also regulate ions. The cell wall of gram –ve
bacteria contains only 3-12%of mucopeptides,the rest being lipoprotein and polysaccharide.
Differences between gram+ve
and gram-ve
bacteria
Gram+ve
Gram-ve
1.Teichoic acid present 1. Teichoic acid absent
2.homogenois layer 2. three(3)layers
3.major portion of cell wall is
mucopeptides (85%)
3. mucopetides (3-12%)
4.protoplast completely digested
cellwall
4. sphaeroplast
5.L,P rings are present 5. L,P,M,S rings are present
6. while stating it produce
violet/purple in colour
6. while stating it produce pink colour
7.Ex.bacillus,streptomycin,
Corynebacterium
7. most of the bacterium are gram-ve
8.Much rigid due to the presence of
greater amount of muciopeptides
8. Less rigid due to the plastic nature of
lipoprotein, lipopolysaccaride

26. Pili/ fimbriae - fimbriae are hair like structure that are observed as surface appendages on
some bacteria ,fimbriae are common in plant pathogenic bacteria. Pili are also hair like
structure found in some bacteria which are elongate, rigid, tubular appendages made of
special protein called pilin, these have so far been reported in gram negative bacterium
where they serve to connect to cells during conjugation (also called sex pili )and allows the
DNA to pass from donor to recipient.
Flagella : these are the organs used for locomotion in motile forms and many times longer
than bacteria (4-5 times) than the bacterial cell, they are fundamentally different from the
flagella or cilia of eukaryotes in lacking the ‘9+2’ arrangements. Flagella or cilia of eukaryotic
cells are , morphologically and physiologically similar.
Types of bacterial flagella
1. Atrichous : no flagella are present on the bacterial cell surface
2. Monotrichous : single flagella are present on the bacterial surface
3. Amphitrichous :single flagella are present on the either side of the bacterial surface
4. Peritrichous: flagella are present on all over the body
5. Cepalotrichous: turfts of flagella are present on either side of the bacterial surface
6. Lophotrichous: tufts of flagella are present on both the sides
The plasmids: bacterial plasmid is circular, extra chromosomal double standard DNA , which
provides additional genetic information which, tought not essential for basic life process,
help the bacteria in various ways. Although plasmids usually contains 1-5% of the DNA, The
affect of the small genetic information can decide survival, as happens with the antibiotic
resistance gene.
Capsule/ slime layer – which protects the bacteria from desiccation
(refere slide share for more diagrammatic representation and inflation – Hima Shankar)

27. Growth and reproduction in bacteria:
Bacteria multiply by all the known methods of reproduction. The novel methods of
sexual reproduction that occurs in bacteria, though different from classical types involving
karyogamy and meiosis, bring about the same end result Viz., genetic recombination.
The bacteria reproduce asexually by fission, endospores, cysts, fragmentation,
sporangiospores, and conidia. The asexual reproduction is represented by conjugation,
transformation, transduction, transduction and lysogenic conversion.
I. Asexual reproduction:
Fission: The bacterial cell divided into two by fission. Mostly it is a binary fission in which
the two daughter cells are identical. Division is a very quick process and it is
completed in 30 minutes.
II. Sexual reproduction:
Until 1940 ,ant idea of sexual reproduction in bacteria was considered ridiculous. Bacterial
cytology was a diffuse and a controversial subject.even the genetic material was not clearey
demonstrated.
1 .Conjugation: The transfer of genetic material from one bacterial cell to another
bacterial cell during conjugation. The two cells are genetically different, the donor
cell transferred part of its genome to the recipient cell. This was discovered by
Lederberg and Tatum in 1946 on Escherichia coli.
2. Transformation: In 1928 Frederik Griffith, an english bacteriologist, made an
important observation which initiated a biological revolution. When he was working
with the bacterium Pneumococcus pneumonia (then called diplococcus) the causal
organism of pneumonia, he observed DNA from one type of bacterium is
incorporated into the genetic makeup of another organism during transformation, A
new individual which derives some of its genes from two genetically different
parents is formed during this process.
3. Transduction: Lederberg and his student Zinder in 1951 started looking for
recombination in salmonella tymphimurium , They used the same techniques which
Lederberg and Tatum had used with E.coli. They obtained the nutritionally deficient

28. mutants (auxotrophs) which failed to grow on the mineral medium. When a mixture
of the two mutants are plated together ,recombination appers in a few cases but not
with other stains, When they analysed the cause they discoverd a new type of gene
exchange, , Which involved the medium bacteriophage. Zinder and Lederberg
described the new method of of gene transfer in 1952 as Transduction.
Genetic mechanism Organism Scientist discovered Year
Conjugation E. coli Lederberg and Tatum 1946
Transformation Pneumonia Griffith 1928
Transduction Salmonella Lederberg and Zinder berg 1952
(For easy remembering to students CTT = EPS
Where C – conjugation, T- Transformation, T – Transduction that happens in
organisms of - E – E. Coli, P – Pneumonia, S – Salmonella, in an order makes
the right sense of answers)
(Bacteriophage: A virus which infects the bacterium is called bacteriophage. Bacterophage
grows within a cell. That infects the bacterial cell bursts and bacteriophages particle are
liberated)
 The 1st
plant pathogenic bacteria the genome which was completely sequenced was
- Xylella fastidiosa (in 2000 by a Brazilian consortium/association, scientist
associated with genome sequencing is A. J. G. Simpson)
 Pierce disease of grapes is transmitted by – Glassy winged sharp shooter
(Homolodisca coagulata later name changed to Homolodisca vitripennis)
Mode of entry of plant pathogenic bacteria
Specialized structure
(enters through)
Causal organism Causal organism
Hydathodes Black rot of cabbage/
Crucifers
Xanthomonas campestris pv.
campestris
Floral parts (Nectaris) Fire blight of apple and pear Erwinia amylovora
Lenticels Potato common scab Streptomyces scabies
Trichomes Bacterial canker of tomato Clavibacter michiganensis
Stomata Bacterial leaf streak Xanthomonas oryzae pv.
oryzicola
Citrus canker Xanthomonas citri
Bacterial classification is mainly based on :-
 Bergey’s manual of determinative bacteriology (1923)
 Bergey’s manual of systemic bacteriology, 1st
edition (1984)
 Bergey’s manual of systemic bacteriology 2nd
edition (2004)

29. Virology
 Study of plant virus is called Plant Virology
 The term virus was derived from ‘Latin’ word which means Poison/ venom/ slimy
liquid
 Virus – virus is a sub-microscopic, infectious, obligate intracellular parasite which do
not replicate without host
 Capsid – protein coat or shell which encloses the viral genome
 Vector – An agent/ organism which carries virus
 Bacteriophage - virus which infects the bacteria (which means bacteria eater)
 General characters of plant viruses
 Virus is acellular which only contains singe type of nucleic acid, either DNA or
RNA
 They are smaller than bacteria, and can pass through bacteriologic filter
 Contains Nucleic acid (NA), packed inside the protein coat
 Plants viruses transmitted through seeds, vegetative propagation, mechanical
and vectors.
 Morphology, structure of plant viruses
 All plant viruses contains two major components i.e. nucleic acid and protein
coat
 Nucleic acid (NA) is considered as infectious material of plant virus, which is
protected or coved by protein coat
 Protein coat only protects nucleic acid (NA), which having no role in disease
transmission and spread.
 GENOME: The genome may be RNA or DNA, either of which may be single
stranded (ss) or double stranded (ds).
 CAPSID SYMMETRY: Found in either of two geometric configuration helical (rod
shaped or coiled) or icosahedral (spherical or symmetrical).
 COMPOSITION OF VIRUSES: Plant viruses contain selective amounts of nucleic
acids and protein. Viruses with isometric particles may contain between 15%
and 45% nucleic acid whereas viruses with rod shaped particles have only about
5% nucleic acid. They also contain polyamines, enzymes and lipids.
 Almost all plant pathogenic viruses contains – 5-40 % NA, 60-95 % protein
coat
 TMV contains 5 % NA, 95 % protein coat
 All plant pathogenic viruses are inactivated/ killed at 50 - 60 0
C, whereas
TMV requires 93 0
C
 Cell to cell movement of virus is mediated by Plasmodesmata

30.  Short note on TMV
 Positive (+) ss RNA viruses which infects wide range of plants, especially
tobacco
 TMV belongs to the genus Tobamovirus
 TMV is a rod shaped which measures about 300 × 15-18 nm
 TMV contains 158 amino acids
 TMV contains 2130 capsomere subunits
 TMV contains approximately 6400 nucleotides
 Multiplication of plant viruses
 Virus initially enters into the host through wounds or physical injuries made by
vectors
 Uncoating of protein coat
 Production of mRNA
 Translation of mRNA
 Replication of viral genome
 Assembly of progeny of virus
Note – RNA viruses multiply in ‘Cytoplasm’
DNA viruses multiply in ‘Nucleus’
COMMON SYMPTOMS OF VIRUS DISEASES
‘Symptoms’ are the manifestation of the effects that a virus causes on the growth,
development and metabolism of an infected host plant, which are mostly visible to the
naked eye.
1. Stunting and dwarfing. Reduced plant size is a common symptom of most virus
infections and is most likely to be found in association with other symptoms. Growth may
be reduced evenly throughout the plant or the stunting may be confined to certain parts or
organs of the plant. Along with the aerial parts of the infected plant, root growth may also
be stunted
(e-g) Pea stunt disease caused by Red clover vein mosaic virus; Rice dwarf disease; Peanut
stunt disease; Barley yellow dwarf disease.
2. Mosaic. Mosaic is one of the most important symptoms caused by virus infection in
many plant species. The infected areas are usually pale green or chlorotic due to loss or
reduced production of chlorophyll.
(e-g) Tobacco mosaic; Tomato mosaic; Cucumber mosaic;
3. Yellow mosaic. The leaves of infected plants develop more of irregular yellow patches
than the green portion and the infected plants are stunted
(e-g) Bean yellow mosaic; Barley yellow mosaic.
4. Chlorosis. In the infected plants, the whole leaf may become chlorotic due to decreased
chlorophyll production and break down of chloroplasts.

31. (e-g) Wheat yellow leaf; Potato yellow dwarf; Barley yellow dwarf; Cowpea chlorotic mottle;
Beet yellows.
5. Vein clearing. Here the cells adjacent to the vein becomes translucent, while the
interveinal areas remain green (e-g) Okra vein clearing; Lettuce vein clearing.
6. Vein banding. In the infected plant, the area adjacent to the veins of the leaf remain
green, in contrast to the remaining areas of the leaf, which may be chlorotic (e-g) Chilli vein
banding caused by Tobacco etch virus.
7. Ring-spotting. The disease is restricted to a ring or broken ring of infected cells. The
infected cells may be chlorotic or necrotic and sometimes the rings may occur in concentric
circles. (e-g) Cabbage necrotic ringspot; Chlorotic ringspot and Broken ringspot of celery;
Tobacco chlorotic ringspot;
8. Necrosis. In some cases, the veins may become necrotic and the necrosis may spread to
the stem and root apices and ultimately the plant may be killed. Necrosis may occur on
fruits or seeds also. (e-g) Tobacco necrosis; Cucumber necrosis; Cacao necrosis; Clover
necrotic mosaic.
9. Enations or tumors. Due to infection by some viruses, characteristic tumor-like
outgrowths are formed on the leaves and roots. (e-g) Pea enation mosaic; Sugarcane Fiji
disease; Maize rough dwarf - wart-like outgrowths are produced on the lower surface of
leaves due to abnormal proliferation of the underlying phloem tissues; tumors on clover
roots caused by Wound tumor virus.
10. Leaf distortion. In some virus infections, the leaf lamina is affected and it may become
irregularly distorted or become strap-like. (e-g) Bean common mosaic in Phaseolus vulgaris;
Strawberry latent ringspot in celery; Tobacco mosaic virus in tomatoes; Bean leaf roll virus in
Vicia faba; Beet leaf curl; Tobacco leaf curl
11. Leaf roll. The leaf lamina roll and curl upwards (e-g) Potato leaf roll, Bean leaf roll and
Pea leaf roll.
Virus classified based in ICNV and ICTV
ICNV – international committee on nomenclature of virus (1966)
ICTV – international committee on taxonomy of virus (1973)

32. Viroids
 Viroids – Small circular, single standard RNA without protein coat(nucleic acid devoid
of protein coat), consists of 250-370 nucleotides
 Viroid was discovered by Diener (1971)
 1st
viroid disease – Potato spine tuber viroid
 Examples – Potato spindle tuber viroid (357-359 nucleotides)
Citrus exocortosis viroid (371 nucleotides)
Coconut cudang cudang viroid (246 nucleotides)
 Difference between virus and viroid
Virus Viroid
Discovered by Beijerinck (1898) Discovered by Diener (1971)
Infects all types of organisms (both
plants and animals)
Infects only plants
Contains protein coat Contains no protein coat
Contains genetic material as DNA or
RNA, but not both
Only RNA as genetic material
Transmitted by insects, seeds and
pollen
Mainly mechanical or contact
Rod and spherical in shape Circular in shape
Eg - TMV Eg – Potato spindle tuber viroid
 PHYTOPLASMA
 Lack of cell wall, pleomorphic and filamentous shape
 Discovered by Doi et al., 1967
 Initially called as mycoplasma like organisms (MLOs), then renamed as
phytoplasma in 1994
 Contains both DNA and RNA as genetic material
 Size ranges from 0.1 – 1 µm
 Phytoplasma cannot be cultured on artificial media
 Transmitted by leafhoppers, plant hoppers and psyllids but not seeds
 Resistant to penicillin and sensitive to tetracycline
 1st
phytoplasmal disease – Mulberry dwarf
 Eg – Little leaf of brinjal
Sesame phyllody
Coconut lethal yellowing
Rice yellow dwarf
Apple proliferation

33.  SPIOPLASMA
 It is the smallest, wall less, helical, self-replicating prokaryote
 Discovered by Davis et al., 1972
 Contains both DNA and RNA
 It can be cultured in the artificial nutrient media
 Cultural colonies are appeared as fried egg appearance
 Resistant to penicillin and sensitive to tetracycline
 1st
spiroplasmal disease – Corn stunt
 Eg – citrus stub born
Pear decline
NEMATODES
 Study of nematodes – Nematology
 Father of modern nematology – N. A. Cobb
Nematode Scientific name / causal organims
Wheat/ rye ear cockle nematode (seed
gall nematode)
Anguna tritici
Cyst nematode Heterodera, Globodera
Dagger nematode Xiphinema
Stubby root nematode Trichodorous
Potato cyst nematode/ Potato root
nematode
Globodera rostochiensis
Golden nematode
Golden eelworm or
Yellow potato cyst nematode
Globodera rostochiensis
Reniform nematode Rotylenchulus reniformis
Banana burrowing nematode Rhadopholus similis
Rice white tip nematode/ leaf and bud
nematode
Aphelenchoides besseyi
ALGAE
 Study of algae is called – Phycology/ Algology
 Father of Modern Phycology/ Algology - William Henry Harvey
 Father of Indian Algology – M. O. P. Iyengar
 Red rust of guava is caused by – Cephaleuros parasiticus

34. Some important plant diseases
Oomycota –
 Damping off – Pythium aphanidermatum
 White rust of crucifers – Albugo candida
 White rust of amaranthus – Albugo bliti
 Late blight of potato – Phytophthora infestans
 Downy mildew of grapes – Plasmopara viticola
 Downy mildew/ green ear of cumbu – Sclerospora graminicola
Chytridiomycota –
 Potato wart – Sychytrium endobioticum
 Jack fruit rot – Rhizopus atrocarpi
Ascomycota
 Peach leaf curl – Taphrina deformans
 Banana sigatoka leaf spot – Mycosphearella musicola
 Brown leaf spot of rice – Helminthosporium oryzae/ Bipolaris oryzae
 Early blight of tomato and potato – Alternaria solani
 Apple scab – Venturia inaequalis
 Root rot of pulses – Macrophomina phaseolina
 Rice blast – Pyricularia oryzae
Basidiomycota
 Button mushroom – Agaricus bisporus
 Milky mushroom – Calocybe indica
 Paddy straw – Volvariella volvacea
 Oyster mushroom – Plerotus sojar caju
 Sheath blight of rice – Rhizoctona solani
 Wheat stem rust – Puccinia graminis tritici
 Coffee rust – Hemileia vastratrix
 Flax seed rust – Melampsora lini