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.
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)
·
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)
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
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".
·
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 –
Ø Discovery of Mycoplasma like
organisms (in mulberry dwarf disease
Ø 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)
VIROLOGY
Ø Virus :-
·
Plant viruses are
sub-microscopic, infectious, obligate intracellular
parasites, which do not replicate without a living host.
|
‘A
virus is a virus’. It is neither a living organism nor a non-living
chemical, but something between and betwixt
Andrew Lwoff
|
Ø Virus is
derived from Latin word which means
- Poison/ Venom/Slimy liquid
Ø Study of
Plant viruses and virus like pathogens is called – Plant Virology
HISTORY:-
Ø 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.
Ø 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.
Ø 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
Ø 1915 – Twort, 1917 -F. D. Herelle – Individually discovered bacteriophages
Ø 1929 – Mckinney –
·
Developed cross protection/ pre-immunization technique
for control of citrus tristeza virus (CTV)
·
Cross protection was 1st used against TMV
Ø 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
·
Molecular plant pathology work can
be initiated with W. M. Stanley
Ø 1936 – F. E. Bawden and N. W. Pirie –
·
Demonstrated that virus is a nucleoprotein which
consists both nucleic acid and protein
Ø 1939 – Kausche
et al –
Saw virus particles (TMV) for the first time with the help of
electron microscope
Ø 1956 – Gierrer and Schramm –
·
Showed that nucleic acid is the infectious agent
·
Also investigated about double standard RNA viruses
(ds RNA)
Ø 1967 – Doi et
al – First
observed Phytoplasma (In mulberry
dwarf disease)
Ø 1971 – Dienner and Raymer – reported 1st
viroid disease potato spindle tuber
viroid.
Ø 1972 – Davis et al – First
observed the Spiroplasma (in Corn
stunt disease)
Ø 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
|
General characters of fungi
Ø The
branch of biology that deals with fungi is called ‘Mycology’
Ø Fungus is
a Latin word which means ‘Mushroom’
Ø 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
Ø 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
Ø 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
Ø 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)
|
Septa – The
cross walls which divide the hypha into cells are called septa
|
Ø
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.
Ø Plasmodium – Naked,motile multinucleated mass of protoplasm is called plasmodium
Ø Rhizomorphs: Thicker
root like aggregates. Also called mycelial cords
Ø 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
Ø Stroma: some
fungi also develop mat like structures which contain the fruiting bodies.
Ø 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
Ø 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
Ø 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
Ø 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)
Ø 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
ü 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
|
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
|
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
|
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
|
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
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
|
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
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
|
Hypertrophy –
abnormal enlargement of cells (increase in number of cells)
Hyperplasia –
increase in number of cells (increase cell divisions)
|
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
·
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.
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.
·
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.
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
|
Types of rust –
Ø Autoecious rust – Completes its entire life cycle
in a single host
Ø Heteroecious rust
- Requires genetically two hosts to complete their life cycle
Ø Autoecious macrocyclic rust – Eg – B
– Bean rust
F – Flax rust
S
- Sunflower rust
S
- Safflower rust
Ø Autoecious demicyclic rust – Eg – Rubus orange rust – Gymnoconia peckiana
Ø Heteroecious macrocyclic – Eg –
Wheat stem rust – Puccinia graminis
tritici
White pine blister blight – Cronartium rubicola
Ø Heteroecious demicyclic – Eg – Cedar apple rust – Gymnosporangium juniperi
viriginianae
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 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
|
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
|
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
|
Bacteria
Ø The term bacteria was coined
by – Ehrenberg
Ø Size of bacteria ranges from
– 0.5
to 1.0 µm breadth and 2.0 to 5.0 µm in
length
Ø 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
Ø Anton van leeuwenhoek (1676
) discovered the microbial world with his simple microscope .
‘’Dear god
what marvels they are in so small a creature’’
Leeuwenhoek
|
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
|
Ø 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
Ø 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
|
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)
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 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)
Ø 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)
Ø 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)
Virology
Ø Study of
plant virus is called Plant Virology
Ø The term
virus was derived from ‘Latin’ word which means Poison/ venom/ slimy liquid
Ø Virus – virus is a sub-microscopic,
infectious, obligate intracellular parasite which do not replicate without host
Ø Capsid – protein coat or shell which
encloses the viral genome
Ø Vector – An agent/ organism which carries
virus
Ø Bacteriophage - virus which infects the bacteria (which
means bacteria eater)
Ø 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.
Ø 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).
·
|
·
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
|
Ø 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
Ø 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.
(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)
|
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)
Ø 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
|
Ø 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
Ø 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
Ø Study of
nematodes – Nematology
Ø 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
Ø Study of
algae is called – Phycology/ Algology
Ø Father of
Modern Phycology/ Algology - William Henry Harvey
Ø Father of
Indian Algology – M. O. P. Iyengar
Ø Red rust of
guava is caused by – Cephaleuros parasiticus
Some important plant diseases
Oomycota –
Ø Damping off – Pythium
aphanidermatum
Ø White rust of crucifers – Albugo candida
Ø White rust of amaranthus – Albugo bliti
Ø Late blight of potato – Phytophthora infestans
Ø Downy mildew of grapes – Plasmopara viticola
Ø Downy mildew/ green ear of cumbu – Sclerospora graminicola
Chytridiomycota
–
Ø Potato wart – Sychytrium
endobioticum
Ø Jack fruit rot – Rhizopus
atrocarpi
Ascomycota
Ø Peach leaf curl – Taphrina
deformans
Ø Banana sigatoka leaf spot – Mycosphearella musicola
Ø Brown leaf spot of rice – Helminthosporium oryzae/ Bipolaris
oryzae
Ø Early blight of tomato and potato – Alternaria solani
Ø Apple scab – Venturia
inaequalis
Ø Root rot of pulses – Macrophomina phaseolina
Ø Rice blast – Pyricularia
oryzae
Basidiomycota
Ø Button mushroom – Agaricus
bisporus
Ø Milky mushroom – Calocybe
indica
Ø Paddy straw – Volvariella
volvacea
Ø Oyster mushroom – Plerotus
sojar caju
Ø Sheath blight of rice – Rhizoctona solani
Ø Wheat stem rust – Puccinia
graminis tritici
Ø Coffee rust – Hemileia
vastratrix
Ø Flax seed rust – Melampsora
lini
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