2. Losses caused by Plant Diseases
• 20 % yield loss due to Plant Pathogens
• Varied from country to country
• Epidemic situation loss may reach 100 %
About 34% of the crop produce is lost annually due to diseases,
insect-pests and weeds on the global basis; out of which, 12% is
lost due to diseases (caused by fungi, bacteria or viruses), 11% due
to nematodes, 7% due to insect-pests and 3% due to weeds.
When plant protection measures are not implemented, annual loss
of 30-50% are common in major crops including horticulture
3. Irish famine
• 1845- late blight of potato
• Phytophthora infestans
• Ireland- approximately 1.0
million people lost their lives
due to starvation
• People shifted to maize
cultivation
4. Large Emigration
1.5 million emigrated from
Ireland
to north America
• John F. Kennedy, the 35th
president of USA
forefathers were the
immigrants from Ireland
6. Grapevine downy mildew in France
• Plasmopara viticola
• 1878-1882
• France and other European
countries
• Introduced from USA
through root Aphid
resistant clones
• 50-75 % crop loss
• Bordeaux mixture
developed by Millardet in
1885
7. Coffee Leaf rust in Ceylon
• 1875-1889
• Hemileia vastatrix
• Production reduced from
100 mil. tonnes to 2.3
mil. tonnes
• Planters shifted to tea
cultivation
8. Panama wilt of banana
Fusarium wilt (Panama disease)
Fusarium oxysporum f.sp.
cubense
It first became epidemic in
Panama in 1890
Central American and
Caribbean banana industries
Threatening 80% of the world's
banana production
A new race TR4 pose threat to
Grand naine
9. Sigatoka leaf spot in Fiji island
• Mycosphaerella musicola
• First recognized in the
Sigatoka Valley of Fiji in
1963
• Yield losses of >50%
• Pre-mature ripening
10. Citrus Tristeza in Argentina
• Quick decline
• Citrus tristeza virus
• Aphid Toxoptera citricidus
• 18 million citrus trees were
dead since 1930
• Sour orange rootstock- highly
susceptible root stock
11. St. Antony fire or Holy fire or Ergot
• Due to consumption of
ergot contaminated rye
or jowar or Bajra
• Ergotism
• Claviceps spp
• Ergotoxin, ergometrine
and ergatamine
• Europe and India in
seventeenth century
12. Bengal Famine -1942
• Brown spot of rice
• Helminthosporium oryzae
• 2 million people died of
starvation
13. Bunchy top of banana
• BBTV- virus
• Black aphid
• Destroy hill banana or virupakshi
• Lower palani hills, sirumalai and Kolli hills
14. Chestnut blight
Fungus: Chryphonectria parasitica
1904 - introduced to North America
from Europe
1940- most mature American
chestnut trees wiped out
4 billion trees have succumbed to the
disease
Turmoil of furniture, tanning and
Leather industry
15. Citrus canker in Florida
• Caused by Bacterium
Xanthomonas axanopodis pv citri
• The disease was first found
around 1912, spread throughout
the southeastern U.S. on imported
seedlings from Japan
• It was declared eradicated from
Florida and the adjacent states in
1933
16. Other evidences
• Wheat rust epidemics in 1946-47 in
Northern plains of India
• Bacterial leaf blight of rice in 1963 in Bihar
• Red rot of sugarcane during 1938-39 in
Bihar, Punjab and U.P
• 1985-86 – Rice Tungro viral disease in TN
• 1985-88- Rice blast infection on IR8 variety
in TN
18. Terms related to Plant Pathology
Parasite: An organism living upon or in
another living organism (the host) and
obtaining the food from the invading host
Pathogen: An entity, usually a micro-
organism that can cause the disease by its
constant association
All pathogen are parasite, but all
parasites are not pathogen
19. Terms related to plant pathology
Saprophyte: Organism derive food
material from dead organic matters
Etiology: Study of the causal agent of the
diseases and its relation to susceptible plant
Host: Plant that is diseased
20. Terms related to Plant Pathology
Pathogenesis: Chain of events that lead to the
development of disease in the host
Pathogenicity: Ability of the pathogen to cause disease
Symptom: The external and internal reaction or
alterations of a plant as a result of disease
Sign: Manifestation of the pathogen in diseased plants .
Eg: Powdery mildew and downy mildew
Syndrome: Sum of all signs and symptoms
21. Parasite
Obligate / biotrop: never been grown in
dead or artificial media and require living
host to complete life cycle.
Eg: Downy mildew, Rust , viruses
Facultative parasite: Usually saprophyte ,
certain conditions they become parasite
Eg: Pythium , Fusarium
22. Parasite
Facultative saprophyte
Usually Parasite, certain conditions they
become saprophyte
Eg: Smuts
Necrotrophs
Parasite kill tissue by advance penetration
and live saprophytically
Eg: Sclerotium rolfsii
23. Symbiosis/ Mutualism
• Relationship of two dissimilar organism
living together in close association for
mutual benefits
• Litchens: Fungi + Algae
• Mycorrhizae - Fungus+ plant roots
24. Antagonism
• One organism is injured by another through
competition for food or other demands or
through secretion of toxic substances
• Eg: pathogens which cause diseases on
plants
• Pathogen + Biocontrol agents
25. Causes of Plant Diseases
I. Animate or biotic causes: Pathogens of living nature
(i) Fungi
(ii) Bacteria
(iii) Phytoplasma
(iv) Rickettsia-like organisms
(v) Algae
(vi) Phanerogams
(vii) Protozoa
(viii) Nematodes
26. II. Mesobiotic causes
These disease incitants are neither living or
non-living,
• (i) Viruses
• (ii) Viroides
• (iii) Virusoids
27. III. Inanimate or abiotic causes
• (i) Deficiencies or excess of nutrients
e.g. ‘Khaira’ disease of rice due to Zn deficiency
• (ii) Light
• (iii) Moisture – Damping off, Root rot
• (iv) Temperature – High temp. Powdery
mildew; Low: DM
28. Inanimate or abiotic causes
(v) Air pollutants (e.g. black tip of mango)
(vi) Lack of oxygen (e.g. hollow and black heart of
potato)
(vii) Toxicity of pesticides
(viii) Improper cultural practices
(ix) Abnormality in soil conditions (acidity,-- Club
root; alkalinity- Scab)
29. Protozoa
• Eukaryotic, obligate parasite
• Vegetative thallus : plasmodium
• Asexual spore: Zoospores
• Sexual spore : Resting spore
• Club root of crucifers and powdery scab of
potato
• Plasmodiophora
• Spongospora
38. Fungi - Mycology
• Microscopic, eukaryotic, spore-bearing,
achlorophyllus organisms that generally
reproduce sexually and asexually, and
whose usually filamentous, branched
somatic structures are typically surrounded
by cell walls containing chitin or cellulose,
or both
49. Bacteria
• A unicellular, Prokaryotic, microscopic
organism that lack of chlorophyll and
multiplied by fission. They are either
spherical or rod or spiral form and most of
the plant pathogenic bacteria are motile and
cause diseases in plants
51. Fastidious Phloem Colonizing Bacteria
(Rickettsia like organism)
• FPCB are non-motile, Gram-negative,
non-sporeforming, highly pleomorphic
bacteria that can present as cocci (0.1 μm in
diameter), rods (1–4 μm long) or thread-like
(10 μm long).
• Obligate intracellular parasites, the
Rickettsia survival depends on entry,
growth, and replication within the
cytoplasm of eukaryotic host cells (typically
endothelial cells)
52. FPCB - Diseases
• Citrus Greening-Candidatus Liberobacter
asiaticum and Candidatus L. africanum
• Papaya bunchy top
• Clover club leaf
53. Fastidious Xylem-Limited Bacteria (XLB)
• Fastidious, slow-growing Gram-positive
bacilli of variable form that often appear
coryneform (club-shaped) and often occur
in pairs linked at one end to form a V-shape
• Clavibacter xyli subsp. xyli (sugarcane
ratoon stunting disease)
• Curtobacterium flaccumfaciens that cause
vascular diseases of beets, beans and
soybeans,
55. Spiroplasma
Genus of Mollicutes, a group of small bacteria
without cell walls. Spiroplasma shares the simple
metabolism, parasitic lifestyle, fried-egg colony
morphology.
It has a spiral shape and moves in a corkscrew
motion.
Most spiroplasmas are found either in the gut or
hemolymph of insects, or in the phloem of plants.
Spiroplasmas are fastidious organisms, which
require a rich culture medium. Typically they grow
well at 30°C, but not at 37°C
57. Candidatus Phytoplasma
A group of very small bacteria like organism
intermediate between virus and bacteria
Unicellular, non motile, prokaryote
Grown on cell free media
Pleomorphic, present in Phloem cells
Covered by triple layered membrane
Filterable through bacteriological filters
Resistant to penicillin, sensitive to tetracycline
Require sterol for growth
61. Virus
• Ultra microscopic disease producing entities
• No metabolic enzymes
• Only one type of nucleic acid (DNA/RNA) ,
• Obligate parasite of varying shape
• Pass through bacteriological filters
• Transmitted by insect, seed, sap, etc.,
64. Viroids
• Viroids are plant pathogens that consist of a
short stretch (a few hundred nucleobases) of
highly complementary, circular, single-
stranded RNA without the protein coat
• Diseases
Spindle tuber Cadang cadang
65. Algae
• Unicellular or multicellular organisms
formerly classified as plants, occurring in
fresh or salt water or moist ground, that
have chlorophyll and other pigments but
lack true stems, roots, and leaves
Red rust- Cephaleuros virescens
66. Phanerogamic parasites/
Parasitic weeds
• Parasitic seed-producing plants attack the
other plants.
• They may be total or partial and it may be
root parasite or stem parasites.
• They lack true root system and possess
haustoria to absorb water and nutrients
