This document defines key terms related to plant diseases and their causal organisms. It discusses the objectives of studying plant diseases and provides examples of major plant disease epidemics throughout history. It also summarizes the disease cycle, types of plant pathogens, examples of specific diseases like late blight of potato and rust diseases of wheat, and control measures for these diseases. Overall, the document serves as a reference for understanding the terminology, mechanisms, and management of important plant diseases.

5. TERMS
• HOST : An organism that supports the activities of a parasite is known as
host.
• INOCULUM : It is the infectious material that can cause disease, and is that
portion of pathogens that comes in contact with the host.
• FUNGITOXIC : These are the substances which are harmful to the fungi
and these include fungicides.
• FUNGICIDE : These are the chemicals which are capable of killing fungi
• ACERVULUS : A subepidermal , saucer- shaped , asexual fruiting body
producing conidia on short conidiophores.

6. TERMS
• ASCUS : A sac-like cell of a hypha in which meiosis occurs and that
contain ascospores.
• AVIRULENCE : The inability of a pathogen to infect a certain plant
variety .
• PUSTULE : Small blister-like elevation of epidermis created as spores
from underneath and push outward.
• SMUT : These are the fungal diseases which cause the ears to turn
black. It also cause other parts of the plant.
• RUST : These are the fungal diseases that appear on the host surface
as small, coloured pustules – red , brown, orange, black in colour

7. TERMS
• WHITE BLISTERS : These are white, shining ,blister like pustules found on
the leaves of cruciferous plant . These pustules visible as powdery masses of
spores.
• BLIGHT : In many plants leaves, stems in response to the attack of
pathogen undergo rapid discolouration and leads to death.
• ROT : It is a disease in which the affected tissues die and undergo decay .It
may effect leaves, roots , stem , buds of the host plant.
• WARTS : These are the outgrowths that develop on tubers and stems
showing discoloured cauliflower like appearance .
• MILDEW : These are the fungal diseases of plants in which pathogen has
superficial on host surface (leaves , stems) in the form of patches of varying
sizes and colours.

8. TO STUDY THE BIOTIC , ABIOTIC CAUSES OF PLANT
DISEASES.
TO STUDY THE MECHANISM OF DISEASE
DEVELOPMENT.
TO STUDY THE INTERACTION BETWEEN PLANT
AND PATHOGEN.
TO DEVELOP THE METHODS OF PLANT DISEASE
MANAGEMENT/CONTROL.

9. • 1845-46 LATE BLIGHT OF POTATO / IRISH FAMINE.
• 1867 COFFEE RUST IN SRI LANKA
• 1869 COFFEE RUST IN SOUTHERN INDIA
• 1918-19 BROWN LEAF SPOT OF RICE IN DELTA OF KRISHNA AND
GODAWARI RIVERS
• 1943 BROWN LEAF SPOT OF RICE/BENGAL FAMINE
• 1956-57 RUSTS IN BIHAR

10. PEST LOSS(%)
WEED 33
DISEASES 26
INSECTS 20
STORAGE PESTS 7
RODENTS 6
OTHERS 8
TOTAL 100

11. A DISEASE IS A PARTICULAR ABNORMAL
CONDITION THAT NEGATIVELY AFFECTS
THE STRUCTURE OR FUNCTION OF PART
OR ALL OF AN ORGANISM.

12. INFECTIOUS OR BIOTIC,PLANTDISEASES
• DISEASES CAUSED BY FUNGI
• DISEASES CAUSED BY PARASITIC
HIGHER PLANTS
• DISEASES CAUSED BY VIRUSES
• DISEASES CAUSED BY NEMATODES
• DISEASES CAUSED BY BACTERIA
NON-INFECTIOUS,OR ABIOTICPLANT
DISEASES
• DISEASES CAUSED BY
TEMPERATURE
• DISEASES CAUSED BY SOIL
MOISTURE
• DISEASES CAUSED BY POLLUTION
• DISEASES CAUSED BY LIGHT

14. INFECTIOUS DISEASES
• A) ENDEMIC DISEASES : A disease which is present from year to year in a
certain region ( country) or a part of a region (district ) is a referred to as
endemic. The environmental conditions are favourable for its development.
The causal agent is well established in the locality.
• B) EPIDEMIC DISEASES : Diseases which spread widely but occur
periodically. The causal agent may be regularly present in the locality but the
environmental conditions are favourable but occur periodically.
• C) SPORADIC DISEASES : These are the plant diseases which occur at
irregular intervals or occasionally.

15. •
•
•

16. ▪ THE PLANTDISEASESARE CAUSEDBY FOLLOWING PATHOGENS:
1) PARASITIC FUNGI : They produce a great majority of the parasitic plant
diseases called fungal diseases. These diseases cause damage and destruction.
Ex : Albugo candida cause white rust of crucifers
2) PARASITIC BACTERIA : They also cause many plant diseases .
Ex : Xanthomonas sp. cause citrus canker
3) PARASITIC SEED PLANTS : There are few phanerogamic parasites which
cause plant diseases.
Ex: Dodders (Cuscuta) etc.
Cntd…...

17. 4) PARASITIC ALGAE : There are very few parasitic algae that cause plant
diseases.
Ex : Cephaleuros parasitica cause orange rust of tea
5) VIRUSES : These are the pathogens which almost completely dependent
upon their host for their growth and replication. They cause serious plant and
animal diseases.
Ex : Yellow vein mosaic virus in bhindi

18. TYPES OF PLANT PATHOGENS

20. DISEASE CYCLE
• The chain of events that leads to the development of a disease is
called disease cycle .
• ELEMENTS OF THE DISEASE CYCLE :
1) Host
2) Pathogen
3) Environment

21. TYPICAL DISEASE CYCLE

22. PLANT DISEASES ANDTHEIRCAUSALORGANISMS

23. S.NO.
DISEASES
PATHOGENS
1) WART DISEASE OF POTATO Synchytrium endobioticum
2) LATE BLIGHT OF POTATO Phytophthora infestans
3) WHITE RUST OF CRUCIFERS Albugo candida
4) DOWNY MILDEW OF BAJRA Sclerospora graminicola
5) POWDERY MILDEW OF GRAPEVINE Uncinula necator
6) BROWN RUST OF WHEAT Puccinia triticina
7) BLACK RUST OF WHEAT Puccinia graminis tritici
8) YELLOW RUST OF WHEAT Puccinia striiformis

24. S.NO. DISEASES
PATHOGENS
9) LOOSE SMUT OF WHEAT Ustilago tritici
10) RED ROT OF SUGARCANE Colletotrichum falcatum
11) TIKKA DISEASE OF GROUNDNUT Cercospora sp.
12) ROOT KNOT OF VEGETABLE CROPS Root – knot nematodes
13) EAR COCKLE OF WHEAT Anguina tritici
14) KARNAL BUNT OF WHEAT Tilletia indica
15) YELLOW VEIN MOSAIC OF BHINDI Monopartite begomovirus
16) LITTLE LEAF OF BRINJAL Phytoplasma

25. WART DISEASE OF POTATO
host
• Solanum tuberosum
• Synchytrium endobioticum
• The disease occur on the underground
parts except roots i.e. tubers , buds ,
stems, and stolons.
• There is a Cauliflower like outgrowths on
infected parts.
• In the early growing season they are
greenish white in colour.
• In advanced stages, the warts become
dark black in colour.

26. WART DISEASE OF POTATO
Resting spore

27. DISEASECYCLE CONTROL MEASURES
• The diseased potato area should be
discarded.
• Soil treatment may control the disease to
a large extent .This include steam
sterilization, mercuric chloride and
copper sulphate application and formalin.
It is very costly.
• Cultivation of disease resistant varieties
continuously for 8-10 years.

28. LATE BLIGHT OF POTATO
HOST
• Solanum tuberosum
PATHOGEN
• Phytophthora infestans
• The disease appears on the top of the plant
i.e. on the tip and margins of the leaflets ,
petiole , stem and this is mainly infected in
the field.
• The disease makes its appearance as dead
,small , brownish to purplish black areas.
• There is more discoloration of the skin of
those parts of the tubers which lie nearest to
the surface of the soil.

29. LATE BLIGHT OF POTATO
Lemon shaped sporangia

30. LATE BLIGHT OF POTATO
DISEASECYCLE CONTROLMEASURES
• The seed tubers should be free from
the disease.
• Storage of potato tubers in cold
storage.
• By spraying fungicides such as Blitox-
50 etc. in proper time.
• The tubers should be dipped in
mercuric chloride solution for 90
minutes before storage.

31. WHITE RUSTOF CRUCIFERS
HOST
• Members of Crucifers like Brassica sp.
, Raphnus sativus, etc.
• Pathogen
• Albugo candida
• The disease affects all the aerial parts of
the plant, roots are not affected.
• There are 2 types of infection : Local
and Systematic .
• In local infection, spots appear on
leaves, stems . These spots have variable
size.
• In systematic infection, young stems
and inflorescence are infected.

32. Conidia

33. DISEASECYCLE CONTROLMEASURES
• Cultivation practices should be
followed and destruction of weed
should be done.
• Crop rotation prevent the disease.
• Disease resistant varieties should
be preferred.

34. DOWNY MILDEWOF BAJRA
HOST
• Pennisetum glaucum
PATHOGEN
• Sclerospora graminicola
• In this there are two stages of symptoms.
• One is downy mildew stage, in which leaf
is affected and leaves then start showing
chlorotic streaks on their upper surface
and just opposite to streaks on lower
surface.
• Other is the green ear stage, affecting
inflorescence. In this a whole or a part of
inflorescence is transformed into twisted
leafy structure.

35. DOWNY MILDEWOF BAJRA
Sporangia of Sclerospora
SEM
Inflorescence of Bajra Diseased spikelet

36. DOWNY MILDEWOF BAJRA
DISEASECYCLE CONTROL MEASURES
• Removal of the infected tissues
• Crop rotation
• Deep ploughing
• Use fungicides
• Some of the resistant cultivars like NHB
10 etc. are resistant to downy mildew.

37. POWDERY MILDEWOF GRAPEVINE
HOST
• Vitis vinifera
• PATHOGEN
• Uncinula necator
• The disease attacks the vines at any
stage of their growth
• All aerial parts of the plant are
attacked
• Floral infection results in shedding
of flowers
• Powdery growth is visible on berries
and the infection results in the
cracking of skin of the berries.

38. POWDERY MILDEWOF GRAPEVINE
Lower Surface of LeafOn fruit surface

39. POWDERY MILDEWOF GRAPEVINE
DISEASECYCLE CONTROL MEASURES
• Resistant varieties should be grown
• Fungicides like Sulphur etc. should
be used to control the disease
• The use of fungicides for control
of powdery mildew should begin
during early stages of vine
development

40. BROWN RUST OF WHEAT (leaf rust)
host
• Triticum vulgare
PATHOGEN
• Puccinia triticina
• Pustules appear on the leaf ,on the
upper surface.
• Pustule is orange brown in colour.
• Pustule have random arrangement
• They may group into patches
• Losses takes place between 5% and
20%

41. BROWN RUST OF WHEAT
Diseased leaf

42. BROWN RUST OF WHEAT
DISEASECYCLE CONTROL MEASURES
• Use of fungicides is useful to
control infections.
• Cultivars are the best method of
controlling the disease.
• Variety resistance is important
• Wheat should be sown as early as
possible to avoid rust periods.

43. BLACK RUST OF WHEAT (stem rust)
host
• Triticum vulgare
PATHOGEN
• Puccinia graminis tritici
• Pustules appear on the stem,leaf
bases.
• Pustules have reddish brown colour
• Large number of uredo spores are
released
• Towards the end black telia are
produced

44. BLACK RUST OF WHEAT
Uredospores
Teleutospores

45. BLACK RUST OF WHEAT
DISEASECYCLE CONTROL MEASURES
• Use resistant varieties.
• Use of fungicides
• Cultivars is the method of
controlling disease

46. YELLOWRUST OF WHEAT (stripe rust)
host
• Triticum vulgare
PATHOGEN
• Puccinia striiformis
• There is a appearance of yellow
pustules on the upper surface of
leaf.
• Pustules are round ,blister like
and small
• Yellow coloured uredo spores
are released

47. YELLOWRUST OF WHEAT

48. YELLOWRUST OF WHEAT
DISEASECYCLE CONTROL MEASURES
• Resistant varieties is the most
effective method to control this
rust.
• Use of fungicides
• Cultivars are also used to control
disease

49. LOOSE SMUT OF WHEAT
HOST
• Triticum vulgare
PATHOGEN
• Ustilago tritici
• They bear loose, black ,powdery
masses of smut spores instead of
flowers.
• All the floral parts except the awns
are converted into masses of smut
spores.
• Membrane bursts and smut spore
release
• Group of smut spore called sorus

50. LOOSE SMUT OF WHEAT
Teliospores

51. LOOSE SMUT OF WHEAT
DISEASECYCLE CONTROL MEASURES
• Use of healthy seed for sowing
• Seeds are treated with the
fungicide to kill any fungus
which is present inside.
• Use of resistant varieties
• By heat treating the seed to kill
the fungus before planting

52. REDROT OF SUGARCANE
host
• Saccharum officinarum
PATHOGEN
• Colletotrichum falcatum
• Glomerella tucumanensis
• Appear after rainy season when
plant growth stops
• In the early stage, yellowing and
drooping of upper leaves is there
• In the later stage, the stem shrivels
and loses its bright colour
• At advanced stage of disease blood
red colour with dark margins
develop on the midribs of the
leaves

53. REDROT OF SUGARCANE
Sickle shaped conidia

54. REDROT OF SUGARCANE
DISEASECYCLE CONTROL MEASURES
• By collection and burning of
sugarcane trash in the field
• Crop rotation
• Use of resistant varieties is the
most effective method of
controlling the disease.

55. TIKKADISEASE OF GROUNDNUT
HOST
• Arachis hypogaea
PATHOGEN
• Cercospora sp.
1) Cercospora personata
2) Cercospora arachidicola

56. Cercospora personata
• Leaf spots are small , more circular
• The mycelium consists of internal
hyphae.
• The conidiophores occur on the
lower surface of the host leaf
• The conidia are light in colour
Cercospora arachidicola
• Leaf spots are larger in size ,and are
irregularly circular.
• The mycelium consists of both
external and internal hyphae.
• The conidiophores occur on the
upper surface of the host leaf
• The conidia are pale yellow in colour

57. TIKKA DISEASE OF GROUNDNUT
Conidia

58. TIKKADISEASE OF GROUNDNUT
DISEASECYCLE CONTROL MEASURES
• By crop rotation
• By spraying fungicides
• Burning of the diseased plant
debris will reduce the infection

59. ROOT KNOT OF VEGETABLE CROPS
• This disease is caused by root knot nematodes.
• Most of the vegetable crops serve as the host plant : carrot , sweet
potato , okra , brinjal , chili , tomato etc.

60. ROOT KNOT OF tomato
HOST
• Solanum lycopersicum
PATHOGEN
• Meloidogyne sp.
• Leaf size decreases
• Yellowing of leaves
• Slow growth and dwarfing
• Yield reduces and it also kills the
plant
• This root knot nematode produces
root galls

61. ROOT KNOT OF tomato

62. DISEASE CYCLE

63. ROOT KNOT OF TOMATO
CONTROLMEASURES
● Crop rotation
● Field sanitation
● Use of resistant varieties
● Deep ploughing
● Use of fungicides

64. EAR COCKLE OF WHEAT
HOST
• Triticum vulgare
PATHOGEN
• Anguina tritici
• Affects all growing stages
• There is a rolling and twisting of
the leaves
• A rolled leaves traps the next
growing leaf and inflorescence
within it and causes it to become
bent
• Base of the stem are bent and
generally stunted.

65. EAR COCKLE OF WHEAT

66. EAR COCKLE OF WHEAT
DISEASECYCLE CONTROL MEASURES
• Use of healthy seed from
healthy crop.
• Use of fungicides
• By crop rotation
• Hot water treatment of seed ,
first soaking seed in cold water
for 4-5 hours and treating at 54C

67. KARNAL BUNT OF WHEAT
HOST
• Triticum vulgare
PATHOGEN
• Tilletia indica
• The fungus causes a reduction
in the length of ears
• Not whole grain but partially are
infected so, called as Partial
Bunt
• Ovoid sori develop, containing
dusty, brown to black spore
masses.

68. KARNAL BUNT OF WHEAT
sporangium

69. KARNAL BUNT OF WHEAT
DISEASECYCLE CONTROL MEASURES
• Use of healthy seed
• By crop rotation
• By spraying fungicides
• Use of resistant varieties

70. YELLOWVEINMOSAICOF BHINDI
HOST
• Abelmoschus esculentus
PATHOGEN
• Monopartite Begomovirus
• Yellowing of the entire network of
veins in the leaf
• In severe infections younger leaves
turn yellow ,become reduced in size
• The veins of the leaves will be
cleared by the virus and intervenal
area becomes completely yellow
• Virus is spread by whitefly

71. YELLOWVEINMOSAICOF BHINDI

72. YELLOWVEINMOSAICOF BHINDI
DISEASECYCLE
• The virus penetrates in the several hosts
• This virus is transmitted by whitefly
• The insect vector acquires virus , so viruses
undergo incubation period of 7 hours
within the vector body
• Further vector inoculates them on crop
plants
• Vectors retain viruses in them and may
infect host plant until they die
CONTROL MEASURES
• By selecting varieties resistant to
yellow vein mosaic.
• Organic neem oil is used to kill
whitefly
• For sowing during the summer
season ,when whitefly activity is
high, the susceptible varieties
should be avoided

73. LITTLE LEAF OF BRINJAL
host
• Solanum melongena
PATHOGEN
• Phytoplasma ( Mycoplasma like organism)
• There is a production of very short
leaves by affected plant.
• The petioles are reduced in size
• Leaves are narrow, soft , yellowish
• Internodes are also reduced in size. This
gives whole plant a bushy appearance
• Fruiting is rare

74. LITTLE LEAF OF BRINJAL
Diseased leaf Diseased fruit

75. LITTLE LEAF OF BRINJAL
DISEASECYCLE
• Disease is transmitted from diseased to
healthy plants by vectors.
• This is mainly transmitted by leafhoppers
• This leafhopper is inhabitants of brinjal
leaves
CONTROL MEASURES
• Removal of weeds and infected
plants
• Spraying of insecticides
• Spray tetracycline which helps to
control the disease.
• Use disease resistant varieties

76. ● Plants are grown for beautiful flowers, fruits, seeds, vegetables but plants also
affected by many diseases.
● Plant diseases cause great loses annually throughout the world and reduce the yield
even with the use of improved varieties and technologies. Because of the dependence
of humans for food, fiber and other resources, plant diseases and their control is vital
for our survival.
● There is need to increase the productivity of crops for future generation to achieve
the goal of sustainable development.
● Plant pathology is intimately related to the health of plant and production of more
crop yield.
● Many new techniques and chemicals have been evolved to fight plant diseases.
Efforts have been made to understand the nature of diseases at molecular levels and
the relationship between host and pathogen.

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• Singh , R.P. 2005. Plant Pathology. Kalyani Publ., Noida.
• Mehrotra , R.S. and Aggarwal , A. 2013. Fundamentals of plant pathology.
Tata McGraw Hill.
• Singh , R.S. 1970. Plant Diseases. Oxford and IBH Publ., CO. PVT. LTD.
New Delhi.