Introduction to Plant Pathogens

1. PP-401 Introduction to Plant Pathogens 2(1-2)
Why we want to study plants pathogens ???

2. ➢ Plants provide us food, fiber and shelter
➢They also provide us mineral, vitamins, carbohydrates and
fiber

3. Plants are always under stress
Ground WaterSoil pH

5. BASIC TERMINOLOGY
➢ Pathogen : Any organism that can incite disease
➢Pathogenicity : The capability of a pathogen to cause disease
➢Parasite : An organism living on or in another living organism (host)and obtaining
its food from the latter.
➢ Pathogen vs Parasite
➢Host :An organism plant that is invaded by a parasite and from which
the parasite obtains its nutrients.
➢Disease Any malfunctioning of host cells and tissues that results from continuous
irritation by a pathogenic agent or environmental factor and leads to development
of symptoms.
a. Infectious
b. Progressive
Infestation Infection
➢ Injury: loss of plant vigor resulting from an sudden event, such as a lightning
strike, hail damage, chemical burn or mechanical damage.

6. ➢Plant Pathology : The study of plant diseases
Plant pathology is an interdisciplinary science that includes knowledge of botany,
microbiology, crop science, soil science, ecology, genetics, biochemistry,
molecular biology, and physiology.
How we come to know Plants is Sick?
➢Symptom : Abnormal appearance of a plant
➢Sign : Appearance of the actual pathogen (fruiting bodies, spores, hyphae)
Causes of Diseases
Biotic Diseases(Plant Pathogens) Abiotic Diseases
Fungi Environmental (freezing, flooding,
drought,light,wind, hail)
Bacteria Cultural: (mechanical damage, planting
problems)
Virus Chemical:(fertilizers, herbicides, pets)
Nematode Physiological Disorders (abnormal growth
Higher Parasitic Plants due to genetic and/or environmental
Viriods interaction
Phytoplasma

7. ➢Conducive Environment
Susceptible Host: Lacking the inherent ability to resist disease or attack by a
given pathogen
Susceptibility The inability of a plant to resist the effect of a pathogen or other
damaging factor
➢ Virulent Pathogen Capable of causing a severe disease; strongly pathogenic.n
Pathogenicity: Ability pathogen to cause the diseaase
Virulence : The degree of pathogenicity of a given pathogen.
➢ Adequate Time
Components of a Plant Disease
Disease Triangle

8. Why do we study Pathogens?
• Plant Pathology is the study of;
• living entities and the environmental conditions that cause
disease in plants
• mechanisms by which these factors produce disease in plants
• interactions between the disease-causing agents and the diseased
plant and
• methods of preventing or controlling disease and alleviating the
damage it causes

9. What is Plant Pathology?
Plant pathology is about
• plants and
• organisms that cause diseases on them economic
value of plant is important
• focus of plant pathology - plant health rather than
plant production
What is health?
The ability to carry out normal physiological
functions at a acceptable level consistent to genetic
potential.

10. Fungi
Nematode
Bacteria
Infected Plant
Virus
Plant Pathogen

11. Species richness in major groups of organisms

12. Prokaryotes Eukaryotes
- A single celled microorganisms
- genetic material is not organized
into a membrane bound nucleus
e.g. Bacteria & Mollicutes
- Cell organelles (nuclei, and
mitochondria) are not
membrane bound.
-Only 70 S ribosomes within
cytoplasm
-Single/multi cellular organisms
- genetic material is organized
into a membrane bound
nucleus
-Cell organelles (nuclei, and
mitochondria) are membrane
bound.
Have two types of ribosomes
Larger one in cytoplasm (80 S)
Smaller one in
mitochondria(70S)
Prokaryotes VS Eukaryotes

13. Fungi
• A eukaryotic, heterotrophic organism devoid of
chlorophyll that obtains its nutrients by absorption, and
reproduces by spores.
• The primary carbohydrate storage product of fungi is
glycogen.
• Most fungi have a thallus composed of hyphae (sing.
hypha) that elongate by tip growth
• Cell must be made Chitin

14. Aspergillus Wheat Smut
Wheat Rust

15. Bacteria
Bacillus
Staphyllococus
Pseudomonas

16. Bacteria Mollicutes
A single celled microorganisms
Belong to the kingdom
Prokaryotae
Genetic material is not bound
by membrane, therefore, is not
organized into a nucleus
The cytoplasm is bounded by
cell membrane and cell wall
A single celled microorganisms
Belong to the kingdom
Prokaryotae
Genetic material is not bound
by membrane, therefore, is not
organized into a nucleus
The cytoplasm is bounded by
cell membrane only

17. Disease Causal Agent /Pathogens
VIRUS
• Word virus is derived from the Latin word “venome”
meaning “poisonous fluid”.
• It is non cellular infectious entity which contain nucleic acid
( RNA or DNA) which is coated with protein.
• It is capable of reproducing only in living cells.
• They use biosynthetic machinery of the host to perform their
own functions.
VIROIDS
• Similar to viruses but with the difference that they lack
protein coat or
• Small low molecular weight RNA that can infect
Plant cells replicate themselves and cause disease.

18. Nematodes
• Generally microscopic, worm like animals, that
live saprophytically in water or soil, or as parasite
of animals and plants.

19. Parasitic Plants
Some higher plant forms live on the surface of or parasitize other
plants and often cause harmful reactions in their hosts.
➢Dodder( Cuscuta sp)
➢Leafy Mistletoe
➢Dwarf Mistletoe

20. Discipline of Plant Pathology Grows with Human Race
PreHistoric:
➢ Ancient Babylon, People are familiar with Smut Disease (1900BC)
➢ Roman celebrated festival called Robigalia (715BC) to please God
Robigus to avoid Rust diseases
➢ Europe Poor people suffered by eating infected Rye with disease called
“Ergot”
Early modern period:
➢ Irish Famine by late Blight of Potato(1845-46)
➢Chest nut blight(1900)
➢Coffee Rust(1800)----- Cultural Impact as Tea replace Coffee in every day
life
Modern Period:
➢ Great Bengal famine(1943) caused by Fungi finally lead to division of
India
➢1970 southern corn blight in USA
➢Cotton Leaf curl Disease(1992-93): loss of thousand of bails in Pakistan
➢ Chickpea Blight

21. Need, Threat and Challenges for Plant Pathology
➢Feeding 9 billion people expected to inhibit our planet by 2050
➢Cost of production increase i.e. Pesticide
➢Limit options for crop production
➢Environment and Health Hazards
➢Biological Warfare
Table
Attainable crop production $1.5 trillion
Actual crop production (-36.5%) $950 b
Production without crop protection $455 b
Losses prevented by crop protection $415 b
Actual annual losses to world crop production $550 b
Losses caused by diseases only (14.1%) $220 b

22. Fungi
• A eukaryotic, heterotrophic organism devoid of
chlorophyll that obtains its nutrients by absorption, and
reproduces by spores.
• The primary carbohydrate storage product of fungi is
glycogen.
• Most fungi have a thallus composed of hyphae (sing.
hypha) that elongate by tip growth

23. Wheat Smut
Wheat Rust

24. Magical Mushrooms, Mischievous Molds
Welcome to the World Of Fungi

25. Comparison of Fungi with Plants and Animals
Features Plants Animals Fungi
1.Cell Type Eukaryotes Eukaryotes Eukaryotes
2.Nuclear Envelope Present Present Present
3.Mitochondia Present Present Present or Absent
4.Chloroplast Present Present Absent
5.Cell Wall Present Absent Present with Chitin
6.Mode of Nutrition Autotrophic Digestion Absorption
7.Motility None Motile None
8.Multicellular Present Present Present
9.Nervous System Absent Present Absent
10.Means of Genetics Meiosis Meiosis Mesiosis

26. Economic Importance of Fungi:
Fungi as Friends
➢ Fungi as antibiotics and drugs
1. Penicillins: Penicillium chrysogenum
2. LCD : Clavicep purpurea
➢Fungi in Food and Industry
1. Mushroom Agaricus sp.
2. Yeast Saccharomyces sp.
3. Wine; Yeast and Botyritis sp.
4. Blue Cheese Penicillium sp.
5. Bread Yeast
➢Fungi as Biological Control Agent
Trichoderma sp.
Fungi as saprophytes: Most of the more than 100,000 known fungus spp are
strictly saprophytic. World is nothing but debris if there is no fungi
➢Fungi as Symbionts
1. Mycorrhiza : Fungus and roots of higher plants
2. Lichens: Fungus and algae
➢ Biological and Genetic Studies:
1. Yeast
2. Neurospora sp

27. Fungi as Foe
➢ Fungi causal agents of human and Animals
1. Athelete foot cause by Trichophyton sp
2. Ergotism by Clavicep pupurea
➢Fungi as food spoiler
Penilcilium sp, Aspergillus sp, Rhizopus sp.etc also
known as Pathogenic Weeds
➢Mycotoxins
e.g Aflatoxins
➢Fungi as Plant Pathogens
1.Rust Diseases
2. Smut Diseases
3. Blight
4. Rots
➢ Post harvest Loses

28. Characteristics of Fungi
►Eukaryotic
►Nonphotosynthetic ( heterotrophic)
►Most are multicellular
►Most are microscopic molds or yeasts
►Food storage is generally in the form of
lipids and glycogen
►Reproduce by spores
The study fungi is known as MYCOLOGY.

29. Heterotrophic by Absorption
• Fungi get carbon from organic sources
• Hyphal tips release enzymes
• Enzymatic breakdown of substrate
• Products diffuse back into hyphae
Product diffuses back
into hypha and is used
Nucleus hangs back
and “directs”
Fungi‘s Mechanism of Absorption

30. Russula
mushroom
mycorrhizas on
Western
Hemlock root
Fungal hyphae
around root and
between cells
Mycorrhiza cross sections
Mycorrhiza Symbionts Lichens

31. Ecology of Fungi
➢Relative humidity over 70%.
➢Temperatures over 30 degrees Celsius for a
period of a few days to a week.
➢Stress to the affected plant, such as drought,
flood, or insect infestation.
➢High moisture content of crop (20% or higher).
➢Must occur in conjunction, or fungal growth
cycle will cease.

32. Fungal Infection
• Can occur at any stage in crop
production.
• While in the field.
• During harvesting.
• While in silage and storage.
• Spores can lay dormant for months to
years, waiting for positive conditions
for germination.

33. Modes of Spore Transmission
• Airborne, wind or indoor ventilation
systems.
• Attachment to insects of birds, thus
transmitted from plant to plant, or
animal to animal, etc.
• Via transportation mechanisms such
as trucks, crop machinery, etc.
g

34. Morphology of Fungi
Fungi can be divided into two basic morphological forms,
yeasts and hyphae.
a. Yeasts are unicellular fungi which reproduce asexually
by blastoconidia formation (budding) or fission.
b. Hyphae are multi-cellular fungi which reproduce asexually
and/or sexually.
Dimorphism is the condition where by a fungus can exhibit
either the yeast form or the hyphal form, depending on growth
conditions.

35. Morhology of Fungi
➢Hypha : Branch of fungi( 2-1-micrometer in thickness)
➢Vegetataive body of Fungi called mycellium which is made up
of Hyphae
➢These filamentous structures either lack cross walls
(coenocytic) or have cross walls acoenocytic or septate
depending on the species.

36. Reproduction in Fungi
➢ Fungi reproduce through spores
➢Spores either produce asexually or sexually
➢Asexual spores either produce in a sac like structure called
sporangium and known as sporangiospores
➢Sporangiospores which can swim with flagella called
zoospores
➢ Another type of asexual spores which are produce by
cutting of special terminal hypha are called Conidia( sing.
Conidium) and terminal hypha which bear these spore is called
conidiphore
➢A type of asexual spores in which terminal hypha form a
thick layer and later become separate from rest of body called
chlamydospores

37. Reproduction in Fungi
➢ Sexual Reproduction occurs in most of Fungi
➢If spore form by the union of two gametes of same size and
shape such spore is called zygospore and group of fungi in
which it form are called Zygomycetes
➢If spore is form by the union of motile gametes of equal or
unequal size is called meisosporangia and group in which they
form is called Chytridiomycetes
➢ In some fungi sexual spores are form inside sac like structure
called ascus and usually eight in number are called ascospores
and group of fungi are called Ascomycetes
➢ In some other Fungi spores are formed on club like zygote cell
and their number is four are called basiospores and group is
called Basidiomycetes

38. Reproduction in Fungi
➢ In fungal like organism which belong to chromista
and called Oomycetes, sexual spores form by the
union of gametes of unequal size called oospores

39. ➢There are fungi in which instead producing spores,
mycelium of two unite with each other result in
exchange of genetic information

40. ➢Large group of fungi in which either sexual
reproduction is not present or if present it is not
discovered are called mitosporic fungi and class is
called deutromycetes

41. Classification of Fungi
Fungal like organisms(Flo’o) and True Fungi
➢Fungal like organisms include
a) Protozoa include
1. Myxomycetes
2. Plasmodiophoromycetes
Features:
Unicellular
Plasmodial
Colonial
Very simple multicells or phagotrophic, i.e., feeding by engulfing
their food e.g Plasmodiophora brassicae club root of crucifers

42. Fungal like organisms(Flo’o)
b) Kingdom Chromista include
Oomycetes
Phyllum Oomycota
•Have biflagellate zoospores, with longer tinsel flagellum
directed forward and a shorter whiplash flagellum directed
backward.
•Diploid thallus, with meiosis occurring in the developing
gametangia.
• Sexual resting spores (oospores) produced by the union of
morphologically different gametangia called antheridia (male)
and oogonia (female)
•Cell walls composed of glucans and small amounts of
hydroxyproline and cellulose (chitin is missing)

43. Oospore
Oocyte
Anthiridium
Oogonium
Sporangia
Zoospore with flagella
Plant Pathogenic Genera
1. Phyophthora infestans
Late Blight of Potato
2. Pythium sp.
Damping off disease
3.Plasmopara viticola
Downy mildew of grapes
4. Albugo candida
White rust of Crucifers
Fungal like organisms(Flo’o)

44. Late Blight of Potato: Phytophthora infestans
DAMING OFF White Rust

45. Classification of Fungi
True Fungi Lower Fungi (hyphae lack cross walls)
•Lack chlorophyll
•Cell wall made of Chitin
Phyllum Chytridiomycota
Class Chytriomycetes
Features:
•Non-sepate mycellium
•Produce zoospores
e.g synchytrium endobioticum Black wart of potato
Olpidium brassicae parasitic on cabbage roots and can
transmit viruses

46. Classification of Fungi
True Fungi Lower Fungi
Phyllum Zygomycota
Class Zygomycetes
•Produce nonmotile asexual spores in sporangia.
•No zoospores.
•The resting spore is a zygospore, produced by the fusion of
two morphologically similar gametes
Examples Rhizopus, causing bread molds and soft rot of fruits
and vegetables
Mucor, causing bread mold and storage rots of fruits and
vegetables
• Glomus Endomycorrhiza

47. True Fungi
Classification of Fungi
Higher Fungi (Hyphae have cross walls)
Phylum Ascomycota
Class Ascomycetes
•Most have a sexual stage (teleomorph or Perfect) and
an asexual stage (anamorph or imperfect).
•Produce sexual spores, called ascospores, generally in groups
of eight within an ascus.
•Produce asexual spores (conidia) on free hyphae or in asexual
fruiting bodies
•Structures (pycnidia, acervuli, etc.)
•

48. i. Ascostromata — Produce asci within locules (cavities)preformed in
a stroma.
ii. Cleitothecium– Closed shape fruiting body
iii. Perithecium----- A saucer shaped fruiting body with small opening
iv. Apothecium------- Open shape fruiting body

49. Classification of Fungi
True Fungi Higher Fungi
Phylum Ascomycota
Class Ascomycetes
I. Archiascomycetes
A group of diverse fungi,
difficult to characterize
e.g Taphrina sp Peach leaf
curl

50. II. Saccharomycetes or Yeast
Asci are naked. No ascocarp. Unicellular fungi
reproduce by budding

51. III. Filamentous ascomycetes
a. Pyrenomycetes
b. Loculoascomycete
c. Discomycetes
d. Deuteromycetes or mitosporic fungi (imperfect
or asexual fungi)

52. Classification of Fungi
True Fungi Higher Fungi
Phylum Ascomycota
Class Ascomycetes
III. Filamentous Ascomycetes
Order Ersiphales: Close fruiting body(ascocarp) called
cleistothecium
Obligate parasites(Biotroph)
e.g Erysiphe sp. Powdery mildew of herbaceous plants

53. a. Pyrenomycetes
Fruiting body is cleistothecium.
e.g Claviceps purpurea causing ergot of grain crops
e.g Giberella fujikuroi Foolish disease of rice

54. b. Loculoascomycetes
Loculoascomycetes: Ascomycetes with
ascostromata — Produce asci within locules
(cavities)preformed in a stroma.
e.g Venturia inaequalis cause apple scab

55. Classification of Fungi
True Fungi Higher Fungi
Phylum Ascomycota
Class Ascomycetes
III. Filamentous Ascomycetes
c. Discomycetes
Ascomycetes with apothecia
e.g Sclerotinia sclerotiorum cause white mold
or soft rot vegetable

56. d. Deuteromycetes or mitosporic
fungi (imperfect or asexual fungi)
•Mycelium well developed,septate,
branched.
•Sexual reproduction and structures rare,
lacking, or unknown.
•Asexual spores (conidia) formed on
conidiophores or produced in structures
known as pycnidia and acervuli.
e.g Penicilllium sp., Aspergilus sp.

57. Classification of Fungi
True Fungi Higher Fungi
Phylum: Basidiomycota (Basidiomycetes, the club and mushroom
•Sexual spores called basidiospores, are produced externally on a club-
like, one- or four-celled spore producing structure called a basidium
Order: Ustiliginales Smut Fungi
•Basidium has cross walls or is nonseptate.
• It is the promycelium of the teliospore. Teliospores single or united
into crusts or columns, remaining in host tissue or bursting through the
epidermis.
• Fertilization by union of compatible spores, hyphae, etc.
•Only teliospores and basidiospores are produced
e.g Ustilago tritici Wheat smut
Tilletia india Karnal Bunt

58. Classification of Fungi
True Fungi Higher Fungi
Phylum: Basidiomycota (basidiomycetes,the club and mushroom
Order Uredinales: Rust Fungi
•Basidium with cross walls.
•Sperm cells called spermatia fertilize special receptive hyphae
in spermagonia. Produce two to several types of spores:
teliospores, basidiospores, aeciospores, and uredospores
(sometimes called “urediniospores”).
•Uredioospores can be repeating spores.
•Obligate parasites
Puccinia sp. Wheat rusts

59. Agaricales (the mushrooms) —
Basidium
without cross walls, produced
on radiating gills or lamellae.
Many are mycorrhizal fungi
e.g Agaricus bisporus
Button Mushroom

60. Some relevant terms
➢ Plasmogamy: Fusion of cytoplasm
➢Karyogamy: Fusion of Nuclei
➢Dikaryotic Mycellium: Mycelium or spores containing two
sexually compatible nuclei per cell. Common in the basidiomycetes
➢Heterokaryon: Mycellium contain genetically two different
nuclei
➢Homothallic Fungus: Fungus producing compatible male and
female gametes on the same mycelium
➢Heterothallic: Fungi producing compatible male and female
gametes on physiologically distinct mycelia
➢Parasexualism: A mechanism whereby recombination of
hereditary properties occurs within fungal heterokaryons
➢Anastomosis: The union of a hypha with another, resulting in
intercommunication of their genetic material.

61. Life Cycle and Disease Cycle
➢ Life Cycle: The stage or successive stages in the growth and
development of an organism that occur between the appearance and
reappearance of the same stage(e.g., spore) of the organism.
➢Disease Cycle: The chain of events involved in disease development,
including the stages of development of the pathogen and the effect of
the disease on the host.