this ppt will be useful to agricultural students

1. WELCOME…

2. Mesobiotic
Virus
Viroid
Virusoid
Abiotic
Nutrient Deficiency
Environment
Biotic
Fungi
Bacteria
Fastidious Vascular Bacteria
Phytoplasma
Spiroplasma
Algae
Phanerogamic Parasites
Causes of Plant Diseases

3. 1. FUNGI
Eukaryotic,
Achlorophyllous
Sexually and (or) asexually reproduced,
filamentous-branched somatic structures
surrounded by cell wall containing cellulose or
chitin.
2–10 µm in diameter and up to
several centimeters in length.

4. 2. BACTERIA
Microscopic,
Unicellular prokaryotes
Lack chlorophyll
Smaller than fungi
commonly multiplying asexually by fission
Majority of them are saprophytes.
1 to 2 microns in diameter and 5
to 10 microns long.

5. Protozoa
Single-celled eukaryotes,
Either free-living or parasitic,
Heterotrophic.
Obtain food by absorption

6. Protozoan disease
Plasmodiophora brassicae
(Endoparasitic slime mould)
Clubroot of Cabbage

7. 3. Fastidious vascular bacteria (Rickettsia-like bacteria
– RLB / Rickettsia-like organism – RLO)
Typical Gram-negative bacteria
Fastidious in their nutritional requirements,
Refusing to grow on routine bacteriological media.
They have a cell wall unlike MLO and spiroplasma.
MLO is restricted to phloem tissues where as RLB are
restricted mostly to xylem or phloem.
They reproduce by binary fission.

8. Transmission
Insect vector
Nematode (Xiphinema index) (yellow disease of
grapevine)
Mechanical inoculations (Pierce's disease of
Grape)
vegetative propagation
Penicillin is effective against RLB.
The RLB can be divided into three groups.
i. Xylem-limited RLB ii. Phloem-limited RLB
iii. Non-tissue restricted RLB

9. i. Xylem-limited RLB (Xylella fastidiosa)
Elongated cells of 0.2 to 0.5 into 1.4 m size
Well defined cell wall and plasma membrane
Both are triple layered in structure
Susceptible to tetracyclines but not to penicillin.
E.g., Pierce's disease of grapevine.
(Davis et. al., 1981).

10. ii. Phloem-limited RLB
Rigid rods and Gram-negative (0.2-0.5 into 1.2-1.6
m size)
 sensitive to penicillin.
Transmission is by leafhoppers, dodder and
grafting. Citrus greening - citrus psyllid
iii. Non-tissue restricted RLB
Found in parenchyma and meristematic cells.
e.g.Yellows of grapevine.
It is transmitted by a nematode, Xiphinema index.

11. Citrus greening
Citrus greening
Citrus greening
Phloem-limited FVB
Citrus Psylla-
Diaphorina citri

13. 4. PHYTOPLASMA
They lack cell wall, are bounded by a unit membrane.
They are pleomorphic.
 They have fried egg appearance of colony.
They have both DNA and RNA.
They are mostly transmitted by leafhoppers.
They are insensitive to penicillin and
sensitive to tetracycline.
e.g. Phyllody of sesame, little leaf of brinjal

14. 500 nm in diameter.

15. Little leaf of brinjal
Phytoplasma

16. 5. SPIROPLASMA
Helical, wall-less prokaryotes
Requiring cholesterol for growth
Cause diseases in plants, insects and rats.
They are insensitive to penicillin and sensitive to
erythrocin and tetracycline.
e.g. Corn stunt, Citrus stubborn

17. 5. SPIROPLASMA
100 to 240 nanometers or larger in diameter

18. 6. VIRUS
Ultramicroscopic,
Nucleoprotein entities,
Infectious agents
Obligate parasite
20–200 nm in diameter in size
They have only one type of nucleic acid viz.,
either RNA or DNA.
Matured virus particles - Virions
Most of the plant virus is having RNA. E.g. TMV.
Few viruses contain DNA.
E.g. Cauliflower mosaic virus, banana bunchy top virus.

19. Cassava Mosaic Disease

20. 7. Viroids
Small, single-stranded, circular RNA particles
 Minivirus
 They do not have a capsid or outer envelope, but,
as with viruses, can reproduce only within a host cell.
They produce only a single, specific RNA molecule.
 Size 220 and 450 nucleotides
E.g. Potato spindle tuber, Chrysanthemum stunt,
Coconut cadang cadang

21. Viroids

22. Virusoids are circular single-stranded RNA(s)
dependent on viruses for replication and
encapsidation.
The genome of virusoids consist of several hundred
(200–400) nucleotides and does not code for any
proteins.
Virusoids are essentially viroids that have been
encapsulated by a helper virus coat protein.

23. 8. ALGAE
Eukaryotic, unicellular or multicellular
organisms and mostly occur in aquatic environments.
Some algae thrive as terrestrial or subterranean algae.
1.0mm to many cm in length.
They contain chlorophyll and are photosynthetic.
Asexual and sexual processes.
The study of algae is called phycology or algalogy.

24. 9. PHANEROGAMIC PARASITES
Phanerogamic parasites are flowering plants or
seed plants, which lead a parasitic life on other living
plants.
Semi or partial parasites – Partially depend on plants
Holo or total parasites – Totally depend on plants
Classification based on their mode of parasitism:
1. Stem parasite
Total stem parasite – Dodder (Cuscuta)
Partial Stem Parasite – Loranthus (Dendrophthoe)
2. Root parasite
Total Root parasite – Broom rape (Orobanche)
Partial Root Parasite – Witch weed (Striga)

25. Total stem parasite - Dodder (Cuscuta sp)

26. Partial Stem Parasite – Loranthus (Dendrophthoe sp)

27. Total Root parasite – Broom rape (Orobanche sp)

28. Partial Root Parasite – Witch weed (Striga sp)

29. Striga densiflora Striga asiatica

30. Non-parasites or Abiotic agents: These are also called as non-
infectious or physiological disorders. These diseases occur because
of disturbances in the plant system by the improper environmental
conditions. They are listed below.
i. Too low or too high temperature
ii. Lack or excess of soil moisture
iii. Lack or excess of light
iv. Lack of oxygen
v. Air pollution
vi. Mineral deficiencies or toxicities
vii. Soil acidity or alkalinity
viii. Toxicity of pesticides (Iatrogenic)
ix. Improper agricultural practices.

31. Koch’s postulates
1. Association
Pathogen must show constant association with
disease
2. Isolation
The microorganism must be isolated from
diseased host
3. Inoculation
The microorganism should be inoculated
(injected) in healthy plants
4. Re- isolation
The artificially produced disease should yield
the same microorganism on re-isolation

32. Thank you …