Plant pathogens secrete various toxins which causes disease to the plant host by infecting the metabolic process of the host. The toxins secreted may be Host specific or non host specific.

1. ANNAMALAI UNIVERSITY
Faculty of Agriculture
DEPARTMENT OF PLANT PATHOLOGY
PAT 032 Credit seminar (0+1)
CHAIRMA
N :
Dr. D. John Christopher
Professor
Department of Plant Pathology
MEMBERS
:
1. Dr. V. Jaiganesh
Assistant Professor
Department of Plant Pathology
2. Dr. C. Kathirvelu
Associate Professor
Department of Entomology
Presented by,
P. SABARI GRISH,
217090010
II- M.sc.,(Ag)Plant Pathology
ROLE OF TOXINS IN PLANT PATHOGENESIS AND
METHODS OF DETECTION OF MYCOTOXINS

2. TOXIN –
Ludwig Brieger (1888).
A toxin can be defined as a substance of
microbial origin involved in host pathogenesis.
They damage or
kill the host cells.
Both plant pathogenic fungi and bacteria
produces toxins during pathogenesis.
TOXINS IN PATHOGENESIS

3. Toxins are non-enzymic substances that cause harm to plant
cells or disturb their metabolism in the host.
Anton de Bary proposed the poison theory in 1886.
A toxin hypothesis states that "toxins play a causative role in
disease etiology and cell death." Sclerotinia spp. released oxalic
acid, which De Bary said was responsible for cell death.

4. • Alternaric acid, Ten toxin,
Fumaric acid, Tab toxin,
Ophiobolin, Fusicoccin
Non host
specific/Non host
selective toxin
• Victorin, AK toxin, AL toxin,
HC toxin
Host specific/Host
selective toxin

5. The toxins produced
by the bacteria are
classified as
Exotoxin Endotoxin

6. Cell wall breaks up

7. Phytotoxin
Vivotoxin
Pathotoxin
Wheeler and Luke
(1963)

8. EFFECT OF TOXINS
ON HOST TISSUES:
1. Changes in cell wall
permeability:
Cellular transport system, especially, H+/K+ exchange at
the cell membrane is affected.
Toxins kill plant cells by altering the plasma membrane
permeability.
( Singh, 2001)

9. 2. Disruption of normal
metabolic processes:
Increase in respiration due to
disturbed salt balance, opening
and closure of stomata.
Malfunctioning of enzyme system.
(Singh, 2001)

10. Interfere with the
growth regulatory
system of the host
plant.
Some toxins
inhibit root
growth.
Eg: Fusarium moniliforme causes
browning of root and restricted
development.
(Singh, 2001)
Other mechanisms

11. MODE OF ACTION
HOST
SPECIFIC
TOXINS :
1.Victorin:
Helminthosporium
victoriae
Discovered by
Meehan and
Murphy (1947)
It affects plasma
membrane
permeability.

13. 2. T- TOXIN – Helminthosporium maydis
It disrupts the
mitochondria.
T toxin bind to
inner
mitochondrial
membrane protein
(URF-13),
inhibiting ATP
synthesis.

15. 3.AAL TOXIN - Alternaria alternata f.sp. lycopersici
AAL-toxin was first
isolated by Bottini and
Gilchrist
The toxin targets the
Aspartate carbamoyl
transferase; sphinganine
N-acyltransferase
There are five types of
AAL toxins - Among
them are- sphingosine,
phytosphingosine
ALT1 gene

16. Discovered by Tanaka
(1933)
It causes damage to the
cellular membrane of
the host plant.
Targets the Sulfhydryl-
containing molecules in
membrane protein. AKT gene
4. AK Toxin: Alternaria
kikuchiana

17. 5. AM TOXIN –
Alternaria mali
Chloroplasts are the
important cellular organelles
which serve as the primary
site for AM-toxins.
AMT gene

18. 6. DESTRUXIN B – Alternaria brassicae
It inhibits vacuolar-type ATPase (V-ATPase) activity.

19. Chemical structures of the toxins produced by
Alternaria spp.

20. 7. ACR TOXIN- Alternaria alternata f.sp. citri
It acts on the
mitochondria
of the host.
ACRTS1 and
ACRTS2
genes

21. TARGET SITES OF ACTION OF HOST SPECIFIC TOXINS

22. 8.HC TOXIN – Helminthosporium carbonum
It inhibits
maize
histone
deacetylase
.

23. 9. HS TOXIN - Helminthosporium sacchari
It disrupts chloroplast,
lamellae and
plasmalemma

24. Toxins produced by the
pathogens
Host specific toxin Disease
Cochliobolus victoriae VICTORIN Victoria blight
Cochliobolus carbonum HC-TOXIN Leaf spot of corn
Cochliobolus sacchari HS- TOXIN Sugarcane leaf spot
Cochliobolus heterosporus T- TOXIN Southern corn leaf blight
Alternaria kikuchiana AK TOXIN Pear black spot
Alternaria brassicae DESTRUXIN Brassicaceae
Alternaria mali AM- TOXIN Apple spot
Phyllosticta maydis PM- TOXIN Maize leaf spot
Periconia circinata PC- TOXIN Sorghum blight
Akpaninyang, F. E., & Opara, E. U. (2017)
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25. NON HOST
SPECIFIC TOXINS :
1.Tab toxin –
Pseudomonas
syringae pv. tabaci
Also known as wild fire
toxin.
The active toxin,
Tabtoxinine inactivates
the enzyme glutamine
synthetase, resulting in
reduced glutamine levels

26. 2.CERCOSPO
RIN
Cercosporin
is a non-
host-
selective,
light-
activated
toxin.
Exposure of plant
cells and tissues to
cercosporin results
in peroxidation of
the membrane
lipids, leading to
membrane
breakdown and
death of the cells.

27. 3.TEN TOXIN – Alternaria spp.
It induces stomatal
closure and inhibits
photophosphorylation.

28. 4. FUSICOCCIN – Fusicoccum amydgali
• It induces stomata to open.

29. 5. PHASEOLOTOXIN – Pseudomonas syringae pv. phaseolicola
Toxin causes growth reduction of
newly expanding leaves,
disruption of apical dominance,
and accumulation of ornithine.
It interferes with lipid synthesis,
change the permeability of
membranes.

30. 6.OPHIOBOLIN- Bipolaris oryzae
Ophiobolin A was isolated
from the pathogenic plant
fungus Ophiobolus
miyabeanus by Nakamura
and Ishibashi in 1958 It affects phenol metabolism.

31. 7.FUSARIC ACID – Fusarium oxysporum f.sp. lycopersici
It affects photosynthesis,
membrane permeability and
transpiration.
Toxicity - Gauman et al. in
1952
Fusarium oxysporum f.sp.
lycopersici, Fusarium
oxysporum f.sp. vasinfectum,

32. 8. OXALIC ACID – Sclerotinia sclerotiorum
Oxalic acid interferes with
defense mechanisms of host
plants by inhibiting the activities
of polyphenol oxidases by
suppressing the oxidative burst.

33. Toxin producer pathogen Non host
specific toxin
Disease
Pseudomonas syringae pv.tabaci TAB TOXIN Tobacco wild fire
P.syringae pv.phaseolicola PHASEOLOTOXIN Bean blight
Erwinia amylovora AMYLOVORIN Apple fire blight
Streptomyces spp. THAXTOMINS Scab of potato
P.syringae pv.atroseptica CORONOTINE Rot of Potato
P.syringae pv.syringae SYRINGOMYCIN Bacterial canker
Ferguson, A. R., & Johnston, J. S. (1980)
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34. PATHOGEN NON HOST SPECIFIC TOXIN DISEASE
Alternaria alternata Ten toxin Leaf spot
Cercospora spp. Cercosporin Leaf spot
Rhizopus spp. Fumaric acid Rots
Magnaporthe grisea Pyricularin Rice blast
Fusarium oxysporum Fusaric acid, Lycomarasmin Wilts
Alternaria spp. Alternaric acid Leaf spot
Sclerotium and Sclerotiorum Oxalic acid Wide host diseases
Ceratocystis ulmi Ceratoulmin Dutch elm
Cochliobolus spp. Ophiobolin Grain disease
Daub, M. E., & Ehrenshaft, M. (2000)
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35. MYCOTOXINS DURING STORAGE:
1. Aflatoxins:
Aspergillus flavus
Aspergillus parasiticus
Penicillium puberulum
Penicillium islandicum
2. Ochratoxins:
Aspergillus ochraceous
Penicillium viridicatum

36. TECHNIQUES FOR DETECTING THE TOXINS PRODUCED BY PATHOGEN
HPLC
method
(Kong et al,
2013)
LC-MS
method
(Cho et al,
2018)
GC-MS
method
(Cunha et
al, 2010)
DART
method
(Busman et
al, 2015)
SWIR
technique
(Kandpal et
al, 2015)

37. HPLC

38. GC-MS

39. Direct Analysis in Real Time (DART)

41. Fluorescence polarization immunoassay (FPIA)
Zheng et al

42. COLD PLASMA:

43. MODE OF ACTION:

44. Case studies

49. CONCLUSION…