Fungicide resistance

1. Fungicide
Resistance
Speaker: Sudarshna Negi

2. Fungi are small, microscopic
eukaryotic, usually filamentous,
branched, spore bearing
organisms that lack chlorophyll
and Cell wall contains chitin
and glucan as the skeletal
components includes
mushrooms, molds and yeasts
Fungi

3. Fungal pathogen of plants
A wide range of
fungi cause
diseases of plants
to be classified as
fungal pathogen
or phytopathogen.
Fungi cause local
or general necrosis
of plant tissue,
they often cause
reduced growth of
plants.
E.g. Botrytis cinera
cause gray mold rots
on many plants.
Penicillin, cause blue
mold and rots

4. symptoms caused by fungi
Spots: localized lesion on host leaves
e.g., Mycosphaerella musicola cause
banana leaf spot
Scab: Localized lesion of scabby
appearance on host fruite.g.,
Venturia inaequalis cause apple scab
Blight: Browning of leaves,
branches, twigs e.g., Late blight of
potato caused by Phytophthora
infestens

5. Mildew: Area on leaves, stem,
blossoms and fruits covered with
whitish mycilium e.g., Plasmopara
viticola cause mildew of grape
Canker: Necritic lesion on the
stem or fleshy organ e.g.,
Botryospheria dothia cause
canker on peach
Rust: Many small lesion on
leaves or stem, usually of rusty
colour.e.g., Puccinia graminis
cause yellow rust of wheat

7. Disease Cycle

8. Diseases are a major
source of crop and plant
damage that can be
caused by a number of
plant pathogenic
(disease-causing)
organisms. Fungi are
the number one cause
of crop loss worldwide

9. Fungicides
A fungicide is a specific type of pesticide that
controls fungal disease by specifically
inhibiting or killing the fungus causing the
diseases.
Benzimidazoles
Phenylamide
Organophosphorus
Carboxamides
Thiophnates,
, Demethylation
Inhibitors (DMI)

10. History of Fungicide
“Development" of the first fungicide was the
result of good observations.
The first use of brining of wheat grain with
salt water followed by liming took place in
the middle of the 17th century to control
bunt, and followed the observation that
grains of wheat was free of bunt.
In France in 1882 by Millardet, noticed that grape vines
that had been sprayed with a bluish-white mixture of
copper sulfate and lime, retained their leaves through the
season, whereas the unsprayed vines lost their leaves.
After numerous spraying experiments Millardet concluded
that a mixture of copper sulfate and hydrated lime could
effectively control downy mildew of grape.

11. Classification Of Fungicides
Protectant
• Donot penetrate the plant, but affect pathogen viability
and Germination on the surface of the host plant.e.g.,
mancozeb and coppers
Systemic
• Act on the plant surface and be translocated throughout the
pant vascular system to kill the fungus.e.g., Mefenoxam
Eradacative
• They are applied post-infection and act on contact by killing the
organism or by preventing its further growth and reproduction
e.g.,Lime sulfur
Translaminar.
• These compounds move into and through the leaf but do not move as
readily in the transpiration stream.e.g.,strobilurin

13. Why are Fungicides Needed?
To control a disease
during the establishment
and development of a
crop.
To increase productivity
of a crop and to reduce
blemishes.
To improve the storage
life and quality of
harvested plants and
produce.
Pesticide Usage in India

14. Fungicide Resistance?
Resistance: A
stable, heritable
trait that results in
a reduction in
sensitivity to a
fungicide by an
individual
Practical resistance:
labeled rates of a
fungicide no longer
provide
commercially
acceptable control
of a disease

15. How Does Resistance Occur?
Origin: rare genetic mutation(s) that alter the
target site in the fungus to block the action of
the fungicide
Natural selection: fungicide causes selection
of the fittest (resistant) individuals
Resistant individuals are more likely to survive to
reproduce
When the fungus reproduces, resistant
individuals pass on the mutation

17. Types Of
Resistance
Qualitative
resistance
Quantitative
resistance
Cross-
resistance
Negative
cross
resistance

18. Qualitative resistance: sudden loss of control
Resistance results from a single mutation in one gene

19. Quantitative resistance: gradual reduction in control
Resistance results from mutations in several genes that interact

20. • when a pathogen resistant to
one fungicide exhibits
resistance to other fungicides in
the same chemical class, even
without exposure
Cross-
resistance
• whindependently en a
pathogen develops resistance
to fungicides in different
chemical classes
Negative
cross
resistance

21. Basic process of Resistance
development
Resistance can only develop in spore populations where there is
the genetic potential to resist the disease
Resistant spores occur at extremely low numbers
When a fungicide spray is applied some of the sensitive spores also survived,
because they “escaped” the fungicide treatment
This can result from incomplete spray coverage
If environmental conditions favors continued disease activity, the surviving
spores grow and produce a new spores
This spores has a higher percentage of resistant spores

22. Build up of resistant pathogen
population

23. Mode of action
Fungicides inhibit
fungal growth by
interfering with
critical cellular
processes. Mode of
action (MOA) refers to
the specific cellular
process inhibited by a
particular fungicide.
There are specific sites of
action, these sites of
action or target sites are
the specific enzymes in a
cellular process to which
the fungicides are
binding.
e.g., both strobilurin
fungicides and SDHI
fungicides share the
same MOA (inhibition
of respiration) but
have different sites of
action in the
respiratory pathway;
SDHI’s inhibit complex
II while strobilurins
inhibit complex III.

24. Single and Multiple Site Mode of Action

25. Altered target site:
• A fungicide has a
specific target site
where it acts to
disrupt a particular
biochemical process
• If this site altered
fungicide no longer
binds to site of
action and unable to
exert its toxic effect

26. Detoxification or metabolism:
• Metabolism within the
fungal cell
•Detoxify a foreign compound
such as fungicide
Removal:
• A fungal cell may rapidly
export the fungicide before it
can reach the site of action

27. Reduced uptake :
• The resistant pathogen
simply absorbs the fungicide
much more slowly than the
susceptible type

28. HOW much more?
Depends on...
Fungicide and
its target site
Characteristics
Of target fungi
and disease

29. • It binds to tubulin and Inhibit the assembly of
microtubules and formation of spindle
• resistance in cucumber powdery mildew
Benzimidazoles
and Thiophnates
•
• Site of action – mitochondria
• Resistance – chrysanthemum rust Ustilago
mydis
Carboxamides
• systemic activity against oomycetes
• Resistance- Phytophothora infestans
Phenylamide
Examples of Fungicides That Become Resistance

30. Case study
Laura E. Hayes and Kathryn E. Sackett, (2016) Zymoseptoria
tritici, causal agent of Septoria tritici blotch, is a major fungal
pathogen of wheat that has evolved resistance to chemical
control products in four fungicide classes in Europe. resistance
to strobilurins conferred by the G143A mutation occurred over
the course of a single growing season of Z. tritici.
S. Rupp et al 2017 Botrytis cinerea causes pre- and
postharvest decay of many fruit and vegetable crops. Isolates
of B. fragariae were detected in strawberry fields throughout
Germany, sometimes at frequencies similar to those of B.
cinerea, B. fragariae strains showed resistance to one or
several chemical classes of fungicides and an efflux-based
multidrug resistance (MDR1)

31. Mitchell Bauske 2017 Resistance to chemistries of the succinate dehydrogenase
inhibiting (SDHI) and quinone outside inhibiting (QoI) fungicides has
developed rapidly in populations of Alternaria solani, the cause of early blight
of potato. Reduced sensitivity to the anilinopyrimidine (AP) fungicide
pyrimethanil has also been identified recently, determining that resistance to
three chemical classes of fungicides is present within the A. solani population.
Villani and Sara 2016: Apple scab, caused by the fungal
pathogen Venturia inaequalis the highly specific nature and
repetitive use of fungicides has led to their diminished efficacy
and widespread resistance in V. inaequalis. The identification of
the prevalence of single-site resistance in populations of V.
inaequalisthe results of this dissertation contribute to the
identification and understanding of mechanisms associated with
single-site fungicide resistance in V. inaequalis.

32. Management Of Resistance
• Under-application can lead to fungal pathogens that
are not fully controlled, leading to a greater chance of
survival and adaption of the disease.
Apply the
correct
rates
• Multi-site mode of action fungicides have low
resistance risk and thus play an important role in
resistance management for the single-site mode of
action fungicides.
Multi-site
MOA

33. • Follow the manufacturer’s directions on
best use and maintain application limits
during each season/year. Following best
practice guidelines for a number of
consecutive applications will help reduce
resistance development.
Restrict
use
• The use of preventative application
maintains a much lower pathogen
population. The reduced numbers of
pathogens limits the opportunity of a
natural mutations that lead to resistance
development.
Preventatiave
applications

34. Microbes In Management
• Bacillus-based biological control agents (BCAs) have great potential
in integrated resistance management.
• Use of Bacillus based BCAs with disease management tools,
including resistant cultivars, fungicides or bactericides, or other
BCAs.
• Integration of BCAs with other disease management tools often
provides broader crop adaptation and both more efficacious and
consistent levels of disease control.
• The Bacillus-based BCAs use in fungicide resistance management

35. Use of Bacillus-based BCAs in fungicide
resistance management.
• Bacillus-based BCAs have modes of action
different from that of synthetic chemical
fungicides, it is logical that they can be used in
fun
• By using different modes of action, The BCA
contributed to a fungicide resistance
management

36. Conclusion
• Resistance is the evolutionary response of a
fungus to a threat to its survival: the fungicide
• Fungicides that act at a single site are more prone
to resistance development
• How quickly resistance will develop, and how
much control will be lost, depend on both the
fungicide and the target fungus
• Resistance to most newer fungicides will occur,
but we can prolong their effective life by careful
use