2. Introduction
Fungicides have been used for over 200 years to protect
plants against disease
With the introduction of the systemic fungicides, the
incidence of resistance increased greatly
Repeated use of the fungicide
Once it arises, resistance is heritable
Mechanism of resistance may or may not related to
fungicidal action
B. cinerea was one of the first fungi for which
resistance was described
2
3. Stable , inheritable adjustment by a fungus to
a fungicide, resulting in a less than normal
sensitivity to that fungicide
(FAO)
3
4. Resistance risk
Single site of action in the target fungus
Cross-resistance with existing fungicides
Facile generation of fit, resistant mutants
in the laboratory
Use of repetitive or sustained treatments
in practice
Extensive areas of use
Large populations and rapid multiplication
of target pathogen
No complementary use of other types of
fungicide
Lack of non-chemical control measures
4
6. 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
6
7. 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
7
8. If environmental conditions favour continued
disease activity, the surviving spores grow and
produce a new crop of spores
This spores has a higher percentage of resistant
spores
8
9. Mechanisms
Altered target site:
o A fungicide has a specific
target site where it acts
to disrupt a particular
biochemical process
o If this site altered
fungicide no longer binds
to site of action and
unable to exert its toxic
effect
9
11. Removal:
o A fungal cell may rapidly
export the fungicide
before it can reach the
site of action
11
12. Reduced uptake :
o The resistant pathogen
simply absorbs the fungicide
much more slowly than the
susceptible type
12
13. 1. Genetic variability: The fungus has spores
with the genes necessary to resist the
toxin
2. Selection: The toxin is used repeatedly
13
14. Benzimidazoles and
Thiophnates
Carbendazim
It binds to tubulins
Inhibit the assembly of microtubules and
formation of spindle
Leads to general disturbance of cellular
function
Eg: Benomyl resistance in cucumber
powdery mildew
14
15. Mutation - at loci ben A, ben B, ben C
Changes in tubulin structure which enables
microtubule to function in the presence
of benzimidazoles
15
16. Carboxamides
Vitavax, plantvax, calirus, panorm, basizac
Seed treatment- cereals
Leaf rust
Site of action – mitochondria
Interferes with respiration by specific inhibition of
succinate
Resistance –
chrysanthemum rust
Ustilago mydis
Mutation - change at the target site in the succinate
dehydrogenase complex
16
17. Phenylamide
Metalxyl, furalaxyl, benalaxyl
systemic activity against oomycetes
Inhibition of the RNA polymerase enzyme
Ribosomal RNA is selectively inhibited
Metalaxyl resistance- Phytophothora infestans
Mutation – uridine incorporation into RNA
Chandge in target site
17
19. Organophosphorus
Pyrazophos, edefenphos, kitazin P
Metabolite of pyzarophos is the fungitoxic
principle
Resistance- inability of the strains to
convert pyrazophos to toxic compound
Rice blast(Pyricularia oryzae) in japan
19
21. The type of fungicide
1. Monogenic or polygenic resistance
Monogenic- develops in one step
Highest level of resistance
More than one locus involved
Polygenic- many mutant genes are
required
21
22. 2.Fitness of resistant strains
Genetic changes in sensitive cell influence
other characteristics of the cell
Strains with lower fitness will be less
competitive
Slow down the build up of a resistant
pathogen population
22
23. Nature and life cycle of the pathogen
Build up will be faster in heavily
sporulating pathogen on aerial parts
Late blight (Phytophthora infestans) faster
than avocado root disease(P.cinnamomi)
23
24. Selection pressure by the fungicide
Continuous high selection pressure favour
build up of resistant population
High doses of fungicide, frequency,
method of application , persistence of the
fungicide
Environmental factors
24
25. Management
Do not use the product exclusively
Apply it as a mixture with one
More fungicides of a different type
As one component in a rotation or
alternation of different fungicide
treatments
25
26. Use other fungicides both beforehand and
subsequently
Reduces the total number of applications
of the at-risk fungicide
slow down selection to some extent
It can favour decline of resistant strains
that have a fitness deficit
26
27. Restrict the number of treatments applied
per season, and apply only when strictly
necessary
Maintain manufacturers’ recommended
dose
Avoid eradicant use
Integrated disease management
Chemical diversity
27
28. FARC
In 1994 the Fungicide Resistance Action
Committee (FRAC)
FRAC is a Specialist Technical Group of
CropLife International
To provide fungicide resistance
management guidelines to prolong the
effectiveness of "at risk" fungicides and to
limit crop losses
28
29. Reference
Altman, J., 1993. Pesticide Interactions In
Crop Production- Beneficial And
Deleterious Effects. Boca raton ann arbor.
London
Brent , K. J. and Holloman, W. D., 2007.
Fungicide Resistance In Crop Pathogens:
How Can It Be Managed?. FARC
29
Editor's Notes
This means that they were lucky enough to be in a microsite that was not treated with fungicide
because the resistant spores preferentially survived the fungicide treatment