Chemical/Microbial/Physical inducers/ Precision Agriculture/

1. George Karaoglanidis
PLANT RESISTANCE INDUCERS

2. Difficulties in controlling plant diseases
•Lack of resistance genes for many diseases
•Not possible the control of viral and many bacterial diseases with
chemical fungicides
•Fungicide resistance development
•Restrictions in the number of active ingredients with detectable
Residues
•Environmental and social restrictions for the use of chemicals
Necessity: Development and application of new
control methods for incorporation in Integrated
Disease Management schemes (IPM)

3. PLANT DISEASE RESISTANCE INDUCERS
The activation of plant defense mechanisms
with the use of natural molecules that
mimic the induction of resistance
after infection by pathogens

4. SYSTEMIC AND INDUCED AQUIRED RESISTANCE
SAR:
• Is activated by plant pathogenic organisms or chemical substances
• Salicylic Acid (SA)- mediated
• Effective mostly against biotrophic
and semi biotrophic pathogens
ISR:
• Is activated by non pathogenic
microorganisms (i.e. rhizobacteria)
• Jasmonic Acid/Ethylene (JA/ET) –
mediated
• Effective mostly against necrotrophic
pathogens

5. Recognition of the pathogen by the plant
• MAMPs/PAMPS
Microbe/Pathogen associated molecular
patterns
Molecular structures with vital role in the
biology of the microorganisms
• Flaggelin in bacteria
• Chitin in fungi
• Glycoproteins in cell walls
• carbonhydrates
• PAMPS – triggered immunity
(PTI)
SYSTEMIC AND INDUCED AQUIRED RESISTANCE

6. • DAMPs
Damage associated molecular
patterns – risk alarms associated with
the plant
The outcome of the enzymatic/toxic
activity of the pathogen on the plant tissues
i.e
• Pectin oligogalacturonases
• peptides
SYSTEMIC AND INDUCED AQUIRED RESISTANCE
Recognition of the pathogen by the plant

7. Pathogen Recognition Receptors
Receptors (proteins or kinases in the
cytoplasmic membranes of plant cells)
SYSTEMIC AND INDUCED AQUIRED RESISTANCE
Recognition of the pathogen by the plant

8. Pathogen Recognition Receptors
Signaling of recognition
• Ion efflux from the cytoplasmic
membrane
• Accumulation of ROS
• Accumulation of nitrate oxides
• Accumulation of Ca-dependent
• protein kinases
Increased activity of
transcription factors
SYSTEMIC AND INDUCED AQUIRED RESISTANCE
Recognition of the pathogen by the plant

9. Activated defense mechanisms
1. Pathogenesis related proteins (PR proteins)
2. Synthesis of phytoalexins
3. Lignification of cell walls
4. Production of ROS
5. Stomata closure
The role of the plant hormones SA, JA, ET
for the signaling of resistance induction
SYSTEMIC AND INDUCED AQUIRED RESISTANCE

10. • Effectors
Molecules that change the structure
and the functions of the host cells
facilitating the infection process
(virulence factors) or by triggering
resistance mechanisms
(avirulence factors)
Hyper-sensitivity response the most common induced mechanism of
resistance
• Effectors – triggered
immunity (ETI)
SYSTEMIC AND INDUCED AQUIRED RESISTANCE
Recognition of the pathogen by the plant

11. Plant resistance inducers
• Chemical inducers
• Plant extracts
• Microbial inducers
• Physical inducers
• Microorganisms (Biological Control)

12. Chemical inducers of resistance
Characteristics
•They do not exhibit antimicrobial activity and they are not
metabolized to substances with antimicrobial activity
•They change the response of the plant to the pathogen in the
presence of the pathogen
•They protect the plants against different pathogens (non pathogen-
specific activity)

13. Application of the inducer
3 possible outcomes
•Induction of resistance – no further response in the presence of the
pathogen
•Induction of resistance – further increase in the defense ability in the
presence of the pathogen
•Induction of resistance only after the infection by the pathogen
(Priming)
Chemical inducers of resistance

14. acibenzolar –S – methyl
•The older and better studied chemical inducer
•Structural and functional analog of SA
•Induces resistance against fungi/bacteria/viruses/nematodes
•Induces the SA pathway (SAR)
•Accumulation of PR-proteins (PR1-PR4)
•Its use is not correlated with yield reduction (if the pathogen is
absent)
Chemical inducers of resistance

15. acibenzolar –S – methyl
TSWV on tobacco
Successful applications against several pathogens
Direct antimicrobial activity in some cases
(i.e. Rhizoctonia solani)
Chemical inducers of resistance

16. Control of Psa in kiwifruit with the use of ASM
•At least 2 applications in 21 days
intervals
•Maximum number of spray
applications 6
•Initiation of spray applications after
the emergence of the leaves
•End of spray applications at the fruit set
• Combinations with copper compounds is necessary during rainy
periods
Chemical inducers of resistance

17. Lower
leaves
Medium
leaves
Upper
leaves
4 weeks before the application
Lower
leaves
Medium
leaves
Upper
leaves
4 weeks after the application
Συγκέντρωση
ιού
Συγκέντρωση
ιού
ASM reduces the concentration of CCYV and reduces or delay the appearance of
the symptoms
Application of ASM prior the
inoculation with the virus
Application of ASM after the
inoculation with the virus
Control of CCYV on mrlon with the use of ASM
Chemical inducers of resistance

18. ASM – Apple scab in the orchard
Significant reduction in the incidence/severity
of infections with the combined use of
ASM and fungicides
Chemical inducers of resistance

19. ASM – Apple scab in the orchard
Significant effect of the variety
Stronger induction of
resistance in varieties
with tolerance to the scab
Chemical inducers of resistance

20. β- aminobutyric acid
(ΒΑΒΑ)
•Non proteinaceous aminoacid
•Induces resistance against Downy mildews (Β. lactucae, P.
viticola, P. infestans)
Chemical inducers of resistance

21. •Spray application before the infections
•In some cases applications 1 day after the inoculation may
lead to hypersensitive response υπερευαισθησίας
Chemical inducers of resistance
β- aminobutyric acid (ΒΑΒΑ)

22. •Induces increased concentrations of SA
•Production of ROS (hypersensitive response)
•Production of callose around the lesions
•Indications for direct mycotoxic activity (Laeptosphaeria
maculans)
PR-proteins (PR-1, glucanases, chitinases)
Chemical inducers of resistance
β- aminobutyric acid (ΒΑΒΑ)

23. Phosphate salts (K2HPO4, K3PO4)
•Affect the permeability of the cytoplasmic
membrane and contributes to liberation of
oligogalacturonides in plant cells
•Induces increase in the SA concentration
•They have been evaluated in several
pathosystems but only in the lab
Increase of PAL and Lox
DAMPS
Chemical inducers of resistance

24. Phosphonic ions (H2PO3
-, H2PO4
-)
Increase in
-phytoalexins
-PR-proteins
Stronger cell walls (PAL)
Activates the JA/ET pathways
• Phosetyl-Al is a widely distributed commercial product
• Low direct mycotoxic activity
• Strong defence inducer
Chemical inducers of resistance

25. Probenazole
• Applications in rice crop against
Magnaporthe grisea and Xanthomonas oryzae
• Low direct mycotoxic activity (inhibition of mycelial growth or conidia
germination)
• Induces SAR
SA pathway
Increased concentrations of
PR1 and PR2
Chemical inducers of resistance

26. Resistance inducers of microbial origin
Fungal substances Chitin - Chitosan
Chitin:
• The second most common
carbohydrate in the earth
• Basic structural component of
fungal cell wall
Chitosan:
• Deacetylated derivative of chitin
• Less common structural element of
fungal cell wall

27. Chitin – one of the best characterized MAMPs
• Activates the phenylpropanoid pathway (PAL)
• PR-proteins production (peroxidases, chitinases,
thaumatins)
• Its activity is related to the size of the chain
Resistance inducers of microbial origin
Substances of fungi Chitin - Chitosan

28. Substances of fungi Chitin - Chitosan
Chitosan
• Phytoalexin production
• Increased callose in plant cell walls
• PR-proteins production (peroxidases, chitinases)
• Hypersensitive response
direct antimicrobial activity
Depends on
• Molecular weight
• Acetylation level
Resistance inducers of microbial origin

29. • Less important than chitin or chitosan
• Phytoalexin biosynthesis
• ROS production
• PR-proteins production (PR-2, PR-3, chitinases)
• Increased callose deposition
• PAL
Poly-oligo glucanes
Resistance inducers of microbial origin
Substances of fungi Poly-oligo glucanes

30. Resistance inducers of plant origin
Algae extracts
Laminarin
•Low molecular weight
β-1,3- glucane
•Natural origin (green algae Laminaria digitata)
•Induces the SA pathway (SAR) and JA/ET (ISR)
•Accumulation of PR proteins (PR1-PR4) and phytoalexins
•It does not induce hypersensitive response (HR)
•Use for the control of several diseases on pome fruit, strawberry, grapes ,
tomato, lettuce

31. •Effective protection
(≈ 60%)
•Significant reduction in post
harvest scab
•Laminarin applications should
primarily target the inhibition of secondary infections
•Spray intervals of 8-10 days
•Efficacy similar to that of protective fungicides (dithianon, captan)
Resistance inducers of plant origin
Control of apple scab with
laminarin

32. Control of olive peacock spot with
laminarin
Resistance inducers of plant origin

33. Use of inducers combinations
Aim: simultaneous induction of different signaling pathways
Increase in resistance levels
Numerous research applications of different inducers in different
pathosystems

34. Limiting factors for the use of resistance inducers
• Reduced efficacy at field level
• Crucial factors for successful applications
- host genotype
- Environmental conditions
- nutritional physiological plant status
-disease severity
• In the field lower ability for induction because plant are already in interaction
with other microorganisms
• Ability for massive production – Is this the case for all the inducers ???
In most cases stronger induction in varieties with a certain level
of resistance to the pathogen

35. Fitness cost
•The induction of resistance has a cost!!!!!
•Utilizes energy and metabolites that
otherwise could be used for the
growth of the plants
•Reductions in yield, reduction in plant
height, reduction in seed or fruit size,
Reduction in protein content
•Induction of resistance without the
presence of a pathogen may be
harmful for the plant
Limiting factors for the use of resistance inducers

36. Resistance Inducers
Can they be used in practice??
Resistance Inducers – Necessity for the incorporation in IPM programs
Against which diseases????
Easier their use against diseases that are not successfully controlled
with conventional fungicides or against diseases for which there are
no resistant cultivars οποίες δεν υπάρχουν ανθεκτικές ποικιλίες

37. Resistance inducers & fungicides : Can they be combined???
•Only rarely resistance inducers provide efficacy higher than that
provided by chemical fungicide
•Combination of inducers with conventional fungicides may increase
the control efficacy
•Use of inducers early in the season provided higher efficacy
•Lower disease incidence
•Production of less secondary inoculum
•Reduction in the total number of applications with conventional
fungicides
Resistance Inducers
Can they be used in practice??

38. Resistance Inducers – How often have to be used?
•Necessity for repetitive applications
•Reduction in the application`s efficacy 9-12 days after the application
Resistance Inducers & Biological Control: Can they be combined???
• the combined use of resistance inducers and biological control may
increase the efficacy of biological control
Resistance Inducers
Can they be used in practice??

39. The reaction to inducers depends on:
α) plant genotype
β) pathogen strain
Main aim the control of the reaction of several cultivars to different inducers
Selection of cultivars with stronger expression of
resistance
Alternatively, breeding for genes encoding stronger resistance
Resistance Inducers
Research priorities
Incorporation of mechanisms of resistance induction to breeding
programs

40. Incorporation of mechanisms of resistance induction to breeding
programs
• Which is the risk for resistance development in cultivars expressing the
introduced mechanisms?
• Is there any fitness cost in the varieties after the introduction of resistance
mechanisms?
• Which is the risk for increased susceptibility to other pathogens due to
discrepancies in the communication between different signaling pathways?
Resistance Inducers
Research priorities

41. Resistance Inducers in the era of climate change
Components of climate change
• Higher temperatures
• Changes in water availability
• Changes in Relative Humidity levels
• Increased concentrations of CO2
• Changes in the geographical
distribution of the pathogens
• Changes in the plant-microbe
interactions
• Changes in the physiological
status of the plants
(immune system)
Few research data until now
Increased variance in the results depending on the
pathosystem and the inducer under evaluation
Resistance Inducers
Research priorities

42. Resistance Inducers
Research priorities
Incorporation of resistance inducers in IPM and Precision Agriculture
schemes
Precision Agriculture
Development of tools of phenotyping disease on plants and the response of
them (remote sensing)
Development of Decision Support Systems (DSS)
On time disease diagnosis and prevision of weather conditions favoring
Disease development may optimize the use of resistance inducers

43. •New control methods are required providing satisfactory and long term
control efficacy
•Resistance inducers could play a complementary role in disease control
•Disadvantage the instability of the efficacy of resistance inducers
•Growers have to accept the lower efficacy of inducers
Applied research is a necessity to successfully incorporate resistance
inducers in the agricultural practice
Conclusions

44. Conclusions
•“Omic” applications have provided a huge amount of information
related to the activity of plant resistance inducers
•Can they be combined with applications of Precision Agriculture?
•How they will be registered for use in practice?
However there are still several questions without answer
• How they affect the microbiome of the rhizosphere or the phyllosphere?
• How they behave in a changing environment?

45. Future Research Directions