1. Plant defense mechanisms

2. Whatever concerns plant defense or resistance, it is controlled by genes of the plant and pathogen

3. Nonhost resistance The most common case:
Apple tree cannot be infected by pathogens specific to tomato and vice versa

4. Partial, polygenic, quantitative or horizontal resistance
Result of more or many minor genes
Present in all plants
Different levels against different pathogens
Basically against necrotrophic or semibiotrophic pathogens as Botrytis, fusarium, sclerotinia etc.

5. Race-specific, monogenic or vertical resistance
Result of one major gen
Usually against biotrophic pathogens as downy mildews, powdery mildews and rusts
Gen to gen theory

6. Preexisting structural defense
Wax, cuticle, structure of cell wall, stomata and lenticels, presence of thick-walled tissues (sclerenchyma) etc.

7. Preexisting chemical defense
Released into environment:
Fungitoxic exudates, phenolic compounds (eg. Red and yellow onion cannot be infected by smudge, whereas white one can be infected because of lacking catechol), coumarins

9. Preexisting chemical defense
Inhibitors in plant cells before infection:
tannins, catechin, saponins (eg. Tomatine, avenacine), low molecular proteins – phytocystatins, lectins, glucanases and chitinases contained in surface cells

10. Defense through lack of essential factors
Lack of recognition between host and pathogen
Lack of host receptors and sensitive sites for toxins
Lack of essential substances for the pathogen

11. Induced structural and biochemical defenses

12. Induced structural and biochemical defenses
Recognition of the pathogens by the host plant:
- Pathogen elicitors
Host plant receptors
=> Mobilization of defenses and transmission of alarm signal

13. Induced structural defenses
Cytoplasmic defense reaction
Cell wall defense structures

14. Cell wall defense structures

15. Induced structural defenses - Histological defense structures:
Cork layers

16. Induced structural defenses - Histological defense structures:
Cork layers

17. Induced structural defenses - Histological defense structures:
Tyloses
Deposition of gums

18. Induced structural defenses - Histological defense structures:
Abscission layers

19. NECROTIC STRUCTURAL DEFENSE REACTION

20. NECROTIC STRUCTURAL DEFENSE REACTION

21. HYPERSENSITIVE REACTION

22. INDUCED BIOCHEMICAL DEFENSES
ACTIVE OXYGEN SPECIES: SUPEROXIDE (O -2), HYDROGEN PEROXIDE (H2O2) AND HYDROXYL RADICAL (OH)

23. INDUCED BIOCHEMICAL DEFENSES
REINFORCEMENT OF HOST CELL WALLS BY
CALLOSE
GLYCOPROTEINS (EXTENSIN)
PHENOLIC COMPOUNDS (SUBERIN, LIGNIN)
MINERAL ELEMENTS (SILICON, CALCIUM)

24. INDUCED BIOCHEMICAL DEFENSES
PRODUCTION OF ANTIMICROBIAL SUBSTANCES IN ATTACKED CELLS:
PATHOGENESIS RELATED PROTEINS

25. INDUCED BIOCHEMICAL DEFENSES
PRODUCTION OF SECONDARY METABOLITES:
PHENOLIC COMPOUNDS LIKE CHLOROGENIC ACID, CAFFEIC ACID AND FERULIC ACID
PHENOL OXIDIZING ENZYMES – QUINONES (MORE TOXIC THAN ORIGINAL COMPOUND)

26. INDUCED BIOCHEMICAL DEFENSES
PRODUCTION OF SECONDARY METABOLITES:
PHYTOALEXINS – PHASEOLIN, PISATIN, GOSSYPOL, CAPSIDIOL ETC.
ELICITORS OF PHA ARE RELEASED FROM PATHOGEN CELL WALL BY HOST ENZYMES OR PRODUCET BY HOST CELL ITSELF

27. DETOXIFICATION OF PATHOGEN TOXINS BY PLANTS
E.G. HC TOXIN, PYRICULARIN

28. IMMUNIZATION OF PLANTS AGAINST PATHOGENS
PLANTIBODIES

29. SYSTEMIC ACQUIRED RESISTANCE

30. DEFENSE THROUGH GENETICALLY ENGINEERING DISEASE-RESISTANT PLANTS
PLANT-DERIVED GENES:
E.G. Hml GENE FOR ENZYME INACTIVATING HC TOXIN
GENES ACTIVATED BY AVR GENES OF PATHOGENS
ANTIVIRAL GENES

31. DEFENSE THROUGH GENETICALLY ENGINEERING DISEASE-RESISTANT PLANTS
PATHOGEN-DERIVED GENES
SEE VIROLOGY
GENE FROM ASPERGILLUS NIGER FOR H2O2 GENERATING GLUCOSE OXIDASE INCREASES RESISTANCE AGAINST P. INFESTANS, A. SOLANI

32. DEFENSE THROUGH GENETICALLY ENGINEERING DISEASE-RESISTANT PLANTS
PATHOGEN-DERIVED GENES
T4 GENE FOR LYSOZYME DEGRADING CELL WALL OF SOME BACTERIA AND FUNGI
GENE FOR CHITINASE FROM T. HARZIANUM AGAINST APPLE SCAB

33. RNA SILENCING