Host Plant Resistance against Pathogens

1. Department of Entomology and Agricultural Zoology
Institute of Agricultural Sciences
Banaras Hindu University
Presented by:
Mamoon Rasheed
M.Sc. (Ag.) Prev
Department of Mycology and Plant Pathology

2. • Disease resistance is the ability of a plant to prevent, restrict, or
retard disease development, and occurs at high, moderate, or
low levels.
• Capabilities of plants to dissuade the adversaries depend a
great deal on the preformed structures and pathogen induced
responses.
• These are
• Passive Defence
• Active Defence
Introduction
Source : Santaram, Akundi. (2000). Biochemical and Molecular Aspects of Disease Resistance in Plants. Geobios.
27. 205-216.

3. • The Cuticle : Cutin and waxes together comprise the cuticle
• Carbohydrate Appositions : the resistant host responds by
synthesizing new carbohydrates, particularly callose and cellulose
• Gels and Tyloses : Vascular gels coat the walls and fill the infected
vessels in numerous plant species infected with fungi
• Structural Proteins : b-proteins of tobacco
Passive Defense

4. • Phytoalexins
• Protein synthesis inhibitors
• PR Proteins
• Tannins and melanins
Active Defense

5. • Ribosome inactivating proteins found in the seed extracts
are known to prevent protein synthesis
• They act on the large ribosomal subunit to inactivate the
ribosome to carry out the polypeptide chain elongation
Protein synthesis inhibitors
Source : Jimenez, A., and D. Vazquez. "Plant and fungal protein and glycoprotein toxins inhibiting
eukaryote protein synthesis." Annual review of microbiology 39.1 (1985): 649-672.

6. • These antibiotics, produced after infection, include a variety of natural
compounds:
• Isoflavonoids, Flavonoids
• Dihydrophenanthrenes
• Stilbenes
• coumarins, isocoumarins
• Terpenoids
• furanoacetylenes, polyacetylenes, and polyenes.
Phytoalexins
Source : Ingham, J. L., Harhorne, J. B. 1976. Phytoalexin induction as a new dynamic approach to the study of
systematic relationships among higher plants. Nature 260:241-43

7. Phytoalexins
Source : Ingham, J. L., Harhorne, J. B. 1976. Phytoalexin induction as a new dynamic approach to the study of
systematic relationships among higher plants. Nature 260:241-43

8. • Necrosis associated with race-specific resistance normally is characterized by the
formation of brown to black pigments (melanin) throughout the cell walls and the
collapsed protoplasts.
• Melanins in plants are formed principally from various ortho-dihydroxyphenolic
compounds
• The enzymes polyphenoloxidase (PPO) and peroxidase (PO) oxidize the colorless
dihydroxyphenols to give the colored ortho-quinones
Production of tannins and melanins
Source : Mayer, A. M., Harel, E. 1979. Review: polyphenol oxidases in plants. Phytochemistry 18:193-215

9. • Proteins encoded by the host plant but induced only in
pathological or related situations, the latter implying situations of
non-pathogenic origin
• PR 2 : Shows β-1,3-glucanase activity
• PR 3 :Shows Chitinase activity
• PR 12 : Plant defensins
PR Proteins
Source : Edreva, A. (2005). Pathogenesis-related proteins: research progress in the last 15 years. Gen Appl Plant
Physiol, 31(1-2), 105-24.

10. PR2 Mode of action
β-1,3-glucanases are involves in hydrolytic cleavage of the 1,3-β-D-glucosidic linkages in β- 1,3-
glucans, a major componant of fungi cell wall. So that cell lysis and cell death occur as a result
of hydrolysis of glucans present in the cell wall of fungi.

11. • Cleaves the cell wall chitin polymers , resulting in a weakened cell wall and
rendering fungal cells osmotically sensitive
• These Chitinases have Significant antifungal activities against plant
pathogenic fungi like
• Alternaria sp.
• Bipolaris oryzae for brown spot of rice
PR3 Mode of action
Source : Nejad, M. S., Bonjar, G. H. S., & Dehkaei, F. P. (2014). Control of Bipolaris oryzae the causal agent of rice
brown spot disease via soil Streptomyces sp. isolate G. International Journal of Advanced Biological and Biomedical
Research, New Delhi, 2, 310-317.

12. PR12 Mode of action
Source https://www.macmillanhighered.com/BrainHoney/Resource/6716/digital_first_content/trunk/test/hillis2e/hillis2e_ch28_2.html

13. Conclusion
• These play important role in disease resistance and also help the plant to adapt to the
environmental stress.
• The increasing knowledge about the these gives better idea regarding the development
and defense system of plants.
• Primary aspects of the gene regulation of the biochemical factors are understood but the
study of exact mechanism of gene regulation and receptor cascade will open new ways
for the plant genetic engineering technology for crop improvement.