Enzymes & Pathogenesis

1. Cutinase, cellulase, and pectinase help pathogens penetrate host tissues.
2. Ligninase and protease degrade structural and defense proteins.
3. Polygalacturonase degrades pectin in plant cell walls.
4. Amylases degrade starch reserves in host cells.
5. Lipases destroy lipid membranes during infection.
6. Pectolytic enzymes are mainly involved in soft rot diseases.
7. Pectin methyl esterase converts pectin into pectic acid.
8. Cellulolytic enzymes help fungi penetrate cellulose layers of plants.
9. Oxalic acid secreted by Sclerotinia sclerotiorum aids in infection.
10. Siderophores chelate iron, helping pathogens survive in iron-deficient conditions.

Plant Defense Mechanisms

1. Phytoalexins are antimicrobial compounds produced by plants after infection.
2. Phaseollin – phytoalexin in beans; resveratrol – in grapes.
3. Gossypol – defense compound in cotton.
4. Camalexin – phytoalexin found in Arabidopsis thaliana.
5. Lignification strengthens cell walls, restricting pathogen spread.
6. Callose deposition occurs at infection sites as a mechanical barrier.
7. Phenolics have antifungal properties and enhance resistance.
8. Hypersensitive response (HR) involves programmed cell death to stop pathogen spread.
9. Systemic Acquired Resistance (SAR) is induced after a local infection and protects the whole plant.
10. Salicylic acid (SA) plays a key role in SAR activation.

Disease Diagnosis & Management

1. ELISA (Enzyme-Linked Immunosorbent Assay) is used to detect plant viruses.
2. PCR (Polymerase Chain Reaction) helps in molecular detection of pathogens.
3. Integrated Disease Management (IDM) combines biological, cultural, and chemical control methods.
4. Hot water treatment is effective against seed-borne bacterial and fungal diseases.
5. Crop rotation helps control soil-borne pathogens like Fusarium.
6. Resistant varieties provide the most sustainable disease control.
7. Sanitation (removal of infected plant debris) reduces inoculum load.
8. Soil solarization uses sunlight to sterilize soil before planting.
9. Biocontrol agents like Trichoderma viride, Pseudomonas fluorescens, and Bacillus subtilis are widely used.
10. Copper oxychloride and mancozeb are broad-spectrum fungicides.

Disease Types & Transmission

1. Seed-borne diseases – loose smut of wheat, bacterial blight of rice.
2. Air-borne diseases – rust, late blight, powdery mildew.
3. Soil-borne diseases – wilt, damping-off, collar rot.
4. Water-borne diseases – paddy blast and downy mildew.
5. Insect-transmitted diseases – leaf curl virus, little leaf of brinjal.
6. Mechanical transmission – tobacco mosaic virus.
7. Nematode-transmitted diseases – tundu disease of wheat.
8. Seed certification ensures freedom from seed-borne pathogens.
9. Vector control is essential in viral disease management.
10. Eradication of alternate host (like barberry for rust) prevents pathogen survival.