6. Localized symptoms
(in a particular part of the plant)
leaf blight
(death of cells in restricted areas)
(death of cells: not restricted)
leaf spot
bacterial canker
7. (Death of cells and tissues)
dry rot: fungi
Rots
soft rot: bacteria
anthracnose
22. Diagnostic Techniques
1. Visual inspection of symptoms
2. Microscopic examination
3. Isolation for pure culture of pathogen
and Identification of pure culture
4. Biochemical & physiological methods
5. Nucleic acid-based methods
(molecular methods)
29. • Transmission test
• Indicator plant
• Serology
• Electron microscope
• Nucleic Acid, DNA
Virus and phytoplasma
30. Nematode Damage
root knot (gall)
Nematodes in
stained root
Symptom, Population density in soil & root
poor growth
31. Principles of Plant Disease Control
1. Reducing Initial Inoculum
2. Reducing Rate of Development
32. Reducing Initial Inoculum
Exclusion - no introduction of pathogen
Eradication - eliminate pathogen
inoculum
Therapy - eliminate pathogen from living host
33. Reducing Rate of Development
(To Slow Rate of Increase)
• Host resistance - horizontal resistance
• Protection - protect the host from infection
• Avoidance - avoid contact of host and
pathogen under conditions favorable for
disease
34. Reducing Rate of Development
Avoidance
Avoid putting host & pathogen in contact with
one another under a favorable environment
A. Geographic Selection
B. Site Selection
C. Environmental Management
D. Cultural Practices
– Planting/Harvest dates
– Short season cultivars
– Cultivation practices, plant spacing
– Irrigation management, fertility management
35. Reducing Rate of Development
Protection
A. Biological control
– Antagonistic organisms (Streptomyces, Bacillus,
Trichoderma, Paecillomyces, Verticillium)
– Cross protection (inoculate mild strain to induce
resistance for virulent strain of pathogen)
B. Chemical control
– Protectant, Eradicant
– Contact, systemic pesticides
– Fungicides, bactericides, nematicides
