Summary of "Curso de Fitopatología: Clase 2. Enfermedades monocíclicas y policíclicas."

Summary of Curso de Fitopatología: Clase 2. Enfermedades monocíclicas y policíclicas

Main Ideas and Concepts

1. Introduction to Epidemiology and Disease Physiology in Plants

Epidemiology (Epi-physiology) studies the temporal and spatial changes during the development of plant diseases.
It covers how inoculum arrives, infects, colonizes, disperses, and produces symptoms in plants.
Understanding disease behavior is fundamental for effective disease management.

2. Disease Measurement: Incidence and Severity

Incidence
- The proportion (%) of visibly diseased units (plants, leaves, fruits) over the total units evaluated.
- Units must be consistent (e.g., leaves over leaves, plants over plants).
- Incidence is easy to measure and has low observer variability.
- Example: 7 diseased plants out of 100 = 7% incidence.
Severity
- The proportion (%) of affected tissue area over the total tissue area.
- More complex to measure due to observer variability.
- Requires training and use of severity scales or diagrams for consistency.
- Severity scales help standardize assessments among different evaluators.

3. Disease Dynamics and Classification: Monocyclic vs. Polycyclic Diseases

Diseases are generally grouped into monocyclic and polycyclic based on their infection cycles per crop cycle.

Monocyclic Diseases

Caused mainly by soilborne pathogens affecting roots and stem bases.
Pathogens have low dispersal capacity (limited movement in soil).
Disease appears in localized patches in the field.
Do not produce secondary inoculum during the crop cycle; only one infection cycle per crop.
Management focuses on:
- Preventing initial inoculum introduction into the field.
- Reducing inoculum in soil before planting (crop rotation, soil solarization, biological control).
- Using healthy seeds and disinfecting tools and equipment.
- Genetic resistance is highly recommended.
Once a plant is infected and shows symptoms (e.g., wilting), no curative treatment is possible.
Examples: Fusarium wilt, Sclerotinia diseases, some root rots.

Polycyclic Diseases

Affect mainly aerial parts: leaves, stems, flowers, fruits.
Pathogens produce large amounts of secondary inoculum (e.g., rust pustules producing thousands of spores per day).
High dispersal capacity through wind, rain, and vectors.
Disease spreads rapidly and extensively in the field, often beyond initial patches.
Management focuses on:
- Reducing or stopping the number of secondary infection cycles during the crop.
- Chemical, biological, or cultural controls to interrupt pathogen reproduction and dispersal.
- Reducing initial inoculum is important but controlling secondary cycles is critical.
- Genetic resistance remains a primary tool.
Examples: Wheat rusts, potato late blight (Phytophthora infestans), downy mildew, powdery mildew.

4. Disease Progress Curves

Monocyclic disease curve: Disease increases slowly, directly related to the amount of initial inoculum. No exponential increase since no secondary cycles occur.
Polycyclic disease curve: Disease increases exponentially due to multiple secondary infection cycles. Management aims to flatten this curve by interrupting secondary cycles.
Examples are illustrated with graphs showing disease incidence over crop cycle time.

5. Case Studies and Examples

Sclerotinia diseases showing monocyclic behavior despite affecting aerial parts (due to lack of secondary inoculum).
Wheat seed-borne diseases that infect systemically but do not produce secondary inoculum during the crop cycle.
The Irish Potato Famine as a historical example of a devastating polycyclic disease outbreak caused by potato late blight.
The importance of integrated management combining preventive measures, genetic resistance, and timely interventions.

6. Practical Recommendations for Disease Management

For monocyclic diseases:
- Prevent pathogen entry and reduce soil inoculum.
- Use crop rotation, soil treatments, biological controls, and healthy seeds.
- No curative treatments once symptoms appear.
For polycyclic diseases:
- Early detection and timely application of fungicides or biocontrol agents to reduce secondary inoculum.
- Use resistant varieties and cultural practices to reduce disease spread.
- Continuous monitoring and multiple interventions may be necessary.

7. Final Notes

These concepts are generalities; exceptions exist and disease-specific knowledge is essential.
Genetic resistance is the most effective and sustainable management strategy for both disease types.
The speaker encourages proper disease quantification and understanding disease dynamics to inform management decisions.

Methodology / Instructions for Disease Assessment and Management

Disease Sampling and Incidence Calculation
- Sample plants/leaves/fruits randomly and consistently (e.g., zigzag pattern).
- Count total units and visibly diseased units.
- Calculate incidence = (Number of diseased units / Total units) × 100.
Severity Assessment
- Use severity scales with reference diagrams for affected tissue percentage.
- Train evaluators to standardize severity estimation.
- Assign severity values based on comparison with scale examples.
Monocyclic Disease Management
- Avoid introduction of primary inoculum.
- Reduce soil inoculum via:
  - Crop rotation (several years if needed).
  - Soil solarization.
  - Biological control (e.g., Trichoderma spp.).
- Use healthy seeds and disinfect tools and equipment.
- No chemical cure once plants show symptoms.
Polycyclic Disease Management
- Reduce initial inoculum by using healthy seeds and crop rotation.
- Monitor disease incidence regularly.
- Apply fungicides or biocontrol agents to reduce secondary inoculum production and dispersal.
- Use resistant cultivars.
- Implement cultural practices to reduce disease spread (e.g., spacing, pruning).

Speakers / Sources Featured

Nicolás Escarlo Agricultural Engineer and creator of the “Academic Phytopathology” page; main presenter and lecturer in the video.
References Mentioned:
- Fernández Valiela (author of phytopathology bibliography).
- Other unspecified phytopathology books and scientific sources (listed at the end of the video).

This summary captures the key teaching points on plant disease epidemiology, disease measurement, monocyclic vs. polycyclic disease behavior, and management strategies as presented by Nicolás Escarlo in the video.