🧵 General Characteristics of Viroids
Structure, replication, and disease importance of viroids as subviral plant pathogens.
Viroids are the smallest known infectious agents of plants and are important because they cause systemic diseases despite lacking a protein coat.
What Are Viroids
Viroids are:
- Small circular single-stranded RNA molecules.
- Non-coding and coatless.
- Entirely dependent on host enzymes for replication.
How Viroids Differ from Viruses
Key differences:
- No capsid protein.
- Much smaller genome.
- Do not encode proteins.
- Disease caused through host gene regulation disruption.
Replication and Movement
Replication occurs in host cellular compartments using host polymerases. Viroids move cell-to-cell and long-distance via plasmodesmata and vascular tissues.
Transmission and Symptoms
Transmission routes:
- Vegetative propagation.
- Mechanical handling and tools.
- Grafting.
- Seed or pollen in some pathosystems.
Common outcomes:
- Stunting.
- Distortion.
- Chlorosis and yield reduction.
Management Strategy
Best control relies on exclusion and sanitation:
- Certified viroid-free propagules.
- Tool disinfection.
- Rogueing infected stock plants.
- Strict nursery hygiene.
Summary Cheat Sheet
| Parameter | Viroid Feature |
|---|---|
| Genome | Circular ssRNA |
| Protein coat | Absent |
| Coding capacity | None |
| Multiplication | Host-dependent |
| Main control | Clean planting material + sanitation |
References
1 source • [1]
References
[1]
Used for: Introductory concepts of viroid biology, transmission, and crop disease impact.
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