Pathology L2 Viruses Flashcards
How are classes of biotic stress categorized
Size
Phylogenetic context
Levels of biological complexity
Importance as casual agents
________ of infectious disease in plants are caused by viruses
Around 50%
Tulipomania
First known financial bubble causes by a virus that made a marbled tulip
Kochs Postulates
- Must be found in diseased but not healthy organisms
- Must be extracted and isolated from the diseased organism and grown in culture
- Must cause disease when introduced to a healthy plant
- The re-isolated organism from the inoculated plant must be same as original
Who worked on the mosaic disease of tobacco
Mayer, Ivanovski, and Beijerunck
What did Mayer find about mosaic disease of tobacco plants
Could not produce and culture or find the reason for disease under a microscope
What did Ivanovski show about the mosaic disease of tobacco
Showed the filterability of the causal agent with a chamberland filter
What did Beijerinck suggest about the mosaic disease of tobacco
Suggested presence of non-cellular organism (virus)
Virus
Obligatory cellular parasites with minimal genetic info that utilize host cell resources for translocation, replication and assembly
Viruses have a ______________ genome consisting of DNA or RNA
Very small
How are viruses classified
Baltimore scheme
T or F: RNA viruses are more common in plants
T
2 parts of virus structure
Capsid (protein shell)
A nucleic acid genome
2 forms of capsids
Helical - rod or filaments
Spherical- icoshedral
Viroids
Infectious piece of RNA that doe not have a protein coat or produce proteins
How do viruses cause disease
Using plant cellular substances during multiplication
Taking up spc3 and disrupting cellular processes
Upsetting metabolism and cell function
Viral disease symptoms
Necrotic spot/ring
Mosaic yellowing
Stunted growth
What can chlorosis be caused by
Nutrient deficiency
Herbicide drift
Virus infection
Types of transmission of viruses
Seed transmission
Mechanical transmission
Vegetative propagation and grafting
Vectors
Seed transmission
Use of seed derived from an infected plant
Mechanical transmission
Contact between infected and healthy leaves (wind, shears, knives)
Vegetative propagation and grafting
Placing infected plant parts with healthy plants
Most common disease vector
Insects
How does the triangle change in viruses
Environment in replaced with vector
Strategies of virus disease management
Resistance variety
Virus-free materials
Sanitary measures
Vector control
Scouting/early detection and removal of infected plants
Example of virus resistant varieties
Peas. En gene=resistance to pea enation mosaic virus. Mo gene=resistance to bean yellow mosaic virus
Why is it so hard to identify viruses
No visual sign
Symptoms can be confused with other factors
Viruses cannot be seen or cultured
How to detect viruses
Must be done with molecular tests with either commercial ones or plant matter sent to a lab
Steps and approaches of virus control
Field scouting
Seed selection/resistance variety
Crop rotation
Remove weeds
Manage insect vectors
Tobacco mosaic virus
Family - vigraviridae
Genus - tobamovirus
First described virus, transmitted mechanically
Pepper mild mottle virus
Family- virgraviridae
Genus - tobamovirus
Positive sense RNA virus
Wheat streak mosaic virus
Family - potyviridae
Genus - tritimovirus
Transmitted by wheat curl mite and infects wheat, barley, oat, corn, and rye
Pea seedborne mosaic virus
Family - potyviridae
Genus - potyvirus
Transmitted by pea aphid or infected seed and affects pea, lentil and faba bean
Potato virus Y
Family - potyviridae
Genus - potyvirus
Transmitted by aphids, mostly in Alberta
Bean leaf curl virus
Family - tombusviridae
Genus - luteovirus
On pea and chickpea leaves found in Saskatchewan
