Plant virology basics

1- Examples of diseases, hosts

A- Tobacco - tobacco mosaic virus
B- Wheat - wheat streak mosaic virus, WSMV, soil-borne wheat mosaic virus, SBWMV
2- Virology is new field - first journal in 1956

A- Archives of Virology
3- Journals

A- Virology
B- Journal of General Virology
C- Journal of Virology
D- Plant pathology journals
E- Web site
4- Textbooks - more complete references

A- Agrios, George (1997) Plant Pathology, 4th edition
B- Bos, L. (1999) Plant viruses, unique and intriguing pathogens
C- Hull, Roger (2001) Matthews' Plant Virology, 4th edition
D- Khan, J.A., and Dijkstra. J. (2002) Plant viruses as molecular pathogens
5- Information on internet - Search engines - web iris, also do text searches through IRIS by telnet
A- Agricola
B- Biological Abstracts
C- CAB Abstracts
C- Web of Science
6- Ways of looking at viruses

A- Physical particle
B- Disease (symptoms, damage to plants)
C- Microbiological agent (infectivity, local lesions)
D- Ecological agent (source, transmission mechanism)
E- Genetic element (genome map)
F- Physiological agent (affects plant development)
G- Evolving organism (variation, selection)

7- Virus life cycle

A- Transmission to plant
B- Entry and uncoating (no attachment)
C- Translation of nucleic acid
D- Replication of RNA
E- Assembly of progeny particles
F- Cell to cell transport (plamodesmata)
G- Movement of through vascular system (phloem, xylem)
8- Recognizing virus disease in the field

A- Symptoms (compare to known endemic viruses)
B- Field pattern (how did it spread)
C- Crop genetics (is crop resistant to some viruses)
D- Disease progress (is it spreading?, how?)
9- Diagnosis

A- Symptoms
B- Transmission (host range)
C- Serology (ELISA)
D- EM (negative staining)
E- Biophysical (capsid protein, dsRNA)
10- Seed transmission

A- Only ~10% seed transmitted
B- Normally inefficient (0.1 to 10%) - hinders International trade
C- Through egg or pollen
D- Therapy to eliminate virus (heat)
11- Common soil vectors (move virus slowly)

A- Plasmodiophorid fungi (Wheat soilborne mosaic)
B- Nematodes (Tobacco ringspot virus)
12- Aerial vectors

A- Aphids - see also
I- Nonpersistent (stylet borne - potyviruses, maize dwarf mosaic)
II- Persistent (circulative - luteoviruses, barley yellow dwarf)
B- Leafhoppers (Beet curly top)
C- Whiteflies (Bean golden mosaic)
D- Mites (Wheat streak mosaic)
F- Beetles (Bean pod mottle)
13- Aphid biology

A- Complex life cycles
B- Often alternate hosts (Myzus persicae - peach potato aphid)
C- Winged forms
D- Multiply rapidly (parthenogenesis, live birth)
14- Aphid feeding behavior (aphids are usually host specific)

A- Fly toward sun (UV)
B- After a few hours repelled by UV, attracted by yellow)
C- Settle on a plant and taste
D- If they don't like host fly on
E- When they find host, feed, lose wings, give birth parthenogenetically
15- Nonpersistent (stylet borne) transmission

A- Immediate acquisition (seconds to minutes)
B- Immediate transmission
C- Ability to transmit lost in minutes to hours
D- Virus lost during molt
E- Fasting improves acquisition
F- Virus acquired from epidermis, bound to stylet tip
16- Persistent (circulative) transmission

A- Acquisition requires 10s of minutes
B- Latent period (hours to days)
C- Transmission persists days to weeks
D- Virus retained through molt
E- Circulative (virus detectable in hemolymph)
F- Virus acquired from phloem
G- Viruses usually not mechanically transmissible
17- Variations on persistent transmission

A- Circulative
B- Propagative
C- Transovarial passage