Plant Virology

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Plant Virology

• The 30 minute semester
• with 3 examples from MT

PVY
WSMV
BYDV
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Diagnosis

• Symptoms
• Mechanical or insect transmission
• Immunological (ELISA)
• Nucleic acid (PCR)

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How do viruses move from plant to plant?

• Insect vectors, nematodes
• Mechanically (sap on clothing/tools/equipment)
• Seed, tubers
• Pollen

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Virus diseases in MT

• Occur sporadically
• Difficult to predict

• Potato virus Y
• Wheat streak mosaic virus
• Barley yellow dwarf virus

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Insect transmission of plant viruses The Jargon

• Vector insect (or other means) of transmitting
  the virus from plant to plant
• Nonpersistant (stylet-borne)
• Semipersistant
• Persistant
• Circulative, propogative
• Circulative, nonpropogative

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Insect transmission of plant viruses The Jargon,
contd
Type Acquisition Time to start transmitting Retention
Nonpersistant Seconds Seconds Min to Hours
Semipersistant (foregut-borne) Min. to Hours Min to Hours Hours (until molt)
Circulative Propagative Min. to Hours Hours to Days Life
Circulative Nonpropagative Min. to Hours Hours to Days Days to Life

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Control of nonpersistant vs. persistant

• Insecticides are effective against persistant,
  but not nonpersistant viruses
• Plant resistance can be effective, but viruses
  evolve rapidly
• Prevent introducing the virus inoculum (seed,
  tubers)
• Prevent movement from volunteer plants by getting
  rid of volunteers before planting (green bridge)

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Potato virus Y (PVY) The Host

• Solanum tuberosum (potato)
• Capsicum spp. (peppers)
• Nicotiana spp. (tobacco)
• Lycopersicon esculentum (tomato)

Primary source of inoculum Seed potatoes
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Potato virus Y (PVY) The Pathogen

• Potyvirus (40 all known plant viruses)
• Nonpersistant (stylet-borne)
• Aphid transmitted

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Nonpersistant viruses stick to the stylet

• Mediated by a protein, HC-Pro
• Specific relationship

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PVY The Environment (control)

• PVY does not spread rapidly in the absence of the
  aphid vector
• Can be transmitted mechanically
• Insecticides are not effective
• Best option is preventing inoculum introduction
• Some variety resistance

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PVY Disease triangle
Resistance
Avoidance
Exclusion certified seed
Scouting Roguing
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Wheat streak mosaic virus The Host

• Infects both winter and spring wheat
• Symptoms in spring
• Earlier infection greater yield loss
• Grassy weeds, volunteer wheat, corn, etc. can
  harbor both WSMV and the mite vector

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WSMV The Pathogen

• Family Potyviridae, genus Rymovirus
• Mite-transmitted virus
• Wheat curl mite survives on green tissue

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WSMV The Environment

• Warm, dry conditions favor mite reproduction

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Wheat streak mosaic virus control

• Early seeding of winter wheat favors mite and
  WSMV spread
• Eliminate the green bridge
• 3 week gap between herbicide
• and planting
• Avoid spraying herbicide on volunteer wheat near
  spring wheat fields during cool, moist, windy
  weather
• Do not plant wheat next to late-maturing (green)
  corn, which is also a mite host

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Disease cycle of WSMV
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Role of the predominant grassy weeds as
reservoirs of WSMV
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Weed Host Volunteer Wheat
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WSMV Disease triangle
Resistance
Avoidance
Seed transmission (dont use seed from
heavily infected plants)
be aware of the weather
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Barley yellow dwarf virus The Host

• Infects barley, wheat, oats, rye, corn,
  triticale, rice
• Resistance has been developed, but predicting the
  virus and aphid populations from year to year can
  be difficult

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BYDV The Pathogen

• Family Luteoviridae
• Persistant, circulative, nonpropagative
• First classified by primary aphid vector
• MAV Macrosiphum (Sitobion) avenae
• PAV Rhopalosiphum padi
• RMV Rhopalosiphum maidis
• SGV Schizaphis graminum
• RPV Rhopalosiphum padi

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Insect transmission of plant viruses
Type Acquisition Time to start transmitting Retention
Nonpersistant Seconds Seconds Min to Hours
Semipersistant (foregut-borne) Min. to Hours Min to Hours Hours (until molt)
Circulative Propagative Min. to Hours Hours to Days Life
Circulative Nonpropagative Min. to Hours Hours to Days Days to Life

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Circulative nonpropagative (Another very
specific relationship)
Hemocoel
ASG
PSG
Midgut
Hindgut
Phloem
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BYDV The environment

• Inoculum
• Wild grasses, perennial grassy weeds
• Aphid flights from other wheat-growing areas
• Insecticides can be very effective at controlling
  the aphid and virus transmission, if applied early

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BYDV Disease triangle
Resistance
Insecticide
Control grassy weeds
Scouting
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Wheat streak mosaic virus The Host

• Infects both winter and spring wheat
• Symptoms in spring
• Earlier infection greater yield loss
• Grassy weeds, volunteer wheat, corn, etc. can
  harbor both WSMV and the mite vector

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WSMV The Pathogen

• Family Potyviridae, genus Rymovirus
• Mite-transmitted virus
• Wheat curl mite survives on green tissue