Plant virology
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Plant Virology. The 30 minute semester with 3 examples from MT. PVY. WSMV. BYDV. Diagnosis. Symptoms Mechanical or insect transmission Immunological (ELISA) Nucleic acid (PCR). How do viruses move from plant to plant?. Insect vectors, nematodes

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Plant Virology

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Plant Virology

The 30 minute semester

with 3 examples from MT

PVY

WSMV

BYDV


Diagnosis

  • Symptoms

  • Mechanical or insect transmission

  • Immunological (ELISA)

  • Nucleic acid (PCR)


How do viruses move from plant to plant?

  • Insect vectors, nematodes

  • Mechanically (sap on clothing/tools/equipment)

  • Seed, tubers

  • Pollen


Host

Vector

Pathogen

Environment

Virus diseases in MT

  • Occur sporadically

  • Difficult to predict

  • Potato virus Y

  • Wheat streak mosaic virus

  • Barley yellow dwarf virus


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


Insect transmission of plant viruses: The Jargon, cont’d


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)


Potato virus Y (PVY): The Host

  • Solanum tuberosum (potato)

  • Capsicum spp. (peppers)

  • Nicotiana spp. (tobacco)

  • Lycopersicon esculentum (tomato)

Primary source of inoculum = Seed potatoes


125I-TEV

Potato virus Y (PVY): The Pathogen

  • Potyvirus (40% all known plant viruses)

  • Nonpersistant (stylet-borne)

  • Aphid transmitted


X

Nonpersistant viruses stick to the stylet

Mediated by a protein, HC-Pro

Specific relationship


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


Host

Vector

Pathogen

Environment

PVY: Disease triangle

: Resistance

: Avoidance

: Exclusion – certified seed

: Scouting

: Roguing


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


WSMV: The Pathogen

  • Family Potyviridae, genus Rymovirus

  • Mite-transmitted virus

  • Wheat curl mite survives on green tissue


WSMV: The Environment

  • Warm, dry conditions favor mite reproduction


X

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


Disease cycle of WSMV


Role of the predominant grassy weeds as reservoirs of WSMV


Weed Host: Volunteer Wheat


Host

Vector

X

Pathogen

Environment

WSMV: Disease triangle

: Resistance

: Avoidance

: Seed transmission

(don’t use seed from

heavily infected plants)

:be aware of the

weather


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


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


Insect transmission of plant viruses


Circulative – nonpropagative

(Another very specific relationship)

Food

Salivary

Canal

Canal

Hemocoel

ASG

PSG

Midgut

Hindgut

Phloem


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


Host

Vector

Pathogen

Environment

BYDV: Disease triangle

: Resistance

: Insecticide

: Control grassy weeds

: Scouting


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


WSMV: The Pathogen

  • Family Potyviridae, genus Rymovirus

  • Mite-transmitted virus

  • Wheat curl mite survives on green tissue


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