Plant Virology The 30 minute semester with 3 examples from MT PVYWSMVBYDV

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

Virus diseases in MT Occur sporadically Difficult to predict Host PathogenEnvironment Vector 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 TypeAcquisition Time to start transmittingRetention NonpersistantSeconds Min to Hours Semipersistant (foregut-borne) Min. to Hours Min to Hours Hours (until molt) Circulative Propagative Min. to Hours Hours to DaysLife Circulative Nonpropagative Min. to Hours Hours to DaysDays to Life

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

Potato virus Y (PVY): The Pathogen Potyvirus (40% all known plant viruses) Nonpersistant (stylet-borne) Aphid transmitted 125 I-TEV

Nonpersistant viruses stick to the stylet Mediated by a protein, HC-Pro Specific relationship X

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 PathogenEnvironment Vector 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

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 X

Disease cycle of WSMV

Role of the predominant grassy weeds as reservoirs of WSMV

Weed Host: Volunteer Wheat

Host PathogenEnvironment Vector WSMV: Disease triangle : Resistance : Avoidance X :be aware of the weather : Seed transmission (don’t use seed from heavily infected plants)

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 TypeAcquisition Time to start transmittingRetention NonpersistantSeconds Min to Hours Semipersistant (foregut-borne) Min. to Hours Min to Hours Hours (until molt) Circulative Propagative Min. to Hours Hours to DaysLife Circulative Nonpropagative Min. to Hours Hours to DaysDays to Life

Circulative – nonpropagative (Another very specific relationship) Phloem Hindgut ASG PSG Midgut Food Canal Salivary Canal Hemocoel

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 PathogenEnvironment Vector BYDV: Disease triangle : Resistance : Control grassy weeds: Scouting : Insecticide

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