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Plant Virology - MSU Extension

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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
Virus diseases in MT
• Occur sporadically
• Difficult to predict
Host
Vector
Pathogen
• Potato virus Y
• Wheat streak mosaic virus
• Barley yellow dwarf virus
Environment
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
Type
Acquisition
Time to start
transmitting
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
Retention
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
125I-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
PVY: Disease triangle
Host : Resistance
Vector : Avoidance
Pathogen
: Exclusion – certified seed
Environment
: 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
X
• 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
Table 2. Capacity of prevalent grassy weeds in Montana to serve as mite and virus hosts.*
Common name
Scientific name
Life cycle Mite host WSMV host
Jointed goatgrass
Aegilops cylindricae
Annual
Yes
Yes
Crested wheatgrass
Agropyron cristatum
Perennial Unknown Unknown
Wild oat
Avena fatua
Annual
No
Yes
Smooth brome
Bromus inermis
Perennial
Yes
No
Bromus japonicus
Japanese brome
Perennial
No
Unknown
Downy brome/Cheatgrass Bromus tectorum
Annual
Yes
Yes
Persian darnell
Lolium persicum
Annual
Unknown Unknown
Western wheatgrass
Pascopyrum smithii
Perennial
Yes
No
Feral rye
Secale cereale
Annual
Unknown Unknown
Yellow foxtail
Setaria glauca
Annual
No
No
Green foxtail
Setaria viridis
Annual
Yes
Yes
*data taken from literature cited in text
WSMV: Disease triangle
Host : Resistance
X
Pathogen
: Seed transmission
(don’t use seed from
heavily infected plants)
Vector : Avoidance
Environment
: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
Type
Acquisition
Time to start
transmitting
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
Retention
Circulative – nonpropagative
(Another very specific relationship)
Hemocoel
PSG
ASG
Midgut
Hindgut
Food
Salivary
Canal
Phloem
Canal
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
BYDV: Disease triangle
Host : Resistance
Vector : Insecticide
Pathogen
: Control grassy weeds
Environment
: 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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