Potato viruses and vectors

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Potato viruses and vectors

• Brendan Rodoni
• Plant Virologist
• Vic DPI

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• Potato Viruses of Significance in Victoria
• Potato leafroll virus (aphid transmitted
  persistent)
• Potato virus Y (aphid transmitted non
  persistent)
• Potato virus S (aphid transmitted non
  persistent)
• Tomato spotted wilt virus (thrips transmitted)

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Plant viruses and viroids

• very small (PLRV 28 nm sphere)
• usually made of RNA coated with proteins
• vectored from plant to plant by other organisms,
  mainly insects (aphids, thrips)

Agrios, 2005
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Incidence of potato viruses in ViCSPA seed
potatoes in 2005/06 and 06/07
Source of data ViCSPA 13th Annual Report
2006/07, 20/9/07

• Concerns
• PVY
• PVS
• TSWV sporadic incidence

BUT In 2007/08 45 hectares of seed potatoes -
estimated value 1.35 million
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Host
Virus
Insect vector
The Virus-Vector-Disease triangle
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Plant Viruses and Potatoes

• Viruses are spread by either .
• Vectors.
• Aphids
• Thrips
• Nematodes
• Fungi
• Leaf hoppers (PYDV)
• Mechanical transmission
• Sap inoculation by leaves rubbing against each
  other
• Infected material
• Diseased tubers
• Self sown/volunteers
• Weeds

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Aphids as vectors of potato viruses

• Persistent mode of transmission
• Mode of transmission for PLRV.
• Aphid requires a feeding period of up to two
  hours to acquire the virus.
• The aphid remains infectious for life.
• Once infected every feed potentially can transmit
  the virus.
• Sprays effective to some extent, as chemical
  will kill the aphid before the required
  acquisition period.
• Non-persistent transmission
• Mode of transmission for viruses such as PVY and
  PVS.
• Aphid acquires virus in first 15 - 30 seconds of
  feeding.
• Transmission time is very short.
• Basically the virus is attached to the lining of
  the stylet.
• Chemicals not as effective as aphid is infectious
  before chemical kill.

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Aphids persistent transmission (PLRV)

• Adult female and immature wingless (apterous)
  bird cherry-oat aphid, Rhopalosiphum padi.

• B. Diagram of an aphid vector feeding on a plant
  host showing the internal route of the viruses
  (Diagram courtesy L.L. Domier, from DArcy and
  Domier 2000).

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PLRV is transmitted by aphids in a persistent
manner

• Potato leafroll virus (PLRV)
• Is transmitted in a persistent manner by aphids,
  of which Myzus persicae is the most efficient
  vector.
• Transmission occurs when an aphid carrying the
  virus feeds on a leaf or tuber, exchanging saliva
  in the process.
• Aphids require a 1 - 2 hour acquisition period on
  infected plant material before it has the ability
  to transmit the virus.
• PLRV is also spread on infected material, through
  seed and self-sown potatoes, and can over-winter
  in solaneceous and other weeds.

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• Management options for PLRV Control
• Use certified seed
• Remove symptomatic plants
• Control broad leafed weeds within and adjacent to
  the crop
• control self sown potatoes
• Avoid overlapping crops
• Time planting dates carefully to avoid exposure
  of young plants when aphid numbers are high
• Use appropriate insecticides

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Non-persistent transmission (PVY and PVS)
X
X
X
Moves only in to the bottom portion of the
salivary duct
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PVY is transmitted by aphids in a non-persistent
manner

• PVY - (Potyvirus)
• Several strains, (O, C, N) some more
  devastating than others
• Incidence of PVY is increasing
• Symptoms vary depending on strain (stunting,
  necrosis, crinkling)
• Yield losses of 10-80 have been reported
• is strain and cultivar dependant
• more severe if PVY is present with other viruses
  (ie PVS, PVX)

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PVY Transmission

• Aphids - Non-persistent transmission
• Aphid acquires virus in first 15 - 30 seconds of
  feeding
• Aphid transmits virus to healthy plant in 5 30
  seconds of feeding
• Basically the virus is attached to the lining of
  the stylet
• Chemicals not effective in control as aphid
  acquires and/or transmits the virus before the
  chemical can kill it
• aphid is only infectious for 1- 2 feeds after
  acquiring the virus

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PVY Transmission (Cont)

• Readily transferred from one generation to next
  via potato tubers (seed)

• There are reports that PVY may be transmitted
  mechanically by plant contact/seed cutters
• Strain dependant

• Alternate Hosts
• has a wide natural host range (41 species in
  four plant families)
• includes tomatoes, capsicum and many weeds of
  potato crops including nightshade

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• Control
• Plant certified seed stocks
• Use good Crop Hygiene
• Control alternate hosts (weeds) and self-sowns
• Early rouging
• Clean seed cutters
• Use border crops (Oats, Barley, Maize etc)
• Avoid spread from nearby potato crops and
  volunteers
• Use crop rotation
• Inspect crops regularly

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Potato virus S non-persistently transmitted by
aphids

• PVS
• Classified as a Carlavirus,
• Well spread throughout Victoria and Australia.
• It is a latent virus, virtually symptomless in
  most cultivars.
• It is transmitted in a non-persistent manner by
  aphids. Frequency of transmission may differ
  depending on the isolate.
• Transmission occurs during probing of leaf or
  tuber material.
• Aphids require short acquisition periods before
  they have the ability to transmit.
• PVS is also spread by infected plant material,
  and can over-winter in solaneceous and other
  weeds .

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• PVS Mechanical Transmission
• PVS is very easily transmitted mechanically by
  infected sap, e.g.
• by plant to plant contact,
• machinery contact in the field,
• seed graders and cutters etc.
• PVS is also tuber transmitted.

• PVS Yield loss
• Does PVS alone consistently reduces yield?
• losses of 10-20 have been reported.
• Will increase yield loss when in combination
  with other viruses

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Tomato spotted wilt virus (TSWV)
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• TSWV
• causes significant yield losses in seed and ware
  potato crops in Australia
• Aus environment provides an abundance of thrips
  vectors and alternate weed hosts
• control of TSWV is difficult in many districts
• chemical control is difficult and expensive and
  not compatible with IPM programs

• TSWV as a disease of potatoes is a unique
  Australian problem
• as a result there has been very little work
  towards the development of TSWV resistance in
  potato germplasm

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• Transmitted by adults from 4 different Thrips
  species, Thrips tabaci (Onion Thrips) is the
  greatest concern in southern Victoria.
• Adult thrips transmit the virus when feeding on
  leaves, or more commonly on flowers.

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• Management options for TSWV Control
• Use certified seed for planting
• Practise Good Crop Hygiene
• remove and destroy any plants with symptoms
• remove weeds
• remove tubers completely after harvest
• Leave a fallow break from one crop to the next
• Monitor crops regularly
• Use appropriate insecticides

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• Vector transmission and control of PLRV, PVY, PVS
  and TSWV
• PLRV (aphid transmitted persistent)
• Chemicals can be effective
• PVY and PVS (aphid transmitted non persistent)
• Chemicals not effective
• TSWV (thrips transmitted)
• Chemicals not effective
• Generic control measures
• Plant certified seed
• Control weeds in and around potato crops
• Consider planting border crops (grasses) for PVY
  and PVS