viruses of potato - ahdb potatoes · • while virus levels remains low, potato virus y (pvyn)...

SASA © Crown Copyright

Viruses of Potato–

Virus Incidence in Scottish Seed Crops

Epidemiology & Management

Christophe Lacomme

Science & Advice for Scottish Agriculture, Edinburgh, UK


Viruses of Potato: Epidemiology & Management

Outline

Virus epidemiology– Population dynamics of viruses in Scottish seed crops – Survey of growing crops

– Risk posed to crops

– What drives PVY prevalence?

– Transmission & spread of Potato virus Y (PVY) in field conditions

Control & Management of Viruses and their Aphid vectors– Aphid monitoring in the UK / Scotland

– Association between aphid species & PVY transmission

Summary: Implications for the Management of Viruses & their Vectors


Acknowledgements

AHDB-Potato Council Project R428 - Aphids & virus transmission in seed potato The James Hutton Institute, Fera, SASA, SRUC, Scottish Agronomy, Rothamsted Research http://potatoes.ahdb.org.uk/publications/r428-aphids-virus-transmission-seed-crops

AHDB-Potato Council Project R449 –Effectiveness of Mineral oilsScottish Agronomy, NIAB, SASA, SRUChttp://potatoes.ahdb.org.uk/publications/r449-effectiveness-mineral-oils

Scottish Government AFRC-RPID Potato InspectorsSASA Virology & Entomology staff


Virus Incidence – Epidemiology – ManagementSeed Potatoes

All Scottish seed crops are inspected for visual symptoms of virus infection

Growing Crop Inspection: Symptomatic leaf samples are tested at SASA Virology Laboratory ELISA / Real-Time RT-PCR for 11 most common virus species:

PLRV, PMTV, PVA, PVM, PVS, PVV, PVX, PVYN, PVYO/C, TRV, TBRV

Post-harvest testing for viruses for selected seed crops (export, certification)

Sources of data for epidemiology studies - virus incidence in Scottish seed potatoes

Use of Suction Trap Data Aphid Monitoring for supporting decisions on aphid management during the growing season


Virus Symptoms in Seed Crops

0%

10%

20%

30%

40%

50%

60%

70%

80%

1969 1974 1979 1984 1989 1994 1999 2004 2009

Are

a of

see

d cr

ops

cont

aini

ng a

t lea

st o

ne

plan

t exh

ibiti

ng v

irus

sym

ptom

s

Mosaics Leafroll

2014

• Prevalence of mosaic causing viruses over leaf roll over the past two decades


Net necrosis (PLRV)

Tuber cracking (PVA, PVV, PVY)PTNRD (PVYNTN)

Spraing (TRV, PMTV)

Potato Viruses & Tuber Symptoms


Symptoms Virus Species Consequences

Leaf roll PLRV Yield, marketability, downgrade,fail export tolerances. (conversion starch to sucrose resulting inbad chipping quality)

Mild & Severe Mosaic Potyviruses, Yield(PVA, PVV,PVYC, PVYO, PVYN) USA (2008): 1% virus = loss 170 Kg/Ha Potexviruses (PVX) Synergism: Severe Mosaic observed in

mixed infection Potyviruses + PVX

Potato Tuber Necrotic PVYN, PVYN-Wilga, PVYNTN

Ringspot Disease (PTNRD)

Tuber Cracking PVA, PVV, PVY

Spraing soil-borne virusesTRV, PMTV

Mild Mosaic Carlaviruses Yield, marketability, fail export tolerance(PVS, PVM) Synergism: Severe Mosaic

in mixed infections with PVY or PVX

Economic Impact of Viruses

Yield, marketability, downgrade,Fail export tolerance


Seed Area Downgraded per Fault

(figures expressed as a % of seed area entered for inspection)


Virus Incidence in SymptomaticSeed Crops

• While virus levels remains low, Potato virus Y (PVYN) relative incidence is increasing

o Trend observed since early 2000’s

• PVYN account for 67% of all virus cases in 2015

• ~ 80% of virus cases are aphid-transmitted viruses !


• Infected plants are stunted, leaf roll upwards

• Phloem–restricted virus

• Relative importance of PLRV has decreased Healthy seeds

Breeding PLRV-resistant variety

• Transmitted persistently by the peach potato aphid Myzus persicae

• Acquisition of PLRV by feeding (uptake phloem sap)

• Relatively well-controlled:

Control of aphid vector by aphicides M. persicae clones resistant to carbamates, organophosphates,

pyrethroid have been reported

Potato leaf roll virus (PLRV)


Potyviruses: PVY (PVA, PVV)

• Mild & Severe Mosaic on leaves

• PVY is the most important virus of potato (used to be PLRV) Important cause of cultivar degeneration worldwide

• Occasionally associated with tuber growth cracks PVA + PVV (Scotland), PVY (Norway)

• PVY is the cause of Potato Ringspot Necrosis Disease (PTRND) Outbreak central Europe (1980’s – 1990’s)

Not observed in the SPCS

• Transmitted non-persistently by aphids More than 40 aphid species are known vectors of PVY

Level of transmission vary between aphid species

While M. persicae is the most efficient vector, in Scotland cereal aphids

(M. dirhodum, S. avenae) are strongly associated with PVY transmission

Very short period (second-mins) of acquisition & transmission (leaf probing)

Aphicides are not efficient in controlling aphids vectors & virus transmission


Diagnostic & Characterisation of Viruses

ELISA:– Monoclonal & Polyclonal antibodies

Molecular diagnoses & characterisation of PVY variants:– Real-Time RT-PCR– Sequencing Virus Genome

Biological characterisation: – Symptoms development on indicator plants

• Tobacco (Vein Necrosis / Mosaic)• Hypersensitive Response on Potato

cultivars of genotype Nc, Ny, Nz• PTNRD on Potato

SASA © Crown CopyrightAdapted from Schubert et al, 2007

Characterisation of PVY Species

ELISA

NO/CO/C

Biotype Molecular Type

NOC

NOC

Wilg

a

N

N, NTN

NTN, E, Z

ON

N

O/C

O/C

NANA-NTN

EU-NTN

N, EU-NO

N-WilgaN:O


Rel

ativ

e P

erce

ntag

e of

PV

Y ca

ses

(%)

Population Dynamics of PVY Variants

PVYN

PVYO/C

Serotype

• Yearly survey PVY species Increased relative incidence of PVYN species vs PVYO


Rel

ativ

e P

erce

ntag

e of

PV

Y ca

ses

(%)

Population Dynamics of PVYO Variants

• Yearly survey PVYO species: Diversity of PVYO recombinant species (NA:O, N:O, N-Wilga) None of these species is prevalent in Scotland (prevalent in mainland Europe & USA)


R1 10038R1 10001R1R RC9832R1 9773R1 10059R1 9725R1 9736R1 9583R1 9676R1 9787Hun-NTNR1 10039R1 9586R1 9748R1 10057L26SASA390-R1DV76-1 R1 9640R1 9919R1 10040R1 9681R1 9550R1 9747R1 9631R1 9863R1 10539R1 9799R1 9845R1 10538R1 9838R1 9743R1 9562R1 9597R1 9542R1 9529R1 9816R1 9654R1 10076R1 9523R1 9758R1 10088R1 9651R1F 9579R1 9730R1 10042R1 9827R1 10537R1 11301SASA207L56SCRI-ODV71-4 O R1R RC9792SASA110R1 9592R1 9580R1 9552N605New-ZealandSCRI-NRRA-1R1 9737Nicola GermanyR1 9575R1 9941SASA61DV69-1 R1 9561SASA154-R1

100

82

9586

80EU-NTN

N-WilgaOEU-N

NA-NTN/N

Survey of PVYN Species-

2010-2011

EU-NTN = 85%

EU-N = 3%

NA-NTN = 12%

PVYN PopulationStructure


Rel

ativ

e P

erce

ntag

e of

PV

Y ca

ses

(%)

Population Dynamics of PVYN Variants

PVYN

PVYO/C

SerotypePVYEU-NTN

PVYNA-NTN

Molecular type

PVYEU-N

•Yearly survey PVYN group: PVYEU-NTN is the most prevalent PVY subspecies


Ranking Isolate Molecular type Average score

1 9561 NA-N/NTN 4

2 9529 EU-NTN 3.5

3 9737 NA-N/NTN 3.5

4 9552 EU-N 3

5 10057 EU-NTN 3

610088 (PVYE) EU-NTN 2

7 9792 O 1.5

8 10766 N-Wilga 0.2PTNRD Indexing on cv. Nadine

PTNRD Disease Index (DI)PTNRD Index


Potato Tuber Necrotic Ringspot Disease (PTNRD) Development – A Risk Assessment

PVY Isolate

EU-NTN 9529

NA-NTN 95619737

N-Wilga

EU-N 9552

O

Varieties

NadineIgor

Hermes

Maris Piper

Spunta

Nicola

Bintje

.

.

.

.

.

.Desiree

Yukon Gold

Environment

20°C

10°C - 15°C

.

.

.

.

.

.

.

.

.

High

Low

Tuber storage

PVY isolates

Environmentalconditions

Potato varieties

PTNRD

King Edward

Glasshouse(18°C - 20°C)

.

.

.

.

.

Plant Growth

Field Grown(variable –

10°C – 15°C)N-Wilga 10766

O9792

PTNRD Risk

EU-NTN 1005710088

.

Lady Rosetta

Markies

Maris Peer

Saxon

Marfona

Dis.Index

• All PVY isolates have the ability to cause PTNRD given the right conditions• PTNRD development is highly dependant on cultivar & environmental conditions• No obvious association between PVY resistance/susceptibility & PTNRD sensitivity • So far no obvious association between PVY genetic determinants and PTNRD …


What drives PVY prevalence ?

Aphid / Virus Interactions?– Timing transmission– Aphid species– Frequency & Efficiency of transmission

Plant / Virus Interactions?– Replication & Movement – Ability to overcome Host Resistance Mechanisms

Interactions between virus species?– Competition between PVY variants

Environmental conditions ?- Climate, Symptoms development, …


PVYO PVYN

MARIS PIPERKING EDWARDMARIS PEERATLANTICDESIREEHARMONYSLANEYMARFONACHARLOTTECABARETWILJADUKE OF YORKPENTLAND DELLVALORWINSTONCARA ESTIMAGOLDEN WONDERKERR'S PINKVALES SOVEREIGNHERMES

PVA

Distribution of Viruses per Variety

M. Piper

K. Edward

M. Peer

M. Piper

M. Peer

Valor

Desiree

Estima

Hermes

• PVYN is found in twice more varieties than PVYO & PVA

• Susceptibility to PVYN is frequent

• Resistance to PVYO and PVA is frequent

• Information on varietal virus resistanceavailable mainly for PVYO

http://varieties.ahdb.org.uk/https://www.europotato.org/menu.php?


PVY Incidence in Tubers in Relation to Plant Development

Suggest higher incidence of plants infected by PVYEU-NTN in older plants as opposed to PVYO

PVYEU-NTN overcome MPR more efficiently than PVYO ?

Conundrum!: Whilst potato plants become less susceptible to virus acquisition as they mature, relationships with suction trap data only ‘become’ significant if catches to day 210 or 220 are included (i.e. 29 July, 8 August) Management of viruses:

• advise early planting to maximise development of Mature Plant Resistance.• virus management is required through to burn down of the crop

Rel

ativ

e pr

opor

tion

of p

lant

s in

fect

ed (%

)

0

20

40

60

80

100

1 WPE 2 WPE 3 WPE 5 WPE 6 WPE 7 WPE 8 WPE 10 WPE

PVYEU-NTN

PVYO


Aphid / Virus Interactions?– Timing of transmission– Frequency & Efficiency of transmission by aphid

species

Plant / Virus Interactions?– Replication & Movement – Ability to overcome Host Resistance Mechanisms

Interactions between virus species?– Competition between PVY variants

Environmental conditions ?- Climate, Symptoms development (latent infection), …

What drives PVY prevalence ?


Field Transmission Studies of PVY Variants

- Design of the trial :- 7 “Infectors” for each PVYO, PVYNA-NTN and PVYEU-NTN isolate- Tobacco (60 plants per week) and Potato (450 plants Maris Piper) bait plants (~4.5% inoculum)- Trials run over a 3-year period

- Purpose of the trial:- Timing of transmission, frequency of transmission, & nature of aphid species

- Spatial distribution & frequency transmission at post harvest (virus PH test individual potato plant)

PVY EU-NTN PVYNA-NTN PVYO

10 m

8 m


Aphid monitoring – Transmission of PVYTransmission Field trials

Yellow water pan trapsSuction trap

- Monitor weekly virus transmission & aphid catches using ST & YWT• Timing of transmission, frequency of transmission & nature of aphid species


Epidemiology of PVY-

Timing and Frequency of Transmission of PVY isolatesW

eekl

y Fr

eque

ncy

of tr

ansm

issi

on

Aph

id v

ecto

r pre

ssur

e

10%

20%

30%

40%

50%

60%

70%

80%

90%

01/06/11 08/06 15/06 22/06 29/06 06/07 13/07 20/07 27/07/110

50

100

150

200

250

300

350

400

PVYO

Aphid VectorPressure

PVYEU-NTN

PVYNA-NTN

PVY Field Transmission – Year 2

• Higher frequency of transmission for PVYEU-NTN vs PVYNA-NTN and PVYO

• Comparable transmission pattern: o PVY isolates likely to be transmitted by similar aphid species


Field Transmission Studies of PVY Variants

- Spatial & Frequency of distribution: assess virus incidence in tubers for each potato plant

PVY EU-NTN PVYNA-NTN PVYO


PVY- EU-NTN PVY-NA-NTN PVY-O

Distribution and Incidence of PVY Speciesat Post Harvest

Higher incidence of PVYEU-NTN in comparison to PVYNA-NTN and PVYO


0

20

40

60

80

100%

PVY

inci

denc

e

Cumulative Relative Incidence of Aphid TransmittedPVY strains at Post-Harvest

Year 1Year 2Year 3Overall

PVYEU-NTN PVYNA-NTN PVYO

Transmission Efficiency of PVY variants-

Incidence of PVYO, PVYEU-NTN and PVYNA-NTN in field conditions

• Higher incidence of PVYEU-NTN in progeny tubers (3-fold > PVYNA-NTN & 5-fold > PVYO)• PVYEU-NTN might outcompete others PVY isolates in field conditions


Summary - Part 1• While virus incidence is low, aphid transmitted viruses represent ~ 80% of

virus cases

Cereal aphids are the main vectors of PVY in Scotland

• PVYN species are found worldwide however PTNRD is not observed in the SPCS

PTNRD can be observed upon infection by different types of PVY strains dependant on environmental conditions & on PVY species / variety

combination

• Control and management of viruses: Viruses (PVY) are efficiently transmitted to tubers:

o Plant high quality seedo Ensure seed crops are free of viruses

A wide range of colonizing & non-colonizing aphid species can transmit PVY:o Control potential sources of inoculum (roguing, proximity of ware crops)o Prevent aphid build up in crops & when possible neighbouring crops

Advise early planting to maximise development of Mature Plant Resistance. Virus management is required through to burn down of the crop


http://www.rothamsted.ac.uk/insect-survey-bulletins/count-maps

http://aphmon.fera.defra.gov.uk/ https://www.sasa.gov.uk/wildlife-environment/aphid-monitoring/

Control & Management of Viruses & their Aphid VectorsAphid Monitoring in the UK


Aphid Monitoring: Dissemination

SASA website: Weekly Suction Trap Data Weekly aphid bulletins Aphid Prediction Email on request (let us know…) / SMS alert from AHDB (Claire Hodge)

Suction Trap Data can be used to support decisions on aphid management during the growing season- Assist decision making: Haulm destruction, spraying (insecticide, mineral oil,…)

https://www.sasa.gov.uk/wildlife-environment/aphid-monitoring/


Population development of cereal aphids monitored by suction traps


Virus symptoms in crops are the result of transmission in the previous season in Scotland

There is a strong relationship between transmission of Potato Leafroll (PLRV) and Suction Trap catches of Peach-Potato aphids Myzus persicae

Significant relationships exist between transmission of Potato Virus Y (PVY) and Suction Trap catches of three species of cereal aphids: Metopolophiumdirhodum, Sitobion avenae and Rhopalosiphum padi (see Model next slide)

Field trial and laboratory data support the role of Metopolophium dirhodumand Sitobion avenae in PVY transmission

Suction Trap Data can be used to support decisions on aphid management during the growing season

Peach-Potato aphids Myzus persicae have not played a major role in virus transmission in recent years – this may not be the case in England!

Aphid Monitoring & Virus Transmission - ScotlandSummary - Part 2


The strongest relationship with PVY transmission is produced using the mean catch of cereal aphids prior to 29 July and the incidence of PVY in the previous year

• The incidence of PVY in 2015 was 6.0%• The incidence of PVY in 2016 is predicted to be 2.4%


Aphid Monitoring & Virus Transmission - Scotland Virus symptoms in crops are the result of transmission in the previous season

in Scotland

There is a strong relationship between transmission of Potato Leafroll (PLRV) and Suction Trap catches of Peach-Potato aphids Myzus persicae

Significant relationships exist between transmission of Potato Virus Y (PVY) and Suction Trap catches of three species of cereal aphids: Metopolophiumdirhodum, Sitobion avenae and Rhopalosiphum padi

Field trial and laboratory data support the role of Metopolophium dirhodumand Sitobion avenae in PVY transmission

Suction Trap Data can be used to support decisions on aphid management during the growing season

Peach-Potato aphids Myzus persicae have not played a major role in virus transmission in recent years – this may not be the case in England!

Summary - Part 2


Conclusions: Implications for the Management of Viruses Viruses (PVY) are efficiently transmitted “horizontally” (plant-to-plant) and

“vertically” (tuber progeny) Reduce the level of initial inoculum in the crop

o Eliminate overwintering sources of viruseso Rogue volunteers early in the season o Planting high quality seed

Ensure seed crops are free of viruses Virus testing of input crop

Maximise the use of host resistance mechanism: o Use resistant cultivars (low propensity*)

http://varieties.ahdb.org.uk/ ; https://www.europotato.org/menu.php? https://www.sasa.gov.uk/seed-ware-potatoes/virology/varietal-propensity-virus-infection

o Advise early planting to maximise development of Mature Plant Resistance before aphid build up

A wide range of colonizing & non-colonizing aphid species can transmit PVY Reduce virus spread:

o Avoid proximity of ware crops / lower grade seed crops to high grade seed cropso Eliminate weed reservoirs of aphids & potential PVY hostso Control aphid vectors

Prevent aphid build up in crops & aphid feeding Prevent aphid build up when possible in neighbouring crops (ware, cereals, …) Liaise with agronomists for best practice (Insecticide / Mineral oil treatments)

Virus management is required through to burn down of the crop!


Acknowledgements

AHDB-Potato Council Project R428 Aphids & virus transmission in seed potato The James Hutton Institute, Fera, SASA, SRUCScottish Agronomy, Rothamsted Research

http://potatoes.ahdb.org.uk/publications/r428-aphids-virus-transmission-seed-crops

AHDB-Potato Council Project R449 –Effectiveness of Mineral oilsScottish Agronomy, NIAB, SASA, SRUChttp://potatoes.ahdb.org.uk/publications/r449-effectiveness-mineral-oils

Scottish Government, AFRC-RPID Potato InspectorsSASA Virology & Entomology staff

Weblinks / contacts:[email protected]

https://www.sasa.gov.uk/ https://www.sasa.gov.uk/diagnostics/virus-testinghttps://www.sasa.gov.uk/wildlife-environment/aphid-monitoring/


Effect of Variety - Propensity

We are proposing the term ‘varietal propensity’ as a measure of the extent to which a disease is present in that variety compared with the norm:

– Propensity = %age of diseased crops of a variety / %age of diseased crops of all varieties

– e.g. Maris Piper constitutes 8% of Scottish seed crops but is responsible for 36% of the leafroll seen.

• Propensity of Maris Piper to leafroll is 36/8 = 4.5

A propensity of 1 is what would be expected if viruses/symptoms were evenly distributed across all varieties

Values > 1virus/symptom more likely found in a given variety

Values < 1virus/symptom less likely found in a given variety

https://www.sasa.gov.uk/seed-ware-potatoes/virology/varietal-propensity-virus-infection


Summary of Varietal Propensity(Data for Mosaics from symptom expression at crop inspection)

(Data for viruses are from leaf test diagnosis)

Variety Crops Mosaics PVYN PVYO/C PVA PVV LeafrollHERMES 1771 0.5 0.1 0.6 1.8 0.0 0.3MARIS PIPER 1746 1.7 1.7 1.0 0.1 0.0 4.4DESIREE 1031 2.0 1.1 1.2 5.9 0.0 1.4MARIS PEER 714 2.2 2.4 2.9 0.3 0.0 0.5ESTIMA 592 1.1 0.2 0.8 5.4 26.4 1.5MARKIES 426 0.3 0.1 0.0 1.5 0.0 0.4KING EDWARD 395 2.3 4.7 3.2 0.2 0.0 1.5MARFONA 363 0.9 1.2 2.2 0.2 0.0 1.0PENTLAND DELL 357 0.5 0.9 0.0 0.3 0.0 1.1CABARET 331 1.1 1.3 1.4 4.9 0.0 0.5LADY ROSETTA 330 0.2 0.0 0.0 0.0 0.0 0.4SAXON 323 0.1 0.1 0.0 0.3 0.0 0.2VALOR 314 3.8 2.7 4.0 0.0 0.0 0.9ATLANTIC 296 1.9 4.4 4.2 0.3 0.0 0.2CHARLOTTE 288 1.1 1.7 2.2 0.0 0.0 0.2CARA 280 0.5 0.5 0.6 0.0 0.0 1.4WINSTON 274 2.3 0.8 5.7 0.0 0.0 0.8HARMONY 269 2.3 2.0 0.6 0.0 0.0 1.1

https://www.sasa.gov.uk/seed-ware-potatoes/virology/varietal-propensity-virus-infection


Vector efficiencyIn

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ion

by te

st s

peci

es d

ivid

ed b

y in

fect

ion

by th

e in

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ontro

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PCL Project – R428


Aphids - Vector Efficiency Results

Aphid species PVY PVA PVY PVAAcyrthosiphon pisum 0.7 ? 0.55 0.19

Aphis fabae group 0.1 ? 0.06 0.47

Aulacorthum solani 0.2 No (1933) Brachycaudus helichrysi 0.21 Yes (1963) Hyperomyzus lactucae 0.16 ? 0 0

Macrosiphum euphorbiae 0.2 Yes (2002) 0.49 0.94

Metopolophium dirhodum 0.3 ? 0.37 0.02

Myzus ascolonicus 0.2 ? Myzus persicae 1 Yes (1933, 1996, 2002) 1 1

Rhoplalosiphum padi 0.4 Yes (2002) 0.81 0.02

Sitobion avenae 0.01 ? 0.68 0.63

Brevicoryne brassicae 0.01 ? 0 0

Aphis frangulae Yes (1996) Aphis nasturtii 0.4 Yes (1996, 2002) Neomyzus circumflexum Yes (1933) Cavariella aegopodii 0 ? 0.78 0.55

Drepanosiphum platanoides 0 ? 0 0

Microlophium carnosum 0 ? 0 0

PCL – R428

viruses of potato - ahdb potatoes · • while virus levels remains low, potato virus y (pvyn)...

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