Viruses of Potato. Virus Incidence in Scottish Seed Crops Epidemiology & Management. Christophe Lacomme

Transcription

1 Viruses of Potato Virus Incidence in Scottish Seed Crops Epidemiology & Management Christophe Lacomme Science & Advice for Scottish Agriculture, Edinburgh, UK

2 Viruses of Potato: Epidemiology & Management Virus epidemiology Outline 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

3 Acknowledgements AHDB-Potato Council Project R428 - Aphids & virus transmission in seed potato The James Hutton Institute, Fera, SASA, SRUC, Scottish Agronomy, Rothamsted Research AHDB-Potato Council Project R449 Effectiveness of Mineral oils Scottish Agronomy, NIAB, SASA, SRUC Scottish Government AFRC-RPID Potato Inspectors SASA Virology & Entomology staff

4 Virus Incidence Epidemiology Management Seed 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, PVY N, PVY O/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

5 Virus Symptoms in Seed Crops Area of seed crops containing at least one plant exhibiting virus symptoms 80% 70% 60% Mosaics Leafroll 50% 40% 30% 20% 10% 0% Prevalence of mosaic causing viruses over leaf roll over the past two decades

6 Potato Viruses & Tuber Symptoms Net necrosis (PLRV) Spraing (TRV, PMTV) Tuber cracking (PVA, PVV, PVY) PTNRD (PVY NTN )

7 Economic Impact of Viruses Symptoms Virus Species Consequences Leaf roll PLRV Yield, marketability, downgrade, fail export tolerances. (conversion starch to sucrose resulting in bad chipping quality) Mild & Severe Mosaic Potyviruses, Yield (PVA, PVV,PVY C, PVY O, PVY N ) USA (2008): 1% virus = loss 170 Kg/Ha Potexviruses (PVX) Synergism: Severe Mosaic observed in mixed infection Potyviruses + PVX Potato Tuber Necrotic Ringspot Disease (PTNRD) Tuber Cracking PVY N, PVY N-Wilga, PVY NTN PVA, PVV, PVY Yield, marketability, downgrade, Fail export tolerance Spraing soil-borne viruses TRV, PMTV Mild Mosaic Carlaviruses Yield, marketability, fail export tolerance (PVS, PVM) Synergism: Severe Mosaic in mixed infections with PVY or PVX

8 Seed Area Downgraded per Fault (figures expressed as a % of seed area entered for inspection)

9 Virus Incidence in Symptomatic Seed Crops While virus levels remains low, Potato virus Y (PVY N ) relative incidence is increasing o Trend observed since early 2000 s PVY N account for 67% of all virus cases in 2015 ~ 80% of virus cases are aphid-transmitted viruses!

10 Potato leaf roll virus (PLRV) 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

11 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

12 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

13 Characterisation of PVY Species ELISA Biotype Molecular Type N O/C O/C N O C N O C N O/C N O N, EU-N O Wilga O/C N, NTN N-Wilga N:O EU-NTN N NTN, E, Z NA-NTN NA Adapted from Schubert et al, 2007

14 Population Dynamics of PVY Variants Relative Percentage of PVY cases (%) Serotype PVY N PVY O/C Yearly survey PVY species Increased relative incidence of PVY N species vs PVY O

15 Population Dynamics of PVY O Variants Relative Percentage of PVY cases (%) Yearly survey PVY O species: Diversity of PVY O recombinant species (NA:O, N:O, N-Wilga) None of these species is prevalent in Scotland (prevalent in mainland Europe & USA)

16 Survey of PVY N Species PVY N Population Structure EU-NTN = 85% EU-N = 3% NA-NTN = 12% R R R1R RC9832 R R R R R R R Hun-NTN R R R R L26 SASA390-R1 DV76-1 R R R R R R R R R R R R R R R R R R R R R R R R R R1F 9579 R R R R R SASA207 L56 SCRI-O DV71-4 O R1R RC9792 SASA110 R R R N605 New-Zealand SCRI-N RRA-1 R Nicola Germany R R SASA61 DV69-1 R SASA154-R1 EU-NTN N-Wilga O EU-N NA-NTN/N

17 Population Dynamics of PVY N Variants Relative Percentage of PVY cases (%) Serotype PVY N PVY O/C Molecular type PVY EU-NTN PVY NA-NTN PVY EU-N Yearly survey PVY N group: PVY EU-NTN is the most prevalent PVY subspecies

18 PTNRD Index Ranking Isolate Molecular type Average score PTNRD Disease Index (DI) NA-N/NTN EU-NTN NA-N/NTN EU-N EU-NTN (PVY E ) EU-NTN O N-Wilga 0.2 PTNRD Indexing on cv. Nadine

19 Potato Tuber Necrotic Ringspot Disease (PTNRD) Development A Risk Assessment PTNRD Risk Dis.Index High PVY Isolate EU-NTN 9529 NA-NTN EU-N 9552 EU-NTN N-Wilga O 9792 N-Wilga O Varieties Nadine Igor Yukon Gold Nicola Hermes Marfona Markies... Desiree Saxon... Bintje Spunta Maris Peer Lady Rosetta King Edward Maris Piper Environment Tuber storage 20 C C - 15 C. Plant Growth Glasshouse (18 C - 20 C)... Field Grown (variable 10 C 15 C).. PVY isolates Environmental conditions PTNRD Potato varieties Low 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

20 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,

21 Distribution of Viruses per Variety Valor PVY O M. Piper M. Peer PVY N M. Piper K. Edward M. Peer MARIS PIPER KING EDWARD MARIS PEER ATLANTIC DESIREE HARMONY SLANEY MARFONA CHARLOTTE CABARET WILJA DUKE OF YORK PENTLAND DELL VALOR WINSTON CARA ESTIMA GOLDEN WONDER KERR'S PINK VALES SOVEREIGN HERMES Hermes PVY N is found in twice more varieties than PVY O & PVA Estima PVA Desiree Susceptibility to PVY N is frequent Resistance to PVY O and PVA is frequent Information on varietal virus resistance available mainly for PVY O

22 PVY Incidence in Tubers in Relation to Plant Development Relative proportion of plants infected (%) PVY EU-NTN PVY O 0 1 WPE 2 WPE 3 WPE 5 WPE 6 WPE 7 WPE 8 WPE 10 WPE Suggest higher incidence of plants infected by PVY EU-NTN in older plants as opposed to PVY O PVY EU-NTN overcome MPR more efficiently than PVY O? 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

23 What drives PVY prevalence? 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),

24 Field Transmission Studies of PVY Variants PVY EU-NTN PVY NA-NTN PVY O 8 m 10 m - Design of the trial : - 7 Infectors for each PVY O, PVY NA-NTN and PVY EU-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)

25 Aphid monitoring Transmission of PVY Transmission Field trials Suction trap Yellow water pan traps - Monitor weekly virus transmission & aphid catches using ST & YWT Timing of transmission, frequency of transmission & nature of aphid species

26 Epidemiology of PVY - Timing and Frequency of Transmission of PVY isolates Weekly Frequency of transmission 90% 80% 70% 60% 50% 40% 30% 20% 10% PVY Field Transmission Year 2 PVY EU-NTN PVY NA-NTN PVY O Aphid Vector Pressure 01/06/11 08/06 15/06 22/06 29/06 06/07 13/07 20/07 27/07/ Aphid vector pressure Higher frequency of transmission for PVY EU-NTN vs PVY NA-NTN and PVY O Comparable transmission pattern: o PVY isolates likely to be transmitted by similar aphid species

27 Field Transmission Studies of PVY Variants PVY EU-NTN PVY NA-NTN PVY O - Spatial & Frequency of distribution: assess virus incidence in tubers for each potato plant

28 Distribution and Incidence of PVY Species at Post Harvest PVY- EU-NTN PVY-NA-NTN PVY-O Higher incidence of PVY EU-NTN in comparison to PVY NA-NTN and PVY O

29 Transmission Efficiency of PVY variants - Incidence of PVY O, PVY EU-NTN and PVY NA-NTN in field conditions 100 Cumulative Relative Incidence of Aphid Transmitted PVY strains at Post-Harvest % PVY incidence Year 1 Year 2 Year 3 Overall 0 PVY EU-NTN PVY NA-NTN PVY O Higher incidence of PVY EU-NTN in progeny tubers (3-fold > PVY NA-NTN & 5-fold > PVY O ) PVY EU-NTN might outcompete others PVY isolates in field conditions

30 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 PVY N 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 seed o 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

31 Control & Management of Viruses & their Aphid Vectors Aphid Monitoring in the UK

32 Aphid Monitoring: Dissemination SASA website: Weekly Suction Trap Data Weekly aphid bulletins Aphid Prediction 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, )

33 Population development of cereal aphids monitored by suction traps

34

35 Summary - Part 2 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: Metopolophium dirhodum, Sitobion avenae and Rhopalosiphum padi (see Model next slide) Field trial and laboratory data support the role of Metopolophium dirhodum and 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!

36 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%

37 Summary - Part 2 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: Metopolophium dirhodum, Sitobion avenae and Rhopalosiphum padi Field trial and laboratory data support the role of Metopolophium dirhodum and 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!

38 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 o o Eliminate overwintering sources of viruses Rogue volunteers early in the season Planting high quality seed Ensure seed crops are free of viruses Virus testing of input crop Maximise the use of host resistance mechanism: o o Use resistant cultivars (low propensity*) ; 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 o o Avoid proximity of ware crops / lower grade seed crops to high grade seed crops Eliminate weed reservoirs of aphids & potential PVY hosts 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!

39 Acknowledgements AHDB-Potato Council Project R428 Aphids & virus transmission in seed potato The James Hutton Institute, Fera, SASA, SRUC Scottish Agronomy, Rothamsted Research AHDB-Potato Council Project R449 Effectiveness of Mineral oils Scottish Agronomy, NIAB, SASA, SRUC Scottish Government, AFRC-RPID Potato Inspectors SASA Virology & Entomology staff Weblinks / contacts: virology@sasa.gsi.gov.uk

40 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

41 Summary of Varietal Propensity (Data for Mosaics from symptom expression at crop inspection) (Data for viruses are from leaf test diagnosis) Variety Crops Mosaics PVY N PVY O/C PVA PVV Leafroll HERMES MARIS PIPER DESIREE MARIS PEER ESTIMA MARKIES KING EDWARD MARFONA PENTLAND DELL CABARET LADY ROSETTA SAXON VALOR ATLANTIC CHARLOTTE CARA WINSTON HARMONY

42 Vector efficiency PCL Project R428 Infection by test species divided by infection by the internal control

43 Aphids - Vector Efficiency Results Aphid species PVY PVA PVY PVA Acyrthosiphon pisum 0.7? Aphis fabae group 0.1? Aulacorthum solani 0.2 No (1933) Brachycaudus helichrysi 0.21 Yes (1963) Hyperomyzus lactucae 0.16? 0 0 Macrosiphum euphorbiae 0.2 Yes (2002) Metopolophium dirhodum 0.3? Myzus ascolonicus 0.2? Myzus persicae 1 Yes (1933, 1996, 2002) 1 1 Rhoplalosiphum padi 0.4 Yes (2002) Sitobion avenae 0.01? Brevicoryne brassicae 0.01? 0 0 Aphis frangulae Yes (1996) Aphis nasturtii 0.4 Yes (1996, 2002) Neomyzus circumflexum Yes (1933) Cavariella aegopodii 0? Drepanosiphum platanoides 0? 0 0 Microlophium carnosum 0? 0 0 PCL R428