Virus Diseases in the UK:A Case Study of Current

Problems and Future Challenges

Virus problems in field crops

• Only two groups cause significant problems:– Aphid-borne diseases– Soil-borne diseases

Current problems in field crops• Cereals

– BYDV / CYDV, BaYMV & BaMMV, SBCMV• Oilseed rape

– BWYV, (TuMV), (CaMV)• Sugar beet

– BYV, BMYV, BNYVV• Potato

– PVY, (PLRV), TRV, (PMTV)• Carrot

– Motley dwarf complex• Field brassicas

– BWYV, TuMV, CaMV• Pea

– PEMV, (PSbMV), (PEBV)

A. Aphid-borne

B. Soil-borne

C. Seed & aphid

Control of viruses in field crops

• Aphid-borne diseases– Use of insecticides has proved relatively successful

• e.g. seed treatments on sugar beet• e.g. PLRV control in seed potatoes

– Seed potato certification / testing• e.g. PVY and other viruses

• Soil-borne diseases– Deployment of natural resistance is key

• e.g. rhizomania• e.g. Barley mosaic viruses

Virus problems in protected crops

• Simple model of virus transmission:– Long-distance spread (between greenhouses)

• via propagation material (seed, cuttings or young plants)

– Short-distance spread (within greenhouses)• Mechanically (esp. protected vegetables)• Insect-borne (esp. ornamentals)

Current problems in protected crops

• Tomato– PepMV, ToMV

• Cucumber– CGMMV, (BPYV)

• Pepper– PMMoV

• Ornamentals– CMV, TSWV, INSV…..– many others………..

A. Propagation & Mechanical

B. Propagation & Insect

C. Insect alone

Control of viruses in protected crops

• Spread via propagation– Need for effective screening – Often inadequate esp. for ‘new’ viruses

• Mechanically-transmitted diseases– Often extremely hard to control once introduced

• Resistance can work but limited sources– e.g. Tomato mosaic virus

• Insect-borne diseases– Often extremely hard to control: difficult pests &

viruses with broad host ranges– e.g. Western flower thrips & TSWV

Virus problems in fruit crops

• Most spread via movement of propagation material– Budwood and rootstocks

• Secondary spread via variety of means:– Aphids, nematodes, Pollen, mites– Generally very limited due to supply ‘clean’

planting material

Current problems in fruit crops

• Apple– (ApMV, ASPV, ACLSV, ASGV)

• Pear– (ASPV)

• Plum– (PPV)

• Strawberry– SCV, SMoV, SMYEV, (nepoviruses)

• Rapsberry– RBDV, (nepoviruses)

• Blackcurrant– BRV

A. Propagation

B. Other transmission

Control of viruses in fruit crops

• Viruses spread by propagation– Use of certification schemes is highly successful– e.g. PPV

• Insecticide control of aphid vectors has proved successful– e.g. control of strawberry viruses in propagation

stocks• Deployment of natural resistance has been effective

– e.g. Raspberry bushy dwarf virus

Potential future problems

• Bemisia–transmitted viruses – esp. protected vegetables

• Thrips-transmitted viruses– esp. protected vegetables & ornamentals

• Viroid diseases– In particular PSTVd on tomato, pepper & potato

• New viruses introduced via ornamental trade– e.g. solanaceous hosts from South America

• Soil-borne viruses – Arable crops

New viruses found in UK since 1970

‘Bedford virus’ (Aubian mosaic virus?)Beet necrotic yellow vein virusBeet soil-borne virusOat chlorotic stunt virusSoil-borne cereal mosaic virusBarley yellow mosaic virusBarley mild mosaic virusBeet pseudo yellows virusBeet yellow stunt virusPepino mosaic virusZucchini yellow mosaic virusPotato spindle tuber viroid (erad.)Calibrochoa mottle virusCanna yellow mottle virusClover yellow mosaic virusDatura Colombian virusImpatiens necrotic spot virusPetunia vein clearing virusChrysanthemum stem necrosis virus (erad.)Nemesia necrotic ring virus

Soil-borne

Vegetables

Ornamentals

Future issues

• Reduction in use of aphicides– Withdrawal from use / residue issues– Particularly on fruit & vegetable crops

• Continued expansion of world trade– Esp. movement of cuttings/seed from outside EU

• Lack of priority for disease resistance in breeding programs– Other factors often of more commercial importance

• Rapid production of new varieties– Esp. in ornamentals sector– Appearance of new, unexpected problems

The next steps• Members of EG1 revise questionnaire to capture

more information e.g. crop and control data• Send questionnaire to all consortium members• Engage with other key stakeholders e.g. industry

and specialist virus groups• Collect information on future risks• Compile all information in a spreadsheet• Summarise key virus problems and future risks