PVY and potato viruses
Viruses build up in seed from one generation to the next, and aphids carry them between plants. PVY is the most widespread and most damaging, and the main defence is virus-free seed, short seed generation counts and seed grown where aphids are scarce.
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| At a glance | |
|---|---|
| Main viruses | PVY, PLRV (severe); PVX, PVS, PVM (mild) |
| PVY strains | PVYO, PVYN and PVYNTN (tuber necrotic ringspot) |
| Spread | Seed tubers and aphids |
| Chemical cure | None; aphid control only |
Cause
Potato virus Y is a potyvirus. Scottish certification rules divide viruses into severe (PLRV and PVY, which cause large yield loss) and mild (PVX, PVS and PVM). Strains of PVY differ: PVYNTN causes tuber necrotic ringspot disease, which damages tubers, and breeders rate varieties for resistance to it separately.
Symptoms
- PVY: mottling, crinkling and necrosis of leaves, and in some strains necrotic rings on tubers. Symptoms vary with variety, strain and temperature, and some varieties carry the virus with few signs.
- PLRV (leafroll): upward rolling and a leathery feel in leaves, and net necrosis in tubers in some varieties.
- Mild viruses: slight mosaic and little yield loss, but they are tested for in seed.
How it spreads
Infected seed tubers carry the virus into the next crop. PVY is then carried plant to plant by aphids, including species that only visit the crop briefly, so field control is difficult.
Because the virus passes through the tuber, it accumulates over generations, which is why certification limits the number of field generations from tissue culture.
Where the risk is highest
Everywhere potatoes are grown from tubers. Seed is produced in cooler, windier or higher areas where aphid pressure is lower: for example Segovia and Avila in Spain, northern Scotland and the Dutch seed areas. True potato seed is free of all major potato viruses, which is one attraction of TPS (CIP).
Management: cultural
- Use certified virus-tested seed and replace it regularly.
- Rogue infected plants early in seed crops, kill haulm early to limit the window for aphid transmission, and use mineral-oil sprays and border crops where they are recommended.
- Monitor aphid flights and keep seed crops away from older potato crops.
Management: resistant varieties
Variety ratings for PVY range widely on the 1 to 9 scale. Payette Russet and Castle Russet have complete immunity to PVY, but are largely ignored by the industry because of dormancy and defect problems, and are of interest as breeding parents (research reviews summarised in the corpus). Gene-based resistance (Ry genes) is the target of modern breeding.
Management: chemical and regulatory notes
No chemical cures an infected plant. Insecticides against aphids give limited protection against PVY, because the virus is transmitted within seconds of probing. Regulatory notes are product-specific, so check national approvals.
Seed certification
Laboratories test seed by ELISA for PVY, PLRV, PVX, PVS and PVM. Scotland's SPCS caps severe virus at 0 percent in Pre-Basic 1, 0.5 percent in Super Elite, 1.0 percent in Elite and 2.0 percent in Certified 1, with higher mild-virus caps (SASA technical notes, as summarised in the corpus).
In the Dutch NAK system, maximum virus tolerances run from 0.1 percent in the highest field class to 10 percent in the lowest certified class.
Seed certification schemes set maximum tolerances for disease by class, from Pre-Basic to Certified, and regulated bacteria such as ring rot and brown rot are held at zero in every class (EU Directive 2002/56/EC framework; Scottish SPCS and Dutch NAK schemes as summarised in the Potatopedia corpus).