Seed Potato Buyer Guide · Preliminary Quality Assessment

How to Check Seed Potato Quality Before You Buy

A practical guide for growers, importers and agricultural projects covering field inspection, tuber examination, internal cutting checks and laboratory verification. Visual assessment helps identify obvious risks, but it does not replace virus testing, traceability or phytosanitary documentation.

Seed Potato Quality CheckField InspectionTuber Cutting TestVirus TestingELISA & PCRSeed Lot TraceabilityPhytosanitary Documents

InspectField and tuber condition

CutInternal tissue and vascular ring

VerifyLab reports and traceability

Important Limitation

Visual inspection is useful—but it cannot confirm virus-free status

A healthy-looking crop or tuber can still carry latent infection. Visual screening should therefore be used to identify obvious quality risks, while final purchasing decisions should be supported by representative sampling, laboratory testing, field records and destination-country phytosanitary requirements.

Vascular browning is a warning sign, not a virus test.

Brown or black vascular tissue may be associated with bacterial, fungal or physiological disorders. It does not provide a reliable measure of virus load, and normal-looking tissue does not prove that a tuber is virus-free.

Inspect the seed crop before haulm destruction or harvest

Where possible, visit the multiplication field approximately one to two weeks before haulm destruction or harvest. At this stage, canopy development and visible disease expression are usually easier to assess.

Check varietal uniformity, plant height, canopy structure and maturity.
Look for mosaic, leaf rolling, crinkling, chlorosis, stunting or premature decline.
Inspect for late blight, early blight, blackleg, stem necrosis and wilting.
Review drainage, ridge condition, aphid pressure, volunteer potatoes and field hygiene.
Confirm that diseased and off-type plants have been removed through regular roguing.

Examine the harvested seed potato lot under good lighting

Remove enough soil to expose the tuber surface and inspect a representative sample from different bags, pallets or storage positions—not only the cleanest tubers at the top of the lot.

Correct varietal shape, skin colour and agreed size grade.
Firm tubers without excessive dehydration, shrivelling or abnormal sprouting.
Limited cuts, bruising, pressure damage and skinning injury.
No active soft rot, dry rot, late blight lesions or extensive scab.
No severe greening, frost injury, unpleasant odour or wet packaging.

Internal Examination

Cut a representative sample to reveal defects hidden beneath the skin

Internal cutting is useful for detecting rot, tissue breakdown, vascular abnormalities and other defects that may not be visible externally. Use a clean, disinfected knife and avoid transferring contamination between samples.

What a healthy cut surface should look like

The flesh should be firm and evenly coloured for the variety, without water-soaked tissue, abnormal odour, extensive necrosis, internal cavities or active decay. A uniform cut surface is a positive visual indicator of tuber condition, but it does not confirm freedom from potato viruses.

Brown, black or water-soaked vascular tissueIsolate the sample and investigate possible internal disease or physiological injury.

Creamy or sticky bacterial oozeMay indicate a serious bacterial problem and requires professional laboratory diagnosis.

Dry rot, soft rot or tissue collapseSuggests poor tuber health, handling damage or storage-related disease.

Necrotic arcs, rings or net-like patternsDo not assume the cause; submit representative samples for diagnostic testing.

Document Verification

Ask for evidence behind the seed lot—not only a good-looking sample

Professional buyers should combine visual assessment with documentary verification. This is especially important for international projects, long-distance shipment and seed lots intended for further multiplication.

Four questions every buyer should ask

What is the variety and seed generation? Which pathogens were tested? When and how was the lot sampled? Can the supplier link the test results to the exact lot offered for sale?

Virus Test ResultsRequest the tested virus panel, such as PVY, PLRV, PVX and PVS, together with ELISA or PCR results.

Seed GenerationConfirm the multiplication stage, lot identity and the terminology used in the supplier’s national seed system.

Field Inspection RecordReview roguing, varietal purity, disease observations and production-field traceability.

Phytosanitary ComplianceConfirm import permits, phytosanitary certificates and destination-country quarantine requirements.

Storage InformationAsk about temperature history, dormancy, sprout status, ventilation and pre-shipment grading.

Representative SamplingEnsure tests and visual checks represent the commercial lot rather than a specially selected display sample.

Technical notice: Visual inspection is intended for preliminary quality screening only. It cannot independently confirm varietal purity, virus status or freedom from quarantine pathogens. Final acceptance criteria should be written into the purchase specification and supported by representative sampling, laboratory testing, field records and phytosanitary documents.

Buyer FAQ

Common questions about seed potato quality assessment

Can healthy-looking seed potatoes still carry viruses?

Yes. Some infections remain latent or produce mild symptoms. Laboratory testing and lot-specific records are needed for reliable assessment.

Does a clean vascular ring prove that the seed potato is virus-free?

No. A clean cut surface is a positive visual indicator of internal condition, but it cannot establish virus status.

How many tubers should be cut for inspection?

The sample should be representative of the lot and taken from multiple bags, pallets or storage positions. The exact sampling plan should be agreed according to lot size and buyer requirements.

Which documents matter most for an international buyer?

Lot-specific virus test results, seed-generation records, field inspection information, traceability data, storage history and the required phytosanitary documentation.