Potato Viruses: Understanding Their Impact on Global Potato Production

Potato Viruses and Why They Matter

Potato viruses are among the most serious biotic constraints on potato production worldwide. More than 50 viruses and one viroid have been reported in potato, yet only a handful cause major losses on a global scale, according to the International Potato Center review of viral diseases in potato. The most damaging of them reduce yield, spoil tuber quality and cause seed lots to be downgraded or rejected.

What makes viruses so important in potato is the way the crop is grown. Most potatoes are planted from tubers rather than true seed, so a virus that infects a plant this season usually travels inside its daughter tubers into the next crop. Without clean seed, virus levels build up from one generation to the next, a process known as seed degeneration. There is no treatment that cures an infected plant, which is why control depends on prevention: virus-tested seed, vector management, field hygiene and resistant varieties.

Viruses sit alongside fungi, bacteria, nematodes and insects among the main potato pests and diseases, and many of them depend on those same insects and nematodes to move from plant to plant.

Potato Viruses: From Leaf to Tuber

Key Facts About Potato Viruses: Global Impact and Transmission

What Are Potato Viruses?

A plant virus is a very small infectious particle made of genetic material, RNA or DNA, wrapped in a protein coat. It cannot grow or multiply on its own; it has to enter a living plant cell and use the cell's machinery to make copies of itself. Most potato viruses carry their genes as single-stranded RNA. A few, such as the whitefly-borne begomoviruses, carry DNA.

How a virus infects the plant: Viruses enter a potato plant through a wound: the feeding puncture of an aphid or other insect, a rub between leaves, a cut during seed handling, or the root damage caused by soil nematodes. Once inside, the virus multiplies in the first cells it reaches, then moves from cell to cell through the fine channels that connect plant cells. When it reaches the phloem, the plant's sugar-transport tissue, it is carried with the flow of nutrients to the growing tips and down the stolons into the developing tubers.

How far and how fast a virus spreads inside the plant depends on the virus, the variety and the age of the crop. Plants infected early in the season usually pass the virus to most of their tubers. Infections that start late, close to haulm destruction, may not reach the tubers at all, which is why the timing of haulm killing matters so much in seed crops.

Viruses, viroids and phytoplasmas: Several potato disorders are often grouped with viruses but have different causes. Potato spindle tuber viroid (PSTVd) is a viroid: a small circle of naked RNA with no protein coat, which spreads mainly by contact and through infected tubers, and is regulated as a quarantine pest in many countries. Purple top and aster yellows are caused by phytoplasmas, which are wall-less bacteria spread by leafhoppers. Zebra chip is caused by the bacterium Candidatus Liberibacter solanacearum, carried by the potato psyllid. The distinction matters because diagnostic tests and control measures differ for each group.

Why potatoes are especially exposed: Grain crops start each season from true seed, which carries very few viruses. Potato starts from tubers, which carry almost any virus their mother plant had. Every season a seed stock spends in the field is another chance for aphids and other vectors to bring in new infections, and the virus load then compounds in the following generation. Smallholder practice can make the problem worse: farmers who sell or eat the largest tubers and keep the small ones as seed may be selecting the progeny of infected plants, which tend to produce smaller tubers, as noted in the CIP chapter on potato virus diseases.

Understanding Potato Viruses and How They Infect Plants

Main Potato Viruses at a Glance

The viruses that matter most to the potato industry are best understood by the way they spread, since the route of transmission decides which control measures work. The table groups the most widespread potato viruses by their main route of spread.

Aphid-borne viruses: Aphids are the most important vectors of potato viruses. The group includes the potyviruses potato virus Y, now the most damaging potato virus worldwide, and potato virus A, together with potato leafroll virus, which for decades was the leading virus problem before PVY overtook it. The carlavirus potato virus M is also aphid-borne. Alfalfa mosaic virus and cucumber mosaic virus reach potato from other host crops and weeds, usually causing scattered infections rather than epidemics.

Contact-transmitted viruses: Potato virus X spreads when infected and healthy plants touch, and on machinery, tools and hands. Potato virus S spreads the same way, and some of its strains are also aphid-borne. Both viruses are common worldwide and often cause mild or no visible symptoms, which allowed them to persist in seed schemes that relied only on visual inspection.

Soil-borne viruses: Two viruses survive in the soil inside their vectors rather than in plant debris. Tobacco rattle virus is spread by stubby-root nematodes of the genera Trichodorus and Paratrichodorus. Potato mop-top virus is spread by Spongospora subterranea, the cause of powdery scab. Both can cause spraing, brown arcs and rings inside the tuber flesh, and both can persist in infested fields for many years.

Warm-region and highland viruses: Viruses that are rare in temperate seed regions can dominate elsewhere. In the Indo-Gangetic plains of India, tomato leaf curl New Delhi virus, a whitefly-borne begomovirus that causes apical leaf curl, was first seen in potato around 1999 and has since become the leading virus problem in Indian potato. Tomato spotted wilt virus, spread by thrips, affects potato in warmer regions. In the Andes, the crop's centre of origin, growers also face viruses such as potato yellow vein virus and Andean potato mottle virus that are rarely found elsewhere.

Mixed infections and synergy: Field plants often carry more than one virus, especially where seed is saved for several seasons. Some combinations do far more damage than either virus alone. The best-known case is PVX with PVY or PVA: the viruses interact inside the plant and tuber yield losses can reach 80%, compared with 10–40% for PVX on its own. Mixed infections also change and mask symptoms, which is one reason laboratory testing has replaced visual diagnosis in modern seed certification.

Impact on Yield, Tuber Quality and Seed Potatoes

The economic impact of potato viruses comes through three channels: lower yield, poorer tuber quality and lost seed value. Their relative weight depends on where the potatoes are grown. In regions with strong certified seed systems, the main cost is seed lot downgrading and rejection. Where formal seed systems are weak, yield loss on farmers' fields is the larger burden.

Yield losses: Losses vary widely with the virus, the strain, the variety, the share of infected seed and when infection happened. PVY and PLRV in single infections already reduce yield, and in combination with other viruses tuber yield losses can pass 80%, according to the CIP review. Field studies have put PVY losses alone at between 10% and 80%. PVX causes 10–40% loss alone, PVA up to 40%, while PVS and PVM usually cause only minor losses unless severe strains or mixed infections are involved.

Tuber quality and processing defects: Several viruses damage the tuber itself. PLRV can cause net necrosis, a brown network in the vascular tissue. Some recombinant strains of PVY cause potato tuber necrotic ringspot disease, with sunken rings on the skin. The soil-borne viruses TRV and PMTV cause spraing, and tomato spotted wilt virus can also cause internal necrosis in warmer regions. Necrotic defects are often invisible from outside, show up only when tubers are cut, peeled or fried, and can lead to rejection of whole loads by processors and fresh packers. Such tubers are safe to eat, but they fail quality specifications.

Seed lot downgrading and rejection: Seed potatoes are certified against strict virus tolerances, so a small rise in infection can push a lot into a lower class or out of certification altogether. In the United States, PVY has been the main reason for seed lot rejections over the past two decades. In Colorado's certification programme, PVY incidence in certified seed lots ranged from 2.6% in 2017 to 6.5% in 2022. Seed exporters face an extra layer of risk, because importing countries set their own tolerances and may refuse whole shipments.

Routes of Potato Virus Transmission: From Seed Tubers to Insect Vectors

Potato viruses reach a crop by five main routes: infected seed tubers, aphids, other insect vectors, plant-to-plant contact and soil-borne vectors. In most fields the first source of infection is the seed itself; vectors then spread the virus to neighbouring plants during the season.

Infected seed tubers: An infected seed tuber produces an infected plant from the day it emerges. Such plants, often called secondary or tuber-borne infections, are usually more stunted than plants infected during the season, and they act as sources from which vectors pick up the virus and carry it through the field. Even a low share of infected seed can lead to a much higher level of infection at harvest when vector pressure is high, which is why seed quality is the starting point of every control programme.

Aphids: How a virus travels with its aphid vector explains most management choices. Non-persistent viruses, such as PVY, PVA and PVM, are picked up and passed on within seconds to about a minute as an aphid probes a leaf, and the aphid usually loses them within one to two hours. Winged aphids that do not colonise potato, flying in from cereals, legumes or weeds and tasting plants on their way, are important carriers of these viruses. At least 70 aphid species can transmit PVY.

Persistent viruses, of which PLRV is the main example in potato, behave very differently. The aphid has to feed in the phloem for a long time to take up the virus, which then passes through its gut into the blood and salivary glands. After a latent period of hours, the aphid stays infective for the rest of its life. The green peach aphid (Myzus persicae) is the most efficient vector.

Other insect vectors: Whiteflies, especially Bemisia tabaci, transmit begomoviruses such as tomato leaf curl New Delhi virus in South Asia and the Middle East, and the greenhouse whitefly transmits potato yellow vein virus in the Andes. Thrips spread tomato spotted wilt virus. In dry areas of the Americas, Europe and Asia, the beet leafhopper transmits beet curly top virus, which occasionally infects potato.

Contact and mechanical spread: PVX, PVS and PSTVd move easily in sap. They spread when leaves of neighbouring plants rub together, on tractor wheels and sprayer booms passing through the crop, on knives used to cut seed, on hands and clothing during roguing, and through sprout contact in storage. In seed production, equipment hygiene and the order in which fields are entered (high-grade stocks first) matter for these viruses.

Soil-borne spread: TRV and PMTV survive in the soil inside their vectors, nematodes and Spongospora resting spores, and infect potatoes through the roots and stolons. Once a field is infested, rotation alone has limited effect, because both vectors persist for years and have alternative hosts. They can also be moved to new fields in soil on machinery and seed.

Volunteers, weeds and other reservoirs: Volunteer potatoes from the previous crop, cull piles, garden potatoes and weeds such as nightshades act as reservoirs from which vectors carry viruses into new crops. Studies in Colombia have detected PVY and PLRV in a single volunteer plant growing beside a seed store, illustrating how easily such plants can sustain infection between seasons.

Recognising Virus Symptoms and Diagnosing Infection

Potato virus symptoms can point to a problem, but they rarely identify the virus. The same virus can look very different in two varieties, and different viruses can look alike. For a reliable diagnosis, growers and seed inspectors combine field observation with laboratory tests.

Common potato virus symptoms: The most common foliar symptoms are mosaic (patches of light and dark green), mottling, crinkling or rugosity of the leaf surface, rolling of the leaflets, yellowing, dwarfing and dead spots or streaks on leaves and stems. In tubers, viruses can cause internal necrosis, rings and arcs in the flesh, cracking and reduced size. Symptom expression is also affected by temperature, plant age and whether the plant grew from an infected tuber or was infected during the season.

Why visual inspection is not enough: Many modern varieties show only mild or no foliar symptoms when infected, and some viruses, such as PVS, are almost always symptomless. The rise of recombinant PVY strains shows the risk: strains that cause mild leaf symptoms escaped roguing and spread through seed systems. In Idaho and Washington seed potatoes, the recombinant strains PVY^N-Wi and PVY^NTNa together accounted for 98% of PVY-positive samples by 2021, after the ordinary strain dropped sharply from 2011. Similar shifts have been reported in Europe, which is why most certification schemes now combine field inspection with laboratory testing.

ELISA and lateral flow strips: ELISA (enzyme-linked immunosorbent assay) detects virus proteins with specific antibodies. It is cheap, can process large numbers of samples and remains the standard test in many certification laboratories, although it is less sensitive than molecular methods. Lateral flow devices use the same principle on a paper strip, giving a result in the field within minutes, but they share ELISA's sensitivity limits and are not available for every virus.

RT-PCR, real-time RT-PCR and LAMP: Reverse transcription polymerase chain reaction (RT-PCR) copies a section of the viral RNA many millions of times so that even very small amounts can be detected. Real-time RT-PCR measures the product as it builds up, which makes it faster, quantitative and suitable for testing several viruses in one reaction. These methods are used to detect viruses in dormant tubers and to identify virus strains, for example to tell tuber-necrotic PVY strains from others. Loop-mediated isothermal amplification (LAMP) works at a single temperature, tolerates crude sample extracts and can run on portable battery-powered devices, making sensitive testing possible outside the laboratory.

High-throughput sequencing: High-throughput sequencing (HTS) reads all the genetic material in a sample, so it can detect every virus present, including new or unexpected ones, without knowing in advance what to look for. A 2024 review in Frontiers in Horticulture describes its growing use in testing seed and vegetative planting material and in post-entry quarantine. In Colorado, HTS of inconclusive seed samples identified PVY^N-Wi as the main strain and revealed variants that could escape standard strain-typing tests. HTS is still too costly and complex for routine testing of every seed lot, but it is becoming a reference tool for laboratories and plant health authorities.

When seed lots are tested: Certification programmes test at different points. Leaf samples are tested during the growing season. After harvest, many schemes test a sample of tubers from each seed lot, either directly by RT-PCR on dormant tubers or by a grow-out test, in which tubers are sprouted and grown in a greenhouse or a warmer region and the leaves are tested. Viruses are harder to detect in dormant tubers because their concentration is low and unevenly distributed, which is why sensitive molecular methods are preferred for direct tuber testing.

Preventing and Managing Potato Viruses

Potato virus management is preventive and works best as an integrated programme. No product cures an infected plant, so the aim is to plant healthy seed, keep vectors from spreading viruses within the crop and stop infections from reaching the tubers. The main steps are:

1. Plant certified, virus-tested seed of a suitable class.
2. Inspect fields regularly and remove infected plants early.
3. Manage vectors with methods suited to the type of virus.
4. Remove volunteers, cull piles and weed hosts.
5. Adjust planting date and destroy haulms before late infections reach the tubers.
6. Grow resistant or less susceptible varieties where available.

Certified, virus-free seed: Certified seed is the single most effective protection against potato viruses, because it limits the number of infected plants present from the start of the season. Seed class matters: higher classes have stricter tolerances and fewer generations in the field. Growers producing their own seed for more than one or two seasons should test it before replanting.

Field inspection and roguing: Roguing means removing infected plants, including the mother tuber and daughter tubers, before vectors spread the virus further. It is most effective early in the season, when plants are small and symptoms are easier to see, and in seed crops with low infection levels. For smallholders without access to certified seed, positive selection, marking healthy-looking plants during the season and keeping only their tubers for seed, has reduced virus incidence by 35–40% and raised yields by about 30% in trials in East Africa.

Vector management: The right vector control depends on how the virus is transmitted. For persistent viruses such as PLRV, insecticides are effective because they kill colonising aphids before they have fed long enough to pass on the virus. For non-persistent viruses such as PVY, insecticides are of limited use, because an aphid can transmit the virus in a brief probe before the insecticide acts. Here, refined mineral oils sprayed on the foliage interfere with virus transmission, and border crops of a non-host such as cereals or soybean act as places where incoming winged aphids lose the virus from their mouthparts before reaching the potatoes.

In field trials in New Brunswick, Canada, PVY spread to 18% and 22% of initially virus-free plants in unsprayed plots in 2014 and 2015. Combining mineral oil with insecticide sprays cut this to 4% and 12%, while insecticide-only sprays gave no significant reduction, as reported in the American Journal of Potato Research. Straw mulch and intercropping can also reduce PVY spread, although their cost is usually justified only in seed production. Product choice and spray timing depend on local registrations and aphid monitoring; crop protection suppliers and extension services can advise on options approved in each country.

Crop hygiene: Destroying volunteer potatoes and cull piles, controlling weed hosts, cleaning machinery between fields and disinfecting cutting knives all reduce the sources from which viruses spread. Seed farms usually work from the highest seed class to the lowest, so that equipment and workers do not carry contact-transmitted viruses into the cleanest stocks.

Planting date and haulm destruction: Planting early, so that plants reach mature-plant resistance before the main aphid flights, reduces the risk of infection. In seed crops, killing the haulms before aphid numbers reach a critical level prevents late-season infections from moving into the tubers. In India, the seed plot technique combines these principles: seed crops are grown in the season of low aphid pressure on the plains and the haulms are destroyed before vector numbers rise. Aphid monitoring with suction traps or yellow water traps helps time both decisions.

Resistant varieties: Host resistance is the most cost-effective way to control viruses where formal seed systems are weak. Potato breeders use two main types of resistance genes: extreme resistance genes, which stop virus multiplication without visible symptoms, and hypersensitive resistance genes, which kill infected cells to confine the virus. Many genes work only against certain virus strains, and resistance-breaking strains have emerged, so variety choice should be based on local virus populations.

Soil-borne viruses: For TRV and PMTV, prevention starts with field choice. Testing soil for the vector or the virus before planting, avoiding fields with a history of spraing for susceptible varieties, and choosing less susceptible varieties are the main tools. Because Spongospora also causes powdery scab, measures that limit powdery scab, such as avoiding over-irrigation at tuber initiation, also reduce the risk of PMTV.

Virus Control in Seed Potato Systems

Seed potato certification is the backbone of virus control in most major potato-producing countries. It combines clean starting material, a limited number of field generations, field inspection and laboratory testing, so that virus levels stay within set limits as seed is multiplied.

From tissue culture to certified seed: Certified seed starts from nuclear stock: plantlets grown in tissue culture and tested free of the regulated viruses, often after meristem culture or heat treatment to eliminate infections. The plantlets produce minitubers in insect-proof greenhouses or screenhouses, which are then multiplied in isolated fields as pre-basic, basic and finally certified seed. Each season in the field adds risk, so certification schemes limit the number of generations. In the European Union, up to seven generations are allowed across pre-basic and basic seed, and up to two for certified seed.

Virus tolerances and standards: Each seed class has a maximum permitted level of virus infection, measured during field inspection and, in most schemes, by post-harvest testing. Tolerances are strictest for the top classes and wider for certified seed sold to ware growers. International references include the EPPO certification scheme for seed potatoes (PM 4/28) and the UNECE Standard S-1 for seed potatoes, while national rules set the binding limits. Some viruses, such as PMTV and potato virus V, are tested for only in nuclear stock, because they rarely cause problems further down the chain.

Informal seed systems: In much of Asia, Africa and Latin America, formal certified seed reaches only a small share of farmers. Most plant seed from their own previous crop or buy it through informal trade, and virus levels in this seed can be very high. A survey of commercial tuber-seed lots in Antioquia, Colombia, found PVY in 81.7% and potato yellow vein virus in 70.0% of samples. Programmes led by the International Potato Center and national institutes combine rapid multiplication of clean seed, decentralised seed producers, positive selection and resistant varieties to improve this situation. In the Andes and the Himalayas, farmers traditionally refresh their seed by sourcing it from higher altitudes, where aphid pressure is lower.

Potato Viruses Around the World

Which viruses matter most depends on climate, vector populations, varieties and seed systems. The importance of individual viruses also shifts over time, with changes in trade, cropping patterns and testing regimes.

Temperate seed regions: In Europe, North America and Oceania, strong seed systems keep most viruses at low levels, and PVY is the main concern. Over the past three decades, tuber-necrotic and other recombinant PVY strains have caused heavy losses in Europe and North America, although some areas, such as south-west Australia, were reported in 2020 as still free of them. In cooler, wetter areas such as northern Europe, soil-borne TRV and PMTV are a recurring quality problem for processors and fresh packers.

Subtropical lowlands: In the subtropical plains of South Asia, potatoes are grown as a winter crop, when aphid numbers are lower. Tomato leaf curl New Delhi virus has become a major problem in the Indo-Gangetic plains of India, especially in early-planted crops exposed to whiteflies moving from cotton and vegetables. Elsewhere in warm regions, including North Africa and the Middle East, thrips-borne tomato spotted wilt virus and whitefly-borne viruses add to the familiar aphid-borne viruses.

Andean and East African highlands: The Andes hold the greatest diversity of potato viruses, including several found nowhere else, and some strains there can overcome resistance genes used in other regions. In the East African highlands, where most farmers save their own seed, PVY, PLRV and mixed infections cause seed degeneration over successive seasons, and improving access to clean seed is a central part of potato development programmes.

Climate change: Warmer seasons can bring earlier and larger aphid and whitefly flights and allow vectors to spread to higher altitudes and latitudes. Researchers at the James Hutton Institute have described PLRV as a re-emerging threat, linking its return to changes in agronomic practice and a warmer environment. Because climate, trade, seed systems and vectors interact, the future importance of individual viruses is difficult to predict, which makes ongoing surveillance essential.

New Research in Potato Virus Management

Research on potato viruses is moving fastest in diagnostics and resistance. Some of the tools below are already used in seed programmes; others are still at the laboratory or greenhouse stage.

Faster field diagnostics: Multiplex real-time RT-PCR panels and LAMP assays are already in use, and portable devices are bringing sensitive testing closer to the field. HTS is being adopted by plant health authorities and reference laboratories to check nuclear stock and imported material and to discover new viruses and strains.

Breeding and gene editing: Breeders are stacking several resistance genes into new varieties and using molecular markers to speed up selection. Gene editing approaches are being studied in two directions: switching off plant genes that viruses need to multiply, and using RNA-targeting CRISPR-Cas13 systems to cut viral RNA. A 2025 laboratory study reported that Cas13 constructs reduced PVY and PLRV levels in potato plants, but such approaches still need field testing and regulatory approval.

RNA-based sprays: Spray-applied double-stranded RNA (dsRNA) can trigger the plant's own RNA silencing defence against a specific virus without genetic modification of the crop. In a 2022 study, PVY-specific dsRNA sprayed on potato suppressed PVY but not the unrelated PVX, showing the sequence-specific nature of the protection. Stability on leaves, cost of production and regulation remain the main hurdles to practical use.

Forecasting and decision tools: Aphid suction-trap networks, weather-based models and online alert systems help seed growers time oil sprays, insecticide applications and haulm destruction. Combined with field test results, they are moving virus management from fixed calendars towards risk-based decisions.