The potato industry increasingly asks how a new variety can reach growers faster. But the familiar 15-year timeline conceals several different biological problems. Looking beyond genomics alone reveals a deeper story involving heterozygosity, vegetative multiplication, diploid genetics, unreduced gametes — and the possibility of redesigning the breeding system itself.
By Lukie Pieterse, Editor/Publisher of Potato News Today,
and Dr Herman J. van Eck, Wageningen University & Research
When Potatoes USA recently convened approximately two dozen researchers in Denver to discuss a national roadmap for potato variety development, one figure captured attention: moving from identifying a useful trait to having a variety in growers’ fields can take around 15 years.
The July 21, 2026 meeting considered faster and cheaper genotyping and phenotyping, improved genetic markers, better data sharing, germplasm exchange, coordinated testing and more durable research funding. All are credible ways of making potato breeding more efficient.
Yet that raises a question that is easy to overlook: what precisely consumes those 15 years?
The answer is not one bottleneck. Potato breeding is slowed by several biological and operational processes, and technologies that accelerate one may have little effect on another.
A useful starting point is to separate two fundamental constraints: the genetic consequences of breeding a highly heterozygous outcrossing crop, and the practical consequences of multiplying commercial potatoes vegetatively.
That distinction leads eventually to a further question. Should breeders simply become better at identifying winners within enormous segregating populations, or can they change the breeding system so that fewer genetic “lottery tickets” need to be bought in the first place?
Why every conventional potato cross reshuffles the deck
A successful potato cultivar is an intricate genetic package. Yield, maturity, disease resistance, tuber size and shape, skin characteristics, dormancy, storage behaviour, cooking quality, fry colour, dry matter and numerous other characteristics are determined by many genes interacting with one another and with the environment.
Most commercial potatoes are autotetraploid and highly heterozygous. When two such parents are crossed, their favourable combinations of alleles do not simply remain intact. Meiosis reshuffles them, and the offspring segregate widely.
This distinguishes potato from highly homozygous self-pollinating crops in which breeders can often improve an established variety incrementally.
Suppose an otherwise successful inbred variety lacks one resistance gene. A breeder may introduce that resistance from another parent and repeatedly backcross to the original variety, recovering much of the original genome while retaining the desired new allele.
With a heterozygous outbreeder such as potato, the problem is much more difficult. Crossing a successful variety breaks apart many of the combinations that made it successful in the first place.
A breeder therefore produces large seedling populations and searches through them for rare individuals in which enough desirable characteristics have come together again.
It is, in one useful analogy, a genetic lottery.
The more tickets available, the greater the chance of finding an exceptional combination.
But buying, growing, testing and eliminating those tickets takes time and money.
Fixation changes the mathematics
Diploid breeding offers one way of simplifying this genetic problem. Consider a single diploid locus with genotype Aa. After self-fertilisation, offspring segregate approximately one AA : two Aa : one aa. Once AA has been selected, that locus is homozygous and therefore fixed: it no longer segregates for A versus a.
This simple principle becomes enormously important when expanded across the genome. If useful alleles can be fixed, breeders begin retaining rather than repeatedly reshuffling favourable genetic information.
That thinking underlies much of the modern interest in self-compatible diploid potato breeding.
Self-compatibility itself was once regarded as difficult to obtain in potato. Research by Corentin Clot, Herman van Eck and colleagues, however, showed in 2020 that Sli-based self-compatibility was more widespread in potato germplasm than had often been assumed.
Yet self-compatibility and fertility are not the same thing. A plant may be genetically capable of accepting its own pollen while still producing inadequate pollen or seed. Repeated inbreeding can expose deleterious recessive alleles and reduce vigour and fertility.
That is one of the central difficulties confronting F1 hybrid potato breeding: achieving enough homozygosity to make parental lines genetically predictable without losing the biological vigour and fertility required to make the system practical.
The breeding debate is much older than today’s hybrid potato programmes
None of this began recently. In 1963, S.S. Chase described what he called “analytic breeding” in potato, proposing the use of parthenotes and other diploid material to simplify genetic manipulation.
During subsequent decades, researchers including Stan Peloquin and colleagues in Wisconsin, Jacob Hermsen and M.S. Ramanna at Wageningen, scientists associated with the International Potato Center, and many others investigated diploid breeding, polyploidisation and mechanisms for moving genetic material between ploidy levels.
Ramanna’s 1979 examination of 2n gamete formation was especially important in describing meiotic mechanisms capable of producing unreduced gametes and considering how they might be exploited in potato breeding. Research on 2n pollen and eggs was also being pursued in North America, including extensive contributions from the Wisconsin programme.
Later developments included the Wageningen-associated F1 hybrid work published in 2011 and renewed international interest in diploid inbred-line breeding during the following decade.
The important point is not to assign the modern potato breeding revolution to one laboratory, university or country. Its foundations were laid through decades of interacting — and sometimes competing — scientific ideas.
That historical perspective also reveals that there has never been only one route to simplifying potato genetics.
A third route: fixation without extreme inbreeding
One particularly interesting alternative is now being developed under the name fixation–restitution breeding. The idea attempts to combine advantages from both diploid and tetraploid breeding.
At diploid level, genetics is simpler. Useful traits can be identified and fixed more efficiently than in a highly heterozygous tetraploid population. But instead of driving the whole genome towards extreme homozygosity, as required for classic F1 hybrid parental lines, fixation–restitution seeks to retain substantial heterozygosity elsewhere in the genome.
That matters because heterozygosity contributes to vigour and can help avoid the inbreeding depression and fertility problems associated with highly inbred diploid lines.
The second part of the concept — restitution — relies on unreduced, or 2n, gametes. Normally a diploid potato produces gametes containing one set of chromosomes. During certain forms of abnormal or modified meiosis, however, chromosome reduction fails and the resulting pollen or egg retains the somatic chromosome number.
In first-division restitution, much of the parental heterozygosity can be transmitted through the unreduced gamete rather than being separated in the conventional way. Ramanna’s 1979 work described mechanisms producing such gametes, and numerous researchers subsequently examined their value in potato breeding.
This provides a biological bridge from diploid breeding back towards tetraploid commercial material.
In simplified terms, breeders can work at diploid level where inheritance is easier to manage, fix a particular desirable locus while retaining substantial heterozygosity elsewhere, and then use unreduced gametes to create tetraploid offspring carrying much of that selected diploid genome.
Wageningen University & Research currently lists Fixation–Restitution Breeding among projects led by van Eck, together with earlier projects explicitly aimed at using diploid inbreds for fixation and unreduced gametes for tetraploidy. A 2024 Wageningen-linked conference contribution described the concept as a middle ground between conventional tetraploid breeding and diploid F1 hybrid breeding.
The eventual commercial product need not be true potato seed.
Tetraploid offspring can be evaluated, the best individual selected and that genotype propagated clonally, just as a conventional potato variety is.
This distinction is crucial because it separates the breeding method from the form in which growers receive the variety.
True seed and better breeding are not the same question
F1 hybrid breeding is often discussed alongside true potato seed, and understandably so. Highly defined parental lines can produce more genetically uniform botanical seed, opening possibilities very different from traditional seed tuber production.
True seed offers important logistical and phytosanitary advantages. Thousands of seeds can be transported in a small package rather than tonnes of tubers, while botanical seed avoids many of the disease problems accumulated through repeated vegetative propagation.
These characteristics could be particularly important in regions where certified seed tubers are expensive, difficult to store or unavailable in sufficient quantities. But true potato seed addresses a different group of problems from the question of how to organise the genetics of a breeding programme.
It is therefore useful to separate three discussions that are often blended together: How should potato genetics be manipulated most efficiently? Should the commercial variety ultimately be delivered as botanical seed or as a selected clone? And how should planting material be multiplied, transported and kept healthy?
One breeding system need not provide the same answer to all three.
The second clock: vegetative multiplication
Even a dramatically improved breeding system would not automatically eliminate another contributor to the 15-year timeline. A promising conventional potato clone initially exists in tiny quantities. Seed stock must then be multiplied while material is simultaneously required for disease testing, agronomic trials, storage evaluation, processing tests and multi-location comparisons.
A single seed tuber may yield perhaps a dozen or more daughter tubers under suitable conditions, but that multiplication factor is modest compared with seed-propagated crops.
Furthermore, breeders cannot economically multiply every early candidate to commercial scale. Most will eventually be discarded. Expansion therefore tends to accelerate only after confidence in a candidate has grown. Selection and multiplication consequently proceed partly in sequence rather than perfectly in parallel.
This is a fundamental reason why shortening genetic selection does not necessarily remove all of the years between cross and commercial acreage.
The 15 years contain several different clocks.
Genomics: finding the winners sooner
Where, then, does genomics fit? Very prominently. Marker-assisted selection allows breeders to identify plants carrying particular genes or genomic regions at an early stage, eliminating unsuitable material before expensive testing begins. Genomic prediction extends that principle to complex traits, using genome-wide markers and statistical relationships between genotype and observed performance to estimate which individuals are most promising.
This can make the genetic lottery substantially more efficient.
Van Eck offers a useful conceptual distinction. Imagine a conventional breeding population containing 100,000 lottery tickets. Genomic prediction can help identify many tickets that are unlikely to win before the costly draw of years of field testing.
That is a substantial advance.
But changing the genetic architecture of the breeding programme asks a different question: can breeders design a lottery in which far fewer tickets are needed to begin with?
This should not be framed as genetics versus genomics. Modern breeding programmes routinely combine them. Genomics helps breeders see. Breeding-system innovation changes what they are looking at.
The greatest gains may ultimately come when both are used together.
Why ploidy matters to the numbers game
A simplified example illustrates the point. At a diploid locus, Aa × Aa gives AA, Aa and aa offspring in the familiar 1:2:1 ratio. One-quarter is therefore homozygous AA. Tetraploid inheritance allows considerably more allele configurations and more complicated segregation. At a single locus, combinations can include AAAA, AAAa, AAaa, Aaaa and aaaa.
The real genome is, of course, vastly more complicated than one locus. But the principle scales: tetraploid polysomic inheritance increases the number of possible genetic combinations through which breeders must search.
Diploids can therefore make fixation and genetic analysis more efficient.
That does not automatically mean the best commercial potato must itself remain diploid.
Fixation–restitution illustrates why. Simpler diploid genetics can potentially be used during breeding, while unreduced gametes provide a route back to tetraploid offspring where favourable heterozygosity and commercial performance can again be exploited.
So what is actually taking 15 years?
The more closely the timeline is examined, the less useful it becomes to speak of “slow potato breeding” as though it were one problem.
Part of the delay arises because highly heterozygous parental genomes segregate, forcing breeders to search large populations.
Part comes from evaluating complex traits that cannot be predicted perfectly from DNA.
Part comes from testing varieties across locations, seasons and production systems.
Part comes from storage, processing and disease evaluation.
And part comes from the stubborn arithmetic of vegetatively multiplying enough healthy seed potatoes to support commercial adoption.
Different technologies shorten different parts of that sequence. Genomics can improve early selection. Diploid genetics can simplify inheritance. F1 hybrid breeding aims to produce predictable parental combinations and potentially uniform true seed. Fixation–restitution seeks another path: exploit diploid genetics without demanding genome-wide homozygosity, then restore tetraploidy using unreduced gametes.
True potato seed can transform multiplication, logistics and parts of phytosanitary management.
Better research coordination can reduce duplication and move useful material between programmes faster.
The central question raised by the Potatoes USA roadmap may therefore be even more important than the original 15-year figure suggests.
Before asking how do we shorten potato breeding?, it may be necessary to ask: Which part of those 15 years are we trying to shorten — and what biological process is responsible for it?
Once the problem is defined correctly, the industry can choose the appropriate tool.
The future of potato breeding may not belong to one technology or one breeding philosophy. After more than half a century of experimentation with ploidy, unreduced gametes, diploid genetics, markers, genomics and hybrid breeding, several once-separate lines of research are beginning to intersect.
The real breakthrough may come not from declaring one of them the winner, but from understanding how the pieces fit together.
Authors’ note
This article arose from an exchange between the two authors following Potato News Today’s earlier reporting on the Potatoes USA variety-development roadmap. Lukie Pieterse initiated and developed the journalistic article and independently researched the broader literature. Dr Herman J. van Eck contributed the central genetic framework, historical context, the distinction between breeding genetics and vegetative multiplication, the explanation of fixation–restitution breeding, and technical review. Both authors share responsibility for the final published version.
Sources consulted
- Potatoes USA. Potato Researchers Convene to Shape a National Roadmap for New Potato Variety Development. July 21, 2026.
https://potatoesusa.com/news-events/ - Ramanna, M.S. (1979). A re-examination of the mechanisms of 2n gamete formation in potato and its implications for breeding. Euphytica 28, 537–561.
https://link.springer.com/article/10.1007/BF00038921 - Chase, S.S. (1963). Analytic Breeding in Solanum tuberosum L. — A Scheme Utilizing Parthenotes and Other Diploid Stocks. Canadian Journal of Genetics and Cytology 5, 359–363.
https://cdnsciencepub.com/doi/10.1139/g63-049 - Clot, C.R. et al. (2020). The origin and widespread occurrence of Sli-based self-compatibility in potato. Theoretical and Applied Genetics.
https://link.springer.com/article/10.1007/s00122-020-03627-8 - Wageningen University & Research. Herman J. van Eck — research profile, publications and projects.
https://research.wur.nl/en/persons/herman-van-eck/ - Wageningen University & Research. Fixation–Restitution Breeding – analysis and synthesis of haplotype compositions of diploid potato germplasm.
https://research.wur.nl/en/persons/herman-van-eck/ - Clot, C.R. et al. (2024). Innovative potato breeding through FIXATION and RESTITUTION – the happy medium between conventional tetraploid and diploid F1 hybrid breeding. 22nd EAPR Triennial Conference, Oslo.
https://research.wur.nl/en/persons/corentin-clot-2/ - Clot, C. et al. (2024). Crossover shortage in potato is caused by StMSH4 mutant alleles and leads to either highly uniform unreduced pollen or sterility. Genetics 226(1).
https://academic.oup.com/genetics/article/226/1/iyad194/7378811 - Ramanna, M.S. (1983). First division restitution gametes through fertile desynaptic mutants of potato. Euphytica 32, 337–350.
https://link.springer.com/article/10.1007/BF00021442 - Jansky, S.H. et al. (2016). Reinventing Potato as a Diploid Inbred Line-Based Crop. Crop Science 56, 1412–1422.
https://acsess.onlinelibrary.wiley.com/doi/full/10.2135/cropsci2015.12.0740
Image: Credit Thomas from Pixabay
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