New evidence of evolution of potatoes

Also why they are hard to breed.
https://www.nhm.ac.uk/discover/news/2025/july/we-finally-solved-the-mystery-of-how-potatoes-evolved.html?utm_source=join1440&utm_medium=email&utm_placement=newsletter&user_id=66c4bb9f5d78644b3a946ddc

Neat!

From another article of theirs that that one links to:

'Potato breeding is very difficult because it is a clonally reproduced crop, so new potatoes are grown from pieces of old ones,' Sandy explains. 'It means they have accumulated lots of deleterious mutations, which impact their health and growth and cannot easily be gotten rid of using traditional breeding methods.'

Can anyone explain that? Why do vegetatively produced crops concentrate deleterious mutations? (That sounds crazy, but I assume I'm just missing a piece of the puzzle.)

'It means they have accumulated lots of deleterious mutations, which impact their health and growth and cannot easily be gotten rid of using traditional breeding methods.'

A lot of bad DNA accumulated after years and years of cloning.

The opposite of landrace.

Since potatoes have been around since the Incas that is a long time.

Where did the bad DNA come from if it's cloning? It sort of sounds like they're talking about viral-load, and maybe there's a horizontal gene transfer mechanism from the viruses to the host...or something?

Where did the bad DNA come from if it's cloning?

Clones still accumulate mutations, and most mutations are either bad or neutral. Without sexual reproduction, there's no means for the mutations to be removed. Imagine a parental plant that has a deleterious mutation in one allele, but not in the other allele (in other words, it's heterozygous at that particular gene). All of its cloned offspring will carry that deleterious mutation, but only half of its sexually produced offspring will have the bad allele. Selection can then eliminate the mutation in the sexual line.

True seed from potato flowers is still used today for potato improvement and I was glad to see that some home gardeners are even delving into this approach:  https://heritagerevived.com/growing-potatoes-from-true-potato-seeds/

Nevertheless, clonal selection still is widely used as a means of identifying and advancing potato for yield, quality traits, and disease resistance.   https://www.nature.com/articles/s41598-021-87284-x

Cool to see some discovery on he hybrid origins of potato through genome reconstruction in the links above in this thread.

Oh, right, I get it...duh. Thanks, Jake! The mutations are taking place in the normal tuber tissue due to environmental exposures. (For some reason I got stuck on haploid mutation being the only thing...)

(I grow potato from seed most years. Then we have a taste-test and let some vanish and save the tiny first-year tubers from the ones that aren't too bitter.)

It's a bit more complicated, yet potentially beneficial, that the bulk of domesticated/commercial potato is tetraploid instead of diploid.  There can be 'gene dosage' effects that factor into the negative impacts of a deleterious mutation.  Thus, in a diploid, if a mutation occurs in one of the two copies of a given gene, there may be (a) no effect (mutation fully recessive), (b) full deleterious effect of that mutation (mutation fully dominant), or (c) partial effect on the organism/plant even when a "good" copy of that gene exists on the paired chromosome. In a tetrapolid, you have 4 genes in question because there are 4 chromosome 'equivalents' that harbor those gene copies.  If one copy becomes mutated, a masking effect by the other 3 good copies of that gene *can* occur in certain circumstances.  Also, when we think about how sexual reproduction can eliminate deleterious genes through the act of genome recombination, we forget about other mechanisms that can aid clonal organisms, especially those with polyploid genomes.  For the purposes of this discussion, we can consider the saving of 'seed' tubers in your root cellar and planting anew each spring from stock that is saved from the previous year as the cultivation of a clonal organism. To be sure, depending on the genetic diversity in the potato seed tubers you first obtained or purchased, the genetic diversity in your potato root cellar that you will start from each year is likely to be quite low as a consequence of using the nearly same tuber batch each new year to start the crop.  But this ignores the paired effects of mutation, selection, and even perhaps rarer, gene conversion.  So in the above discussion, we can indeed have both deleterious and beneficial mutations occuring.  Under most circumstances, the deleterious ones will be lost simply by exclusion of those tubers if the mutation causes a significant immediate undesirable product during growth, harvest, storge, or palatability.  Likewise, a beneficial mutation (greater disease resistance, larger tuber size, Paisley skin color ... :-) ) is more likely to be kept out of novelty and saved for planting again in the following year.  But many mutations, both good and bad, can also be eliminated through mitotic gene conversion.  In this case, even though sexual reproduction is not occuring, the pairing of chromosomes during mitosis (cell division while tuber is growing), can lead to a repair of the 'bad' mutation while aligned with the 'good' gene copy.  Thus, there are many forces and mechanisms at work in that underground tuber that can bestow nutrition and resilience in this 'clonal' cosmopolitan comestible.

https://www.cultivariable.com/the-practicality-of-growing-diploid-potatoes-in-north-america/

https://www.biorxiv.org/content/10.1101/2024.08.30.610445v2.full

I've grown some TPS out two seasons ago and am hoping to see the results ones they lay down. Some have flowers so i might get some new seed. I am happy already. people keep saying breeding potatos is difficult because of this tetraploidy or something. I'm not that interested if it's difficult, i don't see how it's difficult. I just get them out, taste them( they tasted of potato) and replant them. I'll dig up the ones that were left behind in spring and move them to the new bed.
Meanwhile i expect to learn a thing or two reading up about them every so often.

It bothers me people keep saying it is difficult, potatos are a wondrous crop, so much result for so little effort. From TPS the results are a bit less spectecular. So what?

If enough people do a difficult thing, progress will be made. Just like the people in South-America who have grown potatos forever and have reached an enormous diversity. They can grow them in whatever climate. I believe we'll be doing humanity a favor by trying to be a bit like them and just respect diversity as is. Because the mindset of those people is very different to ours.

They respect all diversity, they see a change in phenotype as a good sign and share results far and wide. Some change might be good for somewhere else so spread the diversity... I guess that's the message.
I was at 'Sow your resistance' in Antibes in 2024, and spoke to a Peruvian farmer who explained it in simple words. He shared some wonderfull fava seeds with me and told me that the crop originates in Europe, but they have more diversity. Because they look for it and cherish it.

I can only hope that mentality will finally prevail over the 'it is difficult, don't do it!' one we currently abide to in the West.

Christopher Weeks wrote:Where did the bad DNA come from if it's cloning? It sort of sounds like they're talking about viral-load, and maybe there's a horizontal gene transfer mechanism from the viruses to the host...or something?

Just guessing., though it sounds to me like from your quote:

a clonally reproduced crop, so new potatoes are grown from pieces of old ones

How much do you know about DNA?

Been out to get some.. Bit early. No idea if they're good. Many small ones. But I like how they look.