Friday, 16 February 2007

Woohoo! My potatoes germinated

Potato seedball harvested last July. I'm now in the process of growing its seeds.

It may not seem like much to get excited about, but it is for me. It's the first time I've tried growing potatoes from seed. That's right, not the usual tubers left sprouting in eggboxes on windowsills (though I have plenty of those too) but real, true seeds.

Just to confuse things, the term 'seed potatoes' or 'potato seed' usually refers to tubers which are supplied for planting. But they're not seeds really, they're vegetative cuttings. Potatoes do produce real actual seeds though, and to differentiate them from seed tubers they are called 'true potato seed', or TPS.

If you've been looking at the blog for any length of time you may remember the small green 'apples' I collected from my potato plants last year. Not all potatoes produce them, because many these days don't have fertile pollen in their flowers and so have lost the ability to set top fruit (or seedballs, as they're properly called). But every now and then they appear.

They look very like miniature green tomatoes, for the very good reason that potatoes and tomatoes are closely related (hence their susceptibility to blight). When you open up a potato fruit it has juicy white flesh full of small tomato-like seeds. I saved some last year, not knowing whether they would be viable or not, and they have taken a couple of weeks to germinate ... but there they are, little pale green noses poking up out of the compost just like tomato seedlings.

You may be wondering why I'm bothering to grow potatoes from seed when it's easier to grow them from tubers. In fact, it will take two seasons to get a decent harvest from them this way. But the appeal (for me) is that each seed is unique, and effectively a brand new variety. Some will be worth keeping and some won't, but they'll all be unique.

When I do my pea breeding projects I know which genes control the traits I want, and I can predict to some extent what I'm going to get if I cross Plant X with Plant Y, even down to the likely ratio of particular characteristics in each batch of offspring. But that's because peas are efficient inbreeders, genetically stable and easy to control. Potatoes are the opposite. They are a gene lottery. I don't even need to do any crosses ... I can take self-pollinated seeds from one plant and the resulting offspring will all be different from the parent plant and from each other.

The reasons for this are a bit complicated, and if you're not interested in plant genetics you may want to hum a pleasant tune to yourself while you read the next bit. It's basically down to potatoes having twice as much genetic material as normal.

Here goes then. Genes are carried on chromosomes, which are chunks of DNA. In most plants chromosomes are arranged in matched pairs, which means there are two copies of each gene. Each gene pair may consist of two dominants, two recessives, or one of each, and these combinations determine which traits are expressed in the plant. The technical name for this gene arrangement is diploid. When a diploid plant is fertilised and produces seed, the chromosome pairs are torn apart down the middle and only one half is passed on by each parent. The seed (and the plant that grows from it) inherits one set of chromosomes from the ovule of the flower which produces it and one from the pollen which fertilised it. The two sets match up into their correct pairs, so the seed ends up with a new diploid (paired) arrangement made up of one set of chromosomes from each parent.

Potatoes are not diploid though, they're tetraploid. Instead of having two sets of chromosomes they have four. So when they reproduce by setting fruit, each seed inherits two complete sets of genes from each parent instead of one. Every chromosome carries many thousands of genes, and as both parents have four sets of chromosomes each, and the chromosomes break up into parts which randomly recombine, it becomes quite a major reshuffle ... more or less any combination of genes could end up being passed on to the offspring (or not). Which makes for a right mixed bag.

And suddenly the system of one gene being dominant over its neighbour becomes a lot more complicated. Instead of a simple 'either-or' situation you get four copies of each gene vying for dominance. You may get one dominant and three recessives, two of each, four recessives, four dominants, etc. Recessive traits which have been hidden for generations suddenly emerge. The likelihood of a seed-raised potato having the same genetic makeup as its parent(s) is very small indeed.

One way of looking at it is to imagine a diploid plant is like a one-armed-bandit fruit machine with only two wheels spinning inside it. The number of combinations possible with two wheels is relatively small. Increase the number of wheels to four though, and suddenly you have a massive increase in possible combinations and much less chance of predicting what you might get. That's basically what happens with a tetraploid.


Even if my potato seeds come from a flower which pollinated itself, the number of possible different combinations of genes should ensure that every plant I grow is a new variety. Some will be crap and may not even survive. Most will be good, but probably not very interesting. But with any luck a few will be excitingly different. At the end of the first season I will harvest the tubers from each plant and select the ones I like best. They will only be mini-tubers, not full sized potatoes. To evaluate them properly I will have to save them over next winter and replant them in 2008, when they should reward me with a decent crop. And once I've done that, I can select any I want to keep long-term, and that's how I get my new variety.

OK ... so how the hell do you maintain a new variety, when there's so much unavoidable variability every time you reproduce it? Well actually that bit is easy. Once you've grown a potato variety you like from seed, you just save and replant its tubers. The great random genetic lucky dip is only an issue when plants reproduce sexually by producing seed. Because tubers reproduce by vegetative propagation they are actually root stem cuttings (clones) from the parent plant. So each new plant grown from a tuber is genetically identical to the plant which produced it, and remains so in successive generations. This is true of all commercial potatoes too of course. If I plant a tuber of King Edward, for example, I'm essentially growing a cutting from the original King Edward plant which flourished in a Northumbrian field back in 1902.

So that's the genetic basis for wanting to grow potatoes from seed. But there are other benefits. Tubers are genetically identical to the parent plant but they also very efficiently store and pass on all the viruses and nematodes the parent plant may have had. These can build up over successive generations and become a serious problem, which is why most countries have laws requiring commercially available seed tubers to be tested and certified disease free (usually involving hefty blasts of chemicals). However, potatoes raised from seed are generally virus-free anyway, because there are very very few seed-borne potato diseases. And growing from seed represents a good opportunity to select new varieties with better disease resistance, specially adapted for your own garden, because most modern commercial varieties are pretty rubbish in that department.

If you're interested in developing your own potatoes I highly recommend a fantastic eBook, Amateur Potato Breeder's Manual by Raoul A. Robinson, which the author has generously made available as a free download. It's angled towards breeding for sustainable disease resistance, but the information is so thorough and clearly explained it's a gift to anyone who wants to grow spuds from seed. He even explains how to graft a potato scion onto a tomato rootstock so that it has to put all its energy into forming flowers and seedballs instead of tubers. Now that sounds like fun!


2010 update
As this page still gets a lot of hits, I thought it worth mentioning that I've written a new and updated article about growing potatoes from seed, with more pictures.

21 comments:

Patrick said...

This is really interesting! I have never heard of tetraploid chromosomes before. I'll bet now is when you wished your garden was really, really big so you could grow out all these potentially interesting new potato varieties!

Rebsie Fairholm said...

Too right! I live in hope that one day some nice person in my neighbourhood will lend me a small field.

Anonymous said...

Dude, that was seriously fascinating. My folks will be amazed to hear that potatoes are tetraploid-- I'd always wondered why everyone just composted the little fruitballs.

Great blog!

Anonymous said...

just last week i found the little green seed balls on my potatoes and i had wondered about the process of bringing them to bear plants and googled the phrase `potatoes from see' and found your fascinating article. Now i shall certainly try to grow these into plants!
arthur beaudarc, Canada

Mitch said...

This year our potatoes had many seed pods on them.They started to fall off the plant while still green. I am interested in trying to grow potatoes from these.

Will the fact them fell off the parent plant while green keep them from growing? Do you plant the whole seed pod or do you open them and take out the very small seeds and plant those?

Any info will be deeply appreciated.

Mitch

Rebsie Fairholm said...

Hello Mitch

It depends how mature the seedballs were when they fell off. It's quite common - normal even - for them to fall off. Just pick the largest and most mature looking ones. They tend to go slightly soft as they ripen, so if any of them have reached this stage they should germinate well.

Open up the seedball and scrape out the tiny seeds. I usually do it into a small bowl of water to clean the pulp off. Once you have the seeds extracted, you grow them in the same way as tomatoes.

Good luck.

maria said...

Hello fellow folksinger/Earthmother. I am a seed collector/spokesperson [for Seeds of Diversity Canada] living in Toronto, Canada, and also a folk singer, for the last 40 odd years or so. I was just going to try the potato seed experiment because I am becoming increasingly alarmed about the amount of plant material that is cloned/grafted. This is pretty risky, as far a disease resistance and climate adaptability is concerned. Your pointers for doing this are going to be very helpful. Have you ever tried "fermenting" the potato fruit as you would a tomato to prepare them for storage or planting? We do this for tomatoes to kill viruses and to rot off the enzyme that retards germination. I am going to try this with some of the "BC Blue" potatoes I have in the garden. If you would like me to send you my CD, "Love Songs for the Homeless Guy," please send your mailing address to my email: mariakasstan@gmail.com I would be happy to send it to you, FREE, as it were, as I am very grateful for the rich info on your site. I have some other [older] things on myspace as well, but I don't run the site, and get too impatient with the computer to spend all day. Much luck with the harvest! Maria Kasstan

Garden Geezer said...

I am a very "new at it" veggie gardener and I had tomatoes on one side of my 20 x25 foot plot and taters on the other with a lot of other veggies in-between. Imagine my surprise when little green maters started sprouting up in my taters. Needless to say I now know from reading your blog that those little green beauties were potato seeds !!!! You should have heard me bragging to my wife about my miniature green tomatoes growing wild in the garden, good thing I am too ignorant to have been embarrassed at the time lol.

Lynda said...

How did the seedlings grow for you this year? Any updates?

Kayla said...

Thank you for describing what those little fruits are on the potatoes because this year was the first time i have ever seen on my potatoe plants... my dad and i are willing to try next season to plant them and see how they go... cant wait... we are going to get my grandparents involved in trying the seeds our next season along with our tubers... thank you :)

Jenn said...

So?? How did they grow? I see this is an older post, but I found it when doing a search. I am so excited to hear how it went for you. I hope it went well. I am going to save your post to my favs and try this myself. Good luck to everyone else who is going to try it too!!!!! ~Jenn

Tom Wagner said...

I am posting here because updates on this subject are dear to me. I am offering True Potato Seed (TPS) in 2010 for interested parties. This work of mine in now entering the 6th decade of breeding potatoes and handling of those potato berries.

I was in Coventry and Oxford this past fall offering TPS during my talks there, and I know several people there will be growing potatoes from my seed. You can find me on the internet by googling Tater Mater and Tom Wagner along with TPS and you will locate my blogs, forums, etc. Patrick, who posted here first, is my main contact in Europe about my potato work.

Tom Wagner

Anonymous said...

Hi, I was given some potato seeds and found this blog while looking up how to grow them.

Now I need to know - what do the emerging seedlings look like?

Thanks, Margaret

Rebsie Fairholm said...

Margaret, I've just posted a new and more detailed article about true potato seeds, including photographs of seedlings:
http://daughterofthesoil.blogspot.com/2010/04/sowing-potatoes-from-tps.html

Laurie Darcey said...

Thank you for this info. I have my true potato seeds ready to go! I don't suppose they would overwinter in our zone, but I will check out that eBook!

Anonymous said...

I'm a New Zealander and I stumbled across TPS a few years back. I dug over my aunt's garden in spring not realising she hadn't removed the tops of last season's spuds. I inadvertently scattered TPS everywhere and they came up like hair on a dog's back. Once I realised they weren't growing from leftovers I let them go. I got a lovely spud I call Hangover - its got pink eyes and it feels a bit rough :-) Since then, I've grown TPS deliberately. I'm trying seed from Maori potatos this year. The Maori traded for spuds with whalers and explorers for at least 6 centuries so it should be interesting.......

Anonymous said...

im trying to do this myself, I grew Desiree in 2010 and many of them fruited heavily, so naturally I saved the healthiest fruit and processed the seed. The following weeks after a good time in the fridge I tested them for germination rates and it was very high, the strongest seedlings were potted on (carefully)and have since aquired some small golfball sized tubers to experiment with, there was one downfall....I havent successfully been able to get these seed plants to flower! or the new tubers! so Ive looked into the whole R.Robinson potato breeding manual (its online from sharebooks) which talks about grafting them (using an approach graft) onto tomato stock, thus all the plants energy is rendered into producing fruits not tubers, if this fails then they are not deemed suitable for breeding, which will be a disapointment (although i will still have the tiny tubers to grow on to produce more.........gotta be worth as try! excellent blog by the way! be back to see how things are going.wezza2009@live.co.uk

Rebsie Fairholm said...

Ah, but you've already bred your own variety simply by sowing those Desiree seeds! You don't need to worry about whether they flower - unlike other plants, potatoes don't need to keep creating more seed from one generation to the next. Just evaluate the tubers you have grown from your Desiree seed - they should all be slightly different from one another and from their parent variety - and if there are any you like, you can keep them going simply by re-planting the tubers from year to year.

Golfball sized tubers is exactly what you can expect for a successful first year - so you've obviously done everything right so far. Next year they will be bigger.

I haven't tried the method of grafting onto tomato roots, but for most purposes it's extreme and unnecessary. Raoul Robinson's book is excellent, but it's aimed at people growing on a large scale and for a specific purpose - i.e. multi-gene disease resistance. For home gardeners breeding potatoes for fun, it's all a lot more simple! Just sow whatever seed you can get, and if you like the results, keep and replant the tubers. Job done!

Anonymous said...

What a delightful thing to do. I didn't wonder for one moment why you grow you potatoes from seed.

Y Al-Khatib said...

I have been doing it for years with exciting results.

Anonymous said...

NAug.31 2014 This was my first time to notice the seed balls on my potatos. I was,as every one else,very suprised and had to see what they were. Thank you for the complete information.It was very helpful,and glad I wasn't thinking about eating them.Keep up the good work.Susan