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I was watching The Martian, and there is a scene with Mark harvests his potatoes and says that he keeps the larger ones for his food supply and replants the smaller ones.

Wouldn't this create a genetic propensity for the next harvest to favor smaller potatoes on average?

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    While not strictly gardening related, I vaguely remember from the book that the timeframe he was aiming at was pretty short (e.g. survive months, maybe couple of years). The risk of "cultivating small potato breed" is rather insignificant as far as selection in a couple of generations, even if (see accepted answer) it was a risk at all
    – DVK
    Commented Apr 2 at 17:02
  • I always like to point out this answer at the sister site scifi.stackexchange.com, whenever there is a question about Mark Watney's potatoes.
    – davidbak
    Commented Apr 5 at 2:39

3 Answers 3

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Great question, this is one of the cool things about potatoes!

Mark is creating clones of the mother plant when he uses the small potatoes as seed potatoes. All of the plant's potatoes have the same genetics, it doesn't matter which particular potato is used as the seed potato.

The small potatoes are smaller for non-genetic reasons, which won't be passed on.

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    However, if he has several mother plants, he would have genetic diversity among the plants, and by replanting the smaller potatoes, he would be creating clones of those plants which tended to have smaller potatoes. Probably not much of an issue (as potato size is largely a matter of how long the potato has been forming, and so Mark's strategy is probably a good one for maximising calorie intake over the short to medium term.
    – James K
    Commented Apr 2 at 7:48
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    Also of note is that he intends to survive on potatoes until the next transport, which is in two years IIRC, and if that doesn't come, he will die regardless of potatoes, due to running out of other resources. And in such a short time period, genetic drift does not play any significant role, even if it was an issue (which this answer shows it is not). Unless he cares about having better potatoes 20 years later, it is not an issue which ones he eats and which ones he plants, even if it mattered.
    – vsz
    Commented Apr 2 at 11:42
  • Reading for other potato enthusiasts: intechopen.com/books/10750
    – MackM
    Commented Apr 2 at 13:14
  • @JamesK Also, even if there are several mother plants, they are probably clones of each other, since they will all be the same variety, and the farm they come from probably isn't using an open-pollinated variety.
    – Eonema
    Commented Apr 14 at 23:29
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My high-school biology textbook (~1985) contains exactly potatoes as an example for a bad strategy for selection because the new potatoes all carry the same genes as the one seeded and one gets the same distribution of sizes.

This is why here, on Earth, we use the same strategy when planting potatoes - we use the smaller ones for seeding.

What is less known about potatoes is that they also have a real seeds. This is what you get from their flowers. The seeds do have some genetic diversity because the potato flowers are cross-polinated by bees.

If one does the whole hassle of collecting and planting the potato seeds, one COULD exert selection pressure on them and (at least, in theory) select them for favorable properties.

From the comments: Getting potato seeds implies polination of their flowers and thus having bees. I am yet to see the movie, but one of the comment stated that the movie character had no bees.

Potato (and almost all other) flowers could be hand-polinated. This is routinely done in indoor gardening and this is also how an important discovery was made long ago by Gregor Mendel.

Hand-polination does not scale well, but it looks like potatoes in fact do need sexual / seed-based reproduction once in a while (few years) in order to maintain health and yield.

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    @gerrit should the matter be this much important, one could cross-polinate flowers by hand. This is what Gregor Mendel did to pea and this is what many amateur botanists do in their homes. This does not scale well, but it looks that potatoes in fact do need sexual / seed-based reproduction once in a while in order to maintain health and yield.
    – fraxinus
    Commented Apr 2 at 6:52
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    FWIW, Mark himself is a botanist, definitely familiar with the basics of genetics. It's a pity it wasn't explained to the audience, though.
    – Trang Oul
    Commented Apr 2 at 19:36
  • The advantage in the movie of using potato seed for the next crop rather than seed potatoes would be a slight extra supply of potatoes in the short term; in the artificial environment he'd presumably have to hand-pollinate anyway so would be free to choose whether to cross them or pollinate within a variety. However he would be at the mercy of germination of the seeds in harsh conditions
    – Chris H
    Commented Apr 4 at 20:21
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+100

Gardener here.

Planting small potatoes will yield bigger potatoes. Planting big potatoes will yield smaller potatoes.

That's because potatoes are tubers that grows along the stem of the plant, if the stem is underground. And bigger potatoes have more sprouts than small potatoes (each "node" or "eye" on a potato will give you a sprout => a stem), so they have more stems, so they grow more "units" of potatoes, so the energy of the plant is divided among more of them, so each of them grows smaller (that's similar to how fruit trees bearing a lot of fruits will tend to yield smaller, less sweet fruit, hence thinning apples for instance).

So if you want to grow early potatoes, you'll likely plant big potatoes, whereas if you want storage potatoes, you'll likely plant smaller ones.

Also, early potatoes are often planted earlier than storage potatoes. I haven't seen the movie, but depending on where you live, this could mean risk of frosts (and potato plant doesn't handle it very well). I think that potentially, if the potato you're planting is bigger, this means that there's more energy for the plant to bounce back to health if the first shoots were affected by frost.

I'm a bit interested in botany but aren't a botanist (only horticulturist). From my basic understanding of it, other answers are quite right about the whole genetic aspect of potatoes.

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  • Fascinating! Welcome to the site, I hope you stick around :-)
    – MackM
    Commented Apr 6 at 20:47

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