A Horn Of Potato Plenty

KATHLEEN DAVIS: This is Science Friday. I’m Kathleen Davis. For the rest of the hour, a bit of science for you to chew on at the Thanksgiving dinner table. We’re talking about meat and potatoes.

First, the humble potato, a versatile vegetable– baked, roasted, fried, mashed. What can’t they do? But how exactly do these tasty tubers end up on our tables?

Joining me now to give us a crash course in the science of potatoes is my guest, Dr. Rhett Spear, assistant professor in the plant sciences department at the University of Idaho based in Aberdeen, Idaho. Dr. Spear, welcome to Science Friday.

RHETT SPEAR: Hi, Kathleen. Thank you for having me.

KATHLEEN DAVIS: Well, thank you so much for being here. I want to start with a little bit of potato 101. Can you tell us a little bit about how they grow?

RHETT SPEAR: Absolutely. So unlike a lot of plants that grow from an actual little seed that you plant in the ground, most potatoes are what they call vegetatively propagated. So what that means is if you take a potato and you cut it into pieces and throw it in the ground that it will grow another plant, and that new plant will be genetically identical to the parent plant.

KATHLEEN DAVIS: So let’s back up here. So if I have a pile of potato peels and other bits, is it possible that a potato would grow from that pile?

RHETT SPEAR: It depends on how big those bits are. If you have a decent-sized piece and as long as you look at the potato and you see those little divots on the outside of it that we call eyes, those eyes are actually where the stems grow from. So if you have a piece that’s big enough and it has at least one eye on it, you can plant that piece, and as long as the conditions are right– it’s not too cold, it’s not too wet, not too dry– that little piece will grow into a new potato plant.

KATHLEEN DAVIS: So I think most people are familiar with maybe two distinctly different potatoes that they might come across in the grocery store. We’ve got the white potatoes, and we’ve got sweet potatoes. What is the difference between the two?

RHETT SPEAR: So if you go back far enough into their family tree so to speak, they are very, very distantly related. But more importantly sweet potatoes are more part of the morning glory family, and potatoes are in the solanacearum family. So their– potatoes are in the same family as tomatoes and tobacco and eggplants.

KATHLEEN DAVIS: So let’s go back to our good old white potatoes. How did we arrive at the common potato varieties that we see in the grocery store? So I’m thinking russets, Yukon golds, redskin potatoes. How did we come to this conclusion of these are the ones that we’re going to find at basically every grocery store?

RHETT SPEAR: So a lot of that comes down to there’s been something in their development that has been beneficial to the farmer or to the consumer. So a lot of these white potatoes, a lot of them will store fairly well and for a long time. Potatoes like Yukon gold, they have a really good taste, and they’re visually appealing. But most of these potatoes while they do have lots of good things that have got them into the grocery store, oftentimes they’ll have– I don’t know if you want to call them speed bumps in their growth that could be a bigger hindrance, but the farmers know how to grow them. They’ve been growing them for long enough that they know how much fertilizer they need, how much water they need, when to plant and harvest them, and what they need in the season.

KATHLEEN DAVIS: You have I think one of the coolest jobs out there. You helped to develop new potato varieties. So as an expert in this, what makes for a good new potato?

RHETT SPEAR: So we’re always looking for things like efficiency and sustainability. We want to see potato varieties that will turn a better profit for growers. So an example of this would be– we’re looking for maybe potato varieties that use less fertilizer or are less impacted by stresses like heat or water, things that will make that variety easier to grow or better to grow or something that will help the industry to be better.

KATHLEEN DAVIS: And I suspect that you also want those potatoes to taste good, right?

RHETT SPEAR: Oh, of course.

KATHLEEN DAVIS: So what are the factors that actually contribute to the flavor of a potato?

RHETT SPEAR: So there’s a lot of things that will actually contribute to the flavor. Anything from the soil that it’s grown in to the different chemicals and volatiles and things that are actually in the potato that vary by variety. So if you eat a russet potato, it’s probably going to taste different than if you eat a Yukon gold or a red or a purple potato.

KATHLEEN DAVIS: So we talked a little bit about the people who are actually growing these potatoes. How does weather affect the growing process for potatoes?

RHETT SPEAR: So weather is a huge factor when it comes to growing potatoes. The plant, based on the weather, can start growing and stop growing. I don’t know if that makes sense, but if it gets too cold, the plant just– it doesn’t grow as fast. And if you have potato tubers that are already growing at that point, they stop receiving nutrients also.

So when the potato starts growing again and especially if it starts growing really fast, you could have one end of the tuber that’s a lot smaller than the rest of the tuber. And if you have tubers that maybe receive some kind of stress in the middle of the growing season like it got too hot or the farmer didn’t get the water on or something like that, you might have that plant stop growing and/or grow very slowly, and once it can start growing at its full-rate again, you might have a tuber that looks like a dumbbell.

KATHLEEN DAVIS: OK. I don’t know if I’ve ever seen a dumbbell-shaped potato. I have to say.

RHETT SPEAR: Well, quite often now, they’ll cull those out, and they’ll pull them before they get to the store because they’re not visually appealing. Nobody wants to buy that kind of potato.

KATHLEEN DAVIS: We talk about climate change a lot on this show because it tends to affect everything. Does climate change play a factor into how you are thinking about developing new varieties of potatoes into how these potatoes might grow?

RHETT SPEAR: Absolutely. So we really want to find varieties that are less susceptible to heat stress or water stress that they– like they can handle it a little bit better than some of the varieties that we currently use. So we do trials at the university where we’ll stress these varieties on purpose. We won’t give them enough water, or we’ll give them not enough fertilizer. And we’ll see at the end of the season how that affects the yield and the quality of those potatoes.

KATHLEEN DAVIS: So let’s shift gears here back to nutrition for a minute. Potatoes get a bad rap I would say for being unhealthy, but can you set the record straight for us? Are potatoes nutritious?

RHETT SPEAR: Absolutely they’re nutritious. Potatoes actually have quite a bit of a lot of the nutrients we need like potassium and vitamin C and protein. So I used to know some guys that did long distance bike rides, and they would actually cook potatoes, little potatoes, and just put them in a bag on their back. And as they were riding these long distance rides, they would eat potatoes because it gave them a lot of the nutrients they needed for those big expenditures of energy.

KATHLEEN DAVIS: What an amazing idea. I’ve never thought about that.

RHETT SPEAR: I think a lot of the bad rap comes from how the potatoes are prepared because I mean don’t go to Thanksgiving dinner with just a potato and no butter or no sour cream or no bacon or–

KATHLEEN DAVIS: Right. Right.

RHETT SPEAR: You don’t eat french fries that are not cooked in oil.

KATHLEEN DAVIS: I have seen blue potatoes in the store, a shocking sight. Are blue potatoes different nutritionally from white potatoes?

RHETT SPEAR: Yes. So there’s been some research done that’s looked at the nutrition of colorful potatoes like that compared to a white potato, and they do have higher concentrations of nutrients, of carotenoids, and other things that our bodies need. And so colored potatoes really do have a little bit more nutrients in them than just a regular white potato.

KATHLEEN DAVIS: So as the potato expert, I have to ask you. Do you have a favorite type of potato?

RHETT SPEAR: I really do like specialty potatoes or these colorful potatoes. Our program released one called Huckleberry gold, and it actually has a purple skin and a yellow flesh. And it is just excellent for making mashed potatoes.

KATHLEEN DAVIS: That sounds beautiful. Do you have a least favorite type of potato that we should be avoiding?

RHETT SPEAR: Well, given my employment, I don’t know if I should be badmouthing the potatoes that I don’t like so much. But there are some that I wish that we could replace because they’re not efficient to grow. They take a lot of nutrients and water, and any little tiny hiccup will give you a bad yield or bad quality at the end of the season.

KATHLEEN DAVIS: So one little safety question to end us off here. Let’s just say that I forgot about a potato in my pantry and it has turned green. Is it safe for me to eat that green potato?

RHETT SPEAR: That green usually doesn’t go very deep into the potato. So if you peeled it past the green, you’d probably be just fine. The potato plant does produce a toxic chemical called solanine that’s usually pretty much concentrated in the leaves and the stems or the parts that we don’t eat. But potatoes that have been left in the light can develop higher concentrations of that chemical, so I wouldn’t recommend eating a green potato. I would probably peel that off first, but you’d probably have to eat a lot of them to get sick.

KATHLEEN DAVIS: Good to know and thank you so much for being here, Dr. Spear.

RHETT SPEAR: Yeah, thank you very much. Dr. Rhett Spear, assistant professor in the plant sciences department at the University of Idaho based in Aberdeen, Idaho.

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