Landrace sweet corn question

Adaptation Projects
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Hey there,

This year I will be growing 4 different varieties of corn together to start a sweet corn landrace (will add many more varieties in the following years).

Three of the four varieties are definitely sweet corn (Inca Rainbow, True gold, and a local Catalan sweet corn). The fourth variety I acquired from a local permaculture gardener who swears by it. He told me “You can eat it not only as sweet corn, but you can also pop it when it is dry and you can even press the cane for a sweet syrup”.

The thing is, these seeds are not wrinkled like the other three varieties. I always thought that sweet corn seeds are always wrinkled, but maybe I am wrong. I am wondering if I am risking introducing an undesirable trait (I don’t even know what non-sweet corn is called. Never understood the jargon, because there seems to be so many types: flint, flour, pop, grain…).

Anyways, in case it helps, the suspicious seeds are red.

Would you introduce them in the mix?

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From what I understand sweet corn is the result of a naturally occurring genetic “defect”, for lack of a better word. There are a number of heritable genes that can cause it with names like “su” and “se”. More modern commercial breeders have stacked those genes and came up with new things they call, synergistic and some other names I don’t recall. In my own work with sweet corn, I have avoided all but the older su and se types.

When the seed grows it first produces sugars which then convert to starch as it matures, the starch is the food for the baby corn plant when it first sprouts. If the “sugar” genes are present the starch conversion is inhibited or delayed or maybe in the more modern types prevented completely, I don’t know.

Almost any corn is sweet corn if harvested at exactly the right time, but that exact time is very short. If you want sweet corn that is sweet for a period of a few days instead of maybe hours and that doesn’t immediately start losing the sweet the second it is picked then you grow “sweet corn”, those that have the defective genes.

The “endosperm” inside the corn kernel is the starch and the food for the seedling. In flint corn it is very hard and that is used for polenta and things like that. In flour corn it is soft and that can be ground into flour for tortillas and things like that. I think popcorn is basically like flint corn except the endosperm is even harder.

In sweet corn the endosperm is partly missing. That is why the kernel is wrinkled up or puckered looking. It’s also why sweet corn seed is often coated with poisons, to protect the baby sprout, which is basically starving until it develops good roots, from soil organisms.

I don’t know how exactly the sweet genes are inherited, whether they are dominate or recessive and so on, but it sort of doesn’t matter because that wrinkled appearance is a visual tell-tell that a seed indeed has one or more of them.

General advice I think is to avoid mixing non-sweet varieties with your sweet corn. In my own work with sweet corn, I completely ignored that advise in order to bring other traits like stalk strength, disease resistance and generally greater genetic diversity into my mix. For a period, I ended up with sweet and non-sweet kernels mixed on the same ear but just a few years of planting only the shrunken, or wrinkled kernels brought it back to all sweet.

A bit long winded there but in a nutshell, I would say, leave out the non-sweet, if you’re in a hurry. If you got a few years, include the locally adapted seeds for a more robust population in the long term.

Remember almost all corn is sweet corn, if you time the picking just right and have the water boiling on the stove before you go out to pick it. :laughing: The color of the seeds is not related to the sweetness.

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Thanks for the great tutorial, Mark! I guess I will continue to include mostly the wrinkled kernels in my grex. I do prefer to have the less sweet varieties so I guess it would be okay for my situation if there were some of the stronger, “non-defective” genetics included.

Chapi, your friend’s corn sounds like an interesting one to try. Maybe you could grow it far away for your sweet corn grex? Or maybe try some of his this summer?

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The sweet genes, su and sh2, are recessive. If the kernel is wrinkled when dry, it has two copies of at least one of these genes. The se gene enhances the su gene. The sh2 corns are also called supersweets. I don’t particularly like this type of sweet corn because to my taste buds it is just sweet, no corn flavour. I like the su sweets, with or without the se enhancer gene as the flavour is more corny, at least to me.
Mixing in non-sweets: no problem here really. Imagine a block of sweet corn (all from wrinkled seeds) plus a non-sweet. If you were to detassel the non-sweet, any kernels formed on this plant would be half sweet but would look non-sweet, i.e., not wrinkled.
Grow these out and in the next generation you’ll get a mix of wrinkled and non-wrinkled seeds. All the wrinkled ones will be full sweet and into the landrace they go. The rest can go to the chooks.
It gets a little messy if you’re mixing su and sh2 corns, You only have to remember that any wrinkled dry kernel is fully sweet.

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Wow! Thanks a lot for the thorough answer! Will follow your instructions. Maybe I will plant some of the suspicious corn on its own. I can’t separate it too much from the rest, but I can always save seeds from the plants farthest away.