Hybrids versus open pollinated corn

That depends on what type of corn you’re eating. Hybrid corn is as much a loser for taste if we’re talking field corn (cornmeal, grits, hominy, etc.), which is what I assume the article was about, as it is a loser for protein/nutrients. Of course, hybrid sweet corn, on the other hand, has been bred very aggressively for sweetness.

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There are technically 3 types of corn, hybrid, gmo, open pollinated.

I don’t eat a lot of corn flower, or even feed lot, corn fed meat, but I eat some and now that you’ve shown me this I’m inclined to try to find sources of food that are from OP corn. I hope it becomes a foodie movement so such products become available and identifiable.

I’ve long preferred my open pollinated sweet corn to the sugary types now in vogue and even popular on this forum. I want to grow corn that tastes corny, not corn syrupy- that stuff I can buy anyway. It tastes about the same way after a couple weeks in storage as fresh picked. When I bought sweet corn instead of growing it I purchased it from Amish farmers when I could. They only seem to grow OP types.

I brought this up in 2015 here Blackberries by the gallons - #11 by clarkinks again here Raccoon, squirrel or opossum damage? - #30 by clarkinks one more time here Interesting short article on new GM tomatoes ... thought I'd share - #3 by clarkinks . Im a reader of Eco-Farm by the late Charles Walters of Acres magazine as well but i love the way the author plantlover68 describes the problem on the other website. Im glad other people get it because the modified sweet corns, field corns etc will not end well. Furthermore people drink pasteurized milk now as well since there is more need to do so now. People are creating problems they are unaware of. I could go on but eating the same convenient food as everyone just less of it i feel like a hypocrit. We need to solve these,problems at home first. Gmos and hybrid are also polluting our open pollinated seeds genes. I have open pollinated seeds but i question all seeds now. There is a tipping point we are approaching as farmers.

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To my knowledge, there is only one company left that aggressively markets hybrid and open pollinated corn i.e. does not sell any gmo seed corn.

Corn breeding has been oriented toward increasing production of starch to the exclusion of protein and other nutrients. To illustrate this, a corn variety was found in North Korea about 20 years ago that produces much higher oil content than any corn in the U.S. When it was brought to the U.S., it was tested and found to have genetics that had been removed from commercial breeding lines of corn. The best I recall, it was an open pollinated corn that produced 20+ percent oil. This corn currently has been used in breeding at university of Minnesota to create a hybrid that produces the highest oil content of any currently available corn. It has not been released to the public due to concerns about property rights. Some search terms that work are “Bernardo High Oil Corn” and “Korean High Oil Corn”. A stable hybrid AHO-1 was developed. The traits of this corn are smaller kernel, larger embyro, less starch, and less volume. In a world where corn farm income depends on volume, you can bet there is not much demand.

I grow a high protein corn that came from crossing Cherokee Squaw with a numbered line from ARS-Grin. I fed the corn to my chickens a few years ago to see what impact it had on egg production. The chickens ate more of the corn than the commercial egg ration. They also produced about 10% more eggs. Don’t read too much into this. It basically means the high protein corn met the needs to produce eggs. I attribute this mostly to increased consumption plus the benefit of more lysine and more methionine in the corn. If you want to read about this more, search for methionine corn. How could I further improve this corn as animal feed? One way would be to increase the content of beta carotene. Search for professor Torbert orange corn to read about this a bit.

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Nobody in my family does anymore. We drink the milk substitutes. I myself was never a fan of milk. I recently had a physical, like last week! My calcium and well everything else is normal. Calcium was very high, seem not to have any problem with it not drinking milk. I never actually drink the substitutes straight, never have my whole life. Real milk or substitute. I need it for cooking, I also use half and half, depends what I’m cooking.
As far as substitutes, I’m not a fan of the almond. I have not tried the cashew, I use coconut milk substitute. I only drink it straight if I get heartburn. I don’t use tums or other stomach products as the milk substitute relieves it instantly. My wife still prefers tums rolaids etc. I tend to get heartburn when I have too many cups of coffee. What I love about the substitutes is their long shelf life. We consume little and every container of real milk when we did use it would always go bad before we finished it. Even though we bought small sizes. Those days are gone now. No more waste.

It’s interesting how corn can vary so much and the different niches it can fill. For me I like the (se/sh2) hybrids the best. All I ever grow, I only grow corn every other year. It’s a no grow year this year. Yeah I tried some of the other types of sweet and was always disappointed so I just grow se/sh2 hybrids like Honey Select or Serendipity triple sweets.

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This is the growing list of gmo’s and yes apples are on the new list https://gmoanswers.com/current-gmo-crops?gclid=EAIaIQobChMIkOLXkq_g5wIVRv_jBx3yywnnEAAYASAAEgKb1vD_BwE
Sticking to just corn for a minute which im qualafied to talk about since i grew round up ready corn in the late 1990s. Had grown open pollinated corn many times before and after those years where i grew soybeans and corn that was modified for roundup. The amount of chemicals needed for the program is staggering.
This is from the website above

Know who your dealing with i did not when i grew these products. The gentleman Paul W who taught me to farm using roundup died of bone cancer by the way. He was a close friend of the family. This website gives some info on these companies and what they do and who they are Five things to know about Bayer and Monsanto . Im not going to go there on chemicals / gmos because that is a seperate thing and causes heated disagreements. Going to limit this to corn because as a society we are addicted to what these chemicals do for us. When i mean us i mean me to. I limit my chemicals to the bare minimum i think i need and my conscience stays pretty clear doing that. I have 5 gallons of rodeo in my barn as we speak and countless fruit tree chemicals because with a large farm we need some at times when all else fails. Ignorance has been much of my problem at times and other people have that trouble too because we dont always know a better way. Corn is however very different from other crops because we used thousands of gallons of spray on our gmo corn crops. My fruit crops take less than a quart of concentrates a year all total. I mean Copper, fungicide etc. And i handle most insects with traps. By the way open pollinated corn i grew spray free but there were some ear worms at the tips of the ears the last several times i grew it. There are traps for those to. Open pollinated wheat and many others can be grown spray free as well.

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I have no desire to send my topic from general gardening to lounge so lets (im the worst offender) please limit the rest of the topic to hybrid versus open pollinated corn and leave gmo corn out of it. The distinction needs to be made their is a difference between the first two and the latter. Please flag me anywhere where you feel i crossed the line. I have complete respect for those individuals who are professional farmers, the chemical sellers, goverment regulators etc we are all in this together looking for a better way to put food on the table. Ive been on both sides of the fence. Organic farms may be limited by geography as well. My farm may never be a candidate for 100% spray free but i cut way back.

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Im going to also point out hybrids and gmos cost us power over our own lives if we let them. Growing those puts others in charge of our food. I love this recent topic on popcorn which is clearly open pollinated if seed is being saved it must be open pollinated Selecting new Corn from Old . This link has just a few open pollinated sweet corns Southern Exposure Seed Exchange . Here are some additional op corns Open-Pollinated & Heirloom Corn Open-Pollinated & Heirloom Corn - Territorial Seed Company and more Sweet Corn (Maize) Seed Varieties - Heirloom, Open Pollinated, Non-hybrid Seeds from Victory Seeds® and more https://www.ufseeds.com/product-category/vegetables/corn-seed/heirloom-corn/ and more Heirloom, Open Pollinated, Non-Hybrid Field and Sweet Corn Seed from the New Hope Seed Company and more https://www.stokeseeds.com/us/catalogsearch/result/?q=+Corn+seeds
I enjoyed reading this but know nothing of this gentleman Breeding Sugary Enhanced (se) Multi-Colored Open Pollinated Sweet Corn again we can expect more of these op types https://www.restorationseeds.com/products/tux-multi-color-corn-sweet. There is always alot more to learn about open pollinated corns and ive grown them a long time . “There are six types of corn kernels: flint, flour, dent, pop, sweet, and waxy.” As seen and discussed more here The Types of Corn Grown in the U.S. and How We Use Them
" A Corny Guide to the 6 Types of Corn Grown in the U.S.

Corn is literally in everything. You can’t go through a day without encountering types of corn in one form or another, whether it’s the hand soap in your bathroom (both the plastic bottle and the cleanser itself), your morning bowl of cereal , the gas in your car made in part of ethanol, the aspirin you take for a headache, the crayons your kids draw with, or the roasted corn you serve as a side dish for dinner (and it fed the cow you fixed as the main dish, too).

In 2017, the United States produced 14.6 billion bushels of corn. Most of that produce went to places other than your dinner table, such as livestock feed and industrial products, but corn is still a staple of human consumption from breakfast all the way through snack time. And because we rely on corn for so many things other than eating, the diversity in corn grown in the U.S. has decreased. Large corn farmers are producing the corn needed for feed and fuel and food products like corn starch and corn syrup, which is not the corn we eat off the cob.

There are six types of corn kernels: flint, flour, dent, pop, sweet, and waxy. Flour corn is mostly grown in the Andean region of South America and is used to make corn flour. Waxy corn is grown in China and has a texture that is more like glutinous rice. Grab some butter and salt, and let’s look at some of the different types of corn and how a few farmers are trying to keep corn diversity alive.

TYPES OF CORN

1. DENT CORN

Dent corn, which is also known as “field corn,” is an easy type of corn to spot – there’s a dent in the crown of each individual kernel of corn. It has a high starch and low sugar content, which means it’s not sweet and juicy like the corn you buy to eat from the grocery store or farmers market. Because it’s not meant to be eaten fresh, dent corn is harvested in its mature stage when the kernels are dry and then processed.

Most dent corn grown in the U.S. winds up as animal feed, though because of its soft starch, dent corn is used as a grain in products like chips and masa (a corn flour used to make corn tortillas). Dent corn is also used to make moonshine and bourbon . The majority of corn grown in the U.S. is yellow dent corn, though you may also find dent corn in a range of colors.

2. SWEET CORN

Sweet corn is what you eat for dinner (or breakfast or lunch – there’s no bad time to eat fresh corn). It has a high sugar content, which is why it’s desirable as a fresh corn. It’s picked while immature, before the sugar has a chance to turn into starch, in what is known as the milk stage. Fresh, sweet corn is juicy; the juice, or “milk,” is how you get the creaminess of cream corn.

This type of corn comes in white, yellow, and colored varieties, and at the grocery store, you’re generally just going to find it labeled as “corn.” You may also see super-sweet corn; this variety is sweet corn with the sugar content enhanced for a sweeter flavor.

3. FLINT CORN

Flint corn is also known as Indian corn or calico corn, and it’s even harder than dent corn. If you see decorative corn (those fall-colored ears with the husks still on them), it’s almost certain to be flint corn. However, flint corn has a high nutrient value and once the grains are dried, they can be used for any number of foods, including corn meal, corn flour, hominy, polenta, and grits.

Flint corn that has a hard outer shell is what gets turned into popcorn. The kernels are dried to a point where they have a certain moisture content left; then when the dried kernels are heated, the remaining moisture turns into steam and causes the kernel to turn inside out, or pop.

This type of corn is grown mostly in South America in countries like Argentina. In the U.S., you may find it at local stores and farmers markets as popcorn.

4. HEIRLOOM CORN

There used to be far more variety in corn than there is today, but industrial farming has led to a narrower selection, with only a few types of corn being grown by large farmers. The end users of corn want a standardized product that’s the same every year, so that’s what large-scale farmers tend to grow. Heirloom corn refers to corn that’s not mass produced and tends to be varieties that have all but disappeared.

Fortunately, there are farmers working to bring back heirloom varieties of corn. It’s not always an easy process, though, saving corn. In the case of Jimmy Red, it came down to two ears and a South Carolina farmer.

Jimmy Red is a crimson red dent corn with a rich and oily germ that, back in the day, was known for making outstanding moonshine. When the last bootlegger died in the early 2000s, South Carolina farmer Ted Chewning got his hands on the last two ears of Jimmy Red corn. Chewning, a well-known seed saver, turned those two ears into seed and by carefully cultivating the seeds year after year. He gave seeds to other local farms and a few chefs, and the heirloom corn now has its own cult following.

This type of corn is used by famed Charleston chef Sean Brock; he even has a tattoo of the corn on his arm. Other Charleston chefs, including Forrest Parker and Jason Stanhope, use the corn as well, especially for making grits .

And Jimmy Red still makes a fine hooch. High Wire Distilling, also based in Charleston, was able to make two barrels of bourbon using only the red corn from a 2014 crop. Cementing Jimmy Red’s legendary status, the 570 bottles from those two barrels sold out in 11 minutes.

Today, you can buy heirloom corn varieties to grow or to cook with, including a corn that creates pink unicorn grits. If you can’t find it in your local store, it’s available online from places like Anson Mills or Geechie Boy Mill .

This article was originally published on April 23, 2018.
"
and then here is more about growing , spacing etc. https://myfarmlife.com/home-garden/the-best-varieties-of-heirloom-corn/
" The Best Varieties of Heirloom Corn
Seven varieties of heirloom corn that are as easy to grow as they are to eat.

BY KAREN K. WILL

If you have a patch of well-drained soil, you’ve got most of what it takes to grow heirloom corn. Many old-line, open-pollinated heirloom varieties are surprisingly easy to grow and provide delicious produce, perfect for eating fresh, canning or grinding into meal.

Heirloom Corn Basics

Many varieties are drought-resistant, and plenty can yield a good crop with 90 frost-free days or fewer. Some of these corns prefer to be grown in hills (four to six plants per) spaced on a 3- or 4-foot grid. Others will do fine in rows. Adding nitrogen in the form of composted manure at planting and blood meal at the final hoeing should be all the corn needs in good soils.

Most heirlooms can be planted about two weeks before your last frost date, and will survive light frosts until seedlings are at the four-leaf stage. In addition to the main stalk, some old varieties produce tillers; you can pinch them off or allow them to grow, reaping the reward of miniature nubbin ears.

When it isn’t possible to irrigate, opt for wider row spacing, up to 36 inches. Cultivate as soon after germination as needed, and then once or twice more before hilling. It’s imperative to use shallow cultivation and to hill at speed so soil will be thrown into the row without damaging the plants’ lateral roots.

WEB EXCLUSIVE: Five More Heirloom Corn Growing Tips

Most of the older corn varieties don’t have uniform seed sizes and shapes, so you should adjust your planting equipment for best results. If you have vegetable-seeding equipment, experiment with different plates; tape off holes if the spacing is too close for corn.

If your seed is untreated, don’t worry. Most of the old varieties are quick to germinate and relatively resistant to cold, damp conditions. However, if you typically plant a month before your last frost date, you might want to wait a couple of weeks for a more favorable outlook to plant untreated seeds.

Hilling is imperative for standability of old corns. If you planted in rows, adjust your cultivator shovels to take a shallow cut in the center between rows and move that soil into the row. The combination of depth and speed will allow you to throw sufficient soil into the row to cover the first exposed node. If you planted in hills, simply pull sufficient additional soil to the hill to cover the first node.

In the event your plot is hit with a strong wind and the corn experiences a high frequency of lodging, just wait it out. Most of these old corns will recover completely, sometimes even after being flattened.

Some old varieties, especially those adapted to grow in dry conditions, have not been bred for ear decline, so they remain erect with the tips pointing up. These ears won’t shed rain or heavy dew as well as varieties that decline at maturity; thus, molding of ears can be a problem. Time the planting so the grain will be maturing during typically drier periods, or choose other varieties.

Heirloom Corn Varieties

All varieties listed below can be combined, except where noted.

Oaxacan Green Dent

Oaxacan Green Dent (75 to 100 days; rows) An ancient corn of the Zapotec people of southern Mexico, it’s traditionally used to make green-flour tamales. Ground Oaxacan Green also adds color and flavor to homemade tortillas, polenta, corn mush and even breading for deep-frying. Ten-inch ears are born on 7-foot stalks, producing 12 or more rows of emerald-green kernels. This variety is very drought-resistant and, if watered too often, will tend to lodge under windy conditions.

Hopi Blue (90 to 110 days; hills or rows) With 30% higher protein content than conventional dent corns, this drought-tolerant flint corn is delicious boiled or roasted in the early milk stage, and makes wonderful, antioxidant-rich cornmeal when dried and ground. Don’t overwater this variety or it will tend to lodge more easily.

Mandan Bride (85 to 90 days; hills or rows) A multicolored corn that produces a mixture of flour and flint kernels on every ear, it’s developed from traditional Mandan corns and is highly prized by chefs as a grinding corn for use in polentas and cornbread. Like other Mandan corns, it won’t stand for combining or machine picking, but for the home garden or restaurant market, hand-picking makes it worthwhile. Best shelled right before grinding—or shelled and frozen— to preserve peak flavor.

Painted Mountain (70 to 90 days; hills or rows) Developed over the last 40 years from a number of Northern Native American corns, it’s cold-tolerant and perfect for short growing seasons in relatively dry conditions. This multicolored eight-row corn is good roasted when immature, and ground into meal and flour, imparting a nutty flavor. The plants won’t stand for combining.

(https://www.myfarmlife.com/wp-content/uploads/2014/03/1_14_corn1-200x300.jpg)](https://www.myfarmlife.com/wp-content/uploads/2014/03/1_14_corn1.jpg)

Bloody Butcher

Bloody Butcher (100 to 110 days; rows) Developed commercially in Virginia by around 1845, some say it was long a part of Native American commerce by then. This dent corn will produce two to six 8- to 12-inch-long ears on stalks that can reach 12 feet. This corn is delicious when roasted or boiled in the very early milk stage—don’t expect the sugar of modern sweet corns—and is wonderful when ground into meal or parched to make corn nuts.

Golden Bantam (75 to 85 days; rows) A traditional old sweet corn that offers real corn flavor with just the right amount of sugar, this yellow variety was first offered by W. Atlee Burpee in 1902, and it’s been with us ever since. Look for improved strains for longer ears with more than 10 rows of succulent kernels. The plants should stand about 6 feet tall and bear two 8- to 10-inch ears under good conditions.

Stowell’s Evergreen (85 to 105 days; rows) A white sweet corn developed by Nathaniel Stowell and released in about 1848, it’s terrific for canning and fresh eating. Stowell’s produces two 8-inch ears with up to 20 rows of kernels on stalks that might just reach 8 feet tall. Although not as sweet as today’s supersweet hybrids, Stowell’s is famous for holding the sugar longer after picking than most others."

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This article legitmately brings up some valid points on the otherside of the fence http://thinkbioenergy.com/did-you-know-there-were-6-different-types-of-corn/ some claim 4 types only exist https://www.popcorn.org/Different-Types-of-Corn. My goal is education not to necessarily persuade you to be on strictly one side or the other of hybrid or open pollinated. My side right now leans towards open pollinated due to nutrition levels when grown for animal and people food. I think for fuel i would lean towards hybrid to increase production. Great article here https://www.farmanddairy.com/top-stories/how-to-tell-the-difference-between-types-of-corn/279825.html
corn-kinds
More to educate us on types Types of Corn – Native-Seeds-Search
Finally how do we grow the best open pollinated corn ourselves? Much has been summarized here Improving Your Own Open-pollinated Corn | EcoFarming Daily based on this https://www.acresusa.com/products/how-to-grow-top-quality-corn .

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Here’s a recent trend in sweet corn breeding that seems long overdue: modern breeding for new open-pollinated sweet corn, in the following case a sugary enhanced (se) variety. It seems like there was at least a half century without any new open-pollinated varieties of sweet corn being released.

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@cousinfloyd
Thanks for posting this i was not sure it was stabalized yet when i read of this a few years ago. I had no further details other than to know they existed but no experience growing it or if it was available. You posted exactly what i wanted.
Open pollinated types like this are the best because the seeds grow true to type as you know whereas hybrids do not , they revert to an undesirable type. This is very hard to grow corn thats an se type of yellow and white corn. Seeds of change sold an open pollinated small eared 5-6" indian type sweet corn that was exceptional that i cannot find any longer. It was not theirs they merely sold it for the expert who developed it. I grew it 5 years until i finally lost the seed to multiple droughts and carelessness. It was a delicious light multicolored pinkish type sweet corn.

Isn’t Stowell Evergreen an OP variety? I have seen it advertised on some seed sites.

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There are several such smaller seed companies selling mostly to home gardeners, right? Are you talking about a larger seed company selling modern varieties to commodity farmers?

Can you remind me what variety you grow? Have you compared it to other o-p varieties and found it significantly superior? I’ve grown maybe 6-8 different varieties (including complete crop failures that may or may not have been failures regardless of the variety) of open-pollinated sweet corn, and if I were to try one of those again it would probably be Golden Bantam, but I’d almost just as soon eat the heirloom field corn I’ve been growing in what people here call the roasting ear stage. I think what most of the local older generation ate when they were young for sweet corn was just early harvested field corn (harvested in the roasting ear stage.) I quit growing sweet corn mainly because I’ve been saving my own field corn and popcorn seed, and corn requires really big isolation distances (although it offers significant potential for isolating in time since it can be planted (even transplanted) over a fairly long season.)

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Going on memory, it was blue river seeds selling commercial corn varieties. Smaller companies are out there by the hundreds but in the scheme of corn seed marketing they are minor players.

I’m working on a se+ variety developed from Country Gentleman crossed to Silver King. Stabilizing the shoepeg trait with se has been a problem so far. I’ll get it eventually.

If you are growing corn to feed animals, I highly recommend growing higher protein content varieties. For sweet corn, pick your particular pleasure. I happen to like se+ because of the tender pericarp and increased sweetness. If you want to get into the nitty gritty details, there are about 9 different genes that play a part in corn sweetness. This includes the standard su (golden bantam), se+ (from Narrow Leaf Evergreen), super sweet (many varieties similar to Illini Extra Sweet), and often enhanced by combining with other genes such as du (dull, boosts total sugar content).

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Just Golden Bantam and that white one with Evergreen in the name.

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Certainly RU-ready corn would presumably be sprayed with RU, maybe several times. And RU acts as a chelating agent binding to and tying up some minerals. So as far as this mineral comparison goes, if the hybrids were RU-ready then I’d be surprised not to see a reduction in minerals.

But @cousinfloyd says, it’s not just RU-ready hybrids which have had the nutrition bred out of them. We often breed with just one or two goals in mind (disease resistance, color, early ripening, etc) and I doubt that many check for nutrients as part of their breeding programs.

This line of thought hearkens back to the old analysis of crops which the USDA used to publish every 10 years (I think). They suddenly stopped publishing it around 1970 saying that it wasn’t needed anymore. Even though for decades it was showing a steady decline in the nutrition of most of the crops it covered. But since no one is paying attention to this anymore, no one did any research as what the causes were of the steady decline, then or now. I suspect some would be due to the varieties people were growing now and some due to the health of our soils. But who knows.

As far as hybrid vs open pollinated goes, I tend to favor open pollinated, and not just for corn but for everything. Main reason is with OP you can save your own seed and select for traits which you want or do well in your area. Can’t do that with hybrids. (Well you can a bit, several folks have bred lines of hybrid corn, some even being marketed now)

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Alan, I could name a few hundred varieties of corn with su of which Golden Bantam is an example. I’ve grown about 50 such over the years including Luther Hill, Whipple White, Buhl, and others that I sold to Sandhill Preservation for seed. Varieties with se+ are much more limited as it is a gene found after 1950 therefore was widely used in hybrids such as Kandy Korn which was available in the 1970’s. The original variety where se was found was Narrow Leaf Evergreen. One of the complications with se is that for many years it was thought to be on chromsome 4 along with su. Better analysis about 30 years ago finally determined it is on chromosome 2 therefore can be readily combined with other genes for enhanced sweetness. This is the source of the “synergistic” and “augmented” varieties commonly sold today. Synergistic combines sh2 + su + se in varying combinations so that each ear has a few kernels of each type. The usual mix is to stack sh2 and se on top of su such that 50% of kernels are su, 25% are sh2, and 25% are se. Augmented is homozygous for sh2 with se and su stacked on top such that 100% are sh2 with varying percentages of kernels on the same ear having se and su. The reason for stacking these genes is to enhance texture and flavor while boosting overall sweetness.

One problem with sweet corn is that there are very few really good open pollinated varieties. By this, I mean that combining large ears with excellent sweetness and good flavor in an OP line is very rare.

One item of trivia to know about sweet corn is that it is derived from flint corn. A single gene mutation turns flint corn into sugary corn like Golden Bantam. If you combine sugary with ordinary dent corn, too much starch is retained in the kernel resulting in odd textures and flavors.

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Years have taught us very little apparently

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Front Plant Sci. 2021; 12: 768523.

Published online 2021 Nov 16. doi: 10.3389/fpls.2021.768523

PMCID: PMC8635114

PMID: 34868165

Cobalt: An Essential Micronutrient for Plant Growth?

Xiu Hu, 1 Xiangying Wei, 2 , * Jie Ling, 3 and Jianjun Chen 4 , *

Author information Article notes Copyright and License information PMC Disclaimer

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Abstract

Cobalt is a transition metal located in the fourth row of the periodic table and is a neighbor of iron and nickel. It has been considered an essential element for prokaryotes, human beings, and other mammals, but its essentiality for plants remains obscure. In this article, we proposed that cobalt (Co) is a potentially essential micronutrient of plants. Co is essential for the growth of many lower plants, such as marine algal species including diatoms, chrysophytes, and dinoflagellates, as well as for higher plants in the family Fabaceae or Leguminosae. The essentiality to leguminous plants is attributed to its role in nitrogen (N) fixation by symbiotic microbes, primarily rhizobia. Co is an integral component of cobalamin or vitamin B12, which is required by several enzymes involved in N2 fixation. In addition to symbiosis, a group of N2 fixing bacteria known as diazotrophs is able to situate in plant tissue as endophytes or closely associated with roots of plants including economically important crops, such as barley, corn, rice, sugarcane, and wheat. Their action in N2 fixation provides crops with the macronutrient of N. Co is a component of several enzymes and proteins, participating in plant metabolism. Plants may exhibit Co deficiency if there is a severe limitation in Co supply. Conversely, Co is toxic to plants at higher concentrations. High levels of Co result in pale-colored leaves, discolored veins, and the loss of leaves and can also cause iron deficiency in plants. It is anticipated that with the advance of omics, Co as a constitute of enzymes and proteins and its specific role in plant metabolism will be exclusively revealed. The confirmation of Co as an essential micronutrient will enrich our understanding of plant mineral nutrition and improve our practice in crop production.

Keywords: cobalamin, cobalt, endophytes, essential nutrients, micronutrients, symbiosis, vitamin B12, transporter

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Introduction

Cobalt is an essential nutrient for prokaryotes, human beings, and other mammals but has not been considered an essential micronutrient for plants. Instead, this element, along with other elements, such as aluminum (Al), selenium (Se), silicon (Si), sodium (Na), and titanium (Ti), has been considered as a beneficial element for plant growth (Pilon-Smits et al., 2009; Lyu et al., 2017). An element that can improve plant health status at low concentrations but has toxic effects at high concentrations is known as a beneficial element (Pais, 1992). For an element to be considered essential, it must be required by plants to complete its life cycle, must not be replaceable by other elements, and must directly participate in plant metabolism (Arnon and Stout, 1939). It has been well-documented that there are 92 naturally occurring elements on the earth, wherein 82 of which have been found in plants (Reimann et al., 2001). Plants are able to absorb elements from soils either actively or passively due to their sessile nature. The occurrence of an element in plants, particularly in shoots, must have a purpose. Active transport of an element from roots to shoots may indicate a certain role it plays in plants. As stated in the study by Bertrand (1912), potentially, every element has a biological function that can be assessed properly against a background of a deficiency state, and every element is toxic when present at high enough concentrations, which is known as Bertrand’s rule of metal necessity.

Significant progress has been made in plant mineral nutrition since the publication of Bertrand’s rule (Bertrand, 1912) and the essentiality concept (Arnon and Stout, 1939). Among the beneficial elements, cobalt (Co) could potentially be an essential plant micronutrient. Co is a core element of cobalamin (vitamin B12 and its derivatives) and a cofactor of a wider range of enzymes and a component of different proteins in prokaryotes and animals (Maret and Vallee, 1993; Kobayashi and Shimizu, 1999; Harrop and Mascharak, 2013; Odaka and Kobayashi, 2013). Co-containing enzymes and proteins in plants require further investigation and clarification. Rhizobia and other nitrogen (N)-fixation bacteria require Co and cobalamin for fixing atmosphere dinitrogen (N2) into ammonia (NH3), providing plants with the essential macronutrient of N. Co plays a vital role in interaction with iron (Fe), nickel (Ni), and zinc (Zn) in maintaining cellular homeostasis. Similar to other essential micronutrients, plants respond to Co concentrations in soil: at low concentrations, it promotes plant growth but causes phytotoxicity at higher concentrations. However, it is different from other beneficial elements, as plants do exhibit Co deficiency when grown in soils with limited supply.

The objective of this article was to concisely review the importance of Co as a plant micronutrient including its role in N fixation, the occurrence of coenzyme or proteins, and its effects on plant growth as well as Co deficiency and toxicity. We intended that this review could raise an awareness that Co is a potentially essential micronutrient of plants, and further research is needed to confirm this proposition.

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Cobalt and Nitrogen-Fixation in Plants

Cobalt was isolated by Brandt in 1735 and recognized as a new element by Bergman in 1780 (Lindsay and Kerr, 2011). The importance of Co to living things was realized in the 1930s during the investigation of ruminant livestock nutrition in Australia (Underwood and Filmer, 1935). Co was discovered to be essential for animals as it is a component of cobalamin. Five scientists were awarded Nobel Prizes for the investigation of cobalamin (Carpenter, 2004).

Cobalt Is a Core Element of Cobalamin

Cobalamin is a large molecule (C63H88O14N14PCo) comprised of a modified tetrapyrrole ring known as corrin with Co3+ in the center (Osman et al., 2021). Co is not inter-exchangeable with other metals in the cobalamin and cannot be released from the ring unless the ring is broken (Yamada, 2013), implying the significance of Co to cobalamin. There are two biologically active forms of cobalamin, namely, methylcobalamin and adenosylcobalamin in ruminants (Gonzalez-Montana et al., 2020). In human beings, Co is a cofactor of two enzymes, namely, ethylmalonyl-CoA mutase (MCM) and methionine synthase. MCM catalyzes the reversible isomerisation of l-methylmalonyl-CoA to succinyl-CoA. A deficiency of MCM causes an inherited metabolism disorder commonly known as methylmalonic aciduria. Methionine synthase utilizes cobalamin as a cofactor to produce methionine from homocysteine (Table 1). Reduced activity of this enzyme leads to megaloblastic anemia (Tjong et al., 2020). Ruminant animals produce vitamin B12 if there is an appropriate supply of Co in their diet. It was reported that 3 to 13% of the Co was incorporated into cobalamin by bacteria in the ruminant animals (Huwait et al., 2015).

Cobalamin Biosynthesis in Bacteria and Archaea

The natural forms of vitamin B12 are 1,5-deoxyadenosylcobalamin, hydroxycobalamin, and methylcobalamin (Nohwar et al., 2020). They are synthesized by a selected subset of bacteria and archaea (Heal et al., 2017; Guo and Chen, 2018), which include Bacillus, Escherichia, Fervidobacterium, Kosmotoga, Lactobacillus, Mesotoga, Nitrosopumilus, Petrotoga, Propionibacterium, Proteobacteria, Pseudomonas, Rhodobacter, Rhizobium, Salmonella, Sinorhizobium, Thermosipho, and Thermotoga (Doxey et al., 2015; Fang et al., 2017). Cyanocobalamin is not a natural form but commercially synthesized B12. The production of vitamin B12 by these microbes involves about 30 enzymatic steps through either aerobic or anaerobic pathways. In addition to being essential for fat and carbohydrate metabolism and synthesis of DNA, vitamin B12 is a cofactor of many enzymes. There are more than 20 cobalamin-dependent enzymes in those prokaryotes including diol dehydratase, ethanolamine ammonia-lyase, glutamate, and methylmalonyl-CoA mutase, methionine synthase, and ribonucleotide reductase (Marsh, 1999) (Table 1). These enzymes catalyze a series of transmethylation and rearrangement reactions (Rodionov et al., 2003). Thus, Co is essential for those archaea and bacteria.

Cobalt Plays an Important Role in Biological Nitrogen Fixation

Biological N fixation is a process of converting N2 from the atmosphere into plant-usable form, primarily NH3. Biological N fixation (BNF) is carried out by a group of prokaryotes known as diazotrophs, which are listed in Table 2, including bacteria, mainly Rhizobium, Frankia, Azotobacter, Mycobaterium, Azospirillum, and Bacillus; Archaea, such as Methanococcales, Methanobacteriatles, and Methanomicrobiales, and cyanobacteria, like Anabaena, Nostoc, Toypothrix, and Anabaenopsis (Soumare et al., 2020). N2-fixing organisms are also classified into three categories: symbiotic, endophytic, and associated groups (Figure 1). Such classifications may not be accurate as some of them, such as those from Acetobacter and Azospirillum, could be associated, as well as endophytic bacteria."

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The relation of cobalt is important

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