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Boost corn yields, cut costs: Part 1

Where grass is greener

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POSTED: April 27, 2011 10:20 a.m.

Genetically speaking, we are more like our moms than we are our dads. Yes, mom and dad each gave us half of the DNA in the nuclei of our cells, but those are not the only genes in our cells.
The mitochondria in our cells and all other cellular life forms have their own genetic material. The chloroplasts in green plants have their own genetic material that controls how they work.
All those genes found outside the nucleus are called extra-nucleic genes, not because they are optional, but because they are outside the nucleus. Think exit – the outside. All those extra-nucleic genes are always and only inherited from our mothers, not our fathers.
Your mitochondria control how your body uses energy. If mom is plump and dad is skinny and they are eating the same food, all other things being equal, we would expect the kids to be plump, because they got mom’s mitochondria. If we reversed it and mom is skinny and dad is plump, the kids will tend to be skinny – because mom’s body tends to burn energy rather than store it.
So what does this have to do with corn? Patience, it will all come together, I promise.
Corn has been cultivated by humans for more than 5,500 years. It started out as a couple kernels on an ear the size of your little finger. The best yielding plants were selected for planting the following season, and slowly the plant developed by human selection into the plant grown by the Native Americans and introduced to European colonists. There are three or four books hidden in those last two sentences, so forgive me if I do not elaborate.
The corn plant naturally is self-fertile. Pollen is produced in the tassel at the top of the plant. The pollen sheds and drifts in the air. If the pollen lands on the silk of a young ear, usually an ear on the same plant that holds the tassel, it digests its way down the silk and down to the ovule and fertilizes it.
A single kernel develops from this process. It takes a lot of pollen to fertilize all those kernels on all those ears of corn in all those square miles of corn fields.
Around 1909, the benefits of hybrid vigor were discovered. Purebred (inbred) corn varieties were found to increase yields by about 20 percent if the pollen that fertilized the kernels came from an entirely different corn variety. The crossed or hybrid varieties that resulted from this breeding also were less susceptible to disease and weather extremes.
Farmers would plant nine or 10 rows of the corn from which they wanted to collect the ears – the female plant – and then plant one row next to it of a different variety of corn whose purpose was to supply the pollen – the bull row. The problem was that the female or ear plants still were self-fertile.
The tassel of each female plant had to be manually removed. At first this was done by hand while walking down the row. Later, it was done by a tractor pulling a tall wheeled frame down the rows upon which workers would lie face down and reach out and manually cut off each tassel of each female corn plant.
Still later, machines were used to cut off the tassels. All these detasseling methods were expensive and added to the cost of the crop.
In 1944, a single corn plant was discovered in Texas that had a gene in its cytoplasm (outside the cell nucleus) that made its pollen sterile. We are simple farming folk, so even our technical shorthand is pretty easy.
The trait that caused the pollen (male) flower to be sterile is a cytoplasmic gene discovered and developed by Texas A&M and was called Tcms corn, which stands for Texas cytoplasm male sterile gene. This gene was backcrossed into the female or ear-producing plants, and viola! No more detasseling was necessary.
By 1956 – just 12 years later – 85 percent of all the corn grown in the United States and Canada carried the Tcms gene. This rapidly brought down production costs (lots less equipment, fuel and labor). How about that – a 20-percent yield increase from just one gene.
Not everyone planted Tcms corn. There still were some farmers who, being an independent bunch, did not change over to Tcms. Still, others were growing corn for seed for the seed companies.
But with as risky a business as farming, one cannot blame a grower for taking advantage of the things he could control. We were manipulating what we found in the environment, brilliantly to be sure, but this still was a naturally occurring phenomenon.
Tcms corn was not some new designer plant. It was a great step toward feeding the world. In spite of our brilliance with Tcms corn, we unknowingly stepped into a right cross 20 years in the making.
Next time – learning to value diversity …

Gardner is the extension agent for Bryan County. He can be reached at dgardner@uga.edu.

 

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