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What’s meant by hybrid diversity?

When an agronomist recommends farmers plant a diversity of corn hybrids, what does that mean? Here’s the dictionary definition of diverse: 1: having a different kind, form, character or quality 2: dissimilar, unlike.

What does diversity look like in corn hybrids, and is it important? The popular open-pollinated variety Reid Yellow Dent was widely grown from the late 19th century through nearly the first half of the 20th century.

Reid Yellow Dent

In fact, the 1907 Pascal ear I wrote about in the August Corn Source column was Reid Yellow Dent. The variety was included from the early 1920s through the 1930s as an entry in Iowa’s Corn Yield Tests, conducted by the Agriculture Experiment Station, Iowa State College.

In 1936 it was the most popular variety in the United States. And it’s important now, too, as 50% of the U.S. hybrid corn family tree originated from Reid Yellow Dent.

Think about it, a popular corn variety grown across the country 100 years ago, and its progeny are still seen everywhere. Is that diversity? No, but of course Reid Yellow Dent as an open-pollinated variety was inherently diverse; every ear, every kernel contained a different set of genes.

We learned too much about the dangers of relying on a narrow genetic base in 1970; some of us remember well southern corn leaf blight that devastated corn across the country that year.

The concept and perils of “genetic vulnerability” were easily engrained in my memory when I saw entire fields of nubbins. Lack of diversity hurt.

Fast turnover these days

Also think about this, a single popular corn variety grown for perhaps half a century! Today’s long-lived hybrids might last only two or three years in the marketplace. Unfortunately, by the time we know where and how a hybrid fits into a cropping system, it’s replaced.

Last month’s Corn Source column summarized briefly the 2011 growing season. In the context of the long hot spell we experienced during pollination, I wrote: “I’m not sure we could have avoided a yield reduction, even with good hybrid selection, management practices, etc.

In any case, you should always plant a diverse set of hybrids … so fields aren’t silking at the same time. That way you can avoid the consequences of a week or several days perhaps of stress occurring during the pollination period.”

Do we have to concern ourselves with genetic diversity in the 21st century? Of course we do. But there are two ways to think about diversity: the regional or national scale, which hit us hard in 1970, and the local scale, your own farm, in 2012.

Make an informed decision

Let’s talk about the latter category here — your farm. It is possible today to plant what you may think are diverse hybrids, when in fact they may be quite similar. That’s like putting all of your eggs in a basket, which briefly brings up a bad memory of mine: As the third son, my job was the egg collecting — enough said!

Now, back to corn. What do you look for to ensure a diverse set of genetics? The first thing you clearly don’t want to compromise is yield. Use hybrid performance data from unbiased sources like the “Iowa Crop Performance Test — Corn.” It’s available at

After looking for high-yielding hybrids and sorting them out, what do you look for to help ensure that the hybrids you are thinking about planting are indeed diverse? That takes a little more explanation than we have room for here. We explain the performance differences in the accompanying story on the next page.

Elmore is the Iowa State University Extension corn agronomist.

Visit for more corn management information.

This article published in the December, 2011 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.