focus on: hybrid crosses
Corn is a versatile crop. It's a food staple for humans – from fresh corn on the cob, to corn meal and flour, to popcorn. Corn is processed into cornstarch, which is used as a thickener in foods, corn oil, which is used for cooking, and high fructose corn syrup, a sweetener in so many of our food and drink products. But corn doesn't just feed us; livestock eat corn and it's also processed to make bio-diesel fuel as well as ethanol that's mixed with gasoline that we use in our cars. The market for corn is enormous.

However, a long, long time ago – in the late 1800s and early 1900s – US corn but they faced a significant problem: farmers wanted to produce more corn, but they couldn't figure out how to increase their yield. Corn farmers didn't have any more land into which they could expand, so they needed to figure out how to grow more corn on the land they had. They needed new varieties of corn that grew well and produced lots of kernels. Despite farmers' best efforts, however, the amount of corn produced per acre - the yield - was stable.

How could corn farmers harvest more corn from the same amount of land? The key to higher yields was understanding how desirable traits – like corn cob size and plant height - were passed from generation to generation. Read on to learn about how the emerging science of genetics in the early 1900s transformed corn plant breeding, addressed the yield problem and shaped the corn industry into what it is today.
About the organism
Corn, also known as maize, is an annual grass that was domesticated nearly 9000 years ago from a wild relative, teosinte, in Central America. Today's plants grow 3-13 ft tall, (1-4 m), with a tall central stalk, off of which come long leaf blades.

Corn plants have separate male and female flowers. At the top of the plant is the tassel. It contains the male reproductive flowers in which the pollen is made. Down lower on the plant, where the leaf blades form on the stem, are the ears or cobs, on which are found the female flowers that contain the ovules. Each ovule has a long, thin silk that grows up to the top of the cob. The silks contain the sticky stigma, which traps pollen, and the style. After the silks at the top of the cob capture the pollen grains, the male reproductive cells travel down the long style to pollinate the ovules.

Placeholder: Baseball Card

Placeholder: Baseball Card
Although corn can self-pollinate, that doesn't typically happen in a field. Usually corn is cross-pollinated, as the wind blows the pollen from one plant to the silks of other corn plants. Because the genetic information from two different parents is combined during fertilization of the ovule, cross-pollination increases the genetic diversity of a species.

Each fertilized ovule grows into a little fruit that we call a corn kernel or seed as long as the plants gets the right amount of light and water. A cob is covered with many, many kernels. The kernels are the support package for the next generation. Each
kernel contains a plant embryo and the energy reserves to sustain it until it can start producing its own energy. Those starchy energy reserves contain the energy we capitalize on when we eat the kernels! Although each plant produces a few cobs, usually only the uppermost cob produces a large, complete ear.
Growing Corn
Corn was domesticated nearly 9000 years ago by indigenous people in what is now Mexico and has been grown in what is now the United States since 2000 BCE. The "discovery" of the Americas by the Europeans has also been called the discovery of corn. Corn seed travelled global trade routes and now is grown in temperate and tropical climates worldwide, between 58[Symbol] North latitude to 40[Symbol] South latitude. Worldwide, 1 billion metric tons of corn were grown in 2016. The US grows the most corn; other top growing countries include China, Brazil, Mexico and Argentina.
Different varieties of corn are grown for different purposes. Corn is planted from seed and harvested after the plants have matured to the point appropriate for their use. If the plant is grown as baby corn and green animal feed, it's harvested just after the female flowers develop and silk emerges, but before pollination. In contrast, sweet corn (Zea mays var. saccharata), eaten as corn on the cob, is harvested about 15-20 days after pollination, when the kernels have a high level of sugar. Field corn, on the other hand, is left to mature further and dry in the field, so that it's easy to store and process. Field corn, also called dent corn (Zea mays var. indentata), is used as animal feed or made into corn meal, corn syrup, ethanol and many other products. Zea mays var. everta is grown for popcorn and is also harvested later in the season.
Think and Apply
Examine the two pie charts below and describe how the regional production of corn has changed between 1961 and 2016.
How Nutritious
Sweet corn is a delicious and nutritious vegetable. A one cup serving of sweet corn provides 125 calories of energy, with much of energy coming from carbohydrates in the sweet and starchy kernels. Low in fat and sodium, corn provides some protein and a healthy amount of dietary fiber as well. A serving of sweet corn also provides good amounts of potassium, magnesium, and Vitamin C.

Think and Apply
Compare the nutrition information of sweet corn, above, with other products made from corn. Note that the serving sizes are different than the 1 cup of sweet corn, but for each serving size, compare the calories, where those calories come from (protein, fat, carbohydrates), the amount of dietary fiber, and the amount of various nutrients in each food.
The Challenge
In the late 1800s and 1900s, US corn farmers faced a problem. The demand for corn was high. People were eating corn as food, canning it to have in the winter, and grinding it into flour. Livestock farmers were becoming more interested in corn as feed for cows. Farmers needed to grow more corn, but the farmland available for growing corn was already in use, so farmers' only option was to increase the productivity of their land. Farmers needed to grow more corn per acre. Unfortunately, that wasn't easy.

Farmers were interested in increasing yields, so they worked with each other and with state agricultural extension workers. They would grow different varieties of corn, select the best seed, and even win prizes for that seed in agricultural shows and fairs. They saved the best seed and grew plants from that seed the next year. But that best seed didn't produce greater yields of corn. The next year's crop was variable and yields still didn't increase. Despite farmers' best efforts to develop the highest quality seed, yields were flat. They were stuck.
Think and Apply
Examine the graph of US Corn Yields between 1860 and 1930. Describe the trend in corn yields during that time.
Despite the stagnant yields, thousands of years of farming knowledge provided a possibility for the corn farmers; better yet, that knowledge was being supported by ideas from scientific experiments. For centuries, farmers had known that crossing different species sometimes resulted in a more vigorous offspring. The mule, useful because of its strength and endurance, is a cross between a horse and a donkey; there are also examples of crossing donkeys with other closely related species. A related concept had been observed in plants. Archeological evidence indicates that Native Americans likely saw some increase in production because in some areas they regularly planted two different strains of corn together to facilitate crossing between those strains. Throughout the late 1700s and through the next century, a number of plant scientists shared results of experiments that indicated that there were positive benefits found in cross-pollinated plants versus those that were self-pollinated.

One such scientist was Gregor Mendel, who published his results in the late 1800s. Mendel investigated inheritance of traits in pea plants, which he chose because he could easily control the pollination. In addition to outlining the basic principles of inheritance, Mendel made some interesting observations about certain offspring, noting that the hybrid plants – those that were the result of a cross between two different inbred lines of parents - tended to grow much more robustly than the plants that were self-pollinated.

"It must be noted that the longer of the two parental axes is usually even exceeded by the hybrid, which perhaps can only be ascribed to the great luxuriance that appears in all plant parts once axes of very different length are joined. Thus, for example, in repeated experiments, axes of 1' and 6' length in hybrid union yielded axes whose length fluctuated between 6 and 7½' without exception." (page 11, Versuche über Pflanzen-Hybriden, Mendel 1866)

Another giant in science, Charles Darwin (best known for On the Origin of Species), being the prolific observer and writer that he was, also published book on plant breeding – The Effects of Cross and Self Fertilization in the Vegetable Kingdom, in 1876. In this book, he provides data from plant crosses and provides more support for the idea that self-pollinated plants tend to make less vigorous, less pest-resistant, lower-yielding offspring than plants that are hybrids, or crosses between two strains. In short, there was growing evidence that for some plants hybrids tend to be more robust. Darwin's work was highly influential to many scientists, including William Beal, who, in the 1880s, studied pollination control as a way to minimize the negative effects of inbreeding in corn.

The late 1800s into the early 1900s was a time of great change in our understanding of traits and inheritance from generation. Corn farmers had tried crossing different varieties of corn, but they weren't able to maintain the quality they did sometimes find. Could science integrate new data about inheritance with centuries of farming knowledge to maximize the effects of cross-pollination and provide the answers that corn farmers needed to increase their yields?
The Solution
Darwin, Beale and others noted the deleterious impact of inbreeding in corn plants and the positive impacts of outbreeding due to cross-pollination. Creating corn varieties with desired traits, however, required connecting the pollination work findings with the in recently rediscovered work of Gregor Mendel - the fundamentals of inheritance and ideas about what we now call alleles. In the early 1900s, George Shull applied Mendel's ideas to understanding inbreeding and outbreeding in corn and conducted experiments that led to a hybrid revolution.
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