There’s nothing more disappointing than discovering that your carefully stored corn harvest has been gnawed apart by insects. After harvest, corn (or maize as it’s called in much of the world), can last for months and is a crucial element of the diets of many people across Africa, America, and Asia. However, the hard work of growing and harvesting the crop can be severely curtailed by pest infestation during storage. Small farmers in developing countries lose an incredible portion of their maize to insects like the large grain borer and the maize weevil.
Fortunately, many varieties of maize are selectively bred to be less accessible to pests. In a study published in the November-December issue of Crop Science, Silverio García-Lara and David Bergvinson discuss the details of maize breeding lines that not only resist certain pests but also have potential health benefits.
“Pests are the major constraint to low income farmers, especially in developing countries,” says García-Lara. “They account for almost 40% of total food losses in marginal areas.”
The insects pollute the crop while it’s still in the field or after it’s been stored. Insects thrive in moist, warm environments and love to hide in old storage bins that haven't been thoroughly cleaned. They come out of hiding and can decimate the year’s crop in a matter of months.
“Storage pests are a real problem for food security,” says Bergvinson. “I’ve seen grain so severely damaged that even the poultry won’t eat it.”
In fact, many low income farmers sell off their maize at rock-bottom prices immediately after harvest to avoid the inevitable losses to infestation. Wealthier maize farmers are able to hold on to their crop for longer and wait for a better price. They protect their crop by stock piling it in climate-controlled storage silos and monitoring it for insect damage. If insects are found, the crop is fumigated with insecticides, a dangerous process with many associated health risks.
Small farmers in developing countries often can’t afford the luxury of large sealed containers or expensive chemicals. Therefore, there is a demand for maize varieties that are naturally pest resistant.
García-Lara and Bergvinson worked with the International Maize and Wheat Improvement Center from 1995 to 2007 to develop maize lines resistant to pests. They were able to build on existing maize varieties that have been stored in seed banks over generations for their valuable traits.
“Farmers have been selecting maize for resistance traits for a millennium,” says Bergvinson. “Seed banks all over the world have maize varieties with desirable traits, and that’s where we started. For this breeding line we nursed a few populations along, recombining for different grain characteristics.”
Selecting recombinant inbred lines in the CIMMYT (International Maize and Wheat Improvement Center) experimental station in Morelos, Mexico.
The goal was maize varieties that the more voracious pests like the large grain borer and the maize weevil found unappealing. The end result was a productive line of maize featuring kernels with a thick outer layer that insects can’t burrow into.
Specific kernel characteristics, like a thick outer layer, can also lead to other benefits. “During the last 15 years, we discovered that pest resistant traits in the maize kernel are also related with some nutritional properties never before discovered,” says García-Lara. In other words, these crops are both pest resistant and better for you.
“We selected for kernels with a thick outer layer that acts as a physical barrier for pests,” says Bergvinson. The thick outer layer, known as the pericarp, is also nutritious and contains phytochemicals.
Phytochemicals are compounds that act as a defense mechanism against pests and diseases. Research shows that they also have beneficial nutritional properties for humans.
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