Gardening Articles: Edibles :: Vegetables

Sweet Corn - It's A-maize-ing!

by Susan Littlefield

If there is one vegetable that truly says "summer," it's corn. A freshly picked ear of corn, its sweet, tender kernels dripping with butter, is a seasonal treat we associate with long, hot days, picnics and barbecues, and the bounty of the midsummer garden.

This native member of the grass family has been cultivated in our hemisphere since before Columbus first saw it growing on the island of Hispaniola in 1492. It has undergone a lot of breeding changes since then. Thanks to a recessive gene that keeps all its sugars from converting to starch as it matures, we now have the delicious "sweet" varieties that we so enjoy eating fresh in summer.

Sugary, Sugary Enhanced, Supersweet or Synergistic?

The characteristics of each kernel of corn come from the genes of both the plant that produces the ear and the pollen that fertilized it. The genes that give corn it sweetness are recessive, meaning that the genetic contribution from both parents must contain genes that code for sugar formation. (The field, or dent, corns have dominant starch-producing genes.)

Standard sweet corn varieties contain the sugary (SU-1) gene that gives them their sweet taste and creamy texture. But the sugars in these varieties begin changing to starch as soon as the corn is picked. These traditional varieties are responsible for the old saying that you should have the water boiling in the pot before you head out to pick the corn.

Sugary enhanced (SE) hybrid varieties have a gene that increases both sugar content and tenderness and creaminess, compared to the standard varieties. Because of their enhanced sugar content, SE varieties stay sweeter longer than standard sweet corn, especially if they are kept at cool temperatures. So gardeners have a little more flexibility when it comes to harvesting and cooking the corn. Heterozygous hybrids have one copy of the SE gene, with about 25 percent sugary enhanced kernels, while homozygous hybrids with two copies of the SE gene are extra sweet, having 100 percent sugary enhanced kernels.

Supersweet corn carries the SH-2 gene that dramatically slows the conversion of sugar to starch in the kernels, so ears remain sweet for many days after harvest. Because even the mature seeds contain so little starch, they can be harder to grow from seed. Most of these varieties must also be be isolated from plantings of standard and sugary-enhanced varieties to avoid cross-pollination that can result in starchy kernels.

Synergistic (SYN) hybrids really go to town genetically in the sweetness department. They contain not only SU-1 and SE genes, but the SH2 gene from supersweet corn as well, a combination that results in tender kernels with a very high sugar content that has a very slow rate of conversion to starch.

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