In order for a kernel to be pollenated, a grain of pollen must 1) Drop from a tassel, 2) Land on the silk, which would be protruding from the ear, 3) the genetic content from the pollen must travel inside the silk to the kernel, and 4) The pollen genetics (male) must meet up with the kernel genetics (female) to finally pollenate the ear. It’s quite an incredible journey. On mature kernels, you can find a small bump of scar tissue where the silk was attached. I like to tell kids that is the kernels belly button. You can see the scar on mature corn kernels, and even on the sweet corn you have for dinner. Photo by Jeff Burbrink.

By Jeff Burbrink
Ag & Natural Resources Extension Educator, Purdue Extension LaGrange County

LAGRANGE — Earlier, I wrote about the V, or vegetative stage, of corn development, when the plants grow fast and tall, while setting the stage for tassels, ears and pollination. This week, the focus is the R, or reproductive stage of development.

A corn tassel is the “male” portion of the plant. On a single tassel, there are over 6,000 pollen-bearing structures, with millions of pollen grains inside, ready to drop when the plant matures. If you live next to fields where hybrid corn is grown, you may be asked not to grow sweetcorn in your backyard. The pollen from just one of your sweetcorn plants can contaminate as much as three acres of hybrid corn if it reaches the female seed corn silk at the wrong time.

Pollen is sensitive to temperature and drought. Fortunately, the plants have adapted to conditions, and typically drop pollen in the morning when it is cooler. Pollen drop can even adapt to rainfall! When conditions are rainy, a tassel can hang onto pollen grains to reduce the amount of pollen washed straight to the soil. The pollen is spread primarily by wind and gravity.

The target for the pollen is the silk, part of the “female” portion of the plant, that also includes the ear and kernels. Each kernel is attached to one silk that emerges from the tip of the ear. As the ears form, the silks begin to grow longer, heading for the tip of the ear, happening about the same time the first tassels begin appear. Silks from the butt end of the ear typically emerge first, while the silks near the tip emerge last, growing as much as 1.5 inches a day in the process.

When viable pollen lands on the silk, it germinates, meaning it releases the male genetic material, which travels down the inside of the silk in a tunnel called a pollen tube. It takes less than 24 hours for the male genetic material to travel the length of the silk, reach the kernel, and fertilize the ovule.

Since each silk is attached to just one kernel, then each silk must receive pollen or there will be gaps among the kernels on the ear. There are a number of ways the pollination process can fail. Extreme heat (over 100 degrees) can kill pollen before it transfers its genetics. Severe droughts can cause silks to grow slower or not emerge from the ear tip. Insects such as Japanese beetle or corn rootworm beetles can clip off the silk and reduce the target size for the pollen.

When proper fertilization does not occur on an ear, one symptom you might see is long green silk. The silk will continue to grow for about 10 days once they emerge from the tip or the ear. Once the fertilization process is complete, the silk turns brown, signaling successful fertilization.

If you look carefully, you may be able to see a small bump on the top of a mature corn kernel, which is scar tissue where the silk was attached to the kernel. When I show that to children, I like to say that is the kernel’s belly button!