SEX in the Corn Field:
How's It Done?

To better understand potential problems that can occur during pollination, you should first understand how the pollination process is orchestrated. Remember that corn has both male flowers and female flowers on the same plant (a flowering habit called monoecious for you trivia fans.) When the male flowers in the tassel mature, anthers emerge from the spikelet flowers, and pollen is dispersed through pores that open at the tips of the anthers.

Pollen Shed.

The anthers are those gizmos that hang from the tassel during pollination. Under a magnifying lens, anthers look somewhat like the double-barrel of a shotgun. Don't mistake anthers for the pollen itself. Pollen is contained inside the anthers.

The yellow 'dust-like' pollen that falls from the anthers of the tassel actually represent two to five million individual, nearly microscopic, spherical, yellowish-translucent pollen grains. Each pollen grain contains the male genetic material necessary for fertilizing the ovary of one potential kernel.

All of the pollen from a single anther may be released in as little as three minutes. An individual tassel may take as long as seven days to finish shedding its pollen, although the greatest volume of pollen may be shed during the second and third day of anther emergence. Because of natural field variability in plant development, a whole field may take as long as 14 days to complete pollen shed.

If the anthers are wet, the pores will not open and pollen will not be released. Thus, on an average Indiana summer morning following a heavy evening dew, pollen shed will not begin until the dew dries and the anther pores open. Cool, cloudy, humid conditions also delay the onset of pollen shed. Similarly, pollen is not shed during rainy conditions. So, growers need not worry about pollen being washed off the tassel during heavy rainfall.

Silks.

The silks that emerge from the ear shoot are the functional stigmas of the female flowers. Every potential kernel (ovule) on an ear develops its own silk that must be pollinated in order for the ovary to be fertilized and develop into a kernel. Typically, up to 1000 ovules form per ear, even though we typically harvest only 400 to 600 actual kernels per ear.

Silk elongation begins 7 to 10 days prior to silk emergence from the husk. Complete silk emergence from an ear generally occurs within two to seven days. Silks from the basal portion of the ear typically emerge first, while the tip silks generally emerge last.

Pollination and Fertilization.

For those of you serious about semantics, let's review two definitions relevant to sex in the corn field. Pollination is the act of transferring the pollen grains to the silks by wind or insects. Fertilization is the union of the male gametes from the pollen with the female gametes from the ovary. Technically, pollination usually occurs successfully (i.e., the pollen reaches the silks), but unsuccessful fertilization results in poor kernel set on the ears.

Pollen grain germination occurs within minutes after a pollen grain lands on a receptive silk. A pollen tube, containing the male genetic material, develops and grows inside the silk, and fertilizes the ovary within 24 hours. Pollen grains can land and germinate anywhere along the length of an exposed silk.

Pollen grain germination occurs within minutes after a pollen grain lands on a receptive silk. A pollen tube, containing the male genetic material, develops and grows inside the silk, and fertilizes the ovary within 24 hours. Pollen grains can land and germinate anywhere along the length of an exposed silk.

Silk clipping by certain insects like the corn rootworm beetle not only removes viable silk tissue, but also injures a certain length of the remaining silk. Generally, silk length on these injured ear shoots must be at least 1/2 inch to ensure that a sufficient length of uninjured silk tissue is exposed for pollen germination to occur.

Silk receptivity to pollen grain germination exists up to 10 days after silk emergence. After 10 days, silk receptivity decreases rapidly. Silk elongation continues until pollination is successful, although elongation eventually ceases as unfertilized silks senesce.

Return to The Corn Growers Guidebook , a WWW resource for corn management systems in Indiana and the eastern CornBelt.

Return to Chapter 2. Corn Management Information .

The Chat 'n Chew Cafe.

Purdue University Agronomy Extension WWW Home Page.

Purdue Agronomy On-Line! , Purdue's Agronomy Department WWW Home Page.

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