P&PDL Picture of the Week for
June 23, 2008

Ear Size Determination in Corn

Bob Nielsen, Extension Corn Specialist, Department of Agronomy, Purdue University

Row number and kernel number per row are two of several yield components in corn. Typically, from 750 to 1000 ovules (potential kernels) develop on each ear shoot. The number of kernel rows multiplied by the number of kernels per row determines total kernel number per ear. Actual (harvestable) kernel number per ear averages between 400 and 600. For a 16-row ear, one kernel per row is equal to about five bushels per acre (for average populations).

Like so many other processes in the corn plant, kernel row number determination on an ear proceeds in an acropetal fashion (from base to tip). Kernel row number determination of the uppermost ear begins shortly after the ear shoot is initiated (V5 to V6) and is thought to be complete as early as V8.

Kernel rows first initiate as "ridges" of cells that eventually differentiate into pairs of rows. Thus, row number on ears of corn is always even unless some sort of stress disrupts the developmental process. True row number is often difficult to visualize in tiny ears dissected from plants younger than about the 12-leaf stage.

The potential number of kernels per row is complete by at least V15 and maybe as early as V12. Kernel number (ear length) is strongly affected by environmental stresses. This means that potential ear length will vary dramatically from year to year as growing conditions vary. Severe stress can greatly reduce potential kernel number per row. Conversely, excellent growing conditions can encourage unusually high potential kernel number.

For more information on ear size determination, see my lengthier article on the Web at http://www.kingcorn.org/news/timeless/EarSize.html.

Click image to enlarge

Ear shoot at Node #6 on a V6 corn plant

Upper ear shoots and tassel dissected from a V9 corn plant

Tip of uppermost ear shoot dissected from a V14 corn plant

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service