Corn Breeding: Lessons From the Past
Anatomy and Reproduction of Corn
Most corn plants have a single stem, called a stalk, which grows vertically upward from the ground (Figure 2a). The height of the stalk depends both on the variety of the corn and the environment in which a corn plant is grown. As the stalk grows, leaves emerge. A typical corn plant grown by a farmer in the central United States will have a stalk that is 7 to 10 feet tall and has 16 to 22 leaves. The lower part of each leaf wraps around the stalk and is attached to the stalk at a juncture called a node. Typically the lowest four nodes are below ground. Roots develop from each of these nodes. Sometimes, roots develop from the first aboveground node, and these are known as brace roots (Figure 2b). Some varieties of corn in certain environments produce secondary stalks, known as tillers, which grow outward from near the base of the main stalk.
The female floral organ is called an ear. The ear develops at the tip of a shank, which is a small, stalk-like structure that grows out from a leaf node located approximately midway between the ground and the tassel (Figure 3). Occasionally, a plant will produce an ear at several consecutive nodes, but the one that is located uppermost on the stalk becomes the largest ear. The immature ear consists of a cob, eggs that develop into kernels after pollination, and silks. The cob is a cylindrical structure upon which kernel development occurs. The kernels are arranged on the cob in pairs of rows. From each egg, a hair-like structure called a silk grows and eventually emerges from the tip of the husk, which is a group of leaves attached to the shank that encloses the entire ear. Pollination occurs when pollen falls on the exposed silks. Following pollination, a male sex cell grows down each silk to a single egg and fertilization (the union of the male and female sex cells) occurs. The fertilized egg develops into a kernel and inside each kernel is a single embryo (a new plant). A vigorous corn plant may have 500 to 1000 kernels on a single ear.
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