Early Corn Root Development
Published: May 23, 2012
Corn plants, like most annual grass plants, produce two root systems. The first root system (primary) is composed of the radical and up to three pairs of seminal roots (Figure 1). All of these roots arise from within the seed. The term seminal means "of the seed" and describes their origin. These roots anchor the seeding in the soil and sustain the seedling for the first couple of weeks after emergence. This root system is called primary, not because of its importance, but because is forms first.
The main root system (secondary) of the corn plant is composed of numerous roots that originate from stem tissue outside of the seed. Because they arise from tissues other than roots they are called "adventitious roots", and because they arise from stem nodes they are also called "nodal roots". Again, the name of the root system, secondary, should not be confused with a description of their importance. It is merely a chronological term. The secondary root system is composed of the roots that provide water, nutrients, and anchorage to the plant through nearly its entire life.
Adventitious roots are located at nodes along the stem, both below and above ground. They begin their development shortly after the seedling has emerged, but it takes several weeks before the roots are capable of sustaining the plant. The first node on a corn stem (other than the scutellar node in the seed) is located at the top of the mesocotyl (Figure 1). During germination and emergence, the mesocotyl elongates and pushes the coleoptile toward the soil surface. As the mesocotyl elongates the coleoptile is also elongating. The junction between the mesocotyl and coleoptiles is visible as a slightly swollen area that surrounds the stem. Perched on top of the mesocotyl and covered by the coleoptile is an area of rapid cell division or the growing point. When the coleoptile nears the surface it senses light and signals the mesocotyl to stop elongating. Under most situations the junction between the mesocotyl and the coleoptile will be located about 3/4 of an inch below the soil surface when elongation stops.
It is at this junction between the mesocotyl and the coleoptile that the first set of adventitious roots form. The first sign of developing nodal roots are small bumps that appear around the stem at the node (Figure 2). If soil conditions are conducive to root growth these bumps will transform into easily recognized roots (Figure 3). Although timing varies because of conditions, by the time the plant is at V3 stage, nodal roots extend past well past where the kernel was placed during planting. As the plant continues to develop multiple roots from multiple nodes will be evident (Figure 4). The first four stem internodes elongate very little. So, the accompanying nodes remain underground. Other stem internode elongate, so that their accompanying nodes are above ground. Roots can and often do from several of these above ground nodes. These nodes are called brace roots, but they perform all the functions other corn roots including anchorage in the soil.