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Germination events in the cornfield

May 22, 2009
From Wayne Schoper, Brown/Nicollet Extension Educator

The corn has been planted for awhile and farmers are out looking to see what kind of stand that they have and if everything emerged the way it is supposed to. The corn plant is a very unique organism and has a very specific way that it grows. According to Dave Nicolai, Regional Extension Educator, there are some uniform steps that the corn seedling follows.

The seed of corn (kernel) consists of an embryo surrounded by a mass of stored food called endosperm and an outer covering called the pericarp. The pericarp consists of several layers of cells which help protect the endosperm and embryo from disease organisms and moisture loss. The endosperm provides about 75 percent of the weight of a kernel and is the stored energy reserve. It is about 90 percent starch and 10 percent protein, oils and minerals. The embryo is a miniature plant consisting of a plumule (5-6 embryonic leaves) at one end and a radicle (root) at the opposite end. A cotyledon is connected to the midpoint of the embryo axis and serves as the absorption site for the food stored in the endosperm.

Germination is triggered by absorption of water through the seed coat. Corn kernels must absorb (imbibe) about 30 percent of their weight in water before germination begins. Less than optimum absorption of water (perhaps due to a rapidly drying seed zone) may slow or stop germination. Repeated wetting/drying cycles can decrease seed viability.

Article Photos

Wayne Schoper

The radicle root emerges first, near the tip end of the kernel, within two to three days in warm soils with adequate moisture. In cooler or drier soils, the radicle root may not emerge until one to two weeks after planting. The coleoptile (commonly called the "spike") emerges next from the embryo side of the kernel within one to several days of the appearance of the radicle, depending on soil temperature. The coleoptile initially negotiates its way toward the dent end of the kernel by virtue of the elongation of the mesocotyl. The coleoptile is a rigid piece of plant tissue that completely encloses the four to five embryonic leaves (plumule) that formed during grain development of the seed development last year. The plumule leaves slowly enlarge and eventually cause the coleoptile to split open as it nears the soil surface. The tip of this coleoptile can reach the surface in about 6-10 days, at which time light causes it to split open revealing the first leaves of the corn plant.

Soon after the coleoptile reaches the surface, the first adventitious roots develop from the elongated mesocotyl. This occurs just below the soil surface. Crown roots, which ultimately become the main root system of the corn plant, will develop later from the lower nodes on the main stem. The mesocotyl should remain firm, white and healthy through at least the 6-leaf stage, if not longer. If it is mushy, discolored, or damaged prior to this stage, then it is likely part of the crop problem being investigated.

The lateral seminal roots are the last to emerge, near the dent end of the kernel. Even though these and the radicle root are technically nodal roots, they do not compromise what is typically referred to as the permanent nodal root system. The first set of so-called "permanent" roots begins elongating at approximately the V1 leaf stage (1 leaf with a visible leaf collar) and is clearly visible by V2. Under warm soil conditions, the calendar time from planting to emergence can be as little as 5 - 7 days. Under cold soil conditions, emergence can easily take up to four weeks.

The point to remember is to take the time and go out and scout your fields and see what is happening out there.



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