Potential ears are initiated at each node up to about the 12th to 14th leaf node, but typically only the uppermost ear fully develops. The female florets are located in paired rows along the surface of the ear. The florets contain the ovules that will become kernels upon successful fertilization. A primary ear may develop up to 1, ovules, and around are usually harvested.
Row number is determined shortly after ear initiation, but ear length is not set until just before tasseling. Silks develop and elongate from the surface of each ovary on the ear.
The silk functions as the stigma and style of the female flower providing a pathway for the male reproductive cells to reach the ovule. Silks begin growing from ovaries at the base of the ear, then progress toward the tip. Pollination occurs when pollen grains are transferred from the tassel to the silks.
Fertilization does not occur until the male reproductive cells pollen unite with female reproductive cells from the ovule.
Therefore, successful pollination does not always result in fertilization. Pollen shed begins shortly after the corn tassel is fully emerged from the whorl VT stage. Pollen shed usually lasts for 5 to 8 days with peak shed by the 3rd day. Hot, dry conditions can reduce pollen viability and decrease length of shed. Silks from the base of the ear are the first to emerge from the husk, and continue up to the ear tip. Silk longevity is around 10 days under typical growing conditions, but because not all silks are exposed simultaneously, viable silks may be present for around 14 days.
Variable flowering dates in a given field may reduce total pollen available to receptive silks. Severe heat or moisture stress may delay silking and hasten pollen shed reducing fertilization. Poor pollination can cause barren ears or unfertilized ovules near the tips of the ears. Pollen that lands on a silk is captured by small hairs called trichomes.
The pollen grain germinates immediately, producing a pollen tube that grows down the length of the silk, resulting in fertilization of the ovule within 12 to 28 hours. Normally, pollination is a continuous process with fertilization occurring gradually along the ear as silks emerge.
Also unique among grain crops, these flower types are separated on a plant by a distance of several feet. Successful kernel formation is dependent upon both flower types developing in sync with each other nick , pollen grains landing on exposed silks pollination , the joining of a male gamete with a female gamete to form the kernel embryo fertilization , and the joining of another male gamete with two other female nuclei to form the endosperm second fertilization.
This double fertilization is truly a miracle and happens millions of times in our cornfields. Unfortunately, the weather events that most of Missouri has experienced this summer can interfere with each of these events. In Parts 1 and 2, I described the development of the male and female flowers. Under normal conditions the growth and maturing of these two flower types prepare them so that pollen shed occurs within a day or two after silk emergence from husks.
This timing is given a colloquial term — nick. Pollen shed and silk receptivity to that pollen last for at least six days, so some leeway is built into corn plant development to help ensure that pollen is shed when silks are available to catch the pollen. Water pressure turgor drives silk elongation. Silks are highly susceptible to water loss and loss of turgor pressure. They are highly elongated so their surface area to volume ratio is extremely large. They appear to lack much ability to regulate the amount of dissolved molecules in their cells.
Dissolved molecules, like sugars, is one way that plant cells can cause water to flow from outside the cell to inside the cell.
And, they must elongate a long distance from their source of water. Water enters silks from the ovary to which they are attached. The ovary receives water from the cob, and the cob receives water from the stem through the shank. Silks must compete with nearly all other plant parts for water.
They are at the end of a long chain of these plant parts. So, they are at a competitive disadvantage when water becomes scarce. Fortunately, the place where the silk attaches to the ovary and nearly the entire length of the silk is covered by multiple layers of husks.
This helps protect them from harsh environments. But, when water availability is limited silks are often affected first and to a greater amount than other plant parts, such as leaves.
Figure 2. Closeup of corn silks. Notice small hairs that help capture pollen grains. When soil moisture content is low or heat causes increased water loss from plants, silk turgor pressure decreases and silk growth slows.
In fact, there are clear diurnal growth patterns for silk. Most rapid elongation of 1. During the afternoon, when plant water status decreases, silk elongation also decreases — sometimes to zero.
Drought will extenuate this pattern, and if drought stress lasts through the night, silk growth may be nearly zero for the entire day. Elongation rate changes with days after initial silk growth. Excellent pollination produces ears that are filled with wall-to-wall kernels; poor pollination leads to ears with lots of missing kernels.
There are three main ways to go about it:. The orgy ends when the tassels stop shedding pollen and the silks dry to brown. There are three main ways to go about it: Take a broad, dry pan such as a pie tin plucked from the recycling bin , and hold it beneath tassels as you go through the patch and tap the stalks to shake out pollen.
However, the pollen grain starts growth of the pollen tube down the silk channel within minutes of coming in contact with a silk and the pollen tube grows the length of the silk and enters the female flower ovule in 12 to 28 hours.
A well-developed ear shoot should have to 1, ovules potential kernels each producing a silk. The silks from near the base of the ear emerge first and those from the tip appear last. Under good conditions, all silks will emerge and be ready for pollination within 3 to 5 days.
This usually provides adequate time to pollinate all silks before pollen shed ceases. Pollen of a given plant rarely fertilizes all the silks of the same plant.
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