The ovary is formed from the diploid tissue of the mother plant. Like other flowering plants the female sex organ is called the pistil, consisting of the ovary, a style and stigma. The style, like in other flowering plants allows the movement of the pollen sperm to be transmitted to the ovule. In corn, this style is exceptionally long and is known as the silk. Towards the outer end of the silk is a portion that has many hairs (trichomes) that aid in capturing pollen and encourage them to germinate. This is known, botanically, as the stigma. Each silk is part of a single flower of the female plant and thus leading to a single ovary with its enclosed ovule. Cells making up the silk elongate basically due to osmotic pressure as water is transported to the cells as well as photosynthetic sugars for energy. Environmental conditions including soil moisture, leaf disease and light intensity interact with genetics to influence the movement of essential elements to the growing silk cells. The oldest ovaries at the base of the forming ear are the first to develop and elongate, but they also have the furthest to go before emerging from the surrounding leaves. First to emerge often is those a short distance from the base of the ear.
Corn silk emergence may occur over a 10-day period as those at the tip of the developing ear eventually emerge. Without pollination or stresses, an individual silk remains viable for about 10 days. A viable pollen grain germinates within minutes of adherence to the silk. Growth of the pollen germ tube into the silk initiates the halt to that silk’s elongation. As the pollen tube progresses down the silk channel towards the ovule, silk cells dehydrate and collapse, effectively inhibiting infection by fungi. Timing of the pollination and silk emergence is essential to successful fertilization of the ovule cells. Water pressure being more essential to silk emergence than the production of pollen, makes corn seed production very dependent on field conditions. Genetics vary for vulnerability to stress related silk extension. Inbreds and hybrids vary in root growth patterns for absorption of water from soil as well as the tendency to move water to the developing silks. Duration of silk emergence without pollination also influences the vulnerability to ear mold fungi. Aspergillus infection, often causing aflatoxin, is related to drought delaying silk emergence and thus poor pollination. Diplodia ear rot is often related to long silk emergence periods without pollination when rain inhibits movement of viable pollen to the silk, adding to the vulnerability of the silk to infection by this fungus. Insect feeding of fresh silk also is linked to fungus infection.
Environment and genetics greatly influence the biology of flowering in corn.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.