Pollination is one of the most critical stages in the life of a corn plant.
Unfortunately, pollination is also one of the least controllable aspects of grain production since its success or failure is mainly influenced by environmental conditions. At this stage, the corn plant is switching from the vegetative stage of the corn plant to the reproductive stage. We'll see this switch when tassels & silks start appearing. From this point forward all of the corn plant's resources are going to be used to produce grain.
The Tassel
The corn tassel is the male flower of corn. The tassel has been developing deep in the whorl of the plant since approximately the 6th leaf stage. The tassel consists of many spikelets, which are located along the main spike and lateral branches of the tassel. Anthers emerge from these spikelets. An individual tassel produces approximately 6,000 pollen-bearing anthers, although the number can vary greatly with different hybrids. The pollen grains are held on the anthers, which are located at the end of a thin stem called the filament.
The Process: Pollination and Fertilization
Pollen landing on silks is called Pollination.
The successful merging of the pollen with the ovule is called Fertilization.
Pollen (yellow dust-like) grains are contained in anthers. An anther can have from two to 25 million pollen grains. The anthers open and the pollen grains pour out, but only after the tassel is dry. Pollen is light and can be carried up to 600 feet by wind. However, most of it drops within the first 20 to 50 feet. Pollen shed is not a continuous process. It stops when the tassel is too wet or too dry and begins again when temperature conditions are favourable. A pollen grain stands little chance of being washed off the silk during rain storms as little to none is shed when the tassel is wet.
Each pollen grain contains the male genetic material necessary for fertilizing the ovary of one potential kernel. Under favourable conditions, pollen that lands on a silk is captured by fine, sticky hairs on the surface of the silk. 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. Although many pollen grains may germinate along the surface of the silk, only one grain will generate a pollen tube resulting in fertilization.
Pollen from a corn plant rarely fertilizes the silks of the same plant. Silk elongation begins seven to 10 days prior to silk emergence from the husk. Every potential kernel (ovule) on an ear develops its own silk that must be pollinated in order for the ovary to be fertilized and develop into a kernel. 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 three to five days and this usually provides adequate time for all silks to be pollinated before pollen shed stops.
The Ear
Beginning at about the 6th leaf stage, potential ears are initiated at each node up to the 12th to 14th leaf node, but it is normally only the uppermost ear that fully develops. The female ovules that will become kernels upon successful fertilization, are located in paired rows along the surface of the ear. A primary ear may develop up to 1,000 ovules, of which only around 400-700 will be fertilized and harvested as corn kernels.
Mid-20 C daytime temperatures and low-20 C night temperatures are ideal for pollinations. This combination of day and night temperatures maximizes photosynthesis during the day and minimizes respiration during the night. These temperatures will maximize pollination, fertilization and kernel growth rate. Extreme heat stress (37 C or greater) can kill corn pollen. Fortunately corn pollen does not mature or shed all at once. Pollen maturity and shed occur over several days and up to two weeks. Therefore, a day or two of very high heat usually does not affect the entire pollen supply.
