Pollination and Fertilization in Corn
Key Points
 The processes that take place
during pollen shed and silk
emergence have a great
influence on potential grain yield.
 Pollination is the transfer of
pollen from the anthers to the
silks and fertilization is when the
male reproductive cells unite
with the female reproductive
cells.
The processes that take place during pollen shed and silk emergence have a great
influence on potential grain yield. Understanding what problems may arise during
reproductive development stages should start with a basic understanding of the
reproductive parts of the corn plant and the processes of pollination and fertilization.
Corn plants have both male and female flowers on each plant. Unlike most plants with
both male and female flowers though, the two reproductive structures are in different
locations on the plant. The tassel is the male flower and the ear is the female flower of
the plant. Their distance apart from each other on an individual plant combined with
the vast quantity of pollen drifting around within a corn field, easily explains why corn
is primarily cross-pollinated.
Tassel
Attached to the tassel of the corn
plant are several thousand anthers
which are responsible for releasing
pollen (Figure 1). Pollen transfers
the male genetic material needed to
 Pollination is one aspect of corn
fertilize the ovary for one potential
production growers have little
kernel. One tassel produces
control over because its
millions of pollen grains. Pollen
success is primarily influenced
shed is usually highest mid-morning
by environmental conditions.
and is influenced by temperature
and moisture conditions. Plants
tend to regulate pollen shed to
occur when temperatures are not too hot and conditions are not too wet. Because
pollen is not all shed at once, even a couple days of extreme heat stress should
not affect the entire pollen supply. Due to natural variability of plants within a field,
it can take up to two weeks to complete pollen shed for an entire field.
Figure 1. Tassel with anthers visible on central spike.
Ear
The ear of a corn plant is the female flower. Silks that emerge from the ear shoot
are the pathways responsible for transporting male genetic material to the ovules,
or potential kernels, of the ear (Figure 2). Silks develop and elongate from the
surface of each ovule on the ear. In order for an ovule to be fertilized and develop
into a kernel, its silk must be pollinated. There may be up to 1000 ovules formed
per ear, but typically only between 400-600 kernels are harvested per ear. Silks
begin to elongate from the ovules about 10 to 14 days before R1 growth stage, or
around V12. Elongation occurs first from the base of the ear, then progresses
toward the tip. Silks can remain receptive to pollen up to 10 days after their
emergence, but typically successful germination occurs within the first 4-5 days.
Extremely long, green silks is an indication that the ear has not yet been
successfully fertilized.
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Figure 2. A corn plant at silking stage. Silk strands can
grow 1 to 1.5 inches per day until pollination of the
individual silk occurs.
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Pollination and Fertilization in Corn
Pollination and Fertilization
The term pollination defines the transfer of pollen from the anthers to the
silks which can occur by wind or insects. Fertilization does not occur until
the male reproductive cells from the pollen unite with the female
reproductive cells in the ovary. Successful pollination does not always
result in fertilization.
Within minutes of a pollen grain landing on a receptive silk, germination
occurs and a pollen tube is initiated and grows within the silk. Through this
pollen tube, male genetic material is transferred to the ovary and fertilizes it
within about 24 hours. While many pollen grains may germinate along the
length of a receptive silk, only one will successfully fertilize the ovule.
Within a few days of successful fertilization, the silks will detach from the
fertilized ovules. To observe this, you can complete the “ear shake test.”
After making a single cut through the husk leaves from the base of the ear
to the top, slowly peel off the husk leaves being careful not to remove any Figure 3. The ear shake test. Fertilization has not yet occurred in
ovules that still have silks attached.
silks. Grasp the ear by the base and give it a gentle shake (Figure 3). Silks
will either drop away from the cob or remain attached. When the majority of silks easily drop away from the cob, successful
fertilization has occurred.
Sometimes even successful fertilization does not result in a harvestable kernel. Anything reducing photosynthesis in the weeks after
fertilization such as cloudy conditions or moisture and heat stress can cause kernels to abort. The sharp reduction in photosynthesis
prevents them from receiving enough nutrients to develop properly. This can usually be observed in the youngest kernels at the tip of
the ear.
Potential Stresses at Pollination
Severe heat or moisture stress. Severe moisture stress can sometimes slow silk elongation to the extent that pollen shed may be
almost finished by the time receptive silks are available. Poor pollination resulting from asynchronous pollen shed and silking can
cause barren ears or unfertilized ovules occurring mainly toward the tips of the ears. After silk emergence, severe drought stress
coupled with low relative humidity can dry out silks to the extent they are no longer receptive to pollen germination.
Silk clipping insects. Insects that feed on corn silks, such as corn rootworm beetles and Japanese beetles, can hinder pollination by
eating exposed silk tissue and damaging what remains. Continued silk elongation until fertilization occurs or growth finally ceases
can expose new silk tissue; however, viability is dependent upon insect damage, available pollen, and environment.
Hail damage. Corn plants are most vulnerable to yield loss from hail damage at VT (tasseling) because all the leaves are exposed.
Even if pollination occurs and results in successful fertilization, with little leaf area left, plants are rarely able to produce enough
carbohydrates necessary to complete grain fill.
Unfortunately, pollination is one aspect of corn production growers have little control over because its success or failure is primarily
influenced by environmental conditions. However, taking steps to reduce variability in corn growth stages and flowering can increase
the likelihood of pollen shed and silking occurring at the proper time. Additional management considerations to keep in mind when
trying to promote successful pollination and fertilization include: use of corn products with adequate heat and drought tolerance for
your growing conditions, use of irrigation where available and when necessary, ensuring adequate fertility for kernel set and reducing
mobilization of nutrients from the stalk, and monitoring fields for corn rootworm and Japanese beetle clipping.
Sources:
Nielsen, R.L. 2012. A fast & accurate pregnancy test for corn. Corny News Network. Purdue University. http://www.agry.purdue.edu/.; Nielsen, R.L. 2010. Silk development and
emergence in corn. Corny News Network, Purdue University. http://www.agry.purdue.edu/.; Nielsen, R.L. 2010. Tassel emergence and pollen shed. Corny News Network, Purdue
University. http://www.agry.purdue.edu/.; Thomison, P. Corn pollination – an overview. AGF-128-95. Ohio State University Extension. http://ohioline.osu.edu/.
Web sources verified 05/05/15.
This publication was developed in partnership with Technology, Development & Agronomy by Monsanto.
Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may obtain as local growing, soil and
weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible. ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Channel®
and the Arrow Design® and Seedsmanship At Work® are trademarks of Channel Bio, LLC. All other trademarks are the property of their respective owners. ©2015 Monsanto Company.
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