Pollination Success is Critical to Final Yield
- The number of kernels set is largely determined near the time of pollination.
- Yield losses due to reduced kernel set at pollination cannot be fully regained.
Kernel set requires the successful completion of several plant processes.
- Production of viable pollen by the tassel.
- Interception of pollen by receptive silks.
- Embryo and endosperm development.
- Pollen shed or anthesis is controlled by a combination of genetic and environmental factors.
- Once pollen grains have matured inside corn anthers, these anthers begin to dry or dehisce.
- Anthers typically shed pollen around midmorning as anthers dry in the heat and sunlight.
- As anthers dehisce, they split apart to allow pollen grains to fall into the open air.
- Pollen grains are viable for only a few minutes after they are shed until they desiccate.
- A tassel normally sheds pollen for about 5 days.
- Pollen shed in a field can last up to 2 weeks.
- Each silk that emerges from an ear shoot connects to a single ovule, or potential kernel.
- A silk must be pollinated for the ovule to develop into a kernel.
- Silk emergence proceeds from the base to the tip of the ear over the course of 4 to 8 days.
- Silks will continue to elongate for up to 10 days after emergence or until they are pollinated.
- Silk receptivity decreases over time following emergence due to the senescence of silk tissue.
Stress at Pollination Can Reduce Yield
- Stress susceptible period extends from 1 week prior to silking to approximately 2 weeks after silking.
- Yield losses during this period result from reduction in kernel number and are therefore irreversible.
Drought Effects on Silk Growth
- Reduction in kernel number may result from asynchrony of pollen shed and silking.
- Silk elongation requires high water potential ― drought stress can delay silking and increase the anthesis-silking interval (ASI) ― the time between the start of pollen shed and silk emergence.
- Silks that emerge after most of the pollen is shed may not be pollinated.
- Moderate silk delay can cause poorly filled ear tips, whereas more severe stress can result in ears that are nearly or completely barren.
Heat Effects on Pollen Shed
- The location of the tassel exposes it to high radiation and potential temperature extremes.
- Extreme heat stress (over 100 F) can reduce pollen production and viability.
- Severe losses in pollen production or viability are necessary to affect kernel set, which would require an extended period of extremely high temperatures.
- Drought stress can prevent pollination, as well as cause successfully pollinated kernels to abort.
- Drought stress causes kernel abortion by reducing photosynthesis and carbohydrate availability following pollination.
- Aborted kernels will appear white and shriveled. The yellow embryo may also be visible.
- Insects such as corn rootworm beetles and Japanese beetles can interfere with pollination by clipping silks.
- Clipped silks can still elongate and receive pollen; however continuous intense insect activity can result in reduced seed set.
Nielsen, R. L. 2007. Silk Emergence. Purdue Univ.
Nielsen, R.L. 2007. Tassel Emergence & Pollen Shed. Purdue Univ.