Corn Pollination Success

Author: Mark Jeschke 

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
  • Fertilization
  • Embryo and endosperm development

corn polination success

Pollination

  • 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 mid-morning as anthers dry in the heat and sunlight

corn polination success

  • 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

corn polination success

Silk Emergence

  • 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

corn polination success

  • 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

corn polination success

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

corn polination success

corn polination success

Heat effects on pollen shed

  • The location of the tassel exposes it to high radiation and potential temperature extremes
  • Extreme heat stress (over 100º F)  can reduce pollen prod-uction 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.

Kernel abortion

  • 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

corn polination success

Aborted kernels will appear white and shriveled. The yellow embryo may also be visible

Silk clipping

  • 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

corn polination success

References:

Nielsen, R. L. 2007. Silk Emergence. Purdue Univ. http://www.kingcorn.org/news/timeless/Silks.html

Nielsen, R.L.  2007. Tassel Emergence & Pollen Shed. Purdue Univ. http://www.kingcorn.org/news/timeless/Tassels.html