Obtaining reliable predictions of percentage of occurrence of any biological feature within a population is extremely difficult. Hybrid seed corn in which two parent inbreds, rarely perfectly homozygous for all genetics, needs to be evaluated for potential problems with purity problems due to contamination within the parent seed or outside pollen fertilizing the ovules.
Seed producers use all reasonable approaches to limit these possibilities but environments within the seed field can affect the purity as well. Extreme dry areas can delay silk emergence but rarely delay pollen production by the male inbred. Consequently, female silks remain viable for potential fertilization by pollen from hybrid fields. Such outside pollen can be genetically segregating, resulting in genetics varying from the correct hybrid, but with each of the resulting plants different from the correct hybrid and different from each other. Corn pollen can remain viable while carried by wind for at least a mile. Lack of timely distribution of correct male inbred pollen, increases the potential contamination by foreign corn pollen.
Stressed plants in a hybrid production seed field also may cause delayed tassel production leading to the possibility of missing a few plants from having tassels removed from the female inbred parent. This can lead to self-pollination of the female parent resulting in inbreds within the hybrid seed corn.
Hybrid seed corn producers are well aware of these potential problems and use multiple methods to avoid purity problems. Despite their field management and care, there are circumstances that are difficult to overcome. Consequently, checking the purity and germination of the resulting seed needs to be done after the seed is harvested.
Each kernel of seed corn can be distinct in origin. Those at the base of the female parent ear were probably fertilized a few days earlier than those at the tip. It is possible that the source of pollen could be different simply because of timing conditions at that location of the field. Seed producers are aware of these possibilities and significant problems to hybrid corn performance are rarely released to sales. Testing for purity of the hybrid seed sizes allows the eventual discard of any highly contaminated seed sizes from those being sold.
Seed companies give considerable effort to produce and sell pure hybrid seed. These are tasks easily overlooked as one views uniform hybrid corn fields from the roadway.
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.