Variety parent seed is identical to the final seed product. Parents of hybrid seed are not identical to the hybrid. Single cross corn hybrids are inbreds selected primarily for favorable performance when combined as a hybrid but each with homozygosity for repeatable genetics. This inbreeding process does result in some genetic expression of negative characters in one parent that are covered up by the other when combined as hybrids. After identifying such a combination of inbreds, selection of which parent will become the source of the seed and which will become the pollinator becomes significant to the commercial production of hybrid seed.
The corn kernel is a fruit. The outer layer, the pericarp, is a structure of the female plant. It does not include any genetics of the inbred chosen to be the pollen source. The bulk of the corn seed within the kernel is the endosperm where storage of starch is made available as energy utilized for germination of the seed. Cells within the endosperm include 2 copies of female plant chromosomes and one of the pollen parent. Only the embryo has equal genetics from both parents of hybrid seed.
Commercially acceptable female parents of hybrids need to have reliable and consistent elongation of silks even when under some moisture stress. Silks need to be receptive to fertilization after pollenated. High number of ovules is favored. Pericarp structure must be inclined to withstand stress with minimal cracking. The most important character of the female parent is consistently high percentage of germination. A major factor linking this to the female seed parent is the genetics of the mitochondria within the embryo cells. Mitochondrial genetics originate only from the ovule. These sources of transforming energy stored as carbohydrates into that needed for cell metabolism are full of membranes that can be damaged by rapid swelling when water infuses into dry seed. Maintenance of the integrity of these membranes become essential to the germination process. Tolerance of natural stresses on emergence of silks, of pathogens and stresses on pericarps and of function of mitochondria are all associated with the female parent of a corn hybrid.
Pollen sources for hybrid seed production do have some responsibility as well. Most critical is reliable and timely production of live pollen grains. Release of pollen grains from the anthers is affected by genetics, as the anther chambers must dehisce as the relative humidity drops. Timing with the presence of receptive silks on the female parent is essential. It is probable that part of the pressure for selecting parents that increase grain yield involves shifting the genetics for energy needed to produce pollen to that of more grain results in less pollen.
Commercial hybrid corn breeding programs identify which hybrid parent is best as the female or male based upon quantity and germination of the seed. These are determined by the genetics affecting the biology within the corn seed.
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.