Corn Diversity is great (usually)
Zea mays plant structure with the strong distance between the male and female flowers and the ease of pollen movement in wind allows cross pollination of among corn plants. Easy transport of seed both of its historic movement from those initial development in Mexico as well as in recent times has allowed diversity among the 25-30000 genes in the species. This phenomenon is the major contributor to corn’s success to converting solar energy for human’s use.
Each gene of corn is a long chain of nucleic acid components in which one small substitution of that DNA can affect the performance of the resulting protein. That protein may be an important contributor to some physiological event in the plants cells. Diploid plants have a code for the same gene on the other string of DNA in that chromosome. This allows compensation for potential negative affect of any mutation in a gene on one of the pair of chromosomes.
Self pollinated plants have the advantage and disadvantage of eventually getting the same mutations in both members of the chromosome pairs. This can result in selection by breeders to stabilize favorable characters but the large number of genes and probability of also getting ‘negative’ genes on both members of a chromosome pair is especially high. Inbred plants have little genetic diversity among each other. This allows for retaining genetics when in a controlled field environment like a seedstock increase isolation where all plants have identical, homozygous genes. Unfortunately, some of the affect is negative affect of some genes affecting plant size and perhaps some specific traits such as resistance to a pathogen. It is the corn breeders objective to match inbreds that will have dominant genes to reduce the negative affect when crossed with a specific inbred.
After identifying the pair of inbreds that make desired hybrids with maximum expression of desired traits a commercial hybrid can be produced. Controlled pollination of one parent onto the other parent is essential for resulting seed to uniformly express the hybrid genetics. Few pollen from the female plant landing on its own ear silk, will result in seed with the female inbred and not that of the hybrid genetics. Such ‘self’ will be small, unproductive plants in the hybrid field. If female silks are pollinated by the wrong plants, such as from other hybrid fields, resulting seed will not be identical to the desired hybrid. Pollen produced by hybrid plants are not genetically identical to each other and therefore such contaminating pollen on a female plant in a hybrid seed production field results in seed with wide variation. Each outcross plant from this type of contamination will be different from the desired hybrid but also from each other, varying in plant height, ear placement and size and other noticed traits.
Corn diversity benefits availability of traits and needs to be carefully controlled to maximize its advantages.
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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.