Not only is our species dependent upon diversity for survival as our environment, including pathogens, changes. We are depended upon diversity among our crops as well. Corn being naturally cross-pollinated and diploid provides this opportunity for the diversity that comes from naturally occurring mutations. It is basic to providing the eventual variability that has driven and continually drives evolution. It allowed the deviants in Teosinte that was selected by people in Mexico 10000 years ago and the multiple selections in corn as it was moved worldwide since then. Most research has verified that most of these genetic mutations result in recessive genes and thus the presence of the mutation is not often expressed in a diploid present in which the dominant member of the paired gene is expressed. The su genes resulting in sweet corn is only expressed when the recessive gene is expressed in both members of the diploid plant. Same is true of the mutants wx for waxy. This is true for multiple other homozygous recessive traits.
Occurrence of mutations can be an advantage or a disadvantage. In most cases, being recessive, the mutation may not be detected by performance of the hybrid. Selfing to achieve homozygosity during the inbred development reflects the negative affect of making some recessive genes more homozygous. This is reflected in reduction of plant size from the heterozygous parent used for inbred development. The selection process with each generation does allow elimination of some negative homozygous recessives. Double haploid systems do not allow generational selection because the homozygous condition is fixed.
Expression of hybrid vigor when an inbred is crossed with another specific inbred is mostly due to dominant versions of the negative recessive genes of the inbred parents. That is probably why prospective commercial hybrids are from crosses of inbreds with distinct ‘families’, each not likely to share the same negative recessive versions of important genes. Corn has 40000 genes, including some negative recessives, perhaps due to mutations. The seed industry uses hybrid testing, and inbred development to select for hybrid performance. Further selection among those near-inbreds can allow for selection against the few negative traits found among some plants to improve inbred performance in hybrid production. That has been consistent with our experience in our proprietary Rapid Inbreeding® program. Diversity is good!
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.