How Many Maize U. S. Commercial Heterotic Groups are Available?.

The answer is ‘not too many’. Even though confidentiality between seed companies and public institutions do not allow us to know for sure, there is a general concern about corn genetic diversity available at the farm level. The major factor for improved corn grain yield remains the same: good germplasm choice. Specific breeding methods and/or the most sophisticated genetic tools available will have limited success if poor choices of source germplasm are made in initiating inbred line and hybrid development programs. The inbred-hybrid concept was developed by the public sector in the early 1900s The development of the hybrid corn industry was, therefore, successful because of input by both public and private sectors of corn research. Development of improved inbred lines via recycling is still the main method of corn breeding. In addition, germplasm improvement (e.g. pre-breeding) with use of recurrent selection procedures have created useful genetic diversity, prevented genetic vulnerability, and will provide backup germplasm for possible future needs. B73 is a successful example of a genetically-broad based line that produced billions of dollars. To enhance the expression of heterosis of corn yield, heterotic groups have been identified, and inbred lines are still developed within heterotic groups. The concept of heterotic groups is different from the one for heterotic patterns. Heterotic patterns are crosses between known genotypes that express a high level of heterosis. The specific combinations of dominance and epistatic effects are different for each hybrid. Therefore, the heterotic effects will be unique for each hybrid. As with any genetically complex trait the use of molecular tools and/or other technologies will seem to be more useful on simple inherited traits that are still difficult to accurately phenotype on already chosen germplasm. The presentation will focus on early maturing corn challenges and needs for diversity.

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