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Title:   Author  item
                                            Edwards, Jode
  Submitted to: American Seed Trade Association Conference Proceedings
                                    Publication Type: Proceedings
                                    Publication Acceptance Date: 12/7/2007
                                    Publication  Date: 12/7/2007
                                    Citation: Edwards, J.W. 2007. Genetic Perspectives on Loss of Diversity in Elite Maize Breeding Germplasm. Proceedings of the American Seed Trade Association Conference, December 4-7, 2007, Chicago, Illinois. p. 01.Interpretive Summary: The germplasm base of the U.S. hybrid seed industry is known to be quite narrow.  Current hybrid corn yield in the U.S. continues to rise by nearly two bushels/acre/year, and these rates of improvement need to be maintained or increased to meet future demands.  However, the narrow range of genetic diversity within U.S. maize breeding germplasm may be placing constraints on current genetic improvement.  Domesticated maize has an enormous amount of genetic diversity, but much of the diversity is difficult to use because genetic differences between elite maize hybrids and most of the diverse accessions of maize still available.  Some genetic processes that account for these differences are discussed.  It is argued that a much better understanding of genetic processes that shape and erode diversity is needed in order to maintain current improvement in corn yield in the U.S.  The customers of such research will be seed producers, corn producers, and consumers of corn-based products.
                                Technical Abstract: Selection and genetic drift are two processes that are very well understood if treated separately, but very poorly understood when acting in concert.  As a result, existing quantitative genetic theory does not provide any good methods for developing optimal strategies for maintaining sustainable selection response in the long term.  In order to maintain or increase current selection response patterns in elite materials, a science based-approach is needed to better understand changes in diversity within current pools and to develop strategies in introduce new germplasm.  A population genetics context is presented for maize breeding.  Three basic genetic processes are important in maize breeding, population bottleneck effects, linkage disquilibrium, and epistasis.  It is argued that a better fundamental understanding of these processes in selected maize populations is needed to develop more effective strategies to maintain longer term selection response.


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