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Title:   Author  item
                                            Edwards, Jode
  Submitted to: Crop Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 10/26/2009
                                    Publication  Date: 9/1/2010
                                    Citation: Edwards, J.W. 2010. Testcross Response to Four Cycles of Half-sib and S2 Recurrent Selection in the BS13 Maize (Zea mays L.) Population. Crop Science. 50:1840-1847.Interpretive Summary: The poor relationship between inbred and hybrid performance is an important issue in the hybrid seed corn industry.  Seed companies need high performance hybrids for producers but also need high performing inbreds to reduce seed production costs.  Inbred and hybrid yields tend to have low correlations, meaning it is very difficult to improve inbred performance and hybrid performance simultaneously.  The present study shows that selection on the basis of inbred performance does not improve hybrid performance.  The study also presents results of selection for hybrid performance in the same maize population to show that improved hybrid performance comes only from selecting on hybrid performance.  This study is a follow-up study to several others that will be instrumental in building a line to support a genetic hypothesis, namely a pseudo-overdominance hypothesis, to explain why selecting for inbred-line performance does not improve hybrid performance.  If we can understand why selecting on inbred line performance does not improve hybrid performance, then breeding programs can be altered to more efficiently improve both inbred and hybrid performance, an enhancement that could have immense economic value to the seed industry.
                                Technical Abstract: Inbred progeny recurrent selection was shown to be superior to several forms of outbred-progeny recurrent selection for improving population per se performance based on theoretical arguments.  However, recent improvements to theory and mounting empirical evidence suggest that inbred-progeny recurrent selection is not a superior method of recurrent selection.  In the BS13(S)C0 population, inbred-progeny recurrent selection has not been effective at improving population per se performance.  However, no other selection programs have been evaluated in BS13(S)C0, so there is no basis to compare inbred-progeny recurrent selection in BS13(S)C0 to other methods to determine if other methods might be more effective.  Four cycles of half-sib selection with inbred line B97 as tester have been completed.  The first four cycles of half-sib selection and first four cycles of inbred-progeny selection were testcrossed to B97 and evaluated in a replicated experiment in 2007 and 2008.  Half-sib selection improved grain yield, grain moisture, stalk lodging, root lodging, test weight, and final plant density, whereas inbred-progeny selection did not improve any of these phenotypes, and in fact, stalk lodging had a significant increase.  This study adds to growing empirical literature suggesting that inbred-progeny recurrent selection is inferior to outbred-progeny selection methods whereas early theoretical predictions were the inbred-progeny selection should be the superior method.


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