Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/22/2005
Publication Date: 10/27/2005
Citation: Hinze, L.L., Kresovich, S., Nason, J.D., Lamkey, K.R. 2005. Population genetic diversity in a maize reciprocal recurrent selection program. Crop Science. 45:2435-2442. Interpretive Summary: The current research was conducted to gather information on a selection program designed to develop improved corn varieties. The objective was to more thoroughly understand genetic and structural changes that have occurred in two corn populations that are a part of this selection program. Over time, genetic similarity between the two populations has decreased while similarity within each population has increased. Evolutionary forces, such as selection, have forced these populations to diverge and thus have created a distinct structure. Our findings provide evidence to support the theory written more than 50 years ago that forms the basis of this selection program. The information gained here is important to help breeders understand how this strategy affects between and within population genetic and structural variables. It is valuable to understand this selection program and the material evaluated because they serve as a model for development of modern commercial corn grown by America's farmers and farmers around the world.
Technical Abstract: The genetic structures of the Iowa Corn Borer Synthetic #1 (CB) and Iowa Stiff Stalk Synthetic (SS) maize [Zea mays (L.)] populations are of particular significance because these populations serve as the model for development of modern commercial hybrids. In 1949, CB and SS were used to start a reciprocal recurrent selection (RRS) breeding program at Iowa State University. We measured the progress of this program in terms of between- and within-population genetic differentiation by analyzing the variation at 86 SSR loci among 448 plants sampled from eight groups (progenitors, Cycle 0, Cycle 1, Cycle 3, Cycle 6, Cycle 9, Cycle 12, and Cycle 15) in each population. The progenitors used to form these populations show a high amount of variation (3.38 alleles/locus). As the RRS program proceeds, the variation decreases (Cycle 15, 1.88 alleles/locus). Over all 448 plants and eight groups (66%) than among groups within populations (13%) or between populations (21%). The repartitioning of variation from within populations (96% in progenitors) to between populations (58% in Cycle 15) over time is consistent with theoretical expectations of divergence between the populations. We have estimated genetic diversity statistics for more intermediate cycles of selection than any previous work in these populations. These intermediate time points provide a comprehensive genetic view of CB and SS permitting evaluation of the molecular-level changes occuring as a result of reciprocal recurrent selection.