Date of Award
Doctor of Philosophy
A. R. Hallauer
An experiment was conducted to evaluate the progress from use of S2 recurrent selection in BS16, BS2, and BSTL maize populations representing 100, 50, and 25% exotic germplasm. The objectives were to evaluate the response to selection, its genetic basis, the heterotic pattern among populations, and the changes in combining ability with cycles of selection. The study was conducted at eight environments and included the following entries: the original populations, an intermediate, and on advanced cycle of selection evaluated per se and selfed; a complete diallel among populations; testcrosses of the populations with four elite inbred testers (B73, B84, Mo17, and Oh43); and checks that included crosses between BS10 and BS11 (cycles 0, 4, and 8) and their testcrosses with elite inbreds, and the single crosses among the four elite testers;The response to selection in grain yield was significant in the intermediate cycle of selection, with no further changes in BS2 and BSTL, and a significant reduction for BS16 in the advanced cycle. Changes in frequency of alleles with additive effects were responsible for the observed changes in yield. Genetic drift was important for the advanced cycles of selection in BS16. Significant changes were obtained for most of the other evaluated traits;Changes in general combining ability (GCA) were associated with the observed direct response to selection for all the traits. Specific combining ability (SCA) and population heterosis did not determine differences among population crosses. The three populations can be classified in the same heterotic group with respect to grain yield. The superior testcross performance with B73 and B84 indicates that the populations can be grouped with Lancaster Sure Crop Composite, and lines as good as Oh43 can be derived from advanced cycles of BS2 and BSTL. Low performing testers were the most effective in discriminating changes in combining ability with cycles of selection. The testcrossed populations compared well with check hybrids for the other agronomic traits except for stalk lodging;S2 recurrent selection resulted in a significant direct response for a limited number of cycles. Changes in GCA and testcross performance were associated to the direct response to selection. The method can provide the means to improve the performance of lines and hybrids developed from populations with restricted number of cycles of S2 recurrent selection.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Carlos Ariel Iglesias
Iglesias, Carlos Ariel, "Efficiency of S2 recurrent selection for improvement of exotic and semi-exotic populations in maize (Zea mays L.) " (1989). Retrospective Theses and Dissertations. 9199.