GENETIC-EFFECTS ASSOCIATED WITH RECIPROCAL RECURRENT SELECTION IN BSSS AND BSCB1 MAIZE POPULATIONS

Reciprocal recurrent selection (RRS) was designed to capitalize on both additive and nonadditive genetic effects for improvement of the cross between two populations by complementary changes in allelic frequencies between populations. Eleven cycles of RRS have been completed in the lowa Stiff Stalk Synthetic (BSSS) and lowa Corn Borer Synthetic No. 1 (BSCB1) maize (Zea mays L.) populations. The objectives of this study were to partition the response to selection into that due to additive and dominance genetic effects and to evaluate the effects of genetic drift. A population diallel of the C0, C4, C7, C9, and C11 cycles of BSSS(R) and BSCB1(R) and the C8 and C10 interpopulation crosses of BSSS(R) and BSCB1(R) were evaluated. The populations per se selfed and interpopulation crosses selfed of the C0, C4, C7, C8, C9, C10, C11 cycles also were included in the study. The study was evaluated at four locations in 1988 and three locations in 1989. The response of the interpopulation cross for grain yield was 0.28 +/- 0.04 Mg ha-1 cycle-1 and was primarily due to dominance effects. Responses in the populations per se, adjusted for the effects of genetic drift, were similar to the direct effects in the interpopulation cross. Improvement in BSSS(R) was due to both additive and dominance effects, but only dominance effects were important in BSCB1(R). The results showed that selection response occurred at loci with alleles with partial to complete dominance with no evidence for overdominant alleles contributing to selection response. There were no significant changes in grain moisture, and the responses for root and stalk lodging were in the desired direction. It is concluded that RRS was effective for improving the interpopulation cross and inbreeding depression from genetic drift limited the observed response in the populations per se.