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Iowa Stiff Stalk Synthetic (BSSSC0) maize (Zea mays L.) population has been used in two long-term recurrent selection programs: reciprocal recurrent selection (R) and half-sib followed by S2-progeny (S) recurrent selection. Advanced populations after nine cycles of reciprocals recurrent selection [BSSS(R)C9] and seven cycles of half-sib and three cycels of S2 progeny selection [BS13(S)C3] were evaluated. Objectives of this study were to compare performance and amount of genetic variation present among S1 lines from BSSSC0, BSSS(R)C9, BS13(S)C3, and BSSS(R)C9 ✕ BS13(S)C3(C3 ✕ C9) and, also, to compare performance and genetic variation among testcrosses of the S1 lines by using two testers of different heterotic background, B73 and Mo17. The S1 lines from BSSS(S)C9 and BS13(S)C3 showed significant increases in grain yield compared with S1 lines from BSSSC0. The C3 ✕ C9 S1 lines showed high-parent heterosis for grain yield. Genetic variance component estimates of S1 lines were significant in all four populations, and C3 ✕ C9 reflected midparent estimates between the estimates for C3 and C9. Mean grain yield for Mo17 testcrosses was significantly greater than for B73 testcrosses within each of the four populations. Testcrosses involving C3 and a related inbred, B73, showed a nonsignificant grain yield variance estimate. The average yield for the testcrosses of S1 lines from C3 ✕ C9 for both testers was intermediate between the testcrosses of S1 lines from C3 and C9; thus, the high-parent heterosis observed for C3 ✕ C9 S1 lines was not observed for the testcross means.
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Walters, S. P.; Russell, W. A.; and Lamkey, K. R., "Performance and Genetic Variance among S1 Lines and Testcrosses of Iowa Stiff Stalk Synthetic Maize" (1991). Agronomy Publications. 265.