Yields of S1 Lines from Original and Advanced Synthetic Varieties of Maize1

Abstract

Four maize (Zea mays L.) synthetic varieties were selfed and approximately 200 S1 lines of each were grown in separate replicated yield trials with the parental populations to compare inbreeding depressions and yield distributions among the S1 lines. The four parental populations were (i) ‘iowa Stiff Stalk Synthetic,’ SSS, (ii) an advanced synthetic derived from SSS by seven cycles of recurrent selection based on half‐sib yield, SSS(HT)C7, (iii) ‘Virginia Corn Belt‐Southern Synthetic,’ CBS, and (iv) an advance synthetic derived from CBS by four cycles of recurrent selection for S1 yield, CBS(S)C4.Inbreeding depression was lower for S1 lines from each of the advanced synthetics than for those of the corresponding original and was lowest for the S1 lines from SSS(HT)C7. Inbreeding depressions were 39.1 and 27.8%, respectively, for S1 lines from SSS and SSS(HT)C7, and 38.3 and 32.5%, respectively, for S1 lines from CBS and CBS(S)C4. S1 lines from SSS(HT)C7 averaged 9.3% higher in yield than those from SSS, although the range of yields was less at both extremes for lines from the advanced population. S1 lines from CBS(S)C4 averaged 27.2% higher than those from CBS with a comparable range of yields.SSS(HT)C7 yielded slightly less than SSS. CBS(S)C4 yielded approximately 19% more than CBS. In all populations the maximum S1 yield approximated that of the parental source. Two S1 lines from CBS(S)C4 were comparable in yield to that of a double‐cross hybrid check variety. One effective means of increasing inbred line yields appears to be increasing the yields of parental source populations.