Twenty‐Seven Cycles of Divergent Mass Selection for Ear Length in Maize

Knowledge of the associations between yield and its components is fiseful in selection among and within progenies. Twenty‐seven cycles of divergent mass selection for ear length in maize (Zea mays L.) were completed in the Iowa Long Ear Synthetic (BSLE) cultivar determine the effect of ear length selection on grain yield. The original population, selected cycles, and their crosses were evaluated at five Iowa sites for 2 yr to estimate direct and correlated responses to selection. S1 lines from the original population and from the 24Th cycles of selection were evaluated to determine the effect of selection on the genetic variability for ear length and correlated traits. Divergent mass selection was effective to modify ear length: ear length increased 1.4% (b1 = 0.27 cm ± 0.03) cycle−1 of selection for longer ears and decreased 1.9% (b1 = −0.37 cm ± 0.03) cycle−1 of selection for shorter ears. Selection for shorter ears was accompanied by a significant decrease of grain yield of 1.7% (b1 = −0.08 Mg ha−1 ± 0.01) cycle−1 of selection, with no change in yield with selection for longer ears. Selection for shorter ears significantly increased kernel‐row number per cycle (b1 = 0.11 ± .01) and ear diameter (b1 = 0.10 cm ± 0.01); whereas, selection for longer ears significantly reduced kernel‐row number per cycle (b1 = −0.06 ± 0.01) and ear diameter (b1 = −0.20 cm ± 0.01). No heterosis was observed in the crosses between corresponding cycles of selection. There was some evidence that genetic variation had decreased with selection.